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Sample records for open-shell singlet formation

  1. Decamethylytterbocene Complexes of Bipyridines and Diazabutadienes: Multiconfigurational Ground States and Open-Shell Singlet Formation

    Energy Technology Data Exchange (ETDEWEB)

    Booth, Corwin H.; Walter, Marc D.; Kazhdan, Daniel; Hu, Yung-Jin; Lukens, Wayne W.; Bauer, Eric D.; Maron, Laurent; Eisenstein, Odile; Andersen, Richard A.

    2009-04-22

    Partial ytterbium f-orbital occupancy (i.e., intermediate valence) and open-shell singlet formation are established for a variety of bipyridine and diazabutadiene adducts with decamethylytterbocene, (C5Me5)2Yb, abbreviated as Cp*2Yb. Data used to support this claim include ytterbium valence measurements using Yb LIII-edge X-ray absorption near-edge structure spectroscopy, magnetic susceptibility, and complete active space self-consistent field (CASSCF) multiconfigurational calculations, as well as structural measurements compared to density functional theory calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground-state wave function that has both an open-shell singlet f13(?*)1, where pi* is the lowest unoccupied molecular orbital of the bipyridine or dpiazabutadiene ligands, and a closed-shell singlet f14 component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the lack of temperature dependence of the measured intermediate valence. These results have implications for understanding chemical bonding not only in organolanthanide complexes but also for f-element chemistry in general, as well as understanding magnetic interactions in nanoparticles and devices.

  2. Decamethylytterbocene complexes of bipyridines and diazabutadines: multiconfigurational ground states and open-shell singlet formation

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, Eric D [Los Alamos National Laboratory; Booth, C H [LBNL; Walter, M D [LBNL; Kazhdan, D [LBNL; Hu, Y - J [LBNL; Lukens, Wayne [LBNL; Maron, Laurent [INSA TOULOUSE; Eisentein, Odile [UNIV MONTPELLIER 2; Anderson, Richard [LBNL

    2009-01-01

    Partial ytterbium f-orbital occupancy (i.e. intermediate valence) and open-shell singlet Draft 12/formation are established for a variety of bipyridine and diazabutadiene adducts to decamethylytterbocene, (C{sub 5}Me{sub 5}){sub 2}Yb or Cp*{sub 2}Yb. Data used to support this claim includes ytterbium valence measurements using Yb Lm-edge x-ray absorption near-edge structure (XANES) spectroscopy, magnetic susceptibility and Complete Active Space Self-Consistent Field (CASSCF) multi configurational calculations, as well as structural measurements compared to density-functional theory (DFT) calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground state wave function that has both an open-shell singlet f{sup 13} and a closed-shell singlet f{sup 14} component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the presence of intermediate valence and its lack of any significant temperature dependence. These results have implications for understanding chemical bonding not only in organolanthanide complexes, but also for organometallic chemistry in general, as well as understanding magnetic interactions in nanopartic1es and devices.

  3. Diradical character dependences of the first and second hyperpolarizabilities of asymmetric open-shell singlet systems.

    Science.gov (United States)

    Nakano, Masayoshi; Champagne, Benoît

    2013-06-28

    The static first and second hyperpolarizabilities (referred to as β and γ, respectively) of asymmetric open-shell singlet systems have been investigated using the asymmetric two-site diradical model within the valence configuration interaction level of theory in order to reveal the effect of the asymmetric electron distribution on the diradical character and subsequently on β and γ. It is found that the increase of the asymmetric electron distribution causes remarkable changes in the amplitude and the sign of β and γ, and that their variations are intensified with the increase of the diradical character. These results demonstrate that the asymmetric open-shell singlet systems with intermediate diradical characters can exhibit further enhancements of β and γ as compared to conventional asymmetric closed-shell systems and also to symmetric open-shell singlet systems with intermediate diradical characters.

  4. Soluble and stable heptazethrenebis(dicarboximide) with a singlet open-shell ground state

    KAUST Repository

    Sun, Zhe

    2011-08-10

    A soluble and stable heptazethrene derivative was synthesized and characterized for the first time. This molecule exhibits a singlet biradical character in the ground state, which is the first case among zethrene homologue series. Exceptional stability of this heptazethrenebis(dicarboximide) raises the likelihood of its practical applications in materials science. © 2011 American Chemical Society.

  5. Finite-field method with unbiased polarizable continuum model for evaluation of the second hyperpolarizability of an open-shell singlet molecule in solvents.

    Science.gov (United States)

    Inui, Tomoya; Shigeta, Yasuteru; Okuno, Katsuki; Baba, Takeshi; Kishi, Ryohei; Nakano, Masayoshi

    2013-10-15

    The static second hyperpolarizability γ of the complexes composed of open-shell singlet 1,3-dipole molecule involving a boron atom and a water molecule in aqueous phase are investigated by the finite-field (FF) method combined with a standard polarized continuum model (PCM) and with a newly proposed unbiased PCM (UBPCM). On the basis of the comparison with the results calculated by the FF method using the full quantum and the quantum-mechanical/molecular-mechanical and molecular-dynamics (QM/MM-MD) treatments, the present FF-UBPCM method is demonstrated to remedy the artificial overestimation of the γ caused by standard FF-PCM calculations and to well reproduce the FF-QM/MM-MD and FF-full-QM results with much lower costs.

  6. Excitation energies and properties of open-shell singlet molecules applications to a new class of molecules for nonlinear optics and singlet fission

    CERN Document Server

    Nakano, Masayoshi

    2014-01-01

    This brief investigates the diradical character, which is one of the ground-state chemical indices for 'bond weakness' or 'electron correlation' and which allows researchers to explore the origins of the electron-correlation-driven physico-chemical phenomena concerned with electronic, optical and magnetic properties as well as to control them in the broad fields of physics and chemistry. It then provides the theoretical fundamentals of ground and excited electronic structures of symmetric and asymmetric open-shell molecular systems by using model molecular systems. Moreover, it presents the th

  7. Carbon-Carbon Bond Formation in a Weak Ligand Field: Leveraging Open Shell First Row Transition Metal Catalysts.

    Science.gov (United States)

    Chirik, Paul James

    2017-01-12

    Unique features of Earth abundant transition metal catalysts are reviewed in the context of catalytic carbon-carbon bond forming reactions. Aryl-substituted bis(imino)pyridine iron and cobalt dihalide compounds, when activated with alkyl aluminum reagents, form highly active catalysts for the polymerization of ethylene. Open shell iron and cobalt alkyl complexes have been synthesized that serve as single component olefin polymerization catalysts. Reduced bis(imino)pyridine iron- and cobalt dinitrogen compounds have also been discovered that promote the unique [2+2] cycloaddition of unactivated terminal alkenes. Electronic structure studies support open shell intermediates, a deviation from traditional strong field organometallic compounds that promote catalytic C-C bond formation.

  8. Excimer formation and singlet-singlet energy transfer of organoluminophores in the premicellar and micellar-polyelectrolytes solutions

    Science.gov (United States)

    Bisenbaev, Adel K.; Levshin, L. V.; Saletsky, A. M.

    1991-05-01

    Recently the investigation of photoprocesses in organized synthetical structures (ionic micelles, vesicles, linear polyelectrolytes, polymer gels etc.), intermolecular interactions of which are formed by hydrophobic and electric forces, have been of great interest.12 These systems are of particular interest due to the possibility of using luminescent data, which reflected the peculiarities of photoprocesses in organized assemblies. This can be used to establishing the mechanism of photobiological processes. Due to the very complex nature of biostructures our approximation can be considered phenomenological, however it gives the possibility of revealing the energy dissipation path in biosystems. Such model approach is based on a principal resemblance between a living matter and synthetical polymolecular structures with a certain degree of organization. This resemblance is displayed in theoretical models of synthetic polymers,3 which are the foundation of modern ideas on biomolecule conformation. Organized synthetical structures like ionic micelles, polymer gel, bilayer and strong polyelectrolytes could be made to represent biosystems like cell, protoplasm, membrane and NADH, respectively. In this paper we report some new results on the complex formation of dyes and detergents in premicellar region and singlet-singlet energy transfer from pyrene (Py) excimer to dye monomers in ionic micellar-polyion-water system.

  9. Phenomenological model of photoluminescence degradation and photoinduced defect formation in silicon nanocrystal ensembles under singlet oxygen generation

    Energy Technology Data Exchange (ETDEWEB)

    Gongalsky, Maxim B., E-mail: mgongalsky@gmail.com; Timoshenko, Victor Yu. [Faculty of Physics, Moscow State M.V. Lomonosov University, 119991 Moscow (Russian Federation)

    2014-12-28

    We propose a phenomenological model to explain photoluminescence degradation of silicon nanocrystals under singlet oxygen generation in gaseous and liquid systems. The model considers coupled rate equations, which take into account the exciton radiative recombination in silicon nanocrystals, photosensitization of singlet oxygen generation, defect formation on the surface of silicon nanocrystals as well as quenching processes for both excitons and singlet oxygen molecules. The model describes well the experimentally observed power law dependences of the photoluminescence intensity, singlet oxygen concentration, and lifetime versus photoexcitation time. The defect concentration in silicon nanocrystals increases by power law with a fractional exponent, which depends on the singlet oxygen concentration and ambient conditions. The obtained results are discussed in a view of optimization of the photosensitized singlet oxygen generation for biomedical applications.

  10. Spin-adapted open-shell time-dependent density functional theory. II. Theory and pilot application.

    Science.gov (United States)

    Li, Zhendong; Liu, Wenjian; Zhang, Yong; Suo, Bingbing

    2011-04-07

    The excited states of open-shell systems calculated by unrestricted Kohn-Sham-based time-dependent density functional theory (U-TD-DFT) are often heavily spin-contaminated and hence meaningless. This is solved ultimately by the recently proposed spin-adapted time-dependent density functional theory (TD-DFT) (S-TD-DFT) [J. Chem. Phys. 133, 064106 (2010)]. Unlike the standard restricted open-shell Kohn-Sham-based TD-DFT (R-TD-DFT) which can only access the singlet-coupled single excitations, the S-TD-DFT can capture both the singlet- and triplet-coupled single excitations with the same computational effort as the U-TD-DFT. The performances of the three approaches (U-TD-DFT, R-TD-DFT, and S-TD-DFT) are compared for both the spin-conserving and spin-flip excitations of prototypical open-shell systems, the nitrogen (N(2)(+)) and naphthalene (C(10)H(8)(+)) cations. The results show that the S-TD-DFT gives rise to balanced descriptions of excited states of open-shell systems.

  11. Time-resolved luminescence and singlet oxygen formation after illumination of the hypericin-low-density lipoprotein complex.

    Science.gov (United States)

    Gbur, Peter; Dedic, Roman; Chorvat, Dusan; Miskovsky, Pavol; Hala, Jan; Jancura, Daniel

    2009-01-01

    Time-resolved fluorescence and phosphorescence study of hypericin (Hyp) in complex with low-density lipoproteins (LDL) as well as the evolution of singlet oxygen formation and annihilation after illumination of Hyp/LDL complexes at room temperature are presented in this work. The observed shortening of the fluorescence lifetime of Hyp at high Hyp/LDL molar ratios (>25:1) proves the self-quenching of the excited singlet state of monomeric Hyp at these concentration ratios. The very short lifetime ( approximately 0.5 ns) of Hyp fluorescence at very high Hyp/LDL ratios (>150:1) suggests that at high local Hyp concentration inside LDL molecules fast and ultrafast nonradiative decay processes from excited singlet state of Hyp become more important. Contrary to the lifetime of the singlet excited state, the lifetime (its shorter component) of Hyp phosphorescence is not dependent on Hyp/LDL ratio in the studied concentration range. The amount of singlet oxygen produced as well as the integral intensity of Hyp phosphorescence after illumination of Hyp/LDL complexes resemble the dependence of the concentration of molecules of Hyp in monomeric state on Hyp/LDL until a concentration ratio of 60:1. This fact confirms that only monomeric Hyp is able to produce the excited triplet state of Hyp, which in aerobic conditions leads to singlet oxygen production. The value of singlet oxygen lifetime ( approximately 8 micros) after its formation from the excited triplet state of Hyp in LDL proves that molecules of singlet oxygen remain for a certain period of time inside LDL particles and are not immediately released to the aqueous surrounding. That Hyp exists in the complex with LDL in the monodeprotonated state is also demonstrated.

  12. Mechanism of Rh-Catalyzed Oxidative Cyclizations: Closed versus Open Shell Pathways.

    Science.gov (United States)

    Park, Yoonsu; Ahn, Seihwan; Kang, Dahye; Baik, Mu-Hyun

    2016-06-21

    A conceptual theory for analyzing and understanding oxidative addition reactions that form the cornerstone of many transition metal mediated catalytic cycles that activate C-C and C-H bonds, for example, was developed. The cleavage of the σ- or π-bond in the organic substrate can be envisioned to follow a closed or an open shell formalism, which is matched by a corresponding electronic structure at the metal center of the catalyst. Whereas the assignment of one or the other mechanistic scenario appears formal and equivalent at first sight, they should be recognized as different classes of reactions, because they lead to different reaction optimization and control strategies. The closed-shell mechanism involves heterolytic bond cleavages, which give rise to highly localized charges to form at the transition state. In the open-shell pathway, bonds are broken homolytically avoiding localized charges to accumulate on molecular fragments at the transition states. As a result, functional groups with inductive effects may exert a substantial influence on the energies of the intermediate and transition states, whereas no such effect is expected if the mechanism proceeds through the open-shell mechanism. If these functional groups are placed in a way that opens an electronic communication pathway to the molecular sites where charges accumulate, for example, using hyperconjugation, electron donating groups may stabilize a positive charge at that site. An instructive example is discussed, where this stereoelectronic effect allowed for rendering the oxidative addition diastereoselective. No such control is possible, however, when the open-shell reaction pathway is followed, because the inductive effects of functional groups have little to no effect on the stabilities of radical-like substrate states that are encountered when the bonds are broken in a homolytic fashion. Whether the closed-shell or open-shell mechanism for oxidative addition is followed is determined by the

  13. Geminate recombination kinetics of solute radical ions. Singlet excited state formation in cyclohexane solutions of biphenyl

    Science.gov (United States)

    Tagawa, S.; Washio, M.; Tabata, Y.; Kobayashi, H.

    Transient absorption spectra of the solute anion, cation and triplet state and the solute fluorescence in the pulse radiolysis of 0.1 mole 1 -1 biphenyl in cyclohexane were observed on a nanosecond timescale longer than 1 ns after a 20 ps pulse. The formation of the solute excited singlet state is mainly due to the geminate ion recombination reaction even in the high concentrated solutions. The decay of the solute ions obeys the reciprocal square root dependence on time longer than 10 ns from the end of a 10 ps pulse. The slope of this reciprocal square root plots agrees with the literature value on a longer timescale obtained by microwave absorption. The yield of free ions obtained from the intercept of the slope agrees also with the literature values obtained by the field clearing method. Ratio of the formation rate of the solute excited triplet state to the decay rate of the solute anion changes in a time range between 5 and 20 ns. It is very well correlated with a theoretical calculation of spin correlation decay of the germinate ion pairs by Brocklehurst, although the formation of the solute triplet state was observed even on a timescale shorter than 5 ns from the end of a 20 ps pulse, where loss of spin correlation is negligibly small.

  14. Spin-adapted open-shell time-dependent density functional theory. III. An even better and simpler formulation.

    Science.gov (United States)

    Li, Zhendong; Liu, Wenjian

    2011-11-21

    The recently proposed spin-adapted time-dependent density functional theory (S-TD-DFT) [Z. Li and W. Liu, J. Chem. Phys. 133, 064106 (2010)] resolves the spin-contamination problem in describing singly excited states of high spin open-shell systems. It is an extension of the standard restricted open-shell Kohn-Sham-based TD-DFT which can only access those excited states due to singlet-coupled single excitations. It is also far superior over the unrestricted Kohn-Sham-based TD-DFT (U-TD-DFT) which suffers from severe spin contamination for those excited states due to triplet-coupled single excitations. Nonetheless, the accuracy of S-TD-DFT for high spin open-shell systems is still inferior to TD-DFT for well-behaved closed-shell systems. The reason can be traced back to the violation of the spin degeneracy conditions (SDC) by approximate exchange-correlation (XC) functionals. Noticing that spin-adapted random phase approximation (S-RPA) can indeed maintain the SDC by virtue of the Wigner-Eckart theorem, a hybrid ansatz combining the good of S-TD-DFT and S-RPA can immediately be envisaged. The resulting formalism, dubbed as X-TD-DFT, is free of spin contamination and can also be viewed as a S-RPA correction to the XC kernel of U-TD-DFT. Compared with S-TD-DFT, X-TD-DFT leads to much improved results for the low-lying excited states of, e.g., N(2)(+), yet with much reduced computational cost. Therefore, X-TD-DFT can be recommended for routine calculations of excited states of high spin open-shell systems.

  15. Kinetically blocked stable heptazethrene and octazethrene: Closed-shell or open-shell in the ground state?

    KAUST Repository

    Li, Yuan

    2012-09-12

    Polycyclic aromatic hydrocarbons with an open-shell singlet biradical ground state are of fundamental interest and have potential applications in materials science. However, the inherent high reactivity makes their synthesis and characterization very challenging. In this work, a convenient synthetic route was developed to synthesize two kinetically blocked heptazethrene (HZ-TIPS) and octazethrene (OZ-TIPS) compounds with good stability. Their ground-state electronic structures were systematically investigated by a combination of different experimental methods, including steady-state and transient absorption spectroscopy, variable temperature NMR, electron spin resonance (ESR), superconducting quantum interfering device (SQUID), FT Raman, and X-ray crystallographic analysis, assisted by unrestricted symmetry-broken density functional theory (DFT) calculations. All these demonstrated that the heptazethrene derivative HZ-TIPS has a closed-shell ground state while its octazethrene analogue OZ-TIPS with a smaller energy gap exists as an open-shell singlet biradical with a large measured biradical character (y = 0.56). Large two-photon absorption (TPA) cross sections (σ(2)) were determined for HZ-TIPS (σ(2)max = 920 GM at 1250 nm) and OZ-TIPS (σ(2)max = 1200 GM at 1250 nm). In addition, HZ-TIPS and OZ-TIPS show a closely stacked 1D polymer chain in single crystals. © 2012 American Chemical Society.

  16. Hyper Open-Shell States: The Lowest Excited Spin States of O Atom, Fe(2+) Ion, and FeF2.

    Science.gov (United States)

    Varga, Zoltan; Verma, Pragya; Truhlar, Donald G

    2017-09-13

    Excited spin states are important for reactivity, catalysis, and magnetic applications. This work examines the relative energies of the spin states of O atom, Fe(2+) ion, and FeF2 and characterizes their excited spin states. Both single-configuration and multireference methods are used to establish the character of the lowest singlet excited state of all three systems and the lowest triplet excited state of Fe(2+) and FeF2. We find that the conventional representation of the orbital occupancies is incorrect in that the states have more unpaired electrons than the minimum number required by their total electron spin quantum number. In particular, we find that, for a given spin state, an electronic configuration with more than 2S unpaired electrons is more stable than the configuration with 2S unpaired electrons (where S is the spin of the system). For instance, triplet FeF2 with four unpaired electrons is lower in energy than triplet FeF2 with two unpaired electrons. Such highly open-shell configurations are labeled as hyper open-shell electronic configurations in this work and are compared to ordinary open-shell or closed-shell electronic configurations. The hyper open-shell states considered in this work are especially interesting because, unlike typical biradicals and polyradicals, the unpaired electrons are all on the same center. This work shows that the conventional perspective on spin-state energetics that usually assumes ordinary open shells for single-centered radicals needs modification to take into account, whenever possible, hyper open-shell configurations as well.

  17. Three-nucleon forces in exotic open-shell isotopes

    CERN Document Server

    Soma, V; Cipollone, A; Duguet, T; Navratil, P

    2013-01-01

    Advances in the self-consistent Green's function approach to finite nuclei are discussed, including the implementation of three-nucleon forces and the extension to the Gorkov formalism. We report results on binding energies in the nitrogen and fluorine isotopic chains, as well as spectral functions of 22O. The application to medium-mass open-shell systems is illustrated by separation energy spectra of two argon isotopes, which are compared to one-neutron removal experiments.

  18. VIRTUAL MASS EFFECT ON CONSTRAINED OSCILLATION OF OPEN SHELLS

    Directory of Open Access Journals (Sweden)

    Mr. Oleg Ye. Sysoyev  Doctor of Engineering, Professor, the Civil construction and Architecture Department, Dean of the Cadastre and Civil construction faculty, Komsomolsk-on-Amur State Technical University (Russia, Komsomolsk-on-Amur. E-mail: fks@knastu.ru.

    2016-09-01

    Full Text Available In the laboratory of constructions of Komsomolsk-on-Amur State Technical University (KnAGTU an experiment has been carried on. The aim of the experiment was to identify patterns of influence of magnitude of fluctuations in the virtual mass on constrained oscillation of open shells. Constrained oscillation of curved and open-shell carrying the virtual mass was measured with the help of induction accelerometers. Steel shell is pin supported along the edges, rectangular in the plan. Pin supported open shells along both sides, as the most frequently used in the construction have not yet been investigated. The calculation was made based on the general equation of oscillation of a shell, as well as Donnell - Mushtari - Vlasov equations. In the theoretical calculation, assumptions about the flatness were not taken into account. But it seemed that the magnitude of the stresses from bending moments are comparable in magnitude to the stress of the effort. In consequence, substantial increase in the differentiation was obtained. As a result, values of theoretical constrained oscillation of a shell were obtained. We compared the theoretical and analytical data.

  19. Singlet Molecular Oxygen on Ice: Rates of Formation and Steady State Concentrations

    Science.gov (United States)

    Bower, J. P.; Anastasio, C.

    2007-12-01

    Singlet molecular oxygen (1O2*), the first electronically excited state of molecular oxygen, reacts rapidly with certain types of environmental pollutants such as furans, phenols, and polycyclic aromatic hydrocarbons (PAHs). Its formation requires the absorption of light by a chromophore (a.k.a. sensitizer), which subsequently transfers energy to ground state molecular oxygen. In the environment, 1O2* chemistry has been studied primarily in the aqueous phase, such as in surface waters or cloud and fog drops. In this work, we expand our current understanding by investigating the rate of formation (Rf) and steady state concentration ([1O2*]) of 1O2* on ice. To investigate 1O2* kinetics, we use a chemical probe technique in which photoformed 1O2* reacts with furfuryl alcohol (FFA). To generate 1O2*, we illuminated frozen samples containing a sensitizer (Rose Bengal, RB) at 549 nm. The concentration of total solutes in each sample was controlled using sodium sulfate (Na2SO4). Following illumination, the decay of FFA was measured using high performance liquid chromatography (HPLC). Ice tests were conducted at 253, 263, and 268 K. Liquid tests for comparison were conducted at 278 K. Results showed dramatically faster (~104) FFA decay on ice than in liquid samples prepared from the same solutions, in agreement with the calculated solute concentration factor in the quasi-liquid layer (QLL) on ice compared to bulk solution. Varying the concentration of RB resulted in similar changes in both Rf and [1O2*], with magnitudes of change close to those expected. Changing temperature and total solutes, both of which control the volume of the QLL on ice, revealed two model regimes: FFA as a major (1) or minor (2) sink of 1O2*. Experimental results from the former regime show good agreement with expected values for both Rf and [1O2*]. Experiments in the later regime are currently in progress. We will also discuss the potential implications of 1O2* to the chemistry of naturally

  20. Singlet Oxygen Formation during the Charging Process of an Aprotic Lithium-Oxygen Battery.

    Science.gov (United States)

    Wandt, Johannes; Jakes, Peter; Granwehr, Josef; Gasteiger, Hubert A; Eichel, Rüdiger-A

    2016-06-06

    Aprotic lithium-oxygen (Li-O2 ) batteries have attracted considerable attention in recent years owing to their outstanding theoretical energy density. A major challenge is their poor reversibility caused by degradation reactions, which mainly occur during battery charge and are still poorly understood. Herein, we show that singlet oxygen ((1) Δg ) is formed upon Li2 O2 oxidation at potentials above 3.5 V. Singlet oxygen was detected through a reaction with a spin trap to form a stable radical that was observed by time- and voltage-resolved in operando EPR spectroscopy in a purpose-built spectroelectrochemical cell. According to our estimate, a lower limit of approximately 0.5 % of the evolved oxygen is singlet oxygen. The occurrence of highly reactive singlet oxygen might be the long-overlooked missing link in the understanding of the electrolyte degradation and carbon corrosion reactions that occur during the charging of Li-O2 cells.

  1. Generalized seniority with realistic interactions in open-shell nuclei

    CERN Document Server

    Caprio, M A; Cai, K; Constantinou, Ch; Hellemans, V

    2014-01-01

    Generalized seniority provides a truncation scheme for the nuclear shell model, based on pairing correlations, which offers the possibility of dramatically reducing the dimensionality of the nuclear shell-model problem. Systematic comparisons against results obtained in the full shell-model space are required to assess the viability of this scheme. Here, we extend recent generalized seniority calculations for semimagic nuclei, the Ca isotopes, to open-shell nuclei, with both valence protons and valence neutrons. The even-mass Ti and Cr isotopes are treated in a full major shell and with realistic interactions, in the generalized seniority scheme with one broken proton pair and one broken neutron pair. Results for level energies, orbital occupations, and electromagnetic observables are compared with those obtained in the full shell-model space. We demonstrate that, even for the Ti isotopes, significant benefit would be obtained in going beyond the approximation of one broken pair of each type, while the Cr iso...

  2. Third-Order Incremental Dual-Basis Set Zero-Buffer Approach for Large High-Spin Open-Shell Systems.

    Science.gov (United States)

    Zhang, Jun; Dolg, Michael

    2015-03-10

    The third-order incremental dual-basis set zero-buffer approach (inc3-db-B0) is an efficient, accurate, and black-box quantum chemical method for obtaining correlation energies of large systems, and it has been successfully applied to many real chemical problems. In this work, we extend this approach to high-spin open-shell systems. In the open-shell approach, we will first decompose the occupied orbitals of a system into several domains by a K-means clustering algorithm. The essential part is that we preserve the active (singly occupied) orbitals in all the calculations of the domain correlation energies. The duplicated contributions of the active orbitals to the correlation energy are subtracted from the incremental expansion. All techniques of truncating the virtual space such as the B0 approximation can be applied. This open-shell inc3-db-B0 approach is combined with the CCSD and CCSD(T) methods and applied to the computations of a singlet-triplet gap and an electron detachment process. Our approach exhibits an accuracy better than 0.6 kcal/mol or 0.3 eV compared with the standard implementation, while it saves a large amount of the computational time and can be efficiently parallelized.

  3. Critical Assessment of TD-DFT for Excited States of Open-Shell Systems: I. Doublet-Doublet Transitions.

    Science.gov (United States)

    Li, Zhendong; Liu, Wenjian

    2016-01-12

    A benchmark set of 11 small radicals is set up to assess the performance of time-dependent density functional theory (TD-DFT) for the excited states of open-shell systems. Both the unrestricted (U-TD-DFT) and spin-adapted (X-TD-DFT) formulations of TD-DFT are considered. For comparison, the well-established EOM-CCSD (equation-of-motion coupled-cluster with singles and doubles) is also used. In total, 111 low-lying singly excited doublet states are accessed by all the three approaches. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as the benchmark, it is found that both U-TD-DFT and EOM-CCSD perform well for those states dominated by singlet-coupled single excitations (SCSE) from closed-shell to open-shell, open-shell to vacant-shell, or closed-shell to vacant-shell orbitals. However, for those states dominated by triplet-coupled single excitations (TCSE) from closed-shell to vacant-shell orbitals, both U-TD-DFT and EOM-CCSD fail miserably due to severe spin contaminations. In contrast, X-TD-DFT provides balanced descriptions of both SCSE and TCSE. As far as the functional dependence is concerned, it is found that, when the Hartree-Fock ground state does not suffer from the instability problem, both global hybrid (GH) and range-separated hybrid (RSH) functionals perform grossly better than pure density functionals, especially for Rydberg and charge-transfer excitations. However, if the Hartree-Fock ground state is instable or nearly instable, GH and RSH tend to underestimate severely the excitation energies. The SAOP (statistically averaging of model orbital potentials) performs more uniformly than any other density functionals, although it generally overestimates the excitation energies of valence excitations. Not surprisingly, both EOM-CCSD and adiabatic TD-DFT are incapable of describing excited states with substantial double excitation characters.

  4. Formation of Singlet Fermion Pairs in the Dilute Gas of Boson-Fermion Mixture

    Directory of Open Access Journals (Sweden)

    Minasyan V.

    2010-10-01

    Full Text Available We argue the formation of a free neutron spinless pairs in a liquid helium -dilute neutron gas mixture. We show that the term, of the interaction between the excitations of the Bose gas and the density modes of the neutron, meditate an attractive interaction via the neutron modes, which in turn leads to a bound state on a spinless neutron pair. Due to presented theoretical approach, we prove that the electron pairs in superconductivity could be discovered by Frölich earlier then it was made by the Cooper.

  5. Formation of Singlet Fermion Pairs in the Dilute Gas of Boson-Fermion Mixture

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    Samoilov V.

    2010-10-01

    Full Text Available We argue the formation of a free neutron spinless pairs in a liquid helium -dilute neutron gas mixture. We show that the term, of the interaction between the excitations of the Bose gas and the density modes of the neutron, meditate an attractive interaction via the neutron modes, which in turn leads to a bound state on a spinless neutron pair. Due to presented theoretical approach, we prove that the electron pairs in superconductivity could be discovered by Froelich earlier then it was made by the Cooper.

  6. Caffeic Acid Inhibits the Formation of 7-Carboxyheptyl Radicals from Oleic Acid under Flavin Mononucleotide Photosensitization by Scavenging Singlet Oxygen and Quenching the Excited State of Flavin Mononucleotide

    Directory of Open Access Journals (Sweden)

    Marie Asano

    2014-08-01

    Full Text Available We examined the effects of caffeic acid (CA and related compounds on 7-carboxyheptyl radical formation. This analysis was performed using a standard D2O reaction mixture containing 4.3 mM oleic acid, 25 μM flavin mononucleotide (FMN, 160 mM phosphate buffer (pH 7.4, 10 mM cholic acid, 100 mM α-(4-pyridyl-1-oxide-N-tert-butylnitrone, and 1 mM Fe(SO42(NH42 during irradiation with 7.8 J/cm2 at 436 nm. 7-Carboxyheptyl radical formation was inhibited by CA, catechol, gallic acid, chlorogenic acid, ferulic acid, noradrenalin, 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid. Quinic acid, benzoic acid, and p-anisic acid had no effect on radical formation. These results suggest that a phenol moiety is essential for these inhibitory effects. The fluorescence intensity of FMN decreased by 69% ± 2% after CA addition, suggesting that CA quenches the singlet excited state of FMN. When 1 mM CA was added to a standard reaction mixture containing 25 μM FMN, 140 mM phosphate buffer (pH 7.4, and 10 mM 4-oxo-2,2,6,6-tetramethylpiperidine, the electron spin resonance signal of 4-oxo-2,2,6,6-tetramethylpiperidinooxy disappeared. This finding suggests that singlet oxygen was scavenged completely by CA. Therefore, CA appears to inhibit 7-carboxyheptyl radical formation by scavenging singlet oxygen and quenching the excited state of FMN.

  7. Coupled cluster valence bond theory for open-shell systems with application to very long range strong correlation in a polycarbene dimer.

    Science.gov (United States)

    Small, David W; Head-Gordon, Martin

    2017-07-14

    The Coupled Cluster Valence Bond (CCVB) method, previously presented for closed-shell (CS) systems, is extended to open-shell (OS) systems. The theoretical development is based on embedding the basic OS CCVB wavefunction in a fictitious singlet super-system. This approach reveals that the OS CCVB amplitude equations are quite similar to those of CS CCVB, and thus that OS CCVB requires the same level of computational effort as CS CCVB, which is an inexpensive method. We present qualitatively correct CCVB potential energy curves for all low-lying spin states of P2 and Mn2(+). CCVB is successfully applied to the low-lying spin states of some model linear polycarbenes, systems that appear to be a hindrance to standard density functionals. We examine an octa-carbene dimer in a side-by-side orientation, which, in the monomer dissociation limit, exhibits maximal strong correlation over the length of the polycarbene.

  8. Critical Assessment of Time-Dependent Density Functional Theory for Excited States of Open-Shell Systems: II. Doublet-Quartet Transitions.

    Science.gov (United States)

    Li, Zhendong; Liu, Wenjian

    2016-06-14

    Compared with closed-shell systems, open-shell systems place three additional challenges to time-dependent density functional theory (TD-DFT) for electronically excited states: (a) the spin-contamination problem is a serious issue; (b) the exchange-correlation (XC) kernel may be numerically instable; and (c) the single-determinant description of open-shell ground states readily becomes energetically instable. Confined to flip-up single excitations, the spin-contamination problem can largely be avoided by using the spin-flip TD-DFT (SF-TD-DFT) formalism, provided that a noncollinear XC kernel is employed. As for the numerical instabilities associated with such a kernel, only an ad hoc scheme has been proposed so far, viz., the ALDA0 kernel, which amounts to setting the divergent components (arising from density gradients and kinetic energy density) simply to zero. The ground-state instability problem can effectively be avoided by introducing the Tamm-Dancoff approximation (TDA) to TD-DFT. Therefore, on a general basis, the SF-TDA/ALDA0 Ansatz is so far the only promising means within the TD-DFT framework for flip-up single excitations of open-shell systems. To assess systematically the performance of SF-TDA/ALDA0, in total 61 low-lying quartet excited states of the benchmark set of 11 small radicals [J. Chem. Theory Comput. 2016, 12, 238] are investigated with various XC functionals. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as benchmark, it is found that the mean absolute errors of SF-TDA/ALDA0 with the SAOP (statistical averaging of model orbital potentials), global hybrid, and range-separated hybrid functionals are in the range of 0.2-0.4 eV. This is in line not only with the typical accuracy of TD-DFT for singlet and triplet excited states of closed-shell systems but also with the gross accuracy of spin-adapted TD-DFT for spin-conserving excited states of open-shell systems.

  9. Benzoylation of Ergosterol through Nucleophilic Acyl Substitution and Subsequent Formation of Ergosterol Benzoate Endoperoxide by Reaction with Singlet Oxygen Generated by Photosensitization

    Science.gov (United States)

    Roslaniec, Mary C.; Sanford, Elizabeth M.

    2011-01-01

    Reactive oxygen species such as singlet oxygen have been a major focus of research in medicine. The effect of singlet oxygen on sterols within biological membranes is becoming increasingly more important. Ergosterol, a vitamin D precursor, is one such sterol. The benzoylation of ergosterol and subsequent reaction with singlet oxygen to form an…

  10. Third-order nonlinear optical properties of open-shell supermolecular systems composed of acetylene linked phenalenyl radicals.

    Science.gov (United States)

    Nakano, Masayoshi; Kishi, Ryohei; Yoneda, Kyohei; Inoue, Yudai; Inui, Tomoya; Shigeta, Yasuteru; Kubo, Takashi; Champagne, Benoît

    2011-08-11

    toward designing a variety of open-shell NLO supermolecular systems composed of phenalenyl radical building blocks.

  11. Studies on singlet oxygen formation and UVA light-mediated photobleaching of the yellow chromophores in human lenses.

    Science.gov (United States)

    Ortwerth, Beryl J; Chemoganskiy, Vitaliy; Olesen, P R

    2002-02-01

    The protein-bound chromophores, which increase with aging in the human lens, act as UVA sensitizers, producing almost exclusively singlet oxygen in vitro. Direct irradiation of whole, aged human lenses with high intensity UVA light (200 mW cm(-2) for 24 hr), however, failed to produce singlet oxygen damage, as evidenced by the lack of either His or Trp photodestruction. Total homogenates of human lenses prepared in a cuvette under air did show destruction of His and Trp residues by UVA light, but no destruction was seen when equivalent homogenates were prepared under argon. These data are consistent with the idea that the low oxygen levels in the lens prevent singlet oxygen damage in vivo.UVA irradiation of aged human lenses in culture caused an extensive photobleaching of the yellow chromophores. A time course indicated that the photobleaching increased with time, with significant color loss apparent after 6 hr. Homogenization of the irradiated and dark control lenses in 6 M guanidine-HCl, followed by determination of the difference spectrum, showed approximately 50% bleaching of compounds with a lambda(max) at 355 nm. Similarly, fluorophores with a lambda(max) for excitation of 355 nm and for emission of 420 nm were 50% destroyed by the UVA light. Similar results were obtained in vitro by the anaerobic irradiation of a sonication-solubilized WI fraction from type II brunescent cataracts and from aged human lenses. In this system, there was an initial bleaching of 15% after 30 min of irradiation, followed by a slow increase over the next 6 hr to a final bleaching of 30%. The addition of 1.0 m M ascorbic acid, but not 1.0 m M glutathione (GSH), increased the photobleaching to 60% under argon, and the loss of ascorbate could be detected under these anaerobic conditions. In the presence of air, UVA light produced no photobleaching, but rather caused a three-fold increase in absorbance at 345 nm, which was prevented by the inclusion of 1.0 m M ascorbic acid and almost

  12. The spin-unrestricted molecular Kohn-Sham solution and the analogue of Koopmans's theorem for open-shell molecules.

    Science.gov (United States)

    Gritsenko, O V; Baerends, E J

    2004-05-08

    -electron independent-particle model for interpretation and assignment of the experimental photoelectron spectra of open-shell molecules.

  13. The {\\it ab initio} calculation of spectra of open shell diatomic molecules

    CERN Document Server

    Tennyson, Jonathan; McKemmish, Laura K; Yurchenko, Sergei N

    2016-01-01

    The spectra (rotational, rotation-vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell ($^1\\Sigma$) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbations with even larger complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an \\emph{ab initio} approach, these areas are ultracold chemistry and the astrophysics of "cool" stars, brown dwarfs and most recently extraso...

  14. Rate coefficients of open shell molecules and radicals: $R$-matrix method

    Indian Academy of Sciences (India)

    JASMEET SINGH; K L BALUJA; GAGANDEEP LONGIANY

    2017-05-01

    The open shell molecules with even number of electrons have $\\pi^2$ or $\\pi^{2}_{g}$ ground-state electronic configuration. Several homonuclear diatomic molecules like $\\rm{O_2, S_2, B_2}$ have $\\pi^{2}_{g}$ ground state in the $D_{\\infty h}$ point group and heteronuclear diatomic radicals like PH, NH, SO have $\\pi^2$ ground state in the $C_{\\infty v}$ point group. We have computed and presented here the rate coefficient of these open shell molecules $\\rm{(O_2, S_2, B_2)}$ and radicals (PH, NH,SO) from the results of our previous studies using a well-established $\\it {ab-initio}$ formalism: the $R$-matrix method. The rate coefficients for elastic and electron-excited processes are studied over a wide electron temperature range.

  15. Excited states of large open-shell molecules: an efficient, general, and spin-adapted approach based on a restricted open-shell ground state wave function.

    Science.gov (United States)

    Roemelt, Michael; Neese, Frank

    2013-04-11

    A spin-adapted configuration interaction with singles method that is based on a restricted open-shell reference function (ROCIS) with general total spin S is presented. All excited configuration state functions (CSFs) are generated with the aid of a spin-free second quantization formalism that only leads to CSFs within the first order interacting space. By virtue of the CSF construction, the formalism involves higher than singly excited determinants but not higher than singly excited configurations. Matrix elements between CSFs are evaluated on the basis of commutator relationships using a symbolic algebra program. The final equations were, however, hand-coded in order to maximize performance. The method can be applied to fairly large systems with more than 100 atoms in reasonable wall-clock times and also parallelizes well. Test calculations demonstrate that the approach is far superior to UHF-based configuration interaction with single excitations but necessarily falls somewhat short of quantitative accuracy due to the lack of dynamic correlation contributions. In order to implicitly account for dynamic correlation in a crude way, the program optionally allows for the use of Kohn-Sham orbitals in combination with a modest downscaling of two-electron integrals (DFT/ROCIS). All two-electron integrals of Kohn-Sham orbitals that appear in the Hamiltonian matrix are reduced by a total of three scaling parameters that are suitable for a wide range of molecules. Test calculations on open-shell organic radicals as well as transition metal complexes demonstrate the wide applicability of the method and its ability to calculate the electronic spectra of large molecular systems.

  16. Generalized Møller-Plesset Multiconfiguration Perturbation Theory Applied to an Open-Shell Antisymmetric Product of Strongly Orthogonal Geminals Reference Wave Function.

    Science.gov (United States)

    Tarumi, Moto; Kobayashi, Masato; Nakai, Hiromi

    2012-11-13

    The antisymmetric product of strongly orthogonal geminals (APSG) method is a wave function theory that can effectively treat the static electron correlation. Recently, we proposed the open-shell APSG method using one-electron orbitals for open-shell parts. In this paper, we have extended the perturbation correction to the open-shell APSG calculations through Møller-Plesset-type multiconfiguration perturbation theory (MP-MCPT). Numerical applications demonstrate that the present open-shell MP-MCPT can reasonably reproduce the dissociation energies or equilibrium distances for open-shell systems.

  17. The ab initio calculation of spectra of open shell diatomic molecules

    Science.gov (United States)

    Tennyson, Jonathan; Lodi, Lorenzo; McKemmish, Laura K.; Yurchenko, Sergei N.

    2016-05-01

    The spectra (rotational, rotation-vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell (1Σ ) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbed spectra of even greater complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an ab initio approach; these areas are ultracold chemistry and the astrophysics of ‘cool’ stars, brown dwarfs and most recently extrasolar planets. However, the complex electronic structure of these molecules combined with the accuracy requirements of high-resolution spectroscopy render such an approach particularly challenging. This review describes recent progress in developing methods for directly solving the effective Schrödinger equation for open-shell diatomic molecules, with a focus on molecules containing a transtion metal. It considers four aspects of the problem: (i) the electronic structure problem; (ii) non-perturbative treatments of the curve couplings; (iii) the solution of the nuclear motion Schrödinger equation; (iv) the generation of accurate electric dipole transition intensities. Examples of applications are used to illustrate these issues.

  18. Pathological behavior of the open-shell restricted self-consistent-field equations

    Energy Technology Data Exchange (ETDEWEB)

    Moscardo, F.; Alvarez-Collado, J.R.

    1979-02-01

    The possible solutions of open-shell restricted self-consistent-field equations for a doublet are studied for Li and Na atoms, according to the values of the parameters implied in those equations. A similar behavior, characterized by the presence of several variational solutions is observed in both atoms. Some of these solutions can be assigned to excited configurations. Excitation energies are in good agreement with experimental data. Doublet stability for the solutions obtained has been studied, discussing the saddle-point character present in those solutions associated to excited configurations.

  19. Ab initio Bogoliubov coupled cluster theory for open-shell nuclei

    CERN Document Server

    Signoracci, Angelo; Hagen, Gaute; Jansen, Gustav

    2014-01-01

    Ab initio many-body methods address closed-shell nuclei up to mass A ~ 130 on the basis of realistic two- and three-nucleon interactions. Several routes to address open-shell nuclei are currently under investigation, including ideas which exploit spontaneous symmetry breaking. Singly open-shell nuclei can be efficiently described via the sole breaking of $U(1)$ gauge symmetry associated with particle number conservation, to account for their superfluid character. The present work formulates and applies Bogoliubov coupled cluster (BCC) theory, which consists of representing the exact ground-state wavefunction of the system as the exponential of a quasiparticle excitation cluster operator acting on a Bogoliubov reference state. Equations for the ground-state energy and cluster amplitudes are derived at the singles and doubles level (BCCSD) both algebraically and diagrammatically. The formalism includes three-nucleon forces at the normal-ordered two-body level. The first BCC code is implemented in $m$-scheme, wh...

  20. Ab initio Bogoliubov coupled cluster theory for open-shell nuclei

    Science.gov (United States)

    Signoracci, A.; Duguet, T.; Hagen, G.; Jansen, G. R.

    2015-06-01

    Background: Ab initio many-body methods have been developed over the past 10 yr to address closed-shell nuclei up to mass A ≈130 on the basis of realistic two- and three-nucleon interactions. A current frontier relates to the extension of those many-body methods to the description of open-shell nuclei. Several routes to address open-shell nuclei are currently under investigation, including ideas that exploit spontaneous symmetry breaking. Purpose: Singly open-shell nuclei can be efficiently described via the sole breaking of U(1) gauge symmetry associated with particle-number conservation as a way to account for their superfluid character. While this route was recently followed within the framework of self-consistent Green's function theory, the goal of the present work is to formulate a similar extension within the framework of coupled cluster theory. Methods: We formulate and apply Bogoliubov coupled cluster (BCC) theory, which consists of representing the exact ground-state wave function of the system as the exponential of a quasiparticle excitation cluster operator acting on a Bogoliubov reference state. Equations for the ground-state energy and the cluster amplitudes are derived at the singles and doubles level (BCCSD) both algebraically and diagrammatically. The formalism includes three-nucleon forces at the normal-ordered two-body level. The first BCC code is implemented in m scheme, which will permit the treatment of doubly open-shell nuclei via the further breaking of SU(2) symmetry associated with angular momentum conservation. Results: Proof-of-principle calculations in an Nmax=6 spherical harmonic oscillator basis for O,1816 and 18Ne in the BCCD approximation are in good agreement with standard coupled cluster results with the same chiral two-nucleon interaction, while 20O and 20Mg display underbinding relative to experiment. The breaking of U(1) symmetry, monitored by computing the variance associated with the particle-number operator, is relatively

  1. Quantum master equation method based on the broken-symmetry time-dependent density functional theory: application to dynamic polarizability of open-shell molecular systems.

    Science.gov (United States)

    Kishi, Ryohei; Nakano, Masayoshi

    2011-04-21

    A novel method for the calculation of the dynamic polarizability (α) of open-shell molecular systems is developed based on the quantum master equation combined with the broken-symmetry (BS) time-dependent density functional theory within the Tamm-Dancoff approximation, referred to as the BS-DFTQME method. We investigate the dynamic α density distribution obtained from BS-DFTQME calculations in order to analyze the spatial contributions of electrons to the field-induced polarization and clarify the contributions of the frontier orbital pair to α and its density. To demonstrate the performance of this method, we examine the real part of dynamic α of singlet 1,3-dipole systems having a variety of diradical characters (y). The frequency dispersion of α, in particular in the resonant region, is shown to strongly depend on the exchange-correlation functional as well as on the diradical character. Under sufficiently off-resonant condition, the dynamic α is found to decrease with increasing y and/or the fraction of Hartree-Fock exchange in the exchange-correlation functional, which enhances the spin polarization, due to the decrease in the delocalization effects of π-diradical electrons in the frontier orbital pair. The BS-DFTQME method with the BHandHLYP exchange-correlation functional also turns out to semiquantitatively reproduce the α spectra calculated by a strongly correlated ab initio molecular orbital method, i.e., the spin-unrestricted coupled-cluster singles and doubles.

  2. Symmetry-adapted perturbation theory utilizing density functional description of monomers for high-spin open-shell complexes.

    Science.gov (United States)

    Zuchowski, Piotr S; Podeszwa, Rafał; Moszyński, Robert; Jeziorski, Bogumił; Szalewicz, Krzysztof

    2008-08-28

    We present an implementation of symmetry-adapted perturbation theory (SAPT) to interactions of high-spin open-shell monomers forming high-spin dimers. The monomer spin-orbitals used in the expressions for the electrostatic and exchange contributions to the interaction energy are obtained from density functional theory using a spin-restricted formulation of the open-shell Kohn-Sham (ROKS) method. The dispersion and induction energies are expressed through the density-density response functions predicted by the time-dependent ROKS theory. The method was applied to several systems: NH...He, CN...Ne, H2O...HO2, and NH...NH. It provides accuracy comparable to that of the best previously available methods such as the open-shell coupled-cluster method with single, double, and noniterative triple excitations, RCCSD(T), with a significantly reduced computational cost.

  3. Predicted Landé g-factors for open shell diatomic molecules

    Science.gov (United States)

    Semenov, Mikhail; Yurchenko, Sergei. N.; Tennyson, Jonathan

    2016-12-01

    The program DUO (Yurchenko et al., 2016) provides direct solutions of the nuclear motion Schrödinger equation for the (coupled) potential energy curves of open shell diatomic molecules. Wavefunctions from DUO are used to compute Landé g-factors valid for weak magnetic fields; the results are compared with the idealized predictions of both Hund's case (a) and Hund's case (b) coupling schemes. Test calculations are performed for AlO, NO, CrH and C2. The computed gJ 's both provide a sensitive test of the underlying spectroscopic model used to represent the system and an indication of whether states of the molecule are well-represented by the either of the Hund's cases considered. The computation of Landé g-factors is implemented as a standard option in the latest release of DUO.

  4. Infrared-dressed entanglement of cold open-shell polar molecules for universal matchgate quantum computing

    CERN Document Server

    Herrera, Felipe; Kais, Sabre; Whaley, K Birgitta

    2014-01-01

    Implementing a scalable quantum information processor using polar molecules in optical lattices requires precise control over the long-range dipole-dipole interaction between molecules in selected lattice sites. We present here a scheme using trapped open-shell $^2\\Sigma$ polar molecules that allows dipolar exchange processes between nearest and next-nearest neighbors to be controlled to construct a generalized transverse Ising spin Hamiltonian with tunable $XX$, $YY$ and $XY$ couplings in the rotating frame of the driving lasers. The scheme requires a moderately strong bias magnetic field with near-infrared light to provide local tuning of the qubit energy gap, and mid-infrared pulses to perform rotational state transfer via stimulated Raman adiabatic passage. No interaction between qubits is present in the absence of the infrared driving. We analyze the fidelity of the resulting two-qubit matchgate, and demonstrate its robustness as a function of the driving parameters. We discuss a realistic application of...

  5. Open-shell pair interaction energy decomposition analysis (PIEDA): formulation and application to the hydrogen abstraction in tripeptides.

    Science.gov (United States)

    Green, Mandy C; Fedorov, Dmitri G; Kitaura, Kazuo; Francisco, Joseph S; Slipchenko, Lyudmila V

    2013-02-21

    An open-shell extension of the pair interaction energy decomposition analysis (PIEDA) within the framework of the fragment molecular orbital (FMO) method is developed. The open-shell PIEDA method allows the analysis of inter- and intramolecular interactions in terms of electrostatic, exchange-repulsion, charge-transfer, dispersion, and optional polarization energies for molecular systems with a radical or high-spin fragment. Taking into account the low computational cost and scalability of the FMO and PIEDA methods, the new scheme provides a means to characterize the stabilization of radical and open-shell sites in biologically relevant species. The open-shell PIEDA is applied to the characterization of intramolecular interactions in capped trialanine upon hydrogen abstraction (HA) at various sites on the peptide. Hydrogen abstraction reaction is the first step in the oxidative pathway initiated by reactive oxygen or nitrogen species, associated with oxidative stress. It is found that HA results in significant geometrical reorganization of the trialanine peptide. Depending on the HA site, terminal interactions in the radical fold conformers may become weaker or stronger compared to the parent molecule, and often change the character of the non-covalent bonding from amide stacking to hydrogen bonding.

  6. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. I. Triples expansions.

    Science.gov (United States)

    Eriksen, Janus J; Matthews, Devin A; Jørgensen, Poul; Gauss, Jürgen

    2016-05-21

    The accuracy at which total energies of open-shell atoms and organic radicals may be calculated is assessed for selected coupled cluster perturbative triples expansions, all of which augment the coupled cluster singles and doubles (CCSD) energy by a non-iterative correction for the effect of triple excitations. Namely, the second- through sixth-order models of the recently proposed CCSD(T-n) triples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the acclaimed CCSD(T) model for both unrestricted as well as restricted open-shell Hartree-Fock (UHF/ROHF) reference determinants. By comparing UHF- and ROHF-based statistical results for a test set of 18 modest-sized open-shell species with comparable RHF-based results, no behavioral differences are observed for the higher-order models of the CCSD(T-n) series in their correlated descriptions of closed- and open-shell species. In particular, we find that the convergence rate throughout the series towards the coupled cluster singles, doubles, and triples (CCSDT) solution is identical for the two cases. For the CCSD(T) model, on the other hand, not only its numerical consistency, but also its established, yet fortuitous cancellation of errors breaks down in the transition from closed- to open-shell systems. The higher-order CCSD(T-n) models (orders n > 3) thus offer a consistent and significant improvement in accuracy relative to CCSDT over the CCSD(T) model, equally for RHF, UHF, and ROHF reference determinants, albeit at an increased computational cost.

  7. In-medium similarity renormalization group for closed and open-shell nuclei

    Science.gov (United States)

    Hergert, H.

    2017-02-01

    We present a pedagogical introduction to the in-medium similarity renormalization group (IMSRG) framework for ab initio calculations of nuclei. The IMSRG performs continuous unitary transformations of the nuclear many-body Hamiltonian in second-quantized form, which can be implemented with polynomial computational effort. Through suitably chosen generators, it is possible to extract eigenvalues of the Hamiltonian in a given nucleus, or drive the Hamiltonian matrix in configuration space to specific structures, e.g., band- or block-diagonal form. Exploiting this flexibility, we describe two complementary approaches for the description of closed- and open-shell nuclei: the first is the multireference IMSRG (MR-IMSRG), which is designed for the efficient calculation of nuclear ground-state properties. The second is the derivation of non-empirical valence-space interactions that can be used as input for nuclear shell model (i.e., configuration interaction (CI)) calculations. This IMSRG+shell model approach provides immediate access to excitation spectra, transitions, etc, but is limited in applicability by the factorial cost of the CI calculations. We review applications of the MR-IMSRG and IMSRG+shell model approaches to the calculation of ground-state properties for the oxygen, calcium, and nickel isotopic chains or the spectroscopy of nuclei in the lower sd shell, respectively, and present selected new results, e.g., for the ground- and excited state properties of neon isotopes.

  8. Relativistic equation-of-motion coupled-cluster method using open-shell reference wavefunction

    CERN Document Server

    Pathak, Himadri; Nayak, Malaya K; Vaval, Nayana; Pal, Sourav

    2016-01-01

    The open-shell reference relativistic equation-of-motion coupled-cluster method within its four-component description is successfully implemented with the consideration of single- and double- excitation approximation. The one-body and two-body matrix elements required for the correlation calculation are generated using Dirac-Coulomb Hamiltonian. As a first attempt, the implemented method is employed to calculate a few of the low-lying ionized states of heavy atomic (Ag, Cs, Au, Fr, Lr) and valence ionization potential of molecular (HgH, PbF) systems, where the effect of relativity does really matter to obtain highly accurate results. Not only the relativistic effect, but also the effect of electron correlation is crucial in these heavy atomic and molecular systems. To justify the fact, we have taken two further approximations in the four-component relativistic equation-of-motion framework to quantify how the effect of electron correlation plays a role in the calculated values at different level of the approxi...

  9. Time-dependent density functional methods for Raman spectra in open-shell systems.

    Science.gov (United States)

    Aquino, Fredy W; Schatz, George C

    2014-01-16

    We present an implementation of a time-dependent density functional theory (TD-DFT) linear response module in NWChem for unrestricted DFT calculations and apply it to the calculation of resonant Raman spectra in open-shell molecular systems using the short-time approximation. The new source code was validated and applied to simulate Raman spectra on several doublet organic radicals (e.g., benzyl, benzosemiquinone, TMPD, trans-stilbene anion and cation, and methyl viologen) and the metal complex copper phthalocyanine. We also introduce a divide-and-conquer approach for the evaluation of polarizabilities in relatively large systems (e.g., copper phthalocyanine). The implemented tool gives comparisons with experiment that are similar to what is commonly found for closed-shell systems, with good agreement for most features except for small frequency shifts, and occasionally large deviations for some modes that depend on the molecular system studied, experimental conditions not being accounted in the modeling such as solvation effects and extra solvent-based peaks, and approximations in the underlying theory. The approximations used in the quantum chemical modeling include (i) choice of exchange-correlation functional and basis set; (ii) harmonic approximation used in the frequency analysis to determine vibrational normal modes; and (iii) short-time approximation (omission of nuclear motion effects) used in calculating resonant Raman spectra.

  10. Time-dependent density functional theory for nonlinear properties of open-shell systems.

    Science.gov (United States)

    Rinkevicius, Zilvinas; Jha, Prakash Chandra; Oprea, Corneliu I; Vahtras, Olav; Agren, Hans

    2007-09-21

    This paper presents response theory based on a spin-restricted Kohn-Sham formalism for computation of time-dependent and time-independent nonlinear properties of molecules with a high spin ground state. The developed approach is capable to handle arbitrary perturbations and constitutes an efficient procedure for evaluation of electric, magnetic, and mixed properties. Apart from presenting the derivation of the proposed approach, we show results from illustrating calculations of static and dynamic hyperpolarizabilities of small Si(3n+1)H(6n+3) (n=0,1,2) clusters which mimic Si(111) surfaces with dangling bond defects. The results indicate that the first hyperpolarizability tensor components of Si(3n+1)H(6n+3) have an ordering compatible with the measurements of second harmonic generation in SiO2/Si(111) interfaces and, therefore, support the hypothesis that silicon surface defects with dangling bonds are responsible for this phenomenon. The results exhibit a strong dependence on the quality of basis set and exchange-correlation functional, showing that an appropriate set of diffuse functions is required for reliable predictions of the first hyperpolarizability of open-shell compounds.

  11. In-Medium Similarity Renormalization Group for Closed and Open-Shell Nuclei

    CERN Document Server

    Hergert, H

    2016-01-01

    We present a pedagogical introduction to the In-Medium Similarity Renormalization Group (IM-SRG) framework for ab initio calculations of nuclei. The IM-SRG performs continuous unitary transformations of the nuclear many-body Hamiltonian in second-quantized form, which can be implemented with polynomial computational effort. Through suitably chosen generators, it is possible to extract eigenvalues of the Hamiltonian in a given nucleus, or drive the Hamiltonian matrix in configuration space to specific structures, e.g., band- or block-diagonal form. Exploiting this flexibility, we describe two complementary approaches for the description of closed- and open-shell nuclei: The first is the Multireference IM-SRG (MR-IM-SRG), which is designed for the efficient calculation of nuclear ground-state properties. The second is the derivation of nonempirical valence-space interactions that can be used as input for nuclear Shell model (i.e., configuration interaction (CI)) calculations. This IM-SRG+Shell model approach pr...

  12. The nature of singlet exciton fission in carotenoid aggregates.

    Science.gov (United States)

    Musser, Andrew J; Maiuri, Margherita; Brida, Daniele; Cerullo, Giulio; Friend, Richard H; Clark, Jenny

    2015-04-22

    Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission.

  13. Exciton Correlations in Intramolecular Singlet Fission.

    Science.gov (United States)

    Sanders, Samuel N; Kumarasamy, Elango; Pun, Andrew B; Appavoo, Kannatassen; Steigerwald, Michael L; Campos, Luis M; Sfeir, Matthew Y

    2016-06-15

    We have synthesized a series of asymmetric pentacene-tetracene heterodimers with a variable-length conjugated bridge that undergo fast and efficient intramolecular singlet fission (iSF). These compounds have distinct singlet and triplet energies, which allow us to study the spatial dynamics of excitons during the iSF process, including the significant role of exciton correlations in promoting triplet pair generation and recombination. We demonstrate that the primary photoexcitations in conjugated dimers are delocalized singlets that enable fast and efficient iSF. However, in these asymmetric dimers, the singlet becomes more localized on the lower energy unit as the length of the bridge is increased, slowing down iSF relative to analogous symmetric dimers. We resolve the recombination kinetics of the inequivalent triplets produced via iSF, and find that they primarily decay via concerted processes. By identifying different decay channels, including delayed fluorescence via triplet-triplet annihilation, we can separate transient species corresponding to both correlated triplet pairs and uncorrelated triplets. Recombination of the triplet pair proceeds rapidly despite our experimental and theoretical demonstration that individual triplets are highly localized and unable to be transported across the conjugated linker. In this class of compounds, the rate of formation and yield of uncorrelated triplets increases with bridge length. Overall, these constrained, asymmetric systems provide a unique platform to isolate and study transient species essential for singlet fission, which are otherwise difficult to observe in symmetric dimers or condensed phases.

  14. Communication: Spin densities within a unitary group based spin-adapted open-shell coupled-cluster theory: Analytic evaluation of isotropic hyperfine-coupling constants for the combinatoric open-shell coupled-cluster scheme

    Energy Technology Data Exchange (ETDEWEB)

    Datta, Dipayan, E-mail: datta.dipayan@gmail.com; Gauss, Jürgen, E-mail: gauss@uni-mainz.de [Institut für Physikalische Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, D-55128 Mainz (Germany)

    2015-07-07

    We report analytical calculations of isotropic hyperfine-coupling constants in radicals using a spin-adapted open-shell coupled-cluster theory, namely, the unitary group based combinatoric open-shell coupled-cluster (COSCC) approach within the singles and doubles approximation. A scheme for the evaluation of the one-particle spin-density matrix required in these calculations is outlined within the spin-free formulation of the COSCC approach. In this scheme, the one-particle spin-density matrix for an open-shell state with spin S and M{sub S} = + S is expressed in terms of the one- and two-particle spin-free (charge) density matrices obtained from the Lagrangian formulation that is used for calculating the analytic first derivatives of the energy. Benchmark calculations are presented for NO, NCO, CH{sub 2}CN, and two conjugated π-radicals, viz., allyl and 1-pyrrolyl in order to demonstrate the performance of the proposed scheme.

  15. Endohedral metallofullerenes, M@C60 (M = Ca, Na, Sr): selective adsorption and sensing of open-shell NOx gases.

    Science.gov (United States)

    Tawfik, Sherif Abdulkader; Cui, X Y; Ringer, S P; Stampfl, C

    2016-08-21

    Based on density-functional theory and non-equilibrium Green's function calculations, we demonstrate that endohedral metallofullerenes (EMFs) are reactive to open-shell gases, and therefore have the potential application as selective open-shell gas sensors. The adsorption of eight gas species (CO, H2O, H2S, NO2, NO, SO2, O2 and NH3) on three EMFs (M@C60, M = Ca, Na and Sr) shows that the adsorption energies of the EMFs towards NO2 and NO are significantly higher than the closed-shell species. Moreover, the high selectivity appears relatively insensitive to the inserted metal atoms. The calculated current-voltage characteristics of gold-M@C60-gold structures (M = Ca, Na) show that the adsorption of NO2 leads to significant change in conductivity, suggesting a potential application as an EMF gas resistive sensing device.

  16. Second-order Møller-Plesset perturbation theory without basis set superposition error. II. Open-shell systems.

    Science.gov (United States)

    Salvador, P; Mayer, I

    2004-04-01

    The basis set superposition error-free second-order Møller-Plesset perturbation theory of intermolecular interactions, based on the "chemical Hamiltonian approach," which has been introduced in Part I, is applied here to open-shell systems by using a new, effective computer realization. The results of the numerical examples considered (CH(4) em leader HO, NO em leader HF) showed again the perfect performance of the method. Striking agreement has again been found with the results of the a posteriori counterpoise correction (CP) scheme in the case of large, well-balanced basis sets, which is also in agreement with a most recent formal theoretical analysis. The difficulties of the CP correction in open-shell systems are also discussed.

  17. Restricted open-shell Kohn-Sham theory for π-π* transitions. I. Polyenes, cyanines, and protonated imines

    Science.gov (United States)

    Grimm, Stephan; Nonnenberg, Christel; Frank, Irmgard

    2003-12-01

    We present a self-consistent field algorithm for the restricted open-shell Kohn-Sham method which can be used to calculate excited states that have the same spatial symmetry as the corresponding ground states. The method is applied to π-π* transitions in polyenes, cyanines, and protonated imines. Excitation energies obtained with gradient corrected functionals are found to be significantly redshifted; the shift is constant within a homologous series. Planar excited state geometries have been optimized for all systems.

  18. Density functional theory embedding for correlated wavefunctions: improved methods for open-shell systems and transition metal complexes.

    Science.gov (United States)

    Goodpaster, Jason D; Barnes, Taylor A; Manby, Frederick R; Miller, Thomas F

    2012-12-14

    Density functional theory (DFT) embedding provides a formally exact framework for interfacing correlated wave-function theory (WFT) methods with lower-level descriptions of electronic structure. Here, we report techniques to improve the accuracy and stability of WFT-in-DFT embedding calculations. In particular, we develop spin-dependent embedding potentials in both restricted and unrestricted orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and develop an orbital-occupation-freezing technique to improve the convergence of optimized effective potential calculations that arise in the evaluation of the embedding potential. The new techniques are demonstrated in applications to the van-der-Waals-bound ethylene-propylene dimer and to the hexa-aquairon(II) transition-metal cation. Calculation of the dissociation curve for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating errors in the dispersion interactions due to conventional exchange-correlation (XC) functionals while simultaneously avoiding errors due to subsystem partitioning across covalent bonds. Application of WFT-in-DFT embedding to the calculation of the low-spin/high-spin splitting energy in the hexaaquairon(II) cation reveals that the majority of the dependence on the DFT XC functional can be eliminated by treating only the single transition-metal atom at the WFT level; furthermore, these calculations demonstrate the substantial effects of open-shell contributions to the embedding potential, and they suggest that restricted open-shell WFT-in-DFT embedding provides better accuracy than unrestricted open-shell WFT-in-DFT embedding due to the removal of spin contamination.

  19. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. I. Triples expansions

    CERN Document Server

    Eriksen, Janus Juul; Jørgensen, Poul; Gauss, Jürgen

    2015-01-01

    The accuracy with which total energies of open-shell species may be calculated using coupled cluster perturbative triples expansions is investigated. In particular, the acclaimed CCSD(T) model, in which a non-iterative correction for the effect of triple excitations is added to the coupled cluster singles and doubles (CCSD) energy, is compared to the second- through sixth-order models of the recently proposed CCSD(T-n) triples series for both unrestricted as well as restricted open-shell Hartree-Fock (UHF/ROHF) reference determinants. By comparing UHF- and ROHF-based statistical results for a test set of 18 atoms and small radicals with comparable RHF-based results, it is found that not only the numerical consistency of the CCSD(T) model, but also its fortuitous cancellation of errors for closed-shell systems break down in the transition from closed- to open-shell systems. For the higher-order models of the CCSD(T-n) series, however, no behavioral differences are found between the correlated descriptions of c...

  20. Role of a singlet diradical character in carbon nanomaterials: a novel hot spot for efficient nonlinear optical materials.

    Science.gov (United States)

    Muhammad, Shabbir; Nakano, Masayoshi; Al-Sehemi, Abdullah G; Kitagawa, Yasutaka; Irfan, Ahmad; Chaudhry, Aijaz R; Kishi, Ryohei; Ito, Soichi; Yoneda, Kyohei; Fukuda, Kotaro

    2016-10-27

    Carbon atoms have the potential to produce a variety of fascinating all-carbon structures with amazing electronic and mechanical properties. Over the last few decades, several efforts have been made using experimental and computational techniques to functionalize graphene, carbon nanotubes and fullerenes for potential use in modern hi-tech electronic, medicinal, optical and nonlinear optical (NLO) applications. Since photons replaced electrons as a carrier of information, the field of NLO material design has drawn immense interest in contemporary materials science. There have been several reports of bridging the gap between the exciting fields of carbon nanomaterials and NLO materials by functionalizing carbon nanomaterials for potential NLO applications. In contrast to previous reports of the design of third-order NLO materials using conventional closed-shell materials, a novel strategy using open-shell diradical molecular systems has recently been proposed. Quantum chemically, diradical character is explained in terms of the instability of the chemical bonds in open-shell molecular systems. Interestingly, several carbon nanomaterials, which naturally possess open-shell singlet configurations, have recently gained momentum in the design of these classes of open-shell NLO materials with excellent NLO properties, stability and diversity. The present review establishes a systematic sequence of different studies (spanning over two decades of intense research efforts), starting from the simplest theoretical two-site diradical model, continuing to its experimental and theoretical realization in actual chemical systems, and finally applying the abovementioned model/rule to novel carbon nanomaterials to tune their NLO properties, particularly their second hyperpolarizability (γ). In the present report, we highlight several recent efforts to functionalize carbon nanomaterials by exploiting their open-shell diradical character to achieve efficient third-order NLO

  1. Long-range corrected density functional theory study on static second hyperpolarizabilities of singlet diradical systems.

    Science.gov (United States)

    Kishi, Ryohei; Bonness, Sean; Yoneda, Kyohei; Takahashi, Hideaki; Nakano, Masayoshi; Botek, Edith; Champagne, Benoît; Kubo, Takashi; Kamada, Kenji; Ohta, Koji; Tsuneda, Takao

    2010-03-07

    Within the spin-unrestricted density functional theory (DFT) the long-range correction (LC) scheme combined with the Becke-Lee-Yang-Parr exchange-correlation functional, referred to as LC-UBLYP method, has been applied to the calculation of the second hyperpolarizability (gamma) of open-shell singlet diradical systems of increasing complexity and has demonstrated good performance: (i) for the simplest H(2) dissociation model, the gamma values calculated by the LC-UBLYP method significantly overshoot the full configuration interaction result but reproduce qualitatively the evolution of gamma as a function of the diradical character, (ii) for small singlet diradical 1,3-dipole systems, the diradical character dependence of gamma determined by the UCCSD and UCCSD(T) reference methods is reproduced semiquantitatively by the LC-UBLYP method except in the small diradical character region, where the spin-unrestricted solutions coincide with spin-restricted solutions, (iii) the LC-UBLYP method also closely reproduces the UCCSD(T) results on the diradical character dependence of gamma of the p-quinodimethane model system, particularly in the intermediate and large diradical character regions, whereas it shows an abrupt change for a diradical character (y) close to 0.2 originating from the triplet instability, (iv) the reliability of LC-UBLYP to reproduce reference coupled cluster results on open-shell singlet systems with intermediate and large diradical characters has also been substantiated in the case of gamma of 1,4-bis-(imidazol-2-ylidene)-cyclohexa-2,5-diene (BI2Y), then (v), for real systems built from a pair of phenalenyl radicals separated by a conjugated linker, the LC-UBLYP results have been found to closely match the UBHandHLYP values-which, for small systems are in good agreement with those obtained using correlated molecular orbital methods-whereas the UB3LYP results can be much different. These results are not only important from the viewpoint of an efficient

  2. Spin-orbit coupling mechanism of singlet oxygen a1Δg quenching by solvent vibrations

    Science.gov (United States)

    Minaev, B. F.

    2017-02-01

    Degenerate character of the O2(a1Δg) state and of the charge-transfer configurations (CTCs) from solvent to the oxygen open-shell orbitals explains the enhancement of spin-orbit coupling (SOC) which is necessary to overcome spin prohibition during singlet oxygen a1Δg quenching. The former mechanism of non-radiative transition O2(a1Δg) → O2(X3 Σg-) based on electronic energy transfer to the solvent vibrational levels (e-v mechanism) is supplemented here by explicit analysis of SOC effects mediated by solvent and O2 vibrations. The SOC matrix element between one component of the initial electronic excited singlet a1Δg state and the final ground triplet X3 Σg- state in the oxygen moiety is not equal to zero (as in free O2) in the collision complex with solvent molecule (M) when all possible CTCs of the type O2- …M+ are accounted for. Intermolecular configuration interaction between CTC and locally excited states obeys a simple symmetry selection rule which provides finally the SOC matrix element with a guarantee of large orbital rotation around the molecular oxygen axis creating a torque. The CTCs admixtures into the singlet and triplet wave functions in the collision complex O2…M ensure the SOC enhancement inside the O2 moiety and let the spin-prohibited singlet oxygen a1Δg quenching to become effectively allowed in terms of e-v mechanism. In the new model the solvent is not only a passive "sink" for the singlet oxygen excitation energy but serves as an active perturber of the oxygen open shell and finally - of the whole spin dynamics in the collision system.

  3. Singlet oxygen production in the reaction of superoxide with organic peroxides.

    Science.gov (United States)

    MacManus-Spencer, Laura A; Edhlund, Betsy L; McNeill, Kristopher

    2006-01-20

    [reaction: see text] A selective chemiluminescent probe for singlet oxygen has been employed to detect and quantify singlet oxygen in the reactions of superoxide with organic peroxides. The production of singlet oxygen has been quantified in the reaction of superoxide with benzoyl peroxide (BP). No singlet oxygen was detected in the reactions of superoxide with cumyl peroxide, tert-butyl peroxide, or tert-butyl hydroperoxide. On the basis of these results and on the temperature dependence of the reaction, we proposed a mechanism for singlet oxygen formation in the reaction of superoxide with BP.

  4. Singlet Ground State Magnetism:

    DEFF Research Database (Denmark)

    Loidl, A.; Knorr, K.; Kjems, Jørgen;

    1979-01-01

    The magneticGamma 1 –Gamma 4 exciton of the singlet ground state system TbP has been studied by inelastic neutron scattering above the antiferromagnetic ordering temperature. Considerable dispersion and a pronounced splitting was found in the [100] and [110] directions. Both the band width...... and the splitting increased rapidly as the transition temperature was approached in accordance with the predictions of the RPA-theory. The dispersion is analysed in terms of a phenomenological model using interactions up to the fourth nearest neighbour....

  5. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions

    Science.gov (United States)

    Eriksen, Janus J.; Matthews, Devin A.; Jørgensen, Poul; Gauss, Jürgen

    2016-05-01

    We extend our assessment of the potential of perturbative coupled cluster (CC) expansions for a test set of open-shell atoms and organic radicals to the description of quadruple excitations. Namely, the second- through sixth-order models of the recently proposed CCSDT(Q-n) quadruples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the prominent CCSDT(Q) and ΛCCSDT(Q) models. From a comparison of the models in terms of their recovery of total CC singles, doubles, triples, and quadruples (CCSDTQ) energies, we find that the performance of the CCSDT(Q-n) models is independent of the reference used (unrestricted or restricted (open-shell) Hartree-Fock), in contrast to the CCSDT(Q) and ΛCCSDT(Q) models, for which the accuracy is strongly dependent on the spin of the molecular ground state. By further comparing the ability of the models to recover relative CCSDTQ total atomization energies, the discrepancy between them is found to be even more pronounced, stressing how a balanced description of both closed- and open-shell species—as found in the CCSDT(Q-n) models—is indeed of paramount importance if any perturbative CC model is to be of chemical relevance for high-accuracy applications. In particular, the third-order CCSDT(Q-3) model is found to offer an encouraging alternative to the existing choices of quadruples models used in modern computational thermochemistry, since the model is still only of moderate cost, albeit markedly more costly than, e.g., the CCSDT(Q) and ΛCCSDT(Q) models.

  6. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions.

    Science.gov (United States)

    Eriksen, Janus J; Matthews, Devin A; Jørgensen, Poul; Gauss, Jürgen

    2016-05-21

    We extend our assessment of the potential of perturbative coupled cluster (CC) expansions for a test set of open-shell atoms and organic radicals to the description of quadruple excitations. Namely, the second- through sixth-order models of the recently proposed CCSDT(Q-n) quadruples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the prominent CCSDT(Q) and ΛCCSDT(Q) models. From a comparison of the models in terms of their recovery of total CC singles, doubles, triples, and quadruples (CCSDTQ) energies, we find that the performance of the CCSDT(Q-n) models is independent of the reference used (unrestricted or restricted (open-shell) Hartree-Fock), in contrast to the CCSDT(Q) and ΛCCSDT(Q) models, for which the accuracy is strongly dependent on the spin of the molecular ground state. By further comparing the ability of the models to recover relative CCSDTQ total atomization energies, the discrepancy between them is found to be even more pronounced, stressing how a balanced description of both closed- and open-shell species-as found in the CCSDT(Q-n) models-is indeed of paramount importance if any perturbative CC model is to be of chemical relevance for high-accuracy applications. In particular, the third-order CCSDT(Q-3) model is found to offer an encouraging alternative to the existing choices of quadruples models used in modern computational thermochemistry, since the model is still only of moderate cost, albeit markedly more costly than, e.g., the CCSDT(Q) and ΛCCSDT(Q) models.

  7. Efficient and accurate local single reference correlation methods for high-spin open-shell molecules using pair natural orbitals

    Science.gov (United States)

    Hansen, Andreas; Liakos, Dimitrios G.; Neese, Frank

    2011-12-01

    A production level implementation of the high-spin open-shell (spin unrestricted) single reference coupled pair, quadratic configuration interaction and coupled cluster methods with up to doubly excited determinants in the framework of the local pair natural orbital (LPNO) concept is reported. This work is an extension of the closed-shell LPNO methods developed earlier [F. Neese, F. Wennmohs, and A. Hansen, J. Chem. Phys. 130, 114108 (2009), 10.1063/1.3086717; F. Neese, A. Hansen, and D. G. Liakos, J. Chem. Phys. 131, 064103 (2009), 10.1063/1.3173827]. The internal space is spanned by localized orbitals, while the external space for each electron pair is represented by a truncated PNO expansion. The laborious integral transformation associated with the large number of PNOs becomes feasible through the extensive use of density fitting (resolution of the identity (RI)) techniques. Technical complications arising for the open-shell case and the use of quasi-restricted orbitals for the construction of the reference determinant are discussed in detail. As in the closed-shell case, only three cutoff parameters control the average number of PNOs per electron pair, the size of the significant pair list, and the number of contributing auxiliary basis functions per PNO. The chosen threshold default values ensure robustness and the results of the parent canonical methods are reproduced to high accuracy. Comprehensive numerical tests on absolute and relative energies as well as timings consistently show that the outstanding performance of the LPNO methods carries over to the open-shell case with minor modifications. Finally, hyperfine couplings calculated with the variational LPNO-CEPA/1 method, for which a well-defined expectation value type density exists, indicate the great potential of the LPNO approach for the efficient calculation of molecular properties.

  8. Singlet and triplet instability theorems

    Science.gov (United States)

    Yamada, Tomonori; Hirata, So

    2015-09-01

    A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree-Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree-Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree-Fock-theory-based explanations of Hund's rule, a singlet instability in Jahn-Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions.

  9. Nuclear-electronic orbital reduced explicitly correlated Hartree-Fock approach: Restricted basis sets and open-shell systems

    Science.gov (United States)

    Brorsen, Kurt R.; Sirjoosingh, Andrew; Pak, Michael V.; Hammes-Schiffer, Sharon

    2015-06-01

    The nuclear electronic orbital (NEO) reduced explicitly correlated Hartree-Fock (RXCHF) approach couples select electronic orbitals to the nuclear orbital via Gaussian-type geminal functions. This approach is extended to enable the use of a restricted basis set for the explicitly correlated electronic orbitals and an open-shell treatment for the other electronic orbitals. The working equations are derived and the implementation is discussed for both extensions. The RXCHF method with a restricted basis set is applied to HCN and FHF- and is shown to agree quantitatively with results from RXCHF calculations with a full basis set. The number of many-particle integrals that must be calculated for these two molecules is reduced by over an order of magnitude with essentially no loss in accuracy, and the reduction factor will increase substantially for larger systems. Typically, the computational cost of RXCHF calculations with restricted basis sets will scale in terms of the number of basis functions centered on the quantum nucleus and the covalently bonded neighbor(s). In addition, the RXCHF method with an odd number of electrons that are not explicitly correlated to the nuclear orbital is implemented using a restricted open-shell formalism for these electrons. This method is applied to HCN+, and the nuclear densities are in qualitative agreement with grid-based calculations. Future work will focus on the significance of nonadiabatic effects in molecular systems and the further enhancement of the NEO-RXCHF approach to accurately describe such effects.

  10. Two-dimensional Penning ionization electron spectroscopy of open-shell metallocenes: outer valence ionic states of vanadocene and nickelocene.

    Science.gov (United States)

    Kishimoto, Naoki; Kimura, Miku; Ohno, Koichi

    2013-04-11

    In order to investigate outer valence ionic states of open-shell metallocenes, we have applied two-dimensional collision-energy/electron-energy-resolved Penning ionization electron spectroscopy (2D-PIES) upon collision with metastable He*(2(3)S) excited atoms as well as a high level ab initio molecular orbital calculation (the partial third-order quasiparticle theory of the electron propagator (P3)) to ionization from neutral ground states of vanadocene ((4)A2g) and nickelocene ((3)A2g). Assignments of observed Penning ionization electron/He I ultraviolet photoelectron spectra were consistent with the P3 calculation results for ionization of α and β spin electrons except for electron correlation bands observed by PIES. Negative collision energy dependence of partial Penning ionization cross-sections (CEDPICS) indicate attractive interaction with He*(2(3)S) around the molecule. Results by model potential calculation utilizing Li(2(2)S) instead of He*(2(3)S) for interaction between He*(2(3)S) and open-shell metallocenes do not explain the strong negative CEDPICS of the bands observed in PIES.

  11. Electronic fine structure calculation of metal complexes with three-open-shell s, d, and p configurations.

    Science.gov (United States)

    Ramanantoanina, Harry; Daul, Claude

    2017-08-01

    The ligand field density functional theory (LFDFT) algorithm is extended to treat the electronic structure and properties of systems with three-open-shell electron configurations, exemplified in this work by the calculation of the core and semi-core 1s, 2s, and 3s one-electron excitations in compounds containing transition metal ions. The work presents a model to non-empirically resolve the multiplet energy levels arising from the three-open-shell systems of non-equivalent ns, 3d, and 4p electrons and to calculate the oscillator strengths corresponding to the electric-dipole 3d (m)  → ns (1)3d (m) 4p (1) transitions, with n = 1, 2, 3 and m = 0, 1, 2, …, 10 involved in the s electron excitation process. Using the concept of ligand field, the Slater-Condon integrals, the spin-orbit coupling constants, and the parameters of the ligand field potential are determined from density functional theory (DFT). Therefore, a theoretical procedure using LFDFT is established illustrating the spectroscopic details at the atomic scale that can be valuable in the analysis and characterization of the electronic spectra obtained from X-ray absorption fine structure or electron energy loss spectroscopies.

  12. Search for Singlet Fission Chromophores

    Energy Technology Data Exchange (ETDEWEB)

    Havlas, Z.; Akdag, A.; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, J.

    2012-01-01

    Singlet fission, in which a singlet excited chromophore shares its energy with a ground-state neighbor and both end up in their triplet states, is of potential interest for solar cells. Only a handful of compounds, mostly alternant hydrocarbons, are known to perform efficiently. In view of the large number of conditions that a successful candidate for a practical cell has to meet, it appears desirable to extend the present list of high performers to additional classes of compounds. We have (i) identified design rules for new singlet fission chromophores and for their coupling to covalent dimers, (ii) synthesized them, and (iii) evaluated their performance as neat solids or covalent dimers.

  13. Ground and excited states of doubly open-shell nuclei from ab initio valence-space Hamiltonians

    CERN Document Server

    Stroberg, S R; Holt, J D; Bogner, S K; Schwenk, A

    2015-01-01

    We present ab initio predictions for ground and excited states of doubly open-shell fluorine and neon isotopes based on chiral two- and three-nucleon interactions. We use the in-medium similarity renormalization group, in both flow-equation and Magnus formulations, to derive mass-dependent sd valence-space Hamiltonians. The experimental ground-state energies are reproduced through neutron number N=14, beyond which a new targeted normal-ordering procedure improves agreement with data and large-scale multi-reference calculations. For spectroscopy, we focus on neutron-rich 23-26F and 24-26Ne isotopes near N=14,16 magic numbers. In all cases we find an agreement with experiment competitive with established phenomenology. Moreover, yrast states are well described in 20Ne and 24Mg, providing an ab initio description of deformation in the medium-mass region.

  14. Singlet oxygen treatment of tumor cells triggers extracellular singlet oxygen generation, catalase inactivation and reactivation of intercellular apoptosis-inducing signaling.

    Science.gov (United States)

    Riethmüller, Michaela; Burger, Nils; Bauer, Georg

    2015-12-01

    Intracellular singlet oxygen generation in photofrin-loaded cells caused cell death without discrimination between nonmalignant and malignant cells. In contrast, extracellular singlet oxygen generation caused apoptosis induction selectively in tumor cells through singlet oxygen-mediated inactivation of tumor cell protective catalase and subsequent reactivation of intercellular ROS-mediated apoptosis signaling through the HOCl and the NO/peroxynitrite signaling pathway. Singlet oxygen generation by extracellular photofrin alone was, however, not sufficient for optimal direct inactivation of catalase, but needed to trigger the generation of cell-derived extracellular singlet oxygen through the interaction between H2O2 and peroxynitrite. Thereby, formation of peroxynitrous acid, generation of hydroxyl radicals and formation of perhydroxyl radicals (HO2(.)) through hydroxyl radical/H2O2 interaction seemed to be required as intermediate steps. This amplificatory mechanism led to the formation of singlet oxygen at a sufficiently high concentration for optimal inactivation of membrane-associated catalase. At low initial concentrations of singlet oxygen, an additional amplification step needed to be activated. It depended on singlet oxygen-dependent activation of the FAS receptor and caspase-8, followed by caspase-8-mediated enhancement of NOX activity. The biochemical mechanisms described here might be considered as promising principle for the development of novel approaches in tumor therapy that specifically direct membrane-associated catalase of tumor cells and thus utilize tumor cell-specific apoptosis-inducing ROS signaling.

  15. MOLECULAR OPEN-SHELL CONFIGURATION-INTERACTION CALCULATIONS USING THE DIRAC-COULOMB HAMILTONIAN - THE F6-MANIFOLD OF AN EMBEDDED EUO69- CLUSTER

    NARCIS (Netherlands)

    VISSER, O; VISSCHER, L; AERTS, PJC; NIEUWPOORT, WC

    1992-01-01

    We present results of all-electron molecular relativistic (Hartree-Fock-Dirac) and nonrelativistic (Hartree-Fock) calculations followed by a complete open shell configuration interaction (COSCI) calculation on an EuO6(9-) cluster in a Ba2GdNbO6 crystal. The results include the calculated energies of

  16. MOLECULAR OPEN-SHELL CONFIGURATION-INTERACTION CALCULATIONS USING THE DIRAC-COULOMB HAMILTONIAN - THE F6-MANIFOLD OF AN EMBEDDED EUO69- CLUSTER

    NARCIS (Netherlands)

    VISSER, O; VISSCHER, L; AERTS, PJC; NIEUWPOORT, WC

    1992-01-01

    We present results of all-electron molecular relativistic (Hartree-Fock-Dirac) and nonrelativistic (Hartree-Fock) calculations followed by a complete open shell configuration interaction (COSCI) calculation on an EuO6(9-) cluster in a Ba2GdNbO6 crystal. The results include the calculated energies of

  17. Binding of oxygen with titanium dioxide on singlet potential energy surface: An ab initio investigation

    Science.gov (United States)

    Bogdanchikov, Georgii A.; Baklanov, Alexey V.

    2017-01-01

    Ab initio calculations have been carried out to investigate interaction of titanium dioxide TiO2 with oxygen O2 in ground triplet and excited singlet states. On a singlet potential energy surface (PES) formation of a stable compound of titanium peroxide TiO4 is revealed which should appear in reaction of TiO2 with singlet oxygen without activation barrier. This peroxide is lower in energy than the ground state of two individual molecules TiO2 + 3O2 by 34.6 kcal/mol. Location of conical intersection between triplet and singlet PESs of TiO2sbnd O2 is also investigated.

  18. 1,3-Diphenylisobenzofuran: a Model Chromophore for Singlet Fission

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Justin C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Michl, Josef [University of Colorado; Academy of Sciences of the Czech Republic

    2017-09-11

    In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The highest quantum yield of triplet formation by singlet fission, 200% at 80 K, is found in one of the two known crystal modification of the parent. In the other modification and in many derivatives, excimer formation competes successfully and triplet yields are low. A description of solution photophysics of covalent dimers is described in the next section. Triplet yields are very low, but interesting phenomena are uncovered. One is an observation of a separated-charges (charge-transfer) intermediate in highly polar solvents. The other is an observation of excitation isomerism in both singlet and triplet states, where in one isomer the excitation is delocalized over both halves of the covalent dimer, whereas in the other it is localized on one of the halves. In the last section we present the operation of a simple device illustrating the use of triplets generated by singlet fission for charge separation.

  19. Differential magnetometry with multiparticle singlets

    CERN Document Server

    Urizar-Lanz, Inigo; Egusquiza, Inigo; Mitchell, Morgan W; Toth, Geza

    2012-01-01

    We present a method for measuring the magnetic field gradient with singlets realized with spin-1/2 particles. While the singlet state does not change under the influence of homogenous magnetic fields, the variance of the collective spin components start to grow under a field gradient. We compute the dynamics of this variance analytically for a chain of spins and also for an ensemble of particles with a given density distribution. We calculate an upper bound on how exactly the field gradient can be estimated from the measured data. The proposal is relevant for cold atomic ensembles where multiparticle singlet states can be prepared by spin squeezing and the differential magnetometry can be carried out.

  20. Dibenzoheptazethrene isomers with different biradical characters: An exercise of clar's aromatic sextet rule in singlet biradicaloids

    KAUST Repository

    Sun, Zhe

    2013-12-04

    Clar\\'s aromatic sextet rule has been widely used for the prediction of the reactivity and stability of polycyclic aromatic hydrocarbons with a closed-shell electronic configuration. Recent advances in open-shell biradicaloids have shown that the number of aromatic sextet rings plays an important role in determination of their ground states. In order to test the validity of this rule in singlet biradicaloids, the two soluble and stable dibenzoheptazethrene isomers DBHZ1 and DBHZ2 were prepared by different synthetic approaches and isolated in crystalline form. These two molecules have different numbers of aromatic sextet rings in their respective biradical resonance forms and thus are expected to exhibit varied singlet biradical character. This assumption was verified by different experimental methods, including nuclear magnetic resonance (NMR), electron spin resonance (ESR), superconducting quantum interference device (SQUID), steady-state and transient absorption spectroscopy (TA), and X-ray crystallographic analysis, assisted by unrestricted symmetry-broken density functional theory (DFT) calculations. DBHZ2, with more aromatic sextet rings in the biradical form, was demonstrated to possess greater biradical character than DBHZ1; as a result, DBHZ2 exhibited an intense one-photon absorption (OPA) in the near-infrared region (λabs max = 804 nm) and a large two-photon absorption (TPA) cross-section (σ(2)max = 2800 GM at 1600 nm). This investigation together with previous studies indicates that Clar\\'s aromatic sextet rule can be further extended to the singlet biradicaloids to predict their ground states and singlet biradical characters. © 2013 American Chemical Society.

  1. Relativistic equation-of-motion coupled-cluster method using open-shell reference wavefunction: Application to ionization potential

    Science.gov (United States)

    Pathak, Himadri; Sasmal, Sudip; Nayak, Malaya K.; Vaval, Nayana; Pal, Sourav

    2016-08-01

    The open-shell reference relativistic equation-of-motion coupled-cluster method within its four-component description is successfully implemented with the consideration of single- and double- excitation approximations using the Dirac-Coulomb Hamiltonian. At the first attempt, the implemented method is employed to calculate ionization potential value of heavy atomic (Ag, Cs, Au, Fr, and Lr) and molecular (HgH and PbF) systems, where the effect of relativity does really matter to obtain highly accurate results. Not only the relativistic effect but also the effect of electron correlation is crucial in these heavy atomic and molecular systems. To justify the fact, we have taken two further approximations in the four-component relativistic equation-of-motion framework to quantify how the effect of electron correlation plays a role in the calculated values at different levels of theory. All these calculated results are compared with the available experimental data as well as with other theoretically calculated values to judge the extent of accuracy obtained in our calculations.

  2. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions

    CERN Document Server

    Eriksen, Janus J; Jørgensen, Poul; Gauss, Jürgen

    2016-01-01

    We extend our assessment of the potential of perturbative coupled cluster (CC) expansions for a test set of open-shell species to the description of quadruple excitations. In doing so, we compare the prominent CCSDT(Q) and lambda-CCSDT(Q) (a-CCSDT(Q)) models, in which the CC singles, doubles, and triples (CCSDT) energy is augmented by similar corrections for quadruple excitations, to the second- through sixth-order models of the CCSDT(Q-n) quadruples series, which is based on a CCSDT rather than an HF zeroth-order state. By comparing the models in terms of the size-intensive recovery of as well as the total deviation from the quadruples contribution to CC singles, doubles, triples, and quadruples (CCSDTQ) energies, we find (i) that the accuracy offered by the CCSDT(Q) and a-CCSDT(Q) models is strongly dependent on the spin of the molecular ground state - like for the CCSD(T) model in the first part of the present series [arXiv:1512.02846] - and (ii) that the performance of the CCSDT(Q-n) models is practically...

  3. Density functional theory embedding for correlated wavefunctions: Improved methods for open-shell systems and transition metal complexes

    CERN Document Server

    Goodpaster, Jason D; Manby, Frederick R; Miller, Thomas F

    2012-01-01

    Density functional theory (DFT) embedding provides a formally exact framework for interfacing correlated wave-function theory (WFT) methods with lower-level descriptions of electronic structure. Here, we report techniques to improve the accuracy and stability of WFT-in-DFT embedding calculations. In particular, we develop spin-dependent embedding potentials in both restricted and unrestricted orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and we develop an orbital-occupation-freezing technique to improve the convergence of optimized effective potential (OEP) calculations that arise in the evaluation of the embedding potential. The new techniques are demonstrated in applications to the van-der-Waals-bound ethylene-propylene dimer and to the hexaaquairon(II) transition-metal cation. Calculation of the dissociation curve for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating errors in th...

  4. Identification of singlet oxygen photosensitizes in lambs drinking water in an alveld risk area in West Norway

    DEFF Research Database (Denmark)

    Tønnesen, Hanne Hjorth; Mysterud, Ivar; Karlsen, Jan

    2013-01-01

    in order to identify the chromophores responsible for the formation of singlet oxygen, e.g. phycocyanins from the cyanobacteria. The highest level of singlet oxygen formation was detected in lotic (i.e. flowing) water in the period consistent with the outbreak of the alveld disease in the area...

  5. Stable tetrabenzo-Chichibabin's hydrocarbons: Tunable ground state and unusual transition between their closed-shell and open-shell resonance forms

    KAUST Repository

    Zeng, Zebing

    2012-09-05

    Stable open-shell polycyclic aromatic hydrocarbons (PAHs) are of fundamental interest due to their unique electronic, optical, and magnetic properties and promising applications in materials sciences. Chichibabin\\'s hydrocarbon as a classical open-shell PAH has been investigated for a long time. However, most of the studies are complicated by their inherent high reactivity. In this work, two new stable benzannulated Chichibabin\\'s hydrocarbons 1-CS and 2-OS were prepared, and their electronic structure and geometry in the ground state were studied by various experiments (steady-state and transient absorption spectra, NMR, electron spin resonance (ESR), superconducting quantum interference device (SQUID), FT Raman, X-ray crystallographic etc.) and density function theory (DFT) calculations. 1-CS and 2-OS exhibited tunable ground states, with a closed-shell quinoidal structure for 1-CS and an open-shell biradical form for 2-OS. Their corresponding excited-state forms 1-OS and 2-CS were also chemically approached and showed different decay processes. The biradical 1-OS displayed an unusually slow decay to the ground state (1-CS) due to a large energy barrier (95 ± 2.5 kJ/mol) arising from severe steric hindrance during the transition from an orthogonal biradical form to a butterfly-like quinoidal form. The quick transition from the quinoidal 2-CS (excited state) to the orthogonal biradicaloid 2-OS (ground state) happened during the attempted synthesis of 2-CS. Compounds 1-CS and 2-OS can be oxidized into stable dications by FeCl 3 and/or concentrated H 2SO 4. The open-shell 2-OS also exhibited a large two-photon absorption (TPA) cross section (760 GM at 1200 nm). © 2012 American Chemical Society.

  6. The quantum coherent mechanism for singlet fission: experiment and theory.

    Science.gov (United States)

    Chan, Wai-Lun; Berkelbach, Timothy C; Provorse, Makenzie R; Monahan, Nicholas R; Tritsch, John R; Hybertsen, Mark S; Reichman, David R; Gao, Jiali; Zhu, X-Y

    2013-06-18

    The absorption of one photon by a semiconductor material usually creates one electron-hole pair. However, this general rule breaks down in a few organic semiconductors, such as pentacene and tetracene, where one photon absorption may result in two electron-hole pairs. This process, where a singlet exciton transforms to two triplet excitons, can have quantum yields as high as 200%. Singlet fission may be useful to solar cell technologies to increase the power conversion efficiency beyond the so-called Shockley-Queisser limit. Through time-resolved two-photon photoemission (TR-2PPE) spectroscopy in crystalline pentacene and tetracene, our lab has recently provided the first spectroscopic signatures in singlet fission of a critical intermediate known as the multiexciton state (also called a correlated triplet pair). More importantly, we found that population of the multiexciton state rises at the same time as the singlet state on the ultrafast time scale upon photoexcitation. This observation does not fit with the traditional view of singlet fission involving the incoherent conversion of a singlet to a triplet pair. However, it provides an experimental foundation for a quantum coherent mechanism in which the electronic coupling creates a quantum superposition of the singlet and the multiexciton state immediately after optical excitation. In this Account, we review key experimental findings from TR-2PPE experiments and present a theoretical analysis of the quantum coherent mechanism based on electronic structural and density matrix calculations for crystalline tetracene lattices. Using multistate density functional theory, we find that the direct electronic coupling between singlet and multiexciton states is too weak to explain the experimental observation. Instead, indirect coupling via charge transfer intermediate states is two orders of magnitude stronger, and dominates the dynamics for ultrafast multiexciton formation. Density matrix calculation for the crystalline

  7. A new near-linear scaling, efficient and accurate, open-shell domain-based local pair natural orbital coupled cluster singles and doubles theory.

    Science.gov (United States)

    Saitow, Masaaki; Becker, Ute; Riplinger, Christoph; Valeev, Edward F; Neese, Frank

    2017-04-28

    The Coupled-Cluster expansion, truncated after single and double excitations (CCSD), provides accurate and reliable molecular electronic wave functions and energies for many molecular systems around their equilibrium geometries. However, the high computational cost, which is well-known to scale as O(N(6)) with system size N, has limited its practical application to small systems consisting of not more than approximately 20-30 atoms. To overcome these limitations, low-order scaling approximations to CCSD have been intensively investigated over the past few years. In our previous work, we have shown that by combining the pair natural orbital (PNO) approach and the concept of orbital domains it is possible to achieve fully linear scaling CC implementations (DLPNO-CCSD and DLPNO-CCSD(T)) that recover around 99.9% of the total correlation energy [C. Riplinger et al., J. Chem. Phys. 144, 024109 (2016)]. The production level implementations of the DLPNO-CCSD and DLPNO-CCSD(T) methods were shown to be applicable to realistic systems composed of a few hundred atoms in a routine, black-box fashion on relatively modest hardware. In 2011, a reduced-scaling CCSD approach for high-spin open-shell unrestricted Hartree-Fock reference wave functions was proposed (UHF-LPNO-CCSD) [A. Hansen et al., J. Chem. Phys. 135, 214102 (2011)]. After a few years of experience with this method, a few shortcomings of UHF-LPNO-CCSD were noticed that required a redesign of the method, which is the subject of this paper. To this end, we employ the high-spin open-shell variant of the N-electron valence perturbation theory formalism to define the initial guess wave function, and consequently also the open-shell PNOs. The new PNO ansatz properly converges to the closed-shell limit since all truncations and approximations have been made in strict analogy to the closed-shell case. Furthermore, given the fact that the formalism uses a single set of orbitals, only a single PNO integral transformation is

  8. Small -x behavior of the non-singlet and singlet structure functions g_1

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2003-01-01

    Explicit expressions for the non-singlet and singlet structure functions g_1 at the small $x$-region are obtained. They include the total resummation of double-logarithmic contributions and accounting for the running QCD coupling effects. We predict that both the non-singlet and singlet g_1 asymptotically ~ x^{- \\Delta}, with the singlet intercept = 0.86 and being more than twice larger than the non-singlet intercept = 0.4. The impact of the initial quark and gluon densities on the sign of g_1 at x << 1 is discussed.

  9. Ab Initio Exploration of the Potential Energy Surface of the O_2-SO_2 Open-Shell Complex.

    Science.gov (United States)

    Fawzy, Wafaa M.; Hougen, Jon T.

    2016-06-01

    The O_2-SO_2 complex is believed to be a precursor to acid rain. The previously observed FTMW spectrum suggested internal motions within the complex, but their nature was not identified. Development of an effective Hamiltonian for an open-shell molecule with tunneling requires knowledge of the potential energy surface (PES) and the intrinsic reaction coordinates (IRC) for the paths between minima. A recent ab initio study reported two different nonplanar minima in the ground electronic state of O_2-SO_2. These predictions were based on geometry optimization calculations at the MP2/aug-cc-pVnZ level of theory, with n = 2 and 3. The current work is focused on a highly correlated ab initio investigation of the global PES (a 9-D problem) in the ground triplet electronic state of O_2-SO_2. Because of the high dimensionality in the complex, the PES calculations are partitioned into several two-dimensional cuts through the PES. We have so far explored only a 3-D part of the global PES to look for stable planar configurations. These calculations included geometry optimization, frequency, and single point energy calculations. Calculations were performed using UCCSD(T)/aug-cc-pV(n+D)Z,where n = 2 and 3, level of theory. We used an axis system that defines the radial and the angular van der Waals coordinates for a planar complex as RvW, θ_1, and θ_2. The bond length (RvW) is the distance between the center of mass of the O_2 unit and the S atom. θ_1 and θ_2 are the angles between the van der Waals bond and the O_2 internuclear axis or one of the SO bonds in the SO_2 moiety, respectively. Full geometry optimization calculations predicted a minimum of C_s symmetry in which both the O_2 and SO_2 units are tilted with respect to the van der Waals bond, and RvW = 3.63 {Å}. 3-D PES surface calculations, which involve the RvW, θ_1, and θ_2 vdW coordinates, showed that the optimized structure is the global minimum. In addition, a local minimum at RvW = 3.9 {Å}, which

  10. Density Functional Theory of Open-Shell Systems. The 3d-Series Transition-Metal Atoms and Their Cations.

    Science.gov (United States)

    Luo, Sijie; Averkiev, Boris; Yang, Ke R; Xu, Xuefei; Truhlar, Donald G

    2014-01-14

    The 3d-series transition metals (also called the fourth-period transition metals), Sc to Zn, are very important in industry and biology, but they provide unique challenges to computing the electronic structure of their compounds. In order to successfully describe the compounds by theory, one must be able to describe their components, in particular the constituent atoms and cations. In order to understand the ingredients required for successful computations with density functional theory, it is useful to examine the performance of various exchange-correlation functionals; we do this here for 4s(N)3d(N') transition-metal atoms and their cations. We analyze the results using three ways to compute the energy of the open-shell states: the direct variational method, the weighted-averaged broken symmetry (WABS) method, and a new broken-symmetry method called the reinterpreted broken symmetry (RBS) method. We find the RBS method to be comparable in accuracy with the WABS method. By examining the overall accuracy in treating 18 multiplicity-changing excitations and 10 ionization potentials with the RBS method, 10 functionals are found to have a mean-unsigned error of systems, the M06-L functional is the most accurate. And by combining the results with our previous studies of p-block and 4d-series elements as well as databases for alkyl bond dissociation, main-group atomization energies, and π-π noncovalent interactions, we find five functionals, namely, PW6B95, MPW1B95, M08-SO, SOGGA11-X, and MPWB1K, to be highly recommended. We also studied the performance of PW86 and C09 exchange functionals, which have drawn wide interest in recent studies due to their claimed ability to reproduce Hartree-Fock exchange at long distance. By combining them with four correlation functionals, we find the performance of the resulting functionals disappointing both for 3d transition-metal chemistry and in broader tests, and thus we do not recommend PW86 and C09 as components of generalized

  11. Singlet oxygen reactions with flavonoids. A theoretical-experimental study.

    Directory of Open Access Journals (Sweden)

    Javier Morales

    Full Text Available Detection of singlet oxygen emission, λ(max = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, k(T, and the reactive reaction rate constant, k(r, for the reaction between singlet oxygen and several flavonoids. Values of k(T determined in deuterated water, ranging from 2.4×10(7 M(-1 s(-1 to 13.4×10(7 M(-1 s(-1, for rutin and morin, respectively, and the values measured for k(r, ranging from 2.8×10(5 M(-1 s(-1 to 65.7×10(5 M(-1 s(-1 for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid.

  12. Singlet Oxygen Reactions with Flavonoids. A Theoretical – Experimental Study

    Science.gov (United States)

    Morales, Javier; Günther, Germán; Zanocco, Antonio L.; Lemp, Else

    2012-01-01

    Detection of singlet oxygen emission, λmax = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, kT, and the reactive reaction rate constant, kr, for the reaction between singlet oxygen and several flavonoids. Values of kT determined in deuterated water, ranging from 2.4×107 M−1s−1 to 13.4×107 M−1s−1, for rutin and morin, respectively, and the values measured for kr, ranging from 2.8×105 M−1s−1 to 65.7×105 M−1s−1 for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid. PMID:22802966

  13. Collective aspects of singlet fission in molecular crystals

    Energy Technology Data Exchange (ETDEWEB)

    Teichen, Paul E.; Eaves, Joel D., E-mail: joel.eaves@colorado.edu [Department of Chemistry and Biochemistry, The University of Colorado at Boulder, Boulder, Colorado 80309 (United States)

    2015-07-28

    We present a model to describe collective features of singlet fission in molecular crystals and analyze it using many-body theory. The model we develop allows excitonic states to delocalize over several chromophores which is consistent with the character of the excited states in many molecular crystals, such as the acenes, where singlet fission occurs. As singlet states become more delocalized and triplet states more localized, the rate of singlet fission increases. We also determine the conditions under which the two triplets resulting from fission are correlated. Using the Bethe Ansatz and an entanglement measure for indistinguishable bipartite systems, we calculate the triplet-triplet entanglement as a function of the biexciton interaction strength. The biexciton interaction can produce bound biexciton states and provides a source of entanglement between the two triplets even when the triplets are spatially well separated. Significant entanglement between the triplet pair occurs well below the threshold for bound pair formation. Our results paint a dynamical picture that helps to explain why fission has been observed to be more efficient in molecular crystals than in their covalent dimer analogues and have consequences for photovoltaic efficiency models that assume that the two triplets can be extracted independently.

  14. Entanglement routers using macroscopic singlets.

    Science.gov (United States)

    Bayat, Abolfazl; Bose, Sougato; Sodano, Pasquale

    2010-10-29

    We propose a mechanism where high entanglement between very distant boundary spins is generated by suddenly connecting two long Kondo spin chains. We show that this procedure provides an efficient way to route entanglement between multiple distant sites. We observe that the key features of the entanglement dynamics of the composite spin chain are well described by a simple model of two singlets, each formed by two spins. The proposed routing mechanism is a footprint of the emergence of a Kondo cloud in a Kondo system and can be engineered and observed in varied physical settings.

  15. Chemistry of singlet oxygen. 52. Reaction with trans-stilbene

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Byoungmog; Foote, C.S.; Khan, S.I. (Univ. of California, Los Angeles (USA))

    1989-07-07

    Substituted trans-stilbenes react with singlet oxygen to give substituted diendoperoxides along with corresponding epoxides, cis-stilbenes, and benzaldehydes. The diendoperoxides rearrange readily to keto compounds on treatment with base. In methyl alcohol, solvent adducts are isolated. Monoendoperoxides are the primary products isolated from the photooxygenation of mono- and dimethoxystilbenes. Structures of several products were confirmed by NMR and X-ray crystallography. The results suggest that endoperoxide formation occurs via a polar intermediate such as a perepoxide or zwitterion.

  16. Extension of the composite CBS-QB3 method to singlet diradical calculations.

    OpenAIRE

    Sirjean, Baptiste; Fournet, René; Glaude, Pierre-Alexandre; Ruiz-Lopez, M. F.

    2007-01-01

    International audience; The composite CBS-QB3 method is widely used to obtain accurate energies of molecules and radicals although its use in the case of singlet diradicals gives rise to some difficulties. The problem is related to the parameterized correction this method introduces to account for spin-contamination. We report a new term specifically designed to describe singlet diradicals separated by at least one CH2 unit. As a test case, we have computed the formation enthalpy of a series ...

  17. Diphotons from an Electroweak Triplet-Singlet

    Energy Technology Data Exchange (ETDEWEB)

    Howe, Kiel [Fermilab; Knapen, Simon [UC, Berkeley; Robinson, Dean J. [UC, Berkeley

    2016-03-29

    The neutral component of a real pseudoscalar electroweak (EW) triplet can produce a diphoton excess at 750 GeV, if it is somewhat mixed with an EW singlet pseudoscalar. This triplet-singlet mixing allows for greater freedom in the diboson branching ratios than the singlet-only case, but it is still possible to probe the parameter space extensively with 300 fb$^{-1}$. The charged component of the triplet is pair-produced at the LHC, which results in a striking signal in the form of a pair of $W\\gamma$ resonances with an irreducible rate of 0.27 fb. Other signatures include multiboson final states from cascade decays of the triplet-singlet neutral states. A large class of composite models feature both EW singlet and triplet pseudo-Nambu Goldstone bosons in their spectrum, with the diboson couplings generated by axial anomalies.

  18. Density-fitted open-shell symmetry-adapted perturbation theory and application to π-stacking in benzene dimer cation and ionized DNA base pair steps

    Science.gov (United States)

    Gonthier, Jérôme F.; Sherrill, C. David

    2016-10-01

    Symmetry-Adapted Perturbation Theory (SAPT) is one of the most popular approaches to energy component analysis of non-covalent interactions between closed-shell systems, yielding both accurate interaction energies and meaningful interaction energy components. In recent years, the full open-shell equations for SAPT up to second-order in the intermolecular interaction and zeroth-order in the intramolecular correlation (SAPT0) were published [P. S. Zuchowski et al., J. Chem. Phys. 129, 084101 (2008); M. Hapka et al., ibid. 137, 164104 (2012)]. Here, we utilize density-fitted electron repulsion integrals to produce an efficient computational implementation. This approach is used to examine the effect of ionization on π-π interactions. For the benzene dimer radical cation, comparison against reference values indicates a good performance for open-shell SAPT0, except in cases with substantial charge transfer. For π stacking between hydrogen-bonded pairs of nucleobases, dispersion interactions still dominate binding, in spite of the creation of a positive charge.

  19. Analytic first derivatives for a spin-adapted open-shell coupled cluster theory: Evaluation of first-order electrical properties

    Energy Technology Data Exchange (ETDEWEB)

    Datta, Dipayan, E-mail: datta@uni-mainz.de; Gauss, Jürgen, E-mail: gauss@uni-mainz.de [Institut für Physikalische Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10-14, D-55128 Mainz (Germany)

    2014-09-14

    An analytic scheme is presented for the evaluation of first derivatives of the energy for a unitary group based spin-adapted coupled cluster (CC) theory, namely, the combinatoric open-shell CC (COSCC) approach within the singles and doubles approximation. The widely used Lagrange multiplier approach is employed for the derivation of an analytical expression for the first derivative of the energy, which in combination with the well-established density-matrix formulation, is used for the computation of first-order electrical properties. Derivations of the spin-adapted lambda equations for determining the Lagrange multipliers and the expressions for the spin-free effective density matrices for the COSCC approach are presented. Orbital-relaxation effects due to the electric-field perturbation are treated via the Z-vector technique. We present calculations of the dipole moments for a number of doublet radicals in their ground states using restricted open-shell Hartree-Fock (ROHF) and quasi-restricted HF (QRHF) orbitals in order to demonstrate the applicability of our analytic scheme for computing energy derivatives. We also report calculations of the chlorine electric-field gradients and nuclear quadrupole-coupling constants for the CCl, CH{sub 2}Cl, ClO{sub 2}, and SiCl radicals.

  20. Singlet-Doublet Dark Matter

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, Timothy; /SLAC /Michigan U., MCTP; Kearney, John; Pierce, Aaron; /Michigan U., MCTP; Tucker-Smith, David; /Williams Coll.

    2012-02-15

    In light of recent data from direct detection experiments and the Large Hadron Collider, we explore models of dark matter in which an SU(2){sub L} doublet is mixed with a Standard Model singlet. We impose a thermal history. If the new particles are fermions, this model is already constrained due to null results from XENON100. We comment on remaining regions of parameter space and assess prospects for future discovery. We do the same for the model where the new particles are scalars, which at present is less constrained. Much of the remaining parameter space for both models will be probed by the next generation of direct detection experiments. For the fermion model, DeepCore may also play an important role.

  1. Basis set and electron correlation effects on the polarizability and second hyperpolarizability of model open-shell π-conjugated systems

    Science.gov (United States)

    Champagne, Benoı̂t; Botek, Edith; Nakano, Masayoshi; Nitta, Tomoshige; Yamaguchi, Kizashi

    2005-03-01

    The basis set and electron correlation effects on the static polarizability (α) and second hyperpolarizability (γ) are investigated ab initio for two model open-shell π-conjugated systems, the C5H7 radical and the C6H8 radical cation in their doublet state. Basis set investigations evidence that the linear and nonlinear responses of the radical cation necessitate the use of a less extended basis set than its neutral analog. Indeed, double-zeta-type basis sets supplemented by a set of d polarization functions but no diffuse functions already provide accurate (hyper)polarizabilities for C6H8 whereas diffuse functions are compulsory for C5H7, in particular, p diffuse functions. In addition to the 6-31G*+pd basis set, basis sets resulting from removing not necessary diffuse functions from the augmented correlation consistent polarized valence double zeta basis set have been shown to provide (hyper)polarizability values of similar quality as more extended basis sets such as augmented correlation consistent polarized valence triple zeta and doubly augmented correlation consistent polarized valence double zeta. Using the selected atomic basis sets, the (hyper)polarizabilities of these two model compounds are calculated at different levels of approximation in order to assess the impact of including electron correlation. As a function of the method of calculation antiparallel and parallel variations have been demonstrated for α and γ of the two model compounds, respectively. For the polarizability, the unrestricted Hartree-Fock and unrestricted second-order Møller-Plesset methods bracket the reference value obtained at the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples level whereas the projected unrestricted second-order Møller-Plesset results are in much closer agreement with the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples values than the projected unrestricted Hartree

  2. Singlet oxygen-mediated damage to proteins and its consequences

    DEFF Research Database (Denmark)

    Davies, Michael Jonathan

    2003-01-01

    on the identification of reactive peroxide intermediates formed on Tyr, His, and Trp residues is discussed. These peroxides may be important propagating species in protein oxidation as they can initiate further oxidation via both radical and non-radical reactions. Such processes can result in the transmittal of damage......Proteins comprise approximately 68% of the dry weight of cells and tissues and are therefore potentially major targets for oxidative damage. Two major types of processes can occur during the exposure of proteins to UV or visible light. The first of these involves direct photo-oxidation arising from...... the absorption of UV radiation by the protein, or bound chromophore groups, thereby generating excited states (singlet or triplets) or radicals via photo-ionisation. The second major process involves indirect oxidation of the protein via the formation and subsequent reactions of singlet oxygen generated...

  3. Purification of an unpolarized spin ensemble into entangled singlet pairs

    CERN Document Server

    Greiner, Johannes N; Wrachtrup, Jörg

    2016-01-01

    Dynamical polarization of nuclear spin ensembles is of central importance for magnetic resonance studies, precision sensing and for applications in quantum information theory. Here we propose a scheme to generate long-lived singlet pairs in an unpolarized nuclear spin ensemble which is dipolar coupled to the electron spins of a Nitrogen Vacancy center in diamond. The quantum mechanical back-action induced by frequent spin-selective readout of the NV centers allows the nuclear spins to pair up into maximally entangled singlet pairs. Counterintuitively, the robustness of the pair formation to dephasing noise improves with increasing size of the spin ensemble. We also show how the paired nuclear spin state allows for enhanced sensing capabilities of NV centers in diamond.

  4. Indolo[2,3-b]carbazoles with tunable ground states: How Clar's aromatic sextet determines the singlet biradical character

    KAUST Repository

    Luo, Ding

    2014-01-01

    Polycyclic hydrocarbons (PHs) with a singlet biradical ground state have recently attracted extensive interest in physical organic chemistry and materials science. Replacing the carbon radical center in the open-shell PHs with a more electronegative nitrogen atom is expected to result in the more stable aminyl radical. In this work, two kinetically blocked stable/persistent derivatives (1 and 2) of indolo[2,3-b]carbazole, an isoelectronic structure of the known indeno[2,1-b]fluorene, were synthesized and showed different ground states. Based on variable-temperature NMR/ESR measurements and density functional theory calculations, it was found that the indolo[2,3-b]carbazole derivative 1 is a persistent singlet biradical in the ground state with a moderate biradical character (y0 = 0.269) and a small singlet-triplet energy gap (ΔES-T ≅ -1.78 kcal mol-1), while the more extended dibenzo-indolo[2,3-b]carbazole 2 exhibits a quinoidal closed-shell ground state. The difference can be explained by considering the number of aromatic sextet rings gained from the closed-shell to the open-shell biradical resonance form, that is to say, two for compound 1 and one for compound 2, which determines their different biradical characters. The optical and electronic properties of 2 and the corresponding aromatic precursors were investigated by one-photon absorption, transient absorption and two-photon absorption (TPA) spectroscopies and electrochemistry. Amphoteric redox behaviour, a short excited lifetime and a moderate TPA cross section were observed for 2, which can be correlated to its antiaromaticity and small biradical character. Compound 2 showed high reactivity to protic solvents due to its extremely low-lying LUMO energy level. Unusual oxidative dimerization was also observed for the unblocked dihydro-indolo[2,3-b]carbazole precursors 6 and 11. Our studies shed light on the rational design of persistent aminyl biradicals with tunable properties in the future. This journal

  5. Quantum Chemistry on Quantum Computers: A Polynomial-Time Quantum Algorithm for Constructing the Wave Functions of Open-Shell Molecules.

    Science.gov (United States)

    Sugisaki, Kenji; Yamamoto, Satoru; Nakazawa, Shigeaki; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji

    2016-08-18

    Quantum computers are capable to efficiently perform full configuration interaction (FCI) calculations of atoms and molecules by using the quantum phase estimation (QPE) algorithm. Because the success probability of the QPE depends on the overlap between approximate and exact wave functions, efficient methods to prepare accurate initial guess wave functions enough to have sufficiently large overlap with the exact ones are highly desired. Here, we propose a quantum algorithm to construct the wave function consisting of one configuration state function, which is suitable for the initial guess wave function in QPE-based FCI calculations of open-shell molecules, based on the addition theorem of angular momentum. The proposed quantum algorithm enables us to prepare the wave function consisting of an exponential number of Slater determinants only by a polynomial number of quantum operations.

  6. Reaching the cold regime: S(^1D) + H_2 and the Role of Long-Range Interactions in Open Shell Reactive Collisions

    CERN Document Server

    Lara, Manuel; Launay, J -M

    2010-01-01

    Reactive cross-sections for the collision of open shell S(^1D) atoms with ortho- and para-hydrogen, in the kinetic energy range 1-120 K, have been calculated using the hyperspherical quantum reactive scattering method developed by Launay et al. [Chem. Phys. Lett. 169, 473 (1990)]. Short-range interactions, described using the {\\em ab initio} potential energy surface by Ho et al. were complemented with an accurate description of the long-range interactions, where the main electrostatic (~R^{-5}) and dispersion (~ R^{-6}) contributions were considered. This allows the comparison with recent experimental measurements of rate constants and excitation functions for the title reaction at low temperatures [Berteloite et al., Phys. Rev. Lett., 2010]. The agreement is fairly good. The behavior in the considered energy range can be understood on the average in terms of a classical Langevin (capture) model, where the centrifugal barriers determine the amount of reactive flux which reaches the barrierless transition stat...

  7. Detection prospects of singlet fermionic dark matter

    CERN Document Server

    Esch, Sonja; Yaguna, Carlos E

    2013-01-01

    A singlet fermion which interacts only with a new singlet scalar provides a viable and minimal scenario that can explain the dark matter. The singlet fermion is the dark matter particle whereas the new scalar mixes with the Higgs boson providing a link between the dark matter sector and the Standard Model. In this paper, we present an updated analysis of this model focused on its detection prospects. Both, the parity-conserving case and the most general case are considered. First, the full parameter space of the model is analyzed, and the regions compatible with the dark matter constraint are obtained and characterized. Then, the implications of current and future direct detection experiments are taken into account. Specifically, we determine the regions of the multidimensional parameter space that are currently excluded and those that are going to be probed by next generation experiments. Finally, indirect detection prospects are discussed and the expected signal at neutrino telescopes is calculated.

  8. Detection prospects of singlet fermionic dark matter

    Science.gov (United States)

    Esch, Sonja; Klasen, Michael; Yaguna, Carlos E.

    2013-10-01

    A singlet fermion which interacts only with a new singlet scalar provides a viable and minimal scenario that can explain the dark matter. The singlet fermion is the dark matter particle whereas the new scalar mixes with the Higgs boson providing a link between the dark matter sector and the standard model. In this paper, we present an updated analysis of this model focused on its detection prospects. Both the parity-conserving case and the most general case are considered. First, the full parameter space of the model is analyzed, and the regions compatible with the dark matter constraint are obtained and characterized. Then, the implications of current and future direct detection experiments are taken into account. Specifically, we determine the regions of the multidimensional parameter space that are currently excluded and those that are going to be probed by next generation experiments. Finally, indirect detection prospects are discussed and the expected signal at neutrino telescopes is calculated.

  9. Global solutions of restricted open-shell Hartree-Fock theory from semidefinite programming with applications to strongly correlated quantum systems.

    Science.gov (United States)

    Veeraraghavan, Srikant; Mazziotti, David A

    2014-03-28

    We present a density matrix approach for computing global solutions of restricted open-shell Hartree-Fock theory, based on semidefinite programming (SDP), that gives upper and lower bounds on the Hartree-Fock energy of quantum systems. While wave function approaches to Hartree-Fock theory yield an upper bound to the Hartree-Fock energy, we derive a semidefinite relaxation of Hartree-Fock theory that yields a rigorous lower bound on the Hartree-Fock energy. We also develop an upper-bound algorithm in which Hartree-Fock theory is cast as a SDP with a nonconvex constraint on the rank of the matrix variable. Equality of the upper- and lower-bound energies guarantees that the computed solution is the globally optimal solution of Hartree-Fock theory. The work extends a previously presented method for closed-shell systems [S. Veeraraghavan and D. A. Mazziotti, Phys. Rev. A 89, 010502-R (2014)]. For strongly correlated systems the SDP approach provides an alternative to the locally optimized Hartree-Fock energies and densities with a certificate of global optimality. Applications are made to the potential energy curves of C2, CN, Cr2, and NO2.

  10. Ab Initio Description of Open-Shell Nuclei: Merging No-Core Shell Model and In-Medium Similarity Renormalization Group

    CERN Document Server

    Gebrerufael, Eskendr; Hergert, Heiko; Roth, Robert

    2016-01-01

    We merge two successful ab initio nuclear-structure methods, the no-core shell model (NCSM) and the multi-reference in-medium similarity renormalization group (IM-SRG) to define a new many-body approach for the comprehensive description of ground and excited states of closed and open-shell nuclei. Building on the key advantages of the two methods---the decoupling of excitations at the many-body level in the IM-SRG and the access to arbitrary nuclei, eigenstates, and observables in the NCSM---their combination enables fully converged no-core calculations for an unprecedented range of nuclei and observables at moderate computational cost. We present applications in the carbon and oxygen isotopic chains, where conventional NCSM calculations are still feasible and provide an important benchmark. The efficiency and rapid convergence of the new approach make it ideally suited for ab initio studies of the complete spectroscopy of nuclei up into the medium-mass regime.

  11. Global solutions of restricted open-shell Hartree-Fock theory from semidefinite programming with applications to strongly correlated quantum systems

    Energy Technology Data Exchange (ETDEWEB)

    Veeraraghavan, Srikant; Mazziotti, David A., E-mail: damazz@uchicago.edu [Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)

    2014-03-28

    We present a density matrix approach for computing global solutions of restricted open-shell Hartree-Fock theory, based on semidefinite programming (SDP), that gives upper and lower bounds on the Hartree-Fock energy of quantum systems. While wave function approaches to Hartree-Fock theory yield an upper bound to the Hartree-Fock energy, we derive a semidefinite relaxation of Hartree-Fock theory that yields a rigorous lower bound on the Hartree-Fock energy. We also develop an upper-bound algorithm in which Hartree-Fock theory is cast as a SDP with a nonconvex constraint on the rank of the matrix variable. Equality of the upper- and lower-bound energies guarantees that the computed solution is the globally optimal solution of Hartree-Fock theory. The work extends a previously presented method for closed-shell systems [S. Veeraraghavan and D. A. Mazziotti, Phys. Rev. A 89, 010502–R (2014)]. For strongly correlated systems the SDP approach provides an alternative to the locally optimized Hartree-Fock energies and densities with a certificate of global optimality. Applications are made to the potential energy curves of C{sub 2}, CN, Cr {sub 2}, and NO {sub 2}.

  12. Exchange effects in elastic collisions of spin-polarized electrons with open-shell molecules with $^3\\Sigma_g^-$ symmetry

    CERN Document Server

    Tashiro, Motomichi

    2007-01-01

    The spin-exchange effect in spin-polarized electron collisions with unpolarized open-shell molecules, O$_2$, B$_2$, S$_2$ and Si$_2$, has been studied by the R-matrix method with the fixed-bond approximation. All of these molecules have ${}^3 \\Sigma_{g}^{-}$ symmetry in their ground states. Usual integrated cross sections with unpolarized electrons has also been studied. We used the complete active space self consistent field orbitals and put more than 10 target electronic states in the R-matrix models. In electron O$_2$ elastic collisions, calculated polarization fractions agree well with the experimental results, especially around the ${}^4 \\Sigma_u^-$ resonance. In e-B$_2$, S$_2$ and Si$_2$ elastic collisions, larger spin-exchange effect is observed compared to the e-O$_2$ elastic collisions. In all four cases, spin-exchange effect becomes prominent near resonances. This association of resonance and magnitude of the spin-exchange effect was studied by explicitly removing the resonance configurations from t...

  13. Ab Initio Description of Open-Shell Nuclei: Merging No-Core Shell Model and In-Medium Similarity Renormalization Group.

    Science.gov (United States)

    Gebrerufael, Eskendr; Vobig, Klaus; Hergert, Heiko; Roth, Robert

    2017-04-14

    We merge two successful ab initio nuclear-structure methods, the no-core shell model (NCSM) and the multireference in-medium similarity renormalization group (IM-SRG) to define a new many-body approach for the comprehensive description of ground and excited states of closed and open-shell nuclei. Building on the key advantages of the two methods-the decoupling of excitations at the many-body level in the IM-SRG and the access to arbitrary nuclei, eigenstates, and observables in the NCSM-their combination enables fully converged no-core calculations for an unprecedented range of nuclei and observables at moderate computational cost. We present applications in the carbon and oxygen isotopic chains, where conventional NCSM calculations are still feasible and provide an important benchmark. The efficiency and rapid convergence of the new approach make it ideally suited for ab initio studies of the complete spectroscopy of nuclei up into the medium-mass regime.

  14. Extension of the composite CBS-QB3 method to singlet diradical calculations

    Science.gov (United States)

    Sirjean, Baptiste; Fournet, René; Glaude, Pierre-Alexandre; Ruiz-López, Manuel F.

    2007-02-01

    The composite CBS-QB3 method is widely used to obtain accurate energies of molecules and radicals although its use in the case of singlet diradicals gives rise to some difficulties. The problem is related to the parameterized correction this method introduces to account for spin-contamination. We report a new term specifically designed to describe singlet diradicals separated by at least one CH 2 unit. As a test case, we have computed the formation enthalpy of a series of diradicals that includes hydrocarbons as well as systems involving heteroatoms (nitrogen, oxygen). The resulting CBS-QB3 energies are very close to experiment.

  15. Singlet oxygen induced advanced glycation end-product photobleaching of in vivo human fingertip autofluorescence

    Science.gov (United States)

    Deng, Bin; Simental, Anabel; Lutz, Patrick; Shaheen, George; Chaiken, Joseph

    2012-01-01

    Nonenzymatic glycation and oxidation of ubiquitous proteins in vivo leads to irreversible formation of advanced glycation end products (AGEs). Due to their relatively long half life and low clearance rate AGEs tend to accumulate within static tissues and the circulatory system. Spectra obtained using 830 nm near-infrared (NIR) excitation suggest that the so-called "autofluorescence" from all tissues has a finite number of sources but the fact that senior and diabetic subjects produce more than other members of the general population suggests that a significant portion of the total autofluorescence from all sources originates from AGEs. Using pentosidine generated in a reaction mixture as described by Monnier as representative, an in vitro study unveiled very similar fluorescence and photobleaching pattern as observed for autofluorescence in vivo. A series of oxygen, air and argon purging experiments on the pentosidine-generating reaction mixture suggests that pentosidine is a singlet oxygen sensitizer and secondary reactions between the pentosidine itself and/or other fluorophores and the photosensitized singlet oxygen explain the observed photobleaching. Ab initio Gaussian calculations on pentosidine reveal the existence of low-lying triplet excited states required for the sensitization of ground state oxygen. A commercially available product known as singlet oxygen sensor green (SOSG) that specifically serves as a singlet oxygen detection reagent confirms the generation of singlet oxygen from NIR irradiated pentosidine trimixture. This study provides one definite chemical mechanism for understanding in vivo human skin autofluorescence and photobleaching.

  16. Singlet-Oxygen Generation From Individual Semiconducting and Metallic Nanostructures During Near-Infrared Laser Trapping

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Bennett E.; Roder, Paden B.; Hanson, Jennifer L.; Manandhar, Sandeep; Devaraj, Arun; Perea, Daniel E.; Kim, Woo-Joong; Kilcoyne, Arthur L.; Pauzauskie, Peter J.

    2015-03-13

    Photodynamic therapy has been used for several decades in the treatment of solid tumors through the generation of reactive singlet-oxygen species (1O2). Recently, nanoscale metallic and semiconducting materials have been reported to act as photosensitizing agents with additional diagnostic and therapeutic functionality. To date there have been no reports of observing the generation of singlet-oxygen at the level of single nanostructures, particularly at near infrared (NIR) wavelengths. Here we demonstrate that NIR laser-tweezers can be used to observe the formation of singlet-oxygen produced from individual silicon and gold nanowires via use of a commercially available reporting dye. The laser trap also induces 2-photon photoexcitation of the dye following a chemical reaction with singlet oxygen. Corresponding 2-photon emission spectra confirms the generation of singlet oxygen from individual silicon nanowires at room temperature (30°C), suggesting a range of applications in understanding the impact of 1O2 on individual cancer cells.

  17. Involvement of singlet oxygen in biochemical systems

    Energy Technology Data Exchange (ETDEWEB)

    Singh, A. (Whiteshell Nuclear Research Establishment, Pinawa, Manitoba, Canada); Singh, H.; Kremers, W.; Koroll, G.W.

    1981-01-01

    Reliable monitoring of singlet oxygen in biological systems is complicated by reactions of superoxide anions and hydroxyl radicals, which can often be present. However, tryptophan is now emerging as a potential monitor of singlet oxygen and other reactive oxy-species, in aqueous solutions, on the basis of the following results. Tryptophan reacts with singlet oxygen to produce N-form lykynurenine (FK), kynurenine (K), 2-carboxy-3a hydroxy-1,2,3,3a,8,8a-hexahydropyrrlo-(2,3b)-indole (HPI) and an unidentified product. It also reacts with hydroxyl radicals; in the presence of oxygen, six products are formed which include 5-hydroxy-tryptophan, FK, K, and HPI; in the absence of oxygen, K and HPI are not formed and a different unidentified product is formed. The relative yields of the common products in these three cases are different. Trytophan does not react with superoxide anions. Thus, by comparing the products formed and their ratios, tyrptophan can be used as a discriminating monitor for singlet oxygen, superoxide anions and hydroxyl radicals. On direct irradiation of tryptophan, at 280 nm, only two products (FK and HPI) are formed in measurable yields. In reaction with high concentrations of hydrogen peroxide, seven products result. Again, the relative ratios of the common products in these cases are different than the ones described above. In radiolysis, in the absence of oxygen, the decomposition of tryptophan is negligible. (JMT)

  18. Size of colour singlets in QCD jets

    Science.gov (United States)

    Bertolini, S.; Marchesini, G.

    1982-11-01

    By using the jet calculus technique, the size of the colour singlet clusters of emitted partons of mass Q0 is estimated. For α(Q20)/πapplications of preconfinement in pertubbative QCD. This result is very sensitive to the correct treatment of infrared singularities. Permanent address: Istituto di Fisica, Università di Parma, Parma, Italy.

  19. Oxygen measurements to improve singlet oxygen dosimetry

    Science.gov (United States)

    Kim, Michele M.; Penjweini, Rozhin; Ong, Yi Hong; Finlay, Jarod C.; Zhu, Timothy C.

    2017-02-01

    Photodynamic therapy (PDT) involves interactions between the three main components of light fluence, photosensitizer concentration, and oxygenation. Currently, singlet oxygen explicit dosimetry (SOED) has focused on the first two of these components. The macroscopic model to calculate reacted singlet oxygen has previously involved a fixed initial ground state oxygen concentration. A phosphorescence-based oxygen probe was used to measure ground state oxygen concentration throughout treatments for mice bearing radioactively induced fibroscarcoma tumors. Photofrin-, BPD-, and HPPH-mediated PDT was performed on mice. Model-calculated oxygen and measured oxygen was compared to evaluate the macroscopic model as well as the photochemical parameters involved. Oxygen measurements at various depths were compared to calculated values. Furthermore, we explored the use of noninvasive diffuse correlation spectroscopy (DCS) to measure tumor blood flow changes in response to PDT to improve the model calculation of reacted singlet oxygen. Mice were monitored after treatment to see the effect of oxygenation on long-term recurrence-free survival as well as the efficacy of using reacted singlet oxygen as a predictive measure of outcome. Measurement of oxygenation during treatment helps to improve SOED as well as confirm the photochemical parameters involved in the macroscopic model. Use of DCS in predicting oxygenation changes was also investigated.

  20. Recycling and imaging of nuclear singlet hyperpolarization

    DEFF Research Database (Denmark)

    Pileio, Giuseppe; Bowen, Sean; Laustsen, Christoffer

    2013-01-01

    observation of the same batch of polarized nuclei over a period of 30 min and more. We report a recycling protocol in which the enhanced nuclear polarization achieved by dissolution-DNP is observed with full intensity and then returned to singlet order. MRI experiments may be run on a portion of the available...

  1. Radiative neutrino masses in the singlet-doublet fermion dark matter model with scalar singlets

    CERN Document Server

    Restrepo, Diego; Sánchez-Peláez, Marta; Zapata, Oscar; Tangarife, Walter

    2015-01-01

    When the singlet-doublet fermion dark matter model is extended with additional $Z_2$--odd real singlet scalars, neutrino masses and mixings can be generated at one-loop level. In this work, we discuss the salient features arising from the combination of the two resulting simplified dark matter models. When the $Z_2$-lightest odd particle is a scalar singlet, $\\operatorname{Br}(\\mu\\to e \\gamma)$ could be measurable provided that the singlet-doublet fermion mixing is small enough. In this scenario, also the new decay channels of vector-like fermions into scalars can generate interesting leptonic plus missing transverse energy signals at the LHC. On the other hand, in the case of doublet-like fermion dark matter, scalar coannihilations lead to an increase in the relic density which allow to lower the bound of doublet-like fermion dark matter.

  2. Photophysical characterization and time-resolved spectroscopy of a anthradithiophene dimer: exploring the role of conformation in singlet fission.

    Science.gov (United States)

    Dean, Jacob C; Zhang, Ruomeng; Hallani, Rawad K; Pensack, Ryan D; Sanders, Samuel N; Oblinsky, Daniel G; Parkin, Sean R; Campos, Luis M; Anthony, John E; Scholes, Gregory D

    2017-08-30

    Quantitative singlet fission has been observed for a variety of acene derivatives such as tetracene and pentacene, and efforts to extend the library of singlet fission compounds is of current interest. Preliminary calculations suggest anthradithiophenes exhibit significant exothermicity between the first optically-allowed singlet state, S1, and 2 × T1 with an energy difference of >5000 cm(-1). Given the fulfillment of this ingredient for singlet fission, here we investigate the singlet fission capability of a difluorinated anthradithiophene dimer (2ADT) covalently linked by a (dimethylsilyl)ethane bridge and derivatized by triisobutylsilylethynyl (TIBS) groups. Photophysical characterization of 2ADT and the single functionalized ADT monomer were carried out in toluene and acetone solution via absorption and fluorescence spectroscopy, and their photo-initiated dynamics were investigated with time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopy. In accordance with computational predictions, two conformers of 2ADT were observed via fluorescence spectroscopy and were assigned to structures with the ADT cores trans or cis to one another about the covalent bridge. The two conformers exhibited markedly different excited state deactivation mechanisms, with the minor trans population being representative of the ADT monomer showing primarily radiative decay, while the dominant cis population underwent relaxation into an excimer geometry before internally converting to the ground state. The excimer formation kinetics were found to be solvent dependent, yielding time constants of ∼1.75 ns in toluene, and ∼600 ps in acetone. While the difference in rates elicits a role for the solvent in stabilizing the excimer structure, the rate is still decidedly long compared to most singlet fission rates of analogous dimers, suggesting that the excimer is neither a kinetic nor a thermodynamic trap, yet singlet fission was still not observed. The result

  3. Photophysical characterization and time-resolved spectroscopy of a anthradithiophene dimer: exploring the role of conformation in singlet fission

    KAUST Repository

    Dean, Jacob C.

    2017-08-18

    Quantitative singlet fission has been observed for a variety of acene derivatives such as tetracene and pentacene, and efforts to extend the library of singlet fission compounds is of current interest. Preliminary calculations suggest anthradithiophenes exhibit significant exothermicity between the first optically-allowed singlet state, S1, and 2 × T1 with an energy difference of >5000 cm−1. Given the fulfillment of this ingredient for singlet fission, here we investigate the singlet fission capability of a difluorinated anthradithiophene dimer (2ADT) covalently linked by a (dimethylsilyl)ethane bridge and derivatized by triisobutylsilylethynyl (TIBS) groups. Photophysical characterization of 2ADT and the single functionalized ADT monomer were carried out in toluene and acetone solution via absorption and fluorescence spectroscopy, and their photo-initiated dynamics were investigated with time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopy. In accordance with computational predictions, two conformers of 2ADT were observed via fluorescence spectroscopy and were assigned to structures with the ADT cores trans or cis to one another about the covalent bridge. The two conformers exhibited markedly different excited state deactivation mechanisms, with the minor trans population being representative of the ADT monomer showing primarily radiative decay, while the dominant cis population underwent relaxation into an excimer geometry before internally converting to the ground state. The excimer formation kinetics were found to be solvent dependent, yielding time constants of ∼1.75 ns in toluene, and ∼600 ps in acetone. While the difference in rates elicits a role for the solvent in stabilizing the excimer structure, the rate is still decidedly long compared to most singlet fission rates of analogous dimers, suggesting that the excimer is neither a kinetic nor a thermodynamic trap, yet singlet fission was still not observed. The result

  4. Singlet oxygen generation as a major cause for parasitic reactions during cycling of aprotic lithium-oxygen batteries

    Science.gov (United States)

    Mahne, Nika; Schafzahl, Bettina; Leypold, Christian; Leypold, Mario; Grumm, Sandra; Leitgeb, Anita; Strohmeier, Gernot A.; Wilkening, Martin; Fontaine, Olivier; Kramer, Denis; Slugovc, Christian; Borisov, Sergey M.; Freunberger, Stefan A.

    2017-03-01

    Non-aqueous metal-oxygen batteries depend critically on the reversible formation/decomposition of metal oxides on cycling. Irreversible parasitic reactions cause poor rechargeability, efficiency, and cycle life, and have predominantly been ascribed to the reactivity of reduced oxygen species with cell components. These species, however, cannot fully explain the side reactions. Here we show that singlet oxygen forms at the cathode of a lithium-oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products. The amount increases during discharge, early stages of charge, and charging at higher voltages, and is enhanced by the presence of trace water. Superoxide and peroxide appear to be involved in singlet oxygen generation. Singlet oxygen traps and quenchers can reduce parasitic reactions effectively. Awareness of the highly reactive singlet oxygen in non-aqueous metal-oxygen batteries gives a rationale for future research towards achieving highly reversible cell operation.

  5. A Hirshfeld interpretation of the charge, spin distribution, and polarity of the dipole moment of the open shell (3Sigma-) nitrogen halides: NF, NCl, and NBr.

    Science.gov (United States)

    Harrison, James F

    2009-07-28

    We calculated the dipole moment function for the ground (3)Sigma(-)(m(S) = +1) state of the open shell molecules, NF, NCl, and NBr, and analyzed it in terms of the charge and spin distribution and the induced atomic dipoles using the Hirshfeld partitioning of the electron density. The smallest dipole moment (0.026ea(0)) obtains with NF, in which the atoms have the largest difference in electronegativity, while the dipole moments in NCl and NBr are 0.441ea(0) and 0.506ea(0), respectively. All dipoles have the N(-)X(+) polarity. In the sigma system alpha spin electrons flow from N to the halogen while beta spin electrons flow in the opposite direction and interestingly from both the sigma and the pi systems of the halogen to the sigma system of N. In NF the number of beta spins lost by F is essentially equal to the number of alpha spins gained and the atomic charges are essentially 0. The small dipole in NF is the result of a slight imbalance in the induced atomic dipoles. For NCl and NBr the halogen loses more beta spins than it gains alpha spins resulting in the polarity N(-)X(+). It is interesting that at equilibrium N gained electrons in the pi system while the halogen lost pi electrons relative to the separated atoms. This however is not back donation in the usual sense because the electrons gained by N have alpha spin while those lost by the halogen have beta spin. Detailed examination of the spin flow shows that the excess alpha electrons in the pi system of N come from an intra-atomic transfer from the N sigma system. The induced atomic dipole moments essentially cancel at all internuclear separations and the polarity of the dipole moment accurately reflects the molecular charge distribution.

  6. Neutrino Masses and Scalar Singlet Dark Matter

    CERN Document Server

    Bhattacharya, Subhaditya; Nandi, S

    2016-01-01

    We propose a simple extension of the Standard Model (SM) which has a viable dark matter (DM) candidate, as well as can explain the generation of tiny neutrino masses. The DM is an electroweak (EW) singlet scalar $S$, odd under an imposed exact $Z_2$ symmetry, interacting to SM through `Higgs-portal' coupling, while all other particles are even under $Z_2$. The model also has an EW isospin $3/2$ scalar, $\\Delta$ and a pair of EW isospin vector, $\\Sigma$ and $\\bar{\\Sigma}$, responsible for generating tiny neutrino mass via the effective dimension seven operator. Thanks to the additional interactions with $\\Delta$, the scalar singlet DM $S$ survives a large region of parameter space by relic density constraints from WMAP/PLANCK and direct search bounds from updated LUX data. Constraints on the model from Large Hadron Collider (LHC) has also been discussed.

  7. Neutrino masses and scalar singlet dark matter

    Science.gov (United States)

    Bhattacharya, Subhaditya; Jana, Sudip; Nandi, S.

    2017-03-01

    We propose a simple extension of the Standard Model (SM) which has a viable dark matter (DM) candidate and can explain the generation of tiny neutrino masses. The DM is an electroweak (EW) singlet scalar S , odd under an imposed exact Z2 symmetry, that interacts with the SM through the "Higgs portal" coupling, while all other particles are even under Z2. The model also has an EW isospin 3 /2 scalar Δ and a pair of EW isospin vectors Σ and Σ ¯, which are responsible for generating tiny neutrino mass via the effective dimension-seven operator. Thanks to the additional interactions with Δ , the scalar singlet DM S survives a large region of parameter space by relic density constraints from WMAP/Planck and direct search bounds from updated LUX data. Constraints on the model from the LHC are also discussed.

  8. Singlet fission: Towards efficient solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Havlas, Zdeněk; Wen, Jin [Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610 Prague 6 (Czech Republic); Michl, Josef [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215 (United States); Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610 Prague 6 (Czech Republic)

    2015-12-31

    Singlet fission (SF) offers an opportunity to improve solar cell efficiency, but its practical use is hindered by the limited number of known efficient materials, limited knowledge of SF mechanism, mainly the relation between the dimer structure and SF efficiency and diffusion of the triplet states allowing injection of electrons into the solar cell semiconductor band. Here we report on our attempt to design new classes of chromophores and to study the relation between the structure and SF efficiency.

  9. Astrophysical Constraints on Singlet Scalars at LHC

    CERN Document Server

    Hertzberg, Mark P

    2016-01-01

    We consider the viability of new heavy gauge singlet scalar particles at the LHC. Our motivation for this study comes from the possibility of a new particle with mass ~ 750 GeV decaying significantly into two photons at LHC, but our analysis applies more broadly. We show that there are significant constraints from astrophysics and cosmology on the simplest UV complete models that incorporate such a particle and its associated collider signal. The simplest and most obvious UV complete model that incorporates the signal is that it arises from a new singlet scalar (or pseudo-scalar) coupled to a new electrically charged and colored heavy fermion. Here we show that these new fermions (and anti-fermions) would be produced in the early universe, then form new color singlet heavy mesons with light quarks, obtain a non-negligible freeze-out abundance, and remain in kinetic equilibrium until decoupling. These heavy mesons possess interesting phenomenology, dependent on their charge, including forming new bound states ...

  10. Helicity Evolution at Small $x$: Flavor Singlet and Non-Singlet Observables

    CERN Document Server

    Kovchegov, Yuri V; Sievert, Matthew D

    2016-01-01

    We extend our earlier results for the quark helicity evolution at small $x$ to derive the small-$x$ asymptotics of the flavor singlet and flavor non-singlet quark helicity TMDs and PDFs and of the $g_1$ structure function. In the flavor singlet case we re-derive the evolution equations obtained in our previous paper on the subject, performing additional cross-checks of our results. In the flavor non-singlet case we construct new small-$x$ evolution equations by employing the large-$N_c$ limit. All evolution equations resum double-logarithmic powers of $\\alpha_s \\, \\ln^2 (1/x)$ in the polarization-dependent evolution along with the single-logarithmic powers of $\\alpha_s \\, \\ln (1/x)$ in the unpolarized evolution which includes saturation effects. We solve the linearized flavor non-singlet equation analytically, obtaining an intercept which agrees with the one calculated earlier by Bartels, Ermolaev and Ryskin using the infra-red evolution equations. Our numerical solution of the linearized large-$N_c$ evolutio...

  11. The development of efficient two-photon singlet oxygen sensitizers

    DEFF Research Database (Denmark)

    Nielsen, Christian Benedikt

    The development of efficient two-photon singlet oxygen sensitizers is addressed focusing on organic synthesis. Photophysical measurements were carried out on new lipophilic molecules, where two-photon absorption cross sections and singlet oxygen quantumyields were measured. Design principles...... for making efficient two-photon singlet oxygen sensitizers were then constructed from these results. Charge-transfer in the excited state of the prepared molecules was shown to play a pivotal role in the generationof singlet oxygen. This was established through studies of substituent effects on both...... the singlet oxygen yield and the two-photon absorption cross section, where it was revealed that a careful balancing of the amount of charge transfer present in theexcited state of the sensitizer is necessary to obtain both a high singlet oxygen quantum yield and a high two-photon cross section. An increasing...

  12. Dynamic zero modes of Dirac fermions and competing singlet phases of antiferromagnetic order

    Science.gov (United States)

    Goswami, Pallab; Si, Qimiao

    2017-06-01

    In quantum spin systems, singlet phases often develop in the vicinity of an antiferromagnetic order. Typical settings for such problems arise when itinerant fermions are also present. In this paper, we develop a theoretical framework for addressing such competing orders in an itinerant system, described by Dirac fermions strongly coupled to an O(3) nonlinear sigma model. We focus on two spatial dimensions, where upon disordering the antiferromagnetic order by quantum fluctuations the singular tunneling events also known as (anti)hedgehogs can nucleate competing singlet orders in the paramagnetic phase. In the presence of an isolated hedgehog configuration of the nonlinear sigma model field, we show that the fermion determinant vanishes as the dynamic Euclidean Dirac operator supports fermion zero modes of definite chirality. This provides a topological mechanism for suppressing the tunneling events. Using the methodology of quantum chromodynamics, we evaluate the fermion determinant in the close proximity of magnetic quantum phase transition, when the antiferromagnetic order-parameter field can be described by a dilute gas of hedgehogs and antihedgehogs. We show how the precise nature of emergent singlet order is determined by the overlap between dynamic fermion zero modes of opposite chirality, localized on the hedgehogs and antihedgehogs. For a Kondo-Heisenberg model on the honeycomb lattice, we demonstrate the competition between spin Peierls order and Kondo singlet formation, thereby elucidating its global phase diagram. We also discuss other physical problems that can be addressed within this general framework.

  13. Astrophysical constraints on singlet scalars at LHC

    Science.gov (United States)

    Hertzberg, Mark P.; Masoumi, Ali

    2017-04-01

    We consider the viability of new heavy gauge singlet scalar particles at colliders such as the LHC . Our original motivation for this study came from the possibility of a new heavy particle of mass ~ TeV decaying significantly into two photons at colliders, such as LHC, but our analysis applies more broadly. We show that there are significant constraints from astrophysics and cosmology on the simplest UV complete models that incorporate such new particles and its associated collider signal. The simplest and most obvious UV complete model that incorporates such signals is that it arises from a new singlet scalar (or pseudo-scalar) coupled to a new electrically charged and colored heavy fermion. Here we show that these new fermions (and anti-fermions) would be produced in the early universe, then form new color singlet heavy mesons with light quarks, obtain a non-negligible freeze-out abundance, and remain in kinetic equilibrium until decoupling. These heavy mesons possess interesting phenomenology, dependent on their charge, including forming new bound states with electrons and protons. We show that a significant number of these heavy states would survive for the age of the universe and an appreciable number would eventually be contained within the earth and solar system. We show that this leads to detectable consequences, including the production of highly energetic events from annihilations on earth, new spectral lines, and, spectacularly, the destabilization of stars. The lack of detection of these consequences rules out such simple UV completions, putting pressure on the viability of such new particles at LHC . To incorporate such a scalar would require either much more complicated UV completions or even further new physics that provides a decay channel for the associated fermion.

  14. Doublet-singlet model and unitarity

    Science.gov (United States)

    Cynolter, G.; Kovács, J.; Lendvai, E.

    2016-12-01

    We study the renormalizable singlet-doublet fermionic extension of the Standard Model (SM). In this model, the new vector-like fermions couple to the gauge bosons and to the Higgs via new Yukawa couplings that allow for nontrivial mixing in the new sector, providing a stable, neutral dark matter candidate. Approximate analytic formulae are given for the mass spectrum around the blind spots, where the dark matter candidate coupling to h or Z vanishes. We calculate the two particle scattering amplitudes in the model, impose the perturbative unitarity constraints and establish bounds on the Yukawa couplings.

  15. Doublet-singlet model and unitarity

    CERN Document Server

    Cynolter, G; Lendvai, E

    2016-01-01

    We study the renormalizable singlet-doublet fermionic extension of the Standard Model. In this model, the new vector-like fermions couple to the gauge bosons and to the Higgs via new Yukawa couplings, that allow for nontrivial mixing in the new sector, providing a stable, neutral dark matter candidate. Approximate analytic formulae are given for the mass spectrum around the blind spots, where the dark matter candidate coupling to $h$ or $Z$ vanishes. We calculate the two particle scattering amplitudes in the model, impose the perturbative unitarity constraints and establish bounds on the Yukawa couplings.

  16. Singlet deflected anomaly/gauge mediation

    Energy Technology Data Exchange (ETDEWEB)

    Blas, J. de, E-mail: jdeblasm@nd.edu [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Delgado, A., E-mail: antonio.delgado@nd.edu [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)

    2012-02-28

    We study an extension of the standard anomaly/gauge mediation scenario where the messenger fields have direct interactions with an extra gauge singlet. This realizes a phenomenologically viable NMSSM-like scenario free of the {mu}-b{sub {mu}} problem. Current cosmological constraints imply a small size for the anomaly-mediation contributions, unless some source of R-parity violation is permitted. In the latter case the allowed regions in the parameter space can be substantially larger than in the corresponding gauge-mediation scenario.

  17. Excited singlet states of "hairpin" polyenes

    OpenAIRE

    Froelich, Wolfgang; Dewey, Harry J.; Deger, Hans; Dick, Bernhard; Klingensmith, Kenneth A.; Puettmann, Wilhelm; Vogel, Emanuel; Hohlneicher, Georg; Michl, Josef

    1983-01-01

    The synthesis and UV-visible, polarized-fluorescence and MCD spectra of 6 U-shaped hairpin polyenes (e.g., I) are reported. Qual. arguments and results of p-electron calcns. permit the identification of 4 excited singlet states and their assignment to mixts. of singly and doubly excited configurations. The hairpin polyenes represent a link between the all-trans-polyenes on the 1 hand and the annulenes and acenes on the other; they have the topol. of the former and a geometry near that of the ...

  18. Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

    Science.gov (United States)

    Palumbo, Fabrizio; Bosca, Francisco; Morera, Isabel Maria

    2016-01-01

    Summary Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen (1O2). Suprofen (SP) is a nonsteroidal anti-inflammatory drug that contains the 2-benzoylthiophene (BZT) chromophore and has a π,π* lowest triplet excited state. In the present work, dyads (S)- and (R)-SP-α-Ch (1 and 2), as well as (S)-SP-β-Ch (3) have been prepared from β- or α-Ch and SP to investigate the possible competition between photogeneration of biradicals and 1O2, the key mechanistic steps in Ch photooxidation. Steady-state irradiation of 1 and 2 was performed in dichloromethane, under nitrogen, through Pyrex, using a 400 W medium pressure mercury lamp. The spectral analysis of the separated fractions revealed formation of two photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C–C coupling of the generated biradicals. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Transient absorption spectra obtained for 1–3 were very similar and matched that described for the SP triplet excited state (typical bands with maxima at ca. 350 nm and 600 nm). Direct kinetic analysis of the decay traces at 620 nm led to determination of triplet lifetimes that were ca. 4.1 μs for 1 and 2 and 5.8 μs for 3. From these data, the intramolecular quenching rate constants in 1 and 2 were determined as 0.78 × 105 s−1. The capability of dyads 1–3 to photosensitize the production of singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (ΦΔ) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-α-Ch dyads are unique in the sense that they

  19. Solution phase isomerization of vibrationally excited singlet nitrenes to vibrationally excited 1,2-didehydroazepine.

    Science.gov (United States)

    Burdzinski, Gotard T; Middleton, Chris T; Gustafson, Terry L; Platz, Matthew S

    2006-11-22

    Photolysis of phenyl and o-biphenylyl azide (at 270 nm) releases vibrationally excited singlet nitrene which isomerizes to the corresponding hot 1,2-didehydroazepine at a rate competitive with thermal relaxation. Using ultrafast vibrational spectroscopy we observe the formation of vibrationally excited 1,2-4,6-azacycloheptatetraene (1,2-didehydroazepine) in picoseconds following photolysis of phenyl azide in chloroform and o-biphenylyl azide in acetonitrile at ambient temperature.

  20. Flavour singlets in gauge theory as Permutations

    CERN Document Server

    Kimura, Yusuke; Suzuki, Ryo

    2016-01-01

    Gauge-invariant operators can be specified by equivalence classes of permutations. We develop this idea concretely for the singlets of the flavour group $SO(N_f)$ in $U(N_c)$ gauge theory by using Gelfand pairs and Schur-Weyl duality. The singlet operators, when specialised at $N_f =6$, belong to the scalar sector of ${\\cal N}=4$ SYM. A simple formula is given for the two-point functions in the free field limit of $g_{YM}^2 =0$. The free two-point functions are shown to be equal to the partition function on a 2-complex with boundaries and a defect, in a topological field theory of permutations. The permutation equivalence classes are Fourier transformed to a representation basis which is orthogonal for the two-point functions at finite $N_c , N_f$. Counting formulae for the gauge-invariant operators are described. The one-loop mixing matrix is derived as a linear operator on the permutation equivalence classes.

  1. Stability of singlet and triplet trions in carbon nanotubes

    DEFF Research Database (Denmark)

    Rønnow, Troels Frimodt; Pedersen, Thomas Garm; Cornean, Horia

    2009-01-01

    We investigate singlet and triplet trion states in semiconducting carbon nanotubes using a one-dimensional model. It is concluded that singlet trion states in bind up to 13.5% stronger than exciton states, and that they lower the optical transition energy with up to 50% of the tight binding band ...

  2. Magnetic excitons in singlet-ground-state ferromagnets

    DEFF Research Database (Denmark)

    Birgeneau, R.J.; Als-Nielsen, Jens Aage; Bucher, E.

    1971-01-01

    The authors report measurements of the dispersion of singlet-triplet magnetic excitons as a function of temperature in the singlet-ground-state ferromagnets fcc Pr and Pr3Tl. Well-defined excitons are observed in both the ferromagnetic and paramagnetic regions, but with energies which are nearly...

  3. Lycopene inhibits the isomerization of β-carotene during quenching of singlet oxygen and free radicals.

    Science.gov (United States)

    Heymann, Thomas; Heinz, Philipp; Glomb, Marcus A

    2015-04-01

    The present study aimed to investigate the influence of singlet oxygen and radical species on the isomerization of carotenoids. On the one hand, lycopene and β-carotene standards were incubated with 1,4-dimethylnaphthalene-1,4-endoperoxide that produced singlet oxygen in situ. (13Z)- and (15Z)-β-carotene were preferentially generated at low concentrations of singlet oxygen, while high concentrations resulted in formation of (9Z)-β-carotene. The addition of different concentrations of lycopene led to the same isomerization progress of β-carotene, but resulted in a decreased formation of (9Z)-β-carotene and retarded degradation of (all-E)-β-carotene. On the other hand, isomerization of β-carotene and lycopene was induced by ABTS-radicals, too. As expected from the literature, chemical quenching was observed especially for lycopene, while physical quenching was preferred for β-carotene. Mixtures of β-carotene and lycopene resulted in a different isomerization progress compared to the separate β-carotene model. As long as lycopene was present, almost no isomerization of β-carotene was triggered; after that, strong formation of (13Z)-, (9Z)-, and (15Z)-β-carotene was initiated. In summary, lycopene protected β-carotene against isomerization during reactions with singlet oxygen and radicals. These findings can explain the pattern of carotenoid isomers analyzed in fruits and vegetables, where lycopene containing samples showed higher (all-E)/(9Z)-β-carotene ratios, and also in in vivo samples such as human blood plasma.

  4. In situ Formation and Electron-Spectroscopic Study of Bis(arene) V and Cr Compounds ona Graphite Surface

    Science.gov (United States)

    2013-03-07

    ECPs that replace only the metal 1s, 2s, and 2p shells . Spin-unrestricted calculations were done for species having an unpaired electron, and all results... ghosts ” due to excitation of the HOMO by the 23.09 eV HeI satellite; however, they also correspond to theoretically pre- dicted CrBz2 and VBz2...be a Jahn-Teller-distorted open- shell triplet rather than a closed- shell singlet. In the adsorbed state, the IPs will be reduced by 1–1.5 eV due to

  5. Color Singlet Production at NNLO in MCFM

    Energy Technology Data Exchange (ETDEWEB)

    Boughezal, Radja [Argonne; Campbell, John M. [Fermilab; Ellis, R. Keith [Durham U., IPPP; Focke, Christfried [Northwestern U.; Giele, Walter [Fermilab; Liu, Xiaohui [Maryland U.; Petriello, Frank [Northwestern U.; Williams, Ciaran [SUNY, Buffalo

    2016-05-25

    We present the implementation of several color-singlet final-state processes at Next-to-Next-to Leading Order (NNLO) accuracy in QCD to the publicly available parton-level Monte Carlo program MCFM. Specifically we discuss the processes $pp\\rightarrow H$, $pp\\rightarrow Z$, $pp\\rightarrow W$, $pp\\rightarrow HZ$, $pp\\rightarrow HW$ and $pp\\rightarrow\\gamma\\gamma$. Decays of the unstable bosons are fully included, resulting in a flexible fully differential Monte Carlo code. The NNLO corrections have been calculated using the non-local $N$-jettiness subtraction approach. Special attention is given to the numerical aspects of running MCFM for these processes at this order. We pay particular attention to the systematic uncertainties due to the power corrections induced by the $N$-jettiness regularization scheme and the evaluation time needed to run the hybrid openMP/MPI version of MCFM at NNLO on multi-processor systems.

  6. Singlet Scalar Resonances and the Diphoton Excess

    CERN Document Server

    McDermott, Samuel D; Ramani, Harikrishnan

    2015-01-01

    ATLAS and CMS recently released the first results of searches for diphoton resonances in 13 TeV data, revealing a modest excess at an invariant mass of approximately 750 GeV. We find that it is generically possible that a singlet scalar resonance is the origin of the excess while avoiding all other constraints. We highlight some of the implications of this model and how compatible it is with certain features of the experimental results. In particular, we find that the very large total width of the excess is difficult to explain with loop-level decays alone, pointing to other interesting bounds and signals if this feature of the data persists. Finally we comment on the robust Z-gamma signature that will always accompany the model we investigate.

  7. Monitoring of singlet oxygen in the lower troposphere and processes of ozone depletion.

    Science.gov (United States)

    Iasenko, Egor; Chelibanov, Vladimir; Marugin, Alexander; Kozliner, Marat

    2016-04-01

    The processes of ozone depletion in the atmosphere are widely discussed now in a connection with the problem of a global climate changes. It is known fact that photolysis of ozone in the upper atmosphere is the source of metastable molecules of oxygen. But, metastable molecules of oxygen can be formed as a result of photo initiated heterogeneous oxidation of molecules adsorbed on the surface of natural aerosol particles. During the outdoor experiment, we observed a formation of Singlet oxygen (1Δg) at concentration level of 2 ... 5 ppb when ice crystals have been exposed to the sun light. In experiments, we used Analyzers of Singlet oxygen and Ozone (produced by JSC "OPTEC") that utilize solid-state chemiluminescence technology. We assumed that the singlet oxygen is formed in the active centers on the surface of ice crystals in the presence or absence of anthropogenic pollutants in the atmosphere. Identified efficiency of heterogeneous reaction of O2 (1Δg) formation suggests the importance of the additional channel O3 + O2 (1Δg) → 2O2 + O (3P) of atmospheric ozone removal comparable with other well known cycles of ozone depletion.

  8. Self-assembled benzophenone bis-urea macrocycles facilitate selective oxidations by singlet oxygen.

    Science.gov (United States)

    Geer, Michael F; Walla, Michael D; Solntsev, Kyril M; Strassert, Cristian A; Shimizu, Linda S

    2013-06-07

    This manuscript investigates how incorporation of benzophenone, a well-known triplet sensitizer, within a bis-urea macrocycle, which self-assembles into a columnar host, influences its photophysical properties and affects the reactivity of bound guest molecules. We further report the generation of a remarkably stable organic radical. As expected, UV irradiation of the host suspended in oxygenated solvents efficiently generates singlet oxygen similar to the parent benzophenone. In addition, this host can bind guests such as 2-methyl-2-butene and cumene to form stable solid host-guest complexes. Subsequent UV irradiation of these complexes facilitated the selective oxidation of 2-methyl-2-butene into the allylic alcohol, 3-methyl-2-buten-1-ol, at 90% selectivity as well as the selective reaction of cumene to the tertiary alcohol, α,α'-dimethyl benzyl alcohol, at 63% selectivity. However, these products usually arise through radical pathways and are not observed in the presence of benzophenone in solution. In contrast, typical reactions with benzophenone result in the formation of the reactive singlet oxygen that reacts with alkenes to form endoperoxides, diooxetanes, or hydroperoxides, which are not observed in our system. Our results suggest that the confinement, the formation of a stable radical species, and the singlet oxygen photoproduction are responsible for the selective oxidation processes. A greater understanding of the mechanism of this selective oxidation could lead to development of greener oxidants.

  9. Kinetics of oxygen species in an electrically driven singlet oxygen generator

    Science.gov (United States)

    Azyazov, V. N.; Torbin, A. P.; Pershin, A. A.; Mikheyev, P. A.; Heaven, M. C.

    2015-12-01

    The kinetics of oxygen species in the gaseous medium of a discharge singlet oxygen generator has been revisited. Vibrationally excited ozone O3(υ) formed in O + O2 recombination is thought to be a significant agent in the deactivation of singlet oxygen O2(a1Δ), oxygen atom removal and ozone formation. It is shown that the process O3(υ ⩾ 2) + O2(a1Δ) → 2O2 + O is the main O2(a1Δ) deactivation channel in the post-discharge zone. If no measures are taken to decrease the oxygen atom concentration, the contribution of this process to the overall O2(a1Δ) removal is significant, even in the discharge zone. A simplified model for the kinetics of vibrationally excited ozone is proposed. Calculations based on this model yield results that are in good agreement with the experimental data.

  10. The electroweak phase transition in models with gauge singlets

    Energy Technology Data Exchange (ETDEWEB)

    Ahriche, A.

    2007-04-18

    A strong first order phase transition is needed for generating the baryon asymmetry; and also to save it during the electroweak phase transition (EWPT). However this condition is not fulfilled within the Standard Model (SM), but in its extensions. It is widely believed that the existence of singlet scalars in some Standard Model extensions can easily make the EWPT strongly first order. In this work, we will examine the strength of the EWPT in the simplest extension of the SM with a real gauge singlet using the sphaleron energy at the critical temperature. We find that the phase transition is stronger by adding a singlet; and also that the criterion for a strong phase transition {omega}(T{sub c})/T{sub c} >or similar 1, where {omega} = (v{sup 2} + (x - x{sub 0}){sup 2}){sup (}1)/(2) and x(x{sub 0}) is the singlet vacuum expectation value in the broken (symmetric) phase, is not valid for models containing singlets, even though often used in the literature. The usual condition v{sub c}/T{sub c} >or similar 1 is more meaningful, and it is satisfied for the major part of the parameter space for physically allowed Higgs masses. Then it is convenient to study the EWPT in models with singlets that couple only to the Higgs doublets, by replacing the singlets by their vevs. (orig.)

  11. The Helium Golden Ratios: triplet-singlet and G for He-like X-ray Emission

    Science.gov (United States)

    Stancil, Phillip C.; Miller, Ansley; Terry, Jason; Cumbee, Renata; Mullen, Patrick Dean; Schultz, David R.

    2017-06-01

    The existence of a mere two electrons manifests a multitude of interesting and diverse phenomena in the atomic structure of He-like ions including separate spin manifolds (singlets and triplets), unusual ordering of angular momentum states, and intercombination (i) and forbidden (f) radiative transitions. This rich behavior extends also to the dynamics involving He-like ions and various perturbers. While electrons have a propensity for exciting resonant (r) dipole-allowed transitions, heavy particles are far less selective. In this presentation, I'll illustrate how these properties play out in ion-neutral charge exchange (CX) processes which result in He-like product ions. The focus will be on the spin-multiplicity of the atomic ions and the quasi-molecular states involved in the interactions, how these affect the CX cross sections, and their impact on the resulting X-ray spectrum. In particular, the G-ratio, the ratio of Kα line intensities (f+i)/r, is very sensitive to the spin-dependent cross sections which in turn is dependent on the neutral target, whether open-shell like H (Nolte et al. 2012, 2017; Wu et al. 2012) or closed-shell like He or H2 (Cumbee et al. 2017; Mullen et al. 2016, 2017). Preliminary evidence also suggests that multielectron capture processes may influence the G-ratio when multielectron targets are involved.Cumbee R. S. et al. 2017, ApJ, submittedMullen, P. D. et al. 2016, ApJS, 224, 31Mullen, P. D. et al. 2017, ApJ, submittedNolte, J. et al. 2012, JPB, 45, 245202; 2017, to be submittedWu, Y. et al. 2012, JPB, 84, 022711This work was partially supported by NASA grants NNX09AC46G and NNG09WF24I.

  12. Photochemical Dynamics of Intramolecular Singlet Fission

    Science.gov (United States)

    Lin, Zhou; Iwasaki, Hikari; Van Voorhis, Troy

    2017-06-01

    Singlet fission (SF) converts a singlet exciton (S_1) into a pair of triplet ones (T_1) via a ``multi-exciton'' (ME) intermediate: S_1 \\longleftrightarrow ^1ME \\longleftrightarrow ^1(T_1T_1) \\longrightarrow 2T_1. In exothermic cases, e.g., crystalline pentacene or its derivatives, the quantum yield of SF can reach 200%. With SF doubling the electric current generated by an incident high-energy photon, the solar conversion efficiency in pentacene-based organic photovoltaics (OPVs) can exceed the Shockley-Queisser limit of 33.7%. The ME state is popularly considered to be a dimeric state with significant charge transfer (CT) character that is strongly coupled to both S_1 and ^1(T_1T_1), while this local model lacks strong support from full quantum dynamics studies. Intramolecular SF (ISF) occurring to covalently-bound dimers in the solution phase is an excellent model for a straightforward dynamics simulation of local excitons. In the present study, we investigate the ISF mechanisms for three covalently-bound dimers of pentacene derivatives, including ortho-, meta-, and para-bis(6,13-bis(triisopropylsilylethynyl)pentacene)benzene, in non-protic solvents. Specifically, we propagate the real-time, non-adiabatic quantum mechanical/molecular mechanical (QM/MM) dynamics on the potential energy surfaces associated with the states of S_1, ^1(T_1T_1) and CT. We explore how the energies of these ISF-relevant states and the non-adiabatic couplings between each other fluctuate with time and the instantaneous molecular configuration (e.g., intermonomer distance and orientation). We also quantitatively compare Condon and non-Condon ISF dynamics with solution-phase spectroscopic data. Our results allow us to understand the roles of CT energy levels in the ISF mechanism and propose a design strategy to maximize ISF efficiency. M. B. Smith and J. Michl, Chem. Rev. 110, 6891 (2010). W. Shockley and H. J. Queisser, J. Appl. Phys. 32, 510 (1961). T. C. Berkelbach, M. S. Hybertsen

  13. Photoluminescence dynamics in singlet fission chromophore liquid melts

    Science.gov (United States)

    Piland, Geoffrey B.; Bardeen, Christopher J.

    2017-02-01

    The effect of high temperature melting on the photophysics of three prototypical singlet fission molecules is investigated. Time-resolved photoluminescence is used to look at the melt phase of the molecules tetracene, diphenylhexatriene and rubrene. Chemical decomposition of tetracene precluded any detailed measurements on this molecule. In the diphenylhexatriene melt, a rapid singlet state nonradiative relaxation process outcompetes singlet fission. In the rubrene melt, singlet fission occurs at a rate similar to that of the crystal, but the decay of the delayed fluorescence is much more rapid. The rapid decay of the delayed fluorescence suggests that either the triplet lifetime is shortened, or the fusion probability decreases, or that both factors are operative at higher temperatures.

  14. Singlet exciton fission in nanostructured organic solar cells.

    Science.gov (United States)

    Jadhav, Priya J; Mohanty, Aseema; Sussman, Jason; Lee, Jiye; Baldo, Marc A

    2011-04-13

    Singlet exciton fission is an efficient multiexciton generation process in organic molecules. But two concerns must be satisfied before it can be exploited in low-cost solution-processed organic solar cells. Fission must be combined with longer wavelength absorption in a structure that can potentially surpass the single junction limit, and its efficiency must be demonstrated in nanoscale domains within blended devices. Here, we report organic solar cells comprised of tetracene, copper phthalocyanine, and the buckyball C(60). Short wavelength light generates singlet excitons in tetracene. These are subsequently split into two triplet excitons and transported through the phthalocyanine. In addition, the phthalocyanine absorbs photons below the singlet exciton energy of tetracene. To test tetracene in nanostructured blends, we fabricate coevaporated bulk heterojunctions and multilayer heterojunctions of tetracene and C(60). We measure a singlet fission efficiency of (71 ± 18)%, demonstrating that exciton fission can efficiently compete with exciton dissociation on the nanoscale.

  15. Singlet model interference effects with high scale UV physics

    Science.gov (United States)

    Dawson, S.; Lewis, I. M.

    2017-01-01

    One of the simplest extensions of the Standard Model (SM) is the addition of a scalar gauge singlet, S . If S is not forbidden by a symmetry from mixing with the Standard Model Higgs boson, the mixing will generate non-SM rates for Higgs production and decays. In general, there could also be unknown high energy physics that generates additional effective low energy interactions. We show that interference effects between the scalar resonance of the singlet model and the effective field theory (EFT) operators can have significant effects in the Higgs sector. We examine a non-Z2 symmetric scalar singlet model and demonstrate that a fit to the 125 GeV Higgs boson couplings and to limits on high mass resonances, S , exhibit an interesting structure and possible large cancellations of effects between the resonance contribution and the new EFT interactions, that invalidate conclusions based on the renormalizable singlet model alone.

  16. Theoretical study on the oxidation of zigzag silicon carbide nanotubes (SiCNTs) by singlet O2

    Science.gov (United States)

    Wang, Hong; Liu, Wei; Zhao, Jing-xiang

    2012-11-01

    Singlet O2 produced upon photoexcitation is a very important oxidative reagent. The study on its reaction with nanotube might be useful not only to evaluate the stability of the nanotube upon air exposure and sunlight, but also to modify the properties of the nanotube. Considering the unique properties and wide applications of silicon carbide nanotube (SiCNT), in this paper, we performed extensive density functional theory (DFT) calculations to study the oxidation of a series of zigzag (n,0) SiCNTs (n=6 to 12) by singlet O2. It is found that the reaction process contains two steps, namely, (i) [2+2] cycloaddition of a singlet O2 to the Si-C bond, followed by (ii) the dissociation of the O-O bond, leading to the formation of an epoxide configuration with a highly exothermicity (>4.00 eV). Compared with pure SiCNT, the cycloaddition of singlet O2 on tube leads to the decrease of the band gap, while the formation of the stable epoxy structure render band gap increase. Our results indicate that the SiCNT is more prone to be degraded after exposure to air and sunlight.

  17. Theoretical study on the oxidation of zigzag silicon carbide nanotubes (SiCNTs) by singlet O{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Wang Hong [School of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150040 (China); Liu Wei [Academy of Environmental Science of Heilongjiang, Harbin, 150056 (China); Zhao Jingxiang, E-mail: xjz_hmily@yahoo.com.cn [Department of Chemistry, Harbin Normal University, Harbin 150080 (China)

    2012-11-01

    Singlet O{sub 2} produced upon photoexcitation is a very important oxidative reagent. The study on its reaction with nanotube might be useful not only to evaluate the stability of the nanotube upon air exposure and sunlight, but also to modify the properties of the nanotube. Considering the unique properties and wide applications of silicon carbide nanotube (SiCNT), in this paper, we performed extensive density functional theory (DFT) calculations to study the oxidation of a series of zigzag (n,0) SiCNTs (n=6 to 12) by singlet O{sub 2}. It is found that the reaction process contains two steps, namely, (i) [2+2] cycloaddition of a singlet O{sub 2} to the Si-C bond, followed by (ii) the dissociation of the O-O bond, leading to the formation of an epoxide configuration with a highly exothermicity (>4.00 eV). Compared with pure SiCNT, the cycloaddition of singlet O{sub 2} on tube leads to the decrease of the band gap, while the formation of the stable epoxy structure render band gap increase. Our results indicate that the SiCNT is more prone to be degraded after exposure to air and sunlight.

  18. Singlet Oxygen Generation Mediated By Silicon Nanocrystal Assemblies

    Science.gov (United States)

    2011-01-01

    respect to conventional sources. Absorption maxima of dye photosensitizers used for singlet oxygen generation are between 630 to 700 nm. On the other hand...in aqueous solutions is its photodegradation due to photooxidation. This process drastically reduces photosensitizing ability of Si nanocrystals in a...above. Thus, the efficiency of photodegradation of organic molecules by singlet oxygen generated by PSi strongly depends on the nature of

  19. Optical detection of singlet oxygen from single cells

    DEFF Research Database (Denmark)

    Snyder, John; Skovsen, Esben; Lambert, John D. C.;

    2006-01-01

    The lowest excited electronic state of molecular oxygen, singlet molecular oxygen, O2(a 1g), is a reactive species involved in many chemical and biological processes. To better understand the roles played by singlet oxygen in biological systems, particularly at the sub-cellular level, optical too...... for mechanistic studies of intra- and inter-cellular signaling and events that ultimately lead to photo-induced cell death....

  20. Singlet Fission in Rubrene Derivatives: Impact of Molecular Packing

    KAUST Repository

    Sutton, Christopher

    2017-03-13

    We examine the properties of six recently synthesized rubrene derivatives (with substitutions on the side phenyl rings) that show vastly different crystal structures. In order to understand how packing in the solid state affects the excited states and couplings relevant for singlet fission, the lowest excited singlet (S), triplet (T), multiexciton (TT), and charge-transfer (CT) states of the rubrene derivatives are compared to known singlet fission materials [tetracene, pentacene, 5,12-diphenyltetracene (DPT), and rubrene itself]. While a small difference of less than 0.2 eV is calculated for the S and TT energies, a range of 0.50 to 1.2 eV in the CT energies and nearly 3 orders of magnitude in the electronic couplings are computed for the rubrene derivatives in their crystalline packings, which strongly affects the role of the CT state in facilitating SF. To rationalize experimental observations of singlet fission occurring in amorphous phases of rubrene, DPT, and tetracene, we use molecular dynamics (MD) simulations to assess the impact of molecular packing and orientations and to gain a better understanding of the parameters that control singlet fission in amorphous films compared to crystalline packings. The MD simulations point to a crystalline-like packing for thin films of tetracene; on the other hand, DPT, rubrene, and the rubrene derivatives all show various degrees of disorder with a number of sites that have larger electronic couplings than in the crystal, which can facilitate singlet fission in such thin films. Our analysis underlines the potential of these materials as promising candidates for singlet fission and helps understand how various structural motifs affect the critical parameters that control the ability of a system to undergo singlet fission.

  1. [Decrease of singlet oxygen chemiluminescence by the presence of carnosine].

    Science.gov (United States)

    Svachko, A G; Formaziuk, V E; Sergienko, V I

    1990-08-01

    To test antiradical medicines effect the chemical production of singlet oxygen (NaClO + H2O2) was investigated. The quantity singlet oxygen chemiluminescence was decreased in the presence of Japanese Catalin and Chine Baineiting, antirheumatic Voltaren and less strong Finish Catachrome and Carnosine. American Quinax does not possess such an effect. One of the possible starting mechanisms causing different diseases (atherosclerosis, cataract etc.) is destruction of biomembranes by active forms of oxygen.

  2. The role of vasoactive intestinal peptide in scavenging singlet oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Misra, B.R.; Misra, H.P. (Virginia Polytechnic Inst. and State Univ., Blacksburg (United States))

    1990-02-26

    The neuropeptide vasoactive intestinal peptide (VIP), a highly basic 28 amino acid peptide, has a widespread distribution in the body. The functional specificity of this peptide not only includes its potent vasodilatory activity, but also its role in protecting lungs against acute injury, in preventing T-lymphocyte proliferation and in modulating immune function. The purpose of this study was to examine the possible antioxidant properties of VIP. The authors found that VIP up to 50 {mu}g/ml had no inhibitory effect on its reduction of cytochrome C by xanthine and xanthine oxidase, indicating that the peptide does not have significant O{sub 2} scavenging ability. However, VIP was found to inhibit, in a dose-dependent manner, the {sup 1}O{sub 2} dependent 2, 2, 6, 6 tetramethyl piperidine oxide (TEMPO) formation. {sup 1}O{sub 2} was produced by rose benzal photosensitizing system and was detected as TEMP-{sup 1}O{sub 2} adduct (TEMPO) by electron paramagnetic resonance (EPR) spectroscopic technique. The formation of TEMPO signal was strongly inhibited by {beta}-carotene, histidine as well as azide, but not by superoxide dismutase (48 {mu}g/ml), catalase (20 {mu}g/ml) and mannitol (6mM), indicating that TEMPO signal was a TEMP-{sup 1}O{sub 2} adduct. These results indicate that VIP has potent antioxidant activity and may serve as a singlet O{sub 2} scavenger, thus it may modulate the oxidative tissue injury caused by this reactive oxygen species.

  3. The photophysics of monomeric bacteriochlorophylls c and d and their derivatives: properties of the triplet state and singlet oxygen photogeneration and quenching

    Science.gov (United States)

    Krasnovsky, A. A. Jr; Cheng, P.; Blankenship, R. E.; Moore, T. A.; Gust, D.

    1993-01-01

    Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen.

  4. Rates and singlet/triplet ratios from TADF transients

    CERN Document Server

    Nelson, Mitchell C

    2016-01-01

    Thermally activated delayed fluorescence has been reported in a number of OLED emitter materials engineered to have low singlet-triplet energy gaps. Here we derive closed solutions for steady state and transient behaviors and apply these results to data provided in recent reports. Earlier work has used yields, rates and a supplied forward crossing rate to estimate the reverse crossing rate and then obtain the singlet-triplet energy gap in a log-linear fit. In this work we use only the system relaxation times and obtain all five of the system constants: the singlet and triplet relaxation rates, the forward and reverse crossing rates and the singlet-triplet energy gap. These are then used to calculate the fluorescent/phosphorescent ratio and the singlet/triplet population ratio. Good fits are obtained for data from 4CzIPN and from the excimer m-MTDATA:t-Bu-PBD and the results appear to be consistent with the reported behaviors of OLEDS using these materials.

  5. Impurities near an antiferromagnetic-singlet quantum critical point

    Science.gov (United States)

    Mendes-Santos, T.; Costa, N. C.; Batrouni, G.; Curro, N.; dos Santos, R. R.; Paiva, T.; Scalettar, R. T.

    2017-02-01

    Heavy-fermion systems and other strongly correlated electron materials often exhibit a competition between antiferromagnetic (AF) and singlet ground states. Using exact quantum Monte Carlo simulations, we examine the effect of impurities in the vicinity of such an AF-singlet quantum critical point (QCP), through an appropriately defined "impurity susceptibility" χimp. Our key finding is a connection within a single calculational framework between AF domains induced on the singlet side of the transition and the behavior of the nuclear magnetic resonance (NMR) relaxation rate 1 /T1 . We show that local NMR measurements provide a diagnostic for the location of the QCP, which agrees remarkably well with the vanishing of the AF order parameter and large values of χimp.

  6. Probing scalar coupling differences via long-lived singlet states

    Science.gov (United States)

    DeVience, Stephen J.; Walsworth, Ronald L.; Rosen, Matthew S.

    2016-01-01

    We probe small scalar coupling differences via the coherent interactions between two nuclear spin singlet states in organic molecules. We show that the spin-lock induced crossing (SLIC) technique enables the coherent transfer of singlet order between one spin pair and another. The transfer is mediated by the difference in syn and anti vicinal or long-range J couplings among the spins. By measuring the transfer rate, we calculate a J coupling difference of 8 ± 2 mHz in phenylalanine-glycine-glycine and 2.57 ± 0.04 Hz in glutamate. We also characterize a coherence between two singlet states in glutamate, which may enable the creation of a long-lived quantum memory.

  7. Probing Scalar Coupling Differences via Long-Lived Singlet States

    CERN Document Server

    DeVience, Stephen J; Rosen, Matthew S

    2015-01-01

    We probe small scalar coupling differences via the coherent interactions between two nuclear spin singlet states in organic molecules. We show that the spin-lock induced crossing (SLIC) technique enables the coherent transfer of singlet order between one spin pair and another. The transfer is mediated by the difference in cis and trans vicinal J couplings among the spins. By measuring the transfer rate, we calculate a J coupling difference of $8 \\pm 2$ mHz in phenylalanine-glycine-glycine and $2.57 \\pm 0.04$ Hz in glutamate. We also characterize a coherence between two singlet states in glutamate, which may enable the creation of a long-lived quantum memory.

  8. The role of EDS1 (enhanced disease susceptibility) during singlet oxygen-mediated stress responses of Arabidopsis.

    Science.gov (United States)

    Ochsenbein, Christian; Przybyla, Dominika; Danon, Antoine; Landgraf, Frank; Göbel, Cornelia; Imboden, André; Feussner, Ivo; Apel, Klaus

    2006-08-01

    Upon a dark/light shift the conditional flu mutant of Arabidopsis starts to generate singlet oxygen (1O2) that is restricted to the plastid compartment. Distinct sets of genes are activated that are different from those induced by hydrogen peroxide/superoxide. One of the genes that is rapidly upregulated is EDS1 (enhanced disease susceptibility). The EDS1 protein has been shown to be required for the resistance to biotrophic pathogens and the accumulation of salicylic acid (SA) that enhances the defenses of a plant by inducing the synthesis of pathogen-related (PR) proteins. Because of the similarity of its N-terminal portion to the catalytic site of lipases, EDS1 has also been implicated with the release of polyunsaturated fatty acids and the subsequent formation of various oxylipins. The release of singlet oxygen in the flu mutant triggers a drastic increase in the concentration of free SA and activates the expression of PR1 and PR5 genes. These changes depend on the activity of EDS1 and are suppressed in flu/eds1 double mutants. Soon after the beginning of singlet oxygen production, the synthesis of oxylipins such as jasmonic acid (JA) and 12-oxophytodienoic acid (OPDA) also start and plants stop growing and induce a cell-death response. The inactivation of EDS1 does not affect oxylipin synthesis, growth inhibition and the initiation of cell death, but it does allow plants to recover much faster from singlet oxygen-mediated growth inhibition and it also suppresses the spread of necrotic lesions in leaves. Hence, singlet oxygen activates a complex stress-response program with EDS1 playing a key role in initiating and modulating several steps of it. This program includes not only responses to oxidative stress, but also responses known to be activated during plant-pathogen interactions and wounding.

  9. Identification of singlet oxygen photosensitizes in lambs drinking water in an alveld risk area in West Norway.

    Science.gov (United States)

    Tønnesen, Hanne Hjorth; Mysterud, Ivar; Karlsen, Jan; Skulberg, Olav M; Laane, Carl M M; Schumacher, Trond

    2013-02-05

    Alveld is a hepatogenous photosensitivity disorder in lambs. Although alveld has been known in Norway for more than 100years, there are still questions related to the cause of the disease. Phytoporphyrin has long been incriminated as the photosensitizer in hepatogenous photosensitivity diseases but previous findings suggest that the photosensitizing mechanism in alveld is more complex, possibly involving other co-factors. The current work investigates the presence of non-hepatogenous photosensitizers originating in lamb's drinking water from various sources. In addition samples of two of the predominent cyanobacteria found in a representative biofilm (i.e. aggregates of microbes) were identified and isolated in axenic (i.e. pure) cultures. Information from the absorption-, fluorescence emission-, and -excitation spectra and the action spectrum for the formation of singlet oxygen was combined in order to identify the chromophores responsible for the formation of singlet oxygen, e.g. phycocyanins from the cyanobacteria. The highest level of singlet oxygen formation was detected in lotic (i.e. flowing) water in the period consistent with the outbreak of the alveld disease in the area. Meteorological data indicate a warm and wet May with a high radiation exposure leading up to a colder and wet June with an even higher solar irradiance. The seasonal variation in the amount of photosensitizers in lamb's drinking water combined meteorological data can be important to predict the outbreak of alveld. Copyright © 2012 Elsevier B.V. All rights reserved.

  10. The Higgs singlet extension at LHC Run 2

    CERN Document Server

    Chalons, Guillaume; Robens, Tania; Stefaniak, Tim

    2016-01-01

    We discuss the current status of theoretical and experimental constraints on the real Higgs singlet extension of the Standard Model. For the second neutral (non-standard) Higgs boson the full mass range from 1 GeV to 1 TeV accessible at past and current collider experiments is considered. We present benchmark scenarios for searches for an additional Higgs state in the real Higgs singlet extension of the Standard Model in Run 2 of the LHC. We furthermore discuss electroweak corrections to the H to hh partial decay width within this model.

  11. Blind spots for neutralinos in NMSSM with light singlet scalar

    CERN Document Server

    Badziak, M; Szczerbiak, P

    2016-01-01

    A substantial contribution to the SM-like Higgs mass may come from the mixing with the lightest singlet-dominated scalar in NMSSM for moderate or large values of $\\tan\\beta$ [1]. The LSP neutralino in this model may also contain the singlet component - singlino. In this work we analyze the direct detection cross section for a Higgsino-singlino LSP with the emphasis on possible direct detection blind spots in the parameter space. Correlations between the LSP properties and the effects in the Higgs sector coming from the mixing are also discussed.

  12. Effective t-J model of pairing: singlet versus triplet

    Directory of Open Access Journals (Sweden)

    J.Spałek

    2008-09-01

    Full Text Available The t-J model is regarded as a canonical model of spin-singlet pairing induced by the kinetic exchange interaction also responsible for an antiferromagnetic ordering in the strongly correlated narrow-band systems. In the orbitally degenerate systems both ferromagnetic and antiferromagnetic kinetic exchange interactions occur. I briefly review the analogy between the singlet and triplet types of pairing, as well as draw some general conclusions about the pairing induced by these exchange interactions. The general discussion is also illustrated with a concrete case of a two-dimensional lattice with the spin triplet pairing.

  13. Generation of singlet oxygen by the glyoxal-peroxynitrite system.

    Science.gov (United States)

    Massari, Júlio; Tokikawa, Rita; Medinas, Danilo B; Angeli, José P F; Di Mascio, Paolo; Assunção, Nilson A; Bechara, Etelvino J H

    2011-12-28

    Diacetyl, methylglyoxal, and glyoxal are α-dicarbonyl catabolites prone to nucleophilic additions of amino groups of proteins and nucleobases, thereby triggering adverse biological responses. Because of their electrophilicity, in aqueous medium, they exist in a phosphate-catalyzed dynamic equilibrium with their hydrate forms. Diacetyl and methylglyoxal can be attacked by peroxynitrite (k(2) ≈ 1.0 × 10(4) M(-1) s(-1) and k(2) ≈ 1.0 × 10(5) M(-1) s(-1), respectively), a potent biological nucleophile and oxidant, yielding the acetyl radical from the homolysis of peroxynitrosocarbonyl adducts, and acetate or formate ions, respectively. We report here that glyoxal also reacts with peroxynitrite, yielding formate ion at rates at least 1 order of magnitude greater than does methylglyoxal. A triplet EPR signal (1:2:1; a(H) = 0.78 mT) attributable to hydrated formyl radical was detected by direct flow experiments. In the presence of the spin trap 2-methyl-2-nitrosopropane, the EPR spectrum displays the di-tert-butyl nitroxide signal, another signal assignable to the spin trapping adduct with hydrogen radical (a(N) = a(H) = 1.44 mT), probably formed from formyl radical decarbonylation, and a third EPR signal assignable to the formyl radical adduct of the spin trap (a(N) = 0.71 mT and a(H) = 0.14 mT). The novelty here is the detection of singlet oxygen ((1)Δ(g)) monomol light emission at 1270 nm during the reaction, probably formed by subsequent dioxygen addition to formyl radical and a Russell reaction of nascent formylperoxyl radicals. Accordingly, the near-infrared emission increases upon raising the peroxynitrite concentration in D(2)O buffer and is suppressed upon addition of O(2) ((1)Δ(g)) quenchers (NaN(3), l-His, H(2)O). Unequivocal evidence of O(2) ((1)Δ(g)) generation was also obtained by chemical trapping of (18)O(2) ((1)Δ(g)) with anthracene-9,10-divinylsulfonate, using HPLC/MS/MS for detection of the corresponding 9,10-endoperoxide derivative. Our

  14. Preparation of Nuclear Spin Singlet States using Spin-Lock Induced Crossing

    CERN Document Server

    DeVience, Stephen J; Rosen, Matthew S

    2013-01-01

    We introduce a broadly applicable technique to create nuclear spin singlet states in organic molecules and other many-atom systems. We employ a novel pulse sequence to produce a spin-lock induced crossing (SLIC) of the spin singlet and triplet energy levels, which enables triplet/singlet polarization transfer and singlet state preparation. We demonstrate the utility of the SLIC method by producing a long-lived nuclear spin singlet state on two strongly-coupled proton pairs in the tripeptide molecule phenylalanine-glycine-glycine dissolved in D2O, and by using SLIC to measure the J-couplings, chemical shift differences, and singlet lifetimes of the proton pairs. We show that SLIC is more efficient at creating nearly-equivalent nuclear spin singlet states than previous pulse sequence techniques, especially when triplet/singlet polarization transfer occurs on the same timescale as spin-lattice relaxation.

  15. Formats

    Directory of Open Access Journals (Sweden)

    Gehmann, Ulrich

    2012-03-01

    Full Text Available In the following, a new conceptual framework for investigating nowadays’ “technical” phenomena shall be introduced, that of formats. The thesis is that processes of formatting account for our recent conditions of life, and will do so in the very next future. It are processes whose foundations have been laid in modernity and which will further unfold for the time being. These processes are embedded in the format of the value chain, a circumstance making them resilient to change. In addition, they are resilient in themselves since forming interconnected systems of reciprocal causal circuits.Which leads to an overall situation that our entire “Lebenswelt” became formatted to an extent we don’t fully realize, even influencing our very percep-tion of it.

  16. Reactive species formed on proteins exposed to singlet oxygen

    DEFF Research Database (Denmark)

    Davies, Michael Jonathan

    2004-01-01

    Singlet oxygen ((1)O(2)) is believed to be generated in biological systems by a range of endogenous processes (e.g. enzymatic and chemical reactions) and exogenous stimuli (e.g. UV or visible light in the presence of a sensitiser). Kinetic data is consistent with proteins being a major target...

  17. Singlet oxygenation in microemulsion catalysed by vanadium chloroperoxidase

    NARCIS (Netherlands)

    Renirie, R.; Pierlot, C.; Wever, R.; Aubry, J.-M.

    2009-01-01

    Non-ionic microemulsions compatible with the enzyme vanadium chloroperoxidase were designed to perform singlet oxygenation of apolar substrates. The media were based on mono- and polydisperse ethoxylated fatty alcohols (CiEj). octane and aqueous buffer. "Fish" diagrams were determined to identify

  18. High throughput jet singlet oxygen generator for multi kilowatt SCOIL

    Science.gov (United States)

    Rajesh, R.; Singhal, Gaurav; Mainuddin; Tyagi, R. K.; Dawar, A. L.

    2010-06-01

    A jet flow singlet oxygen generator (JSOG) capable of handling chlorine flows of nearly 1.5 mol s -1 has been designed, developed, and tested. The generator is designed in a modular configuration taking into consideration the practical aspects of handling high throughput flows without catastrophic BHP carry over. While for such high flow rates a cross-flow configuration has been reported, the generator utilized in the present study is a counter flow configuration. A near vertical extraction of singlet oxygen is effected at the generator exit, followed by a 90° rotation of the flow forming a novel verti-horizontal COIL scheme. This allows the COIL to be operated with a vertical extraction SOG followed by the horizontal arrangement of subsequent COIL systems such as supersonic nozzle, cavity, supersonic diffuser, etc. This enables a more uniform weight distribution from point of view of mobile and other platform mounted systems, which is highly relevant for large scale systems. The present study discusses the design aspects of the jet singlet oxygen generator along with its test results for various operating ranges. Typically, for the intended design flow rates, the chlorine utilization and singlet oxygen yield have been observed to be ˜94% and ˜64%, respectively.

  19. Singlet-like Higgs bosons at present and future colliders

    CERN Document Server

    Buttazzo, Dario; Tesi, Andrea

    2015-01-01

    The presence of extra scalar singlets is a feature of several motivated extensions of the Standard Model, and the mixing of such a singlet with the Higgs boson is allowed to be quite large by current experiments. In this paper we perform a thorough phenomenological study of this possibility. We consider both direct and indirect searches, and we quantify the current constraints as well as the prospects for future hadron and lepton machines - from the forthcoming LHC run up to a futuristic 100 TeV proton-proton collider. The direct reaches are obtained extrapolating the current limits with a technique that we discuss and check with various tests. We find a strong complementarity between direct and indirect searches, with the former dominating for lower values of the singlet mass. We also find that the trilinear Higgs coupling can have sizeable deviations from its Standard Model value, a fact for which we provide an analytical understanding. The results are first presented in a general scalar singlet extension o...

  20. Explorative computational study of the singlet fission process

    NARCIS (Netherlands)

    Havenith, Remco W. A.; de Gier, Hilde D.; Broer, Ria

    2012-01-01

    Different ab initio methods, namely multi-reference and nonorthogonal configuration interaction techniques, are explored for their applicability in studying the singlet fission problem. It has been shown for 2-methyl-1,5-hexadiene that the (TT)-T-1 state can be identified using multi-reference techn

  1. Universal higher order singlet QED corrections to unpolarized lepton scattering

    Energy Technology Data Exchange (ETDEWEB)

    Bluemlein, J. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Kawamura, H. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany)]|[Radiation Laboratory, RIKEN (Japan)

    2006-12-15

    We calculate the universal flavor-singlet radiative QED corrections to unpolarized lepton scattering applicable to general differential scattering cross sections, involving charged fermions or photons in initial or final states. The radiators are derived to O(({alpha} ln (Q{sup 2}/m{sub f}{sup 2})){sup 5}) in analytic form. Numerical illustrations are given. (orig.)

  2. Electroweak interacting dark matter with a singlet scalar portal

    CERN Document Server

    Chiang, Cheng-Wei

    2015-01-01

    We investigate an electroweak interacting dark matter (DM) model in which the DM is the neutral component of the SU$(2)_L$ triplet fermion that couples to the standard model (SM) Higgs sector via an SM singlet Higgs boson. In this setup, the DM can have a CP-violating coupling to the singlet Higgs boson at the renormalizable level. As long as the nonzero Higgs portal coupling (singlet-doublet Higgs boson mixing) exists, we can probe CP violation of the DM via the electric dipole moment of the electron. Assuming the $\\mathcal{O}(1)$ CP-violating phase in magnitude, we investigate the relationship between the electron EDM and the singlet-like Higgs boson mass and coupling. It is found that for moderate values of the Higgs portal couplings, current experimental EDM bound is not able to exclude the wide parameter space due to a cancellation mechanism at work. We also study the spin-independent cross section of the DM in this model. It is found that although a similar cancellation mechanism may diminish the leadin...

  3. The study of the action of self-friction field on the atom and molecular structures by using combined Hartree-Fock-Roothaan theory for closed and open shells of any symmetry

    Science.gov (United States)

    Mamedov, B. A.; Çopuroğlu, E.

    2016-06-01

    In this work, we study the effects of self-friction field on the states of a single configuration of closed and open shells by using the Combined Hartree-Fock-Roothaan equations for atomic-molecular and nuclear systems. Here, we present a program that implements the evaluation of the various properties of atoms and molecular systems with respect to the various values of self-friction quantum numbers. An especially fast and accurate algorithm for the calculation of the self-friction multicenter molecular integrals is obtained by using one-range addition theorems. To demonstrate the action of self-friction field on the atomic and molecular systems we have performed the calculations of H2O, CH3, CH2 and NH3 molecules. For the derivations of the orbital, kinetic and total energies and linear combination coefficients, the results are given for various values of self-friction quantum numbers. For various values of self-friction quantum numbers the obtained results of the orbital, kinetic and total energies and linear combination coefficients have been analyzed.

  4. An assessment of pure, hybrid, meta, and hybrid-meta GGA density functional theory methods for open-shell systems: the case of the nonheme iron enzyme 8R-LOX.

    Science.gov (United States)

    Bushnell, Eric A C; Gauld, James W

    2013-01-15

    The performance of a range density functional theory functionals combined in a quantum mechanical (QM)/molecular mechanical (MM) approach was investigated in their ability to reliably provide geometries, electronic distributions, and relative energies of a multicentered open-shell mechanistic intermediate in the mechanism 8R-Lipoxygenase. With the use of large QM/MM active site chemical models, the smallest average differences in geometries between the catalytically relevant quartet and sextet complexes were obtained with the B3LYP(*) functional. Moreover, in the case of the relative energies between (4) II and (6) II, the use of the B3LYP(*) functional provided a difference of 0.0 kcal mol(-1). However, B3LYP(±) and B3LYP also predicted differences in energies of less than 1 kcal mol(-1). In the case of describing the electronic distribution (i.e., spin density), the B3LYP(*), B3LYP, or M06-L functionals appeared to be the most suitable. Overall, the results obtained suggest that for systems with multiple centers having unpaired electrons, the B3LYP(*) appears most well rounded to provide reliable geometries, electronic structures, and relative energies. Copyright © 2012 Wiley Periodicals, Inc.

  5. Singlet exciton fission in polycrystalline pentacene: from photophysics toward devices.

    Science.gov (United States)

    Wilson, Mark W B; Rao, Akshay; Ehrler, Bruno; Friend, Richard H

    2013-06-18

    Singlet exciton fission is the process in conjugated organic molecules bywhich a photogenerated singlet exciton couples to a nearby chromophore in the ground state, creating a pair of triplet excitons. Researchers first reported this phenomenon in the 1960s, an event that sparked further studies in the following decade. These investigations used fluorescence spectroscopy to establish that exciton fission occurred in single crystals of several acenes. However, research interest has been recently rekindled by the possibility that singlet fission could be used as a carrier multiplication technique to enhance the efficiency of photovoltaic cells. The most successful architecture to-date involves sensitizing a red-absorbing photoactive layer with a blue-absorbing material that undergoes fission, thereby generating additional photocurrent from higher-energy photons. The quest for improved solar cells has spurred a drive to better understand the fission process, which has received timely aid from modern techniques for time-resolved spectroscopy, quantum chemistry, and small-molecule device fabrication. However, the consensus interpretation of the initial studies using ultrafast transient absorption spectroscopy was that exciton fission was suppressed in polycrystalline thin films of pentacene, a material that would be otherwise expected to be an ideal model system, as well as a viable candidate for fission-sensitized photovoltaic devices. In this Account, we review the results of our recent transient absorption and device-based studies of polycrystalline pentacene. We address the controversy surrounding the assignment of spectroscopic features in transient absorption data, and illustrate how a consistent interpretation is possible. This work underpins our conclusion that singlet fission in pentacene is extraordinarily rapid (∼80 fs) and is thus the dominant decay channel for the photoexcited singlet exciton. Further, we discuss our demonstration that triplet excitons

  6. Morphological Tuning of the Energetics in Singlet Fission Organic Solar Cells

    NARCIS (Netherlands)

    Lin, Yun Hui L; Fusella, Michael A.; Kozlov, Oleg V.; Lin, Xin; Kahn, Antoine; Pshenichnikov, Maxim S.; Rand, Barry P.

    2016-01-01

    Effective singlet fission solar cells require both fast and efficient singlet fission as well as favorable energetics for harvesting the resulting triplet excitons. Notable progress has been made to engineer materials with rapid and efficient singlet fission, but the ability to control the energetic

  7. Singlet Fission of Non-polycyclic Aromatic Molecules in Organic Photovoltaics.

    Science.gov (United States)

    Kawata, So; Pu, Yong-Jin; Saito, Ayaka; Kurashige, Yuki; Beppu, Teruo; Katagiri, Hiroshi; Hada, Masaki; Kido, Junji

    2016-02-24

    Singlet fission of thienoquinoid compounds in organic photovoltaics is demonstrated. The escalation of the thienoquinoid length of the compounds realizes a suitable packing structure and energy levels for singlet fission. The magnetic-field dependence of the photocurrent and the external quantum efficiency of the devices reveal singlet fission of the compounds and dissociation of triplet excitons into charges.

  8. High-Yield Excited Triplet States in Pentacene Self-Assembled Monolayers on Gold Nanoparticles through Singlet Exciton Fission.

    Science.gov (United States)

    Kato, Daiki; Sakai, Hayato; Tkachenko, Nikolai V; Hasobe, Taku

    2016-04-18

    One of the major drawbacks of organic-dye-modified self-assembled monolayers on metal nanoparticles when employed for efficient use of light energy is the fact that singlet excited states on dye molecules can be easily deactivated by means of energy transfer to the metal surface. In this study, a series of 6,13-bis(triisopropylsilylethynyl)pentacene-alkanethiolate monolayer protected gold nanoparticles with different particle sizes and alkane chain lengths were successfully synthesized and were employed for the efficient generation of excited triplet states of the pentacene derivatives by singlet fission. Time-resolved transient absorption measurements revealed the formation of excited triplet states in high yield (172±26 %) by suppressing energy transfer to the gold surface.

  9. Singlet oxygen-mediated protein oxidation

    DEFF Research Database (Denmark)

    Wright, Adam; Bubb, William A; Hawkins, Clare Louise

    2002-01-01

    methods. The yield of these species is significantly enhanced in D2O and decreased by azide. Nuclear magnetic resonance and mass spectroscopic analysis of reaction mixtures, or materials separated by high-performance liquid chromatography, are consistent with the initial formation of an (undetected...... temperatures to give the corresponding alcohol. Their rate of decay is enhanced at 37 degrees C, or on exposure to UV light or metal ions, and gives rise to reactive radicals, via cleavage of the peroxide bond. These radicals have been characterized by electron paramagnetic resonance spin trapping...

  10. Filter-filter interactions. Photostabilization, triplet quenching and reactivity with singlet oxygen.

    Science.gov (United States)

    Lhiaubet-Vallet, Virginie; Marin, Mireia; Jimenez, Oscar; Gorchs, Olga; Trullas, Carles; Miranda, Miguel Angel

    2010-04-01

    In most sunscreens, the presence of two UV filters usually leads to synergistic effects regarding both the final performance and photostabilization of the active principles. However, this may also result in an accelerated decomposition if a photoreaction occurs between the single components. Thus, the understanding of photophysics and photochemistry of UV filter combinations is important to improve sunscreen photostability. In this context, photoreactivity of a commonly used UVA filter, namely tert-butylmethoxydibenzoylmethane (BM-DBM, also known as avobenzone, Parsol 1789, etc.), has been studied in the presence of six commercial solar filters: octyl methoxycinnamate, bis-ethylhexyloxyphenol methoxyphenyl triazine, octocrylene, diethylamino hydroxybenzoyl hexyl benzoate, octyl triazone and dioctyl butamido triazone. To achieve this goal, a mechanism-based strategy has been designed in order to investigate the photostability of sunscreens in a more systematic way, taking into account different processes: tautomerization of BM-DBM, formation of triplet excited state of BM-DBM in its diketo form and its quenching in the presence of UV filters, reactivity of UV filters under triplet photosensitization, quenching of singlet oxygen by UV filters and degradation of the latter under singlet oxygenation conditions.

  11. Single Cell Responses to Spatially Controlled Photosensitized Production of Extracellular Singlet Oxygen

    DEFF Research Database (Denmark)

    Pedersen, Brian Wett; Sinks, Louise E.; Breitenbach, Thomas;

    2011-01-01

    to localize the sensitized production of singlet oxygen. Cells in close proximity to the domain of singlet oxygen production showed morphological changes commonly associated with necrotic cell death. The elapsed post-irradiation “waiting period” before necrosis became apparent depended on (a) the distance...... between the cell membrane and the domain irradiated, (b) the incident laser fluence and, as such, the initial concentration of singlet oxygen produced, and (c) the lifetime of singlet oxygen. The data imply that singlet oxygen plays a key role in this process of light-induced cell death. The approach...... of using extracellularly-generated singlet oxygen to induce cell death can provide a solution to a problem that often limits mechanistic studies of intracellularly photosensitized cell death: it can be difficult to quantify the effective light dose, and hence singlet oxygen concentration, when using...

  12. Spin Density Distribution in Open-Shell Transition Metal Systems: A Comparative Post-Hartree-Fock, Density Functional Theory, and Quantum Monte Carlo Study of the CuCl2 Molecule.

    Science.gov (United States)

    Caffarel, Michel; Giner, Emmanuel; Scemama, Anthony; Ramírez-Solís, Alejandro

    2014-12-09

    We present a comparative study of the spatial distribution of the spin density of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell and the delocalization of the 3d hole over the chlorine atoms. More generally, this problem is representative of the difficulties encountered when studying open-shell metal-containing molecular systems. Here, it is shown that qualitatively different results for the spin density distribution are obtained from the various quantum-mechanical approaches. At the DFT level, the spin density distribution is found to be very dependent on the functional employed. At the QMC level, Fixed-Node Diffusion Monte Carlo (FN-DMC) results are strongly dependent on the nodal structure of the trial wave function. Regarding wave function methods, most approaches not including a very high amount of dynamic correlation effects lead to a much too high localization of the spin density on the copper atom, in sharp contrast with DFT. To shed some light on these conflicting results Full CI-type (FCI) calculations using the 6-31G basis set and based on a selection process of the most important determinants, the so-called CIPSI approach (Configuration Interaction with Perturbative Selection done Iteratively) are performed. Quite remarkably, it is found that for this 63-electron molecule and a full CI space including about 10(18) determinants, the FCI limit can almost be reached. Putting all results together, a natural and coherent picture for the spin distribution is proposed.

  13. Non-singlet Baryons in Less Supersymmetric Backgrounds

    CERN Document Server

    Giataganas, Dimitrios; Picos, Marco; Siampos, Konstadinos

    2012-01-01

    We analyze the holographic description of non-singlet baryons in various backgrounds with reduced supersymmetries and/or confining. We show that they exist in all AdS_5xY_5 backgrounds with Y_5 an Einstein manifold bearing five form flux, for a number of quarks 5N/8< k< N, independently on the supersymmetries preserved. This result still holds for gamma_i deformations. In the confining Maldacena-Nunez background non-singlet baryons also exist, although in this case the interval for the number of quarks is reduced as compared to the conformal case. We generalize these configurations to include a non-vanishing magnetic flux such that a complementary microscopical description can be given in terms of lower dimensional branes expanding into fuzzy baryons. This description is a first step towards exploring the finite 't Hooft coupling region.

  14. Singlet fermion Dark Matter within Left-Right Model

    CERN Document Server

    Patra, Sudhanwa

    2015-01-01

    We discuss singlet fermion dark matter within a left-right symmetric model promoting baryon and lepton number as separate gauge symmetries. We add a simple Dirac fermionic dark matter singlet under $SU(2)_{L,R}$ with nonzero and equal baryon and lepton number which ensures charge neutrality. Such a dark matter candidate interacts with SM particles through the extra $Z_{B,\\ell}$ gauge bosons. This can give rise to a dark matter particle of a few hundred GeV that couples to $\\sim$ TeV scale gauge bosons to give the correct relic density. This model thus accommodates TeV scale $Z_{B,\\ell}$ gauge bosons and other low scale BSM particles, which can be easily probed at LHC.

  15. Activated singlet exciton fission in a semiconducting polymer.

    Science.gov (United States)

    Musser, Andrew J; Al-Hashimi, Mohammed; Maiuri, Margherita; Brida, Daniele; Heeney, Martin; Cerullo, Giulio; Friend, Richard H; Clark, Jenny

    2013-08-28

    Singlet exciton fission is a spin-allowed process to generate two triplet excitons from a single absorbed photon. This phenomenon offers great potential in organic photovoltaics, but the mechanism remains poorly understood. Most reports to date have addressed intermolecular fission within small-molecular crystals. However, through appropriate chemical design chromophores capable of intramolecular fission can also be produced. Here we directly observe sub-100 fs activated singlet fission in a semiconducting poly(thienylenevinylene). We demonstrate that fission proceeds directly from the initial 1Bu exciton, contrary to current models that involve the lower-lying 2Ag exciton. In solution, the generated triplet pairs rapidly recombine and decay through the 2Ag state. In films, exciton diffusion breaks this symmetry and we observe long-lived triplets which form charge-transfer states in photovoltaic blends.

  16. Power Counting in Peripheral Partial Waves: The Singlet Channels

    CERN Document Server

    Valderrama, M Pavón; Yang, C -J; Long, Bingwei; Carbonell, Jaume; van Kolck, U

    2016-01-01

    We analyze the power counting of the peripheral singlet partial waves in nucleon-nucleon scattering. In agreement with conventional wisdom, we find that pion exchanges are perturbative in the peripheral singlets. We quantify from the effective field theory perspective the well-known suppression induced by the centrifugal barrier in the pion-exchange interactions. By exploring perturbation theory up to fourth order, we find that the one-pion-exchange potential in these channels is demoted from leading to subleading order by a given power of the expansion parameter that grows with the orbital angular momentum. We discuss the implications of these demotions for few-body calculations: though higher partial waves have been known for a long time to be irrelevant in these calculations (and are hence ignored), here we explain how to systematize the procedure in a way that is compatible with the effective field theory expansion.

  17. Singlet scalar dark matter: Monochromatic gamma rays and metastable vacua

    Science.gov (United States)

    Profumo, Stefano; Ubaldi, Lorenzo; Wainwright, Carroll

    2010-12-01

    We calculate the pair-annihilation cross section of real scalar singlet dark matter into two monoenergetic photons. We derive constraints on the theory parameter space from the Fermi limits on gamma-ray lines, and we compare with current limits from direct dark matter detection. We show that the new limits, albeit typically relevant only when the dark matter mass is close to half the standard model Higgs mass, rule out regions of the theory parameter space that are otherwise not constrained by other observations or experiments. In particular, the new excluded regions partly overlap with the parameter space where real scalar singlet dark matter might explain the anomalous signals observed by CDMS. We also calculate the lifetime of unstable vacuum configurations in the scalar potential, and show that the gamma-ray limits are quite relevant in regions where the electroweak vacuum is metastable with a lifetime longer than the age of the Universe.

  18. On the potential of a singlet scalar enhanced Standard Model

    CERN Document Server

    Ghosh, Swagata; Ray, Shamayita

    2015-01-01

    We investigate the parameter space of the Standard Model enhanced by a gauge singlet real scalar $S$. Taking into account all the theoretical and experimental constraints, we show the allowed parameter space for two different types of such singlet-enhanced Standard Model. For the first case, the scalar potential has an explicit $Z_2$-symmetry, and may lead to a dark matter candidate under certain conditions. For the second case, the scalar potential does not respect any $Z_2$. This is again divided into two subcategories: one where the Standard Model vacuum is stable, and one where it is unstable and can decay into a deeper minimum. We show how the parameters in the scalar potential control the range of validity of all these models. Finally, we show the effect of one-loop correction on the positions and depths of the minima of the potential.

  19. Triplet-triplet energy transfer and protection mechanisms against singlet oxygen in photosynthesis

    Science.gov (United States)

    Kihara, Shigeharu

    In photosynthesis, (bacterio)chlorophylls ((B)Chl) play a crucial role in light harvesting and electron transport. (B)Chls, however, are known to be potentially dangerous due to the formation of the triplet excited state which forms the singlet oxygen (1O2*) when exposed to the sunlight. Singlet oxygen is highly reactive and all modern organisms incorporate special protective mechanisms to minimize the oxidative damage. One of the conventional photoprotective mechanisms used by photosynthetic organisms is by the nearby carotenoids quenching the excess energy and releasing it by heat. In this dissertation, two major aspects of this process are studied. First, based on experimental data and model calculations, the oxygen content in a functioning oxygenic photosynthetic oxygen cell was determined. These organisms perform water splitting and as a result significant amount of oxygen can be formed within the organism itself. It was found, that contrary to some published estimates, the excess oxygen concentration generated within an individual cell is extremely low -- 0.025 ... 0.25 microM, i.e. about 103-104 times lower than the oxygen concentration in air saturated water. Such low concentrations imply that the first oxygenic photosynthetic cells that evolved in oxygen-free atmosphere of the Earth ~2.8 billion years ago might have invented the water splitting machinery (photosystem II) without the need for special oxygen-protective mechanisms, and the latter mechanisms could have evolved in the next 500 million years during slow rise of oxygen in the atmosphere. This result also suggests that proteins within photosynthetic membranes are not exposed to significant O2 levels and thus can be studied in vitro under the usual O2 levels. Second, the fate of triplet excited states in the Fenna Matthew Olson (FMO) pigment-protein complex is studied by means of time-resolved nanosecond spectroscopy and exciton model simulations. For the first time, the properties of several

  20. Towards building artificial light harvesting complexes: enhanced singlet-singlet energy transfer between donor and acceptor pairs bound to albumins.

    Science.gov (United States)

    Kumar, Challa V; Duff, Michael R

    2008-12-01

    Specific donor and acceptor pairs have been assembled in bovine serum albumin (BSA), at neutral pH and room temperature, and these dye-protein complexes indicated efficient donor to acceptor singlet-singlet energy transfer. For example, pyrene-1-butyric acid served as the donor and Coumarin 540A served as the acceptor. Both the donor and the acceptor bind to BSA with affinity constants in excess of 2x10(5) M(-1), as measured in absorption and circular dichroism (CD) spectral titrations. Simultaneous binding of both the donor and the acceptor chromophores was supported by CD spectra and one chromophore did not displace the other from the protein host, even when limited concentrations of the host were used. For example, a 1:1:1 complex between the donor, acceptor and the host can be readily formed, and spectral data clearly show that the binding sites are mutually exclusive. The ternary complexes (two different ligands bound to the same protein molecule) provided opportunities to examine singlet-singlet energy transfer between the protein-bound chromophores. Donor emission was quenched by the addition of the acceptor, in the presence of limited amounts of BSA, while no energy transfer was observed in the absence of the protein host, under the same conditions. The excitation spectra of the donor-acceptor-host complexes clearly show the sensitization of acceptor emission by the donor. Protein denaturation, as induced by the addition of urea or increasing the temperature to 360 K, inhibited energy transfer, which indicate that protein structure plays an important role. Sensitization also proceeded at low temperature (77 K) and diffusion of the donor or the acceptor is not required for energy transfer. Stern-Volmer quenching plots show that the quenching constant is (3.1+/-0.2)x10(4) M(-1), at low acceptor concentrations (albumins such as human and porcine proteins also served as good hosts for the above experiments. For the first time, non-natural systems have been self

  1. 5-Azido-2-aminopyridine, a new nitrene/nitrenium ion photoaffinity labeling agent that exhibits reversible intersystem crossing between singlet and triplet nitrenes.

    Science.gov (United States)

    Panov, Maxim S; Voskresenska, Valentyna D; Ryazantsev, Mikhail N; Tarnovsky, Alexander N; Wilson, R Marshall

    2013-12-26

    The photochemistry of a new photoaffinity labeling (PAL) agent, 5-azido-2-(N,N-diethylamino)pyridine, was studied in aprotic and protic solvents using femtosecond-to-microsecond transient absorption and product analysis, in conjunction with ab initio multiconfigurational and multireference quantum chemical calculations. The excited singlet S1 state is spectroscopically dark, whereas photoexcitation to higher-lying singlet excited S2 and S3 states drives the photochemical reaction toward a barrierless ultrafast relaxation path via two conical intersections to S1, where N2 elimination leads to the formation of the closed-shell singlet nitrene. The singlet nitrene undergoes intersystem crossing (ISC) to the triplet nitrene in aprotic and protic solvents as well as protonation to form the nitrenium ion. The ISC rate constants in aprotic solvents increase with solvent polarity, displaying a "direct" gap effect, whereas an "inverse" gap effect is observed in protic solvents. Transient absorption actinometry experiments suggest that a solvent-dependent fraction from 20% to 50% of nitrenium ions is generated on a time scale of a few tens of picoseconds. The closed-shell singlet and triplet nitrene are separated by a small energy gap in protic solvents. As a result, the unreactive triplet state nitrene undergoes delayed, thermally activated reverse ISC to reform the reactive closed-shell singlet nitrene, which subsequently protonates, forming the remaining fraction of nitrenium ions. The product studies demonstrate that the resulting nitrenium ion stabilized by the electron-donating 4-amino group yields the final cross-linked product with high, almost quantitative efficiency. The enhanced PAL function of this new azide with respect to the widely applied 4-amino-3-nitrophenyl azide is discussed.

  2. Triplet exciton dissociation in singlet exciton fission photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Jadhav, Priya J.; Mohanty, Aseema; Bulovic, Vladimir; Baldo, Marc A. [Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA (United States); Brown, Patrick R. [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA (United States); Thompson, Nicholas [Department of Materials Science, Massachusetts Institute of Technology, Cambridge, MA (United States); Wunsch, Benjamin [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA (United States); Yost, Shane R.; Hontz, Eric; Van Voorhis, Troy; Bawendi, Moungi G. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA (United States)

    2012-12-04

    Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Gradient Index Polymer Optics: Achromatic Singlet Lens Design

    Science.gov (United States)

    2010-01-01

    achromatic singlet lenses. The designs are based on gradient index lenses fabricated from nanolayered polymer materials. Raytraced results confirm the...fabricated from nanolayered polymer materials. Raytraced results confirm the achromatic performance of the designs. OCIS codes: (110.2760) Gradient...lenses in Zemax®. In order to model these lenses, user-defined surfaces had to be developed for the software. RL RG z y • • Δz • tc •n0 n1• Raytrace

  4. On threshold resummation of singlet structure and fragmentation functions

    CERN Document Server

    Grunberg, Georges

    2011-01-01

    The large x behavior of the physical evolution kernels appearing in the second order evolution equation of the F_2 singlet structure function is investigated. The validity of a leading logarithmic threshold resummation, analoguous to the one prevailing for the non-singlet physical kernel, is established, allowing to recover the predictions of Soar et al. for the double-logarithmic contributions (\\ln^i(1-x), i=4,5,6) to the four loop splitting function P^{(3)}_{qg}(x). Threshold resummation at the next-to-leading logarithmic level is found however to break down in the three loop kernel, except in the "supersymmetric" case C_A=C_F. Assuming a full threshold resummation does hold in this case also beyond three loop gives some information on the leading and next-to-leading single-logarithmic contributions (\\ln^i(1-x), i=2,3) to P^{(3)}_{qg}(x). Similar results are obtained for singlet fragmentation functions up to two loop, where a large x Gribov-Lipatov relation in the physical kernels is pointed out. Assuming t...

  5. Helicity evolution at small x : Flavor singlet and nonsinglet observables

    Science.gov (United States)

    Kovchegov, Yuri V.; Pitonyak, Daniel; Sievert, Matthew D.

    2017-01-01

    We extend our earlier results for the quark helicity evolution at small x [J. High Energy Phys. 01 (2016) 072, 10.1007/JHEP01(2016)072] to derive the small-x asymptotics of the flavor singlet and flavor nonsinglet quark helicity TMDs and PDFs and of the g1 structure function. In the flavor singlet case we rederive the evolution equations obtained in our previous paper on the subject [J. High Energy Phys. 01 (2016) 072, 10.1007/JHEP01(2016)072], performing additional cross-checks of our results. In the flavor nonsinglet case we construct new small-x evolution equations by employing the large-Nc limit. All evolution equations resum double-logarithmic powers of αsln2(1 /x ) in the polarization-dependent evolution along with the single-logarithmic powers of αsln (1 /x ) in the unpolarized evolution which includes saturation effects. We solve the linearized flavor nonsinglet equation analytically, obtaining an intercept which agrees with the one calculated earlier by Bartels, Ermolaev and Ryskin [Z. Phys. C 70, 273 (1996)] using the infrared evolution equations. Our numerical solution of the linearized large-Nc evolution equations for the flavor singlet case is presented in the accompanying Letter [Phys. Rev. Lett. 118, 052001 (2017), 10.1103/PhysRevLett.118.052001] and is further discussed here.

  6. IDMS: inert dark matter model with a complex singlet

    Science.gov (United States)

    Bonilla, Cesar; Sokolowska, Dorota; Darvishi, Neda; Diaz-Cruz, J. Lorenzo; Krawczyk, Maria

    2016-06-01

    We study an extension of the inert doublet model (IDM) that includes an extra complex singlet of the scalars fields, which we call the IDMS. In this model there are three Higgs particles, among them a SM-like Higgs particle, and the lightest neutral scalar, from the inert sector, remains a viable dark matter (DM) candidate. We assume a non-zero complex vacuum expectation value for the singlet, so that the visible sector can introduce extra sources of CP violation. We construct the scalar potential of IDMS, assuming an exact Z 2 symmetry, with the new singlet being Z 2-even, as well as a softly broken U(1) symmetry, which allows a reduced number of free parameters in the potential. In this paper we explore the foundations of the model, in particular the masses and interactions of scalar particles for a few benchmark scenarios. Constraints from collider physics, in particular from the Higgs signal observed at the Large Hadron Collider with {M}h≈ 125 {{GeV}}, as well as constraints from the DM experiments, such as relic density measurements and direct detection limits, are included in the analysis. We observe significant differences with respect to the IDM in relic density values from additional annihilation channels, interference and resonance effects due to the extended Higgs sector.

  7. Singlet-Doublet model: dark matter searches and LHC constraints

    Energy Technology Data Exchange (ETDEWEB)

    Calibbi, Lorenzo [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,Chinese Academy of Sciences,Beijing 100190 (China); Service de Physique Théorique, Université Libre de Bruxelles,C.P. 225, B-1050, Brussels (Belgium); Mariotti, Alberto; Tziveloglou, Pantelis [Theoretische Natuurkunde and IIHE/ELEM, Vrije Universiteit Brussel,and International Solvay Institutes,Pleinlaan 2, B-1050 Brussels (Belgium)

    2015-10-19

    The Singlet-Doublet model of dark matter is a minimal extension of the Standard Model with dark matter that is a mixture of a singlet and a non-chiral pair of electroweak doublet fermions. The stability of dark matter is ensured by the typical parity symmetry, and, similar to a ‘Bino-Higgsino’ system, the extra matter content improves gauge coupling unification. We revisit the experimental constraints on the Singlet-Doublet dark matter model, combining the most relevant bounds from direct (spin independent and spin dependent) and indirect searches. We show that such comprehensive analysis sets strong constraints on a large part of the 4-dimensional parameter space, closing the notorious ‘blind-spots’ of spin independent direct searches. Our results emphasise the complementarity of direct and indirect searches in probing dark matter models in diverse mass scale regimes. We also discuss the LHC bounds on such scenario, which play a relevant role in the low mass region of the dark matter candidate.

  8. Singlet-Doublet Model: Dark matter searches and LHC constraints

    CERN Document Server

    Calibbi, Lorenzo; Tziveloglou, Pantelis

    2015-01-01

    The Singlet-Doublet model of dark matter is a minimal extension of the Standard Model with dark matter that is a mixture of a singlet and a non-chiral pair of electroweak doublet fermions. The stability of dark matter is ensured by the typical parity symmetry, and, similar to a "Bino-Higgsino" system, the extra matter content improves gauge coupling unification. We revisit the experimental constraints on the Singlet-Doublet dark matter model, combining the most relevant bounds from direct (spin independent and spin dependent) and indirect searches. We show that such comprehensive analysis sets strong constraints on a large part of the 4-dimensional parameter space, closing the notorious "blind-spots" of spin independent direct searches. Our results emphasise the complementarity of direct and indirect searches in probing dark matter models in diverse mass scale regimes. We also discuss the LHC bounds on such scenario, which play a relevant role in the low mass region of the dark matter candidate.

  9. keV sterile neutrino dark matter from singlet scalar decays: basic concepts and subtle features

    Energy Technology Data Exchange (ETDEWEB)

    Merle, Alexander; Totzauer, Maximilian [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, 80805 München (Germany)

    2015-06-08

    We perform a detailed and illustrative study of the production of keV sterile neutrino Dark Matter (DM) by decays of singlet scalars in the early Universe. In the current study we focus on providing a clear and general overview of this production mechanism. For the first time we study all regimes possible on the level of momentum distribution functions, which we obtain by solving a system of Boltzmann equations. These quantities contain the full information about the production process, which allows us to not only track the evolution of the DM generation but to also take into account all bounds related to the spectrum, such as constraints from structure formation or from avoiding too much dark radiation. In particular we show that this simple production mechanism can, depending on the regime, lead to strongly non-thermal DM spectra which may even feature more than one peak in the momentum distribution. These cases could have particularly interesting consequences for cosmological structure formation, as their analysis requires more refined tools than the simplistic estimate using the free-streaming horizon. Here we present the mechanism including all concepts and subtleties involved, for now using the assumption that the effective number of relativistic degrees of freedom is constant during DM production, which is applicable in a significant fraction of the parameter space. This allows us to derive analytical results to back up our detailed numerical computations, thus leading to the most comprehensive picture of keV sterile neutrino DM production by singlet scalar decays that exists up to now.

  10. Influence of clay minerals on curcumin properties: Stability and singlet oxygen generation

    Science.gov (United States)

    Gonçalves, Joyce L. S.; Valandro, Silvano R.; Poli, Alessandra L.; Schmitt, Carla C.

    2017-09-01

    Curcumin (CUR) has showed promising photophysical properties regarding to biological and chemical sciences. However, the main barrier for those applications are their low solubility and stability in aqueous solution. The effects of two different clay minerals, the montmorillonite (SWy-2) and the Laponite RD (Lap) nanoclay, on the stabilization of Curcumin were investigated. Their effects were compared with two well-established environments (acidic and neutral aqueous media). CUR/clay hybrids were prepared using a simple and fast method, where CUR solution was added into clay suspensions, to obtain well dispersed hybrids in water. The degradation process of CUR and CUR/clays hybrids was investigated using UV-Vis spectroscopic. For both studied hybrids, the CUR degradation process was suppressed by the presence of the clay particles. Furthermore, the Lap showed a great stabilization effect than SWy-2. This behavior was due to the smaller particle size and higher exfoliation ability of Lap, providing a large surface for CUR adsorption compared to SWy-2. The degradation process of CUR solutions and CUR/clay hybrids was also studied in the presence of light. CUR photodegradation process was faster not only in the aqueous solution but also in the clay suspension compared to those studied in the dark. The presence of clay particles accelerated the photodegradation of CUR due to the products formation in the reactions between CUR and oxygen radicals. Our results showed that the singlet oxygen quantum yield (ΦΔ) of CUR were about 59% higher in the clay suspensions than CUR in aqueous solution. Therefore, the formation of CUR/clay hybrids, in particularly with Lap, suppressed the degradation in absence light of CUR and increased the singlet oxygen generation, which makes this hybrids of CUR/clay a promising material to enlarge the application of CUR in the biological sciences.

  11. Direct spectroscopic observation of singlet oxygen quenching and kinetic studies of physical and chemical singlet oxygen quenching rate constants of synthetic antioxidants (BHA, BHT, and TBHQ) in methanol.

    Science.gov (United States)

    Lee, Jun Hyun; Jung, Mun Yhung

    2010-08-01

    Singlet oxygen quenching by synthetic antioxidants (BHA, BHT, and TBHQ) was directly observed by spectroscopic monitoring of luminescence at 1268 nm. The luminescence data showed unambiguous evidence of singlet oxygen quenching by synthetic phenolic antioxidants with the highest activity for TBHQ, followed by BHA and BHT. The protective activities of these synthetic antioxidants on alpha-terpinene oxidation with chemically-induced singlet oxygen under dark further confirmed their singlet oxygen quenching abilities. Total singlet oxygen quenching rate constants (k(r) + k(q)) of BHA, BHT, and TBHQ were determined in a system containing alpha-terpinene (as a singlet oxygen trap) and methylene blue (as a sensitizer) during light irradiation, and the values were 5.14 x 10(7), 3.41 x 10(6), and 1.99 x 10(8) M(-1)s(-1), respectively. After the k(r) value of alpha-terpinene was first determined, the k(r) values of the synthetic antioxidants were calculated by measuring their relative reaction rates with singlet oxygen to that of alpha-terpinene under the identical conditions. The k(r) values of the BHA, BHT, and TBHQ were 3.90 x 10(5), 1.23 x 10(5), and 2.93 x 10(6), M(-1)s(-1). The percent partition of chemical quenching over total singlet oxygen quenching (k(r) x 100)/(k(r) + k(q)) for BHA, BHT, and TBHQ were 0.76%, 3.61%, and 1.47%, respectively. The results showed that the synthetic antioxidants quench singlet oxygen almost exclusively through the mechanism of physical quenching. This represents the first report on the singlet oxygen quenching mechanism of these synthetic antioxidants. Practical Application: The synthetic antioxidants, especially TBHQ, have been found to have a strong singlet oxygen quenching ability. This article also clearly showed that singlet oxygen quenching by synthetic antioxidants was mainly by the physical quenching mechanism. The results suggested that these synthetic antioxidants, especially TBHQ, could be used practically for the protection

  12. Long-Lived Heteronuclear Spin-Singlet States in Liquids at a Zero Magnetic field

    Science.gov (United States)

    Emondts, M.; Ledbetter, M. P.; Pustelny, S.; Theis, T.; Patton, B.; Blanchard, J. W.; Butler, M. C.; Budker, D.; Pines, A.

    2014-02-01

    We report an observation of long-lived spin-singlet states in a C-H113 spin pair in a zero magnetic field. In C13-labeled formic acid, we observe spin-singlet lifetimes as long as 37 s, about a factor of 3 longer than the T1 lifetime of dipole polarization in the triplet state. In contrast to common high-field experiments, the observed coherence is a singlet-triplet coherence with a lifetime T2 longer than the T1 lifetime of dipole polarization in the triplet manifold. Moreover, we demonstrate that heteronuclear singlet states formed between a H1 and a C13 nucleus can exhibit longer lifetimes than the respective triplet states even in the presence of additional spins that couple to the spin pair of interest. Although long-lived homonuclear spin-singlet states have been extensively studied, this is the first experimental observation of analogous singlet states in heteronuclear spin pairs.

  13. New strategies to produce and detect singlet oxygen in a cell

    DEFF Research Database (Denmark)

    Gollmer, Anita

    2012-01-01

    Singlet oxygen, the first excited electronic state of molecular oxygen, plays a major role in oxygen-dependent photo-induced cell death. In such systems, singlet oxygen is generally produced in a photosensitized process wherein light is absorbed by a molecule (the so-called sensitizer) which...... of the general methodology to generate and detect singlet oxygen is currently of great importance in order to better understand the roles played by singlet oxygen in photo-induced cell death. From a mechanistic perspective, experiments performed at the level of a single cell provide unique insight...... of a new, commercially available fluorescent probe called Singlet Oxygen Sensor Green® (SOSG) was examined in this dissertation. The pertinent methodology involves a trapping reaction with singlet oxygen that in turn changes the fluorescence quantum yield of the probe. First, it is shown that the immediate...

  14. Antiviral agents derived from novel 1-adamantyl singlet nitrenes.

    Science.gov (United States)

    Kesel, Andreas J; Weiss, Hans-Christoph; Schönleber, Andreas; Day, Craig W; Barnard, Dale L; Detorio, Mervi A; Schinazi, Raymond F

    2012-12-07

    Amantadine constitutes an interesting, diamond crystal lattice-shaped, antivirally active amine with an inhibitory effect on influenza A viruses causing common 'flu' in humans. Unfortunately, amantadine forfeited most of its therapeutic potential because of resistance development in recent influenza A virus isolates. The antiviral efficacy of amantadine congeners can be chemically modified, resulting in re-constitution, improvement and/or extension of antiviral activities mediated by amino-adamantyls. Newly synthesized compounds were evaluated towards HIV type-1 (HIV-1) replication in primary human lymphocytes. One N-phenacyl amantadine derivative was investigated for inhibiting the in vitro replication of respiratory viruses (influenza A viruses, influenza B virus, human parainfluenza virus type 3 and severe acute respiratory syndrome coronavirus). Two ketone-stabilized 1-adamantyl singlet nitrenes were discovered serendipitously. To our best knowledge these are the first persistently stable nitrenes to be reported. Their structure was proved by determining the X-ray single crystal structure of one hydrolytic elaboration product. This salt adduct revealed an incommensurately modulated crystal structure, which was solved by extensive computational refinement. We could show that ketone-stabilized 1-adamantyl singlet nitrenes are versatile synthons for the synthesis of antiviral drug candidates. An amantadine-folate conjugate was inhibitory on HIV-1 replication in primary human lymphocytes, and one N-phenacyl amantadine derivative was inhibitory towards low pathogenic avian influenza A virus (H5N1) replication in vitro. These results indicate that the aromatic-aliphatic ketone-stabilized 1-adamantyl singlet nitrenes, beyond being of fundamental interest in organic chemistry, represent versatile synthons for the synthesis of new amantadine-related potentially antiviral drugs.

  15. Distinct properties of the triplet pair state from singlet fission.

    Science.gov (United States)

    Trinh, M Tuan; Pinkard, Andrew; Pun, Andrew B; Sanders, Samuel N; Kumarasamy, Elango; Sfeir, Matthew Y; Campos, Luis M; Roy, Xavier; Zhu, X-Y

    2017-07-01

    Singlet fission, the conversion of a singlet exciton (S1) to two triplets (2 × T1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state (1)(TT). Despite extensive research, the nature of the (1)(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound (1)(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of the S1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to (1)(TT)→Sn and S1→Sn' transitions; Sn and Sn' likely come from the antisymmetric and symmetric linear combinations, respectively, of the S2 state localized on each pentacene unit in the dimer molecule. The (1)(TT)→Sn transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound (1)(TT) state also shows chemical reactivity that is distinctively different from that of an individual T1 state. Using an electron-accepting iron oxide molecular cluster [Fe8O4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T1 in pentacene but not from the tightly bound (1)(TT) state. Thus, reducing intertriplet electronic coupling in (1)(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.

  16. Measuring Long-Lived ^{13}C-Singlet State Lifetimes at Natural Abundance

    CERN Document Server

    Claytor, Kevin E; Feng, Yesu; Warren, Warren

    2013-01-01

    Long-lived singlet states hold the potential to drastically extend the lifetime of hyperpolarization in molecular tracers for in-vivo magnetic resonance imaging (MRI). Such long lived hyperpolarization can be used for elucidation of fundamental metabolic pathways, early diagnosis, and optimization of clinical tests for new medication. All previous measurements of 13C singlet state lifetimes rely on costly and time consuming syntheses of 13C labeled compounds. Here we show that it is possible to determine 13C singlet state lifetimes by detecting the naturally abundant doubly-labeled species. This approach allows for rapid and low cost screening of potential molecular biomarkers bearing long-lived singlet states.

  17. Singlet vs Nonsinglet Perturbative Renormalization of Fermion Bilinears

    CERN Document Server

    Constantinou, M; Panagopoulos, H; Spanoudes, G

    2016-01-01

    In this paper we present the perturbative evaluation of the difference between the renormalization functions of flavor singlet and nonsinglet bilinear quark operators on the lattice. The computation is performed to two loops and to lowest order in the lattice spacing, for a class of improved lattice actions, including Wilson, tree-level (TL) Symanzik and Iwasaki gluons, twisted mass and SLiNC Wilson fermions, as well as staggered fermions with twice stout-smeared links. In the staggered formalism, the stout smearing procedure is also applied to the definition of bilinear operators.

  18. Singlet scalar Dark Matter in Dark Two Higgs Doublet Model

    CERN Document Server

    Gaitan, R; de Oca, J H Montes

    2014-01-01

    We consider the case of the Dark Two Higgs Doublet Model (D2HDM) where a $U(1)'$ symmetry group and an extra Higgs doublet are added to the Standard Model. This model leads to a gauge singlet particle as an interesting Dark Matter (DM) candidate. We obtain phenomenological constraints to the parameter space of the model considering the one necessary to produce the correct density of thermal relic dark matter $\\Omega h^2$. We find a relation between the masses of the DM matter candidate $m_S$ and $m_{Z'}$ that satisfy the relic density for given values of $\\tan\\beta$.

  19. Entanglement and Metrology with Singlet-Triplet Qubits

    Science.gov (United States)

    Shulman, Michael Dean

    Electron spins confined in semiconductor quantum dots are emerging as a promising system to study quantum information science and to perform sensitive metrology. Their weak interaction with the environment leads to long coherence times and robust storage for quantum information, and the intrinsic tunability of semiconductors allows for controllable operations, initialization, and readout of their quantum state. These spin qubits are also promising candidates for the building block for a scalable quantum information processor due to their prospects for scalability and miniaturization. However, several obstacles limit the performance of quantum information experiments in these systems. For example, the weak coupling to the environment makes inter-qubit operations challenging, and a fluctuating nuclear magnetic field limits the performance of single-qubit operations. The focus of this thesis will be several experiments which address some of the outstanding problems in semiconductor spin qubits, in particular, singlet-triplet (S-T0) qubits. We use these qubits to probe both the electric field and magnetic field noise that limit the performance of these qubits. The magnetic noise bath is probed with high bandwidth and precision using novel techniques borrowed from the field of Hamiltonian learning, which are effective due to the rapid control and readout available in S-T 0 qubits. These findings allow us to effectively undo the undesired effects of the fluctuating nuclear magnetic field by tracking them in real-time, and we demonstrate a 30-fold improvement in the coherence time T2*. We probe the voltage noise environment of the qubit using coherent qubit oscillations, which is partially enabled by control of the nuclear magnetic field. We find that the voltage noise bath is frequency-dependent, even at frequencies as high as 1MHz, and it shows surprising and, as of yet, unexplained temperature dependence. We leverage this knowledge of the voltage noise environment, the

  20. Tetraphenylhexaazaanthracenes: 16π Weakly Antiaromatic Species with Singlet Ground States.

    Science.gov (United States)

    Constantinides, Christos P; Zissimou, Georgia A; Berezin, Andrey A; Ioannou, Theodosia A; Manoli, Maria; Tsokkou, Demetra; Theodorou, Eleni; Hayes, Sophia C; Koutentis, Panayiotis A

    2015-08-21

    Tetraphenylhexaazaanthracene, TPHA-1, is a fluorescent zwitterionic biscyanine with a closed-shell singlet ground state. TPHA-1 overcomes its weak 16π antiaromaticity by partitioning its π system into 6π positive and 10π negative cyanines. The synthesis of TPHA-1 is low yielding and accompanied by two analogous TPHA isomers: the deep red, non-charge-separated, quinoidal TPHA-2, and the deep green TPHA-3 that partitions into two equal but oppositely charged 8π cyanines. The three TPHA isomers are compared.

  1. [Photosensitized luminescence of singlet oxygen in aqueous solutions].

    Science.gov (United States)

    Krasnovskiĭ, A A

    1979-01-01

    The photoluminescence of singlet oxygen has been observed in air saturated solutions of riboflavin in D2O and mixtures of D2O and H2O. The excitation spectrum coincides with the absorption spectrum of the pigment, the emission maximum lies at 1275 nm. In D2O the quantum yield is approximately 1,2 x 10(-7). H2O quenches the luminescence. Analysis of quenching has shown that the quantum yield in H2O is less than in D2O by the factor of 20.

  2. Electroweak baryogenesis and gravitational waves from a real scalar singlet

    CERN Document Server

    Vaskonen, Ville

    2016-01-01

    We consider a real scalar singlet field which provides a strong first order electroweak phase transition via its coupling to the Higgs boson, and gives a CP violating contribution on the top quark mass via a dimension 6 operator. We study the correlation between the baryon-to-entropy ratio produced by electroweak baryogenesis, and the gravitational wave signal from the electroweak phase transition. We show that the future gravitational wave experiments can test in particular the region of the model parameter space where the observed baryon-to-entropy ratio can be obtained even if the new physics scale, which is explicit in the dimension 6 operator, is high.

  3. A Flippon Related Singlet at the LHC II

    CERN Document Server

    Li, Tianjun; Mayes, Van E; Nanopoulos, Dimitri V

    2016-01-01

    We consider the 750 GeV diphoton resonance at the 13 TeV LHC in the ${\\cal F}$-$SU(5)$ model with a Standard Model (SM) singlet field which couples to TeV-scale vector-like particles, dubbed $flippons$. This singlet field assumes the role of the 750 GeV resonance, with production via gluon fusion and subsequent decay to a diphoton via the vector-like particle loops. We present a numerical analysis showing that the observed 8 TeV and 13 TeV diphoton production cross-sections can be generated in the model space with realistic electric charges and Yukawa couplings, for light and heavy vector-like masses. We further discuss the experimental viability of the light vector-like masses in a General No-Scale ${\\cal F}$-$SU(5)$ model, offering a few benchmark scenarios that can satisfy all experimental constraints imposed by the LHC and other essential experiments.

  4. Natural NMSSM with a light singlet Higgs and singlino LSP

    Energy Technology Data Exchange (ETDEWEB)

    Potter, C.T. [University of Oregon, Physics Department, Eugene (United States)

    2016-01-15

    Supersymmetry (SUSY) is an attractive extension of the Standard Model (SM) of particle physics which solves the SM hierarchy problem. Motivated by the theoretical μ-term problem of the Minimal Supersymmetric Model (MSSM), the Next-to MSSM (NMSSM) can also account for experimental deviations from the SM like the anomalous muon magnetic moment and the dark matter relic density. Natural SUSY, motivated by naturalness considerations, exhibits small fine tuning and a characteristic phenomenology with light higgsinos, stops, and gluinos. We describe a scan in NMSSM parameter space motivated by Natural SUSY and guided by the phenomenology of an NMSSM with a slightly broken Peccei-Quinn symmetry and a lightly coupled singlet. We identify a scenario which survives experimental constraints with a light singlet Higgs and a singlino lightest SUSY particle. We then discuss how the scenario is not presently excluded by searches at the Large Hadron Collider (LHC) and which channels are promising for discovery at the LHC and International Linear Collider. (orig.)

  5. Singlet Oxygen Detection Using Red Wine Extracts as Photosensitizers.

    Science.gov (United States)

    Lagunes, Irene; Vázquez-Ortega, Fernanda; Trigos, Ángel

    2017-09-01

    Moderate consumption of red wine provides beneficial effects to health. This is attributed to polyphenol compounds present in wine such as resveratrol, quercetin, gallic acid, rutin, and vanillic acid. The amount of these antioxidants is variable; nevertheless, the main beneficial effects of red wine are attributed to resveratrol. However, it has been found that resveratrol and quercetin are able to photosensitize singlet oxygen generation and conversely, gallic acid acts as quencher. Therefore, and since resveratrol and quercetin are some of the most important antioxidants reported in red wines, the aim of this research was to evaluate the photosensitizing ability of 12 red wine extracts through photo-oxidation of ergosterol. The presence of (1) O2 was detected by ergosterol conversion into peroxide of ergosterol through (1) H NMR analysis. Our results showed that 10 wine extracts were able to act as photosensitizers in the generation of singlet oxygen. The presence of (1) O2 can damage other compounds of red wine and cause possible organoleptic alterations. Finally, although the reaction conditions employed in this research do not resemble the inherent conditions in wine making processing or storing, or even during its consumption, this knowledge could be useful to prevent possible pro-oxidant effects and avoid detrimental effects in red wines. © 2017 Institute of Food Technologists®.

  6. Discrete R symmetries for the MSSM and its singlet extensions

    CERN Document Server

    Lee, Hyun Min; Ratz, Michael; Ross, Graham G; Schieren, Roland; Schmidt-Hoberg, Kai; Vaudrevange, Patrick K S

    2011-01-01

    We determine the anomaly free discrete R symmetries, consistent with the MSSM, that commute with SU(5) and suppress the $\\mu$ parameter and nucleon decay. We show that the order M of such $Z_M^R$ symmetries has to divide 24 and identify 5 viable symmetries. The simplest possibility is a $Z_4^R$ symmetry which commutes with SO(10). We present a string-derived model with this $Z_4^R$ symmetry and the exact MSSM spectrum below the GUT scale; in this model $Z_4^R$ originates from the Lorentz symmetry of compactified dimensions. We extend the discussion to include the singlet extensions of the MSSM and find $Z_4^R$ and $Z_8^R$ are the only possible symmetries capable of solving the $\\mu$ problem in the NMSSM. We also show that a singlet extension of the MSSM based on a $Z_{24}^R$ symmetry can provide a simultaneous solution to the $\\mu$ and strong CP problem with the axion coupling in the favoured window.

  7. Discrete R symmetries for the MSSM and its singlet extensions

    Science.gov (United States)

    Lee, Hyun Min; Raby, Stuart; Ratz, Michael; Ross, Graham G.; Schieren, Roland; Schmidt-Hoberg, Kai; Vaudrevange, Patrick K. S.

    2011-09-01

    We determine the anomaly free discrete R symmetries, consistent with the MSSM, that commute with SU(5) and suppress the μ parameter and nucleon decay. We show that the order M of such ZMR symmetries has to divide 24 and identify 5 viable symmetries. The simplest possibility is a Z4R symmetry which commutes with SO(10). We present a string-derived model with this Z4R symmetry and the exact MSSM spectrum below the GUT scale; in this model Z4R originates from the Lorentz symmetry of compactified dimensions. We extend the discussion to include the singlet extensions of the MSSM and find Z4R and Z8R are the only possible symmetries capable of solving the μ problem in the NMSSM. We also show that a singlet extension of the MSSM based on a Z24R symmetry can provide a simultaneous solution to the μ and strong CP problem with the axion coupling in the favoured window.

  8. CP violation in the Standard Model with a complex singlet

    CERN Document Server

    Darvishi, Neda

    2016-01-01

    CP violation of the Standard Model (SM) is insufficient to explain the baryon asymmetry in the Universe and therefore an additional source of CP violation is needed. Here we consider the extension of the SM by a neutral complex singlet and discuss the physical conditions for a spontaneous CP violation in such model. In the model there are three neutral Higgs particles. Assuming the lightest one to be the 125 GeV Higgs boson found at LHC we calculate masses of the additional Higgs scalars and perform a numerical study of the allowed region of parameters. The scenario according to which the SM-like Higgs particle comes mostly from the SM-like SU(2) doublet, with a small modification coming from the singlet, is in agreement with the newest $R_{\\gamma \\gamma}$ and precise EW (parameters S, T) data. We have found that the Jarlskog invariant, measuring the strength of the CP violation, can be enhanced as compared to the one in the SM, at the same time there is no corresponding enhancements expected for the Electric...

  9. Renormalon Model Predictions for Power-Corrections to Flavour Singlet Deep Inelastic Structure Functions

    CERN Document Server

    Stein, E; Mankiewicz, L; Schäfer, A

    1998-01-01

    We analyze power corrections to flavour singlet deep inelastic scattering structure functions in the framework of the infrared renormalon model. Our calculations, together with previous results for the non-singlet contribution, allow to model the x-dependence of higher twist corrections to F_2, F_L and g_1 in the whole x domain.

  10. Two Birds with One Stone: Tailoring Singlet Fission for Both Triplet Yield and Exciton Diffusion Length

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Tong [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA; Wan, Yan [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA; Guo, Zhi [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA; Johnson, Justin [National Renewable Energy Laboratory, 15013 Denver West Pkwy Golden CO 80401 USA; Huang, Libai [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA

    2016-06-27

    By direct imaging of singlet and triplet populations with ultrafast microscopy, it is shown that the triplet diffusion length and singlet fission yield can be simultaneously optimized for tetracene and its derivatives, making them ideal structures for application in bilayer solar cells.

  11. Search for Colour Singlet and Colour Reconnection Effects in Hadronic Z Decays at LEP

    CERN Document Server

    Achard, P; Aguilar-Benítez, M; Alcaraz, J; Alemanni, G; Allaby, James V; Aloisio, A; Alviggi, M G; Anderhub, H; Andreev, V P; Anselmo, F; Arefev, A; Azemoon, T; Aziz, T; Bagnaia, P; Bajo, A; Baksay, G; Baksay, L; Baldew, S V; Banerjee, S; Banerjee, Sw; Barczyk, A; Barillère, R; Bartalini, P; Basile, M; Batalova, N; Battiston, R; Bay, A; Becattini, F; Becker, U; Behner, F; Bellucci, L; Berbeco, R; Berdugo, J; Berges, P; Bertucci, B; Betev, B L; Biasini, M; Biglietti, M; Biland, A; Blaising, J J; Blyth, S C; Bobbink, Gerjan J; Böhm, A; Boldizsar, L; Borgia, B; Bottai, S; Bourilkov, D; Bourquin, Maurice; Braccini, S; Branson, J G; Brochu, F; Burger, J D; Burger, W J; Cai, X D; Capell, M; Cara Romeo, G; Carlino, G; Cartacci, A M; Casaus, J; Cavallari, F; Cavallo, N; Cecchi, C; Cerrada, M; Chamizo-Llatas, M; Chang, Y H; Chemarin, M; Chen, A; Chen, G; Chen, G M; Chen, H F; Chen, H S; Chiefari, G; Cifarelli, Luisa; Cindolo, F; Clare, I; Clare, R; Coignet, G; Colino, N; Costantini, S; de la Cruz, B; Cucciarelli, S; van Dalen, J A; De Asmundis, R; Déglon, P L; Debreczeni, J; Degré, A; Dehmelt, K; Deiters, K; Della Volpe, D; Delmeire, E; Denes, P; De Notaristefani, F; De Salvo, A; Diemoz, M; Dierckxsens, M; Dionisi, C; Dittmar, M; Doria, A; Dova, M T; Duchesneau, D; Duda, M; Echenard, B; Eline, A; El-Hage, A; El-Mamouni, H; Engler, A; Eppling, F J; Extermann, P; Falagán, M A; Falciano, S; Favara, A; Fay, J; Fedin, O; Felcini, M; Ferguson, T; Fesefeldt, H S; Fiandrini, E; Field, J H; Filthaut, F; Fisher, P H; Fisher, W; Fisk, I; Forconi, G; Freudenreich, Klaus; Furetta, C; Galaktionov, Yu; Ganguli, S N; García-Abia, P; Gataullin, M; Gentile, S; Giagu, S; Gong, Z F; Grenier, G; Grimm, O; Grünewald, M W; Guida, M; van Gulik, R; Gupta, V K; Gurtu, A; Gutay, L J; Haas, D; Hatzifotiadou, D; Hebbeker, T; Hervé, A; Hirschfelder, J; Hofer, H; Hohlmann, M; Holzner, G; Hou, S R; Hu, Y; Jin, B N; Jones, L W; de Jong, P; Josa-Mutuberria, I; Käfer, D; Kaur, M; Kienzle-Focacci, M N; Kim, J K; Kirkby, Jasper; Kittel, E W; Klimentov, A; König, A C; Kopal, M; Koutsenko, V F; Kräber, M H; Krämer, R W; Krüger, A; Kunin, A; Ladrón de Guevara, P; Laktineh, I; Landi, G; Lebeau, M; Lebedev, A; Lebrun, P; Lecomte, P; Lecoq, P; Le Coultre, P; Le Goff, J M; Leiste, R; Levtchenko, M; Levchenko, P M; Li, C; Likhoded, S; Lin, C H; Lin, W T; Linde, Frank L; Lista, L; Liu, Z A; Lohmann, W; Longo, E; Lü, Y S; Luci, C; Luminari, L; Lustermann, W; Ma Wen Gan; Malgeri, L; Malinin, A; Maña, C; Mans, J; Martin, J P; Marzano, F; Mazumdar, K; McNeil, R R; Mele, S; Merola, L; Meschini, M; Metzger, W J; Mihul, A; Milcent, H; Mirabelli, G; Mnich, J; Mohanty, G B; Muanza, G S; Muijs, A J M; Musicar, B; Musy, M; Nagy, S; Natale, S; Napolitano, M; Nessi-Tedaldi, F; Newman, H; Nisati, A; Novák, T; Nowak, H; Ofierzynski, R A; Organtini, G; Pal, I; Palomares, C; Paolucci, P; Paramatti, R; Passaleva, G; Patricelli, S; Paul, T; Pauluzzi, M; Paus, C; Pauss, Felicitas; Pedace, M; Pensotti, S; Perret-Gallix, D; Petersen, B; Piccolo, D; Pierella, F; Pioppi, M; Piroué, P A; Pistolesi, E; Plyaskin, V; Pohl, M; Pozhidaev, V; Pothier, J; Prokofev, D; Prokofiev, D O; Quartieri, J; Rahal-Callot, G; Rahaman, M A; Raics, P; Raja, N; Ramelli, R; Rancoita, P G; Ranieri, R; Raspereza, A V; Razis, P A; Ren, D; Rescigno, M; Reucroft, S; Riemann, S; Riles, K; Roe, B P; Romero, L; Rosca, A; Rosier-Lees, S; Roth, S; Rosenbleck, C; Rubio, J A; Ruggiero, G; Rykaczewski, H; Sakharov, A; Saremi, S; Sarkar, S; Salicio, J; Sánchez, E; Schäfer, C; Shchegelskii, V; Schopper, Herwig Franz; Schotanus, D J; Sciacca, C; Servoli, L; Shevchenko, S; Shivarov, N; Shoutko, V; Shumilov, E; Shvorob, A V; Son, D; Souga, C; Spillantini, P; Steuer, M; Stickland, D P; Stoyanov, B; Strässner, A; Sudhakar, K; Sultanov, G G; Sun, L Z; Sushkov, S; Suter, H; Swain, J D; Szillási, Z; Tang, X W; Tarjan, P; Tauscher, Ludwig; Taylor, L; Tellili, B; Teyssier, D; Timmermans, C; Ting, Samuel C C; Ting, S M; Tonwar, S C; Tóth, J; Tully, C; Tung, K L; Ulbricht, J; Valente, E; Van de Walle, R T; Vásquez, R; Veszpremi, V; Vesztergombi, G; Vetlitskii, I; Vicinanza, D; Viertel, Gert M; Villa, S; Vivargent, M; Vlachos, S; Vodopyanov, I; Vogel, H; Vogt, H; Vorobev, I; Vorobyov, A A; Wadhwa, M; Wang, Q; Wang, X L; Wang, Z M; Weber, M; Wienemann, P; Wilkens, H; Wynhoff, S; Xia, L; Xu, Z Z; Yamamoto, J; Yang, B Z; Yang, C G; Yang, H J; Yang, M; Yeh, S C; Zalite, A; Zalite, Yu; Zhang, Z P; Zhao, J; Zhu, G Y; Zhu, R Y; Zhuang, H L; Zichichi, A; Zimmermann, B; Zöller, M

    2004-01-01

    A search is performed in symmetric 3-jet hadronic Z decay events for evidence of colour singlet production or colour reconnection effects. Asymmetries in the angular separation of particles are found to be sensitive indicators of such effects. Upper limits on the level of colour singlet production and colour reconnection effects are established for a variety of models.

  12. Discrimination between closed and open shell pistachio nuts using machine vision%基于机器视觉的开心果闭壳与开壳识别

    Institute of Scientific and Technical Information of China (English)

    郭晓伟

    2011-01-01

    To improve the quality of pistachio nuts, it is necessary to remove the closed shell pistachio nuts. A single row equally spacing method was taken to carry the pistachio nuts on the conveyor belt, and every pistachio nut image was captured by camera during the transmission. Then the image processing algorithm was used to detect whether its shell was open or not.Finally, gas nozzle, which was at the end of the conveyor belt, was used to blow away the closed shell pistachio nuts.Pistachio image was reduced to 0.2 times, and then the centroid of binary pistachio image was searched. After that, three horizontal pixel lines were described from the binary pistachio image, which was positioned in the centroid of pistachio, the middle of the upper part of pistachio and the middle of the lower part of pistachio. The gray value changes of all pixels of three lines were calculated respectively, and the features of those three pixel lines were integrated to judge whether the pistachio shell was open or not. Experiment results prove that the correct discrimination rates of the open shell pistachio nuts and the closed shell pistachio nuts are 93% and 100% respectively.%为从开心果中选出开壳果和去除闭壳果以提高开心果的品质.采用以单排等间距方式在传送带上输送开心果,输送过程中用摄像头拍摄每个开心果的图像,传输至电脑,经图像处理算法识别出开心果壳是否裂开,最后在传送带末端利用气嘴吹走闭壳果实以实现开心果自动分级.开心果图像缩小至原来的0.2倍,然后寻找出二值化图像中开心果的质心,再在开心果的质心、上半部分二分之一和下半部分二分之一处各取横向像素线,分别求取3条像素线上所有像素点灰度值变化之和,最后每个开心果综合3条像素线特征判断开心果是否开壳.实验证明开心果开壳果正确识别率为93%,闭壳果正确识别率达100%.

  13. Highly efficient spin-conversion effect leading to energy up-converted electroluminescence in singlet fission photovoltaics

    Science.gov (United States)

    Pandey, Ajay K.

    2015-01-01

    Free charge generation in donor-acceptor (D-A) based organic photovoltaic diodes (OPV) progresses through formation of charge-transfer (CT) and charge-separated (CS) states and excitation decay to the triplet level is considered as a terminal loss. On the other hand a direct excitation decay to the triplet state is beneficial for multiexciton harvesting in singlet fission photovoltaics (SF-PV) and the formation of CT-state is considered as a limiting factor for multiple triplet harvesting. These two extremes when present in a D-A system are expected to provide important insights into the mechanism of free charge generation and spin-character of bimolecular recombination in OPVs. Herein, we present the complete cycle of events linked to spin conversion in the model OPV system of rubrene/C60. By tracking the spectral evolution of photocurrent generation at short-circuit and close to open-circuit conditions we are able to capture spectral changes to photocurrent that reveal the triplet character of CT-state. Furthermore, we unveil an energy up-conversion effect that sets in as a consequence of triplet population build-up where triplet-triplet annihilation (TTA) process effectively regenerates the singlet excitation. This detailed balance is shown to enable a rare event of photon emission just above the open-circuit voltage (VOC) in OPVs.

  14. WIMP Dark Matter and Unitarity-Conserving Inflation via a Gauge Singlet Scalar

    CERN Document Server

    Kahlhoefer, Felix

    2015-01-01

    A gauge singlet scalar with non-minimal coupling to gravity can drive inflation and later freeze out to become cold dark matter. We explore this idea by revisiting inflation in the singlet direction (S-inflation) and Higgs Portal Dark Matter in light of the Higgs discovery, limits from LUX and observations by Planck. We show that large regions of parameter space remain viable, so that successful inflation is possible and the dark matter relic abundance can be reproduced. Moreover, the scalar singlet can stabilise the electroweak vacuum and at the same time overcome the problem of unitarity-violation during inflation encountered by Higgs Inflation, provided the singlet is a real scalar. The 2-$\\sigma$ Planck upper bound on $n_s$ imposes that the singlet mass is below 2 TeV, so that almost the entire allowed parameter range can be probed by XENON1T.

  15. Theoretical studies on kinetics of singlet oxygen in nonthermal plasma

    Science.gov (United States)

    Frolov, Mikhail P.; Ionin, Andrei A.; Kotkov, Andrei A.; Kochetov, Igor V.; Napartovich, Anatolii P.; Podmarkov, Yurii P.; Seleznev, Leonid V.; Sinitsyn, Dmitrii V.; Vagin, Nikolai P.; Yuryshev, Nikolay N.

    2004-09-01

    An idea to replace singlet delta oxygen (SDO) generator working with wet chemistry by electric discharge generator has got much attention last years. Different kinds of discharge were examined for this purpose, but without a great success. The existing theoretical models are not validated by well-characterized experimental data. To describe complicated kinetics in gas discharge with oxygen one needs to know in detail processes involving numerous electronic excited oxygen molecules and atoms. To gain new knowledge about these processes experimental studies were made on electric discharge properties in gas mixture flow with independent control of inlet SDO concentration. The theoretical model extended to include minor additives like oxygen atoms, water molecules, ozone was developed. Comparison with careful experimental measurements of electric characteristics along with gas composition allows us to verify the model and make theoretical predictions more reliable. Results of numerical simulations using this model for an electron-beam sustained discharge are reported and compared with the experimental data.

  16. Intercepts of the non-singlet structure functions

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2001-01-01

    Infrared evolution equations for small-$x$ behaviour of the non-singlet structure functions $f_1^{NS}$ and $g_1^{NS}$ are obtained and solved in the next-to-leading approximation, to all orders in $\\alpha_s$, and including running $\\alpha_s$ effects. The intercepts of these structure functions, i.e. the exponents of the power-like small-$x$ behaviour, are calculated. A detailed comparison with the leading logarithmic approximation (LLA) and DGLAP is made. We explain why the LLA predictions for the small-$x$ dependence of the structure functions may be more reliable than the prediction for the $Q^2$ dependence in the range of $Q^2$ explored at HERA.

  17. Demonstration of entanglement of electrostatically coupled singlet-triplet qubits.

    Science.gov (United States)

    Shulman, M D; Dial, O E; Harvey, S P; Bluhm, H; Umansky, V; Yacoby, A

    2012-04-13

    Quantum computers have the potential to solve certain problems faster than classical computers. To exploit their power, it is necessary to perform interqubit operations and generate entangled states. Spin qubits are a promising candidate for implementing a quantum processor because of their potential for scalability and miniaturization. However, their weak interactions with the environment, which lead to their long coherence times, make interqubit operations challenging. We performed a controlled two-qubit operation between singlet-triplet qubits using a dynamically decoupled sequence that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography, we measured the full density matrix of the system and determined the concurrence and the fidelity of the generated state, providing proof of entanglement.

  18. Singlet Fission: Progress and Prospects in Solar Cells.

    Science.gov (United States)

    Xia, Jianlong; Sanders, Samuel N; Cheng, Wei; Low, Jonathan Z; Liu, Jinping; Campos, Luis M; Sun, Taolei

    2016-12-14

    The third generation of photovoltaic technology aims to reduce the fabrication cost and improve the power conversion efficiency (PCE) of solar cells. Singlet fission (SF), an efficient multiple exciton generation (MEG) process in organic semiconductors, is one promising way to surpass the Shockley-Queisser limit of conventional single-junction solar cells. Traditionally, this MEG process has been observed as an intermolecular process in organic materials. The implementation of intermolecular SF in photovoltaic devices has achieved an external quantum efficiency of over 100% and demonstrated significant promise for boosting the PCE of third generation solar cells. More recently, efficient intramolecular SF has been reported. Intramolecular SF materials are modular and have the potential to overcome certain design constraints that intermolecular SF materials possess, which may allow for more facile integration into devices.

  19. Exchange-only singlet-only spin qubit

    Science.gov (United States)

    Sala, Arnau; Danon, Jeroen

    2017-06-01

    We propose a feasible and scalable quantum-dot-based implementation of a singlet-only spin qubit which is to leading order intrinsically insensitive to random effective magnetic fields set up by fluctuating nuclear spins in the host semiconductor. Our proposal thus removes an important obstacle for further improvement of spin qubits hosted in high-quality III-V semiconductors such as GaAs. We show how the resulting qubit could be initialized, manipulated, and read out by electrical means only, in a way very similar to a triple-dot exchange-only spin qubit. Due to the intrinsic elimination of the effective nuclear fields from the qubit Hamiltonian, we find an improvement of the dephasing time T2* of several orders of magnitude as compared to similar existing spin qubits.

  20. On the low lying singlet states of BeO

    Science.gov (United States)

    Bauschlicher, C. W., Jr.; Lengsfield, B. H.; Yarkony, D. R.

    1980-01-01

    Calculations of the ground and low-lying singlet states of BeO are performed in order to gain an understanding of the techniques needed to treat the excited states of other, more complex, ionic molecules. The MCSCF and CI calculations are based on a Gaussian basis set of slightly better than double zeta plus polarization quality for single configuration descriptions of the states. The calculated X-A and X-B state separations are found to be in agreement with experimental measurements. The 1 Sigma - and 1 Delta states are predicted to lie approximately 40,000 kaysers above the ground state and are identified as the C and D states.The 2 1 Pi state is found to be approximately 15,000 kaysers and the 3 1 Sigma + state is found to be approximately 65,000 kaysers above the ground state.

  1. Device-independent parallel self-testing of two singlets

    Science.gov (United States)

    Wu, Xingyao; Bancal, Jean-Daniel; McKague, Matthew; Scarani, Valerio

    2016-06-01

    Device-independent self-testing offers the possibility of certifying the quantum state and measurements, up to local isometries, using only the statistics observed by querying uncharacterized local devices. In this paper we study parallel self-testing of two maximally entangled pairs of qubits; in particular, the local tensor product structure is not assumed but derived. We prove two criteria that achieve the desired result: a double use of the Clauser-Horne-Shimony-Holt inequality and the 3 ×3 magic square game. This demonstrate that the magic square game can only be perfectly won by measuring a two-singlet state. The tolerance to noise is well within reach of state-of-the-art experiments.

  2. The SUSY Higgs Mass: the Singlet Saves the Day

    CERN Document Server

    Delgado, Antonio; Olson, J Pocahontas; de la Puente, Alejandro

    2010-01-01

    We present a generalization of the Next-to-Minimal Supersymmetric Standard Model (NMSSM), with an explicit mu-term and a supersymmetric mass for the singlet superfield, as a route to alleviating the little hierarchy problem of the Minimal Supersymmetric Standard Model (MSSM). Though this model does not address the mu-problem of the MSSM, we are able to generate masses for the lightest neutral Higgs boson up to 140 GeV with top squarks below the TeV scale, all couplings perturbative to the gauge unification scale, and with no need to fine tune parameters in the scalar potential. This model, which we call the S-MSSM, more closely resembles the MSSM phenomenologically than the NMSSM as usually defined.

  3. Global fits of scalar singlet dark matter with GAMBIT

    CERN Document Server

    Cornell, Jonathan M

    2016-01-01

    The wide range of probes of physics beyond the standard model leads to the need for tools that combine experimental results to make the most robust possible statements about the validity of theories and the preferred regions of their parameter space. Here we introduce a new code for such analyses: GAMBIT, the Global and Modular BSM Inference Tool. GAMBIT is a flexible and extensible framework for global fits of essentially any BSM theory. The code currently incorporates direct and indirect searches for dark matter, limits on production of new particles from the LHC and LEP, complete flavor constraints from LHCb, LHC Higgs production and decay measurements, and various electroweak precision observables. Here we present an overview of the code's capabilities, followed by preliminary results from scans of the scalar singlet dark matter model.

  4. keV sterile neutrino dark matter from singlet scalar decays: the most general case

    Energy Technology Data Exchange (ETDEWEB)

    König, Johannes; Merle, Alexander; Totzauer, Maximilian [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, 80805 München (Germany)

    2016-11-21

    We investigate the early Universe production of sterile neutrino Dark Matter by the decays of singlet scalars. All previous studies applied simplifying assumptions and/or studied the process only on the level of number densities, which makes it impossible to give statements about cosmic structure formation. We overcome these issues by dropping all simplifying assumptions (except for one we showed earlier to work perfectly) and by computing the full course of Dark Matter production on the level of non-thermal momentum distribution functions. We are thus in the position to study a broad range of aspects of the resulting settings and apply a broad set of bounds in a reliable manner. We have a particular focus on how to incorporate bounds from structure formation on the level of the linear power spectrum, since the simplistic estimate using the free-streaming horizon clearly fails for highly non-thermal distributions. Our work comprises the most detailed and comprehensive study of sterile neutrino Dark Matter production by scalar decays presented so far.

  5. On couplings and excimers: lessons from studies of singlet fission in covalently linked tetracene dimers.

    Science.gov (United States)

    Feng, Xintian; Krylov, Anna I

    2016-03-21

    Electronic factors controlling singlet fission (SF) rates are investigated in covalently linked dimers of tetracene. Using covalent linkers, relative orientation of the individual chromophores can be controlled, maximizing the rates of SF. Structures with coplanar and staggered arrangements of tetracene moieties are considered. The electronic structure calculations and three-state kinetic model for SF rates provide explanations for experimentally observed low SF yields in coplanar dimers and efficient SF in staggered dimers. The calculations illuminate the role of the excimer formation in SF process. The structural relaxation in the S1 state leads to the increased rate of the multi-exciton (ME) state formation, but impedes the second step, separation of the ME state into independent triplets. The slower second step reduces SF yield by allowing other processes, such as radiationless relaxation, to compete with triplet generation. The calculations of electronic couplings also suggest an increased rate of radiationless relaxation at the excimer geometries. Thus, the excimer serves as a trap of the ME state. The effect of covalent linkers on the electronic factors and SF rates is investigated. In all considered structures, the presence of the linker leads to larger couplings, however, the effect on the overall rate is less straightforward, since the linkers generally result in less favorable energetics. This complex behavior once again illustrates the importance of integrative approaches that evaluate the overall rate, rather than focusing on specific electronic factors such as energies or couplings.

  6. Impact of double-logarithmic electroweak radiative corrections on the non-singlet structure functions at small x

    CERN Document Server

    Ermolaev, B I

    2008-01-01

    In the QCD context, the non-singlet structure functions of u and d -quarks are identical, save the initial quark densities. Electroweak radiative corrections, being flavor-dependent, bring further difference between the non-singlets. This difference is calculated in the double-logarithmic approximation and the impact of the electroweak corrections on the non-singlet intercepts is estimated numerically.

  7. Photosensitized oxidation of 9,10-dimethylanthracene with singlet oxygen by using a safranin O/silica composite under visible light.

    Science.gov (United States)

    Albiter, Elim; Alfaro, Salvador; Valenzuela, Miguel A

    2015-03-01

    The photosensitized oxidation of 9,10-dimethylanthracene with singlet oxygen in acetonitrile was investigated using a safranin O/silica composite as an heterogeneous delivery system of the photosensitizer. The only detected product was the corresponding endoperoxide (9,10-endoperoxianthracene) and its formation rate depended on the initial concentration of DMA, the light intensity and the amount of the composite. The kinetics of this reaction was compared with that of the reported kinetic model of photosensitized oxidations of organic compounds in homogeneous reactions. It was found that both reactions followed the same model, suggesting that the actual reaction between photoproduced singlet oxygen and 9,10-dimethylanthracene was performed in homogeneous media and the surface of the composite was not involved in the reaction.

  8. Phosphoprotein SAK1 is a regulator of acclimation to singlet oxygen in Chlamydomonas reinhardtii.

    Science.gov (United States)

    Wakao, Setsuko; Chin, Brian L; Ledford, Heidi K; Dent, Rachel M; Casero, David; Pellegrini, Matteo; Merchant, Sabeeha S; Niyogi, Krishna K

    2014-05-23

    Singlet oxygen is a highly toxic and inevitable byproduct of oxygenic photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is capable of acclimating specifically to singlet oxygen stress, but the retrograde signaling pathway from the chloroplast to the nucleus mediating this response is unknown. Here we describe a mutant, singlet oxygen acclimation knocked-out 1 (sak1), that lacks the acclimation response to singlet oxygen. Analysis of genome-wide changes in RNA abundance during acclimation to singlet oxygen revealed that SAK1 is a key regulator of the gene expression response during acclimation. The SAK1 gene encodes an uncharacterized protein with a domain conserved among chlorophytes and present in some bZIP transcription factors. The SAK1 protein is located in the cytosol, and it is induced and phosphorylated upon exposure to singlet oxygen, suggesting that it is a critical intermediate component of the retrograde signal transduction pathway leading to singlet oxygen acclimation.DOI: http://dx.doi.org/10.7554/eLife.02286.001.

  9. Phosphoprotein SAK1 is a regulator of acclimation to singlet oxygen in Chlamydomonas reinhardtii

    Science.gov (United States)

    Wakao, Setsuko; Chin, Brian L; Ledford, Heidi K; Dent, Rachel M; Casero, David; Pellegrini, Matteo; Merchant, Sabeeha S; Niyogi, Krishna K

    2014-01-01

    Singlet oxygen is a highly toxic and inevitable byproduct of oxygenic photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is capable of acclimating specifically to singlet oxygen stress, but the retrograde signaling pathway from the chloroplast to the nucleus mediating this response is unknown. Here we describe a mutant, singlet oxygen acclimation knocked-out 1 (sak1), that lacks the acclimation response to singlet oxygen. Analysis of genome-wide changes in RNA abundance during acclimation to singlet oxygen revealed that SAK1 is a key regulator of the gene expression response during acclimation. The SAK1 gene encodes an uncharacterized protein with a domain conserved among chlorophytes and present in some bZIP transcription factors. The SAK1 protein is located in the cytosol, and it is induced and phosphorylated upon exposure to singlet oxygen, suggesting that it is a critical intermediate component of the retrograde signal transduction pathway leading to singlet oxygen acclimation. DOI: http://dx.doi.org/10.7554/eLife.02286.001 PMID:24859755

  10. Flavour changing neutral currents in the standard model and its extensions with singlet quarks

    CERN Document Server

    Bejlin, V A; Kuksa, V I

    2001-01-01

    The review is devoted to the phenomenology of singlet quarks, which are singlets with respect to the SU(2), have hypercharges Y = -1/3 masses m > m sub t. It is shown, that experimental data on rare processes and the corresponding theoretical predictions of the Standard Model (SM) allow to invoke the SM extensions for the analysis of the phenomena stimulated by flavor changing neutral current. The extended matrix of standard and singlet quark mixing is constructed, the restriction on mixing angles and the estimate of low bound of singlet quark mass m sub D >= 0.5 TeV are obtained. Besides the direct observation the perspectives to increase the confidence level of the singlet quark existence are discussed. The cross-sections of nondiagonal production of singlet quark in pair with standard one in e sup - e sup + -, ep- and pp-bar-collisions are analyzed and the unique signature of such events is described. The model of up-singlet quark with the hypercharge Y sub U 2/3 and its applications to the physics of t-qu...

  11. Singlet oxygen production by PSII under light stress: mechanism, detection and the protective role of β-carotene.

    Science.gov (United States)

    Telfer, Alison

    2014-07-01

    In this review, I outline the indirect evidence for the formation of singlet oxygen ((1)O(2)) obtained from experiments with the isolated PSII reaction center complex. I also review the methods we used to measure singlet oxygen directly, including luminescence at 1,270 nm, both steady state and time resolved. Other methods we used were histidine-catalyzed molecular oxygen uptake (enabling (1)O(2) yield measurements), and dye bleaching and difference absorption spectroscopy to identify where quenchers of (1)O(2) can access this toxic species. We also demonstrated the protective behavior of carotenoids bound within Chl-protein complexes which bring about a substantial amount of (1)O(2) quenching within the reaction center complex. Finally, I describe how these techniques have been used and expanded in research on photoinhibition and on the role of (1)O(2) as a signaling molecule in instigating cellular responses to various stress factors. I also discuss the current views on the role of (1)O(2) as a signaling molecule and the distance it might be able to travel within cells. © The Author 2014. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.

  12. Solving the Hierarchy Problem with a Light Singlet and Supersymmetric Mass Terms

    CERN Document Server

    Delgado, Antonio; de la Puente, Alejandro

    2011-01-01

    A generalization of the Next-to-Minimal Supersymmetric Model (NMSSM) is studied in which an explicit \\mu-term as well as a small supersymmetric mass term for the singlet superfield are incorporated. We study the possibility of raising the Standard Model-like Higgs mass at tree level through its mixing with a light, mostly-singlet, CP-even scalar. We are able to generate Higgs boson masses up to 145 GeV with top squarks below 1.1 TeV and without the need to fine tune parameters in the scalar potential. This model yields light singlet-like scalars and pseudoscalars passing all collider constraints.

  13. Solving the little hierarchy problem with a light singlet and supersymmetric mass terms

    Energy Technology Data Exchange (ETDEWEB)

    Delgado, Antonio, E-mail: antonio.delgado@nd.edu [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Kolda, Christopher [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Puente, Alejandro de la [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States)

    2012-04-12

    A generalization of the Next-to-Minimal Supersymmetric Model (NMSSM) is studied in which an explicit {mu}-term as well as a small supersymmetric mass term for the singlet superfield are incorporated. We study the possibility of raising the Standard Model-like Higgs mass at tree level through its mixing with a light, mostly-singlet, CP-even scalar. We are able to generate Higgs boson masses up to 145 GeV with top squarks below 1.1 TeV and without the need to fine tune parameters in the scalar potential. This model yields light singlet-like scalars and pseudoscalars passing all collider constraints.

  14. Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering

    Science.gov (United States)

    Lukman, Steven; Chen, Kai; Hodgkiss, Justin M.; Turban, David H. P.; Hine, Nicholas D. M.; Dong, Shaoqiang; Wu, Jishan; Greenham, Neil C.; Musser, Andrew J.

    2016-12-01

    Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.

  15. A Simple Singlet Fermionic Dark-Matter Model Revisited

    Institute of Scientific and Technical Information of China (English)

    QIN Hong-Yi; WANG Wen-Yu; XIONG Zhao-Hua

    2011-01-01

    We evaluate the spin-independent elastic dark matter-nucleon scattering cross section in the framework of the simple singlet fermionic dark matter extension of the standard model and constrain the model parameter space with the following considerations:(i) new dark matter measurement,in which,apart from WMAP and CDMS,the results from the XENON experiment are also used in constraining the model;(ii) new fitted value of the quark fractions in nucleons,in which the updated value of fTs from the recent lattice simulation is much smaller than the previous one and may reduce the scattering rate significantly;(iii) new dark matter annihilation channels,in which the scenario where top quark and Higgs pairs produced by dark matter annihilation was not included in the previous works.We find that unlike in the minimal supersymmetric standard model,the cross section is just reduced by a factor of about 1/4 and dark matter lighter than 100 GeV is not favored by the WMAP,CDMS and XENON experiments.It is well known that about 20% of the energy density of the Universe[1] is composed of dark matter (DM).Probing the properties of DM and searching for DM candidates are the most important motivations for the research of new physics beyond the standard model (SM).%We evaluate the spin-independent elastic dark matter-nucleon scattering cross section in the framework of the simple singlet fermionic dark matter extension of the standard model and constrain the model parameter space with the following considerations: (I) new dark matter measurement, in which, apart from WMAP and CDMS, the results from the XENON experiment are also used in constraining the model; (ii) new fitted value of the quark fractions in nucleons, in which the updated value of fT8 from the recent lattice simulation is much smaller than the previous one and may reduce the scattering rate significantly; (Hi) new dark matter annihilation channels, in which the scenario where top quark and Higgs pairs produced by dark

  16. On the origin of regio- and stereoselectivity in singlet oxygen addition to enecarbamates.

    Science.gov (United States)

    Rajeev, Ramanan; Sunoj, Raghavan B

    2012-03-02

    The reactions of excited state singlet molecular oxygen ((1)Δ(g),(1)O(2)) continue to witness interesting new developments. In the most recent manifestation, (1)O(2) is tamed to react with enecarbamates in a stereoselective manner, which is remarkable, in view of its inherently high reactivity (Acc. Chem. Res. 2008, 41, 387). Herein, we employed the CAS-MP2(8,7)/6-31G* as well as the CAS-MP2(10,8)/6-31G* computations to unravel the origin of (i) diastereoselectivities in dioxetane or hydroperoxide formation and (ii) regioselectivity leading to a [2 + 2] cycloadduct or an ene product when (1)O(2) reacts with an oxazolidinone tethered 2-phenyl-1-propenyl system. The computed Gibbs free energy profiles for E- and Z-isomers when (1)O(2) approaches through the hindered and nonhindered diastereotopic faces (by virtue of chiral oxazolidinone) of the enecarbamates exhibit distinct differences. In the case of E-isomer, the relative energies of the transition structures responsible for hydroperoxide (ene product) are lower than that for dioxetane formation. On the other hand, the ene pathway is predicted to involve higher barriers as compared to the corresponding dioxetane pathway for Z-isomer. The energy difference between the rate-determining diastereomeric transition structures involved in the most favored ene reaction for E-enecarbamate suggests high diastereoselectivity. In contrast, the corresponding energy difference for Z-enecarbamate in the ene pathway is found to be diminishingly close, implying low diastereoselectivity. However, the dioxetane formation from Z-enecarbamate is predicted to exhibit high diastereoselectivity. The application of activation strain model as well as the differences in stereoelectronic effects in the stereocontrolling transition structures is found to be effective toward rationalizing the origin of selectivities reported herein. These predictions are found to be in excellent agreement with the experimental observations.

  17. On the influence of singlet oxygen molecules on characteristics of HCCI combustion: A numerical study

    Science.gov (United States)

    Starik, A. M.; Kozlov, V. E.; Titova, N. S.

    2013-08-01

    Mechanisms of homogeneous charge compression ignition (HCCI) combustion enhancement are investigated numerically when excited O2(a 1Δg) molecules are produced at different points in the compression stroke. The analysis is conducted with the use of an extended kinetic model involving the submechanism of nitric oxide formation in the presence of singlet oxygen O2(a 1Δg) or O2(b 1Σg +) molecules in the methane-air mixture. It is demonstrated that the abundance of excited O2(a 1Δg) molecules in the mixture even in a small amounts intensifies the ignition and combustion and allows one to control the ignition event in the HCCI engine. Such a method of energy supply in the HCCI engine is much more effective in advancement of combustion timing than mere heating of the mixture, because it leads to acceleration of the chain-branching mechanism. The excitation of O2 molecules to the a 1Δg electronic state makes it possible to organise the successful combustion in the cylinder at diminished initial temperature of the mixture and increase the effective energy released during HCCI combustion. The advance in the value of this energy is much higher than the energy needed for the excitation of oxygen molecules. Moreover, in this case, the output concentration of NO and CO can be reduced significantly.

  18. Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

    Science.gov (United States)

    Mahato, Prasenjit; Yanai, Nobuhiro; Sindoro, Melinda; Granick, Steve; Kimizuka, Nobuo

    2016-05-25

    Photon upconversion (UC) based on triplet-triplet annihilation (TTA) has the potential to enhance significantly photovoltaic and photocatalytic efficiencies by harnessing sub-bandgap photons, but the progress of this field is held back by the chemistry problem of how to preorganize multiple chromophores for efficient UC under weak solar irradiance. Recently, the first maximization of UC quantum yield at solar irradiance was achieved using fast triplet energy migration (TEM) in metal-organic frameworks (MOFs) with ordered acceptor arrays, but at the same time, a trade-off between fast TEM and high fluorescence efficiency was also found. Here, we provide a solution for this trade-off issue by developing a new strategy, triplet energy migration, annihilation and upconverted singlet energy collection (TEM-UPCON). The porous structure of acceptor-based MOF crystals allows triplet donor molecules to be accommodated without aggregation. The surface of donor-doped MOF nanocrystals is modified with highly fluorescent energy collectors through coordination bond formation. Thanks to the higher fluorescence quantum yield of surface-bound collectors than parent MOFs, the implementation of the energy collector greatly improves the total UC quantum yield. The UC quantum yield maximization behavior at ultralow excitation intensity was retained because the TTA events take place only in the MOF acceptors. The TEM-UPCON concept may be generalized to collectors with various functions and would lead to quantitative harvesting of upconverted energy, which is difficult to achieve in common molecular diffusion-based systems.

  19. Magnetic field protects plants against high light by slowing down production of singlet oxygen.

    Science.gov (United States)

    Hakala-Yatkin, Marja; Sarvikas, Päivi; Paturi, Petriina; Mäntysaari, Mika; Mattila, Heta; Tyystjärvi, Taina; Nedbal, Ladislav; Tyystjärvi, Esa

    2011-05-01

    Recombination of the primary radical pair of photosystem II (PSII) of photosynthesis may produce the triplet state of the primary donor of PSII. Triplet formation is potentially harmful because chlorophyll triplets can react with molecular oxygen to produce the reactive singlet oxygen (¹O₂). The yield of ¹O₂ is expected to be directly proportional to the triplet yield and the triplet yield of charge recombination can be lowered with a magnetic field of 100-300 mT. In this study, we illuminated intact pumpkin leaves with strong light in the presence and absence of a magnetic field and found that the magnetic field protects against photoinhibition of PSII. The result suggests that radical pair recombination is responsible for significant part of ¹O₂ production in the chloroplast. The magnetic field effect vanished if leaves were illuminated in the presence of lincomycin, an inhibitor of chloroplast protein synthesis, or if isolated thylakoid membranes were exposed to light. These data, in turn, indicate that ¹O₂ produced by the recombination of the primary charge pair is not directly involved in photoinactivation of PSII but instead damages PSII by inhibiting the repair of photoinhibited PSII. We also found that an Arabidopsis thaliana mutant lacking α-tocopherol, a scavenger of ¹O₂, is more sensitive to photoinhibition than the wild-type in the absence but not in the presence of lincomycin, confirming that the target of ¹O₂ is the repair mechanism.

  20. X-ray induced singlet oxygen generation by nanoparticle-photosensitizer conjugates for photodynamic therapy: determination of singlet oxygen quantum yield

    Science.gov (United States)

    Clement, Sandhya; Deng, Wei; Camilleri, Elizabeth; Wilson, Brian C.; Goldys, Ewa M.

    2016-01-01

    Singlet oxygen is a primary cytotoxic agent in photodynamic therapy. We show that CeF3 nanoparticles, pure as well as conjugated through electrostatic interaction with the photosensitizer verteporfin, are able to generate singlet oxygen as a result of UV light and 8 keV X-ray irradiation. The X-ray stimulated singlet oxygen quantum yield was determined to be 0.79 ± 0.05 for the conjugate with 31 verteporfin molecules per CeF3 nanoparticle, the highest conjugation level used. From this result we estimate the singlet oxygen dose generated from CeF3-verteporfin conjugates for a therapeutic dose of 60 Gy of ionizing radiation at energies of 6 MeV and 30 keV to be (1.2 ± 0.7) × 108 and (2.0 ± 0.1) × 109 singlet oxygen molecules per cell, respectively. These are comparable with cytotoxic doses of 5 × 107-2 × 109 singlet oxygen molecules per cell reported in the literature for photodynamic therapy using light activation. We confirmed that the CeF3-VP conjugates enhanced cell killing with 6 MeV radiation. This work confirms the feasibility of using X- or γ- ray activated nanoparticle-photosensitizer conjugates, either to supplement the radiation treatment of cancer, or as an independent treatment modality.

  1. Interference effects of two scalar boson propagators on the LHC search for the singlet fermion DM

    CERN Document Server

    Ko, P

    2016-01-01

    A gauge invariant UV-completion for singlet fermion DM interacting with the standard model (SM) particles involves a new singlet scalar. Therefore the model contains two scalar mediators, mixtures of the SM Higgs boson and a singlet scalar boson. Collider phenomenology of the interference effect between these two scalar propagators is studied in this work. This interference effect can be either constructive or destructive in the DM production cross section depending on both singlet scalar and DM masses, and it will soften the final state jets in the full mass region. Applying the CMS mono-jet search to our model, we find the interference effect plays a very important role in the DM search sensitivity, and the DM production cross section of our model is more than one order of magnitude below the LHC sensitivity at current stage.

  2. Dependence of nuclear spin singlet lifetimes on RF spin-locking power

    CERN Document Server

    DeVience, Stephen J; Rosen, Matthew S

    2012-01-01

    We measure the lifetime of long-lived nuclear spin singlet states as a function of the strength of the RF spin-locking field and present a simple theoretical model that agrees well with our measurements, including the low-RF-power regime. We also measure the lifetime of a long-lived coherence between singlet and triplet states that does not require a spin-locking field for preservation. Our results indicate that for many molecules, singlet states can be created using weak RF spin-locking fields: more than two orders of magnitude lower RF power than in previous studies. Our findings suggest that in many biomolecules, singlets and related states with enhanced lifetimes might be achievable in vivo with safe levels of RF power.

  3. New strategies to produce and detect singlet oxygen in a cell

    DEFF Research Database (Denmark)

    Gollmer, Anita

    2012-01-01

    then transfers its energy of excitation to oxygen. Systems with light, light absorbing molecules and molecular oxygen are present everywhere in nature, so this is a pertinent process. It is also conveniently reproduced with lamps and/or lasers to purposely kill undesired cells. The development and improvement......, and that is the perspective of this study. Although the direct optical detection of singlet oxygen by its near IR phosphorescence is the ideal way to monitor this species, it suffers from the problem of weak signal intensity. Fluorescent probes can be a more sensitive way to detect singlet oxygen. The photochemical behavior......” is designed. Aarhus Green relies on the use of a modified fluorescein derivative that precludes the photosensitization of singlet oxygen. Two-photon excitation of a sensitizer with a focused laser improves the spatial resolution to generate singlet oxygen. With this approach, experiments were performed...

  4. Novel fully-BODIPY functionalized cyclotetraphosphazene photosensitizers having high singlet oxygen quantum yields

    Science.gov (United States)

    Şenkuytu, Elif; Eçik, Esra Tanrıverdi

    2017-07-01

    Novel fully-BODIPY functionalized dendrimeric cyclotetraphosphazenes (FBCP 1 and 2) have been synthesized and characterized by 1H, 13C and 31P NMR spectroscopies. The photophysical and photochemical properties of FBCP 1 and 2 are investigated in dichloromethane solution. The effectiveness of singlet oxygen generation was measured for FBCP 1 and 2 by UV-Vis spectra monitoring of the solution of 1,3-diphenylisobenzofuran (DPBF), which is a well-known trapping molecule used in detection of singlet oxygen. FBCP 1 and 2 show high molar extinction coefficients in the NIR region, good singlet oxygen quantum yields and appropriate photo degradation. The data presented in the work indicate that the dendrimeric cyclotetraphosphazenes are effective singlet oxygen photosensitizers that might be used for various areas of applications such as photodynamic therapy and photocatalysis.

  5. Interference effects of two scalar boson propagators on the LHC search for the singlet fermion DM

    Science.gov (United States)

    Ko, P.; Li, Jinmian

    2017-02-01

    A gauge invariant UV-completion for singlet fermion DM interacting with the standard model (SM) particles involves a new singlet scalar. Therefore the model contains two scalar mediators, mixtures of the SM Higgs boson and a singlet scalar boson. Collider phenomenology of the interference effect between these two scalar propagators is studied in this work. This interference effect can be either constructive or destructive in the DM production cross section depending on both singlet scalar and DM masses, and it will soften the final state jets in the full mass region. Applying the CMS mono-jet search to our model, we find the interference effect plays a very important role in the DM search sensitivity, and the DM production cross section of our model is more than one order of magnitude below the LHC sensitivity at current stage.

  6. NIR area array CCD-based singlet oxygen luminescence imaging for photodynamic therapy

    Energy Technology Data Exchange (ETDEWEB)

    Hu Bolin; He Yonghong; Liu Zhiyi, E-mail: heyh@sz.tsinghua.edu.cn [Laboratory of Optical Imaging and Sensing, Graduate School at Shenzhen, Tsinghua University, Shenzhen, 518055 (China)

    2011-01-01

    In this work, a near-infrared CCD-based singlet oxygen luminescence two-dimensional imaging method is proposed to detect singlet oxygen by its 1270nm luminescence. Two-dimensional singlet oxygen images with its near-infrared luminescence during photosensitization could be obtained with a CCD integration time of 1s, without scanning. The data presented shows a linear relationship between the singlet oxygen luminescence intensity and sample concentration. This method provides a detection sensitivity of 0.00189mg/ml (Hematoporphyrin monomethyl Ether dissolved in ethanol) and a spatial resolution better than 100{mu}m. We applied this method in vivo to demonstrate its potential in monitoring photodynamic therapy.

  7. Gamma ray signals of the annihilation of Higgs-portal singlet dark matter

    CERN Document Server

    Sage, Frederick S

    2016-01-01

    This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detection bounds. We also find that singlets in the mass range of 250-1000 GeV are consistent with both the Fermi-LAT IGRB observations and direct detection bounds. Additionally, bounds from gamma ray observations of the dwarf spheroidal galaxy Segue I are translated into bounds on the Higgs-portal couplings.

  8. Quenching of singlet oxygen by pyocyanin and related phenazines.

    Science.gov (United States)

    Reszka, Krzysztof J; Bilski, Piotr J; Britigan, Bradley E

    2010-01-01

    Pseudomonas aeruginosa is a human pathogen, which causes infections of various organs, including lung, skin and eye, particularly in individuals who are immunocompromised. Pyocyanin (1-hydroxy-5-methylphenazine), a cytotoxic pigment secreted by the bacterium, is among the factors that contribute to virulence of this pathogen. We have previously shown that rose bengal and riboflavin photosensitize oxidation of pyocyanin to a product(s) with diminished reactivity and toxicity. Singlet oxygen was suggested as the major oxidant, based on the inhibitory effect of sodium azide. In the present study, we used the time resolved technique to investigate direct interaction of pyocyanin and related phenazines (1-hydroxyphenazine [1-OH-Phen], 1-methoxy-5-methylphenazine [1-MeO-PCN] and phenazine methosulfate [PMS]) with (1)O(2). The rate constants for the (1)O(2) quenching (physical + chemical) by pyocyanin and 1-OH-Phen in D(2)O buffer (pD approximately 7.2) have been determined to be 4.8 x 10(8) and 6.8 x 10(8) M(-1) s(-1), respectively. 1-MeO-PCN and PMS were markedly less efficient (1)O(2) quenchers. Among the phenazines studied only phenazine methosulfate photogenerated (1)O(2) (Phi((1)O(2)) = 0.56 in acetonitrile). Interaction of (1)O(2) with pyocyanin and other related phenazines produced by the bacteria may be important in determining the potential utility of photochemical/pharmacological approaches to eradicate P. aeruginosa from infected tissues.

  9. Effect of oxygen concentration on singlet oxygen luminescence detection

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Longchao; Lin, Lisheng; Li, Yirong; Lin, Huiyun; Qiu, Zhihai [MOE Key Laboratory of OptoElectronic Science and Technology for Medicine, Fujian Provincial Key Laboratory for Photonics Technology, Fujian Normal University, Fuzhou 350007 (China); Gu, Ying [Department of Laser Medicine, Chinese PLA General Hospital, Beijing 100853 (China); Li, Buhong, E-mail: bhli@fjnu.edu.cn [MOE Key Laboratory of OptoElectronic Science and Technology for Medicine, Fujian Provincial Key Laboratory for Photonics Technology, Fujian Normal University, Fuzhou 350007 (China)

    2014-08-01

    Singlet oxygen ({sup 1}O{sub 2}) is a major phototoxic component in photodynamic therapy (PDT) and its generation is dependent on the availability of tissue oxygen. To examine the effect of oxygen concentration on {sup 1}O{sub 2} detection, two hydrophilic photosensitizer (PS), rose bengal (RB) and meso-metra (N-methyl-4-pyridyl) porphine tetra tosylate (TMPyP) were used as model PS. Irradiation was carried out using 523 nm under hypoxic (2%, 13%), normoxic (21%) and hyperoxic (65%) conditions. The spectral and spatial resolved {sup 1}O{sub 2} luminescence was measured by near-infrared (NIR) photomultiplier tube (PMT) and camera, respectively. Upon the irradiation, the emission signal mainly consisted of background scattering light, PS fluorescence and phosphorescence, and {sup 1}O{sub 2} luminescence. The PS phosphorescence was evidently dependent on the oxygen concentration and PS type, which resulted in the change of emission profile of {sup 1}O{sub 2} luminescence. This change was further demonstrated on {sup 1}O{sub 2} luminescence image. The present study suggests that the low oxygen concentration could affect {sup 1}O{sub 2} luminescence detection. - Highlights: • Both spectral and spatial resolved {sup 1}O{sub 2} luminescence measurements were performed. • Effect of oxygen concentration on {sup 1}O{sub 2} generation was quantitatively evaluated. • Low oxygen concentration could affect {sup 1}O{sub 2} luminescence detection.

  10. Noise filtering of composite pulses for singlet-triplet qubits

    Science.gov (United States)

    Yang, Xu-Chen; Wang, Xin

    2016-01-01

    Semiconductor quantum dot spin qubits are promising candidates for quantum computing. In these systems, the dynamically corrected gates offer considerable reduction of gate errors and are therefore of great interest both theoretically and experimentally. They are, however, designed under the static-noise model and may be considered as low-frequency filters. In this work, we perform a comprehensive theoretical study of the response of a type of dynamically corrected gates, namely the supcode for singlet-triplet qubits, to realistic 1/f noises with frequency spectra 1/ωα. Through randomized benchmarking, we have found that supcode offers improvement of the gate fidelity for α  1 and the improvement becomes exponentially more pronounced with the increase of the noise exponent in the range 1  α ≤ 3 studied. On the other hand, for small α, supcode will not offer any improvement. The δJ-supcode, specifically designed for systems where the nuclear noise is absent, is found to offer additional error reduction than the full supcode for charge noises. The computed filter transfer functions of the supcode gates are also presented. PMID:27383129

  11. Noise filtering of composite pulses for singlet-triplet qubits

    Science.gov (United States)

    Yang, Xu-Chen; Wang, Xin

    2016-07-01

    Semiconductor quantum dot spin qubits are promising candidates for quantum computing. In these systems, the dynamically corrected gates offer considerable reduction of gate errors and are therefore of great interest both theoretically and experimentally. They are, however, designed under the static-noise model and may be considered as low-frequency filters. In this work, we perform a comprehensive theoretical study of the response of a type of dynamically corrected gates, namely the SUPCODE for singlet-triplet qubits, to realistic 1/f noises with frequency spectra 1/ωα. Through randomized benchmarking, we have found that SUPCODE offers improvement of the gate fidelity for α  1 and the improvement becomes exponentially more pronounced with the increase of the noise exponent in the range 1  α ≤ 3 studied. On the other hand, for small α, SUPCODE will not offer any improvement. The δJ-SUPCODE, specifically designed for systems where the nuclear noise is absent, is found to offer additional error reduction than the full SUPCODE for charge noises. The computed filter transfer functions of the supcode gates are also presented.

  12. The nature of singlet excitons in oligoacene molecular crystals

    KAUST Repository

    Yamagata, H.

    2011-01-01

    A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0-0) vibronic band of only -32cm-1, far smaller than the measured value of 631cm-1 and of the wrong sign-a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0-0 DS of 601cm-1 and a nearly quantitative reproduction of the relative spectral intensities of the 0-n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications of these results on exciton dissociation and transport. © 2011 American Institute of Physics.

  13. Analyzing of singlet fermionic dark matter via the updated direct detection data

    Energy Technology Data Exchange (ETDEWEB)

    Ettefaghi, M.M.; Moazzemi, R. [University of Qom, Department of Physics, Qom (Iran, Islamic Republic of)

    2017-05-15

    We revisit the parameter space of singlet fermionic cold dark matter model in order to determine the role of the mixing angle between the standard model Higgs and a new singlet one. Furthermore, we restudy the direct detection constraints with the updated and new experimental data. As an important conclusion, this model is completely excluded by recent XENON100, PandaX II and LUX data. (orig.)

  14. Solar water disinfection by singlet oxygen photogenerated with polymer-supported Ru(II) sensitizers

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez-Hernandez, M. Emilia; Manjon, Francisco; Garcia-Fresnadillo, David; Orellana, Guillermo [Laboratory of Applied Photochemistry, Department of Organic Chemistry, Faculty of Chemistry, Universidad Complutense de Madrid, 28040 Madrid (Spain)

    2006-10-15

    Using Escherichia coli and Enterococcus faecalis as model microorganisms, water disinfection has been demonstrated with singlet molecular oxygen (a reactive oxygen species) photogenerated by polymer-supported Ru(II) sensitizers and solar light. Both laboratory and sunlight tests were performed. The Ru(II) polypyridyl complex and its insoluble support have been optimized to provide maximum efficiency of singlet oxygen production and contact with the microorganism. (author)

  15. Running coupling effects for the singlet structure function g_1 at small x

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2004-01-01

    The running of the QCD coupling is incorporated into the infrared evolution equations for the flavour singlet component, g_1^S of g_1. The explicit expressions for g_1^S including the total resummation of the double-logarithmic contributions and accounting for the running coupling are obtained. We predict that asymptotically g_1^S ~ x^{- \\Delta_S}, with the intercept \\Delta_S = 0.8, which is a factor of 2 larger than the non-singlet intercept.

  16. Eta bound states in nuclei: a probe of flavour-singlet dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Steven D. Bass; Anthony W. Thomas

    2005-07-01

    We argue that eta bound states in nuclei are sensitive to the singlet component in the eta. The bigger the singlet component, the more attraction and the greater the binding. Thus, measurements of eta bound states will yield new information about axial U(1) dynamics and glue in mesons. Eta - etaprime mixing plays an important role in understanding the value of the eta-nucleon scattering length.

  17. Towards photodynamic therapy with ionizing radiation: nanoparticle-mediated singlet oxygen generation (Conference Presentation)

    Science.gov (United States)

    Clement, Sandhya; Deng, Wei; Camilleri, Elizabeth; Wilson, Brian; Goldys, Ewa

    2016-03-01

    Photodynamic therapy (PDT) is a clinically approved method for the treatment of cancer by using singlet oxygen, a highly reactive oxygen generated from a photosensitizer drug upon photoactivation. Limited light penetration depth into to the tissue means that PDT is unsuitable for deep tissue cancer treatments. This can be overcome by using X-ray /gamma rays activated nanoparticles able to trigger the photosensitizer drug and generate singlet oxygen. Additionally, inorganic nanoparticles interact more strongly with X and/or gamma rays than the tissue, allowing to concentrate the effects of radiation near nanoparticle surface and they can also be molecularly targeted to cancer cells. In this work we synthesized and characterized CeF3 nanoparticles, a well-known scintillator material. The nanoparticles were conjugated with Verteporfin, a photosensitizer drug by electrostatic interaction. We assessed the performance of CeF3 and the conjugates to generate singlet oxygen exposed to X-ray radiation. The X-ray singlet oxygen quantum yield of the nanoparticle-photosensitizer system was accurately quantified for the first time. This provided realistic estimates of the singlet oxygen dose taking into consideration the dose partition of the radiation between CeF3 and the tissue. Furthermore, we investigated gold nanoparticle-photosensitizer systems. We confirmed that pure gold nanoparticles itself generate singlet oxygen which is attributed to plasmonic effects. We found enhanced singlet oxygen generation from gold-Rose Bengal conjugates and gold nanorod-verteporfin conjugates. These singlet-oxygen-generating nanomaterials add a new dimension to radiation-assisted PDT.

  18. Long-lived heteronuclear spin-singlet states in liquids at a zero magnetic field.

    Science.gov (United States)

    Emondts, M; Ledbetter, M P; Pustelny, S; Theis, T; Patton, B; Blanchard, J W; Butler, M C; Budker, D; Pines, A

    2014-02-21

    We report an observation of long-lived spin-singlet states in a 13C-1H spin pair in a zero magnetic field. In 13C-labeled formic acid, we observe spin-singlet lifetimes as long as 37 s, about a factor of 3 longer than the T1 lifetime of dipole polarization in the triplet state. In contrast to common high-field experiments, the observed coherence is a singlet-triplet coherence with a lifetime T2 longer than the T1 lifetime of dipole polarization in the triplet manifold. Moreover, we demonstrate that heteronuclear singlet states formed between a 1H and a 13C nucleus can exhibit longer lifetimes than the respective triplet states even in the presence of additional spins that couple to the spin pair of interest. Although long-lived homonuclear spin-singlet states have been extensively studied, this is the first experimental observation of analogous singlet states in heteronuclear spin pairs.

  19. One-Pot Synthesis of (+-Nootkatone via Dark Singlet Oxygenation of Valencene: The Triple Role of the Amphiphilic Molybdate Catalyst

    Directory of Open Access Journals (Sweden)

    Bing Hong

    2016-11-01

    Full Text Available Efficient one-pot catalytic synthesis of (+-nootkatone was performed from (+-valencene using only hydrogen peroxide and amphiphilic molybdate ions. The process required no solvent and proceeded in three cascade reactions: (i singlet oxygenation of valencene according to the ene reaction; (ii Schenck rearrangement of one hydroperoxide into the secondary β-hydroperoxide; and (iii dehydration of the hydroperoxide into the desired (+-nootkatone. The solvent effect on the hydroperoxide rearrangement is herein discussed. The amphiphilic dimethyldioctyl ammonium molybdate, which is also a balanced surfactant, played a triple role in this process, as molybdate ions catalyzed at both Step 1 and Step 3 and it allowed the rapid formation of a three-phase microemulsion system that highly facilitates product recovery. Preparative synthesis of the high added value (+-nootkatone was thus performed at room temperature with an isolated yield of 46.5%. This is also the first example of a conversion of allylic hydroperoxides into ketones catalyzed by molybdate ions.

  20. Targeted oxidation of Torpedo californica acetylcholinesterase by singlet oxygen.

    Science.gov (United States)

    Weiner, Lev; Roth, Esther; Silman, Israel

    2011-01-01

    The photosensitizer, methylene blue (MB), is a strong reversible inhibitor of Torpedo californica acetylcholinesterase (AChE) in the dark. Under illumination it causes irreversible inactivation. Loss of fluorescence of the singlet oxygen ((1)O(2)) trap, 9,10-dimethylanthracene, was retarded in the presence of AChE, and the rate of photo-inactivation was increased in the presence of D(2)O, indicating that inactivation was due to (1)O(2) generated by the photosensitizer. CD revealed slightly reduced far-UV ellipticity, and slightly enhanced binding of an amphiphilic probe, indicating limited unfolding of the photo-oxidized AChE. However, both near-UV ellipticity and intrinsic fluorescence were markedly reduced, suggesting photo-oxidative damage to tryptophans, (Trp) supported by appearance of novel emission peaks ascribed to N'-formylkynurenine and/or kynurenine. Like other partially unfolded forms, the photo-oxidized AChE was sensitive to proteolysis. Photosensitized inactivation produced exclusively chemically cross-linked dimers, whereas irradiation of a partially unfolded state generated higher-order oligomers. The active-site gorge of AChE contains Trp in inhibitor-binding sites that might be targets for photo-oxidation. Indeed, reversible inhibitors retard photo-inactivation, and photo-inactivation destroys their binding sites. An excess of AChE protects paraoxonase from photo-inactivation by sequestering the photosensitizer. Affinity photo-oxidation of AChE by MB thus provides a valuable model for studying site-specific photo-inactivation of enzymes in both fundamental and clinical contexts. © 2010 The Authors. Photochemistry and Photobiology © 2010 The American Society of Photobiology.

  1. Topological spin-singlet superconductors with underlying sublattice structure

    Science.gov (United States)

    Dutreix, C.

    2017-07-01

    Majorana boundary quasiparticles may naturally emerge in a spin-singlet superconductor with Rashba spin-orbit interactions when a Zeeman magnetic field breaks time-reversal symmetry. Their existence and robustness against adiabatic changes is deeply related, via a bulk-edge correspondence, to topological properties of the band structure. The present paper shows that the spin-orbit may be responsible for topological transitions when the superconducting system has an underlying sublattice structure, as it appears in a dimerized Peierls chain, graphene, and phosphorene. These systems, which belong to the Bogoliubov-de Gennes class D, are found to have an extra symmetry that plays the role of the parity. It enables the characterization of the topology of the particle-hole symmetric band structure in terms of band inversions. The topological phase diagrams this leads to are then obtained analytically and exactly. They reveal that, because of the underlying sublattice structure, the existence of topological superconducting phases requires a minimum doping fixed by the strength of the Rashba spin orbit. Majorana boundary quasiparticles are finally predicted to emerge when the Fermi level lies in the vicinity of the bottom (top) of the conduction (valence) band in semiconductors such as the dimerized Peierls chain and phosphorene. In a two-dimensional topological superconductor based on (stretched) graphene, which is semimetallic, Majorana quasiparticles cannot emerge at zero and low doping, that is, when the Fermi level is close to the Dirac points. Nevertheless, they are likely to appear in the vicinity of the van Hove singularities.

  2. Photo-excitation of carotenoids causes cytotoxicity via singlet oxygen production

    Energy Technology Data Exchange (ETDEWEB)

    Yoshii, Hiroshi, E-mail: yoshii@nirs.go.jp [Research Center for Radiation Emergency Medicine, National Institute of Radiological Science, Chiba 263-8555 (Japan); Faculty of Medical Sciences, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Yoshii, Yukie, E-mail: yukiey@nirs.go.jp [Molecular Imaging Center, National Institute of Radiological Science, Chiba 263-8555 (Japan); Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Asai, Tatsuya [Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Faculty of Engineering, University of Fukui, Fukui 910-8507 (Japan); Furukawa, Takako [Molecular Imaging Center, National Institute of Radiological Science, Chiba 263-8555 (Japan); Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Takaichi, Shinichi [Department of Biology, Nippon Medical School, Kawasaki, Kanagawa 211-0063 (Japan); Fujibayashi, Yasuhisa [Molecular Imaging Center, National Institute of Radiological Science, Chiba 263-8555 (Japan); Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan)

    2012-01-06

    Highlights: Black-Right-Pointing-Pointer Some photo-excited carotenoids have photosensitizing ability. Black-Right-Pointing-Pointer They are able to produce ROS. Black-Right-Pointing-Pointer Photo-excited fucoxanthin can produce singlet oxygen through energy transfer. -- Abstract: Carotenoids, natural pigments widely distributed in algae and plants, have a conjugated double bond system. Their excitation energies are correlated with conjugation length. We hypothesized that carotenoids whose energy states are above the singlet excited state of oxygen (singlet oxygen) would possess photosensitizing properties. Here, we demonstrated that human skin melanoma (A375) cells are damaged through the photo-excitation of several carotenoids (neoxanthin, fucoxanthin and siphonaxanthin). In contrast, photo-excitation of carotenoids that possess energy states below that of singlet oxygen, such as {beta}-carotene, lutein, loroxanthin and violaxanthin, did not enhance cell death. Production of reactive oxygen species (ROS) by photo-excited fucoxanthin or neoxanthin was confirmed using a reporter assay for ROS production with HeLa Hyper cells, which express a fluorescent indicator protein for intracellular ROS. Fucoxanthin and neoxanthin also showed high cellular penetration and retention. Electron spin resonance spectra using 2,2,6,6-tetramethil-4-piperidone as a singlet oxygen trapping agent demonstrated that singlet oxygen was produced via energy transfer from photo-excited fucoxanthin to oxygen molecules. These results suggest that carotenoids such as fucoxanthin, which are capable of singlet oxygen production through photo-excitation and show good penetration and retention in target cells, are useful as photosensitizers in photodynamic therapy for skin disease.

  3. Robust conversion of singlet spin order in coupled spin-1/2 pairs by adiabatically switched RF-fields

    CERN Document Server

    Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Vieth, Hans-Martin; Ivanov, Konstantin L

    2016-01-01

    We propose a robust and highly efficient NMR technique to create singlet spin order from longitudinal spin magnetization in coupled spin-1/2 pairs and to perform backward conversion (singlet order)$\\to$magnetization. In this method we exploit adiabatic switching of an RF-field in order to drive transitions between the singlet state and the $T_\\pm$ triplet states of a spin pair under study. We demonstrate that the method works perfectly for both strongly and weakly coupled spin pairs, providing a conversion efficiency between the singlet spin order and magnetization, which is equal to the theoretical maximum. We anticipate that the proposed technique is useful for generating long-lived singlet order, for preserving spin hyperpolarization and for assessing singlet spin order in nearly equivalent spin pairs in specially designed molecules and in low-field NMR studies.

  4. Understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells.

    Science.gov (United States)

    Ran, Niva A; Kuik, Martijn; Love, John A; Proctor, Christopher M; Nagao, Ikuhiro; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    Electroluminescence (EL) from the charge-transfer state and singlet excitons is observed at low applied voltages from high-performing small-molecule bulk-heterojunction solar cells. Singlet emission from the blends emerges upon altering the processing conditions, such as thermal annealing and processing with a solvent additive, and correlates with improved photovoltaic performance. Low-temperature EL measurements are utilized to access the physics behind the singlet emission.

  5. Singlet Oxygen Generation on Porous Superhydrophobic Surfaces: Effect of Gas Flow and Sensitizer Wetting on Trapping Efficiency

    Science.gov (United States)

    2015-01-01

    We describe physical-organic studies of singlet oxygen generation and transport into an aqueous solution supported on superhydrophobic surfaces on which silicon–phthalocyanine (Pc) particles are immobilized. Singlet oxygen (1O2) was trapped by a water-soluble anthracene compound and monitored in situ using a UV–vis spectrometer. When oxygen flows through the porous superhydrophobic surface, singlet oxygen generated in the plastron (i.e., the gas layer beneath the liquid) is transported into the solution within gas bubbles, thereby increasing the liquid–gas surface area over which singlet oxygen can be trapped. Higher photooxidation rates were achieved in flowing oxygen, as compared to when the gas in the plastron was static. Superhydrophobic surfaces were also synthesized so that the Pc particles were located in contact with, or isolated from, the aqueous solution to evaluate the relative effectiveness of singlet oxygen generated in solution and the gas phase, respectively; singlet oxygen generated on particles wetted by the solution was trapped more efficiently than singlet oxygen generated in the plastron, even in the presence of flowing oxygen gas. A mechanism is proposed that explains how Pc particle wetting, plastron gas composition and flow rate as well as gas saturation of the aqueous solution affect singlet oxygen trapping efficiency. These stable superhydrophobic surfaces, which can physically isolate the photosensitizer particles from the solution may be of practical importance for delivering singlet oxygen for water purification and medical devices. PMID:24885074

  6. UVA Photoirradiation of Oxygenated Benz[a]anthracene and 3-Methylcholanthene - Generation of Singlet Oxygen and Induction of Lipid Peroxidation

    Directory of Open Access Journals (Sweden)

    Diógenes Herreño Sáenz

    2008-03-01

    Full Text Available Polycyclic aromatic hydrocarbons (PAHs are widespread genotoxic environmental pollutants and potentially pose a health risk to humans. Although the biological and toxicological activities, including metabolism, mutagenicity, and carcinogenicity, of PAHs have been thoroughly studied, their phototoxicity and photo-induced biological activity have not been well examined. We have long been interested in phototoxicity of PAHs and their derivatives induced by irradiation with UV light. In this paper we report the photoirradiation of a series of oxygenated benz[a]anthracene (BA and 3-methylcholanthene (3-MC by UVA light in the presence of a lipid, methyl linoleate. The studied PAHs include 2-hydroxy-BA (2-OH-BA, 3-hydroxy-BA (3-OH-BA, 5-hydroxymethyl-BA (5-CH2OH-BA, 7-hydroxymethyl-BA (7-CH2OH-BA, 12-hydroxymethyl-BA (12-CH2OH-BA, 7-hydroxymethyl-12-methyl-BA (7-CH2OH-12-MBA, 5-formyl-BA (5-CHO-BA, BA 5,6-cis-dihydrodiol (BA 5,6-cis-diol, 1-hydroxy-3- methylcholanthene (1-OH-3-MC, 1-keto-3-methylcholanthene (1-keto-3-MC, and 3-MC 1,2-diol. The results indicate that upon photoirradiation by UVA at 7 and 21 J/cm2, respectively all these compounds induced lipid peroxidation and exhibited a relationship between the dose of the light and the level of lipid peroxidation induced. To determine whether or not photoirradiation of these compounds by UVA light produces ROS, an ESR spin-trap technique was employed to provide direct evidence. Photoirradiation of 3-keto-3-MC by UVA (at 389 nm in the presence of 2,2,6,6-tetramethylpiperidine (TEMP, a specific probe for singlet oxygen, resulted in the formation of TEMPO, indicating that singlet oxygen was generated. These overall results suggest that UVA photoirradiation of oxygenated BA and 3-methylcholanthrene generates singlet oxygen, one of the reactive oxygen species (ROS, which induce lipid peroxidation.

  7. Time and spectral resolved phosphorescence of singlet oxygen and pigments in photosystem II particles

    Energy Technology Data Exchange (ETDEWEB)

    Dedic, R.; Svoboda, A.; Psencik, J.; Lupinkova, L.; Komenda, J.; Hala, J. E-mail: hala@karlov.mff.cuni.cz

    2003-05-01

    Singlet oxygen generated via chlorophyll triplets in photosynthetic systems can destroy basic components of photosynthetic apparatus. In order to study this process a sensitive spectroscopic experimental set-up was built to detect both weak infrared (IR) chlorophyll phosphorescence (between 900 and 1000 nm) and singlet oxygen phosphorescence (at 1270 nm). The spectral and time resolution of the used monochromator and photon counting multiscaler are sufficient to provide two-dimensional matrix of temporally and spectrally resolved IR luminescence data. We have studied IR emission of photosystem II particles in D{sub 2}O and H{sub 2}O buffer including the effect of the sodium dodecyl sulphate (SDS) detergent. Both sub-microsecond lifetime of chlorophyll triplet states and microsecond lifetime of singlet oxygen were determined. The singlet oxygen lifetime in D{sub 2}O (of 18 {mu}s) was approximately five times longer than that in H{sub 2}O. Quantum efficiency of singlet oxygen generation in photosystem II particles was significantly lower than that in chlorophyll a in acetone, however, it could be substantially increased by addition of SDS.

  8. Cytotoxicity But No Mutagenicity In Bacteria With Externally Generated Singlet Oxygen

    Science.gov (United States)

    Midden, W. Robert; Dahl, Thomas A.; Hartman, Philip E.

    1988-02-01

    Singlet oxygen is believed to be an important intermediate responsible for the cytotoxicity of HpD phototherapy. It has been recognized as a possible intermediate in photosensitization for more than 20 years. However, it has been difficult to obtain conclusive evidence of its biological characteristics in the past because most of the methods available for its generation that are compatible with biological systems also generate other reactive intermediates whose effects are difficult to distinguish from singlet oxygen. We have used a recently devised separated-surface-sensi-tizer (S-S-S) system for singlet oxygen generation' to measure the cytotoxicity and mutagenicity of singlet oxygen in bacteria. The S-S-S system employs rose bengal as a sensitizer immobilized on one surface of a glass plate. The glass plate is placed sensitizer-side down a small distance (Salmonella bacteria than hydrogen peroxide, on a molar basis. We have not observed mutagenicity in these bacteria exposed to sufficient singlet oxygen to kill 60-90% using a variety of bacterial strains and assays.

  9. Two-photon induced photoluminescence and singlet oxygen generation from aggregated gold nanoparticles.

    Science.gov (United States)

    Jiang, Cuifeng; Zhao, Tingting; Yuan, Peiyan; Gao, Nengyue; Pan, Yanlin; Guan, Zhenping; Zhou, Na; Xu, Qing-Hua

    2013-06-12

    Metal nanoparticles have potential applications as bioimaging and photosensitizing agents. Aggregation effects are generally believed to be adverse to their biomedical applications. Here we have studied the aggregation effects on two-photon induced photoluminescence and singlet oxygen generation of Au nanospheres and Au nanorods of two different aspect ratios. Aggregated Au nanospheres and short Au nanorods were found to display enhanced two-photon induced photoluminescence and singlet oxygen generation capabilities compared to the unaggregated ones. The two-photon photoluminescence of Au nanospheres and short Au nanorods were enhanced by up to 15.0- and 2.0-fold upon aggregation, and the corresponding two-photon induced singlet oxygen generation capabilities were enhanced by 8.3 and 1.8-fold, respectively. The two-photon induced photoluminescence and singlet oxygen generation of the aggregated long Au nanorods were found to be lower than the unaggregated ones. These results support that the change in their two-photon induced photoluminescence and singlet oxygen generation originate from aggregation modulated two-photon excitation efficiency. This finding is expected to foster more biomedical applications of metal nanoparticles as Au nanoparticles normally exist in an aggregated form in the biological environments. Considering their excellent biocompatibility, high inertness, ready conjugation, and easy preparation, Au nanoparticles are expected to find more applications in two-photon imaging and two-photon photodynamic therapy.

  10. 750 GeV diphoton resonance from singlets in an exceptional supersymmetric standard model

    Energy Technology Data Exchange (ETDEWEB)

    King, Stephen F. [Physics and Astronomy, University of Southampton,SO17 1BJ Southampton (United Kingdom); Nevzorov, Roman [ARC Centre of Excellence for Particle Physics at the Terascale,Department of Physics, The University of Adelaide,Adelaide, South Australia 5005 (Australia)

    2016-03-21

    The 750–760 GeV diphoton resonance may be identified as one or two scalars and/or one or two pseudoscalars contained in the two singlet superfields S{sub 1,2} arising from the three 27-dimensional representations of E{sub 6}. The three 27s also contain three copies of colour-triplet charge ∓1/3 vector-like fermions D,D̄ and two copies of charged inert Higgsinos H̃{sup +},H̃{sup −} to which the singlets S{sub 1,2} may couple. We propose a variant of the E{sub 6}SSM where the third singlet S{sub 3} breaks a gauged U(1){sub N} above the TeV scale, predicting Z{sub N}{sup ′}, D,D̄, H̃{sup +},H̃{sup −} at LHC Run 2, leaving the two lighter singlets S{sub 1,2} with masses around 750 GeV. We calculate the branching ratios and cross-sections for the two scalar and two pseudoscalar states associated with the S{sub 1,2} singlets, including possible degeneracies and maximal mixing, subject to the constraint that their couplings remain perturbative up to the unification scale.

  11. Development of Singlet Oxygen Luminescence Kinetics during the Photodynamic Inactivation of Green Algae.

    Science.gov (United States)

    Bornhütter, Tobias; Pohl, Judith; Fischer, Christian; Saltsman, Irena; Mahammed, Atif; Gross, Zeev; Röder, Beate

    2016-04-13

    Recent studies show the feasibility of photodynamic inactivation of green algae as a vital step towards an effective photodynamic suppression of biofilms by using functionalized surfaces. The investigation of the intrinsic mechanisms of photodynamic inactivation in green algae represents the next step in order to determine optimization parameters. The observation of singlet oxygen luminescence kinetics proved to be a very effective approach towards understanding mechanisms on a cellular level. In this study, the first two-dimensional measurement of singlet oxygen kinetics in phototrophic microorganisms on surfaces during photodynamic inactivation is presented. We established a system of reproducible algae samples on surfaces, incubated with two different cationic, antimicrobial potent photosensitizers. Fluorescence microscopy images indicate that one photosensitizer localizes inside the green algae while the other accumulates along the outer algae cell wall. A newly developed setup allows for the measurement of singlet oxygen luminescence on the green algae sample surfaces over several days. The kinetics of the singlet oxygen luminescence of both photosensitizers show different developments and a distinct change over time, corresponding with the differences in their localization as well as their photosensitization potential. While the complexity of the signal reveals a challenge for the future, this study incontrovertibly marks a crucial, inevitable step in the investigation of photodynamic inactivation of biofilms: it shows the feasibility of using the singlet oxygen luminescence kinetics to investigate photodynamic effects on surfaces and thus opens a field for numerous investigations.

  12. Glutathione modifies the oxidation products of 2'-deoxyguanosine by singlet molecular oxygen.

    Science.gov (United States)

    Peres, Patrícia S; Valerio, Andressa; Cadena, Silvia M S C; Winnischofer, Sheila M B; Scalfo, Alexsandra C; Di Mascio, Paolo; Martinez, Glaucia R

    2015-11-15

    The oxidation of the free nucleoside 2'-deoxyguanosine (dGuo) by singlet molecular oxygen ((1)O2) has been studied over the three last decades due to the major role of DNA oxidation products in process such as ageing, mutation and carcinogenesis. In the present work we investigated the dGuo oxidation by (1)O2 in the presence of the important low molecular antioxidant, glutathione, in its reduced (GSH) and oxidized (GSSG) forms. There were applied different conditions of concentration, pH, time of incubation, and the use of a [(18)O]-labeled thermolabile endoperoxide naphthalene derivative as a source of [(18)O]-labeled (1)O2. Data was obtained through high performance liquid chromatography (HPLC) and HPLC coupled to micrOTOF Q-II analysis of the main oxidation products: the diastereomers of spiroiminodihydantoin-2'-deoxyribonucleosides (dSp) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). An intriguing result was that 8-oxodGuo levels increased by 100 fold when dGuo was oxidized by (1)O2 in the presence of GSH and by 2 fold in the presence of GSSG, while dSp levels dropped to zero for both conditions. All data from dGuo, 8-oxodGuo and dSp quantification together with the analysis of residual GSH/GSSG content in each sample strongly suggest that glutathione modifies the mechanism of dGuo oxidation by (1)O2 by disfavoring the pathway of dSp formation. Copyright © 2015. Published by Elsevier Inc.

  13. Determining the contribution of singlet molecular oxygen to the decay of pollutants on snow and ice

    Science.gov (United States)

    Bower, J. P.; Anastasio, C.

    2009-12-01

    Singlet molecular oxygen (1O2*) reacts rapidly with certain types of environmental pollutants such as furans, phenols, and polycyclic aromatic hydrocarbons (PAHs). It is formed when a sensitizer, or chromophore, absorbs light and subsequently transfers energy to dissolved oxygen. 1O2* chemistry has been studied primarily in the aqueous phase, such as in surface waters or cloud and fog drops. In our prior work, we showed that the rate of formation (Rf) and steady state concentration ([1O2*]) of 1O2* can be orders of magnitude higher in frozen solutions, relative to those in the liquid phase. Here we investigate methods to discern the contribution of 1O2* - rather than oxidants such as hydroxyl radical (●OH) - to the decay of pollutants on snow and ice. Ice and liquid samples containing a known sensitizer (Rose Bengal) for 1O2* were illuminated in a temperature-controlled solar simulator. Following illumination, the decay of our probe species (furfuryl alcohol) was measured using high performance liquid chromatography. Initial tests were conducted in laboratory solutions made to simulate the concentrations and characteristics of natural (melted) snow, with low concentrations of glycerol added to simulate natural scavengers of ●OH. We show our method to detect reactions by 1O2* apart from other oxidants, particularly ●OH, and show examples of its application in real snow samples. The results of these experiments will allow us to determine the contribution of 1O2* to the decay of the pollutant species in illuminated snow.

  14. Interplay between singlet and triplet excited states in a conformationally locked donor–acceptor dyad

    KAUST Repository

    Filatov, Mikhail A.

    2015-10-13

    The synthesis and photophysical characterization of a palladium(II) porphyrin – anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By using steady-state and time-resolved photoluminescence spectroscopy it was shown that excitation of the singlet excited state of the anthracene leads to energy transfer to the lower-lying singlet state of porphyrin. Alternatively, excitation of the porphyrin followed by intersystem crossing to the triplet state leads to very fast energy transfer to the triplet state of anthracene. The rate of this energy transfer has been determined by transient absorption spectroscopy. Comparative studies of the dynamics of triplet excited states of the dyad and reference palladium octaethylporphyrin (PdOEP) have been performed.

  15. Singlet oxygen generation in PUVA therapy studied using electronic structure calculations

    Energy Technology Data Exchange (ETDEWEB)

    Serrano-Perez, Juan Jose; Olaso-Gonzalez, Gloria; Merchan, Manuela [Instituto de Ciencia Molecular, Universitat de Valencia, Apartado 22085, ES-46071 Valencia (Spain); Serrano-Andres, Luis, E-mail: Luis.Serrano@uv.es [Instituto de Ciencia Molecular, Universitat de Valencia, Apartado 22085, ES-46071 Valencia (Spain)

    2009-06-12

    The ability of furocoumarins to participate in the PUVA (Psoralen + UV-A) therapy against skin disorders and some types of cancer, is analyzed on quantum chemical grounds. The efficiency of the process relies on its capability to populate its lowest triplet excited state, and then either form adducts with thymine which interfere DNA replication or transfer its energy, generating singlet molecular oxygen damaging the cell membrane in photoactivated tissues. By determining the spin-orbit couplings, shown to be the key property, in the intersystem crossing yielding the triplet state of the furocoumarin, the electronic couplings in the triplet-triplet energy transfer process producing the singlet oxygen, and the reaction rates and lifetimes, the efficiency in the phototherapeutic action of the furocoumarin family is predicted as: khellin < 5-methoxypsoralen (5-MOP) < 8-methoxypsoralen (8-MOP) < psoralen < 4,5',8-trimethylpsoralen (TMP) < 3-carbethoxypsoralen (3-CPS), the latter being the most efficient photosensitizer and singlet oxygen generator.

  16. Non-singlet structure functions: Combining the leading logarithms resummation at small-x with DGLAP

    Energy Technology Data Exchange (ETDEWEB)

    Ermolaev, B.I. [Ioffe Physico-Technical Institute, 194021 St. Petersburg (Russian Federation)]. E-mail: ermolaev@mail.cern.ch; Greco, M. [Department of Physics and INFN, University Rome III, Rome (Italy); Troyan, S.I. [St. Petersburg Institute of Nuclear Physics, 188300 Gatchina (Russian Federation)

    2005-08-25

    The explicit expressions for the non-singlet DIS structure functions F{sub 1} and g{sub 1}, obtained at small-x by resumming the leading logarithmic contributions to all orders, are discussed and compared in detail with the DGLAP evolution for different values of x and Q{sup 2}. The role played by the DGLAP inputs for the initial parton densities on the small-x behavior of the non-singlet structure functions is discussed. It is shown that the singular factors included into the fits ensure the Regge asymptotics of the non-singlet structure functions and mimic the impact of the total resummation of the leading logarithms found explicitly in our approach. Explicit expressions are presented which implement the NLO DGLAP contributions with our small-x results.

  17. A Novel Foamy Origin for Singlet Fermion Masses arXiv

    CERN Document Server

    Ellis, John; Nanopoulos, Dimitri V.

    We show how masses for singlet fermions can be generated by interactions with a D-particle model of space-time foam inspired by brane theory. It has been shown previously by one of the authors (N.E.M.) such interactions may generate generate dynamically small masses for charged fermions via the recoils of D-particle defects interacting with photons. In this work we consider the direct interactions of D-particle with uncharged singlet fermions such as right-handed neutrinos. Quantum fluctuations of the lattice of D-particles have massless vector (spin-one) excitations that are analogues of phonons. These mediate forces between the singlet fermions, generating large dynamical masses that may be communicated to light neutrinos via the seesaw mechanism.

  18. The nuMSM, leptonic asymmetries, and properties of singlet fermions

    CERN Document Server

    Shaposhnikov, Mikhail

    2008-01-01

    We study in detail the mechanism of baryon and lepton asymmetry generation in the framework of the nuMSM (an extension of the Standard Model by three singlet fermions with masses smaller than the electroweak scale). We clarify the question of quantum-mechanical coherence, essential for the lepton asymmetry generation in singlet fermion oscillations and compute the relevant damping rates. The range of masses and couplings of singlet leptons which can lead to successful baryogenesis is determined. The conditions which insure survival of primordial (existing above the electroweak temperatures) asymmetries in different leptonic numbers are analysed. We address the question whether CP-violating reactions with lepton number non-conservation can produce leptonic asymmetry {\\em below} the sphaleron freeze-out temperature. This asymmetry, if created, leads to resonant production of dark matter sterile neutrinos. We show that the requirement that a significant lepton asymmetry be produced puts stringent constraints on ...

  19. Direct detection of singlet dark matter in classically scale-invariant standard model

    Directory of Open Access Journals (Sweden)

    Kazuhiro Endo

    2015-10-01

    Full Text Available Classical scale invariance is one of the possible solutions to explain the origin of the electroweak scale. The simplest extension is the classically scale-invariant standard model augmented by a multiplet of gauge singlet real scalar. In the previous study it was shown that the properties of the Higgs potential deviate substantially, which can be observed in the International Linear Collider. On the other hand, since the multiplet does not acquire vacuum expectation value, the singlet components are stable and can be dark matter. In this letter we study the detectability of the real singlet scalar bosons in the experiment of the direct detection of dark matter. It is shown that a part of this model has already been excluded and the rest of the parameter space is within the reach of the future experiment.

  20. The Forward-Backward Top Asymmetry in a Singlet extension of the MSSM

    CERN Document Server

    de la Puente, Alejandro

    2011-01-01

    The CDF and D0 collaborations have recently reported a large forward-backward asymmetry in the ttbar system which deviates from the next to-leading order QCD standard model prediction. We study the asymmetry in the ttbar system within the framework of singlet extensions of the Minimal Supersymmetric Standard Model. For this purpose, we introduce non-renormalizable couplings between first and third generation of quarks to scalars. We analyze two limiting cases of the model, characterized by the size of the supersymmetric mass for the singlet superfield. We study both the small and large limits of this mass parameter. We find that in the region of small singlet supersymmetric mass we can obtain a large asymmetry while being consistent with limits on the ttbar production cross section. These results are also consistent with constraints arising from flavor physics, quark masses and top quark decays.

  1. Baryogenesis in the two doublet and inert singlet extension of the Standard Model

    DEFF Research Database (Denmark)

    Alanne, Tommi; Kainulainen, Kimmo; Tuominen, Kimmo

    2016-01-01

    We investigate an extension of the Standard Model containing two Higgs doublets and a singlet scalar field (2HDSM). We show that the model can have a strongly first-order phase transition and give rise to the observed baryon asymmetry of the Universe, consistent with all experimental constraints....... In particular, the constraints from the electron and neutron electric dipole moments are less constraining here than in pure two-Higgs-doublet model (2HDM). The two-step, first-order transition in 2HDSM, induced by the singlet field, may lead to strong supercooling and low nucleation temperatures in comparison...... with the critical temperature, Tn Tc, which can significantly alter the usual phase-transition pattern in 2HD models with Tn ≈ Tc. Furthermore, the singlet field can be the dark matter particle. However, in models with a strong first-order transition its abundance is typically but a thousandth of the observed dark...

  2. Molecular Tuning of Phenylene-Vinylene Derivatives for Two-Photon Photosensitized Singlet Oxygen Production

    DEFF Research Database (Denmark)

    Nielsen, Christian B.; Arnbjerg, Jacob; Johnsen, Mette

    2009-01-01

    that can deviate from the norm, a full investigation of the photophysical properties of the system is generally required. For example, it is acknowledged that the introduction of a ketone moiety to the sensitizer chromophore often results in more efficient production of singlet oxygen. However, we show...... here that the introduction of a carbonyl into a given phenylene-vinylene can, rather, have adverse effects on the yield of singlet oxygen produced. Using these molecules, we show that care must also be exercised when using qualitative symmetry-derived arguments to predict the relationship between one...

  3. The SM extensions with additional light scalar singlet, nonrenormalizable Yukawa interactions and $(g-2)_{\\mu}$

    CERN Document Server

    Gninenko, S N

    2016-01-01

    We consider the SM extension with additional light real singlet scalar, right-handed neutrino and nonrenormalizable Yukawa interaction for the first two generations. We show that the proposed model can explain the observed $(g - 2)$ muon anomaly. Phenomenological consequences as flavour violating decays $\\tau \\rightarrow \\mu\\mu\\mu, \\mu \\mu e, \\mu e e $ are briefly discussed. We also propose the $U_R(1)$ gauge generalization of the SM with complex scalar singlet and nonzero right-handed charges for the first two generations.

  4. Non-singlet structure functions: Combining the leading logarithms resummation at small-x with DGLAP

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2005-01-01

    The explicit expressions for the non-singlet DIS structure functions obtained at small x by resumming the most singular logarithmic contributions are discussed and compared in detail with the DGLAP evolution for different values of x and Q^2. The role played by the initial conditions for the parton densities currently used in the DGLAP analysis, on the small-$x$ behavior of the non-singlet structure functions is discussed. Explicit expressions are presented which implement the NLO DGLAP contributions with our small-x results.

  5. QCD running coupling effects for the non-singlet structure function at small x

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2000-01-01

    A generalization of the leading-order DGLAP evolution at small x is performed for the non-singlet structure function by resumming the leading-order DGLAP anomalous dimension to all orders in the QCD coupling. Explicit expressions are obtained for the non-singlet structure function of the deep inelastic scattering, taking into account both the double-logarithmic and the single-logarithmic contributions, including the running alpha_s effects. It is shown that when these contributions are included, the asymptotic small-x behaviour is power-like, with an exponent of about 0.4.

  6. A Direct Mechanism of Ultrafast Intramolecular Singlet Fission in Pentacene Dimers

    Science.gov (United States)

    2016-08-24

    acscentsci.6b00063 ACS Cent. Sci. 2016, 2, 316−324 This is an open access article published under an ACS AuthorChoice License, which permits copying and...and correspond to the ground state gg, the ME state, tt, the two singlet LE states, eg and ge, the two CT states, ac and ca, and the doubly excited...singlet fission (τiSF) and the rate of triplet pair (2×T1) recombination (τrec). ACS Central Science Research Article DOI: 10.1021/acscentsci.6b00063

  7. Photostabilizing effects of singlet oxygen quenchers on long chain cyanine dyes

    Institute of Scientific and Technical Information of China (English)

    曾万学; 陈萍; 郑德水; Tsuneki Okazaki; Masaaki Hayami

    1995-01-01

    The total rate constants of the reaction of six antioxidants with singlet oxygen were measuredby fluorospectroscopy,and the effects of these antioxidants on the photostability of the dyes were alsoinvestigated kinetically.The results reveal that the six antioxidants are the effective quenchers of singlet oxygen(1O2)and can increase the photostability of the dyes.The power of metal chelates to quench 1O2 is thestrongest,and the chelates show the most effects on the photostability of the dyes.The photostability of thedyes has something to do with the relative amount of the antioxidant used.

  8. Singlet Ground State Magnetism: III Magnetic Excitons in Antiferromagnetic TbP

    DEFF Research Database (Denmark)

    Knorr, K.; Loidl, A.; Kjems, Jørgen

    1981-01-01

    The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined.......The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined....

  9. Dimensional reduction of the Standard Model coupled to a new singlet scalar field

    CERN Document Server

    Brauner, Tomáš; Tranberg, Anders; Vuorinen, Aleksi; Weir, David J

    2016-01-01

    We derive an effective dimensionally reduced theory for the Standard Model augmented by a real singlet scalar. We treat the singlet as a superheavy field and integrate it out, leaving an effective theory involving only the Higgs and $\\mathrm{SU}(2)_\\mathrm{L} \\times \\mathrm{U}(1)_Y$ gauge fields, identical to the one studied previously for the Standard Model. This opens up the possibility of efficiently computing the order and strength of the electroweak phase transition, numerically and nonperturbatively, in this extension of the Standard Model. Understanding the phase diagram is crucial for models of electroweak baryogenesis and for studying the production of gravitational waves at thermal phase transitions.

  10. Simulating Entanglement Dynamics of Singlet-Triplet Qubits Coupled to a Classical Transmission Line Resonator

    Science.gov (United States)

    Wolfe, Michael; Kestner, Jason

    Electrons confined in lateral quantum dots are promising candidates for scalable quantum bits. Particularly, singlet-triplet qubits can entangle electrostatically and offer long coherence times due to their weak interactions with the environment. However, fast two-qubit operations are challenging. We examine the dynamics of singlet triplet qubits capacitively coupled to a classical transmission line resonator driven near resonance. We numerically simulate the dynamics of the von Neumann entanglement entropy and investigate parameters of the coupling element that optimizes the operation time for the qubit.

  11. The four-qubit singlet state and decoherence-free subspaces

    CERN Document Server

    Cabello, A

    2002-01-01

    It is pointed out that the recent experimental preparation of the four-qubit singlet state by Weinfurter's group is a fundamental achievement for the encoding of quantum information in decoherence-free (DF) subspaces. This state is the DF state orthogonal to the tensor product of two two-qubit singlet states, whose DF properties were experimentally checked by P. G. Kwiat et al. [Science 290, 498 (2000)], and thus provides the missing state for the simplest nontrivial encoding of quantum information in a DF subspace. An experiment to study this DF subspace is suggested.

  12. Out-of-Plane Coordinated Porphyrin Nanotubes with Enhanced Singlet Oxygen Generation Efficiency

    Science.gov (United States)

    Zhao, Qiang; Wang, Yao; Xu, Yanshuang; Yan, Yun; Huang, Jianbin

    2016-08-01

    A supramolecular porphyrin nanotube displaying J-aggregation feature was constructed by out-of-plane coordinated bismuth-porphyrin. Significantly, compared to traditional J-aggregated porphyrin suffering from fluorescence and singlet oxygen quenching, the nanotube exhibits excellent bio-imaging ability and enhanced production efficiency of singlet oxygen. The out-of-plane structure of bismuth to porphyrin makes the aggregation an appropriate material for theranostics. Furthermore, it is also a potential radio-therapeutic drug owing to the presence of radio-active bismuth. Thus, the self-assembly of out-of-plane coordinated porphyrin can be a facile approach toward effective therapy of tumors and other diseases.

  13. The vacuum structure of the Higgs complex singlet-doublet model

    CERN Document Server

    Ferreira, P M

    2016-01-01

    The complex singlet-doublet model is a popular theory to account for dark matter and electroweak baryogenesis, wherein the Standard Model particle content is supplemented by a complex scalar gauge singlet, with certain discrete symmetries imposed. The scalar potential which results thereof can have seven different types of minima at tree-level, which may coexist for specific choices of parameters. There is therefore the possibility that a given minimum is not global but rather a local one, and may tunnel to a deeper extremum, thus causing vacuum instability. This rich vacuum structure is explained and discussed in detail.

  14. Synthesis of DGLAP and total resummation of leading logarithms for the non-singlet spin structure function $g_{1}$

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2005-01-01

    The explicit expressions for the non-singlet DIS structure function g_1 at small $x$ are obtained by resumming the leading logarithmic contributions. The role played by the fits for the initial parton densities currently used in the DGLAP on the small-x behavior of the non-singlet g_1 is discussed. Explicit expressions combining DGLAP with our results are presented.

  15. Spin-state dependent radical stabilization in nitrenes: the unusually small singlet-triplet splitting in 2-furanylnitrene.

    Science.gov (United States)

    Wenthold, Paul G

    2012-01-06

    Geometries and energies of the triplet and singlet states of 2-furanylnitrene and 3-furanylnitrene have been calculated by using spin-flip coupled-cluster methods. Calculations with triple-ζ basis sets predict a singlet-triplet splitting of 10.9 kcal/mol for 2-furanylnitrene, 4.5 kcal/mol smaller than that in phenylnitrene. In contrast, the singlet-triplet splitting in 3-furanylnitrene is computed to be 1.9 kcal/mol larger than that in phenylnitrene. The differences in the singlet-triplet splittings for the furanylnitrenes are attributed to the differences in the radical stabilizing abilities of the 2-furanyl- and 3-furanyl-groups compared to a phenyl ring. Comparison of the singlet-triplet splittings of more than 20 substituted aromatic nitrenes and the radical stabilizing ability of the aromatic systems reveals a high degree of correlation between the singlet-triplet splitting and the radical stabilizing ability, indicating that singlet states of aromatic nitrenes are preferentially stabilized by radical stabilizing substituents. The preferential stabilization of the singlet states is attributed to the decrease in electron pair repulsion resulting from increased delocalization of the radical electron.

  16. OLEDs under high current densities. Transient electroluminescence turn-on peaks and singlet-triplet quenching

    Energy Technology Data Exchange (ETDEWEB)

    Kasemann, Daniel

    2012-02-27

    This work focuses on a better understanding of the behavior of organic light emitting devices (OLEDs) under intense electrical excitation. Attaining high exciton densities in organic semiconductors by electrical excitation is of special interest for the field of organic semiconductor lasers (OSLs). In these devices, the high singlet exciton density needed in the active layer to obtain population inversion is easily created by pulsed optical pumping, but direct electrical pumping has not been achieved yet. First, the steps necessary to achieve stable high current densities in organic semiconductors are discussed. After determining the optimal excitation scheme using single p-doped transport layers, the device complexity is increased up to full p-i-n OLEDs with their power dependent emission spectra. For this purpose, two exemplary emitter systems are chosen: the fluorescent laser dye 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) doped into Aluminum(III)bis (2-methyl-8-quinolinato)-4-phenylphenolate (Alq{sub 3}) and the efficient phosphorescent emitter system N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine (alpha-NPD) doped by Iridium(III) bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate) (Ir(MDQ){sub 2}(acac)). For pulsed excitation using 50 ns pulses and a repetition rate of 1 kHz, single 100 nm thin p- and n-doped transport layers sustain current densities of over 6 kA/cm{sup 2}. While the maximum current density decreases with increasing device thickness, the full OLEDs still sustain current densities beyond 800 A/cm{sup 2} and exhibit a continuously increasing emission intensity with increasing input power. Next, the time-resolved emission behavior of the singlet and triplet emitter device at high excitation densities is analyzed on the nanosecond scale. Here, the peak emission intensity of the phosphorescent emitter system is found to be more than eight times lower than for the singlet emitter system at comparable current

  17. Crossing behavior of the singlet and triplet State of the negatively charged magneto-exciton in a GaAs/AlGaAs quantum well

    Energy Technology Data Exchange (ETDEWEB)

    MUNTEANU,F.M.; KIM,YONGMIN; PERRY,C.H.; RICKEL,D.G.; SIMMONS,JERRY A.; RENO,JOHN L.

    2000-01-27

    Polarized magneto-photoluminescence (MPL) measurements on a high mobility {delta}-doped GaAs/AlGaAs single quantum well from 0--60 T at temperatures between 0.37--2.1 K are reported. In addition to the neutral heavy hole magneto-exciton (X{sup 0}), the singlet (X {sub s}{sup {minus}}) and triplet (X {sub t}{sup {minus}}) states of the negatively charged magneto-exciton are observed in both polarizations. The energy dispersive and time-resolved MPL data suggest that their development is fundamentally related to the formation of the neutral magneto-exciton. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher energy subbands in their energetic evolution, confirming theoretical predictions. The authors also observed the formation of two higher energy peaks. One of them is completely right circularly polarized and its appearance can be considered a result of the electron-hole exchange interaction enhancement with an associated electron g-factor of 3.7 times the bulk value. The other peak completely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previous anomalies observed in the integer and fractional quantum Hall regimes.

  18. Crossing behavior of the singlet and triplet State of the negatively charged magneto-exciton in a GaAs/AlGaAs quantum well

    Energy Technology Data Exchange (ETDEWEB)

    MUNTEANU,F.M.; KIM,YONGMIN; PERRY,C.H.; RICKEL,D.G.; SIMMONS,JERRY A.; RENO,JOHN L.

    2000-01-27

    Polarized magneto-photoluminescence (MPL) measurements on a high mobility {delta}-doped GaAs/AlGaAs single quantum well from 0--60 T at temperatures between 0.37--2.1 K are reported. In addition to the neutral heavy hole magneto-exciton (X{sup 0}), the singlet (X {sub s}{sup {minus}}) and triplet (X {sub t}{sup {minus}}) states of the negatively charged magneto-exciton are observed in both polarizations. The energy dispersive and time-resolved MPL data suggest that their development is fundamentally related to the formation of the neutral magneto-exciton. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher energy subbands in their energetic evolution, confirming theoretical predictions. The authors also observed the formation of two higher energy peaks. One of them is completely right circularly polarized and its appearance can be considered a result of the electron-hole exchange interaction enhancement with an associated electron g-factor of 3.7 times the bulk value. The other peak completely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previous anomalies observed in the integer and fractional quantum Hall regimes.

  19. Benchmarking Compound Methods (CBS-QB3, CBS-APNO, G3, G4, W1BD) against the Active Thermochemical Tables: Formation Enthalpies of Radicals.

    Science.gov (United States)

    Somers, Kieran P; Simmie, John M

    2015-08-20

    The 298.15 K formation enthalpies of 38 radicals with molecular formula CxHyOz have been computed via the atomization procedure using the five title methods. The computed formation enthalpies are then benchmarked against the values recommended in the Active Thermochemical Tables (ATcT). The accuracy of the methods have been interpreted in terms of descriptive statistics, including the mean-signed error, mean-unsigned error, maximum average deviation, 2σ uncertainties, and 2×root-mean-square-deviations (2RMSD). The results highlight the following rank order of accuracy for the methods studied G4 > G3 > W1BD > CBS-APNO > CBS-QB3. The findings of this work are also considered in light of a recent companion study, which took an identical approach to quantifying the accuracies of these methods for 48 closed-shell singlet CxHyOz compounds. A similar order of accuracies and precisions were observed therein: G3 > G4 > W1BD > CBS-APNO > CBS-QB3. Both studies highlight systematic biases/deviations from the ATcT for the methods investigated, which are discussed in some detail, with methods having clear tendencies to over- or underpredict the recommended formation enthalpies for radical and/or closed-shell CxHyOz compounds. We show that one can improve the accuracy of their computation, and simultaneously reduce the uncertainty, by taking unweighted average formation enthalpies from various combinations of methods used. The reader should note that the statistical analyses preceding these conclusions also highlight that these error cancellation effects are unique for closed-shell and radical species. By extension, these error-cancellation effects can be expected to be different for various homologous series and chemical functionalities and their closed- and open-shell subgroups. Hence, further benchmarking studies are advised for other homologous series, such that the scientists and engineers (e.g., combustion/atmospheric/astrochemical) who frequently use these methods can

  20. Photosensitized production of singlet oxygen: spatially-resolved optical studies in single cells

    DEFF Research Database (Denmark)

    Breitenbach, Thomas; Kuimova, Marina; Gbur, Peter;

    2009-01-01

    be monitored using viability assays. Time- and spatially-resolved optical measurements of both singlet oxygen and its precursor, the excited state sensitizer, reflect the complex and dynamic morphology of the cell. These experiments help elucidate photoinduced, oxygen-dependent events that compromise cell...

  1. Technicolor Models with Color-Singlet Technifermions and their Ultraviolet Extensions

    DEFF Research Database (Denmark)

    Ryttov, Thomas; Shrock, Robert

    2011-01-01

    We study technicolor models in which all of the technifermions are color-singlets, focusing on the case in these fermions transform according to the fundamental representation of the technicolor gauge group. Our analysis includes a derivation of restrictions on the weak hypercharge assignments...

  2. Singlet aided infinite resource reduction in the comparison of distant fields

    CERN Document Server

    Bose, S; Plenio, M B

    2001-01-01

    We present a task which can be faithfully solved with finite resources only when aided by particles prepared in a particular entangled state: the singlet state. The task consists of identifying the mutual parallelity or orthogonality of weak distant magnetic fields whose absolute directions are completely unknown.

  3. Disjoint nonclassical hydrocarbons have very unstable lowest-lying singlet states: a PM3 study

    Directory of Open Access Journals (Sweden)

    Richard Francis Langler

    2001-12-01

    Full Text Available Earlier workers have suggested that disjoint hydrocarbons have nearly-degenerate lowest-lying singlet and triplet states while non-disjoint (or joint hydrocarbons should be ground-state triplets. PM3 results for an appropriate selection of alternant hydrocarbons are inconsistent with that generalization: disjoint, nonclassical, alternant hydrocarbons show the strongest predilection for triplet ground states.

  4. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    KAUST Repository

    Dimitrov, Stoichko

    2016-01-13

    The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  5. Spin-slip structure and central peak phenomena in singlet-doublet system: Praseodymium

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1997-01-01

    A theory is given for the central peaks observed in praseodymium, which is an effective singlet-doublet System of localized spins. The dominant peak is due to induced longitudinal magnetic ordering, which can be accounted for by mode-mode coupling theory. The second, broader peak is due to an ind...

  6. A Covalently Linked Tetracene Trimer: Synthesis and Singlet Exciton Fission Property.

    Science.gov (United States)

    Liu, Heyuan; Wang, Rui; Shen, Li; Xu, Yanqing; Xiao, Min; Zhang, Chunfeng; Li, Xiyou

    2017-02-03

    A linear tetracene trimer linked by phenyl groups has been prepared for the first time. The triplet quantum yield formed via intramolecular singlet fission can reach up to 96% in this trimer, which is enhanced significantly compared with that in the dimer. This can be attributed to the stronger electronic coupling between tetracene subunits and more delocalized excitons in the trimer.

  7. Voltage-sensitive styryl dyes as singlet oxygen targets on the surface of bilayer lipid membrane.

    Science.gov (United States)

    Sokolov, V S; Gavrilchik, A N; Kulagina, A O; Meshkov, I N; Pohl, P; Gorbunova, Yu G

    2016-08-01

    Photosensitizers are widely used as photodynamic therapeutic agents killing cancer cells by photooxidation of their components. Development of new effective photosensitive molecules requires profound knowledge of possible targets for reactive oxygen species, especially for its singlet form. Here we studied photooxidation of voltage-sensitive styryl dyes (di-4-ANEPPS, di-8-ANEPPS, RH-421 and RH-237) by singlet oxygen on the surface of bilayer lipid membranes commonly used as cell membrane models. Oxidation was induced by irradiation of a photosensitizer (aluminum phthalocyanine tetrasulfonate) and monitored by the change of dipole potential on the surface of the membrane. We studied the drop of the dipole potential both in the case when the dye molecules were adsorbed on the same side of the lipid bilayer as the photosensitizer (cis-configuration) and in the case when they were adsorbed on the opposite side (trans-configuration). Based on a simple model, we determined the rate of oxidation of the dyes from the kinetics of change of the potential during and after irradiation. This rate is proportional to steady-state concentration of singlet oxygen in the membrane under irradiation. Comparison of the oxidation rates of various dyes reveals that compounds of ANEPPS series are more sensitive to singlet oxygen than RH type dyes, indicating that naphthalene group is primarily responsible for their oxidation.

  8. Single Molecule Atomic Force Microscopy Studies of Photosensitized Singlet Oxygen Behavior on a DNA Origami Template

    DEFF Research Database (Denmark)

    Helmig, Sarah Wendelboe; Rotaru, Alexandru; Arian, Dumitru

    2010-01-01

    photosensitizer molecule conjugated to a selected DNA origami staple strand on an origami structure. We demonstrate a distance-dependent oxidation of organic moieties incorporated in specific positions on DNA origami by singlet oxygen produced from a single photosensitizer located at the center of each origami....

  9. Storage of magnetization as singlet order by optimal control designed pulses

    DEFF Research Database (Denmark)

    Laustsen, Christoffer; Bowen, Sean; Vinding, Mads Sloth

    2014-01-01

    . With this aim, optimal control theory was applied to create pulses that for near‐equivalent spins accomplish transfers in and out of the singlet state with maximum efficiency while ensuring robustness toward variations in the nuclear spin system Hamiltonian (chemical shift, J‐couplings, B1 and B magnetic field...

  10. Singlet fission/silicon solar cell exceeding 100% EQE (Conference Presentation)

    Science.gov (United States)

    Pazos, Luis M.; Lee, Jumin; Kirch, Anton; Tabachnyk, Maxim; Friend, Richard H.; Ehrler, Bruno

    2016-09-01

    Current matching limits the commercialization of tandem solar cells due to their instability over spectral changes, leading to the need of using solar concentrators and trackers to keep the spectrum stable. We demonstrate that voltage-matched systems show far higher performance over spectral changes; caused by clouds, dust and other variations in atmospheric conditions. Singlet fission is a process in organic semiconductors which has shown very efficient, 200%, down-conversion yield and the generated excitations are long-lived, ideal for solar cells. As a result, the number of publications has grown exponentially in the past 5 years. Yet, so far no one has achieved to combine singlet fission with most low bandgap semiconductors, including crystalline silicon, the dominating solar cell material with a 90% share of the PV Market. Here we show that singlet fission can facilitate the fabrication of voltage-matched systems, opening a simple design route for the effective implementation of down-conversion in commercially available photovoltaic technologies, with no modification of the electronic circuitry of such. The implemention of singlet fission is achieved simply by decoupling the fabrication of the individual subcells. For this demonstration we used an ITO/PEDOT/P3HT/Pentacene/C60/Ag wide-bandgap subcell, and a commercial silicon solar cell as the low-bandgap component. We show that the combination of the two leads to the first tandem silicon solar cell which exceeds 100% external quantum efficiency.

  11. Solving the liar detection problem using the four-qubit singlet state

    CERN Document Server

    Cabello, A

    2003-01-01

    A method for solving the Byzantine generals problem [M. Fitzi, N. Gisin, and U. Maurer, Phys. Rev. Lett. 87, 217901 (2001)] and the liar detection problem [A. Cabello, Phys. Rev. Lett. 89, 100402 (2002)] is introduced. The main advantage of this proposal is that it is based on the four-qubit singlet state recently obtained experimentally by Weinfurter's group.

  12. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    Directory of Open Access Journals (Sweden)

    Stoichko D. Dimitrov

    2016-01-01

    Full Text Available The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  13. Laser-induced generation of singlet oxygen and its role in the cerebrovascular physiology

    Science.gov (United States)

    Semyachkina-Glushkovskaya, O. V.; Sokolovski, S. G.; Goltsov, A.; Gekaluyk, A. S.; Saranceva, E. I.; Bragina, O. A.; Tuchin, V. V.; Rafailov, E. U.

    2017-09-01

    For over 55 years, laser technology has expanded from laboratory research to widespread fields, for example telecommunication and data storage amongst others. Recently application of lasers in biology and medicine presents itself as one of the emerging areas. In this review, we will outline the recent advances in using lasers for the generation of singlet oxygen, traditionally used to kill tumour cells or induce thrombotic stroke model due to damage vascular effects. Over the last two decade, completely new results on cerebrovascular effects of singlet oxygen generated during photodynamic therapy (PDT) have been shown alongside promising applications for delivery of drugs and nanoparticles into the brain for therapy of brain cancer. Furthermore, a ;gold key; has been found to overcome the limitations of PDT, such as low light penetration and high toxicity of photosensitizers, by direct generation of singlet oxygen using quantum-dot laser diodes emitting in the near infrared (NIR) spectral range. It is our motivation to highlight these pioneering results in this review, to improve understanding of the biological role of singlet oxygen and to provide new perspectives for improving clinical application of laser based therapy in further research.

  14. Graphene oxide functionalized with methylene blue and its performance in singlet oxygen generation

    Energy Technology Data Exchange (ETDEWEB)

    Wojtoniszak, M., E-mail: mwojtoniszak@zut.edu.pl [West Pomeranian University of Technology in Szczecin, Institute of Chemical and Environment Engineering, Pulaskiego 10, 70-322 Szczecin (Poland); Rogińska, D.; Machaliński, B. [Pomeranian Medical University, Department of General Pathology, Powstańców Wlkp. 72, 70-111 Szczecin (Poland); Drozdzik, M. [Pomeranian Medical University, Department of Pharmacology, Powstańców Wlkp. 72, 70-111 Szczecin (Poland); Mijowska, E. [West Pomeranian University of Technology in Szczecin, Institute of Chemical and Environment Engineering, Pulaskiego 10, 70-322 Szczecin (Poland)

    2013-07-15

    Graphical abstract: - Highlights: • Adsorption of methylene blue (MB) on graphene oxide (GO). • Characterization of graphene oxide–methylene blue nanocomposite (MB–GO). • Examination of MB–GO efficiency in singlet oxygen generation (SOG). • MB–GO performs higher SOG efficiency than pristine MB. - Abstract: Due to unique electronic, mechanical, optical and structural properties, graphene has shown promising applications in many fields, including biomedicine. One of them is noninvasive anticancer therapy – photodynamic therapy (PDT), where singlet oxygen (SO), generated under the irradiation of light with appropriate wavelengths, kills cancer cells. In this study, authors report graphene oxide (GO) noncovalent functionalization with methylene blue (MB). MB molecules underwent adsorption on the surface of GO. Detailed characterization of the obtained material was carried out with UV–vis spectroscopy, Raman spectroscopy, FT-IR spectroscopy, and confocal laser scanning microscopy. Furthermore, its performance in singlet oxygen generation (SOG) under irradiation of laser with excitation wavelengths of 785 nm was investigated. Interestingly, GO functionalized with MB (MB–GO) showed enhanced efficiency in singlet oxygen generation compared to pristine MB. The efficiency in SOG was detected by photobleaching of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABMDMA). These results indicate the material is promising in PDT anticancer therapy and further in vitro and in vivo studies are required.

  15. Calculation of excitation energies of open-shell molecules with spatially degenerate ground states. I. Transformed reference via an intermediate configuration Kohn-Sham density-functional theory and applications to d1 and d2 systems with octahedral and tetrahedral symmetries.

    Science.gov (United States)

    Seth, Michael; Ziegler, Tom

    2005-10-08

    A method for calculating the UV-vis spectra of molecules with spatially degenerate ground states using time-dependent density-functional theory (TDDFT) is proposed. The new transformed reference via an intermediate configuration Kohn-Sham TDDFT (TRICKS-TDDFT) method avoids the difficulties caused by the multireference nature of spatially degenerate states by rather than utilizing the ground state instead taking a nondegenerate excited state with desirable properties as the reference for the TDDFT calculation. The scope and practical application of the method are discussed. Like all open-shell TDDFT calculations this method at times suffers from the inability to produce transitions to states that are eigenfunctions of the total spin operator. A technique for alleviating this difficulty to some extent is proposed. The applicability and accuracy of the TRICKS-TDDFT method is demonstrated through example calculations of several d(1) and d(2) transition metal complexes with tetrahedral and octahedral symmetries. For the most part, the results of these calculations are similar in quality to to those obtained from standard TDDFT calculations.

  16. Formation and dynamics of van der Waals molecules in buffer-gas traps

    CERN Document Server

    Brahms, Nathan; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G

    2011-01-01

    We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calc...

  17. Efeitos de oxigenio singlete gerado fotoquimica e enzimaticamente sobre o acido ribonucleico de transferencia de E. coli

    OpenAIRE

    Maria Cristina Marcucci

    1986-01-01

    Resumo: O malonaldeído e o ácido indol-3-acético são oxidados aerobicamente pela peroxidase, produzindo oxigênio singlete em ambos os processos, e no último caso também indol-3-aldeído excitado. Estes processos são chamados de biofotoenergizados. Entretanto, existem outras vias de geração de oxigênio singlete como processos fotoquímicos, pelo uso de sensibilizadores. Foi comprovada a similaridade entre os efeitos de oxigênio singlete gerado fotoquimica e enzimaticamenle sobre o ácido ribonucl...

  18. The effect of solvent polarity on the balance between charge transfer and non-charge transfer pathways in the sensitization of singlet oxygen by pipi triplet states.

    Science.gov (United States)

    Schmidt, Reinhard

    2006-05-11

    A large set of literature kinetic data on triplet (T(1)) sensitization of singlet oxygen by two series of biphenyl and naphthalene sensitizers in solvents of strongly different polarity has been analyzed. The rate constants and the efficiencies of singlet oxygen formation are quantitatively reproduced by a model that assumes the competition of a non-charge transfer (nCT) and a CT deactivation channel. nCT deactivation occurs from a fully established spin-statistical equilibrium of (1)(T(1)(3)Sigma) and (3)(T(1)(3)Sigma) encounter complexes by internal conversion (IC) to lower excited complexes that dissociate to yield O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)), and O(2)((3)Sigma(g)(-)). IC of (1,3)(T(1)(3)Sigma) encounter complexes is controlled by an energy gap law that is generally valid for the transfer of electronic energy to and from O(2). (1,3)(T(1)(3)Sigma) nCT complexes form in competition to IC (1)(T(1)(3)Sigma) and (3)(T(1)(3)Sigma) exciplexes if CT interactions between T(1) and O(2) are important. The rate constants of exciplex formation depend via a Marcus type parabolic model on the corresponding free energy change DeltaG(CT), which varies with sensitizer triplet energy, oxidation potential, and solvent polarity. O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)), and O(2)((3)Sigma(g)(-)) are formed in the product ratio (1/6):(1/12):(3/4) in the CT deactivation channel. The balance between nCT and CT deactivation is described by the relative contribution p(CT) of CT induced deactivation calculated for a sensitizer of known triplet energy from its quenching rate constant. It is shown how the change of p(CT) influences the quenching rate constant and the efficiency of singlet oxygen formation in both series of sensitizers. p(CT) is sensitive to differences of solvent polarity and varies for the biphenyls and the naphthalenes as sigmoidal with DeltaG(CT). This quantitative model represents a realistic and general mechanism for the quenching of pipi triplet states by O

  19. Reaction of protonated tyrosine with electronically excited singlet molecular oxygen (a1Delta(g)): an experimental and trajectory study.

    Science.gov (United States)

    Fang, Yigang; Liu, Jianbo

    2009-10-22

    Reaction of protonated tyrosine with the lowest electronically excited singlet state of molecular oxygen, (1)O(2) (a(1)Delta(g)), is reported over the center-of-mass collision energy (E(col)) range from 0.1 to 3.0 eV, using an electrospray-ionization, guided-ion-beam scattering instrument, in conjunction with ab initio electronic structure calculations and direct dynamics trajectory simulations. Only one product channel is observed, corresponding to generation of hydrogen peroxide via transfer of two hydrogen atoms from protonated tyrosine. Despite being exoergic, the reaction is in competition with physical quenching of (1)O(2) and is very inefficient. At low E(col), the reaction may be mediated by intermediate complexes and shows strong inhibition by collision energy. At high E(col), the reaction efficiency drops to approximately 1% and starts to have contribution from a direct mechanism. Quasi-classical trajectory simulations were performed to probe the mechanism at high collision energies. Analysis of trajectories shows that, at E(col) of 3.0 eV, a small fraction of hydrogen peroxide (25%) is produced via a direct, concerted mechanism where two hydrogen atoms are transferred simultaneously, but most hydrogen peroxide (75%) is formed by dissociation of hydroperoxide intermediates. According to ab initio calculations and trajectory simulations, collisions also lead to formation of various endoperoxides, and dissociation of endoperoxides may play a role in physical quenching of (1)O(2). The apparatus and experimental techniques are described in detail.

  20. A novel approach to nonperturbative renormalization of singlet and nonsinglet lattice operators

    Directory of Open Access Journals (Sweden)

    A.J. Chambers

    2015-01-01

    Full Text Available A novel method for nonperturbative renormalization of lattice operators is introduced, which lends itself to the calculation of renormalization factors for nonsinglet as well as singlet operators. The method is based on the Feynman–Hellmann relation, and involves computing two-point correlators in the presence of generalized background fields arising from introducing additional operators into the action. As a first application, and test of the method, we compute the renormalization factors of the axial vector current Aμ and the scalar density S for both nonsinglet and singlet operators for Nf=3 flavors of SLiNC fermions. For nonsinglet operators, where a meaningful comparison is possible, perfect agreement with recent calculations using standard three-point function techniques is found.

  1. Singlet states and the estimation of eigenstates and eigenvalues of an unknown Controlled-U gate

    CERN Document Server

    Hillery, M; Hillery, Mark; Buzek, Vladimir

    2001-01-01

    We consider several problems that involve finding the eigenvalues and generating the eigenstates of unknown unitary gates. We first examine Controlled-U gates that act on qubits, and assume that we know the eigenvalues. It is then shown how to use singlet states to produce qubits in the eigenstates of the gate. We then remove the assumption that we know the eigenvalues and show how to both find the eigenvalues and produce qubits in the eigenstates. Finally, we look at the case where the unitary operator acts on qutrits and has eigenvalues of 1 and -1, where the eigenvalue 1 is doubly degenerate. The eigenstates are unknown. We are able to use a singlet state to produce a qutrit in the eigenstate corresponding to the -1 eigenvalue.

  2. Fluorescence Behaviour and Singlet Oxygen Production of Aluminium Phthalocyanine in the Presence of Upconversion Nanoparticles.

    Science.gov (United States)

    Watkins, Zane; Taylor, Jessica; D'Souza, Sarah; Britton, Jonathan; Nyokong, Tebello

    2015-09-01

    NaYF4:Yb/Er/Gd upconversion nanoparticles (UCNP) were synthesised and the photoemission stabilised by embedding them in electrospun fibers. The photophysical behaviour of chloro aluminium tetrasulfo phthalocyanine (ClAlTSPc) was studied in the presence of UCNPs when the two are mixed in solution. The fluorescence quantum yield value of ClAlTSPc decreased in the presence of UCNPs due to the heavy atom effect of UCNPs. This effect also resulted in increase in triplet quantum yields for ClAlTSPc in the presence of UCNPs. The fluorescence lifetimes for UCNPs were shortened at 658 nm in the presence of ClAlTSPc when the former was embedded in fiber and suspended in a dimethyl sulfoxide solution of the latter. A clear singlet oxygen generation by ClAlTSPc though Förster resonance energy transfer was demonstrated using a singlet oxygen quencher, 1,3-diphenylisobenzofuran.

  3. Photophysical Properties and Singlet Oxygen Generation Efficiencies of Water-Soluble Fullerene Nanoparticles

    Science.gov (United States)

    Stasheuski, Alexander S; Galievsky, Victor A; Stupak, Alexander P; Dzhagarov, Boris M; Choi, Mi Jin; Chung, Bong Hyun; Jeong, Jin Young

    2014-01-01

    As various fullerene derivatives have been developed, it is necessary to explore their photophysical properties for potential use in photoelectronics and medicine. Here, we address the photophysical properties of newly synthesized water-soluble fullerene-based nanoparticles and polyhydroxylated fullerene as a representative water-soluble fullerene derivative. They show broad emission band arising from a wide-range of excitation energies. It is attributed to the optical transitions from disorder-induced states, which decay in the nanosecond time range. We determine the kinetic properties of the singlet oxygen (1O2) luminescence generated by the fullerene nanoparticles and polyhydroxylated fullerene to consider the potential as photodynamic agents. Triplet state decay of the nanoparticles was longer than 1O2 lifetime in water. Singlet oxygen quantum yield of a series of the fullerene nanoparticles is comparably higher ranging from 0.15 to 0.2 than that of polyhydroxylated fullerene, which is about 0.06. PMID:24893622

  4. Transient photocurrent in molecular junctions: singlet switching on and triplet blocking.

    Science.gov (United States)

    Petrov, E G; Leonov, V O; Snitsarev, V

    2013-05-14

    The kinetic approach adapted to describe charge transmission in molecular junctions, is used for the analysis of the photocurrent under conditions of moderate light intensity of the photochromic molecule. In the framework of the HOMO-LUMO model for the single electron molecular states, the analytic expressions describing the temporary behavior of the transient and steady state sequential (hopping) as well as direct (tunnel) current components have been derived. The conditions at which the current components achieve their maximal values are indicated. It is shown that if the rates of charge transmission in the unbiased molecular diode are much lower than the intramolecular singlet-singlet excitation/de-excitation rate, and the threefold degenerated triplet excited state of the molecule behaves like a trap blocking the charge transmission, a possibility of a large peak-like transient switch-on photocurrent arises.

  5. Singlet oxygen mediated DNA degradation by copper nanoparticles: potential towards cytotoxic effect on cancer cells

    Science.gov (United States)

    2011-01-01

    The DNA degradation potential and anti-cancer activities of copper nanoparticles of 4-5 nm size are reported. A dose dependent degradation of isolated DNA molecules by copper nanoparticles through generation of singlet oxygen was observed. Singlet oxygen scavengers such as sodium azide and Tris [hydroxyl methyl] amino methane were able to prevent the DNA degradation action of copper nanoparticles confirming the involvement of activated oxygen species in the degradation process. Additionally, it was observed that the copper nanoparticles are able to exert cytotoxic effect towards U937 and Hela cells of human histiocytic lymphoma and human cervical cancer origins, respectively by inducing apoptosis. The growth characteristics of U937 and Hela cells were studied applying various concentrations of the copper nanoparticles. PMID:21439072

  6. Singlet-triplet annihilation limits exciton yield in poly(3-hexylthiophene)

    CERN Document Server

    Steiner, Florian; Lupton, John M

    2014-01-01

    Control of chain length and morphology in combination with single-molecule spectroscopy techniques provide a comprehensive photophysical picture of excited-state losses in the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT). A universal self-quenching mechanism is revealed, based on singlet-triplet exciton annihilation, which accounts for the dramatic loss in fluorescence quantum yield of a single P3HT chain between its solution (unfolded) and bulk-like (folded) state. Triplet excitons fundamentally limit the fluorescence of organic photovoltaic materials, which impacts on the conversion of singlet excitons to separated charge carriers, decreasing the efficiency of energy harvesting at high excitation densities. Interexcitonic interactions are so effective that a single P3HT chain of >100 kDa weight behaves like a two-level system, exhibiting perfect photon-antibunching.

  7. Actinide chemistry using singlet-paired coupled cluster and its combinations with density functionals

    CERN Document Server

    Garza, Alejandro J; Scuseria, Gustavo E

    2015-01-01

    Singlet-paired coupled cluster doubles (CCD0) is a simplification of CCD that relinquishes a fraction of dynamic correlation in order to be able to describe static correlation. Combinations of CCD0 with density functionals that recover specifically the dynamic correlation missing in the former have also been developed recently. Here, we assess the accuracy of CCD0 and CCD0+DFT (and variants of these using Brueckner orbitals) as compared to well-established quantum chemical methods for describing ground-state properties of singlet actinide molecules. The $f^0$ actinyl series (UO$_2^{2+}$, NpO$_2^{2+}$, PuO$_2^{2+}$), the isoelectronic NUN, and Thorium (ThO, ThO$^{2+}$) and Nobelium (NoO, NoO$_2$) oxides are studied.

  8. Prediction of Tetraoxygen Reaction Mechanism with Sulfur Atom on the Singlet Potential Energy Surface

    Directory of Open Access Journals (Sweden)

    Ashraf Khademzadeh

    2014-01-01

    Full Text Available The mechanism of S+O4 (D2h reaction has been investigated at the B3LYP/6-311+G(3df and CCSD levels on the singlet potential energy surface. One stable complex has been found for the S+O4 (D2h reaction, IN1, on the singlet potential energy surface. For the title reaction, we obtained four kinds of products at the B3LYP level, which have enough thermodynamic stability. The results reveal that the product P3 is spontaneous and exothermic with −188.042 and −179.147 kcal/mol in Gibbs free energy and enthalpy of reaction, respectively. Because P1 adduct is produced after passing two low energy level transition states, kinetically, it is the most favorable adduct in the 1S+1O4 (D2h atmospheric reactions.

  9. Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors

    CERN Document Server

    Moroz, Sergej; Gurarie, Victor; Radzihovsky, Leo

    2016-01-01

    Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for $s$-wave, $d+id$, and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of low-energy excitations and incorporate global continuous symmetries - specifically, spin rotation and conservation of magnetic flux - present in all singlet superconductors. We compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly-coupled phase of a chiral state paired in the even $k^{\\text{th}}$ partial wave has a spin Hall coefficient $\

  10. Jet Production via Strongly Interacting Color-Singlet Exchange in pp¯ Collisions

    Science.gov (United States)

    Abachi, S.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adam, I.; Adams, D. L.; Adams, M.; Ahn, S.; Aihara, H.; Alitti, J.; Álvarez, G.; Alves, G. A.; Amidi, E.; Amos, N.; Anderson, E. W.; Aronson, S. H.; Astur, R.; Avery, R. E.; Baden, A.; Balamurali, V.; Balderston, J.; Baldin, B.; Bantly, J.; Bartlett, J. F.; Bazizi, K.; Bendich, J.; Beri, S. B.; Bertram, I.; Bezzubov, V. A.; Bhat, P. C.; Bhatnagar, V.; Bhattacharjee, M.; Bischoff, A.; Biswas, N.; Blazey, G.; Blessing, S.; Bloom, P.; Boehnlein, A.; Bojko, N. I.; Borcherding, F.; Borders, J.; Boswell, C.; Brandt, A.; Brock, R.; Bross, A.; Buchholz, D.; Burtovoi, V. S.; Butler, J. M.; Carvalho, W.; Casey, D.; Castilla-Valdez, H.; Chakraborty, D.; Chang, S.-M.; Chekulaev, S. V.; Chen, L.-P.; Chen, W.; Chevalier, L.; Chopra, S.; Choudhary, B. C.; Christenson, J. H.; Chung, M.; Claes, D.; Clark, A. R.; Cobau, W. G.; Cochran, J.; Cooper, W. E.; Cretsinger, C.; Cullen-Vidal, D.; Cummings, M. A.; Cutts, D.; Dahl, O. I.; de, K.; Demarteau, M.; Demina, R.; Denisenko, K.; Denisenko, N.; Denisov, D.; Denisov, S. P.; Diehl, H. T.; Diesburg, M.; di Loreto, G.; Dixon, R.; Draper, P.; Drinkard, J.; Ducros, Y.; Dugad, S. R.; Durston-Johnson, S.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Engelmann, R.; Eno, S.; Eppley, G.; Ermolov, P.; Eroshin, O. V.; Evdokimov, V. N.; Fahey, S.; Fahland, T.; Fatyga, M.; Fatyga, M. K.; Featherly, J.; Feher, S.; Fein, D.; Ferbel, T.; Finocchiaro, G.; Fisk, H. E.; Fisyak, Y.; Flattum, E.; Forden, G. E.; Fortner, M.; Frame, K. C.; Franzini, P.; Fuess, S.; Gallas, E.; Galyaev, A. N.; Geld, T. L.; Genik, R. J., II; Genser, K.; Gerber, C. E.; Gibbard, B.; Glebov, V.; Glenn, S.; Gobbi, B.; Goforth, M.; Goldschmidt, A.; Gómez, B.; Goncharov, P. I.; González Solís, J. L.; Gordon, H.; Goss, L. T.; Graf, N.; Grannis, P. D.; Green, D. R.; Green, J.; Greenlee, H.; Griffin, G.; Grossman, N.; Grudberg, P.; Grünendahl, S.; Gu, W. X.; Guglielmo, G.; Guida, J. A.; Guida, J. M.; Guryn, W.; Gurzhiev, S. N.; Gutierrez, P.; Gutnikov, Y. E.; Hadley, N. J.; Haggerty, H.; Hagopian, S.; Hagopian, V.; Hahn, K. S.; Hall, R. E.; Hansen, S.; Hatcher, R.; Hauptman, J. M.; Hedin, D.; Heinson, A. P.; Heintz, U.; Hernández-Montoya, R.; Heuring, T.; Hirosky, R.; Hobbs, J. D.; Hoeneisen, B.; Hoftun, J. S.; Hsieh, F.; Hu, Tao; Hu, Ting; Hu, Tong; Huehn, T.; Igarashi, S.; Ito, A. S.; James, E.; Jaques, J.; Jerger, S. A.; Jiang, J. Z.-Y.; Joffe-Minor, T.; Johari, H.; Johns, K.; Johnson, M.; Johnstad, H.; Jonckheere, A.; Jones, M.; Jöstlein, H.; Jun, S. Y.; Jung, C. K.; Kahn, S.; Kalbfleisch, G.; Kang, J. S.; Kehoe, R.; Kelly, M. L.; Kernan, A.; Kerth, L.; Kim, C. L.; Kim, S. K.; Klatchko, A.; Klima, B.; Klochkov, B. I.; Klopfenstein, C.; Klyukhin, V. I.; Kochetkov, V. I.; Kohli, J. M.; Koltick, D.; Kostritskiy, A. V.; Kotcher, J.; Kourlas, J.; Kozelov, A. V.; Kozlovski, E. A.; Krishnaswamy, M. R.; Krzywdzinski, S.; Kunori, S.; Lami, S.; Landsberg, G.; Lebrat, J.-F.; Leflat, A.; Li, H.; Li, J.; Li, Y. K.; Li-Demarteau, Q. Z.; Lima, J. G.; Lincoln, D.; Linn, S. L.; Linnemann, J.; Lipton, R.; Liu, Y. C.; Lobkowicz, F.; Loken, S. C.; Lökös, S.; Lueking, L.; Lyon, A. L.; Maciel, A. K.; Madaras, R. J.; Madden, R.; Mandrichenko, I. V.; Mangeot, Ph.; Mani, S.; Mansoulié, B.; Mao, H. S.; Margulies, S.; Markeloff, R.; Markosky, L.; Marshall, T.; Martin, M. I.; Marx, M.; May, B.; Mayorov, A. A.; McCarthy, R.; McKibben, T.; McKinley, J.; McMahon, T.; Melanson, H. L.; de Mello Neto, J. R.; Merritt, K. W.; Miettinen, H.; Milder, A.; Mincer, A.; de Miranda, J. M.; Mishra, C. S.; Mohammadi-Baarmand, M.; Mokhov, N.; Mondal, N. K.; Montgomery, H. E.; Mooney, P.; Mudan, M.; Murphy, C.; Murphy, C. T.; Nang, F.; Narain, M.; Narasimham, V. S.; Narayanan, A.; Neal, H. A.; Negret, J. P.; Neis, E.; Nemethy, P.; NešiĆ, D.; Nicola, M.; Norman, D.; Oesch, L.; Oguri, V.; Oltman, E.; Oshima, N.; Owen, D.; Padley, P.; Pang, M.; Para, A.; Park, C. H.; Park, Y. M.; Partridge, R.; Parua, N.; Paterno, M.; Perkins, J.; Peryshkin, A.; Peters, M.; Piekarz, H.; Pischalnikov, Y.; Pluquet, A.; Podstavkov, V. M.; Pope, B. G.; Prosper, H. B.; Protopopescu, S.; Pušeljić, D.; Qian, J.; Quintas, P. Z.; Raja, R.; Rajagopalan, S.; Ramirez, O.; Rao, M. V.; Rapidis, P. A.; Rasmussen, L.; Read, A. L.; Reucroft, S.; Rijssenbeek, M.; Rockwell, T.; Roe, N. A.; Rubinov, P.; Ruchti, R.; Rusin, S.; Rutherfoord, J.; Santoro, A.; Sawyer, L.; Schamberger, R. D.; Schellman, H.; Sculli, J.; Shabalina, E.; Shaffer, C.; Shankar, H. C.; Shao, Y. Y.; Shivpuri, R. K.; Shupe, M.; Singh, J. B.; Sirotenko, V.; Smart, W.; Smith, A.; Smith, R. P.; Snihur, R.; Snow, G. R.; Snyder, S.; Solomon, J.; Sood, P. M.; Sosebee, M.; Souza, M.; Spadafora, A. L.; Stephens, R. W.; Stevenson, M. L.; Stewart, D.; Stoianova, D. A.; Stoker, D.; Streets, K.; Strovink, M.; Sznajder, A.; Taketani, A.; Tamburello, P.; Tarazi, J.; Tartaglia, M.; Taylor, T. L.; Teiger, J.; Thompson, J.; Trippe, T. G.; Tuts, P. M.; Varelas, N.; Varnes, E. W.; Virador, P. R.; Vititoe, D.; Volkov, A. A.; Vorobiev, A. P.; Wahl, H. D.; Wang, G.; Warchol, J.; Wayne, M.; Weerts, H.; Wen, F.; White, A.; White, J. T.; Wightman, J. A.; Wilcox, J.; Willis, S.; Wimpenny, S. J.; Wirjawan, J. V.; Womersley, J.; Won, E.; Wood, D. R.; Xu, H.; Yamada, R.; Yamin, P.; Yanagisawa, C.; Yang, J.; Yasuda, T.; Yoshikawa, C.; Youssef, S.; Yu, J.; Yu, Y.; Zhang, D. H.; Zhu, Q.; Zhu, Z. H.; Zieminska, D.; Zieminski, A.; Zylberstejn, A.

    1996-01-01

    A study of the particle multiplicity between jets with large rapidity separation has been performed using the D0 detector at the Fermilab Tevatron pp¯ Collider operating at s = 1.8 TeV. A significant excess of low-multiplicity events is observed above the expectation for color-exchange processes. The measured fractional excess is 1.07+/-0.10\\(stat\\)+0.25-0.13\\(syst\\)%, which is consistent with a strongly interacting color-singlet (colorless) exchange process and cannot be explained by electroweak exchange alone. A lower limit of 0.80% (95% C.L.) is obtained on the fraction of dijet events with color-singlet exchange, independent of the rapidity gap survival probability.

  11. Singlet exciton condensation and bond-order-wave phase in the extended Hubbard model

    Science.gov (United States)

    Hafez-Torbati, Mohsen; Uhrig, Götz S.

    2017-09-01

    The competition of interactions implies the compensation of standard mechanisms, which leads to the emergence of exotic phases between conventional phases. The extended Hubbard model (EHM) is a fundamental example for the competition of the local Hubbard interaction and the nearest-neighbor density-density interaction, which at half-filling and in one dimension leads to a bond-order wave (BOW) between a charge-density wave (CDW) and a quasi-long-range order Mott insulator. We study the full momentum-resolved excitation spectrum of the one-dimensional EHM in the CDW phase, and we clarify the relation between different elementary energy gaps. We show that the CDW-to-BOW transition is driven by the softening of a singlet exciton at momentum π . The BOW is realized as the condensate of this singlet exciton.

  12. Dynamic zero modes of Dirac fermions and competing singlet phases of antiferromagnetic order

    CERN Document Server

    Goswami, Pallab

    2016-01-01

    In quantum spin systems, singlet phases often develop in the vicinity of an antiferromagnetic order. Typical settings for such problems arise when itinerant fermions are also present. In this work, we develop a theoretical framework for addressing such competing orders in an itinerant system, described by Dirac fermions strongly coupled to an O(3) nonlinear sigma model. We focus on two spatial dimensions, where upon disordering the antiferromagnetic order by quantum fluctuations the singular tunneling events also known as (anti)hedgehogs can nucleate competing singlet orders in the paramagnetic phase. In the presence of an isolated hedgehog configuration of the nonlinear sigma model field, we show that the fermion determinant vanishes as the dynamic Euclidean Dirac operator supports fermion zero modes of definite chirality. This provides a topological mechanism for suppressing the tunneling events. Using the methodology of quantum chromodynamics, we evaluate the fermion determinant in the close proximity of m...

  13. Triplet-singlet conversion in ultracold Cs$_2$ and production of ground state molecules

    CERN Document Server

    Bouloufa, Nadia; Aymar, Mireille; Dulieu, Olivier

    2010-01-01

    We propose a process to convert ultracold metastable Cs$_2$ molecules in their lowest triplet state into (singlet) ground state molecules in their lowest vibrational levels. Molecules are first pumped into an excited triplet state, and the triplet-singlet conversion is facilitated by a two-step spontaneous decay through the coupled $A^{1}\\Sigma_{u}^{+} \\sim b ^{3}\\Pi_{u}$ states. Using spectroscopic data and accurate quantum chemistry calculations for Cs$_2$ potential curves and transition dipole moments, we show that this process has a high rate and competes favorably with the single-photon decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels.

  14. Singlet oxygen mediated DNA degradation by copper nanoparticles: potential towards cytotoxic effect on cancer cells

    Directory of Open Access Journals (Sweden)

    Sengupta Tapas K

    2011-03-01

    Full Text Available Abstract The DNA degradation potential and anti-cancer activities of copper nanoparticles of 4-5 nm size are reported. A dose dependent degradation of isolated DNA molecules by copper nanoparticles through generation of singlet oxygen was observed. Singlet oxygen scavengers such as sodium azide and Tris [hydroxyl methyl] amino methane were able to prevent the DNA degradation action of copper nanoparticles confirming the involvement of activated oxygen species in the degradation process. Additionally, it was observed that the copper nanoparticles are able to exert cytotoxic effect towards U937 and Hela cells of human histiocytic lymphoma and human cervical cancer origins, respectively by inducing apoptosis. The growth characteristics of U937 and Hela cells were studied applying various concentrations of the copper nanoparticles.

  15. Photopolymer material sensitized by xanthene dyes for holographic recording using forbidden singlet-triplet electronic transitions

    Science.gov (United States)

    Shelkovnikov, Vladimir; Vasiljev, Evgeny; Russkih, Vladimlen; Berezhnaya, Viktoria

    2016-07-01

    A new holographic photopolymer material is developed. The photopolymer material is sensitized by dyes of xanthene and thioxanthene series which contain iodine and bromine heavy atoms. Holographic recording was carried out during excitation of forbidden singlet-triplet electron transitions of dyes. Thioerythrosin triethylammonium was identified as the most effective sensitizer among a number of tested dyes. The spectral absorption area of the singlet-triplet electronic transition of the dye is conveyed in the red spectral range from 600 to 700 nm. The sensitivity of the photopolymer material to radiation with 633 nm wavelength is 180 mJ cm-2. Optimization of concentration of the main components of the photopolymer compositions was carried out in order to achieve maximum efficiency of holographic recording.

  16. Multiple-point principle with a scalar singlet extension of the standard model

    Science.gov (United States)

    Haba, Naoyuki; Ishida, Hiroyuki; Okada, Nobuchika; Yamaguchi, Yuya

    2017-01-01

    We suggest a scalar singlet extension of the standard model, in which the multiple-point principle (MPP) condition of a vanishing Higgs potential at the Planck scale is realized. Although there have been lots of attempts to realize the MPP at the Planck scale, a realization maintaining naturalness is quite difficult. Our model can easily achieve the MPP at the Planck scale without large Higgs mass corrections. It is worth noting that the electroweak symmetry can be radiatively broken in our model. In the naturalness point of view, the singlet scalar mass should be of calligraphy">O(1) TeV or less. We also consider a right-handed neutrino extension of the model for neutrino mass generation. The model does not affect the MPP scenario, and might keep the naturalness with the new particle mass scale beyond TeV, thanks to accidental cancellation of Higgs mass corrections.

  17. 750-GeV Diphoton Resonance as the Singlet of Custodial Higgs Triplet Model

    CERN Document Server

    Chiang, Cheng-Wei

    2016-01-01

    The observation of diphoton excess around the mass of 750~GeV at the LHC motivates us to consider the singlet Higgs boson in the custodial Higgs triplet model as a good candidate. Based on an earlier study of comprehensive parameter scan for viable mass spectra, we show that the diphoton resonance data fall well within the allowed space. Moreover, we point out that a definite mass hierarchy emerges among the exotic Higgs bosons in the model. Further search channels for the singlet and those for the other exotic Higgs bosons in LHC Run-II are discussed. In particular, we present a simulation of distributions of two kinematic variables for the search of the doubly-charged Higgs boson.

  18. Conformal Complex Scalar Singlet Extensions of the Standard Model: Symmetry Breaking Patterns and Phenomenology

    CERN Document Server

    Wang, Zhi-Wei; Steele, T G; Mann, R B; Hanif, T

    2016-01-01

    We consider a conformal complex singlet extension of the Standard Model with a Higgs portal interaction. Two different scenarios depending on whether the global U(1) symmetry is broken or not have been studied. In the unbroken phase, the decay of the complex singlet is protected by the global U(1) symmetry which leads to an ideal cold dark matter candidate. In the broken phase, we are able to provide a second Higgs at $554\\,\\rm{GeV}$. In addition, gauging the global U(1) symmetry, we can construct an asymptotically safe U(1)' leptophobic model. We combine the notion of asymptotic safety with conformal symmetry and use the renormalization group equations as a bridge to connect UV boundary conditions and Electroweak/ TeV scale physics. We also provide a detailed example to show that these boundary conditions will lead to phenomenological signatures such as diboson excesses which could be tested at the LHC.

  19. A novel approach to nonperturbative renormalization of singlet and nonsinglet lattice operators

    Energy Technology Data Exchange (ETDEWEB)

    Chambers, A.J. [CSSM, Department of Physics, University of Adelaide, Adelaide, SA 5005 (Australia); Horsley, R. [School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Nakamura, Y. [RIKEN Advanced Institute for Computational Science, Kobe, Hyogo 650-0047 (Japan); Perlt, H., E-mail: perlt@itp.uni-leipzig.de [Institut für Theoretische Physik, Universität Leipzig, 04103 Leipzig (Germany); Rakow, P.E.L. [Theoretical Physics Division, Department of Mathematical Sciences, University of Liverpool, Liverpool L69 3BX (United Kingdom); Schierholz, G. [Deutsches Elektronen-Synchrotron DESY, 22603 Hamburg (Germany); Schiller, A. [Institut für Theoretische Physik, Universität Leipzig, 04103 Leipzig (Germany); Zanotti, J.M. [CSSM, Department of Physics, University of Adelaide, Adelaide, SA 5005 (Australia)

    2015-01-05

    A novel method for nonperturbative renormalization of lattice operators is introduced, which lends itself to the calculation of renormalization factors for nonsinglet as well as singlet operators. The method is based on the Feynman–Hellmann relation, and involves computing two-point correlators in the presence of generalized background fields arising from introducing additional operators into the action. As a first application, and test of the method, we compute the renormalization factors of the axial vector current A{sub μ} and the scalar density S for both nonsinglet and singlet operators for N{sub f}=3 flavors of SLiNC fermions. For nonsinglet operators, where a meaningful comparison is possible, perfect agreement with recent calculations using standard three-point function techniques is found.

  20. Singlet-Triplet Transitions of a P(o)schl-Teller Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang

    2006-01-01

    We study the energy spectra of a two-dimensional two-electron quantum dot (QD) with P(o)schl-Teller confining potential under the influence of perpendicular homogeneous magnetic field. Calculations are made by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. A ground-state behavior (spin singlet-triplet transitions) as a function of the strength of a magnetic field is found. We find that the dot radius R of a P(o)schl-Teller potential is important for the ground-state transition and the feature of ground-state for a P(o)schl-Teller QD and a parabolic QD is similar when R is larger. The larger the well depth, the higher the magnetic field for the singlet-triplet transition of the ground-state of two interacting electrons in a P(o)schl-Teller QD.

  1. Multiple-point principle with a scalar singlet extension of the Standard Model

    CERN Document Server

    Haba, Naoyuki; Okada, Nobuchika; Yamaguchi, Yuya

    2016-01-01

    We suggest a scalar singlet extension of the standard model, in which the multiple-point principle (MPP) condition of a vanishing Higgs potential at the Planck scale is realized. Although there have been lots of attempts to realize the MPP at the Planck scale, the realization with keeping naturalness is quite difficult. Our model can easily achieve the MPP at the Planck scale without large Higgs mass corrections. It is worth noting that the electroweak symmetry can be radiatively broken in our model. In the naturalness point of view, the singlet scalar mass should be of ${\\cal O}(1)\\,{\\rm TeV}$ or less. We also consider right-handed neutrino extension of the model for neutrino mass generation. The model does not affect the MPP scenario, and might keep the naturalness with the new particle mass scale beyond TeV, thanks to accidental cancellation of Higgs mass corrections.

  2. Singlet oxygen luminescence detecting in presence of hybrid associates of colloidal Ag2S quantum dots with methylene blue molecules

    Science.gov (United States)

    Ovchinnikov, O. V.; Kondratenko, T. S.; Smirnov, M. S.; Perepelitsa, A. S.; Grevtseva, I. G.; Vinokur, Y. A.; Aslanov, S. V.; Matsukovich, A. S.

    2016-12-01

    In our work we demonstrate some spectroscopic investigation of colloidal Ag2S QDs associates with methylene blue. The photosensitizing of singlet oxygen by associates of colloidal Ag2S QDs with methylene blue was found.

  3. Transport and noise properties of a normal metal-superconductor-normal metal junction with mixed singlet and chiral triplet pairings

    Science.gov (United States)

    Paul, Ganesh C.; Dutta, Paramita; Saha, Arijit

    2017-01-01

    We study transport and zero frequency shot noise properties of a normal metal-superconductor-normal metal (NSN) junction, with the superconductor having mixed singlet and chiral triplet pairings. We show that in the subgapped regime when the chiral triplet pairing amplitude dominates over that of the singlet, a resonance phenomena emerges out at zero energy where all the quantum mechanical scattering probabilities acquire a value of 0.25. At the resonance, crossed Andreev reflection mediating through such junction, acquires a zero energy peak. This reflects as a zero energy peak in the conductance as well depending on the doping concentration. We also investigate shot noise for this system and show that shot noise cross-correlation is negative in the subgapped regime when the triplet pairing dominates over the singlet one. The latter is in sharp contrast to the positive shot noise obtained when the singlet pairing is the dominating one.

  4. Forbidden Electronic Transitions between the Singlet Ground State and the Triplet Excited State of Pt(II) Complexes.

    Science.gov (United States)

    Zheng, Greg Y.; Rillema, D. Paul; DePriest, Jeff; Woods, Clifton

    1998-07-13

    Direct access to the triplet emitting state from the ground state is observed for Pt(II) complexes containing heterocyclic (CwedgeC', CwedgeN, NwedgeN') and bis(diphenylphosphino)alkane (PwedgeP') ligands. Extinction coefficients for such transitions are in the range 4-25 M(-)(1) cm(-)(1). Emission quantum yields resulting from singlet-to-triplet excitation are as high as 61-77 times the emission quantum yields resulting from singlet-to-singlet excitation at 296 K. The intersystem crossing quantum yield from the singlet excited state to triplet emitting state is lower than 2% at 296 K but is greatly enhanced at 77 K. The forbidden electronic transition observed for Pt(II) complexes is attributed to result from spin-orbit coupling due to the presence of Pt(II) in the skeleton structure. The importance of excitation spectra on the computation of emission quantum yields is discussed.

  5. PHOTOGENERATION OF SINGLET OXYGEN AND FREE RADICALS IN DISSOLVED ORGANIC MATTER ISOLATED FROM THE MISSISSIPPI AND ATCHAFALAYA RIVER PLUMES

    Science.gov (United States)

    The photoreactivity to UV light of ultrafiltered dissolved organic matter (DOM) collected during cruises along salinity transects in the Mississippi and Atchafalaya River plumes was examined by measuring photogenerated free radicals and singlet molecular oxygen (1O2) photosensiti...

  6. Enhancing triplet superconductivity by the proximity to a singlet superconductor in oxide heterostructures

    Science.gov (United States)

    Horsdal, Mats; Khaliullin, Giniyat; Hyart, Timo; Rosenow, Bernd

    2016-06-01

    We show how in principle a coherent coupling between two superconductors of opposite parity can be realized in a three-layer oxide heterostructure. Due to strong intraionic spin-orbit coupling in the middle layer, singlet Cooper pairs are converted into triplet ones and vice versa. This results in a large enhancement of the triplet superconductivity, persisting well above the native triplet critical temperature.

  7. Quantum Computing via Singlet-Triplet Spin Qubits in Nanowire Double Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    XUE Peng

    2011-01-01

    We propose a new structure for quantum computing via spin qubits with high fidelity.Each spin qubit corresponds to two electrons in a nanowire double quantum dot,with the singlet and one of the triplets as the logical qubit states.The entangling gate is effected by virtual charge dipole transitions.We include noise to show the feasibility of this scheme under current experimental conditions.

  8. Entropy balance and evidence for local spin singlets in a Kagome-like magnet

    NARCIS (Netherlands)

    Ramirez, A.P.; Hessen, B.; Winklemann, M.

    2000-01-01

    We have measured the specific heat C(T) of the S = 3/2 Kagomé-lattice-containing compound SrCr9pGa12-9pO19. We find little field dependence of the low-temperature C(T), consistent with a low-energy spectrum dominated by many-body singlet excitations. At high temperatures, we recover only ~50% of the

  9. Extension of Standard Model with a Complex Singlet and Iso-Doublet Vector Quarks

    Science.gov (United States)

    Darvishi, Neda

    2017-07-01

    In this paper the extension of the SM by a neutral complex scalar singlet with a nonzero vacuum expectation value and a heavy vector quark pair is considered. This model provides an extra source of spontaneous CP violation. The focus of this article is to obtain the rate of baryon number generation. We show that the considered model provides a strong enough first-order electroweak phase transition to suppress the baryon-violating sphaleron process.

  10. Enhanced Singlet Oxygen Generation in Oxidized Graphitic Carbon Nitride for Organic Synthesis.

    Science.gov (United States)

    Wang, Hui; Jiang, Shenlong; Chen, Shichuan; Li, Dandan; Zhang, Xiaodong; Shao, Wei; Sun, Xianshun; Xie, Junfeng; Zhao, Zhi; Zhang, Qun; Tian, Yupeng; Xie, Yi

    2016-08-01

    Experimental data reveal that the incorporation of carbonyl groups into polymer matrix can significantly enhance singlet oxygen ((1) O2 ) generation and suppress production of other reactive oxygen species. Excitonic processes investigated by phosphorescence spectroscopy reveal enhanced triplet-exciton generation in the modified g-C3 N4 , which facilitate (1) O2 generation through an energy transfer process. Benefiting from this, the modified g-C3 N4 shows excellent conversion and selectivity in organic synthesis.

  11. Flavonoids in Microheterogeneous Media, Relationship between Their Relative Location and Their Reactivity towards Singlet Oxygen

    OpenAIRE

    Germán Günther; Eduardo Berríos; Nancy Pizarro; Karina Valdés; Guillermo Montero; Francisco Arriagada; Javier Morales

    2015-01-01

    In this work, the relationship between the molecular structure of three flavonoids (kaempferol, quercetin and morin), their relative location in microheterogeneous media (liposomes and erythrocyte membranes) and their reactivity against singlet oxygen was studied. The changes observed in membrane fluidity induced by the presence of these flavonoids and the influence of their lipophilicity/hydrophilicity on the antioxidant activity in lipid membranes were evaluated by means of fluorescent prob...

  12. Some Attempts to Employ the Singlet Oxygen Generated from H2O2

    Institute of Scientific and Technical Information of China (English)

    JIN Hong-Xia金红霞; LIU He-Hua刘鹤华; WU Yi-Kang伍贻康

    2004-01-01

    Some attempts to employ the singlet oxygen generated from molybdate-catalyzed decomposition of hydrogen peroxide are presented. Reduction of ascaridole with diimide is also described, along with the preliminary results of the cleavage study using Fe-cysteinate as a simple model for F.e-S type redox species. There were strong indications that S-alkylation occurred as observed in similar cleavage of the potent antimalarial qinghaosu.

  13. Singlet particles as cold dark matter in θ-exact non-commutative space-time

    Directory of Open Access Journals (Sweden)

    S A A Alavi

    2017-02-01

    Full Text Available First, singlet dark matter annihilation into pair charged fermions and pair  bosons was studied to the first order of non-commutativity parameter in perturbative model. Our results are different from the results reported in some previous studies. Then the problem is formulated in -exact non-commutative space-time and non-perturbative model, then the exact results are presented

  14. De novo generation of singlet oxygen and ammine ligands by photoactivation of a platinum anticancer complex.

    Science.gov (United States)

    Zhao, Yao; Farrer, Nicola J; Li, Huilin; Butler, Jennifer S; McQuitty, Ruth J; Habtemariam, Abraha; Wang, Fuyi; Sadler, Peter J

    2013-12-16

    Worth the excitement: Highly reactive oxygen and nitrogen species are generated by photoactivation of the anticancer platinum(IV) complex trans,trans,trans-[Pt(N3 )2 (OH)2 (MA)(Py)] (MA=methylamine, Py=pyridine). Singlet oxygen is formed from the hydroxido ligands and not from dissolved oxygen, and ammine ligands are products from the conversion of azido ligands to nitrenes. Both processes can induce oxidation of guanine.

  15. Real singlet scalar dark matter extension of the Georgi-Machacek model

    CERN Document Server

    Campbell, Robyn; Logan, Heather E; Poulin, Alexandre

    2016-01-01

    The Georgi-Machacek model extends the Standard Model Higgs sector with the addition of isospin-triplet scalar fields in such a way as to preserve the custodial symmetry. The presence of higher-isospin scalars contributing to electroweak symmetry breaking offers the interesting possibility that the couplings of the 125 GeV Higgs boson to both gluons and vector boson pairs could be larger than those of the Standard Model Higgs boson. Constraining this possibility using measurements of Higgs production and decay at the CERN Large Hadron Collider is notoriously problematic if a new, non-Standard Model decay mode of the 125 GeV Higgs boson is present. We study an implementation of this scenario in which the Georgi-Machacek model is extended by a real singlet scalar dark matter candidate, and require that the singlet scalar account for all the dark matter in the universe. The combination of the observed dark matter relic density and direct detection constraints exclude singlet scalar masses below about 57 GeV. Higg...

  16. One-Loop Radiative Correction to the Triple Higgs Coupling in the Higgs Singlet Model

    CERN Document Server

    He, Shi-Ping

    2016-01-01

    Though the 125 GeV Higgs boson is consistent with the standard model (SM) prediction until now, the triple coupling can deviate from the SM value in the physics beyond the SM (BSM). In this paper, the radiative correction to the triple Higgs coupling is calculated in the minimal extension of the SM by adding a real gauge singlet scalar. In this model there are two scalars $h$ and $H$ and both of them are mixed states of the doublet and singlet. Provided that the mixing angle is set to be zero, $h$ is the pure left-over of the doublet and its behavior is the same as that of the SM except the triple $h$ couping. In this SM limit case, the effect of the singlet $H$ will decouple from the fermions and gauge bosons, and firstly shown up in the triple $h$ coupling. Our numerical results show that the deviation is sizable. For $\\lambda_{\\Phi{S}}=1$ (see text for the parameter definition), the deviation $\\delta_{hhh}^{(1)}$ can be $40\\%$. For $\\lambda_{\\Phi{S}}=1.5$, the $\\delta_{hhh}^{(1)}$ can reach $140\\%$. The si...

  17. Variable aberration generator using a high-order even aspheric singlet for testing optical surfaces

    Science.gov (United States)

    Lu, Jinfeng; Chen, Shanyong; Xue, Shuai

    2016-10-01

    Traditional null optics is generally designed for a particular optical surface. It must be redesigned when the test surface is changed no matter the null optic is reflective, transmitted or a CGH. Development of advanced optical machining and testing based on deterministic figuring and null test makes it possible to apply high-order aspheres. This paper presents a plano-concave singlet to realize variable aberration correction for testing different surfaces. The concave surface is an even asphere with high-order terms. By changing the axial distances among the transmission sphere, the null singlet and the test surface, variable aberrations are generated to meet the aberration balance requirement for various surfaces. The residual aberrations are confirmed within the vertical dynamic range of measurement of the interferometer. It enables flexible testing of optical surfaces without dedicated null optics. The optical design verifies that the aspheric singlet can be used to test conic surfaces with different conic constant and radius of curvature ranging from ellipsoid, paraboloid to hyperboloid and an even asphere.

  18. Experimental evidences of singlet to triplet transition in a spin cluster compound

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Tanmoy [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, PO: BCKV Campus Main Office, Nadia, Mohanpur 741246, West Bengal (India); Experimental Physics III, Fakultät Physik, TU Dortmund, 44221 Dortmund (Germany); Singh, Harkirat [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, PO: BCKV Campus Main Office, Nadia, Mohanpur 741246, West Bengal (India); Department of Condensed Matter Physics and Material Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005 (India); Mitra, Chiranjib, E-mail: chiranjib@iiserkol.ac.in [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, PO: BCKV Campus Main Office, Nadia, Mohanpur 741246, West Bengal (India)

    2015-12-15

    Experimental realization of magnetic field induced singlet to triplet transition is reported for NH{sub 4}CuPO{sub 4}·H{sub 2}O, a two spin cluster material with isotropic Heisenberg interaction. Experimental magnetization and specific heat data have been collected as a function of temperature and magnetic field. Experimental data have been analyzed in terms of Heisenberg dimer model. Two quantum complementary observables representing local and non-local properties of the spins are constructed using the experimental data and a clear evidence of singlet to triplet transition is observed through partial quantum information sharing when the magnetic field is swept through a particular value. Signature of this transition has also been captured when specific heat is measured as a function of magnetic field. Furthermore, using the experimental specific heat data, magnetic energy values are calculated and their variations are captured as a function of magnetic field and temperature. - Highlights: • Magnetic field induced energy level crossing is reported for NH{sub 4}CuPO{sub 4}·H{sub 2}O. • Magnetic data are analyzed within the framework of spin 1/2 dimer model. • Singlet-triplet transition is captured employing quantum complementarity principle. • Field dependent specific heat data also provides the signature of the transition.

  19. Baryogenesis in the two doublet and inert singlet extension of the Standard Model

    Energy Technology Data Exchange (ETDEWEB)

    Alanne, Tommi [CP" 3-Origins, University of Southern Denmark,Campusvej 55, DK-5230 Odense M (Denmark); Kainulainen, Kimmo [Department of Physics, University of Jyväskylä,P.O. Box 35 (YFL), FI-40014 Jyväskylä (Finland); Helsinki Institute of Physics, University of Helsinki,P.O. Box 64, FI-00014 Helsinki (Finland); Tuominen, Kimmo [Department of Physics, University of Helsinki,P.O. Box 64, FI-00014 Helsinki (Finland); Helsinki Institute of Physics, University of Helsinki,P.O. Box 64, FI-00014 Helsinki (Finland); Vaskonen, Ville [Department of Physics, University of Jyväskylä,P.O. Box 35 (YFL), FI-40014 Jyväskylä (Finland); Helsinki Institute of Physics, University of Helsinki,P.O. Box 64, FI-00014 Helsinki (Finland)

    2016-08-25

    We investigate an extension of the Standard Model containing two Higgs doublets and a singlet scalar field (2HDSM). We show that the model can have a strongly first-order phase transition and give rise to the observed baryon asymmetry of the Universe, consistent with all experimental constraints. In particular, the constraints from the electron and neutron electric dipole moments are less constraining here than in pure two-Higgs-doublet model (2HDM). The two-step, first-order transition in 2HDSM, induced by the singlet field, may lead to strong supercooling and low nucleation temperatures in comparison with the critical temperature, T{sub n}≪T{sub c}, which can significantly alter the usual phase-transition pattern in 2HD models with T{sub n}≈T{sub c}. Furthermore, the singlet field can be the dark matter particle. However, in models with a strong first-order transition its abundance is typically but a thousandth of the observed dark matter abundance.

  20. Baryogenesis in the two doublet and inert singlet extension of the Standard Model

    CERN Document Server

    Alanne, Tommi; Tuominen, Kimmo; Vaskonen, Ville

    2016-01-01

    We investigate an extension of the Standard Model containing two Higgs doublets and a singlet scalar field (2HDSM). We show that the model can have a strongly first-order phase transition and give rise to the observed baryon asymmetry of the Universe, consistent with all experimental constraints. In particular, the constraints from the electron and neutron electric dipole moments are less constraining here than in pure two-Higgs-doublet model (2HDM). The two-step, first-order transition in 2HDSM, induced by the singlet field, may lead to strong supercooling and low nucleation temperatures in comparison with the critical temperature, $T_n \\ll T_c$, which can significantly alter the usual phase-transition pattern in 2HD models with $T_n \\approx T_c$. Furthermore, the singlet field can be the dark matter particle. However, in models with a strong first-order transition its abundance is typically but a thousandth of the observed dark matter abundance.

  1. Topological order, symmetry, and Hall response of two-dimensional spin-singlet superconductors

    Science.gov (United States)

    Moroz, Sergej; Prem, Abhinav; Gurarie, Victor; Radzihovsky, Leo

    2017-01-01

    Fully gapped two-dimensional superconductors coupled to dynamical electromagnetism are known to exhibit topological order. In this work, we develop a unified low-energy description for spin-singlet paired states by deriving topological Chern-Simons field theories for s -wave, d +i d , and chiral higher even-wave superconductors. These theories capture the quantum statistics and fusion rules of Bogoliubov quasiparticles and vortices and incorporate global continuous symmetries—specifically, spin rotation and conservation of magnetic flux—present in all singlet superconductors. For all such systems, we compute the Hall response for these symmetries and investigate the physics at the edge. In particular, the weakly coupled phase of a chiral d +i d chiral state has a spin Hall coefficient νs=2 and a vanishing Hall response for the magnetic flux symmetry. We argue that the latter is a generic result for two-dimensional superconductors with gapped photons, thereby demonstrating the absence of a spontaneous magnetic field in the ground state of chiral superconductors. It is also shown that the Chern-Simons theories of chiral spin-singlet superconductors derived here fall into Kitaev's 16-fold classification of topological superconductors.

  2. Helical Self-Assembly-Induced Singlet-Triplet Emissive Switching in a Mechanically Sensitive System.

    Science.gov (United States)

    Wu, Hongwei; Zhou, Yunyun; Yin, Liyuan; Hang, Cheng; Li, Xin; Ågren, Hans; Yi, Tao; Zhang, Qing; Zhu, Liangliang

    2017-01-18

    In nanoscience, chirality has shown a significant ability to tune materials' electronic properties, whereas imposing macrochirality into the regulation of singlet-triplet features of organic optoelectronics remains a challenging research topic. Since the tuning for singlet and triplet excited-state properties in a single π-functional molecule connects to its multicolor luminescent application and potential improvement of internal quantum efficiency, we here report that supramolecular chirality can be employed to toggle the singlet and triplet emissions in a well-designed asterisk-shaped molecule. Employing a hexathiobenzene-based single luminophore as a prototype and functionalizing it with chiral α-lipoiate side groups, we find that helical nanoarchitectures can accordingly form in mixed DMF/H2O solution. On this basis, switching between fluorescence and phosphorescence of the material can be realized upon helical self-assembly and dissociation. Such a behavior can be attributed to a helical-conformation-dependent manipulation of the intersystem crossing. Furthermore, reversible mechanoluminescence of the corresponding solid sample was also observed to rely on an analogous molecular self-assembly alternation. These results can probably provide new visions for the development of next-generation supramolecular chiral functional materials.

  3. Enhancement of carotenoid-to-chlorophyll singlet energy transfer by carotenoid-carotenoid interaction.

    Science.gov (United States)

    Zurdo, J; Fernández-Cabrera, C; Ramírez, J M

    1992-06-01

    The apparent quantum yield of singlet-singlet spirilloxanthin-to-bacteriochlorophyll a energy transfer increases linearly with the residual spirilloxanthin content in Rhodospirillum rubrum membrane vesicles from which this carotenoid has been partially removed. Since it has been previously shown that carotenoid-carotenoid interaction is a linear function of the residual spirilloxanthin level in the major pigment-protein complex of those vesicles (Zurdo, J., R. M. Lozano, C. Fernandez-Cabrera, and J. M. Ramirez. 1991. Biochem. J. 274:881-884), it appears that such degenerate interaction enhances singlet energy transfer. Part of the enhancement may be explained if the energy donor is the spirilloxanthin 1Bu----1Ag (S2----S0) transition, because exciton coupling probably brings its energy closer to that of the Qx (S2----S0) transition of bacteriochlorophyll. In contrast, it seems that the possible stabilization of the spirilloxanthin 2Ag (S1) state would hardly improve energy transfer, because this hidden state probably lies below the S1 bacteriochlorophyll state. In any case, the stabilizing effects of carotenoid-carotenoid interactions seem insufficient to explain the enhancement of energy transfer. Direct or indirect effects of carotenoid dimerization on the three-dimensional structure of the pigment cluster appear to be required to account for such enhancement.

  4. Quantum dynamics study of singlet-triplet transitions in s-trans-1,3-butadiene

    Science.gov (United States)

    Nikoobakht, Behnam; Köppel, Horst

    2016-05-01

    The intersystem crossing dynamics of s-trans-1,3-butadiene in its lowest singlet and triplet states is studied theoretically, employing a fully quantal approach for the first time. The electronic states 21Ag, 11Bu, 13Bu and 13Ag, which interact vibronically and via the spin-orbit coupling are treated in the calculation, thus covering the lowest spin-forbidden electronic transitions. Up to five nuclear degrees of freedom, including out-of-plane dihedral angles are included in our investigation. The calculation of potential energy surfaces relies on the CASPT2 method, and the evaluation of spin-orbit coupling matrix elements using the full two-electron Breit-Pauli Hamiltonian is performed by utilizing the MRCI wavefunction. The latter dependence on the nuclear coordinates is included for the first time. An electronic population transfer on the sub-picosecond time scale due to intersystem crossing is obtained, a mechanism that can contribute to the singlet-triplet transitions in the electron energy loss spectrum of s-trans-1, 3-butadiene. It is found that the dependence of the spin-orbit coupling on the out-of-plane coordinates plays a dominant role in these singlet-triplet transitions. The amount of population transfer to the 13Ag and 13Bu states is roughly of the same order of magnitude.

  5. Lamb shift in radical-ion pairs produces a singlet-triplet energy splitting in photosynthetic reaction centers

    OpenAIRE

    Vitalis, K. M.; Kominis, I. K.

    2013-01-01

    Radical-ion pairs, fundamental for understanding photosynthesis and the avian magnetic compass, were recently shown to be biological open quantum systems. We here show that the coupling of the radical-pair's spin degrees of freedom to its decohering vibrational reservoir leads to a shift of the radical-pair's magnetic energy levels. The Lamb shift Hamiltonian is diagonal in the singlet-triplet basis, and results in a singlet-triplet energy splitting physically indistinguishable from an exchan...

  6. Highly efficient oxidation of amines to imines by singlet oxygen and its application in Ugi-type reactions.

    Science.gov (United States)

    Jiang, Gaoxi; Chen, Jian; Huang, Jie-Sheng; Che, Chi-Ming

    2009-10-15

    A variety of secondary benzylic amines were oxidized to imines in 90% to >99% yields by singlet oxygen generated from oxygen and a porphyrin photosensitizer. On the basis of these reactions, a protocol was developed for oxidative Ugi-type reactions with singlet oxygen as the oxidant. This protocol has been used to synthesize C1- and N-functionalized benzylic amines in up to 96% yields.

  7. Open-shell organometallics: reactivity at the ligand

    NARCIS (Netherlands)

    W.I. Dzik; B. de Bruin

    2011-01-01

    The purpose of this review is to show that (cooperative) ligand radical reactivity can be effectively employed in synthetic organometallic chemistry and catalysis to achieve selectivity in radical-type transformations. The ‘redox non-innocence’ of ligands, and the controlled reactivity of ‘ligand ra

  8. Singlet oxygen generation during the oxidation of L-tyrosine and L-dopa with mushroom tyrosinase

    Energy Technology Data Exchange (ETDEWEB)

    Miyaji, Akimitsu [Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259-G1-14, Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan); Kohno, Masahiro [Department of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259-G1-25 Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan); Inoue, Yoshihiro [Showa Pharmaceutical University, 3-3165 Higashi-tamagawagakuen, Machida, Tokyo 194-8543 (Japan); Baba, Toshihide, E-mail: tbaba@chemenv.titech.ac.jp [Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259-G1-14, Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan)

    2016-03-18

    The generation of singlet oxygen during the oxidation of tyrosine and L-dopa using mushroom tyrosinase in a phosphate buffer (pH 7.4), the model of melanin synthesis in melanocytes, was examined. The reaction was performed in the presence of 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP), an acceptor of singlet oxygen and the electron spin resonance (ESR) of the spin adduct, 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (4-oxo-TEMPO), was measured. An increase in the ESR signal attributable to 4-oxo-TEMPO was observed during the oxidation of tyrosine and L-dopa with tyrosinase, indicating the generation of singlet oxygen. The results suggest that {sup 1}O{sub 2} generation via tyrosinase-catalyzed melanin synthesis occurs in melanocyte. - Highlights: • Generation of singlet oxygen was observed during tyrosinase-catalyzed tyrosine oxidation. • The singlet oxygen generated when tyrosine was converted into dopachrome. • The amount of singlet oxygen is not sufficient for cell toxicity. • It decreased when the hydroxyl radicals and/or superoxide anions were trapped.

  9. Spectral- and time-resolved phosphorescence of photosensitizers and singlet oxygen: From in vitro towards in vivo

    Energy Technology Data Exchange (ETDEWEB)

    Vyklický, Vojtěch [Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3, 121 16 Praha 2 (Czech Republic); Dědic, Roman, E-mail: Roman.Dedic@mff.cuni.cz [Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3, 121 16 Praha 2 (Czech Republic); Curkaniuk, Natalija [Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3, 121 16 Praha 2 (Czech Republic); Vilnius University, Faculty of Physics, Universiteto st. 3, LT-01513 Vilnius (Lithuania); Hála, Jan [Charles University in Prague, Faculty of Mathematics and Physics, Department of Chemical Physics and Optics, Ke Karlovu 3, 121 16 Praha 2 (Czech Republic)

    2013-11-15

    Spectral- and time-resolved infrared phosphorescence set-up was adapted for detection from surfaces of solid samples by utilizing fiber optics. Its abilities are demonstrated on the detection of singlet oxygen photosensitization by intrinsic (protoporphyrin IX synthesized from ALA) and extrinsic (TPPS{sub 4} and TMPyP) photosensitizers in in vitro layers of cultured 3T3 murine fibroblasts and HeLa cells mimicking in vivo tissues. Complex decays of phosphorescence of the photosensitizers were detected. The data were approximated by multi-exponential decays, however, no straightforward explanation of the individual components was found. Singlet oxygen phosphorescence kinetics were obtained with rise-times corresponding to singlet oxygen lifetimes ranging from 0.7μs to 1.0μs and single-exponential decay times between 5.3μs and 6.5μs for different photosensitizers and cell lines. -- Highlights: ► Spectral- and time-resolved IR phosphorescence excited and collected by lightguides. ► Detection of singlet oxygen photosensitization in in vitro layers of cultured cells. ► Complex decays of PS phosphorescence approximated by multi-exponential decays. ► Singlet oxygen life-times ranging from 0.7μs to 1.0μs. ► Singlet oxygen exponential decay times 5.3–6.5μs for different PS and cell lines.

  10. Singlet oxygen generation from the decomposition of alpha-linolenic acid hydroperoxide by cytochrome c and lactoperoxidase.

    Science.gov (United States)

    Sun, Shuna; Bao, Zhijuan; Ma, Huimin; Zhang, Deqing; Zheng, Xiaoping

    2007-06-01

    Generation of singlet oxygen is first investigated in the decomposition of polyunsaturated lipid peroxide, alpha-linolenic acid hydroperoxide (LAOOH), by heme-proteins such as cytochrome c and lactoperoxidase. Chemiluminescence and electron spin resonance methods are used to confirm the singlet oxygen generation and quantify its yield. Decomposition products of LAOOH are characterized by HPLC-ESI-MS, which suggests that singlet oxygen is produced via the decomposition of a linear tetraoxide intermediate (Russell's mechanism). Free radicals formed in the decomposition are also identified by the electron spin resonance technique, and the results show that peroxyl, alkyl, and epoxyalkyl radicals are involved. The changes of cytochrome c and lactoperoxidase in the reaction are monitored by UV-visible spectroscopy, revealing the action of a monoelectronic and two-electronic oxidation for cytochrome c and lactoperoxidase, respectively. These results suggest that cytochrome c causes a homolytic reaction of LAOOH, generating alkoxyl radical and then peroxyl radical, which in turn releases singlet oxygen following the Russell mechanism, whereas lactoperoxidase leads to a heterolytic reaction of LAOOH, and the resulting ferryl porphyryl radical of lactoperoxidase abstracts the hydrogen atom from LAOOH to give peroxyl radical and then singlet oxygen. This observation would be important for a better understanding of the damage mechanism of cell membrane or lipoprotein by singlet oxygen and various radicals generated in the peroxidation and decomposition of lipids induced by heme-proteins.

  11. Zethrenes, Extended p -Quinodimethanes, and Periacenes with a Singlet Biradical Ground State

    KAUST Repository

    Sun, Zhe

    2014-08-19

    ConspectusResearchers have studied polycyclic aromatic hydrocarbons (PAHs) for more than 100 years, and most PAHs in the neutral state reported so far have a closed-shell electronic configuration in the ground state. However, recent studies have revealed that specific types of polycyclic hydrocarbons (PHs) could have a singlet biradical ground state and exhibit unique electronic, optical, and magnetic activities. With the appropriate stabilization, these new compounds could prove useful as molecular materials for organic electronics, nonlinear optics, organic spintronics, organic photovoltaics, and energy storage devices. However, before researchers can use these materials to design new devices, they need better methods to synthesize these molecules and a better understanding of the fundamental relationship between the structure and biradical character of these compounds and their physical properties. Their biradical character makes these compounds difficult to synthesize. These compounds are also challenging to physically characterize and require the use of various experimental techniques and theoretic methods to comprehensively describe their unique properties.In this Account, we will discuss the chemistry and physics of three types of PHs with a significant singlet biradical character, primarily developed in our group. These structures are zethrenes, Z-shaped quinoidal hydrocarbons; hydrocarbons that include a proaromatic extended p-quinodimethane unit; and periacenes, acenes fused in a peri-Arrangement. We used a variety of synthetic methods to prepare these compounds and stabilized them using both thermodynamic and kinetic approaches. We probed their ground-state structures by electronic absorption, NMR, ESR, SQUID, Raman spectroscopy, and X-ray crystallography and also performed density functional theory calculations. We investigated the physical properties of these PHs using various experimental methods such as one-photon absorption, two-photon absorption

  12. The effect of laparotomy on hydroxyl radicals, singlet oxygen and antioxidants measured by EPR method in the tails of rats.

    Science.gov (United States)

    Fricova, Jitka; Stopka, Pavel; Krizova, Jana; Yamamotova, Anna; Rokyta, Richard

    2009-01-01

    The aim of the study was to demonstrate that direct measurement of hydroxyl radicals and singlet oxygen in the tail of living rats is possible. The basic level of hydroxyl radicals and singlet oxygen were measured and the effects of antioxidants on their levels were studied in the tail of living anaesthetized rats after acute postoperative pain. Laparotomy was performed as the source of acute abdominal pain. After closure of the abdominal cavity, the animals began to awaken within 30-60 minutes. They were left to recover for 2-3 hours; then they were reanesthetized and the effect of antioxidants was measured on the numbers of hydroxyl radicals and singlet oxygen via blood in the tail. The laparotomy was preformed under general anesthesia (Xylazin and Ketamin) using Wistar rats. After recovery and several hours of consciousness they were reanaesthetized and free radicals and singlet oxygen were measured. An antioxidant mixture (vitamins A, C, D and Selenium) was administered intramuscularly prior to the laparotomy. All measurements were done on the tail of anaesthetized animals. In this particular article, the effect of antioxidants is only reported for hydroxyl radicals. After laparotomy, which represented both somatic and visceral pain, hydroxyl radicals and singlet oxygen were increased. Antioxidant application prior to laparotomy decreased the numbers of hydroxyl radicals. Results are in agreement with our previous finding regarding the increase in hydroxyl free radicals and singlet oxygen following nociceptive stimulation, in this case a combination of both somatic and visceral pain. The administered antioxidants mitigated the increase. This is further confirmation that direct measurement of free radicals and singlet oxygen represents a very useful method for the biochemical evaluation of pain and nociception.

  13. One-loop radiative correction to the triple Higgs coupling in the Higgs singlet model

    Science.gov (United States)

    He, Shi-Ping; Zhu, Shou-hua

    2017-01-01

    Though the 125 GeV Higgs boson is consistent with the standard model (SM) prediction until now, the triple Higgs coupling can deviate from the SM value in the physics beyond the SM (BSM). In this paper, the radiative correction to the triple Higgs coupling is calculated in the minimal extension of the SM by adding a real gauge singlet scalar. In this model there are two scalars h and H and both of them are mixing states of the doublet and singlet. Provided that the mixing angle is set to be zero, namely the SM limit, h is the pure left-over of the doublet and its behavior is the same as that of the SM at the tree level. However the loop corrections can alter h-related couplings. In this SM limit case, the effect of the singlet H may show up in the h-related couplings, especially the triple h coupling. Our numerical results show that the deviation is sizable. For λΦS = 1 (see text for the parameter definition), the deviation δhhh(1) can be 40%. For λΦS = 1.5, the δhhh(1) can reach 140%. The sizable radiative correction is mainly caused by three reasons: the magnitude of the coupling λΦS, light mass of the additional scalar and the threshold enhancement. The radiative corrections for the hVV, hff couplings are from the counter-terms, which are the universal correction in this model and always at O(1%). The hZZ coupling, which can be precisely measured, may be a complementarity to the triple h coupling to search for the BSM. In the optimal case, the triple h coupling is very sensitive to the BSM physics, and this model can be tested at future high luminosity hadron colliders and electron-positron colliders.

  14. Probing hard color-singlet exchange in pp¯ collisions at sqrt(s) = 630 GeV and 1800 GeV

    Science.gov (United States)

    D0 Collaboration; Abbott, B.; Abolins, M.; Abramov, V.; Acharya, B. S.; Adam, I.; Adams, D. L.; Adams, M.; Ahn, S.; Aihara, H.; Alves, G. A.; Amos, N.; Anderson, E. W.; Astur, R.; Baarmand, M. M.; Babintsev, V. V.; Babukhadia, L.; Baden, A.; Baldin, B.; Banerjee, S.; Bantly, J.; Barberis, E.; Baringer, P.; Bartlett, J. F.; Belyaev, A.; Beri, S. B.; Bertram, I.; Bezzubov, V. A.; Bhat, P. C.; Bhatnagar, V.; Bhattacharjee, M.; Biswas, N.; Blazey, G.; Blessing, S.; Bloom, P.; Boehnlein, A.; Bojko, N. I.; Borcherding, F.; Boswell, C.; Brandt, A.; Breedon, R.; Brock, R.; Bross, A.; Buchholz, D.; Burtovoi, V. S.; Butler, J. M.; Carvalho, W.; Casey, D.; Casilum, Z.; Castilla-Valdez, H.; Chakraborty, D.; Chang, S.-M.; Chekulaev, S. V.; Chen, W.; Choi, S.; Chopra, S.; Choudhary, B. C.; Christenson, J. H.; Chung, M.; Claes, D.; Clark, A. R.; Cobau, W. G.; Cochran, J.; Coney, L.; Cooper, W. E.; Cretsinger, C.; Cullen-Vidal, D.; Cummings, M. A. C.; Cutts, D.; Dahl, O. I.; Davis, K.; de, K.; del Signore, K.; Demarteau, M.; Denisov, D.; Denisov, S. P.; Diehl, H. T.; Diesburg, M.; di Loreto, G.; Draper, P.; Ducros, Y.; Dudko, L. V.; Dugad, S. R.; Dyshkant, A.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Engelmann, R.; Eno, S.; Eppley, G.; Ermolov, P.; Eroshin, O. V.; Evdokimov, V. N.; Fahland, T.; Fatyga, M. K.; Feher, S.; Fein, D.; Ferbel, T.; Finocchiaro, G.; Fisk, H. E.; Fisyak, Y.; Flattum, E.; Forden, G. E.; Fortner, M.; Frame, K. C.; Fuess, S.; Gallas, E.; Galyaev, A. N.; Gartung, P.; Gavrilov, V.; Geld, T. L.; Genik, R. J., II; Genser, K.; Gerber, C. E.; Gershtein, Y.; Gibbard, B.; Gobbi, B.; Gómez, B.; Gómez, G.; Goncharov, P. I.; González Solís, J. L.; Gordon, H.; Goss, L. T.; Gounder, K.; Goussiou, A.; Graf, N.; Grannis, P. D.; Green, D. R.; Greenlee, H.; Grinstein, S.; Grudberg, P.; Grünendahl, S.; Guglielmo, G.; Guida, J. A.; Guida, J. M.; Gupta, A.; Gurzhiev, S. N.; Gutierrez, G.; Gutierrez, P.; Hadley, N. J.; Haggerty, H.; Hagopian, S.; Hagopian, V.; Hahn, K. S.; Hall, R. E.; Hanlet, P.; Hansen, S.; Hauptman, J. M.; Hedin, D.; Heinson, A. P.; Heintz, U.; Hernández-Montoya, R.; Heuring, T.; Hirosky, R.; Hobbs, J. D.; Hoeneisen, B.; Hoftun, J. S.; Hsieh, F.; Hu, Ting; Hu, Tong; Ito, A. S.; James, E.; Jaques, J.; Jerger, S. A.; Jesik, R.; Joffe-Minor, T.; Johns, K.; Johnson, M.; Jonckheere, A.; Jones, M.; Jöstlein, H.; Jun, S. Y.; Jung, C. K.; Kahn, S.; Kalbfleisch, G.; Karmanov, D.; Karmgard, D.; Kehoe, R.; Kelly, M. L.; Kim, S. K.; Klima, B.; Klopfenstein, C.; Ko, W.; Kohli, J. M.; Koltick, D.; Kostritskiy, A. V.; Kotcher, J.; Kotwal, A. V.; Kozelov, A. V.; Kozlovsky, E. A.; Krane, J.; Krishnaswamy, M. R.; Krzywdzinski, S.; Kuleshov, S.; Kulik, Y.; Kunori, S.; Landry, F.; Landsberg, G.; Lauer, B.; Leflat, A.; Li, J.; Li-Demarteau, Q. Z.; Lima, J. G. R.; Lincoln, D.; Linn, S. L.; Linnemann, J.; Lipton, R.; Lobkowicz, F.; Loken, S. C.; Lucotte, A.; Lueking, L.; Lyon, A. L.; Maciel, A. K. A.; Madaras, R. J.; Madden, R.; Magaña-Mendoza, L.; Manankov, V.; Mani, S.; Mao, H. S.; Markeloff, R.; Marshall, T.; Martin, M. I.; Mauritz, K. M.; May, B.; Mayorov, A. A.; McCarthy, R.; McDonald, J.; McKibben, T.; McKinley, J.; McMahon, T.; Melanson, H. L.; Merkin, M.; Merritt, K. W.; Miao, C.; Miettinen, H.; Mincer, A.; Mishra, C. S.; Mokhov, N.; Mondal, N. K.; Montgomery, H. E.; Mooney, P.; Mostafa, M.; da Motta, H.; Murphy, C.; Nang, F.; Narain, M.; Narasimham, V. S.; Narayanan, A.; Neal, H. A.; Negret, J. P.; Nemethy, P.; Norman, D.; Oesch, L.; Oguri, V.; Oliveira, E.; Oltman, E.; Oshima, N.; Owen, D.; Padley, P.; Para, A.; Park, Y. M.; Partridge, R.; Parua, N.; Paterno, M.; Pawlik, B.; Perkins, J.; Peters, M.; Piegaia, R.; Piekarz, H.; Pischalnikov, Y.; Pope, B. G.; Prosper, H. B.; Protopopescu, S.; Qian, J.; Quintas, P. Z.; Raja, R.; Rajagopalan, S.; Ramirez, O.; Reucroft, S.; Rijssenbeek, M.; Rockwell, T.; Roco, M.; Rubinov, P.; Ruchti, R.; Rutherfoord, J.; Sánchez-Hernández, A.; Santoro, A.; Sawyer, L.; Schamberger, R. D.; Schellman, H.; Sculli, J.; Shabalina, E.; Shaffer, C.; Shankar, H. C.; Shivpuri, R. K.; Shpakov, D.; Shupe, M.; Singh, H.; Singh, J. B.; Sirotenko, V.; Smith, E.; Smith, R. P.; Snihur, R.; Snow, G. R.; Snow, J.; Snyder, S.; Solomon, J.; Sosebee, M.; Sotnikova, N.; Souza, M.; Steinbrück, G.; Stephens, R. W.; Stevenson, M. L.; Stewart, D.; Stichelbaut, F.; Stoker, D.; Stolin, V.; Stoyanova, D. A.; Strauss, M.; Streets, K.; Strovink, M.; Sznajder, A.; Tamburello, P.; Tarazi, J.; Tartaglia, M.; Thomas, T. L. T.; Thompson, J.; Trippe, T. G.; Tuts, P. M.; Vaniev, V.; Varelas, N.; Varnes, E. W.; Vititoe, D.; Volkov, A. A.; Vorobiev, A. P.; Wahl, H. D.; Wang, G.; Warchol, J.; Watts, G.; Wayne, M.; Weerts, H.; White, A.; White, J. T.; Wightman, J. A.; Willis, S.; Wimpenny, S. J.

    1998-11-01

    We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at sqrt(s)=630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.

  15. Singlet oxygen detection in water by means of digital holography and digital holographic tomography

    Science.gov (United States)

    Belashov, A. V.; Petrov, N. V.; Semenova, I. V.; Vasyutinskii, O. S.

    2016-04-01

    The paper presents results on singlet oxygen detection in aqueous solutions of a photosensitizer based on the reconstruction of 3D temperature gradients resulting from nonradiative deactivation of excited oxygen molecules. 3D temperature distributions were reconstructed by means of the inverse Abel transformation from a single digital hologram in the case of cylindrically symmetric distribution of the temperature gradient and using holographic tomography algorithm with filtered back projection in the case of nonsymmetrical distribution. Major features of the applied techniques are discussed and results obtained by the two methods are compared.

  16. Blue-light emission of Cu(I) complexes and singlet harvesting.

    Science.gov (United States)

    Czerwieniec, Rafał; Yu, Jiangbo; Yersin, Hartmut

    2011-09-05

    Strongly luminescent neutral copper(I) complexes of the type Cu(pop)(NN), with pop = bis(2-(diphenylphosphanyl)phenyl)ether and NN = bis(pyrazol-1-yl)borohydrate (pz(2)BH(2)), tetrakis(pyrazol-1-yl)borate (pz(4)B), or bis(pyrazol-1-yl)-biphenyl-borate (pz(2)Bph(2)), are readily accessible in reactions of Cu(acetonitrile)(4)(+) with equimolar amounts of the pop and NN ligands at ambient temperature. All products were characterized by means of single crystal X-ray diffractometry. The compounds exhibit very strong blue/white luminescence with emission quantum yields of up to 90%. Investigations of spectroscopic properties and the emission decay behavior in the temperature range between 1.6 K and ambient temperature allow us to assign the emitting electronic states. Below 100 K, the emission decay times are in the order of many hundreds of microseconds. Therefore, it is concluded that the emission stems from the lowest triplet state. This state is assigned to a metal-to-ligand charge-transfer state (3MLCT) involving Cu-3dand pop-π* orbitals. With temperature increase, the emission decay time is drastically reduced, e.g. to 13 μs [corrected] (Cu(pop)-(pz(2)Bph(2))), at ambient temperature. At this temperature, the complexes exhibit high emission quantum yields, as neat material or doped into poly(methyl methacrylate) (PMMA). This behavior is assigned to an efficient thermal population of a singlet state (being classified as (1)MLCT), which lies only 800 to 1300 cm(-1) above the triplet state, depending on the individual complex. Thus, the resulting emission at ambient temperature largely represents a fluorescence. For applications in OLEDs and LEECs, for example, this type of thermally activated delayed fluorescence (TADF) creates a new mechanism that allows to harvest both singlet and triplet excitons (excitations) in the lowest singlet state. This effect of singlet harvesting leads to drastically higher radiative rates than obtainable for emissions from triplet

  17. Photochromic metal-organic frameworks: reversible control of singlet oxygen generation.

    Science.gov (United States)

    Park, Jihye; Feng, Dawei; Yuan, Shuai; Zhou, Hong-Cai

    2015-01-07

    The controlled generation of singlet oxygen is of great interest owing to its potential applications including industrial wastewater treatment, photochemistry, and photodynamic therapy. Two photochromic metal-organic frameworks, PC-PCN and SO-PCN, have been developed. A photochromic reaction has been successfully realized in PC-PCN while maintaining its single crystallinity. In particular, as a solid-state material which inherently integrates the photochromic switch and photosensitizer, SO-PCN has demonstrated reversible control of (1)O2 generation. Additionally, SO-PCN shows catalytic activity towards photooxidation of 1,5-dihydroxynaphthalene.

  18. Singlet-state creation and universal quantum computation in NMR using a genetic algorithm

    Science.gov (United States)

    Manu, V. S.; Kumar, Anil

    2012-08-01

    The experimental implementation of a quantum algorithm requires the decomposition of unitary operators. Here we treat unitary-operator decomposition as an optimization problem, and use a genetic algorithm—a global-optimization method inspired by nature's evolutionary process—for operator decomposition. We apply this method to NMR quantum information processing, and find a probabilistic way of performing universal quantum computation using global hard pulses. We also demonstrate the efficient creation of the singlet state (a special type of Bell state) directly from thermal equilibrium, using an optimum sequence of pulses.

  19. Singlet state creation and Universal quantum computation in NMR using Genetic Algorithm

    CERN Document Server

    Manu, V S

    2012-01-01

    Experimental implementation of a quantum algorithm requires unitary operator decomposition. Here we treat the unitary operator decomposition as an optimization problem and use Genetic Algorithm, a global optimization method inspired by nature's evolutionary process for operator decomposition. As an application, we apply this to NMR Quantum Information Processing and find a probabilistic way of doing universal quantum computation using global hard pulses. We also demonstrate efficient creation of singlet state (as a special case of Bell state) directly from thermal equilibrium using an optimum sequence of pulses.

  20. Finite-bias conductance anomalies at a singlet-triplet crossing

    DEFF Research Database (Denmark)

    Stevanato, Chiara; Leijnse, Martin Christian; Flensberg, Karsten;

    2012-01-01

    Quantum dots and single-molecule transistors may exhibit level crossings induced by tuning external parameters such as magnetic eld or gate voltage. For Coulomb blockaded devices, this shows up as an inelastic cotunneling threshold in the dierential conductance, which can be tuned to zero...... at the crossing. Here we show that, in addition, level crossings can give rise to a nearly vertical step-edge, ridge or even a Fano-like ridge-valley feature in the dierential conductance inside the relevant Coulomb diamond. We study a gate-tunable quasidegeneracy between singlet and triplet ground states...

  1. Singlet structure function g_1 at small x and small Q^2

    CERN Document Server

    Ermolaev, B I; Troyan, S I

    2006-01-01

    Explicit expressions for the singlet g_1 at small x and small Q^2 are obtained with the total resummation of the leading logarithmic contributions. It is shown that g_1 practically does not depend on Q^2 in this kinematic region. In contrast, it would be interesting to investigate its dependence on the invariant energy 2pq because, being g_1 positive at small 2pq, it can turn negative at greater values of this variable. The position of the turning point is sensitive to the ratio between the initial quark and gluon densities, so its experimental detection would enable to estimate this ratio

  2. Hidden-variable models for the spin singlet: I. Non-local theories reproducing quantum mechanics

    CERN Document Server

    Di Lorenzo, Antonio

    2011-01-01

    A non-local hidden variable model reproducing the quantum mechanical probabilities for a spin singlet is presented. The non-locality is concentrated in the distribution of the hidden variables. The model otherwise satisfies both the hypothesis of outcome independence, made in the derivation of Bell inequality, and of compliance with Malus's law, made in the derivation of Leggett inequality. It is shown through the prescription of a protocol that the non-locality can be exploited to send information instantaneously provided that the hidden variables can be measured, even though they cannot be controlled.

  3. Ultrafast internal conversion of excited cytosine via the lowest pipi electronic singlet state.

    Science.gov (United States)

    Merchán, Manuela; Serrano-Andrés, Luis

    2003-07-09

    Computational evidence at the CASPT2 level supports that the lowest excited state pipi* contributes to the S1/S0 crossing responsible for the ultrafast decay of singlet excited cytosine. The computed radiative lifetime, 33 ns, is consistent with the experimentally derived value, 40 ns. The nOpi* state does not play a direct role in the rapid repopulation of the ground state; it is involved in a S2/S1 crossing. Alternative mechanisms through excited states pisigma* or nNpi* are not competitive in cytosine.

  4. Hybrid spin and valley quantum computing with singlet-triplet qubits.

    Science.gov (United States)

    Rohling, Niklas; Russ, Maximilian; Burkard, Guido

    2014-10-24

    The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

  5. Singlet-triplet gaps in substituted carbenes predicted from block-correlated coupled cluster method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The block correlated coupled cluster (BCCC) method, with the complete active-space self-consistent-field (CASSCF) reference function, has been applied to investigating the singlet-triplet gaps in several substituted carbenes including four halocarbenes (CHCl, CF2, CCl2, and CBr2) and two hydroxycar-benes (CHOH and C(OH)2). A comparison of our results with the experimental data and other theoretical estimates shows that the present approach can provide quantitative descriptions for all the studied carbenes. It is demonstrated that the CAS-BCCC method is a promising theoretical tool for calculating the electronic structures of diradicals.

  6. Singlet oxygen generation from water-soluble quantum dot-organic dye nanocomposites.

    Science.gov (United States)

    Shi, Lixin; Hernandez, Billy; Selke, Matthias

    2006-05-17

    Water-soluble quantum dot-organic dye nanocomposites have been prepared via electrostatic interaction. We used CdTe quantum dots with diameters up to 3.4 nm, 2-aminoethanethiol as a stabilizer, and meso-tetra(4-sulfonatophenyl)porphine dihydrochloride (TSPP) as an organic dye. The photophysical properties of the nanocomposite have been investigated. The fluorescence of the parent CdTe quantum dot is largely suppressed. Instead, indirect excitation of the TSPP moiety leads to production of singlet oxygen with a quantum yield of 0.43. The nanocomposite is sufficiently photostable for biological applications.

  7. A Singlet Extension of the MSSM with a Dark Matter Portal

    CERN Document Server

    de La Puente, Alejandro

    2014-01-01

    The minimal extension of the MSSM (NMSSM) has been widely studied in the search for a natural solution to the $\\mu$ problem. In this work, we consider a variation of the NMSSM where an extra singlet is added and a Peccei-Quinn symmetry is imposed. We study its neutralino sector and compute the annihilation cross section of the lightest neutralino. We use existent cosmological and collider data to constrain the parameter space and consider the lightest neutralino, which is very light, as a dark matter candidate.

  8. Standard model extended by a heavy singlet: Linear vs. nonlinear EFT

    Directory of Open Access Journals (Sweden)

    G. Buchalla

    2017-04-01

    Full Text Available We consider the Standard Model extended by a heavy scalar singlet in different regions of parameter space and construct the appropriate low-energy effective field theories up to first nontrivial order. This top-down exercise in effective field theory is meant primarily to illustrate with a simple example the systematics of the linear and nonlinear electroweak effective Lagrangians and to clarify the relation between them. We discuss power-counting aspects and the transition between both effective theories on the basis of the model, confirming in all cases the rules and procedures derived in previous works from a bottom-up approach.

  9. Standard model extended by a heavy singlet: Linear vs. nonlinear EFT

    Energy Technology Data Exchange (ETDEWEB)

    Buchalla, G., E-mail: gerhard.buchalla@lmu.de; Catà, O.; Celis, A.; Krause, C.

    2017-04-15

    We consider the Standard Model extended by a heavy scalar singlet in different regions of parameter space and construct the appropriate low-energy effective field theories up to first nontrivial order. This top-down exercise in effective field theory is meant primarily to illustrate with a simple example the systematics of the linear and nonlinear electroweak effective Lagrangians and to clarify the relation between them. We discuss power-counting aspects and the transition between both effective theories on the basis of the model, confirming in all cases the rules and procedures derived in previous works from a bottom-up approach.

  10. Inhibition of glyceraldehyde-3-phosphate dehydrogenase by peptide and protein peroxides generated by singlet oxygen attack

    DEFF Research Database (Denmark)

    Morgan, Philip E; Dean, Roger T; Davies, Michael Jonathan

    2002-01-01

    the active-site thiol of the enzyme and the peroxide. A number of low-molecular-mass compounds including thiols and ascorbate, but not Trolox C, can prevent inhibition by removing the initial peroxide, or species derived from it. In contrast, glutathione reductase and lactate dehydrogenase are poorly......Reaction of certain peptides and proteins with singlet oxygen (generated by visible light in the presence of rose bengal dye) yields long-lived peptide and protein peroxides. Incubation of these peroxides with glyceraldehyde-3-phosphate dehydrogenase, in the absence of added metal ions, results...

  11. Exact Wave Packet Dynamics of Singlet Fission in Unsubstituted and Substituted Polyene Chains within Long-Range Interacting Models

    CERN Document Server

    Prodhan, Suryoday

    2016-01-01

    Singlet fission is a potential pathway for significant enhancement of efficiency in organic solar cells. In this article, we have studied singlet fission in a pair of polyene molecules employing exact many-body wave packet dynamics. The individual molecules are treated within Hubbard and Pariser-Parr-Pople (PPP) models and the interaction between them involves transfer terms, intersite electron repulsions and site charge-bond charge repulsion terms. Initial wave packet is constructed from excited singlet state of one molecule and ground state of the other. Time development of this wave packet under the influence of intermolecular interactions is followed within the Schr\\"{o}dinger picture by an efficient predictor-corrector scheme. In unsubstituted Hubbard and PPP chains, $2{}^1A$ excited singlet state leads to significant fission yield while the $1{}^1B$ state gives negligible fission yield. On substitution by donor-acceptor groups of moderate strength, singlet state derived from $1{}^1B$ state also gives si...

  12. Exact wave packet dynamics of singlet fission in unsubstituted and substituted polyene chains within long-range interacting models

    Science.gov (United States)

    Prodhan, Suryoday; Ramasesha, S.

    2017-08-01

    Singlet fission (SF) is a potential pathway for significant enhancement of efficiency in organic solar cells (OSC). In this paper, we study singlet fission in a pair of polyene molecules in two different stacking arrangements employing exact many-body wave packet dynamics. In the noninteracting model, the SF yield is absent. The individual molecules are treated within Hubbard and Pariser-Parr-Pople (PPP) models and the interaction between them involves transfer terms, intersite electron repulsions, and site-charge-bond-charge repulsion terms. Initial wave packet is constructed from excited singlet state of one molecule and ground state of the other. Time development of this wave packet under the influence of intermolecular interactions is followed within the Schrödinger picture by an efficient predictor-corrector scheme. In unsubstituted Hubbard and PPP chains, 2 1A excited singlet state leads to significant SF yield while the 1 1B state gives negligible fission yield. On substitution by donor-acceptor groups of moderate strength, the lowest excited state will have sufficient 2 1A character and hence results in significant SF yield. Because of rapid internal conversion, the nature of the lowest excited singlet will determine the SF contribution to OSC efficiency. Furthermore, we find the fission yield depends considerably on the stacking arrangement of the polyene molecules.

  13. Properties of the random-singlet phase: From the disordered Heisenberg chain to an amorphous valence-bond solid

    Science.gov (United States)

    Shu, Yu-Rong; Yao, Dao-Xin; Ke, Chih-Wei; Lin, Yu-Cheng; Sandvik, Anders W.

    2016-11-01

    We use a strong-disorder renormalization group (SDRG) method and ground-state quantum Monte Carlo (QMC) simulations to study S =1 /2 spin chains with random couplings, calculating disorder-averaged spin and dimer correlations. The QMC simulations demonstrate logarithmic corrections to the power-law decaying correlations obtained with the SDRG scheme. The same asymptotic forms apply both for systems with standard Heisenberg exchange and for certain multispin couplings leading to spontaneous dimerization in the clean system. We show that the logarithmic corrections arise in the valence-bond (singlet pair) basis from a contribution that cannot be generated by the SDRG scheme. In the model with multispin couplings, where the clean system dimerizes spontaneously, random singlets form between spinons localized at domain walls in the presence of disorder. This amorphous valence-bond solid is asymptotically a random-singlet state and only differs from the random-exchange Heisenberg chain in its short-distance properties.

  14. Singlet-triplet fission of carotenoid excitation in light-harvesting LH2 complexes of purple phototrophic bacteria.

    Science.gov (United States)

    Klenina, I B; Makhneva, Z K; Moskalenko, A A; Gudkov, N D; Bolshakov, M A; Pavlova, E A; Proskuryakov, I I

    2014-03-01

    The current generally accepted structure of light-harvesting LH2 complexes from purple phototrophic bacteria conflicts with the observation of singlet-triplet carotenoid excitation fission in these complexes. In LH2 complexes from the purple bacterium Allochromatium minutissimum, a drop in the efficiency of carotenoid triplet generation is demonstrated, which correlates with the extent of selective photooxidation of bacteriochlorophylls absorbing at ~850 nm. We conclude that singlet-triplet fission of carotenoid excitation proceeds with participation of these excitonically coupled bacteriochlorophylls. In the framework of the proposed mechanism, the contradiction between LH2 structure and photophysical properties of carotenoids is eliminated. The possibility of singlet-triplet excitation fission involving a third mediator molecule was not considered earlier.

  15. Comparative study of singlet oxygen production by photosensitiser dyes encapsulated in silicone: towards rational design of anti-microbial surfaces.

    Science.gov (United States)

    Noimark, Sacha; Salvadori, Enrico; Gómez-Bombarelli, Rafael; MacRobert, Alexander J; Parkin, Ivan P; Kay, Christopher W M

    2016-10-12

    Surfaces with built-in antimicrobial activity have the potential to reduce hospital-acquired infections. One promising strategy is to create functionalised surfaces which, following illumination with visible light, are able to generate singlet oxygen under aerobic conditions. In contrast to antibiotics, the mechanism of bacterial kill by species derived from reactions with singlet oxygen is completely unselective, therefore offering little room for evolutionary adaptation. Here we consider five commercially available organic photosensitiser dyes encapsulated in silicone polymer that show varied antimicrobial activity. We correlate density functional theory calculations with UV-Vis spectroscopy, electron paramagnetic resonance spectroscopy and singlet oxygen production measurements in order to define and test the elements required for efficacious antimicrobial activity. Our approach forms the basis for the rational in silico design and spectroscopic screening of simple and efficient self-sterilising surfaces made from cheap, low toxicity photosensitiser dyes encapsulated in silicone.

  16. Forbidden singlet exciton transitions induced by localization in polymer light-emitting diodes in a strong electric field.

    Science.gov (United States)

    Sun, Zheng; Xu, Yuan-Ping; Li, Sheng; George, Thomas F

    2011-02-10

    Through combining the electron transition process and dipole moment evolution as well as electron-phonon coupling, molecular dynamics calculations show that the radiative decay of singlet excitons in a conjugated polymer, such as a polymer light-emitting diode (PLED), is largely determined by the evolution of the dipole moment. Without an electric field, the decay life of a singlet exciton is about 1 ns. Once an electric field is applied and exceeds a critical value, with electron-phonon coupling, the original lattice structure evolves into two new localized lattice distortions, consistent with the experimental results. Owing to the new lattice structure and self-trapping, the dipole moment rapidly decreases to zero within 5 fs, eliminating the radiative decay of the singlet exciton.

  17. Sizable NSI from the $SU(2)_L$ scalar doublet-singlet mixing and the implications in DUNE

    CERN Document Server

    Forero, David V

    2016-01-01

    We propose a novel and simple mechanism where sizable effects of non-standard interactions (NSI) in neutrino propagation are induced from the mixing between an electrophilic second Higgs doublet and a charged singlet. The mixing arises from a dimensionful coupling of the scalar doublet and singlet to the standard model Higgs boson. In light of the small mass, the light mass eigenstate from the doublet-singlet mixing can generate much larger NSI than those from the heavy eigenstate. We show that a sizable NSI $\\varepsilon_{e\\tau}$ ($\\sim 0.3$) can be attained without being excluded by a variety of experimental constraints. Furthermore, we demonstrate that NSI can mimic effects of the Dirac CP phase in the neutrino mixing matrix but they can potentially be disentangled by future long-baseline neutrino experiments, such as the Deep Underground Neutrino Experiment (DUNE).

  18. Implications of the observation of dark matter self-interactions for singlet scalar dark matter

    CERN Document Server

    Campbell, Robyn; Logan, Heather E; Peterson, Andrea D; Poulin, Alexandre

    2015-01-01

    Evidence for dark matter self-interactions has recently been reported based on the observation of a spatial offset between the dark matter halo and the stars in a galaxy in the cluster Abell 3827. Interpreting the offset as due to dark matter self-interactions leads to a cross section measurement of sigma_DM/m ~ (1-1.5) cm^2/g, where m is the mass of the dark matter particle. We use this observation to constrain singlet scalar dark matter coupled to the Standard Model and to two-Higgs-doublet models. We show that the most natural scenario in this class of models is very light dark matter, below about 0.1 GeV, whose relic abundance is set by freeze-in, i.e., by slow production of dark matter in the early universe via extremely tiny interactions with the Higgs boson, never reaching thermal equilibrium. We also show that the dark matter abundance can be established through the usual thermal freeze-out mechanism in the singlet scalar extension of the Yukawa-aligned two-Higgs-doublet model, but that it requires ra...

  19. Singlet Oxygen-Mediated Oxidation during UVA Radiation Alters the Dynamic of Genomic DNA Replication

    Science.gov (United States)

    Graindorge, Dany; Martineau, Sylvain; Machon, Christelle; Arnoux, Philippe; Guitton, Jérôme; Francesconi, Stefania; Frochot, Céline; Sage, Evelyne; Girard, Pierre-Marie

    2015-01-01

    UVA radiation (320–400 nm) is a major environmental agent that can exert its deleterious action on living organisms through absorption of the UVA photons by endogenous or exogenous photosensitizers. This leads to the production of reactive oxygen species (ROS), such as singlet oxygen (1O2) and hydrogen peroxide (H2O2), which in turn can modify reversibly or irreversibly biomolecules, such as lipids, proteins and nucleic acids. We have previously reported that UVA-induced ROS strongly inhibit DNA replication in a dose-dependent manner, but independently of the cell cycle checkpoints activation. Here, we report that the production of 1O2 by UVA radiation leads to a transient inhibition of replication fork velocity, a transient decrease in the dNTP pool, a quickly reversible GSH-dependent oxidation of the RRM1 subunit of ribonucleotide reductase and sustained inhibition of origin firing. The time of recovery post irradiation for each of these events can last from few minutes (reduction of oxidized RRM1) to several hours (replication fork velocity and origin firing). The quenching of 1O2 by sodium azide prevents the delay of DNA replication, the decrease in the dNTP pool and the oxidation of RRM1, while inhibition of Chk1 does not prevent the inhibition of origin firing. Although the molecular mechanism remains elusive, our data demonstrate that the dynamic of replication is altered by UVA photosensitization of vitamins via the production of singlet oxygen. PMID:26485711

  20. Enhanced Higgs associated production with a top quark pair in the NMSSM with light singlets

    Science.gov (United States)

    Badziak, Marcin; Wagner, Carlos E. M.

    2017-02-01

    Precision measurements of the 125 GeV Higgs resonance recently discovered at the LHC have determined that its properties are similar to the ones of the Standard Model (SM) Higgs boson. However, the current uncertainties in the determination of the Higgs boson couplings leave room for significant deviations from the SM expectations. In fact, if one assumes no correlation between the top-quark and gluon couplings to the Higgs, the current global fit to the Higgs data lead to central values of the Higgs couplings to the bottom-quark and the top-quark that are about 2 σ away from the SM predictions. In a previous work, we showed that such a scenario could be realized in the Next to Minimal Supersymmetric extension of the SM (NMSSM), for heavy singlets and light MSSM-like Higgs bosons and scalar top quarks, but for couplings that ruined the perturbative consistency of the theory up to the GUT scale. In this work we show that a perturbative consistent scenario, for somewhat heavier stops, may be obtained in the presence of light singlets. An interesting bonus of this scenario is the possibility of explaining an excess of events observed in CP-even Higgs searches at LEP2.

  1. Experimental and theoretical dipole moments of purines in their ground and lowest excited singlet states

    Science.gov (United States)

    Aaron, Jean-Jacques; Diabou Gaye, Mame; Párkányi, Cyril; Cho, Nam Sook; Von Szentpály, László

    1987-01-01

    The ground-state dipole moments of seven biologically important purines (purine, 6-chloropurine, 6-mercaptopurine, hypoxanthine, theobromine, theophylline and caffeine) were determined at 25°C in acetic acid (all the above compounds with the exception of purine) and in ethyl acetate (purine, theophylline and caffeine). Because of its low solubility, it was not possible to measure the dipole moment of uric acid. The first excited singlet-state dipole moments were obtained on the basis of the Bakhshiev and Chamma—Viallet equations using the variation of the Stokes shift with the solvent dielectric constant-refractive index term. The theoretical dipole moments for all the purines listed above and including uric acid were calculated by combining the use of the PPP (π-LCI-SCF-MO) method for the π-contribution to the overall dipole moment with the σ-contribution obtained as a vector sum of the σbond moments and group moments. The experimental and theoretical values were compared with the data available in the literature for some of the purines under study. For several purines, the calculations were carried out for different tautomeric forms. Excited singlet-state dipole moments are smaller than the ground-state values by 0.8 to 2.2 Debye units for all purines under study with the exception of 6-chloropurine. The effects of the structure upon the ground- and excited-state dipole moments of the purines are discussed.

  2. Efficiency factors of singlet oxygen generation from core-modified expanded porphyrin: tetrathiarubyrin in ethanol

    CERN Document Server

    Ha, J H; Kim, Y R; Jung, G Y; Lee, Y H; Shin, K

    2001-01-01

    The photophysical properties and the singlet oxygen generation efficiency of tetrathiarubyrin have been investigated to elucidate the possibility of its use as a photodynamic therapy (PDT) photosensitizer by steady-state and time-resolved spectroscopic methods. The observed photophysical properties were affected by various molecular aspects, such as extended pi conjugation, structural distortion, and internal heavy atom. The steady-state electronic absorption spectrum was red-shifted due to the extended pi-conjugation, and the spin orbital coupling was enhanced by the structural distortion and the internal heavy atom effect. As a result of the enhanced spin orbital coupling, the triplet quantum yield increased to 0.90 +- 0.10 and the triplet state lifetime was shortened to 7.0 +- 1.2 mu s. Since the triplet state decays at a relatively faster rate, the efficiency of the oxygen quenching of the triplet state decreases. The singlet oxygen quantum yield was estimated to be 0.52 +- 0.02, which is somewhat lower t...

  3. Singlet-Catalyzed Electroweak Phase Transitions in the 100 TeV Frontier

    CERN Document Server

    Kotwal, Ashutosh V; No, Jose Miguel; Winslow, Peter

    2016-01-01

    We study the prospects for probing a gauge singlet scalar-driven strong first order electroweak phase transition with a future proton-proton collider in the 100 TeV range. Singlet-Higgs mixing enables resonantly-enhanced di-Higgs production, potentially aiding discovery prospects. We perform Monte Carlo scans of the parameter space to identify regions associated with a strong first-order electroweak phase transition, analyze the corresponding di-Higgs signal, and select a set of benchmark points that span the range of di-Higgs signal strengths. For the $b\\bar{b}\\gamma\\gamma$ and $4\\tau$ final states, we investigate discovery prospects for each benchmark point for the high luminosity phase of the Large Hadron Collider and for a future $pp$ collider with $\\sqrt{s}$ = 50, 100, or 200 TeV. We find that any of these future collider scenarios could significantly extend the reach beyond that of the high luminosity LHC, and that with $\\sqrt{s}$ = 100 TeV (200 TeV) and 30 ab$^{-1}$, the full region of parameter space ...

  4. Randomized Benchmarking of Barrier versus Tilt Control of a Singlet-Triplet Qubit

    Science.gov (United States)

    Zhang, Chengxian; Throckmorton, Robert E.; Yang, Xu-Chen; Wang, Xin; Barnes, Edwin; Das Sarma, S.

    2017-05-01

    Decoherence due to charge noise is one of the central challenges in using spin qubits in semiconductor quantum dots as a platform for quantum information processing. Recently, it has been experimentally demonstrated in both Si and GaAs singlet-triplet qubits that the effects of charge noise can be suppressed if qubit operations are implemented using symmetric barrier control instead of the standard tilt control. Here, we investigate the key issue of whether the benefits of barrier control persist over the entire set of single-qubit gates by performing randomized benchmarking simulations. We find the surprising result that the improvement afforded by barrier control depends sensitively on the amount of spin noise: for the minimal nuclear spin noise levels present in Si, the coherence time improves by more than 2 orders of magnitude whereas in GaAs, by contrast the coherence time is essentially the same for barrier and tilt control. However, we establish that barrier control becomes beneficial if qubit operations are performed using a new family of composite pulses that reduce gate times by up to 90%. With these optimized pulses, barrier control is the best way to achieve high-fidelity quantum gates in singlet-triplet qubits.

  5. Singlet Oxygen-Mediated Oxidation during UVA Radiation Alters the Dynamic of Genomic DNA Replication.

    Science.gov (United States)

    Graindorge, Dany; Martineau, Sylvain; Machon, Christelle; Arnoux, Philippe; Guitton, Jérôme; Francesconi, Stefania; Frochot, Céline; Sage, Evelyne; Girard, Pierre-Marie

    2015-01-01

    UVA radiation (320-400 nm) is a major environmental agent that can exert its deleterious action on living organisms through absorption of the UVA photons by endogenous or exogenous photosensitizers. This leads to the production of reactive oxygen species (ROS), such as singlet oxygen (1O2) and hydrogen peroxide (H2O2), which in turn can modify reversibly or irreversibly biomolecules, such as lipids, proteins and nucleic acids. We have previously reported that UVA-induced ROS strongly inhibit DNA replication in a dose-dependent manner, but independently of the cell cycle checkpoints activation. Here, we report that the production of 1O2 by UVA radiation leads to a transient inhibition of replication fork velocity, a transient decrease in the dNTP pool, a quickly reversible GSH-dependent oxidation of the RRM1 subunit of ribonucleotide reductase and sustained inhibition of origin firing. The time of recovery post irradiation for each of these events can last from few minutes (reduction of oxidized RRM1) to several hours (replication fork velocity and origin firing). The quenching of 1O2 by sodium azide prevents the delay of DNA replication, the decrease in the dNTP pool and the oxidation of RRM1, while inhibition of Chk1 does not prevent the inhibition of origin firing. Although the molecular mechanism remains elusive, our data demonstrate that the dynamic of replication is altered by UVA photosensitization of vitamins via the production of singlet oxygen.

  6. Correlated Pair States Formed by Singlet Fission and Exciton-Exciton Annihilation.

    Science.gov (United States)

    Scholes, Gregory D

    2015-12-24

    Singlet fission to form a pair of triplet excitations on two neighboring molecules and the reverse process, triplet-triplet annihilation to upconvert excitation, have been extensively studied. Comparatively little work has sought to examine the properties of the intermediate state in both of these processes-the bimolecular pair state. Here, the eigenstates constituting the manifold of 16 bimolecular pair excitations and their relative energies in the weak-coupling regime are reported. The lowest-energy states obtained from the branching diagram method are the triplet pairs with overall singlet spin |X1⟩ ≈ (1)[TT] and quintet spin |Q⟩ ≈ (5)[TT]. It is shown that triplet pair states can be separated by a triplet-triplet energy-transfer mechanism to give a separated, yet entangled triplet pair (1)[T···T]. Independent triplets are produced by decoherence of the separated triplet pair. Recombination of independent triplets by exciton-exciton annihilation to form the correlated triplet pair (i.e., nongeminate recombination) happens with 1/3 of the rate of either triplet migration or recombination of the separated correlated triplet pair (geminate recombination).

  7. Magnetic dipolar interaction between correlated triplets created by singlet fission in tetracene crystals

    CERN Document Server

    Wang, Rui; Zhang, Bo; Liu, Yunlong; Wang, Xiaoyong; Xiao, Min

    2015-01-01

    Singlet fission (SF) can potentially break the Shockley-Queisser efficiency limit in single-junction solar cells by splitting one photo-excited singlet exciton (S1) into two triplets (2T1) in organic semiconductors. A dark multi-exciton (ME) state has been proposed as the intermediate connecting S1 to 2T1. However, the exact nature of this ME state, especially how the doubly-excited triplets interact, remains elusive. Here, we report a quantitative study on the magnetic dipolar interaction between SF-induced correlated triplets in tetracene crystals by monitoring quantum beats relevant to the ME sublevels at room temperature. The resonances of ME sublevels approached by tuning an external magnetic field are observed to be avoided, which agrees well with the theoretical predictions considering a magnetic dipolar interaction of ~ 0.008 GHz. Our work paves a way to quantify the magnetic dipolar interaction in organic materials and marks an important step towards understanding the underlying physics of the ME sta...

  8. Amplified Singlet Oxygen Generation in Semiconductor Polymer Dots for Photodynamic Cancer Therapy.

    Science.gov (United States)

    Li, Shouying; Chang, Kaiwen; Sun, Kai; Tang, Ying; Cui, Ni; Wang, Yu; Qin, Weiping; Xu, Hong; Wu, Changfeng

    2016-02-17

    This paper described the energy-transfer amplified singlet oxygen generation in semiconductor polymer dots (Pdots) for in vitro and in vivo photodynamic therapy. Hydrophobic photosensitizer tetraphenylporphyrin was facilely doped in the nanoparticles consisting of densely packed semiconductor polymers. Optical characterizations indicated that the fluorescence of Pdots was completely quenched by the photosensitizer, yielding an energy transfer efficiency of nearly 100% and singlet-oxygen generation quantum yield of ∼50%. We evaluated the cellular uptake, dark toxicity, and photodynamic therapy of the Pdot photosensizer in human gastric adenocarcinoma cells. The in vitro studies indicated that cancer cells were efficiently destroyed at very low dose of the Pdots such as 1 μg/mL by using the light dose of 90 J/cm(2), which is considerably less than that in clinical practice. The antitumor effect of the Pdots was further evaluated in vivo with human gastric adenocarcinoma xenografts in Balb/c nude mice, which show that the xenograft tumors were significantly inhibited and eradicated in some cases. Our results indicate the energy transfer amplified Pdot platforms have great therapeutic potential for treating malignant cancers.

  9. Inverse Amplitude Method for Perturbative Electroweak Symmetry Breaking Sector: The Singlet Higgs Portal as a Study Case

    CERN Document Server

    Corbett, Tyler; Gonzalez-Garcia, M C

    2015-01-01

    We explore the use of the Inverse Amplitude Method for unitarization of scattering amplitudes to derive the existence and properties of possible new heavy states associated with perturbative extensions of the electroweak breaking sector of the Standard Model starting from the low energy effective theory. We use a toy effective theory generated by integrating out a heavy singlet scalar and compare the pole mass and width of the unitarized amplitudes with those of the original model. Our results show that the Inverse Amplitude Method reproduces correctly the singlet mass up to factors of O(1-3), but its width is overestimated.

  10. Non-singlet spin structure function $g^{NS}_{1} (x,t)$ in the DGLAP approach

    Indian Academy of Sciences (India)

    Neelakshi N K Borah; D K Choudhury; P K Sahariah

    2012-10-01

    An analytical solution of the non-singlet polarized parton distribution $ q^{NS} (x, Q^{2}) = ( u(x, Q^{2}) − d(x, Q^{2}))$ is obtained by solving the DGLAP (Gribov and Lipatov, Sov. J. Nucl. Phys. 15, 438 (1972); Lipatov, ibid, 20, 94 (1975); Dokshitzer, Sov. Phys. JETP 46, 641 (1997); Altarelli and Parisi, Nucl. Phys. B126, 298 (1977)) equation by the method of characteristics. We then evaluate the non-singlet spin-dependent structure function $g^{NS}_{1}$ . The result is compared with the data from HERMES (Airapetian et al, Phys. Rev. D75, 012007 (2007)).

  11. Analytical singlet α{/s 4} QCD contributions into the e + e --annihilation Adler function and the generalized Crewther relations

    Science.gov (United States)

    Kataev, A. L.

    2012-02-01

    The generalized Crewther relations in the channels of the non-singlet and vector quark currents are considered. These relations follow from the double application of the operator product expansion approach to the same axial vector-vector-vector triangle amplitude in two regions, adjoining to the angle sides ( x, y) (or p 2, q 2). We assume that the generalized Crewther relations in these two kinematic regimes result in the existence of the same perturbation expression for two products of the coefficient functions of annihilation and deepinelastic scattering processes in the non-singlet and vector channels. This feature explains the conformal symmetry motivated cancellations between the singlet α{/s 3} corrections to the Gross-Llewellyn Smith sum rule S GLS of ν N deep inelastic scattering and the singlet α{/s 3} correction to the e + e --annihilation Adler function D {/A V } in the product of the corresponding perturbative series. Taking into account the Baikov-Chetyrkin-Kuhn fourth order result for S GLS and the perturbative effects of the violation of the conformal symmetry in the generalized Crewther relation, we obtain the analytical contribution to the singlet α{/s 4} correction to the D {/A V } function. Its a-posteriori comparison with the recent result of direct diagram-by-diagram evaluation of the singlet fourth order corrections to D {/A V } function demonstrates the coincidence of the predicted and obtained ζ{3/2}-contributions to the singlet term. They can be obtained in the conformal invariant limit from the original Crewther relation. Therefore, on the contrary to previous belief, the appearance of ζ3-terms in the perturbative series in quantum field theory gauge models does not contradict to the property of the conformal symmetry and can be considered as regular feature. The Banks-Zaks motivated relation between our predicted and the obtained directly fourth order corrections is mentioned. It confirms the expectation, previously made by Baikov

  12. Focal point analysis of the singlet-triplet energy gap of octacene and larger acenes.

    Science.gov (United States)

    Hajgató, Balázs; Huzak, Matija; Deleuze, Michael S

    2011-08-25

    A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet-triplet (ST) excitation energies of n-acenes (C(4n+2)H(2n+4)) ranging from octacene (n = 8) to undecacene (n = 11) is presented. The T1 diagnostics of coupled cluster theory and further energy-based criteria demonstrate that all investigated systems exhibit predominantly a (1)A(g) singlet closed-shell electronic ground state. Singlet-triplet (S(0)-T(1)) energy gaps can therefore be very accurately determined by applying the principle of a focal point analysis (FPA) onto the results of a series of single-point and symmetry-restricted calculations employing correlation consistent cc-pVXZ basis sets (X = D, T, Q, 5) and single-reference methods [HF, MP2, MP3, MP4SDQ, CCSD, and CCSD(T)] of improving quality. According to our best estimates, which amount to a dual extrapolation of energy differences to the level of coupled cluster theory including single, double, and perturbative estimates of connected triple excitations [CCSD(T)] in the limit of an asymptotically complete basis set (cc-pV∞Z), the S(0)-T(1) vertical (adiabatic) excitation energies of these compounds amount to 13.40 (8.21), 10.72 (6.05), 8.05 (3.67), and 7.10 (2.58) kcal/mol, respectively. In line with the absence of Peierls distortions (bond length alternations), extrapolations of results obtained at this level for benzene (n = 1) and all studied n-acenes so far (n = 2-11) indicate a vanishing S(0)-T(1) energy gap, in the limit of an infinitely large polyacene, within an uncertainty of 1.5 kcal/mol (0.06 eV). Lacking experimental values for the S(0)-T(1) energy gaps of n-acenes larger than hexacene, comparison is made with recent optical and electrochemical determinations of the HOMO-LUMO band gap. Further issues such as scalar relativistic, core correlation, and diagonal Born-Oppenheimer corrections (DBOCs) are tentatively examined.

  13. Vibronic exciton theory of singlet fission. I. Linear absorption and the anatomy of the correlated triplet pair state

    Science.gov (United States)

    Tempelaar, Roel; Reichman, David R.

    2017-05-01

    Recent time-resolved spectroscopic experiments have indicated that vibronic coupling plays a vital role in facilitating the process of singlet fission. In this work, which forms the first article of a series, we set out to unravel the mechanisms underlying singlet fission through a vibronic exciton theory. We formulate a model in which both electronic and vibrational degrees of freedom are treated microscopically and non-perturbatively. Using pentacene as a prototypical material for singlet fission, we subject our theory to comparison with measurements on polarization-resolved absorption of single crystals, and employ our model to characterize the excited states underlying the absorption band. Special attention is given to the convergence of photophysical observables with respect to the basis size employed, through which we determine the optimal basis for more expensive calculations to be presented in subsequent work. We furthermore evaluate the energetic separation between the optically prepared singlet excited state and the correlated triplet pair state, as well as provide a real-space characterization of the latter, both of which are of key importance in the discussion of fission dynamics. We discuss our results in the context of recent experimental studies.

  14. Gravitational waves at aLIGO and vacuum stability with a scalar singlet extension of the standard model

    Science.gov (United States)

    Balázs, Csaba; Fowlie, Andrew; Mazumdar, Anupam; White, Graham A.

    2017-02-01

    A new gauge singlet scalar field can undergo a strongly first-order phase transition (PT) leading to gravitational waves (GW) potentially observable at aLIGO and stabilizes the electroweak vacuum at the same time by ensuring that the Higgs quartic coupling remains positive up to at least the grand unification (GUT) scale. aLIGO (O5) is potentially sensitive to cosmological PTs at 1 07- 1 08 GeV , which coincides with the requirement that the singlet scale is less than the standard model (SM) vacuum instability scale, which is between 1 08 GeV and 1 014 GeV . After sampling its parameter space, we identify three benchmark points with a PT at about T ≈1 07 GeV in a gauge singlet extension of the SM. We calculate the nucleation temperature, order parameter, characteristic time scale, and peak amplitude and frequency of GW from bubble collisions during the PT for the benchmarks and find that, in an optimistic scenario, GW from such a PT may be in reach of aLIGO (O5). We confirm that the singlet stabilizes the electroweak vacuum while remaining consistent with zero-temperature phenomenology as well. Thus, this scenario presents an intriguing possibility that aLIGO may detect traces of fundamental physics motivated by vacuum stability at an energy scale that is well above the reach of any other experiment.

  15. Hermitian separability and transition from singlet to adjoint BFKL equations in $\\mathcal{N}=4$ super Yang-Mills Theory

    CERN Document Server

    Bondarenko, S

    2015-01-01

    We revisit the next-to-leading order~(NLO) correction to the eigenvalue of the BFKL equation in the adjoint representation and investigate its properties in analogy with the singlet BFKL in planar $\\mathcal{N}=4$ super Yang-Mills Theory~(SYM). We show that the adjoint NLO BFKL eigenvalue is needed to be slightly modified in order to have a property of hermitian separability present for the singlet BFKL. After this modification the adjoint NLO BFKL eigenvalue is expressed through holomorphic and antiholomophic parts of the leading order eigenvalue and their derivatives. The proposed choice of the modified NLO expression is supported by the fact that it is possible to obtain the same result in a relatively straightforward way directly from the singlet NLO BFKL eigenvalue replacing alternating series by series of constant sign. This transformation corresponds to changing cylindrical topology of the singlet BFKL to the planar topology of the adjoint BFKL. We believe that the original NLO calculation of Fadin and ...

  16. Gravitational waves at aLIGO and vacuum stability with a scalar singlet extension of the Standard Model

    CERN Document Server

    Balazs, Csaba; Mazumdar, Anupam; White, Graham

    2016-01-01

    A new gauge singlet scalar field can undergo a strongly first-order PT leading to gravitational waves (GW) observable at aLIGO and stabilizes the electroweak vacuum at the same time. In fact, aLIGO (O5) should be sensitive to cosmological PTs at scales $10^7$ GeV to $10^8$ GeV, which coincides with the requirement that the singlet scale is less than the Standard Model (SM) instability scale, which is between $10^8$ GeV and $10^{14}$ GeV. Extending the SM with such a singlet, we calculate the nucleation temperature and order parameter of the PT during which the singlet acquires a vacuum expectation value in terms of Lagrangian parameters. Relating the thermodynamic quantities to the peak frequency and amplitude of the GW created during the PT, we present three benchmark points for which not only are GW observable at aLIGO (O5) but the electroweak vacuum is stable and the zero temperature phenomenology is acceptable. This scenario offers an intriguing possibility for aLIGO to detect traces of fundamental physic...

  17. Toward industrial scale synthesis of ultrapure singlet nanoparticles with controllable sizes in a continuous gas-phase process.

    Science.gov (United States)

    Feng, Jicheng; Biskos, George; Schmidt-Ott, Andreas

    2015-10-29

    Continuous gas-phase synthesis of nanoparticles is associated with rapid agglomeration, which can be a limiting factor for numerous applications. In this report, we challenge this paradigm by providing experimental evidence to support that gas-phase methods can be used to produce ultrapure non-agglomerated "singlet" nanoparticles having tunable sizes at room temperature. By controlling the temperature in the particle growth zone to guarantee complete coalescence of colliding entities, the size of singlets in principle can be regulated from that of single atoms to any desired value. We assess our results in the context of a simple analytical model to explore the dependence of singlet size on the operating conditions. Agreement of the model with experimental measurements shows that these methods can be effectively used for producing singlets that can be processed further by many alternative approaches. Combined with the capabilities of up-scaling and unlimited mixing that spark ablation enables, this study provides an easy-to-use concept for producing the key building blocks for low-cost industrial-scale nanofabrication of advanced materials.

  18. Interactions of dietary carotenoids with singlet oxygen (1O2) and free radicals: potential effects for human health.

    Science.gov (United States)

    Böhm, Fritz; Edge, Ruth; Truscott, T George

    2012-01-01

    The dietary carotenoids provide photoprotection to photosynthetic organisms, the eye and the skin. The protection mechanisms involve both quenching of singlet oxygen and of damaging free radicals. The mechanisms for singlet oxygen quenching and protection against free radicals are quite different - indeed, under some conditions, quenching of free radicals can lead to a switch from a beneficial anti-oxidant process to damaging pro-oxidative situation. Furthermore, while skin protection involves β-carotene or lycopene from a tomato-rich diet, protection of the macula involves the hydroxyl-carotenoids (xanthophylls) zeaxanthin and lutein. Time resolved studies of singlet oxygen and free radicals and their interaction with carotenoids via pulsed laser and fast electron spectroscopy (pulse radiolysis) and the possible involvement of amino acids are discussed and used to (1) speculate on the anti- and pro-oxidative mechanisms, (2) determine the most efficient singlet oxygen quencher and (3) demonstrate the benefits to photoprotection of the eye from the xanthophylls rather than from hydrocarbon carotenoids such as β-carotene.

  19. Production of singlet oxygen by the reaction of non-basic hydrogen peroxide with chlorine gas.

    Science.gov (United States)

    Tian, Wenming; Shi, Wenbo; Yang, Heping; Cui, Rongrong; Deng, Liezheng

    2012-10-14

    Non-basic hydrogen peroxide was found to be very easy to react with Cl(2) to produce singlet oxygen O(2)(a(1)Δ(g)) (i.e. the molecular oxygen in its first electronic excited state) when an H(+) absorbent such as C(5)H(5)N, CH(3)COONH(4), HCOONH(4) or NH(4)F was added into H(2)O(2) aqueous solution, and the long concealed fact that molecular H(2)O(2) can react with Cl(2) to produce O(2)(a(1)Δ(g)) was then uncovered. It is only when an H(+) absorbent has provided a stronger base than H(2)O to absorb the H(+) produced during the reaction that O(2)(a(1)Δ(g)) can be produced.

  20. Au nanorods modulated NIR fluorescence and singlet oxygen generation of water soluble dendritic zinc phthalocyanine.

    Science.gov (United States)

    Zhou, Xuefei; He, Xiaohong; Wei, Shiliang; Jia, Kun; Liu, Xiaobo

    2016-11-15

    A novel cyano-terminated zinc phthalocyanine (ZnPc-CN) exhibiting visible near infrared (vis-NIR) emitting around 690nm in N,N-dimethylformamide (DMF) solvent has been synthesized. Furthermore, the peripheral cyano groups of newly synthesized zinc phthalocyanine were hydrolyzed in strong basic solution, leading to water soluble carboxylated zinc phthalocyanine (ZnPc-COOH) with completely quenched fluorescence in aqueous solution. Interestingly, we found that the NIR fluorescence of aqueous ZnPc-COOH was dramatically recovered in the presence of gold nanorods (Au NR), which was due to the alternation of ZnPc-COOH molecules self-assembling via electrostatic interaction between cetyltrimethylammonium bromide (CTAB) on the surface of Au NR and peripheral carboxyl of ZnPc-COOH. In addition, ZnPc-COOH/Au NR conjugates demonstrated an improved singlet oxygen generation, which could be served as potential bioimaging probe and photosensitizer for photodynamic therapy.

  1. Collider Constraints and Prospects of a Scalar Singlet Extension to Higgs Portal Dark Matter

    CERN Document Server

    Dupuis, Grace

    2016-01-01

    This work considers an extension of the Standard Model (SM) Higgs sector by a real, scalar singlet field, including applicability to a dark matter (DM) model with the addition of a Yukawa coupling to a Dirac fermion. The collider signatures and constraints on the mixed two-Higgs scenario are determined, including limits from Higgs production signals and exclusion searches, as well as constraints arising from the Higgs total and invisible widths. As there is overwhelming Higgs data which is consistent with a SM scenario, the case in which an additional scalar has evaded detection is further explored in the context of Higgs precision measurement. The discovery reach and prospective signatures of the model at a proposed linear collider are investigated, with particular focus on the Higgs triple coupling, and di-Higgs production processes.

  2. The 750 GeV diphoton resonance as a singlet scalar in an extra dimensional model

    CERN Document Server

    Cai, Chengfeng; Zhang, Hong-Hao

    2015-01-01

    We interpret the 750~GeV diphoton excess recently found in the 13~TeV LHC data as a singlet scalar in an extra dimensional model, where one extra dimension is introduced. In the model, the scalar couples to multiple vector-like fermions, which are just the KK modes of SM fermions. Mediated by the loops of these vector-like fermions, the $\\phi$ effective couplings to gluons and photons can be significantly large. Therefore, it is quite easy to obtain an observed cross section for the diphoton excess. We also calculate the cross sections for other decay channels of $\\phi$, and find that this interpretation can evade the bounds from the 8~TeV LHC data.

  3. Effect of CP violation in the singlet-doublet dark matter model

    Directory of Open Access Journals (Sweden)

    Tomohiro Abe

    2017-08-01

    Full Text Available We revisit the singlet-doublet dark matter model with a special emphasis on the effect of CP violation on the dark matter phenomenology. The CP violation in the dark sector induces a pseudoscalar interaction of a fermionic dark matter candidate with the SM Higgs boson. The pseudoscalar interaction helps the dark matter candidate evade the strong constraints from the dark matter direct detection experiments. We show that the model can explain the measured value of the dark matter density even if dark matter direct detection experiments do not observe any signal. We also show that the electron electric dipole moment is an important complement to the direct detection for testing this model. Its value is smaller than the current upper bound but within the reach of future experiments.

  4. Singlet structure function g{sub 1} at small x and small Q{sup 2}

    Energy Technology Data Exchange (ETDEWEB)

    Ermolaev, B.I. [Ioffe Physico-Technical Institute, St. Petersburg (Russian Federation); Greco, M. [Rome III Univ. (Italy). Dept. of Physics; INFN, Rome (Italy); Troyan, S.I. [St. Petersburg Institute of Nuclear Physics, Gatchina (Russian Federation)

    2007-05-15

    Explicit expressions for the singlet spin structure function g{sub 1} at small x and small Q{sup 2} are obtained with a total resummation of the leading logarithmic contributions. It is shown that g{sub 1} practically does not depend on x in this kinematic region. In contrast, it would be interesting to investigate its dependence on the invariant energy 2pq, because g{sub 1}, being positive at small 2pq, can turn negative at greater values of this variable. The position of the turning point is sensitive to the ratio of the initial quark and gluon densities, so its experimental detection would enable one to estimate this ratio. (orig.)

  5. Inclusive J/\\psi Production In \\Upsilon Decay Via Color-singlet Mechanism

    CERN Document Server

    He, Zhi-Guo

    2009-01-01

    We reconsider the tree level color-singlet contribution for the inclusive J/\\psi production in \\Upsilon decay with the \\alpha_{s}^{5} order QCD process \\Upsilon\\to J/\\psi+c\\bar{c}+g and \\alpha^{2}\\alpha_s^{2} order QED processes \\Upsilon\\to\\gamma^{\\ast}\\to J/\\psi+c\\bar{c} and \\Upsilon\\to J/\\psi+gg. It is found that the contribution of the QED process is compatible with that of the QCD process, and the numerical results for the QCD process alone is an order of magnitude smaller than the previous theoretical predictions, and our theoretical prediction in total is about an order of magnitude smaller than the recent CLEO measurement on the branching fraction B(\\Upsilon\\to J/\\psi+X). It indicates that the J/\\psi production mechanism in \\Upsilon decay is not well understood, and further theoretical work and experimental analysis are still necessary.

  6. Effective Theory of WIMP Dark Matter supplemented by Simplified Models: Singlet-like Majorana fermion case

    CERN Document Server

    Matsumoto, Shigeki; Tsai, Yue-Lin Sming

    2016-01-01

    We enumerate the set of simplified models which match onto the complete set of gauge invariant effective operators up to dimension six describing interactions of a singlet-like Majorana fermion dark matter with the standard model. Tree level matching conditions for each case are worked out in the large mediator mass limit, defining a one to one correspondence between the effective operator coefficients and the simplified model parameters for weakly interacting models. Utilizing such a mapping, we compute the dark matter annihilation rate in the early universe, as well as other low-energy observables like nuclear recoil rates using the effective operators, while the simplified models are used to compute the dark matter production rates at high energy colliders like LEP, LHC and future lepton colliders. Combining all relevant constraints with a profile likelihood analysis, we then discuss the currently allowed parameter regions and prospects for future searches in terms of the effective operator parameters, red...

  7. [Pt(mesBIAN)(tda)]: a near-infrared emitter and singlet oxygen sensitizer.

    Science.gov (United States)

    Rachford, Aaron A; Hua, Fei; Adams, Christopher J; Castellano, Felix N

    2009-05-28

    The synthesis and subsequent photophysical investigation of [Pt(mesBIAN)(tda)], where mesBIAN is bis(mesitylimino)acenaphthene and tda is tolan-2,2'-diacetylide, reveal excited-state characteristics best described as triplet charge transfer ((3)CT) in nature upon visible light excitation. Large ground-state dipole moments are apparent as the absorption spectrum dramatically red-shifts with decreasing solvent polarity. The (3)CT excited state is significantly lower in energy than the ligand-centered (3)tda excited-state, as confirmed by steady-state and time-resolved techniques. Singlet oxygen sensitization studies demonstrate that (1)O(2) production occurs by diffusive quenching from the photo-excited (3)CT state (Phi(Delta) = 0.24, lambda(max) approximately 1270 nm) in oxygen-saturated dichloromethane.

  8. Charge noise and dynamical decoupling in singlet-triplet spin qubits

    Science.gov (United States)

    Ramon, Guy

    2013-03-01

    We consider theoretically the effects of an ensemble of fluctuating charges on the coherence of a singlet-triplet qubit in gate-defined double quantum dots. We predict a crossover behavior of the system between non-Gaussian noise and 1/f spectrum, going from mesoscopic single-qubit devices to multi-qubit larger devices. With increasing size of the fluctuator ensemble we find a narrowed distribution of qubit dephasing times that result from random sets of fluctuators. At the same time the noise becomes Markovian with a characteristic Gaussian spectrum and it is dominated by a large collection of weakly-coupled fluctuators. The efficiency of dynamical decoupling pulse sequences in restoring coherence is examined as a function of the qubit's working position and the fluctuator ensemble size. Analytical solutions for qubit dephasing in the limits of weak and strong qubit-fluctuator coupling shed light on the distinct dynamics at different parameter regimes. Supported by Research Corporation

  9. Singlet oxygen luminescence detection with a fiber-coupled superconducting nanowire single-photon detector

    CERN Document Server

    Gemmell, Nathan R; Liu, Baochang; Tanner, Michael G; Dorenbos, Sander N; Zwiller, Valery; Patterson, Michael S; Buller, Gerald S; Wilson, Brian C; Hadfield, Robert H; 10.1364/OE.21.005005

    2013-01-01

    Direct monitoring of singlet oxygen (1O2) luminescence is a particularly challenging infrared photodetection problem. 1O2, an excited state of the oxygen molecule, is a crucial intermediate in many biological processes. We employ a low noise superconducting nanowire single-photon detector to record 1O2 luminescence at 1270 nm wavelength from a model photosensitizer (Rose Bengal) in solution. Narrow band spectral filtering and chemical quenching is used to verify the 1O2 signal, and lifetime evolution with the addition of protein is studied. Furthermore, we demonstrate the detection of 1O2 luminescence through a single optical fiber, a marked advance for dose monitoring in clinical treatments such as photodynamic therapy.

  10. Stability of O/W Emulsion with Synthetic Perfumes Oxidized by Singlet Oxygen

    Directory of Open Access Journals (Sweden)

    Naoki Watabe

    2013-01-01

    Full Text Available We prepared O/W emulsion composed of a synthetic perfume, n-dodecane, protoporphyrin IX disodium salt (PpIX-2Na, sodium dodecyl sulfate, and water and investigated oxidative decomposition of the synthetic perfume in the emulsion and change in the stability of the emulsion by singlet oxygen (1O2 generated by photosensitization of PpIX-2Na. We used eugenol, linalool, benzyl acetate, α-ionone, α-hexylcinnamaldehyde, and d-limonene as a synthetic perfume. The stability of the O/W emulation including eugenol and linalool significantly decreased with increasing light irradiation time. The decrease in the emulsion stability may be attributable to oxidative decomposition of eugenol and linalool by 1O2 and enlargement of the oil droplet size.

  11. Analytic quantification of the singlet nonlocality for the first Bell inequality

    Science.gov (United States)

    Parisio, Fernando

    2016-03-01

    Recently an alternative way to quantifying the Bell nonlocality has been proposed [E. A. Fonseca and F. Parisio, Phys. Rev. A 92, 030101(R) (2015), 10.1103/PhysRevA.92.030101]. In this work we further develop this concept, the volume of violation, and analytically calculate its value for the spin-singlet state with respect to the settings of the first Bell inequality. These settings correspond to three directions in space, or three arbitrary points on the unit sphere. It is shown that the triples of directions that lead to violations in local causality correspond to 1 /3 of all possible configurations. From the perspective of quantum communication, this means that two distant parties that were able to align their measurements in one direction only (the remaining direction in each site being random) have a probability of about 33.3 % to certify their entanglement.

  12. Tunneling Conductance in Ferromagnetic Metal/Normal Metal/Spin-Singlet -Wave Ferromagnetic Superconductor Junctions

    Directory of Open Access Journals (Sweden)

    Hamidreza Emamipour

    2013-01-01

    Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.

  13. 750 GeV diphoton resonance as a singlet scalar in an extra dimensional model

    Science.gov (United States)

    Cai, Chengfeng; Yu, Zhao-Huan; Zhang, Hong-Hao

    2016-04-01

    We interpret the 750 GeV diphoton excess recently found in the 13 TeV LHC data as a singlet scalar in an extra dimensional model, where one extra dimension is introduced. In the model, the scalar couples to multiple vectorlike fermions, which are just the Kaluza-Klein modes of SM fermions. Mediated by the loops of these vectorlike fermions, the ϕ effective couplings to gluons and photons can be significantly large. Therefore, it is quite easy to obtain an observed cross section for the diphoton excess. We also calculate the cross sections for other decay channels of ϕ , and find that this interpretation can evade the bounds from the 8 TeV LHC data.

  14. LHC Benchmark Scenarios for the Real Higgs Singlet Extension of the Standard Model

    CERN Document Server

    Robens, Tania

    2016-01-01

    We present benchmark scenarios for searches for an additional Higgs state in the real Higgs singlet extension of the Standard Model in Run 2 of the LHC. The scenarios are selected such that they fulfill all relevant current theoretical and experimental constraints, but can potentially be discovered at the current LHC run. We take into account the results presented in earlier work and update the experimental constraints from relevant LHC Higgs searches and signal rate measurements. The benchmark scenarios are given separately for the low mass and high mass region, i.e. the mass range where the additional Higgs state is lighter or heavier than the discovered Higgs state at around 125 GeV. They have also been presented in the framework of the LHC Higgs Cross Section Working Group.

  15. Singlet-triplet gaps in substituted carbenes predicted from block-correlated coupled cluster method

    Institute of Scientific and Technical Information of China (English)

    SHEN Jun; FANG Tao; LI Shuhua

    2008-01-01

    Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, ChinaThe block correlated coupled cluster (BCCC) method, with the complete active-space self-consistent-field (CASSCF) reference function, has been applied to investigating the singlet-triplet gaps in several substituted carbenes including four halocarbenes (CHCl, CF2, CCl2, and CBr2) and two hydroxycar-bones (CHOH and C(OH)2). A comparison of our results with the experimental data and other theoretical estimates shows that the present approach can provide quantitative descriptions for all the studied carbenes. It is demonstrated that the CAS-BCCC method is a promising theoretical tool for calculating the electronic structures of diradicals.

  16. Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls

    Energy Technology Data Exchange (ETDEWEB)

    Niedzwiedzki, Dariusz; Blankenship, R. E.

    2010-11-18

    Ten naturally occurring chlorophylls (a, b, c{sub 2}, d) and bacteriochlorophylls (a, b, c, d, e, g) were purified and studied using the optical spectroscopic techniques of both steady state and time-resolved absorption and fluorescence. The studies were carried out at room temperature in nucleophilic solvents in which the central Mg is hexacoordinated. The comprehensive studies of singlet excited state lifetimes show a clear dependency on the structural features of the macrocycle and terminal substituents. The wide-ranging studies of triplet state lifetime demonstrate the existence of an energy gap law for these molecules. The knowledge of the dynamics and the energies of the triplet state that were obtained in other studies allowed us to construct an energy gap law expression that can be used to estimate the triplet state energies of any (B)chlorophyll molecule from its triplet lifetime obtained in a liquid environment.

  17. Enhanced singlet oxygen generation from PLGA loaded with verteporfin and gold nanoparticles

    Science.gov (United States)

    Deng, Wei; Kautzka, Zofia; Goldys, Ewa M.

    2016-12-01

    In this study, poly(lactic-co-glycolic acid) (PLGA) nanocomposites were developed by incorporating a photosensitizer, verteporfin and gold nanoparticles into this polymeric matrix and utilised for enhanced photoynamic therapy. Both enhanced fluorescence and singlet oxygen generation from verteporfin were observed in this new formulation under both 425nm LED and 405nm laser illumination. A maximum enhancement factor of 2.5 for fluorescence and 1.84 for 1O2 generation was obtained when the molar ratio of gold:VP was 5:1 and excited at 425 nm, compared with PLGA doped with verteporfin only. The experiment results could be explained by the local electric field enhancement of gold nanoparticles. Furthermore, in vitro cell-killing effect on human pancreatic cancer cells was also demonstrated by using this new formulation following light exposure, indicating the utility of these nanocomposites for enhanced photodynamic therapy.

  18. Predicting the singlet vector channel in a partially Higgsed gauge theory

    CERN Document Server

    Maas, A

    2016-01-01

    We study a toy version of a grand-unified theory on the lattice: An $SU(3)$ gauge theory, which experiences a Brout-Englert-Higgs effect due to a single Higgs field in the fundamental representation. This yields a perturbative breaking pattern $SU(3) \\rightarrow SU(2)$. We investigate the singlet vector channel, finding an apparently non-degenerate and massive ground state. This is in contradistinction to the perturbative prediction of three massless and five massive vector states, even though the correlation functions of the gauge bosons exhibit a weak-coupling behavior, being almost tree-level-like. However, a combination of perturbation theory with the Fr\\"ohlich-Morchio-Strocchi mechanism allows to predict the physical spectrum in this channel.

  19. Functional renormalization group approach to the singlet-triplet transition in quantum dots.

    Science.gov (United States)

    Magnusson, E B; Hasselmann, N; Shelykh, I A

    2012-09-12

    We present a functional renormalization group approach to the zero bias transport properties of a quantum dot with two different orbitals and in the presence of Hund's coupling. Tuning the energy separation of the orbital states, the quantum dot can be driven through a singlet-triplet transition. Our approach, based on the approach by Karrasch et al (2006 Phys. Rev. B 73 235337), which we apply to spin-dependent interactions, recovers the key characteristics of the quantum dot transport properties with very little numerical effort. We present results on the conductance in the vicinity of the transition and compare our results both with previous numerical renormalization group results and with predictions of the perturbative renormalization group.

  20. A Singlet Thiophosphoryl Nitrene and Its Interconversion with Thiazyl and Thionitroso Isomers.

    Science.gov (United States)

    Li, Hongmin; Wu, Zhuang; Li, Dingqing; Zeng, Xiaoqing; Beckers, Helmut; Francisco, Joseph S

    2015-09-02

    Thiophosphoryl nitrenes, R2P(S)N, are thiazirine-like intermediates that have been chemically inferred from trapping products in early solution studies. In this work, photolysis of the simplest thiophosphoryl azide, F2P(S)N3, in solid noble-gas matrices enabled a first-time spectroscopic (IR and UV-vis) identification of the thiophosphoryl nitrene F2P(S)N in its singlet ground state. Upon visible-light irradiation (≥495 nm), it converts into the thionitroso isomer F2P-N═S, which can also be produced in the gas phase from flash vacuum pyrolysis of F2P(S)N3. Further irradiation of F2P-NS with 365 nm UV light leads to the reformation of F2P(S)N and isomerization to the thiazyl species F2P-S≡N.

  1. The effect of axial ligands on the quantum yield of singlet oxygen of new silicon phthalocyanine

    Science.gov (United States)

    Lv, Huafei; Zhang, Xuemei; Yu, Xinxin; Pan, Sujuan; Xie, Shusen; Yang, Hongqin; Peng, Yiru

    2016-10-01

    The singlet oxygen (1O2) production abilitity is an important factor to assess their potential as effective of photosensitizers. In this paper, the 1O2 production rate, production rate constant and quantum yield of silicon(IV) phthalocyanine axially bearing 1-3 generation dendritic substituents were evaluated by a high performance liquid chromatographic method. The results show that the 1O2 production rate and production rate constant of these compounds increase gradually with dendritic generations increase. And the 1O2 quantum yield of silicon(IV) phthalocyanine with first generation dendritic ligand was the highest. This may be due to the isolation effect of the dendritic ligands on the phthalocyanine core. The parameters of the observed 1O2 production properties will provide valuable data for these dendrimer phthalocyanines as promising photosensitizer in PDT application.

  2. Effect of intramolecular charge transfer on fluorescence and singlet oxygen production of phthalocyanine analogues.

    Science.gov (United States)

    Vachova, Lenka; Novakova, Veronika; Kopecky, Kamil; Miletin, Miroslav; Zimcik, Petr

    2012-10-14

    Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties were compared to corresponding macrocycles that do not bear any donor centers. The data showed high feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of non-donor peripheral substituents on ICT was also described. The results imply that tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in applications based on ICT.

  3. LHC benchmark scenarios for the real Higgs singlet extension of the standard model

    Energy Technology Data Exchange (ETDEWEB)

    Robens, Tania [TU Dresden, Institut fuer Kern- und Teilchenphysik, Dresden (Germany); Stefaniak, Tim [University of California, Department of Physics and Santa Cruz Institute for Particle Physics, Santa Cruz, CA (United States)

    2016-05-15

    We present benchmark scenarios for searches for an additional Higgs state in the real Higgs singlet extension of the Standard Model in Run 2 of the LHC. The scenarios are selected such that they fulfill all relevant current theoretical and experimental constraints, but can potentially be discovered at the current LHC run. We take into account the results presented in earlier work and update the experimental constraints from relevant LHC Higgs searches and signal rate measurements. The benchmark scenarios are given separately for the low-mass and high-mass region, i.e. the mass range where the additional Higgs state is lighter or heavier than the discovered Higgs state at around 125 GeV. They have also been presented in the framework of the LHC Higgs Cross Section Working Group. (orig.)

  4. Properties of pseudoscalar flavour-singlet mesons from 2+1+1 twisted mass lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Cichy, Krzysztof [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Poznan Univ. (Poland). Faculty of Physics; Drach, Vincent; Garcia Ramos, Elena; Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Michael, Chris [Liverpool Univ. (United Kingdom). Dept. of Mathematical Sciences; Ottnad, Konstantin; Urbach, Carsten; Zimmermann, Falk [Bonn Univ. (Germany). Inst. fuer Strahlen- und Kernphysik

    2012-11-15

    We study properties of pseudoscalar flavour-singlet mesons from Wilson twisted mass lattice QCD with N{sub f}=2+1+1 dynamical quark flavors. Results for masses are presented at three values of the lattice spacing and light quark masses corresponding to values of the pion mass from 230 MeV to 500 MeV. We briefly discuss scaling effects and the light and strange quark mass dependence of M{sub {eta}}. In addition we present an exploratory study using Osterwalder-Seiler type strange and charm valence quarks. This approach avoids some of the complications of the twisted mass heavy doublet. We present first results for matching valence and unitary actions and a comparison of statistical uncertainties.

  5. Planck scale boundary conditions in the standard model with singlet scalar dark matter

    CERN Document Server

    Haba, Naoyuki; Takahashi, Ryo

    2013-01-01

    We investigate Planck scale boundary conditions on the Higgs sector of the standard model with a gauge singlet scalar dark matter. We will find that vanishing self-coupling and Veltman condition at the Planck scale are realized with the 126 GeV Higgs mass and top pole mass, 171.8 GeV $\\lesssim M_t\\lesssim$ 173.5 GeV, where a correct abundance of scalar dark matter is obtained with mass of 300 GeV $\\lesssim m_S \\lesssim$ 1 TeV. It means that the Higgs potential is flat at the Planck scale, and this situation can not be realized in the standard model with the top pole mass.

  6. Planck scale boundary conditions in the standard model with singlet scalar dark matter

    Energy Technology Data Exchange (ETDEWEB)

    Haba, Naoyuki [Graduate School of Science and Engineering, Shimane University, Matsue, Shimane 690-8504 (Japan); Kaneta, Kunio [Kavli IPMU (WPI), The University of Tokyo, Kashiwa, Chiba 277-8568 (Japan); Takahashi, Ryo [Graduate School of Science and Engineering, Shimane University, Matsue, Shimane 690-8504 (Japan)

    2014-04-04

    We investigate Planck scale boundary conditions on the Higgs sector of the standard model with a gauge singlet scalar dark matter. We will find that vanishing self-coupling and Veltman condition at the Planck scale are realized with the 126 GeV Higgs mass and top pole mass, 172 GeV≲M{sub t}≲173.5 GeV, where a correct abundance of scalar dark matter is obtained with mass of 300 GeV≲m{sub S}≲1 TeV. It means that the Higgs potential is flat at the Planck scale, and this situation can not be realized in the standard model with the top pole mass.

  7. Vanishing Higgs potential at the Planck scale in singlets extension of the standard model

    CERN Document Server

    Haba, Naoyuki; Kaneta, Kunio; Takahashi, Ryo

    2014-01-01

    We discuss the realization of a vanishing Higgs potential at the Planck scale, which is required by the multiple point criticality principle, in the standard model with singlet scalar dark matter and a right-handed neutrino. We find the scalar dark matter and the right-handed neutrino play crucial roles, and their masses, $m_S$ and $M_R$, must be $8.0\\times10^2~{\\rm GeV}\\leq m_S\\leq1.2\\times10^3~{\\rm GeV}$ and $6.3\\times10^{13}~{\\rm GeV}\\leq M_R\\leq1.6\\times10^{14}~{\\rm GeV}$ within current experimental values of the Higgs and top masses. This scenario is consistent with current dark matter direct search experiments, and will be confirmed by future experiments such as LUX with further exposure and/or XENON1T.

  8. Simplified Models for Higgs Physics: Singlet Scalar and Vector-like Quark Phenomenology

    CERN Document Server

    Dolan, Matthew J; Krämer, M; Rizzo, T G

    2016-01-01

    Simplified models provide a useful tool to conduct the search and exploration of physics beyond the Standard Model in a model-independent fashion. In this work we consider the complementarity of indirect searches for new physics in Higgs couplings and distributions with direct searches for new particles, using a simplified model which includes a new singlet scalar resonance and vector-like fermions that can mix with the SM top-quark. We fit this model to the combined ATLAS and CMS 125 GeV Higgs production and coupling measurements and other precision electroweak constraints, and explore in detail the effects of the new matter content upon Higgs production and kinematics. We highlight some novel features and decay modes of the top partner phenomenology, and discuss prospects for Run II.

  9. Simplified models for Higgs physics: singlet scalar and vector-like quark phenomenology

    Science.gov (United States)

    Dolan, Matthew J.; Hewett, J. L.; Krämer, M.; Rizzo, T. G.

    2016-07-01

    Simplified models provide a useful tool to conduct the search and exploration of physics beyond the Standard Model in a model-independent fashion. In this work we consider the complementarity of indirect searches for new physics in Higgs couplings and distributions with direct searches for new particles, using a simplified model which includes a new singlet scalar resonance and vector-like fermions that can mix with the SM top-quark. We fit this model to the combined ATLAS and CMS 125 GeV Higgs production and coupling measurements and other precision electroweak constraints, and explore in detail the effects of the new matter content upon Higgs production and kinematics. We highlight some novel features and decay modes of the top partner phenomenology, and discuss prospects for Run II.

  10. Universal doublet-singlet Higgs couplings and phenomenology at the CERN Large Hadron Collider

    CERN Document Server

    Bhattacharyya, Gautam; Nandi, S

    2008-01-01

    We consider a minimal extension of the Standard Model where a real, gauge singlet scalar field is added to the standard spectrum. Introducing the Ansatz of universality of scalar couplings, we are led to a scenario which has a set of very distinctive and testable predictions: (i) the mixing between the SM Higgs and the new state is near maximal, (ii) the ratio of the two Higgs mass eigenstates is fixed ($\\sim \\sqrt{3}$), (iii) the decay modes of each of the two eigenstates are Standard Model like. We also study how electroweak precision tests constrain this scenario. We predict the lighter Higgs to lie in the range of 114 and 145 GeV, and hence the heavier one between 198 and 250 GeV. The predictions of the model can be tested at the upcoming LHC.

  11. Efficient cyanoaromatic photosensitizers for singlet oxygen production: synthesis and characterization of the transient reactive species.

    Science.gov (United States)

    Ronzani, Filippo; Arzoumanian, Emmanuel; Blanc, Sylvie; Bordat, Patrice; Pigot, Thierry; Cugnet, Cyril; Oliveros, Esther; Sarakha, Mohamed; Richard, Claire; Lacombe, Sylvie

    2013-10-28

    In order to graft cyanoaromatic molecules onto various inert supports, we designed two new cyanoanthracene derivatives of benzo[b]triphenylene-9,14-dicarbonitrile (DBTP, 1), which already demonstrated good photosensitizing properties. We synthesized 3-(N-hydroxypropyl)carboxamido-9,14-dicyanobenzo[b]triphenylene, 3 and 3-(N-N0-Boc-aminohexyl)carboxamido-9,14-dicyanobenzo[b]triphenylene, 4 and compared their photophysical properties in acetonitrile relative to those of the parent compound 1 and its carboxylic derivative 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid, 2. The transient species were analysed and the quantum yields of singlet oxygen production (ΦΔ) determined in acetonitrile. The effect of chemical functionalization can be considered negligible, since absorption spectra, fluorescence emission spectra and fluorescence lifetimes do not significantly change with the substituent. The triplet-triplet absorption spectra and the triplet excited state lifetimes are similar for the whole series. For compounds 1-4 high values of ΦΔ, close to that of the standard sensitizer 1H-phenalen-1-one (PN, ΦΔ ≈ 1), and higher than that of the well-known photosensitizer 9,10-dicyanoanthracene (DCA), are due to very efficient intersystem crossing from the singlet to the triplet excited state and subsequent energy transfer to ground state oxygen ((3)O2). They belong to a class of very efficient photosensitizers, absorbing visible light and stable under irradiation, they may be functionalized without significant changes to their photophysical behaviour, and grafted onto various supports.

  12. Photoinduced C—I bond homolysis of 5-iodouracil: A singlet predissociation pathway

    Science.gov (United States)

    Dai, Xiaojuan; Song, Di; Liu, Kunhui; Su, Hongmei

    2017-01-01

    5-Iodouracil (5-IU) can be integrated into DNA and acts as a UV sensitive chromophore suitable for probing DNA structure and DNA-protein interactions based on the photochemical reactions of 5-IU. Here, we perform joint studies of time-resolved Fourier transform infrared (TR-FTIR) spectroscopy and ab initio calculations to examine the state-specific photochemical reaction mechanisms of the 5-IU. The fact that uracil (U) is observed in TR-FTIR spectra after 266 nm irradiation of 5-IU in acetonitrile and ascribed to the product of hydrogen abstraction by the uracil-5-yl radical (U.) provides experimental evidence for the C—I bond homolysis of 5-IU. The excited state potential energy curves are calculated with the complete active space second-order perturbation//complete active space self-consistent field method, from which a singlet predissociation mechanism is elucidated. It is shown that the initially populated 1(ππ*) state crosses with the repulsive 1(πσ*) or 1(nIσ*) state, through which 5-IU undergoes dissociation to the fragments of (U.) radical and iodine atom. In addition, the possibility of intersystem crossing (ISC) is evaluated based on the calculated vertical excitation energies. Although a probable ISC from 1(ππ*) state to 3(nOπ*) and then to the lowest triplet 3(ππ*) could occur in principal, there is little possibility for the excited state populations bifurcating to triplet manifold, given that the singlet state predissociation follows repulsive potential and should occur within dozens to hundreds of femtoseconds. Such low population of triplet states means that the contribution of triplet state to photoreactions of 5-IU should be quite minor. These results demonstrate clearly a physical picture of C—I bond homolysis of 5-IU and provide mechanistic illuminations to the interesting applications of 5-IU as photoprobes and in radiotherapy of cancer.

  13. A heterogeneous optimization algorithm for reacted singlet oxygen for interstitial PDT

    Science.gov (United States)

    Zhu, Timothy C.; Altschuler, Martin D.; Hu, Yida; Wang, Ken; Finlay, Jarod C.; Dimofte, Andreea; Cengel, Keith; Hahn, Stephen M.

    2015-01-01

    Singlet oxygen (1O2) is the major cytotoxic agent for type II photodynamic therapy (PDT). The production of 1O2 involves the complex reactions among light, oxygen molecule, and photosensitizer. From universal macroscopic kinetic equations which describe the photochemical processes of PDT, the reacted 1O2 concentration, [1O2]rx, with cell target can be expressed in a form related to time integration of the product of 1O2 quantum yield and the PDT dose rate. The object of this study is to develop optimization procedures that account for the optical heterogeneity of the patient prostate, the tissue photosensitizer concentrations, and tissue oxygenation, thereby enable delivery of uniform reacted singlet oxygen to the gland. We use the heterogeneous optical properties measured for a patient prostate to calculate a light fluence kernel. Several methods are used to optimize the positions and intensities of CDFs. The Cimmino feasibility algorithm, which is fast, linear, and always converges reliably, is applied as a search tool to optimize the weights of the light sources at each step of the iterative selection. Maximum and minimum dose limits chosen for sample points in the prostate constrain the solution for the intensities of the linear light sources. The study shows that optimization of individual light source positions and intensities is feasible for the heterogeneous prostate during PDT. To study how different photosensitizer distributions as well as tissue oxygenation in the prostate affect optimization, comparisons of light fluence rate were made with measured distribution of photosensitizer in prostate under different tissue oxygenation conditions. PMID:25995533

  14. A heterogeneous optimization algorithm for reacted singlet oxygen for interstitial PDT

    Science.gov (United States)

    Zhu, Timothy C.; Altschuler, Martin D.; Hu, Yida; Wang, Ken; Finlay, Jarod C.; Dimofte, Andreea; Cengel, Keith; Hahn, Stephen M.

    2010-02-01

    Singlet oxygen (1O2) is the major cytotoxic agent for type II photodynamic therapy (PDT). The production of 1O2 involves the complex reactions among light, oxygen molecule, and photosensitizer. From universal macroscopic kinetic equations which describe the photochemical processes of PDT, the reacted 1O2 concentration, [1O2]rx, with cell target can be expressed in a form related to time integration of the product of 1O2 quantum yield and the PDT dose rate. The object of this study is to develop optimization procedures that account for the optical heterogeneity of the patient prostate, the tissue photosensitizer concentrations, and tissue oxygenation, thereby enable delivery of uniform reacted singlet oxygen to the gland. We use the heterogeneous optical properties measured for a patient prostate to calculate a light fluence kernel. Several methods are used to optimize the positions and intensities of CDFs. The Cimmino feasibility algorithm, which is fast, linear, and always converges reliably, is applied as a search tool to optimize the weights of the light sources at each step of the iterative selection. Maximum and minimum dose limits chosen for sample points in the prostate constrain the solution for the intensities of the linear light sources. The study shows that optimization of individual light source positions and intensities is feasible for the heterogeneous prostate during PDT. To study how different photosensitizer distributions as well as tissue oxygenation in the prostate affect optimization, comparisons of light fluence rate were made with measured distribution of photosensitizer in prostate under different tissue oxygenation conditions.

  15. Spin-Free CC2 Implementation of Induced Transitions between Singlet Ground and Triplet Excited States.

    Science.gov (United States)

    Helmich-Paris, Benjamin; Hättig, Christof; van Wüllen, Christoph

    2016-04-12

    In most organic molecules, phosphorescence has its origin in transitions from triplet exited states to the singlet ground state, which are spin-forbidden in nonrelativistic quantum mechanics. A sufficiently accurate description of phosphorescence lifetimes for molecules that contain only light elements can be achieved by treating the spin-orbit coupling (SOC) with perturbation theory (PT). We present an efficient implementation of this approach for the approximate coupled cluster singles and doubles model CC2 in combination with the resolution-of-the-identity approximation for the electron repulsion integrals. The induced oscillator strengths and phosphorescence lifetimes from SOC-PT are computed within the response theory framework. In contrast to previous work, we employ an explicitly spin-coupled basis for singlet and triplet operators. Thereby, a spin-orbital treatment can be entirely avoided for closed-shell molecules. For compounds containing only light elements, the phosphorescence lifetimes obtained with SOC-PT-CC2 are in good agreement with those of exact two-component (X2C) CC2, whereas the calculations are roughly 12 times faster than with X2C. Phosphorescence lifetimes computed for two thioketones with the SOC-PT-CC2 approach agree very well with reference results from experiment and are similar to those obtained with multireference spin-orbit configuration interaction and with X2C-CC2. An application to phosphorescent emitters for metal-free organic light-emitting diodes (OLEDs) with almost 60 atoms and more than 1800 basis functions demonstrates how the approach extends the applicability of coupled cluster methods for studying phosphorescence. The results indicate that other decay channels like vibrational relaxation may become important in such systems if lifetimes are large.

  16. Considerations on describing non-singlet spin states in variational second order density matrix methods.

    Science.gov (United States)

    van Aggelen, Helen; Verstichel, Brecht; Bultinck, Patrick; Van Neck, Dimitri; Ayers, Paul W

    2012-01-07

    Despite the importance of non-singlet molecules in chemistry, most variational second order density matrix calculations have focused on singlet states. Ensuring that a second order density matrix is derivable from a proper N-electron spin state is a difficult problem because the second order density matrix only describes one- and two-particle interactions. In pursuit of a consistent description of spin in second order density matrix theory, we propose and evaluate two main approaches: we consider constraints derived from a pure spin state and from an ensemble of spin states. This paper makes a comparative assessment of the different approaches by applying them to potential energy surfaces for different spin states of the oxygen and carbon dimer. We observe two major shortcomings of the applied spin constraints: they are not size consistent and they do not reproduce the degeneracy of the different states in a spin multiplet. First of all, the spin constraints are less strong when applied to a dissociated molecule than when they are applied to the dissociation products separately. Although they impose correct spin expectation values on the dissociated molecule, the dissociation products do not have correct spin expectation values. Secondly, both under "pure spin state conditions" and under "ensemble spin state" conditions is the energy a convex function of the spin projection. Potential energy surfaces for different spin projections of the same spin state may give a completely different picture of the molecule's bonding. The maximal spin projection always gives the most strongly constrained energy, but is also significantly more expensive to compute than a spin-averaged ensemble. In the dissociation limit, both the problem of nondegeneracy of equivalent spin projections, size-inconsistency and unphysical dissociation can be corrected by means of subspace energy constraints.

  17. Interaction of phosphatidylcholine and α-tocopherol on the oxidation of sunflower oil and content changes of phosphatidylcholine and tocopherol in the emulsion under singlet oxygen.

    Science.gov (United States)

    Lee, Yoosung; Choe, Eunok

    2011-04-01

    Interaction of phosphatidylcholine (PC) and α-tocopherol (α-Toc) on the oxidation of oil in the emulsion consisting of sunflower oil and water under singlet oxygen at 25 °C was studied by determining peroxide value (PV) and conjugated dienoic acid (CDA) contents. Singlet oxygen was produced by chlorophyll b under 1700 lux. Single addition of PC or α-Toc decreased the values of peroxides and CDAs of oil in the emulsion via singlet oxygen quenching. PC and α-Toc showed simply additive interaction in decreasing the singlet oxygen oxidation of oil in the emulsion. α-Toc was a physical quencher of singlet oxygen in the emulsion, but PC involved chemical quenching in the antioxidant action. Chlorophyll and PC contents were decreased in the emulsion under singlet oxygen, while α-Toc was not. α-Toc protected chlorophyll and PC from degradation, and was a more important component than PC in the oil oxidation under singlet oxygen in the emulsion.

  18. Sensitization of singlet oxygen via encounter complexes and via exciplexes of pipi* triplet excited sensitizers and oxygen.

    Science.gov (United States)

    Mehrdad, Zahra; Noll, Astrid; Grabner, Erich-Walter; Schmidt, Reinhard

    2002-04-01

    Both excited singlet states, 1sigma(g)+ and 1delta(g), and the triplet ground state, 3sigma(g)-, of molecular oxygen are competitively formed during the quenching by O2 of triplet (T1) excited sensitizers of sufficient energy. The corresponding overall rate constants kT(1sigma), kT(1delta), and kT(3sigma) as well as the T1 state energies E(T) and the oxidation potentials E(ox), have been determined for a series of six fluorene derivatives. Graduated and in part strong charge transfer (CT) effects on kT(1sigma), kT(1delta), and kT(3sigma) are observed. These and literature data strongly indicate that quenching occurs in two different channels each capable of producing O2(1sigma(g)-), O2(1delta(g)), and O2(3sigma(g)-). One proceeds via internal conversion (IC) of excited 1,3(T1 x 3sigma) complexes with no CT character (nCT), which cannot be distinguished from encounter complexes, the other via IC of 1,3(T1 x 3sigma) exciplexes with partial CT character (pCT). The contributions of nCT and pCT deactivation channels to the overall formation of O2(1sigma(g)+), O2(1delta(g)). and O2(3sigma(g)-) depend on E(T) and E(ox). The rate constants of the nCT channel are controlled by the excess energies of the respective IC processes by an energy gap law. The rate constants of the pCT channel depend on the change of free energy deltaG(CET) for complete electron transfer from T1 excited sensitizer to O2. Equations are presented which show the functional form of the dependence of the oxygen quenching rate constants on E(T) and E(ox). Particular emphasis is laid on the question of whether these relations could generally be valid for pipi* triplet sensitizers.

  19. Strongly-interacting color-singlet exchange in $\\bar{p}$-p collisions at √s = 1800 GeV

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Tracy Lea Taylor [Northwestern Univ., Evanston, IL (United States)

    1997-12-01

    Results are presented from an analysis of the particle multiplicity between high transverse energy jets in $\\bar{p}$-p collisions at √s = 1,800 GeV. The data were collected using the D0 Detector at Fermi National Accelerator Laboratory. The authors observe an excess of events at low multiplicity which is consistent with strongly interacting color-singlet exchange. The fraction of events due to color-singlet exchange is measured as a function of the transverse energy and rapidity separation of the jets and is compared to several theoretical models for color-singlet exchange.

  20. Toward Designed Singlet Fission: Electronic States and Photophysics of 1,3-Diphenylisobenzofuran

    Energy Technology Data Exchange (ETDEWEB)

    Schwerin, A.F.; Miller, J.; Johnson, J.C.; Smith, M.B.; Sreearunothai, P.; Popovic, D.; Cerny, J.; Havlas, Z.; Paci, I.; Akdag, A.; MacLeod, M.K.; Chen, X.; David, D.E.; Ratner, M.A.; Nozik, A.J.; Mich, J.

    2009-12-21

    Single crystal molecular structure and solution photophysical properties are reported for 1,3-diphenylisobenzofuran (1), of interest as a model compound in studies of singlet fission. For the ground state of 1 and of its radical cation (1{sup +{sm_bullet}}) and anion (1{sup -{sm_bullet}}), we report the UV-visible absorption spectra, and for neutral 1, also the magnetic circular dichroism (MCD) and the decomposition of the absorption spectrum into purely polarized components, deduced from fluorescence polarization. These results were used to identify a series of singlet excited states. For the first excited singlet and triplet states of 1, the transient visible absorption spectra, S{sub 1} {yields} S{sub x} and sensitized T{sub 1} {yields} T{sub x}, and single exponential lifetimes, {tau}{sub F} = {approx} 5.3 ns and {tau}{sub T} = {approx}200 {mu}s, are reported. The spectra and lifetimes of S{sub 1} {yields} S{sub 0} fluorescence and sensitized T{sub 1} {yields} T{sub x} absorption of 1 were obtained in a series of solvents, as was the fluorescence quantum yield, {Phi}{sub F} = 0.95-0.99. No phosphorescence has been detected. The first triplet excitation energy of solid 1 (11,400 cm{sup -1}) was obtained by electron energy loss spectroscopy, in agreement with previously reported solution values. The fluorescence excitation spectrum suggests an onset of a nonradiative channel at {approx} 37,000 cm{sup -1}. Excitation energies and relative transition intensities are in agreement with those of ab initio (CC2) calculations after an empirical 3000 cm{sup -1} adjustment of the initial state energy to correct differentially for a better quality description of the initial relative to the terminal state of an absorption transition. The interpretation of the MCD spectrum used the semiempirical PPP method, whose results for the S{sub 0} {yields} S{sub x} spectrum require no empirical adjustment and are otherwise nearly identical with the CC2 results in all respects

  1. A Singlet Oxygen Photogeneration and Luminescence Study of Unsymmetrically Substituted Mesoporphyrinic Compounds

    Directory of Open Access Journals (Sweden)

    Anabela Sousa Oliveira

    2009-01-01

    Full Text Available This paper deals with a series of new unsymmetrically substituted mesoporphyrins: 5-(2-hydroxyphenyl-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHO, 5-(3-hydroxyphenyl-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHM, 5-(4-hydroxyphenyl-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHP, 5-(2-hydroxyphenyl-10,15,20-tris-butyl-21,23-H-porphyrin (TBPOHO, and their parent nonsubstituted compounds, respectively, 5,10,15,20-tetrakis-phenyl-21,23-H-porphyrin (TPP and 5,10,15,20-tetrakis-butyl-21,23-H-porphyrin (TBP. Several photophysical studies were carried out to access the influence of the unsymmetrical substitution at the porphyrinic macrocycle on porthyrin's photophysical properties, especially porthyrin's efficiency as singlet oxygen sensitizers. The quantum yields of singlet oxygen generation were determined in benzene (ΦΔ(TPP = 0.66 ± 0.05; ΦΔ(TPPOHO = 0.69 ± 0.04; ΦΔ(TPPOHM = 0.62 ± 0.04; ΦΔ(TPPOHP = 0.73 ± 0.03; ΦΔ(TBP = 0.76 ± 0.03; ΦΔ(TBPOHO = 0.73 ± 0.02 using the 5,10,15,20-tetraphenyl-21,23-H-porphine (ΦΔ(TPP = 0.66 and Phenazine (ΦΔ(Phz = 0.83 as reference compounds. Their fluorescence quantum yields were found to be (Φf(TPPOHO = 0.10 ± 0.04; Φf(TPPOHM = 0.09 ± 0.03; Φf(TPPOHP = 0.13 ± 0.02; Φf(TBP = 0.08 ± 0.03 and Φf(TBPOHO = 0.08 ± 0.02 using 5,10,15,20-tetraphenyl-21,23-H-porphine as reference Φf(TPP = 0.13. Singlet state lifetimes were also determined in the same solvent. All the porphyrins presented very similar fluorescence lifetimes (mean values of τS (with O2, air equilibrated = 9.6 ± 0.3 nanoseconds and (without O2, argon purged = 10.1 ± 0.6 nanoseconds, resp.. The phosphorescence emission was found to be negligible for this series of unsymmetrically substituted mesoporphyrins, but an E-type, thermally activated, delayed fluorescence process was proved to occur at room temperature.

  2. Light flavor-singlet scalars and walking signals in Nf=8 QCD on the lattice

    Science.gov (United States)

    Aoki, Yasumichi; Aoyama, Tatsumi; Bennett, Ed; Kurachi, Masafumi; Maskawa, Toshihide; Miura, Kohtaroh; Nagai, Kei-ichi; Ohki, Hiroshi; Rinaldi, Enrico; Shibata, Akihiro; Yamawaki, Koichi; Yamazaki, Takeshi; LatKMI Collaboration

    2017-07-01

    Based on the highly improved staggered quark action, we perform lattice simulations of Nf=8 QCD and confirm our previous observations, both of a flavor-singlet scalar meson (denoted as σ ) as light as the pion and of various "walking signals" through the low-lying spectra, with higher statistics, smaller fermion masses mf, and larger volumes. We measure Mπ, Fπ, Mρ, Ma0,Ma 1, Mb 1, MN, Mσ, Fσ, ⟨ψ ¯ψ ⟩ (both directly and through the Gell-Mann-Oakes-Renner relation), and the string tension. The data are consistent with the spontaneously broken phase of the chiral symmetry, in agreement with the previous results: Ratios of the quantities to Mπ monotonically increase in the smaller mf region towards the chiral limit similarly to Nf=4 QCD, in sharp contrast to Nf=12 QCD where the ratios become flattened. We perform fits to chiral perturbation theory, with the value of Fπ found in the chiral limit extrapolation reduced dramatically to roughly 2 /3 of the previous result, suggesting the theory is much closer to the conformal window. In fact, each quantity obeys the respective hyperscaling relation throughout a more extensive mf region compared with earlier works. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, γm≃1 , with the notable exception of Mπ with γm≃0.6 as in the previous results, which reflects the above growing up of the ratios towards the chiral limit. This is a salient feature (walking signal) of Nf=8 , unlike either Nf=4 , which has no hyperscaling relation at all, or Nf=12 QCD, which exhibits universal hyperscaling. The effective γm≡γm(mf) of Mπ defined for each mf region has a tendency to grow towards unity near the chiral limit, in conformity with the Nambu-Goldstone boson nature, as opposed to the case of Nf=12 QCD where it is almost constant. We further confirm the previous observation of the light σ with mass comparable to the pion in the studied mf region. In a chiral limit

  3. Ferrnion Mass Hierarchies in Singlet-Extended Minimal-Supersymmetric-Standard-Model Quivers

    Institute of Scientific and Technical Information of China (English)

    Salah Eddine Ennadifi; Adil Belhaj; El Hassan Saidi

    2011-01-01

    In the context of type-ⅡA orientifold compactifications,we discuss the fermion masses in a two-singlet-extended minimal-supersymmetric-standard-model four-stack quiver with U(3) × Sp(1) × U(1) × U(1) gauge symmetry.The corresponding effective superpotential exhibits hierarchical coupling term scales giving a partial solution to the fermion masses problem.Using the known data with upper bound neutrino masses mvτ <~ 2 eV,we estimate the relevant scales for the model.It has been shown that important particle physics can be realized in type-Ⅱ superstring models by using the mechanism of intersecting D-branes in orientifold compactifications.[1-6] In such compactifications,the gauge groups arise from stacks of D-branes that fill four-dimensional spacetime and wrap the three-cycles in the internal Calabi-Yau threefold.However,matter fields arise at the intersection of two different D-brane stacks in internal space and their multiplicity is given by the topological intersection numbers of the respective three-cycles.Their interactions are subject to restrictions of additional global U(1)'s exhibited by orientifold compactifications.[7-10] Stringy effects have a crucial role in this regard,as they give corrections to the superpotential by inducing the missing couplings relevant for fermion masses.This method provides an acceptable effective low energy description reproducing the standard model or some extensions.[11,12]%In the context of type-IIA orientifold compactifications, we discuss the fermion masses in a two-singlet-extended minimal-supersymmetric-standard-model four-stack quiver with U(3)×Sp(1)×U(1)×U(1) gauge symmetry. The corresponding effective superpotential exhibits hierarchical coupling term scales giving a partial solution to the fermion masses problem. Using the known data with upper bound neutrino masses mvτ≤2 eV, we estimate the relevant scales for the model.

  4. Formation and dynamics of van der Waals molecules in buffer-gas traps.

    Science.gov (United States)

    Brahms, Nathan; Tscherbul, Timur V; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G

    2011-11-14

    We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, (3)He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag(3)He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag(3)He, and report on our spectroscopic search for Ag(3)He, which produced a null result.

  5. Magnetic-Field Dependence of the Electroluminescence of Organic Light-Emitting Diodes: A Competition between Exciton Formation and Spin Mixing

    Science.gov (United States)

    Kersten, S. P.; Schellekens, A. J.; Koopmans, B.; Bobbert, P. A.

    2011-05-01

    We explore the magnetoelectroluminescence (MEL) of organic light-emitting diodes by evaluating the magnetic-field dependent fraction of singlet excitons formed. We use two- and multisite polaron-hopping models with spin mixing by hyperfine fields and different singlet and triplet exciton formation rates kS and kT. A huge MEL is predicted when exciton formation is in competition with spin mixing and when kT is significantly larger than kS. This competition also leads to a low-field structure in the MEL that is in agreement with recent experiments.

  6. Effects of the cryptochrome CryB from Rhodobacter sphaeroides on global gene expression in the dark or blue light or in the presence of singlet oxygen.

    Science.gov (United States)

    Frühwirth, Sebastian; Teich, Kristin; Klug, Gabriele

    2012-01-01

    Several regulators are controlling the formation of the photosynthetic apparatus in the facultatively photosynthetic bacterium Rhodobacter sphaeroides. Among the proteins affecting photosynthesis gene expression is the blue light photoreceptor cryptochrome CryB. This study addresses the effect of CryB on global gene expression. The data reveal that CryB does not only influence photosynthesis gene expression but also genes for the non-photosynthetic energy metabolism like citric acid cycle and oxidative phosphorylation. In addition several genes involved in RNA processing and in transcriptional regulation are affected by a cryB deletion. Although CryB was shown to undergo a photocycle it does not only affect gene expression in response to blue light illumination but also in response to singlet oxygen stress conditions. While there is a large overlap in these responses, some CryB-dependent effects are specific for blue-light or photooxidative stress. In addition to protein-coding genes some genes for sRNAs show CryB-dependent expression. These findings give new insight into the function of bacterial cryptochromes and demonstrate for the first time a function in the oxidative stress response.

  7. Tetramer spin singlet instability in the fluorine-substituted pyrochlore superconducting system Cd2Re2O7-x F x.

    Science.gov (United States)

    Haraguchi, Yuya; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi

    2016-09-01

    We synthesized polycrystalline samples of the fluorine-substituted pyrochlore rhenates Cd2Re2O7-x F x , and investigated their magnetic, transport and structural properties. The transition temperature T s1, where each Re4 tetrahedron in the Re pyrochlore network alternately expands and contracts, decreases with increasing x from 200 K at x  =  0 to 100 K at x  =  0.5. The strong x dependence of the magnetic and transport properties at the low-temperature phase indicates that the driving force of structural phase transition is fluctuations of the tetramer spin singlet formation in order to release the spin frustration in the pyrochlore lattice. Furthermore, we found unconventional superconducting properties in Cd2Re2O7-x F x . It was found that the superconducting phase transition temperature T c markedly decreases with increasing x, suggesting that the addition of imperfection suppresses a condensation of Cooper-pair. In addition, the estimated upper critical field at zero temperature exceeds the Pauli paramagnetic limit and increases with increasing x in spite of the reduction of T c. Hence, Cd2Re2O7-x F x is suggested to be an exotic superconductor realized in the itinerant electron systems on a spin frustrated lattice.

  8. Tetramer spin singlet instability in the fluorine-substituted pyrochlore superconducting system Cd2Re2O7-x F x

    Science.gov (United States)

    Haraguchi, Yuya; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi

    2016-09-01

    We synthesized polycrystalline samples of the fluorine-substituted pyrochlore rhenates Cd2Re2O7-x F x , and investigated their magnetic, transport and structural properties. The transition temperature T s1, where each Re4 tetrahedron in the Re pyrochlore network alternately expands and contracts, decreases with increasing x from 200 K at x  =  0 to 100 K at x  =  0.5. The strong x dependence of the magnetic and transport properties at the low-temperature phase indicates that the driving force of structural phase transition is fluctuations of the tetramer spin singlet formation in order to release the spin frustration in the pyrochlore lattice. Furthermore, we found unconventional superconducting properties in Cd2Re2O7-x F x . It was found that the superconducting phase transition temperature T c markedly decreases with increasing x, suggesting that the addition of imperfection suppresses a condensation of Cooper-pair. In addition, the estimated upper critical field at zero temperature exceeds the Pauli paramagnetic limit and increases with increasing x in spite of the reduction of T c. Hence, Cd2Re2O7-x F x is suggested to be an exotic superconductor realized in the itinerant electron systems on a spin frustrated lattice.

  9. Effects of the cryptochrome CryB from Rhodobacter sphaeroides on global gene expression in the dark or blue light or in the presence of singlet oxygen.

    Directory of Open Access Journals (Sweden)

    Sebastian Frühwirth

    Full Text Available Several regulators are controlling the formation of the photosynthetic apparatus in the facultatively photosynthetic bacterium Rhodobacter sphaeroides. Among the proteins affecting photosynthesis gene expression is the blue light photoreceptor cryptochrome CryB. This study addresses the effect of CryB on global gene expression. The data reveal that CryB does not only influence photosynthesis gene expression but also genes for the non-photosynthetic energy metabolism like citric acid cycle and oxidative phosphorylation. In addition several genes involved in RNA processing and in transcriptional regulation are affected by a cryB deletion. Although CryB was shown to undergo a photocycle it does not only affect gene expression in response to blue light illumination but also in response to singlet oxygen stress conditions. While there is a large overlap in these responses, some CryB-dependent effects are specific for blue-light or photooxidative stress. In addition to protein-coding genes some genes for sRNAs show CryB-dependent expression. These findings give new insight into the function of bacterial cryptochromes and demonstrate for the first time a function in the oxidative stress response.

  10. Interpretation of 750 GeV Diphoton Excess at LHC in Singlet Extension of Color-octet Neutrino Mass Model

    CERN Document Server

    Ding, Ran; Liao, Yi; Ma, Xiao-Dong

    2016-01-01

    We propose that the possible 750 GeV diphoton excess can be explained in the color-octet neutrino mass model extended with a scalar singlet $\\Phi$. The model generally contains $N_s$ species of color-octet, electroweak doublet scalars $S$ and $N_f$ species of color-octet, electroweak triplet $\\chi$ or singlet $\\rho$ fermions. While both scalars and fermions contribute to the production of $\\Phi$ through gluon fusion, only the charged members induce the diphoton decay of $\\Phi$. The diphoton rate can be significantly enhanced due to interference between the scalar and fermion loops. We show that the diphoton cross section can be from 3 to 10 fb for O(TeV) color-octet particles while evading all current LHC limits.

  11. Interpretation of 750 GeV diphoton excess at LHC in singlet extension of color-octet neutrino mass model

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Ran [Peking University, Center for High Energy Physics, Beijing (China); Han, Zhi-Long; Ma, Xiao-Dong [Nankai University, School of Physics, Tianjin (China); Liao, Yi [Peking University, Center for High Energy Physics, Beijing (China); Nankai University, School of Physics, Tianjin (China); Chinese Academy of Sciences, State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Beijing (China)

    2016-04-15

    We propose that the possible 750 GeV diphoton excess can be explained in the color-octet neutrino mass model extended with a scalar singlet Φ. The model generally contains N{sub s} species of color-octet, electroweak doublet scalars S and N{sub f} species of color-octet, electroweak triplet χ or singlet ρ fermions. While both scalars and fermions contribute to the production of Φ through gluon fusion, only the charged members induce the diphoton decay of Φ. The diphoton rate can be significantly enhanced due to interference between the scalar and fermion loops.We show that the diphoton cross section can be from 3 to 10 fb for O(TeV) color-octet particles while evading all current LHC limits. (orig.)

  12. Fluorescence behavior and singlet oxygen generating abilities of aluminum phthalocyanine in the presence of anisotropic gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Mthethwa, Thandekile; Nyokong, Tebello, E-mail: t.nyokong@ru.ac.za

    2015-01-15

    Gold nanoparticles (spheres, rods and bipyramids) were synthesized. The nanocrystals were characterized by UV–visible spectrometry, transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The as prepared gold nanoparticles were then conjugated to a quaternized 2,(3)-tetra [2-(dimethylamino) ethanethio] substituted Al(OH) phthalocyanine (complex 1). The conjugation of phthalocyanines with gold nanoparticles resulted in a decrease in the fluorescence quantum yields and lifetimes. Conversely, an increase in the singlet oxygen quantum yields was observed for the conjugated complex 1 in the presence of AuNPs. - Highlights: • Gold nanoparticles (spheres, rods and bipyramids) were synthesized. • Gold nanoparticles were then conjugated to a quaternized ClAl phthalocyanine. • Conjugation of phthalocyanines with gold nanoparticles resulted in a decrease in the fluorescence quantum yields. • An increase in the singlet oxygen quantum yields was observed for the phthalocyanine in the presence of nanoparticles.

  13. Non-singlet structure function of the 3He-3H system and divergence of the Gottfried integral

    CERN Document Server

    Guzey, V; Strikman, M I; Thomas, A W; Tsushima, K

    2001-01-01

    We study shadowing and antishadowing corrections to the flavor non-singlet structure function F_2(3He)-F_2(3H) and show that the difference between the one-particle density distributions of 3He and 3H plays an important role at very small x. We find that the flavor non-singlet structure function in these mirror nuclei is enhanced at small x by nuclear shadowing, which increases the nuclear Gottfried integral, integrated from 10^{-4} to 1, by 11-36 %. When integrated from zero, the Gottfried integral is divergent for these mirror nuclei. It seems likely that, as a consequence of charge symmetry breaking, this may also apply to the proton-neutron system.

  14. Singlet oxygen generation using a porous monolithic polymer supported photosensitizer: potential application to the photodynamic destruction of melanoma cells.

    Science.gov (United States)

    Burguete, M Isabel; Galindo, Francisco; Gavara, Raquel; Luis, Santiago V; Moreno, Miguel; Thomas, Paul; Russell, David A

    2009-01-01

    Photogeneration of singlet oxygen (1O2) by rose bengal is improved through the use of a porous monolithic polymer (PMP) as a support, as compared to a classic gel-type resin matrix. This type of monolithic polymeric matrix can be made at a multigram scale in quantitative yields enabling the preparation of large amounts of supported photosensitizer at low cost. The singlet oxygen induced oxidation of 9,10-diphenylanthracene has been used as a benchmark reaction, and a comparative study using rose bengal in solution, entrapped within gel-type derived polymer and entrapped within a porous monolithic polymer (PMP) has been performed. The enhanced photoreactivity of the PMP-rose bengal conjugates has been utilised for the successful photodynamic therapy (PDT) of melanoma cells.

  15. Radiative corrections to the Higgs boson couplings in the model with an additional real singlet scalar field

    CERN Document Server

    Kanemura, Shinya; Yagyu, Kei

    2015-01-01

    We calculate renormalized Higgs boson couplings with gauge bosons and fermions at the one-loop level in the model with an additional isospin singlet real scalar field. These coupling constants can deviate from the predictions in the standard model due to tree-level mixing effects and one-loop contributions of the extra neutral scalar boson. We investigate how they can be significant under the theoretical constraints from perturbative unitarity and vacuum stability and also the condition of avoiding the wrong vacuum. Furthermore, comparing with the predictions in the Type I two Higgs doublet model, we numerically demonstrate how the singlet extension model can be distinguished and identified by using precision measurements of the Higgs boson couplings at future collider experiments.

  16. All-electrical measurement of the triplet-singlet spin relaxation time in self-assembled quantum dots

    Science.gov (United States)

    Eltrudis, K.; Al-Ashouri, A.; Beckel, A.; Ludwig, A.; Wieck, A. D.; Geller, M.; Lorke, A.

    2017-08-01

    We have measured the spin relaxation time of an excited two-electron spin-triplet state into its singlet ground state in self-assembled InAs/GaAs quantum dots. We use a time-resolved measurement scheme that combines transconductance spectroscopy with spin-to-charge conversion to address the |s ↑,p ↑ 〉 triplet state, where one electron is in the quantum dot s-shell and a second one in the p-shell. The evaluation of the state-selective tunneling times from the dots into a nearby two-dimensional electron gas allows us to determine the s- and p-shell occupation and extract the relaxation time from a rate equation model. A comparably long triplet-to-singlet spin relaxation time of 25 μs is found.

  17. Higgs inflation with singlet scalar dark matter and right-handed neutrino in the light of BICEP2

    CERN Document Server

    Haba, Naoyuki

    2014-01-01

    We discuss the Higgs inflation scenario with singlet scalar dark matter and a right-handed neutrino. The singlet scalar and the right-handed neutrino play crucial roles for realizing a suitable plateau of Higgs potential with the center value of the top mass of Tevatron and LHC measurements. This Higgs inflation scenario predicts about 1 TeV scalar dark matter and $\\mathcal{O}(10^{14})$ GeV right-handed neutrino by use of 125.6 GeV Higgs mass, 173.34 GeV top mass, and a non-minimal gravity coupling $\\xi\\simeq10.1$. This inflation model is consistent with the recent result of tensor-to-scalar ratio $r=0.20_{-0.05}^{+0.07}$ by the BICEP2 collaboration.

  18. A Singlet Extension of the Minimal Supersymmetric Standard Model: Towards a More Natural Solution to the Little Hierarchy Problem

    Energy Technology Data Exchange (ETDEWEB)

    de la Puente, Alejandro [Univ. of Notre Dame, IN (United States)

    2012-05-01

    In this work, I present a generalization of the Next-to-Minimal Supersymmetric Standard Model (NMSSM), with an explicit μ-term and a supersymmetric mass for the singlet superfield, as a route to alleviating the little hierarchy problem of the Minimal Supersymmetric Standard Model (MSSM). I analyze two limiting cases of the model, characterized by the size of the supersymmetric mass for the singlet superfield. The small and large limits of this mass parameter are studied, and I find that I can generate masses for the lightest neutral Higgs boson up to 140 GeV with top squarks below the TeV scale, all couplings perturbative up to the gauge unification scale, and with no need to fine tune parameters in the scalar potential. This model, which I call the S-MSSM is also embedded in a gauge-mediated supersymmetry breaking scheme. I find that even with a minimal embedding of the S-MSSM into a gauge mediated scheme, the mass for the lightest Higgs boson can easily be above 114 GeV, while keeping the top squarks below the TeV scale. Furthermore, I also study the forward-backward asymmetry in the t¯t system within the framework of the S-MSSM. For this purpose, non-renormalizable couplings between the first and third generation of quarks to scalars are introduced. The two limiting cases of the S-MSSM, characterized by the size of the supersymmetric mass for the singlet superfield is analyzed, and I find that in the region of small singlet supersymmetric mass a large asymmetry can be obtained while being consistent with constraints arising from flavor physics, quark masses and top quark decays.

  19. One-loop corrections to the Higgs self-couplings in the singlet extension

    CERN Document Server

    Kanemura, Shinya; Yagyu, Kei

    2016-01-01

    We investigate predictions on the triple Higgs boson couplings with radiative corrections in the model with an additional real singlet scalar field. In this model, the second physical scalar state ($H$) appears in addition to the Higgs boson ($h$) with the mass 125 GeV. The $hhh$ vertex is calculated at the one-loop level, and its possible deviation from the predictions in the standard model is evaluated under various theoretical constraints. The decay rate of $H \\to hh$ is also computed at the one-loop level. We also take into account the bound from the precise measurement of the $W$ boson mass, which gives the upper limit on the mixing angle $\\alpha$ between two physical Higgs bosons for a given value of the mass of $H$ ($m_H^{}$). We find that the deviation in the $hhh$ coupling from the prediction in the standard model can maximally be about 250\\%, 150\\% and 75\\% for $m_H^{}=300$, 500 and 1000 GeV, respectively, under the requirement that the cutoff scale of the model is higher than 3 TeV. We also discuss...

  20. Secluded singlet fermionic dark matter driven by the Fermi gamma-ray excess

    CERN Document Server

    Kim, Yeong Gyun; Park, Chan Beom; Shin, Seodong

    2016-01-01

    We examine the possibility that the dark matter (DM) interpretation of the GeV scale Fermi gamma-ray excess at the Galactic Center can be realized in a specific framework - secluded singlet fermionic dark matter model with small mixing between the dark and Standard Model sector. Within this framework it is shown that the DM annihilation into bottom-quark pair, Higgs pair, and new scalar pair can give good fits to the Fermi gamma-ray data. Moreover unavoidable constraints from the antiproton ratio by the PAMELA and AMS-02, the gamma-ray emission from the dwarf spheroidal galaxies by the Fermi-LAT, and the Higgs measurements by the LHC are also considered. Then we found our best-fit parameters for the Fermi gamma-ray excess without conflicting other experimental and cosmological constraints if uncertainties on the DM density profile of the Milky Way Galaxy are taken into account. Successfully surviving parameters are benchmark points for future study on the collider signals.