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.

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

Investigation of the generation of singlet oxygen in ensembles of photoexcited silicon nanocrystals by electron paramagnetic resonance spectroscopy

International Nuclear Information System (INIS)

Konstantinova, E. A.; Demin, V. A.; Timoshenko, V. Yu.

2008-01-01

The generation of singlet oxygen is investigated and its concentration upon photoexcitation of silicon nanocrystals in porous silicon layers is determined using electron paramagnetic resonance spectroscopy. The relaxation times of spin centers, i.e., silicon dangling bonds, in vacuum and in an oxygen atmosphere in the dark and under illumination of the samples are measured for the first time. It is revealed that the spin-lattice relaxation in porous silicon is retarded as compared to that in a single-crystal substrate. From analyzing experimental data, a microscopic model is proposed for interaction of oxygen molecules in the triplet state and spin centers at the surface of silicon nanocrystals. The results obtained have demonstrated that porous silicon holds promise for the use as a photosensitizer of molecular oxygen in biomedical applications

4-spin plaquette singlet state in the Shastry-Sutherland compound SrCu2(BO3)2

Science.gov (United States)

Zayed, M. E.; Rüegg, Ch.; Larrea J., J.; Läuchli, A. M.; Panagopoulos, C.; Saxena, S. S.; Ellerby, M.; McMorrow, D. F.; Strässle, Th.; Klotz, S.; Hamel, G.; Sadykov, R. A.; Pomjakushin, V.; Boehm, M.; Jiménez-Ruiz, M.; Schneidewind, A.; Pomjakushina, E.; Stingaciu, M.; Conder, K.; Rønnow, H. M.

2017-10-01

The study of interacting spin systems is of fundamental importance for modern condensed-matter physics. On frustrated lattices, magnetic exchange interactions cannot be simultaneously satisfied, and often give rise to competing exotic ground states. The frustrated two-dimensional Shastry-Sutherland lattice realized by SrCu2(BO3)2 (refs ,) is an important test case for our understanding of quantum magnetism. It was constructed to have an exactly solvable 2-spin dimer singlet ground state within a certain range of exchange parameters and frustration. While the exact dimer state and the antiferromagnetic order at both ends of the phase diagram are well known, the ground state and spin correlations in the intermediate frustration range have been widely debated. We report here the first experimental identification of the conjectured plaquette singlet intermediate phase in SrCu2(BO3)2. It is observed by inelastic neutron scattering after pressure tuning to 21.5 kbar. This gapped singlet state leads to a transition to long-range antiferromagnetic order above 40 kbar, consistent with the existence of a deconfined quantum critical point.

Signaling pathways regulating the expression of Prx1 and Prx2 in the Chick Mandibular Mesenchyme

Science.gov (United States)

Doufexi, Aikaterini-El; Mina, Mina

2009-01-01

Prx1 and Prx2 are members of the aristaless-related homeobox genes shown to play redundant but essential roles in morphogenesis of the mandibular processes. To gain insight into the signaling pathways that regulate expression of Prx genes in the mandibular mesenchyme, we used the chick as a model system. We examined the patterns of gene expression in the face and the roles of signals derived from the epithelium on the expression of Prx genes in the mandibular mesenchyme. Our results demonstrated stage-dependent roles of mandibular epithelium on the expression of Prx in the mandibular mesenchyme and provide evidence for positive roles of members of the fibroblast and hedgehog families derived from mandibular epithelium on the expression of Prx genes in the mandibular mesenchyme. Our studies suggest that endothelin-1 signaling derived from the mesenchyme is involved in restricting the expression of Prx2 to the medial mandibular mesenchyme. PMID:18942149

Prx1 and Prx2 cooperatively regulate the morphogenesis of the medial region of the mandibular process

Science.gov (United States)

Balic, Anamaria; Adams, Douglas; Mina, Mina

2009-01-01

Mice lacking both Prx1 and Prx2 display severe abnormalities in the mandible. Our analysis showed that complete loss of Prx gene products leads to growth abnormalities in the mandibular processes evident as early as E10.5 associated with changes in the survival of the mesenchyme in the medial region. Changes in the gene expression in the medial and lateral regions were related to gradual loss of a subpopulation of mesenchyme in the medial region expressing eHand. Our analysis also showed that Prx gene products are required for the initiation and maintenance of chondrogenesis and terminal differentiation of the chondrocytes in the caudal and rostral ends of Meckel’s cartilage. The fusion of the mandibular processes in the Prx1/Prx2 double mutants is caused by accelerated ossification. These observations together show that during mandibular morphogenesis Prx gene products play multiple roles including the cell survival, the region-specific terminal differentiation of Meckelian chondrocytes and osteogenesis. PMID:19777594

Unified model for singlet fission within a non-conjugated covalent pentacene dimer

Science.gov (United States)

Basel, Bettina S.; Zirzlmeier, Johannes; Hetzer, Constantin; Phelan, Brian T.; Krzyaniak, Matthew D.; Reddy, S. Rajagopala; Coto, Pedro B.; Horwitz, Noah E.; Young, Ryan M.; White, Fraser J.; Hampel, Frank; Clark, Timothy; Thoss, Michael; Tykwinski, Rik R.; Wasielewski, Michael R.; Guldi, Dirk M.

2017-01-01

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron–hole pairs, leading to a predicted ∼50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures. PMID:28516916

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.

Photoexcited singlet and triplet states of a UV absorber ethylhexyl methoxycrylene.

Science.gov (United States)

Kikuchi, Azusa; Hata, Yuki; Kumasaka, Ryo; Nanbu, Yuichi; Yagi, Mikio

2013-01-01

The excited states of UV absorber, ethylhexyl methoxycrylene (EHMCR) have been studied through measurements of UV absorption, fluorescence, phosphorescence and electron paramagnetic resonance (EPR) spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states of EHMCR were determined. The energy levels of the S1 and T1 states of EHMCR are much lower than those of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The energy levels of the S1 and T1 states of EHMCR are lower than those of octyl methoxycinnamate. The weak phosphorescence and EPR B(min) signals were observed and the lifetime was estimated to be 93 ms. These facts suggest that the significant proportion of the S1 molecules undergoes intersystem crossing to the T1 state, and the deactivation process from the T1 state is predominantly radiationless. The photostability of EHMCR arises from the (3)ππ* character in the T1 state. The zero-field splitting (ZFS) parameter in the T1 state is D** = 0.113 cm(-1). © 2012 The Authors Photochemistry and Photobiology © 2012 The American Society of Photobiology.

Singlet oxygen quenching by oxygen in tetraphenyl-porphyrin solutions

International Nuclear Information System (INIS)

Dedic, Roman; Korinek, Miloslav; Molnar, Alexander; Svoboda, Antonin; Hala, Jan

2006-01-01

Time-resolved measurement of singlet oxygen infrared phosphorescence is a powerful tool for determination of quantum yields and kinetics of its photosensitization. This technique was employed to investigate in detail the previously observed effect of singlet oxygen quenching by oxygen. The question whether the singlet oxygen is quenched by oxygen in ground or in excited state was addressed by study of two complementary dependencies of singlet oxygen lifetimes: on dissolved oxygen concentration and on excitation intensity. Oxygen concentration dependence study of meso-tetra(4-sulphonato)phenylporphyrin (TPPS 4 ) phosphorescence kinetics showed linearity of the dependence of TPPS 4 triplet state rate-constant. Corresponding bimolecular quenching constant of (1.5±0.1)x10 9 l/mol s was obtained. On the other hand, rate constants of singlet oxygen depopulation exhibit nonlinear dependence on oxygen concentration. Comparison of zero oxygen concentration-extrapolated value of singlet oxygen lifetime of (6.5±0.4) μs to (3.7±0.1) μs observed under air-saturated conditions indicates importance of the effect of quenching of singlet oxygen by oxygen. Upward-sloping dependencies of singlet oxygen depopulation rate-constant on excitation intensity evidence that singlet oxygen is predominantly quenched by oxygen in excited singlet state

Fate of the open-shell singlet ground state in the experimentally accessible acenes: A quantum Monte Carlo study

Science.gov (United States)

Dupuy, Nicolas; Casula, Michele

2018-04-01

By means of the Jastrow correlated antisymmetrized geminal power (JAGP) wave function and quantum Monte Carlo (QMC) methods, we study the ground state properties of the oligoacene series, up to the nonacene. The JAGP is the accurate variational realization of the resonating-valence-bond (RVB) ansatz proposed by Pauling and Wheland to describe aromatic compounds. We show that the long-ranged RVB correlations built in the acenes' ground state are detrimental for the occurrence of open-shell diradical or polyradical instabilities, previously found by lower-level theories. We substantiate our outcome by a direct comparison with another wave function, tailored to be an open-shell singlet (OSS) for long-enough acenes. By comparing on the same footing the RVB and OSS wave functions, both optimized at a variational QMC level and further projected by the lattice regularized diffusion Monte Carlo method, we prove that the RVB wave function has always a lower variational energy and better nodes than the OSS, for all molecular species considered in this work. The entangled multi-reference RVB state acts against the electron edge localization implied by the OSS wave function and weakens the diradical tendency for higher oligoacenes. These properties are reflected by several descriptors, including wave function parameters, bond length alternation, aromatic indices, and spin-spin correlation functions. In this context, we propose a new aromatic index estimator suitable for geminal wave functions. For the largest acenes taken into account, the long-range decay of the charge-charge correlation functions is compatible with a quasi-metallic behavior.

Exact ground and excited states of an antiferromagnetic quantum spin model

International Nuclear Information System (INIS)

Bose, I.

1989-08-01

A quasi-one-dimensional spin model which consists of a chain of octahedra of spins has been suggested for which a certain parameter regime of the Hamiltonian, the ground state, can be written down exactly. The ground state is highly degenerate and can be other than a singlet. Also, several excited states can be constructed exactly. The ground state is a local RVB state for which resonance is confined to rings of spins. Some exact numerical results for an octahedron of spins have also been reported. (author). 16 refs, 2 figs, 1 tab

Absence of Intramolecular Singlet Fission in Pentacene-Perylenediimide Heterodimers: The Role of Charge Transfer State.

Science.gov (United States)

Wang, Long; Wu, Yishi; Chen, Jianwei; Wang, Lanfen; Liu, Yanping; Yu, Zhenyi; Yao, Jiannian; Fu, Hongbing

2017-11-16

A new class of donor-acceptor heterodimers based on two singlet fission (SF)-active chromophores, i.e., pentacene (Pc) and perylenediimide (PDI), was developed to investigate the role of charge transfer (CT) state on the excitonic dynamics. The CT state is efficiently generated upon photoexcitation. However, the resulting CT state decays to different energy states depending on the energy levels of the CT state. It undergoes extremely rapid deactivation to the ground state in polar CH 2 Cl 2 , whereas it undergoes transformation to a Pc triplet in nonpolar toluene. The efficient triplet generation in toluene is not due to SF but CT-mediated intersystem crossing. In light of the energy landscape, it is suggested that the deep energy level of the CT state relative to that of the triplet pair state makes the CT state actually serve as a trap state that cannot undergoes an intramolecular singlet fission process. These results provide guidance for the design of SF materials and highlight the requisite for more widely applicable design principles.

Singlet oxygen-mediated damage to proteins and its consequences

DEFF Research Database (Denmark)

Davies, Michael Jonathan

2003-01-01

by the transfer of energy to ground state (triplet) molecular oxygen by either protein-bound, or other, chromophores. Singlet oxygen can also be generated by a range of other enzymatic and non-enzymatic reactions including processes mediated by heme proteins, lipoxygenases, and activated leukocytes, as well...... 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...... as radical termination reactions. This paper reviews the data available on singlet oxygen-mediated protein oxidation and concentrates primarily on the mechanisms by which this excited state species brings about changes to both the side-chains and backbone of amino acids, peptides, and proteins. Recent work...

High orbital angular momentum states in H2 and D2. III. Singlet--triplet splittings, energy levels, and ionization potentials

International Nuclear Information System (INIS)

Jungen, C.; Dabrowski, I.; Herzberg, G.; Vervloet, M.

1990-01-01

The 5g--4 f Rydberg groups of H 2 and D 2 first studied in paper I have been obtained with a tenfold increase in resolution which made it possible to resolve the singlet from the triplet components. As a result we can now establish separately precise values for the energy levels in the triplet and singlet systems. For this purpose we have remeasured a number of transitions between the lower energy levels for which at present only old measurements are available. In particular we obtain accurate values for the energies of the lowest (stable) triplet state a 3 Σ + g relative to the singlet ground state, as well as of the ionization potential. The values obtained for the former are more accurate than obtained from singlet--triplet anticrossings while the latter are of similar accuracy as those reported recently by McCormack et al. [Phys. Rev. A 39, 2260 (1989)] and fit well within this accuracy with the most recent ab initio values

Cluster expansion of the wavefunction. Calculation of electron correlations in ground and excited states by SAC and SAC CI theories

International Nuclear Information System (INIS)

Nakatsuji, H.

1979-01-01

The SAC and SAC CI theories are formulated for actual calculations of singlet ground states and their excited states of arbitrary spin multiplicity. Approximations are considered for the variational methods since time-consuming terms are involved. The results of test calculations for singlet states have shown, with much smaller numbers of variables (sizes of the matrices involved), excellent agreement with the full CI and close-to-full CI results. This shows the utility of the SAC theory for ground states and especially of the SAC CI theory for excited states, since the slow convergence of the CI theory is much more critical for excited states than for ground states. (Auth.)

Spin-singlet quantum Hall states and Jack polynomials with a prescribed symmetry

International Nuclear Information System (INIS)

Estienne, Benoit; Bernevig, B. Andrei

2012-01-01

We show that a large class of bosonic spin-singlet Fractional Quantum Hall model wavefunctions and their quasihole excitations can be written in terms of Jack polynomials with a prescribed symmetry. Our approach describes new spin-singlet quantum Hall states at filling fraction ν=(2k)/(2r-1) and generalizes the (k,r) spin-polarized Jack polynomial states. The NASS and Halperin spin-singlet states emerge as specific cases of our construction. The polynomials express many-body states which contain configurations obtained from a root partition through a generalized squeezing procedure involving spin and orbital degrees of freedom. The corresponding generalized Pauli principle for root partitions is obtained, allowing for counting of the quasihole states. We also extract the central charge and quasihole scaling dimension, and propose a conjecture for the underlying CFT of the (k,r) spin-singlet Jack states.

Toward Singlet-Triplet Bistable Nonalternant Kekulé Hydrocarbons: Azulene-to-Naphthalene Rearrangement.

Science.gov (United States)

Das, Soumyajit; Wu, Jishan

2015-12-04

Recent developments of open-shell singlet diradicaloids motivated the search for stable singlet-triplet bistable nonalternant polycyclic hydrocarbons. During the synthesis of this type of molecule, such as the dibenzo-cyclohepta[def]fluorene 3, an unexpected azulene-to-naphthalene rearrangement was observed at room temperature, which resulted in new nonalternant hydrocarbons 8a/8b with a closed-shell singlet ground state. These studies provided insight into the unique chemistry of azulene and challenges for the synthesis of singlet-triplet bistable polycyclic hydrocarbons.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission.

Science.gov (United States)

Hart, Stephanie M; Silva, W Ruchira; Frontiera, Renee R

2018-02-07

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes.

Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State

KAUST Repository

Pace, Natalie A.; Zhang, Weimin; Arias, Dylan H.; McCulloch, Iain; Rumbles, Garry; Johnson, Justin C.

2017-01-01

The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission rate and triplet yield in two polymers differing only by side chain motif in both solution and the solid state. Whereas solid-state films show singlet fission rates identical to those measured in solution, the average lifetime of the triplet population increases dramatically, and is strongly dependent on side-chain identity. These results show that it may be necessary to carefully engineer the solid-state microstructure of these “singlet fission polymers” in order to produce the long-lived triplets needed to realize efficient photovoltaic devices.

Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State

KAUST Repository

Pace, Natalie A.

2017-11-30

The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission rate and triplet yield in two polymers differing only by side chain motif in both solution and the solid state. Whereas solid-state films show singlet fission rates identical to those measured in solution, the average lifetime of the triplet population increases dramatically, and is strongly dependent on side-chain identity. These results show that it may be necessary to carefully engineer the solid-state microstructure of these “singlet fission polymers” in order to produce the long-lived triplets needed to realize efficient photovoltaic devices.

Magnetic field effects on the soft mode in a singlet ground-state dimer system: a neutron scattering study of Cs3Cr2Br9

DEFF Research Database (Denmark)

Leuenberger, Bruno; Gudel, Hans U.; Feile, Rudolf

1985-01-01

Neutron scattering experiments in a magnetic field have been performed on the singlet ground-state dimer system Cs3Cr2Br9. At low fields the Zeeman splitting of the soft mode evolves in agreement with the isotropic random-phase approximation (RPA) model, with the notable absence of a quasielastic...... peak. At a temperature of 1.7K the expected long-range magnetic order is not found at the predicted field of 2.8 T, indicating the shortcomings of the isotropic RPA model in the critical region. Magnetic intensity on the weak nuclear Bragg peak (1¯1¯4) indicates a probable ordering with a ferromagnetic...

New possibilities for using laser polarimetry technology to study electron paramagnetic resonance

Energy Technology Data Exchange (ETDEWEB)

Aleksandrov, E V; Zapasskii, V S

1982-01-01

Optical methods of recording electron paramagnetic resonance which arose in the early 50's as applied to the problem of recording the magnetic resonance of excited atoms is at the present time widely used in studying the electron paramagnetic resonance of the ground and excited states of free atoms and paramagnetic centers in condensed media. At the present time attention is devoted to the additional possibilities of optical methods of electron paramagnetic resonance which are realized using laser sources.

Para-quinodimethane-bridged perylene dimers and pericondensed quaterrylenes: The effect of the fusion mode on the ground states and physical properties

KAUST Repository

Das, Soumyajit

2014-07-23

Polycyclic hydrocarbon compounds with a singlet biradical ground state show unique physical properties and promising material applications; therefore, it is important to understand the fundamental structure/biradical character/physical properties relationships. In this study, para-quinodimethane (p-QDM)-bridged quinoidal perylene dimers 4 and 5 with different fusion modes and their corresponding aromatic counterparts, the pericondensed quaterrylenes 6 and 7, were synthesized. Their ground-state electronic structures and physical properties were studied by using various experiments assisted with DFT calculations. The proaromatic p-QDM-bridged perylene monoimide dimer 4 has a singlet biradical ground state with a small singlet/triplet energy gap (-2.97 kcalmol-1), whereas the antiaromatic s-indacene-bridged N-annulated perylene dimer 5 exists as a closed-shell quinoid with an obvious intramolecular charge-transfer character. Both of these dimers showed shorter singlet excited-state lifetimes, larger two-photon-absorption cross sections, and smaller energy gaps than the corresponding aromatic quaterrylene derivatives 6 and 7, respectively. Our studies revealed how the fusion mode and aromaticity affect the ground state and, consequently, the photophysical properties and electronic properties of a series of extended polycyclic hydrocarbon compounds. A matter of fusion mode! Fusion of a para-quinodimethane (p-QDM) subunit at the peri and β positions of perylene dimers leads to systems with different ground states, that is, open and closed shell (see picture). These systems showed large two-photon absorption cross sections and ultrafast excited-state dynamics relative to their corresponding pericondensed aromatic quaterrylene counterparts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Probability of color singlet chain states in e+e- annihilation

International Nuclear Information System (INIS)

Wang, Qun; Gustafson, Gosta; Jin, Yi; Xie, Qu-bing

2001-01-01

We use the method of the color effective Hamiltonian to study the structure of color singlet chain states in N c =3 and in the large N c limit. In order to obtain their total fraction when N c is finite, we illustrate how to orthogonalize these nonorthogonal states. We give numerical results for the fraction of orthogonalized states in e + e - ->q bar qgg. With the help of a diagram technique, we derive their fraction up to O(1/N c 2 ) for the general multigluon process. For large N c the singlet chain states correspond to well-defined color topologies. Therefore we may expect that the fraction of non-color-singlet-chain states is an estimate of the fraction of events where color reconnection is possible. In the case of soft gluon bremsstrahlung, we give an explicit form for the color effective Hamiltonian which leads to the dipole cascade formulation for parton showering in leading order in N c . The next-to-leading order corrections are also given for e + e - ->qbar qg 1 g 2 and e + e - ->qbar qg 1 g 2 g 3

Hexameric oligomerization of mitochondrial peroxiredoxin PrxIIF and formation of an ultrahigh affinity complex with its electron donor thioredoxin Trx-o.

Science.gov (United States)

Barranco-Medina, Sergio; Krell, Tino; Bernier-Villamor, Laura; Sevilla, Francisca; Lázaro, Juan-José; Dietz, Karl-Josef

2008-01-01

Mitochondria from plants, yeast, and animals each contain at least one peroxiredoxin (Prx) that is involved in peroxide detoxification and redox signalling. The supramolecular dynamics of atypical type II Prx targeted to the mitochondrion was addressed in pea. Microcalorimetric (ITC) titrations identified an extremely high-affinity binding between the mitochondrial PsPrxIIF and Trx-o with a K(D) of 126+/-14 pM. Binding was driven by a favourable enthalpy change (DeltaH= -60.6 kcal mol(-1)) which was counterbalanced by unfavourable entropy changes (TDeltaS= -47.1 kcal mol(-1)). This is consistent with the occurrence of large conformational changes during binding which was abolished upon site-directed mutaganesis of the catalytic C59S and C84S. The redox-dependent interaction was confirmed by gel filtration of mitochondrial extracts and co-immunoprecipitation from extracts. The heterocomplex of PsPrxIIF and Trx-o reduced peroxide substrates more efficiently than free PsPrxIIF suggesting that Trx-o serves as an efficient and specific electron donor to PsPrxIIF in vivo. Other Trx-s tested by ITC analysis failed to interact with PsPrxIIF indicating a specific recognition of PsPrxIIF by Trx-o. PsPrxIIF exists primarily as a dimer or a hexamer depending on the redox state. In addition to the well-characterized oligomerization of classical 2-Cys Prx the results also show that atypical Prx undergo large structural reorganization with implications for protein-protein interaction and function.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission† †Electronic supplementary information (ESI) available: Actinic pump spectrum, discussion on ground state addition process, peak fitting procedure, transient absorption data, power dependence measurements, etalon pulse shaping, TIPS-pentacene FSRS data, and optimized geometry and frequency calculation results. See DOI: 10.1039/c7sc03496b

Science.gov (United States)

Hart, Stephanie M.; Silva, W. Ruchira

2017-01-01

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes. PMID:29675170

The low-lying electronic states of pentacene and their roles in singlet fission.

Science.gov (United States)

Zeng, Tao; Hoffmann, Roald; Ananth, Nandini

2014-04-16

We present a detailed study of pentacene monomer and dimer that serves to reconcile extant views of its singlet fission. We obtain the correct ordering of singlet excited-state energy levels in a pentacene molecule (E (S1) pentacene, we use a well-developed diabatization scheme to characterize the six low-lying singlet states of a pentacene dimer that approximates the unit cell structure of crystalline pentacene. The local, single-excitonic diabats are not directly coupled with the important multiexcitonic state but rather mix through their mutual couplings with one of the charge-transfer configurations. We analyze the mixing of diabats as a function of monomer separation and pentacene rotation. By defining an oscillator strength measure of the coherent population of the multiexcitonic diabat, essential to singlet fission, we find this population can, in principle, be increased by small compression along a specific crystal direction.

Cross sections for the vibrational excitation of the H2 X 1Σ+g(v) levels generated by electron collisional excitation of the higher singlet states

International Nuclear Information System (INIS)

Hiskes, J.R.

1991-01-01

The excitation cross sections, σ(v,v double-prime), for an H 2 molecule initially in any one of the 15 vibrational levels, v belonging to the ground electronic state and excited to a final vibrational level, v double-prime are evaluated for direct excitations via all members of the excited electronic singlet spectrum. Account is taken of predissociation, autoionization, and radiative decay of the excited electronic spectrum that leads to a final population distribution for the ground electronic state, X 1 Σ + g (v double-prime). For v=0, account is taken explicitly of transitions via the B, C, B', and D electronic states in evaluating the cross sections. The additional contribution of excitations via all Rydberg states lying above the D state enhances these cross sections by approximately 10%. For v>0, cross sections are evaluated taking explicit account of transitions through the B and C states; higher singlet excitations enhance these values by 25%. The choice of the reference total cross sections remains a subjective one, causing the values calculated here to have a possible uncertainty of +20% -30% . For excitations occurring within a hydrogen discharge, collisional excitation-ionization events among the intermediate singlet states will effectively quench the v, v double-prime excitation process for discharge densities in excess of the range 10 15 --10 16 electrons/cm -3

Glow discharge in singlet oxygen

International Nuclear Information System (INIS)

Vagin, N.P.; Ionin, A.A.; Klimachev, Yu.M.; Sinitsyn, D.V.; Yuryshev, N.N.; Kochetov, I.V.; Napartovich, A.P.

2003-01-01

Currently, there is no experimental data on the plasma balance in gas mixtures with a high content of singlet delta oxygen O 2 ( 1 Δ g ). These data can be obtained by studying the parameters of an electric discharge in singlet oxygen produced by a chemical generator. The O 2 ( 1 Δ g ) molecules significantly change the kinetics of electrons and negative ions in plasma. Hence, the discharge conditions at low and high O 2 ( 1 Δ g ) concentrations are very different. Here, the parameters of the positive column of a glow discharge in a gas flow from a chemical singlet-oxygen generator are studied. It is experimentally shown that, at an O 2 ( 1 Δ g ) concentration of 50% and at pressures of 1.5 and 2 torr, the electric field required to sustain the discharge is considerably lower than in the case when all of the oxygen molecules are in the ground state. A theoretical model of the glow discharge is proposed whose predictions are in good agreement with the experimental data

Confinement sensitivity in quantum dot singlet-triplet relaxation

Science.gov (United States)

Wesslén, C. J.; Lindroth, E.

2017-11-01

Spin-orbit mediated phonon relaxation in a two-dimensional quantum dot is investigated using different confining potentials. Elliptical harmonic oscillator and cylindrical well results are compared to each other in the case of a two-electron GaAs quantum dot subjected to a tilted magnetic field. The lowest energy set of two-body singlet and triplet states are calculated including spin-orbit and magnetic effects. These are used to calculate the phonon induced transition rate from the excited triplet to the ground state singlet for magnetic fields up to where the states cross. The roll of the cubic Dresselhaus effect, which is found to be much more important than previously assumed, and the positioning of ‘spin hot-spots’ are discussed and relaxation rates for a few different systems are exhibited.

Highly twisted 1,2:8,9-dibenzozethrenes: Synthesis, ground state, and physical properties

KAUST Repository

Sun, Zhe; Zheng, Bin; Hu, Pan; Huang, Kuo-Wei; Wu, Jishan

2014-01-01

Two soluble and stable 1,2:8,9-dibenzozethrene derivatives (3a,b) are synthesized through a palladium-catalyzed cyclodimerization reaction. X-ray crystallographic analysis shows that these molecules are highly twisted owing to congestion at the cove region. Broken-symmetry DFT calculations predict that they have a singlet biradical ground state with a smaller biradical character and a large singlet-triplet energy gap; these predictions are supported by NMR and electronic absorption measurements. They have small energy gaps and exhibit farred/near-infrared absorption/emission and amphoteric redox behaviors.

Highly twisted 1,2:8,9-dibenzozethrenes: Synthesis, ground state, and physical properties

KAUST Repository

Sun, Zhe

2014-08-08

Two soluble and stable 1,2:8,9-dibenzozethrene derivatives (3a,b) are synthesized through a palladium-catalyzed cyclodimerization reaction. X-ray crystallographic analysis shows that these molecules are highly twisted owing to congestion at the cove region. Broken-symmetry DFT calculations predict that they have a singlet biradical ground state with a smaller biradical character and a large singlet-triplet energy gap; these predictions are supported by NMR and electronic absorption measurements. They have small energy gaps and exhibit farred/near-infrared absorption/emission and amphoteric redox behaviors.

OsPRX2 contributes to stomatal closure and improves potassium deficiency tolerance in rice.

Science.gov (United States)

Mao, Xiaohui; Zheng, Yanmei; Xiao, Kaizhuan; Wei, Yidong; Zhu, Yongsheng; Cai, Qiuhua; Chen, Liping; Xie, Huaan; Zhang, Jianfu

2018-01-01

Peroxiredoxins (Prxs) which are thiol-based peroxidases have been implicated in the toxic reduction and intracellular concentration regulation of hydrogen peroxide. In Arabidopsis thaliana At2-CysPrxB (At5g06290) has been demonstrated to be essential in maintaining the water-water cycle for proper H 2 O 2 scavenging. Although the mechanisms of 2-Cys Prxs have been extensively studied in Arabidopsis thaliana, the function of 2-Cys Prxs in rice is unclear. In this study, a rice homologue gene of At2-CysPrxB, OsPRX2 was investigated aiming to characterize the effect of 2-Cys Prxs on the K + -deficiency tolerance in rice. We found that OsPRX2 was localized in the chloroplast. Overexpressed OsPRX2 causes the stomatal closing and K + -deficiency tolerance increasing, while knockout of OsPRX2 lead to serious defects in leaves phenotype and the stomatal opening under the K + -deficiency tolerance. Detection of K + accumulation, antioxidant activity of transgenic plants under the starvation of potassium, further confirmed that OsPRX2 is a potential target for engineering plants with improved potassium deficiency tolerance. Copyright © 2017 Elsevier Inc. All rights reserved.

Finite-bias conductance anomalies at a singlet-triplet crossing

DEFF Research Database (Denmark)

Stevanato, Chiara; Leijnse, Martin Christian; Flensberg, Karsten

2012-01-01

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...

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.

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

KAUST Repository

Filatov, Mikhail A.; Etzold, Fabian; Gehrig, Dominik; Laquai, Fré dé ric; Busko, Dmitri; Landfester, Katharina; Baluschev, Stanislav

2015-01-01

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.

Theoretical study of singlet oxygen molecule generation via an exciplex with valence-excited thiophene.

Science.gov (United States)

Sumita, Masato; Morihashi, Kenji

2015-02-05

Singlet-oxygen [O2((1)Δg)] generation by valence-excited thiophene (TPH) has been investigated using multireference Møller-Plesset second-order perturbation (MRMP2) theory of geometries optimized at the complete active space self-consistent field (CASSCF) theory level. Our results indicate that triplet TPH(1(3)B2) is produced via photoinduced singlet TPH(2(1)A1) because 2(1)A1 TPH shows a large spin-orbit coupling constant with the first triplet excited state (1(3)B2). The relaxed TPH in the 1(3)B2 state can form an exciplex with O2((3)Σg(-)) because this exciplex is energetically more stable than the relaxed TPH. The formation of the TPH(1(3)B2) exciplex with O2((3)Σg(-)) whose total spin multiplicity is triplet (T1 state) increases the likelihood of transition from the T1 state to the singlet ground or first excited singlet state. After the transition, O2((1)Δg) is emitted easily although the favorable product is that from a 2 + 4 cycloaddition reaction.

Singlet oxygen produced by quasi-continuous photo-excitation of hypericin in dimethyl-sulfoxide

Energy Technology Data Exchange (ETDEWEB)

Varchola, J.; Želonková, K. [Department of Biophysics, Faculty of Science, P. J. Šafárik University, Jesenná 5, 041 54 Košice (Slovakia); Chorvat Jr, D. [International Laser Centre, Ilkovicova 3, 841 05 Bratislava (Slovakia); Jancura, D. [Department of Biophysics, Faculty of Science, P. J. Šafárik University, Jesenná 5, 041 54 Košice (Slovakia); Center for Interdisciplinary Biosciences, Faculty of Science, P. J. Šafárik University, Jesenná 5, 041 54 Košice (Slovakia); Miskovsky, P. [Department of Biophysics, Faculty of Science, P. J. Šafárik University, Jesenná 5, 041 54 Košice (Slovakia); International Laser Centre, Ilkovicova 3, 841 05 Bratislava (Slovakia); Center for Interdisciplinary Biosciences, Faculty of Science, P. J. Šafárik University, Jesenná 5, 041 54 Košice (Slovakia); and others

2016-09-15

Singlet oxygen (O{sub 2}({sup 1}Δ{sub g})) production by photo-excited hypericin (Hyp) dissolved in dimethyl-sulfoxide (DMSO) was studied by means of time-resolved phosphorescence measurements. In order to minimize photo-bleaching, the samples were excited in quasi-continuous mode using long-pulse (35 μs) laser excitation. The measured lifetime of singlet oxygen is τ{sub Δ}=5.5±0.3 μs. This result helps to resolve the discrepancy existing in the literature concerning singlet oxygen lifetime in DMSO. The obtained quantum yield of singlet oxygen photosensitized by Hyp in air-saturated DMSO is Φ{sub Δ}=0.4±0.03. The rate constant for Hyp triplet state depopulation in reaction with ground state molecular oxygen is measured to be k{sub q}=1.6±0.3×10{sup 9} M{sup −1} s{sup −1}.

Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer.

Science.gov (United States)

Nardi, Giacomo; Manet, Ilse; Monti, Sandra; Miranda, Miguel A; Lhiaubet-Vallet, Virginie

2014-12-01

For many biological and biomedical studies, it is essential to detect the production of (1)O2 and quantify its production yield. Among the available methods, detection of the characteristic 1270-nm phosphorescence of singlet oxygen by time-resolved near-infrared (TRNIR) emission constitutes the most direct and unambiguous approach. An alternative indirect method is electron paramagnetic resonance (EPR) in combination with a singlet oxygen probe. This is based on the detection of the TEMPO free radical formed after oxidation of TEMP (2,2,6,6-tetramethylpiperidine) by singlet oxygen. Although the TEMPO/EPR method has been widely employed, it can produce misleading data. This is demonstrated by the present study, in which the quantum yields of singlet oxygen formation obtained by TRNIR emission and by the TEMPO/EPR method are compared for a set of well-known photosensitizers. The results reveal that the TEMPO/EPR method leads to significant overestimation of singlet oxygen yield when the singlet or triplet excited state of the photosensitizer is efficiently quenched by TEMP, acting as electron donor. In such case, generation of the TEMP(+) radical cation, followed by deprotonation and reaction with molecular oxygen, gives rise to an EPR-detectable TEMPO signal that is not associated with singlet oxygen production. This knowledge is essential for an appropriate and error-free application of the TEMPO/EPR method in chemical, biological, and medical studies. Copyright © 2014 Elsevier Inc. All rights reserved.

Scattering Properties of Ground-State 23Na Vapor Using Generalized Scattering Theory

Science.gov (United States)

Al-Harazneh, A. A.; Sandouqa, A. S.; Joudeh, B. R.; Ghassib, H. B.

2018-04-01

The scattering properties of ground-state 23Na vapor are investigated within the framework of the Galitskii-Migdal-Feynman formalism. Viewed as a generalized scattering theory, this formalism is used to calculate the medium phase shifts. The scattering properties of the system—the total, viscosity, spin-exchange, and average cross sections—are then computed using these phase shifts according to standard recipes. The total cross section is found to exhibit the Ramsauer-Townsend effect as well as resonance peaks. These peaks are caused by the large difference between the potentials for electronic spin-singlet and spin-triplet states. They represent quasi-bound states in the system. The results obtained for the complex spin-exchange cross sections are particularly highlighted because of their importance in the spectroscopy of the Na2 dimer. So are the results for the scattering lengths pertaining to both singlet and triplet states. Wherever possible, comparison is made with other published results.

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.

Electron paramagnetic resonance and optical absorption of uranium ions diluted in CdF2 single crystals

International Nuclear Information System (INIS)

Pereira, J.J.C.R.

1976-08-01

The electron paramagnetic resonance (EPR) has been studied in conection with the optical absortion spectra of Uranium ions diluted in CdF 2 single crystals. Analyses of the EPR and optical absorption spectra obtained experimentally, and a comparison with known results in the isomorfic CaF 2 , SrF 2 and BaF 2 , allowed the identification of two paramagnetic centers associated with Uranium ions. These are the U(2+) ion in cubic symmetry having the triplet γ 5 as ground state, and the U(3+) ion in cubic symmetry having the dublet γ 6 as ground state. (Author) [pt

EPR studies of excited state exchange and crystal-field effects in rare earth compounds

International Nuclear Information System (INIS)

Huang, C.Y.; Sugawara, K.; Cooper, B.R.

1976-01-01

EPR in excited crystal-field states of Tm 3+ , Pr 3+ , and Tb 3+ in singlet-ground-state systems and in the excited state of Ce 3+ in CeP are reviewed. Because one is looking at a crystal-field excited state resonance, the exchange, even if isotropic, does not act as a secular perturbation. This means that one obtains different effects and has access to more information about the dynamic effects of exchange than in conventional paramagnetic resonance experiments. The Tm and Pr monopnictides studied are paramagnetic at all temperatures. The most striking feature of the behavior of the GAMMA 5 /sup (2)/ EPR in the Tm compounds is the presence of an anomalous maximum in the temperature dependence of the g-factor. The relationship of this effect to anisotropic exchange is discussed. The results of the EPR of the excited GAMMA 5 /sup (2)/ level of Tb 3 + (g-factor becomes very large at T/sub N/ in antiferromagnetic TbX (X = P, As, Sb) and that of the excited GAMMA 8 level of Ce 3+ in antiferromagnetic CeP will also be reported. For sufficient dilution of the Tb 3+ in the terbium monopnictides, the systems become paramagnetic (Van Vleck paramagnets) down to 0 0 K. The Tb 3+ excited state resonance EPR in Tb/sub 0.1/ La/sub 0.9/P was studied as an example of behavior in such systems. 10 fig

A rigorous nonorthogonal configuration interaction approach for the calculation of electronic couplings between diabatic states applied to singlet fission

NARCIS (Netherlands)

Wibowo, Meilani; Broer, Ria; Havenith, Remco W. A.

2017-01-01

For the design of efficient singlet fission chromophores, knowledge of the factors that govern the singlet fission rate is important. This rate is approximately proportional to the electronic coupling between the lowest (diabatic) spin singlet state that is populated following photoexcitation state

Calculation of the ground and excited states of the Ne2 molecule by the variational cellular method

International Nuclear Information System (INIS)

Dias, A.M.; Rosato, A.

1981-07-01

The potential curves for the ground state 1 Σ + sub(g) and for the first singlet excited state 1 Σ + sub (u) of the Ne 2 molecule are determined by the Variational Cellular Method. From these curves some spectroscopical constants are obtained. Ionization energies of the excited state 1 Σ + sub (u) are calculated. (Author) [pt

Study of a Quantum Dot in an Excited State

Science.gov (United States)

Slamet, Marlina; Sahni, Viraht

We have studied the first excited singlet state of a quantum dot via quantal density functional theory (QDFT). The quantum dot is represented by a 2D Hooke's atom in an external magnetostatic field. The QDFT mapping is from an excited singlet state of this interacting system to one of noninteracting fermions in a singlet ground state. The results of the study will be compared to (a) the corresponding mapping from a ground state of the quantum dot and (b) to the similar mapping from an excited singlet state of the 3D Hooke's atom.

Scheme for generating the singlet state of three atoms trapped in distant cavities coupled by optical fibers

Energy Technology Data Exchange (ETDEWEB)

Wang, Dong-Yang [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Wen, Jing-Ji [College of Foundation Science, Harbin University of Commerce, Harbin, Heilongjiang 150028 (China); Bai, Cheng-Hua; Hu, Shi; Cui, Wen-Xue [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Wang, Hong-Fu, E-mail: hfwang@ybu.edu.cn [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Zhu, Ai-Dong [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Zhang, Shou, E-mail: szhang@ybu.edu.cn [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China)

2015-09-15

An effective scheme is proposed to generate the singlet state with three four-level atoms trapped in three distant cavities connected with each other by three optical fibers, respectively. After a series of appropriate atom–cavity interactions, which can be arbitrarily controlled via the selective pairing of Raman transitions and corresponding optical switches, a three-atom singlet state can be successfully generated. The influence of atomic spontaneous decay, photon leakage of cavities and optical fibers on the fidelity of the state is numerically simulated showing that the three-atom singlet state can be generated with high fidelity by choosing the experimental parameters appropriately.

Calculation of the ground and excited states of the Ne2 molecule by the Variational Cellular Method

International Nuclear Information System (INIS)

Dias, A.M.; Rosato, A.

1982-01-01

The potential curves for the ground 1 μ + sub(g) and for the first singlet excited state 1 μ + sub(u) of the Ne 2 molecule are determined by the Variational Cellular Method. From these curves some spectroscopical constants are obtained. Ionization energies of the excited state 1 μ + sub(u) are calculated. (Author) [pt

Optical and electron paramagnetic resonance studies of the excited triplet states of UV-B absorbers: 2-ethylhexyl salicylate and homomenthyl salicylate.

Science.gov (United States)

Sugiyama, Kazuto; Tsuchiya, Takumi; Kikuchi, Azusa; Yagi, Mikio

2015-09-26

The energy levels and lifetimes of the lowest excited triplet (T1) states of UV-B absorbers, 2-ethylhexyl salicylate (EHS) and homomenthyl salicylate (HMS), and their deprotonated anions (EHS(-) and HMS(-)) were determined through measurements of phosphorescence and electron paramagnetic resonance (EPR) spectra in rigid solutions at 77 K. The observed T1 energies of EHS and HMS are higher than those of butylmethoxydibenzoylmethane, the most widely used UV-A absorber, and octyl methoxycinnamate, the most widely used UV-B absorber. The T1 states of EHS, HMS, EHS(-) and HMS(-) were assigned to almost pure (3)ππ* state from the observed T1 lifetimes and zero-field splitting parameters. EHS and HMS with an intramolecular hydrogen bond show a photoinduced phosphorescence enhancement in ethanol at 77 K. The EPR signals of the T1 states of EHS and HMS also increase in intensity with UV-irradiation time (photoinduced EPR enhancement). The T1 lifetimes of EHS and HMS at room temperature were determined through triplet-triplet absorption measurements in ethanol. The quantum yields of singlet oxygen production by EHS and HMS were determined by using time-resolved near-IR phosphorescence.

Fermionic spin liquid analysis of the paramagnetic state in volborthite

Science.gov (United States)

Chern, Li Ern; Schaffer, Robert; Sorn, Sopheak; Kim, Yong Baek

2017-10-01

Recently, thermal Hall effect has been observed in the paramagnetic state of volborthite, which consists of distorted kagome layers with S =1 /2 local moments. Despite the appearance of magnetic order below 1 K , the response to external magnetic field and unusual properties of the paramagnetic state above 1 K suggest possible realization of exotic quantum phases. Motivated by these discoveries, we investigate possible spin liquid phases with fermionic spinon excitations in a nonsymmorphic version of the kagome lattice, which belongs to the two-dimensional crystallographic group p 2 g g . This nonsymmorphic structure is consistent with the spin model obtained in the density functional theory calculation. Using projective symmetry group analysis and fermionic parton mean field theory, we identify twelve distinct Z2 spin liquid states, four of which are found to have correspondence in the eight Schwinger boson spin liquid states we classified earlier. We focus on the four fermionic states with bosonic counterpart and find that the spectrum of their corresponding root U (1 ) states features spinon Fermi surface. The existence of spinon Fermi surface in candidate spin liquid states may offer a possible explanation of the finite thermal Hall conductivity observed in volborthite.

Effects of Intermolecular Coupling on Excimer Formation and Singlet Fission

Science.gov (United States)

Mauck, Catherine McKay

compelling strategy for improving organic photovoltaic device efficiencies. The formation of triplet states through singlet fission can be characterized using femtosecond visible transient absorption spectroscopy (fsTA). However, in PDI, the triplet-triplet absorption spectrum is strongly overlapped with the ground state bleach absorption. Here, a dyad molecule where PDI is covalently attached to an apocarotene triplet acceptor is synthesized, and studied in solution aggregates and thin films with fsTA, to demonstrate that apocarotene can be used as a sensitive spectral tag for triplet formation in PDI due to triplet-triplet energy transfer from PDI to the carotenoid. The efficiency of singlet fission in DPP can be tuned by modulating the crystal packing in the solid state. By synthesizing 3,6-bis(thiophene) derivatives of DPP with a series of different sidechains, thin film DPP singlet fission is related to the crystal structure intermolecular geometries, to more precisely determine the relationship between interchromophore coupling and singlet fission rate, which will inform the design of more robust chromophores for singlet fission. Finally, the role of the dielectric environment and stabilization of charge transfer configurations and charge transfer states is explored in DPP singlet fission, through aqueous nanoparticles of 3,6-bis(phenylthiophene) with different surface area-to-volume ratios, and a covalently linked dimer of DPP in solvents of varying polarity which can undergo symmetry-breaking charge separation.

Ground States of Ultracold Spin-1 Atoms in a Deep Double-Well Optical Superlattice in a Weak Magnetic Field

International Nuclear Information System (INIS)

Zheng Gong-Ping; Qin Shuai-Feng; Wang Shou-Yang; Jian Wen-Tian

2013-01-01

The ground states of the ultracold spin-1 atoms trapped in a deep one-dimensional double-well optical superlattice in a weak magnetic field are obtained. It is shown that the ground-state diagrams of the reduced double-well model are remarkably different for the antiferromagnetic and ferromagnetic condensates. The transition between the singlet state and nematic state is observed for the antiferromagnetic interaction atoms, which can be realized by modulating the tunneling parameter or the quadratic Zeeman energy. An experiment to distinguish the different spin states is suggested. (general)

Hypoxia and Prx1 in Malignant Progression of Prostate Cancer

Science.gov (United States)

2007-09-01

promoter composition of human prx1 gene and identified EpRE elements and Nrf2 as critical regulatory component of its up- regulation in prostate cancer...nucleus as well as in the cytoplasm in the rat kidney (42). The presence of Prx1 in the nucleolus of hepatic parenchymal cells has also been shown in the...Gpx; KO, knock-out; JNK, c-Jun N-terminal kinase. THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 282, NO. 30, pp. 22011–22022, July 27, 2007 © 2007 by The

Electron scattering from the ground state of mercury

International Nuclear Information System (INIS)

Fursa, D.; Bray, I.

2000-01-01

Full text: Close-coupling calculations have been performed for electron scattering from the ground state of mercury. We have used non-relativistic convergent close-coupling computer code with only minor modifications in order to account for the most prominent relativistic effects. These are the relativistic shift effect and singlet-triplet mixing. Very good agreement with measurements of differential cross sections for elastic scattering and excitation of 6s6p 1 P state at all energies is obtained. It is well recognised that a consistent approach to electron scattering from heavy atoms (like mercury, with nuclear charge Z=80) must be based on a fully relativistic Dirac equations based technique. While development of such technique is under progress in our group, the complexity of the problem ensures that results will not be available in the near future. On other hand, there is considerable interest in reliable theoretical results for electron scattering from heavy atoms from both applications and the need to interpret existing experimental data. This is particularly the case for mercury, which is the major component in fluorescent lighting devices and has been the subject of intense experimental study since nineteen thirties. Similarly to our approach for alkaline-earth atoms we use a model of two valence electrons above an inert Hartree-Fock core to describe the mercury atom. Note that this model does not account for any core excited states which are present in the mercury discrete spectrum. The major effect of missing core-excited states is substantial underestimation of the static dipole polarizability of the mercury ground state (34 a.u.) and consequent underestimation of the forward scattering elastic cross sections. We correct for this by adding in the scattering calculations a phenomenological polarization potential. In order to obtain correct ground state ionization energy for mercury one has to account for the relativistic shift effect. We model this

Concentration of paramagnetic centres at low-temperature thermal destruction of asphaltenes of heavy petroleum distillates

Directory of Open Access Journals (Sweden)

Dolomatov M.U., Rodionov A.A., Gafurov M.R., Petrov A.V., Biktagirov T.B., Bakhtizin R.Z., Makarchikov S.O., Khairudinov I.Z., Orlinskii S.B.

2016-11-01

Full Text Available Changes of paramagnetic centers (PC concentration in dispersed petroleum systems were studied in the process of low-temperature thermolysis. The kinetic model of PC concentration dynamics based on the processes of unpaired electrons formation during singlet-triplet transitions, weak chemical bonds dissociation and recombination of free radicals is proposed.

Metal bacteriochlorins which act as dual singlet oxygen and superoxide generators.

Science.gov (United States)

Fukuzumi, Shunichi; Ohkubo, Kei; Zheng, Xiang; Chen, Yihui; Pandey, Ravindra K; Zhan, Riqiang; Kadish, Karl M

2008-03-06

A series of stable free-base, Zn(II) and Pd(II) bacteriochlorins containing a fused six- or five-member diketo- or imide ring have been synthesized as good candidates for photodynamic therapy sensitizers, and their electrochemical, photophysical, and photochemical properties were examined. Photoexcitation of the palladium bacteriochlorin affords the triplet excited state without fluorescence emission, resulting in formation of singlet oxygen with a high quantum yield due to the heavy atom effect of palladium. Electrochemical studies revealed that the zinc bacteriochlorin has the smallest HOMO-LUMO gap of the investigated compounds, and this value is significantly lower than the triplet excited-state energy of the compound in benzonitrile. Such a small HOMO-LUMO gap of the zinc bacteriochlorin enables intermolecular photoinduced electron transfer from the triplet excited state to the ground state to produce both the radical cation and the radical anion. The radical anion thus produced can transfer an electron to molecular oxygen to produce superoxide anion which was detected by electron spin resonance. The same photosensitizer can also act as an efficient singlet oxygen generator. Thus, the same zinc bacteriochlorin can function as a sensitizer with a dual role in that it produces both singlet oxygen and superoxide anion in an aprotic solvent (benzonitrile).

Antiaromatic bisindeno-[n]thienoacenes with small singlet biradical characters: Syntheses, structures and chain length dependent physical properties

KAUST Repository

Shi, Xueliang

2014-01-01

Recent studies demonstrated that aromaticity and biradical character play important roles in determining the ground-state structures and physical properties of quinoidal polycyclic hydrocarbons and oligothiophenes, a kind of molecular materials showing promising applications for organic electronics, photonics and spintronics. In this work, we designed and synthesized a new type of hybrid system, the so-called bisindeno-[n]thienoacenes (n = 1-4), by annulation of quinoidal fused α-oligothiophenes with two indene units. The obtained molecules can be regarded as antiaromatic systems containing 4n π electrons with small singlet biradical character (y0). Their ground-state geometry and electronic structures were studied by X-ray crystallographic analysis, NMR, ESR and Raman spectroscopy, assisted by density functional theory calculations. With extension of the chain length, the molecules showed a gradual increase of the singlet biradical character accompanied by decreased antiaromaticity, finally leading to a highly reactive bisindeno[4]thienoacene (S4-TIPS) which has a singlet biradical ground state (y0= 0.202). Their optical and electronic properties in the neutral and charged states were systematically investigated by one-photon absorption, two-photon absorption, transient absorption spectroscopy, cyclic voltammetry and spectroelectrochemistry, which could be correlated to the chain length dependent antiaromaticity and biradical character. Our detailed studies revealed a clear structure-aromaticity-biradical character-physical properties-reactivity relationship, which is of importance for tailored material design in the future. This journal is

Fermi Surfaces in the Antiferromagnetic, Paramagnetic and Polarized Paramagnetic States of CeRh2Si2 Compared with Quantum Oscillation Experiments

Science.gov (United States)

Pourret, Alexandre; Suzuki, Michi-To; Palaccio Morales, Alexandra; Seyfarth, Gabriel; Knebel, Georg; Aoki, Dai; Flouquet, Jacques

2017-08-01

The large quantum oscillations observed in the thermoelectric power in the antiferromagnetic (AF) state of the heavy-fermion compound CeRh2Si2 disappear suddenly when entering in the polarized paramagnetic (PPM) state at Hc ˜ 26.5 T, indicating an abrupt reconstruction of the Fermi surface. The electronic band structure was calculated using [LDA+U] for the AF state taking the correct magnetic structure into account, for the PPM state, and for the paramagnetic state (PM). Different Fermi surfaces were obtained for the AF, PM, and PPM states. Due to band folding, a large number of branches was expected and observed in the AF state. The LDA+U calculation was compared with the previous LDA calculations. Furthermore, we compared both calculations with previously published de Haas-van Alphen experiments. The better agreement with the LDA approach suggests that above the critical pressure pc CeRh2Si2 enters in a mixed-valence state. In the PPM state under a high magnetic field, the 4f contribution at the Fermi level EF drops significantly compared with that in the PM state, and the 4f electrons contribute only weakly to the Fermi surface in our approach.

Generation of macroscopic singlet states in atomic ensembles

Science.gov (United States)

Tóth, Géza; Mitchell, Morgan W.

2010-05-01

We study squeezing of the spin uncertainties by quantum non-demolition (QND) measurement in non-polarized spin ensembles. Unlike the case of polarized ensembles, the QND measurements can be performed with negligible back-action, which allows, in principle, perfect spin squeezing as quantified by Tóth et al (2007 Phys. Rev. Lett. 99 250405). The generated spin states approach many-body singlet states and contain a macroscopic number of entangled particles even when individual spin is large. We introduce the Gaussian treatment of unpolarized spin states and use it to estimate the achievable spin squeezing for realistic experimental parameters. Our proposal might have applications for magnetometry with a high spatial resolution or quantum memories storing information in decoherence free subspaces.

Singlet and triplet states of trions in Zinc Selenide-based quantum wells probed by magnetic fields to 50 Tesla

International Nuclear Information System (INIS)

Astakhov, G.V.; Yakovlev, D.R.; Crooker, Scott A.; Barrick, Todd; Dzyubenko, A.B.; Sander, Thomas; Kochereshko, V.P.; Ossau, W.; Faschinger, W.; Waag, A.

2002-01-01

Singlet and triplet states of positively (X + ) and negatively (X - ) charged excitons in ZnSe-based quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. The binding energy of the X - singlet state shows a monotonic increase with magnetic field with a tendency to saturation, while that of the X + slightly decreases. The triplet X + and X - states, being unbound at zero magnetic field, noticeably increase their binding energy in high magnetic fields. The experimental evidence for the interaction between the triplet and singlet states of lTions leading to their anticrossing in magnetic fields has been found.

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.

Sub-Doppler spectroscopy of thioformaldehyde: Excited state perturbations and evidence for rotation-induced vibrational mixing in the ground state

International Nuclear Information System (INIS)

Clouthier, D.J.; Huang, G.; Adam, A.G.; Merer, A.J.

1994-01-01

High-resolution intracavity dye laser spectroscopy has been used to obtain sub-Doppler spectra of transitions to 350 rotational levels in the 4 1 0 band of the A 1 A 2 --X 1 A 1 electronic transition of thioformaldehyde. Ground state combination differences from the sub-Doppler spectra, combined with microwave and infrared data, have been used to improve the ground state rotational and centrifugal distortion constants of H 2 CS. The upper state shows a remarkable number of perturbations. The largest of these are caused by nearby triplet levels, with matrix elements of 0.05--0.15 cm -1 . A particularly clear singlet--triplet avoided crossing in K a ' = 7 has been shown to be caused by interaction with the F 1 component of the 3 1 6 2 vibrational level of the a 3 A 2 state. At least 53% of the S 1 levels show evidence of very small perturbations by high rovibronic levels of the ground state. The number of such perturbations is small at low J, but increases rapidly beyond J=5 such that 40%--80% of the observed S 1 levels of any given J are perturbed by ground state levels. Model calculations show that the density and J dependence of the number of perturbed levels can be explained if there is extensive rotation-induced mixing of the vibrational levels in the ground state

Singlet and triplet states of trions in ZuSe-based quantum wells probed by magnetic fields to 50 Tesla

Energy Technology Data Exchange (ETDEWEB)

Astakhov, G. V.; Yakovlev, D. R.; Crooker, S. A. (Scott A.); Barrick, T. (Todd); Dzyubenko, A. B.; Sander, Thomas; Kochereshko, V. P.; Ossau, W.; Faschinger, W.; Waag, A.

2002-01-01

Singlet and triplet states of positively (X{sup +}) and negatively (X{sup -}) charged excitons in ZnSe-based quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. The binding energy of the X{sup -} singlet state shows a monotonic increase with magnetic field with a tendency to saturation, while that of the X{sup +} slightly decreases. The triplet X{sup +} and X{sup -} states, being unbound at zero magnetic field, noticeably increase their binding energy in high magnetic fields. The experimental evidence for the interaction between the triplet and singlet states of lTions leading to their anticrossing in magnetic fields has been found.

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

KAUST Repository

Sun, Zhe; Lee, Sangsu; Park, Kyuhyung; Zhu, Xiaojian; Zhang, Wenhua; Zheng, Bin; Hu, Pan; Zeng, Zebing; Das, Soumyajit; Li, Yuan; Chi, Chunyan; Li, Runwei; Huang, Kuo-Wei; Ding, Jun; Kim, Dongho; Wu, Jishan

2013-01-01

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

Singlet fission in pentacene dimers

Science.gov (United States)

Zirzlmeier, Johannes; Lehnherr, Dan; Coto, Pedro B.; Chernick, Erin T.; Casillas, Rubén; Basel, Bettina S.; Thoss, Michael; Tykwinski, Rik R.; Guldi, Dirk M.

2015-01-01

Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photon-to-current conversion efficiencies beyond the 30% Shockley–Queisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule. PMID:25858954

Preclinical and first-in-human evaluation of PRX-105, a PEGylated, plant-derived, recombinant human acetylcholinesterase-R

International Nuclear Information System (INIS)

Atsmon, Jacob; Brill-Almon, Einat; Nadri-Shay, Carmit; Chertkoff, Raul; Alon, Sari; Shaikevich, Dimitri; Volokhov, Inna; Haim, Kirsten Y.; Bartfeld, Daniel; Shulman, Avidor; Ruderfer, Ilya; Ben-Moshe, Tehila; Shilovitzky, Orit; Soreq, Hermona; Shaaltiel, Yoseph

2015-01-01

PRX-105 is a plant-derived recombinant version of the human ‘read-through’ acetylcholinesterase splice variant (AChE-R). Its active site structure is similar to that of the synaptic variant, and it displays the same affinity towards organophosphorus (OP) compounds. As such, PRX-105 may serve as a bio-scavenger for OP pesticides and chemical warfare agents. To assess its potential use in prophylaxis and treatment of OP poisoning we conducted several preliminary tests, reported in this paper. Intravenous (IV) PRX-105 was administered to mice either before or after exposure to an OP toxin. All mice who received an IV dose of 50 nmol/kg PRX-105, 2 min before being exposed to 1.33 × LD 50 and 1.5 × LD 50 of toxin and 10 min after exposure to 1.5 × LD 50 survived. The pharmacokinetic and toxicity profiles of PRX-105 were evaluated in mice and mini-pigs. Following single and multiple IV doses (50 to 200 mg/kg) no deaths occurred and no significant laboratory and histopathological changes were observed. The overall elimination half-life (t ½ ) in mice was 994 (± 173) min. Additionally, a first-in-human study, to assess the safety, tolerability and pharmacokinetics of the compound, was conducted in healthy volunteers. The t ½ in humans was substantially longer than in mice (average 26.7 h). Despite the small number of animals and human subjects who were assessed, the fact that PRX-105 exerts a protective and therapeutic effect following exposure to lethal doses of OP, its favorable safety profile and its relatively long half-life, renders it a promising candidate for treatment and prophylaxis against OP poisoning and warrants further investigation. - Highlights: • PRX-105 is a PEGylated plant-derived recombinant human acetylcholinesterase-R. • PRX-105 is a promising bio-scavenger for organophosphorous toxins at lethal doses. • PRX-105 was shown to protect animals both prophylactically and post-poisoning. • First-in-human study exhibited its safety

Preclinical and first-in-human evaluation of PRX-105, a PEGylated, plant-derived, recombinant human acetylcholinesterase-R

Energy Technology Data Exchange (ETDEWEB)

Atsmon, Jacob [Clinical Research Center, Tel Aviv Sourasky Medical Center, Tel Aviv (Israel); Sackler Faculty of Medicine, Tel Aviv University (Israel); Brill-Almon, Einat; Nadri-Shay, Carmit; Chertkoff, Raul; Alon, Sari [Protalix Biotherapeutics, Science Park, Carmiel (Israel); Shaikevich, Dimitri; Volokhov, Inna; Haim, Kirsten Y. [Clinical Research Center, Tel Aviv Sourasky Medical Center, Tel Aviv (Israel); Sackler Faculty of Medicine, Tel Aviv University (Israel); Bartfeld, Daniel [Protalix Biotherapeutics, Science Park, Carmiel (Israel); Shulman, Avidor, E-mail: avidors@protalix.com [Protalix Biotherapeutics, Science Park, Carmiel (Israel); Ruderfer, Ilya; Ben-Moshe, Tehila; Shilovitzky, Orit [Protalix Biotherapeutics, Science Park, Carmiel (Israel); Soreq, Hermona [Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem (Israel); Shaaltiel, Yoseph [Protalix Biotherapeutics, Science Park, Carmiel (Israel)

2015-09-15

PRX-105 is a plant-derived recombinant version of the human ‘read-through’ acetylcholinesterase splice variant (AChE-R). Its active site structure is similar to that of the synaptic variant, and it displays the same affinity towards organophosphorus (OP) compounds. As such, PRX-105 may serve as a bio-scavenger for OP pesticides and chemical warfare agents. To assess its potential use in prophylaxis and treatment of OP poisoning we conducted several preliminary tests, reported in this paper. Intravenous (IV) PRX-105 was administered to mice either before or after exposure to an OP toxin. All mice who received an IV dose of 50 nmol/kg PRX-105, 2 min before being exposed to 1.33 × LD{sub 50} and 1.5 × LD{sub 50} of toxin and 10 min after exposure to 1.5 × LD{sub 50} survived. The pharmacokinetic and toxicity profiles of PRX-105 were evaluated in mice and mini-pigs. Following single and multiple IV doses (50 to 200 mg/kg) no deaths occurred and no significant laboratory and histopathological changes were observed. The overall elimination half-life (t{sub ½}) in mice was 994 (± 173) min. Additionally, a first-in-human study, to assess the safety, tolerability and pharmacokinetics of the compound, was conducted in healthy volunteers. The t{sub ½} in humans was substantially longer than in mice (average 26.7 h). Despite the small number of animals and human subjects who were assessed, the fact that PRX-105 exerts a protective and therapeutic effect following exposure to lethal doses of OP, its favorable safety profile and its relatively long half-life, renders it a promising candidate for treatment and prophylaxis against OP poisoning and warrants further investigation. - Highlights: • PRX-105 is a PEGylated plant-derived recombinant human acetylcholinesterase-R. • PRX-105 is a promising bio-scavenger for organophosphorous toxins at lethal doses. • PRX-105 was shown to protect animals both prophylactically and post-poisoning. • First-in-human study

AgInS{sub 2}-ZnS nanocrystals: Evidence of bistable states using light-induced electron paramagnetic resonance and photoluminescence

Energy Technology Data Exchange (ETDEWEB)

Nobre, Sonia S.; Renard, Olivier; Chevallier, Theo; Le Blevennec, Gilles [Laboratoire d' Innovation pour les Technologies des Energies Nouvelles et les Nanomateriaux, Departement de Technologie des Nano-Materiaux, Service d' Elaboration de Nanomateriaux, Laboratoire de Synthese et Integration des Nanomateriaux, CEA-Grenoble (France); Lombard, Christian; Pepin-Donat, Brigitte [Laboratoire Structure et Proprietes d' Architecture Moleculaire (UMR 5819) CEA-CNRS - UJF/INAC/CEA-Grenoble (France)

2014-04-15

The precursor (AgIn){sub x} Zn{sub 2(1-x)}(S{sub 2}CN(C{sub 2}H{sub 5}){sub 2}){sub 4} was used to prepared AgInS{sub 2}-ZnS nanocrystals with different compositions (x = 0.4 and x = 0.7) and with different time of reaction (10 min and 75 min). The photoluminescence features of the nanocrystals were addressed by combining steady-state spectroscopy and light-induced electron paramagnetic resonance. Both techniques showed the contribution of at least two components for the emission, previously assigned to surface and intrinsic states. Light-induced electron paramagnetic resonance allowed detection of the photocreation both of irreversible paramagnetic species that are likely responsible for the nano-crystals degradation assigned to surface states and of reversible paramagnetic species assigned to intrinsic states. Moreover, reversible bistable paramagnetic states were observed. This Letter provides a scheme that might be useful in addressing the well-known problem of aging of the nanocrystals. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Singlet and triplet polaron relaxation in doubly charged self-assembled quantum dots

International Nuclear Information System (INIS)

Grange, T; Zibik, E A; Ferreira, R; Bastard, G; Carpenter, B A; Phillips, P J; Stehr, D; Winnerl, S; Helm, M; Steer, M J; Hopkinson, M; Cockburn, J W; Skolnick, M S; Wilson, L R

2007-01-01

Polaron relaxation in self-assembled InAs/GaAs quantum dot samples containing 2 electrons per dot is studied using far-infrared, time-resolved pump-probe measurements for transitions between the s-like ground and p-like first excited conduction band states. Spin-flip transitions between singlet and triplet states are observed experimentally in the decay of the absorption bleaching, which shows a clear biexponential dependence. The initial fast decay (∼30 ps) is associated with the singlet polaron decay, while the decay component with the longer time constant (∼5 ns) corresponds to the excited state triplet lifetime. The results are explained by considering the intrinsic Dresselhaus spin-orbit interaction, which induces spin-flip transitions by acoustic phonon emission or phonon anharmonicity. We have calculated the spin-flip decay times, and good agreement is obtained between the experiment and the simulation of the pump-probe signal. Our results demonstrate the importance of spin-mixing effects for intraband energy relaxation in InAs/GaAs quantum dots

Theory of singlet-doublet excitations in praseodymium

International Nuclear Information System (INIS)

Bak, P.

1975-10-01

The magnetic excitation spectrum in a paramagnetic singlet-doublet system is calculated using a diagrammatic high density expansion technique. The lowest order diagrams, which correspond to the random phase approximation (RPA), give a detailed description of the wave vector and temperature dependence of the four exciton modes in praseodymium in terms of a Hamiltonian including isotropic Heisenberg exchange interactions and anisotropic, dipolar-like interactions. The leading contributions to the linewidths of the excitations are obtained by extending the 1/Z expansion of the generalized susceptibility propagators one order beyond the random phase approximation. This damping corresponds to spin wave scattering on single-site fluctuations. The theoretical spectral functions are in detailed agreement with experiment

Time-dependent broken-symmetry density functional theory simulation of the optical response of entangled paramagnetic defects: Color centers in lithium fluoride

Science.gov (United States)

Janesko, Benjamin G.

2018-02-01

Parameter-free atomistic simulations of entangled solid-state paramagnetic defects may aid in the rational design of devices for quantum information science. This work applies time-dependent density functional theory (TDDFT) embedded-cluster simulations to a prototype entangled-defect system, namely two adjacent singlet-coupled F color centers in lithium fluoride. TDDFT calculations accurately reproduce the experimental visible absorption of both isolated and coupled F centers. The most accurate results are obtained by combining spin symmetry breaking to simulate strong correlation, a large fraction of exact (Hartree-Fock-like) exchange to minimize the defect electrons' self-interaction error, and a standard semilocal approximation for dynamical correlations between the defect electrons and the surrounding ionic lattice. These results motivate application of two-reference correlated ab initio approximations to the M-center, and application of TDDFT in parameter-free simulations of more complex entangled paramagnetic defect architectures.

The magnetic structure on the ground state of the equilateral triangular spin tube

International Nuclear Information System (INIS)

Matsui, Kazuki; Goto, Takayuki; Manaka, Hirotaka; Miura, Yoko

2016-01-01

The ground state of the frustrated equilateral triangular spin tube CsCrF_4 is still hidden behind a veil though NMR spectrum broaden into 2 T at low temperature. In order to investigate the spin structure in an ordered state by "1"9F-NMR, we have determined the anisotropic hyperfine coupling tensors for each three fluorine sites in the paramagnetic state. The measurement field was raised up to 10 T to achieve highest resolution. The preliminary analysis using the obtained hyperfine tensors has shown that the archetypal 120°-type structure in ab-plane does not accord with the NMR spectra of ordered state.

Preferential elevation of Prx I and Trx expression in lung cancer cells following hypoxia and in human lung cancer tissues.

Science.gov (United States)

Kim, H J; Chae, H Z; Kim, Y J; Kim, Y H; Hwangs, T S; Park, E M; Park, Y M

2003-10-01

Transient/chronic microenvironmental hypoxia that exists within a majority of solid tumors has been suggested to have a profound influence on tumor growth and therapeutic outcome. Since the functions of novel antioxidant proteins, peroxiredoxin I (Prx I) and II, have been implicated in regulating cell proliferation, differentiation, and apoptosis, it was of our special interest to probe a possible role of Prx I and II in the context of hypoxic tumor microenvironment. Since both Prx I and II use thioredoxin (Trx) as an electron donor and Trx is a substrate for thioredoxin reductase (TrxR), we investigated the regulation of Trx and TrxR as well as Prx expression following hypoxia. Here we show a dynamic change of glutathione homeostasis in lung cancer A549 cells and an up-regulation of Prx I and Trx following hypoxia. Western blot analysis of 10 human lung cancer and paired normal lung tissues also revealed an elevated expression of Prx I and Trx proteins in lung cancer tissues. Immunohistochemical analysis of the lung cancer tissues confirmed an augmented Prx I and Trx expression in cancer cells with respect to the parenchymal cells in adjacent normal lung tissue. Based on these results, we suggest that the redox changes in lung tumor microenvironment could have acted as a trigger for the up-regulation of Prx I and Trx in lung cancer cells. Although the clinical significance of our finding awaits more rigorous future study, preferential augmentation of the Prx I and Trx in lung cancer cells may well represent an attempt of cancer cells to manipulate a dynamic redox change in tumor microenvironment in a manner that is beneficial for their proliferation and malignant progression.

Spin nematics next to spin singlets

Science.gov (United States)

Yokoyama, Yuto; Hotta, Chisa

2018-05-01

We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neither the frustration effect nor spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that interdimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose-Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves includes the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first-order transition.

Actinide chemistry using singlet-paired coupled cluster and its combinations with density functionals

Science.gov (United States)

Garza, Alejandro J.; Sousa Alencar, Ana G.; Scuseria, Gustavo E.

2015-12-01

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 f0 actinyl series (UO22+, NpO23+, PuO24+), the isoelectronic NUN, and thorium (ThO, ThO2+) and nobelium (NoO, NoO2) oxides are studied.

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

On the Josephson effect between superconductors in singlet and triplet spin-pairing states

International Nuclear Information System (INIS)

Pals, J.A.; Haeringen, W. van

1977-01-01

An expression is derived for the Josephson current between two weakly coupled superconductors of which one or both have pairs in a spin-triplet state. It is shown that there can be no Josephson effect up to second order in the transition matrix elements between a superconductor with spin-triplet pairs and one with spin-singlet pairs if the coupling between the two superconductors can be described with a spin-conserving tunnel hamiltonian. This is shown to offer a possibility to investigate experimentally whether a particular superconductor has spin-triplet pairs by coupling it weakly to a well-known spin-singlet pairing superconductor. (Auth.)

Proteomic identification of an embryo-specific 1Cys-Prx promoter and analysis of its activity in transgenic rice.

Science.gov (United States)

Kim, Je Hein; Jung, In Jung; Kim, Dool Yi; Fanata, Wahyu Indra; Son, Bo Hwa; Yoo, Jae Yong; Harmoko, Rikno; Ko, Ki Seong; Moon, Jeong Chan; Jang, Ho Hee; Kim, Woe Yeon; Kim, Jae-Yean; Lim, Chae Oh; Lee, Sang Yeol; Lee, Kyun Oh

2011-04-29

Proteomic analysis of a rice callus led to the identification of 10 abscisic acid (ABA)-induced proteins as putative products of the embryo-specific promoter candidates. 5'-flanking sequence of 1 Cys-Prx, a highly-induced protein gene, was cloned and analyzed. The transcription initiation site of 1 Cys-Prx maps 96 nucleotides upstream of the translation initiation codon and a TATA-box and putative seed-specific cis-acting elements, RYE and ABRE, are located 26, 115 and 124 bp upstream of the transcription site, respectively. β-glucuronidase (GUS) expression driven by the 1 Cys-Prx promoters was strong in the embryo and aleurone layer and the activity reached up to 24.9 ± 3.3 and 40.5 ± 2.1 pmol (4 MU/min/μg protein) in transgenic rice seeds and calluses, respectively. The activity of the 1 Cys-Prx promoters is much higher than that of the previously-identified embryo-specific promoters, and comparable to that of strong endosperm-specific promoters in rice. GUS expression driven by the 1 Cys-Prx promoters has been increased by ABA treatment and rapidly induced by wounding in callus and at the leaf of the transgenic plants, respectively. Furthermore, ectopic expression of the GUS construct in Arabidopsis suggested that the 1 Cys-Prx promoter also has strong activity in seeds of dicot plants. Copyright © 2011 Elsevier Inc. All rights reserved.

Singlet versus Triplet Excited State Mediated Photoinduced Dehalogenation Reactions of Itraconazole in Acetonitrile and Aqueous Solutions.

Science.gov (United States)

Zhu, Ruixue; Li, Ming-de; Du, Lili; Phillips, David Lee

2017-04-06

Photoinduced dehalogenation of the antifungal drug itraconazole (ITR) in acetonitrile (ACN) and ACN/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA, respectively) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR 3 ) experiments. An excited resonance energy transfer is found to take place from the 4-phenyl-4,5-dihydro-3H-1,2,4-triazol-3-one part of the molecule to the 1,3-dichlorobenzene part of the molecule when ITR is excited by ultraviolet light. This photoexcitation is followed by a fast carbon-halogen bond cleavage that leads to the generation of radical intermediates via either triplet and/or singlet excited states. It is found that the singlet excited state-mediated carbon-halogen cleavage is the predominant dehalogenation process in ACN solvent, whereas a triplet state-mediated carbon-halogen cleavage prefers to occur in the ACN/water mixed solutions. The singlet-to-triplet energy gap is decreased in the ACN/water mixed solvents and this helps facilitate an intersystem crossing process, and thus, the carbon-halogen bond cleavage happens mostly through an excited triplet state in the aqueous solutions examined. The ns-TA and ns-TR 3 results also provide some evidence that radical intermediates are generated through a homolytic carbon-halogen bond cleavage via predominantly the singlet excited state pathway in ACN but via mainly the triplet state pathway in the aqueous solutions. In strong acidic solutions, protonation at the oxygen and/or nitrogen atoms of the 1,2,4-triazole-3-one group appears to hinder the dehalogenation reactions. This may offer the possibility that the phototoxicity of ITR due to the generation of aryl or halogen radicals can be reduced by protonation of certain moieties in suitably designed ITR halogen-containing derivatives.

First-Principle Characterization for Singlet Fission Couplings.

Science.gov (United States)

Yang, Chou-Hsun; Hsu, Chao-Ping

2015-05-21

The electronic coupling for singlet fission, an important parameter for determining the rate, has been found to be too small unless charge-transfer (CT) components were introduced in the diabatic states, mostly through perturbation or a model Hamiltonian. In the present work, the fragment spin difference (FSD) scheme was generalized to calculate the singlet fission coupling. The largest coupling strength obtained was 14.8 meV for two pentacenes in a crystal structure, or 33.7 meV for a transition-state structure, which yielded a singlet fission lifetime of 239 or 37 fs, generally consistent with experimental results (80 fs). Test results with other polyacene molecules are similar. We found that the charge on one fragment in the S1 diabatic state correlates well with FSD coupling, indicating the importance of the CT component. The FSD approach is a useful first-principle method for singlet fission coupling, without the need to include the CT component explicitly.

Solid-state NMR paramagnetic relaxation enhancement immersion depth studies in phospholipid bilayers

KAUST Repository

Chu, Shidong; Maltsev, Sergey B.; Emwas, Abdul-Hamid M.; Lorigan, Gary A.

2010-01-01

A new approach for determining the membrane immersion depth of a spin-labeled probe has been developed using paramagnetic relaxation enhancement (PRE) in solid-state NMR spectroscopy. A DOXYL spin label was placed at different sites of 1-palmitoyl-2

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...

Is the Chemical Strategy for Imbuing "Polyene" Character in Diketopyrrolopyrrole-Based Chromophores Sufficient for Singlet Fission?

OpenAIRE

Mukhopadhyay, T; Musser, AJ; Puttaraju, B; Dhar, J; Friend, Richard Henry; Patil, S

2017-01-01

In this work, we have rationally designed and synthesized a novel thiophene-diketopyrrolopyrrole (TDPP)-vinyl-based dimer. We have investigated the optical and electronic properties and have probed the photophysical dynamics using transient absorption to investigate the possibility of singlet exciton fission. These revealed extremely rapid decay to the ground state (

Quantum Monte Carlo study of the singlet-triplet transition in ethylene

International Nuclear Information System (INIS)

El Akramine, Ouafae; Kollias, Alexander C.; Lester, William A. Jr.

2003-01-01

A theoretical study is reported of the transition between the ground state ( 1 A g ) and the lowest triplet state (1 3 B 1u ) of ethylene based on the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo method. Using DMC trial functions constructed from Hartree-Fock, complete active space self-consistent field and multi-configuration self-consistent field wave functions, we have computed the atomization energy and the heat of formation of both states, and adiabatic and vertical energy differences between these states using both all-electron and effective core potential DMC. The ground state atomization energy and heat of formation are found to agree with experiment to within the error bounds of the computation and experiment. Predictions by DMC of the triplet state atomization energy and heat of formation are presented. The adiabatic singlet-triplet energy difference is found to differ by 5 kcal/mol from the value obtained in a recent photodissociation experiment

Differential cross sections for elastic and inelastic n=2 excitation of ground-state helium at 29.6 and 40.1 eV

International Nuclear Information System (INIS)

Brunger, M.J.

1989-11-01

Differential cross sections have been measured for elastic and inelastic scattering of electrons by ground-state helium at 29.6 and 40.1eV. The normalisation of the cross sections is discussed. Theoretical cross sections have been obtained using a 10-state coupled-channels-optical calculation. In general, there is good agreement between theory and experiment for singlet states but not for triplet. 20 refs., 5 tabs., 6 figs

PRX1 knockdown potentiates vitamin K3 toxicity in cancer cells: a potential new therapeutic perspective for an old drug.

Science.gov (United States)

He, Tiantian; Hatem, Elie; Vernis, Laurence; Lei, Ming; Huang, Meng-Er

2015-12-21

significantly up-regulated mRNA and protein levels of NRH:quinone oxidoreductase 2, which was partially responsible for vitK3-induced ROS accumulation and consequent cell death. Our data suggest that PRX1 inactivation could represent an interesting strategy to enhance cancer cell sensitivity to vitK3, providing a potential new therapeutic perspective for this old molecule. Conceptually, a combination of drugs that modulate intracellular redox states and drugs that operate through the generation of ROS could be a new therapeutic strategy for cancer treatment.

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...

Fano-type coupling of a bound paramagnetic state with 2D continuum

International Nuclear Information System (INIS)

Rozhansky, I. V.; Averkiev, N. S.; Lähderanta, E.

2013-01-01

We analyze an effect of a bound impurity state located at a tunnel distance from a quantum well (QW). The study is focused on the resonance case when the bound state energy lies within the continuum of the QW states. Using the developed theory we calculate spin polarization of 2D holes induced by paramagnetic (Mn) delta-layer in the vicinity of the QW and indirect exchange interaction between two impurities located at a tunnel distance from electron gas

Microscopic theory of singlet exciton fission. III. Crystalline pentacene

International Nuclear Information System (INIS)

Berkelbach, Timothy C.; Reichman, David R.; Hybertsen, Mark S.

2014-01-01

We extend our previous work on singlet exciton fission in isolated dimers to the case of crystalline materials, focusing on pentacene as a canonical and concrete example. We discuss the proper interpretation of the character of low-lying excited states of relevance to singlet fission. In particular, we consider a variety of metrics for measuring charge-transfer character, conclusively demonstrating significant charge-transfer character in the low-lying excited states. The impact of this electronic structure on the subsequent singlet fission dynamics is assessed by performing real-time master-equation calculations involving hundreds of quantum states. We make direct comparisons with experimental absorption spectra and singlet fission rates, finding good quantitative agreement in both cases, and we discuss the mechanistic distinctions that exist between small isolated aggregates and bulk systems

Microscopic theory of singlet exciton fission. III. Crystalline pentacene

Energy Technology Data Exchange (ETDEWEB)

Berkelbach, Timothy C., E-mail: tcb2112@columbia.edu; Reichman, David R., E-mail: drr2103@columbia.edu [Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027 (United States); Hybertsen, Mark S., E-mail: mhyberts@bnl.gov [Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)

2014-08-21

We extend our previous work on singlet exciton fission in isolated dimers to the case of crystalline materials, focusing on pentacene as a canonical and concrete example. We discuss the proper interpretation of the character of low-lying excited states of relevance to singlet fission. In particular, we consider a variety of metrics for measuring charge-transfer character, conclusively demonstrating significant charge-transfer character in the low-lying excited states. The impact of this electronic structure on the subsequent singlet fission dynamics is assessed by performing real-time master-equation calculations involving hundreds of quantum states. We make direct comparisons with experimental absorption spectra and singlet fission rates, finding good quantitative agreement in both cases, and we discuss the mechanistic distinctions that exist between small isolated aggregates and bulk systems.

Singlet ground state in the spin-1/2 weakly coupled dimer compound NH4[ (V2O3)2(4,4'-b p y ) 2(H2PO4)(PO4)2] .0.5 H2O

Science.gov (United States)

Arjun, U.; Kumar, Vinod; Anjana, P. K.; Thirumurugan, A.; Sichelschmidt, J.; Mahajan, A. V.; Nath, R.

2017-05-01

We present the synthesis and a detailed investigation of structural and magnetic properties of polycrystalline NH4[(V2O3)2(4,4'-b p y ) 2(H2PO4) (PO4)2] .0.5 H2O by means of x-ray diffraction, magnetic susceptibility, electron spin resonance, and 31P nuclear magnetic resonance measurements. Temperature-dependent magnetic susceptibility could be described well using a weakly coupled spin-1/2 dimer model with an excitation gap Δ /kB≃26.1 K between the singlet ground state and triplet excited states and a weak interdimer exchange coupling J'/kB≃4.6 K. A gapped chain model also describes the data well with a gap of about 20 K. The electron spin resonance intensity as a function of temperature traces the bulk susceptibility nicely. The isotropic Landé g factor is estimated to be about g ≃1.97 , at room temperature. We are able to resolve the 31P NMR signal as coming from two inequivalent P sites in the crystal structure. The hyperfine coupling constant between 31P nucleus and V4 + spins is calculated to be Ahf(1 ) ≃2963 Oe/μB and Ahf(2 ) ≃1466 Oe/μB for the P(1) and P(2) sites, respectively. Our NMR shift and spin-lattice relaxation rate for both the 31P sites show an activated behavior at low temperatures, further confirming the singlet ground state. The estimated value of the spin gap from the NMR data measured in an applied field of H =9.394 T is consistent with the gap obtained from the magnetic susceptibility analysis using the dimer model. Because of a relatively small spin gap, NH4[(V2O3)2(4,4'-b p y ) 2(H2PO4) (PO4)2] .0.5 H2O is a promising compound for further experimental studies under high magnetic fields.

Stability of singlet and triplet trions in carbon nanotubes

International Nuclear Information System (INIS)

Ronnow, Troels F.; Pedersen, Thomas G.; Cornean, Horia D.

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 13.6% stronger than exciton states, and that they lower the optical transition energy with up to 50% of the tight binding band gap energy.

Is the Chemical Strategy for Imbuing "Polyene" Character in Diketopyrrolopyrrole-Based Chromophores Sufficient for Singlet Fission?

Science.gov (United States)

Mukhopadhyay, Tushita; Musser, Andrew J; Puttaraju, Boregowda; Dhar, Joydeep; Friend, Richard H; Patil, Satish

2017-03-02

In this work, we have rationally designed and synthesized a novel thiophene-diketopyrrolopyrrole (TDPP)-vinyl-based dimer. We have investigated the optical and electronic properties and have probed the photophysical dynamics using transient absorption to investigate the possibility of singlet exciton fission. These revealed extremely rapid decay to the ground state (TDPP-V-TDPP under direct photoexcitation. This may be a consequence of significant singlet stabilization in the dimer, bringing it below the energy needed to form two triplets. Our studies on this model compound set valuable lessons for design of novel triplet-forming materials and highlight the need for more broadly applicable design principles.

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.

Coherent-state representation for the QCD ground state

International Nuclear Information System (INIS)

Celenza, L.S.; Ji, C.; Shakin, C.M.

1987-01-01

We make use of the temporal gauge to construct a coherent state which is meant to describe the gluon condensate in the QCD vacuum under the assumption that the condensate is in a zero-momentum mode. The state so constructed is a color singlet and will yield finite, nonperturbative vacuum expectation values such as . (This matrix element is found to have a value of about 0.012 GeV 4 in QCD sum-rule studies.)

Probing the singlet character of the two-hole states in cuprate superconductors

NARCIS (Netherlands)

Ghiringhelli, G; Brookes, NB; Tjeng, LH; Mizokawa, T; Tjernberg, O; Menovsky, AA; Steeneken, P.G.

Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the

Examining tissue composition, whole-bone morphology and mechanical behavior of GorabPrx1 mice tibiae: A mouse model of premature aging.

Science.gov (United States)

Yang, Haisheng; Albiol, Laia; Chan, Wing-Lee; Wulsten, Dag; Seliger, Anne; Thelen, Michael; Thiele, Tobias; Spevak, Lyudmila; Boskey, Adele; Kornak, Uwe; Checa, Sara; Willie, Bettina M

2017-12-08

Gerodermia osteodysplastica (GO) is a segmental progeroid disorder caused by loss-of-function mutations in the GORAB gene, associated with early onset osteoporosis and bone fragility. A conditional mouse model of GO (Gorab Prx1 ) was generated in which the Gorab gene was deleted in long bones. We examined the biomechanical/functional relevance of the Gorab Prx1 mutants as a premature aging model by characterizing bone composition, tissue-level strains, and whole-bone morphology and mechanical properties of the tibia. MicroCT imaging showed that Gorab Prx1 tibiae had an increased anterior convex curvature and decreased cortical cross-sectional area, cortical thickness and moments of inertia, compared to littermate control (LC) tibiae. Fourier transform infrared (FTIR) imaging indicated a 34% decrease in mineral/matrix ratio and a 27% increase in acid phosphate content in the posterior metaphyseal cortex of the Gorab Prx1 tibiae (p finite element analysis showed ∼two times higher tissue-level strains within the Gorab Prx1 tibiae relative to LC tibiae when subjected to axial compressive loads of the same magnitude. Three-point bending tests suggested that Gorab Prx1 tibiae were weaker and more brittle, as indicated by decreasing whole-bone strength (46%), stiffness (55%), work-to-fracture (61%) and post-yield displacement (47%). Many of these morphological and biomechanical characteristics of the Gorab Prx1 tibia recapitulated changes in other animal models of skeletal aging. Future studies are necessary to confirm how our observations might guide the way to a better understanding and treatment of GO. Copyright © 2017 Elsevier Ltd. All rights reserved.

Entanglement sharing via qudit channels: Nonmaximally entangled states may be necessary for one-shot optimal singlet fraction and negativity

Science.gov (United States)

Pal, Rajarshi; Bandyopadhyay, Somshubhro

2018-03-01

We consider the problem of establishing entangled states of optimal singlet fraction and negativity between two remote parties for every use of a noisy quantum channel and trace-preserving local operations and classical communication (LOCC) under the assumption that the parties do not share prior correlations. We show that for a family of quantum channels in every finite dimension d ≥3 , one-shot optimal singlet fraction and entanglement negativity are attained only with appropriate nonmaximally entangled states. A consequence of our results is that the ordering of entangled states in all finite dimensions may not be preserved under trace-preserving LOCC.

Robust singlet fission in pentacene thin films with tuned charge transfer interactions.

Science.gov (United States)

Broch, K; Dieterle, J; Branchi, F; Hestand, N J; Olivier, Y; Tamura, H; Cruz, C; Nichols, V M; Hinderhofer, A; Beljonne, D; Spano, F C; Cerullo, G; Bardeen, C J; Schreiber, F

2018-03-05

Singlet fission, the spin-allowed photophysical process converting an excited singlet state into two triplet states, has attracted significant attention for device applications. Research so far has focused mainly on the understanding of singlet fission in pure materials, yet blends offer the promise of a controlled tuning of intermolecular interactions, impacting singlet fission efficiencies. Here we report a study of singlet fission in mixtures of pentacene with weakly interacting spacer molecules. Comparison of experimentally determined stationary optical properties and theoretical calculations indicates a reduction of charge-transfer interactions between pentacene molecules with increasing spacer molecule fraction. Theory predicts that the reduced interactions slow down singlet fission in these blends, but surprisingly we find that singlet fission occurs on a timescale comparable to that in pure crystalline pentacene. We explain the observed robustness of singlet fission in such mixed films by a mechanism of exciton diffusion to hot spots with closer intermolecular spacings.

Spin-polarized ground state and exact quantization at ν=5/2

Science.gov (United States)

Pan, Wei

2002-03-01

The nature of the even-denominator fractional quantum Hall effect at ν=5/2 remains elusive, in particular, its ground state spin-polarization. An earlier, so-called "hollow core" model arrived at a spin-unpolarized wave function. The more recent calculations based on a model of BCS-like pairing of composite fermions, however, suggest that its ground state is spin-polarized. In this talk, I will first review the earlier experiments and then present our recent experimental results showing evidence for a spin-polarized state at ν=5/2. Our ultra-low temperature experiments on a high quality sample established the fully developed FQHE state at ν=5/2 as well as at ν=7/3 and 8/3, manifested by a vanishing R_xx and exact quantization of the Hall plateau. The tilted field experiments showed that the added in-plane magnetic fields not only destroyed the FQHE at ν=5/2, as seen before, but also induced an electrical anisotropy, which is now interpreted as a phase transition from a paired, spin-polarized ν=5/2 state to a stripe phase, not unlike the ones at ν=9/2, 11/2, etc in the N > 1 higher Landau levels. Furthermore, in the experiments on the heterojunction insulated-gate field-effect transistors (HIGFET) at dilution refrigerator temperatures, a strong R_xx minimum and a concomitant developing Hall plateau were observed at ν=5/2 in a magnetic field as high as 12.6 Tesla. This and the subsequent density dependent studies of its energy gap largely rule out a spin-singlet state and point quite convincingly towards a spin-polarized ground state at ν=5/2.

Antiferrodistortive phase transitions and ground state of PZT ceramics

International Nuclear Information System (INIS)

Pandey, Dhananjai

2013-01-01

resolution neutron powder diffraction data, we have shown that the superlattice peaks of the pure PZT and the 6% Sr 2+ substituted PZT are not singlets ruling out the R3c space group for the ground state phase. Rietveld refinements results reconfirm the Cc space group for the ground state phase. In this talk I propose to discuss these findings which have led to significant modification of the phase diagram of the PZT. (author)

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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetism of singlet - singlet ions interacting with an electron gas: application to PrAl2

International Nuclear Information System (INIS)

Palermo, L.

1986-01-01

Various magnetic quantities are investigated for a system consisting of singlet-singlet ions interacting with an electron gas. In obtaining the magnetic state equations, the molecular field approximation is used. At T=0, an onset magnetic order condition in function of crystal field and exchange parameters and eletronic density of states at Fermi level is derived. A parametric study of the model is performed numerically. Main results are shown on diagrams. From the experimental data existent in the literature for magnetisation, susceptibility and magnetic specific heat of the PrAl 2 , a fitting with the model predictions is obtained using the following parameters: exchange interaction: 611meV; crystal field parameters: 2,5 meV; band with: 10 eV (of a rectangular density of states with 0,8 el/atom). (author) [pt

Fermi surface properties of paramagnetic NpCd11 with a large unit cell

Science.gov (United States)

Homma, Yoshiya; Aoki, Dai; Haga, Yoshinori; Settai, Rikio; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Takeuchi, Tetsuya; Yamagami, Hiroshi; Ōnuki, Yoshichika

2010-03-01

We succeeded in growing a high-quality single crystal of NpCd11 with the cubic BaHg11-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 105 to 1.9 x 107 Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd11 is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np3+(5f4) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m0, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K2·mol, revealing no hybridization between the 5f electrons and conduction electrons.

Photo-excitation of carotenoids causes cytotoxicity via singlet oxygen production

International Nuclear Information System (INIS)

Yoshii, Hiroshi; Yoshii, Yukie; Asai, Tatsuya; Furukawa, Takako; Takaichi, Shinichi; Fujibayashi, Yasuhisa

2012-01-01

Highlights: ► Some photo-excited carotenoids have photosensitizing ability. ► They are able to produce ROS. ► 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 β-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.

Nuclear and solid state investigations for the non-cubic paramagnetic system europium in samarium

International Nuclear Information System (INIS)

Boehm, R.

1979-01-01

By means of the time-differential perturbed angular gamma distribution after a nuclear reaction (TDPAD) the g-values of the isomer 1 1/2 - states are measured in 145 Eu and 147 Eu in the host metal Sm. The results are g ( 145 Eu) = + 1.356 + 0.008 g ( 147 Eu) = + 1.28 +- 0.01. The temperature dependence of the paramagnetic correction β obeys a Curie-Weiss law β = 1 + C/CT-, with C = -(50 +- 2) K and THETA = -(29 +- 5) K between 90 K and 1000 K, for both systems, 145 EU Sm and 147 Eu Sm. For room temperature the quadrupole coupling constant νsub(Q) is determined for 145 Eu Sm for the 1 1/2 - state: νsub(Q) = (12.5 +- 0.5) MHz and the paramagnetic relaxation time tausub(p) >= 1 μs. The g values are investigated also theoretically. (BHO)

Unveiling Singlet Fission Mediating States in TIPS-pentacene and its Aza Derivatives.

Science.gov (United States)

Herz, Julia; Buckup, Tiago; Paulus, Fabian; Engelhart, Jens U; Bunz, Uwe H F; Motzkus, Marcus

2015-06-25

Femtosecond pump-depletion-probe experiments were carried out in order to shed light on the ultrafast excited-state dynamics of triisopropylsilylethynyl (TIPS)-pentacene and two nitrogen-containing derivatives, namely, diaza-TIPS-pentacene and tetraaza-TIPS-pentacene. Measurements performed in the visible and near-infrared spectral range in combination with rate model simulations reveal that singlet fission proceeds via the extremely short-lived intermediate (1)TT state, which absorbs in the near-infrared spectral region only. The T1 → T3 transition probed in the visible region shows a rise time that comprises two components according to a consecutive reaction (S1 → (1)TT → T1). The incorporation of nitrogen atoms into the acene structure leads to shorter dynamics, but the overall triplet formation follows the same kinetic model. This is of particular importance, since experiments on tetraaza-TIPS-pentacene allow for investigation of the triplet state in the visible range without an overlapping singlet contribution. In addition, the pump-depletion-probe experiments show that the triplet absorption in the visible (T1 → T3) and near-infrared (T1 → T2) regions occurs from the same initial state, which was questioned in previous studies. Furthermore, an additional ultrafast transfer between the excited triplet states (T3 → T2) is identified, which is also in agreement with the rate model simulation. By applying depletion pulses, which are resonant with higher vibrational levels, we gain insight into internal vibrational energy redistribution processes within the triplet manifold. This additional information is of great relevance regarding the study of loss channels within these materials.

Isolation of EPR spectra and estimation of spin-states in two-component mixtures of paramagnets.

Science.gov (United States)

Chabbra, Sonia; Smith, David M; Bode, Bela E

2018-04-26

The presence of multiple paramagnetic species can lead to overlapping electron paramagnetic resonance (EPR) signals. This complication can be a critical obstacle for the use of EPR to unravel mechanisms and aid the understanding of earth abundant metal catalysis. Furthermore, redox or spin-crossover processes can result in the simultaneous presence of metal centres in different oxidation or spin states. In this contribution, pulse EPR experiments on model systems containing discrete mixtures of Cr(i) and Cr(iii) or Cu(ii) and Mn(ii) complexes demonstrate the feasibility of the separation of the EPR spectra of these species by inversion recovery filters and the identification of the relevant spin states by transient nutation experiments. We demonstrate the isolation of component spectra and identification of spin states in a mixture of catalyst precursors. The usefulness of the approach is emphasised by monitoring the fate of the chromium species upon activation of an industrially used precatalyst system.

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 tools...... including across the cell membrane into the extracellular environment. On one hand, these results demonstrate that the behavior of singlet oxygen in an intact cell can be significantly different from that inferred from model bulk studies. More generally, these results provide a new perspective...

Paramagnetic properties of the low- and high-spin states of yeast cytochrome c peroxidase

International Nuclear Information System (INIS)

Vanwetswinkel, Sophie; Nuland, Nico A. J. van; Volkov, Alexander N.

2013-01-01

Here we describe paramagnetic NMR analysis of the low- and high-spin forms of yeast cytochrome c peroxidase (CcP), a 34 kDa heme enzyme involved in hydroperoxide reduction in mitochondria. Starting from the assigned NMR spectra of a low-spin CN-bound CcP and using a strategy based on paramagnetic pseudocontact shifts, we have obtained backbone resonance assignments for the diamagnetic, iron-free protein and the high-spin, resting-state enzyme. The derived chemical shifts were further used to determine low- and high-spin magnetic susceptibility tensors and the zero-field splitting constant (D) for the high-spin CcP. The D value indicates that the latter contains a hexacoordinate heme species with a weak field ligand, such as water, in the axial position. Being one of the very few high-spin heme proteins analyzed in this fashion, the resting state CcP expands our knowledge of the heme coordination chemistry in biological systems

Paramagnetic properties of the low- and high-spin states of yeast cytochrome c peroxidase

Energy Technology Data Exchange (ETDEWEB)

Vanwetswinkel, Sophie; Nuland, Nico A. J. van; Volkov, Alexander N., E-mail: ovolkov@vub.ac.be [Vrije Universiteit Brussel, Jean Jeener NMR Centre, Structural Biology Brussels (Belgium)

2013-09-15

Here we describe paramagnetic NMR analysis of the low- and high-spin forms of yeast cytochrome c peroxidase (CcP), a 34 kDa heme enzyme involved in hydroperoxide reduction in mitochondria. Starting from the assigned NMR spectra of a low-spin CN-bound CcP and using a strategy based on paramagnetic pseudocontact shifts, we have obtained backbone resonance assignments for the diamagnetic, iron-free protein and the high-spin, resting-state enzyme. The derived chemical shifts were further used to determine low- and high-spin magnetic susceptibility tensors and the zero-field splitting constant (D) for the high-spin CcP. The D value indicates that the latter contains a hexacoordinate heme species with a weak field ligand, such as water, in the axial position. Being one of the very few high-spin heme proteins analyzed in this fashion, the resting state CcP expands our knowledge of the heme coordination chemistry in biological systems.

Optical and paramagnetic properties of Ti in LiF

International Nuclear Information System (INIS)

Krystek, M.

1982-01-01

Titanium replaces substitutionally Li + at its lattice site in LiF. The resulting deep impurity must be understood as TiF 6 -cluster. The symmetry of this cluster is octahedral in the case of the unoccupied impurity. If the impurity will be occupied by an electron, a trigonal distortion of the cluster results, whereby the orbital degeneracy of the ground state will be liftet. Since the occupied impurity is paramagnetic, the symmetry reduction could be proved by ENDOR measurements. Using a calculated term diagram of the impurity inside the crystal a model is offered to explain the photoluminescence and the thermoluminescence of LiF:Ti. (orig./HP) [de

Solid-state NMR paramagnetic relaxation enhancement immersion depth studies in phospholipid bilayers

KAUST Repository

Chu, Shidong

2010-11-01

A new approach for determining the membrane immersion depth of a spin-labeled probe has been developed using paramagnetic relaxation enhancement (PRE) in solid-state NMR spectroscopy. A DOXYL spin label was placed at different sites of 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholine (PSPC) phospholipid bilayers as paramagnetic moieties and the resulting enhancements of the longitudinal relaxation (T1) times of 31P nuclei on the surface of the bilayers were measured by a standard inversion recovery pulse sequence. The 31P NMR spin-lattice relaxation times decrease steadily as the DOXYL spin label moves closer to the surface as well as the concentration of the spin-labeled lipids increase. The enhanced relaxation vs. the position and concentration of spin-labels indicate that PRE induced by the DOXYL spin label are significant to determine longer distances over the whole range of the membrane depths. When these data were combined with estimated correlation times τc, the r-6-weighted, time-averaged distances between the spin-labels and the 31P nuclei on the membrane surface were estimated. The application of using this solid-state NMR PRE approach coupled with site-directed spin labeling (SDSL) may be a powerful method for measuring membrane protein immersion depth. © 2010 Elsevier Inc. All rights reserved.

A novel chalcone-analogue as an optical sensor based on ground and excited states intramolecular charge transfer: A combined experimental and theoretical study

International Nuclear Information System (INIS)

Fayed, Tarek A.

2006-01-01

Steady-state absorption and emission spectroscopic techniques as well as semiempirical quantum calculations at the AM1 and ZINDO/S levels have been used to investigate the intramolecular charge transfer (ICT) behaviour of a novel chalcone namely; 1-(2-pyridyl)-5-(4-dimethylaminophenyl)-penta-2,4-diene-1-one, DMAC. The ground state DMAC has a significant ICT character and a great sensitivity to the hydrogen bond donating ability of the medium as reflected from the change of the absorption spectra in pure and mixed organic solvents. On the other hand, its excited singlet state exhibits high ICT characters as manifested by the drastic solvatochromic effects. These results are consistent with the data of charge density calculations in both the ground and excited state, which indicates enhancement of the charge transfer from the dimethyl-amino group to the carbonyl oxygen upon excitation. Also, the dipole moment calculations indicates a highly dipolar excited singlet state (Δμ eg = 15.5 D). The solvent dependence of the fluorescence quantum yield of DMAC was interpreted on the basis of positive and negative solvatokinetic as well as the hydrogen bonding effects. Incorporation of the 2-pyridyl group in the chemical structure of the present DMAC led to design of a potential optical sensor for probing acidity of the medium and metal cations such as Zn 2+ , Cd 2+ and Hg 2+ . This was concluded from the high acidochromic and metallochromic behaviour of DMAC on adding such cations to its acetonitrile solutions

Singlet oxygen: photosensitized generation, detection and reaction with organic molecules

Energy Technology Data Exchange (ETDEWEB)

Barik, Atanu; Indira Priyadarsini, K; Mohan, Hari; Bajaj, P N; Sapre, A V; Mittal, J P; Mukherjee, T [Radiation and Photochemistry Div., Bhabha Atomic Research Centre, Mumbai (India)

2006-10-15

Singlet molecular oxygen ({sup 1}O{sub 2}) is an excited state of molecular oxygen, having antiparallel spin in the same {pi} antibonding orbital. The study of singlet oxygen production and reactivity has emerged as a rich and diverse area, with implication in diverse fields, such as synthetic chemistry, polymer chemistry, photodynamic therapy, etc. There are several known methods to produce singlet oxygen, and also various techniques employed to detect it. Out of these, photosensitization method is the most popular one. In this article, photosensitized production of singlet oxygen from triplet oxygen and photosensitizers in presence of light, and its detection by the infrared luminescence at 1270 nm have been presented. Further, some results using different types of photosensitizers, effect of solvent on singlet oxygen quantum yields and lifetime have been discussed. The quenching rate constants of singlet oxygen have been determined with different types of organic molecules such as derivatives of thiourea and its analogues, hydroxy indoles and antioxidants and the results have been presented. (author)

Singlet oxygen: photosensitized generation, detection and reaction with organic molecules

International Nuclear Information System (INIS)

Barik, Atanu; Indira Priyadarsini, K.; Hari Mohan; Bajaj, P.N.; Sapre, A.V.; Mittal, J.P.; Mukherjee, T.

2006-10-01

Singlet molecular oxygen ( 1 O 2 ) is an excited state of molecular oxygen, having antiparallel spin in the same π antibonding orbital. The study of singlet oxygen production and reactivity has emerged as a rich and diverse area, with implication in diverse fields, such as synthetic chemistry, polymer chemistry, photodynamic therapy, etc. There are several known methods to produce singlet oxygen, and also various techniques employed to detect it. Out of these, photosensitization method is the most popular one. In this article, photosensitized production of singlet oxygen from triplet oxygen and photosensitizers in presence of light, and its detection by the infrared luminescence at 1270 nm have been presented. Further, some results using different types of photosensitizers, effect of solvent on singlet oxygen quantum yields and lifetime have been discussed. The quenching rate constants of singlet oxygen have been determined with different types of organic molecules such as derivatives of thiourea and its analogues, hydroxy indoles and antioxidants and the results have been presented. (author)

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

Quinoidal Oligo(9,10-anthryl)s with Chain-Length-Dependent Ground States: A Balance between Aromatic Stabilization and Steric Strain Release

KAUST Repository

Lim, Zhenglong

2015-11-12

Quinoidal π-conjugated polycyclic hydrocarbons have attracted intensive research interest due to their unique optical/electronic properties and possible magnetic activity, which arises from a thermally excited triplet state. However, there is still lack of fundamental understanding on the factors that determine the electronic ground states. Herein, by using quinoidal oligo(9,10-anthryl)s, it is demonstrated that both aromatic stabilisation and steric strain release play balanced roles in determining the ground states. Oligomers with up to four anthryl units were synthesised and their ground states were investigated by electronic absorption and electron spin resonance (ESR) spectroscopy, assisted by density functional theory (DFT) calculations. The quinoidal 9,10-anthryl dimer 1 has a closed-shell ground state, whereas the tri- (2) and tetramers (3) both have an open-shell diradical ground state with a small singlet-triplet gap. Such a difference results from competition between two driving forces: the large steric repulsion between the anthryl/phenyl units in the closed-shell quinoidal form that drives the molecule to a flexible open-shell diradical structure, and aromatic stabilisation due to the gain of more aromatic sextet rings in the closed-shell form, which drives the molecule towards a contorted quinoidal structure. The ground states of these oligomers thus depend on the overall balance between these two driving forces and show chain-length dependence. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Colour-singlet exchange and tests of models of diffractive DIS

International Nuclear Information System (INIS)

Williams, J.C.

2000-03-01

Diffractive deep-inelastic scattering events observed at the HERA electron-proton collider are interpreted as an interaction involving a virtual photon scattering off a colour-singlet state within the proton. Models which attempt to describe the colour-singlet exchanged in diffractive interactions range from the purely phenomenological Donnachie-Landshoff form factor approach to the QCD-motivated gluon-exchange models and the scalar-pomeron model. It is important to find ways to test these models. In this thesis colour-singlet exchange models of diffractive DIS are compared with cross section and structure function data from the H1 detector. H1 select diffractive data by requiring there to be a large angle between the forward proton direction and any other significant detector activity. This pseudo-rapidity gap cut extracts colour-singlet exchange events from the standard DIS data sample. For a wide range of the parameter space covered by the HERA experiments, however, the pseudo-rapidity gap cuts restrict the final-state phase space available for diffractive scattering. One consequence is that pseudo-rapidity gap cuts can be used to select diffractive events in which the colour-singlet only couples to off-shell partons. To leading order in the strong coupling constant, the diffractive final state consists of a quark-antiquark pair. Higher-order events include diffractive production of quark-antiquark-gluon states. In the region where pseudo-rapidity gap cuts restrict the accessible phase space, the cuts reject low transverse momentum quark-antiquark diffractive events. Pseudo-rapidity gap data selection cuts also allow selection of an enhanced 3-jet data sample. The structure function and transverse momentum distribution data can be described by either a two-gluon model or by the Donnachie-Landshoff model, both models requiring a significant contribution from quark-antiquark-gluon diffractive final states to fit the full kinematic range of the diffractive data

Singlet channel coupling in deuteron elastic scattering at intermediate energies

International Nuclear Information System (INIS)

Al-Khalili, J.S.; Tostevin, J.A.; Johnson, R.C.

1990-01-01

Intermediate energy deuteron elastic scattering is investigated in a three-body model incorporating relativistic kinematics. The effects of deuteron breakup to singlet spin intermediate states, on the elastic scattering observables for the 58 Ni(d vector, d) 58 Ni reaction at 400 and 700 MeV, are studied quantitatively. The singlet-breakup contributions to the elastic amplitude are estimated within an approximate two-step calculation. The calculation makes an adiabatic approximation in the intermediate states propagator which allows the use of closure over the np intermediate states continuum. The singlet channel coupling is found to produce large effects on the calculated reaction tensor analysing power A yy , characteristic of a dynamically induced second-rank tensor interaction. By inspection of the calculated breakup amplitudes we show this induced interaction to be of the T L tensor type. (orig.)

The ground state magnetic moment and susceptibility of a two electron Gaussian quantum dot

Science.gov (United States)

Boda, Aalu; Chatterjee, Ashok

2018-04-01

The problem of two interacting electrons moving in a two-dimensional semiconductor quantum dot with Gaussian confinement under the influence of an external magnetic field is studied by using a method of numerical diagonalization of the Hamiltonian matrix with in the effective-mass approximation. The energy spectrum is calculated as a function of the magnetic field. We find the ground state magnetic moment and the magnetic susceptibility show zero temperature diamagnetic peaks due to exchange induced singlet-triplet oscillations. The position and the number of these peaks depend on the size of the quantum dot and also strength of the electro-electron interaction. The theory is applied to a GaAs quantum dot.

Electron paramagnetic resonance

CERN Document Server

Al'tshuler, S A

2013-01-01

Electron Paramagnetic Resonance is a comprehensive text on the field of electron paramagnetic resonance, covering both the theoretical background and the results of experiment. This book is composed of eight chapters that cover theoretical materials and experimental data on ionic crystals, since these are the materials that have been most extensively studied by the methods of paramagnetic resonance. The opening chapters provide an introduction to the basic principles of electron paramagnetic resonance and the methods of its measurement. The next chapters are devoted to the theory of spectra an

Detection of Multiconfigurational States of Hydrogen-Passivated Silicene Nanoclusters.

Science.gov (United States)

Pablo-Pedro, Ricardo; Lopez-Rios, Hector; Fomine, Serguei; Dresselhaus, Mildred S

2017-02-02

Utilizing density functional theory (DFT) and a complete active space self-consistent field (CASSCF) approach,we study the electronic properties of rectangular silicene nano clusters with hydrogen passivated edges denoted by H-SiNCs (n z ,n a ), with n z and n a representing the zigzag and armchair directions, respectively. The results show that in the n z direction, the H-SiNCs prefer to be in a singlet (S = 0) ground state for n z > n a . However, a transition from a singlet (S = 0) to a triplet (S = 1) ground state is revealed for n a > n z . Through the calculated Raman spectrum, the S = 0 and S = 1 ground states can be observed by the E 2g (G) and A (D) Raman modes. Furthermore, H-SiNC clusters are shown to have HOMO-LUMO (HL) energy gaps, which decrease as a function of n a and n z for S = 0 and S = 1 states. The H-SiNC with a S = 1 ground state can be potentially used for silicene-based spintronic devices.

Detection of Multiconfigurational States of Hydrogen-Passivated Silicene Nanoclusters

KAUST Repository

Pablo-Pedro, Ricardo; Lopez-Rios, Hector; Fomine, Serguei; Dresselhaus, Mildred S.

2017-01-01

Utilizing density functional theory (DFT) and a complete active space self-consistent field (CASSCF) approach,we study the electronic properties of rectangular silicene nano clusters with hydrogen passivated edges denoted by H-SiNCs (nz,na), with nz and na representing the zigzag and armchair directions, respectively. The results show that in the nz direction, the H-SiNCs prefer to be in a singlet (S = 0) ground state for nz > na. However, a transition from a singlet (S = 0) to a triplet (S = 1) ground state is revealed for na > nz. Through the calculated Raman spectrum, the S = 0 and S = 1 ground states can be observed by the E2g (G) and A (D) Raman modes. Furthermore, H-SiNC clusters are shown to have HOMO–LUMO (HL) energy gaps, which decrease as a function of na and nz for S = 0 and S = 1 states. The H-SiNC with a S = 1 ground state can be potentially used for silicene-based spintronic devices.

Detection of Multiconfigurational States of Hydrogen-Passivated Silicene Nanoclusters

KAUST Repository

Pablo-Pedro, Ricardo

2017-01-16

Utilizing density functional theory (DFT) and a complete active space self-consistent field (CASSCF) approach,we study the electronic properties of rectangular silicene nano clusters with hydrogen passivated edges denoted by H-SiNCs (nz,na), with nz and na representing the zigzag and armchair directions, respectively. The results show that in the nz direction, the H-SiNCs prefer to be in a singlet (S = 0) ground state for nz > na. However, a transition from a singlet (S = 0) to a triplet (S = 1) ground state is revealed for na > nz. Through the calculated Raman spectrum, the S = 0 and S = 1 ground states can be observed by the E2g (G) and A (D) Raman modes. Furthermore, H-SiNC clusters are shown to have HOMO–LUMO (HL) energy gaps, which decrease as a function of na and nz for S = 0 and S = 1 states. The H-SiNC with a S = 1 ground state can be potentially used for silicene-based spintronic devices.

New strategies to produce and detect singlet oxygen in a cell

DEFF Research Database (Denmark)

Gollmer, Anita

2012-01-01

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......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......, 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...

Origins of Singlet Fission in Solid Pentacene from an ab initio Green's Function Approach

Science.gov (United States)

Refaely-Abramson, Sivan; da Jornada, Felipe H.; Louie, Steven G.; Neaton, Jeffrey B.

2017-12-01

We develop a new first-principles approach to predict and understand rates of singlet fission with an ab initio Green's-function formalism based on many-body perturbation theory. Starting with singlet and triplet excitons computed from a G W plus Bethe-Salpeter equation approach, we calculate the exciton-biexciton coupling to lowest order in the Coulomb interaction, assuming a final state consisting of two noninteracting spin-correlated triplets with finite center-of-mass momentum. For crystalline pentacene, symmetries dictate that the only purely Coulombic fission decay process from a bright singlet state requires a final state consisting of two inequivalent nearly degenerate triplets of nonzero, equal and opposite, center-of-mass momenta. For such a process, we predict a singlet lifetime of 30-70 fs, in very good agreement with experimental data, indicating that this process can dominate singlet fission in crystalline pentacene. Our approach is general and provides a framework for predicting and understanding multiexciton interactions in solids.

Nonlinear magnetoelectric effect and magnetostriction in piezoelectric CsCuCl{sub 3} in paramagnetic and antiferromagnetic states

Energy Technology Data Exchange (ETDEWEB)

Kharkovskiy, A. I., E-mail: akharkovskiy@inbox.ru [International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, 53-421 Wrocław (Poland); L.F. Vereshchagin Institute for High Pressure Physics RAS, 142190 Troitsk, Moscow (Russian Federation); Shaldin, Yu. V. [International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, 53-421 Wrocław (Poland); Institute for Crystallography RAS, Lenin' s Avenue 59, 119333 Moscow (Russian Federation); Nizhankovskii, V. I. [International Laboratory of High Magnetic Fields and Low Temperatures, Gajowicka 95, 53-421 Wrocław (Poland)

2016-01-07

The direct nonlinear magnetoelectric (ME) effect and the magnetostriction of piezoelectric CsCuCl{sub 3} single crystals were comprehensively studied over a wide temperature range in stationary magnetic fields of up to 14 T. The direct nonlinear ME effect measurements were also performed in pulsed magnetic fields up to 31 T, at liquid helium temperature in the antiferromagnetic (AF) state for the crystallographic direction in which effect has the maximum value. The nonlinear ME effect was quadratic in the paramagnetic state for the whole range of magnetic fields. In the AF state the phase transition between different configurations of spins manifested itself as plateau-like peculiarity on the nonlinear ME effect. The nonlinear ME effect was saturated by the phase transition to the spin-saturated paramagnetic state. Two contributions to the nonlinear ME effects in CsCuCl{sub 3} were extracted from the experimental data: the intrinsic ME effect originated from the magnetoelectric interactions, and the extrinsic one, which resulted from a magnetostriction-induced piezoelectric effect.

Explicit role of dynamical and nondynamical electron correlation on singlet-triplet splitting in carbenes

International Nuclear Information System (INIS)

Seal, Prasenjit; Chakrabarti, Swapan

2007-01-01

Density functional theoretical studies have been performed on carbene systems to determine the singlet-triplet splitting and also to explore the role of electron correlation. Using an approximate method of separation of dynamical and nondynamical correlation, it is found that dynamical and nondynamical electron correlation stabilizes the singlet state relative to the triplet for halo carbenes in both BLYP and B3LYP methods. Calculations performed on higher homologues of methylene suggest that beyond CH(CH 3 ), both the electron correlations have leveling effect in stabilizing the singlet state relative to the triplet. It has also been observed while dynamical electron correlation fails to provide any substantial degree of stabilization to the singlet states of higher homologues of methylene in B3LYP method, an opposite trend is observed for nondynamical counterpart. Among the larger systems studied (9-triptycyl)(α-naphthyl)-carbene has the highest stability of the triplet state whereas bis-imidazol-2-ylidenes has the most stable singlet state. Interestingly, the values of the dynamical electron correlation for each state of each system studied are different for the two methods used. The reason behind this apparent discrepancy lies in the fact that the coefficients of the LYP part in B3LYP and BLYP functionals are different

Singlet-triplet annihilation in single LHCII complexes

NARCIS (Netherlands)

Gruber, J.M.; Chmeliov, J.; Kruger, T.P.J.; Valkunas, L.; van Grondelle, R.

2015-01-01

In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching

Study of actinide paramagnetism in solution

International Nuclear Information System (INIS)

Autillo, Matthieu

2015-01-01

The physiochemical properties of actinide (An) solutions are still difficult to explain, particularly the behavioral differences between An(III) and Ln(III). The study of actinide paramagnetic behavior may be a 'simple' method to analyze the electronic properties of actinide elements and to obtain information on the ligand-actinide interaction. The objective of this PhD thesis is to understand the paramagnetic properties of these elements by magnetic susceptibility measurements and chemical shift studies. Studies on actinide electronic properties at various oxidation states in solution were carried out by magnetic susceptibility measurements in solution according to the Evans method. Unlike Ln(III) elements, there is no specific theory describing the magnetic properties of these ions in solution. To obtain accurate data, the influence of experimental measurement technique and radioactivity of these elements was analyzed. Then, to describe the electronic structure of their low energy states, the experimental results were complemented with quantum chemical calculations from which the influence of the ligand field was studied. Finally, these interpretations were applied to better understand the variations in the magnetic properties of actinide cations in chloride and nitrate media. Information about ligand-actinide interactions may be determined from an NMR chemical shift study of actinide complexes. Indeed, modifications induced by a paramagnetic complex can be separated into two components. The first component, a Fermi contact contribution (δ_c) is related to the degree of covalency in coordination bonds with the actinide ions and the second, a dipolar contribution (δ_p_c) is related to the structure of the complex. The paramagnetic induced shift can be used only if we can isolate these two terms. To achieve this study on actinide elements, we chose to work with the complexes of dipicolinic acid (DPA). Firstly, to characterize the geometrical parameters, a

Intramolecular singlet-singlet energy transfer in antenna-substituted azoalkanes.

Science.gov (United States)

Pischel, Uwe; Huang, Fang; Nau, Werner M

2004-03-01

Two novel azoalkane bichromophores and related model compounds have been synthesised and photophysically characterised. Dimethylphenylsiloxy (DPSO) or dimethylnaphthylsiloxy (DNSO) serve as aromatic donor groups (antenna) and the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as the acceptor. The UV spectral window of DBO (250-300 nm) allows selective excitation of the donor. Intramolecular singlet-singlet energy transfer to DBO is highly efficient and proceeds with quantum yields of 0.76 with DPSO and 0.99 with DNSO. The photophysical and spectral properties of the bichromophoric systems suggest that energy transfer occurs through diffusional approach of the donor and acceptor within a van der Waals contact at which the exchange mechanism is presumed to dominate. Furthermore, akin to the behaviour of electron-transfer systems in the Marcus inverted region, a rate of energy transfer 2.5 times slower was observed for the system with the more favourable energetics, i.e. singlet-singlet energy transfer from DPSO proceeded slower than from DNSO, although the process is more exergonic for DPSO (-142 kJ mol(-1) for DPSO versus-67 kJ mol(-1) for DNSO).

Exact exchange-correlation potentials of singlet two-electron systems

Science.gov (United States)

Ryabinkin, Ilya G.; Ospadov, Egor; Staroverov, Viktor N.

2017-10-01

We suggest a non-iterative analytic method for constructing the exchange-correlation potential, v XC ( r ) , of any singlet ground-state two-electron system. The method is based on a convenient formula for v XC ( r ) in terms of quantities determined only by the system's electronic wave function, exact or approximate, and is essentially different from the Kohn-Sham inversion technique. When applied to Gaussian-basis-set wave functions, the method yields finite-basis-set approximations to the corresponding basis-set-limit v XC ( r ) , whereas the Kohn-Sham inversion produces physically inappropriate (oscillatory and divergent) potentials. The effectiveness of the procedure is demonstrated by computing accurate exchange-correlation potentials of several two-electron systems (helium isoelectronic series, H2, H3 + ) using common ab initio methods and Gaussian basis sets.

Flavor-singlet spectrum in multi-flavor QCD

Energy Technology Data Exchange (ETDEWEB)

Aoki, Yasamichi; Rinaldi, Enrico

2017-06-18

Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

Flavor-singlet spectrum in multi-flavor QCD

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

2018-03-01

Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

Electronic and ionic transport in Ce0.8PrxTb0.2-xO2-δ and evaluation of performance as oxygen permeation membranes

DEFF Research Database (Denmark)

Chatzichristodoulou, Christodoulos; Hendriksen, Peter Vang

2012-01-01

is significantly enhanced relative to that of a Ce0.9Gd0.1O1.95-δ membrane at high oxygen activities of the permeate gas (aO2 an > 10-15) due to the enhanced electronic conductivity of the Ce0.8PrxTb0.2-xO2-δ compounds. Interference between the ionic and electronic flows has a significant positive effect......The electronic conductivity of Ce0.8PrxTb0.2-xO2-δ (x = 0, 0.05, 0.10, 0.15, 0.20) was determined in the oxygen activity range aO2 ≈ 103 to aO2 ≈ 10-17 at 700- 900 °C by means of Hebb-Wagner polarisation. The electronic conductivity of all the Ce0.8PrxTb0.2-xO2-δ compositions was significantly...... enhanced as compared to that of Ce0.9Gd0.1O1.95-δ, and its value was found to increase with increasing Pr/Tb ratio. The ionic mobility of Ce0.8PrxTb0.2-xO2-δ is similar to that of Ce1- 2δGd2δO2-δ at the same oxygen vacancy concentration. The calculated oxygen flux of a Ce0.8PrxTb0.2-xO2-δ membrane...

Paramagnetic limiting of the upper critical field of the layered organic superconductor κ-(BEDT-TTF)2Cu(SCN)2

International Nuclear Information System (INIS)

Zuo, F.; Brooks, J.S.; McKenzie, R.H.; Schlueter, J.A.; Williams, J.M.

2000-01-01

We report detailed measurements of the interlayer magnetoresistance of the layered organic superconductor κ-(BEDT-TTF) 2 Cu(SCN) 2 for temperatures down to 0.5 K and fields up to 30 T. The upper critical field is determined from the resistive transition for a wide range of temperatures and field directions. For magnetic fields parallel to the layers, the upper critical field increases approximately linearly with decreasing temperature. The upper critical field at low temperatures is compared to the Pauli paramagnetic limit, at which singlet superconductivity should be destroyed by the Zeeman splitting of the electron spins. The measured value is comparable to a value for the paramagnetic limit calculated from thermodynamic quantities but exceeds the limit calculated from BCS theory. The angular dependence of the upper critical field shows a cusplike feature for fields close to the layers, consistent with decoupled layers.

Does the concept of Clar's aromatic sextet work for dicationic forms of polycyclic aromatic hydrocarbons?--testing the model against charged systems in singlet and triplet states.

Science.gov (United States)

Dominikowska, Justyna; Palusiak, Marcin

2011-07-07

The concept of Clar's π-electron aromatic sextet was tested against a set of polycyclic aromatic hydrocarbons in neutral and doubly charged forms. Systems containing different types of rings (in the context of Clar's concept) were chosen, including benzene, naphthalene, anthracene, phenanthrene and triphenylene. In the case of dicationic structures both singlet and triplet states were considered. It was found that for singlet state dicationic structures the concept of aromatic sextet could be applied and the local aromaticity could be discussed in the context of that model, whereas in the case of triplet state dicationic structures Clar's model rather failed. Different aromaticity indices based on various properties of molecular systems were applied for the purpose of the studies. The discussion about the interdependence between the values of different aromaticity indices applied to neutral and charged systems in singlet and triplet states is also included. This journal is © the Owner Societies 2011

Electron Transfer from Triplet State of TIPS-Pentacene Generated by Singlet Fission Processes to CH3NH3PbI3 Perovskite.

Science.gov (United States)

Lee, Sangsu; Hwang, Daesub; Jung, Seok Il; Kim, Dongho

2017-02-16

To reveal the applicability of singlet fission processes in perovskite solar cell, we investigated electron transfer from TIPS-pentacene to CH 3 NH 3 PbI 3 (MAPbI 3 ) perovskite in film phase. Through the observation of the shorter fluorescence lifetime in TIPS-pentacene/MAPbI 3 perovskite bilayer film (5 ns) compared with pristine MAPbI 3 perovskite film (20 ns), we verified electron-transfer processes between TIPS-pentacene and MAPbI 3 perovskite. Furthermore, the observation of singlet fission processes, a faster decay rate, TIPS-pentacene cations, and the analysis of kinetic profiles of the intensity ratio between 500 and 525 nm in the TA spectra of the TIPS-pentacene/MAPbI 3 perovskite bilayer film indicate that electron transfer occurs from triplet state of TIPS-pentacene generated by singlet fission processes to MAPbI 3 perovskite conduction band. We believe that our results can provide useful information on the design of solar cells sensitized by singlet fission processes and pave the way for new types of perovskite solar cells.

Evolution of ground-state wave function in CeCoIn5 upon Cd or Sn doping

Science.gov (United States)

Chen, K.; Strigari, F.; Sundermann, M.; Hu, Z.; Fisk, Z.; Bauer, E. D.; Rosa, P. F. S.; Sarrao, J. L.; Thompson, J. D.; Herrero-Martin, J.; Pellegrin, E.; Betto, D.; Kummer, K.; Tanaka, A.; Wirth, S.; Severing, A.

2018-01-01

We present linear polarization-dependent soft-x-ray absorption spectroscopy data at the Ce M4 ,5 edges of Cd- and Sn-doped CeCoIn5. The 4 f ground-state wave functions have been determined for their superconducting, antiferromagnetic, and paramagnetic ground states. The absence of changes in the wave functions in CeCo (In1-xCdx) 5 suggests that the 4 f -conduction-electron (c f ) hybridization is not affected by global Cd doping, thus supporting the interpretation of magnetic droplets nucleating long-range magnetic order. This is contrasted by changes in the wave function due to Sn substitution. Increasing Sn in CeCo (In1-ySny) 5 compresses the 4 f orbitals into the tetragonal plane of these materials, suggesting enhanced c f hybridization with the in-plane In(1) atoms and a homogeneous altering of the electronic structure. As these experiments show, the 4 f wave functions are a very sensitive probe of small changes in the hybridization of 4 f and conduction electrons, even conveying information about direction dependencies.

Long-Lived Triplet Excited States of Bent-Shaped Pentacene Dimers by Intramolecular Singlet Fission.

Science.gov (United States)

Sakuma, Takao; Sakai, Hayato; Araki, Yasuyuki; Mori, Tadashi; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

2016-03-24

Intramolecular singlet fission (ISF) is a promising photophysical process to construct more efficient light energy conversion systems as one excited singlet state converts into two excited triplet states. Herein we synthesized and evaluated bent-shaped pentacene dimers as a prototype of ISF to reveal intrinsic characters of triplet states (e.g., lifetimes of triplet excited states). In this study, meta-phenylene-bridged TIPS-pentacene dimer (PcD-3Ph) and 2,2'-bipheynyl bridged TIPS-pentacene dimer (PcD-Biph) were newly synthesized as bent-shaped dimers. In the steady-state spectroscopy, absorption and emission bands of these dimers were fully characterized, suggesting the appropriate degree of electronic coupling between pentacene moieties in these dimers. In addition, the electrochemical measurements were also performed to check the electronic interaction between two pentacene moieties. Whereas the successive two oxidation peaks owing to the delocalization were observed in a directly linked-pentacene dimer (PcD) by a single bond, the cyclic voltammograms in PcD-Biph and PcD-3Ph implied the weaker interaction compared to that of p-phenylene-bridged TIPS-pentacene dimer (PcD-4Ph) and PcD. The femtosecond and nanosecond transient absorption spectra clearly revealed the slower ISF process in bent-shaped pentacene dimers (PcD-Biph and PcD-3Ph), more notably, the slower relaxation of the excited triplet states in PcD-Biph and PcD-3Ph. Namely, the quantum yields of triplet states (ΦT) by ISF approximately remain constant (ca. 180-200%) in all dimer systems, whereas the lifetimes of the triplet excited states became much longer (up to 360 ns) in PcD-Biph as compared to PcD-4Ph (15 ns). Additionally, the lifetimes of the corresponding triplet states in PcD-Biph and PcD-3Ph were sufficiently affected by solvent viscosity. In particular, the lifetimes of PcD-Biph triplet state in THF/paraffin (1.0 μs) increased up to approximately three times as compared to that in THF

Electron paramagnetic resonance g-tensors from state interaction spin-orbit coupling density matrix renormalization group

Science.gov (United States)

Sayfutyarova, Elvira R.; Chan, Garnet Kin-Lic

2018-05-01

We present a state interaction spin-orbit coupling method to calculate electron paramagnetic resonance g-tensors from density matrix renormalization group wavefunctions. We apply the technique to compute g-tensors for the TiF3 and CuCl42 - complexes, a [2Fe-2S] model of the active center of ferredoxins, and a Mn4CaO5 model of the S2 state of the oxygen evolving complex. These calculations raise the prospects of determining g-tensors in multireference calculations with a large number of open shells.

Electron paramagnetic resonance of the ns1 centers in crystals

International Nuclear Information System (INIS)

Nistor, S.V.; Ursu, I.

1993-05-01

The results of the EPR studies concerning the paramagnetic centers with ns 1 (N=n>2) outer electronic configuration contained in crystals are reviewed. Such centers, with 2 S 1/2 ground state, are produced by electron trapping at impurities of the IB and IIB group or by hole trapping at impurities of the IIIB and IV group of elements. The production and structural properties of such centers consisting of ns 1 ions (atoms) at various sites in the crystal lattice with different configurations of neighbouring defects are discussed in connection with their EPR characteristics. Tables containing the spin Hamiltonian parameters of all ns 1 centers reported in the literature until the end of year 1992 are given. (author). 146 refs, 14 tabs

Electron paramagnetic resonance detection of carotenoid triplet states

International Nuclear Information System (INIS)

Frank, H.A.; Bolt, J.D.; deCosta, S.M.; Sauer, K.

1980-01-01

Triplet states of carotenoids have been detected by X-band electron paramagnetic resonance (EPR) and are reported here for the first time. The systems in which carotenoid triplets are observed include cells of photosynthetic bacteria, isolated bacteriochlorophyll-protein complexes, and detergent micelles which contain β-carotene. It is well known that if electron transfer is blocked following the initial acceptor in the bacterial photochemical reaction center, back reaction of the primary radical pair produces a bacteriochlorophyll dimer triplet. Previous optical studies have shown that in reaction centers containing carotenoids the bacteriochlorophyll dimer triplet sensitizes the carotenoid triplet. We have observed this carotenoid triplet state by EPR in reaction centers of Rhodopseudomonas sphaeroides, strain 2.4.1 (wild type), which contain the carotenoid spheroidene. The zero-field splitting parameters of the triplet spectrum are /D/ = 0.0290 +- 0.0005 cm -1 and /E/ = 0.0044 +-0.0006 cm -1 , in contrast with the parameters of the bacteriochlorophyll dimer triplet, which are /D/ = 0.0189 +- 0.0004 cm -1 and /E/ = 0.0032 +- 0.004 cm -1 . Bacteriochlorophyll in a light harvesting protein complex from Rps. sphaeroides, wild type, also sensitizes carotenoid triplet formation. In whole cells the EPR spectra vary with temperature between 100 and 10 K. Carotenoid triplets also have been observed by EPR in whole cells of Rps. sphaeroides and cells of Rhodospirillum rubrum which contain the carotenoid spirilloxanthin. Attempts to observe the triplet state EPR spectrum of β-carotene in numerous organic solvents failed. However, in nonionic detergent micelles and in phospholipid bilayer vesicles β-carotene gives a triplet state spectrum with /D/ = 0.0333 +- 0.0010 cm -1 and /E/ = 0.0037 +- 0.0010 cm -1 . 6 figures, 1 table

Nonequilibrium ensembles. 3. Spin 1/2 paramagnets

International Nuclear Information System (INIS)

Sobouti, Y.; Khajeh-Pour, M.R.H.

1990-07-01

The thermodynamic state of a paramagnetic substance in which the spin vectors precess coherently is investigated. The state is a time dependent one. The corresponding density matrix and the thermodynamics emerging from it is worked out. A laboratory preparation of such a system is discussed. (author). 3 refs

Graphene ground states

Science.gov (United States)

Friedrich, Manuel; Stefanelli, Ulisse

2018-06-01

Graphene is locally two-dimensional but not flat. Nanoscale ripples appear in suspended samples and rolling up often occurs when boundaries are not fixed. We address this variety of graphene geometries by classifying all ground-state deformations of the hexagonal lattice with respect to configurational energies including two- and three-body terms. As a consequence, we prove that all ground-state deformations are either periodic in one direction, as in the case of ripples, or rolled up, as in the case of nanotubes.

Local structural changes in paramagnetic and charge-ordered phases of Sm0.2Pr0.3Sr0.5MnO3: an EXAFS study

International Nuclear Information System (INIS)

Priolkar, K R; Kulkarni, Vishwajeet; Sarode, P R; Emura, S

2008-01-01

Sm 0.5-x Pr x Sr 0.5 MnO 3 exhibits a variety of ground states as x is varied from 0 to 0.5. At an intermediate doping of x = 0.3 a charge-ordered CE-type antiferromagnetic insulating (AFI) ground state is seen. The transition to this ground state is from a paramagnetic-insulating (PMI) phase through a ferromagnetic-metallic phase (FMM). Local structures in PMI and AFI phases of the x = 0.3 sample have been investigated using Pr K-edge and Sm K-edge extended x-ray absorption fine structure (EXAFS). It can be seen that the tilting and rotation of the MnO 6 octahedra about the b-axis are responsible for the charge-ordered CE-type antiferromagnetic ground state at low temperatures. In addition a shift in the position of the rare-earth ion along the c-axis has to be considered to account for observed distribution of bond distances around the rare-earth ion

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

The use of hyperpolarization to enhance the sensitivity of MRI has so far been limited by the decay of the polarization through T1 relaxation. Recently, methods have been proposed that extend the lifetime of the hyperpolarization by storing the spin order in slowly relaxing singlet states....... 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...

Ground states of a spin-boson model

International Nuclear Information System (INIS)

Amann, A.

1991-01-01

Phase transition with respect to ground states of a spin-boson Hamiltonian are investigated. The spin-boson model under discussion consists of one spin and infinitely many bosons with a dipole-type coupling. It is shown that the order parameter of the model vanishes with respect to arbitrary ground states if it vanishes with respect to ground states obtained as (biased) temperature to zero limits of thermic equilibrium states. The ground states of the latter special type have been investigated by H. Spohn. Spohn's respective phase diagrams are therefore valid for arbitrary ground states. Furthermore, disjointness of ground states in the broken symmetry regime is examined

Theoretical rationalization of the singlet-triplet gap in OLEDs materials: impact of charge-transfer character.

Science.gov (United States)

Moral, M; Muccioli, L; Son, W-J; Olivier, Y; Sancho-García, J C

2015-01-13

New materials for OLED applications with low singlet-triplet energy splitting have been recently synthesized in order to allow for the conversion of triplet into singlet excitons (emitting light) via a Thermally Activated Delayed Fluorescence (TADF) process, which involves excited-states with a non-negligible amount of Charge-Transfer (CT). The accurate modeling of these states with Time-Dependent Density Functional Theory (TD-DFT), the most used method so far because of the favorable trade-off between accuracy and computational cost, is however particularly challenging. We carefully address this issue here by considering materials with small (high) singlet-triplet gap acting as emitter (host) in OLEDs and by comparing the accuracy of TD-DFT and the corresponding Tamm-Dancoff Approximation (TDA), which is found to greatly reduce error bars with respect to experiments thanks to better estimates for the lowest singlet-triplet transition. Finally, we quantitatively correlate the singlet-triplet splitting values with the extent of CT, using for it a simple metric extracted from calculations with double-hybrid functionals, that might be applied in further molecular engineering studies.

Benchmarking singlet and triplet excitation energies of molecular semiconductors for singlet fission: Tuning the amount of HF exchange and adjusting local correlation to obtain accurate functionals for singlet-triplet gaps

Science.gov (United States)

Brückner, Charlotte; Engels, Bernd

2017-01-01

Vertical and adiabatic singlet and triplet excitation energies of molecular p-type semiconductors calculated with various DFT functionals and wave-function based approaches are benchmarked against MS-CASPT2/cc-pVTZ reference values. A special focus lies on the singlet-triplet gaps that are very important in the process of singlet fission. Singlet fission has the potential to boost device efficiencies of organic solar cells, but the scope of existing singlet-fission compounds is still limited. A computational prescreening of candidate molecules could enlarge it; yet it requires efficient methods accurately predicting singlet and triplet excitation energies. Different DFT formulations (Tamm-Dancoff approximation, linear response time-dependent DFT, Δ-SCF) and spin scaling schemes along with several ab initio methods (CC2, ADC(2)/MP2, CIS(D), CIS) are evaluated. While wave-function based methods yield rather reliable singlet-triplet gaps, many DFT functionals are shown to systematically underestimate triplet excitation energies. To gain insight, the impact of exact exchange and correlation is in detail addressed.

Two-dimensional H2O-Cl2 and H2O-Br2 potential surfaces: an ab initio study of ground and valence excited electronic states.

Science.gov (United States)

Hernandez-Lamoneda, Ramón; Rosas, Victor Hugo Uc; Uruchurtu, Margarita I Bernal; Halberstadt, Nadine; Janda, Kenneth C

2008-01-10

All electron ab initio calculations for the interaction of H2O with Cl2 and Br2 are reported for the ground state and the lowest triplet and singlet Pi excited states as a function of both the X-X and O-X bond lengths (X = Cl or Br). For the ground state and lowest triplet state, the calculations are performed with the coupled cluster singles, doubles, and perturbative triple excitation level of correlation using an augmented triple-zeta basis set. For the 1Pi state the multireference average quadratic coupled cluster technique was employed. For several points on the potential, the calculations were repeated with the augmented quadruple-zeta basis set. The ground-state well depths were found to be 917 and 1,183 cm-1 for Cl2 and Br2, respectively, with the triple-zeta basis set, and they increased to 982 and 1,273 cm-1 for the quadruple-zeta basis set. At the geometry of the ground-state minimum, the lowest energy state corresponding to the unperturbed 1Pi states of the halogens increases in energy by 637 and 733 cm-1, respectively, relative to the ground-state dissociation limit of the H2O-X2 complex. Adding the attractive ground-state interaction energy to that of the repulsive excited state predicts a blue-shift, relative to that of the free halogen molecules, of approximately 1,600 cm-1 for H2O-Cl2 and approximately 2,000 cm-1 for H2O-Br2. These vertical blue-shifts for the dimers are greater than the shift of the band maximum upon solvation of either halogen in liquid water.

Magnetic excitations in intermediate valence semiconductors with singlet ground state

International Nuclear Information System (INIS)

Kikoin, K.A.; Mishchenko, A.S.

1994-01-01

The explanation of the origin inelastic peaks in magnetic neutron scattering spectra of the mixed-valent semiconductor SmB 6 is proposed. It is shown that the excitonic theory of intermediate valence state not only gives the value of the peak frequency but also explains the unusual angular dependence of intensity of inelastic magnetic scattering and describes the dispersion of magnetic excitations in good agreement with experiment

Probing Spin Crossover in a Solution by Paramagnetic NMR Spectroscopy.

Science.gov (United States)

Pavlov, Alexander A; Denisov, Gleb L; Kiskin, Mikhail A; Nelyubina, Yulia V; Novikov, Valentin V

2017-12-18

Spin transitions in spin-crossover compounds are now routinely studied in the solid state by magnetometry; however, only a few methods exist for studies in solution. The currently used Evans method, which relies on NMR spectroscopy to measure the magnetic susceptibility, requires the availability of a very pure sample of the paramagnetic compound and its exact concentration. To overcome these limitations, we propose an alternative NMR-based technique for evaluating spin-state populations by only using the chemical shifts of a spin-crossover compound; those can be routinely obtained for a solution that contains unknown impurities and paramagnetic admixtures or is contaminated otherwise.

Wavelength dependence of the efficiency of singlet oxygen generation upon photoexcitation of photosensitizers

Directory of Open Access Journals (Sweden)

Starukhin A.

2017-01-01

Full Text Available The dependence of the efficiency of singlet oxygen (1Δg generation upon excitation of photosensitizer at different wavelength was observed for several derivatives of palladium porphyrin in carbon tetrachloride. The efficiency of singlet oxygen generation upon excitation in a blue region of the spectrum (Soret band exceeds by several times the efficiency at excitation in the red spectral region (Q band. The effect of enhancement of singlet oxygen generation upon CW photoexcitation to Soret band of photosensitizer may be explained by influence of high laying triplet states of a donor molecule on the triplet-triplet energy transfer.

Spectroscopy and intramolecular relaxation of methyl salicylate in its first excited singlet state

Science.gov (United States)

Kuper, Jerry W.; Perry, David S.

1984-05-01

High resolution fluorescence excitation experiments are reported for the blue emitting rotamer of methyl salicylate in its first excited singlet state. These experiments employ moderate expansions of methyl salicylate seeded in argon ( P0D=5-8 Torr cm) to achieve rotational and vibrational cooling in a pulsed supersonic jet. The rotational contour of the electronic origin at 30 055.3 cm-1 is shown to be consistent with a geometrically distorted π-π* excited state, partially polarized along the A axis and with a rotational temperature of 5-7 K. A noticeable broadening of the spectral features beyond the rotational contour begins at 500 cm-1 above the origin and then increases rapidly above 900 cm-1 reaching a width of 12 cm-1 near 1200 cm-1. The constancy of fluorescence decay lifetimes in this region indicate that intramolecular vibrational relaxation in the S1 manifold is the broadening mechanism.

Photocurrent enhanced by singlet fission in a dye-sensitized solar cell.

Science.gov (United States)

Schrauben, Joel N; Zhao, Yixin; Mercado, Candy; Dron, Paul I; Ryerson, Joseph L; Michl, Josef; Zhu, Kai; Johnson, Justin C

2015-02-04

Investigations of singlet fission have accelerated recently because of its potential utility in solar photoconversion, although only a few reports definitively identify the role of singlet fission in a complete solar cell. Evidence of the influence of singlet fission in a dye-sensitized solar cell using 1,3-diphenylisobenzofuran (DPIBF, 1) as the sensitizer is reported here. Self-assembly of the blue-absorbing 1 with co-adsorbed oxidation products on mesoporous TiO2 yields a cell with a peak internal quantum efficiency of ∼70% and a power conversion efficiency of ∼1.1%. Introducing a ZrO2 spacer layer of thickness varying from 2 to 20 Å modulates the short-circuit photocurrent such that it is initially reduced as thickness increases but 1 with 10-15 Å of added ZrO2. This rise can be explained as being due to a reduced rate of injection of electrons from the S1 state of 1 such that singlet fission, known to occur with a 30 ps time constant in polycrystalline films, has the opportunity to proceed efficiently and produce two T1 states per absorbed photon that can subsequently inject electrons into TiO2. Transient spectroscopy and kinetic simulations confirm this novel mode of dye-sensitized solar cell operation and its potential utility for enhanced solar photoconversion.

On the intramolecular proton transfer of 3-hydroxyflavone in the first singlet excited state: A theoretical study

International Nuclear Information System (INIS)

Casadesus, Ricard; Vendrell, Oriol; Moreno, Miquel; Lluch, Jose M.; Morokuma, Keiji

2006-01-01

The intramolecular proton-transfer reaction in 3-hydroxyflavone (3HF) is theoretically studied both in the ground (S 0 ) and first singlet excited (S 1 ) electronic states. In S 0 the proton-transfer reaction is shown to be quite unfavorable at the DFT (B3LYP) level. However, the back proton transfer is found to be a feasible process with a small energy barrier, both results being in qualitative agreement with known experimental facts. Different theoretical levels are considered and compared for S 1 . The ab initio configuration interaction singles (CIS) method overestimates the energy of S 1 and give too high energy barriers for the proton-transfer reaction. The complete active space SCF (CASSCF) method gives a more reasonable value but the inclusion of the dynamical correlation through second-order perturbation theory (CASPT2) upon CASSCF geometries or the use of the time-dependent DFT (TDDFT) method upon CIS geometries gives a barrierless process. Optimization of geometries (minima and transition-state structures) at the TDDFT level leads to a small but non-negligible energy barrier for the proton-transfer reaction in S 1 and global energies that fit quite well with the known experimental (spectroscopic and femtochemistry) data. Finally the effect of a polar environment is analyzed through a continuum model, which gives only a small difference from the previous gas-phase results. This points out that the remarkable changes in the photochemistry of 3HF observed experimentally are not to be solely attributed to the polarity of the surrounding media

On the intramolecular proton transfer of 3-hydroxyflavone in the first singlet excited state: A theoretical study

Energy Technology Data Exchange (ETDEWEB)

Casadesus, Ricard [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322 (United States); Vendrell, Oriol [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Moreno, Miquel [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain)], E-mail: mmf@klingon.uab.es; Lluch, Jose M. [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Morokuma, Keiji [Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322 (United States)

2006-06-20

The intramolecular proton-transfer reaction in 3-hydroxyflavone (3HF) is theoretically studied both in the ground (S{sub 0}) and first singlet excited (S{sub 1}) electronic states. In S{sub 0} the proton-transfer reaction is shown to be quite unfavorable at the DFT (B3LYP) level. However, the back proton transfer is found to be a feasible process with a small energy barrier, both results being in qualitative agreement with known experimental facts. Different theoretical levels are considered and compared for S{sub 1}. The ab initio configuration interaction singles (CIS) method overestimates the energy of S{sub 1} and give too high energy barriers for the proton-transfer reaction. The complete active space SCF (CASSCF) method gives a more reasonable value but the inclusion of the dynamical correlation through second-order perturbation theory (CASPT2) upon CASSCF geometries or the use of the time-dependent DFT (TDDFT) method upon CIS geometries gives a barrierless process. Optimization of geometries (minima and transition-state structures) at the TDDFT level leads to a small but non-negligible energy barrier for the proton-transfer reaction in S{sub 1} and global energies that fit quite well with the known experimental (spectroscopic and femtochemistry) data. Finally the effect of a polar environment is analyzed through a continuum model, which gives only a small difference from the previous gas-phase results. This points out that the remarkable changes in the photochemistry of 3HF observed experimentally are not to be solely attributed to the polarity of the surrounding media.

The off-shell nucleon-nucleon interaction in the singlet s-state

International Nuclear Information System (INIS)

Groot, H. de

1975-01-01

This thesis studies the off-shell behaviour of the neutron-proton interaction in the singlet state. To generate phase-shift-equivalent potentials a particular type of inversion problem is solved. It requires the potential to contain a non-local, separable part which is supposed to describe part of the short-range interaction. A special solution of the general inversion problem that produces potentials consisting of two separable terms is studied. Criteria to accept or reject particular inversion solutions are discussed. Neutron-proton potentials in the 1 S 0 partial wave which form part of the input for the general inversion procedure are defined. Different local potential tails are chosen, as well as varying short-range interactions, both local and non-local. The input phase shifts are discussed including three extrapolations of the phase shifts at high energy. The half-shell transition matrix for the potentials defined is studied. Some problems introduced by the additional electromagnetic interaction in the proton-proton system is investigated. (Auth.)

Singlets of fermionic gauge symmetries

NARCIS (Netherlands)

Bergshoeff, E.A.; Kallosh, R.E.; Rahmanov, M.A.

1989-01-01

We investigate under which conditions singlets of fermionic gauge symmetries which are "square roots of gravity" can exist. Their existence is non-trivial because there are no fields neutral in gravity. We tabulate several examples of singlets of global and local supersymmetry and κ-symmetry and

Exchange coupled pairs of dangling bond spins as a new type of paramagnetic defects in nanodiamonds

Energy Technology Data Exchange (ETDEWEB)

Osipov, V. Yu., E-mail: osipov@mail.ioffe.r [Ioffe Physico-Technical Institute, Polytechnicheskaya 26, 194021 St. Petersburg (Russian Federation); Faculty of Electronics, St. Petersburg State Electrotechnical University (LETI), 197376 (Russian Federation); Shames, A.I. [Department of Physics, Ben-Gurion University of the Negev, 84105 Be' er-Sheva (Israel); Vul' , A. Ya. [Ioffe Physico-Technical Institute, Polytechnicheskaya 26, 194021 St. Petersburg (Russian Federation)

2009-12-15

EPR in detonation nanodiamonds (DND) reveals two different signals associated with intrinsic carbon inherited paramagnetic defects. Main carbon inherited EPR signal is narrow intensive Lorentzian-like singlet with g=2.0028 and spin concentration N{sub s}=(6-7)x10{sup 19} spin/g that yields on average 13-15 spins per each DND particle. Additional chemical treatment of DND powder allows practically complete removal of trace amounts of transition metal impurities that reveals a new doublet EPR signal consisting of two relatively narrow lines within the half-field region (gapprox4) separated by a distance of 10.4 mT. The intensity of the doublet signal is five orders of magnitude lower than that of the main singlet signal. The former signal has been observed in a wide variety of DND samples disregarding of the impurity level reached and thus may be attributed to some intrinsic defects in DND particles. Such half-field EPR signals correspond to 'forbidden' DELTAM{sub s}=2 transitions within thermally populated triplet (S=1) levels observed in polycrystalline samples containing exchange dimers-antiferromagnetically coupled spin pairs. Estimates suggest that the concentration of such defects is about one dimer per hundreds DND particles.

Rearrangement of van der Waals stacking and formation of a singlet state at T = 90 K in a cluster magnet

Energy Technology Data Exchange (ETDEWEB)

Sheckelton, John P.; Plumb, Kemp W.; Trump, Benjamin A.; Broholm, Collin L.; McQueen, Tyrel M.

2017-01-01

Insulating Nb3Cl8 is a layered chloride consisting of two-dimensional triangular layers of Seff = 1/2 Nb3Cl13 clusters at room temperature. Magnetic susceptibility measurement show a sharp, hysteretic drop to a temperature independent value below T = 90 K. Specific heat measurements show that the transition is first order, with ΔS ≈ 5 J K-1 mol-1 f.u.-1, and a low temperature T-linear contribution originating from defect spins. Neutron and X-ray diffraction show a lowering of symmetry from trigonal P[3 with combining macron]m1 to monoclinic C2/m symmetry, with a change in layer stacking from –AB–AB– to –AB'–BC'–CA'– and no observed magnetic order. This lowering of symmetry and rearrangement of successive layers evades geometric magnetic frustration to form a singlet ground state. It is the lowest temperature at which a change in stacking sequence is known to occur in a van der Waals solid, occurs in the absence of orbital degeneracies, and suggests that designer 2-D heterostructures may be able to undergo similar phase transitions.

First-Principles Quantum Dynamics of Singlet Fission: Coherent versus Thermally Activated Mechanisms Governed by Molecular π Stacking

Science.gov (United States)

Tamura, Hiroyuki; Huix-Rotllant, Miquel; Burghardt, Irene; Olivier, Yoann; Beljonne, David

2015-09-01

Singlet excitons in π -stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states. By contrast, the electronic couplings for singlet fission strictly vanish at the C2 h symmetric equilibrium π stacking of rubrene. In this case, singlet fission is driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence. Design rules for optimal singlet fission materials therefore need to account for the interplay of molecular π -stacking symmetry and phonon-induced coherent or thermally activated mechanisms.

Competition of ground states in URu2Si2 and UCoGe

International Nuclear Information System (INIS)

Hassinger, E.

2010-10-01

In this thesis, two uranium based heavy fermion compounds are studied under pressure. URu2Si2 has a mysterious ground state below T0 = 17.5 K at ambient pressure. The order parameter has not been identified yet which led to the name 'hidden order' (HO). In addition, below 1.5 K the system becomes superconducting. With pressure, the ground state switches from the HO phase to an antiferromagnetic (AF) phase at a critical pressure and superconductivity is concomitantly suppressed. Shubnikov-de Haas measurements under pressure show that the Fermi surface doesn't change between the two phases. The folding of the Fermi surface which occurs in the high pressure AF phase therefore already happens in the HO phase, indicating a unit cell doubling. Our measurements of the complete angular dependence of the oscillation frequencies test the electronic structure and support new theoretical band structure calculations with rather itinerant 5f electrons. The second part of my research focuses on another uranium compound, UCoGe. It is one of the few known materials where superconductivity (Tsc = 0.6 K) coexists with ferromagnetism (T Curie = 2.8 K). Precise studies of the pressure phase diagram by resistivity, ac calorimetry and ac susceptibility show that the ferromagnetic phase is suppressed at a pressure of about 1 GPa and the superconducting phase extends into the paramagnetic phase induced by pressure. When ferromagnetism is suppressed to the superconducting transition no further distinct ferromagnetic anomalies are observed. Thus, the pressure phase diagram of UCoGe is unique in the class of ferromagnetic superconductors. (author)

Towards improved solubility of poorly water-soluble drugs: cryogenic co-grinding of piroxicam with carrier polymers.

Science.gov (United States)

Penkina, Anna; Semjonov, Kristian; Hakola, Maija; Vuorinen, Sirpa; Repo, Timo; Yliruusi, Jouko; Aruväli, Jaan; Kogermann, Karin; Veski, Peep; Heinämäki, Jyrki

2016-01-01

Amorphous solid dispersions (SDs) open up exciting opportunities in formulating poorly water-soluble active pharmaceutical ingredients (APIs). In the present study, novel catalytic pretreated softwood cellulose (CPSC) and polyvinylpyrrolidone (PVP) were investigated as carrier polymers for preparing and stabilizing cryogenic co-ground SDs of poorly water-soluble piroxicam (PRX). CPSC was isolated from pine wood (Pinus sylvestris). Raman and Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) were used for characterizing the solid-state changes and drug-polymer interactions. High-resolution scanning electron microscope (SEM) was used to analyze the particle size and surface morphology of starting materials and final cryogenic co-ground SDs. In addition, the molecular aspects of drug-polymer interactions and stabilization mechanisms are presented. The results showed that the carrier polymer influenced both the degree of amorphization of PRX and stabilization against crystallization. The cryogenic co-ground SDs prepared from PVP showed an enhanced dissolution rate of PRX, while the corresponding SDs prepared from CPSC exhibited a clear sustained release behavior. In conclusion, cryogenic co-grinding provides a versatile method for preparing amorphous SDs of poorly water-soluble APIs. The solid-state stability and dissolution behavior of such co-ground SDs are to a great extent dependent on the carrier polymer used.

A spin exchange model for singlet fission

Science.gov (United States)

Yago, Tomoaki; Wakasa, Masanobu

2018-03-01

Singlet fission has been analyzed with the Dexter model in which electron exchange occurs between chromophores, conserving the spin for each electron. In the present study, we propose a spin exchange model for singlet fission. In the spin exchange model, spins are exchanged by the exchange interaction between two electrons. Our analysis with simple spin functions demonstrates that singlet fission is possible by spin exchange. A necessary condition for spin exchange is a variation in exchange interactions. We also adapt the spin exchange model to triplet fusion and triplet energy transfer, which often occur after singlet fission in organic solids.

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

2015-01-01

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. PMID:26225731

Ground-state and spectral properties of an asymmetric Hubbard ladder

Science.gov (United States)

Abdelwahab, Anas; Jeckelmann, Eric; Hohenadler, Martin

2015-04-01

We investigate a ladder system with two inequivalent legs, namely, a Hubbard chain and a one-dimensional electron gas. Analytical approximations, the density-matrix renormalization group method, and continuous-time quantum Monte Carlo simulations are used to determine ground-state properties, gaps, and spectral functions of this system at half-filling. Evidence for the existence of four different phases as a function of the Hubbard interaction and the rung hopping is presented. First, a Luttinger liquid exists at very weak interchain hopping. Second, a Kondo-Mott insulator with spin and charge gaps induced by an effective rung exchange coupling is found at moderate interchain hopping or strong Hubbard interaction. Third, a spin-gapped paramagnetic Mott insulator with incommensurate excitations and pairing of doped charges is observed at intermediate values of the rung hopping and the interaction. Fourth, the usual correlated band insulator is recovered for large rung hopping. We show that the wave numbers of the lowest single-particle excitations are different in each insulating phase. In particular, the three gapped phases exhibit markedly different spectral functions. We discuss the relevance of asymmetric two-leg ladder systems as models for atomic wires deposited on a substrate.

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, 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.

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.

Probing color-singlet exchange at D0

International Nuclear Information System (INIS)

Abbott, B.; Abolins, M.; Acharya, B.S.

1997-07-01

We present latest preliminary results on hard color-singlet exchange in proton-antiproton collisions. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, dijet pseudorapidity separation, and proton-antiproton center-of-mass energy. These results are qualitatively consistent with a color-singlet fraction that increases with increasing quark-initiated processes

Electronic and Ionic Transport in Ce0.8PrxTb0.2−xO2−δ and Evaluation of Performance as Oxygen Permeation Membranes

DEFF Research Database (Denmark)

Chatzichristodoulou, Christodoulos; Hendriksen, Peter Vang

2012-01-01

to that of Ce0.9Gd0.1O1.95−δ, and was found to increase with increasing Pr/Tb ratio. The oxide ion mobility in Ce0.8PrxTb0.2−xO2−δ is similar to that in Ce1−2δGd2δO2−δ at the same oxygen vacancy concentration. Based on the measured ionic and electronic conductivities, fluxes through thin film Ce0.8PrxTb0.2−xO2......The electronic conductivity of Ce0.8PrxTb0.2−xO2−δ (x = 0, 0.05, 0.10, 0.15, 0.20) was determined in the oxygen activity range aO2 ≈ 103 – 10−17 at 700–900°C by Hebb-Wagner polarization. The electronic conductivity of all the Ce0.8PrxTb0.2−xO2−δ compositions was significantly enhanced as compared......−δ membranes were calculated. Calculated fluxes exceed 10 Nml min−1 cm−2 under oxyfuel relevant conditions (T = 800°C, aO2,permeate side = 10−3). Hence, in terms of transport properties, these materials are promising for this application. Interference between the ionic and electronic flows has...

Recent results on some columnar paramagnetic metallomesogens

Indian Academy of Sciences (India)

A broader view on some physical properties of columnar paramagnetic ... was evident by X-ray crystal structure determination in the solid state on a homologous ... leading to interfacial polarization as described for other LC materials before [9]. ... dodecyloxy tail on the phenyl rings) was described to exhibit a Colho phase ...

New ab initio adiabatic potential energy surfaces and bound state calculations for the singlet ground X˜ 1A1 and excited C˜ 1B2(21A') states of SO2

Science.gov (United States)

Kłos, Jacek; Alexander, Millard H.; Kumar, Praveen; Poirier, Bill; Jiang, Bin; Guo, Hua

2016-05-01

We report new and more accurate adiabatic potential energy surfaces (PESs) for the ground X˜ 1A1 and electronically excited C˜ 1B2(21A') states of the SO2 molecule. Ab initio points are calculated using the explicitly correlated internally contracted multi-reference configuration interaction (icMRCI-F12) method. A second less accurate PES for the ground X ˜ state is also calculated using an explicitly correlated single-reference coupled-cluster method with single, double, and non-iterative triple excitations [CCSD(T)-F12]. With these new three-dimensional PESs, we determine energies of the vibrational bound states and compare these values to existing literature data and experiment.

The effect of gold nanoparticles on exchange processes in collision complexes of triplet and singlet oxygen molecules with excited eosin molecules

Science.gov (United States)

Bryukhanov, V. V.; Minaev, B. M.; Tsibul'nikova, A. V.; Slezhkin, V. A.

2015-07-01

We have studied exchange processes in contact complexes of triplet eosin molecules with oxygen molecules in the triplet (3Σ{/g -}) and singlet (1Δ g ) states in thin polyvinylbutyral films in the presence of gold nanoparticles. Upon resonant excitation of surface plasmons in gold nanoparticles into the absorption band of eosin molecules-singlet oxygen sensitizers-we have obtained an increase in the intensity of the delayed fluorescence and an increase in the lifetime of the dye with simultaneous quenching of the luminescence of singlet oxygen. The kinetics of the delayed fluorescence of the dye as a result of singlet-triplet annihilation of triplet eosin molecules with singlet oxygen molecules has been investigated. To compare theoretical and experimental data, we have numerically simulated energy transfer processes. Rate constants of energy transfer and of singlet-triplet annihilation, as well as quenching constants of triplet states of the dye by molecular oxygen, have been calculated. Luminescence quantum yield 1Δ g of polyvinylbutyral has been estimated. We have analyzed quantum-chemically electronic mechanisms of singlet-triplet annihilation of oxygen and eosin.

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.

Demonstrating Paramagnetism Using Liquid Nitrogen.

Science.gov (United States)

Simmonds, Ray; And Others

1994-01-01

Describes how liquid nitrogen is attracted to the poles of neodymium magnets. Nitrogen is not paramagnetic, so the attraction suggests that the liquid nitrogen contains a small amount of oxygen, which causes the paramagnetism. (MVL)

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. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Spin Singlet Quantum Hall Effect and nonabelian Landau-Ginzburg theory

International Nuclear Information System (INIS)

Balatsky, A.

1991-01-01

In this paper we present a theory of Singlet Quantum Hall Effect (SQHE). We show that the Halperin-Haldane SQHE wave function can be written in the form of a product of a wave function for charged semions in a magnetic field and a wave function for the Chiral Spin Liquid of neutral spin-1/2 semions. We introduce field-theoretic model in which the electron operators are factorized in terms of charged spinless semions (holons) and neutral spin-1/2 semions (spinons). Broken time reversal symmetry and short ranged spin correlations lead to Su(2) κ=1 Chern-Simons term in Landau-Ginzburg action for SQHE phase. We construct appropriate coherent states for SQHE phase and show the existence of SU(2) valued gauge potential. This potential appears as a result of ''spin rigidity'' of the ground state against any displacements of nodes of wave function from positions of the particles and reflects the nontrivial monodromy in the presence of these displacenmants. We argue that topological structure of Su(2) κ=1 Chern-Simons theory unambiguously dictates semion statistics of spinons. 19 refs

Singlet-to-triplet ratio in the deuteron breakup reaction pd → pnp at 585 MeV

International Nuclear Information System (INIS)

Uzikov, Yu.N.; Komarov, V.I.; Rathmann, F.; Seyfarth, H.

2001-01-01

Available experimental data on the exclusive pd → pnp reaction at 585 MeV show a narrow peak in the proton-neutron final-state interaction region. It was supposed previously, on the basis of a phenomenological analysis of the shape of this peak, that the final spin-singlet pn state provided about one third of the observed cross section. By comparing the absolute value of the measured cross section with that of pd elastic scattering using the Faeldt-Wilkin extrapolation theorem, it is shown here that the pd → pnp data can be explained mainly by the spin-triplet final state with a singlet admixture of a few percent. The smallness of the singlet contribution is compatible with existing pN → pNπ data and the one-pion exchange mechanism of the pd → pnp reaction

Ground states of quantum spin systems

International Nuclear Information System (INIS)

Bratteli, Ola; Kishimoto, Akitaka; Robinson, D.W.

1978-07-01

The authors prove that ground states of quantum spin systems are characterized by a principle of minimum local energy and that translationally invariant ground states are characterized by the principle of minimum energy per unit volume

Sensitivity and Resolution Enhanced Solid-State NMR for Paramagnetic Systems and Biomolecules under Very Fast Magic Angle Spinning

KAUST Repository

Parthasarathy, Sudhakar

2013-09-17

Recent research in fast magic angle spinning (MAS) methods has drastically improved the resolution and sensitivity of NMR spectroscopy of biomolecules and materials in solids. In this Account, we summarize recent and ongoing developments in this area by presenting (13)C and (1)H solid-state NMR (SSNMR) studies on paramagnetic systems and biomolecules under fast MAS from our laboratories. First, we describe how very fast MAS (VFMAS) at the spinning speed of at least 20 kHz allows us to overcome major difficulties in (1)H and (13)C high-resolution SSNMR of paramagnetic systems. As a result, we can enhance both sensitivity and resolution by up to a few orders of magnitude. Using fast recycling (∼ms/scan) with short (1)H T1 values, we can perform (1)H SSNMR microanalysis of paramagnetic systems on the microgram scale with greatly improved sensitivity over that observed for diamagnetic systems. Second, we discuss how VFMAS at a spinning speed greater than ∼40 kHz can enhance the sensitivity and resolution of (13)C biomolecular SSNMR measurements. Low-power (1)H decoupling schemes under VFMAS offer excellent spectral resolution for (13)C SSNMR by nominal (1)H RF irradiation at ∼10 kHz. By combining the VFMAS approach with enhanced (1)H T1 relaxation by paramagnetic doping, we can achieve extremely fast recycling in modern biomolecular SSNMR experiments. Experiments with (13)C-labeled ubiquitin doped with 10 mM Cu-EDTA demonstrate how effectively this new approach, called paramagnetic assisted condensed data collection (PACC), enhances the sensitivity. Lastly, we examine (13)C SSNMR measurements for biomolecules under faster MAS at a higher field. Our preliminary (13)C SSNMR data of Aβ amyloid fibrils and GB1 microcrystals acquired at (1)H NMR frequencies of 750-800 MHz suggest that the combined use of the PACC approach and ultrahigh fields could allow for routine multidimensional SSNMR analyses of proteins at the 50-200 nmol level. Also, we briefly discuss the

A Theoretical Study of the Photodissociation Mechanism of Cyanoacetylene in Its Lowest Singlet and Triplet Excited States

Science.gov (United States)

Luo, Cheng; Du, Wei-Na; Duan, Xue-Mei; Li, Ze-Sheng

2008-11-01

Cyanoacetylene (H5-C4 ≡ C3-C2 ≡ N1) is a minor constituent of the atmosphere of Titan, and its photochemistry plays an important role in the formation of the haze surrounding the satellite. In this paper, the complete active space self-consistent field (CASSCF) and multiconfigurational second-order perturbation (CASPT2) approaches are employed to investigate the photochemical processes for cyanoacetylene in its first singlet and triplet excited states with the cc-pVTZ basis set. Fissions of the C4-H5 and C2-C3 bonds in S1 yield H(2S) + CCCN(A2Π) and HCC(A2Π) + CN(X2Σ+), respectively. In T1, the corresponding dissociation products are H(2S) + CCCN(X2Σ+) and HCC(X2Σ) + CN(X2Σ+). At the CASPT2(14,13)//CASSCF(14,13) + ZPE level, the barriers for the adiabatic dissociation of the C4-H5 and C2-C3 bonds are 6.11 and 6.94 eV in S1 and 5.71 and 6.39 eV in T1, respectively, taking the energy of S0 minimum as reference. Based on the calculated potential energy surfaces, the existence of a metastable excited molecule is anticipated upon 260-230 nm photoexcitation, which provides a probable approach for cyanoacetylene to polymerize. The internal conversion (IC) process through vibronic interaction followed by C4-H5 fission in the ground state is found to account for the observed diffuse character in the UV absorption spectrum below 240 nm.

Microscopic time-resolved imaging of singlet oxygen by delayed fluorescence in living cells.

Science.gov (United States)

Scholz, Marek; Dědic, Roman; Hála, Jan

2017-11-08

Singlet oxygen is a highly reactive species which is involved in a number of processes, including photodynamic therapy of cancer. Its very weak near-infrared emission makes imaging of singlet oxygen in biological systems a long-term challenge. We address this challenge by introducing Singlet Oxygen Feedback Delayed Fluorescence (SOFDF) as a novel modality for semi-direct microscopic time-resolved wide-field imaging of singlet oxygen in biological systems. SOFDF has been investigated in individual fibroblast cells incubated with a well-known photosensitizer aluminium phthalocyanine tetrasulfonate. The SOFDF emission from the cells is several orders of magnitude stronger and much more readily detectable than the very weak near-infrared phosphorescence of singlet oxygen. Moreover, the analysis of SOFDF kinetics enables us to estimate the lifetimes of the involved excited states. Real-time SOFDF images with micrometer spatial resolution and submicrosecond temporal-resolution have been recorded. Interestingly, a steep decrease in the SOFDF intensity after the photodynamically induced release of a photosensitizer from lysosomes has been demonstrated. This effect could be potentially employed as a valuable diagnostic tool for monitoring and dosimetry in photodynamic therapy.

Optimal free will on one side in reproducing the singlet correlation

International Nuclear Information System (INIS)

Banik, Manik; Gazi, MD. Rajjak; Das, Subhadipa; Rai, Ashutosh; Kunkri, Samir

2012-01-01

Bell’s theorem teaches us that there are quantum correlations that cannot be simulated by just shared randomness (local hidden variable). There are some recent results which simulate the singlet correlation by using either 1 bit or a binary (no-signaling) correlation which violates Bell’s inequality maximally. But there is one more possible way to simulate quantum correlation by relaxing the condition of independency of measurement on shared randomness. Recently, Hall showed that the statistics of a singlet state can be generated by sacrificing measurement independence where underlying distribution of hidden variables depends on measurement directions of both parties (Hall 2010 Phys. Rev. Lett. 105 250404). He also proved that for any model of singlet correlation, 86% measurement independence is optimal. In this paper, we show that 59% measurement independence is optimal for simulating the singlet correlation when the underlying distribution of hidden variables depends only on the measurements of one party. We also show that a distribution corresponding to this optimal lack of free will already exists in the literature which first appeared in the context of detection efficiency loophole (Gisin and Gisin 1999 Phys. Lett. A 323–7). (paper)

Computational studies of a paramagnetic planar dibenzotetraaza[14]annulene Ni(II) complex.

Science.gov (United States)

Rabaâ, Hassan; Khaledi, Hamid; Olmstead, Marilyn M; Sundholm, Dage

2015-05-28

A square-planar Ni(II) dibenzotetraaza[14]annulene complex substituted with two 3,3-dimethylindolenine groups in the meso positions has recently been synthesized and characterized experimentally. In the solid-state, the Ni(II) complex forms linear π-interacting stacks with Ni···Ni separations of 3.448(2) Å. Measurements of the temperature dependence of the magnetic susceptibility revealed a drastic change in the magnetic properties at a temperature of 13 K, indicating a transition from low-to-high spin states. The molecular structures of the free-base ligand, the lowest singlet, and triplet states of the monomer and the dimer of the Ni complex have been studied computationally using density functional theory (DFT) and ab initio correlation levels of theory. In calculations at the second-order Møller-Plesset (MP2) perturbation theory level, a large energy of 260 kcal mol(-1) was obtained for the singlet-triplet splitting, suggesting that an alternative explanation of the observed magnetic properties is needed. The large energy splitting between the singlet and triplet states suggests that the observed change in the magnetism at very low temperatures is due to spin-orbit coupling effects originating from weak interactions between the fine-structure states of the Ni cations in the complex. The lowest electronic excitation energies of the dibenzotetraaza[14]annulene Ni(II) complex calculated at the time-dependent density functional theory (TDDFT) levels are in good agreement with values deduced from the experimental UV-vis spectrum. Calculations at the second-order algebraic-diagrammatic construction (ADC(2)) level on the dimer of the meso-substituted 3,3-dimethylindolenine dibenzotetraaza[14] annulene Ni(II) complex yielded Stokes shifts of 85-100 nm for the lowest excited singlet states. Calculations of the strength of the magnetically induced ring current for the free-base 3,3-dimethylindolenine-substituted dibenzotetraaza[14]annulene show that the annulene

Deep inelastic singlet structure functions and scaling violation

Energy Technology Data Exchange (ETDEWEB)

Wen-zhu, Li; Bing-xun, Hu

1984-02-01

The flavour singlet structure functions of deep inelastic scattering processes can yield more decisive tests of QCD than the non-singlet. We give analytical expression for flavour singlet structure functions through analysing the lepton-nucleon deep inelastic scattering processes by means of QCD and using Jacobi polynomials. This expression contains 4 to 5 parameters and shows the changes of the singlet structure functions with x and Q/sup 2/ very well. In QCD leading order, the conclusion is in reasonable agreement with experimental data.

Mechanisms involved in the chemical inhibition of the Eosin-sensitized photooxidation of trypsin

Energy Technology Data Exchange (ETDEWEB)

Rizzuto, F.; Spikes, J.D.

1975-01-01

A large series of compounds was screened for ability to protect trypsin from eosin-sensitized photodynamic inactivation. Eosin-sensitized photooxidation reactions of this type typically proceed via the triplet state of the dye and often involve singlet state oxygen as the oxidizing entity. In order to determine the mechanisms by which trypsin is protected from photoinactivation, a number of good protective agents (inhibitors) and some non-protective agents were selected for more detailed flash photolysis studies. Good inhibitors such as p-phenylenediamine, n-propyl gallate, serotonin creatinine sulfate and p-toluenediamine competed efficiently with oxygen and with trypsin for reaction with the triplet state of eosin. The inhibitors were shown to quench triplet eosin to the ground state and/or reduce triplet eosin to form the semireduced eosin radical and an oxidized form of the inhibitor. In the latter case, oxidized inhibitor could react by a reverse electron transfer reaction with the semireduced eosin radical to regenerate ground state eosin and the inhibitor. The good inhibitors also competed effectively with trypsin for oxidation by semioxidized eosin, thus giving another possible protective mechanism. Non-inhibitors such as halogen ions and the paramagnetic ions Co/sup + +/, Cu/sup + +/ and Mn/sup + +/ reacted only slowly with triplet and with semioxidized eosin. The primary pathway for the eosin-sensitized photooxidation of trypsin at pH 8.0 involved singlet oxygen, although semioxidized eosin may also participate.

Antiferromagnetic–paramagnetic state transition of NiO synthesized by pulsed laser deposition

CSIR Research Space (South Africa)

Nkosi, SS

2013-01-01

Full Text Available respectively from Raman spectroscopy study. These particle sizes are known be affected by substrate temperature during the deposition. Electron spin resonance (ESR) results demonstrated a strange antiferromagnetic to paramagnetic transition at a room...

A Possible Role for Singlet Oxygen in the Degradation of Various Antioxidants. A Meta-Analysis and Review of Literature Data

Directory of Open Access Journals (Sweden)

Athinoula L. Petrou

2018-02-01

Full Text Available The thermodynamic parameters Eact, ΔH≠, ΔS≠, and ΔG≠ for various processes involving antioxidants were calculated using literature kinetic data (k, T. The ΔG≠ values of the antioxidants’ processes vary in the range 91.27–116.46 kJmol−1 at 310 K. The similarity of the ΔG≠ values (for all of the antioxidants studied is supported to be an indication that a common mechanism in the above antioxidant processes may be taking place. A value of about 10–30 kJmol−1 is the activation energy for the diffusion of reactants depending on the reaction and the medium. The energy 92 kJmol−1 is needed for the excitation of O2 from the ground to the first excited state (1Δg, singlet oxygen. We suggest the same role of the oxidative stress and specifically of singlet oxygen to the processes of antioxidants as in the processes of proteinaceous diseases. We therefore suggest a competition between the various antioxidants and the proteins of proteinaceous diseases in capturing singlet oxygen’s empty π* orbital. The concentration of the antioxidants could be a crucial factor for the competition. Also, the structures of the antioxidant molecules play a significant role since the various structures have a different number of regions of high electron density.

Technicolor Models with Color-Singlet Technifermions and their Ultraviolet Extensions

DEFF Research Database (Denmark)

Ryttov, Thomas; Shrock, Robert

2011-01-01

for the technifermions and additional color-singlet, technisinglet fermions arising from the necessity of avoiding stable bound states with exotic electric charges. Precision electroweak constraints on these models are also discussed. We determine some general properties of extended technicolor theories containing...

Paramagnetic moments in YBa2Cu3O7−δ nanocomposite films

International Nuclear Information System (INIS)

Dias, F.T.; Vieira, V.N.; Silva, D.L.; Albino Aguiar, J.; Valadão, D.R.B.; Obradors, X.; Puig, T.; Wolff-Fabris, F.; Kampert, E.

2014-01-01

Highlights: • The paramagnetic Meissner effect was observed in a nanocomposite YBaCuO thin film. • The paramagnetic moments in FC experiments were observed up to 10 T. • The paramagnetic Meissner effect increases when the magnetic field is increased. • Results may be explained based on the flux compression scenario and vortex pinning. • An apparent saturation tendency of the paramagnetic moments could be observed. - Abstract: We report on magnetization studies in YBa 2 Cu 3 O 7−δ thin films with dispersed Ba 2 YTaO 6 nanoparticles. The magnetization measurements were made using a superconducting quantum interference device (SQUID) and a vibrating sample magnetometer (VSM). Magnetic moments were measured as functions temperature using zero-field cooling (ZFC) and field-cooled (FC) prescriptions for magnetic fields up to 10 T applied parallel and perpendicular to the ab planes. A paramagnetic response related to the superconducting state was observed during the FC experiments. This effect, known as paramagnetic Meissner effect (PME), apparently increases when the magnetic field is increased. We discuss our PME results in terms of the strong pinning scenario modulated by Ba 2 YTaO 6 nanoparticles dispersed into the superconducting matrix

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.

Astrophysical constraints on singlet scalars at LHC

Energy Technology Data Exchange (ETDEWEB)

Hertzberg, Mark P.; Masoumi, Ali, E-mail: mark.hertzberg@tufts.edu, E-mail: ali@cosmos.phy.tufts.edu [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States)

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.

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

Electron paramagnetic resonance and optical properties of Cr3+ doped YAl3(BO3)4

International Nuclear Information System (INIS)

Wells, Jon-Paul R; Yamaga, Mitsuo; Han, Thomas P J; Honda, Makoto

2003-01-01

We report on the electron paramagnetic resonance (EPR) and optical absorption and fluorescence spectroscopy of YAl 3 (BO 3 ) 4 single crystals doped with 0.2 mol% of trivalent chromium. From EPR we determine that the Cr 3+ ions reside in sites of essentially octahedral symmetry with an orthorhombic distortion. The ground state 4 A 2 splitting is determined to be 2√D 2 + 3E 2 ∼ 1.05 ± 0.04 cm -1 , where D and E are fine-structure parameters, and we can attribute this splitting to the combined effect of a low-symmetry distortion and spin-orbit coupling. The g-values and fine-structure parameters D and E of the ground state 4 A 2 are measured to be g x ∼ g y ∼ g z = 1.978 ± 0.005, vertical bar D vertical bar = 0.52 ± 0.02 cm -1 and vertical bar E vertical bar 0.010 ± 0.005 cm -1 respectively. From 10 K optical absorption we have measured the position and crystal-field splittings of the 2 E, 2 T 1 , 4 T 2 , 2 T 2 and 4 T 1 states with the 4 T 2 and 4 T 1 levels appearing as vibronically broadened bands

On the ground state of Yang-Mills theory

International Nuclear Information System (INIS)

Bakry, Ahmed S.; Leinweber, Derek B.; Williams, Anthony G.

2011-01-01

Highlights: → The ground state overlap for sets of meson potential trial states is measured. → Non-uniform gluonic distributions are probed via Wilson loop operator. → The locally UV-regulated flux-tube operators can optimize the ground state overlap. - Abstract: We investigate the overlap of the ground state meson potential with sets of mesonic-trial wave functions corresponding to different gluonic distributions. We probe the transverse structure of the flux tube through the creation of non-uniform smearing profiles for the string of glue connecting two color sources in Wilson loop operator. The non-uniformly UV-regulated flux-tube operators are found to optimize the overlap with the ground state and display interesting features in the ground state overlap.

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

Flavor-singlet baryons in the graded symmetry approach to partially quenched QCD

Science.gov (United States)

Hall, Jonathan M. M.; Leinweber, Derek B.

2016-11-01

Progress in the calculation of the electromagnetic properties of baryon excitations in lattice QCD presents new challenges in the determination of sea-quark loop contributions to matrix elements. A reliable estimation of the sea-quark loop contributions represents a pressing issue in the accurate comparison of lattice QCD results with experiment. In this article, an extension of the graded symmetry approach to partially quenched QCD is presented, which builds on previous theory by explicitly including flavor-singlet baryons in its construction. The formalism takes into account the interactions among both octet and singlet baryons, octet mesons, and their ghost counterparts; the latter enables the isolation of the quark-flow disconnected sea-quark loop contributions. The introduction of flavor-singlet states enables systematic studies of the internal structure of Λ -baryon excitations in lattice QCD, including the topical Λ (1405 ).

Singlet oxygen generator for a solar powered chemically pumped iodine laser

Science.gov (United States)

Busch, G. E.

1984-01-01

The potential of solid phase endoperoxides as a means to produce single-delta oxygen in the gas phase in concentrations useful to chemical oxygen-iodine lasers was investigated. The 1,4 - endoperoxide of ethyl 3- (4-methyl - 1-naphthyl) propanoate was deposited over an indium-oxide layer on a glass plate. Single-delta oxygen was released from the endoperoxide upon heating the organic film by means of an electrical discharge through the conductive indium oxide coating. The evolution of singlet-delta oxygen was determined by measuring the dimol emission signal at 634 nm. Comparison of the measured signal with an analytic model leads to two main conclusions: virtually all the oxygen being evolved is in the singlet-delta state and in the gas phase, and there is no significant quenching other than energy pooling on the time scale of the experiment (approximately 10 msec). The use of solid phase endoperoxide as a singlet-delta oxygen generator for an oxygen-iodine laser appears promising.

Search for the QCD ground state

International Nuclear Information System (INIS)

Reuter, M.; Wetterich, C.

1994-05-01

Within the Euclidean effective action approach we propose criteria for the ground state of QCD. Despite a nonvanishing field strength the ground state should be invariant with respect to modified Poincare transformations consisting of a combination of translations and rotations with suitable gauge transformations. We have found candidate states for QCD with four or more colours. The formation of gluon condensates shows similarities with the Higgs phenomenon. (orig.)

The influence of microscopic disorder on electron paramagnetic resonance spectra of Eu2+ ions in Pb1-xGexTe

International Nuclear Information System (INIS)

Radzynski, T; Lusakowski, A; Swiatek, K; Story, T

2009-01-01

In mixed crystals, because of the different ionic radii of cations or anions and the randomness in the placement of ions of different kinds, the crystal lattice is locally deformed. Such local deformations have significant influence on the ground state splitting of magnetic ions. Because this ground state splitting is responsible for the position of the electron paramagnetic resonance (EPR) lines, microscopic disorder is one of the factors which lead to the broadening of the lines, and eventually to their disappearance. This paper is devoted to semi-quantitative analysis of the influence of microscopic disorder on EPR spectra. The theory is compared against measurements performed on mono-crystalline Pb 1-x Ge x Te epitaxial layers containing Eu 2+ ions for different germanium and europium contents. With increasing germanium content we observe gradual disappearance of the EPR lines, although macroscopically, on the basis of x-ray diffraction analysis, each layer might have been considered as a perfect crystal.

Is the ground state of Yang-Mills theory Coulombic?

Science.gov (United States)

Heinzl, T.; Ilderton, A.; Langfeld, K.; Lavelle, M.; Lutz, W.; McMullan, D.

2008-08-01

We study trial states modelling the heavy quark-antiquark ground state in SU(2) Yang-Mills theory. A state describing the flux tube between quarks as a thin string of glue is found to be a poor description of the continuum ground state; the infinitesimal thickness of the string leads to UV artifacts which suppress the overlap with the ground state. Contrastingly, a state which surrounds the quarks with non-Abelian Coulomb fields is found to have a good overlap with the ground state for all charge separations. In fact, the overlap increases as the lattice regulator is removed. This opens up the possibility that the Coulomb state is the true ground state in the continuum limit.

Holographic monitoring of spatial distributions of singlet oxygen in water

Science.gov (United States)

Belashov, A. V.; Bel'tyukova, D. M.; Vasyutinskii, O. S.; Petrov, N. V.; Semenova, I. V.; Chupov, A. S.

2014-12-01

A method for monitoring spatial distributions of singlet oxygen in biological media has been developed. Singlet oxygen was generated using Radachlorin® photosensitizer, while thermal disturbances caused by nonradiative deactivation of singlet oxygen were detected by the holographic interferometry technique. Processing of interferograms yields temperature maps that characterize the deactivation process and show the distribution of singlet oxygen species.

EPR in characterization of seeds paramagnetic species

International Nuclear Information System (INIS)

Luiz, A.P.C.; Mauro, M.F.F.L.; Portugal, K.O.; Barbana, V.M.; Guedes, C.L.B.; Mauro, E. di; Carneiro, C.E.A.; Zaia, D.A.M.; Prete, C.E.C.

2011-01-01

Full text. In Brazil, since 1970s, renewable fuel programs has been developed in order to replace petroleum. Today a program that has been discussed is the bio diesel, which intend to replace diesel fuel, fossil oil, to bio diesel, renewal fuel. As seeds are the basis for production of oil and consequently processed into bio diesel, the goal of this work is to characterize and compare paramagnetic species present in the seeds by Electron Paramagnetic Resonance (EPR). Samples used in this study were seeds of sorghum, barley, corn, peanuts, soy beans, cotton, wheat, oats, mustard, rice, sunflower and turnip. Some paramagnetic species present in soil was also investigated as goethite (FeOOH), hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), and ferrihydrite (Fe 5 HO 8 · 4H 2 O), since, these species present in appreciable quantities in the soil can be present in the seeds and analyzed for comparison. The characterization of these species is essential to understand the EPR seeds spectra. Each sample is placed in a thin quartz tube 4 mm in diameter, and it is inserted into the cavity of the spectrometer at room temperature, at low temperature (77 K) and variable temperature using liquid nitrogen flow and hot flow through a compressor air. It was used as standard Mg O:Mn 2+ , which is also inserted into the cavity. Shortly after the potency is regulated, frequency, amplitude and sweep the field. The spectroscopic analysis by EPR X-band (∼ 9:5GHz), were performed at the Fluorescence and Electron Paramagnetic Resonance Laboratory, Exact Sciences Center, State University of Londrina, Parana state, Brazil, through an EPR spectrometer JEOL brand (JES-PE-3X). In the EPR spectra, spectroscopic factor or g factor and line width were determined in paramagnetic species. Studies from several seeds with EPR technique detected in all of them presence of same complex of Fe 3+ present in the goethite at g ∼ 2, and in the seeds exist free radicals at g = 2:004, at room temperature

EPR in characterization of seeds paramagnetic species

Energy Technology Data Exchange (ETDEWEB)

Luiz, A.P.C.; Mauro, M.F.F.L.; Portugal, K.O.; Barbana, V.M.; Guedes, C.L.B.; Mauro, E. di; Carneiro, C.E.A.; Zaia, D.A.M.; Prete, C.E.C. [Universidade Estadual de Londrina (UEL), PR (Brazil)

2011-07-01

Full text. In Brazil, since 1970s, renewable fuel programs has been developed in order to replace petroleum. Today a program that has been discussed is the bio diesel, which intend to replace diesel fuel, fossil oil, to bio diesel, renewal fuel. As seeds are the basis for production of oil and consequently processed into bio diesel, the goal of this work is to characterize and compare paramagnetic species present in the seeds by Electron Paramagnetic Resonance (EPR). Samples used in this study were seeds of sorghum, barley, corn, peanuts, soy beans, cotton, wheat, oats, mustard, rice, sunflower and turnip. Some paramagnetic species present in soil was also investigated as goethite (FeOOH), hematite (Fe{sub 2}O{sub 3}), magnetite (Fe{sub 3}O{sub 4}), and ferrihydrite (Fe{sub 5}HO{sub 8} {center_dot} 4H{sub 2}O), since, these species present in appreciable quantities in the soil can be present in the seeds and analyzed for comparison. The characterization of these species is essential to understand the EPR seeds spectra. Each sample is placed in a thin quartz tube 4 mm in diameter, and it is inserted into the cavity of the spectrometer at room temperature, at low temperature (77 K) and variable temperature using liquid nitrogen flow and hot flow through a compressor air. It was used as standard Mg O:Mn{sup 2+}, which is also inserted into the cavity. Shortly after the potency is regulated, frequency, amplitude and sweep the field. The spectroscopic analysis by EPR X-band ({approx} 9:5GHz), were performed at the Fluorescence and Electron Paramagnetic Resonance Laboratory, Exact Sciences Center, State University of Londrina, Parana state, Brazil, through an EPR spectrometer JEOL brand (JES-PE-3X). In the EPR spectra, spectroscopic factor or g factor and line width were determined in paramagnetic species. Studies from several seeds with EPR technique detected in all of them presence of same complex of Fe{sup 3+} present in the goethite at g {approx} 2, and in the seeds

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

OpenAIRE

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 ...

Point defects in crystalline zircon (zirconium silicate), ZrSiO4: electron paramagnetic resonance studies

Science.gov (United States)

Tennant, W. C.; Claridge, R. F. C.; Walsby, C. J.; Lees, N. S.

This article outlines the present state of knowledge of paramagnetic defects in crystalline zircon as obtained mainly, but not exclusively, from electron paramagnetic resonance (EPR) studies in crystalline zircon (zirconium silicate, ZrSiO4). The emphasis is on single-crystal studies where, in principle, unambiguous analysis is possible. Firstly, the crystallography of zircon is presented. Secondly, the relationships between available crystal-site symmetries and the symmetries of observed paramagnetic species in zircon, and how these observations lead to unambiguous assignments of point-group symmetries for particular paramagnetic species are detailed. Next, spin-Hamiltonian (SH) analysis is discussed with emphasis on the symmetry relationships that necessarily exist amongst the Laue classes of the crystal sites in zircon, the paramagnetic species occupying those sites and the SH itself. The final sections of the article then survey the results of EPR studies on zircon over the period 1960-2002.

Generalized valence bond description of the ground states (X(1)Σg(+)) of homonuclear pnictogen diatomic molecules: N2, P2, and As2.

Science.gov (United States)

Xu, Lu T; Dunning, Thom H

2015-06-09

The ground state, X1Σg+, of N2 is a textbook example of a molecule with a triple bond consisting of one σ and two π bonds. This assignment, which is usually rationalized using molecular orbital (MO) theory, implicitly assumes that the spins of the three pairs of electrons involved in the bonds are singlet-coupled (perfect pairing). However, for a six-electron singlet state, there are five distinct ways to couple the electron spins. The generalized valence bond (GVB) wave function lifts this restriction, including all of the five spin functions for the six electrons involved in the bond. For N2, we find that the perfect pairing spin function is indeed dominant at Re but that it becomes progressively less so from N2 to P2 and As2. Although the perfect pairing spin function is still the most important spin function in P2, the importance of a quasi-atomic spin function, which singlet couples the spins of the electrons in the σ orbitals while high spin coupling those of the electrons in the π orbitals on each center, has significantly increased relative to N2 and, in As2, the perfect pairing and quasi-atomic spin couplings are on essentially the same footing. This change in the spin coupling of the electrons in the bonding orbitals down the periodic table may contribute to the rather dramatic decrease in the strengths of the Pn2 bonds from N2 to As2 as well as in the increase in their chemical reactivity and should be taken into account in more detailed analyses of the bond energies in these species. We also compare the spin coupling in N2 with that in C2, where the quasi-atomic spin coupling dominants around Re.

Is the ground state of Yang-Mills theory Coulombic?

OpenAIRE

Heinzl, Thomas; Ilderton, Anton; Langfeld, Kurt; Lavelle, Martin; Lutz, Wolfgang; McMullan, David

2008-01-01

We study trial states modelling the heavy quark-antiquark ground state in SU(2) Yang-Mills theory. A state describing the flux tube between quarks as a thin string of glue is found to be a poor description of the continuum ground state; the infinitesimal thickness of the string leads to UV artifacts which suppress the overlap with the ground state. Contrastingly, a state which surrounds the quarks with non-abelian Coulomb fields is found to have a good overlap with the ground state for all ch...

Magnetic Circular X-ray Dichroism Study of Paramagnetic and Anti-Ferromagnetic States in SrFeO3 Using a 10-T Superconducting Magnet

International Nuclear Information System (INIS)

Okamoto, J.; Mamiya, K.; Fujimori, S.-I.; Okane, T.; Saitoh, Y.; Muramatsu, Y.; Fujimori, A.; Ishiwata, S.; Takano, M.

2004-01-01

Magnetic circular x-ray dichroism (MCXD) measurements in Fe 2p absorption have been done on SrFeO3, which shows a spiral anti-ferromagnetism, by using a 10-T superconducting magnet. Finite MCXD structures have been observed under magnetic field of 8 T even in the paramagnetic and anti-ferromagnetic states. The intensity of the MCXD structure at hv ∼ 710 eV increases linearly as magnetic field increases linearly and the total magnetic moments estimated by MCXD sum rules roughly corresponds to the magnetization measured by SQUID measurements. MCXD study of paramagnetic and/or anti-ferromagnetic samples can be done by using a superconducting magnet that generates a strong magnetic field enough to induce finite magnetization

Crystalline beam ground state

International Nuclear Information System (INIS)

Wei, Jie; Li, Xiao-Ping; Sessler, A.M.

1993-01-01

In order to employ Molecular Dynamics method, commonly used in condensed matter physics, we have derived the equations of motion for a beam of charged particles in the rotating rest frame of the reference particle. We include in the formalism that the particles are confined by the guiding and focusing magnetic fields, and that they are confined in a conducting vacuum pipe while interacting with each other via a Coulomb force. Numerical simulations has been performed to obtain the equilibrium structure. The effects of the shearing force, centrifugal force, and azimuthal variation of the focusing strength are investigated. It is found that a constant gradient storage ring can not give a crystalline beam, but that an alternating-gradient (AG) structure can. In such a machine the ground state is, except for one-dimensional (1-D) crystals, time-dependent. The ground state is a zero entropy state, despite the time-dependent, periodic variation of the focusing force. The nature of the ground state, similar to that found by Rahman and Schiffer, depends upon the density and the relative focusing strengths in the transverse directions. At low density, the crystal is 1-D. As the density increases, it transforms into various kinds of 2-D and 3-D crystals. If the energy of the beam is higher than the transition energy of the machine, the crystalline structure can not be formed for lack of radial focusing

Crystalline beam ground state

International Nuclear Information System (INIS)

Wei, Jie; Li, Xiao-Ping

1993-01-01

In order to employ molecular dynamics (MD) methods, commonly used in condensed matter physics, we have derived the equations of motion for a beam of charged particles in the rotating rest frame of the reference particle. We include in the formalism that the particles are confined by the guiding and focusing magnetic fields, and that they are confined in a conducting vacuum pipe while interacting with each other via a Coulomb force. Numerical simulations using MD methods has been performed to obtain the equilibrium crystalline beam structure. The effect of the shearing force, centrifugal force, and azimuthal variation of the focusing strength are investigated. It is found that a constant gradient storage ring can not give a crystalline beam, but that an alternating-gradient (AG) structure can. In such a machine the ground state is, except for one-dimensional (1-D) crystals, time dependent. The ground state is a zero entropy state, despite the time-dependent, periodic variation of the focusing force. The nature of the ground state, similar to that found by Schiffer et al. depends upon the density and the relative focusing strengths in the transverse directions. At low density, the crystal is 1-D. As the density increases, it transforms into various kinds of 2-D and 3-D crystals. If the energy of the beam is higher than the transition energy of the machine, the crystalline structure can not be formed for lack of radial focusing

Crystalline beam ground state

International Nuclear Information System (INIS)

Wei, J.; Li, X.P.

1993-01-01

In order to employ the Molecular Dynamics method, commonly used in condensed matter physics, the authors have derived the equations of motion for a beam of charged particles in the rotating rest frame of the reference particle. They include in the formalism that the particles are confined by the guiding and focusing magnetic fields, and that they are confined in a conducting vacuum pipe while interacting with each other via a Coulomb force. Numerical simulations has been performed to obtain the equilibrium structure. The effects of the shearing force, centrifugal force, and azimuthal variation of the focusing strength are investigated. It is found that a constant gradient storage ring can not give a crystalline beam, but that an alternating-gradient (AG) structure can. In such a machine the ground state is, except for one-dimensional (1-D) crystals, time-dependent. The ground state is a zero entropy state, despite the time-dependent, periodic variation of the focusing force. The nature of the ground state, similar to that found by Rahman and Schiffer, depends upon the density and the relative focusing strengths in the transverse directions. At low density, the crystal is 1-D. As the density increases, it transforms into various kinds of 2-D and 3-D crystals. If the energy of the beam is higher than the transition energy of the machine, the crystalline structure can not be formed for lack of radial focusing

α-decay half-lives of some nuclei from ground state to ground state using different nuclear potential

Directory of Open Access Journals (Sweden)

Akrawy Dashty T.

2018-01-01

Full Text Available Theoretical α-decay half-lives of some nuclei from ground state to ground state are calculated using different nuclear potential model including Coulomb proximity potential (CPPM, Royer proximity potential and Broglia and Winther 1991. The calculated values comparing with experimental data, it is observed that the CPPM model is in good agreement with the experimental data.

Nuclear ground state

International Nuclear Information System (INIS)

Negele, J.W.

1975-01-01

The nuclear ground state is surveyed theoretically, and specific suggestions are given on how to critically test the theory experimentally. Detailed results on 208 Pb are discussed, isolating several features of the charge density distributions. Analyses of 208 Pb electron scattering and muonic data are also considered. 14 figures

Levitation in paramagnetic liquids

Energy Technology Data Exchange (ETDEWEB)

Dunne, P.A. [School of Physics and CRANN, Trinity Collge, Dublin 2 (Ireland)]. E-mail: pdunne2@tcd.ie; Hilton, J. [School of Physics and CRANN, Trinity Collge, Dublin 2 (Ireland); Coey, J.M.D. [School of Physics and CRANN, Trinity Collge, Dublin 2 (Ireland)

2007-09-15

Magnetic levitation of diamagnetic and paramagnetic substances in a paramagnetic liquid is explored. Materials ranging from graphite to tin and copper can be made to float at ambient temperature in concentrated solutions of dysprosium nitrate, when an electromagnet or four-block permanent magnet array is used to produce a gradient field. Simulations illustrate the stable regions for levitation above the permanent magnets; and a novel eight-block configuration is proposed, which allows denser materials such as gold or lead to be levitated.

Levitation in paramagnetic liquids

International Nuclear Information System (INIS)

Dunne, P.A.; Hilton, J.; Coey, J.M.D.

2007-01-01

Magnetic levitation of diamagnetic and paramagnetic substances in a paramagnetic liquid is explored. Materials ranging from graphite to tin and copper can be made to float at ambient temperature in concentrated solutions of dysprosium nitrate, when an electromagnet or four-block permanent magnet array is used to produce a gradient field. Simulations illustrate the stable regions for levitation above the permanent magnets; and a novel eight-block configuration is proposed, which allows denser materials such as gold or lead to be levitated

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

Energy Technology Data Exchange (ETDEWEB)

Ko, P., E-mail: pko@kias.re.kr; Li, Jinmian, E-mail: jmli@kias.re.kr

2017-02-10

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.

In-vivo singlet oxygen threshold doses for PDT.

Science.gov (United States)

Zhu, Timothy C; Kim, Michele M; Liang, Xing; Finlay, Jarod C; Busch, Theresa M

2015-02-01

Dosimetry of singlet oxygen ( 1 O 2 ) is of particular interest because it is the major cytotoxic agent causing biological effects for type-II photosensitizers during photodynamic therapy (PDT). An in-vivo model to determine the singlet oxygen threshold dose, [ 1 O 2 ] rx,sh , for PDT was developed. An in-vivo radiation-induced fibrosarcoma (RIF) tumor mouse model was used to correlate the radius of necrosis to the calculation based on explicit PDT dosimetry of light fluence distribution, tissue optical properties, and photosensitizer concentrations. Inputs to the model include five photosensitizer-specific photochemical parameters along with [ 1 O 2 ] rx,sh . Photosensitizer-specific model parameters were determined for benzoporphyrin derivative monoacid ring A (BPD) and compared with two other type-II photosensitizers, Photofrin ® and m-tetrahydroxyphenylchlorin (mTHPC) from the literature. The mean values (standard deviation) of the in-vivo [ 1 O 2 ] rx,sh are approximately 0.56 (0.26) and 0.72 (0.21) mM (or 3.6×10 7 and 4.6×10 7 singlet oxygen per cell to reduce the cell survival to 1/e) for Photofrin ® and BPD, respectively, assuming that the fraction of generated singlet oxygen that interacts with the cell is 1. While the values for the photochemical parameters (ξ, σ, g , β) used for BPD were preliminary and may need further refinement, there is reasonable confidence for the values of the singlet oxygen threshold doses. In comparison, the [ 1 O 2 ] rx,sh value derived from in-vivo mouse study was reported to be 0.4 mM for mTHPC-PDT. However, the singlet oxygen required per cell is reported to be 9×10 8 per cell per 1/ e fractional kill in an in-vitro mTHPC-PDT study on a rat prostate cancer cell line (MLL cells) and is reported to be 7.9 mM for a multicell in-vitro EMT6/Ro spheroid model for mTHPC-PDT. A theoretical analysis is provided to relate the number of in-vitro singlet oxygen required per cell to reach cell killing of 1/ e to in-vivo singlet

Deep two-photon microscopic imaging through brain tissue using the second singlet state from fluorescent agent chlorophyll α in spinach leaf.

Science.gov (United States)

Shi, Lingyan; Rodríguez-Contreras, Adrián; Budansky, Yury; Pu, Yang; Nguyen, Thien An; Alfano, Robert R

2014-06-01

Two-photon (2P) excitation of the second singlet (S₂) state was studied to achieve deep optical microscopic imaging in brain tissue when both the excitation (800 nm) and emission (685 nm) wavelengths lie in the "tissue optical window" (650 to 950 nm). S₂ state technique was used to investigate chlorophyll α (Chl α) fluorescence inside a spinach leaf under a thick layer of freshly sliced rat brain tissue in combination with 2P microscopic imaging. Strong emission at the peak wavelength of 685 nm under the 2P S₂ state of Chl α enabled the imaging depth up to 450 μm through rat brain tissue.

Exchange interactions in two-state systems: rare earth pyrochlores

Science.gov (United States)

Curnoe, S. H.

2018-06-01

The general form of the nearest neighbour exchange interaction for rare earth pyrochlores is derived based on symmetry. Generally, the rare earth angular momentum degeneracy is lifted by the crystal electric field (CEF) into singlets and doublets. When the CEF ground state is a doublet that is well-separated from the first excited state the CEF ground state doublet can be treated as a pseudo-spin of some kind. The general form of the nearest neighbour exchange interaction for pseudo-spins on the pyrochlore lattice is derived for three different types of pseudo-spins. The methodology presented in this paper can be applied to other two-state spin systems with a high space group symmetry.

Reliable Prediction with Tuned Range-Separated Functionals of the Singlet-Triplet Gap in Organic Emitters for Thermally Activated Delayed Fluorescence (TADF)

KAUST Repository

Sun, Haitao; Zhong, Cheng; Bredas, Jean-Luc

2015-01-01

excited states. Here, we demonstrate that time-dependent density functional theory (TD-DFT) in the Tamm-Dancoff Approximation can be very successful in the calculations of the lowest singlet and triplet excitation energies and the corresponding singlet

Characterization of photoactivated singlet oxygen damage in single-molecule optical trap experiments.

Science.gov (United States)

Landry, Markita P; McCall, Patrick M; Qi, Zhi; Chemla, Yann R

2009-10-21

Optical traps or "tweezers" use high-power, near-infrared laser beams to manipulate and apply forces to biological systems, ranging from individual molecules to cells. Although previous studies have established that optical tweezers induce photodamage in live cells, the effects of trap irradiation have yet to be examined in vitro, at the single-molecule level. In this study, we investigate trap-induced damage in a simple system consisting of DNA molecules tethered between optically trapped polystyrene microspheres. We show that exposure to the trapping light affects the lifetime of the tethers, the efficiency with which they can be formed, and their structure. Moreover, we establish that these irreversible effects are caused by oxidative damage from singlet oxygen. This reactive state of molecular oxygen is generated locally by the optical traps in the presence of a sensitizer, which we identify as the trapped polystyrene microspheres. Trap-induced oxidative damage can be reduced greatly by working under anaerobic conditions, using additives that quench singlet oxygen, or trapping microspheres lacking the sensitizers necessary for singlet state photoexcitation. Our findings are relevant to a broad range of trap-based single-molecule experiments-the most common biological application of optical tweezers-and may guide the development of more robust experimental protocols.

Acceleration of Singlet Fission in an Aza-Derivative of TIPS-Pentacene.

Science.gov (United States)

Herz, Julia; Buckup, Tiago; Paulus, Fabian; Engelhart, Jens; Bunz, Uwe H F; Motzkus, Marcus

2014-07-17

The influence of the carbon to nitrogen substitution on the photoinduced dynamics of TIPS-pentacene was investigated by ultrafast transient absorption measurements on spin-coated thin films in the visible and in the near-infrared spectral region. A global target analysis was performed to provide a detailed picture of the excited-state dynamics. We found that the chemical modification has a high impact on the triplet formation and leads to shorter dynamics; hence it speeds up the singlet fission process. A faster relaxation from the singlet into the triplet manifold implies a higher efficiency because other relaxation channels are avoided. The air-stable aza-derivatives have the potential to exceed the energy conversion efficiency of TIPS-pentacene.

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.)

The electroweak phase transition in models with gauge singlets

International Nuclear Information System (INIS)

Ahriche, A.

2007-01-01

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 Ω(T c )/T c >or similar 1, where Ω = (v 2 + (x - x 0 ) 2 ) ( 1)/(2) and x(x 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 c /T 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.)

Identification of quenchers of photoexcited States as novel agents for skin photoprotection.

Science.gov (United States)

Wondrak, Georg T; Jacobson, Myron K; Jacobson, Elaine L

2005-02-01

Photooxidative stress is a key mechanism in UVA-induced skin photodamage. Photoexcited states of endogenous UVA chromophores such as porphyrins, melanin precursors, and cross-link-fluorophores of skin collagen exert skin photodamage by direct reaction with substrate molecules (type I photosensitization) or molecular oxygen (type II), leading to formation of reactive oxygen species. Based on our previous research on the role of photoexcited states of endogenous skin chromophores as sensitizers of photooxidative stress, we describe here the identification of a novel class of chemopreventive agents for topical skin photoprotection: quenchers of photoexcited states (QPES). QPES compounds antagonize the harmful excited state chemistry of endogenous sensitizers by physical quenching, facilitating the harmless return of the sensitizer excited state to the electronic ground state by energy dissipation. To identify QPES compounds suitable for development, we designed a primary screening assay based on QPES suppression of photosensitized plasmid cleavage using conditions that exclude antioxidants. This screen is followed with a screen to test for nonsacrificial quenching of dye-sensitized singlet oxygen ((1)O(2)) formation by electron paramagnetic resonance detection of 2,2,6,6-tetramethyl-piperidine-1-oxyl, a stable free radical indicative of (1)O(2) formation. These initial screens identified a pyrrolidine pharmacophore with pronounced QPES activity, and l-proline and other noncytotoxic proline derivatives containing this pharmacophore were then screened for efficacy in cellular models of sensitized photodamage. These compounds showed QPES protection against dye-sensitized and psoralen-UVA-induced apoptosis and suppression of proliferation in cultured human skin keratinocytes and fibroblasts. Furthermore, QPES photoprotection of reconstructed full thickness human skin exposed to solar simulated light has been demonstrated.

Derivation of the RPA (Random Phase Approximation) Equation of ATDDFT (Adiabatic Time Dependent Density Functional Ground State Response Theory) from an Excited State Variational Approach Based on the Ground State Functional.

Science.gov (United States)

Ziegler, Tom; Krykunov, Mykhaylo; Autschbach, Jochen

2014-09-09

The random phase approximation (RPA) equation of adiabatic time dependent density functional ground state response theory (ATDDFT) has been used extensively in studies of excited states. It extracts information about excited states from frequency dependent ground state response properties and avoids, thus, in an elegant way, direct Kohn-Sham calculations on excited states in accordance with the status of DFT as a ground state theory. Thus, excitation energies can be found as resonance poles of frequency dependent ground state polarizability from the eigenvalues of the RPA equation. ATDDFT is approximate in that it makes use of a frequency independent energy kernel derived from the ground state functional. It is shown in this study that one can derive the RPA equation of ATDDFT from a purely variational approach in which stationary states above the ground state are located using our constricted variational DFT (CV-DFT) method and the ground state functional. Thus, locating stationary states above the ground state due to one-electron excitations with a ground state functional is completely equivalent to solving the RPA equation of TDDFT employing the same functional. The present study is an extension of a previous work in which we demonstrated the equivalence between ATDDFT and CV-DFT within the Tamm-Dancoff approximation.

EPR and optical absorption studies of paramagnetic molecular ion (VO2+) in Lithium Sodium Acid Phthalate single crystal

Science.gov (United States)

Subbulakshmi, N.; Kumar, M. Saravana; Sheela, K. Juliet; Krishnan, S. Radha; Shanmugam, V. M.; Subramanian, P.

2017-12-01

Electron Paramagnetic Resonance (EPR) spectroscopic studies of VO2+ ions as paramagnetic impurity in Lithium Sodium Acid Phthalate (LiNaP) single crystal have been done at room temperature on X-Band microwave frequency. The lattice parameter values are obtained for the chosen system from Single crystal X-ray diffraction study. Among the number of hyperfine lines in the EPR spectra only two sets are reported from EPR data. The principal values of g and A tensors are evaluated for the two different VO2+ sites I and II. They possess the crystalline field around the VO2+ as orthorhombic. Site II VO2+ ion is identified as substitutional in place of Na1 location and the other site I is identified as interstitial location. For both sites in LiNaP, VO2+ are identified in octahedral coordination with tetragonal distortion as seen from the spin Hamiltonian parameter values. The ground state of vanadyl ion in the LiNaP single crystal is dxy. Using optical absorption data the octahedral and tetragonal parameters are calculated. By correlating EPR and optical data, the molecular orbital bonding parameters have been discussed for both sites.

Colour singlets in perturbative QCD

International Nuclear Information System (INIS)

Bassetto, A.

1979-01-01

In the axial gauge and at the leading log level, a definite and consistent picture seems to emerge of a parton decay into states in which many partons are found just before confinement should take place. They are grouped into colourless clusters in a number sufficient to exhaust the ''final'' state, still possessing a finite average mass. This result is peculiar of QCD, in particular of its non-abelian nature. Large transverse momenta or more generally average invariant quantities of partons are mainly due to the multiplicities involved in the branching processes. If eventually confinement would convert these clusters into hadrons (and this is of course the main issue which has still to be proven) without a large rearrangement of the colour lines, the picture we have found for colour singlets could apply to the real hadronic world. (author)

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...

Does interchain stacking morphology contribute to the singlet-triplet interconversion dynamics in polymer heterojunctions?

Energy Technology Data Exchange (ETDEWEB)

Bittner, Eric R. [Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, TX 77204 (United States)], E-mail: bittner@uh.edu; Burghardt, Irene [Departement de Chimie, Ecole Normale Superieure, 24 rue Lhomond, F-75231 Paris cedex 05 (France); Friend, Richard H. [Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE (United Kingdom)

2009-02-23

Time-dependent density functional theory (TD-DFT) is used to examine the effect of stacking in a model semiconducting polymer hetrojunction system consisting of two co-facially stacked oligomers. We find that the excited electronic states are highly sensitive to the alignment of the monomer units of the two chains. In the system we examined, the exchange energy is nearly identical to both the and band off-set at the heterojunction and to the exciton binding energy. Our results indicate that the triplet excitonic states are nearly degenerate with the singlet exciplex states opening the possibility for the interconversion of singlet and triplet electronic states at the heterojunction interface via spin-orbit coupling localized on the heteroatoms. Using Russell-Saunders theory, we estimate this interconversion rate to be approximately 700-800 ps, roughly a 5-10-fold increase compared to isolated organic polymer chains.

NMR study on the low-temperature state of LaMn4Al8

International Nuclear Information System (INIS)

Muro, Y.; Nakamura, H.; Kohara, T.

2007-01-01

The ground state of the quasi-one-dimensional itinerant electron magnet LaMn 4 Al 8 with strong electron correlation has been investigated by NMR. The presence of weak and broad zero-field 55 Mn resonance, corresponding to internal field of 8-11T, indicates slowing down of spins partially released from the spin-singlet-like state in the spin chains

Classical many-particle systems with unique disordered ground states

Science.gov (United States)

Zhang, G.; Stillinger, F. H.; Torquato, S.

2017-10-01

Classical ground states (global energy-minimizing configurations) of many-particle systems are typically unique crystalline structures, implying zero enumeration entropy of distinct patterns (aside from trivial symmetry operations). By contrast, the few previously known disordered classical ground states of many-particle systems are all high-entropy (highly degenerate) states. Here we show computationally that our recently proposed "perfect-glass" many-particle model [Sci. Rep. 6, 36963 (2016), 10.1038/srep36963] possesses disordered classical ground states with a zero entropy: a highly counterintuitive situation . For all of the system sizes, parameters, and space dimensions that we have numerically investigated, the disordered ground states are unique such that they can always be superposed onto each other or their mirror image. At low energies, the density of states obtained from simulations matches those calculated from the harmonic approximation near a single ground state, further confirming ground-state uniqueness. Our discovery provides singular examples in which entropy and disorder are at odds with one another. The zero-entropy ground states provide a unique perspective on the celebrated Kauzmann-entropy crisis in which the extrapolated entropy of a supercooled liquid drops below that of the crystal. We expect that our disordered unique patterns to be of value in fields beyond glass physics, including applications in cryptography as pseudorandom functions with tunable computational complexity.

Cavity optomechanics -- beyond the ground state

Science.gov (United States)

Meystre, Pierre

2011-05-01

The coupling of coherent optical systems to micromechanical devices, combined with breakthroughs in nanofabrication and in ultracold science, has opened up the exciting new field of cavity optomechanics. Cooling of the vibrational motion of a broad range on oscillating cantilevers and mirrors near their ground state has been demonstrated, and the ground state of at least one such system has now been reached. Cavity optomechanics offers much promise in addressing fundamental physics questions and in applications such as the detection of feeble forces and fields, or the coherent control of AMO systems and of nanoscale electromechanical devices. However, these applications require taking cavity optomechanics ``beyond the ground state.'' This includes the generation and detection of squeezed and other non-classical states, the transfer of squeezing between electromagnetic fields and motional quadratures, and the development of measurement schemes for the characterization of nanomechanical structures. The talk will present recent ``beyond ground state'' developments in cavity optomechanics. We will show how the magnetic coupling between a mechanical membrane and a BEC - or between a mechanical tuning fork and a nanoscale cantilever - permits to control and monitor the center-of-mass position of the mechanical system, and will comment on the measurement back-action on the membrane motion. We will also discuss of state transfer between optical and microwave fields and micromechanical devices. Work done in collaboration with Dan Goldbaum, Greg Phelps, Keith Schwab, Swati Singh, Steve Steinke, Mehmet Tesgin, and Mukund Vengallatore and supported by ARO, DARPA, NSF, and ONR.

On the ground state of Yang-Mills theory

OpenAIRE

Bakry, Ahmed S.; Leinweber, Derek B.; Williams, Anthony G.

2011-01-01

We investigate the overlap of the ground state meson potential with sets of mesonic-trial wave functions corresponding to different gluonic distributions. We probe the transverse structure of the flux tube through the creation of non-uniform smearing profiles for the string of glue connecting two color sources in Wilson loop operator. The non-uniformly UV-regulated flux-tube operators are found to optimize the overlap with the ground state and display interesting features in the ground state ...

On the ground state of Yang-Mills theory

Science.gov (United States)

Bakry, Ahmed S.; Leinweber, Derek B.; Williams, Anthony G.

2011-08-01

We investigate the overlap of the ground state meson potential with sets of mesonic-trial wave functions corresponding to different gluonic distributions. We probe the transverse structure of the flux tube through the creation of non-uniform smearing profiles for the string of glue connecting two color sources in Wilson loop operator. The non-uniformly UV-regulated flux-tube operators are found to optimize the overlap with the ground state and display interesting features in the ground state overlap.

Unitarity constraints in the standard model with a singlet scalar field

International Nuclear Information System (INIS)

Kang, Sin Kyu; Park, Jubin

2015-01-01

Motivated by the discovery of a new scalar field and amelioration of the electroweak vacuum stability ascribed to a singlet scalar field embedded in the standard model (SM), we examine the implication of the perturbative unitarity in the SM with a singlet scalar field. Taking into account the full contributions to the scattering amplitudes, we derive unitarity conditions on the scattering matrix which can be translated into bounds on the masses of the scalar fields. In the case that the singlet scalar field develops vacuum expectation value (VEV), we get the upper bound on the singlet scalar mass varying with the mixing between the singlet and Higgs scalars. On the other hand, the mass of the Higgs scalar can be constrained by the unitarity condition in the case that the VEV of the singlet scalar is not generated. Applying the upper bound on the Higgs mass to the scenario of the unitarized Higgs inflation, we discuss how the unitarity condition can constrain the Higgs inflation. The singlet scalar mass is not constrained by the unitarity itself when we impose Z 2 in the model because of no mixing with the Higgs scalar. But, regarding the singlet scalar field as a cold dark matter candidate, we derive upper bound on the singlet scalar mass by combining the observed relic abundance with the unitarity condition.

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.

Electron affinity and excited states of methylglyoxal

Science.gov (United States)

Dauletyarov, Yerbolat; Dixon, Andrew R.; Wallace, Adam A.; Sanov, Andrei

2017-07-01

Using photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X2A″ electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closed-shell singlet ground state (X1A'), the lowest triplet state (a3A″), and the open-shell singlet state (A1A″). The adiabatic electron affinity (EA) of the ground state, EA(X1A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a3A″) = 3.27(2) eV and EA(A1A″) = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a3A″ ← X2A″ and A1A″ ← X2A″ photodetachment transitions are dominated by intense peaks at their respective origins. The lowest-energy photodetachment transition, on the other hand, involves significant geometry relaxation in the X1A' state, which corresponds to a 60° internal rotation of the methyl group, compared to the anion structure. Accordingly, the X1A' ← X2A″ transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equation-of-motion methodologies, combined with coupled-cluster theory.

Induced Orbital Paramagnetism and Paratropism in Closed-Shell Molecules

Science.gov (United States)

Pelloni, Stefano; Lazzeretti, Paolo; Zanasi, Riccardo

2009-07-01

Three-dimensional models of the quantum-mechanical current density induced by a uniform magnetic field in the electron cloud have been obtained for closed-shell systems BeH-, BH, and CH+, characterized by induced orbital paramagnetism, and in planar unsaturated hydrocarbons C4H4 and clamped C8H8, exhibiting π paramagnetism. It is shown that, even for these paramagnetic systems, the paramagnetic contributions to magnetic susceptibilities and nuclear magnetic shielding, customarily taken into account in perturbation theory approaches, can formally be eliminated via the procedure of continuous transformation of the origin of the current density-paramagnetic zero. The definition of magnetic response properties can therefore be recast as a sum of two formally "diamagnetic" terms for any molecule, including systems showing strong induced orbital paramagnetism. It is shown that the paramagnetism in the compounds studied arises from the nodal topology of the electronic wave function. In particular, paratropic vortices circulate about stagnation lines at the intersection of nodal surfaces of the highest-occupied zero-order molecular orbital and corresponding first-order orbital.

Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds.

Science.gov (United States)

Siddique, Zainul Abedin; Yamamoto, Yuichi; Ohno, Takeshi; Nozaki, Koichi

2003-10-06

The photophysical properties of singlet and triplet metal-to-ligand charge transfer (MLCT) states of [Cu(I)(diimine)(2)](+), where diimine is 2,9-dimethyl-1,10-phenanthroline (dmphen), 2,9-dibutyl-1,10-phenanthroline (dbphen), or 6,6'-dimethyl-2,2'-bipyridine (dmbpy), were studied. On 400 nm laser excitation of [Cu(dmphen)(2)](+) in CH(2)Cl(2) solution, prompt (1)MLCT fluorescence with a quantum yield of (2.8 +/- 0.8) x 10(-5) was observed using a picosecond time-correlated single photon counting technique. The quantum yield was dependent on the excitation wavelength, suggesting that relaxation of the Franck-Condon state to the lowest (1)MLCT competes with rapid intersystem crossing (ISC). The fluorescence lifetime of the copper(I) compound was 13-16 ps, unexpectedly long despite a large spin-orbit coupling constant of 3d electrons in copper (829 cm(-1) ). Quantum chemical calculations using a density functional theory revealed that the structure of the lowest (1)MLCT in [Cu(dmphen)(2)](+) (1(1)B(1)) was flattened due to the Jahn-Teller effect in 3d(9) electronic configuration, and the dihedral angle between the two phenanthroline planes (dha) was about 75 degrees with the dha around 90 degrees in the ground state. Intramolecular reorganization energy for the radiative transition of 1(1)B(1) was calculated as 2.1 x 10(3) cm(-1), which is responsible for the large Stokes shift of the fluorescence observed (5.4 x 10(3) cm(-1)). To understand the sluggishness of the intersystem crossing (ISC) of (1)MLCT of the copper(I) compounds, the strength of the spin-orbit interaction between the lowest (1)MLCT (1(1)B(1)) and all (3)MLCT states was calculated. The ISC channels induced by strong spin-orbit interactions (ca. 300 cm(-1)) between the metal-centered HOMO and HOMO - 1 were shown to be energetically unfavorable in the copper(I) compounds because the flattening distortion caused large splitting (6.9 x 10(3) cm(-1)) between these orbitals. The possible ISC is therefore

On the paramagnetism of spin in the classical limit

International Nuclear Information System (INIS)

Hogreve, H.

1985-12-01

We consider particles with spin 1/2 in external electromagnetic fields. Although in many quantum mechanical situations they show a paramagnetic behaviour, within non-relativistic quantum theory a universal paramagnetic influence of spin fails to be true in general. Here we investigate the paramagnetism of spin in the framework of a classical theory. Applying previous results for the classical limit slash-h→O we obtain a classical expression corresponding to the quantum partition function of Hamiltonians with spin variables. For this classical partition function simple estimates lead to a paramagnetic inequality which demonstrates that indeed in the classical limit the spin shows a general paramagnetic behaviour. (author)

Hyperpolarized singlet NMR on a small animal imaging system

DEFF Research Database (Denmark)

Laustsen, Christoffer; Pileio, Giuseppe; Tayler, Michael C. D.

2012-01-01

Nuclear spin hyperpolarization makes a significant advance toward overcoming the sensitivity limitations of in vivo magnetic resonance imaging, particularly in the case of low-gamma nuclei. The sensitivity may be improved further by storing the hyperpolarization in slowly relaxing singlet...... populations of spin- 1/2 pairs. Here, we report hyperpolarized 13C spin order transferred into and retrieved from singlet spin order using a small animal magnetic resonance imaging scanner. For spins in sites with very similar chemical shifts, singlet spin order is sustained in high magnetic field without...... requiring strong radiofrequency irradiation. The demonstration of robust singlet-to-magnetization conversion, and vice versa, on a small animal scanner, is promising for future in vivo and clinical deployments....

Mild hydrothermal crystal growth of new uranium(IV) fluorides, Na3.13Mg1.43U6F30 and Na2.50Mn1.75U6F30: Structures, optical and magnetic properties

Science.gov (United States)

Yeon, Jeongho; Smith, Mark D.; Tapp, Joshua; Möller, Angela; zur Loye, Hans-Conrad

2016-04-01

Two new uranium(IV) fluorides, Na3.13Mg1.43U6F30 (1) and Na2.50Mn1.75U6F30 (2), were synthesized through an in situ mild hydrothermal route, and were structurally characterized by single crystal X-ray diffraction. The compounds exhibit complex crystal structures composed of corner- or edge-shared UF9 and MF6 (M=Mg, Mn) polyhedra, forming hexagonal channels in the three-dimensional framework, in which ordered or disordered divalent metal and sodium atoms reside. The large hexagonal voids contain the nearly regular M(II)F6 octahedra and sodium ions, whereas the small hexagonal cavities include M(II) and sodium ions on a mixed-occupied site. Magnetic susceptibility measurements yielded effective magnetic moments of 8.36 and 11.6 μB for 1 and 2, respectively, confirming the presence and oxidation states of U(IV) and Mn(II). The large negative Weiss constants indicate the spin gap between a triplet and a singlet state in the U(IV). Magnetization data as a function of applied fields revealed that 2 exhibits paramagnetic behavior due to the nonmagnetic singlet ground state of U(IV) at low temperature. UV-vis diffuse reflectance and X-ray photoelectron spectroscopy data were also analyzed.

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...

Impact of Dielectric Constant on the Singlet-Triplet Gap in Thermally Activated Delayed Fluorescence (TADF) Materials

KAUST Repository

Sun, Haitao

2017-04-28

Thermally activated delayed fluorescence (TADF) relies on the presence of a very small energy gap, ΔEST, between the lowest singlet and triplet excited states. ΔEST is thus a key factor in the molecular design of more efficient materials. However, its accurate theoretical estimation remains challenging, especially in the solid state due to the influence of polarization effects. We have quantitatively studied ΔEST as a function of dielectric constant, ε, for four representative organic molecules using the methodology we recently proposed at the Tamm-Dancoff approximation ωB97X level of theory, where the range-separation parameter ω is optimized with the polarizable continuum model. The results are found to be in very good agreement with experimental data. Importantly, the polarization effects can lead to a marked reduction in the ΔEST value, which is favorable for TADF applications. This ΔEST decrease in the solid state is related to the hybrid characters of the lowest singlet and triplet excited states, whose dominant contribution switches to charge-transfer-like with increasing ε. The present work provides a theoretical understanding on the influence of polarization effect on the singlet-triplet gap and confirms our methodology to be a reliable tool for the prediction and development of novel TADF materials.

Paramagnetic contrast material

International Nuclear Information System (INIS)

McNamara, M.T.

1987-01-01

Paramagnetic contrast materials have certainly demonstrated clinical utility in a variety of organ systems for improved detection of various neoplastic, inflammatory, infectious, and physiologic abnormalities. Although the more commonly employed extracellular agents, such as Gd-DTPA, have been quite safe and useful, particularly in the CNS, it is almost certain that other substances will achieve more success in various other organs, such as iron oxides in the reticuloendothelial system and persisting extracellular agents in the cardiovascular system. Finally, as MRI technology continues to evolve, producing such exciting new sequences as gradient-echo fast scans, the roles of currently existing and newly discovered paramagnetic pharmaceuticals must be continuously reevaluated both to obtain maximum clinical benefit and to guide the search for newer agents that may further optimize the diagnostic efficacy of MRI

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.

Ground state searches in fcc intermetallics

International Nuclear Information System (INIS)

Wolverton, C.; de Fontaine, D.; Ceder, G.; Dreysse, H.

1991-12-01

A cluster expansion is used to predict the fcc ground states, i.e., the stable phases at zero Kelvin as a function of composition, for alloy systems. The intermetallic structures are not assumed, but derived regorously by minimizing the configurational energy subject to linear constraints. This ground state search includes pair and multiplet interactions which spatially extend to fourth nearest neighbor. A large number of these concentration-independent interactions are computed by the method of direct configurational averaging using a linearized-muffin-tin orbital Hamiltonian cast into tight binding form (TB-LMTO). The interactions, derived without the use of any adjustable or experimentally obtained parameters, are compared to those calculated via the generalized perturbation method extention of the coherent potential approximation within the context of a KKR Hamiltonian (KKR-CPA-GPM). Agreement with the KKR-CPA-GPM results is quite excellent, as is the comparison of the ground state results with the fcc-based portions of the experimentally-determined phase diagrams under consideration

High-frequency two-electron photoionization cross section of triplet states

International Nuclear Information System (INIS)

Krivec, R.; Amusia, M.Ya.; Mandelzweig, V.B.

2003-01-01

Using high precision wave functions describing the triplet ground and excited 3 S states of the He atom and heliumlike ions, the cross sections of single- and double-electron photoionization are calculated. The dependence of the ratio R of the double and single ionization cross sections on the nuclear charge Z and the principal quantum number of excitation n is studied. The results obtained are compared to those for previously studied singlet states

Singlet-triplet splittings from the virial theorem and single-particle excitation energies

Science.gov (United States)

Becke, Axel D.

2018-01-01

The zeroth-order (uncorrelated) singlet-triplet energy difference in single-particle excited configurations is 2Kif, where Kif is the Coulomb self-energy of the product of the transition orbitals. Here we present a non-empirical, virial-theorem argument that the correlated singlet-triplet energy difference should be half of this, namely, Kif. This incredibly simple result gives vertical HOMO-LUMO excitation energies in small-molecule benchmarks as good as the popular TD-B3LYP time-dependent approach to excited states. For linear acenes and nonlinear polycyclic aromatic hydrocarbons, the performance is significantly better than TD-B3LYP. In addition to the virial theorem, the derivation borrows intuitive pair-density concepts from density-functional theory.

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

The response of individual HeLa cells to extracellularly produced singlet oxygen was examined. The spatial domain of singlet oxygen production was controlled using the combination of a membrane-impermeable Pd porphyrin-dendrimer, which served as a photosensitizer, and a focused laser, which served...... 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...

Electron paramagnetic resonance study of Ce doped partially stabilized ZrO2 crystals

Directory of Open Access Journals (Sweden)

Mikhail А. Borik

2017-09-01

Full Text Available ZrO2 (PSZ solid solutions crystals stabilized with yttrium and cerium oxides have been studied using electron paramagnetic resonance (EPR in the X and Q ranges. Zr3+ have been observed centers in the as-annealed ZrO2 crystals stabilized only by yttrium oxide (2.8 mol% Y2O3. Another type of paramagnetic-O-centers appear as a result of CeO2 addition to ZrO2 crystals along with yttrium oxide. To estimate the concentration of Ce3+ ions in PZS crystals, we recorded the EPR spectra in the presence of a reference at 7 K. Paramagnetic Ce3+ ions have been identified and their relative amount in the PSZ crystals before and after high-temperature heat treatment has been assessed. Annealing in air leads decreases the concentration of Ce3+ ions for all the test compositions and changes the color of the crystals from red to white. After annealing of the sample 2.0Y0.8Ce3Zr, the amount of paramagnetic Ce3+ ions decreased approximately twofold. Paramagnetic centers from Ce3+ have not been detected in the specimen with a low cerium content of 0.1 mol% after annealing which indicates the complete transition of Ce3+ to the Ce4+ state. We show that the forming cerium paramagnetic centers are bound by strong exchange interactions. No angular dependence of the EPR lines of the paramagnetic Ce3+ cations on the applied external magnetic field has been observed. Probable origin of the absence of angular dependence is that the impurity rare-earth ions are located close to one another, forming impurity clusters with an effective spin of Seff=1/2.

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 (plate is illuminated from above to generate singlet oxygen at the surface of the sensitizer. The singlet oxygen thus generated can diffuse the short dis-tance to the surface of the membrane to react with the bacteria. Because of the short lifetime of singlet oxygen in air, increasing the distance between the sensitizer and the membrane causes a decline in the amount of singlet oxygen reaching the membrane according to a function derived from the Einstein-Smoluchowski equation for net displacement by diffusion. Plotting the log of the effect measured (e.g., cytotoxicity) vs. the square of the distance gives a straight line. The slope of this line can be used to calculate the gas phase half life of the intermediate responsible for the observed effects. We have found that bacteria are rapidly killed in the illuminated S-S-S system and that the gas phase half life of the agent responsible for cell killing is the same as that of singlet oxygen. This observation and other simple chemical tests have conclusively estab-lished that singlet oxygen is responsible for the cytotoxicity observed with bacteria. Dosimetry

Superconductivity without inversion symmetry in CePt3Si

International Nuclear Information System (INIS)

Frigeri, P.A.; Agterberg, D.F.; Koga, A.; Sigrist, M.

2005-01-01

Based on symmetry arguments by Anderson, the following conditions are necessary for the formation of Cooper pairs: spin-singlet pairing relies on time-reversal symmetry, while spin-triplet pairing requires parity in addition. The rather general formulation of this rule has led to the common belief that the lack of an inversion center in a material would prevent spin-triplet pairing indiscriminately. In this presentation, we discuss symmetry aspects of superconductivity in a class of systems without inversion symmetry which is connected with spin-orbit coupling. We can show that, not only spin singlet pairing, but also certain spin triplet states remain unaffected by the loss of inversion symmetry. Moreover, the absence of an inversion center reduces the effect of paramagnetic limiting for spin-singlet pairing states in an external magnetic field. Based on this symmetry analysis, we examine the recently discovered heavy Fermion superconductor CePt 3 Si, where a missing inversion plane leads to the well-known Rashba-type of spin-orbit coupling. In particular, the problem of the pairing symmetry will be addressed as well as several properties of the superconducting phase which appears close to a quantum phase transition between a paramagnetic and antiferromagnetic phase. The same kind of analysis will also be done for another example UIr

Novel mutations in the PRX and the MTMR2 genes are responsible for unusual Charcot-Marie-Tooth disease phenotypes.

Science.gov (United States)

Nouioua, Sonia; Hamadouche, Tarik; Funalot, Benoit; Bernard, Rafaëlle; Bellatache, Nora; Bouderba, Radia; Grid, Djamel; Assami, Salima; Benhassine, Traki; Levy, Nicolas; Vallat, Jean-Michel; Tazir, Meriem

2011-08-01

Autosomal recessive Charcot-Marie-Tooth diseases, relatively common in Algeria due to high prevalence of consanguineous marriages, are clinically and genetically heterogeneous. We report on two consanguineous families with demyelinating autosomal recessive Charcot-Marie-Tooth disease (CMT4) associated with novel homozygous mutations in the MTMR2 gene, c.331dupA (p.Arg111LysfsX24) and PRX gene, c.1090C>T (p.Arg364X) respectively, and peculiar clinical phenotypes. The three patients with MTMR2 mutations (CMT4B1 family) had a typical phenotype of severe early onset motor and sensory neuropathy with typical focally folded myelin on nerve biopsy. Associated clinical features included vocal cord paresis, prominent chest deformities and claw hands. Contrasting with the classical presentation of CMT4F (early-onset Dejerine-Sottas phenotype), the four patients with PRX mutations (CMT4F family) had essentially a late age of onset and a protracted and relatively benign evolution, although they presented marked spine deformities. These observations broaden the spectrum of clinical phenotypes associated with these two CMT4 forms. Copyright © 2011 Elsevier B.V. All rights reserved.

The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: Implications for the enzyme mechanism‡

Science.gov (United States)

Ogura, Hiroshi; Evans, John P.; Peng, Dungeng; Satterlee, James D.; de Montellano, Paul R. Ortiz; Mar, Gerd N. La

2009-01-01

The active site electronic structure of the azide complex of substrate-bound human heme oxygenase-1, (hHO) has been investigated by 1H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. 2D 1H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts, that places the lone iron π-spin in the dxz orbital, rather than the dyz orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy and magnetic susceptibilities argues for a low-spin, (dxy)2(dyz,dxz)3, ground state in both azide and cyanide complexes. The switch from singly-occupied dyz for the cyanide to dxz for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide π-plane in the latter complex, which is ∼90° in-plane rotated from that of the imidazole π-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicate that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 → Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed. PMID:19243105

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

KAUST Repository

Filatov, Mikhail A.; Karuthedath, Safakath; Polestshuk, Pavel M.; Savoie, Huguette; Flanagan, Keith J.; Sy, Cindy; Sitte, Elisabeth; Telitchko, Maxime; Laquai, Fré dé ric; Boyle, Ross W.; Senge, Mathias O.

2017-01-01

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

KAUST Repository

Filatov, Mikhail A.

2017-04-14

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Non-diagonal processes of singlet and ordinary quark production

International Nuclear Information System (INIS)

Bejlin, V.A.; Vereshkov, G.M.; Kuksa, V.I.

1995-01-01

Non-diagonal processes of singlet and ordinary quark production are analyzed in the model where the down singlet quark mixes with the ordinary ones. The possibility of experimental selection of h-quark effects is demonstrated

Large Mn25 single-molecule magnet with spin S = 51/2: magnetic and high-frequency electron paramagnetic resonance spectroscopic characterization of a giant spin state.

Science.gov (United States)

Murugesu, Muralee; Takahashi, Susumu; Wilson, Anthony; Abboud, Khalil A; Wernsdorfer, Wolfgang; Hill, Stephen; Christou, George

2008-10-20

The synthesis and structural, spectroscopic, and magnetic characterization of a Mn25 coordination cluster with a large ground-state spin of S = 51/2 are reported. Reaction of MnCl2 with pyridine-2,6-dimethanol (pdmH2) and NaN3 in MeCN/MeOH gives the mixed valence cluster [Mn25O18(OH)2(N3)12(pdm)6(pdmH)6]Cl2 (1; 6Mn(II), 18Mn(III), Mn(IV)), which has a barrel-like cage structure. Variable temperature direct current (dc) magnetic susceptibility data were collected in the 1.8-300 K temperature range in a 0.1 T field. Variable-temperature and -field magnetization (M) data were collected in the 1.8-4.0 K and 0.1-7 T ranges and fit by matrix diagonalization assuming only the ground state is occupied at these temperatures. The fit parameters were S = 51/2, D = -0.020(2) cm(-1), and g = 1.87(3), where D is the axial zero-field splitting parameter. Alternating current (ac) susceptibility measurements in the 1.8-8.0 K range and a 3.5 G ac field oscillating at frequencies in the 50-1500 Hz range revealed a frequency-dependent out-of-phase (chi(M)'') signal below 3 K, suggesting 1 to be a single-molecule magnet (SMM). This was confirmed by magnetization vs dc field sweeps, which exhibited hysteresis loops but with no clear steps characteristic of resonant quantum tunneling of magnetization (QTM). However, magnetization decay data below 1 K were collected and used to construct an Arrhenius plot, and the fit of the thermally activated region above approximately 0.5 K gave U(eff)/k = 12 K, where U(eff) is the effective relaxation barrier. The g value and the magnitude and sign of the D value were independently confirmed by detailed high-frequency electron paramagnetic resonance (HFEPR) spectroscopy on polycrystalline samples. The combined studies confirm both the high ground-state spin S = 51/2 of complex 1 and that it is a SMM that, in addition, exhibits QTM.

Magnetically Bistable Nitrenes: Matrix Isolation of Furoylnitrenes in Both Singlet and Triplet States and Triplet 3-Furylnitrene.

Science.gov (United States)

Feng, Ruijuan; Lu, Yan; Deng, Guohai; Xu, Jian; Wu, Zhuang; Li, Hongmin; Liu, Qian; Kadowaki, Norito; Abe, Manabu; Zeng, Xiaoqing

2018-01-10

Two simple acylnitrenes, 2-furoylnitrene (2) and 3-furoylnitrene (6), were generated through 266 nm laser photolysis of the corresponding azides. Both are magnetically bistable in cryogenic matrices, as evidenced by the direct observation of the closed-shell singlet state with IR spectroscopy in solid Ne, Ar, Kr, Xe, and N 2 matrices (3-40 K) and the triplet state in toluene (10 K) with EPR spectroscopy ( 3 2: |D/hc| = 1.48 cm -1 and |E/hc| = 0.029 cm -1 ; 3 6: |D/hc| = 1.39 cm -1 and |E/hc|c = 0.039 cm -1 ). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (3 and 7) and ring-opening product 3-cyanoacrolein (9-E and 9-Z), respectively, in which the elusive 3-furylnitrene ( 3 8) was also identified by IR and EPR spectroscopy (|D/hc| = 1.12 cm -1 and |E/hc| = 0.005 cm -1 ).

Symmetric Imidazolium-Based Paramagnetic Ionic Liquids

Science.gov (United States)

2017-11-29

Charts N/A Unclassified Unclassified Unclassified SAR 14 Kamran Ghiassi N/A 1 Symmetric Imidazolium-Based Paramagnetic Ionic Liquids Kevin T. Greeson...NUMBER (Include area code) 29 November 2017 Briefing Charts 01 November 2017 - 30 November 2017 Symmetric Imidazolium-Based Paramagnetic Ionic ... Liquids K. Greeson, K. Ghiassi, J. Alston, N. Redeker, J. Marcischak, L. Gilmore, A. Guenthner Air Force Research Laboratory (AFMC) AFRL/RQRP 9 Antares

Jahn-Teller distortion in the phosphorescent excited state of three-coordinate Au(I) phosphine complexes.

Science.gov (United States)

Barakat, Khaldoon A; Cundari, Thomas R; Omary, Mohammad A

2003-11-26

DFT calculations were used to optimize the phosphorescent excited state of three-coordinate [Au(PR3)3]+ complexes. The results indicate that the complexes rearrange from their singlet ground-state trigonal planar geometry to a T-shape in the lowest triplet luminescent excited state. The optimized structure of the exciton contradicts the structure predicted based on the AuP bonding properties of the ground-state HOMO and LUMO. The rearrangement to T-shape is a Jahn-Teller distortion because an electron is taken from the degenerate e' (5dxy, 5dx2-y2) orbital upon photoexcitation of the ground-state D3h complex. The calculated UV absorption and visible emission energies are consistent with the experimental data and explain the large Stokes' shifts while such correlations are not possible in optimized models that constrained the exciton to the ground-state trigonal geometry.

Singlet-oxygen therapy. Scientific and methodological materials

OpenAIRE

Chukhraiev, N.; Chukhraieva, E.; Gun'ko, M.; Kurik, L.; Lomeiko, S.; Marushko, Y.; Samosyuk, N.; Tkalina, A.; Vladimirov, A.; Unichenko, A.; Zavorotnaya, R.; Zukow, W.

2018-01-01

Radomska Szkoła Wyższa w Radomiu MEDICAL INNOVATIVE TECHNOLOGIES SINGLET-OXYGEN THERAPY Scientific and methodological materials 2018 This edition had extended and translated from ukrainian Edited by Chukhraiev N., Vladimirov A., Zukow W. Radom, Kyiv Radomska Szkoła Wyższa w Radomiu MEDICAL INNOVATIVE TECHNOLOGIES SINGLET-OXYGEN THERAPY Scientific and methodological materials 2018 This edition had extended and translated from ukrainian Edited by ...

Singlet axial constant from QCD sum rules

International Nuclear Information System (INIS)

Belitskij, A.V.; Teryaev, O.V.

1995-01-01

We analyze the singlet axial form factor of the proton for small momentum transferred in the framework of QCD sum rules using the interpolating nucleon current which explicitly accounts for the gluonic degrees of freedom. As the result we come to the quantitative prediction of the singlet axial constant. It is shown that the bilocal power corrections play the most important role in the analysis. 21 refs., 3 figs

Paramagnetic moments in YBa{sub 2}Cu{sub 3}O{sub 7−δ} nanocomposite films

Energy Technology Data Exchange (ETDEWEB)

Dias, F.T.; Vieira, V.N.; Silva, D.L. [Instituto de Física e Matemática, Universidade Federal de Pelotas, C.P. 354, 96010-900 Pelotas, RS (Brazil); Albino Aguiar, J. [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, PE (Brazil); Programa de Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, 50670-901 Recife, PE (Brazil); Valadão, D.R.B., E-mail: danielavaladao.ufpe@gmail.com [Programa de Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, 50670-901 Recife, PE (Brazil); Obradors, X.; Puig, T. [Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus U.A. Barcelona, 08193 Bellaterra (Spain); Wolff-Fabris, F.; Kampert, E. [Dresden High Magnetic Field Laboratory, HZ Dresden-Rossendorf , 01314 Dresden (Germany)

2014-08-15

Highlights: • The paramagnetic Meissner effect was observed in a nanocomposite YBaCuO thin film. • The paramagnetic moments in FC experiments were observed up to 10 T. • The paramagnetic Meissner effect increases when the magnetic field is increased. • Results may be explained based on the flux compression scenario and vortex pinning. • An apparent saturation tendency of the paramagnetic moments could be observed. - Abstract: We report on magnetization studies in YBa{sub 2}Cu{sub 3}O{sub 7−δ} thin films with dispersed Ba{sub 2}YTaO{sub 6} nanoparticles. The magnetization measurements were made using a superconducting quantum interference device (SQUID) and a vibrating sample magnetometer (VSM). Magnetic moments were measured as functions temperature using zero-field cooling (ZFC) and field-cooled (FC) prescriptions for magnetic fields up to 10 T applied parallel and perpendicular to the ab planes. A paramagnetic response related to the superconducting state was observed during the FC experiments. This effect, known as paramagnetic Meissner effect (PME), apparently increases when the magnetic field is increased. We discuss our PME results in terms of the strong pinning scenario modulated by Ba{sub 2}YTaO{sub 6} nanoparticles dispersed into the superconducting matrix.

Singlet-triplet energy differences in divalent five membered cyclic conjugated Arduengo-type carbenes XC2HN2M (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I)

Science.gov (United States)

Vessally, Esmail; Dehbandi, Behnam; Ahmadi, Elaheh

2016-09-01

Singlet-triplet energy differences in Arduengo-type carbenes XC2HN2C compared and contrasted with their sila, germa, stana and plumba analogues; at B3LYP/6-311++G** level of theory. Free Gibbs energy differences between triplet (t) and singlet (s) states (Δ G(t-s)) change in the following order: plumbylenes > stannylenes > germylenes > silylenes > carbenes. The singlet states in XC2HN2C are generally more stable when the electron withdrawing groups such as-F was used at β-position. However, the singlet states in XC2N2HM (M = Si, Ge, Sn, and Pb) are generally more stable when the withdrawing groups such as-F was placed. The puckering energy is investigated for each the singlet and triplet states. The DFT calculations found the linear correlation to size of the group 14 divalent element (M), the ∠N-M-N angle, and the Δ(LUMO-HOMO) of XC2HN2M.

66Ga ground state β spectrum

DEFF Research Database (Denmark)

Severin, Gregory; Knutson, L. D.; Voytas, P. A.

2014-01-01

The ground state branch of the β decay of 66Ga is an allowed Fermi (0+ → 0+) transition with a relatively high f t value. The large f t and the isospin-forbidden nature of the transition indicates that the shape of the β spectrum of this branch may be sensitive to higher order contributions...... to the decay. Two previous measurements of the shape have revealed deviations from an allowed spectrum but disagree about whether the shape factor has a positive or negative slope. As a test of a new iron-free superconducting β spectrometer, we have measured the shape of the ground state branch of the 66Ga β...... spectrum above a positron energy of 1.9 MeV. The spectrum is consistent with an allowed shape, with the slope of the shape factor being zero to within ±3 × 10−3 per MeV. We have also determined the endpoint energy for the ground state branch to be 4.1535 ± 0.0003 (stat.) ±0.0007 (syst.) MeV, in good...

Singlet oxygen production and quenching mechanisms in travelling microwave discharges

International Nuclear Information System (INIS)

Savin, Yu V; Goryachev, L V; Adamenkov, Yu A; Rakhimova, T V; Mankelevich, Yu A; Popov, N A; Adamenkov, A A; Egorov, V V; Ilyin, S P; Kolobyanin, Yu V; Kudryashov, E A; Rogozhnikov, G S; Vyskubenko, B A

2004-01-01

Experimental and theoretical studies of singlet oxygen excitation in travelling microwave (TMW) discharges are presented. Singlet oxygen O 2 (a 1 Δ g ) concentrations and atomic oxygen mole fraction have been measured for different pressures, input powers and distances from the MW resonator. It was shown that a steady-state TMW discharge with a coaxial cavity resonator could provide a maximal O 2 (a 1 Δ g ) yield of 22% for 2 Torr of pure oxygen and 27-30% for He : O 2 = 1 : 1 mixture. The two-dimensional (r, z) model developed for calculations of plasma-chemical kinetics, heat and mass transfer was used for simulation of processes in the TMW discharge under study. Effects of gas pressure, gas flow rate and input power are studied and compared with experimental measurements of O 2 (a 1 Δ g ) concentrations and atomic oxygen mole fractions

Singlet fermionic dark matter with Veltman conditions

Science.gov (United States)

Kim, Yeong Gyun; Lee, Kang Young; Nam, Soo-hyeon

2018-07-01

We reexamine a renormalizable model of a fermionic dark matter with a gauge singlet Dirac fermion and a real singlet scalar which can ameliorate the scalar mass hierarchy problem of the Standard Model (SM). Our model setup is the minimal extension of the SM for which a realistic dark matter (DM) candidate is provided and the cancellation of one-loop quadratic divergence to the scalar masses can be achieved by the Veltman condition (VC) simultaneously. This model extension, although renormalizable, can be considered as an effective low-energy theory valid up to cut-off energies about 10 TeV. We calculate the one-loop quadratic divergence contributions of the new scalar and fermionic DM singlets, and constrain the model parameters using the VC and the perturbative unitarity conditions. Taking into account the invisible Higgs decay measurement, we show the allowed region of new physics parameters satisfying the recent measurement of relic abundance. With the obtained parameter set, we predict the elastic scattering cross section of the new singlet fermion into target nuclei for a direct detection of the dark matter. We also perform the full analysis with arbitrary set of parameters without the VC as a comparison, and discuss the implication of the constraints by the VC in detail.

About kinetics of paramagnetic radiation malformations in beryllium ceramics

International Nuclear Information System (INIS)

Polyakov, A.I.; Ryabinkin, Yu.A.; Zashkvara, O.V.; Bitenbaev, M.I.; Petukhov, Yu.V.

1999-01-01

This paper [1] specifies that γ-radiation of the beryllium-oxide-based ceramics results in development of paramagnetic radiation malformations emerging the ESR spectrum in form of doublet with the splitting rate of oestrasid Δ∼1.6 and g-factor of 2.008. This report presents evaluation outcomes of dependence of paramagnetic radiation malformations concentration in beryllium ceramics on gamma-radiation dose ( 60 Co) within the range of 0-100 Mrad. Total paramagnetic parameters of beryllium ceramics in the range 0-100 Mrad of gamma-radiation dose varied slightly, and were specified by the first type of paramagnetic radiation malformations

NMR study on the low-temperature state of LaMn{sub 4}Al{sub 8}

Energy Technology Data Exchange (ETDEWEB)

Muro, Y. [Graduate School of Material Science, University of Hyogo, Kamigori, Ako-gun, Hyogo 678-1297 (Japan)]. E-mail: rk04j052@stkt.u-hyogo.ac.jp; Nakamura, H. [Graduate School of Material Science, University of Hyogo, Kamigori, Ako-gun, Hyogo 678-1297 (Japan); Kohara, T. [Graduate School of Material Science, University of Hyogo, Kamigori, Ako-gun, Hyogo 678-1297 (Japan)

2007-03-15

The ground state of the quasi-one-dimensional itinerant electron magnet LaMn{sub 4}Al{sub 8} with strong electron correlation has been investigated by NMR. The presence of weak and broad zero-field {sup 55}Mn resonance, corresponding to internal field of 8-11T, indicates slowing down of spins partially released from the spin-singlet-like state in the spin chains.

A minor conformation of a lanthanide tag on adenylate kinase characterized by paramagnetic relaxation dispersion NMR spectroscopy

International Nuclear Information System (INIS)

Hass, Mathias A. S.; Liu, Wei-Min; Agafonov, Roman V.; Otten, Renee; Phung, Lien A.; Schilder, Jesika T.; Kern, Dorothee; Ubbink, Marcellus

2015-01-01

NMR relaxation dispersion techniques provide a powerful method to study protein dynamics by characterizing lowly populated conformations that are in dynamic exchange with the major state. Paramagnetic NMR is a versatile tool for investigating the structures and dynamics of proteins. These two techniques were combined here to measure accurate and precise pseudocontact shifts of a lowly populated conformation. This method delivers valuable long-range structural restraints for higher energy conformations of macromolecules in solution. Another advantage of combining pseudocontact shifts with relaxation dispersion is the increase in the amplitude of dispersion profiles. Lowly populated states are often involved in functional processes, such as enzyme catalysis, signaling, and protein/protein interactions. The presented results also unveil a critical problem with the lanthanide tag used to generate paramagnetic relaxation dispersion effects in proteins, namely that the motions of the tag can interfere severely with the observation of protein dynamics. The two-point attached CLaNP-5 lanthanide tag was linked to adenylate kinase. From the paramagnetic relaxation dispersion only motion of the tag is observed. The data can be described accurately by a two-state model in which the protein-attached tag undergoes a 23° tilting motion on a timescale of milliseconds. The work demonstrates the large potential of paramagnetic relaxation dispersion and the challenge to improve current tags to minimize relaxation dispersion from tag movements

Molecular and Cell Mechanisms of Singlet Oxygen Effect on Biosystems

OpenAIRE

Martusevich А.А.; Peretyagin S.P.; Martusevich А.К.

2012-01-01

There has been considered a poorly studied form of activated oxygen — singlet oxygen. Its physicochemical properties (electron configuration of a molecule, reactive capacity, features) are analyzed, and enzymic and nonenzymic ways of singlet oxygen generation in body are specified. There are shown in detail biological effects of the compound as a regulator of cell activity including that determining the mechanism of apoptosis initiation. The relation of singlet oxygen and photodynamic effect ...

Exact ground-state correlation functions of one-dimenisonal strongly correlated electron models with resonating-valence-bond ground state

International Nuclear Information System (INIS)

Yamanaka, Masanori; Honjo, Shinsuke; Kohmoto, Mahito

1996-01-01

We investigate one-dimensional strongly correlated electron models which have the resonating-valence-bond state as the exact ground state. The correlation functions are evaluated exactly using the transfer matrix method for the geometric representations of the valence-bond states. In this method, we only treat matrices with small dimensions. This enables us to give analytical results. It is shown that the correlation functions decay exponentially with distance. The result suggests that there is a finite excitation gap, and that the ground state is insulating. Since the corresponding noninteracting systems may be insulating or metallic, we can say that the gap originates from strong correlation. The persistent currents of the present models are also investigated and found to be exactly vanishing

Sea quark matrix elements and flavor singlet spectroscopy on the lattice

International Nuclear Information System (INIS)

Lagae, J.F.

1996-01-01

I summarize the results of three recent lattice studies which use stochastic estimator techniques in order to investigate the flavor singlet dynamics in QCD. These include a measurement of the pion-nucleon σ-term, the computation of the flavor singlet axial coupling constant of the nucleon and a determination of flavor singlet meson screening lengths in finite temperature QCD

The application of electron paramagnetic resonance in biomedical research

International Nuclear Information System (INIS)

Qu Ximei; Wang Liqin; Zhang Wenyi; Liu Zhongchao; Cui Songye; Feng Xin; Jiaoling

2013-01-01

Electron paramagnetic resonance technique has been found more than half a century, for free radicals detection application, it has been applied to various research studies, and promotes the development of the biomedicine. This article summarized the various free radicals measurement by the electron paramagnetic resonance in biology tissue, and the application of the spin labeling and electron paramagnetic resonance imaging technology in biomedicine. (authors)

Electronically excited states of chloroethylenes: Experiment and DFT calculations in comparison

International Nuclear Information System (INIS)

Khvostenko, O.G.

2014-01-01

Highlights: • B3LYP/6-311 + G(d,p) calculations of chloroethylenes molecules were performed. • Calculations were correlated with experiment on the molecules ground and excited states. • The general pattern of electron structure of chloroethylenes was obtained. • Necessity of this data for chloroethylenes negative ions study was noted. - Abstract: B3LYP/6-311 + G(d,p) calculations of ground and electronically excited states of ethylene, chloroethylene, 1,1-dichloroethylene, 1,2-dichloroethylene-cis, 1,2-dichloroethylene-trans trichloroethylene and tetrachloroethylene molecules have been performed. Molecular orbitals images and orbital correlation diagram are given. The calculation results for chloroethylenes electronically excited states were compared with experimental data from the energy-loss spectra obtained and generally considered previously by C.F. Koerting, K.N. Walzl and A. Kupperman. Several new additional triplet and singlet transitions were pointed out in these spectra considering the calculation results. The finding of the additional transitions was supported by the UV absorption spectrum of trichloroethylene recorded in big cuvette (10 cm), where the first three triplet and two low-intensive forbidden singlet transitions were registered. The first triplet of this compound was recorded to be at the same energy as was found with the energy-loss spectroscopy

Electronically excited states of chloroethylenes: Experiment and DFT calculations in comparison

Energy Technology Data Exchange (ETDEWEB)

Khvostenko, O.G., E-mail: khv@mail.ru

2014-08-15

Highlights: • B3LYP/6-311 + G(d,p) calculations of chloroethylenes molecules were performed. • Calculations were correlated with experiment on the molecules ground and excited states. • The general pattern of electron structure of chloroethylenes was obtained. • Necessity of this data for chloroethylenes negative ions study was noted. - Abstract: B3LYP/6-311 + G(d,p) calculations of ground and electronically excited states of ethylene, chloroethylene, 1,1-dichloroethylene, 1,2-dichloroethylene-cis, 1,2-dichloroethylene-trans trichloroethylene and tetrachloroethylene molecules have been performed. Molecular orbitals images and orbital correlation diagram are given. The calculation results for chloroethylenes electronically excited states were compared with experimental data from the energy-loss spectra obtained and generally considered previously by C.F. Koerting, K.N. Walzl and A. Kupperman. Several new additional triplet and singlet transitions were pointed out in these spectra considering the calculation results. The finding of the additional transitions was supported by the UV absorption spectrum of trichloroethylene recorded in big cuvette (10 cm), where the first three triplet and two low-intensive forbidden singlet transitions were registered. The first triplet of this compound was recorded to be at the same energy as was found with the energy-loss spectroscopy.

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

Investigation of the biochemical state of paramagnetic ions in vivo using the magnetic field dependence of 1/T1 of tissue protons (NMRD profile): applications to contrast agents for magnetic resonance imaging

International Nuclear Information System (INIS)

Koenig, S.H.; Brown, R.D. III; Spiller, M.; Wolf, G.L.

1988-01-01

Nuclear magnetic relaxation dispersion (NMRD) profiles of protons are obtained in homogenous aqueous solutions of the paramagnetic ions, Mn 2+ and Gd 3+ and their chelate and macromolecular complexes in vitro, giving information regarding the biochemical state of these ions. Similarly NMRD profiles of protons of excised rabbit tissues containing Mn 2+ and Gd 3+ complexes are obtained. These NMRD profiles are shown to be very useful for determining the fate of potentially useful paramagnetic NMR imaging contrast agents in vivo. (U.K.)

Accurate adiabatic singlet-triplet gaps in atoms and molecules employing the third-order spin-flip algebraic diagrammatic construction scheme for the polarization propagator

Energy Technology Data Exchange (ETDEWEB)

Lefrancois, Daniel; Dreuw, Andreas, E-mail: dreuw@uni-heidelberg.de [Interdisciplinary Center for Scientific Computing, Ruprecht-Karls University, Im Neuenheimer Feld 205, 69120 Heidelberg (Germany); Rehn, Dirk R. [Departments of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden)

2016-08-28

For the calculation of adiabatic singlet-triplet gaps (STG) in diradicaloid systems the spin-flip (SF) variant of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator in third order perturbation theory (SF-ADC(3)) has been applied. Due to the methodology of the SF approach the singlet and triplet states are treated on an equal footing since they are part of the same determinant subspace. This leads to a systematically more accurate description of, e.g., diradicaloid systems than with the corresponding non-SF single-reference methods. Furthermore, using analytical excited state gradients at ADC(3) level, geometry optimizations of the singlet and triplet states were performed leading to a fully consistent description of the systems, leading to only small errors in the calculated STGs ranging between 0.6 and 2.4 kcal/mol with respect to experimental references.

The orbital ground state of the azide-substrate complex of human heme oxygenase is an indicator of distal H-bonding: implications for the enzyme mechanism.

Science.gov (United States)

Ogura, Hiroshi; Evans, John P; Peng, Dungeng; Satterlee, James D; Ortiz de Montellano, Paul R; La Mar, Gerd N

2009-04-14

The active site electronic structure of the azide complex of substrate-bound human heme oxygenase 1 (hHO) has been investigated by (1)H NMR spectroscopy to shed light on the orbital/spin ground state as an indicator of the unique distal pocket environment of the enzyme. Two-dimensional (1)H NMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methyl contact shifts that places the lone iron pi-spin in the d(xz) orbital, rather than the d(yz) orbital found in the cyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy, and magnetic susceptibilities argues for a low-spin, (d(xy))(2)(d(yz),d(xz))(3), ground state in both azide and cyanide complexes. The switch from singly occupied d(yz) for the cyanide to d(xz) for the azide complex of hHO is shown to be consistent with the orbital hole determined by the azide pi-plane in the latter complex, which is approximately 90 degrees in-plane rotated from that of the imidazole pi-plane. The induction of the altered orbital ground state in the azide relative to the cyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagnetic relaxivity relative to those in globins, indicates that azide exerts a stronger ligand field in hHO than in the globins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 --> Ala hHO mutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevance of our findings for other HO complexes and the HO mechanism is discussed.

Singlet fermionic dark matter with Veltman conditions

OpenAIRE

Kim, Yeong Gyun; Lee, Kang Young; Nam, Soo-hyeon

2018-01-01

We reexamine a renormalizable model of a fermionic dark matter with a gauge singlet Dirac fermion and a real singlet scalar which can ameliorate the scalar mass hierarchy problem of the Standard Model (SM). Our model setup is the minimal extension of the SM for which a realistic dark matter (DM) candidate is provided and the cancellation of one-loop quadratic divergence to the scalar masses can be achieved by the Veltman condition (VC) simultaneously. This model extension, although renormaliz...

Reliable Prediction with Tuned Range-Separated Functionals of the Singlet-Triplet Gap in Organic Emitters for Thermally Activated Delayed Fluorescence (TADF)

KAUST Repository

Sun, Haitao

2015-07-09

The thermally activated delayed fluorescence (TADF) mechanism has recently attracted much interest in the field of organic light-emitting diodes (OLEDs). TADF relies on the presence of a very small energy gap between the lowest singlet and triplet excited states. Here, we demonstrate that time-dependent density functional theory (TD-DFT) in the Tamm-Dancoff Approximation can be very successful in the calculations of the lowest singlet and triplet excitation energies and the corresponding singlet-triplet gap when using nonempirically tuned range-separated functionals. Such functionals provide very good estimates in a series of 17 molecules used in TADF-based OLED devices, with mean absolute deviations of 0.15 eV for the vertical singlet excitation energies and 0.09 eV [0.07 eV] for the adiabatic [vertical] singlet-triplet energy gaps as well as low relative errors and high correlation coefficients compared to the corresponding experimental values. They significantly outperform conventional functionals, a feature which is rationalized on the basis of the amount of exact-exchange included and the delocalization error. The present work provides a reliable theoretical tool for the prediction and development of novel TADF-based materials with low singlet-triplet energetic splittings.

High-speed ground transportation development outside United States

Energy Technology Data Exchange (ETDEWEB)

Eastham, T.R. [Queen`s Univ., Kingston, Ontario (United Kingdom)

1995-09-01

This paper surveys the state of high-speed (in excess of 200 km/h) ground-transportation developments outside the United States. Both high-speed rail and Maglev systems are covered. Many vehicle systems capable of providing intercity service in the speed range 200--500 km/h are or will soon be available. The current state of various technologies, their implementation, and the near-term plans of countries that are most active in high-speed ground transportation development are reported.

Paramagnetic susceptibility of the Zr{sub 62}Cu{sub 22}Al{sub 10}Fe{sub 5}Dy{sub 1} metallic glass subjected to high-pressure torsion deformation

Energy Technology Data Exchange (ETDEWEB)

Korolev, A.V., E-mail: korolyov@imp.uran.ru [Institute of Metal Physics of the Ural Branch RAS, Ekaterinburg (Russian Federation); Ural Federal University, Ekaterinburg (Russian Federation); Kourov, N.I. [Institute of Metal Physics of the Ural Branch RAS, Ekaterinburg (Russian Federation); Pushin, V.G. [Institute of Metal Physics of the Ural Branch RAS, Ekaterinburg (Russian Federation); Ural Federal University, Ekaterinburg (Russian Federation); Gunderov, D.V. [Saint-Petersburg State University, Saint-Petersburg (Russian Federation); Ufa State Aviation Technical University, Ufa (Russian Federation); Boltynjuk, E.V.; Ubyivovk, E.V. [Saint-Petersburg State University, Saint-Petersburg (Russian Federation); Valiev, R.Z. [Saint-Petersburg State University, Saint-Petersburg (Russian Federation); Ufa State Aviation Technical University, Ufa (Russian Federation)

2017-09-01

Highlights: • Zr-based BMG was subjected to HPT at temperatures of 20 °C and 150 °C. • Magnetic measurements reveal well recordable changes in paramagnetic susceptibility. • Paramagnetic susceptibility may be an indicator of a change in the structural state. - Abstract: The Zr{sub 62}Cu{sub 22}Al{sub 10}Fe{sub 5}Dy{sub 1} bulk metallic glass is studied in the as-cast state and in the state after processing by high-pressure torsion at temperatures of 20 °C and 150 °C. According to the data from X-ray diffraction and transmission electron microscopy, the structural state of the samples depends weakly on the conducted processing. At the same time, magnetic measurements reveal well recordable changes in paramagnetic susceptibility induced by the processing of the samples. It is assumed that, because of high-pressure torsion deformation, there occurs a noticeable change in the material electronic structure, which leads to a change in the full susceptibility of the samples. The performed studies demonstrate that paramagnetic susceptibility may be an indicator of a change in the structural state of paramagnetic amorphous metallic substances.

Singlet Fission and Excimer Formation in Disordered Solids of Alkyl-Substituted 1,3-Diphenylisobenzofurans.

Science.gov (United States)

Dron, Paul I; Michl, Josef; Johnson, Justin C

2017-11-16

We describe the preparation and excited state dynamics of three alkyl derivatives of 1,3-diphenylisobenzofuran (1) in both solutions and thin films. The substitutions are intended to disrupt the slip-stacked packing observed in crystals of 1 while maintaining the favorable energies of singlet and triplet for singlet fission (SF). All substitutions result in films that are largely amorphous as judged by the absence of strong X-ray diffraction peaks. The films of 1 carrying a methyl in the para position of one phenyl ring undergo SF relatively efficiently (≥75% triplet yield, Φ T ) but more slowly than thin films of 1. When the methyl is replaced with a t-butyl, kinetic competition in the excited state favors excimer formation rather than SF (Φ T = 55%). When t-Bu groups are placed in both meta positions of the phenyl substituent, SF is slowed further and Φ T = 35%.

Stacked nickelocenes: synthesis, structural characterization, and magnetic properties.

Science.gov (United States)

Trtica, Sabrina; Prosenc, Marc Heinrich; Schmidt, Michael; Heck, Jürgen; Albrecht, Ole; Görlitz, Detlef; Reuter, Frank; Rentschler, Eva

2010-02-15

The disubstitution of 1,8-diiodonaphthalene (1) with cyclopentadienyl nucleophiles reveals 1,8-(dicyclopentadienyl)-naphthalene, which rapidly undergoes Diels-Alder reaction forming 1,8-(3a',4',7',7a'-tetrahydro-4',7'-methanoindene-7a',8'-diyl)-naphthalene (2). A subsequent retro-Diels-Alder reaction in the presence of sodium hydride yields the disodium salt of 1,8-(dicyclopentadiendiyl)-naphthalene 3. The disodium salt 3 was the starting material to obtain the paramagnetic bisnickelocene derivative 4, which structure was obtained by X-ray structure analysis, revealing two nickelocenes kept together in a stacked fashion by a 1,8-naphthalene clamp. An electronic interaction between the two nickel atoms is found as a result of cyclic voltammetry, indicating five different oxidation states +4, +3, +2, +1, and 0. The magnetic properties of 4 in solution were studied by variable temperature paramagnetic (1)H NMR spectroscopy and Evans method and revealed Curie behavior between 213 and 293 K. The magnetic susceptibility of a powdered sample of 4 was measured, and an antiferromagnetic interaction with an exchange coupling of J(12) = -31.49 cm(-1) is found. In accord with experimental data, broken symmetry density functional theory (DFT) calculations revealed four antiferromagnetically coupled electrons resulting in an open shell singlet ground state.

On kinetics of paramagnetic radiation defects accumulation in beryllium ceramics

International Nuclear Information System (INIS)

Polyakov, A.I.; Ryabikin, Yu.A.; Zashkvara, O.V.; Bitenbaev, M.I.; Petykhov, Yu.V.

1999-01-01

Results of paramagnetic radiation defects concentration dependence study in beryllium ceramics from gamma-irradiation dose ( 60 Co) within interval 0-100 Mrem are cited. Obtained dose dependence has form of accumulation curve with saturation typical of for majority of solids (crystals, different polymers, organic substances and others) , in which under irradiation occur not only formation of paramagnetic radiation defects, but its destruction due to recombination and interaction with radiation fields. Analysis of accumulation curve by the method of distant asymptotics allows to determine that observed in gamma-irradiated beryllium ceramics double line of electron spin resonance is forming of two types of paramagnetic radiation defects. It was defined, that sum paramagnetic characteristics of beryllium ceramics within 1-100 Mrad gamma- irradiation dose field change insignificantly and define from first type of paramagnetic radiation defects

Exact many-electron ground states on diamond and triangle Hubbard chains

International Nuclear Information System (INIS)

Gulacsi, Zsolt; Kampf, Arno; Vollhardt, Dieter

2009-01-01

We construct exact ground states of interacting electrons on triangle and diamond Hubbard chains. The construction requires (1) a rewriting of the Hamiltonian into positive semidefinite form, (2) the construction of a many-electron ground state of this Hamiltonian, and (3) the proof of the uniqueness of the ground state. This approach works in any dimension, requires no integrability of the model, and only demands sufficiently many microscopic parameters in the Hamiltonian which have to fulfill certain relations. The scheme is first employed to construct exact ground state for the diamond Hubbard chain in a magnetic field. These ground states are found to exhibit a wide range of properties such as flat-band ferromagnetism and correlation induced metallic, half-metallic or insulating behavior, which can be tuned by changing the magnetic flux, local potentials, or electron density. Detailed proofs of the uniqueness of the ground states are presented. By the same technique exact ground states are constructed for triangle Hubbard chains and a one-dimensional periodic Anderson model with nearest-neighbor hybridization. They permit direct comparison with results obtained by variational techniques for f-electron ferromagnetism due to a flat band in CeRh 3 B 2 . (author)

Geometry and bonding in the ground and lowest triplet state of D{sub 6h} symmetric crenellated edged C{sub 6[3m(m-1)+1]}H{sub 6(2m-1)} (m = 2,..., 6) graphene hydrocarbon molecules

Energy Technology Data Exchange (ETDEWEB)

Philpott, Michael R., E-mail: philpott@imr.edu [Center for Computational Materials Science, Institute of Materials Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, 980-8577 Sendai (Japan); Kawazoe, Yoshiyuki [Center for Computational Materials Science, Institute of Materials Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, 980-8577 Sendai (Japan)

2009-03-30

Ab initio plane wave all valence electron based DFT calculations were used to explore the dichotomy of perimeter vs. interior in the electronic and geometric structure of the D{sub 6h} singlet ground state and D{sub 2h} lowest triplet state of planar graphene hydrocarbon molecules with crenellated (arm chair) edges and the general formula C{sub 6[3m(m-1)+1]} H{sub 6(2m-1)} where m = 2,...,6. The largest molecule C{sub 546}H{sub 66} was 4.78 nm across and contained 2250 valence electrons. These molecules are nominally 'fully benzenoid hydrocarbons'. However with increasing size, the core of central atoms abandoned any fully benzenoid geometry they had in small systems and organized into single layer graphite (graphene) structure. The perimeter atoms of the crenellation adopted a conjugated geometry with unequal bonds and between core and perimeter there were some C{sub 6} rings retaining remnants of aromatic sextet-type properties. Compared to a zigzag edge the crenellated edge conferred stability in all the systems studied as measured by the singlet homo-lumo level gap BG{sub 0} and the singlet-lowest triplet energy gap {Delta}E{sub ST}. For the largest crenellated system (m = 6) BG{sub 0} and {Delta}E{sub ST} were approximately 0.7 eV, larger in value than for similarly sized hexagonal graphenes with zigzag edges. Triplet states were identified for all the molecules in the series and in the case of the m = 2 molecule hexabenzocoronene C{sub 42}H{sub 18}, two conformations with D{sub 2h} symmetry were identified and compared to features on the triplet state potential energy surface of benzene.

Approximating the ground state of gapped quantum spin systems

Energy Technology Data Exchange (ETDEWEB)

Michalakis, Spyridon [Los Alamos National Laboratory; Hamza, Eman [NON LANL; Nachtergaele, Bruno [NON LANL; Sims, Robert [NON LANL

2009-01-01

We consider quantum spin systems defined on finite sets V equipped with a metric. In typical examples, V is a large, but finite subset of Z{sup d}. For finite range Hamiltonians with uniformly bounded interaction terms and a unique, gapped ground state, we demonstrate a locality property of the corresponding ground state projector. In such systems, this ground state projector can be approximated by the product of observables with quantifiable supports. In fact, given any subset {chi} {contained_in} V the ground state projector can be approximated by the product of two projections, one supported on {chi} and one supported on {chi}{sup c}, and a bounded observable supported on a boundary region in such a way that as the boundary region increases, the approximation becomes better. Such an approximation was useful in proving an area law in one dimension, and this result corresponds to a multi-dimensional analogue.

Triplet energy transfer and triplet exciton recycling in singlet fission sensitized organic heterojunctions

Science.gov (United States)

Hamid, Tasnuva; Yambem, Soniya D.; Crawford, Ross; Roberts, Jonathan; Pandey, Ajay K.

2017-08-01

Singlet exciton fission is a process where an excited singlet state splits into two triplets, thus leading to generation of multiple excitons per absorbed photon in organic semiconductors. Herein, we report a detailed exciton management approach for multiexciton harvesting over a broadband region of the solar spectrum in singlet fission sensitized organic photodiodes. Through systematic studies on the model cascade of pentacene/rubrene/C60, we found that efficient photocurrent generation from pentacene can still occur despite the presence of a >10nm thick interlayer of rubrene in between the pentacene/C60 heterojunction. Our results show that thin rubrene interlayers of thickness pentacene despite having a reasonably thick rubrene interlayer, that too with higher triplet energy (T1=1.12 eV) than pentacene (T1= 0.86 eV), makes its operation a rather interesting result. We discuss the role of rubrene interlayer film discontinuity, triplet exciton reflection from rubrene interlayer and triplet energy transfer from rubrene to pentacene layer followed by diffusion of triplet excitons through rubrene as plausible mechanisms that would enable triplet excitons from pentacene to generate significant photocurrent in a multilayer organic heterojunction.

Pentacene Dimers as a Critical Tool for the Investigation of Intramolecular Singlet Fission.

Science.gov (United States)

Hetzer, Constantin; Guldi, Dirk M; Tykwinski, Rik R

2018-01-11

Singlet fission (SF) involves the spontaneous splitting of a photoexcited singlet state into a pair of triplets, and it holds great promise toward the realization of more efficient solar cells. Although the process of SF has been known since the 1960s, debate regarding the underlying mechanism continues to this day, especially for molecular materials. A number of different chromophores have been synthesized and studied in order to better understand the process of SF. These previous reports have established that pentacene and its derivatives are especially well-suited for the study of SF, since the energetic requirement E(S 1 )≥2E(T 1 ) is fulfilled rendering the process exothermic and unidirectional. Dimeric pentacene derivatives, in which individual pentacene chromophores are tethered by a "spacer", have emerged as the system of choice toward exploring the mechanism of intramolecular singlet fission (iSF). The dimeric structure, and in particular the spacer, allows for controlling and tuning the distance, geometric relationship, and electronic coupling between the two pentacene moieties. This Minireview describes recent advances using pentacene dimers for the investigation of iSF. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ionic/Electronic Conductivity, Thermal/Chemical Expansion and Oxygen Permeation in Pr and Gd Co-Doped Ceria PrxGd0.1Ce0.9-xO1.95-δ

DEFF Research Database (Denmark)

Cheng, Shiyang; Chatzichristodoulou, Christodoulos; Søgaard, Martin

2017-01-01

Pr. A series of compositions of PrxGd0.1Ce0.9-xO1.95-δ (x = 0, 0.02, 0.05, 0.08, 0.15, 0.25, 0.3 and 0.4) was prepared by solid state reaction. X-ray powder diffraction (XPD) indicates that Pr is completely dissolved in the fluorite structure up to 40 at.%. Pronounced nonlinear thermal expansion...... behavior was observed as a function of temperature, due to the simultaneous contributions of both thermal and chemical expansion. The electronic and ionic conductivities were measured as a function of temperature and oxygen partial pressure. Within the range from 10 to 15 at.% Pr, a drastic drop...

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.

Fast Preparation of Critical Ground States Using Superluminal Fronts

Science.gov (United States)

Agarwal, Kartiek; Bhatt, R. N.; Sondhi, S. L.

2018-05-01

We propose a spatiotemporal quench protocol that allows for the fast preparation of ground states of gapless models with Lorentz invariance. Assuming the system initially resides in the ground state of a corresponding massive model, we show that a superluminally moving "front" that locally quenches the mass, leaves behind it (in space) a state arbitrarily close to the ground state of the gapless model. Importantly, our protocol takes time O (L ) to produce the ground state of a system of size ˜Ld (d spatial dimensions), while a fully adiabatic protocol requires time ˜O (L2) to produce a state with exponential accuracy in L . The physics of the dynamical problem can be understood in terms of relativistic rarefaction of excitations generated by the mass front. We provide proof of concept by solving the proposed quench exactly for a system of free bosons in arbitrary dimensions, and for free fermions in d =1 . We discuss the role of interactions and UV effects on the free-theory idealization, before numerically illustrating the usefulness of the approach via simulations on the quantum Heisenberg spin chain.

Ground-state phases of the spin-1 J1-J2 Heisenberg antiferromagnet on the honeycomb lattice

Science.gov (United States)

Li, P. H. Y.; Bishop, R. F.

2016-06-01

We study the zero-temperature quantum phase diagram of a spin-1 Heisenberg antiferromagnet on the honeycomb lattice with both nearest-neighbor exchange coupling J1>0 and frustrating next-nearest-neighbor coupling J2≡κ J1>0 , using the coupled cluster method implemented to high orders of approximation, and based on model states with different forms of classical magnetic order. For each we calculate directly in the bulk thermodynamic limit both ground-state low-energy parameters (including the energy per spin, magnetic order parameter, spin stiffness coefficient, and zero-field uniform transverse magnetic susceptibility) and their generalized susceptibilities to various forms of valence-bond crystalline (VBC) order, as well as the energy gap to the lowest-lying spin-triplet excitation. In the range 0 κc 2=0.340 (5 ) . Two different paramagnetic phases are found to exist in the intermediate region. Over the range κc1<κ<κci=0.305 (5 ) we find a gapless phase with no discernible magnetic order, which is a strong candidate for being a quantum spin liquid, while over the range κci<κ <κc 2 we find a gapped phase, which is most likely a lattice nematic with staggered dimer VBC order that breaks the lattice rotational symmetry.

Ground state energy of a polaron in a superlattice

International Nuclear Information System (INIS)

Mensah, S.Y.; Allotey, F.K.A.; Nkrumah, G.; Mensah, N.G.

2000-10-01

The ground state energy of a polaron in a superlattice was calculated using the double-time Green functions. The effective mass of the polaron along the planes perpendicular to the superlattice axis was also calculated. The dependence of the ground state energy and the effective mass along the planes perpendicular to the superlattice axis on the electron-phonon coupling constant α and on the superlattice parameters (i.e. the superlattice period d and the bandwidth Δ) were studied. It was observed that if an infinite square well potential is assumed, the ground state energy of the polaron decreases (i.e. becomes more negative) with increasing α and d, but increases with increasing Δ. For small values of α, the polaron ground state energy varies slowly with Δ, becoming approximately constant for large Δ. The effective mass along the planes perpendicular to the superlattice axis was found to be approximately equal to the mass of an electron for all typical values of α, d and Δ. (author)

Trapping cold ground state argon atoms.

Science.gov (United States)

Edmunds, P D; Barker, P F

2014-10-31

We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable 4s[3/2](2) state to be (7.3±1.1)×10(-39)  C m(2)/V. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be (3.3±0.8)×10(-10)  cm(3) s(-1).

Status of the scalar singlet dark matter model

Science.gov (United States)

Athron, Peter; Balázs, Csaba; Bringmann, Torsten; Buckley, Andy; Chrząszcz, Marcin; Conrad, Jan; Cornell, Jonathan M.; Dal, Lars A.; Edsjö, Joakim; Farmer, Ben; Jackson, Paul; Kahlhoefer, Felix; Krislock, Abram; Kvellestad, Anders; McKay, James; Mahmoudi, Farvah; Martinez, Gregory D.; Putze, Antje; Raklev, Are; Rogan, Christopher; Saavedra, Aldo; Savage, Christopher; Scott, Pat; Serra, Nicola; Weniger, Christoph; White, Martin

2017-08-01

One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z_2 symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ˜ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.

Correlated ground state and E2 giant resonance built on it

International Nuclear Information System (INIS)

Tohyama, Mitsuru

1995-01-01

Taking 16 O as an example of realistic nuclei, we demonstrate that a correlated ground state can be obtained as a long time solution of a time-dependent density-matrix formalism (TDDM) when the residual interaction is adiabatically treated. We also study in TDDM the E2 giant resonance of 16 O built on the correlated ground state and compare it with that built on the Hartree-Fock ground state. It is found that a spurious mixing of low frequency components seen in the latter is eliminated by using the correlated ground state. (author)

Singlet fission efficiency in tetracene-based organic solar cells

International Nuclear Information System (INIS)

Wu, Tony C.; Thompson, Nicholas J.; Congreve, Daniel N.; Hontz, Eric; Yost, Shane R.; Van Voorhis, Troy; Baldo, Marc A.

2014-01-01

Singlet exciton fission splits one singlet exciton into two triplet excitons. Using a joint analysis of photocurrent and fluorescence modulation under a magnetic field, we determine that the triplet yield within optimized tetracene organic photovoltaic devices is 153% ± 5% for a tetracene film thickness of 20 nm. The corresponding internal quantum efficiency is 127% ± 18%. These results are used to prove the effectiveness of a simplified triplet yield measurement that relies only on the magnetic field modulation of fluorescence. Despite its relatively slow rate of singlet fission, the measured triplet yields confirm that tetracene is presently the best candidate for use with silicon solar cells

Ground-Water Availability in the United States

Science.gov (United States)

Reilly, Thomas E.; Dennehy, Kevin F.; Alley, William M.; Cunningham, William L.

2008-01-01

Ground water is among the Nation's most important natural resources. It provides half our drinking water and is essential to the vitality of agriculture and industry, as well as to the health of rivers, wetlands, and estuaries throughout the country. Large-scale development of ground-water resources with accompanying declines in ground-water levels and other effects of pumping has led to concerns about the future availability of ground water to meet domestic, agricultural, industrial, and environmental needs. The challenges in determining ground-water availability are many. This report examines what is known about the Nation's ground-water availability and outlines a program of study by the U.S. Geological Survey Ground-Water Resources Program to improve our understanding of ground-water availability in major aquifers across the Nation. The approach is designed to provide useful regional information for State and local agencies who manage ground-water resources, while providing the building blocks for a national assessment. The report is written for a wide audience interested or involved in the management, protection, and sustainable use of the Nation's water resources.

Dual excitation acoustic paramagnetic logging tool

Energy Technology Data Exchange (ETDEWEB)

Vail, III, William B. (Bothell, WA)

1989-01-01

New methods and apparatus are disclosed which allow measurement of the presence of oil and water in gelogical formations using a new physical effect called the Acoustic Paramagnetic Logging Effect (APLE). The presence of petroleum in formation causes a slight increase in the earth's magnetic field in the vicinity of the reservoir. This is the phenomena of paramagnetism. Application of an acoustic source to a geological formation at the Larmor frequency of the nucleous present causes the paramagnetism of the formation to disappear. This results in a decrease in the earth's magnetic field in the vicinity of the oil bearing formation. Repetitively frequency sweeping the acoustic source through the Larmor frequency of the nucleons present (approx. 2 kHz) causes an amplitude modulation of the earth's magnetic field which is a consequence of the APLE. The amplitude modulation of the earth's magnetic field is measured with an induction coil gradiometer and provides a direct measure of the amount of oil and water in the excitation zone of the formation. The phase of the signal is used to infer the longitudinal relaxation times of the fluids present, which results in the ability in general to separate oil and water and to measure the viscosity of the oil present. Such measurements may be preformed in open boreholes and in cased well bores. The Dual Excitation Acoustic Paramagnetic Logging Tool employing two acoustic sources is also described.

The ground state energy of a classical gas

International Nuclear Information System (INIS)

Conlon, J.G.

1983-01-01

The ground state energy of a classical gas is treated using a probability function for the position of the particles and a potential function. The lower boundary for the energy when the particle number is large is defined as ground state energy. The coulomb gas consisting of positive and negative particles is also treated (fixed and variable density case) the stability of the relativistic system is investigated as well. (H.B.)

2HDM portal for Singlet-Doublet Dark Matter

OpenAIRE

Arcadi, Giorgio

2018-01-01

We present an extensive analysis of a model in which the (Majorana) Dark Matter candidate is a mixture between a SU(2) singlet and two SU(2) doublets. This kind of setup takes the name of singlet-doublet model. We will investigate in detail an extension of this model in which the Dark Matter sector interactions with a 2-doublet Higgs sector enforcing the complementarity between Dark Matter phenomenology and searches of extra Higgs bosons.

Bound states of quarks calculated with stochastic integration of the Bethe-Salpeter equation

International Nuclear Information System (INIS)

Salomon, M.

1992-07-01

We have computed the masses, wave functions and sea quark content of mesons in their ground state by integrating the Bethe-Salpeter equation with a stochastic algorithm. This method allows the inclusion of a large set of diagrams. Inspection of the kernel of the equation shows that q-q-bar pairs with similar constituent masses in a singlet spin state exhibit a high bound state which is not present in other pairs. The pion, kaon and eta belongs to this category. 19 refs., 2 figs., 2 tabs

Anomalous Ground State of the Electrons in Nano-confined Water

Science.gov (United States)

2016-06-13

Anomalous ground state of the electrons in nano -confined water G. F. Reiter1*, Aniruddha Deb2*, Y. Sakurai3, M. Itou3, V. G. Krishnan4, S. J...electronic ground state of nano -confined water must be responsible for these anomalies but has so far not been investigated. We show here for the first time...using x-ray Compton scattering and a computational model, that the ground state configuration of the valence electrons in a particular nano

Singlet oxygen in the low-temperature plasma of an electron-beam-sustained discharge

International Nuclear Information System (INIS)

Vagin, N. P.; Ionin, A. A.; Klimachev, Yu. M.; Kotkov, A. A.; Kochetov, I. V.; Napartovich, A. P.; Podmar'kov, Yu. P.; Rulev, O. A.; Seleznev, L. V.; Sinitsyn, D. V.; Frolov, M. P.; Yuryshev, N. N.

2006-01-01

Results are presented from experimental and theoretical studies of the production of singlet delta oxygen in a pulsed electron-beam-sustained discharge ignited in a large (∼18-1) volume at a total gas mixture pressure of up to 210 Torr. The measured yield of singlet oxygen reaches 10.5%. It is found that varying the reduced electric field from ∼2 to ∼11 kV/(cm atm) slightly affects singlet oxygen production. It is shown experimentally that an increase in the gas mixture pressure or the specific input energy reduces the duration of singlet oxygen luminescence. The calculated time evolution of the singlet oxygen concentration is compared with experimental results

Multi-frequency EDMR studies of light-activated paramagnetic centers in μc-Si:H thin-film solar cells

International Nuclear Information System (INIS)

Meier, Christoph

2014-01-01

This thesis presents a comprehensive study of paramagnetic centers in fully-processed microcrystalline silicon (μc-Si:H) thin-film solar cells. The heterogeneous material gives rise to a complex band structure with deep defects in the middle of the energy band gap as well as localized states close to the energy band edges. They can act as recombination centers and traps and, thereby, influence the charge transport of photogenerated charge carriers. Thus, they diminish the performance of the cell. To reduce the disadvantageous influence of the defect states on the cell efficiency, a detailed understanding of the charge transport processes via these states is necessary. In this work, light-activated paramagnetic centers are studied with electrically detected magnetic resonance (EDMR) at various microwave frequencies. This technique combines electron paramagnetic resonance spectroscopy (EPR) with the photocurrent measurement in the solar cell, thus, delivering information about the transport processes and magnetic parameters of the involved defect states. Multi-frequency EDMR at low temperatures reveals four paramagnetic states in μc-Si:H. Dangling bond (db) defects and holes in valence band tail (h) states are located in the disordered phase, whereas so-called CE and V states originate from the crystalline phase. The multi-frequency approach allows for a separation of field-dependent and -independent line widths. All EDMR signals are affected by line broadening due to spin-spin interaction, which could be used to estimate mean inter-spin distances of around ∼ 0.5 nm for the V center and of ∼ 1-2 nm for the remaining centers. Based on the strong spin-spin coupling and on transient nutation experiments the V signal could be correlated with a vacancy site in its excited triplet state. From the particular properties of the CE line it was concluded that the corresponding states are located in inversion layers and potential wells close to the conduction band of

Electron Paramagnetic Resonance Spectroscopy

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education; Volume 20; Issue 11. Electron Paramagnetic Resonance Spectroscopy: Biological Applications. B G Hegde. General Article Volume 20 Issue 11 November 2015 pp 1017-1032. Fulltext. Click here to view fulltext PDF. Permanent link:

A laser flash photolysis and quantum chemical study of the fluorinated derivatives of singlet phenylnitrene.

Science.gov (United States)

Gritsan, N P; Gudmundsdóttir, A D; Tigelaar, D; Zhu, Z; Karney, W L; Hadad, C M; Platz, M S

2001-03-07

Laser flash photolysis (LFP, Nd:YAG laser, 35 ps, 266 nm, 10 mJ or KrF excimer laser, 10 ns, 249 nm, 50 mJ) of 2-fluoro, 4-fluoro, 3,5-difluoro, 2,6-difluoro, and 2,3,4,5,6-pentafluorophenyl azides produces the corresponding singlet nitrenes. The singlet nitrenes were detected by transient absorption spectroscopy, and their spectra are characterized by sharp absorption bands with maxima in the range of 300-365 nm. The kinetics of their decay were analyzed as a function of temperature to yield observed decay rate constants, k(OBS). The observed rate constant in inert solvents is the sum of k(R) + k(ISC) where k(R) is the absolute rate constant of rearrangement of singlet nitrene to an azirine and k(ISC) is the absolute rate constant of nitrene intersystem crossing (ISC). Values of k(R) and k(ISC) were deduced after assuming that k(ISC) is independent of temperature. Barriers to cyclization of 4-fluoro-, 3,5-difluoro-, 2-fluoro-, 2,6-difluoro-, and 2,3,4,5,6-pentafluorophenylnitrene in inert solvents are 5.3 +/- 0.3, 5.5 +/- 0.3, 6.7 +/- 0.3, 8.0 +/- 1.5, and 8.8 +/- 0.4 kcal/mol, respectively. The barrier to cyclization of parent singlet phenylnitrene is 5.6 +/- 0.3 kcal/mol. All of these values are in good quantitative agreement with CASPT2 calculations of the relative barrier heights for the conversion of fluoro-substituted singlet aryl nitrenes to benzazirines (Karney, W. L. and Borden, W. T. J. Am. Chem. Soc. 1997, 119, 3347). A single ortho-fluorine substituent exerts a small but significant bystander effect on remote cyclization that is not steric in origin. The influence of two ortho-fluorine substituents on the cyclization is pronounced. In the case of the singlet 2-fluorophenylnitrene system, evidence is presented that the benzazirine is an intermediate and that the corresponding singlet nitrene and benzazirine interconvert. Ab initio calculations at different levels of theory on a series of benzazirines, their isomeric ketenimines, and the transition

Solving satisfiability problems by the ground-state quantum computer

International Nuclear Information System (INIS)

Mao Wenjin

2005-01-01

A quantum algorithm is proposed to solve the satisfiability (SAT) problems by the ground-state quantum computer. The scale of the energy gap of the ground-state quantum computer is analyzed for the 3-bit exact cover problem. The time cost of this algorithm on the general SAT problems is discussed

Calculations of the ground state of 16O

International Nuclear Information System (INIS)

Pieper, S.C.

1989-01-01

One of the central problems in nuclear physics is the description of nuclei as systems of nucleons interacting via realistic potentials. There are two main aspects of this problem: specification of the Hamiltonian, and calculation of the ground states of nuclei with the given interaction. Realistic interactions must contain both two- and three-nucleon potentials and these potentials have a complicated non-central operator structure consisting, for example, of spin, isospin and tensor dependences. This structure results in formidable many-body problems in the computation of the ground states of nuclei. At present, reliable solutions of the Faddeev equations for the A = 3 nuclei with such interactions are routine. Recently, Carlson has made an essentially exact GFMC calculation of the He ground state using just a two-nucleon interaction, and there are reliable variational calculations for more complete potential models. Nuclear matter calculations can also be made with reasonable reliability. However, there have been very few calculations of nuclei with A > 5 using realistic interactions, and none with a modern three-nucleon interaction. In the present paper I present a new technique for variational calculations for such nuclei and apply it to the ground state of 16 O. 15 refs., 2 figs., 3 tabs

Singlet Extensions of the MSSM with ℤ4R Symmetry

International Nuclear Information System (INIS)

Ratz, Michael; Vaudrevange, Patrick K. S.

2015-01-01

We discuss singlet extensions of the MSSM with ℤ 4 R symmetry. We show that holomorphic zeros can avoid a potentially large coefficient of the term linear in the singlet. The emerging model has both an effective μ term and a supersymmetric mass term for the singlet μ N which are controlled by the gravitino mass. The μ term turns out to be suppressed against μ N by about one or two orders of magnitude. We argue that this class of models might provide us with a solution to the little hierarchy problem of the MSSM

Leading relativistic corrections for atomic P states calculated with a finite-nuclear-mass approach and all-electron explicitly correlated Gaussian functions

Science.gov (United States)

Stanke, Monika; Bralin, Amir; Bubin, Sergiy; Adamowicz, Ludwik

2018-01-01

In this work we report progress in the development and implementation of quantum-mechanical methods for calculating bound ground and excited states of small atomic systems. The work concerns singlet states with the L =1 total orbital angular momentum (P states). The method is based on the finite-nuclear-mass (non-Born-Oppenheimer; non-BO) approach and the use of all-particle explicitly correlated Gaussian functions for expanding the nonrelativistic wave function of the system. The development presented here includes derivation and implementation of algorithms for calculating the leading relativistic corrections for singlet states. The corrections are determined in the framework of the perturbation theory as expectation values of the corresponding effective operators using the non-BO wave functions. The method is tested in the calculations of the ten lowest 1P states of the helium atom and the four lowest 1P states of the beryllium atom.

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

International Nuclear Information System (INIS)

Kahlhoefer, Felix; McDonald, John

2015-07-01

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-σ 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.

Intrinsic Paramagnetic Meissner Effect Due to s-Wave Odd-Frequency Superconductivity

Directory of Open Access Journals (Sweden)

A. Di Bernardo

2015-11-01

Full Text Available In 1933, Meissner and Ochsenfeld reported the expulsion of magnetic flux—the diamagnetic Meissner effect—from the interior of superconducting lead. This discovery was crucial in formulating the Bardeen-Cooper-Schrieffer (BCS theory of superconductivity. In exotic superconducting systems BCS theory does not strictly apply. A classical example is a superconductor-magnet hybrid system where magnetic ordering breaks time-reversal symmetry of the superconducting condensate and results in the stabilization of an odd-frequency superconducting state. It has been predicted that under appropriate conditions, odd-frequency superconductivity should manifest in the Meissner state as fluctuations in the sign of the magnetic susceptibility, meaning that the superconductivity can either repel (diamagnetic or attract (paramagnetic external magnetic flux. Here, we report local probe measurements of faint magnetic fields in a Au/Ho/Nb trilayer system using low-energy muons, where antiferromagnetic Ho (4.5 nm breaks time-reversal symmetry of the proximity-induced pair correlations in Au. From depth-resolved measurements below the superconducting transition of Nb, we observe a local enhancement of the magnetic field in Au that exceeds the externally applied field, thus proving the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state.

Electron Paramagnetic Resonance Imaging

Indian Academy of Sciences (India)

Twentieth century bore witness to remarkable scientists whohave advanced our understanding of the brain. Among them,EPR (Electron Paramagnetic Resonance) imaging is particularlyuseful in monitoring hypoxic zones in tumors which arehighly resistant to radiation and chemotherapeutic treatment.This first part of the ...

Computational rationalization for the observed ground-state multiplicities of fluorinated acylnitrenes.

Science.gov (United States)

Sherman, Matthew P; Jenks, William S

2014-10-03

Computational methods are used to investigate the mechanism by which fluorination of acetylnitrene reduces the stabilization of the singlet configuration. ΔEST is made more positive (favoring the triplet state) by 1.9, 1.3, and 0.7 kcal/mol by the addition of the first, second, and third fluorine, respectively, at the CR-CC(2,3)/6-311(3df,2p)//B3LYP/6-31G(d,p) level of theory. Smaller effects observed with substitution of β-fluorines in propanoylnitrene derivatives and examination of molecular geometries and orbitals demonstrate that the effect is due to inductive electron withdrawal by the fluorines, rather than hyperconjugation.

Paramagnetic centers in nanocrystalline TiC/C system

International Nuclear Information System (INIS)

Guskos, N.; Bodziony, T.; Maryniak, M.; Typek, J.; Biedunkiewicz, A.

2008-01-01

Electron paramagnetic resonance is applied to study the defect centers in nanocrystalline titanium carbide dispersed in carbon matrix (TiC x /C) synthesized by the non-hydrolytic sol-gel process. The presence of Ti 3+ paramagnetic centers is identified below 120 K along with a minor contribution from localized defect spins coupled with the conduction electron system in the carbon matrix. The temperature dependence of the resonance intensity of the latter signal indicates weak antiferromagnetic interactions. The presence of paramagnetic centers connected with trivalent titanium is suggested to be the result of chemical disorder, which can be further related to the observed anomalous behavior of conductivity, hardness, and corrosion resistance of nanocrystalline TiC x /C

Paramagnetic resonance and electronic conduction in organic semiconductors

International Nuclear Information System (INIS)

Nechtschein, M.

1963-01-01

As some organic bodies simultaneously display semi-conducting properties and a paramagnetism, this report addresses the study of conduction in organic bodies. The author first briefly recalls how relationships between conductibility and Electron Paramagnetic Resonance (EPR) can be noticed in a specific case (mineral and metallic semiconductors). He discusses published results related to paramagnetism and conductibility in organic bodies. He reviews various categories of organic bodies in which both properties are simultaneously present. He notably addresses radical molecular crystals, non-radical molecular crystals, charge transfer complexes, pyrolyzed coals, and pseudo-ferromagnetic organic structures. He discusses the issue of relationships between conduction (charge transfer by electrons) and ERP (which reveals the existence of non-paired electrons which provide free spins)

Theory of the orthogonal dimer Heisenberg spin model for SrCu sub 2 (BO sub 3) sub 2

CERN Document Server

Miyahara, S

2003-01-01

The magnetic properties of SrCu sub 2 (BO sub 3) sub 2 are reviewed from a theoretical point of view. SrCu sub 2 (BO sub 3) sub 2 is a new two-dimensional spin gap system and its magnetic properties are well described by a spin-1/2 antiferromagnetic Heisenberg model of the orthogonal dimer lattice. The model has a dimer singlet ground state whose exactness was proven by Shastry and Sutherland for a topologically equivalent model more than 20 years ago. The exactness of the ground state is maintained even if interlayer couplings are introduced for SrCu sub 2 (BO sub 3) sub 2. In the two-dimensional model, quantum phase transitions take place between different ground states for which three phases are expected: a gapped dimer singlet state, a plaquette resonating valence bond state and a gapless magnetic ordered state. Analysis of the experimental data shows that the dimer singlet ground state is realized in SrCu sub 2 (BO sub 3) sub 2. The orthogonality of the dimer bonds, which is the underlying symmetry of th...

Electron paramagnetic resonance study of copper impurity charge-states in PbWO.sub.4./sub. scintillator

Czech Academy of Sciences Publication Activity Database

Hofstaetter, A.; Laguta, V. V.; Meyer, B.K.; Nikl, Martin; Rosa, Jan; Zhu, R.Y.

2004-01-01

Roč. 38, - (2004), s. 703-706 ISSN 1350-4487 R&D Projects: GA AV ČR(CZ) KSK1010104 Keywords : electron paramagnetic resonance * tungstates * defects Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.664, year: 2004

Steady state and time-resolved spectroscopic investigations on the photoreactions involved within the electronically excited electron acceptor 9-cyanoanthracene in presence of benzotriazole and benzimidazole donors

International Nuclear Information System (INIS)

Bhattacharya, Sudeshna; Bardhan, Munmun; Ganguly, Tapan

2010-01-01

The electrochemical, 'steady-state' and 'time-resolved' spectroscopic investigations were made on the well-known electron acceptor 9-cyanoanthracene (CNA) when interacted with the electron donors benzotriazole (BZT) and benzimidazole (BMI) molecules. Though electrochemical measurements indicate the thermodynamical possibility of occurrences of photoinduced electron transfer reactions within these reacting systems in the lowest excited singlet state (S 1 ) of the acceptor CNA but the steady-state and time-resolved measurements clearly demonstrate only the triplet-initiated charge separation reactions. It was reported earlier that in the cases of disubstituted indole molecules the occurrences of photoinduced electron transfer reactions were apparent both in the excited singlet and triplet states of the acceptor 9-cyanoanthracene, but the similarly structured present donor molecules benzotriazole (and benzimidazole) behave differently from indoles. The weak ground state complex formations within the presently studied reacting systems appear to be responsible for the observed static quenching phenomena as evidenced from the time-resolved fluorescence studies. Time-resolved spectroscopic investigations demonstrate the formation of the ground state of the reacting components (donor and acceptor) through recombination of triplet ion-pairs via formations of contact neutral radical produced by H-abstraction mechanism.

Ground state energy fluctuations in the nuclear shell model

International Nuclear Information System (INIS)

Velazquez, Victor; Hirsch, Jorge G.; Frank, Alejandro; Barea, Jose; Zuker, Andres P.

2005-01-01

Statistical fluctuations of the nuclear ground state energies are estimated using shell model calculations in which particles in the valence shells interact through well-defined forces, and are coupled to an upper shell governed by random 2-body interactions. Induced ground-state energy fluctuations are found to be one order of magnitude smaller than those previously associated with chaotic components, in close agreement with independent perturbative estimates based on the spreading widths of excited states

Status of the scalar singlet dark matter model

Energy Technology Data Exchange (ETDEWEB)

Athron, Peter; Balazs, Csaba [Monash University, School of Physics and Astronomy, Melbourne, VIC (Australia); Australian Research Council Centre of Excellence for Particle Physics at the Tera-scale (Australia); Bringmann, Torsten; Dal, Lars A.; Krislock, Abram; Raklev, Are [University of Oslo, Department of Physics, Oslo (Norway); Buckley, Andy [University of Glasgow, SUPA, School of Physics and Astronomy, Glasgow (United Kingdom); Chrzaszcz, Marcin [Universitaet Zuerich, Physik-Institut, Zurich (Switzerland); Polish Academy of Sciences, H. Niewodniczanski Institute of Nuclear Physics, Krakow (Poland); Conrad, Jan; Edsjoe, Joakim; Farmer, Ben [AlbaNova University Centre, Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden); Stockholm University, Department of Physics, Stockholm (Sweden); Cornell, Jonathan M. [McGill University, Department of Physics, Montreal, QC (Canada); Jackson, Paul; White, Martin [Australian Research Council Centre of Excellence for Particle Physics at the Tera-scale (Australia); University of Adelaide, Department of Physics, Adelaide, SA (Australia); Kahlhoefer, Felix [DESY, Hamburg (Germany); Kvellestad, Anders; Savage, Christopher [NORDITA, Stockholm (Sweden); McKay, James; Scott, Pat [Imperial College London, Department of Physics, Blackett Laboratory, London (United Kingdom); Mahmoudi, Farvah [Univ. Lyon, Univ. Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Saint-Genis-Laval (France); CERN, Theoretical Physics Department, Geneva (Switzerland); Martinez, Gregory D. [University of California, Physics and Astronomy Department, Los Angeles, CA (United States); Putze, Antje [LAPTh, Universite de Savoie, CNRS, Annecy-le-Vieux (France); Rogan, Christopher [Harvard University, Department of Physics, Cambridge, MA (United States); Saavedra, Aldo [Australian Research Council Centre of Excellence for Particle Physics at the Tera-scale (Australia); The University of Sydney, Centre for Translational Data Science, Faculty of Engineering and Information Technologies, School of Physics, Sydney, NSW (Australia); Serra, Nicola [Universitaet Zuerich, Physik-Institut, Zurich (Switzerland); Weniger, Christoph [University of Amsterdam, GRAPPA, Institute of Physics, Amsterdam (Netherlands); Collaboration: The GAMBIT Collaboration

2017-08-15

One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z{sub 2} symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ∝ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned. (orig.)

Two-nucleon bound states in quenched lattice QCD

International Nuclear Information System (INIS)

Yamazaki, T.; Kuramashi, Y.; Ukawa, A.

2011-01-01

We address the issue of bound state in the two-nucleon system in lattice QCD. Our study is made in the quenched approximation at the lattice spacing of a=0.128 fm with a heavy quark mass corresponding to m π =0.8 GeV. To distinguish a bound state from an attractive scattering state, we investigate the volume dependence of the energy difference between the ground state and the free two-nucleon state by changing the spatial extent of the lattice from 3.1 fm to 12.3 fm. A finite energy difference left in the infinite spatial volume limit leads us to the conclusion that the measured ground states for not only spin triplet but also singlet channels are bounded. Furthermore the existence of the bound state is confirmed by investigating the properties of the energy for the first excited state obtained by a 2x2 diagonalization method. The scattering lengths for both channels are evaluated by applying the finite volume formula derived by Luescher to the energy of the first excited states.

Regulatory redox state in tree seeds

Directory of Open Access Journals (Sweden)

Ewelina Ratajczak

2017-12-01

Full Text Available Peroxiredoxins (Prx are important regulators of the redox status of tree seeds during maturation and long-term storage. Thioredoxins (Trx are redox transmitters and thereby regulate Prx activity. Current research is focused on the association of Trx with Prx in tree seeds differing in the tolerance to desiccation. The results will allow for better understanding the regulation of the redox status in orthodox, recalcitrant, and intermediate seeds. The findings will also elucidate the role of the redox status during the loss of viability of sensitive seeds during drying and long-term storage.

Singlet Oxygen Sensor Green: Photochemical Behavior in Solution and in a Mammalian Cell

DEFF Research Database (Denmark)

Gollmer, Anita; Arnbjerg, Jacob; Blaikie, Frances Helen

2011-01-01

The development of efficient and selective luminescent probes for reactive oxygen species, particularly for singlet molecular oxygen, is currently of great importance. In this study, the photochemical behavior of Singlet Oxygen Sensor Green® (SOSG), a commercially available fluorescent probe...... of the reaction between SOSG and singlet oxygen is, itself, an efficient singlet oxygen photosensitizer. Second, SOSG appears to efficiently bind to proteins which, in turn, can influence uptake by a cell as well as behavior in the cell. As such, incorrect use of SOSG can yield misleading data on yields...

Ground state phase diagram of extended attractive Hubbard model

International Nuclear Information System (INIS)

Robaszkiewicz, S.; Chao, K.A.; Micnas, R.

1980-08-01

The ground state phase diagram of the extended Hubbard model with intraatomic attraction has been derived in the Hartree-Fock approximation formulated in terms of the Bogoliubov variational approach. For a given value of electron density, the nature of the ordered ground state depends essentially on the sign and the strength of the nearest neighbor coupling. (author)

BODIPY-pyrene and perylene dyads as heavy atom-free singlet oxygen sensitizers

KAUST Repository

Filatov, Mikhail A.

2018-02-23

Dyads combining BODIPY as an electron acceptor and pyrene or perylene as electron donor subunits were prepared and studied their photophysical properties studied by steady-state and transient spectroscopy. Depending on the structure of the subunits and polarity of the media, the dyads show either bright fluorescence or photo-induced electron transfer (PeT) in solution. Charge-transfer (CT) states formed as a result of PeT and were found to yield triplet excited states of the BODIPY. In the presence of molecular oxygen, the dyads sensitize singlet oxygen (1O2) with quantum yields of up to 0.75.

BODIPY-pyrene and perylene dyads as heavy atom-free singlet oxygen sensitizers

KAUST Repository

Filatov, Mikhail A.; Karuthedath, Safakath; Polestshuk, Pavel M.; Callaghan, Susan; Flanagan, Keith J.; Wiesner, Thomas; Laquai, Fré dé ric; Senge, Mathias O.

2018-01-01

Dyads combining BODIPY as an electron acceptor and pyrene or perylene as electron donor subunits were prepared and studied their photophysical properties studied by steady-state and transient spectroscopy. Depending on the structure of the subunits and polarity of the media, the dyads show either bright fluorescence or photo-induced electron transfer (PeT) in solution. Charge-transfer (CT) states formed as a result of PeT and were found to yield triplet excited states of the BODIPY. In the presence of molecular oxygen, the dyads sensitize singlet oxygen (1O2) with quantum yields of up to 0.75.

Extended random-phase approximation with three-body ground-state correlations

International Nuclear Information System (INIS)

Tohyama, M.; Schuck, P.

2008-01-01

An extended random-phase approximation (ERPA) which contains the effects of ground-state correlations up to a three-body level is applied to an extended Lipkin model which contains an additional particle-scattering term. Three-body correlations in the ground state are necessary to preserve the hermiticity of the Hamiltonian matrix of ERPA. Two approximate forms of ERPA which neglect the three-body correlations are also applied to investigate the importance of three-body correlations. It is found that the ground-state energy is little affected by the inclusion of the three-body correlations. On the contrary, three-body correlations for the excited states can become quite important. (orig.)

Paramagnetism: an alternative view. Pt. 1

International Nuclear Information System (INIS)

Oudet, X.

1991-01-01

A new calculation of the paramagnetic susceptibility χ is proposed on the basis of the statistical distribution of the thermal energy using the mean value U of this energy as statistical variable. This allows us to replace the molecular field by an equivalent energy barrier that the paramagnetic moment of an atom has to cross to contribute to χ. The variation of χ with U, or T as well, shows a maximum when there is no magnetic order. The asymptotic character of the Curie-Weiss law appears in close connection with that of the Dulong and Petit law. (orig.)

Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

KAUST Repository

Dimitrov, Stoichko; Schroeder, Bob; Nielsen, Christian; Bronstein, Hugo; Fei, Zhuping; McCulloch, Iain; Heeney, Martin; Durrant, James

2016-01-01

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

From Kondo to local singlet state in graphene nanoribbons with magnetic impurities

Science.gov (United States)

Diniz, G. S.; Luiz, G. I.; Latgé, A.; Vernek, E.

2018-03-01

A detailed analysis of the Kondo effect of a magnetic impurity in a zigzag graphene nanoribbon is addressed. An adatom is coupled to the graphene nanoribbon via a hybridization amplitude Γimp in a hollow- or top-site configuration. In addition, the adatom is also weakly coupled to a metallic scanning tunnel microscope (STM) tip by a hybridization function Γtip that provides a Kondo screening of its magnetic moment. The entire system is described by an Anderson-like Hamiltonian whose low-temperature physics is accessed by employing the numerical renormalization-group approach, which allows us to obtain the thermodynamic properties used to compute the Kondo temperature of the system. We find two screening regimes when the adatom is close to the edge of the zigzag graphene nanoribbon: (1) a weak-coupling regime (Γimp≪Γtip ), in which the edge states produce an enhancement of the Kondo temperature TK, and (2) a strong-coupling regime (Γimp≫Γtip ), in which a local singlet is formed, to the detriment of the Kondo screening by the STM tip. These two regimes can be clearly distinguished by the dependence of their characteristic temperature T* on the coupling between the adatom and the carbon sites of the graphene nanoribbon Vimp. We observe that in the weak-coupling regime T* increases exponentially with Vimp2. Differently, in the strong-coupling regime, T* increases linearly with Vimp2.

Buckling of paramagnetic chains in soft gels

Science.gov (United States)

Huang, Shilin; Pessot, Giorgio; Cremer, Peet; Weeber, Rudolf; Holm, Christian; Nowak, Johannes; Odenbach, Stefan; Menzel, Andreas M.; Auernhammer, Günter K.

We study the magneto-elastic coupling behavior of paramagnetic chains in soft polymer gels exposed to external magnetic fields. To this end, a laser scanning confocal microscope is used to observe the morphology of the paramagnetic chains together with the deformation field of the surrounding gel network. The paramagnetic chains in soft polymer gels show rich morphological shape changes under oblique magnetic fields, in particular a pronounced buckling deformation. The details of the resulting morphological shapes depend on the length of the chain, the strength of the external magnetic field, and the modulus of the gel. Based on the observation that the magnetic chains are strongly coupled to the surrounding polymer network, a simplified model is developed to describe their buckling behavior. A coarse-grained molecular dynamics simulation model featuring an increased matrix stiffness on the surfaces of the particles leads to morphologies in agreement with the experimentally observed buckling effects.

Superconductivity switch from spin-singlet to -triplet pairing in a topological superconducting junction

Science.gov (United States)

Tao, Ze; Chen, F. J.; Zhou, L. Y.; Li, Bin; Tao, Y. C.; Wang, J.

2018-06-01

The interedge coupling is the cardinal characteristic of the narrow quantum spin Hall (QSH) insulator, and thus could bring about exotic transport phenomena. Herein, we present a theoretical investigation of the spin-resolved Andreev reflection (AR) in a QSH insulator strip touching on two neighbouring ferromagnetic insulators and one s-wave superconductor. It is demonstrated that, due to the interplay of the interedge coupling and ferromagnetic configuration, there could be not only usual local ARs leading to the spin-singlet pairing with the incident electron and Andreev-reflected hole from different spin subbands, but also novel local ARs giving rise to the spin-triplet pairing from the same spin subband. However, only the latter exists in the absence of the interedge coupling, and therefore the two pairings in turn testify the helical spin texture of the edge states. By proper tuning of the band structures of the ferromagnetic layers, under the resonance bias voltage, the usual and novel local ARs of can be all exhibited, resulting in fully spin-polarized pure spin-singlet superconductivity and pure spin-triplet superconductivity, respectively, which suggests a superconductivity switch from spin-singlet to -triplet pairing by electrical control. The results can be experimentally confirmed by the tunneling conductance and the noise power.

Exposure of vitamins to UVB and UVA radiation generates singlet oxygen.

Science.gov (United States)

Knak, Alena; Regensburger, Johannes; Maisch, Tim; Bäumler, Wolfgang

2014-05-01

Deleterious effects of UV radiation in tissue are usually attributed to different mechanisms. Absorption of UVB radiation in cell constituents like DNA causes photochemical reactions. Absorption of UVA radiation in endogenous photosensitizers like vitamins generates singlet oxygen via photosensitized reactions. We investigated two further mechanisms that might be involved in UV mediated cell tissue damage. Firstly, UVB radiation and vitamins also generate singlet oxygen. Secondly, UVB radiation may change the chemical structure of vitamins that may change the role of such endogenous photosensitizers in UVA mediated mechanisms. Vitamins were irradiated in solution using monochromatic UVB (308 nm) or UVA (330, 355, or 370 nm) radiation. Singlet oxygen was directly detected and quantified by its luminescence at 1270 nm. All investigated molecules generated singlet oxygen with a quantum yield ranging from 0.007 (vitamin D3) to 0.64 (nicotinamide) independent of the excitation wavelength. Moreover, pre-irradiation of vitamins with UVB changed their absorption in the UVB and UVA spectral range. Subsequently, molecules such as vitamin E and vitamin K1, which normally exhibit no singlet oxygen generation in the UVA, now produce singlet oxygen when exposed to UVA at 355 nm. This interplay of different UV sources is inevitable when applying serial or parallel irradiation with UVA and UVB in experiments in vitro. These results should be of particular importance for parallel irradiation with UVA and UVB in vivo, e.g. when exposing the skin to solar radiation.

Impact of Dielectric Constant on the Singlet-Triplet Gap in Thermally Activated Delayed Fluorescence (TADF) Materials

KAUST Repository

Sun, Haitao; Hu, Zhubin; Zhong, Cheng; Chen, Xiankai; Sun, Zhenrong; Bredas, Jean-Luc

2017-01-01

Thermally activated delayed fluorescence (TADF) relies on the presence of a very small energy gap, ΔEST, between the lowest singlet and triplet excited states. ΔEST is thus a key factor in the molecular design of more efficient materials. However

Reversible Photochemical Control of Singlet Oxygen Generation Using Diarylethene Photochromic Switches

NARCIS (Netherlands)

Hou, Lili; Zhang, Xiaoyan; Pijper, Thomas C.; Browne, Wesley R.; Feringa, Bernard

2014-01-01

Reversible noninvasive control over the generation of singlet oxygen is demonstrated in a bicomponent system comprising a diarylethene photochromic switch and a porphyrin photosensitizer by selective irradiation at distinct wavelengths. The efficient generation of singlet oxygen by the

Quantitative measurements of ground state atomic oxygen in atmospheric pressure surface micro-discharge array

Science.gov (United States)

Li, D.; Kong, M. G.; Britun, N.; Snyders, R.; Leys, C.; Nikiforov, A.

2017-06-01

The generation of atomic oxygen in an array of surface micro-discharge, working in atmospheric pressure He/O2 or Ar/O2 mixtures, is investigated. The absolute atomic oxygen density and its temporal and spatial dynamics are studied by means of two-photon absorption laser-induced fluorescence. A high density of atomic oxygen is detected in the He/O2 mixture with up to 10% O2 content in the feed gas, whereas the atomic oxygen concentration in the Ar/O2 mixture stays below the detection limit of 1013 cm-3. The measured O density near the electrode under the optimal conditions in He/1.75% O2 gas is 4.26  ×  1015 cm-3. The existence of the ground state O (2p 4 3 P) species has been proven in the discharge at a distance up to 12 mm away from the electrodes. Dissociative reactions of the singlet O2 with O3 and deep vacuum ultraviolet radiation, including the radiation of excimer \\text{He}2\\ast , are proposed to be responsible for O (2p 4 3 P) production in the far afterglow. A capability of the surface micro-discharge array delivering atomic oxygen to long distances over a large area is considered very interesting for various biomedical applications.

Blinking fluorescence of single donor-acceptor pairs: important role of "dark'' states in resonance energy transfer via singlet levels.

Science.gov (United States)

Osad'ko, I S; Shchukina, A L

2012-06-01

The influence of triplet levels on Förster resonance energy transfer via singlet levels in donor-acceptor (D-A) pairs is studied. Four types of D-A pair are considered: (i) two-level donor and two-level acceptor, (ii) three-level donor and two-level acceptor, (iii) two-level donor and three-level acceptor, and (iv) three-level donor and three-level acceptor. If singlet-triplet transitions in a three-level acceptor molecule are ineffective, the energy transfer efficiency E=I_{A}/(I_{A}+I_{D}), where I_{D} and I_{A} are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FT_{D}/(1+FT_{D}). Here F is the rate of energy transfer, and T_{D} is the donor fluorescence lifetime. In accordance with the last equation, 100% of the donor electronic energy can be transferred to an acceptor molecule at FT_{D}≫1. However, if singlet-triplet transitions in a three-level acceptor molecule are effective, the energy transfer efficiency is described by another theoretical equation, E(F)=F[over ¯](F)T_{D}/[1+F[over ¯](F)T_{D}]. Here F[over ¯](F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F[over ¯](F) are derived. In this case the energy transfer efficiency will be far from 100% even at FT_{D}≫1. The character of the intensity fluctuations of donor and acceptor fluorescence indicates which of the two equations for E(F) should be used to find the value of the rate F. Therefore, random time instants of photon emission in both donor and acceptor fluorescence are calculated by the Monte Carlo method for all four types of D-A pair. Theoretical expressions for start-stop correlators (waiting time distributions) in donor and acceptor fluorescence are derived. The probabilities w_{N}^{D}(t) and w_{N}^{A}(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy

Paramagnetic NMR investigation of dendrimer-based host-guest interactions.

Directory of Open Access Journals (Sweden)

Fei Wang

Full Text Available In this study, the host-guest behavior of poly(amidoamine (PAMAM dendrimers bearing amine, hydroxyl, or carboxylate surface functionalities were investigated by paramagnetic NMR studies. 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO derivatives were used as paramagnetic guest molecules. The results showed that TEMPO-COOH significantly broaden the ¹H NMR peaks of amine- and hydroxyl-terminated PAMAM dendrimers. In comparison, no paramagnetic relaxation enhancement (PRE was observed between TEMPO-NH₂, TEMPO-OH and the three types of PAMAM dendrimers. The PRE phenomenon observed is correlated with the encapsulation of TEMPO-COOH within dendrimer pockets. Protonation of the tertiary amine groups within PAMAM dendrimers plays an important role during this process. Interestingly, the absence of TEMPO-COOH encapsulation within carboxylate-terminated PAMAM dendrimer is observed due to the repulsion of TEMPO-COO- anion and anionic dendrimer surface. The combination of paramagnetic probes and ¹H NMR linewidth analysis can be used as a powerful tool in the analysis of dendrimer-based host-guest systems.

Singlet Oxygen Sensor Green: Photochemical Behavior in Solution and in a Mammalian Cell

DEFF Research Database (Denmark)

Gollmer, Anita; Arnbjerg, Jacob; Blaikie, Frances Helen

2011-01-01

The development of efficient and selective luminescent probes for reactive oxygen species, particularly for singlet molecular oxygen, is currently of great importance. In this study, the photochemical behavior of Singlet Oxygen Sensor Green® (SOSG), a commercially available fluorescent probe...... for singlet oxygen, was examined. Despite published claims to the contrary, the data presented herein indicate that SOSG can, in fact, be incorporated into a living mammalian cell. However, for a number of reasons, caution must be exercised when using SOSG. First, it is shown that the immediate product...... of the reaction between SOSG and singlet oxygen is, itself, an efficient singlet oxygen photosensitizer. Second, SOSG appears to efficiently bind to proteins which, in turn, can influence uptake by a cell as well as behavior in the cell. As such, incorrect use of SOSG can yield misleading data on yields...

Magnetically robust non-fermi liquid behavior due to the competition between crystalline-electric field singlet and Kondo-Yosida singlet in f2-based heavy fermion systems

International Nuclear Information System (INIS)

Nishiyama, Shinya; Matsuura, Hiroyasu; Miyake, Kazumasa

2011-01-01

In f 2 -based heavy fermion systems with a tetragonal symmetry, we investigate the magnetic field dependence of a non-fermi liquid (NFL) which arises related to the quantum critical point (QCP) due to the competition between the crystalline-electric field (CEF) singlet and the Kondo-Yosida singlet states. On the basis of the Wilson numerical renormalization group method, we find that the magnetic field less than a characteristic magnetic field H z * does not affect the characteristic temperature T F * at which the specific heat takes a maximum value. Since such H z * increases as the deviation from the QCP increases, slightly off the QCP, there are parameter regions where NFL behaviors are robust at an observable temperature range T > T F *against a magnetic field of up to H z * which is far larger than T F *. Our result suggests that such robust NFL behaviors can arise also in systems with other CEF symmetries; e.g., magnetically robust NFL behaviors observed in UBe 13 may be understood on this basis.

Magnetostriction-driven ground-state stabilization in 2H perovskites

International Nuclear Information System (INIS)

Porter, D. G.; Senn, M. S.; University of Oxford; Khalyavin, D. D.; Cortese, A.

2016-01-01

In this paper, the magnetic ground state of Sr_3ARuO_6, with A =(Li,Na), is studied using neutron diffraction, resonant x-ray scattering, and laboratory characterization measurements of high-quality crystals. Combining these results allows us to observe the onset of long-range magnetic order and distinguish the symmetrically allowed magnetic models, identifying in-plane antiferromagnetic moments and a small ferromagnetic component along the c axis. While the existence of magnetic domains masks the particular in-plane direction of the moments, it has been possible to elucidate the ground state using symmetry considerations. We find that due to the lack of local anisotropy, antisymmetric exchange interactions control the magnetic order, first through structural distortions that couple to in-plane antiferromagnetic moments and second through a high-order magnetoelastic coupling that lifts the degeneracy of the in-plane moments. Finally, the symmetry considerations used to rationalize the magnetic ground state are very general and will apply to many systems in this family, such as Ca_3ARuO_6, with A = (Li,Na), and Ca_3LiOsO_6 whose magnetic ground states are still not completely understood.

Electron paramagnetic resonance and optical properties of Cr{sup 3+} doped YAl{sub 3}(BO{sub 3}){sub 4}

Energy Technology Data Exchange (ETDEWEB)

Wells, Jon-Paul R [Department of Physics and Astronomy, University of Sheffield, Sheffield (United Kingdom); Yamaga, Mitsuo [Department of Mathematical and Design Engineering, Gifu University, Gifu (Japan); Han, Thomas P J [Department of Physics, University of Strathclyde, Glasgow (United Kingdom); Honda, Makoto [Faculty of Science, Naruto University of Education, Naruto (Japan)

2003-01-29

We report on the electron paramagnetic resonance (EPR) and optical absorption and fluorescence spectroscopy of YAl{sub 3}(BO{sub 3}){sub 4} single crystals doped with 0.2 mol% of trivalent chromium. From EPR we determine that the Cr{sup 3+} ions reside in sites of essentially octahedral symmetry with an orthorhombic distortion. The ground state {sup 4}A{sub 2} splitting is determined to be 2{radical}D{sup 2} + 3E{sup 2} {approx} 1.05 {+-} 0.04 cm{sup -1}, where D and E are fine-structure parameters, and we can attribute this splitting to the combined effect of a low-symmetry distortion and spin-orbit coupling. The g-values and fine-structure parameters D and E of the ground state {sup 4}A{sub 2} are measured to be g{sub x} {approx} g{sub y} {approx} g{sub z} = 1.978 {+-} 0.005, vertical bar D vertical bar = 0.52 {+-} 0.02 cm{sup -1} and vertical bar E vertical bar 0.010 {+-} 0.005 cm{sup -1} respectively. From 10 K optical absorption we have measured the position and crystal-field splittings of the {sup 2}E, {sup 2}T{sub 1}, {sup 4}T{sub 2}, {sup 2}T{sub 2} and {sup 4}T{sub 1} states with the {sup 4}T{sub 2} and {sup 4}T{sub 1} levels appearing as vibronically broadened bands.

The relation between the (N) and (N-1) electrons atomic ground state

International Nuclear Information System (INIS)

Briet, P.

1984-05-01

The relation between the ground state of an N and (N-1) electrons atomic system are studied. We show that in some directions of the configuration space, the ratio of the N electrons atomic ground state to the one particle density is asymptotically equivalent to the (N-1) electrons atomic ground state

Degenerate ground states and multiple bifurcations in a two-dimensional q-state quantum Potts model.

Science.gov (United States)

Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T; Zhou, Huan-Qiang

2014-06-01

We numerically investigate the two-dimensional q-state quantum Potts model on the infinite square lattice by using the infinite projected entangled-pair state (iPEPS) algorithm. We show that the quantum fidelity, defined as an overlap measurement between an arbitrary reference state and the iPEPS ground state of the system, can detect q-fold degenerate ground states for the Z_{q} broken-symmetry phase. Accordingly, a multiple bifurcation of the quantum ground-state fidelity is shown to occur as the transverse magnetic field varies from the symmetry phase to the broken-symmetry phase, which means that a multiple-bifurcation point corresponds to a critical point. A (dis)continuous behavior of quantum fidelity at phase transition points characterizes a (dis)continuous phase transition. Similar to the characteristic behavior of the quantum fidelity, the magnetizations, as order parameters, obtained from the degenerate ground states exhibit multiple bifurcation at critical points. Each order parameter is also explicitly demonstrated to transform under the Z_{q} subgroup of the symmetry group of the Hamiltonian. We find that the q-state quantum Potts model on the square lattice undergoes a discontinuous (first-order) phase transition for q=3 and q=4 and a continuous phase transition for q=2 (the two-dimensional quantum transverse Ising model).

Dosimetry of ionizing radiations by Electron paramagnetic resonance

International Nuclear Information System (INIS)

Azorin N, J.

2005-01-01

In this work, some historical and theoretical aspects about the Electron Paramagnetic Resonance (EPR), its characteristics, the resonance detection, the paramagnetic species, the radiation effects on inorganic and organic materials, the diagrams of the instrumentation for the EPR detection, the performance of an EPR spectrometer, the coherence among EPR and dosimetry and, practical applications as well as in the food science there are presented. (Author)

Coherent Control of Ground State NaK Molecules

Science.gov (United States)

Yan, Zoe; Park, Jee Woo; Loh, Huanqian; Will, Sebastian; Zwierlein, Martin

2016-05-01

Ultracold dipolar molecules exhibit anisotropic, tunable, long-range interactions, making them attractive for the study of novel states of matter and quantum information processing. We demonstrate the creation and control of 23 Na40 K molecules in their rovibronic and hyperfine ground state. By applying microwaves, we drive coherent Rabi oscillations of spin-polarized molecules between the rotational ground state (J=0) and J=1. The control afforded by microwave manipulation allows us to pursue engineered dipolar interactions via microwave dressing. By driving a two-photon transition, we are also able to observe Ramsey fringes between different J=0 hyperfine states, with coherence times as long as 0.5s. The realization of long coherence times between different molecular states is crucial for applications in quantum information processing. NSF, AFOSR- MURI, Alfred P. Sloan Foundation, DARPA-OLE

Spin-Triplet Pairing Induced by Spin-Singlet Interactions in Noncentrosymmetric Superconductors

Science.gov (United States)

Matsuzaki, Tomoaki; Shimahara, Hiroshi

2017-02-01

In noncentrosymmetric superconductors, we examine the effect of the difference between the intraband and interband interactions, which becomes more important when the band splitting increases. We define the difference ΔVμ between their coupling constants, i.e., that between the intraband and interband hopping energies of intraband Cooper pairs. Here, the subscript μ of ΔVμ indicates that the interactions scatter the spin-singlet and spin-triplet pairs when μ = 0 and μ = 1,2,3, respectively. It is shown that the strong antisymmetric spin-orbit interaction reverses the target spin parity of the interaction: it converts the spin-singlet and spin-triplet interactions represented by ΔV0 and ΔVμ>0 into effective spin-triplet and spin-singlet pairing interactions, respectively. Hence, for example, triplet pairing can be induced solely by the singlet interaction ΔV0. We name the pairing symmetry of the system after that of the intraband Cooper pair wave function, but with an odd-parity phase factor excluded. The pairing symmetry must then be even, even for the triplet component, and the following results are obtained. When ΔVμ is small, the spin-triplet p-wave interactions induce spin-triplet s-wave and spin-triplet d-wave pairings in the regions where the repulsive singlet s-wave interaction is weak and strong, respectively. When ΔV0 is large, a repulsive interband spin-singlet interaction can stabilize spin-triplet pairing. When the Rashba interaction is adopted for the spin-orbit interaction, the spin-triplet pairing interactions mediated by transverse magnetic fluctuations do not contribute to triplet pairing.

Experimental Insights into Ground-State Selection of Quantum XY Pyrochlores

Science.gov (United States)

Hallas, Alannah M.; Gaudet, Jonathan; Gaulin, Bruce D.

2018-03-01

Extensive experimental investigations of the magnetic structures and excitations in the XY pyrochlores have been carried out over the past decade. Three families of XY pyrochlores have emerged: Yb2B2O7, Er2B2O7, and, most recently, [Formula: see text]Co2F7. In each case, the magnetic cation (either Yb, Er, or Co) exhibits XY anisotropy within the local pyrochlore coordinates, a consequence of crystal field effects. Materials in these families display rich phase behavior and are candidates for exotic ground states, such as quantum spin ice, and exotic ground-state selection via order-by-disorder mechanisms. In this review, we present an experimental summary of the ground-state properties of the XY pyrochlores, including evidence that they are strongly influenced by phase competition. We empirically demonstrate the signatures for phase competition in a frustrated magnet: multiple heat capacity anomalies, suppressed TN or TC, sample- and pressure-dependent ground states, and unconventional spin dynamics.

Magneto-Optical Properties of Paramagnetic Superrotors

Science.gov (United States)

Milner, A. A.; Korobenko, A.; Floß, J.; Averbukh, I. Sh.; Milner, V.

2015-07-01

We study the dynamics of paramagnetic molecular superrotors in an external magnetic field. An optical centrifuge is used to create dense ensembles of oxygen molecules in ultrahigh rotational states. In is shown, for the first time, that the gas of rotating molecules becomes optically birefringent in the presence of a magnetic field. The discovered effect of "magneto-rotational birefringence" indicates the preferential alignment of molecular axes along the field direction. We provide an intuitive qualitative model, in which the influence of the applied magnetic field on the molecular orientation is mediated by the spin-rotation coupling. This model is supported by the direct imaging of the distribution of molecular axes, the demonstration of the magnetic reversal of the rotational Raman signal, and by numerical calculations.

On the behaviour of non-singlet structure functions at small x

International Nuclear Information System (INIS)

Bluemlein, J.

1995-10-01

The resummation of O(α s l+1 ln 2l x) terms in the evolution kernels of non-singlet combinations of unpolarized and polarized structure functions is investigated. The agreement with complete calculations up to order α s 2 is demonstrated, and the leading small-x contributions to the three-loop non-singlet splitting functions P ± are derived. The additional contributions due to the resummed terms are studied numerically for the most important non-singlet structure functions. They are found to be about 1% or smaller in the kinematical regions accessible at present and in the forseeable future. (orig.)

Chain and ladder models with two-body interactions and analytical ground states

Science.gov (United States)

Manna, Sourav; Nielsen, Anne E. B.

2018-05-01

We consider a family of spin-1 /2 models with few-body, SU(2)-invariant Hamiltonians and analytical ground states related to the one-dimensional (1D) Haldane-Shastry wave function. The spins are placed on the surface of a cylinder, and the standard 1D Haldane-Shastry model is obtained by placing the spins with equal spacing in a circle around the cylinder. Here, we show that another interesting family of models with two-body exchange interactions is obtained if we instead place the spins along one or two lines parallel to the cylinder axis, giving rise to chain and ladder models, respectively. We can change the scale along the cylinder axis without changing the radius of the cylinder. This gives us a parameter that controls the ratio between the circumference of the cylinder and all other length scales in the system. We use Monte Carlo simulations and analytical investigations to study how this ratio affects the properties of the models. If the ratio is large, we find that the two legs of the ladder decouple into two chains that are in a critical phase with Haldane-Shastry-like properties. If the ratio is small, the wave function reduces to a product of singlets. In between, we find that the behavior of the correlations and the Renyi entropy depends on the distance considered. For small distances the behavior is critical, and for long distances the correlations decay exponentially and the entropy shows an area law behavior. The distance up to which there is critical behavior gets larger as the ratio increases.

Ground state of charged Base and Fermi fluids in strong coupling

International Nuclear Information System (INIS)

Mazighi, R.

1982-03-01

The ground state and excited states of the charged Bose gas were studied (wave function, equation of state, thermodynamics, application of Feynman theory). The ground state of the charged Fermi gas was also investigated together with the miscibility of charged Bose and Fermi gases at 0 deg K (bosons-bosons, fermions-bosons and fermions-fermions) [fr

Theory of ground state factorization in quantum cooperative systems.

Science.gov (United States)

Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio

2008-05-16

We introduce a general analytic approach to the study of factorization points and factorized ground states in quantum cooperative systems. The method allows us to determine rigorously the existence, location, and exact form of separable ground states in a large variety of, generally nonexactly solvable, spin models belonging to different universality classes. The theory applies to translationally invariant systems, irrespective of spatial dimensionality, and for spin-spin interactions of arbitrary range.

Antibonding hole ground state in InAs quantum dot molecules

Energy Technology Data Exchange (ETDEWEB)

Planelles, Josep [Departament de Química Física i Analítica, Universitat Jaume I, E-12080, Castelló (Spain)

2015-01-22

Using four-band k⋅p Hamiltonians, we study how strain and position-dependent effective masses influence hole tunneling in vertically coupled InAs/GaAs quantum dots. Strain reduces the tunneling and hence the critical interdot distance required for the ground state to change from bonding to antibonding. Variable mass has the opposite effect and a rough compensation leaves little affected the critical bonding-to-antibonding ground state crossover. An alternative implementation of the magnetic field in the envelope function Hamiltonian is given which retrieves the experimental denial of possible after growth reversible magnetically induced bonding-to-antibonding ground state transition, predicted by the widely used Luttinger-Kohn Hamiltonian.

A Model Ground State of Polyampholytes

International Nuclear Information System (INIS)

Wofling, S.; Kantor, Y.

1998-01-01

The ground state of randomly charged polyampholytes (polymers with positive and negatively charged groups along their backbone) is conjectured to have a structure similar to a necklace, made of weakly charged parts of the chain, compacting into globules, connected by highly charged stretched 'strings' attempted to quantify the qualitative necklace model, by suggesting a zero approximation model, in which the longest neutral segment of the polyampholyte forms a globule, while the remaining part will form a tail. Expanding this approximation, we suggest a specific necklace-type structure for the ground state of randomly charged polyampholyte's, where all the neutral parts of the chain compact into globules: The longest neutral segment compacts into a globule; in the remaining part of the chain, the longest neutral segment (the second longest neutral segment) compacts into a globule, then the third, and so on. A random sequence of charges is equivalent to a random walk, and a neutral segment is equivalent to a loop inside the random walk. We use analytical and Monte Carlo methods to investigate the size distribution of loops in a one-dimensional random walk. We show that the length of the nth longest neutral segment in a sequence of N monomers (or equivalently, the nth longest loop in a random walk of N steps) is proportional to N/n 2 , while the mean number of neutral segments increases as √N. The polyampholytes in the ground state within our model is found to have an average linear size proportional to dN, and an average surface area proportional to N 2/3

Three-body problem in the ground-state representation

International Nuclear Information System (INIS)

Gonzalez, A.

1993-01-01

The ground-state probability density of a three-body system is used to construct a classical potential U whose minimum coincides exactly with the ground-state energy. The spectrum of excited states may approximately be obtained by imposing quasiclassical quantization conditions over the classical motion in U. We show nontrivial one-dimensional models in which either this quantization condition is exact or considerably improves the usual semiclassical quantization. For three-dimensional problems, the small-oscillation frequencies in states with total angular momentum L = 0 are computed. These frequencies could represent an improvement over the frequencies of triatomic molecules computed with the use of ordinary quasiclassics for the motion of the nuclei in the molecular term. By providing a semiclassical description of the first excited quantum states, the sketched approach rises some interesting questions such as, for example, the relevance (once again) of classical chaos to quantum mechanics

Singlet-paired coupled cluster theory for open shells

Science.gov (United States)

Gomez, John A.; Henderson, Thomas M.; Scuseria, Gustavo E.

2016-06-01

Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.

Singlet-paired coupled cluster theory for open shells

International Nuclear Information System (INIS)

Gomez, John A.; Henderson, Thomas M.; Scuseria, Gustavo E.

2016-01-01

Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.

Moessbauer studies on the paramagnetic porton of alkidirat meteorite

International Nuclear Information System (INIS)

Kamal, Huda Mohamed

1995-11-01

This work was performed on a sample from alkidirat meteorite which fell west of Sudan by means of Moessbauer effect spectrometer. results showed the absence of transition temperature from the paramagnetic state to the magnetic state in the temperature range from 300K down to 16K. Also, it was found that olivine and ortho pyroxene exist together in site M 1 , while clinothyroxene exists alone in site M 2 . Formula for the composition of ortho pyroxene in the sample were also obtained and they were in good agreement with previous studies. The disorder parameter was also calculated and it showed that the pyroxene present in the sample is well-ordered.(Author)

Collisional-radiative model for neutral helium in plasma. Excitation cross section and singlet-triplet wavefunction mixing

Energy Technology Data Exchange (ETDEWEB)

Goto, Motoshi [National Inst. for Fusion Science, Toki, Gifu (Japan); Fujimoto, Takashi

1997-10-01

We have revised the collisional-radiative (CR) model code of neutral helium (T. Fujimoto, JQSRT 21, 1979). The spin-orbit interaction gives rise to mixing of the wavefunctions of the singlet and triplet states. The degree of the mixing depends on the magnetic field, and at the field strength of the level-anticrossings complete mixing, or complete breakdown of the L-S coupling scheme, occurs. We have approximately incorporated this effect into the code. We have reviewed the excitation cross section data for electron impacts. For transitions starting from the ground state, the recent assessment by the group led by Dr. de Heer is judged satisfactory. For transitions from the metastable levels the assessment by the same group appears rather conservative; there remains a question about the cross section values near the threshold. For transitions between different-l levels within the same multiplicity and same n, a semi-empirical formula based on the Born cross section gives a good agreement with experiment. Proton impacts are also considered for these transitions. We compare the new cross sections with those used in the original version. These cross sections for transitions starting from the metastable levels are fitted by analytical formulas and the parameter values are given. We also give parameter values for the excitation rate coefficient for these transitions as well as for transitions starting from the ground state. With all the above revisions incorporated into the CR model code, we have calculated the energy loss rates and the line intensity ratios for the purpose of plasma diagnostics, where the effect of a magnetic field is noted. The calculated population distribution over excited levels are compared with experiment, and a tentative conclusion is drawn concerning the excitation cross section from the metastable level. (author)

In-vitro singlet oxygen threshold dose at PDT with Radachlorin photosensitizer

Science.gov (United States)

Klimenko, V. V.; Shmakov, S. V.; Kaydanov, N. E.; Knyazev, N. A.; Kazakov, N. V.; Rusanov, A. A.; Bogdanov, A. A.; Dubina, M. V.

2017-07-01

In this present study we investigate the Radachlorin photosensitizer accumulation in K562 cells and Hela cells and determined the cell viability after PDT. Using the macroscopic singlet oxygen modeling and cellular photosensitizer concentration the singlet oxygen threshold doses for K562 cells and Hela cells were calculated.

Stability of quantum-dot excited-state laser emission under simultaneous ground-state perturbation

Energy Technology Data Exchange (ETDEWEB)

Kaptan, Y., E-mail: yuecel.kaptan@physik.tu-berlin.de; Herzog, B.; Schöps, O.; Kolarczik, M.; Woggon, U.; Owschimikow, N. [Institut für Optik und Atomare Physik, Technische Universität Berlin, Berlin (Germany); Röhm, A.; Lingnau, B.; Lüdge, K. [Institut für Theoretische Physik, Technische Universität Berlin, Berlin (Germany); Schmeckebier, H.; Arsenijević, D.; Bimberg, D. [Institut für Festkörperphysik, Technische Universität Berlin, Berlin (Germany); Mikhelashvili, V.; Eisenstein, G. [Technion Institute of Technology, Faculty of Electrical Engineering, Haifa (Israel)

2014-11-10

The impact of ground state amplification on the laser emission of In(Ga)As quantum dot excited state lasers is studied in time-resolved experiments. We find that a depopulation of the quantum dot ground state is followed by a drop in excited state lasing intensity. The magnitude of the drop is strongly dependent on the wavelength of the depletion pulse and the applied injection current. Numerical simulations based on laser rate equations reproduce the experimental results and explain the wavelength dependence by the different dynamics in lasing and non-lasing sub-ensembles within the inhomogeneously broadened quantum dots. At high injection levels, the observed response even upon perturbation of the lasing sub-ensemble is small and followed by a fast recovery, thus supporting the capacity of fast modulation in dual-state devices.

First-principles calculation of the magnetic properties of paramagnetic fcc iron

International Nuclear Information System (INIS)

Johnson, D.D.; Gyorffy, B.L.; Pinski, F.J.; Staunton, J.; Stocks, G.M.

1985-01-01

Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments

Fast hydrogen elimination from the [Ru(PH3)3(CO)(H)2] and [Ru(PH3)4(H)2] complexes in the first singlet excited states: A diabatic quantum dynamics study

International Nuclear Information System (INIS)

Vendrell, Oriol; Moreno, Miquel; Lluch, Jose M.

2004-01-01

The photodissociation dynamics of [Ru(PH 3 ) 3 (CO)(H) 2 ] and cis-[Ru(PH 3 ) 4 (H) 2 ] is theoretically analyzed in the lowest two excited singlet states. Energies obtained through electronic density functional theory calculations that use the time-dependent formalism are fitted to analytical reduced two-dimensional potential energy surfaces (2D-PES). The metal-H 2 (R) and H-H (r) distances are the variables of these 2D-PES, the rest of the parameters being kept frozen at the values of the minimum energy structure in the ground electronic state. The time evolution in these 2D-PES is exactly followed by means of a fast Fourier transform algorithm applied to solve the time-dependent Schroedinger equation. A simple diabatization scheme is devised to take into account the probability of transitions between both excited states. The quantum dynamics results point out that photoelimination is almost inexistent if the H 2 fragment is to be expelled without further rearrangement of the rest of the complex. Conversely, when the geometries of the complex are optimized by keeping r and R frozen at the hydrogen elimination barrier coordinates, the new 2D-PES so obtained are highly dissociative, the H 2 fragment being expelled in less than 100 fs. Finally the picture of the whole reaction that emerges from our theoretical results is described and the main differences between both complexes are examined

Size-dependent concentration of N0 paramagnetic centres in HPHT nanodiamonds

OpenAIRE

Yavkin, Boris V; Mamin, Georgy V; Gafurov, Marat R.; Orlinskii, Sergei B.

2015-01-01

Size-calibrated commercial nanodiamonds synthesized by high-pressure high-temperature (HPHT) technique were studied by high-frequency W and conventional X band electron paramagnetic resonance (EPR) spectroscopy. The numbers of spins in the studied samples were estimated. The core-shell model of the HPHT nanodiamonds was proposed to explain the observed dependence of the concentration of the N0 paramagnetic centers. Two other observed paramagnetic centers are attributed to the two types of str...

Bromorhodamines - new singlet oxygen photosensitizers for oxidative water and wastewater treatment

Energy Technology Data Exchange (ETDEWEB)

Slivka, L.; Alekseeva, V.; Kuznetsova, N.; Marinina, L.; Savvina, L.; Kaliya, O.; Lukyanets, E.; Vorozhtsov, G. [Organic Intermediates and Dyes Inst., Moscow (Russian Federation); Krasnovsky, A.; Butorina, D. [Inst. of Biochemistry RAS, Moscow (Russian Federation)

2003-07-01

The cationic mono-, di- and tetrabromoderivatives of rhodamine 123 have been synthesized and studied as sensitizers for singlet oxygen formation in application for oxidative water treatment. Singlet oxygen quantum yields for compounds under investigation have been determined by using its near IR luminescence at 1270 nm. Bromorhodamines123 have been shown to sensitize the formation of singlet oxygen in aqueous solution with high quantum yields. Efficient oxidation of tryptophan in aqueous solutions sensitized by dibromorhodamine 123 has been demonstrated. This dye was tested as sensitizer for photodynamic treatment of water contaminated with coliform bacteria. It was shown to participate in the photosensitization of coliform bacteria, resulting in their efficient killing. (orig.)

Direct and indirect singlet scalar dark matter detection in the lepton-specific two-Higgs-doublet model

International Nuclear Information System (INIS)

Boucenna, M. S.; Profumo, S.

2011-01-01

A recent study of gamma-ray data from the Galactic center motivates the investigation of light (∼7-10 GeV) particle dark matter models featuring tau-lepton pairs as dominant annihilation final state. The lepton-specific two-Higgs-doublet model provides a natural framework where light, singlet scalar dark matter can pair-annihilate dominantly into tau leptons. We calculate the nucleon-dark matter cross section for singlet scalar dark matter within the lepton-specific two-Higgs-doublet model framework, and compare with recent results from direct detection experiments. We study how direct dark matter searches can be used to constrain the dark matter interpretation of gamma-ray observations, for different dominant annihilation final states. We show that models exist with the correct thermal relic abundance that could fit the claimed gamma-ray excess from the Galactic center region and have direct detection cross sections of the order of what is needed to interpret recent anomalous events reported by direct detection experiments.

On calculations of the ground state energy in quantum mechanics

International Nuclear Information System (INIS)

Efimov, G.V.

1991-02-01

In nonrelativistic quantum mechanics the Wick-ordering method called the oscillator representation suggested to calculate the ground-state energy for a wide class of potentials allowing the existence of a bound state. The following examples are considered: the orbital excitations of the ground-state in the Coulomb plus linear potential, the Schroedinger equation with a ''relativistic'' kinetic energy √p 2 +m 2 , the Coulomb three-body problem. (author). 22 refs, 2 tabs

Ground-state structures of Hafnium clusters

Energy Technology Data Exchange (ETDEWEB)

Ng, Wei Chun; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technoloty, Multimedia University, Melaca Campus, 75450 Melaka (Malaysia)

2015-04-24

Hafnium (Hf) is a very large tetra-valence d-block element which is able to form relatively long covalent bond. Researchers are interested to search for substitution to silicon in the semi-conductor industry. We attempt to obtain the ground-state structures of small Hf clusters at both empirical and density-functional theory (DFT) levels. For calculations at the empirical level, charge-optimized many-body functional potential (COMB) is used. The lowest-energy structures are obtained via a novel global-minimum search algorithm known as parallel tempering Monte-Carlo Basin-Hopping and Genetic Algorithm (PTMBHGA). The virtue of using COMB potential for Hf cluster calculation lies in the fact that by including the charge optimization at the valence shells, we can encourage the formation of proper bond hybridization, and thus getting the correct bond order. The obtained structures are further optimized using DFT to ensure a close proximity to the ground-state.

Probing quantum frustrated systems via factorization of the ground state.

Science.gov (United States)

Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio

2010-05-21

The existence of definite orders in frustrated quantum systems is related rigorously to the occurrence of fully factorized ground states below a threshold value of the frustration. Ground-state separability thus provides a natural measure of frustration: strongly frustrated systems are those that cannot accommodate for classical-like solutions. The exact form of the factorized ground states and the critical frustration are determined for various classes of nonexactly solvable spin models with different spatial ranges of the interactions. For weak frustration, the existence of disentangling transitions determines the range of applicability of mean-field descriptions in biological and physical problems such as stochastic gene expression and the stability of long-period modulated structures.

Ground-state fidelity in the BCS-BEC crossover

International Nuclear Information System (INIS)

Khan, Ayan; Pieri, Pierbiagio

2009-01-01

The ground-state fidelity has been introduced recently as a tool to investigate quantum phase transitions. Here, we apply this concept in the context of a crossover problem. Specifically, we calculate the fidelity susceptibility for the BCS ground-state wave function, when the intensity of the fermionic attraction is varied from weak to strong in an interacting Fermi system, through the BCS-Bose-Einstein Condensation crossover. Results are presented for contact and finite-range attractive potentials and for both continuum and lattice models. We conclude that the fidelity susceptibility can be useful also in the context of crossover problems.

Ground state correlations and structure of odd spherical nuclei

International Nuclear Information System (INIS)

Mishev, S.; Voronov, V. V.

2006-01-01

It is well known that the Pauli principle plays a substantial role at low energies because the phonon operators are not ideal boson operators. Calculating the exact commutators between the quasiparticle and phonon operators one can take into account the Pauli principle corrections. Besides the ground state correlations due to the quasiparticle interaction in the ground state influence the single particle fragmentation as well. In this paper, we generalize the basic QPM equations to account for both mentioned effects. As an illustration of our approach, calculations on the structure of the low-lying states in "1"3"1Ba have been performed.

Relationship between symmetry of porphyrinic pi-conjugated systems and singlet oxygen (1Delta g) yields: low-symmetry tetraazaporphyrin derivatives.

Science.gov (United States)

Ishii, Kazuyuki; Itoya, Hatsumi; Miwa, Hideya; Fujitsuka, Mamoru; Ito, Osamu; Kobayashi, Nagao

2005-07-07

We have investigated the excited-state properties and singlet oxygen ((1)Delta(g)) generation mechanism in phthalocyanines (4M; M = H(2), Mg, or Zn) and in low-symmetry metal-free, magnesium, and zinc tetraazaporphyrins (TAPs), that is, monobenzo-substituted (1M), adjacently dibenzo-substituted (2AdM), oppositely dibenzo-substituted (2OpM), and tribenzo-substituted (3M) TAP derivatives, whose pi conjugated systems were altered by fusing benzo rings. The S(1)(x) and S(1)(y) states (these lowest excited singlet states are degenerate in D(4)(h) symmetry) split in the low-symmetry TAP derivatives. The excited-state energies were quantitatively determined from the electronic absorption spectra. The lowest excited triplet (T(1)(x)) energies were also determined from phosphorescence spectra, while the second lowest excited triplet (T(1)(y)) states were evaluated by using the energy splitting between the T(1)(x) and T(1)(y) states previously reported (Miwa, H.; Ishii, K.; Kobayashi, N. Chem. Eur. J. 2004, 10, 4422-4435). The singlet oxygen quantum yields (Phi(Delta)) are strongly dependent on the pi conjugated system. In particular, while the Phi(Delta) value of 2AdH(2) is smallest in our system, that of 2OpH(2), an isomer of 2AdH(2), is larger than that of 4Zn, in contrast to the heavy atom effect. The relationship between the molecular structure and Phi(Delta) values can be transformed into a relationship between the S(1)(x) --> T(1)(y) intersystem crossing rate constant (k(ISC)) and the energy difference between the S(1)(x) and T(1)(y) states (DeltaE(S)(x)(T)(y)). In each of the Zn, Mg, and metal-free compounds, the Phi(Delta)/tau(F) values (tau(F): fluorescence lifetime), which are related to the k(ISC) values, are proportional to exp(-DeltaE(S)(x)(T)(y)), indicating that singlet oxygen ((1)Delta(g)) is produced via the T(1)(y) state and that the S(1)(x) --> T(1)(y) ISC process follows the energy-gap law. From the viewpoint of photodynamic therapy, our methodology

Ground-state splitting of ultrashallow thermal donors with negative central-cell corrections in silicon

Science.gov (United States)

Hara, Akito; Awano, Teruyoshi

2017-06-01

Ultrashallow thermal donors (USTDs), which consist of light element impurities such as carbon, hydrogen, and oxygen, have been found in Czochralski silicon (CZ Si) crystals. To the best of our knowledge, these are the shallowest hydrogen-like donors with negative central-cell corrections in Si. We observed the ground-state splitting of USTDs by far-infrared optical absorption at different temperatures. The upper ground-state levels are approximately 4 meV higher than the ground-state levels. This energy level splitting is also consistent with that obtained by thermal excitation from the ground state to the upper ground state. This is direct evidence that the wave function of the USTD ground state is made up of a linear combination of conduction band minimums.

Dynamics of Singlet Fission and Electron Injection in Self-Assembled Acene Monolayers on Titanium Dioxide

Energy Technology Data Exchange (ETDEWEB)

Johnson, Justin C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Pace, Natalie A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Arias, Dylan H [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Christensen, Steven T [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Granger, Devin B. [University of Kentucky; Anthony, John E. [University of Kentucky

2018-02-26

We employ a combination of linear spectroscopy, electrochemistry, and transient absorption spectroscopy to characterize the interplay between electron transfer and singlet fission dynamics in polyacene-based dyes attached to nanostructured TiO2. For triisopropyl silylethynyl (TIPS)-pentacene, we find that the singlet fission time constant increases to 6.5 ps on a nanostructured TiO2 surface relative to a thin film time constant of 150 fs, and that triplets do not dissociate after they are formed. In contrast, TIPS-tetracene singlets quickly dissociate in 2 ps at the molecule/TiO2 interface, and this dissociation outcompetes the relatively slow singlet fission process. The addition of an alumina layer slows down electron injection, allowing the formation of triplets from singlet fission in 40 ps. However, the triplets do not inject electrons, which is likely due to a lack of sufficient driving force for triplet dissociation. These results point to the critical balance required between efficient singlet fission and appropriate energetics for interfacial charge transfer.

Model for paramagnetic Fermi systems

International Nuclear Information System (INIS)

Ainsworth, T.L.; Bedell, K.S.; Brown, G.E.; Quader, K.F.

1983-01-01

We develop a mode for paramagnetic Fermi liquids. This model has both direct and induced interactions, the latter including both density-density and current-current response. The direct interactions are chosen to reproduce the Fermi liquid parameters F/sup s/ 0 , F/sup a/ 0 , F/sup s/ 1 and to satify the forward scattering sum rule. The F/sup a/ 1 and F/sup s/,a/sub l/ for l>1 are determined self-consistently by the induced interactions; they are checked aginst experimental determinations. The model is applied in detail to liquid 3 He, using data from spin-echo experiments, sound attenuation, and the velocities of first and zero sound. Consistency with experiments gives definite preferences for values of m. The model is also applied to paramagnetic metals. Arguments are given that this model should provide a basis for calculating effects of magnetic fields

Singlet Oxygen at the Laundromat

Science.gov (United States)

Keeports, David

1995-09-01

Singlet molecular oxygen is an interesting molecule both visually and theoretically, since its red chemiluminescence can be analyzed by the application of simple molecular orbital theory. It can be produced from the reaction of hydrogen peroxide from either chlorine gas or hypochlorite ion from household bleach. Here we demostrate how to produce it using simple laundry cleansers.

Clean bulk YBaCuO superconductors doped by paramagnetic ions of Sm and Yb

Czech Academy of Sciences Publication Activity Database

Jirsa, Miloš; Volochová, D.; Kováč, J.; Diko, P.

2017-01-01

Roč. 131, č. 4 (2017), s. 1027-1029 ISSN 0587-4246 Institutional support: RVO:68378271 Keywords : YBaCuO * bulk superconductors * paramagnetic ions * microstructure * vortex pinning Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.469, year: 2016

Rearrangements in ground and excited states

CERN Document Server

de Mayo, Paul

1980-01-01

Rearrangements in Ground and Excited States, Volume 3 presents essays on the chemical generation of excited states; the cis-trans isomerization of olefins; and the photochemical rearrangements in trienes. The book also includes essays on the zimmerman rearrangements; the photochemical rearrangements of enones; the photochemical rearrangements of conjugated cyclic dienones; and the rearrangements of the benzene ring. Essays on the photo rearrangements via biradicals of simple carbonyl compounds; the photochemical rearrangements involving three-membered rings or five-membered ring heterocycles;

Size-dependent concentration of N0 paramagnetic centres in HPHT nanodiamonds

Directory of Open Access Journals (Sweden)

B.V. Yavkin, G.V. Mamin, M.R. Gafurov, S.B. Orlinskii

2015-12-01

Full Text Available Size-calibrated commercial nanodiamonds synthesized by high-pressure high-temperature (HPHT technique were studied by high-frequency W- and conventional X-band electron paramagnetic resonance (EPR spectroscopy. The numbers of spins in the studied samples were estimated. The core-shell model of the HPHT nanodiamonds was proposed to explain the observed dependence of the concentration of the N0 paramagnetic centers. Two other observed paramagnetic centers are attributed to the two types of structures in the nanodiamond shell.

Singlet Fission via an Excimer-Like Intermediate in 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives.

Science.gov (United States)

Mauck, Catherine M; Hartnett, Patrick E; Margulies, Eric A; Ma, Lin; Miller, Claire E; Schatz, George C; Marks, Tobin J; Wasielewski, Michael R

2016-09-14

Singlet fission (SF) in polycrystalline thin films of four 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores with methyl (Me), n-hexyl (C6), triethylene glycol (TEG), and 2-ethylhexyl (EH) substituents at the 2,5-positions is found to involve an intermediate excimer-like state. The four different substituents yield four distinct intermolecular packing geometries, resulting in variable intermolecular charge transfer (CT) interactions in the solid. SF from the excimer state of Me, C6, TEG, and EH takes place in τSF = 22, 336, 195, and 1200 ps, respectively, to give triplet yields of 200%, 110%, 110%, and 70%, respectively. The transient spectra of the excimer-like state and its energetic proximity to the lowest excited singlet state in these derivatives suggests that this state may be the multiexciton (1)(T1T1) state that precedes formation of the uncorrelated triplet excitons. The excimer decay rates correlate well with the SF efficiencies and the degree of intermolecular donor-acceptor interactions resulting from π-stacking of the thiophene donor of one molecule with the DPP core acceptor in another molecule as observed in the crystal structures. Such interactions are found to also increase with the SF coupling energies, as calculated for each derivative. These structural and spectroscopic studies afford a better understanding of the electronic interactions that enhance SF in chromophores having strong intra- and intermolecular CT character.

Ground-state densities from the Rayleigh-Ritz variation principle and from density-functional theory.

Science.gov (United States)

Kvaal, Simen; Helgaker, Trygve

2015-11-14

The relationship between the densities of ground-state wave functions (i.e., the minimizers of the Rayleigh-Ritz variation principle) and the ground-state densities in density-functional theory (i.e., the minimizers of the Hohenberg-Kohn variation principle) is studied within the framework of convex conjugation, in a generic setting covering molecular systems, solid-state systems, and more. Having introduced admissible density functionals as functionals that produce the exact ground-state energy for a given external potential by minimizing over densities in the Hohenberg-Kohn variation principle, necessary and sufficient conditions on such functionals are established to ensure that the Rayleigh-Ritz ground-state densities and the Hohenberg-Kohn ground-state densities are identical. We apply the results to molecular systems in the Born-Oppenheimer approximation. For any given potential v ∈ L(3/2)(ℝ(3)) + L(∞)(ℝ(3)), we establish a one-to-one correspondence between the mixed ground-state densities of the Rayleigh-Ritz variation principle and the mixed ground-state densities of the Hohenberg-Kohn variation principle when the Lieb density-matrix constrained-search universal density functional is taken as the admissible functional. A similar one-to-one correspondence is established between the pure ground-state densities of the Rayleigh-Ritz variation principle and the pure ground-state densities obtained using the Hohenberg-Kohn variation principle with the Levy-Lieb pure-state constrained-search functional. In other words, all physical ground-state densities (pure or mixed) are recovered with these functionals and no false densities (i.e., minimizing densities that are not physical) exist. The importance of topology (i.e., choice of Banach space of densities and potentials) is emphasized and illustrated. The relevance of these results for current-density-functional theory is examined.

Moessbauer studies on the paramagnetic porton of alkidirat meteorite

Energy Technology Data Exchange (ETDEWEB)

Kamal, Huda Mohamed [Department of Physics, Faculty of Science, University of Khartoum, Khartoum (Sudan)

1995-11-01

This work was performed on a sample from alkidirat meteorite which fell west of Sudan by means of Moessbauer effect spectrometer. results showed the absence of transition temperature from the paramagnetic state to the magnetic state in the temperature range from 300K down to 16K. Also, it was found that olivine and ortho pyroxene exist together in site M{sup 1}, while clinothyroxene exists alone in site M{sup 2}. Formula for the composition of ortho pyroxene in the sample were also obtained and they were in good agreement with previous studies. The disorder parameter was also calculated and it showed that the pyroxene present in the sample is well-ordered.(Author) 37 refs. , 2 tabs. , 19 figs.

Parabanic acid is the singlet oxygen specific oxidation product of uric acid.

Science.gov (United States)

Iida, Sayaka; Ohkubo, Yuki; Yamamoto, Yorihiro; Fujisawa, Akio

2017-11-01

Uric acid quenches singlet oxygen physically or reacts with it, but the oxidation product has not been previously characterized. The present study determined that the product is parabanic acid, which was confirmed by LC/TOFMS analysis. Parabanic acid was stable at acidic pH (acid at neutral or alkaline pH. The total yields of parabanic acid and oxaluric acid based on consumed uric acid were ~100% in clean singlet oxygen production systems such as UVA irradiation of Rose Bengal and thermal decomposition of 3-(1,4-dihydro-1,4-epidioxy-4-methyl-1-naphthyl)propionic acid. However, the ratio of the amount of uric acid consumed to the total amount of singlet oxygen generated was less than 1/180, indicating that most of the singlet oxygen was physically quenched. The total yields of parabanic acid and oxaluric acid were high in the uric acid oxidation systems with hydrogen peroxide plus hypochlorite or peroxynitrite. They became less than a few percent in peroxyl radical-, hypochlorite- or peroxynitrite-induced oxidation of uric acid. These results suggest that parabanic acid could be an in vivo probe of singlet oxygen formation because of the wide distribution of uric acid in human tissues and extracellular spaces. In fact, sunlight exposure significantly increased human skin levels of parabanic acid.

Ground state correlations and structure of odd spherical nuclei

International Nuclear Information System (INIS)

Mishev, S.; Voronov, V.V.

2008-01-01

It is well known that the Pauli principle plays a substantial role at low energies because the phonon operators are not ideal boson operators. Calculating the exact commutators between the quasiparticle and phonon operators one can take into account the Pauli principle corrections. Besides, the ground state correlations due to the quasiparticle interaction in the ground state influence the single-particle fragmentation as well. In this paper, we generalize the basic equations of the quasiparticle-phonon nuclear model to account for both effects mentioned. As an illustration of our approach, calculations on the structure of the low-lying states in 133 Ba have been performed

Ground state of the parallel double quantum dot system.

Science.gov (United States)

Zitko, Rok; Mravlje, Jernej; Haule, Kristjan

2012-02-10

We resolve the controversy regarding the ground state of the parallel double quantum dot system near half filling. The numerical renormalization group predicts an underscreened Kondo state with residual spin-1/2 magnetic moment, ln2 residual impurity entropy, and unitary conductance, while the Bethe ansatz solution predicts a fully screened impurity, regular Fermi-liquid ground state, and zero conductance. We calculate the impurity entropy of the system as a function of the temperature using the hybridization-expansion continuous-time quantum Monte Carlo technique, which is a numerically exact stochastic method, and find excellent agreement with the numerical renormalization group results. We show that the origin of the unconventional behavior in this model is the odd-symmetry "dark state" on the dots.

Signatures for exotic quark singlets from superstrings

International Nuclear Information System (INIS)

Barger, V.; Deshpande, N.G.; Gunion, J.F.

1986-09-01

We consider various scenarios, at Superconducting Super Collider energy and luminosity, for detection of the extra colored, weak isospin singlet, charge -1/3 heavy fermion resulting from E 6 compactification in superstring theories

Ferro-paramagnetic coupled resonant modes in GdEuCuO4

International Nuclear Information System (INIS)

Fainstein, A.; Tovar, M.

1990-01-01

Two paramagnetic resonances were observed in compound GdEuCuO 4 : one was originated in trivalent gadolinium paramagnetism, while the other is associated to a weak ferromagnetic mode in Cu-O planes. In this work, experimental results are presented that show an anisotropy and a strongly anomalous temperature dependence of Gd 3+ . A theoretical model was introduced which explains the data in terms of coupled ferro-paramagnetic resonant modes originated in spin exchange coupling of Cu and Gd. (Author). 9 refs., 4 figs

Pallidol, a resveratrol dimer from red wine, is a selective singlet oxygen quencher

International Nuclear Information System (INIS)

He Shan; Jiang Liyan; Wu Bin; Pan Yuanjiang; Sun Cuirong

2009-01-01

Pallidol is a naturally occurring resveratrol dimer from red wine with antioxidant and antifungal activities. In this report, with the use of the EPR spin-trapping technique, the scavenging and quenching effects of pallidol on reactive oxygen species (ROS) were investigated. The results demonstrated that pallidol showed strong quenching effects on singlet oxygen at very low concentrations, but it was ineffective to scavenge hydroxyl radicals or superoxide anions. Further kinetic study revealed that the reaction of pallidol with singlet oxygen had an extremely high rate constant (k a = 1.71 x 10 10 ). Therefore, pallidol is a potent and selective singlet oxygen quencher in aqueous systems. It may be used in singlet oxygen-mediated diseases as a pharmacological agent, which may contribute to the health beneficial effects of red wine.

Synchrotron radiation x-ray photoelectron spectroscopy study on the interface chemistry of high-k PrxAl2-xO3 (x=0-2) dielectrics on TiN for dynamic random access memory applications

Science.gov (United States)

Schroeder, T.; Lupina, G.; Sohal, R.; Lippert, G.; Wenger, Ch.; Seifarth, O.; Tallarida, M.; Schmeisser, D.

2007-07-01

Engineered dielectrics combined with compatible metal electrodes are important materials science approaches to scale three-dimensional trench dynamic random access memory (DRAM) cells. Highly insulating dielectrics with high dielectric constants were engineered in this study on TiN metal electrodes by partly substituting Al in the wide band gap insulator Al2O3 by Pr cations. High quality PrAlO3 metal-insulator-metal capacitors were processed with a dielectric constant of 19, three times higher than in the case of Al2O3 reference cells. As a parasitic low dielectric constant interface layer between PrAlO3 and TiN limits the total performance gain, a systematic nondestructive synchrotron x-ray photoelectron spectroscopy study on the interface chemistry of PrxAl2-xO3 (x =0-2) dielectrics on TiN layers was applied to unveil its chemical origin. The interface layer results from the decreasing chemical reactivity of PrxAl2-xO3 dielectrics with increasing Pr content x to reduce native Ti oxide compounds present on unprotected TiN films. Accordingly, PrAlO3 based DRAM capacitors require strict control of the surface chemistry of the TiN electrode, a parameter furthermore of importance to engineer the band offsets of PrxAl2-xO3/TiN heterojunctions.

Theoretical study of the lowest-lying electronic states of Aluminium monoiodide

International Nuclear Information System (INIS)

Taher, F.; Kabbani, A.; Ani-El Houte, W.

2004-01-01

Full text.The spectroscopic study of Aluminium monohalides, especially the Aluminium monoiodide, is important for monitoring such species in high temperature fast-flow reactors. Theoretical calculations of AlI are not available, whereas several studies have been done for the other aluminium monohalides. In this work, CAS-SCF/MRCI calculations are performed for the lowest-lying electronic states of AlI in a range of internuclear distance between 2.30 A and 2.80 A. Ab-initio calculations have been effectuated by using the computational chemistry program Molpro. The basis set used in this study for aluminium atom is that used by Langhoff for aluminium monohalides, of contractions using atomic natural orbitals and a pseudopotential is used for iode. Accurate theoretical spectroscopic constants and potential curves are obtained for the ground state X 1 Σ + and the first excited states a 3 Π and A 1 Π. The calculated values of Te, ωe, ωexe and re of these states are compatible with the experimental results. An ordering of states is represented for the lowest five predicted singlet and lowest five predicted triplet states. These results provide a big support to determine the analogy in the ordering of the electronic states in AlF, AlBr and AlI respectively at lower energies. These theoretical results identify a set of electronic singlet and triplet states unobserved experimentally

Development of QCD jets emitted by color-singlet sources

International Nuclear Information System (INIS)

Ellis, R.K.; Gunion, J.F.; Kalinowski, J.; Webber, B.R.

1985-01-01

We compare the angular-ordering approximation to QCD jet development with full calculations to order αsub(s) in the following cases: emission of quark jets by a color-singlet vector source (as in e + e - annihilation) and emission of gluon jets by a color-singlet scalar (Fsup(a)sub(μν)Fsup(aμν)) source. In contrast to the case of a color-octet (gluon) source, we find that the approximation is good in those regions of phase space where the next-to-leading corrections to the amplitude are large. (orig.)

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.

RPA ground state correlations in nuclei

International Nuclear Information System (INIS)

Lenske, H.

1990-01-01

Overcounting in the RPA theory of ground state correlations is shown to be avoided if exact rather than quasiboson commutators are used. Single particle occupation probabilities are formulated in a compact way by the RPA Green function. Calculations with large configuration spaces and realistic interactions are performed with 1p1h RPA and second RPA (SRPA) including 2p2h mixing in excited states. In 41 Ca valence hole states are found to be quenched by about 10% in RPA and up to 18% in SRPA. Contributions from low and high lying excitations and their relation to long and short range correlations in finite nuclei are investigated. (orig.)

Regulation of singlet oxygen-induced apoptosis by cytosolic NADP+-dependent isocitrate dehydrogenase.

Science.gov (United States)

Kim, Sun Yee; Lee, Su Min; Tak, Jean Kyoung; Choi, Kyeong Sook; Kwon, Taeg Kyu; Park, Jeen-Woo

2007-08-01

Singlet oxygen is a highly reactive form of molecular oxygen that may harm living systems by oxidizing critical cellular macromolecules and it also promotes deleterious processes such as cell death. Recently, we demonstrated that the control of redox balance and the cellular defense against oxidative damage are the primary functions of cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDPc) through supplying NADPH for antioxidant systems. In this report, we demonstrate that modulation of IDPc activity in HL-60 cells regulates singlet oxygen-induced apoptosis. When we examined the protective role of IDPc against singlet oxygen-induced apoptosis with HL-60 cells transfected with the cDNA for mouse IDPc in sense and antisense orientations, a clear inverse relationship was observed between the amount of IDPc expressed in target cells and their susceptibility to apoptosis. The results suggest that IDPc plays an important protective role in apoptosis of HL-60 cells induced by singlet oxygen.

Advanced Singlet Oxygen Generator for a COIL

National Research Council Canada - National Science Library

Kodymova, Jarmila; Zagidullin, M; Nikolaev, V; Svistun, M; Khvatov, N; Hruby, J; Spalek, O; Jirasek, V; Censsky, M

2005-01-01

This report results from a contract tasking Academy of Sciences as follows: The Grantee will develop new and radically different ideas for a high performance, advanced singlet oxygen generator for driving a supersonic COIL...

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.

Paramagnetism in ion-implanted oxides

CERN Document Server

Mølholt, Torben Esmann; Gíslason, Hafliði Pétur; Ólafsson, Sveinn

This thesis describes the investigation on para-magnetism in dilute ion-implanted single-crystal oxide samples studied by on- and off-line $^{57}$Fe emission Mössbauer spectroscopy. The ion-implantation of the radioactive isotopes ( $^{57}$Mn and $^{57}$Co) was performed at the ISOLDE facility at CERN in Geneva, Switzerland. The off-line measurements were performed at Aarhus University, Denmark. Mössbauer spectroscopy is a unique method, giving simultaneously local information on valence/spin state of the $^{57}$Fe probe atoms, site symmetry and magnetic properties on an atomic scale. The utilisation of emission Mössbauer spectroscopy opens up many new possibilities compared with traditional transmission Mössbauer spectroscopy. Among them is the possibility of working with a low concentration below 10$^{-4}$ –10$^{-3}$ at.%, where the implanted Mössbauer $^{57}$Fe probes are truly dilute impurities exclusively interacting with their nearest neighbours and therefore the possibility of crea...

Magnetic properties of sheet silicates

International Nuclear Information System (INIS)

Ballet, O.; Coey, J.M.D.

1982-01-01

Susceptibility, magnetisation and Moessbauer measurements are reported for a representative selection of 2:1 layer phyllosilicates. Eight samples from the mica, vermiculite and smectite groups include examples diluted in iron which are paramagnetic at all temperatures, as well as iron-rich silicates which order magnetically below 10 K. Anisotropic susceptibility of crystals of muscovite, biotite and vermiculite is quantitatively explained with a model where the Fe 2+ ions lie in sites of effective trigonal symmetry, the trigonal axis lying normal to the sheets. The ferrous ground state is an orbital singlet. Ferric iron gives an isotropic contribution to the susceptibility. Fe 2+ -Fe 2+ exchange interactions are ferromagnetic with Gapprox. equal to2 K, whereas Fe 3+ -Fe 3+ coupling is antiferromagnetic in the purely ferric minerals. A positive paramagnetic Curie temperature for glauconite may be attributable to Fe 2+ → Fe 3+ charge transfer. Magnetic order was found to set in inhomogeneously for glauconite at 1-7 K. One biotite sample showed an antiferromagnetic transition at Tsub(N) = 7 K marked by a well-defined susceptibility maximum. Its magnetic structure, consisting of ferromagnetic sheets with moments in their planes coupled antiferromagnetically by other, weak interactions, resembles that found earlier for the 1:1 mineral greenalite. (orig.)

Spray generator of singlet oxygen for a chemical oxygen-iodine laser

Czech Academy of Sciences Publication Activity Database

Jirásek, Vít; Hrubý, Jan; Špalek, Otomar; Čenský, Miroslav; Kodymová, Jarmila

2010-01-01

Roč. 100, č. 4 (2010), s. 779-791 ISSN 0946-2171 Grant - others:European Office of Aerospace R&D(US) FA8655-09-1-3091 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20760514 Keywords : spray generator of singlet oxygen * singlet oxygen * chemical oxygen-iodine laser Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.239, year: 2010

Paramagnetic defects in hydrogenated amorphous carbon powders

International Nuclear Information System (INIS)

Keeble, D J; Robb, K M; Smith, G M; Mkami, H El; Rodil, S E; Robertson, J

2003-01-01

Hydrogenated amorphous carbon materials typically contain high concentrations of paramagnetic defects, the density of which can be quantified by electron paramagnetic resonance (EPR). In this work EPR measurements near 9.5, 94, and 189 GHz have been performed on polymeric and diamond-like hydrogenated amorphous carbon (a-C:H) powder samples. A similar single resonance line was observed at all frequencies for the two forms of a-C:H studied. No contributions to the spectrum from centres with resolved anisotropic g-values as reported earlier were detected. An increase in linewidth with microwave frequency was observed. Possible contributions to this frequency dependence are discussed

Singlet and Triplet Excitation Management in a Bichromophoric Near-Infrared-Phosphorescent BODIPY-Benzoporphyrin Platinum Complex

KAUST Repository

Whited, Matthew T.

2011-01-12

Multichromophoric arrays provide one strategy for assembling molecules with intense absorptions across the visible spectrum but are generally focused on systems that efficiently produce and manipulate singlet excitations and therefore are burdened by the restrictions of (a) unidirectional energy transfer and (b) limited tunability of the lowest molecular excited state. In contrast, we present here a multichromophoric array based on four boron dipyrrins (BODIPY) bound to a platinum benzoporphyrin scaffold that exhibits intense panchromatic absorption and efficiently generates triplets. The spectral complementarity of the BODIPY and porphryin units allows the direct observation of fast bidirectional singlet and triplet energy transfer processes (k ST(1BDP→1Por) = 7.8×1011 s-1, kTT(3Por→3BDP) = 1.0×1010 s-1, kTT(3BDP→ 3Por) = 1.6×1010 s-1), leading to a long-lived equilibrated [3BDP][Por]=[BDP][3Por] state. This equilibrated state contains approximately isoenergetic porphyrin and BODIPY triplets and exhibits efficient near-infrared phosphorescence (λem = 772 nm, φ = 0.26). Taken together, these studies show that appropriately designed triplet-utilizing arrays may overcome fundamental limitations typically associated with core-shell chromophores by tunable redistribution of energy from the core back onto the antennae. © 2010 American Chemical Society.

Ferromagnetism versus slow paramagnetic relaxation in Fe-doped Li3N

Science.gov (United States)

Fix, M.; Jesche, A.; Jantz, S. G.; Bräuninger, S. A.; Klauss, H.-H.; Manna, R. S.; Pietsch, I. M.; Höppe, H. A.; Canfield, P. C.

2018-02-01

We report on isothermal magnetization, Mössbauer spectroscopy, and magnetostriction as well as temperature-dependent alternating-current (ac) susceptibility, specific heat, and thermal expansion of single crystalline and polycrystalline Li2(Li1 -xFex) N with x =0 and x ≈0.30 . Magnetic hysteresis emerges at temperatures below T ≈50 K with coercivity fields of up to μ0H =11.6 T at T =2 K and magnetic anisotropy energies of 310 K (27 meV). The ac susceptibility is strongly frequency-dependent (f =10 -10 000 Hz) and reveals an effective energy barrier for spin reversal of Δ E ≈1100 K (90 meV). The relaxation times follow Arrhenius behavior for T >25 K . For T <10 K , however, the relaxation times of τ ≈1010 s are only weakly temperature-dependent, indicating the relevance of a quantum tunneling process instead of thermal excitations. The magnetic entropy amounts to more than 25 J molFe-1 K-1, which significantly exceeds R ln 2 , the value expected for the entropy of a ground-state doublet. Thermal expansion and magnetostriction indicate a weak magnetoelastic coupling in accordance with slow relaxation of the magnetization. The classification of Li2(Li1 -xFex) N as ferromagnet is stressed and contrasted with highly anisotropic and slowly relaxing paramagnetic behavior.

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

Substituent-dependent features and properties of the sensitizer play an important role in the photosensitized production of singlet oxygen, O2(a1Δg). In this work, we systematically examine the effect of molecular changes in the sensitizer on the efficiency of singlet oxygen production using......, as the sensitizer, oligophenylene-vinylene derivatives designed to optimally absorb light in a nonlinear two-photon process. We demonstrate that one cannot always rely on rule-of-thumb guidelines when attempting to construct efficient two-photon singlet oxygen sensitizers. Rather, as a consequence of behavior...... 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...

Cluster decay of Ba isotopes from ground state and as an excited ...

Indian Academy of Sciences (India)

otherwise, inclusion of excitation energy decreases the T1/2 values. ... penetrates the nuclear barrier and reaches scission configuration after running .... between the ground-state energy levels of the parent nuclei and the ground-state energy.

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.

Probing the spin multiplicity of gas-phase polycyclic aromatic hydrocarbons through their infrared emission spectrum: a theoretical study.

Science.gov (United States)

Falvo, Cyril; Calvo, Florent; Parneix, Pascal

2012-08-14

The anharmonic infrared emission spectrum following an optical excitation has been calculated for a variety of polycyclic aromatic hydrocarbon molecules in their ground singlet electronic state or in their triplet state. The computational protocol relies on second-order perturbation theory and involves a quartic vibrational Hamiltonian, the vibrational quantum numbers being sampled according to a Monte Carlo procedure. In the case of neutral naphthalene, the IR spectrum obtained in the (ground) singlet state differs significantly from the spectrum in the triplet state, especially for out-of-plane CH bending modes. Although not as prominent, spectral differences in larger molecules are still observable.

Gapless Spin-Liquid Ground State in the S =1 /2 Kagome Antiferromagnet