WorldWideScience

Sample records for electronic excitation transfer

  1. Ground and excited state electron transfer dynamics

    OpenAIRE

    Brennan, Jennifer L.

    2002-01-01

    The focus of this work is the investigation of the factors controlling electron transfer in molecular electronic systems, in particular those affecting electron transfer to and from electronically excited states. To achieve this, a number of mono- and trimetallic osmium and ruthenium complexes were synthesised and characterised. Monolayers of an osmium polypyridyl complex bound to a platinum microelectrode via a ¿rara-l,2-bis-(4-pyridyl)ethylene bridge were formed to probe ground state electr...

  2. Electronic excitation transfer in concentrated micelle solutions

    International Nuclear Information System (INIS)

    Electronic excitation transport among interacting clusters of chromophores is investigated as a function of chromophores is investigated as a function of chromophore and cluster concentration. The technique of time-correlated single photon counting is employed to obtain time-resolved fluorescence depolarization data on aqueous octadecylrhodamine B/triton X-100 micelle solutions. The time-dependent fluorescence anisotropy, the energy transport observable, is directly compared to a theory developed to model this system. The theory is based on a first-order cumulant approximation to the solution of the transport master equation. The model depicts the micelles as monodisperse hard spheres with chromophores (octadecylrhodamine B) distributed about their surfaces. At low micelle concentration, the dynamics of excitation transfer depend only on internal micelle structure. At high micelle concentration excitation transfer occurs among chromophores on different micelles in addition to intramicelle transfer. The theoretical treatment provides nearly quantitative descriptions of the time and concentration dependence of the excitation transport. It correctly predicts the concentration at which intermicelle transfer becomes significant. In the low micelle concentration limit (energy transport confined to isolated micelles) the model having a Poisson distribution of chromophores works well for small ? ([chromophores]/[micelle]), but progressively worse as ? is increased. Following the literature, a chromophere interaction parameter (in the form of a two dimensional second virial coefficient) is used to skew the probe distribution. This enables the transport theory to reproduce the data for all the values of ? investigated and provides a determination of the second virial coefficient. 34 refs., 4 figs., 2 tabs

  3. Electronic and Nuclear Factors in Charge and Excitation Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Piotr Piotrowiak

    2004-09-28

    We report the and/or state of several subprojects of our DOE sponsored research on Electronic and Nuclear Factors in Electron and Excitation Transfer: (1) Construction of an ultrafast Ti:sapphire amplifier. (2) Mediation of electronic interactions in host-guest molecules. (3) Theoretical models of electrolytes in weakly polar media. (4) Symmetry effects in intramolecular excitation transfer.

  4. Electron transfer, ionization, and excitation atomic collisions

    International Nuclear Information System (INIS)

    Basic atomic-collision processes at intermediate and high energies are being studied theoretically at Penn State by Alston and Winter. In the high velocity regime, single-electron capture is treated using a high order multiple-scattering approach; extensive comparison with experiment and analysis of mechanisms have been made. Fitting the calculated amplitude with a simple analytic form, the asymptotic velocity dependence of the cross section is obtained. The effect on the capture amplitude of altering the inner part of the internuclear potential has also been explored. In the intermediate velocity regime, earlier work on collisions between protons and hydrogenic-ion targets using a coupled-state approach is being extended to the two-electron helium target. 29 refs

  5. [Electron transfer, ionization, and excitation in atomic collisions]: Progress report

    International Nuclear Information System (INIS)

    The fundamental processes of electron transfer, ionization, and excitation in ion-atom collisions are being studied. These collision processes are treated in the context of simple one- or two-electron systems in order to provide unambiguous results and reveal more clearly the collisional mechanisms. As outlined in the original proposal, three coupled-state calculations are being carried out over the present three-year period: a Sturmian-pseudostate study of ionization in collisions between protons and the hydrogenic ions He+, Li2+, Be3+, ...; a triple-center, atomic-state study of ionization in collisions between ? particles and H(ls) atoms and between protons and He+(ls) ions; and an atomic-state study of electron transfer and excitation in collisions between protons and neutral He atoms. 12 refs

  6. Electron transfer, ionization, and excitation in atomic collisions

    International Nuclear Information System (INIS)

    The research being carried out at Penn State by Winter and Alston addresses the fundamental processes of electron transfer, ionization, and excitation in ion-atom (and ion-ion) collisions. The focus is on intermediate- and higher-energy collisions, corresponding to proton energies of about 25 kilo-electron-volts (keV) or larger. At intermediate energies, where the transition probabilities are not small, many states must be coupled in a large calculation, while at higher energies, perturbative approaches may be used. Several studies have been carried out in the current three-year period; most of these treat systems with only one or two electrons, so that fewer approximations need be made and the basic collisional mechanisms can be more clearly described

  7. Electron excitation and energy transfer rates for H2O in the upper atmosphere

    OpenAIRE

    Brunger Michael; Campbell Laurence; Thorn Penny

    2009-01-01

    Abstract Recent measurements of the cross sections for electronic state excitations in H2O have made it possible to calculate rates applicable to these excitation processes. We thus present here calculations of electron energy transfer rates for electronic and vibrational state excitations in H2O, as well as rates for excitation of some of these states by atmospheric thermal and auroral secondary electrons. The calculation of these latter rates is an important first step towards our aim of in...

  8. Electronic excitation energy transfer between quasi-zero-dimensional systems.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Ostrava : Tanger, 2013. ISBN 978-80-87294-44-4. [International Conference NANOCON 2013 /5./. Brno (CZ), 16.10.2013-18.10.2013] R&D Pro jects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

  9. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations

    Energy Technology Data Exchange (ETDEWEB)

    Filatov, Michael, E-mail: mike.filatov@gmail.com [Department of Chemistry, Southern Methodist University, 3215 Daniel Avenue, Dallas, Texas 75275-0314 (United States); Huix-Rotllant, Miquel; Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main (Germany)

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor–acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene–perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  10. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations

    International Nuclear Information System (INIS)

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor–acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene–perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods

  11. Electron excitation and energy transfer rates for H2O in the upper atmosphere

    Directory of Open Access Journals (Sweden)

    Brunger Michael

    2009-01-01

    Full Text Available Abstract Recent measurements of the cross sections for electronic state excitations in H2O have made it possible to calculate rates applicable to these excitation processes. We thus present here calculations of electron energy transfer rates for electronic and vibrational state excitations in H2O, as well as rates for excitation of some of these states by atmospheric thermal and auroral secondary electrons. The calculation of these latter rates is an important first step towards our aim of including water into a statistical equilibrium model of the atmosphere under auroral conditions. PACS Codes: 34.50.Gb 34.50.Ez

  12. Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes

    Energy Technology Data Exchange (ETDEWEB)

    Westlake, Brittany C.; Brennaman, Kyle M; Concepcion, Javier J; Paul, Jared J.; Bettis, Stephanie E; Hampton, Shaun D; Miller, Stephen A.; Lebedeva, Natalia V.; Forbes, Malcolm D. E.; Moran, Andrew M.; Meyer, Thomas J.; Papanikolas, John M.

    2011-05-24

    The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H? is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated ?H–B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.

  13. Use of electron-excitation energy transfer in dye laser active media

    Energy Technology Data Exchange (ETDEWEB)

    Rodchenkova, V.V.; Reva, M.G.; Akimov, A.I.; Uzhinov, B.M.

    1984-01-01

    A study was made of the spectral luminescence and lasing characteristics of two-component dye mixtures, and of the use of electron-excitation energy transfer to improve the laser emission parameters. A considerable increase in the lasing efficiencyu was found on exciting Trypaflavine by energy transfer from coumarin dyes. The use of electron-excitation energy transfer enabled the laser emission spectrum to be broadened. It was found that by varying the energy donor and acceptor concentrations one could produce laser emission of constant intensity in the spectral range between the donor and acceptor lasing regions.

  14. Electronic excitation energy transfer between quasi-zero-dimensional systems.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav; Mao, H.

    Tokyo : The Surface Science Society of Japan, 2014, s. 11-17. ISSN 1348-0391. [International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures /12/ - International Colloquium on Scanning Probe Microscopy /21./. Tsukuba (JP), 04.11.2013-08.11.2013] R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism https://www.jstage.jst.go.jp/result?item1=4&word1=Atomically+Controlled+Surfaces+AND+kral

  15. Ab initio study on electron excitation and electron transfer in tryptophan-tyrosine system

    International Nuclear Information System (INIS)

    In this article, ab initio calculation has been performed to evaluate the transition energy of electronic excitation in tryptophan and tyrosine by using semiempirical molecular orbital method AM1 and complete active space self-consistent field method. The solvent effect has been considered by means of the conductor-like screening model. After geometric optimizations of isolated tryptophan and tyrosine, and their corresponding radicals and cations, reaction heat of these electron transfer reactions have been obtained by the means of complete active space self-consistent field method. The transition energies from the ground state, respectively, to the lowest excited state and to the lowest triplet state of these two amino acids are also calculated and compared with the experimentally observed values. The ionization potential and electron affinity are also calculated for tryptophan and tyrosine employing Koopmans' theorem and ab initio calculation. Compared with the experimental measurements, the theoretical results are found satisfactory. Theoretical results give good explanations on the experimental phenomena that N3· can preferably oxide the side chain of tryptophan residue and then the electron transfer from tyrosine residue to tryptophan residue follows in peptides involving tryptophan and tyrosine

  16. Superexchange coupling and electron transfer in globular proteins via polaron excitations

    OpenAIRE

    Chuev, G. N.; Lakhno, V. D.; Ustitnin, M.N.

    1999-01-01

    The polaron approach is used to treat long-range electron transfers between globular proteins. A rate expression for the polaron transfer model is given along with a description of appropriate conditions for its use. Assuming that electrons transfer via a superexchange coupling due to a polaron excitation, we have estimated the distance dependence of the rate constant for the self-exchange reactions between globular proteins in solutions. The distance dependence of the polaron coupling and so...

  17. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    Energy Technology Data Exchange (ETDEWEB)

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

    2014-03-03

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  18. Nonlinear response of metal nanoparticles: Double plasmon excitation and electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Shiwu [Beijing Computational Science Research Center, Zhongguancun Software Park II, 100094, Beijing (China)

    2015-06-21

    We investigate the dynamical response of a metal nanoparticle and the electron transfer to a molecule near its surface using time-dependent density functional theory. In addition to the linear response of the Mie resonance, double plasmon excitations and a low-frequency charge transfer band emerge and become prominent at high laser intensities. Both modes are nonlinear processes, which are derived from the re-excitation and decay of the primary plasmon mode, respectively. Our results shed light on the localised characters of the plasmon-molecule coupling and hot electron distributions. These findings have general implications to photoinduced phenomena in nanosystems.

  19. New electron energy transfer rates for vibrational excitation of N2

    Directory of Open Access Journals (Sweden)

    A. V. Pavlov

    Full Text Available In this paper we present the results of a study of the electron cooling rate, the production rates of vibrationally excited N2(v, and the production frequency of the N2 vibrational quanta arising from the collisions of electrons with unexcited N2(0 and vibrationally excited N2(1 molecules as functions of the electron temperature. The electron energy transfer rates for vibrational excitation of N2 have been calculated and fit to analytical expressions by use of the revised vibrationally excited N2 cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations.Key words. Atmospheric composition and structure · Thermosphere · Ionosphere · Modeling and forecasting

  20. Excitational energy and photoinduced electron transfer reactions in Ge(IV) corrole–porphyrin hetero dimers

    International Nuclear Information System (INIS)

    We have constructed hetero dimers by utilizing the axial bonding capabilities as well as known oxophilicity of Germanium(IV) ion of Germanium(IV) corroles as basal scaffolding unit and either free-base or ZnII porphyrin at axial position for the first time. Both the hetero dimers have been completely characterized by elemental analysis, UV–visible, proton nuclear magnetic resonance (1D and 1H–1H COSY) and fluorescence spectroscopies as well as electrochemical methods. The ground state properties indicate that there exists a minimum ?–? interactions between the macrocyclic units of these dyads. Excited state properties showed that there is an electronic energy transfer competing photoinduced electron transfer from singlet state of basal metalloid corrole to the axial porphyrin and a photoinduced electron transfer from excited state of axial porphyrin to the ground state of central metalloid corrole are possible. -- Highlights: ? • We have constructed hetero dimers based on corrole–porphyrin by utilizing axial position of Ge(IV) corrole. • There exists mimum ?–? interactions between the macrocyclic units. • The excited state properties indicate that both excitation energy transfer and photoinduced electron transfer reactions are possible in these hetero dimers

  1. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid.

    Science.gov (United States)

    Rury, Aaron S; Sorenson, Shayne; Dawlaty, Jahan M

    2016-03-14

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm(-1) oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology. PMID:26979698

  2. New electron energy transfer and cooling rates by excitation of O2

    Directory of Open Access Journals (Sweden)

    A. V. Pavlov

    Full Text Available In this work I present the results of a study of the electron cooling rate, the production rates of vibrationally excited O2, and the production frequency of the O2 vibrational quanta arising from the collisions of electrons with O2 molecules as functions of the electron temperature. The electron energy transfer and cooling rates by vibrational excitation of O2 have been calculated and fitted to analytical expressions by use of the revised vibrationally excited O2 cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations. It is also shown that the currently accepted rate of electron energy loss associated with rotational transitions in O2 must be decreased by a factor of 13.

  3. Effect of the excitation pulse frequency on the ultrafast photoinduced electron transfer dynamics

    International Nuclear Information System (INIS)

    The dependence of the ultrafast photoinduced electron transfer dynamics in donor-acceptor complexes on the excitation pulse carrier frequency (spectral effect) has been investigated in the framework of a model involving three electronic state. The spectral effect has been shown to strongly depend on the angle ? between the reaction coordinate directions corresponding to optical and charge transfer transitions. Describing the solvent as a linear homogenous polar medium and accounting for Coulombic interaction of the transferred charge with the medium polarization fluctuations, the angle ? has been found out to be typically in the area 40 deg. -85 deg. Exactly in this area of ? the spectral effect is predicted to be most pronounced

  4. Photo- and radiation chemical studies of intermediates involved in excited-state electron-transfer reactions

    International Nuclear Information System (INIS)

    Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of the most photochemical solar energy conversion schemes. The authors research, which has utilized the techniques of continuous and pulsed photolysis and radiolysis, has focused on three general aspects of these reactions involving transition metal coordination complexes and electron donor-acceptor complexes: i) the effect of solution medium on the properties and quenching of the excited states; ii) the control of the quantum yields of formation of redox products; iii) the mechanism by which reduced species interact with water to yield H2 homogeneously and heterogeneously. EDTA is among the most popular sacrificial electron donors used in model systems. Its role is to scavenge the oxidized form of the photosensitizer in order to prevent its rapid reaction with the reduced form of the electron relay species that results from the electron-transfer quenching of the excited photosensitizer. In systems involving MV2+, the radicals resulting from the oxidation of EDTA can eventually lead to the generation of a second equivalent of MV+; the reducing agent is believed to be a radical localized on the carbon atom alpha to the carboxylate group. The reaction of radiolytically-generated OH/H with EDTA produces this radical directly via H-abstraction or indirectly via deprotonation of the carbon atom adjacent to the nitrogen radical site in the oxidized amine moiety; it reduces MV2+ with rate constants of 2.8 x 109, 7.6 x 109, and 8.5 x 106M-1s-1 at pH 12.5, 8.3, and 4.7, respectively. Degradative decarboxylation of EDTA-radicals and their back electron-transfer reactions are enhanced in acidic solution causing the yield of MV+ to be severely diminished

  5. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    KAUST Repository

    Alsam, Amani A.

    2015-09-02

    We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

  6. Statistical analysis of electronic excitation processes: Spatial location, compactness, charge transfer, and electron-hole correlation.

    Science.gov (United States)

    Plasser, Felix; Thomitzni, Benjamin; Bäppler, Stefanie A; Wenzel, Jan; Rehn, Dirk R; Wormit, Michael; Dreuw, Andreas

    2015-08-01

    We report the development of a set of excited-state analysis tools that are based on the construction of an effective exciton wavefunction and its statistical analysis in terms of spatial multipole moments. This construction does not only enable the quantification of the spatial location and compactness of the individual hole and electron densities but also correlation phenomena can be analyzed, which makes this procedure particularly useful when excitonic or charge-resonance effects are of interest. The methods are first applied to bianthryl with a focus on elucidating charge-resonance interactions. It is shown how these derive from anticorrelations between the electron and hole quasiparticles, and it is discussed how the resulting variations in state characters affect the excited-state absorption spectrum. As a second example, cytosine is chosen. It is illustrated how the various descriptors vary for valence, Rydberg, and core-excited states, and the possibility of using this information for an automatic characterization of state characters is discussed. PMID:26119286

  7. Laser-assisted ionization-excitation of helium by electron impact at large momentum transfer

    International Nuclear Information System (INIS)

    Ionization of a helium atom by electron impact in the presence of laser radiation is studied theoretically. The kinematic regime of high impact energy and large momentum transfer is considered. The S-matrix of the process is treated within the first Born and binary-encounter approximations. Triple differential cross sections are calculated for the cases when the residual He+ ion is left both in the ground (n=1) and in the first excited (n=2) states in the presence of a laser field with frequency ? = 1.55 eV and intensity I = 5*1011 W/cm2. The laser-assisted cross sections corresponding to n=2 are found to be more sensitive to the electron-electron correlations in helium than the field-free ones. (authors)

  8. Electronic excitation energy transfer from dye-loaded zeolite L monolayers to a semiconductor

    Science.gov (United States)

    Li, Huanrong; Devaux, André; Zabala Ruiz, Arantzazu; Calzaferri, Gion

    2006-04-01

    In device engineering, a high degree of supramolecular organisation is required to achieve certain desired macroscopic properties. Dye-loaded zeolite L host-guest materials have been successfully used in the realisation of efficient light-harvesting antenna systems. A new hierarchy of structural order is introduced by arranging the zeolite L crystals into densely packed, oriented monolayers on a substrate. We developed methods to synthesise such monolayers, to fill them with dyes and to terminate them with a luminescent stopcock. By the subsequent insertion of different types of dye molecules in a zeolite L monolayer, the first unidirectional antenna system was realised. Such antenna materials open possibilities for the design of a novel thin layer, silicon based solar cell, where the excitation energy can only migrate in one direction towards the zeolite-semiconductor interface. The electronic excitation energy is then transmitted to the semiconductor by Forster resonance energy transfer (FRET) via stopcock molecules attached to the channel ends. Direct transfer of electrons is prevented by an insulating layer. We report here on the UV-VIS absorption as well as NIR luminescence spectroscopy results obtained from such materials.

  9. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    Energy Technology Data Exchange (ETDEWEB)

    Elkins, Madeline H.; Williams, Holly L. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Neumark, Daniel M. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2015-06-21

    The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

  10. Resonant transfer excitation: Interference effects

    International Nuclear Information System (INIS)

    Interference effects in RTE (Resonant Transfer Excitation) can be studied for low Z projectiles via Auger electrons emitted from highly ionized fast moving projectile ions following collisions with low Z targets. RTE in ion-atom collisions is closely related to dielectronic recombination. In the latter case which is of practical interest to the fusion power program an electron with the proper velocity incident on a highly charged ion is resonantly captured and simultaneously interacts with an inner shell electron to excite it, thus forming a doubly excited state which may decay predominantly by X-ray emission for higher Z ions or by Auger electron decay for lower Z ions. The resonant velocity is that of the Auger electron emitted by the ion in the doubly excited state in RTE the electrons to be captured are in low Z atomic (typically He) or Molecular (typically H2) targets and the ions are produced by accelerators in highly charged states with the appropriate resonant velocity. The resonance is much broadened by the velocity distribution of the target electrons. Thus the resonance width as a function of projectile energy is determined by folding the Compton profile of the target electrons with the dielectronic recombination cross sections. A weaker effect and more speculative is Two Electron Transfer Excitation. Here one target electron excites the projectile 1s electron to the 2p shell for example and the other target electron is captured to an excited state of the projectile. This effect becomes more important at projectile energies higher than the energy where the RTE cross section has its maximum value. The electron--electron interaction has been beautifully demonstrated by Zouros et al. Finally, there might be interference with shakeup. This paper will present angular distribution measurements of Auger lines so that the effects of interference between these various processes can be studied

  11. Triple-center treatment of electron transfer and excitation in p-H collisions

    International Nuclear Information System (INIS)

    Cross sections have been calculated for electron transfer into the 1s, 2s, and 2p states and for excitation into the 2s and 2p states in collisions between 1.5--15-keV protons and hydrogen atoms. The triple-center, coupled-state method of Anderson, Antal, and McElroy has been used: Bound atomic states are centered on each nucleus and on a third center (the center of charge) in order to simulate the molecular character of slow collisions. Convergence of cross sections (and molecular potential-energy curves) with respect to the size of the basis has been studied; the present basis includes up to 36 states (16 gerade, 20 ungerade states). The 1s capture cross section is estimated to be converged, and the 2p and 2s cross sections are estimated to be converged to about 10% and 20%, respectively. Dips are observed in the 2s and 2p excitation cross sections at about 10 keV and in the 2p capture cross section at about 5 keV. Results have been compared with atomic-state, pseudostate, and molecular-state results, as well as with experimental results. The results agree fairly closely with the related AO+ pseudostate results of Fritsch and Lin at the lowest calculated energy, although there are differences at higher energies. There are differences from some of the many experimental results, but overall there is agreement within the experimental error limits

  12. Excited states of the high-frequency vibrational modes and kinetics of ultrafast photoinduced electron transfer

    Science.gov (United States)

    Barykov, V. Yu.; Ivanov, A. I.

    2016-02-01

    The effect of the carrier frequency of the exciting laser pulse on the kinetics of intramolecular photoinduced charge transfer in the multi-channel stochastic model is studied. It is shown that the population of different states of high-frequency intramolecular modes upon varying the frequency of the excitation pulse can considerably alter the rate constant of ultrafast charge transfer. It is found that a negative vibrational spectral effect is expected in the vicinity of a barrier-free area (the rate constant of photoinduced charge transfer decreases along with the carrier frequency of the excitation pulse), while a positive effect is predicted in areas of high and low exergonicity (an inverse dependence). It is concluded that the value of the spectral effect falls along with the time of vibrational relaxation. For ultrafast photo-induced charge transfer, however, it remains considerable up to relaxation times of 100 fs.

  13. Energy transfer quenching of a fluorescent excited radical cation by counter radical anion: dissipation of radical ions generated by photoinduced electron transfer

    Science.gov (United States)

    Ichinose, Nobuyuki; Tanaka, Tomoko; Kawanishi, Shun-ichi; Majima, Tetsuro

    2000-08-01

    Fluorescence from the excited 1,3,5-trimethoxybenzene radical cation (TMB ?+*) coexsisting with 1,4-dicyanonaphthalene radical anion (DCN ?-) in acetonitrile was studied by the two-step two-laser excitation technique. The fluorescence intensity observed as a function of the delay time of the excitation pulse relative to generation pulse for TMB ?+ indicated the quenching by DCN ?- at ?220 ns. From the analysis of the fluorescence behavior by the Förster-type energy transfer theory, the distance between TMB ?+* and DCN ?- during their dissipation after the initial photoinduced electron transfer was estimated as a function of time.

  14. Controlling electron transfer in condensed phase with bond-specific infrared excitation

    Science.gov (United States)

    Delor, Milan; Scattergood, Paul A.; Sazanovich, Igor V.; Keane, Theo; Greetham, Gregory M.; Meijer, Anthony J. H. M.; Towrie, Michael; Parker, Anthony W.; Weinstein, Julia A.

    2015-08-01

    Using an ultrafast electronic-vibrational pulse-sequence, we show that the outcome of light-induced ET can be radically altered by mode-specific infrared (IR) excitation of vibrations which are coupled to the ET-pathway. IR-control is particularly challenging in condensed phase systems due to the ultrafast timescales involved, in particular rapid intramolecular vibrational redistribution. We demonstrate how an IR-pulse following UV-excitation perturbs nuclear-electronic (vibronic) interactions within a donor-bridge-acceptor system similar in design to those utilized in (bio)chemical light-harvesting, and alters charge-transport pathways and product state yields.

  15. Radiation and photo induced electron transfer processes: Exciting possibilities for basic research and applications

    International Nuclear Information System (INIS)

    Radiation and/or photo induced electron transfer reaction results in retrievable storage of information, with extensive applications ranging from dosimetry, efficient light conversion molecular devices (LCMD), photo refraction, optical phase conjunction and holography. These areas gives ample new opportunities to conduct basic investigations to elucidate the mechanistic aspects of photo (radiation) induced electron transfer, and to translate the acquired knowledge into making a device. The talk will focus on the investigation by the author on photo induced electron transfer reaction in photorefractive systems and also on the radiation induced electron transfer processes in dosimetric materials. Furthermore, the recent trends in the light conversion molecular devices using rare earth complexes and the fluorescent molecular sensors for cation recognition will be discussed. (author)

  16. Ab initio study of the excited-state coupled electron-proton-transfer process in the 2-aminopyridine dimer

    International Nuclear Information System (INIS)

    The low-lying 1??* excited states of the 2-aminopyridine dimer have been investigated with multi-reference ab initio methods (CASSCF and MRMP2). The 2-aminopyridine dimer can be considered as a mimetic model of Watson-Crick DNA base pairs. The reaction path and the energy profile for single proton transfer in the lowest 1??* inter-monomer charge-transfer state have been obtained. A weakly avoided crossing of the 1??* surface with the electronic ground-state surface has been found near the single-proton-transfer minimum of the 1??* surface. From the splitting of the adiabatic surfaces at the avoided crossing, an internal-conversion lifetime of the excited state of <100 ps has been estimated. The potential relevance of these results for the rationalization of radiation-induced mutations and the photostability of the genetic code is briefly discussed

  17. Resonant electron transfer and L-shell excitation for 26Fe19+ and 30Zn23+ ions

    OpenAIRE

    RAMADAN, Hassan

    2012-01-01

    Resonant transfer and excitation (RTE) involving simultaneous electron capture and projectile L-shell excitation has been calculated for Fe19+ and Zn23+ ions, in charge states ranging from nitrogen-like to oxygen-like incident on molecular hydrogen over an energy range 0--250 MeV. By the same way the calculations have been performed with helium over an energy range 0--300 MeV. The calculations are carried out using the angular momentum average (AMA) scheme in the isolated resonance app...

  18. Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band

    OpenAIRE

    Chen, Jie; Zhang, Hua; Tomov, Ivan V.; Ding, Xunliang; Rentzepis, Peter M.

    2008-01-01

    The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co–O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox r...

  19. Intermolecular and Intramolecular Excited State Charge Transfer

    OpenAIRE

    Eisenthal, Kenneth B.

    1983-01-01

    A primary mechanism of energy relaxation and chemical change in organic molecules in excited electronic states is charge transfer. 1 The charge transfer process can be intermolecular, involving an excited molecule and a neighboring molecule, one serving as an acceptor and the other as a donor molecule, or intramolecular, involving a charge redistribution in the excited molecule which produces a very large excited state dipole moment.In our investigations of the dynamics of these various charg...

  20. Electron transfer collisions between sulfur dioxide clusters and laser-excited Rydberg atoms

    Energy Technology Data Exchange (ETDEWEB)

    Desfrancois, C.; Khelifa, N.; Lisfi, A.; Schermann, J.P. (Paris-13 Univ., 93 - Villetaneuse (France). Lab. de Physique des Lasers)

    1991-08-01

    Electron attachment to SO{sub 2} clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbers n, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations. (orig.).

  1. Electron transfer collisions between sulfur dioxide clusters and laser-excited Rydberg atoms

    International Nuclear Information System (INIS)

    Electron attachment to SO2 clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbers n, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations. (orig.)

  2. Solvent electronic polarization effects on a charge transfer excitation studied by the mean-field QM/MM method

    Science.gov (United States)

    Nakano, Hiroshi

    2015-12-01

    Electronic polarization effects of a medium can have a significant impact on a chemical reaction in condensed phases. We discuss the effects on the charge transfer excitation of a chromophore, N,N-dimethyl-4-nitroaniline, in various solvents using the mean-field QM/MM method with a polarizable force field. The results show that the explicit consideration of the solvent electronic polarization effects is important especially for a solvent with a low dielectric constant when we study the solvatochromism of the chromophore.

  3. Exciton delocalization, charge transfer, and electronic coupling for singlet excitation energy transfer between stacked nucleobases in DNA: An MS-CASPT2 study

    Energy Technology Data Exchange (ETDEWEB)

    Blancafort, Lluís, E-mail: lluis.blancafort@udg.edu [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Voityuk, Alexander A., E-mail: alexander.voityuk@icrea.cat [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona 08010 (Spain)

    2014-03-07

    Exciton delocalization and singlet excitation energy transfer have been systematically studied for the complete set of 16 DNA nucleobase dimers in their ideal, single-strand stacked B-DNA conformation, at the MS-CASPT2 level of theory. The extent of exciton delocalization in the two lowest (?,?{sup *}) states of the dimers is determined using the symmetrized one-electron transition density matrices between the ground and excited states, and the electronic coupling is calculated using the delocalization measure and the energy splitting between the states [see F. Plasser, A. J. A. Aquino, W. L. Hase, and H. Lischka, J. Phys. Chem. A 116, 11151–11160 (2012)]. The calculated couplings lie between 0.05 eV and 0.14 eV. In the B-DNA conformation, where the interchromophoric distance is 3.38 Å, our couplings deviate significantly from those calculated with the transition charges, showing the importance of orbital overlap components for the couplings in this conformation. The calculation of the couplings is based on a two-state model for exciton delocalization. However, in three stacks with a purine in the 5{sup ?} position and a pyrimidine in the 3{sup ?} one (AT, GC, and GT), there is an energetically favored charge transfer state that mixes with the two lowest excited states. In these dimers we have applied a three-state model that considers the two locally excited diabatic states and the charge transfer state. Using the delocalization and charge transfer descriptors, we obtain all couplings between these three states. Our results are important in the context of DNA photophysics, since the calculated couplings can be used to parametrize effective Hamiltonians to model extended DNA stacks. Our calculations also suggest that the 5{sup ?}-purine-pyrimidine-3{sup ?} sequence favors the formation of charge transfer excited states.

  4. [Electron transfer, ionization, and excitation in atomic collisions]. Final technical report, June 15, 1986 - June 14, 1998

    International Nuclear Information System (INIS)

    The research on theoretical atomic collisions that was funded at The Pennsylvania State University's Wilkes-Barre Campus by DOE from 1986 to 1998 was carried out by Winger from 1986 to 1989 and by Winter and Alston from 1989 to 1998. The fundamental processes of electron transfer, ionization, and excitation in ion-ion, ion-atom, and, more recently, ion-molecule collisions were addressed. These collision processes were treated in the context of simple one-electron, quasi-one-electron, or two-electron systems in order to provide unambiguous results and reveal more clearly the collisional mechanisms. Winter's work generally focused on the intermediate projectile-energy range corresponding to proton energies from about ten to a few hundred keV. In this velocity-matching energy range, the electron-transfer cross section reaches a peak, and many states, including electron-transfer and ionization states, contribute to the overall electron-cloud distribution and transition probabilities; a large number of states are coupled, and therefore perturbative approaches are generally inappropriate. These coupled-state calculations were sometimes also extended to higher energies to join with perturbative results. Alston concentrated on intermediate-energy asymmetric collision systems, for which coupling with the projectile is weaker, but many target states are included, and on high energies (MeV energies). Thus, while perturbation theory for electron transfer is valid, it is not adequate to first order. The studies by Winter and Alston described were often done in parallel. Alston also developed formal perturbative approaches not tied to any particular system. Materials studied included He+, Li2+, Be3+, B4+, C5+, and the H+ + Na system

  5. Evidence for resonance electron transfer in photon excited X-ray satellite spectra of fluorine compounds

    Indian Academy of Sciences (India)

    K Ram Narayana; B Seetharami Reddy; S S Raju; T Seshi Reddy; S Lakshmi Narayana; K Premachand; B M Rao; M V R Murti; L S Mombasawala

    2005-08-01

    The K$\\alpha$L1/K$\\alpha$L0 intensity ratio of fluorine is measured in five fluorine compounds with a crystal spectrometer. An anomalous reduction of this intensity ratio was observed in KF and SrF2, which is attributed to resonance electron transfer from the metal ion to the spectator vacancy in the fluorine ion. K$\\alpha$L2/K$\\alpha$L0 intensity ratio of fluorine is also measured. The measured relative intensities are compared with the theoretical estimates of Aberg.

  6. Chemical Physics Electrons and Excitations

    CERN Document Server

    Larsson, Sven

    2012-01-01

    A full understanding of modern chemistry is impossible without quantum theory. Since the advent of quantum mechanics in 1925, a number of chemical phenomena have been explained, such as electron transfer, excitation energy transfer, and other phenomena in photochemistry and photo-physics. Chemical bonds can now be accurately calculated with the help of a personal computer. Addressing students of theoretical and quantum chemistry and their counterparts in physics, Chemical Physics: Electrons and Excitations introduces chemical physics as a gateway to fields such as photo physics, solid-state ph

  7. Mechanism of electronic-excitation transfer in organic light-emitting devices based on semiconductor quantum dots

    International Nuclear Information System (INIS)

    The results of an experimental study of organic light-emitting diodes (LEDs) with luminescent layers based on two types of CdSe/CdS semiconductor quantum dots (QDs) with an average CdSe core diameter of 3 and 5 nm and a characteristic CdS shell thickness of 0.5 nm are presented. The dependences of the LED efficiency on the QD concentration are determined. The experimental data are used to determine the mechanism of electronic-excitation transfer from the organic matrix to the semiconductor QDs. Ways of optimizing the design of the LEDs in order to improve their efficiency are suggested on this basis

  8. Study of intermediates from transition metal excited-state electron-transfer reactions. Final report, August 4, 1986--August 31, 1997

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, M.Z.

    1997-12-31

    The techniques of continuous photolysis and pulsed laser flash photolysis, continuous and pulse radiolysis, fast-scan cyclic voltammetry, and time-resolved fluorimetry have been used to examine intramolecular electron transfer within the solvent quenching cage, photodynamics of quenching of the excited states of transition-metal photosensitizers, the properties of excites states and one-electron reduced forms, ground- and excited-state interactions with solutes, and photoinduced oxidations of organic solutes in aqueous solution. The following specific areas were examined: (1) the parameters that govern the yields of redox products from excited-state electron-transfer quenching reactions; (2) the mediation of the properties of excited states and one-electron reduced forms by the ligands and the solution medium; (3) the effect of the interactions between the ground state of the complex and the solution components on the behavior of the excited state; (4) the yields of singlet oxygen from excited-state energy-transfer quenching by O{sub 2}; and (5) the oxidations of solutes by singlet oxygen, excited-state electron-transfer quenching, and free radicals. This report contains the abstracts of 50 publications describing the studies.

  9. Inelastic scattering of high transfer moment electrons to the first excited state (Jsup(?)=3-) of 208Pb

    International Nuclear Information System (INIS)

    A determination was made of an angular distribution of the inelastic scattering cross-sections of electrons by the first excited state (Jsup(?)=3-, E*=2.615 MeV) of 208Pb. The statistical accuracy of previous data was improved between 2 and 2.7 fm-1 and the area of transfer of moment was extended up to qsub(max)=3.4 fm-1. Cross-sections up to 10-37cm2/sr were determined whereas the limit reached before was 7x10-35 cm2/sr. In order to determine the transition charge density, it was put into parametric form by a Fourier-Bessel development using 12 coefficients and an 11 fm cut-off radius. The model error inherent in this method is reduced to an insignificant contribution by the sufficiently high transfer of moment. The experimental transition charge density was compared with the theoretical predictions

  10. Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

    KAUST Repository

    Alsulami, Qana

    2015-06-25

    Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

  11. Two-laser studies of E ? V energy transfer reactions involving CO and electronically excited I2, ICl and NO2

    International Nuclear Information System (INIS)

    The relaxation of electronically excited I2, ICl and NO2 by CO has been investigated using a dye laser for electronic excitation (in the 590 nm region) and a cw CO laser for measuring the extent of CO product vibrational excitation. The CO molecules formed in these quenching reactions were found to carry very small fractions of electronic energies, in sharp contrast to the results observed in other E ? V transfer reactions involving atomic species which carry comparable amounts of electronic energies. (Auth.)

  12. Theoretical investigation of electronic excitation transfer between chlorophylls in light-harvesting antenna of photosystem ii using quantum computers

    Directory of Open Access Journals (Sweden)

    Maryam Dehestani

    2012-01-01

    Full Text Available The excitation energy transfer between chlorophylls in major and minor antenna complexes of photosystem II (PSII was investigated using quantum Fourier transforms. These transforms have an important role in the efficiency of quantum algorithms of quantum computers. The equation 2n=N was used to make the connection between excitation energy transfers using quantum Fourier transform, where n is the number of qubits required for simulation of transfers and N is the number of chlorophylls in the antenna complexes.

  13. The Fate of Electronically Excited States : Ultrafast Electron and Energy Transfer in Solvated Donor-Acceptor Systems

    OpenAIRE

    Wallin, Staffan

    2005-01-01

    Processes where a molecule absorbs visible light and then disposes of the excess energy via electron/energy transfer reactions have an important role both in nature (e.g. in photosynthesis) and in many technical applications (e.g. in photography and photovoltaics). This thesis uses different spectroscopical techniques, mainly ultrafast transient absorption, to study such processes. The thesis can roughly be divided into three parts. In the first part, donor-acceptor systems linked by differen...

  14. Influence of macromolecule main chain structure on electron excitation energy transfer in carbazole-containing polymers

    International Nuclear Information System (INIS)

    Efficiencies of energy transfer from singlet excitons to rubrene in poly-N-epoxypropylcarbazole (PEPC) and from triplet excitons to pyrene in poly-N-vinylcarbazole (PVC) were found to increase on heating from 5 to 295 K. At the same time, the transfer efficiency in PVC at rubrene concentration 2x10-3 M decreased in the range T = 100-295 K, which correlated with a rise in the intensity of the fluorescence band of the matrix sandwich-like excimers. However, the transfer efficiency increased upon increasing the concentration, which caused the maximum donor-acceptor distance to approach the critical radius of the Forster model. The observed effects were explained by the fact that the free-path lengths of singlet excitons in PEPC and triplet excitons in PVC increased with increasing temperature and, correspondingly, the probability of them approaching the acceptor within distances where energy transfer was possible increased. Singlet-exciton self-trapping at excimer-forming sites and formation of sandwich-like excimers competed in PVC with energy transfer to rubrene. (authors)

  15. Influence of macromolecule main chain structure on electron excitation energy transfer in carbazole-containing polymers

    Science.gov (United States)

    Skryshevski, Yu. A.

    2013-05-01

    Efficiencies of energy transfer from singlet excitons to rubrene in poly- N-epoxypropylcarbazole (PEPC) and from triplet excitons to pyrene in poly- N-vinylcarbazole (PVC) were found to increase on heating from 5 to 295 K. At the same time, the transfer efficiency in PVC at rubrene concentration 2•10-3 M decreased in the range T = 100-295 K, which correlated with a rise in the intensity of the fluorescence band of the matrix sandwich-like excimers. However, the transfer efficiency increased upon increasing the concentration, which caused the maximum donor-acceptor distance to approach the critical radius of the Forster model. The observed effects were explained by the fact that the free-path lengths of singlet excitons in PEPC and triplet excitons in PVC increased with increasing temperature and, correspondingly, the probability of them approaching the acceptor within distances where energy transfer was possible increased. Singlet-exciton self-trapping at excimer-forming sites and formation of sandwich-like excimers competed in PVC with energy transfer to rubrene.

  16. Influence of macromolecule main chain structure on electron excitation energy transfer in carbazole-containing polymers

    International Nuclear Information System (INIS)

    Efficiencies of energy transfer from singlet excitons to rubrene in poly-N-epoxypropylcarbazole (PEPC) and from triplet excitons to pyrene in poly-N-vinylcarbazole (PVC) were found to increase on heating from 5 to 295 K. At the same time, the transfer efficiency in PVC at rubrene concentration 2*10-3 M decreased in the range T = 100-295 K, which correlated with a rise in the intensity of the fluorescence band of the matrix sandwich-like excimers.However, the transfer efficiency increased upon increasing the concentration, which caused the maximum donor-acceptor distance to approach the critical radius of the Forster model. The observed effects were explained by the fact that the free-path lengths of singlet excitons in PEPC and triplet excitons in PVC increased with increasing temperature and, correspondingly, the probability of them approaching the acceptor within distances where energy transfer was possible increased.Singlet-exciton self-trapping at excimer-forming sites and formation of sandwich-like excimers competed in PVC with energy transfer to rubrene. (author)

  17. Description of electron transfer in the ground and excited states of organic donor–acceptor systems by single-reference and multi-reference density functional methods

    International Nuclear Information System (INIS)

    Electron transfer in the ground and excited states of a model donor–acceptor (D–A) system is investigated using the single-reference and multi-reference density functional theory (DFT) methods. To analyze the results of the calculations, a simple two-site multi-reference model was derived that predicts a stepwise electron transfer in the S0 state and a wave-like dependence of the S1 electron transfer on the external stimulus. The standard single-reference Kohn-Sham (KS) DFT approach and the time-dependent DFT (TDDFT) method failed to describe the correct dependence of the S0 and S1 electron transfer on the external electric field applied along the donor–acceptor system. The multi-reference DFT approach, the spin-restricted ensemble-referenced KS (REKS) method, was able to successfully reproduce the correct behavior of the S0 and S1 electron transfer on the applied field. The REKS method was benchmarked against experimentally measured gas phase charge transfer excitations in a series of organic donor–acceptor complexes and displayed its ability to describe this type of electronic transitions with a very high accuracy, mean absolute error of 0.05 eV with the use of the standard range separated density functionals. On the basis of the calculations undertaken in this work, it is suggested that the non-adiabatic coupling between the S0 and S1 states may interfere with the electron transfer in a weakly coupled donor–acceptor system. It is also suggested that the electronic excitation of a D+–A? system may play a dual role by assisting the further electron transfer at certain magnitudes of the applied electric field and causing the backward transfer at lower electric field strengths

  18. Description of electron transfer in the ground and excited states of organic donor–acceptor systems by single-reference and multi-reference density functional methods

    Energy Technology Data Exchange (ETDEWEB)

    Filatov, Michael, E-mail: mike.filatov@gmail.com [Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Universität Bonn, Beringstr. 4, D-53115 Bonn (Germany)

    2014-09-28

    Electron transfer in the ground and excited states of a model donor–acceptor (D–A) system is investigated using the single-reference and multi-reference density functional theory (DFT) methods. To analyze the results of the calculations, a simple two-site multi-reference model was derived that predicts a stepwise electron transfer in the S{sub 0} state and a wave-like dependence of the S{sub 1} electron transfer on the external stimulus. The standard single-reference Kohn-Sham (KS) DFT approach and the time-dependent DFT (TDDFT) method failed to describe the correct dependence of the S{sub 0} and S{sub 1} electron transfer on the external electric field applied along the donor–acceptor system. The multi-reference DFT approach, the spin-restricted ensemble-referenced KS (REKS) method, was able to successfully reproduce the correct behavior of the S{sub 0} and S{sub 1} electron transfer on the applied field. The REKS method was benchmarked against experimentally measured gas phase charge transfer excitations in a series of organic donor–acceptor complexes and displayed its ability to describe this type of electronic transitions with a very high accuracy, mean absolute error of 0.05 eV with the use of the standard range separated density functionals. On the basis of the calculations undertaken in this work, it is suggested that the non-adiabatic coupling between the S{sub 0} and S{sub 1} states may interfere with the electron transfer in a weakly coupled donor–acceptor system. It is also suggested that the electronic excitation of a D{sup +}–A{sup ?} system may play a dual role by assisting the further electron transfer at certain magnitudes of the applied electric field and causing the backward transfer at lower electric field strengths.

  19. Theoretical investigation of electronic excitation transfer between chlorophylls in light-harvesting antenna of photosystem ii using quantum computers

    Scientific Electronic Library Online (English)

    Maryam, Dehestani; Somaie, Shojaei; Azita, Khosravan.

    Full Text Available The excitation energy transfer between chlorophylls in major and minor antenna complexes of photosystem II (PSII) was investigated using quantum Fourier transforms. These transforms have an important role in the efficiency of quantum algorithms of quantum computers. The equation 2n=N was used to mak [...] e the connection between excitation energy transfers using quantum Fourier transform, where n is the number of qubits required for simulation of transfers and N is the number of chlorophylls in the antenna complexes.

  20. Excitation energy transfer in the photosystem I

    Energy Technology Data Exchange (ETDEWEB)

    Webber, Andrew N

    2012-09-25

    Photosystem I is a multimeric pigment protein complex in plants, green alage and cyanobacteria that functions in series with Photosystem II to use light energy to oxidize water and reduce carbon dioxide. The Photosystem I core complex contains 96 chlorophyll a molecules and 22 carotenoids that are involved in light harvesting and electron transfer. In eucaryotes, PSI also has a peripheral light harvesting complex I (LHCI). The role of specific chlorophylls in excitation and electron transfer are still unresolved. In particular, the role of so-called bridging chlorophylls, located between the bulk antenna and the core electron transfer chain, in the transfer of excitation energy to the reaction center are unknown. During the past funding period, site directed mutagenesis has been used to create mutants that effect the physical properties of these key chlorophylls, and to explore how this alters the function of the photosystem. Studying these mutants using ultrafast absorption spectroscopy has led to a better understanding of the process by which excitation energy is transferred from the antenna chlorophylls to the electron transfer chain chlorophylls, and what the role of connecting chlorophylls and A_0 chlorophylls is in this process. We have also used these mutants to investigate whch of the central group of six chlorophylls are involved in the primary steps of charge separation and electron transfer.

  1. Intermediate vibronic coupling in charge transfer states: comprehensive calculation of electronic excitations in sexithiophene crystal.

    Science.gov (United States)

    Stradomska, Anna; Kulig, Waldemar; Slawik, Micha?; Petelenz, Piotr

    2011-06-14

    A comprehensive theory of linear vibronic coupling in a coupled manifold of Frenkel and charge-transfer states in an infinite molecular crystal is presented and applied for sexithiophene. The approach, valid in the intermediate-coupling regime, includes up to three-particle terms of the Philpott expansion, with the vibronic wavefunctions represented in the Lang-Firsov basis. As a stringent test, the scheme is used to reproduce the complete set of available sexithiophene absorption and electroabsorption spectra within a unified theoretical framework. The input is based primarily on independent calculations and to some extent on independent experiments, with explicit fitting contained within the limits set by the estimated inherent errors of a priori parameter estimates. Reasonably good quantitative agreement with experimental spectra is achieved. The results resolve some existing interpretational ambiguities and expose some peculiarities of electric field effect on vibronic eigenstates of Frenkel parentage, highlighting the role of charge-transfer interactions. PMID:21682523

  2. Synthesis of Biomimetic Systems for Proton and Electron Transfer Reactions in the Ground and Excited State

    OpenAIRE

    Parada, Giovanny A.

    2015-01-01

    A detailed understanding of natural photosynthesis provides inspiration for the development of sustainable and renewable energy sources, i.e. a technology that is capable of converting solar energy directly into chemical fuels. This concept is called artificial photosynthesis. The work described in this thesis contains contributions to the development of artificial photosynthesis in two separate areas. The first one relates to light harvesting with a focus on the question of how electronic pr...

  3. Study of photo-activated electron transfer reactions in the first excited singlet state by picosecond and nanosecond laser spectroscopy

    International Nuclear Information System (INIS)

    Picosecond laser spectroscopy has been used to study two photo-activated electron transfer reactions: - a bimolecular electron transfer reaction between a sensitizer, DODCI, and an electron acceptor, methylviologen. The two radical ions created with an electron transfer efficiency ? ? 0.07 have been identified in picosecond and nanosecond laser absorption spectroscopy by adding selective solutes such as para-benzoquinone (an electron acceptor) or L(+) ascorbic acid (an electron donor). - an intramolecular electron transfer reaction in a triad molecule consisting of a tetra-aryl-porphyrin covalently linked to both a carotenoid and a quinone. The photoinduced charge separation occurs within 30 ps and leads, with a yield of 25 pc, to the formation of a zwitterion whose half-life is 2.5 ?s. The experimental results obtained in these two studies show an effective decrease in the recombination rate of the two radical ions created in the encounter pair. (author)

  4. Electron-excited molecule interactions

    International Nuclear Information System (INIS)

    In this paper the limited but significant knowledge to date on electron scattering from vibrationally/rotationally excited molecules and electron scattering from and electron impact ionization of electronically excited molecules is briefly summarized and discussed. The profound effects of the internal energy content of a molecule on its electron attachment properties are highlighted focusing in particular on electron attachment to vibrationally/rotationally and to electronically excited molecules. The limited knowledge to date on electron-excited molecule interactions clearly shows that the cross sections for certain electron-molecule collision processes can be very different from those involving ground state molecules. For example, optically enhanced electron attachment studies have shown that electron attachment to electronically excited molecules can occur with cross sections 106 to 107 times larger compared to ground state molecules. The study of electron-excited molecule interactions offers many experimental and theoretical challenges and opportunities and is both of fundamental and technological significance. 54 refs., 15 figs

  5. Excited-state intramolecular hydrogen transfer (ESIHT) of 1,8-Dihydroxy-9,10-anthraquinone (DHAQ) characterized by ultrafast electronic and vibrational spectroscopy and computational modeling

    KAUST Repository

    Mohammed, Omar F.

    2014-05-01

    We combine ultrafast electronic and vibrational spectroscopy and computational modeling to investigate the photoinduced excited-state intramolecular hydrogen-transfer dynamics in 1,8-dihydroxy-9,10-anthraquinone (DHAQ) in tetrachloroethene, acetonitrile, dimethyl sulfoxide, and methanol. We analyze the electronic excited states of DHAQ with various possible hydrogen-bonding schemes and provide a general description of the electronic excited-state dynamics based on a systematic analysis of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S 2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S 1 state where DHAQ exhibits ESIHT dynamics. In this equilibration process, the excited-state population is distributed between the 9,10-quinone (S2) and 1,10-quinone (S1) states while undergoing vibrational energy redistribution, vibrational cooling, and solvation dynamics on the 0.1-50 ps time scale. Transient UV/vis pump-probe data in methanol also suggest additional relaxation dynamics on the subnanosecond time scale, which we tentatively ascribe to hydrogen bond dynamics of DHAQ with the protic solvent, affecting the equilibrium population dynamics within the S2 and S1 electronic excited states. Ultimately, the two excited singlet states decay with a solvent-dependent time constant ranging from 139 to 210 ps. The concomitant electronic ground-state recovery is, however, only partial because a large fraction of the population relaxes to the first triplet state. From the similarity of the time scales involved, we conjecture that the solvent plays a crucial role in breaking the intramolecular hydrogen bond of DHAQ during the S2/S1 relaxation to either the ground or triplet state. © 2014 American Chemical Society.

  6. Calculations of Nonlinear Wave-Packet Interferometry Signals in the Pump-Probe Limit as Tests for Vibrational Control over Electronic Excitation Transfer

    CERN Document Server

    Biggs, Jason D

    2009-01-01

    The preceding paper describes a strategy for externally influencing the course of short-time electronic excitation transfer (EET) in molecular dimers and observing the process by nonlinear wave-packet interferometry (nl-WPI). Within a sample of isotropically oriented dimers having a specified internal geometry, a vibrational mode internal to the acceptor chromophore can be preferentially driven by electronically nonresonant impulsive stimulated Raman (or resonant infrared) excitation with a short polarized control pulse. A subsequent electronically resonant polarized pump then preferentially excites the donor, and EET ensues. Here we test both the control strategy and its spectroscopic investigation-with some sacrifice of amplitude-level detail-by calculating the pump-probe difference signal. That signal is the limiting case of the control-influenced nl-WPI signal in which the two pulses in the pump pulse-pair coincide, as do the two pulses in the probe pulse-pair. We present calculated pump-probe difference ...

  7. Calculations of nonlinear wave-packet interferometry signals in the pump-probe limit as tests for vibrational control over electronic excitation transfer

    Science.gov (United States)

    Biggs, Jason D.; Cina, Jeffrey A.

    2009-12-01

    The preceding paper [J. D. Biggs and J. A. Cina, J. Chem. Phys. 131, 224101 (2009)] (referred to here as Paper 1), describes a strategy for externally influencing the course of short-time electronic excitation transfer (EET) in molecular dimers and observing the process by nonlinear wave-packet interferometry (nl-WPI). External influence can, for example, be exerted by inducing coherent intramolecular vibration in one of the chromophores prior to short-pulse electronic excitation of the other. Within a sample of isotropically oriented dimers having a specified internal geometry, a vibrational mode internal to the acceptor chromophore can be preferentially driven by electronically nonresonant impulsive stimulated Raman (or resonant infrared) excitation with a short polarized "control" pulse. A subsequent electronically resonant polarized pump then preferentially excites the donor, and EET ensues. Paper 1 investigates control-pulse-influenced nl-WPI as a tool for the spectroscopic evaluation of the effect of coherent molecular vibration on excitation transfer, presenting general expressions for the nl-WPI difference signal from a dimer following the action of a control pulse of arbitrary polarization and shape. Electronic excitation is to be effected and its interchromophore transfer monitored by resonant pump and probe "pulses," respectively, each consisting of an optical-phase-controlled ultrashort pulse-pair having arbitrary polarization, duration, center frequency, and other characteristics. Here we test both the control strategy and its spectroscopic investigation—with some sacrifice of amplitude-level detail—by calculating the pump-probe difference signal. That signal is the limiting case of the control-influenced nl-WPI signal in which the two pulses in the pump pulse-pair coincide, as do the two pulses in the probe pulse-pair. We present calculated pump-probe difference signals for (1) a model excitation-transfer complex in which two equal-energy monomers each support one moderately Franck-Condon active intramolecular vibration; (2) a simplified model of the covalent dimer dithia-anthracenophane, representing its EET dynamics following selective impulsive excitation of the weakly Franck-Condon active ?12 anthracene vibration at 385 cm-1; and (3) a model complex featuring moderate electronic-vibrational coupling in which the site energy of the acceptor chromophore is lower than that of the donor.

  8. Role of electron-driven proton-transfer processes in the excited-state deactivation of the adenine-thymine base pair.

    Science.gov (United States)

    Perun, Serhiy; Sobolewski, Andrzej L; Domcke, Wolfgang

    2006-07-27

    Exploratory electronic structure calculations have been performed with the CC2 (simplified singles and doubles coupled-cluster) method for two conformers of the adenine (A)-thymine (T) base pair, with emphasis on excited-state proton-transfer reactions. The Watson-Crick conformer and the most stable (in the gas-phase) conformer of the A-T base pair have been considered. The equilibrium geometries of the ground state and of the lowest excited electronic states have been determined with the MP2 (second-order Møller-Plesset) and CC2 methods, respectively. Vertical and adiabatic excitation energies, oscillator strengths, and dipole moments of the excited states are reported. Of particular relevance for the photochemistry of the A-T base pair are optically dark (1)pipi* states of charge-transfer character. Although rather high in energy at the ground-state equilibrium geometry, these states are substantially lowered in energy by the transfer of a proton, which thus neutralizes the charge separation. A remarkable difference of the energetics of the proton-transfer reaction is predicted for the two tautomers of A-T: in the Watson-Crick conformer, but not in the most stable conformer, a sequence of conical intersections connects the UV-absorbing (1)pipi* state in a barrierless manner with the electronic ground state. These conical intersections allow a very fast deactivation of the potentially reactive excited states in the Watson-Crick conformer. The results provide evidence that the specific hydrogen-bonding pattern of the Watson-Crick conformer endows this structure with a greatly enhanced photostability. This property of the Watson-Crick conformer of A-T may have been essential for the selection of this species as carrier of genetic information in early stages of the biological evolution. PMID:16854013

  9. Study of intermediates from transition metal excited-state electron-transfer reactions: Progress report, August 1, 1986--December 31, 1988

    International Nuclear Information System (INIS)

    During the period covered by this progress report, the examination of intermediates from transition metal excited-state electron-transfer reactions followed certain well-defined themes; the techniques of conventional and time-resolved spectrofluorimetry, continuous and pulsed laser flash photolysis, and continuous and pulse radiolysis were employed. Research involves Ru(II) complexes and Cr(III) complexes. 23 refs., 2 tabs

  10. Tautomeric selectivity of the excited-state lifetime of guanine/cytosine base pairs: the role of electron-driven proton-transfer processes.

    Science.gov (United States)

    Sobolewski, Andrzej L; Domcke, Wolfgang; Hättig, C

    2005-12-13

    The UV spectra of three different conformers of the guanine/cytosine base pair were recorded recently with UV-IR double-resonance techniques in a supersonic jet [Abo-Riziq, A., Grace, L., Nir, E., Kabelac, M., Hobza, P. & de Vries, M. S. (2005) Proc. Natl. Acad. Sci. USA 102, 20-23]. The spectra provide evidence for a very efficient excited-state deactivation mechanism that is specific for the Watson-Crick structure and may be essential for the photostability of DNA. Here we report results of ab initio electronic-structure calculations for the excited electronic states of the three lowest-energy conformers of the guanine/cytosine base pair. The calculations reveal that electron-driven interbase proton-transfer processes play an important role in the photochemistry of these systems. The exceptionally short lifetime of the UV-absorbing states of the Watson-Crick conformer is tentatively explained by the existence of a barrierless reaction path that connects the spectroscopic (1)pi pi * excited state with the electronic ground state via two electronic curve crossings. For the non-Watson-Crick structures, the photochemically reactive state is located at higher energies, resulting in a barrier for proton transfer and, thus, a longer lifetime of the UV-absorbing (1)pi pi * state. The computational results support the conjecture that the photochemistry of hydrogen bonds plays a decisive role for the photostability of the molecular encoding of the genetic information in isolated DNA base pairs. PMID:16330778

  11. Electron energy distribution functions and fractional power transfer in "cold" and excited CO2 discharge and post discharge conditions

    Science.gov (United States)

    Pietanza, L. D.; Colonna, G.; D'Ammando, G.; Laricchiuta, A.; Capitelli, M.

    2016-01-01

    A Boltzmann equation, in the presence of superelastic vibrational and electronic collisions and of electron-electron Coulomb collisions, has been solved in CO2 plasma in discharge and post discharge conditions. Superelastic vibrational collisions play an important role in affecting the electron energy distribution function (eedf) in a wide range of the reduced electric field E/N and of vibrational temperatures characterizing the vibrational modes of CO2. An important result is the dependence of fractional power losses and of the relevant rate coefficients on the vibrational temperatures of the system. Superelastic electronic collisions, on the other hand, are the main processes affecting eedf and related quantities in the post discharge conditions (i.e., E/N = 0). In particular at low vibrational temperatures, the superelastic electronic collisions form an important plateau in the eedf, largely influencing the rate coefficients and the fractional power transfer.

  12. Exogenous quinones inhibit photosynthetic electron transfer in Chloroflexus aurantiacus by specific quenching of the excited bacteriochlorophyll c antenna

    DEFF Research Database (Denmark)

    Frigaard, N-U; Tokita, S; Matsuura, K

    1999-01-01

    In the photosynthetic green filamentous bacterium Chloroflexus aurantiacus, excitation energy is transferred from a large bacteriochlorophyll (BChl) c antenna via smaller BChl a antennas to the reaction center. The effects of substituted 1,4-naphthoquinones on BChl c and BChl a fluorescence and on flash-induced cytochrome c oxidation were studied in whole cells under aerobic conditions. BChl c fluorescence in a cell suspension with 5.4 microM BChl c was quenched to 50% by addition of 0.6 microM ...

  13. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.

  14. Electron-excited molecule interactions

    Energy Technology Data Exchange (ETDEWEB)

    Christophorou, L.G. (Oak Ridge National Lab., TN (USA) Tennessee Univ., Knoxville, TN (USA). Dept. of Physics)

    1991-01-01

    In this paper the limited but significant knowledge to date on electron scattering from vibrationally/rotationally excited molecules and electron scattering from and electron impact ionization of electronically excited molecules is briefly summarized and discussed. The profound effects of the internal energy content of a molecule on its electron attachment properties are highlighted focusing in particular on electron attachment to vibrationally/rotationally and to electronically excited molecules. The limited knowledge to date on electron-excited molecule interactions clearly shows that the cross sections for certain electron-molecule collision processes can be very different from those involving ground state molecules. For example, optically enhanced electron attachment studies have shown that electron attachment to electronically excited molecules can occur with cross sections 10{sup 6} to 10{sup 7} times larger compared to ground state molecules. The study of electron-excited molecule interactions offers many experimental and theoretical challenges and opportunities and is both of fundamental and technological significance. 54 refs., 15 figs.

  15. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited.

    Science.gov (United States)

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and CT-like character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) calculations with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals are compared with coupled-cluster (CC) benchmarks. The test set comprises an organic CT complex, two push-pull donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT. It is shown that such CT-like excitations do not have the characteristics of physical charge transfer, and improvements with LC functionals may not be obtained for the right reasons. The TDDFT triplet excitation energies are underestimated for all systems, often severely. For the CT-like candidates, the singlet-triplet (S/T) separation changes from negative with a non-hybrid functional to positive with a tuned LC functional. For the cyanine, the S/T separation is systematically too large with TDDFT, leading to better error compensation for the singlet energy with a non-hybrid functional. PMID:26575765

  16. The electron-electron interaction studied in strong central fields by resonant transfer and excitation with H-like U ions

    CERN Document Server

    Ma, X; Gumberidze, A; Kozhuharov, C; Liesen, D; Mokler, P H; Sierpowski, D; Stachura, Z; Stöhlker, T; Warczak, A

    2003-01-01

    Electron-electron interaction is studied in the strongest possible atomic fields (Z.alpha => 1) in the presence of only two electrons. A quasi-free electron from a hydrogen gas target is resonantly captured into a L sub j subshell of a fast H-like U sup 9 sup 1 sup + ion by simultaneous excitation of the strongly bound K electron also into a L sub j sub ' subshell of the projectile, with j and j' the total angular momenta of 1/2 or 3/2 for the electron of concern. This resonant capture and excitation process, KL sub j L sub j sub ' -RTE, is mediated by electron-electron interaction. It is equivalent to dielectronic recombination (DR) in ion-electron collisions and leads to a doubly excited He-like U sup 9 sup 0 sup + sup * sup * ion, which stabilizes - almost exclusively - via the emission of two successive K X-rays, first a K hypersatellite (K alpha i-H) and then a K satellite (K alpha i'-S) transition. The K X-ray emission characteristics associated with one-electron capture in collisions of U sup 9 sup 1 s...

  17. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens; Waluk, Jacek

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an......, associated with an excited-state intramolecular proton transfer process....

  18. Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(1S) + H2(B 1?/sub u/+)

    International Nuclear Information System (INIS)

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H2(B 1?/sub u/+) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H2(B 1?/sub u/+). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H2(E,F 1?/sub g/+) and with He + H2(X 1?/sub g/+) and cause a local maximum and a deep minimum in the He + H2(B 1?/sub u/+) PES, respectively. The crossing with He + H2(X 1?/sub g/+) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H2(B 1?/sub u/+) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs

  19. Electron transfer reactions

    CERN Document Server

    Cannon, R D

    2013-01-01

    Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

  20. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S

    1995-01-01

    Advances in Electron Transfer Chemistry, Volume 4 presents the reaction mechanisms involving the movement of single electrons. This book discusses the electron transfer reactions in organic, biochemical, organometallic, and excited state systems. Organized into four chapters, this volume begins with an overview of the photochemical behavior of two classes of sulfonium salt derivatives. This text then examines the parameters that control the efficiencies for radical ion pair formation. Other chapters consider the progress in the development of parameters that control the dynamics and reaction p

  1. The electron-electron interaction studied in strong central fields by resonant transfer and excitation with H-like U ions. - Angular distribution of hypersatellite and satellite radiation emitted after resonant and excitation into U91+ ions

    International Nuclear Information System (INIS)

    Electron-electron interaction is studied in the strongest possible atomic fields (Z.? => 1) in the presence of only two electrons. A quasi-free electron from a hydrogen gas target is resonantly captured into a Lj subshell of a fast H-like U91+ ion by simultaneous excitation of the strongly bound K electron also into a Lj' subshell of the projectile, with j and j' the total angular momenta of 1/2 or 3/2 for the electron of concern. This resonant capture and excitation process, KLjLj'-RTE, is mediated by electron-electron interaction. It is equivalent to dielectronic recombination (DR) in ion-electron collisions and leads to a doubly excited He-like U90+** ion, which stabilizes - almost exclusively - via the emission of two successive K X-rays, first a K hypersatellite (K?i-H) and then a K satellite (K?i'-S) transition. The K X-ray emission characteristics associated with one-electron capture in collisions of U91+ ions with a hydrogen target is studied for the three resonance groups of the KLjLj'-RTE and one off-resonance energy, i.e. in the energy range between 100 and 135 MeV/u. The total cross section for the first resonance group KL1/2L1/2 confirms the importance of the Breit contribution to the interaction. The angular distribution for the K?2-H transition (j=1/2) is isotropic in the projectile system whereas the K?1-H transition (j=3/2) indicates a strong alignment for the 3/2 electrons in the doubly excited states for the second resonance group KL1/2L3/2. The experimental results are in agreement with fully relativistic calculations including the generalized Breit interaction. (orig.)

  2. Intramolecular electron transfer rates

    Science.gov (United States)

    Hupp, Joseph T.

    The initial goals of this project were: (1) to construct pulsed-accelerated-flow and pulsed-laser (transient absorbance) instruments for intramolecular electron-transfer rate measurements, (2) to design and synthesize appropriate molecules and perform such measurements, (3) to develop further an electrochemical method for gauging site-to-site electronic coupling, and (4) to apply time-dependent Raman scattering theory to the problem of inner-shell reorganization in charge-transfer reactions. Although all four goals were met, we also found it necessary to pursue studies in some unforeseen directions. For example, early on we discovered that medium effects (aggregation and ion pairing) could play a very large, and previously unrecognized, role in some optical intervalence reactions. Given the importance of the effects to the areas above, we chose to map them in a fairly complete fashion. Also, in anticipation of possible renewal we initiated studies in a new area: bimolecular photoredox kinetics in supercritical media. Finally, in a small project carried out largely by undergraduates we examined solvent tuning effects upon lifetimes of photo-excited ruthenium am(m)ine bipyridine complexes. The key new findings and other highlights of these studies are outlined.

  3. Electron impact excitation of ions

    International Nuclear Information System (INIS)

    In researching electron impact excitation of ions, prediction of cross-section rates is still uncertain. This paper reviews electron-ion beam experiments. Theory is reviewed, then energy levels of the electron and He-like atom, and some of the transitions important in electron impact excitation studied. Close-coupling (coupled state) theory is treated. The distorted wave and Coulomb Born Approximations are applied. Experimental techniques are then reviewed. The plasma-based rate measurements are studied. Electron-ion beam experiments are represented schematically. The optical detection system (to observe photon emissions of electron and ion--collisions) is detailed. The parameters for the best experiments are determined. Finally, simple systems (for He+) and complex systems (for heavy ions), the experiments, and theoretical attention given them, are surveyed

  4. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster-configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

    Science.gov (United States)

    Fukuda, Ryoichi; Ehara, Masahiro

    2014-10-01

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2'-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.

  5. An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster–configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

    International Nuclear Information System (INIS)

    Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2?-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy

  6. Excitation energy transfer and electron-vibrational coupling in phycobiliproteins of the cyanobacterium Acaryochloris marina investigated by site-selective spectroscopy.

    Science.gov (United States)

    Gryliuk, G; Rätsep, M; Hildebrandt, S; Irrgang, K-D; Eckert, H-J; Pieper, J

    2014-09-01

    In adaption to its specific environmental conditions, the cyanobacterium Acaryochloris marina developed two different types of light-harvesting complexes: chlorophyll-d-containing membrane-intrinsic complexes and phycocyanobilin (PCB) - containing phycobiliprotein (PBP) complexes. The latter complexes are believed to form a rod-shaped structure comprising three homo-hexamers of phycocyanin (PC), one hetero-hexamer of phycocyanin and allophycocyanin (APC) and probably a linker protein connecting the PBPs to the reaction centre. Excitation energy transfer and electron-vibrational coupling in PBPs have been investigated by selectively excited fluorescence spectra. The data reveal a rich spectral substructure with a total of five low-energy electronic states with fluorescence bands at 635nm, 645nm, 654nm, 659nm and a terminal emitter at about 673 nm. The electronic states at ~635 and 645 nm are tentatively attributed to PC and APC, respectively, while an apparent heterogeneity among PC subunits may also play a role. The other fluorescence bands may be associated with three different isoforms of the linker protein. Furthermore, a large number of vibrational features can be identified for each electronic state with intense phonon sidebands peaking at about 31 to 37cm?¹, which are among the highest phonon frequencies observed for photosynthetic antenna complexes. The corresponding Huang-Rhys factors S fall in the range between 0.98 (terminal emitter), 1.15 (APC), and 1.42 (PC). Two characteristic vibronic lines at about 1580 and 1634cm?¹ appear to reflect CNH? and CC stretching modes of the PCB chromophore, respectively. The exact phonon and vibrational frequencies vary with electronic state implying that the respective PCB chromophores are bound to different protein environments. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy. PMID:24560813

  7. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    CERN Document Server

    Theophilou, Iris; Thanos, S

    2014-01-01

    Photoinduced charge transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for accurate and computationally inexpensive treatment of charge transfer excitations is a topic that attracts nowadays a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations (M. Tassi, I. Theophilou and S. Thanos, Int. J. Quantum Chem., {113}, 690 (2013), M. Tassi, I. Theophilou and S. Thanos, J. Chem. Phys. {138}, 124107 (2013)) to allow for the description of intermolecular charge transfer excitations. For the description of an excitation where an electron is transferred from a donor system to an acceptor one, it is necessary to keep the excited state orthogonal to the ground sate in order to avoid variational collapse. These conditions are achieved by decomposing the subspace spanned by the Hartree-Fock (HF) ground state orbitals to four subspaces: The subspace spanned ...

  8. Electron excitation of dielectric wedges

    International Nuclear Information System (INIS)

    Recent experimental data of Electron Energy Loss Spectrometry of the interaction between small crystallites and beams travelling at a fixed beam-solid surface distance are analyzed in terms of the surface and bulk excitation modes of parabolically shaped wedges. The probability of excitation of the surface modes is calculated for an electron travelling parallel to the wedge surface, either outside or inside the dielectric wedge. The main features of available experimental data for MgO crystallites can be explained by the theory. 8 figures

  9. Resonant electron transfer and L-shell excitation at 3.6 MeV/u 62Smsup(q+) -> Xe collisions, q=35-52

    International Nuclear Information System (INIS)

    For 3.6 MeV/u Smsup(q+) projectiles a hump in the projectile (Lsub(l)+Lsub(?)) X-ray emission cross section is seen as a function of charge state q for high q with 463-shell electron to the M-shell. The cross section for this L3-shell RTE process gives values of up to 2 . 10-19 cm2 which is seen in single spectra already. To demonstrate the strong existence of the L-shell RTE process for the studied collision system, extensive calculations have been carried out. This concerns especially the L3-shell fluorescence yields for the radiative stabilization process in the highly charged projectile, when simultaneous transfer and excitation has taken place. Our calculated q-dependent cross sections for the RTE process support the given interpretation. (orig.)

  10. Proton-Coupled Electron Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Weinberg, Dave; Gagliardi, Christopher J.; Hull, Jonathan F; Murphy, Christine Fecenko; Kent, Caleb A.; Westlake, Brittany C.; Paul, Amit; Ess, Daniel H; McCafferty, Dewey Granville; Meyer, Thomas J

    2012-07-11

    Proton-Coupled Electron Transfer (PCET) describes reactions in which there is a change in both electron and proton content between reactants and products. It originates from the influence of changes in electron content on acid-base properties and provides a molecular-level basis for energy transduction between proton transfer and electron transfer. Coupled electron-proton transfer or EPT is defined as an elementary step in which electrons and protons transfer from different orbitals on the donor to different orbitals on the acceptor. There is (usually) a clear distinction between EPT and H-atom transfer (HAT) or hydride transfer, in which the transferring electrons and proton come from the same bond. Hybrid mechanisms exist in which the elementary steps are different for the reaction partners. EPT pathways such as PhO•/PhOH exchange have much in common with HAT pathways in that electronic coupling is significant, comparable to the reorganization energy with H{sub DA} ~ ?. Multiple-Site Electron-Proton Transfer (MS-EPT) is an elementary step in which an electron-proton donor transfers electrons and protons to different acceptors, or an electron-proton acceptor accepts electrons and protons from different donors. It exploits the long-range nature of electron transfer while providing for the short-range nature of proton transfer. A variety of EPT pathways exist, creating a taxonomy based on what is transferred, e.g., 1e-/2H+ MS-EPT. PCET achieves “redox potential leveling” between sequential couples and the buildup of multiple redox equivalents, which is of importance in multielectron catalysis. There are many examples of PCET and pH-dependent redox behavior in metal complexes, in organic and biological molecules, in excited states, and on surfaces. Changes in pH can be used to induce electron transfer through films and over long distances in molecules. Changes in pH, induced by local electron transfer, create pH gradients and a driving force for long-range proton transfer in Photosysem II and through other biological membranes. In EPT, simultaneous transfer of electrons and protons occurs on time scales short compared to the periods of coupled vibrations and solvent modes. A theory for EPT has been developed which rationalizes rate constants and activation barriers, includes temperature- and driving force (?G)-dependences implicitly, and explains kinetic isotope effects. The distance-dependence of EPT is dominated by the short-range nature of proton transfer, with electron transfer being far less demanding.Changes in external pH do not affect an EPT elementary step. Solvent molecules or buffer components can act as proton donor acceptors, but individual H2O molecules are neither good bases (pKa(H3O+) = -1.74) nor good acids (pKa(H2O) = 15.7). There are many examples of mechanisms in chemistry, in biology, on surfaces, and in the gas phase which utilize EPT. PCET and EPT play critical roles in the oxygen evolving complex (OEC) of Photosystem II and other biological reactions by decreasing driving force and avoiding high-energy intermediates.

  11. An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption

    Science.gov (United States)

    Janke, Svenja M.; Auerbach, Daniel J.; Wodtke, Alec M.; Kandratsenka, Alexander

    2015-09-01

    We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ?3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.

  12. An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption.

    Science.gov (United States)

    Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander

    2015-09-28

    We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ?3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab. PMID:26429033

  13. Calculation of electronic coupling matrix elements for ground and excited state electron transfer reactions: Comparison of the generalized Mulliken-Hush and block diagonalization methods

    Science.gov (United States)

    Cave, Robert J.; Newton, Marshall D.

    1997-06-01

    Two independent methods are presented for the nonperturbative calculation of the electronic coupling matrix element (Hab) for electron transfer reactions using ab initio electronic structure theory. The first is based on the generalized Mulliken-Hush (GMH) model, a multistate generalization of the Mulliken Hush formalism for the electronic coupling. The second is based on the block diagonalization (BD) approach of Cederbaum, Domcke, and co-workers. Detailed quantitative comparisons of the two methods are carried out based on results for (a) several states of the system Zn2OH2+ and (b) the low-lying states of the benzene-Cl atom complex and its contact ion pair. Generally good agreement between the two methods is obtained over a range of geometries. Either method can be applied at an arbitrary nuclear geometry and, as a result, may be used to test the validity of the Condon approximation. Examples of nonmonotonic behavior of the electronic coupling as a function of nuclear coordinates are observed for Zn2OH2+. Both methods also yield a natural definition of the effective distance (rDA) between donor (D) and acceptor (A) sites, in contrast to earlier approaches which required independent estimates of rDA, generally based on molecular structure data.

  14. Electron transfer in proteins

    DEFF Research Database (Denmark)

    Farver, O; Pecht, I

    1991-01-01

    Electron migration between and within proteins is one of the most prevalent forms of biological energy conversion processes. Electron transfer reactions take place between active centers such as transition metal ions or organic cofactors over considerable distances at fast rates and with remarkable...... specificity. The electron transfer is attained through weak electronic interaction between the active sites, so that considerable research efforts are centered on resolving the factors that control the rates of long-distance electron transfer reactions in proteins. These factors include (in addition to the......-containing proteins. These proteins serve almost exclusively in electron transfer reactions, and as it turns out, their metal coordination sites are endowed with properties uniquely optimized for their function....

  15. Excitation and charge transfer in He/sup +/ + H collisions. A molecular approach including two-electron translation factors

    Energy Technology Data Exchange (ETDEWEB)

    Errea, L.F.; Mendez, L.; Riera, A.

    1983-06-01

    In a previous paper we have pointed out that the common-translation-factor (CTF) method is the only one which, at present, and within the framework of the molecular model of atomic collisions, can be shown to be both convergent and computationally fast, even for many-electron systems. In this Communication we check that this second statement is correct, presenting, for the first time, a molecular calculation involving two-electron translation factors, for He/sup +/ + H collisions. A careful study of the sensitivity of the calculated cross sections to the choice of the CTF is performed, and conclusions on that sensitivity are drawn, for several types of processes.

  16. Excitation and charge transfer in He+ + H collisions. A molecular approach including two-electron translation factors

    International Nuclear Information System (INIS)

    In a previous paper we have pointed out that the common-translation-factor (CTF) method is the only one which, at present, and within the framework of the molecular model of atomic collisions, can be shown to be both convergent and computationally fast, even for many-electron systems. In this Communication we check that this second statement is correct, presenting, for the first time, a molecular calculation involving two-electron translation factors, for He+ + H collisions. A careful study of the sensitivity of the calculated cross sections to the choice of the CTF is performed, and conclusions on that sensitivity are drawn, for several types of processes

  17. Efficient excited-state deactivation of the Gly-Phe-Ala tripeptide via an electron-driven proton-transfer process.

    Science.gov (United States)

    Shemesh, Dorit; Sobolewski, Andrzej L; Domcke, Wolfgang

    2009-02-01

    Ab initio electronic-structure calculations indicate a mechanism for efficient excited-state deactivation of a low-energy conformer of the Gly-Phe-Ala tripeptide. The particularly short excited-state lifetime can explain the unexpected absence of this conformer in resonant two-photon ionization spectra. It is suggested that these ultrafast electronic deactivation processes provide specific conformers of peptides with a high degree of photostability. PMID:19140760

  18. Excitation transfer in stacked quantum dot chains

    Science.gov (United States)

    Kanjanachuchai, Songphol; Xu, Ming; Jaffré, Alexandre; Jittrong, Apichart; Chokamnuai, Thitipong; Panyakeow, Somsak; Boutchich, Mohamed

    2015-05-01

    Stacked InAs quantum dot chains (QDCs) on InGaAs/GaAs cross-hatch pattern (CHP) templates yield a rich emission spectrum with an unusual carrier transfer characteristic compared to conventional quantum dot (QD) stacks. The photoluminescent spectra of the controlled, single QDC layer comprise multiple peaks from the orthogonal QDCs, the free-standing QDs, the CHP, the wetting layers and the GaAs substrate. When the QDC layers are stacked, employing a 10 nm GaAs spacer between adjacent QDC layers, the PL spectra are dominated by the top-most stack, indicating that the QDC layers are nominally uncoupled. Under high excitation power densities when the high-energy peaks of the top stack are saturated, however, low-energy PL peaks from the bottom stacks emerge as a result of carrier transfers across the GaAs spacers. These unique PL signatures contrast with the state-filling effects in conventional, coupled QD stacks and serve as a means to quickly assess the presence of electronic coupling in stacks of dissimilar-sized nanostructures.

  19. Charge Transfer Excitations in Insulating Copper Oxides

    CERN Document Server

    Moskvin, A S; Hayn, R; Malek, J

    2005-01-01

    A semi-quantitative cluster approach is developed to describe the charge transfer (CT) electron-hole excitations in insulating cuprates in a rather wide energy range up to 10- 15 eV. It generalizes the Zhang-Ng (ZN) model of CT excitons by considering the complete set of Cu3d and O2p orbitals within the CuO4 embedded molecular cluster method and by introducing one-center (intra-center) Frenkel-like and two-center (inter-center) excitons. Special attention is paid to the transition matrix element effects both in optical and electron energy loss spectra (EELS). In the latter case we obtain the momentum dependence of matrix elements both for intra-center and inter-center transitions. We are able to give a semi-quantitative description of the optical and EELS spectra for a large number of 0D (like CuB2O4), 1D (Sr2CuO3) and 2D (like Sr2CuO2Cl2) insulating cuprates in a unifying manner. By comparing our analysis with the experimental data we find that the CT gap in insulating cuprates is determined by nearly degene...

  20. Relations among theories of excitation transfer

    International Nuclear Information System (INIS)

    Recent applications of the generalized master equation (GME) theory for the transfer of excitation interacting linearly with phonons results in revision of some previous conclusions about relations between GME and other advanced theories: Haken-Strobl-Reineker (HSR) stochastic Liouville equation (SLE) theory, Grover-Silbey (GS) microscopic theory and Continuous Time Random Walk (CTRW) method. Two-channel memory functions (MF) derived from first principles relate entirely to those corresponding to GS and HRS approaches and unify theories of the excitation transfer. Trapping effects have pronounced influence on MFs. Coherence effects in the excitation transfer lead to a strange behaviour of ''probabilities'' in CTRW. Kenkre-Knox (KK) correspondence between MF and spectral properties has a limited applicability. Decay time obtained in such a manner could have nothing to do with much longer real coherence time. (author). 69 refs

  1. Phonons and charge-transfer excitations in HTS superconductors

    International Nuclear Information System (INIS)

    Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs

  2. Electron impact excitation of methane

    Science.gov (United States)

    Vuskovic, L.; Trajmar, S.

    1983-01-01

    A crossed molecular beam-electron beam apparatus was employed to examine the excitation cross-sections of CH4. Attention was given to 20, 30, and 200 eV impact energies at angles from 8-130 deg. Spectra were obtained in the elastic and inelastic realms as well as in the ionization continuum in the 12.99-15.0 eV energy-loss range. Differential cross-sections were also determined. The results are useful for modeling the behavior of CH4 in planetary atmospheres.

  3. Collective Excitations in Electron-Hole Bilayers

    International Nuclear Information System (INIS)

    We report a combined analytic and molecular dynamics analysis of the collective mode spectrum of a bipolar (electron-hole) bilayer in the strong coupling classical limit. A robust, isotropic energy gap is identified in the out-of-phase spectra, generated by the combined effect of correlations and of the excitation of the bound dipoles. In the in-phase spectra we identify longitudinal and transverse acoustic modes wholly maintained by correlations. Strong nonlinear generation of higher harmonics of the fundamental dipole oscillation frequency and the transfer of harmonics between different modes is observed

  4. Dynamics of excitation energy transfer in phycobiliproteins

    Science.gov (United States)

    Zheng, Xiguang; Wang, He Z.; Zhao, Fuli; Gao, Zhaolan; Yu, Zhenxin

    1994-08-01

    Theoretical descriptions of excitation energy transfer between chromophores in allophycocyanin are presented, including bilateral energy transfer paths between chromophores, and are expressed, based on Foster interaction mechanism, as Pauli master equations. Group analysis in C3 symmetry is performed to carry out analytic expressions for fluorescence decays which is generally of triexponential with effects of chromophore coupling and exciton splitting taken account. It is pointed out that the time constant of each decay component contains mixed information of different energy transfer paths, and therefore show its dependence on subtle configuration of chromophores, probably related to site heterogeneity and thus to inhomogeneous broadening previously observed.

  5. Electronic Excited States of Tungsten(0) Arylisocyanides.

    Science.gov (United States)

    Kvapilová, Hana; Sattler, Wesley; Sattler, Aaron; Sazanovich, Igor V; Clark, Ian P; Towrie, Michael; Gray, Harry B; Záliš, Stanislav; Vl?ek, Antonín

    2015-09-01

    W(CNAryl)6 complexes containing 2,6-diisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited states. These properties are enhanced upon appending another aryl ring, e.g., W(CNdippPh(OMe2))6; CNdippPh(OMe2) = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide (Sattler et al. J. Am. Chem. Soc. 2015, 137, 1198-1205). Electronic transitions and low-lying excited states of these complexes were investigated by time-dependent density functional theory (TDDFT); the lowest triplet state was characterized by time-resolved infrared spectroscopy (TRIR) supported by density functional theory (DFT). The intense absorption band of W(CNdipp)6 at 460 nm and that of W(CNdippPh(OMe2))6 at 500 nm originate from transitions of mixed ??*(C?N-C)/MLCT(W ? Aryl) character, whereby W is depopulated by ca. 0.4 e(-) and the electron-density changes are predominantly localized along two equatorial molecular axes. The red shift and intensity rise on going from W(CNdipp)6 to W(CNdippPh(OMe2))6 are attributable to more extensive delocalization of the MLCT component. The complexes also exhibit absorptions in the 300-320 nm region, owing to W ? C?N MLCT transitions. Electronic absorptions in the spectrum of W(CNXy)6 (Xy = 2,6-dimethylphenyl), a complex with orthogonal aryl orientation, have similar characteristics, although shifted to higher energies. The relaxed lowest W(CNAryl)6 triplet state combines ??* excitation of a trans pair of C?N-C moieties with MLCT (0.21 e(-)) and ligand-to-ligand charge transfer (LLCT, 0.24-0.27 e(-)) from the other four CNAryl ligands to the axial aryl and, less, to C?N groups; the spin density is localized along a single Aryl-N?C-W-C?N-Aryl axis. Delocalization of excited electron density on outer aryl rings in W(CNdippPh(OMe2))6 likely promotes photoinduced electron-transfer reactions to acceptor molecules. TRIR spectra show an intense broad bleach due to ?(C?N), a prominent transient upshifted by 60-65 cm(-1), and a weak down-shifted feature due to antisymmetric C?N stretch along the axis of high spin density. The TRIR spectral pattern remains unchanged on the femtosecond-nanosecond time scale, indicating that intersystem crossing and electron-density localization are ultrafast (<100 fs). PMID:26267759

  6. Quantifying electron transfer reactions in biological systems

    DEFF Research Database (Denmark)

    Sjulstok, Emil Sjulstok; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between......Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling...

  7. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens; Waluk, Jacek

    1998-01-01

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an unusually large fluorescence Stokes shift of 10500 cm?1. The emission appears as a broad band with a maximum at 17500 cm?1 and is characterized by a low and nearly temperature-independent quantum yield. The ...

  8. Resonant transfer and excitation in C3++Li collisions

    International Nuclear Information System (INIS)

    Experimental resonant transfer and excitation (RTE) cross sections were measured for lithiumlike carbon ions in the energy range 5--9 MeV incident on a lithium vapor target. Transfer excitation populates the 1s2s2p23D state predominantly. Subsequent Auger decay of this state to the ground state is studied in high resolution using a 0 degree electron spectrometer. The measured single-differential cross sections at different projectile energies were compared with theoretical calculations based on the impulse-approximation formulation of RTE. The results of these experiments show that while the contribution of the target valence electron is consistent with impulse-approximation theory, no contribution to RTE by the core electrons is seen

  9. Theoretical studies of electronically excited states

    Energy Technology Data Exchange (ETDEWEB)

    Besley, Nicholas A. [School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom)

    2014-10-06

    Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.

  10. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    Energy Technology Data Exchange (ETDEWEB)

    Theophilou, Iris, E-mail: i.theophilou@fz-juelich.de [Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich (Germany); Tassi, M.; Thanos, S. [Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, ‘Demokritos’ National Center for Scientific Research, 15310 Athens (Greece)

    2014-04-28

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.

  11. Vibrational control of electron-transfer reactions: a feasibility study for the fast coherent transfer regime.

    Science.gov (United States)

    Antoniou, P; Ma, Z; Zhang, P; Beratan, D N; Skourtis, S S

    2015-11-18

    Molecular vibrations and electron-vibrational interactions are central to the control of biomolecular electron and energy-transfer rates. The vibrational control of molecular electron-transfer reactions by infrared pulses may enable the precise probing of electronic-vibrational interactions and of their roles in determining electron-transfer mechanisms. This type of electron-transfer rate control is advantageous because it does not alter the electronic state of the molecular electron-transfer system or irreversibly change its molecular structure. For bridge-mediated electron-transfer reactions, infrared (vibrational) excitation of the bridge linking the electron donor to the electron acceptor was suggested as being capable of influencing the electron-transfer rate by modulating the bridge-mediated donor-to-acceptor electronic coupling. This kind of electron-transfer experiment has been realized, demonstrating that bridge-mediated electron-transfer rates can be changed by exciting vibrational modes of the bridge. Here, we use simple models and ab initio computations to explore the physical constraints on one's ability to vibrationally perturb electron-transfer rates using infrared excitation. These constraints stem from the nature of molecular vibrational spectra, the strengths of the electron-vibrational coupling, and the interaction between molecular vibrations and infrared radiation. With these constraints in mind, we suggest parameter regimes and molecular architectures that may enhance the vibrational control of electron transfer for fast coherent electron-transfer reactions. PMID:25909507

  12. Cold transfer between deformed, Coulomb excited nuclei

    International Nuclear Information System (INIS)

    The scattering system 162Dy ? 116Sn has been examined at energies in the vicinity of the Coulomb barrier using the Heidelberg-Darmstadt Crystal Ball spectrometer combined with 5 Germanium-CLUSTER detectors. In order to study pairing correlations as a function of angular momentum cold events were selected in the 2n stripping channel by identifying and suppressing the dominant hot part of the transfer with the Crystal Ball. The CLUSTER detectors with their high ?-efficiency were used to identify the transfer channel and to resolve individual final states. Cross sections for the population of individual yrast states in a cold transfer reaction have been measured for the first time indicating the strong influence of higher transfer multipolarities. At small surface distances Coulomb-nuclear interferences were found to be responsible for the stronger decline of the population of higher yrast states in the transfer channel as compared to the Coulex channel. As a preparatory study for 2n transfer measurements between high spin yrast states in the backbending region of deformed nuclei the Coulomb excitation process in the crossing region of two bands in 162Dy has been analyzed. The gross properties of the measured population probabilities could be interpreted in a simple band mixing model. (orig.)

  13. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    R S Swathi; K L Sebastian

    2012-01-01

    Recently, we have reported theoretical studies on the rate of energy transfer from an electronically excited molecule to graphene. It was found that graphene is a very efficient quencher of the electronically excited states and that the rate -4. The process was found to be effective up to 30 which is well beyond the traditional FRET limit. In this report, we study the transfer of an amount of energy $\\hbar$ from a dye molecule to doped graphene. We find a crossover of the distance dependence of the rate from -4 to exponential as the Fermi level is increasingly shifted into the conduction band, with the crossover occurring at a shift of the Fermi level by an amount $\\hbar$ /2.

  14. Two-electron excitation of an interacting cold Rydberg gas.

    Science.gov (United States)

    Millen, J; Lochead, G; Jones, M P A

    2010-11-19

    We report the creation of an interacting cold Rydberg gas of strontium atoms. We show that the excitation spectrum of the inner valence electron is sensitive to the interactions in the Rydberg gas, even though they are mediated by the outer Rydberg electron. By studying the evolution of this spectrum we observe density-dependent population transfer to a state of higher angular momentum l. We determine the fraction of Rydberg atoms transferred, and identify the dominant transfer mechanism to be l-changing electron-Rydberg collisions associated with the formation of a cold plasma. PMID:21231300

  15. Two-electron excitation of an interacting cold Rydberg gas

    CERN Document Server

    Millen, J; Jones, M P A

    2010-01-01

    We report the creation of an interacting cold Rydberg gas of strontium atoms. We show that the excitation spectrum of the inner valence electron is sensitive to the interactions in the Rydberg gas, even though they are mediated by the outer Rydberg electron. By studying the evolution of this spectrum we observe density-dependent population transfer to a state of higher angular momentum l. We determine the fraction of Rydberg atoms transferred, and identify the dominant transfer mechanism to be l-changing electron-Rydberg collisions associated with the formation of a cold plasma.

  16. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S

    1993-01-01

    Advances in Electron Transfer Chemistry, Volume 3 presents studies that discuss findings in the various aspects of electron chemistry. The book is comprised of four chapters; each chapter reviews a work that tackles an issue in electron transfer chemistry. Chapter 1 discusses the photoinduced electron transfer in flexible biaryl donor-acceptor molecules. Chapter 2 tackles light-induced electron transfer in inorganic systems in homogeneous and heterogeneous phases. The book also covers internal geometry relaxation effects on electron transfer rates of amino-centered systems. The sequential elec

  17. Electron spectra from doubly excited charged ions

    International Nuclear Information System (INIS)

    The report describes spectroscopic investigations of ejected electrons from autoionizing state of doubly-excited He-like ions. Total angular momentum L-distributions in the double electron transfer processes have been discussed for O6+, N5+, C4+ and O4+. Those previous studies suggest that high-angular momentum states are dominantly populated by double-capture collisions of highly charged ions. In the present study, most of the ejected elections (about 80%) come from D and F states rather than S and P. If it is assumed that all of the magnetic sublevels are equally populated, differential cross sections for electron emission in the forward direction will be proportional to the total emission cross sections for the respective L-states. Under this assumption, it can be concluded that high L-states are dominantly populated in the present collision systems for C6+ + He at 67 keV and B5+ + He at 50 keV. At the current stage, however, more systematic observations, which can be expressed as a function of ejection angles, are needed because no accurate information is available on the magnetic sublevel population. (N.K.)

  18. Symmetry characterization of electrons and lattice excitations

    Directory of Open Access Journals (Sweden)

    Schober H.

    2012-03-01

    Full Text Available Symmetry concerns all aspects of a physical system from the electronic orbitals to structural and magnetic excitations. In this article we will try to elaborate the fundamental connection between symmetry and excitations. As excitations are manyfold in physical systems it is impossible to treat them exhaustively. We thus concentrate on the two topics of Bloch electrons and phonons. These two examples are complementary in the sense that Bloch electrons describe single particles in an external periodic potential while phonons exemplify a decoupled system of interacting particles. The way we develop the argument gives as by-product a short account of molecular orbitals and molecular vibrations.

  19. Electron transfer reactions of excited dyes with metal complexes. Progress report, March 1, 1978-February 28, 1979. [Iron-methylene blue

    Energy Technology Data Exchange (ETDEWEB)

    Lichtin, N.N.

    1979-03-15

    An intense absorption band of /sup 3/MBH/sup 2 +/ at 700nm was characterized in several media and its pK/sub A/ was measured to be 7.17 +- .1 in water. Flash photolysis show that semiethylene blue, MBH/sup +/, formed by quenching /sup 3/MBH/sup 2 +/ with Fe/sub II/(H/sub 2/O)/sub 6//sup 2 +/, decays by disproportionation at a diffusion-controlled rate. Rates of decay of the photostationary state of solutions of MB/sup +/ and Fe/sup II/(H/sub 2/O)/sub 6//sup 2 +/ in acidic media were measured using crossed beams to yield specific rates of oxidation of leucomethylene blue (MBH/sub 3//sup 2 +/) by MB/sup +/ (synproportionation) and by Fe(III). Laser flash-photolysis shows that quenching of MB/sup +/(S/sub 1/) by Fe(H/sub 2/O)/sub 6//sup 2 +/ can result in electron transfer to give MBH/sup +/. Profound differences between processes initiated by quenching triplet methylene blue with Fe(H/sub 2/O)/sub 6//sup 2 +/ and with stable coordination complexes of Fe(II) were found. Quenchers included (Fe/sup II/(CN)/sub 6/)/sup 4 -/, (Fe/sup II/(CN)/sub 4/(bpy)/sub 2/)/sup 2 -/, (Fe/sup II/(CN)/sub 2/(bpy))/sup 0/, and (Fe/sup II/(bpy)/sub 3/)/sup 2 +/. Measurements were made in aqueous and aqueous-alcoholic solutions at pH 2, 4.4, and 8.2. Quenching of /sup 3/MBH/sup 2 +/ or /sup 3/MB/sup +/ by a stable complex of Fe(II) is diffusion-controlled and 10/sup 2/ to 10/sup 3/ times the rate at which Fe(H/sub 2/O)/sub 6//sup 2 +/ quenches /sup 3/MBH/sup 2 +/. Net electron transfer accounts for less than 1/3 of total quenching by complexed Fe(II). In contrast, quenching by Fe(H/sub 2/O)/sub 6//sup 2 +/ goes essentially entirely with net electron transfer. It is concluded that quenching of triplet methylene blue by complexes proceeds via electron transfer which is reversible in the encounter complex. The MBH/sup +/ which results from net electron transfer from complexes of Fe(II) decays essentially entirely to MB/sup +/ via oxidation by complexed Fe(III); no disproportionation has been observed.

  20. Electron transfer reactions of excited dyes with metal complexes. Progress report, May 1, 1976--January 31, 1977. [Fe(III)--thionine reaction

    Energy Technology Data Exchange (ETDEWEB)

    Lichtin, N.N.

    1977-02-01

    A study was initiated of the factors which determine quantum efficiency of transfer of reducing equivalents between excited dye molecules and metal complexes in their ground state and composition and dynamics of formation and decay of related photostationary states. A ruby laser capable of delivering a 3.6 J, 19 nsec flash was acquired and assembly of an apparatus for laser flash photolysis begun. At the same time, conventional flash photolysis was used to pursue investigation of the dependence upon solvent, anions, pH, and ionic strength of the kinetics of the spontaneous dark reaction of Fe(H/sub 2/O)/sup 3 +//sub 6/ with leucothionine and with semithionine, reactions which contribute to the composition and dynamics of formation and decay of the photostationary state of the iron-thionine photoredox reaction. Results are consistent with formation of an intermediate complex between leucothionine and Fe(III), K/sub A/ = 380 M/sup -1/ and k(elec. transfer) = 0.88 s/sup -1/ at approximately 22/sup 0/ in water solution at pH2, with sulfate as anion and ..mu.. = .05 - .1 M. Under similar conditions in 50 v/v percent aqueous CH/sub 3/CN, K/sub A/ = 780 M/sup -1/, k(elec. transfer) = 0.55 s/sup -1/. In both solvents, sulfate produces a large positive salt effect. Intermediacy of a complex was not established for the faster reaction of Fe(III) with semithionine under similar conditions: K/sub A/ . k(elec. transfer) approximately 3.5 x 10/sup 5/ M/sup -1/s/sup -1/ in H/sub 2/O, approximately 1.0 x 10/sup 4/ in 50 v/v percent aqueous CH/sub 3/CN.

  1. Excitation transfer, charge transfer and hydrogen abstraction reaction, kinetics studies of modification of DNA components

    International Nuclear Information System (INIS)

    Laser induced acetone-sensitized excitation of DNA components offered, for the first time, T-T absorption spectra and direct triplet states kinetics of cytosine, cytidine, and dCMP, adenine, adenosine and dAMP and guanosine. Mechanisms and kinetics of electron transfer reactions between triplet acetone and purine bases and triplet thymine and electroaffinic modifiers have been elucidated. Rapid electron transfer from hydroxycinnamic acid derivatives to oxidizing OH adducts of pyrimidines have been performed. Fast reduction and repair of oxidizing damage of pyrimidines have been achieved accordingly. (author)

  2. Resonant electron transfer between quantum dots

    OpenAIRE

    Openov, Leonid A.

    1999-01-01

    An interaction of electromagnetic field with a nanostructure composed of two quantum dots is studied theoretically. An effect of a resonant electron transfer between the localized low-lying states of quantum dots is predicted. A necessary condition for such an effect is the existence of an excited bound state whose energy lies close to the top of the barrier separating the quantum dots. This effect may be used to realize the reversible quantum logic gate NOT if the superposition of electron s...

  3. Electron-impact excitation of silver

    Science.gov (United States)

    Toši?, S. D.; Pej?ev, V.; Ševi?, D.; McEachran, R. P.; Stauffer, A. D.; Marinkovi?, B. P.

    2015-05-01

    We measure the differential cross sections (DCSs) for the electron-impact excitation of the combined (two fine-structure levels) resonant 4 d105 p P 1 /2 ,3 /2 2 and 4 d95 s2D 5 /2 2 states in silver from the 4 d105 s S 1 /2 2 ground state. A comparison with the predictions of the relativistic distorted-wave (RDW) approximation model is carried out. Relativistic distorted-wave calculations are performed for each level separately and are combined to compare with the measurements. Both the experimental and theoretical results are obtained at incident electron energies E0 of 10, 20, 40, 60, 80, and 100 eV and scattering angles ? from 10° up to 150° (experiment) and from 0° to 180° (calculations). Absolute values for the experimental DCSs are obtained by normalizing relative DCSs to theoretical RDW results at 40° at all energies except at 10 eV, where we performed the normalization of the relative DCSs at 10° to our previous small-angle experimental DCS values [S. D. Toši? et al., Nucl. Instrum. Methods Phys. Res. Sect. B 279, 53 (2012), 10.1016/j.nimb.2011.10.066]. The integrated cross sections, which include integral QI, momentum transfer QM, and viscosity QV cross sections, are determined by numerical integration of the absolute DCSs.

  4. Neutron scattering investigation of magnetic excitations at high energy transfers

    International Nuclear Information System (INIS)

    With the advance of pulsed spallation neutron sources, neutron scattering investigation of elementary excitations in magnetic materials can now be extended to energies up to several hundreds of MeV. We have measured, using chopper spectrometers and time-of-flight techniques, the magnetic response functions of a series of d and f transition metals and compounds over a wide range of energy and momentum transfer. In PrO2, UO2, BaPrO3 and CeB6 we observed crystal-field transitions between the magnetic ground state and the excited levels in the energy range from 40 to 260 MeV. In materials exhibiting spin-fluctuation or mixed-valent character such as Ce 74Th 26, on the other hand, no sharp crystal-field lines but a broadened quasielastic magnetic peak was observed. The line width of the quasielastic component is thought to be connected to the spin-fluctuation energy of the 4f electrons. The significance of the neutron scattering results in relation to the ground state level structure of the magnetic ions and the spin-dynamics of the f electrons is discussed. Recently, in a study of the spin-wave excitations in itinerant magnetic systems, we have extended the spin-wave measurements in ferromagnetic iron up to about 160 MeV. Neutron scattering data at high energy transfers are of particular interest because they provide direct comparison with recent theories of itinerant magnetism. 26 references, 7 figures

  5. Polarization in nuclear excitation by electron impact

    Science.gov (United States)

    Jakubassa-Amundsen, D. H.

    2015-05-01

    Electron-electron polarization correlations from nuclear excitation by spin-polarized electrons are studied within the distorted-wave Born approximation. Restriction is made to spin-0 and to unpolarized spin-1/2 nuclei. When Coulomb scattering is dominant the resulting spin asymmetries may exceed those from elastic scattering. However, at the backmost scattering angles or for large transition current densities where magnetic scattering prevails, there is a strong suppression of the transverse polarization correlations. Predictions are made for the excitation of the lowest 3- and 5- states of 208Pb and the lowest 5/2- state of 89Y by 60-220 MeV electrons.

  6. Ultrafast electronic relaxation of excited state vitamin B{sub 12} in the gas phase

    Energy Technology Data Exchange (ETDEWEB)

    Shafizadeh, Niloufar [Laboratoire de Photophysique Moleculaire, U.P.R. 3361 CNRS Bat 210, Universite de Paris-Sud, 91405 Orsay, Cedex (France)], E-mail: Niloufar.Shafizadeh@u-psud.fr; Poisson, Lionel; Soep, Benoit [Laboratoire Francis Perrin, CEA/DSM/DRECAM/SPAM - CNRS URA 2453, CEA Saclay, 91191 Gif-sur-Yvette Cedex (France)

    2008-06-23

    The time evolution of electronically excited vitamin B{sub 12} (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  7. Ultrafast electronic relaxation of excited state vitamin B12 in the gas phase

    International Nuclear Information System (INIS)

    The time evolution of electronically excited vitamin B12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states

  8. Theory of laser-induced excitation transfer and atomic association

    International Nuclear Information System (INIS)

    Formulas are derived for the differential and integral cross sections associated with laser-induced excitation transfer. The theory is patterned closely after our recent treatment of laser-induced chemi-ionization. It is found that cross sections specific to single-photon absorption are proportional to the square of the cosine of the angle between the laser polarization and the initial relative velocity of the two colliding atoms. The distortion by a laser of the cross section for an elastic scattering event also is treated. Finally, a cross-section formula is derived for a collision-induced two-photon absorption, mediated by a single intermediate electronic state

  9. Enhanced negative ion formation via electron attachment to electronically-excited states

    International Nuclear Information System (INIS)

    Recent basic studies on electron attachment to laser-excited molecules show that electron attachment to electronically-excited states can have orders of magnitude larger cross sections compared to the respective ground electronic states. Even though systematic studies have not been conducted, there are indications that electronically-excited states may play a significant role in negative ion formation in gas discharges. The high-lying Rydberg states could be of particular significance since, (i) their production efficiencies are high, and (ii) they have comparatively long lifetimes. Such states could be populated in discharge sources via direct electron impact or via excitation transfer from metastable states of inert gases. copyright 1996 American Institute of Physics

  10. Electron-beam-excited gas laser research

    International Nuclear Information System (INIS)

    Net energy gain in laser fusion places requirements on the laser that are not realized by any existing laser. Utilization of relativistic electron beams (REB's), a relatively new source for the excitation of gas laser media, may lead to new lasers that could satisfy these requirements. Already REB's have been utilized to excite gas laser media and produce gas lasers that have not been produced as successfully any other way. Electron-beam-excitation has produced electronic-transition dimer lasers that have not yet been produced by any other excitation scheme (for example, Xe2/ sup *(1)/, Kr:O(21S)/sup 2/, KrF/sup *(3)/). In addition, REB's have initiated chemical reactions to produce HF laser radiation with unique and promising results. Relativistic-electron-beam gas-laser research is continuing to lead to new lasers with unique properties. Results of work carried out at Sandia Laboratories in this pioneering effort of electron-beam-excited-gas lasers are reviewed. (U.S.)

  11. Electron impact excitation of helium atoms

    International Nuclear Information System (INIS)

    Two experiments have been conducted in an apparatus which was designed and constructed to study interactions between electrons and atoms. (1) The polarisation fraction of the ultra violet radiation emitted following electron impact excitation of the n1P states of helium atoms has been deduced from measurements of the angular distribution of the photons for incident electron energies from 40eV to 300eV. (2) Angular correlations between the scattered electrons resulting from the excitation of the 21P state of helium and the photons emitted in the decay of this state have been measured using the delayed coincidence technique for an incident energy of 81.2eV. The measurements extend over the electron scattering angles from 10 deg to 130 deg. (author)

  12. Electronic excitation of Na atom by electron impact

    International Nuclear Information System (INIS)

    Electronic excitation of the 3s-3p transition in the Na atom was studied by intermediate energy electron impact spectroscopy. Differential Cross Sections (DCS) and Generalized Oscillator Strenghts (GOS) were determined experimentally for 1 KeV electrons. Theoretical results within the First Born Approximation as well as Glauber theory, were also performed. (A.C.A.S.)

  13. E-T and near-resonant E-V energy transfer in the quenching of the 1.0 and 2.3 ?m electronically excited states of PuF6 by H2 and D2

    International Nuclear Information System (INIS)

    The quenching and energy transfer of electronically excited PuF6 by H2 and D2 have been measured using laser-induced fluorescence (LIF) from both the 1.0 and 2.3 ?m emitting states of PuF6. Linear Stern--Volmer plots of the single exponential decay data give quenching rate constants (all in units of cm3 molecule-1 s-1) for D2 of (3.7 +- 1.7) x 10-15 and (8.7 +- 0.3) x 10-16 for the 1.0 and and 2.3 ?m states, respectively, and a H2 quenching rate constant of (4.8 +- 0.3) x 10-14 for the 1 ?m LIF. The 2.3 ?m LIF in H2 is not a single exponential decay but a rapid decay followed by an anomalously long tail, which implies almost resonant Earrow-right-leftV energy transfer and storage. Kinetic modeling yields the following new rate constants: m PuF6*+H2?PuF6+H/sup not-equal/2, k = (2.05 +- 0.30) x 10-14; P H2/sup not-equal/+PuF6?H2+PuF6*, k = (3.1 +- 0.5) x 10-14; H PuF6*+H2?PuF6+H2, k = (3.1 +- 2.0) x 10-15; P H2/sup not-equal/+PuF6?H2+PuF6, k = (3.1 +- 3.0) x 10-15; H where PuF6* is the 2.3 ?m emitting electronically excited state of PuF6 and H2/sup not-equal/ is vibrationally excited H2 in the v = 1 state

  14. Electron-impact vibrational excitation of cyclopropane.

    Science.gov (United States)

    ?urík, R; ?ársky, P; Allan, M

    2015-04-14

    We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10° to 180° and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by solving the two-channel Lippmann-Schwinger equation in the momentum space, and the interaction between the scattered electron and the target molecule was described by exact static-exchange potential corrected by a density functional theory (DFT) correlation-polarization interaction that models target's response to the field of incoming electron. The theory is found to quantitatively reproduce the measured spectra for all normal modes, even at the difficult conditions of extreme angles and at low energies, and thus provides full understanding of the excitation mechanism. It is shown that the overlap of individual vibrational bands caused by limited experimental resolution and rotational excitation must be properly taken into account for correct comparison of experiment and theory. By doing so, an apparent discrepancy between published experimental data could be reconciled. A substantial cross section is found for excitation of the non-symmetric HCH twisting mode ?4 of A1 (?) symmetry by the 5.5 eV A2 (') resonance, surprisingly because the currently accepted selection rules predict this process to be forbidden. The DMR theory shows that the excitation is caused by an incoming electron in an f-wave of A2 (') symmetry which causes excitation of the non-symmetric HCH twisting mode ?4 of the A1 (?) symmetry and departs in p- and f-waves of A2 (?) symmetry. PMID:25877583

  15. Electron-impact vibrational excitation of cyclopropane

    Science.gov (United States)

    ?urík, R.; ?ársky, P.; Allan, M.

    2015-04-01

    We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10? to 180? and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by solving the two-channel Lippmann-Schwinger equation in the momentum space, and the interaction between the scattered electron and the target molecule was described by exact static-exchange potential corrected by a density functional theory (DFT) correlation-polarization interaction that models target's response to the field of incoming electron. The theory is found to quantitatively reproduce the measured spectra for all normal modes, even at the difficult conditions of extreme angles and at low energies, and thus provides full understanding of the excitation mechanism. It is shown that the overlap of individual vibrational bands caused by limited experimental resolution and rotational excitation must be properly taken into account for correct comparison of experiment and theory. By doing so, an apparent discrepancy between published experimental data could be reconciled. A substantial cross section is found for excitation of the non-symmetric HCH twisting mode ?4 of A1 ? symmetry by the 5.5 eV A2 ' resonance, surprisingly because the currently accepted selection rules predict this process to be forbidden. The DMR theory shows that the excitation is caused by an incoming electron in an f-wave of A2 ' symmetry which causes excitation of the non-symmetric HCH twisting mode ?4 of the A1 ? symmetry and departs in p- and f-waves of A2 ? symmetry.

  16. Medium effects in photoinduced electron transfer reactions

    International Nuclear Information System (INIS)

    The transfer of an electron between two molecules is a fundamental chemical process of great significance in biochemistry as well as in general chemistry. Electron transfer reactions can be induced by the absorption of light - as in photosynthesis - so that one of the molecules reacts through an electronically excited state; a net storage of chemical energy may then take place. When electron transfer involves molecules in condensed phase, the role of the liquid or solid medium must be considered. In the first place, a polar solvent may promote electron transfer through the stabilization of ion pairs and the separation of ions; but if the polar solvent must reorganize prior to the reaction, then an activation barrier will exist against electron transfer in polar solvents. This article gives a citical review of this field, with some novel ideas concerning the role of the medium (liquid solvent or solid matrix) in the overall energy balance of electron transfer, in the kinetics of the reaction, and in the further process of charge separation. It is suggested in particular that no dielectric screening by a polar solvent can exist when ions are formed in direct contact; and that the extensive reorganization of the solvent prior to electron transfer is so unlikely as to be discounted. In these respects the model presented in this article diverges from the commonly accepted model of Weller and of Marcus and Hush. In the Conclusion section some areas of particular importance for further research in this field are outlined. (author) 28 refs., 20 figs., 2 tabs

  17. High resolution studies of electron capture and excitation by 00 projectile electron spectroscopy

    International Nuclear Information System (INIS)

    A tandem 450 parallel-plate spectrometer has been developed for high resolution electron studies of atomic collision processes using the method of 00 electron spectroscopy. High resolution projectile K-Auger electron spectra have been obtained in a state-selective study of transfer-excitation (TE) and single excitation in collisions of 4.5-33 MeV F6+ with He and H2 targets. A high resolution measurement of 9.5 MeV F7+ with He yielded preliminary information on state-selective capture to the metastable F7+ (1s2s) state. Future plans include studies of Fq+ + T (q: 6-9; T: H2, He, Ne) to determine absolute state-selective cross sections for transfer-excitation, single and double electron capture. (orig.)

  18. Coherence in electron-impact excitation of helium

    International Nuclear Information System (INIS)

    This thesis describes an experimental study into the electron-impact excitation to the 33P, 31D and 33D states of Helium. The scattered electron and the photon, emitted by the excited atom, are measured in coincidence. The parameters, which can be varied, are the scattering angle and the kinetic energy of the projectile. Two parameters, which are used to characterize the excited state, are the angular momentum transferred to the atom, L perpendicular, and the alignment angle ?. It is shown that results of measurements on 31D excitation with photon detection perpendicular to the scattering plane do not agree in the small scattering angle region with any of the model calculations currently available. Remarkable is the sign of L perpendicular, which appears to start of negatively at 60 eV. It is shown that for 33P excitation the predicted large value of ? is indeed found experimentally. This supports the suggestion that exchange scattering is underestimated in model calculations for 1P excitation. Another result is that for 1P and 3P excitation the behaviour of L perpendicular as a function of the scattering angle can be related at different impact energies with the help of a partial wave expansion. A scaling relation can be formulated for the behaviour of L perpendicular. The influence of a negative ion resonance to excitation of the 33D state is investigated. Both in coincidence and non-coincidence measurements the presence of the resonance yields information on both the direct and indirect excitation of the 33D state. It is shown that the coincident measurement gives an unique opportunity to determine the excited 33D state completely. Results of measurements with photon detection in the scattering plane are given. They supplement previous 31D and 33D results and allow physical parameters, such as L perpendicular and ?, to be obtained. (H.W.). 132 refs.; 20 figs.; 18 tabs

  19. Computer simulation of cluster impact induced electronic excitation of solids

    Energy Technology Data Exchange (ETDEWEB)

    Weidtmann, B.; Hanke, S.; Duvenbeck, A. [Fakultät für Physik, Universität Duisburg-Essen, 47048 Duisburg (Germany); Wucher, A., E-mail: andreas.wucher@uni-deu.de [Fakultät für Physik, Universität Duisburg-Essen, 47048 Duisburg (Germany)

    2013-05-15

    We present a computational study of electronic excitation upon bombardment of a metal surface with cluster projectiles. Our model employs a molecular dynamics (MD) simulation to calculate the particle dynamics following the projectile impact. Kinetic excitation is implemented via two mechanisms describing the electronic energy loss of moving particles: autoionization in close binary collisions and a velocity proportional friction force resulting from direct atom–electron collisions. Two different friction models are compared with respect to the predicted sputter yields after single atom and cluster bombardment. We find that a density dependent friction coefficient leads to a significant reduction of the total energy transferred to the electronic sub-system as compared to the Lindhard friction model, thereby strongly enhancing the predicted sputter yield under cluster bombardment conditions. In contrast, the yield predicted for monoatomic projectile bombardment remains practically unchanged.

  20. Excitations and benchmark ensemble density functional theory for two electrons

    Energy Technology Data Exchange (ETDEWEB)

    Pribram-Jones, Aurora; Burke, Kieron [Department of Chemistry, University of California-Irvine, Irvine, California 92697 (United States); Yang, Zeng-hui; Ullrich, Carsten A. [Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211 (United States); Trail, John R.; Needs, Richard J. [Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE (United Kingdom)

    2014-05-14

    A new method for extracting ensemble Kohn-Sham potentials from accurate excited state densities is applied to a variety of two-electron systems, exploring the behavior of exact ensemble density functional theory. The issue of separating the Hartree energy and the choice of degenerate eigenstates is explored. A new approximation, spin eigenstate Hartree-exchange, is derived. Exact conditions that are proven include the signs of the correlation energy components and the asymptotic behavior of the potential for small weights of the excited states. Many energy components are given as a function of the weights for two electrons in a one-dimensional flat box, in a box with a large barrier to create charge transfer excitations, in a three-dimensional harmonic well (Hooke's atom), and for the He atom singlet-triplet ensemble, singlet-triplet-singlet ensemble, and triplet bi-ensemble.

  1. Excitations and benchmark ensemble density functional theory for two electrons

    International Nuclear Information System (INIS)

    A new method for extracting ensemble Kohn-Sham potentials from accurate excited state densities is applied to a variety of two-electron systems, exploring the behavior of exact ensemble density functional theory. The issue of separating the Hartree energy and the choice of degenerate eigenstates is explored. A new approximation, spin eigenstate Hartree-exchange, is derived. Exact conditions that are proven include the signs of the correlation energy components and the asymptotic behavior of the potential for small weights of the excited states. Many energy components are given as a function of the weights for two electrons in a one-dimensional flat box, in a box with a large barrier to create charge transfer excitations, in a three-dimensional harmonic well (Hooke's atom), and for the He atom singlet-triplet ensemble, singlet-triplet-singlet ensemble, and triplet bi-ensemble

  2. Excitations and benchmark ensemble density functional theory for two electrons

    CERN Document Server

    Pribram-Jones, Aurora; Trail, John R; Burke, Kieron; Needs, Richard J; Ullrich, Carsten A

    2014-01-01

    A new method for extracting ensemble Kohn-Sham potentials from accurate excited state densities is applied to a variety of two electron systems, exploring the behavior of exact ensemble density functional theory. The issue of separating the Hartree energy and the choice of degenerate eigenstates is explored. A new approximation, spin eigenstate Hartree-exchange (SEHX), is derived. Exact conditions that are proven include the signs of the correlation energy components, the virial theorem for both exchange and correlation, and the asymptotic behavior of the potential for small weights of the excited states. Many energy components are given as a function of the weights for two electrons in a one-dimensional flat box, in a box with a large barrier to create charge transfer excitations, in a three-dimensional harmonic well (Hooke's atom), and for the He atom singlet-triplet ensemble, singlet-triplet-singlet ensemble, and triplet bi-ensemble.

  3. Neutral excitations in quasi-1D strongly correlated electron systems

    International Nuclear Information System (INIS)

    Novel neutral spin-0 excitation for quasi-1D systems with one electron per site are obtained within a localized scheme. Our ground state wave-function is defined by a variational localized - site cluster - expanded ansatz and these excitations are naturally built upon it. All computations are easily carried out by a transfer matrix technique that enables explicit inclusion of electron - correlation effects and, at the same time, provides a quasi - particle band - theoretic picture of these excitations. This treatment is applied, in particular, to a polyphene strip. At k=0 the energy gap corresponds to a dipole-allowed transition in the visible region, our result compares fairly well with observed decreasing transitions for finite polyphene strips. (author). 14 refs, 1 fig

  4. Femtosecond Timescale Evolution of Pyrrole Electronic Excitation

    Science.gov (United States)

    Montero, Raul; Conde, Alvaro Peralta; Ovejas, Virginia; Castano, Fernando; Longarte, Asier

    2012-06-01

    Pyrrole is a simple aromatic molecule with relevantchromophoric properties in biology. Although its apparent simplicity, it shows a complicated dynamics after excitation in the near part of the UV absorption spectrum, which results from the interplay between the bright ??^* and the dark dissociative ??^* electronic transitions. Herein, we present a time resolved study with ultrafast resolution on the relaxation dynamics of isolated pyrrole, after excitation in the 265-217 nm range. Two lifetimes of 19 and 15 fs, which are associated with the internal conversion from the bright 1B2 ??^* state and the propagation of the wavepacket on the ??^* state, respectively, are found in the studied energy interval. The work also explores the consequences of non resonant adiabatic excitation of the system when broadband femtosecond pulses are employed to prepare the molecule in the targeted electronic states, revealing the key implication of this type of coherent phenomena. The collected data reveal that the bright 1B2 ??^* state is adiabatically populated at excitation wavelengths far away from resonance, providing an efficient way to reach the ??^* state. The recorded transients are fit employing a coherent model that provides a comprehensive view of the dynamical processes pyrrole undergoes after excitation by ultrashort light pulses. M. N. R. Ashfold, B. Cronin, A. L. Devine, R. N. Dixon and M. G. D. Nix Science, 312, 1637-1640, 2006.

  5. Electron-impact excitation of Ar2+

    Science.gov (United States)

    Munoz Burgos, J. M.; Loch, S. D.; Ballance, C. P.; Boivin, R. F.

    2009-06-01

    Context: Emission from Ar III is seen in planetary nebulae, in H II regions, and from laboratory plasmas. The analysis of such spectra requires accurate electron impact excitation data. Aims: The aim of this work is to improve the electron impact excitation data available for Ar2+, for application in studies of planetary nebulae and laboratory plasma spectra. The effects of the new data on diagnostic line ratios are also studied. Methods: Electron-impact excitation collision strengths have been calculated using the R-Matrix Intermediate-Coupling Frame-Transformation method and the R-Matrix Breit-Pauli method. Excitation cross sections are calculated between all levels of the configurations 3s^23p^4, 3s3p^5, 3p^6, 3p^53d, and 3s^23p^3nl (3d ≤ nl ≤ 5s). Maxwellian effective collision strengths are generated from the collision strength data. Results: Good agreement is found in the collision strengths calculated using the two R-Matrix methods. The collision strengths are compared with literature values for transitions within the 3s^23p4 configuration. The new data has a small effect on Te values obtained from the I(λ7135 Å+ λ7751 Å)/ I(λ5192 Å) line ratio, and a larger effect on the Ne values obtained from the I(λ7135 Å)/I(λ9 μm) line ratio. The final effective collision strength data is archived online.

  6. How Geometric Distortions Scatter Electronic Excitations in Conjugated Macromolecules.

    Science.gov (United States)

    Shi, Tian; Li, Hao; Tretiak, Sergei; Chernyak, Vladimir Y

    2014-11-20

    Effects of disorder and exciton-phonon interactions are the major factors controlling photoinduced dynamics and energy-transfer processes in conjugated organic semiconductors, thus defining their electronic functionality. All-atom quantum-chemical simulations are potentially capable of describing such phenomena in complex "soft" organic structures, yet they are frequently computationally restrictive. Here we efficiently characterize how electronic excitations in branched conjugated molecules interact with molecular distortions using the exciton scattering (ES) approach as a fundamental principle combined with effective tight-binding models. Molecule geometry deformations are incorporated to the ES view of electronic excitations by identifying the dependence of the Frenkel-type exciton Hamiltonian parameters on the characteristic geometry parameters. We illustrate our methodology using two examples of intermolecular distortions, bond length alternation and single bond rotation, which constitute vibrational degrees of freedom strongly coupled to the electronic system in a variety of conjugated systems. The effect on excited-state electronic structures has been attributed to localized variation of exciton on-site energies and couplings. As a result, modifications of the entire electronic spectra due to geometric distortions can be efficiently and accurately accounted for with negligible numerical cost. The presented approach can be potentially extended to model electronic structures and photoinduced processes in bulk amorphous polymer materials. PMID:26276475

  7. Electronic excitation of methane molecule by electron impact

    International Nuclear Information System (INIS)

    In this work, it is presented elastic and inelastic differential cross sections for the electronic excitation of the Triplet (3T2) of CH4 molecule calculated for electron incident energies of 20 and 30 eV. It is employed the Schwinger multichannel method and these results are compared to the ones available in the literature. (A.C.A.S.)

  8. Electron plasma behavior during autoresonant dioctron excitation

    Science.gov (United States)

    Baker, C. J.; Danielson, J. R.; Hurst, N. C.; Surko, C. M.

    2014-10-01

    A novel multicell Penning-Malmberg trap is currently being studied as a way to trap and store up to 1012 positrons using kV confinement potentials. A test structure has been constructed to conduct preliminary experiments. It consists of a large diameter ``master'' cell and four smaller diameter ``storage'' cells, three of which are off-axis. To load the multicell trap, plasma in the master cell is moved off-axis to radial displacements D >>rp , where rp is the plasma radius, before being transferred axially into off-axis storage cells. Details of the radial transfer process, which relies upon the autoresonant excitation of the dioctron mode, will be discussed, as well as the plasma behavior during the axial transfer process. This work was supported by the U.S. DTRA.

  9. Electron spectroscopy of collisional excited atoms

    International Nuclear Information System (INIS)

    In this thesis measurements are described in which coincidences are detected between scattered projectiles and emitted electrons. This yields information on two-electron excitation processes. In order to show what can be learnt from coincidence experiments a detailed theoretical analysis is given. The transition amplitudes, which contain all the information, are introduced (ch.2). In ch.3 the experimental set-up is shown. The results for the Li+-He system are shown in ch. 7 and are compared with predictions based on the Molecular-Orbitalmodel which however does not account for two-excitation mechanisms. With the transition amplitudes also the wave function of the excited atom has been completely determined. In ch.8 the shape of the electron cloud, induced by the collision, is derived from the amplitudes. The relation between the oscillatory motion of this cloud after the collision and the correlation between the two electrons of the excited atom is discussed. In ch. 6 it is shown that the broad structures in the non-coincident energy spectra of the Li+-He system are erroneously interpretated as a result of electron emission from the (Li-He)+-quasimolecule. A model is presented which explains, based on the results obtained from the coincidence measurements, these broad structures. In ch. 4 the Post-Collision Interaction process is treated. It is shown that for high-energy collisions, in contrast with general assumptions, PCI is important. In ch. 5 the importance of PCI-processes in photoionization of atoms, followed by Auger decay, are studied. From the formulas derived in ch. 4 simple analytical results are obtained. These are applied to recent experiments and good agreement is achieved. 140 refs.; 55 figs.; 9 tabs

  10. Concepts of Highly Excited Electronic Systems

    Science.gov (United States)

    Berakdar, Jamal

    2003-05-01

    Knowledge of the excitation characteristics of matter is decisive for the descriptions of a variety of dynamical processes, which are of significant technological interest. E.g. transport properties and the optical response are controlled by the excitation spectrum. This self-contained work is a coherent presentation of the quantum theory of correlated few-particle excitations in electronic systems. It begins with a compact resume of the quantum mechanics of single particle excitations. Particular emphasis is put on Green function methods, which offer a natural tool to unravel the relations between the physics of small and large electronic systems. The book contains explicit expressions for the Coulomb Green function of two charge particles and a generalization to three-body systems. Techniques for the many-body Green function of finite systems are introduced and some explicit calculations of the Green functions are given. Concrete examples are provided and the theories are contrasted with experimental data, when available. The second volume presents an up-to-date selection of applications of the developed concepts and a comparison with available experiments is made

  11. Photoinduced energy and electron transfer in rubrene-benzoquinone and rubrene-porphyrin systems

    KAUST Repository

    Khan, Jafar Iqbal

    2014-11-01

    Excited-state electron and energy transfer from singlet excited rubrene (Ru) to benzoquinone (BQ) and tetra-(4-aminophenyl) porphyrin (TAPP) were investigated by steady-state absorption and emission, time-resolved transient absorption, and femtosecond (fs)-nanosecond (ns) fluorescence spectroscopy. The low reduction potential of BQ provides the high probability of electron transfer from the excited Ru to BQ. Steady-state and time-resolved results confirm such an excited electron transfer scenario. On the other hand, strong spectral overlap between the emission of Ru and absorption of TAPP suggests that energy transfer is a possible deactivation pathway of the Ru excited state.

  12. Computer simulation of electronic excitations in beryllium

    OpenAIRE

    A.V. Popov

    2016-01-01

    An effective method for the quantitative description of the electronic excited states of polyatomic systems is developed by using computer technology. The proposed method allows calculating various properties of matter at the atomic level within the uniform scheme. A special attention is paid to the description of beryllium atoms interactions with the external fields, comparable by power to the fields in atoms, molecules and clusters.

  13. Electron impact excitation of SF6

    Science.gov (United States)

    Trajmar, S.; Chutjian, A.

    1977-01-01

    A study of the electron impact energy-loss spectrum of SF6 under both optical (low scattering angle, high impact energy) and non-optical conditions (high scattering angle, low impact energy) has revealed a number of electronic excitation processes. With the help of theoretical calculations, several of these transitions have been assigned and approximate cross sections associated with four features have been determined. In addition, a strong resonance at 12 eV has been observed in both elastic and vibrationally inelastic (delta E = 0.092 eV) channels.

  14. Electron-impact vibrational excitation of furan

    Energy Technology Data Exchange (ETDEWEB)

    Hargreaves, L. R.; Albaridy, R.; Serna, G.; Khakoo, M. A. [Department of Physics, California State University, Fullerton, California 92834 (United States); Lopes, M. C. A. [Departamento de Fisica, ICE, Universidade Federal de Juiz de Fora, Juiz de Fora-MG, CEP 36036-330 (Brazil)

    2011-12-15

    We report measurements of differential cross sections for the vibrational excitation of furan (C{sub 4}H{sub 4}O), obtaining results for nine features spanning the electron energy loss range from 0 to 0.8 eV, at electron-impact energies of 5, 6, 7.5, 10, and 15 eV and for scattering angles ranging from 10{sup o} to 130{sup o}. The normalization of the differential cross sections was done using elastic differential cross sections for furan determined earlier by our group [Khakoo et al., Phys. Rev A 81, 062716 (2010)].

  15. Collapse of an orbit of excited electron

    International Nuclear Information System (INIS)

    The phenomenon of quantum orbit collapse of excited electron in free atoms is considered. Theoretical results on d and f-electron collapse are systematized, main attention being given to configurations of the nlsup(4l+1)n'l+1 type. Collapse regularities in the isoelectronic series are studied. The influence of the potential barrier change on the wave function collapse in the isoelectronic series is discussed. Theoretical calculations carried out in the framework of the Hatree-Fock method correctly predict the collapse role in the periodic system

  16. Tautomeric selectivity of the excited-state lifetime of guanine/cytosine base pairs: The role of electron-driven proton-transfer processes

    OpenAIRE

    Sobolewski, Andrzej L.; Domcke, Wolfgang; Hättig, C.

    2005-01-01

    The UV spectra of three different conformers of the guanine/cytosine base pair were recorded recently with UV-IR double-resonance techniques in a supersonic jet [Abo-Riziq, A., Grace, L., Nir, E., Kabelac, M., Hobza, P. & de Vries, M. S. (2005) Proc. Natl. Acad. Sci. USA 102, 20–23]. The spectra provide evidence for a very efficient excited-state deactivation mechanism that is specific for the Watson–Crick structure and may be essential for the photostability of DNA. Here we report results of...

  17. Excitation of thalium by 20 eV electrons

    International Nuclear Information System (INIS)

    Elastic and inelastic scattering of 20 eV electrons by Thallium atoms were studied. Differential, integral and momentum transfer cross sections were determined for elastic scattering and for the excitation of the 6p 2P sub(3/2), 7s 2S sub(1/2), 7p 2P sub(1/2), 7p 2P sub(3/2) and 6d 2D sub(5/2,3/2) states. In the first ionization continuum a large number of autoionization features were observed and cross section for the intermediate electron shell excitation 6s6p22P sub(1/2,3/2) has also been obtained. (Author)

  18. An excitable electronic circuit as a sensory neuron model

    CERN Document Server

    Medeiros, Bruno N S; Mindlin, Gabriel B; Copelli, Mauro; Leite, José R Rios

    2011-01-01

    An electronic circuit device, inspired on the FitzHugh-Nagumo model of neuronal excitability, was constructed and shown to operate with characteristics compatible with those of biological sensory neurons. The nonlinear dynamical model of the electronics quantitatively reproduces the experimental observations on the circuit, including the Hopf bifurcation at the onset of tonic spiking. Moreover, we have implemented an analog noise generator as a source to study the variability of the spike trains. When the circuit is in the excitable regime, coherence resonance is observed. At sufficiently low noise intensity the spike trains have Poisson statistics, as in many biological neurons. The transfer function of the stochastic spike trains has a dynamic range of 6 dB, close to experimental values for real olfactory receptor neurons.

  19. Combustion enhancement through electronically excited oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Zaehringer, K.; Thevenin, D. [Otto-von-Guericke-Universitaet, Magdeburg (Germany). Lehrstuhl fuer Stroemungsmechanik und Stroemungstechnik; Bourig, A.; Martin, J.P. [ICARE, CNRS, Orleans (France)

    2009-07-01

    The promoting action of electrical discharges on combustion processes results in the reduction of the ignition delay, improvement of flame stability as well as extension of the flammability limits. These features are key technical issues for combustion improvement. One particularly promising approach consists of plasma-enhanced activation of the oxidizing substance, such as when transforming molecular oxygen into its electronically excited singlet delta O{sub 2}(a{sup 1}{delta}{sub g}) and singlet sigma O{sub 2}(b{sup 1}{sigma}{sub g}{sup +}) states. In contrast with non-excited reactants, singlet oxygen molecules display a higher chemical activity and can affect reaction kinetics due to a decrease of the energy barrier associated with endo-energetic reactions, as demonstrated theoretically and numerically [1]. The aim of the present study is to understand experimentally why and how combustion processes are modified in the presence of electronically-excited oxygen molecules, using spontaneous emission of typical flame front marker molecules. (orig.)

  20. Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection

    International Nuclear Information System (INIS)

    Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH3-F2 and on the potential energy curves of NH3 near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces

  1. Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shaohong L.; Truhlar, Donald G., E-mail: truhlar@umn.edu [Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2014-09-14

    Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH{sub 3}-F{sub 2} and on the potential energy curves of NH{sub 3} near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.

  2. Plasmonic coupling and long-range transfer of an excitation along a DNA nanowire.

    Science.gov (United States)

    Toppari, J Jussi; Wirth, Janina; Garwe, Frank; Stranik, Ondrej; Csaki, Andrea; Bergmann, Joachim; Paa, Wolfgang; Fritzsche, Wolfgang

    2013-02-26

    We demonstrate an excitation transfer along a fluorescently labeled dsDNA nanowire over a length of several micrometers. Launching of the excitation is done by exciting a localized surface plasmon mode of a 40 nm silver nanoparticle by 800 nm femtosecond laser pulses via two-photon absorption. The plasmonic mode is subsequently coupled or transformed to excitation in the nanowire in contact with the particle and propagated along it, inducing bleaching of the dyes on its way. In situ as well as ex situ fluorescence microscopy is utilized to observe the phenomenon. In addition, transfer of the excitation along the nanowire to another nanoparticle over a separation of 5.7 ?m was clearly observed. The nature of the excitation coupling and transfer could not be fully resolved here, but injection of an electron into the DNA from the excited nanoparticle and subsequent coupled transfer of charge (Dexter) and delocalized exciton (Frenkel) is the most probable mechanism. However, a direct plasmonic or optical coupling and energy transfer along the nanowire cannot be totally ruled out either. By further studies the observed phenomenon could be utilized in novel molecular systems, providing a long-needed communication method between molecular devices. PMID:23305550

  3. Vibronic speed-up of the excitation energy transfer in the Fenna-Matthews-Olson complex

    CERN Document Server

    Nalbach, P; Thorwart, M

    2013-01-01

    We show that the efficient excitation energy transfer in the Fenna-Matthews-Olson molecular aggregate under realistic physiological conditions is fueled by underdamped vibrations of the embedding proteins. For this, we present numerically exact results for the quantum dynamics of the excitons in the presence of nonadiabatic vibrational states in the Fenna-Matthews-Olson aggregate employing a environmental fluctuation spectral function derived from experiments. Assuming the prominent 180 cm$^{-1}$ vibrational mode to be underdamped, we observe, on the one hand, besides vibrational coherent oscillations between different excitation levels of the vibration also prolonged electronic coherent oscillations between the initially excited site and its neighbours. On the other hand, however, the underdamped vibrations provide additional channels for the excitation energy transfer and by this increase the transfer speed by up to $30\\%$ .

  4. Electronic excitation as a mode of heat dissipation in laser-driven cluster plasmas

    International Nuclear Information System (INIS)

    Electrons streaming out of laser plasma are known for non-local heat transport and energy deposition by the ionization wave. At 100 eV electron temperature, since the electronic excitation cross section is comparable to that of ionization for Ar and CO2, a non-local excitation wave akin to the ionization wave is envisaged where energy deposition in excitations forms a excited cluster sheath beyond the laser focus. Here, we show that nano-cluster systems have the right parameters to form such an exciton sheath and experimentally demonstrate this via charge transfer reactions

  5. Electronic excitation as a mode of heat dissipation in laser-driven cluster plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Rajeev, R.; Rishad, K. P. M.; Madhu Trivikram, T.; Krishnamurthy, M. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-5 (India)

    2013-12-15

    Electrons streaming out of laser plasma are known for non-local heat transport and energy deposition by the ionization wave. At 100 eV electron temperature, since the electronic excitation cross section is comparable to that of ionization for Ar and CO{sub 2}, a non-local excitation wave akin to the ionization wave is envisaged where energy deposition in excitations forms a excited cluster sheath beyond the laser focus. Here, we show that nano-cluster systems have the right parameters to form such an exciton sheath and experimentally demonstrate this via charge transfer reactions.

  6. Role of two-center electron-electron interaction in projectile electron excitation and loss

    International Nuclear Information System (INIS)

    This report discusses the role of two-center electron-electron interaction in projectile cluster excitation and loss. The following topics are explored: PWBA Formalism; Closure Method; Improvements of Closure Method; Molecular Form Factors; SCA Formalism; Impulse Approximation; Higher Order Processes; Projectile-Electron Excitation; Projectile-Electron Loss Cross Section; Projectile-Electron Loss and Capture; Separation of Screening and Antiscreening; Electron-Loss Probability; and Electron Spectroscopy. 94 refs., 23 figs

  7. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    Science.gov (United States)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  8. Motional effects on the efficiency of excitation transfer

    CERN Document Server

    Asadian, Ali; Guerreschi, Gian Giacomo; Cai, Jianming; Popescu, Sandu; Briegel, Hans J

    2010-01-01

    Energy transfer plays a vital role in many natural and technological processes. In this work, we study the effects of mechanical motion on the excitation transfer through a chain of interacting molecules with application to the biological scenario of energy transfer in $\\alpha$-helices. Our investigation demonstrates that, for various types of mechanical oscillations, the transfer efficiency is significantly enhanced over that of comparable static configurations. This enhancement is a genuine quantum signature, and requires the collaborative interplay between the quantum-coherent evolution of the excitation and the mechanical motion of the molecules via their distance-dependent coupling; it has no analogue in the classical incoherent energy transfer. This effect may not only occur naturally, but it could be exploited in artificially designed systems to optimize transport processes. As an application, we discuss simple and hence robust control techniques.

  9. Motional effects on the efficiency of excitation transfer

    International Nuclear Information System (INIS)

    Energy transfer plays a vital role in many natural and technological processes. In this work, we study the effects of mechanical motion on the excitation transfer through a chain of interacting molecules with applications to biological scenarios of transfer processes. Our investigation demonstrates that, for various types of mechanical oscillations, the transfer efficiency is significantly enhanced over that of comparable static configurations. This enhancement is a genuine quantum signature and requires the collaborative interplay between the quantum-coherent evolution of the excitation and the mechanical motion of the molecules; it has no analogue in the classical incoherent energy transfer. This effect may not only occur naturally but also be exploited in artificially designed systems to optimize transport processes. As an application, we discuss a simple and hence robust control technique.

  10. Motional effects on the efficiency of excitation transfer

    Energy Technology Data Exchange (ETDEWEB)

    Asadian, Ali; Tiersch, Markus; Guerreschi, Gian Giacomo; Cai, Jianming; Briegel, Hans J [Institut fuer Theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Popescu, Sandu, E-mail: hans.briegel@uibk.ac.a [H H Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)

    2010-07-15

    Energy transfer plays a vital role in many natural and technological processes. In this work, we study the effects of mechanical motion on the excitation transfer through a chain of interacting molecules with applications to biological scenarios of transfer processes. Our investigation demonstrates that, for various types of mechanical oscillations, the transfer efficiency is significantly enhanced over that of comparable static configurations. This enhancement is a genuine quantum signature and requires the collaborative interplay between the quantum-coherent evolution of the excitation and the mechanical motion of the molecules; it has no analogue in the classical incoherent energy transfer. This effect may not only occur naturally but also be exploited in artificially designed systems to optimize transport processes. As an application, we discuss a simple and hence robust control technique.

  11. Theory of plasmon enhanced interfacial electron transfer

    Science.gov (United States)

    Wang, Luxia; May, Volkhard

    2015-04-01

    A particular attempt to improve the efficiency of a dye sensitized solar cell is it's decoration with metal nano-particles (MNP). The MNP-plasmon induced enhancement of the local field enlarges the photoexcitation of the dyes and a subsequent improvement of the charge separation efficiency may result. In a recent work (2014 J. Phys. Chem. C 118 2812) we presented a theory of plasmon enhanced interfacial electron transfer for perylene attached to a TiO2 surface and placed in the proximity of a spherical MNP. These earlier studies are generalized here to the coupling of to up to four MNPs and to the use of somewhat altered molecular parameters. If the MNPs are placed close to each other strong hybridization of plasmon excitations appears and a broad resonance to which molecular excitations are coupled is formed. To investigate this situation the whole charge injection dynamics is described in the framework of the density matrix theory. The approach accounts for optical excitation of the dye coupled to the MNPs and considers subsequent electron injection into the rutile TiO2-cluster. Using a tight-binding model for the TiO2-system with about 105 atoms the electron motion in the cluster is described. We again consider short optical excitation which causes an intermediate steady state with a time-independent overall probability to have the electron injected into the cluster. This probability is used to introduce an enhancement factor which rates the influence of the MNP. Values larger than 500 are obtained.

  12. Efficiency of excitation transfer in photosynthesis under quantum coherence

    CERN Document Server

    Olaya-Castro, Alexandra; Fassioli-Olsen, Francesca; Johnson, Neil F

    2007-01-01

    We investigate the role of quantum coherence in the efficiency of excitation transfer in a spin-star arrangement of interacting two-level systems, mimicking a light-harvesting antenna connected to a reaction center, similar to a photosynthetic system in nature. By using the quantum jump approach, we show that the efficiency depends intimately on the quantum interference among states in which the excitation is localized on individual sites in the antenna. Our results indicate how efficiency may be used as an indication of quantum coherence in energy transfer.

  13. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    Science.gov (United States)

    Ramon, John Glenn Santos

    The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally, we examine the effect of the nanoscale interfacial morphology and solvation on the electronic excited states of TFB/F8BT. Here, we employ time-dependent density functional theory (TD-DFT) to investigate the relevant excited states of two stacking configurations. We show that the calculated states agree with the excited states responsible for the experimentally observed emission peaks and that these states are blue shifted relative to those of the isolated chain. Furthermore, slight lateral shifts in the stacking orientation not only shift the excited state energies; more importantly, they alter the nature of these states altogether. Lastly, we see that solvation greatly stabilizes the charge-transfer states.

  14. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    International Nuclear Information System (INIS)

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-?*, ?-?*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method

  15. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    Science.gov (United States)

    Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo

    2014-12-01

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-?*, ?-?*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  16. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    Energy Technology Data Exchange (ETDEWEB)

    Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it [Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa (Italy); Koch, Henrik [Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Cappelli, Chiara [Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi, 3 I-56124 Pisa (Italy)

    2014-12-14

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-?{sup *}, ?-?{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  17. Electron Transfer to Vinylaromatic Polymers

    International Nuclear Information System (INIS)

    Aromatic polymers accept electrons from alkali metals to form polyradicalanions. These undergo chain scission as a result of electronic interaction between aromatic rings. Spectrophotometric and chemical evidence led to the conclusion that during the chain-breaking process polymeric fragments were formed which had the properties of ''living polymers'', i.e. the characteristic visible spectra and the capability of initiating the polymerization of a number of vinyl monomers. It was possible to follow the rate of chain scission in the case of poly (4-vinyl biphenyl) and poly(?-vinyl naphthalene) by means of viscosity and spectrophotometric measurements. The postulated mechanism was found to be consistent with the slow decrease in free spin concentration measured by means of the electron spin resonance technique. Chain scission in polyacenaphthalene takes place at a much faster rate than in poly (4-vinyl biphenyl) and this fact is in good agreement with simple LCAO MO calculations. Preliminary experiments indicate that electron transfer to poly-N-vinyl carbazole produces little if any degradation. These investigations led to the examination of the temperature effect on the electron-transfer reaction from sodium to some substituted aromatic hydrocarbons. The details of this effect are discussed. (author)

  18. Excitation of two interacting electrons as a plasmon-decay mechanism in proton-aluminum collisions

    International Nuclear Information System (INIS)

    Projectile-induced plasmon excitation in an electron gas has been studied by several authors who proposed two possible mechanisms for these plasmons to decay. In a previous work we considered one of these mechanisms in which the plasmon transfers its energy to a nearly free electron that makes an interband transition. In this paper, the other mechanism is analyzed. A simple model is developed to describe plasmon decay in aluminum via the excitation of two interacting electrons. Results for the transition probability and the excitation power are presented. When contributions from both mechanisms are considered, they account for more than 60% of the excited plasmons. Also, the slope of the plasmon excitation curve is correctly reproduced. The study of first and second differential spectra in angle and energy show that plasmon decay into two interacting electrons is the main source of low-energy electrons moving in the forward direction (with respect to the projectile initial velocity)

  19. Patterning of insulating surfaces by electronic excitation

    International Nuclear Information System (INIS)

    The interaction of swift heavy ions with any material is governed by a strong electronic excitation. In insulators this often leads to permanent modifications. We have irradiated various insulating materials (SrTiO3,TiO2,Al2O3,CaF2,SrF2,BaF2,andLiF) with swift heavy ions and have studied the irradiated surfaces by means of scanning force microscopy. For all materials used in this study we find one nanosized hillock per incident ion if the beam is oriented perpendicular with respect to the surface. Under oblique angles we find elongated chains of discontinuous nanodots on all crystalline materials investigated here.

  20. Efficient deactivation of a model base pair via excited-state hydrogen transfer.

    Science.gov (United States)

    Schultz, Thomas; Samoylova, Elena; Radloff, Wolfgang; Hertel, Ingolf V; Sobolewski, Andrzej L; Domcke, Wolfgang

    2004-12-01

    We present experimental and theoretical evidence for an excited-state deactivation mechanism specific to hydrogen-bonded aromatic dimers, which may account, in part, for the photostability of the Watson-Crick base pairs in DNA. Femtosecond time-resolved mass spectroscopy of 2-aminopyridine clusters reveals an excited-state lifetime of 65 +/- 10 picoseconds for the near-planar hydrogen-bonded dimer, which is significantly shorter than the lifetime of either the monomer or the 3- and 4-membered nonplanar clusters. Ab initio calculations of reaction pathways and potential-energy profiles identify the mechanism of the enhanced excited-state decay of the dimer: Conical intersections connect the locally excited 1pipi* state and the electronic ground state with a 1pipi* charge-transfer state that is strongly stabilized by the transfer of a proton. PMID:15576616

  1. Excitation energy transfer processes in condensed matter theory and applications

    CERN Document Server

    Singh, Jai

    1994-01-01

    Applying a unified quantum approach, contributors offer fresh insights into the theoretical developments in the excitation energy transfer processes in condensed matter This comprehensive volume examines Frenkel and Wannier excitonic processes; rates of excitonic processes; theory of laser sputter and polymer ablation; and polarons, excitonic polarons and self-trapping

  2. Excitation transfer in atom collisions in helium-neon plasma

    International Nuclear Information System (INIS)

    Due to creation of new types of lasers experimental data on inelastic He* + Ne collisions and results of a theoretic analysis of processes of excitation transfer under atomic collisions in neon-helium plasma are presented. 94 refs., 10 figs., 7 tabs

  3. Excited-state intramolecular charge transfer in 9-aminoacridine derivative.

    Science.gov (United States)

    Pereira, Robson Valentim; Garcia Ferreira, Ana Paula; Gehlen, Marcelo Henrique

    2005-07-14

    A new fluorochromic dye was obtained from the reaction of 9-aminoacridine with ethyl-2-cyano-3-ethoxyacrylate. It displays complex fluorescence that is ascribed to normal emission from the acridine chromophore in addition to excited-state intramolecular charge transfer (ESICT) formed upon light excitation. The analysis of the fluorescence decays in different solvents reveals two short-lived components in the range of 80-450 ps and 0.7-3.2 ns, ascribed to the formation and decay of the intramolecular charge transfer (ICT) state, in addition to a third component of about 9.0 ns, which is related to the normal emission from the acridine singlet excited state, probably in an enol-imine tautomeric form. The ICT emission is readily quenched by water addition to polar solvents, and this effect is ascribed to changes in the keto-amine/enol-imine equilibrium of this fluorochromic dye. PMID:16833932

  4. Orbital-selective electronic excitations in iron arsenides revealed by simulated nonresonant inelastic x-ray scattering

    Science.gov (United States)

    Tsutsui, Kenji; Kaneshita, Eiji; Tohyama, Takami

    2015-11-01

    Nonresonant inelastic x-ray scattering (NIXS) is a possible tool to detect charge excitations in electron systems. In addition, multipole transitions at high-momentum-transfer regions open a new possibility to determine orbital-selective electronic excitations in multiorbital itinerant 3 d electron systems. As a theoretical example, we choose the antiferromagnetic state of iron arsenides and demonstrate that the orbital-selective excitations are detectable by choosing appropriate momentum transfer in NIXS. We propose that both NIXS and resonant inelastic x-ray scattering are complementary to each other for fully understanding the nature of orbital excitations in multiorbital itinerant electron systems.

  5. Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

    CERN Document Server

    Fujita, Takatoshi; Saikin, Semion K; Brookes, Jennifer C; Aspuru-Guzik, Alan

    2013-01-01

    Chlorosomes are the largest and most efficient natural light-harvesting antenna systems. They contain thousands of pigment molecules - bacteriochlorophylls (BChls)- that are organized into supramolecular aggregates and form a very efficient network for excitonic energy migration. Here, we present a theoretical study of excitation energy transfer (EET) in the chlorosome based on experimental evidence of the molecular assembly. Our model for the exciton dynamics throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of supramolecular structure, and electronic structure calculations of the excited states. The simulation results reveal a detailed picture of the EET in the chlorosome. Coherent energy transfer is significant only for the first 50 fs after the initial excitation, and the wavelike motion of the exciton is completely damped at 100 fs. Characteristic time constants of incoherent energy transfer, subsequently, vary from 1 ps to se...

  6. Excitation energy transfer: Study with non-Markovian dynamics

    International Nuclear Information System (INIS)

    In this paper, we investigate the non-Markovian dynamics of a model to mimic the excitation energy transfer (EET) between chromophores in photosynthesis systems. The numerical path integral method is used. This method includes the non-Markovian effects of the environmental affects, and it does not need the perturbation approximation in solving the dynamics of systems of interest. It implies that the coherence helps the EET between chromophores through lasting the transfer time rather than enhancing the transfer rate of the EET. In particular, the non-Markovian environment greatly increases the efficiency of the EET in the photosynthesis systems.

  7. Rerouting Excitation Transfer in the Fenna-Matthews-Olson Complex

    CERN Document Server

    Chen, Guang-Yin; Li, Che-Ming; Chen, Yueh-Nan; Nori, Franco

    2013-01-01

    We investigate, using the Hierarchy method, the entanglement and the excitation transfer efficiency of the Fenna-Matthews-Olson complex under two different local modifications: the suppression of transitions between particular sites and localized changes to the protein environment. We find that inhibiting the connection between the site-5 and site-6, or disconnecting site-5 from the complex completely, leads to an dramatic enhancement of the entanglement between site-6 and site-7. Similarly, the transfer efficiency actually increases if site-5 is disconnected from the complex entirely. We further show that if site-5 and site-7 are conjointly removed, the efficiency falls. This suggests that while not contributing to the transport efficiency in a normal complex, site-5 introduces a redundant transport route in case of damage to site-7. Our results suggest an overall robustness of excitation energy transfer in the FMO complex under mutations, local defects, and other abnormal situations.

  8. Electron Impact Excitation of Noble Gases

    Science.gov (United States)

    Zeman, Vlado; Bartschat, Klaus

    1998-05-01

    We have extended our Breit-Pauli R-matrix work [1,2] to model electron impact excitation of the [np^5(n+1)s] and [np^5(n+1)p] states in the noble gases Ne--Xe. Total and differential cross sections, the polarization of emitted light, and spin asymmetry parameters will be presented for incident electron energies between threshold and 30 eV. The results will be analyzed and compared with a large amount of recent experimental data [3--8]. 1. V. Zeman et al., Phys. Rev. Lett. 79, 1825 (1997) 2. V. Zeman and K. Bartschat, J. Phys. B 30, 4609 (1997) 3. C. Norén et al., Phys. Rev. A53, 3253 (1996) and 54, 510 (1996) 4. T.J. Gay et al., Phys. Rev. A53, 1623 (1996) 5. D.H. Yu et al., Phys. Rev. Lett. 78, 2724 (1997); J. Phys. B 30, L461 5. (1997); J. Phys. B 30, 1799 (1997) 6. J.E. Chilton et al., Phys. Rev. A57, 267 (1998) 7. M.A. Khakoo, private communication (1998) 8. M. Dümmler, G.F. Hanne and J. Kessler, J. Phys. B 28, 2985 (1995)

  9. Collective electronic excitation modes in a superlattice

    International Nuclear Information System (INIS)

    Collective excitation (plasmon) modes of an electron gas in a multilayer system (superlattice) have been studied in great detail in recent years. One important aspect of this fermion system is that the dispersion relation of the plasma frequency shows transitional behavior between the two- and three-dimensional character. An inelastic light scattering experiment was recently conducted in which the intermediate dispersion was observed for a superlattice. The results of the light scattering experiment and earlier calculations based on a superlattice of two-dimensional layers model developed by Fetter and Das Sarma and Quinn are in qualitatively good agreement. Nevertheless there are discrepancies between this theory and experiment, especially for increasing values of q. The objective of this work was to improve Fetter and Das Sarma and Quinn's theory to include the effect of finite thickness of the plasma layers with the objective of better understanding the systematic discrepancy and to describe electronic correlations in a superlattice in a more general way. It proceeds by the determination of the particle-hole channel of the two particle Green's function in the random phase approximation

  10. Nanostructuring graphene by dense electronic excitation

    Science.gov (United States)

    Ochedowski, O.; Lehtinen, O.; Kaiser, U.; Turchanin, A.; Ban-d’Etat, B.; Lebius, H.; Karluši?, M.; Jakši?, M.; Schleberger, M.

    2015-11-01

    The ability to manufacture tailored graphene nanostructures is a key factor to fully exploit its enormous technological potential. We have investigated nanostructures created in graphene by swift heavy ion induced folding. For our experiments, single layers of graphene exfoliated on various substrates and freestanding graphene have been irradiated and analyzed by atomic force and high resolution transmission electron microscopy as well as Raman spectroscopy. We show that the dense electronic excitation in the wake of the traversing ion yields characteristic nanostructures each of which may be fabricated by choosing the proper irradiation conditions. These nanostructures include unique morphologies such as closed bilayer edges with a given chirality or nanopores within supported as well as freestanding graphene. The length and orientation of the nanopore, and thus of the associated closed bilayer edge, may be simply controlled by the direction of the incoming ion beam. In freestanding graphene, swift heavy ion irradiation induces extremely small openings, offering the possibility to perforate graphene membranes in a controlled way.

  11. Electron-electron interactions in K-shell excitation of F6+ ions in fast collisions with H2 targets

    International Nuclear Information System (INIS)

    K-shell excitation of F6+(1s22s) projectile ions in collisions with H2 targets has been studied by measuring 0 degree state-resolved Auger electron production cross sections in the projectile energy range of 0.25 to 2 MeV/u. Projectile 1s?2p excitation due to the interaction with a ''target electron'' (electron-electron Excitation1 [eeE]) has been observed in the production of the 1s(2s2p3P)2P- and 1s(2s2p1P)2P+ states as well as 1s2s2p4P state above the electron impact threshold. Projectile excitation is also produced by the target nucleus (electron-nucleus Excitation [enE]) for the 2P± states. The eeE and enE cross sections were evaluated by Impulse Approximation (IA) and PWBA, respectively. The total KLL Auger electron production cross sections were also determined and exhibited the overall electron-electron interaction effects of eeE and Resonant-Transfer Excitation (RTE) which, in particular, is the 1s?2p excitation with 2p capture to result in 1s2s2p23,1D states

  12. Vibration-translation energy transfer in vibrationally excited diatomic molecules

    International Nuclear Information System (INIS)

    A semiclassical collision model is applied to the study of energy transfer rates between a vibrationally excited diatomic molecule and a structureless atom. The molecule is modeled as an anharmonic oscillator with a multitude of dynamically coupled vibrational states. Three main aspects in the prediction of vibrational energy transfer rates are considered. The applicability of the semiclassical model to an anharmonic oscillator is first evaluated for collinear encounters. Second, the collinear semiclassical model is applied to obtain numerical predictions of the vibrational energy transfer rate dependence on the initial vibrational state quantum number. Thermally averaged vibration-translation rate coefficients are predicted and compared with CO-He experimental values for both ground and excited initial states. The numerical model is also used as a basis for evaluating several less complete but analytic models. Third, the role of rational motion in the dynamics of vibrational energy transfer is examined. A three-dimensional semiclassical collision model is constructed with coupled rotational motion included. Energy transfer within the molecule is shown to be dominated by vibration-rotation transitions with small changes in angular momentum. The rates of vibrational energy transfer in molecules with rational frequencies that are very small in comparison to their vibrational frequency are shown to be adequately treated by the preceding collinear models

  13. Intra- and intermolecular energy transfer in highly excited ozone complexes.

    Science.gov (United States)

    Ivanov, Mikhail V; Grebenshchikov, Sergy Yu; Schinke, Reinhard

    2004-06-01

    The energy transfer of highly excited ozone molecules is investigated by means of classical trajectories. Both intramolecular energy redistribution and the intermolecular energy transfer in collisions with argon atoms are considered. The sign and magnitude of the intramolecular energy flow between the vibrational and the rotational degrees of freedom crucially depend on the projection K(a) of the total angular momentum of ozone on the body-fixed a axis. The intermolecular energy transfer in single collisions between O(3) and Ar is dominated by transfer of the rotational energy. In accordance with previous theoretical predictions, the direct vibrational de-excitation is exceedingly small. Vibration-rotation relaxation in multiple Ar+O(3) collisions is also studied. It is found that the relaxation proceeds in two clearly distinguishable steps: (1) During the time between collisions, the vibrational degrees of freedom are "cooled" by transfer of energy to rotation; even at low pressure equilibration of the internal energy is slow compared to the time between collisions. (2) In collisions, mainly the rotational modes are "cool" by energy transfer to argon. PMID:15268022

  14. Energy traps of excited energy transfer processes in polymer solids

    International Nuclear Information System (INIS)

    In this report, the singlet and triplet exciton behaviors of the polymers containing carbazole (Cz) or phenanthrene (Ph) chromophores as the side group were studied in the solid state. The role of electronic energy traps in energy transfer process will be discussed and controlling factors of energy transfer processes will be given

  15. Electron transfer reactions. Pt. 1

    International Nuclear Information System (INIS)

    The oxidation of the substituted ethylenes, 2,3-dimethylbutene-2 (1), 2-methylbutene-2 (8), and ?-methylstyrene (13), by ferriin or lead dioxide in water and/or methanol has been studied. Product analyses of the reactions, which lead to kinetically controlled product distributions, showed that lead dioxide, just as ferriin, reacts as a one-electron-oxidant. The product distributions, which arise from further reactions of the primary intermediates, i.e. the radical cations formed via one-electron transfer, were found to depend on substituents, acidity and solvent. The results are consistent with three separate reaction paths of the radical cation, each of which leads to specific products. The radical cation can either deprotonate, be nucleophilicly attacked by solvent, or lead to dimeric products. (orig.)

  16. An Accurate and Linear Scaling Method to Calculate Charge-Transfer Excitation Energies and Diabatic Couplings

    CERN Document Server

    Pavanello, Michele; Visscher, Lucas; Neugebauer, Johannes

    2012-01-01

    Quantum--Mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the Frozen Density Embedding formulation of subsystem Density-Functional Theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlap matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against Coupled-Cluster calculations and achieves chemical accuracy for the systems considered...

  17. The mechanism of electronic excitation in the bacterial bioluminescent reaction

    International Nuclear Information System (INIS)

    The current state of the problem of formation of the electron-excited product in the chemiluminescent reaction that underlies the bacterial luminescence is analysed. Various schemes of chemical transformations capable of producing a bacterial bioluminescence emitter are presented. The problem of excitation of secondary emitters is considered; two possible mechanisms of their excitation are analysed.

  18. Electronic excited states of protonated aromatic molecules: Protonated Fluorene

    Energy Technology Data Exchange (ETDEWEB)

    Alata, Ivan [CLUPS (Centre Laser de l' Universite Paris Sud / LUMAT FR 2764) Bat. 106, Univ Paris-Sud 11, 91405 Orsay Cedex (France) and Atomic Energy Commission of Syria, Damascus, P.O. Box 6091 (Syrian Arab Republic); Broquier, Michel; Dedonder, Claude [CLUPS (Centre Laser de l' Universite Paris Sud / LUMAT FR 2764) Bat. 106, Univ Paris-Sud 11, 91405 Orsay Cedex (France); Institut des Sciences Moleculaires d' Orsay (ISMO, UMR8624 CNRS) Bat. 210, Univ Paris-Sud 11, 91405 Orsay Cedex (France); Jouvet, Christophe, E-mail: christophe.jouvet@u-psud.fr [CLUPS (Centre Laser de l' Universite Paris Sud / LUMAT FR 2764) Bat. 106, Univ Paris-Sud 11, 91405 Orsay Cedex (France); Institut des Sciences Moleculaires d' Orsay (ISMO, UMR8624 CNRS) Bat. 210, Univ Paris-Sud 11, 91405 Orsay Cedex (France); Marceca, Ernesto [INQUIMAE-FCEN, UBA, Ciudad Universitaria, 3er piso, Pab. II, 1428 Buenos Aires (Argentina)

    2012-01-17

    Highlights: Black-Right-Pointing-Pointer We report the vibrationally resolved electronic spectrum of protonated fluorene. Black-Right-Pointing-Pointer The ground and excited states of the x possible isomers have been calculated ab initio. Black-Right-Pointing-Pointer Among these isomers, only two may contribute to the two band systems observed. Black-Right-Pointing-Pointer Franck Condon simulations are used to assign the active vibrations. - Abstract: The photo-fragmentation spectrum of protonated fluorene has been recorded in the visible spectral region, evidencing an absorption that appears largely red shifted in comparison to that of the neutral molecule fluorene. The spectrum shows two different vibrational progressions, separated by 0.19 eV. As in the case of protonated linear polycyclic aromatic hydrocarbons (PAHs), comparison of the measured spectra with ab initio calculations allows to associate the observed absorption shift with the charge transfer character of the excited state. The spectra can be properly simulated by geometry optimization of the ground and excited states, followed by Franck Condon analysis. The two vibrational bands progressions observed are assigned, with relatively good confidence, to the existence of two different conformers.

  19. Two-center electron-electron interaction in projectile electron excitation and loss

    International Nuclear Information System (INIS)

    The specific interaction between an electron on the target and an electron on the projectile in an atomic collision is illustrated by means of projectile electron excitation and loss. In that case, the target electron plays a dual role, on the one hand, decreasing the projectile excitation/loss (screening interaction) and, on the other hand, enhancing the excitation/loss (antiscreening interaction). These two interactions have different dynamics and different impact-parameter dependencies, which permit their specific characterization and experimental separation. (orig.)

  20. Electron transfer by singlet excited state of porphyn and electron acceptor affinity in rigid medium: photoacoustic phase angle analysis / Transferência de elétrons via estado singleto excitado de porfirina de base livre e afinidade de elétrons por aceitadores em meio rígido: análise fotoacústica do ângulo de fase

    Scientific Electronic Library Online (English)

    Marinônio Lopes, CORNÉLIO.

    Full Text Available A espectroscopia fotoacústica obtém informações sobre amplitude e fase, da resposta de um sistema submetido a excitação por luz. Este artigo apresenta estudos do ângulo de fase no processo de transfereência de elétrons entre octaetilporfirina (OEP) e derivados de quinona ambos dispersos em uma matri [...] z polimérica. Observou-se uma tendência no comportamento da fase para valores menores na região espectral próximo de 620 nm. Enquanto que para comprimentos de onda menores este efeito não foi apresentado. Estas medidas sugerem que a transferência de elétrons para o aceitador ocorreu com a participação do estado singleto excitado da octaetilporfirina. Abstract in english Photoacoustic spectroscopy provides information about both amplitude and phase of the response of a system to an optical excitation process. This paper presents the studies of the phase in the electron transfer process between octaethylporphyn (OEP) and quinone molecules dispersed in a polymeric mat [...] rix. It was observed a tendency in the phase behavior to small values only in the spectral region near to 620 nm, while for shorter wavelength did not show any tendency. These measurements suggested that the electron transfer to acceptor occurred with the participation of octaethylporphyn singlet excited state.

  1. Protonation of silylenol ether via excited state proton transfer catalysis.

    Science.gov (United States)

    Das, Anjan; Banerjee, Tanmay; Hanson, Kenneth

    2016-01-14

    We demonstrate the photocatalytic protonation of a silylenol ether using 7-bromo-2-naphthol as an ESPT catalyst with phenol as the sacrificial proton source. Greater than 95% conversion is achieved with 1 mol% catalyst. The reaction cycle is dependent on the significantly increased acidity of the catalyst in the excited state as well as the long lifetime for the triplet excited state of 7-bromo-2-naphthol. The reaction does not occur in the absence of light (367 nm) and can readily be controlled by light intensity modulation. We also demonstrate that a 72% reaction yield can be obtained with unsubstituted naphthol as the catalyst by coupling triplet energy transfer, via a visible light absorbing (445 nm) sensitizer, into the catalytic cycle. These results open the door to an entirely new class of sensitized photocatalytic reactions that harness the excited state acidity of ESPT dyes. PMID:26502917

  2. Light induced electron transfer reactions of metal complexes

    International Nuclear Information System (INIS)

    Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed

  3. Excitation of quadrupole vibrations in two-nucleon transfer reactions

    International Nuclear Information System (INIS)

    The spectroscopic factor is considered for two-nucleon transfer reactions involving the excitation of quadrupole one-phonon states. Special attention is payed to the number of particles conservation condition in the dynamically distorted average potential of the deforming nucleus. It is required that the mean square of the time-derivtive of the particle number operator is zero in the collective phonon state. The condition is satisfied by a specially chosen residual interaction terms. (orig.)

  4. Excited State Structural Dynamics of Carotenoids and Charge Transfer Systems

    International Nuclear Information System (INIS)

    This dissertation describes the development and implementation of a visible/near infrared pump/mid-infrared probe apparatus. Chapter 1 describes the background and motivation of investigating optically induced structural dynamics, paying specific attention to solvation and the excitation selection rules of highly symmetric molecules such as carotenoids. Chapter 2 describes the development and construction of the experimental apparatus used throughout the remainder of this dissertation. Chapter 3 will discuss the investigation of DCM, a laser dye with a fluorescence signal resulting from a charge transfer state. By studying the dynamics of DCM and of its methyl deuterated isotopomer (an otherwise identical molecule), we are able to investigate the origins of the charge transfer state and provide evidence that it is of the controversial twisted intramolecular (TICT) type. Chapter 4 introduces the use of two-photon excitation to the S1 state, combined with one-photon excitation to the S2 state of the carotenoid beta-apo-8'-carotenal. These 2 investigations show evidence for the formation of solitons, previously unobserved in molecular systems and found only in conducting polymers Chapter 5 presents an investigation of the excited state dynamics of peridinin, the carotenoid responsible for the light harvesting of dinoflagellates. This investigation allows for a more detailed understanding of the importance of structural dynamics of carotenoids in light harvesting

  5. Fishbone instability excited by electrons in a tokamak

    International Nuclear Information System (INIS)

    Fishbone instability in Tokamak plasma is often produced by deeply trapped suprathermal ions. Theoretical analysis indicates that the instability can be excited by barely trapped suprathermal electrons. Negative magnetic shear help exciting electron fishbone or suppress ion one, while positive shear is opposite. The fishbone instability purely driven by suprathermal trapped electrons is firstly identified by using electron cyclotron resonance heating (ECRH) in the HL-1M Tokamak

  6. Theory of nuclear excitation by electron capture for heavy ions

    OpenAIRE

    Gagyi-Palffy, Adriana

    2006-01-01

    The resonant process of nuclear excitation by electron capture (NEEC) in collisions involving highly-charged ions has been investigated theoretically. NEEC is a rare recombination process in which a free electron is captured into a bound shell of an ion with the simultaneous excitation of the nucleus. Total cross sections for NEEC followed by the radiative decay of the excited nucleus are presented for various collision systems. The possibility to observe the NEEC in scattering experiments wi...

  7. Electronic excitations in fast ion-solid collisions

    International Nuclear Information System (INIS)

    We review recent developments in the study of electronic excitation of projectiles in fast ion-solid collisions. Our focus will be primarily on theory but experimental advances will also be discussed. Topics include the evidence for velocity-dependent thresholds for the existence of bound states, wake-field effects on excited states, the electronic excitation of channeled projectiles, transport phenomena, and the interaction of highly charged ions with surfaces. 44 refs., 14 figs

  8. Search for Excited Electrons in ep Collisions at HERA

    CERN Document Server

    Aaron, F D; Andreev, V; Antunovic, B; Aplin, S; Asmone, A; Astvatsatourov, A; Bacchetta, A; Backovic, S; Baghdasaryan, A; Baranov, P; Barrelet, E; Bartel, Wulfrin; Beckingham, M; Begzsuren, K; Behnke, O; Belousov, A; Berger, N; Bizot, J C; Boenig, M O; Boudry, V; Bozovic-Jelisavcic, I; Bracinik, J; Brandt, G; Brinkmann, M; Brisson, V; Bruncko, D; Bunyatyan, A; Buschhorn, G; Bystritskaya, L; Campbell, A J; Cantun Avila, K B; Cassol-Brunner, F; Cerny, K; Cerny, V; Chekelian, V; Cholewa, A; Contreras, J G; Coughlan, J A; Cozzika, G; Cvach, J; Dainton, J B; Daum, K; Deák, M; De Boer, Y; Delcourt, B; Del Degan, M; Delvax, J; de Roeck, A; De Wolf, E A; Diaconu, C; Dodonov, V; Dossanov, A; Dubak, A; Eckerlin, G; Efremenko, V; Egli, S; Eliseev, A; Elsen, E; Essenov, S; Falkiewicz, A; Faulkner, P J W; Favart, L; Fedotov, A; Felst, R; Feltesse, J; Ferencei, J; Finke, L; Fleischer, M; Fomenko, A; Gabathuler, E; Gayler, J; Ghazaryan, S; Glazov, A; Glushkov, I; Görlich, L; Goettlich, M; Gogitidze, N; Gouzevitch, M; Grab, C; Greenshaw, T; Grell, B R; Grindhammer, G; Habib, S; Haidt, D; Hansson, M; Helebrant, C; Henderson, R C W; Henschel, H; Herrera-Corral, G; Hildebrandt, M; Hiller, K H; Hoffmann, D; Horisberger, R; Hovhannisyan, A; Hreus, T; Jacquet, M; Janssen, M E; Janssen, X; Jemanov, V; Jonsson, L; Johnson, D P; Jung, A W; Jung, H; Kapichine, M; Katzy, J; Kenyon, I R; Kiesling, C; Klein, M; Kleinwort, C; Klimkovich, T; Kluge, T; Knutsson, A; Kogler, R; Korbel, V; Kostka, P; Krämer, M; Krastev, K; Kretzschmar, J; Kropivnitskaya, A; Krüger, K; Kutak, K; Landon, M P J; Lange, W; Lastoviicka-Medin, G; Laycock, P; Lebedev, A; Leibenguth, G; Lendermann, V; Levonian, S; Li, G; Lipka, K; Liptaj, A; List, B; List, J; Loktionova, N; López-Fernandez, R; Lubimov, V; Lucaci-Timoce, A I; Lytkin, L; Makankine, A; Malinovski, E; Marage, P; Marti, L; Martyn, H U; Maxfield, S J; Mehta, A; Meier, K; Meyer, A B; Meyer, H; Meyer, J; Michels, V; Mikocki, S; Milcewicz-Mika, I; Moreau, F; Morozov, A; Morris, J V; Mozer, M U; Mudrinic, M; Müller, K; Murn, P; Nankov, K; Naroska, B; Naumann, T; Newman, P R; Niebuhr, C; Nikiforov, A; Nowak, G; Nowak, K; Nozicka, M; Olivier, B; Olsson, J E; Osman, S; Ozerov, D; Palichik, V; Panagouliasl, I; Pandurovic, M; Papadopouloul, T; Pascaud, C; Patel, G D; Pejchal, O; Peng, H; Pérez, E; Petrukhin, A; Picuric, I; Piec, S; Pitzl, D; Placakyte, R; Polifka, R; Povh, B; Preda, T; Radescu, V; Rahmat, A J; Raicevic, N; Raspiareza, A; Ravdandorj, T; Reimer, P; Rizvi, E; Robmann, P; Roland, B; Roosen, R; Rostovtsev, A; Rotaru, M; Ruiz Tabasco, J E; Rurikova, Z; Rusakov, S; Salek, D; Salvaire, F; Sankey, D P C; Sauter, M; Sauvan, E; Schmidt, S; Schmitt, S; Schmitz, C; Schoeffel, L; Schöning, A; Schultz-Coulon, H C; Sefkow, F; Shaw-West, R N; Shevyakov, I; Shtarkov, L N; Shushkevich, S; Sloan, T; Smiljanic, I; Smirnov, P; Soloviev, Yu; Sopicki, P; South, D; Spaskov, V; Specka, A; Staykova, Z; Steder, M; Stella, B; Straumann, U; Sunar, D; Sykora, T; Tchoulakov, V; Thompson, G; Thompson, P D; Toll, T; Tomasz, F; Tran, T H; Traynor, D; Trinh, T N; Truöl, P; Tsakov, I; Tseepeldorj, B; Tsurin, I; Turnau, J; Tzamariudaki, E; Urban, K; Valkárová, A; Vallée, C; Van Mechelen, P; VargasTrevino, A; Vazdik, Ya; Vinokurova, S; Volchinski, V; Wegener, D; Wessels, M; Wissing, C; Wünsch, E; Yeganov, V; Zácek, J; Zaleisak, J; Zhang, Z; Zhelezov, A; Zhokin, A; Zhu, Y C; Zimmermann, T; Zohrabyan, H; Zomer, F; 10.1016/j.physletb.2008.07.014

    2008-01-01

    A search for excited electrons is performed using the full $e^{\\pm}p$ data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb$^{-1}$. The electroweak decays of excited electrons ${e}^{*}\\to{e}{\\gamma}$, ${e}^{*}\\to{e}Z$ and ${e}^{*}{\\to}\

  9. Measurement of the electronic excitation of atoms in atom-molecule collisions near threshold

    International Nuclear Information System (INIS)

    In first part of the paper the measurement of scattering cross sections is described and the energy transfer in molecule-alkali systems is investigated. The influence of translational and vibrational energy could be separated near the excitation threshold. In the second part of the work measurements are reported on the electronic excitation of the work measurements are reported on the electronic excitation of Xe in Xe-Xe-collisions. The experimental data are compared with theoretical calculations. (KBE) 891 KBE/KBE 892 HIS

  10. Dynamics of Energy Transfer in a Conjugated Dendrimer Driven by Ultrafast Localization of Excitations.

    Science.gov (United States)

    Galindo, Johan F; Atas, Evrim; Altan, Aysun; Kuroda, Daniel G; Fernandez-Alberti, Sebastian; Tretiak, Sergei; Roitberg, Adrian E; Kleiman, Valeria D

    2015-09-16

    Solar energy conversion starts with the harvest of light, and its efficacy depends on the spatial transfer of the light energy to where it can be transduced into other forms of energy. Harnessing solar power as a clean energy source requires the continuous development of new synthetic materials that can harvest photon energy and transport it without significant losses. With chemically-controlled branched architectures, dendrimers are ideally suited for these initial steps, since they consist of arrays of chromophores with relative positioning and orientations to create energy gradients and to spatially focus excitation energies. The spatial localization of the energy delimits its efficacy and has been a point of intense research for synthetic light harvesters. We present the results of a combined theoretical experimental study elucidating ultrafast, unidirectional, electronic energy transfer on a complex molecule designed to spatially focus the initial excitation onto an energy sink. The study explores the complex interplay between atomic motions, excited-state populations, and localization/delocalization of excitations. Our findings show that the electronic energy-transfer mechanism involves the ultrafast collapse of the photoexcited wave function due to nonadiabatic electronic transitions. The localization of the wave function is driven by the efficient coupling to high-frequency vibrational modes leading to ultrafast excited-state dynamics and unidirectional efficient energy funneling. This work provides a long-awaited consistent experiment-theoretical description of excited-state dynamics in organic conjugated dendrimers with atomistic resolution, a phenomenon expected to universally appear in a variety of synthetic conjugated materials. PMID:26122872

  11. Laser pulse control of bridge mediated heterogeneous electron transfer

    International Nuclear Information System (INIS)

    Ultrafast heterogeneous electron transfer from surface attached dye molecules into semiconductor band states is analyzed. The focus is on systems where the dye is separated from the surface by different bridge anchor groups. To simulate the full quantum dynamics of the transfer process a model of reduced dimensionality is used. It comprises the electronic levels of the dye, the bridge anchor group electronic levels and the continuum of semiconductor band states, all defined versus a single intramolecular vibrational coordinate. The effect of the bridge states is demonstrated, firstly, in studying the injection dynamics following an impulsive excitation of the dye. Then, by discussing different control tasks it is demonstrate in which way the charge injection process can be influenced by tailored laser pulses. To highlight the importance of electron wave function interference emphasis is put on asymmetric two-bridge molecule systems which are also characterized by different and complex valued electronic transfer matrix elements.

  12. Excitation transfer through open quantum networks: a few basic mechanisms

    CERN Document Server

    Venuti, Lorenzo Campos

    2011-01-01

    A variety of open quantum networks are currently under intense examination to model energy transport in photosynthetic systems. Here we study the coherent transfer of a quantum excitation over a network incoherently coupled with a structured and small environment that effectively models the photosynthetic reaction center. Our goal is to distill a few basic, possibly universal, mechanisms or "effects" that are featured in simple energy-transfer models. In particular, we identify three different phenomena: the congestion effect, the asymptotic unitarity and the staircase effects. We begin with few-site models, in which these effects can be fully understood, and then proceed to study more complex networks similar to those employed to model energy transfer in light-harvesting complexes. Our numerical studies on such networks seem to suggest that some of the effects observed in simple networks may be of relevance for biological systems, or artificial analogues of them as well.

  13. Initial state dependence of convoy electrons emitted from the excited ions by resonant coherent excitation

    Energy Technology Data Exchange (ETDEWEB)

    Azuma, T; Nakano, Y; Metoki, K [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo (Japan); Hatakeyama, A [Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo (Japan); Nakai, Y [Radioactive Isotope Physics Laboratory, RIKEN Nishina Center, Wako, Saitama (Japan); Komaki, K; Yamazaki, Y [Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro, Tokyo (Japan); Takada, E; Murakami, T, E-mail: azuma@phys.metro-u.ac.j [National Institute of Radiological Sciences, Inage, Chiba (Japan)

    2009-11-01

    Convoy electrons emitted from 416 MeV/u heliumlike Ar{sup 16+} ions excited by three-dimensional resonant coherent excitation (3D-RCE) have been explored. The 1s electron in the ground state was excited to the 2p state by a periodic crystal field during the passage through a Si crystal and released into the continuum by collisions with target atoms to form a cusp-shaped peak in the energy distribution, referred to as convoy electron. Under the resonance condition, we found not only enhancement of the convoy electron yield but also significant narrowing in the energy distribution, reflecting the initial bound state momentum distribution of the excited ions. This suggests that RCE is well-suited to study fast ion collisions involving the specific excited state.

  14. K- and L-shell resonant transfer and excitation in ion-atom collisions

    International Nuclear Information System (INIS)

    Recent experimental studies of resonant transfer and excitation (RTE) in ion-atom collisions are reviewed. In the RTE process correlated electron capture and projectile excitation occur together in a single encounter with a target atom. Measurements of Caq+ + H2 (q=10-19) from 100 to 370 MeV establish the projectile charge-state dependence of K-shell RTE and provide a detailed collision system. A comparison of the Ca17+ + H2 data with previous results for Ca17+ + He demonstrates the effect of the target-electron momentum distribution on the RTE process. Studies of 230-610 MeV Nb31+ + H2 provide information about RTE involing projectile L-shell excitation. All the measurements are in reasonable agreement wit theoretical calculations. (orig.)

  15. Supramolecular host-guest systems as frameworks for excitation energy transfer

    Science.gov (United States)

    Ibrahim, Moustafa Sh; Etaiw, Safaa El-din H.

    2002-01-01

    The antenna behavior of rhodamine 6G and methylene blue loaded novel host supramolecular frameworks is investigated. The geometrical constraints of these supramolecular hosts allows the cationic dye molecules encapsulating within the parallel channels to form novel host-guest systems. The cationic dyes are close together that self-quenching of electronic excitation energy can occur. The excitation energy transfer occurs from rhodamine 6G as a donor (D) to methylene blue as an acceptor (A) within supramolecular systems filled with a mixture of both dyes.

  16. Nonresonant transfer excitation mode in S{sup 15+}+H collisions

    Energy Technology Data Exchange (ETDEWEB)

    Zerarka, A. [Universite de Biskra, Bureau de Poste 145, Inst.-Tronc-C-T, 07000 Biskra (Algeria)

    1997-03-01

    In the context of the independent-electron model, we evaluate the transition amplitude for simultaneous transfer and excitation to occur in ion-atom collisions. For the capture transition amplitude, we use the continuum-distorted-wave approximation, and for the excitation amplitude, we use the first Born approximation. The results are compared directly with the continuum-distorted-wave approximation in a four-body approach for the S{sup 15+}+H system. {copyright} {ital 1997} {ital The American Physical Society}

  17. Correlated electron capture and inner-shell excitation measurements in ion-atom collisions

    International Nuclear Information System (INIS)

    In an ion-atom collision projectile excitation and charge transfer (electron capture) may occur together in a single encounter. If the excitation and capture are correlated, then the process is called resonant transfer and excitation (RTE); if they are uncorrelated, then the process is termed nonresonant transfer and excitation (NTE). Experimental work to date has shown the existence of RTE and provided strong evidence for NTE. Results presented here provide information on the relative magnitudes of RTE and NTE, the charge state dependence of RTE, the effect of the target momentum distribution on RTE, the magnitude of L-shell RTE compared to K-shell RTE, and the target Z dependences of RTE and NTE. 15 refs., 5 figs

  18. Enhanced luminescence excitation via efficient optical energy transfer (Presentation Recording)

    Science.gov (United States)

    Aad, Roy; Nomenyo, Komla D.; Bercu, Bogdan; Couteau, Christophe; Sallet, Vincent; Rogers, David J.; Molinari, Michael; Lérondel, Gilles

    2015-10-01

    Luminescent nanoscale materials (LNMs) have received widespread interest in sensing and lighting applications due to their enhanced emissive properties. For sensing applications, LNMs offer improved sensitivity and fast response time which allow for lower limits of detection. Meanwhile, for lighting applications, LNMs, such as quantum dots, offer an improved internal quantum efficiency and controlled color rendering which allow for better lighting performances. Nevertheless, due to their nanometric dimensions, nanoscale materials suffer from extremely weak luminescence excitation (i.e. optical absorption) limiting their luminescence intensity, which in turn results in a downgrade in the limits of detection and external quantum efficiencies. Therefore, enhancing the luminescence excitation is a major issue for sensing and lighting applications. In this work, we report on a novel photonic approach to increase the luminescence excitation of nanoscale materials. Efficient luminescence excitation increase is achieved via a gain-assisted waveguided energy transfer (G-WET). The G-WET concept consists on placing nanoscale materials atop of a waveguiding active (i.e. luminescent) layer with optical gain. Efficient energy transfer is thus achieved by exciting the nanoscale material via the tail of the waveguided mode of the active layer emission. The G-WET concept is demonstrated on both a nanothin layer of fluorescent sensitive polymer and on CdSe/ZnS quantum dots coated on ZnO thin film, experimentally proving up to an 8-fold increase in the fluorescence of the polymer and a 3-fold increase in the luminescence of the CdSe/ZnS depending of the active layer emission regime (stimulated vs spontaneous emission). Furthermore, we will discuss on the extended G-WET concept which consists on coating nanoscale materials on a nanostructured active layer. The nanostructured active layer offers the necessary photonic modulation and a high specific surface which can presumably lead to a more efficient G-WET concept. Finally, the efficiency as well as the observation conditions of the GWET will be discussed and compared with more conventional charge transfer or dipole-dipole energy transfer.

  19. Local operator partitioning of electronic energy for electronic energy transfer: An efficient algorithm

    CERN Document Server

    Nagesh, Jayashree; Brumer, Paul

    2013-01-01

    An efficient computational algorithm to implement a local operator approach to partitioning electronic energy in general molecular systems is presented. This approach, which rigorously defines the electronic energy on any subsystem within a molecule, gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. We apply the technique to the $9-$(($1-$naphthyl)$-$methyl)-anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH$_2-$naphthyl groups as subsystems, and examine their electronic energies and populations for several excited states using Configuration Interaction Singles method. The implemented approach shows a wide variety of different behaviors amongst these excited electronic states.

  20. Absolute electron transfer efficiency of GEM

    International Nuclear Information System (INIS)

    We report on the absolute single-electron transfer efficiency of a Gas Electron Multiplier (GEM). It is shown that the electron transfer and thus the detection efficiency, depend not only on the GEM geometry and gain but mostly on the electric field and electron diffusion in the gas volume preceding the GEM. We have demonstrated that conditions can be found, including pre-amplification of the single electrons in the gap preceding the GEM, in which full detection efficiency is obtained. The experimental electron transfer efficiency results are confirmed by Monte Carlo simulations

  1. Electron - phonon interaction influence on electron and phonon excitations in amorphous metals

    International Nuclear Information System (INIS)

    The influence of electron-phonon interaction on electron and phonon excitations in amorphous metals is examined. The equation for the gap in the electron spectrum for the transition to the superconducting state is obtained. The renormalization of the energy spectrum and damping of electron and phonon excitations due to electron-phonon interaction is considered. (orig.)

  2. Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

    Energy Technology Data Exchange (ETDEWEB)

    Laursen, S.L.

    1990-01-01

    Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly.

  3. Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

    International Nuclear Information System (INIS)

    Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom ''sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly

  4. Search for excited electrons using the ZEUS detector

    International Nuclear Information System (INIS)

    This paper reports a search for excited electrons at the HERA electron-proton collider. In a sample corresponding to an integrated luminosity of 26 nb-1, no evidence was found for any resonant state decaying into e-?, ?W- or e-Z0. Limits on the coupling strength of an excited electron have been determined for masses between 45 and 225 GeV. This study also reports the observation of the wide-angle e? Compton scattering process. (orig.)

  5. Contribution of excited electrons to the e+e- ? ?? process

    International Nuclear Information System (INIS)

    We have calculated the scattering cross-section of the e+e-??? process in the lowest order of QED. In addition to the single electron exchange diagram we have considered the possible contribution of heavy excited electrons. A symbolic manipulation program, REDUCE, is used for algebraic calculation of the cross section. Illustrations are given or QED tests for possible compositeness of leptons. Also we have studied the QED cuttoff parameters for the excited electrons search. (Author)

  6. SEARCH FOR EXCITED ELECTRONS USING THE ZEUS DETECTOR

    OpenAIRE

    ARZARELLO, F; Basile, M.; Bruni, G.; Bruni, P.; Lin, Q; Diekmann, B; Hilger, E; MENGEL, S; MOLLEN, J; SCHRAMM, D; Wedemeyer, R; Heath, H.; MALOS, J; TAPPER, R; Barillari, T.

    1993-01-01

    This paper reports a search for excited electrons at the HERA electron-proton collider. In a sample corresponding to an integrated luminosity of 26 nb-1, no evidence was found for any resonant state decaying into e-?, ?W- or e-Z0. Limits on the coupling strength of an excited electron have been determined for masses between 45 and 225 GeV. This study also reports the observation of the wide-angle e? Compton scattering process.

  7. Efficiencies of Aloof-Scattered Electron Beam Excitation of Metal and Graphene Plasmons

    CERN Document Server

    Ooi, Kelvin J A; Chu, Hong Son; Tan, Dawn T H; Ang, L K

    2015-01-01

    We assessed the efficiencies of surface plasmon excitation by an aloof-scattered electron beam on metals and graphene. Graphene is shown to exhibit high energy transfer efficiencies at very low electron kinetic energy requirements. We show that the exceptional performance of graphene is due to its unique plasmon dispersion, low electronic density and thin-film structure. The potential applications of these aloof-scattered graphene plasmons are discussed in aspects of coherent radiation.

  8. Attenuation of excited electrons at crystal surfaces

    International Nuclear Information System (INIS)

    Attenuation of the electron current determines surface sensitivity of electron spectroscopies. Pronounced energy and directional dependencies of the electron attenuation in crystals differ strongly from those commonly used for amorphous solids. Quantum descriptions of the electron attenuation can be obtained from the complex band structure of crystal surfaces at energies above the vacuum level. Contributions, specific for concrete processes, are obtained from theoretical description of photoelectron spectroscopy and of electron diffraction.

  9. Application of stepwise electron and laser excitation techniques to electron-photon correlation studies. Pt. 2

    International Nuclear Information System (INIS)

    A stepwise excitation electron-photon correlation experiment is presented in which a combination of electron-photon coincidence and laser excitation techniques is used. Atomic collision parameters were measured for the electron impact excitation of the Hg 61P0-61P1 (185 nm) transition at 16 eV incident electron energy and for electron scattering angles in the range 5o-30o. (Author)

  10. Treatment of semiconductor surfaces by laser-induced electronic excitation

    International Nuclear Information System (INIS)

    We review how semiconductor surfaces can be modified by laser irradiation. We deal solely with phenomena induced by electronic excitation, and compare the processes induced by laser irradiation with that by electrons from STM tips. The ejection of host atoms from perfect surface sites, or of hydrogen from hydrogen-terminated surfaces, takes place either by single excitation for high energy photons or with multiple excitation for low energy photons, even though the quantum yield for ejection by single excitation is extremely low. The atoms neighboring defects on surfaces are ejected with higher probabilities than those on perfect sites. There appear to be anti-bonding states, embedded in the continuum, excitation to which can induce atomic ejection, When the photon energy is too small, multiple photoexcitation or dense excitation is needed to reach these anti-bonding states. Possible applications of laser surface treatments are discussed. (author)

  11. Vibration-assisted resonance in photosynthetic excitation energy transfer

    CERN Document Server

    Irish, E K; Lovett, B W

    2013-01-01

    Coherent quantum energy transfer, as observed in photosynthetic pigment-protein complexes, is inhibited by energetic disorder. While this difficulty can be overcome to some extent by the addition of environmental noise, it has recently has begun to be appreciated that discrete intra- and/or intermolecular vibrational modes may play an important role in quantum dynamics. We present a microscopic mechanism by which intramolecular vibrational modes create resonant energy transfer pathways, enhancing the efficiency of both coherent and dephasing-assisted transfer. The principles of this vibration-assisted resonance are illustrated in a simple model based on one energy-transfer branch of the well-characterised Fenna-Matthews-Olson complex. Despite its simplicity, this model captures the interplay between strong electronic coupling that produces delocalised exciton states and resonance-enhanced weak coupling to local vibrational modes. Analytical and numerical results show that intramolecular vibrations can enhance...

  12. The role of electron-electron interactions in the excitation of fast, highly charged projectile ions

    International Nuclear Information System (INIS)

    The excitation of highly charged projectiles is usually dominated by interactions with the target nucleus, with the target electrons contributing only by screening the nucleus. At high energies, however, the target electrons have enough energy to independently excite the projectile. At the threshold energy, the target electrons give up all of their energy in the projectile frame in order to perform the excitation. These target electrons thereby end up in the continuum of the projectile and can be observed in the laboratory frame as cusp electrons. The authors are studying the electrons' role in these collisions by observing cusp electrons in coincidence with photons emitted from the excited projectiles in collisions of Si13+ with Ar, Ne, and H2, targets. They separate the electron-electron contribution by measuring these coincidences across the threshold energy (? 102 MeV). Initial data indicate that electron-electron interactions do not make a significant contribution in excitation due to the heavy targets

  13. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

    KAUST Repository

    Song, Yin

    2015-06-07

    © 2015 AIP Publishing LLC. Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S (λ 1, T∼ 2, λ 3)) along the population time (T∼ 2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S (λ 1, ν∼ 2, λ 3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ ν∼ 2) in the rephasing beating map and at negative frequency (- ν∼ 2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

  14. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

    International Nuclear Information System (INIS)

    Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S(?1,T~2,?3)) along the population time (T~2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S(?1,?~2,?3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+?~2) in the rephasing beating map and at negative frequency (??~2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems

  15. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film.

    Science.gov (United States)

    Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D

    2015-06-01

    Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S(?1,T?2,?3)) along the population time (T?2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S(?1,??2,?3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+??2) in the rephasing beating map and at negative frequency (-??2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems. PMID:26049430

  16. Cross sections for aluminium atom excitation by electron impact

    International Nuclear Information System (INIS)

    Inelastic collisions of slow electrons with aluminium atoms are studied by the method of extended beams with registration of optical signal from the intersection area. Behaviour of excitation cross sections in the AlI spectral series as well as excitation of radiation transitions with autoionization levels of aluminium atom are studied

  17. Electronic and rotational excitation of H2 by positron impact

    International Nuclear Information System (INIS)

    The body frame fixed nuclei and the laboratory frame rotational close coupling approximations have been employed to calculate electronic excitation of H2 (X 1?+g ? B 1?+u) by positron impact. Two electronic states (X 1?+g and B 1?+u) and three rotational states in both the elastic and excitation channels are retained in the calculations. Results are reported for electronically elastic, excitation and rotational cross sections up to the incident energy 75.0 eV. The elastic cross sections are found to be influenced significantly with the addition of B 1?+u state in the expansion scheme, in both the models used. Above the incident energy of 25.0 eV, the electronic excitation cross sections using the laboratory frame differ significantly from those of the fixed nuclei model. (orig.)

  18. Search for excited electrons in ep collisions at HERA

    International Nuclear Information System (INIS)

    A search for excited electrons is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb-1. The electroweak decays of excited electrons e* ?e?, e* ?eZ and e* ??W with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e* production cross sections and on the ratio f/? of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e* production via contact interactions is also addressed for the first time in ep collisions. (orig.)

  19. Electron-impact dissociative excitation of H3+

    International Nuclear Information System (INIS)

    We report the results of an ab initio calculation of the electron-impact dissociation of H3+ via excitation of the two lowest (3E',1E') excited electronic states, for electron energies between 15 eV, the threshold for excitation of the first electronic state, 3E', and 20.7 eV, corresponding to the excitation energy of the third excited electronic state, 1A2''. The calculations, which were carried out using the complex Kohn variational method, employed extensive correlated target wave functions that accurately reproduced the energy levels and transition dipoles of the ground and excited states of the ion. All open channels were included explicitly in the scattering calculation. Closed-channel effects were included via an ab initio optical potential. The fixed-nuclei excitation cross sections were found to be dominated by a series of sharp resonance structures. However, when the cross sections are averaged over the Franck-Condon envelope of the ground vibrational state, these sharp features are no longer seen

  20. Electron excitation from ground state to first excited state: Bohmian mechanics method

    Science.gov (United States)

    Yang, Song; Shuang, Zhao; Fu-Ming, Guo; Yu-Jun, Yang; Su-Yu, Li

    2016-03-01

    The excitation process of electrons from the ground state to the first excited state via the resonant laser pulse is investigated by the Bohmian mechanics method. It is found that the Bohmian particles far away from the nucleus are easier to be excited and are excited firstly, while the Bohmian particles in the ground state is subject to a strong quantum force at a certain moment, being excited to the first excited state instantaneously. A detailed analysis for one of the trajectories is made, and finally we present the space and energy distribution of 2000 Bohmian particles at several typical instants and analyze their dynamical process at these moments. Project supported by the Doctoral Research Start-up Funding of Northeast Dianli University, China (Grant No. BSJXM-201332), the National Natural Science Foundation of China (Grant Nos. 11547114, 11534004, 11474129, 11274141, 11447192, and 11304116), and the Graduate Innovation Fund of Jilin University, China (Grant No. 2015091).

  1. Excitation energy-transfer in functionalized nanoparticles: Going beyond the Förster approach

    Science.gov (United States)

    Gil, G.; Corni, S.; Delgado, A.; Bertoni, A.; Goldoni, G.

    2016-02-01

    We develop a novel approach to treat excitation energy transfer in hybrid nanosystems composed by an organic molecule attached to a semiconductor nanoparticle. Our approach extends the customary Förster theory by considering interaction between transition multipole moments of the nanoparticle at all orders and a point-like transition dipole moment representing the molecule. Optical excitations of the nanoparticle are described through an envelope-function configuration interaction method for a single electron-hole pair. We applied the method to the prototypical case of a core/shell CdSe/ZnS semiconductor quantum dot which shows a complete suppression of the energy transfer for specific transitions which could not be captured by Förster theory.

  2. Reaction dynamics of electronically excited alkali atoms with simpler molecules

    International Nuclear Information System (INIS)

    The reactions of electronically excited sodium atoms with simple molecules have been studied in crossed molecular beams experiments. Electronically excited Na(32P/sub 3/2/, 42D/sub 5/2/, and 52S/sub 1/2/) were produced by optical pumping using single frequency dye lasers. The effects of the symmetry, and the orientation and alignment of the excited orbital on the chemical reactivity, and detailed information on the reaction dynamics were derived from measurements of the product angular and velocity distributions. 12 refs., 9 figs

  3. Double-electron excitation above Xe K-edge

    International Nuclear Information System (INIS)

    When X-rays fall on any substance, whether solid, liquid, or gaseous, a photoabsorption occurs. Photoabsorption in atoms has been generally treated as a single-electron excitation process. However, the existence of the multi-electron excitation process, where the removal of a core electron by photoabsorption causes excitation of additional electrons in the same atoms, has been known in x-ray absorption spectra for a long time. In x-ray absorption spectra, experimental investigations of the shake processes in inner-shell ionization phenomena have been performed by detecting discontinuities. The shake effect which is a consequence of rearrangement of the atomic electrons, occurs in association with inner-shell excitation and ionization phenomena in x-ray absorption. The shake process has been studied extensively in various gases, because it is usually considered that the measurement of the multi-electron excitation is only possible for monatomic gases or vapors. The x-ray absorption spectra in Kr gas were measured by Ito et al. in order to observe precisely x-ray absorption spectra and to investigate the multi-electron excitation cross sections in Kr as a function of photon energy using synchrotron radiation. However, no suitable measured K x-ray absorption spectra was available to elucidate the shake processes. In the present work, the photoabsorption cross sections in Xe have been precisely measured in order to determine the features on the shake processes resulting from multiple electron excitations as a function of photon energy. Double-electron transitions of [1s4d], [1s4p], [1s4s], and [1s3d] are first detected. (author)

  4. An electron energy-loss study of picene and chrysene based charge transfer salts

    Energy Technology Data Exchange (ETDEWEB)

    Müller, Eric; Mahns, Benjamin; Büchner, Bernd; Knupfer, Martin [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany)

    2015-05-14

    The electronic excitation spectra of charge transfer compounds built from the hydrocarbons picene and chrysene, and the strong electron acceptors F{sub 4}TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and TCNQ (7,7,8,8-tetracyanoquinodimethan) have been investigated using electron energy-loss spectroscopy. The corresponding charge transfer compounds have been prepared by co-evaporation of the pristine constituents. We demonstrate that all investigated combinations support charge transfer, which results in new electronic excitation features at low energy. This might represent a way to synthesize low band gap organic semiconductors.

  5. An electron energy-loss study of picene and chrysene based charge transfer salts

    International Nuclear Information System (INIS)

    The electronic excitation spectra of charge transfer compounds built from the hydrocarbons picene and chrysene, and the strong electron acceptors F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and TCNQ (7,7,8,8-tetracyanoquinodimethan) have been investigated using electron energy-loss spectroscopy. The corresponding charge transfer compounds have been prepared by co-evaporation of the pristine constituents. We demonstrate that all investigated combinations support charge transfer, which results in new electronic excitation features at low energy. This might represent a way to synthesize low band gap organic semiconductors

  6. Two-photon Induced Hot Electron Transfer to a Single Molecule in a Scanning Tunneling Microscope

    OpenAIRE

    Wu, Shiwei; Ho, Wilson

    2010-01-01

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photo-excited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by t...

  7. Total electron scattering and electron state excitations cross sections for O2, CO, and CH4

    International Nuclear Information System (INIS)

    The authors review available cross section data for electron excitation and scattering for O2, CO, and CH4. Their interest is in utilizing available cross section data to obtain total electron state excitation cross sections for these atmospheric molecules in the 1 to 1000 eV electron impact energy range. Available information includes total electron scattering cross sections, ionization cross sections, elastic scattering cross sections, and some vibrational excitation cross section data. Their general conclusion is that derived total electronic state excitation cross sections should be accurate to about 50%, based upon the presently available input data

  8. Anomalous temperature dependence of excitation transfer betweenquantum dots.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Praha : Czechoslovak Association for Crystal Growth (CSACG), 2014 - (Kožíšek, Z.; Nitsch, K.). s. 25-25 ISBN 978-80-260-6599-9. [Joint Seminar Development of Materials Science in Research and Education /24./. 08.09.2014-12.09.2014, Lednice] R&D Pro jects: GA MŠk LH12186 Institutional support: RVO:68378271 Keywords : quantum dots * nanoparticles * electron-phonon interaction * energy transfer Subject RIV: BM - Solid Matter Physics ; Magnetism

  9. Direct conversion of graphite into diamond through electronic excited states

    CERN Document Server

    Nakayama, H

    2003-01-01

    An ab initio total energy calculation has been performed for electronic excited states in diamond and rhombohedral graphite by the full-potential linearized augmented plane wave method within the framework of the local density approximation (LDA). First, calculations for the core-excited state in diamond have been performed to show that the ab initio calculations based on the LDA describe the wavefunctions in the electronic excited states as well as in the ground state quite well. Fairly good coincidence with both experimental data and theoretical prediction has been obtained for the lattice relaxation of the core exciton state. The results of the core exciton state are compared with nitrogen-doped diamond. Next, the structural stability of rhombohedral graphite has been investigated to examine the possibility of the transition into the diamond structure through electronic excited states. While maintaining the rhombohedral symmetry, rhombohedral graphite can be spontaneously transformed to cubic diamond. Tota...

  10. Absorption of waves excited by electron beam in magnetized plasma with longitudinal inhomogeneous density

    International Nuclear Information System (INIS)

    Obtained experimental results confirm the concept of two-dimensional transformation of cold plasma waves into plasma oscillations in the lines ? approximately equal to ?subp, where ? is froquency of electron-excited wave, and ?subp is electron plasma frequency. Efficiency of Cherenkov absorption of oscillations is sufficiently high in this range. Energy transfer from a beam to plasma oscillations is observed to increase in a plasma with a longitudinal density gradient

  11. Electron-electron Thomas peak in fast transfer ionization

    International Nuclear Information System (INIS)

    ''Thomas process'' is a name used for a family of singular two-step processes that can lead to electron transfer. The Thomas process of the ''second kind,'' occurring in reactions with both transfer and ionization, utilizes the e-e scattering in the second step, so this Thomas process requires the dynamics of the electron-electron interaction. We calculate numerically the second order element of an S matrix and corresponding cross sections for the transfer ionization process. We find that the position and shape of the Thomas peak depend on both electron-electron and the electron-nucleus interaction. Also the direct and exchange amplitudes are equal at the peak position. We test the peaking approximation used for transfer ionization. Our results can be compared to experimental results for p++He?H+He2++e-. (c) 2000 The American Physical Society

  12. Excitation functions of slow proton transfer reactions involving negative ions

    International Nuclear Information System (INIS)

    Excitation functions were determined for a series of slow proton and deuteron transfer reactions involving negative ions using a tandem mass spectrometer. Some of the reactions observed, for example, ND2- + D2 ? D- + ND3, exhibit translational energy thresholds, even though they are exothermic. Other reactions, such as CH3COCH2- + CD3COCD3 ? CH3COCH2D + CD3COCD2-, exhibit a complex functional dependence of the cross section upon relative translational energy, which in turn is quite sensitive to the internal energy of the neutral reactant. Rate coefficients determined for these negative ion reactions in the present investigation are compared with analogous data previously reported for thermal energy reactants. The translational energy thresholds observed for several of the reactions are consistent with the existence of a potential energy barrier in the reaction coordinate between the reactants and products. It is demonstrated that the deconvoluted excitation function for the ND2-/D2 reaction is of the form sigma varies as (E/sub rel/ -- E0)/sup 1/2//E/sub rel/, as required by theory, and that the translational energy threshold corresponds to the Arrhenius activation energy for this process

  13. Efficient laser desorption ionization mass spectrometry of polycyclic aromatic hydrocarbons using excitation energy transfer from anthracene

    International Nuclear Information System (INIS)

    Highlights: ? Femtomolar detection of PAHs such as perylene and benzopyrene was achieved. ? Photoexcited anthracene molecules transferred their energy to PAHs. ? Electronically excited PAHs were then excited to be ions. ? Two-photon ionization process was necessary to complete the ionization process. ? The number of defect sites could be reduced by the annealing procedure. - Abstract: Polycyclic aromatic hydrocarbons (PAHs), such as perylene and benzopyrene, doped at amounts on the order of femtomol (?10?15 mol) in anthracene crystals could be detected by laser desorption ionization mass spectrometry. Sensitivity was roughly 103 times higher than that of LDI method in our experimental conditions. It was revealed from the excitation power dependence of the peak intensity of PAHs on the mass spectra that two-photon excitation in one UV pulse was necessary to complete the ionization process. It was also clarified that the number of defect sites that trap excitons generated in anthracene crystals could be reduced by the annealing procedure, by which an efficient energy transfer between anthracene and PAHs became possible

  14. Ultrafast electron diffraction studies of optically excited thin bismuth films

    International Nuclear Information System (INIS)

    This thesis contains work on the design and the realization of an experimental setup capable of providing sub-picosecond electron pulses for ultrafast electron diffraction experiments, and performing the study of ultrafast dynamics in bismuth after optical excitation using this setup. (orig.)

  15. Ultrafast electron diffraction studies of optically excited thin bismuth films

    Energy Technology Data Exchange (ETDEWEB)

    Rajkovic, Ivan

    2008-10-21

    This thesis contains work on the design and the realization of an experimental setup capable of providing sub-picosecond electron pulses for ultrafast electron diffraction experiments, and performing the study of ultrafast dynamics in bismuth after optical excitation using this setup. (orig.)

  16. Double-electron excitation above Xe K-edge

    International Nuclear Information System (INIS)

    The photoabsorption cross-section in Xe has been measured in order to determine the features of the shake processes resulting from multiple electron excitations as a function of photon energy. Double-electron transitions of [1s4d], [1s4p], [1s4s], and [1s3d] have been detected. (author)

  17. Excited baryon program at the Bonn electron stretcher accelerator ELSA

    International Nuclear Information System (INIS)

    The Bonn electron stretcher accelerator ELSA is the first of a new generation of continuous beam machines in the GeV region. It is qualified for experiments with tagged photons and with polarized electrons on polarized nucleons to investigate the electromagnetic properties of excited baryon resonances

  18. Electron-driven excitations and dissociation of molecules

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Greg [Univ. of California, Davis, CA (United States); Orel, Ann E. [Univ. of California, Davis, CA (United States)

    2015-02-13

    This program studied how energy is interchanged in electron and photon collisions with molecules leading to ex-citation and dissociation. Modern ab initio techniques, both for the photoionization and electron scattering, and the subsequent nuclear dynamics studies, are used to accurately treat these problems. This work addresses vibrational ex-citation and dissociative attachment following electron impact, and the dynamics following inner shell photoionzation. These problems are ones for which a full multi-dimensional treatment of the nuclear dynamics is essential and where non-adiabatic effects are expected to be important.

  19. Peculiarities of electron excitations decay in ion-molecular crystals

    International Nuclear Information System (INIS)

    Ionic-molecular crystals (IMC) have wide application in various optical devices. Its are using in capacity of solid state dosimetric materials and isolators. Peculiarities of chemical and energetic states of IMC lead to following number of features of electron excitation decay in comparison with alkaline-halogen crystals: - both an electrons and a holes simultaneously could be captured and localized either on anion or on cation complexes; - in-molecular forces arising in result of charge capture could conduct to decay of anion or cation complex; - decay products od anion or cation complex could participate in following reaction of new products formation. All these processes and new products of electron excitation decay exert strong effect on optical, magnetic and electrical characteristics of IMC. Knowledge of way and mechanisms of electron excitation decay in IMC could allow to control of radiation stability of crystals with help of impurities participating in different channels of solid state reactions

  20. An Exciting Aspect of Nanotechnology: Unimolecular Electronics

    Directory of Open Access Journals (Sweden)

    Metzger R. M.

    2013-08-01

    Full Text Available This is a brief update on our experimental work towards better one-molecule-thick monolayer rectifiers of electrical current, and on theoretical progress towards a one-molecule amplifier of electrical current. This program aims to provide electronic devices at the 2 to 3 nm level, as a dramatic advance towards practical integrated circuits of the future.

  1. Ultrafast relaxation dynamics of optically excited electrons in Ni-3

    Science.gov (United States)

    Pontius, N.; Neeb, M.; Eberhardt, W.; Lüttgens, G.; Bechthold, P. S.

    2003-01-01

    Photon-induced ultrafast energy dissipation in small isolated Ni-3 has been studied by two-color pump-probe photoelectron spectroscopy. The time-resolved photoelectron spectra clearly trace the path from a single-electron excitation to a thermalized cluster via both inelastic electron-electron scattering and electron-vibrational coupling. The relatively short electron-electron-scattering time of 215 fs results from the narrow energy spread of the partially filled d levels in this transition-metal cluster. The relaxation dynamics is discussed in view of the cluster size and in comparison to the totally different relaxation behavior of s/p-metal clusters.

  2. Interfacial electron transfer into functionalized crystalline polyoxotitanate nanoclusters.

    Science.gov (United States)

    Snoeberger, Robert C; Young, Karin J; Tang, Jiji; Allen, Laura J; Crabtree, Robert H; Brudvig, Gary W; Coppens, Philip; Batista, Victor S; Benedict, Jason B

    2012-05-30

    Interfacial electron transfer (IET) between a chromophore and a semiconductor nanoparticle is one of the key processes in a dye-sensitized solar cell. Theoretical simulations of the electron transfer in polyoxotitanate nanoclusters Ti(17)O(24)(OPr(i))(20) (Ti(17)) functionalized with four p-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established by X-ray diffraction measurements, are presented. Complementary experimental information showing IET has been obtained by EPR spectroscopy. Evolution of the time-dependent photoexcited electron during the initial 5 fs after instantaneous excitation to the NPA LUMO + 1 has been evaluated. Evidence for delocalization of the excitation over multiple chromophores after excitation to the NPA LUMO + 2 state on a 15 fs time scale is also obtained. While chromophores are generally considered electronically isolated with respect to neighboring sensitizers, our calculations show that this is not necessarily the case. The present work is the most comprehensive study to date of a sensitized semiconductor nanoparticle in which the structure of the surface and the mode of molecular adsorption are precisely defined. PMID:22548416

  3. Role of excited-state hydrogen detachment and hydrogen-transfer processes for the excited-state deactivation of an aromatic dipeptide: N-acetyl tryptophan methyl amide.

    Science.gov (United States)

    Shemesh, Dorit; Sobolewski, Andrzej L; Domcke, Wolfgang

    2010-05-21

    The excited-state electronic potential-energy surfaces of the three conformers of the capped dipeptide N-acetyl tryptophan methyl amide (NATMA), for which UV and IR spectra have been reported by Dian et al. [J. Chem. Phys., 2003, 118, 2696], have been explored with ab initio electronic-structure methods. The results provide insight into the nonadiabatic electronic coupling mechanisms which are responsible for the pronounced and conformer-specific perturbations of the spectra, such as broad and congested UV spectra as well as the deletion of certain fundamentals in the IR spectrum of the S(1) state. It is shown that the photophysical dynamics of NATMA is governed by at least five excited singlet electronic states: the two spectroscopic (1)L(b) and (1)L(a) states and the dissociative (1)pisigma* state of the indole chromophore, as well as a locally-excited state and a charge-transfer state of the peptide backbone. For the conformer NATMA C, which exhibits a gamma-turn of the backbone, a potentially very efficient excited-state deactivation mechanism to the electronic ground state via three conical intersections has been revealed. The results confirm the important role of hydrogen bonds for rapid excited-state deactivation of peptides, which enhances their photostability. PMID:20445897

  4. Excitation energy transfer in the peridinin-chlorophyll a-protein complex modeled using configuration interaction.

    Science.gov (United States)

    Bricker, William P; Lo, Cynthia S

    2014-08-01

    We modeled excitation energy transfer (EET) in the peridinin-chlorophyll a-protein (PCP) complex of dinoflagellate Amphidinium carterae to determine which pathways contribute dominantly to the high efficiency of this process. We used complete active space configuration interaction (CAS-CI) to calculate electronic structure properties of the peridinin (PID) and chlorophyll a (CLA) pigments in PCP and the transition density cube (TDC) method to calculate Coulombic couplings between energy transfer donors and acceptors. Our calculations show that the S1 ? Qy EET pathway from peridinin to chlorophyll a is the dominant energy transfer pathway in PCP, with two sets of interactions-between PID612 and CLA601 and between PID622 and CLA602-contributing most strongly. EET lifetimes for these two interactions were calculated to be 2.66 and 2.90, with quantum efficiencies of 85.75 and 84.65%, respectively. The calculated Coulombic couplings for EET between two peridinin molecules in the strongly allowed S2 excited states are extremely large and suggest excitonic coupling between pairs of peridinin S2 states. This methodology is also broadly applicable to the study of EET in other photosynthetic complexes and/or organic photovoltaics, where both single and double excitations are present and donor and acceptor molecules are tightly packed. PMID:25007401

  5. Observation of proton transfer in 2-aminopyridine dimer by electron and mass spectroscopy.

    Science.gov (United States)

    Samoylova, Elena; Radloff, Wolfgang; Ritze, Hans-Hermann; Schultz, Thomas

    2009-07-23

    A photoinitiated intermolecular electron-proton transfer reaction in 2-aminopyridine dimer was investigated by femtosecond pump-probe electron-ion coincidence spectroscopy and accompanying theory. Excited-state population dynamics were observed in real time by time-resolved mass spectroscopy, and the respective excited-state character of locally excited and proton/hydrogen transfer states was identified in coincident electron spectra. Two reaction channels for an ultrafast (sub-50 fs) and a slower (approximately 75 ps) proton/hydrogen transfer were observed and indicate that vibrational energy redistribution may lead to efficient population trapping in the excited state. Spectroscopic evidence of an unexpected hydrogen-transfer reaction in photoexcited aminopyridine monomer is also presented. PMID:19569694

  6. Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations.

    Science.gov (United States)

    List, Nanna Holmgaard; Zale?ny, Robert; Murugan, N Arul; Kongsted, Jacob; Bartkowiak, Wojciech; Ågren, Hans

    2015-09-01

    We establish the relationships between the metric of charge transfer excitation (?r) for the bright ??* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push-pull ?-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), ?r is a measure for the average hole-electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push-pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through ?r; if ? ? (?r)(k), then roughly, ?(TPA) ? (?r)(k+1). Second, a simple power relation between ?r and the molecular hyperpolarizabilities of push-pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull ?-conjugated systems through the metric of charge transfer. PMID:26575913

  7. A Qualitative Index of Spatial Extent in Charge-Transfer Excitations.

    Science.gov (United States)

    Le Bahers, Tangui; Adamo, Carlo; Ciofini, Ilaria

    2011-08-01

    With the aim of defining the spatial extent associated to an electronic transition, of particular relevance in the case of charge-transfer (CT) excitations, a new index, evaluated only from the computed density for the ground and excited state, is here derived and tested on a family of molecules that can be considered as prototypes of push-pull chromophores.The index (DCT) allows to define the spatial extent associated to a given transition as well as the associated fraction of electron transferred. By definition of centroids of charges associated to the density increase and depletion zones upon excitation, a qualitative and easy to visualize measure of the spatial extent of the donor and the acceptor moieties within a given molecular system is also given. Finally, an index (t) allowing to define the presence eventually pathologic CT transitions for time-dependent density functional theory treatment in conjunction with standard generalized gradient approximation or hybrid functional, that is through space CT, is disclosed. PMID:26606624

  8. Describing excited state intramolecular proton transfer in dual emissive systems: a density functional theory based analysis.

    Science.gov (United States)

    Wilbraham, Liam; Savarese, Marika; Rega, Nadia; Adamo, Carlo; Ciofini, Ilaria

    2015-02-12

    The excited state intramolecular proton transfer (ESIPT) reaction taking place within 2-(2-hydroxyphenyl)benzoxazole (HBT) and two recently experimentally characterized napthalimide derivatives-known as N-1 and N-4-has been investigated in order to identify and test a possible protocol for the description and complete mechanistic and electronic characterization of the reaction at the excited state. This protocol is based on density functional theory, time-dependent density functional theory, and a recently proposed electron density based index (DCT). This method is able to identify all stable species involved in the reaction, discriminate between possible reaction pathways over potential energy surfaces (PES), which are intrinsically very flat and difficult to characterize, and quantitatively measure the excited state charge transfer character throughout the reaction. The photophysical properties of the molecules (i.e., absorption and emission wavelength) are also quantitatively determined via the implicit inclusion of solvent effects in the case of toluene and, the more polar, tetrahydrofuran. The accuracy obtained with this protocol then opens up the possibility of the ab initio design of molecules exhibiting ESIPT for tailored applications such as highly selective molecular sensors. PMID:25208048

  9. Ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate excited states in molecules: Population and vibrational coherence transfers

    International Nuclear Information System (INIS)

    Graphical abstract: Temporal behaviors due to quantum mechanical interferences between the nonadiabatically coupled quasi-degenerate excited states (b and c) after a coherent excitation. Highlights: ? A nonadiabatic theory of quasi-degenerate ?-electronic states in aromatic molecules. ? Quantum interferences between the nonadiabatically-coupled ?-electronic states. ? Analysis of time-dependent vibrational coherence transfer via nonadiabatic couplings. - Abstract: Results of a theoretical study of ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate ?-electronic excited states of molecules were presented. Analytical expressions for temporal behaviors of population and vibrational coherence were derived using a simplified model to clarify the quantum mechanical interferences between the two coherently excited electronic states, which appeared in the nuclear wavepacket simulations [M. Kanno, H. Kono, Y. Fujimura, S.H. Lin, Phys. Rev. Lett 104 (2010) 108302]. The photon-polarization direction of the linearly polarized laser, which controls the populations of the two quasi-degenerate electronic states, determines constructive or destructive interference. Features of the vibrational coherence transfer between the two coupled quasi-electronic states through nonadiabatic couplings are also presented. Information on both the transition frequency and nonadiabatic coupling matrix element between the two states can be obtained by analyzing signals of two kinds of quantum beats before and after transfer through nonadiabatic coupling.

  10. Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(/sup 1/S) + H/sub 2/(B /sup 1/. sigma. /sub u//sup +/). [Solution for coupled channel equations

    Energy Technology Data Exchange (ETDEWEB)

    Grimes, R.M.

    1986-11-01

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H/sub 2/(B /sup 1/..sigma../sub u//sup +/) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H/sub 2/(B /sup 1/..sigma../sub u//sup +/). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H/sub 2/(E,F /sup 1/..sigma../sub g//sup +/) and with He + H/sub 2/(X /sup 1/..sigma../sub g//sup +/) and cause a local maximum and a deep minimum in the He + H/sub 2/(B /sup 1/..sigma../sub u//sup +/) PES, respectively. The crossing with He + H/sub 2/(X /sup 1/..sigma../sub g//sup +/) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H/sub 2/(B /sup 1/..sigma../sub u//sup +/) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs.

  11. Electron attachment to valence-excited CO

    OpenAIRE

    Kumar, Sanjay; D. Mathur

    1998-01-01

    The possibility of electron attachment to the valence $^{3}\\Pi$ state of CO is examined using an {\\it ab initio} bound-state multireference configuration interaction approach. The resulting resonance has $^{4}\\Sigma^{-}$ symmetry; the higher vibrational levels of this resonance state coincide with, or are nearly coincident with, levels of the parent $a^{3}\\Pi$ state. Collisional relaxation to the lowest vibrational levels in hot plasma situations might yield the possibility of a long-lived CO...

  12. Evolution of microstructure resulting from high electronic excitation during swift heavy ion irradiations

    International Nuclear Information System (INIS)

    This paper is devoted to the specific damage processes resulting from high levels of energy deposition in electronic excitation (a few 10 keV/nm) in metallic targets. Such conditions are fulfilled during irradiations with GeV heavy ions. After a short discussion about the mechanisms of energy deposition in elastic and inelastic collisions, the various microstructural changes observed during swift heavy ion irradiations of metals are described. The damage resulting from electronic excitation is localized along the ion wake and consists mainly in local or long-range order modifications or even phase transformation in crystalline materials and in anisotropic growth in amorphous materials. A tentative model based on the Coulomb explosion mechanism explains how part of the energy deposited in electronic excitation can be transferred to lattice atoms and accounts for the available experimental results. (orig.)

  13. Biotechnological Aspects of Microbial Extracellular Electron Transfer

    OpenAIRE

    Kato, Souichiro

    2015-01-01

    Extracellular electron transfer (EET) is a type of microbial respiration that enables electron transfer between microbial cells and extracellular solid materials, including naturally-occurring metal compounds and artificial electrodes. Microorganisms harboring EET abilities have received considerable attention for their various biotechnological applications, in addition to their contribution to global energy and material cycles. In this review, current knowledge on microbial EET and its appli...

  14. Advances in electron transfer chemistry, v.6

    CERN Document Server

    Mariano, PS

    1999-01-01

    It is clear that electron transfer chemisty is now one of the most active areas of chemical study. Advances in Electron Transfer Chemistry has been designed to allow scientists who are developing new knowledge in this rapidly expanding area to describe their most recent research findings. This volume will serve those interested in learning about current breakthroughs in this rapidly expanding area of chemical research.

  15. Elementary excitations in double electron layers with tunnel coupling

    International Nuclear Information System (INIS)

    The new class of the single-particle excitations in the double electron layers with the tunneling coupling between the layers is studied through the method of the light inelastic scattering. The dispersion law and dependence of the energies of the given excitations on the degree of the layers unbalance are measured. The new spectroscopic method for determining the degree of the double layers unbalance is proposed

  16. Electronic excitation and charge transfer processes in collisions of H{sup +}, H{sub 2}{sup +}, and H{sub 3}{sup +} ions with carbon monoxide at typical solar-wind velocities

    Energy Technology Data Exchange (ETDEWEB)

    Werbowy, S.; Pranszke, B., E-mail: dokws@univ.gda.pl [Institute of Experimental Physics, University of Gdansk, ul. Wita Stwosza 57, PL-80-952 Gdansk (Poland)

    2014-01-10

    Luminescence in the 200-580 nm spectral region was observed in the collisions of H{sup +}, H{sub 2}{sup +}, and H{sub 3}{sup +} with CO in the 50-1000 eV projectile energy range. Using computer simulations, we have identified emission of the following products in the observed spectra: the CO{sup +}(A-X) comet-tail system, CO{sup +}(B-X) first negative system, CO{sup +}(B-A) Baldet-Johnson system, and CO(b-a) third positive system. Also, an emission from atomic hydrogen (H{sub ?} line at 486nm) has been observed. From the analysis of the experimental spectra, we have determined the absolute emission cross-sections for the formation of the observed products. Computer simulations gave the excited-product population distributions over vibrational and rotational energy levels. The vibrational level distribution from the CO{sup +}(A-X) comet-tail system is compared with the data for CO excited by 100 eV electrons and extreme ultraviolet radiation (XUV) photons. We have used these data to analyze the excitation conditions in the comet Humason (1961e). From the vibrational population distributions observed in the comet, we found that this distribution can be reproduced if electrons produce 25%, protons 70%, and XUV photons produce 5% of the emitting molecules. We find that the ratio of the CO{sup +}(B-X) emission to the sum of two main emissions (CO{sup +}(A-X)+CO{sup +}(B-X)) is velocity dependent and does not depend on the projectile ion type. For small velocities (below 100 km s{sup –1}) the ratio is about 5%, while for higher velocities it increases to 30%. For these data, we have found an empirical formula that satisfactorily describes the experimental data: R = R {sub max}(1 – v {sub th}/v), (where R {sub max} = 33%, v {sub th} = 87 km s{sup –1}). This could be used to infer the velocity of ions producing the observed emission of CO{sup +} products.

  17. Tunnelling hot electron transfer amplifiers

    Science.gov (United States)

    Kircher, C. J.

    1993-10-01

    Significant advances were achieved in tunneling hot electron amplifiers and in the understanding of hot electron transport in the work funded by the contract and carried out by M. Heiblum and his co-workers. The results of this work are described in detail in nine papers that have been published in the open literature. (These papers are listed below as references 1-9 and copies of them are attached.) This report summarizes the principal results. There are three aspects of the work in which the results are particularly noteworthy: the demonstration of the first hot hole tunneling transistor and its use to study hot hole transport in GaAs; the successful fabrication of a hot electron 'THETA' transistor with a pseudomorphic InGaAs base which allowed high transistor gains (beta approx. = 30) to be achieved; and the conception and successful fabrication of a lateral hot electron device and its use to investigate ballistic, hot electron transport in a 2-dimensional electron gas in GaAs.

  18. Characterization of adsorption and electronic excited states of quercetin on titanium dioxide nanoparticles

    Science.gov (United States)

    Zdyb, Agata; Krawczyk, Stanis?aw

    2016-03-01

    Adsorption of quercetin on colloidal titanium dioxide nanoparticles in ethanol and its excited-state electronic structure were investigated by means of electronic and vibrational spectroscopies. The changes in electronic charge redistribution as reflected by the dipole moment difference, ??, between the ground and excited electronic states were measured with electroabsorption spectroscopy and analyzed using results of TD DFT computations. Adsorption of quercetin causes a red shift of its absorption spectrum. Raman spectra of quercetin analyzed with reference to analogous data for morin indicate binding of quercetin through the hydroxy groups of the catechol moiety. The difference dipole moment, which is 5.5 D in free quercetin, increases to 11.8 D in opposite direction in adsorbed quercetin, and is associated with charge-transfer to the Ti atom. The computed transition energy, intensity, vector ?? and molecular orbitals involved in the electronic transition at different molecular configurations indicate a bidentate chelating mode of binding of quercetin.

  19. Characterization of adsorption and electronic excited states of quercetin on titanium dioxide nanoparticles.

    Science.gov (United States)

    Zdyb, Agata; Krawczyk, Stanis?aw

    2016-03-15

    Adsorption of quercetin on colloidal titanium dioxide nanoparticles in ethanol and its excited-state electronic structure were investigated by means of electronic and vibrational spectroscopies. The changes in electronic charge redistribution as reflected by the dipole moment difference, ??, between the ground and excited electronic states were measured with electroabsorption spectroscopy and analyzed using results of TD DFT computations. Adsorption of quercetin causes a red shift of its absorption spectrum. Raman spectra of quercetin analyzed with reference to analogous data for morin indicate binding of quercetin through the hydroxy groups of the catechol moiety. The difference dipole moment, which is 5.5D in free quercetin, increases to 11.8D in opposite direction in adsorbed quercetin, and is associated with charge-transfer to the Ti atom. The computed transition energy, intensity, vector ?? and molecular orbitals involved in the electronic transition at different molecular configurations indicate a bidentate chelating mode of binding of quercetin. PMID:26773266

  20. Excitation energy transfer in the antenna system with divinyl-chlorophylls in the vinyl reductase-expressing Arabidopsis

    Science.gov (United States)

    Akimoto, Seiji; Yokono, Makio; Ohmae, Maiko; Yamazaki, Iwao; Nagata, Nozomi; Tanaka, Ryouichi; Tanaka, Ayumi; Mimuro, Mamoru

    2005-06-01

    We examined the excitation energy transfer and electron transfer processes in Arabidopsis thaliana thylakoid membranes following replacement of chlorophyll (Chl) molecules by expression of the vinyl reductase: monovinyl (MV)-Chl was replaced with divinyl (DV)-Chl and the DV-Chl a/DV-Chl b ratio was higher than that of control cells. By this replacement, energy transfer within the photosystem (PS) II became faster, whereas the PS II-to-PS I energy transfer was slower. In the DV-Chl mutant system, the delayed fluorescence from PS II was not resolved. Alternations of the antenna system and the reaction center are discussed in relation to Chl replacement.

  1. Heat Transfer Augmentation for Electronic Cooling

    Directory of Open Access Journals (Sweden)

    Suabsakul Gururatana

    2012-01-01

    Full Text Available Problem statement: The performance of electronic devices has been improving along with the rapid technology development. Cooling of electronic systems is consequently essential in controlling the component temperature and avoiding any hot spot. The study aims to review the present electronic cooling methods which are widely used in electronic devices. Approach: There are several methods to cool down the electronics components such as the pin-fin heat sink, confined jet impingement, heat pipe, micro heat sink and so on. Results: The cooling techniques can obviously increase heat transfer rate. Nonetheless, for active and passive cooling methods the pressure drop could extremely rise, when the heat transfer rate is increased. Conclusion: When the cooling techniques are used, it is clearly seen that the heat transfer increases with pressure drop. To avoid excessive expense due to high pressure drop, optimization method is required to obtain optimum cost and cooling rate.

  2. A stochastic reorganizational bath model for electronic energy transfer

    CERN Document Server

    Fujita, Takatoshi; Aspuru-Guzik, Alan

    2014-01-01

    The fluctuations of optical gap induced by the environment play crucial roles in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker model, in which the energy-gap fluctuation is approximated as a white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to take the thermal fluctuation of excitation energies into account. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equ...

  3. Locally-excited (LE) versus charge-transfer (CT) excited state competition in a series of para-substituted neutral green fluorescent protein (GFP) chromophore models.

    Science.gov (United States)

    Olsen, Seth

    2015-02-12

    In this paper, I provide a characterization of the low-energy electronic structure of a series of para-substituted neutral green fluorescent protein (GFP) chromophore models using a theoretical approach that blends linear free energy relationships (LFERs) with state-averaged complete-active-space self-consistent field (SA-CASSCF) theory. The substituents are chosen to sample the Hammett ?(p) scale from R = F to NH2, and a model of the neutral GFP chromophore structure (R = OH) is included. I analyze the electronic structure for different members of the series in a common complete-active-space valence-bond (CASVB) representation, exploiting an isolobal analogy between active-space orbitals for different members of the series. I find that the electronic structure of the lowest adiabatic excited state is a strong mixture of weakly coupled states with charge-transfer (CT) or locally excited (LE) character and that the dominant character changes as the series is traversed. Chromophores with strongly electron-donating substituents have a CT-like excited state such as expected for a push-pull polyene or asymmetric cyanine. Chromophores with weakly electron-donating (or electron-withdrawing) substituents have an LE-like excited state with an ionic biradicaloid structure localized to the ground-state bridge ? bond. PMID:25343562

  4. Cold transfer between deformed, Coulomb excited nuclei; Kalter Transfer zwischen deformierten, Coulomb-angeregten Kernen

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, H.

    1998-12-31

    The scattering system {sup 162}Dy {yields} {sup 116}Sn has been examined at energies in the vicinity of the Coulomb barrier using the Heidelberg-Darmstadt Crystal Ball spectrometer combined with 5 Germanium-CLUSTER detectors. In order to study pairing correlations as a function of angular momentum cold events were selected in the 2n stripping channel by identifying and suppressing the dominant hot part of the transfer with the Crystal Ball. The CLUSTER detectors with their high {gamma}-efficiency were used to identify the transfer channel and to resolve individual final states. Cross sections for the population of individual yrast states in a cold transfer reaction have been measured for the first time indicating the strong influence of higher transfer multipolarities. At small surface distances Coulomb-nuclear interferences were found to be responsible for the stronger decline of the population of higher yrast states in the transfer channel as compared to the Coulex channel. As a preparatory study for 2n transfer measurements between high spin yrast states in the backbending region of deformed nuclei the Coulomb excitation process in the crossing region of two bands in {sup 162}Dy has been analyzed. The gross properties of the measured population probabilities could be interpreted in a simple band mixing model. (orig.)

  5. Vibrational excitation of molecules by resonant electron scattering

    International Nuclear Information System (INIS)

    A formalism to describe the vibrational excitation of molecules via resonances is presented. For the limiting cases of short and long lifetime of the negative ion the excitation probability can be calculated using a golden rule expression and a simple Hamiltonian. The intensity distribution of the electron energy loss spectrum is expressed in terms of electron-vibration coupling constants which depend on the lifetime of the negative ion. Spectra for resonant scattering on benzene-d6 are calculated and good agreement with experiment is obtained. (orig.)

  6. Structural Phase Transition of Aluminum Induced by Electronic Excitation

    International Nuclear Information System (INIS)

    The dynamics of a structural phase transition induced by interband electronic excitation in aluminum is studied by determining the time evolution of the dielectric constant at 1.55 eV through the measurement of the transient reflectivity induced by an ultrafast pump pulse. The threshold fluence and the time scale for this transition are significantly less than the values necessary for ultrafast heat-induced melting, indicating that this phase change is caused by band structure collapse and lattice instability resulting from strong electronic excitation. (c) 2000 The American Physical Society

  7. Collective modes of laser excited electrons in clusters

    International Nuclear Information System (INIS)

    Complete text of publication follows. Clusters of material at solid state densities can form nanoplasmas after intense laser irradiation. The time evolution of the electron ion system is simulated using semi classical molecular dynamics (MD) simulations. Plasma properties like temperature and density are discussed as function of time. In order to investigated dynamical correlations for finite systems the method of restricted MD simulations has been developed. In this context, we investigate the bi-local frequency dependent structure factor for excited clusters. Within the resonance structure found, different collective excitations have been identified and characterized via the spatial distribution of the momentum auto-correlation function. For demonstration of the applicability of restricted MD simulations, results for resonances in a linear 1D chain are discussed. A systematic behaviour of a dispersion relation typical for plasmon excitations is obtained and agrees well with the bulk limit of an infinite chain. Collective electron excitation modes of 3D clusters are analysed using spherical harmonics. The spatially resolved momentum auto-correlation spectrum is interpreted in terms of collective electron excitation modes. Resonance frequencies of the modes are calculated and identified, for instance as a rigid collective oscillation of all electrons as well as a plane wave like oscillation. Damping rates are discussed. In order to compare with bulk properties, size effects of dynamical properties are investigated. Comparing different cluster sizes at similar ionization degrees, temperatures and densities, we found systematic changes for the Mie mode and the bulk plasmon excitations. In particular, the damping rates are increasing with the cluster size. As already shown for bulk plasmas, the dynamical bi-local structure factor, in particular the current auto-correlation function, is related to optical properties. Scattering as well as absorption of light in excited clusters is influenced by the corresponding collision frequency and subsequently affects the dielectric response function.

  8. Electron transfer induced fragmentation of acetic acid

    International Nuclear Information System (INIS)

    We present negative ion formation driven by electron transfer in atom (K) molecule (acetic acid) collisions. Acetic acid has been found in the interstellar medium, is also considered a biological related compound and as such studying low energy electron interactions will bring new insights as far as induced chemistry is concerned.

  9. Nuclear interlevel transfer driven by electronic transitions

    International Nuclear Information System (INIS)

    We show how a gamma-ray laser might be made by optically exciting a transfer of population from a long-lived isomer to an energetically adjacent short-lived state of the same nucleus. We compare the advantages of using transitions of high multipolarity versus transitions of low multi-polarity. Preliminary numerical investigations of the mechanism show it to be somewhat favorable. 35 refs., 4 figs

  10. Excitation energy transfer in vitro between phycobiliproteins and thylakoid photosystem II of higher plants

    Science.gov (United States)

    Wu, Xiaonan; Tseng, C. K.

    1992-12-01

    The excitation energy transfer from phycobiliproteins to thylakoid PSII of higher plants was investigated. When incubated with spinach thylakoids, phycobiliproteins isolated from red and blue-green algae transferred light energy absorbed to spinach PSII. The efficiency of energy transfer was dependent on the kind of phycobiliproteins used. If spinach thylakoids were replaced by the thylakoids of Brassica chinensis, R-phycoerythin or C-phycocyanin did not transfer their excitation energy to PSII of Brassica chinensis unless allophycocyanin was present.

  11. Distributed Multipolar Expansion Approach to Calculation of Excitation Energy Transfer Couplings.

    Science.gov (United States)

    B?asiak, Bartosz; Maj, Micha?; Cho, Minhaeng; Góra, Robert W

    2015-07-14

    We propose a new approach for estimating the electrostatic part of the excitation energy transfer (EET) coupling between electronically excited chromophores based on the transition density-derived cumulative atomic multipole moments (TrCAMM). In this approach, the transition potential of a chromophore is expressed in terms of truncated distributed multipolar expansion and analytical formulas for the TrCAMMs are derived. The accuracy and computational feasibility of the proposed approach is tested against the exact Coulombic couplings, and various multipole expansion truncation schemes are analyzed. The results of preliminary calculations show that the TrCAMM approach is capable of reproducing the exact Coulombic EET couplings accurately and efficiently and is superior to other widely used schemes: the transition charges from electrostatic potential (TrESP) and the transition density cube (TDC) method. PMID:26575762

  12. Charge-Transfer Excited States in Aqueous DNA: Insights from Many-Body Green's Function Theory

    Science.gov (United States)

    Yin, Huabing; Ma, Yuchen; Mu, Jinglin; Liu, Chengbu; Rohlfing, Michael

    2014-06-01

    Charge-transfer (CT) excited states play an important role in the excited-state dynamics of DNA in aqueous solution. However, there is still much controversy on their energies. By ab initio many-body Green's function theory, together with classical molecular dynamics simulations, we confirm the existence of CT states at the lower energy side of the optical absorption maximum in aqueous DNA as observed in experiments. We find that the hydration shell can exert strong effects (˜1 eV) on both the electronic structure and CT states of DNA molecules through dipole electric fields. In this case, the solvent cannot be simply regarded as a macroscopic screening medium as usual. The influence of base stacking and base pairing on the CT states is also discussed.

  13. Ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate excited states in molecules: Population and vibrational coherence transfers

    Science.gov (United States)

    Mineo, H.; Kanno, M.; Kono, H.; Chao, S. D.; Lin, S. H.; Fujimura, Y.

    2012-01-01

    Results of a theoretical study of ultrafast coherent dynamics of nonadiabatically coupled quasi-degenerate ?-electronic excited states of molecules were presented. Analytical expressions for temporal behaviors of population and vibrational coherence were derived using a simplified model to clarify the quantum mechanical interferences between the two coherently excited electronic states, which appeared in the nuclear wavepacket simulations [M. Kanno, H. Kono, Y. Fujimura, S.H. Lin, Phys. Rev. Lett 104 (2010) 108302]. The photon-polarization direction of the linearly polarized laser, which controls the populations of the two quasi-degenerate electronic states, determines constructive or destructive interference. Features of the vibrational coherence transfer between the two coupled quasi-electronic states through nonadiabatic couplings are also presented. Information on both the transition frequency and nonadiabatic coupling matrix element between the two states can be obtained by analyzing signals of two kinds of quantum beats before and after transfer through nonadiabatic coupling.

  14. Extremely confined gap surface plasmon modes excited by electrons

    CERN Document Server

    Raza, Søren; Pors, Anders; Holmgaard, Tobias; Kadkhodazadeh, Shima; Wagner, Jakob B; Pedersen, Kjeld; Wubs, Martijn; Bozhevolnyi, Sergey I; Mortensen, N Asger

    2013-01-01

    High spatial and energy resolution EELS can be employed for detailed characterization of both localized and propagating surface plasmon excitations supported by metal nanostructures, giving insight into fundamental physical phenomena involved in various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface plasmon (GSP) modes excited by swift electrons in nanometer-wide gaps. Both experimental and theoretical EELS data reveal the resonance behavior associated with the excitation of the antisymmetric (with respect to the transverse electric-field component) GSP mode for extremely small gap widths, down to ~5 nm. It is argued that the excitation of this mode, featuring very strong absorption, plays a crucial role in the experimental realization of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. Occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic...

  15. Single Molecule Spectroscopy of Electron Transfer

    International Nuclear Information System (INIS)

    The objectives of this research are threefold: (1) to develop methods for the study electron transfer processes at the single molecule level, (2) to develop a series of modifiable and structurally well defined molecular and nanoparticle systems suitable for detailed single molecule/particle and bulk spectroscopic investigation, (3) to relate experiment to theory in order to elucidate the dependence of electron transfer processes on molecular and electronic structure, coupling and reorganization energies. We have begun the systematic development of single molecule spectroscopy (SMS) of electron transfer and summaries of recent studies are shown. There is a tremendous need for experiments designed to probe the discrete electronic and molecular dynamic fluctuations of single molecules near electrodes and at nanoparticle surfaces. Single molecule spectroscopy (SMS) has emerged as a powerful method to measure properties of individual molecules which would normally be obscured in ensemble-averaged measurement. Fluctuations in the fluorescence time trajectories contain detailed molecular level statistical and dynamical information of the system. The full distribution of a molecular property is revealed in the stochastic fluctuations, giving information about the range of possible behaviors that lead to the ensemble average. In the case of electron transfer, this level of understanding is particularly important to the field of molecular and nanoscale electronics: from a device-design standpoint, understanding and controlling this picture of the overall range of possible behaviors will likely prove to be as important as designing ia the ideal behavior of any given molecule.

  16. Low-energy charge transfer excitations in NiO

    International Nuclear Information System (INIS)

    Comparative analysis of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of NiO poly- and nanocrystals in the spectral range 2-5.5 eV reveals two PLE bands peaked near 3.7 and 4.6 eV with a dramatic rise in the low-temperature PLE spectral weight of the 3.7 eV PLE band in the nanocrystalline NiO as compared with its polycrystalline counterpart. In frames of a cluster model approach we assign the 3.7 eV PLE band to the low-energy bulk-forbidden p-d (t1g(?)-eg) charge transfer (CT) transition which becomes the allowed one in the nanocrystalline state while the 4.6 eV PLE band is related to a bulk allowed d-d (eg-eg) CT transition scarcely susceptible to the nanocrystallization. The PLE spectroscopy of the nanocrystalline materials appears to be a novel informative technique for inspection of different CT transitions.

  17. Vibrational energy transfer in selectively excited diatomic molecules

    International Nuclear Information System (INIS)

    Single rovibrational states of HCl(v=2), HBr(v=2), DCl(v=2), and CO(v=2) were excited with a pulsed optical parametric oscillator (OPO). Total vibrational relaxation rates near - resonance quenchers were measured at 2950K using time resolved infrared fluorescence. These rates are attributed primarily to V - V energy transfer, and they generally conform to a simple energy gap law. A small deviation was found for the CO(v) + DCl(v') relaxation rates. Upper limits for the self relaxation by V - R,T of HCl(v=2) and HBr(v=2) and for the two quantum exchange between HCl and HBr were determined. The HF dimer was detected at 2950K and 30 torr HF pressure with an optoacoustic spectrometer using the OPO. Pulsed and chopped, resonant and non-resonant spectrophones are analyzed in detail. From experiments and first order perturbation theory, these V - V exchange rates appear to behave as a first order perturbation in the vibrational coordinates. The rotational dynamics are known to be complicated however, and the coupled rotational - vibrational dynamics were investigated theoreticaly in infinite order by the Dillon and Stephenson and the first Magnus approximations. Large ?J transitions appear to be important, but these calculations differ by orders of magnitude on specific rovibrational transition rates. Integration of the time dependent semiclassical equations by a modified Gordon method and a rotationally distorted wave approximation are discussed as methods which would treat the rotational motion more accurately. 225 references

  18. Direct conversion of graphite into diamond through electronic excited states

    International Nuclear Information System (INIS)

    An ab initio total energy calculation has been performed for electronic excited states in diamond and rhombohedral graphite by the full-potential linearized augmented plane wave method within the framework of the local density approximation (LDA). First, calculations for the core-excited state in diamond have been performed to show that the ab initio calculations based on the LDA describe the wavefunctions in the electronic excited states as well as in the ground state quite well. Fairly good coincidence with both experimental data and theoretical prediction has been obtained for the lattice relaxation of the core exciton state. The results of the core exciton state are compared with nitrogen-doped diamond. Next, the structural stability of rhombohedral graphite has been investigated to examine the possibility of the transition into the diamond structure through electronic excited states. While maintaining the rhombohedral symmetry, rhombohedral graphite can be spontaneously transformed to cubic diamond. Total energy in the rhombohedral structure has been calculated as a function of cell volume V, c/a ratio and bond length between layers R. The adiabatic potential energy surfaces for the transition from rhombohedral graphite to diamond in the states after core excitation have been investigated. In core exciton state, the graphite structure is more stable than the diamond. In the valence hole state after the Auger decay process, in contrast, the graphite structure is remarkably unstable compared with the diamond. The conversion into diamond from graphite can be induced spontaneously even at room temperatures due to excited holes. The induced holes decrease the stable interlayer bond length, which can lower the activation energy for buckling displacement of the hexagonal bonds, and the activation energy becomes zero by increasing the concentration of holes up to 0.1/C atom. These results predict that diamond synthesis is possible by a core excitation through the Auger decay process. (topical review)

  19. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    2013-01-01

    The step from ab initio atomic and molecular properties to thermodynamic - or macroscopic - properties requires the combination of several theoretical tools. This dissertation presents constant temperature molecular dynamics with bond length constraints, a hybrid quantum mechanics-molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems to show general (or expected) properties. Properties such as in the physical and (semi-)chemical interface between classical and quantum systems and the effects of molecular bond length constraints on the temperature during simulations. As a second step the methodology is applied to the symmetric and asymmetric charge transfer reactions between several first-row transition metals in water. The results are compared to experiments and rationalised with classical analytic expressions. Shortcomings of the methods are accounted for with clear steps towards improved accuracy. Later the analysis is extended to more complex systems composed of a larger osmium complex in solution and at the solute-substrate interfaces, where in particular the redox state of the complex is controlled through chemical means. The efficiency of the hybrid-classical and quantum mechanics method is used to generate adequate statistics and a simple post-sampling scheme used to generate free energy surfaces - which compare to full ab initio calculations. In the last part both the molecular dynamics and hybrid classical and quantum mechanics method are used to generate a vast data set for the accurate analysis of dynamical structure modes. This is for a large iridium-iridium dimer complex which shows a dramatic structural (and vibrational) change upon electronic excitation.

  20. The particle-hole map: a computational tool to visualize electronic excitations

    CERN Document Server

    Li, Yonghui

    2015-01-01

    We introduce the particle-hole map (PHM), a visualization tool to analyze electronic excitations in molecules in the time or frequency domain, to be used in conjunction with time-dependent density-functional theory (TDDFT) or other ab initio methods. The purpose of the PHM is to give detailed insight into electronic excitation processes which is not obtainable from local visualization methods such as transition densities, density differences, or natural transition orbitals. The PHM is defined as a nonlocal function of two spatial variables and provides information about the origins, destinations, and connections of charge fluctuations during an excitation process; it is particularly valuable to analyze charge-transfer excitonic processes. In contrast with the transition density matrix, the PHM has a statistical interpretation involving joint probabilities of individual states and their transitions, it satisfies several sum rules and exact conditions, and it is easier to read and interpret. We discuss and illu...

  1. DCS - a program for calculating differential cross sections for the electronic excitation of diatomic molecules at fixed nuclei

    International Nuclear Information System (INIS)

    The program DSC computes differential cross sections for the electron-impact electronic excitation of diatomic molecules from the corresponding fixed-nuclei T-matrices. The momentum-transfer formalism is used to derive a convenient expression of the differential cross section. (orig.)

  2. Monte Carlo generators for excited electron and neutrino production

    International Nuclear Information System (INIS)

    'EPEX' and 'NUPEX' are monte carlo event generators, written in standard FORTRAN 77, being able to simulate the production and the decay of the excited leptons e* and ?e* at the electron-proton-colliders HERA and LHC+LEP. A further option of the program 'EPEX' is to simulate the inelastic electron-proton-scattering via contact interactions as: e + p ? e + X. (orig./HSI)

  3. Electron energy distribution in He excited by ions

    International Nuclear Information System (INIS)

    The degradation spectrum of high-energy heavy charged particles which are slowed down in gaseous media is analytically determined. The nonstationary function of the electron energy-distribution in helium by pumping through nuclear reaction products is numerically calculated. The energy areas and times whereby the energy prices for formation of a single electron-ion pair or a single excited atom do not depend on the initial energy and the type of the ionizing heavy particles are determined

  4. Time-resolved spectroscopy of energy and electron transfer processes in the photosynthetic bacterium Heliobacillus mobilis.

    OpenAIRE

    Lin, S.; Chiou, H C; Kleinherenbrink, F A; Blankenship, R E

    1994-01-01

    The kinetics of excitation energy transfer and electron transfer processes within the membrane of Heliobacillus mobilis were investigated using femtosecond transient absorption difference spectroscopy at room temperature. The kinetics in the 725- to 865-nm region, upon excitation at 590 and 670 nm, were fit using global analysis. The fits returned three kinetic components with lifetimes of 1-2 ps and 27-30 ps, and a component that does not decay within several nanoseconds. The 1- to 2-ps comp...

  5. Excitation of electron Langmuir frequency harmonics in the solar atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Fomichev, V. V.; Fainshtein, S. M.; Chernov, G. P. [Russian Academy of Sciences, Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation (Russian Federation)

    2013-05-15

    An alternative mechanism for the excitation of electron Langmuir frequency harmonics as a result of the development of explosive instability in a weakly relativistic beam-plasma system in the solar atmosphere is proposed. The efficiency of the new mechanism as compared to the previously discussed ones is analyzed.

  6. Photoionization of furan from the ground and excited electronic states.

    Science.gov (United States)

    Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došli?, Na?a; Decleva, Piero

    2016-02-28

    Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy. PMID:26931702

  7. Molecular dynamics simulation of electronically excited polyatomic molecules

    International Nuclear Information System (INIS)

    A computer simulation method is proposed for MD study of the photoinduced intramolecular dynamics in polyatomic molecules electronically excited by ultrashort laser pulses. An efficient, partially analytical procedure for calculation of the absorption (emission) spectra is developed and used for determination of molecular potentials in accordance with the experimental supersonic jets spectra. (author). 21 refs, 4 figs, 1 tab

  8. Electron impact excitation processes for carbon-containing molecules

    International Nuclear Information System (INIS)

    Diamond thin films can be made easily by the plasma CVD process which utilizes skillfully the chemical activity of hydrocarbon multi-atom molecules. Accompanying the development of the technology like this, the basic understanding of plasma characteristics at atomic and molecular levels has become an urgent task. In this paper, the research on the elementary process of the collision excitation of low energy electrons and the molecules containing carbon, which plays the main role in the gaseous phase primary reaction process in low temperature plasma, is reported. The collision phenomena in plasma are the collision of accelerated electrons with gas molecules, elastic and inelastic scattering, the excitation and ionization of molecules due to inelastic scattering, the gaseous phase secondary reaction by the excited molecules and ions, and their transport and surface reaction with substrates. As the method of measuring cross sections, electron beam method is explained. On the knowledge obtained from differential cross sections (DCS) on the interaction of electrons and multi-atom molecules, elastic scattering DCS, vibration excitation and unstable negative ion state, dissociative adhesion and stable negative ion formation and so on are described. (K.I.)

  9. Excitation of electron Langmuir frequency harmonics in the solar atmosphere

    International Nuclear Information System (INIS)

    An alternative mechanism for the excitation of electron Langmuir frequency harmonics as a result of the development of explosive instability in a weakly relativistic beam-plasma system in the solar atmosphere is proposed. The efficiency of the new mechanism as compared to the previously discussed ones is analyzed.

  10. Extremely confined gap surface-plasmon modes excited by electrons

    DEFF Research Database (Denmark)

    Raza, Søren; Stenger, Nicolas; Pors, Anders Lambertus; Holmgaard, Tobias; Kadkhodazadeh, Shima; Wagner, Jakob Birkedal; Pedersen, Kjeld; Wubs, Martijn; Bozhevolnyi, Sergey I.; Mortensen, N. Asger

    2014-01-01

    High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying ...

  11. Electron excitation after plasmon decay in proton-aluminum collisions

    International Nuclear Information System (INIS)

    When a projectile travels inside a metal, it interacts with the electron gas, producing both binary and collective excitations (plasmons). Within the nearly-free-electron-gas scheme, Roesler and co-workers showed that plasmons decay in first order and a conduction electron is emitted (interband transition). Working within the frame of atomic collisions, we develop a simple model to describe this decay. The first-order Born expansion is used to approximate the electron wave functions. The influence of the lattice potential on the excited electron is considered in the calculations in order to balance the momentum-conservation equation. It gives contributions associated with sites of the reciprocal lattice. The potential expansion coefficients are obtained following Animalu and co-workers [Philos. Mag. 9, 451 (1964)]. First- and second-differential spectra (in energy and angle) are analyzed discriminating contributions due to different lattice momenta. In all cases, contributions due to binary excitations of the valence electrons and inner-shell ionization are presented to establish a comparison

  12. Localised to intraligand charge-transfer states in cyclometalated platinum complexes: an experimental and theoretical study into the influence of electron-rich pendants and modulation of excited states by ion binding.

    Science.gov (United States)

    Rochester, David L; Develay, Stéphanie; Zális, Stanislav; Williams, J A Gareth

    2009-03-14

    The neopentyl ester of 1,3-di(2-pyridyl)benzene-5-boronic acid (dpy-B) is a useful intermediate in the divergent synthesis of N;C;N-coordinating, 1,3-di(2-pyridyl)benzene ligands, HL(n), that carry aryl substituents at the 5-position of the central ring. The platinum(ii) complexes, PtL(n)Cl, of several such ligands have been prepared, incorporating pendant anisoles, arylamines, an oxacrown, and an azacrown, all of which are strongly luminescent in solution at 298 K. The emission of the complexes is partially quenched by oxygen, and all of the compounds are very efficient sensitisers of singlet oxygen. The quantum yields of (1)O(2) formation have been measured on the basis of the intensity of the O(2)(1)Delta(g) emission at 1270 nm, and are in the range 0.25-0.65. Density functional theory (DFT) calculations have been carried out that include the effect of the solvent, on the unsubstituted complex PtL(1)Cl and on the derivatives incorporating p-dimethylaminophenyl and phenyl-15-mono-N-azacrown-5 pendants (PtL(9)Cl and PtL(12)Cl respectively). Absorption spectra have been simulated on the basis of the calculated singlet excitations: they closely resemble the experimental spectra. In particular, the DFT successfully accounts for the appearance of low-energy absorption bands that accompany the introduction of the aryl pendants, indicating the participation of the aryl group in the HOMO but not significantly in the LUMO. The calculated lowest energy triplet excitation of PtL(1)Cl is close to the observed 0-0 emission maximum of this complex in solution. Taking together data for this series of complexes and related compounds previously studied, the energies of the lowest-energy spin-allowed absorption bands are shown to correlate approximately linearly with the oxidation peak potential. The emission energies show a similar correlation in toluene, but in CH2Cl2 the value for PtL(9)Cl is anomalously low. The differing emission properties of this complex in the two solvents suggest a switch to a TICT-like state in CH2Cl2 (TICT = twisted intramolecular charge transfer), stabilised in the more polar environment. Transient DC photoconductivity measurements confirm that the dipole moment of the triplet excited state is larger in CH2Cl2 than in toluene. The azacrown PtL(12)Cl displays similar behaviour. Binding of metal ions such as Ca2+ to the azacrown unit of this complex leads to a pronounced blue shift in the emission, which can be readily understood in terms of the large increase in the TICT energy that will accompany the binding of the metal ion to the lone pair of the azacrown nitrogen atom. PMID:19240906

  13. Excitation of magnesium ions in slow electron-ion collisions

    International Nuclear Information System (INIS)

    Using the method of crossing modulated beams, the absolute excitation functions for the transitions 3s-3p and 3p-4s in Mg 2 taking place in collisions between electrons and magnesium ions have been measured. The study has been carried out by measuring the flux of photons excited in the transitions indicated. The estimated error of the determination of the absolute cross sections is about 25%. The energy dependences of the cross sections have been investigated from the threshold of excitation to 100 eV. In both cases, an abrupt increase in the effectiveness of excitation can be observed in the near-threshold region, which is consistent (if the electron energy straggling is taken into account) with the concept that at threshold the cross section is finite. As the electron energy increases, one can observe a steady decrease of the above characteristic. At an energy of 11 eV, the resonance doublet excitation functions have a bench, which may be accounted for the cascade contribution to the 3p-state population. The greatest effectiveness of excitation of the 3p-4s transition is attained just at the energy of 11 eV, amounting to about 4% of that for the 3s-3p transition. For comparison also the results of theoretical calculations of the cross sections for excitation of the 3p- and 4s-configurations, have been given, performed in a modified Coulomb-Born approximation. At electron energies of 80 eV and above one observes a reasonable agreement between theory and experiment. The experimental results on the resonance doublet excitation are also compared with the results of calculations of the 3s-3p excitation carried out in the Bethe approximation. The strong-coupling calculations yield the cross-sectional values close to the experimental ones measured in the corresponding energy region. The slope of the theoretical curves is, however, different from that of the experimental ones. The Bethe approximation has been used also at the higher energies

  14. Excited-state kinetics of the carotenoid S//1 state in LHC II and two-photon excitation spectra of lutein and beta-carotene in solution Efficient Car S//1 yields Chl electronic energy transfer via hot S//1 states?

    CERN Document Server

    Walla, P J; Linden, Patricia A; Ohta, Kaoru

    2002-01-01

    The excited-state dynamics of the carotenoids (Car) in light- harvesting complex II (LHC II) of Chlamydomonas reinhardtii were studied by transient absorption measurements. The decay of the Car S //1 population ranges from similar to 200 fs to over 7 ps, depending on the excitation and detection wavelengths. In contrast, a 200 fs Car S//1 yields Chlorophyll (Chl) energy transfer component was the dominant time constant for our earlier two-photon fluorescence up- conversion measurements (Walla, P.J. ; et al. J. Phys. Chem. B 2000, 104, 4799-4806). We also present the two-photon excitation (TPE) spectra of lutein and beta-carotene in solution and compare them with the TPE spectrum of LHC II. The TPE-spectrum of LHC II has an onset much further to the blue and a width that is narrower than expected from comparison to the S//1 fluorescence of lutein and beta-carotene in solution. Different environments may affect the shape of the S//1 spectrum significantly. To explain the blue shift of the TPE spectrum and the d...

  15. Catalytic Olefin Hydroamidation Enabled by Proton-Coupled Electron Transfer

    Science.gov (United States)

    2015-01-01

    Here we report a ternary catalyst system for the intramolecular hydroamidation of unactivated olefins using simple N-aryl amide derivatives. Amide activation in these reactions occurs via concerted proton-coupled electron transfer (PCET) mediated by an excited state iridium complex and weak phosphate base to furnish a reactive amidyl radical that readily adds to pendant alkenes. A series of H-atom, electron, and proton transfer events with a thiophenol cocatalyst furnish the product and regenerate the active forms of the photocatalyst and base. Mechanistic studies indicate that the amide substrate can be selectively homolyzed via PCET in the presence of the thiophenol, despite a large difference in bond dissociation free energies between these functional groups. PMID:26439818

  16. A quadrature excitation coil for longitudinally detected electron spin resonance

    Science.gov (United States)

    Resmer, Frank; Nicholson, Ian; Hutchison, James M. S.

    2001-07-01

    Longitudinally detected electron spin resonance (LODESR) is an alternative method to conventional continuous wave (cw) ESR with transverse detection. LODESR has some practical advantages over cw-ESR for in vivo experiments carried out with excitation at radio frequencies. Sample losses, however, can be a problem and generally limit the LODESR signal to noise ratio for biological samples. We have developed a LODESR coil system with quadrature excitation circuit in order to decrease the sample power deposition. The coil system consists of a high pass birdcage excitation coil operated in quadrature (320 MHz) and a solenoidal coil (325 kHz) for signal detection. Methods of decoupling the excitation and detection circuits are described. Results reported here show the effectiveness of the LODESR coil system with quadrature excitation in reducing the sample power deposition by a factor of 2. The quadrature excitation coil assembly we have described here could be used, without further modification, for LODESR imaging. The coil assembly, including rf screen, could be placed inside the field gradient coils. LODESR imaging, in contrast to nuclear magnetic resonance imaging, uses continuous rather than pulsed gradient wave forms and the copper foil used for the rf screen would not significantly distort the gradients.

  17. Investigations of the electron capture excitation in slow ion-atom collisions

    International Nuclear Information System (INIS)

    Line radiation between 40 and 110 nm from rare gas ions and hydrogen molecules excited by electron impact was observed with a polarization-free arranged vuv-monochromator. Various emission cross sections were measured in dependence of electron impact energy, and were made absolute by comparison with published data. In this way, absolute monochromator calibration could be obtained at several wave lengths. Photon emission in collisions of doubly charged Ne- and Ar ions with Ar, Kr or Xe at impact energies of 10-50 keV was investigated with the absolutely calibrated vuv spectrometer under polarisation-free arrangement. In the collision system (20Ne+2 + Xe) de-excitation after single electron capture was found to proceed with comparable probability via photon emission from excited NeII states and via transfer ionisation causing electron emission. State-resolved studies typical for single electron capture excitation on collisions of singly or multiply charged ions with hydrogen-like target atoms were carried out with the collision systems (20Ne+ + Li) and (20Ne+2 + Li) respectively. For both systems absolute emission cross sections for the strongest NeI and NeII lines emitted in the vuv range respectively were measured together with the respective total single electron capture cross sections. Absolute excitation cross sections were derived from the measured emission cross sections by correcting for the influence of the finite lifetime of the involved excited states. The obtained results could be explained satisfactorily with simple theoretical considerations on the basis of quasimolecular two state transitions. (author)

  18. Analysis of photobleaching in single-molecule multicolor excitation and Förster resonance energy transfer measurements.

    Science.gov (United States)

    Eggeling, Christian; Widengren, Jerker; Brand, Leif; Schaffer, Jörg; Felekyan, Suren; Seidel, Claus A M

    2006-03-01

    Dye photobleaching is a major constraint of fluorescence readout within a range of applications. In this study, we investigated the influence of photobleaching in fluorescence experiments applying multicolor laser as well as Förster resonance energy transfer (FRET) mediated excitation using several red-emitting dyes frequently used in multicolor experiments or as FRET acceptors. The chosen dyes (cyanine 5 (Cy5), MR121, Alexa660, Alexa680, Atto647N, Atto655) have chemically distinct chromophore systems and can be excited at 650 nm. Several fluorescence analysis techniques have been applied to detect photobleaching and to disclose the underlying photophysics, all of which are based on single-molecule detection: (1) fluorescence correlation spectroscopy (FCS) of bulk solutions, (2) fluorescence cross-correlation of single-molecule trajectories, and (3) multiparameter fluorescence detection (MFD) of single-molecule events. The maximum achievable fluorescence signals as well as the survival times of the red dyes were markedly reduced under additional laser irradiation in the range of 500 nm. Particularly at excitation levels at or close to saturation, the 500 nm irradiation effectively induced transitions to higher excited electronic states on already excited dye molecules, leading to a pronounced bleaching reactivity. A theoretical model for the observed laser irradiance dependence of the fluorescence brightness of a Cy5 FRET acceptor dye has been developed introducing the full description of the underlying photophysics. The model takes into account acceptor as well as donor photobleaching from higher excited electronic states, population of triplet states, and energy transfer to both the ground and excited states of the acceptor dye. Also, photoinduced reverse intersystem crossing via higher excited triplet states is included, which was found to be very efficient for Cy5 attached to DNA. Comparing continuous wave (cw) and pulsed donor excitation, a strong enhancement of acceptor photobleaching by a factor of 5 was observed for the latter. Thus, in the case of fluorescence experiments utilizing multicolor pulsed laser excitation, the application of the appropriate timing of synchronized green and red laser pulses in an alternating excitation mode can circumvent excessive photobleaching. Moreover, important new single-molecule analysis diagnosis tools are presented: (1) For the case of excessive acceptor photobleaching, cross-correlation analysis of single-molecule trajectories of the fluorescence signal detected in the donor and acceptor detection channels and vice versa shows an anticorrelated exponential decay and growth, respectively. (2) The time difference, Tg - Tr, of the mean observation times of all photons detected for the donor and acceptor detection channels within a single-molecule fluorescence burst allows one to identify and exclude molecules with an event of acceptor photobleaching. The presented single-molecule analysis methods can be constrained to, for example, FRET-active subpopulations, reducing bias from FRET-inactive molecules. The observations made are of strong relevance for and demand a careful choice of laser action in multicolor and FRET experiments, in particular when performed at or close to saturation. PMID:16509620

  19. Dynamics of two-electron excitations in helium

    Energy Technology Data Exchange (ETDEWEB)

    Caldwell, C.D.; Menzel, A.; Frigo, S.P. [Univ. of Central Florida, Orlando, FL (United States)] [and others

    1997-04-01

    Excitation of both electrons in helium offers a unique window for studying electron correlation at the most basic level in an atom in which these two electrons and the nucleus form a three-body system. The authors utilized the first light available at the U-8 undulator-SGM monochromator beamline to investigate the dynamic parameters, partial cross sections, differential cross sections, and photoelectron angular distribution parameters ({beta}), with a high resolving power for the photon beam and at the highly differential level afforded by the use of their electron spectrometer. In parallel, they carried out detailed calculations of the relevant properties by a theoretical approach that is based on the hyperspherical close-coupling method. Partial photoionization cross sections {sigma}{sub n}, and photoelectron angular distributions {beta}{sub n} were measured for all possible final ionic states He{sup +}(n) in the region of the double excitations N(K,T){sup A} up to the N=5 threshold. At a photon energy bandpass of 12 meV below the thresholds N=3, 4, and 5, this level of differentiation offers the most critical assessment of the dynamics of the two-electron excitations to date. The experimental data were seen to be very well described by the most advanced theoretical calculations.

  20. Statistics of excitations in the electron glass model

    Science.gov (United States)

    Palassini, Matteo

    2011-03-01

    We study the statistics of elementary excitations in the classical electron glass model of localized electrons interacting via the unscreened Coulomb interaction in the presence of disorder. We reconsider the long-standing puzzle of the exponential suppression of the single-particle density of states near the Fermi level, by measuring accurately the density of states of charged and electron-hole pair excitations via finite temperature Monte Carlo simulation and zero-temperature relaxation. We also investigate the statistics of large charge rearrangements after a perturbation of the system, which may shed some light on the slow relaxation and glassy phenomena recently observed in a variety of Anderson insulators. In collaboration with Martin Goethe.

  1. Spodumene and garnet luminescence excited by subnanosecond electron beams

    Science.gov (United States)

    Baksht, E. Kh.; Burachenko, A. G.; Solomonov, V. I.; Tarasenko, V. F.

    2011-11-01

    Pulsed cathodoluminescence of spodumene and yttrium-aluminum garnet crystals activated by Mn2+ and Nd3+ ions, respectively, is investigated. The luminescence was excited upon crystal irradiation by electron beams with current densities of 35 and 100 A/cm2 and average electron energy of ˜ 50 keV for 0.1, 0.25, and 0.65 ns. It is demonstrated that the electron beam duration decreased to several tenth of a nanosecond does not lead to essential changes of the mechanisms of pulsed cathodoluminescence excitation and character of its spectrum, but in this case, the intensity of luminescence of the hole centers increases compared with the intracenter luminescence.

  2. Electron collisions and internal excitation in stored molecular ion beams

    Energy Technology Data Exchange (ETDEWEB)

    Buhr, H.

    2006-07-26

    In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He{sup +}{sub 2}. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He{sup +}{sub 2}, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD{sup +} is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

  3. Electron collisions and internal excitation in stored molecular ion beams

    International Nuclear Information System (INIS)

    In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He+2. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He+2, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD+ is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

  4. Excitement tem-horn antenna by impulsive relativistic electron beam

    CERN Document Server

    Balakirev, V A; Egorov, A M; Lonin, Y F

    2000-01-01

    In the given operation the opportunity of reception powerful electromagnetic irradiation (EMI) is observationally explored by excitation by a impulsive relativistic electronic beam (IREB) of a TEM-horn antenna. It is revealed, that at such expedient of excitation of the TEM-horn antenna, the signal of radiation of the antenna contains three various components caused by oscillation of radiation by forward front IREB, high-voltage discharge between plates irradiation of TEM-horn antenna a and resonant properties of the antenna devices.

  5. Facile Interfacial Electron Transfer of Hemoglobin

    Directory of Open Access Journals (Sweden)

    Chunhai Fan

    2005-12-01

    Full Text Available Abstract: We herein describe a method of depositing hemoglobin (Hb and sulfonated polyaniline (SPAN on GC electrodes that facilitate interfacial protein electron transfer. Well-defined, reproducible, chemically reversible peaks of Hb and SPAN can be obtained in our experiments. We also observed enhanced peroxidase activity of Hb in SPAN films. These results clearly showed that SPAN worked as molecular wires and effectively exchanged electrons between Hb and electrodes.Mediated by Conjugated Polymers

  6. Theory of Ultrafast Photoinduced Heterogeneous Electron Transfer

    OpenAIRE

    May, Volkhard

    2006-01-01

    Abstract Ultrafast heterogeneous electron transfer (HET) between a molecule attached to a semiconductor surface and the conduction band of the semiconductor is discussed theoretically with emphasis on the perylene TiO_2 system. The used description accounts for the specialty of the molecule i.e. its particular electronic level scheme together with its vibrational degrees of freedom. The band continuum of the semiconductor is included and the approach is ready to describe different...

  7. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

    Energy Technology Data Exchange (ETDEWEB)

    Song, Yin [Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6 (Canada); Hellmann, Christoph; Stingelin, Natalie [Department of Materials and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London SW7 2AZ (United Kingdom); Scholes, Gregory D., E-mail: gscholes@princeton.edu [Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6 (Canada); Department of Chemistry, Princeton University, Washington Road, Princeton, New Jersey 08544 (United States)

    2015-06-07

    Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S(λ{sub 1},T{sup ~}{sub 2},λ{sub 3})) along the population time (T{sup ~}{sub 2}) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S(λ{sub 1},ν{sup ~}{sub 2},λ{sub 3})). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ν{sup ~}{sub 2}) in the rephasing beating map and at negative frequency (−ν{sup ~}{sub 2}) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

  8. Defect production and annihilation in metals through electronic excitation by energetic heavy ion bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Iwase, Akihiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1997-03-01

    Defect production, radiation annealing and defect recovery are studied in Ni and Cu irradiated with low-energy ({approx}1-MeV) and high-energy ({approx}100-MeV) ions. Irradiation of Ni with {approx}100-MeV ions causes an anomalous reduction, or even a complete disappearance of the stage-I recovery. This result shows that the energy transferred from excited electrons to lattice atoms through the electron-lattice interaction contributes to the annihilation of the stage-I interstitials. This effect is also observed in Ni as a large radiation annealing during 100-MeV heavy ion irradiation. On the other hand, in Cu thin foils, we find the defect production process strongly associated with electron excitation, where the defect production cross section is nearly proportional to S{sub e}{sup 2}. (author)

  9. Excited electronic states and photophysics of uracil-water complexes

    International Nuclear Information System (INIS)

    The electronically excited singlet states of complexes of uracil with one water molecule have been studied theoretically using ab initio multireference configuration interaction methods. In agreement with previous theoretical and experimental results, four cyclic isomers of uracil forming hydrogen bonds with the water molecule have been located with energies within 0.2 eV from the lowest energy isomer. Focus has been given on the mechanism for radiationless decay to the ground state after initial UV absorption and on the effect of complexation with water on previously reported radiationless decay pathways. Features on the excited state potential energy surfaces, such as minima, transition states and conical intersections, have been located for all isomers and compared with those of free uracil. The hydrogen-bonded water molecule changes the relative energies of these features and may lead to different excited state dynamics and lifetimes, in agreement with experimental observations

  10. Promoting Knowledge Transfer with Electronic Note Taking

    Science.gov (United States)

    Katayama, Andrew D.; Shambaugh, R. Neal; Doctor, Tasneem

    2005-01-01

    We investigated the differences between (a) copying and pasting text versus typed note-taking methods of constructing study notes simultaneously with (b) vertically scaffolded versus horizontally scaffold notes on knowledge transfer. Forty-seven undergraduate educational psychology students participated. Materials included 2 electronic…

  11. Quantum effects in biological electron transfer.

    Czech Academy of Sciences Publication Activity Database

    de la Lande, A.; Babcock, N. S.; ?ezá?, Jan; Levy, B.; Sanders, B. C.; Salahub, D.

    2012-01-01

    Ro?. 14, ?. 17 (2012), s. 5902-5918. ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron transfer * tunnelling * decoherence * semi-classical molecular dynamics * density functional theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012

  12. Vibrationally Assisted Electron Transfer Mechanism of Olfaction: Myth or Reality?

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Chang, Po-Yao

    2012-01-01

    Smell is a vital sense for animals. The mainstream explanation of smell is based on recognition of the odorant molecules through characteristics of their surface, e.g., shape, but certain experiments suggest that such recognition is complemented by recognition of vibrational modes. According to this suggestion an olfactory receptor is activated by electron transfer assisted through odorant vibrational excitation. The hundreds to thousands of different olfactory receptors in an animal recognize odorants over a discriminant landscape with surface properties and vibrational frequencies as the two major dimensions. In the present paper we introduce the vibrationally assisted mechanism of olfaction and demonstrate for several odorants that, indeed, a strong enhancement of an electron tunneling rate due to odorant vibrations can arise. We discuss in this regard the influence of odorant deuteration and explain, thereby, recent experiments performed on Drosophila melanogaster. Our demonstration is based on known physical properties of biological electron transfer and on ab initio calculations on odorants carried out for the purpose of the present study. We identify a range of physical characteristics which olfactory receptors and odorants must obey for the vibrationally assisted electron transfer mechanism to function. We argue that the stated characteristics are feasible for realistic olfactory receptors, noting, though, that the receptor structure presently is still unknown, but can be studied through homology modeling.

  13. Vibrational relaxation pathways in the electronic excited state of carotenoid

    International Nuclear Information System (INIS)

    The intra- and inter-molecular vibrational relaxation in the electronic excited state (1Bu+) of spheroidene derivative (the number of conjugated double bonds, n=8) has been investigated at room temperature by means of femtosecond time-resolved fluorescence spectroscopy based on an optical-Kerr-gate technique. Depending on the photo-excitation either to the 1Bu+(v=1) or 1Bu+(v=2) vibronic level, remarkable differences were observed in hot luminescence spectra related to the vibrational relaxation process of high- and low-frequency modes. Under the excitation to the 1Bu+(v=2) state hot luminescence from the 1Bu+(v=1) state was observed as a dominant feature of the time-resolved spectra while the dynamic Stokes shift originating from the low-frequency-modes dynamics was clearly observed under the excitation to the 1Bu+(v=1). These observations of the excitation energy dependence of time-resolved fluorescence spectra were discussed by analyzing the Franck-Condon factors of transitions from v=0,1, and 2 levels of high-frequency modes

  14. Electronic excitation of the lB2 state of furan by electron impact

    International Nuclear Information System (INIS)

    We report on recent results obtained in studies involving electronically inelastic electron scattering from furan. In particular, we considered the electronic transition from ground state to the 1B2 excited state. The scattering calculations employed the Schwinger multichannel method implemented with pseudopotentials and were carried out up to a nine-state close-coupling plus polarization level of approximation.

  15. Extremely confined gap surface-plasmon modes excited by electrons.

    DEFF Research Database (Denmark)

    Raza, SØren; Stenger, Nicolas

    2014-01-01

    High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5 nm. We argue that excitation of this mode, featuring very strong absorption, has a crucial role in experimental realizations of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. The occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices.

  16. Dynamic correlation of photo-excited electrons: Anomalous levels induced by light–matter coupling

    International Nuclear Information System (INIS)

    Nonlinear light–matter coupling plays an important role in many aspects of modern physics, such as spectroscopy, photo-induced phase transition, light-based devices, light-harvesting systems, light-directed reactions and bio-detection. However, excited states of electrons are still unclear for nano-structures and molecules in a light field. Our studies unexpectedly present that light can induce anomalous levels in the electronic structure of a donor–acceptor nanostructure with the help of the photo-excited electrons transferring dynamically between the donor and the acceptor. Furthermore, the physics underlying is revealed to be the photo-induced dynamical spin–flip correlation among electrons. These anomalous levels can significantly enhance the electron current through the nanostructure. These findings are expected to contribute greatly to the understanding of the photo-excited electrons with dynamic correlations, which provides a push to the development and application of techniques based on photosensitive molecules and nanostructures, such as light-triggered molecular devices, spectroscopic analysis, bio-molecule detection, and systems for solar energy conversion.

  17. EBIT measurements of excitation and ionization by electron impact

    Science.gov (United States)

    Chen, Hui

    2013-05-01

    Electron-impact excitation and electron-impact ionization are fundamental atomic processes that are critical for describing both the ionization balance and the radiative emission of ions in plasmas. The properties of the electron beam ion trap (EBIT) made it a highly useful device for measuring electron-impact cross sections of highly charged ions. Moreover, the recent development and use of x-ray microcalorimeter array detectors made it possible to extend cross section determinations to ions with multiple valence electrons and to measure the ionization equilibrium of complex ions. Since EBIT's inception in the 1980's measurements include cross sections of direct and indirect (resonance) excitation as well as cross sections of single-electron ionization of K-shell and L-shell ions of Ti, V, Cr, Mn, and Fe. Studies of very high-Z elements, such as Xe, Au and U, have been performed, showing the importance of the Breit interaction, which in the case of K-shell uranium ions increases the ionization cross section by 50%. This talk will review the results of such measurements performed at EBIT for nearly three decades. Work at the Lawrence Livermore National Laboratory was performed under auspices of the Department of Energy under contract DE-AC52-07NA-27344.

  18. Toward Highlighting the Ultrafast Electron Transfer Dynamics at the Optically Dark Sites of Photocatalysts

    DEFF Research Database (Denmark)

    Canton, Sophie E.; Zhang, Xiaoyi; Zhang, Jianxin; Brandt van Driel, Tim; Kjaer, Kasper S.; Haldrup, Martin Kristoffer; Chabera, Pavel; Harlang, Tobias; Suarez-Alcantara, Karina; Liu, Yizhu; Pe?rez, Jorge; Bordage, Ame?lie; Pápai, Mátyás Imre; Vanko?, Gyo?rgy; Jennings, Guy; Kurtz, Charles A.; Rovezzi, Mauro; Glatzel, Pieter; Smolentsev, Grigory; Uhlig, Jens; Dohn, Asmus Ougaard; Christensen, Morten; Galler, Andreas; Gawelda, Wojciech; Bressler, Christian; Lemke, Henrik T.; Møller, Klaus Braagaard; Nielsen, Martin Meedom; Lomoth, Reiner; Wa?rnmark, Kenneth; Sundstro?m, Villy

    2013-01-01

    work, transient X-ray absorption spectroscopy highlights the electronic and geometric changes that affect such a center in a bimetallic model complex. Upon selective excitation of the ruthenium chromophore, the cobalt moiety is reduced through intramolecular electron transfer and undergoes a spin flip...

  19. The role of electron-impact vibrational excitation in electron transport through gaseous tetrahydrofuran

    International Nuclear Information System (INIS)

    In this paper, we report newly derived integral cross sections (ICSs) for electron impact vibrational excitation of tetrahydrofuran (THF) at intermediate impact energies. These cross sections extend the currently available data from 20 to 50 eV. Further, they indicate that the previously recommended THF ICS set [Garland et al., Phys. Rev. A 88, 062712 (2013)] underestimated the strength of the electron-impact vibrational excitation processes. Thus, that recommended vibrational cross section set is revised to address those deficiencies. Electron swarm transport properties were calculated with the amended vibrational cross section set, to quantify the role of electron-driven vibrational excitation in describing the macroscopic swarm phenomena. Here, significant differences of up to 17% in the transport coefficients were observed between the calculations performed using the original and revised cross section sets for vibrational excitation

  20. Excitation transfer pathways in excitonic aggregates revealed by the stochastic Schr\\"odinger equation

    CERN Document Server

    Abramavicius, Vytautas

    2014-01-01

    We derive the stochastic Schr\\"odinger equation for the system wave vector and use it to describe the excitation energy transfer dynamics in molecular aggregates. We suggest a quantum-measurement based method of estimating the excitation transfer time. Adequacy of the proposed approach is demonstrated by performing calculations on a model system. The theory is then applied to study the excitation transfer dynamics in a photosynthetic pigment-protein Fenna-Matthews-Olson (FMO) aggregate using both the Debye spectral density and the spectral density obtained from earlier molecular dynamics simulations containing strong vibrational high-frequency modes. The obtained results show that the excitation transfer times in the FMO system are affected by the presence of the vibrational modes, however the transfer pathways remain the same.

  1. Excitation transfer pathways in excitonic aggregates revealed by the stochastic Schrödinger equation

    Energy Technology Data Exchange (ETDEWEB)

    Abramavicius, Vytautas, E-mail: vytautas.ab@gmail.com; Abramavicius, Darius, E-mail: darius.abramavicius@ff.vu.lt [Faculty of Physics, Department of Theoretical Physics, Vilnius University, Saul?tekio 9, LT-10222 Vilnius (Lithuania)

    2014-02-14

    We derive the stochastic Schrödinger equation for the system wave vector and use it to describe the excitation energy transfer dynamics in molecular aggregates. We suggest a quantum-measurement based method of estimating the excitation transfer time. Adequacy of the proposed approach is demonstrated by performing calculations on a model system. The theory is then applied to study the excitation transfer dynamics in a photosynthetic pigment-protein Fenna-Matthews-Olson (FMO) aggregate using both the Debye spectral density and the spectral density obtained from earlier molecular dynamics simulations containing strong vibrational high-frequency modes. The obtained results show that the excitation transfer times in the FMO system are affected by the presence of the vibrational modes; however, the transfer pathways remain the same.

  2. Electronic excitations in semiconductors: Variational Green's-function approach

    Science.gov (United States)

    Lukas, Wolf-Dieter; Fulde, Peter

    1984-07-01

    We develop a Green's-function method for calculating electronic excitations in semiconductors. It is variational in character and takes full account of the local part of the correlation hole as well as the long-ranged polarization cloud. Both contribute significantly to the quasiparticles and their energies. The method is based on the Sauermann functional, the stationary point of which is the one-particle Green's function. For the case of a simple model, a connection is established to an earlier method which required the computation of correlated wave functions in order to obtain the excitation energies. Furthermore, we relate the present approach to the single-mode approximation of Overhauser and others which was devised for describing electron correlations in nearly homogeneous systems.

  3. Electron-lattice Interaction and Nonlinear Excitations in Cuprate Structures

    International Nuclear Information System (INIS)

    A low temperature lattice modulation of the chains of the YBa2Cu3O7 is considered by deriving a Hamiltonian of electron-lattice interaction from density-functional calculations for deformed lattice and solving it for the groundstate. Hubbard-type Coulomb interaction is included. The obtained groundstate is a charge-density-wave state with a pereodicity of four lattice constants and a gap for one-electron excitations of about 1eV, sensitively depending on parameters of the Hamiltonian. There are lots of polaronic and solitonic excitations with formation energies deep in the gap, which can pin the Fermi level and thus produce again metallicity of the chain. They might also contribute to pairing of holes in adjacent CuO2-planes. (author)

  4. Electron densities and the excitation of CN in molecular clouds

    Science.gov (United States)

    Black, John H.; Van Dishoeck, Ewine F.

    1991-01-01

    In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds.

  5. Electron densities and the excitation of CN in molecular clouds

    Energy Technology Data Exchange (ETDEWEB)

    Black, J.H.; Van Dishoeck, E.F. (Onsala Rymdobservatorium (Sweden) Steward Observatory, Tucson, AZ (USA) California Institute of Technology, Pasadena (USA) Leiden Rijksuniversiteit, Sterrewacht (Netherlands))

    1991-03-01

    In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds. 32 refs.

  6. Electron densities and the excitation of CN in molecular clouds

    International Nuclear Information System (INIS)

    In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds. 32 refs

  7. Electron-impact ionization-excitation of atoms

    Energy Technology Data Exchange (ETDEWEB)

    Bartschat, Klaus [Department of Phsyics and Astronomy, Drake University, Des Moines, IA 50311 (United States)], E-mail: klaus.bartschat@drake.edu

    2008-11-01

    As a highly correlated process, simultaneous electron-impact ionization-excitation presents a major challenge to experimentalists and theorists alike. Taking advantage of significant improvements in multi-hit detector technology and the rapid increase of computational power, a number of advances have recently been reported. The current state-of the-art in this field is illustrated by a few key examples.

  8. Total electron scattering and electronic state excitations cross sections for O2, CO, and CH4

    Science.gov (United States)

    Kanik, I.; Trajmar, S.; Nickel, J. C.

    1993-01-01

    Available electron collision cross section data concerning total and elastic scattering, vibrational excitation, and ionization for O2, CO, and CH4 have been critically reviewed, and a set of cross sections for modeling of planetary atmospheric behavior is recommended. Utilizing these recommended cross sections, we derived total electronic state excitation cross sections and upper limits for dissociation cross sections, which in the case of CH4 should very closely equal the actual dissociation cross section.

  9. Excitation of the gas-phase selenium by electron impact

    International Nuclear Information System (INIS)

    Selenium (Se) is an important trace mineral, which plays an active role in many biological systems as it has toxicological and physiological effects. The slow electron excitation of selenium in the gas-phase has been studied using an optical spectroscopy method. The emission spectra of selenium were recorded in the wavelength range of 200-590 nm at the incident electron energies of 20, 30 and 50 eV. In the above spectra, the molecular emissions within the wavelength range of 300-560 nm as well as the selenium atomic spectral lines were observed. The optical excitation functions for the most intense molecular emissions and atomic selenium spectral lines were measured. It has been found that in the selenium vapour the atomic selenium has very low concentration at the 440 K temperature and the main component of the vapour is the Se2 molecule. It has been demonstrated that the excitation of the atomic selenium occurs due to the dissociation of the Se2 molecule by electron impact

  10. Theory of nuclear excitation by electron capture for heavy ions

    Energy Technology Data Exchange (ETDEWEB)

    Gagyi-Palffy, A.

    2006-07-01

    The resonant process of nuclear excitation by electron capture (NEEC) in collisions involving highly-charged ions has been investigated theoretically. NEEC is a rare recombination process in which a free electron is captured into a bound shell of an ion with the simultaneous excitation of the nucleus. Total cross sections for NEEC followed by the radiative decay of the excited nucleus are presented for various collision systems. The possibility to observe the NEEC in scattering experiments with trapped or stored ions was discussed focusing on the cases with the largest calculated resonance strength. As the photons emitted in different channels of the electron recombination process are indistinguishable in the total cross section, the interference between NEEC followed by the radiative decay of the nucleus and radiative recombination was investigated. The angular distribution of the emitted photons in the recombination process provides means to discern the two processes. Angular differential cross sections for the emitted photons in the case of E2 nuclear transitions were presented for several heavy elements. (orig.)

  11. Theory of nuclear excitation by electron capture for heavy ions

    International Nuclear Information System (INIS)

    The resonant process of nuclear excitation by electron capture (NEEC) in collisions involving highly-charged ions has been investigated theoretically. NEEC is a rare recombination process in which a free electron is captured into a bound shell of an ion with the simultaneous excitation of the nucleus. Total cross sections for NEEC followed by the radiative decay of the excited nucleus are presented for various collision systems. The possibility to observe the NEEC in scattering experiments with trapped or stored ions was discussed focusing on the cases with the largest calculated resonance strength. As the photons emitted in different channels of the electron recombination process are indistinguishable in the total cross section, the interference between NEEC followed by the radiative decay of the nucleus and radiative recombination was investigated. The angular distribution of the emitted photons in the recombination process provides means to discern the two processes. Angular differential cross sections for the emitted photons in the case of E2 nuclear transitions were presented for several heavy elements. (orig.)

  12. Indistinguishability in electron-impact excitation-ionization of helium

    International Nuclear Information System (INIS)

    We present fully differential cross section (FDCS) calculations for electron-impact excitation-ionization of helium using the four-body distorted wave-exchange (4DWE) model. This model includes both the direct and exchange amplitudes, which account for the indistinguishability of the free electrons in the final state. The results of the 4DWE model are compared with absolute experimental results, and we find that the exchange amplitude has a minimal impact in determining the shape and magnitude of the FDCS.

  13. Dynamical response function of transverse excitations in electron fluid

    International Nuclear Information System (INIS)

    Dynamical response function of transverse excitations in 3D electron fluid has been studied within moment conserving method by including the effect of many-body correlations beyond the random approximation for various electron densities. It is found that correlation effects bring about qualitative as well as quantitative changes in the behavior of transverse response function as compared to the corresponding non-interacting system. The imaginary part of transverse response function becomes flatter with increase in rs and shows signature of the presence of double peak structure. On the other hand. the width at half maximum of real part decreases with increase in rs. (author)

  14. Electron plasma dynamics during autoresonant excitation of the diocotron mode

    Energy Technology Data Exchange (ETDEWEB)

    Baker, C. J., E-mail: cbaker@physics.ucsd.edu; Danielson, J. R., E-mail: jrdanielson@ucsd.edu; Hurst, N. C., E-mail: nhurst@physics.ucsd.edu; Surko, C. M., E-mail: csurko@ucsd.edu [Physics Department, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093 (United States)

    2015-02-15

    Chirped-frequency autoresonant excitation of the diocotron mode is used to move electron plasmas confined in a Penning-Malmberg trap across the magnetic field for advanced plasma and antimatter applications. Plasmas of 10{sup 8} electrons, with radii small compared to that of the confining electrodes, can be moved from the magnetic axis to ?90% of the electrode radius with near unit efficiency and reliable angular positioning. Translations of ?70% of the wall radius are possible for a wider range of plasma parameters. Details of this process, including phase and displacement oscillations in the plasma response and plasma expansion, are discussed, as well as possible extensions of the technique.

  15. Emission Spectroscopy as a Probe into Photoinduced Intramolecular Electron Transfer in Polyazine Bridged Ru(II,Rh(III Supramolecular Complexes

    Directory of Open Access Journals (Sweden)

    Karen J. Brewer

    2010-08-01

    Full Text Available Steady-state and time-resolved emission spectroscopy are valuable tools to probe photochemical processes of metal-ligand, coordination complexes. Ru(II polyazine light absorbers are efficient light harvesters absorbing in the UV and visible with emissive 3MLCT excited states known to undergo excited state energy and electron transfer. Changes in emission intensity, energy or band-shape, as well as excited state lifetime, provide insight into excited state dynamics. Photophysical processes such as intramolecular electron transfer between electron donor and electron acceptor sub-units may be investigated using these methods. This review investigates the use of steady-state and time-resolved emission spectroscopy to measure excited state intramolecular electron transfer in polyazine bridged Ru(II,Rh(III supramolecular complexes. Intramolecular electron transfer in these systems provides for conversion of the emissive 3MLCT (metal-to-ligand charge transfer excited state to a non-emissive, but potentially photoreactive, 3MMCT (metal-to-metal charge transfer excited state. The details of the photophysics of Ru(II,Rh(III and Ru(II,Rh(III,Ru(II systems as probed by steady-state and time-resolved emission spectroscopy will be highlighted.

  16. Many-body approach to electronic excitations concepts and applications

    CERN Document Server

    Bechstedt, Friedhelm

    2015-01-01

    The many-body-theoretical basis and applications of theoretical spectroscopy of condensed matter, e.g. crystals, nanosystems, and molecules are unified in one advanced text for readers from graduate students to active researchers in the field. The theory is developed from first principles including fully the electron-electron interaction and spin interactions. It is based on the many-body perturbation theory, a quantum-field-theoretical description, and Green's functions. The important expressions for ground states as well as electronic single-particle and pair excitations are explained. Based on single-particle and two-particle Green's functions, the Dyson and Bethe-Salpeter equations are derived. They are applied to calculate spectral and response functions. Important spectra are those which can be measured using photoemission/inverse photoemission, optical spectroscopy, and electron energy loss/inelastic X-ray spectroscopy. Important approximations are derived and discussed in the light of selected computa...

  17. Excitation of heavy hydrogen-like ions by light atoms in relativistic collisions with large momentum transfers

    CERN Document Server

    Najjari, B

    2012-01-01

    We present a theory for excitation of heavy hydrogen-like projectile-ions by light target-atoms in collisions where the momentum transfers to the atom are very large on the atomic scale. It is shown that in this process the electrons and the nucleus of the atom behave as (quasi-) free particles with respect to each other and that their motion is governed by the field of the nucleus of the ion. The effect of this field on the atomic particles can be crucial for the contribution to the excitation of the ion caused by the electrons of the atom. Due to comparatively very large nuclear mass, however, this field can be neglected in the calculation of the contribution to the excitation due to the nucleus of the atom.

  18. Charge-Transfer Excitations in the Model Superconductor HgBa$_2$CuO$_{\\bf 4+\\delta}$

    OpenAIRE

    Lu, L.; Zhao , X.; Chabot-Couture, G.; Hancock, J. N.; Kaneko, N.; Vajk, O. P.; Yu, G; Grenier, S.; Kim, Y.J.; Casa, D.; Gog, T.; Greven, M.

    2005-01-01

    We report a Cu $K$-edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa$_2$CuO$_{4+\\delta}$ at optimal doping ($T_{\\rm c} = 96.5 $ K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly-dispersive ($ < 0.5$ eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitatio...

  19. Electron emission and electron transfer processes in proton-naphthalene collisions at intermediate velocities

    Science.gov (United States)

    Mishra, P. M.; Rajput, J.; Safvan, C. P.; Vig, S.; Kadhane, U.

    2013-11-01

    We investigate the fragmentation and ionization of naphthalene by protons at intermediate velocities (between 1.41 and 2.68 a.u.). Relative cross sections for electron capture (EC), electron emission (EE), and capture ionization are measured. The EC cross sections decrease rapidly over the energy range under consideration (50-150 keV) and are lower than EE cross sections. The EE cross sections, on the other hand, change very slowly in this energy range. The energetics of interactions is quantified by comparing the mass spectra with the photodissociation breakdown curves from literature. In the case of single capture, resonant electron transfer to n = 1 state in H+ is seen to dominate the interaction but is shown to be accompanied by a small amount of electronic energy loss. In the EE mode, two mechanisms are shown to be active in the collision process: large impact parameter plasmon excitation mode, and closer encounters with higher amounts of electronic energy loss.

  20. Regulation of excitation energy transfer in diatom PSII dimer: How does it change the destination of excitation energy?

    Science.gov (United States)

    Yokono, Makio; Nagao, Ryo; Tomo, Tatsuya; Akimoto, Seiji

    2015-10-01

    Energy transfer dynamics in dimeric photosystem II (PSII) complexes isolated from four diatoms, Chaetoceros gracilis, Cyclotella meneghiniana, Thalassiosira pseudonana, and Phaeodactylum tricornutum, are examined. Time-resolved fluorescence measurements were conducted in the range of 0-80ns. Delayed fluorescence spectra showed a clear difference between PSII monomer and PSII dimer isolated from the four diatoms. The difference can be interpreted as reflecting suppressed energy transfer between PSII monomers in the PSII dimer for efficient energy trapping at the reaction center. The observation was especially prominent in C. gracilis and T. pseudonana. The pathways seem to be suppressed under a low pH condition in isolated PSII complexes from C. gracilis, and excitation energy may be quenched with fucoxanthin chlorophyll a/c-binding protein (FCP) that was closely associated with PSII in C. gracilis. The energy transfer between PSII monomers in the PSII dimer may play a role in excitation energy regulation in diatoms. PMID:26188377

  1. Simulação Monte Carlo de mecanismo de transferência de energia de excitação eletrônica: modelo de Perrin para a supressão estática da luminescência / Monte Carlo simulation of electronic excitation energy transfer: Perrin´s model for static luminescence quenching

    Scientific Electronic Library Online (English)

    João Batista Marques, Novo; Lauro Camargo, Dias Júnior.

    Full Text Available [...] Abstract in english A software based in the Monte Carlo method has been developed aiming the teaching of the Perrin´s model for static luminescence quenching. This software allows the student to easily simulate the luminescence decays of emissive molecules in the presence of quenching ones. The software named PERRIN wa [...] s written for FreeBASIC compiler and it can be applied for systems where the molecules remain static during its excited state lifetime. The good agreement found between the simulations and the expected theoretical results shows that it can be used for the luminescence and excited states decay kinetic teaching.

  2. Theory of resonance and threshold effects in the electronic excitation of molecules by electron impact

    International Nuclear Information System (INIS)

    A simple model of electron scattering resonances near electronic excitation thresholds is discussed. The model consists of a single discrete electronic state coupled to several electronic continua. The vibrational dynamics in the resonance state is treated, taking proper account of non-Born-Oppenheimer effects in near-threshold electron-molecule scattering. The effect of long-range potentials is included via the threshold expansion of the partial decay widths of the resonance. The analytic properties of the fixed-nuclei S matrix are analyzed in detail for two special cases (s-wave scattering in the absence of long-range potentials and scattering from a strongly polar target molecule). The dipole potential is shown to lead to a qualitatively new behavior of the trajectories of resonance poles near excitation thresholds. The model yields a qualitative description of the measured excitation function of the B 1?+ state of the CO molecule, where a strong and narrow threshold peak is observed

  3. Bonding electrons visualization in photo-excited state using synchrotron x-ray powder diffractometry

    International Nuclear Information System (INIS)

    The synchrotron X-ray powder diffractometry has been recognized as one of powerful methods for materials science research. By using Maximum Entropy Method (MEM) as an analytical method for the powder diffraction data, bonding electrons can be visualized to reveal the structure-property relationship. The reliability of the MEM change density depends on 'accuracy' and precision' of experimental data. In present studies, we have succeeded in visualizing bonding electrons in the photo-excited state. So far the accuracy of structural analysis under photo irradiation has not reached bonding electrons level. That can be attributed to inhomogeneous excitation caused by large difference between probe light (X-ray) and excitation light (visible laser) energy. In order to overcome the difficulties, we designed sample packing method into a capillary and photo irradiation system for homogeneous excitation. As a result charge density analysis under photo irradiation was successfully achieved in one of spin crossover complexes, Fe(phen)2(NCS)2, which shows a dynamical photo-induced phase transition (PIPT). The bonding nature between Fe and N under photo irradiation is clearly suppressed compared with both ground low-spin phase and temperature induced high-spin phase. The bonding nature created by visible laser may characterize the faster relaxation process of the dynamical PIPT. In my talk, charge density study of persistent PIPT materials (transition metal cyanides) and transient PIPT materials (charge transfer organic materials) will be presented with the dynamical PIPT material. (author)

  4. Electron impact excitation of atoms (ions) by high-energy electron

    International Nuclear Information System (INIS)

    In astrophysics, plasma, quantum chemistry and advanced technique, an increasing demand for collision data is evident. Among those data, cross section of electron impact excitation is important and fundamental data. In this paper, we present the electron impact excitation cross section for some ions at high-energy incident electron. In our calulation, the LS coupling antisymmetric single configuration wavefuction of the target has been used. The plane we BORN approximation has been used in treating the collision problem. Angular part of the transition matrix element of complex atom is treated carefully. We have computed single electron radial wavefunction of atom by means of HARTREE-FOCK-SLATER self consistent field method. We call our computer program as PBA(9). By this computer program, we can compute excitation cross sections, collision strengths, generalized oscillator strengths and optical dipole oscillator strengths. In fact, we have computed widely from H-like to Ne-like isoelectronic sequences. It is made to compare our results with the other ones available. It shows that our results are satisfying for high energy electron. For example, the values of the excitation cross section for C and O fall into the accurate region of recommend data given by Japan's center NAGOYA of atomic data. We conclude that the method used in this paper is reliable and the results are correct. It can provide us with electron-impact excitation useful informantion of light atoms (ions) by high energy electron

  5. Spectroscopy of nitrophenolates in vacuo: effect of spacer, configuration, and microsolvation on the charge-transfer excitation energy

    DEFF Research Database (Denmark)

    Nielsen, Steen Brøndsted; Nielsen, Mogens Brøndsted; Rubio, Angel

    2014-01-01

    Conspectus In a charge-transfer (CT) transition, electron density moves from one end of the molecule (donor) to the other end (acceptor). This type of transition is of paramount importance in nature, for example, in photosynthesis, and it governs the excitation of several protein biochromophores and luminophores such as the oxyluciferin anion that accounts for light emission from fireflies. Both transition energy and oscillator strength are linked to the coupling between the donor and acceptor g...

  6. Influence of donor-donor transport on excitation energy transfer

    International Nuclear Information System (INIS)

    Energy migration and transfer from acriflavine to rhodamine B and malachite green in poly (methylmethacrylate) have been investigated using the decay function analysis. It is found that the influence of energy migration in energy transfer can be described quite convincingly by making use of the theories of Loring, Andersen and Fayer (LAF) and Huber. At high acceptor concentration direct donor-acceptor transfer occurs through Forster mechanism. (author). 17 refs., 5 figs

  7. An efficient implementation of the localized operator partitioning method for electronic energy transfer

    International Nuclear Information System (INIS)

    The localized operator partitioning method [Y. Khan and P. Brumer, J. Chem. Phys. 137, 194112 (2012)] rigorously defines the electronic energy on any subsystem within a molecule and gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. However, an efficient implementation of this approach has been hindered by complicated one- and two-electron integrals arising in its formulation. Using a resolution of the identity in the definition of partitioning, we reformulate the method in a computationally efficient manner that involves standard one- and two-electron integrals. We apply the developed algorithm to the 9 ? ((1 ? naphthyl) ? methyl) ? anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH2 ? naphthyl groups as subsystems and examine their electronic energies and populations for several excited states using configuration interaction singles method. The implemented approach shows a wide variety of different behaviors amongst the excited electronic states

  8. Energy shift of collective electron excitations in highly corrugated graphitic nanostructures: Experimental and theoretical investigation

    Energy Technology Data Exchange (ETDEWEB)

    Sedelnikova, O. V., E-mail: o.sedelnikova@gmail.com; Bulusheva, L. G.; Okotrub, A. V. [Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Science, 3 Acad. Lavrentiev Ave., Novosibirsk 630090 (Russian Federation); Novosibirsk State University, 2 Pirogov Str., Novosibirsk 630090 (Russian Federation); Tomsk State University, 36 Lenina Ave., Tomsk 634050 (Russian Federation); Asanov, I. P. [Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Science, 3 Acad. Lavrentiev Ave., Novosibirsk 630090 (Russian Federation); Novosibirsk State University, 2 Pirogov Str., Novosibirsk 630090 (Russian Federation); Yushina, I. V. [Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Science, 3 Acad. Lavrentiev Ave., Novosibirsk 630090 (Russian Federation)

    2014-04-21

    Effect of corrugation of hexagonal carbon network on the collective electron excitations has been studied using optical absorption and X-ray photoelectron spectroscopy in conjunction with density functional theory calculations. Onion-like carbon (OLC) was taken as a material, where graphitic mantle enveloping agglomerates of multi-shell fullerenes is strongly curved. Experiments showed that positions of ? and ??+?? plasmon modes as well as ? ? ?* absorption peak are substantially redshifted for OLC as compared with those of highly ordered pyrolytic graphite and thermally exfoliated graphite consisted of planar sheets. This effect was reproduced in behavior of dielectric functions of rippled graphite models calculated within the random phase approximation. We conclude that the energy of electron excitations in graphitic materials could be precisely tuned by a simple bending of hexagonal network without change of topology. Moreover, our investigation suggests that in such materials optical exciton can transfer energy to plasmon non-radiatively.

  9. Hot electron mediated desorption rates calculated from excited state potential energy surfaces

    CERN Document Server

    Olsen, Thomas; Schiøtz, Jakob

    2008-01-01

    We present a model for Desorption Induce by (Multiple) Electronic Transitions (DIET/DIMET) based on potential energy surfaces calculated with the Delta Self-Consistent Field extension of Density Functional Theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on various transition metal surfaces, and show that classical nuclear dynamics does not suffice for propagation in the excited state. We present a simple Hamiltonian describing the system, with parameters obtained from the excited state potential energy surface, and show that this model can describe desorption dynamics in both the DIET and DIMET regime, and reproduce the power law behavior observed experimentally. We observe that the internal stretch degree of freedom in the molecules is crucial for the energy transfer between the hot electrons and the molecule when the coupling to the surface is strong.

  10. Electron energy distributions and excitation rates in high-frequency argon discharges

    International Nuclear Information System (INIS)

    The electron energy distribution functions and rate coefficients for excitation and ionisation in argon under the action of an uniform high-frequency electric field were calculated by numerically solving the homogeneous Boltzmann equation. Analytic calculations in the limiting cases ?>>?sub(c) and ?<electron-neutral collision frequency for momentum transfer, are also presented and shown to be in very good agreement with the numerical computations. The results reported here are relevant for the modelling of high-frequency discharges in argon and, in particular, for improving recent theoretical descriptions of a plasma column sustained by surface microwaves. The properties of surface wave produced plasmas make them interesting as possible substitutes for other more conventional plasma sources for such important applications as plasma chemistry laser excitation, plasma etching spectroscopic sources etc...

  11. Biotechnological Aspects of Microbial Extracellular Electron Transfer.

    Science.gov (United States)

    Kato, Souichiro

    2015-01-01

    Extracellular electron transfer (EET) is a type of microbial respiration that enables electron transfer between microbial cells and extracellular solid materials, including naturally-occurring metal compounds and artificial electrodes. Microorganisms harboring EET abilities have received considerable attention for their various biotechnological applications, in addition to their contribution to global energy and material cycles. In this review, current knowledge on microbial EET and its application to diverse biotechnologies, including the bioremediation of toxic metals, recovery of useful metals, biocorrosion, and microbial electrochemical systems (microbial fuel cells and microbial electrosynthesis), were introduced. Two potential biotechnologies based on microbial EET, namely the electrochemical control of microbial metabolism and electrochemical stimulation of microbial symbiotic reactions (electric syntrophy), were also discussed. PMID:26004795

  12. Electronic transfer between low-dimensional nanosystems.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel

    Hoboken : Wiley, 2011 - (Nair, K.; Priya, S.; Jia, Q.), s. 33-40 ISBN 9781118059999. - (Ceramic Transactions. vol. 226). [Materials Science and Technology meeting 2010 (MS&T'10). Dielectric Ceramic Materials and Electronic Devices .. Houston (US), 17.10.2010-21.10.2010] R&D Projects: GA MŠk(CZ) OC10007 Institutional research plan: CEZ:AV0Z10100520 Keywords : electron transfer * nanostructures quantum dots Subject RIV: BM - Solid Matter Physics ; Magnetism http://eu.wiley.com/WileyCDA/WileyTitle/productCd-1118059999,descCd-tableOfContents.html

  13. Ultrafast Intramolecular Electron and Proton Transfer in Bis(imino)isoindole Derivatives.

    Science.gov (United States)

    Driscoll, Eric; Sorenson, Shayne; Dawlaty, Jahan M

    2015-06-01

    Concerted motion of electrons and protons in the excited state is pertinent to a wide range of chemical phenomena, including those relevant for solar-to-fuel light harvesting. The excited state dynamics of small proton-bearing molecules are expected to serve as models for better understanding such phenomena. In particular, for designing the next generation of multielectron and multiproton redox catalysts, understanding the dynamics of more than one proton in the excited state is important. Toward this goal, we have measured the ultrafast dynamics of intramolecular excited state proton transfer in a recently synthesized dye with two equivalent transferable protons. We have used a visible ultrafast pump to initiate the proton transfer in the excited state, and have probed the transient absorption of the molecule over a wide bandwidth in the visible range. The measurement shows that the signal which is characteristic of proton transfer emerges within ?710 fs. To identify whether both protons were transferred in the excited state, we have measured the ultrafast dynamics of a related derivative, where only a single proton was available for transfer. The measured proton transfer time in that molecule was ?427 fs. The observed dynamics in both cases were reasonably fit with single exponentials. Supported by the ultrafast observations, steady-state fluorescence, and preliminary computations of the relaxed excited states, we argue that the doubly protonated derivative most likely transfers only one of its two protons in the excited state. We have performed calculations of the frontier molecular orbitals in the Franck-Condon region. The calculations show that in both derivatives, the excitation is primarily from the HOMO to LUMO causing a large rearrangement of the electronic charge density immediately after photoexcitation. In particular, charge density is shifted away from the phenolic protons and toward the proton acceptor nitrogens. The proton transfer is hypothesized to occur both due to enhanced acidity of the phenolic proton and enhanced basicity of the nitrogen in the excited state. We hope this study can provide insight for better understanding of the general class of excited state concerted electron-proton dynamics. PMID:25932563

  14. Spin effects in intramolecular electron transfer in naproxen- N -methylpyrrolidine dyad

    Science.gov (United States)

    Magin, I. M.; Polyakov, N. E.; Khramtsova, E. A.; Kruppa, A. I.; Tsentalovich, Yu. P.; Leshina, T. V.; Miranda, M. A.; Nuin, E.; Marin, M. L.

    2011-11-01

    The intramolecular electron transfer in the naproxen- N-methylpyrrolidine dyad has been investigated by spin chemistry methods. The existence of CIDNP in a high magnetic field points to electron transfer as a possible mechanism of the quenching of the excited state of a dyad. However, the failure to detect magnetic field effects on triplet yield makes us conclude that this quenching mechanism is not the only one. The observation of CIDNP effects in the dyad in the media of low polarity and the short risetime of triplet state formation indicate a potential role of exciplex in the quenching of the excited state of the dyad.

  15. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Malvankar, Nikhil S.; Liu, Fanghua; Fan, Wei; Nevin, Kelly P.; Lovley, Derek R.

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Ge...

  16. Promoting Interspecies Electron Transfer with Biochar

    OpenAIRE

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Nikhil S. Malvankar; Liu, Fanghua; Fan, Wei; Nevin, Kelly P; Derek R. Lovley

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with...

  17. Neutral histidine and photoinduced electron transfer in DNA photolyases.

    Science.gov (United States)

    Domratcheva, Tatiana

    2011-11-16

    The two major UV-induced DNA lesions, the cyclobutane pyrimidine dimers (CPD) and (6-4) pyrimidine-pyrimidone photoproducts, can be repaired by the light-activated enzymes CPD and (6-4) photolyases, respectively. It is a long-standing question how the two classes of photolyases with alike molecular structure are capable of reversing the two chemically different DNA photoproducts. In both photolyases the repair reaction is initiated by photoinduced electron transfer from the hydroquinone-anion part of the flavin adenine dinucleotide (FADH(-)) cofactor to the photoproduct. Here, the state-of-the-art XMCQDPT2-CASSCF approach was employed to compute the excitation spectra of the respective active site models. It is found that protonation of His365 in the presence of the hydroquinone-anion electron donor causes spontaneous, as opposed to photoinduced, coupled proton and electron transfer to the (6-4) photoproduct. The resulting neutralized biradical, containing the neutral semiquinone and the N3'-protonated (6-4) photoproduct neutral radical, corresponds to the lowest energy electronic ground-state minimum. The high electron affinity of the N3'-protonated (6-4) photoproduct underlines this finding. Thus, it is anticipated that the (6-4) photoproduct repair is assisted by His365 in its neutral form, which is in contrast to the repair mechanisms proposed in the literature. The repair via hydroxyl group transfer assisted by neutral His365 is considered. The repair involves the 5'base radical anion of the (6-4) photoproduct which in terms of electronic structure is similar to the CPD radical anion. A unified model of the CPD and (6-4) photoproduct repair is proposed. PMID:21970417

  18. Degradation of Eu(fod)3 electronic excitation energy in benzene, toluene, and o-xylene solutions

    International Nuclear Information System (INIS)

    Ways of energy dissipation resulting from Eu(fod)3 electronic excitation in homological series of solvents-benzene, toluene and o-xylene have been studied. It is ascertained that probability of the electronic excitation energy degradation increases with an increase in the number of methyl groups at aromatic ring. The values of the activation energy of Eu(fod)3 chelate excited state quenching, which correlate with the number of methyl groups in the series benzene (35.6±1.3 kJ/mol), toluene (39.3±1.3 kJ/mol), o-xylene (54.4±0.8 kJ/mol), have been determined. The results obtained suggest that the main contribution to Eu(3+) electronic excitation energy degradation in homological series benzene, toluene, o-xylene is made by nonradiating energy transfer to high-frequency overtones of oscillations in the solvent C-H groups

  19. Photophysical Model of 10-Hydroxybenzo[h]quinoline: Internal Conversion and Excited State Intramolecular Proton Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Junghwa; Joo, Taiha [Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

    2014-03-15

    Photophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spectral relaxation and anisotropy decay of the keto isomer. We have shown that the ?300 fs component observed frequently in ESIPT dynamics arises from the S{sub 2}?S{sub 1} internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S{sub 1} state to the keto isomer in S{sub 2} state.

  20. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    Science.gov (United States)

    Esboui, Mounir

    2015-07-01

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH3)2 complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH3)2 cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A?(1???) and A'(1n??) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A'(1???) and A?(1n??) potential energy surfaces. For the unconstrained complex, potential energy profiles show two 1???-1??? conical intersections along enol ? keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  1. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer.

    Science.gov (United States)

    Esboui, Mounir

    2015-07-21

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH3)2 complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH3)2 cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A?((1)??*) and A'((1)n?*) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A'((1)??*) and A?((1)n?*) potential energy surfaces. For the unconstrained complex, potential energy profiles show two (1)??*-(1)??* conical intersections along enol ? keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect. PMID:26203026

  2. DOS and electron attachment effects in the electron-induced vibrational excitation of terphenylthiol SAMs.

    Science.gov (United States)

    Houplin, J; Amiaud, L; Dablemont, C; Lafosse, A

    2015-11-11

    Low energy electron scattering on terphenylthiol (TPT, HS-(C6H4)2-C6H5) self-assembled monolayers (SAMs) deposited onto gold was investigated using high resolution electron energy loss spectroscopy (HREELS) by recording specular elastic and inelastic excitation functions. The electron elastic reflectivity could be directly compared to the sample density-of-states (DOS) above vacuum level. A high reflectivity region was observed in the range 7.2-8.6 eV. Inelastic excitation functions were studied to get insights into the mechanisms involved in the excitation of a selection of vibrational modes (dipolar and impact scattering). In particular, a resonant mechanism was observed in the excitation of the stretching mode ?(CC) at 196 meV. The purely resonant contribution to the electron-induced excitation of the stretching modes ?(CH) (379 meV) could be extracted from the overtone excitation. It is located at 7.2 eV above the vacuum level and is characterized by a width of 3.4 eV. PMID:26529112

  3. Computer simulation of electronic excitation in atomic collision cascades

    Energy Technology Data Exchange (ETDEWEB)

    Duvenbeck, A.

    2007-04-05

    The impact of an keV atomic particle onto a solid surface initiates a complex sequence of collisions among target atoms in a near-surface region. The temporal and spatial evolution of this atomic collision cascade leads to the emission of particles from the surface - a process usually called sputtering. In modern surface analysis the so called SIMS technology uses the flux of sputtered particles as a source of information on the microscopical stoichiometric structure in the proximity of the bombarded surface spots. By laterally varying the bombarding spot on the surface, the entire target can be scanned and chemically analyzed. However, the particle detection, which bases upon deflection in electric fields, is limited to those species that leave the surface in an ionized state. Due to the fact that the ionized fraction of the total flux of sputtered atoms often only amounts to a few percent or even less, the detection is often hampered by rather low signals. Moreover, it is well known, that the ionization probability of emitted particles does not only depend on the elementary species, but also on the local environment from which a particle leaves the surface. Therefore, the measured signals for different sputtered species do not necessarily represent the stoichiometric composition of the sample. In the literature, this phenomenon is known as the Matrix Effect in SIMS. In order to circumvent this principal shortcoming of SIMS, the present thesis develops an alternative computer simulation concept, which treats the electronic energy losses of all moving atoms as excitation sources feeding energy into the electronic sub-system of the solid. The particle kinetics determining the excitation sources are delivered by classical molecular dynamics. The excitation energy calculations are combined with a diffusive transport model to describe the spread of excitation energy from the initial point of generation. Calculation results yield a space- and time-resolved excitation energy density profile E(r,t) within the volume affected by the atomic collision cascade.The distribution E(r,t) is then converted into an electron temperature, which in a further step can be utilized to calculate the ionization probabilities of sputtered atoms using published theory. (orig.)

  4. Computer simulation of electronic excitation in atomic collision cascades

    International Nuclear Information System (INIS)

    The impact of an keV atomic particle onto a solid surface initiates a complex sequence of collisions among target atoms in a near-surface region. The temporal and spatial evolution of this atomic collision cascade leads to the emission of particles from the surface - a process usually called sputtering. In modern surface analysis the so called SIMS technology uses the flux of sputtered particles as a source of information on the microscopical stoichiometric structure in the proximity of the bombarded surface spots. By laterally varying the bombarding spot on the surface, the entire target can be scanned and chemically analyzed. However, the particle detection, which bases upon deflection in electric fields, is limited to those species that leave the surface in an ionized state. Due to the fact that the ionized fraction of the total flux of sputtered atoms often only amounts to a few percent or even less, the detection is often hampered by rather low signals. Moreover, it is well known, that the ionization probability of emitted particles does not only depend on the elementary species, but also on the local environment from which a particle leaves the surface. Therefore, the measured signals for different sputtered species do not necessarily represent the stoichiometric composition of the sample. In the literature, this phenomenon is known as the Matrix Effect in SIMS. In order to circumvent this principal shortcoming of SIMS, the present thesis develops an alternative computer simulation concept, which treats the electronic energy losses of all moving atoms as excitation sources feeding energy into the electronic sub-system of the solid. The particle kinetics determining the excitation sources are delivered by classical molecular dynamics. The excitation energy calculations are combined with a diffusive transport model to describe the spread of excitation energy from the initial point of generation. Calculation results yield a space- and time-resolved excitation energy density profile E(r,t) within the volume affected by the atomic collision cascade.The distribution E(r,t) is then converted into an electron temperature, which in a further step can be utilized to calculate the ionization probabilities of sputtered atoms using published theory. (orig.)

  5. The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules

    Energy Technology Data Exchange (ETDEWEB)

    Hou, H [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1995-12-01

    This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O2. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO2 + Na and NaO + NaO. NaO2 products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O2, which is likely a result of a charge transfer from Na2 to the excited state orbital of O2-. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH3 and Na(CH3OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.

  6. Electron transfer and reaction mechanism of laccases.

    Science.gov (United States)

    Jones, Stephen M; Solomon, Edward I

    2015-03-01

    Laccases are part of the family of multicopper oxidases (MCOs), which couple the oxidation of substrates to the four electron reduction of O2 to H2O. MCOs contain a minimum of four Cu's divided into Type 1 (T1), Type 2 (T2), and binuclear Type 3 (T3) Cu sites that are distinguished based on unique spectroscopic features. Substrate oxidation occurs near the T1, and electrons are transferred approximately 13 Å through the protein via the Cys-His pathway to the T2/T3 trinuclear copper cluster (TNC), where dioxygen reduction occurs. This review outlines the electron transfer (ET) process in laccases, and the mechanism of O2 reduction as elucidated through spectroscopic, kinetic, and computational data. Marcus theory is used to describe the relevant factors which impact ET rates including the driving force, reorganization energy, and electronic coupling matrix element. Then, the mechanism of O2 reaction is detailed with particular focus on the intermediates formed during the two 2e(-) reduction steps. The first 2e(-) step forms the peroxide intermediate, followed by the second 2e(-) step to form the native intermediate, which has been shown to be the catalytically relevant fully oxidized form of the enzyme. PMID:25572295

  7. Comparative study on contribution of charge-transfer collision to excitations of iron ion between argon radio-frequency inductively-coupled plasma and nitrogen microwave induced plasma

    Science.gov (United States)

    Satoh, Kozue; Wagatsuma, Kazuaki

    2015-06-01

    This paper describes an ionization/excitation phenomenon of singly-ionized iron occurring in an Okamoto-cavity microwave induced plasma (MIP) as well as an argon radio-frequency inductively-coupled plasma (ICP), by comparing the Boltzmann distribution among iron ionic lines (Fe II) having a wide range of the excitation energy from 4.76 to 9.01 eV. It indicated in both the plasmas that plots of Fe II lines having lower excitation energies (4.76 to 5.88 eV) were fitted on each linear relationship, implying that their excitations were caused by a dominant thermal process such as collision with energetic electron. However, Fe II lines having higher excitation energies (more than 7.55 eV) had a different behavior from each other. In the ICP, Boltzmann plots of Fe II lines assigned to the higher excited levels also followed the normal Boltzmann relationship among the low-lying excited levels, even including a deviation from it in particular excited levels having an excitation energy of ca. 7.8 eV. This deviation can be attributed to a charge-transfer collision with argon ion, which results in the overpopulation of these excited levels, but the contribution is small. On the other hand, the distribution of the high-lying excited levels was non-thermal in the Okamoto-cavity MIP, which did not follow the normal Boltzmann relationship among the low-lying excited levels. A probable reason for the non-thermal characteristics in the MIP is that a charge-transfer collision with nitrogen molecule ion having many vibrational/rotational levels could work for populating the 3d64p (3d54s4p) excited levels of iron ion broadly over an energy range of 7.6-9.0 eV, while collisional excitation by energetic electron would occur insufficiently to excite these high-energy levels.

  8. Compilation of electron collision excitation cross sections for neutro argon

    International Nuclear Information System (INIS)

    The present work presents a compilation and critical analysis of the available data on electron collision excitation cross sections for neutral Argon levels. This study includes: 1.- A detailed description in intermediate coupling for all the levels belonging the 20 configurations 3p''5 ns(n=4 to 12), np(n=4 to 8) and nd(n=3 to 8) of neutral Argon. 2.- Calculation of the electron collision excitation cross sections in Born and Born-Oppenheimer-Ochkur approximations for all the levels in the 14 configurations 3p''5 ns(n=4 to 7), np(n=4 to 7) and nd(n=3 to 8). 3.- Comparison and discussion of the compiled data. These are the experimental and theoretical values available from the literature, and those from this work. 4.- Analysis of the regularities and systematic behaviors in order to determine which values can be considered more reliable. It is show that the concept of one electron cross section results quite useful for this purpose. In some cases it has been possible to obtain in this way approximate analytical expressions interpolating the experimental data. 5.- All the experimental and theoretical values studied are graphically presented and compared. 6.- The last part of the work includes a listing of several general purpose programs for Atomic Physics calculations developed for this work. (Author)

  9. Effect of Electronic Excitation on Thin Film Growth

    Energy Technology Data Exchange (ETDEWEB)

    Elsayed-Ali, Hani E. [Old Dominion University

    2011-01-31

    The effect of nanosecond pulsed laser excitation on surface diffusion during growth of Ge on Si(100) at 250 degrees C was studied. In Situ reflection high-energy electron diffraction (RHEED) was used to measure the surface diffusion coefficient while ex situ atomic force microscopy (AFM) was used to probe the structure and morphology of the grown quantum dots. The results show that laser excitation of the substrate increases the surface diffusion during growth of Ge on Si(100), changes the growth morphology, improves crystalline structure of the grown quantum dots, and decreases their size distribution. A purely electronic mechanism of enhanced surface diffusion of the deposited Ge is proposed. Ge quantum dots were grown on Si(100)-(2x1) by pulsed laser deposition at various substrate temperatures using a femtosecond Ti:sapphire laser. In-situ reflection high-energy electron diffraction and ex-situ atomic force microscopy were used to analyze the fim structure and morphology. The morphology of germanium islands on silicon was studied at differect coverages. The results show that femtosecond pulsed laser depositon reduces the minimum temperature for epitaxial growth of Ge quantum dots to ~280 degrees C, which is 120 degrees C lower then previously observed in nanosecond pulsed laser deposition and more than 200 degrees C lower than that reported for molecular beam epitaxy and chemical vapor deposition.

  10. Excimer Emission using 20keV Electron Beam Excitation

    Science.gov (United States)

    Wieser, J.; Ulrich, A.; Murnick, D. E.

    1996-10-01

    A small, continuously emitting rare gas excimer light source has been developed. The gas is excited by a 20keV dc-electron beam. A 300nm thick, 1×1mm^2 SiNx foil sustaining a pressure difference up to 2bar, separates the target volume from the high vacuum part of the electron gun. Spectra of the rare gases Ar, Kr, and Xe have been studied. The monochromator detector system was intensity calibrated in the wavelength range from 115nm to 320nm. Electron beam currents of typically 1?A were used for excitation. When used as a VUV lamp on the second excimer continua, energy conversion efficiencies of 30% were obtained. Emissions originating from the so called left turning points have been clearly observed at 155, 173, and 222nm in Ar_2^*, Kr_2^*, and Xe_2^*, respectively. The so called third continua between 185nm and 240nm (Ar), 220nm and 250nm (Kr), and at 270nm (Xe) have been studied. A new continuum in Xe at 280nm was found. (Funded by the A.v.Humboldt Foundation and NSF (CTS 94-19440). The authors acknowledge support by H. Huggins, A. Liddle and W.L. Brown (Bell Laboratories, Lucent Technologies))

  11. A new type of localized fast moving electronic excitations in molecular chains

    OpenAIRE

    Korshunova, A. N.; Lakhno, V. D.

    2014-01-01

    It is shown that in a Holstein molecular chain placed in a strong longitudinal electric field some new types of excitations can arise. This excitations can transfer a charge over large distance (more than 1000 nucleotide pairs) along the chain retaining approximately their shapes. Excitations are formed only when a strong electric field either exists or quickly arises under especially preassigned conditions. These excitations transfer a charge even in the case when Holstein polarons are pract...

  12. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Malvankar, Nikhil S.; Liu, Fanghua; Fan, Wei; Nevin, Kelly P.; Lovley, Derek R.

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that...... previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were...... attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why...

  13. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why biochar may enhance methane production from organic wastes under anaerobic conditions.

  14. Interplay between particle-hole excitation and nucleon transfer in deep-inelastic collisions

    International Nuclear Information System (INIS)

    The interplay between particle-hole excitation and nucleon transfer in deep-inelastic collisions is studied within an independent-particle model in which the relative motion is treated classically. The energy and angular momentum loss are evaluated selfconsistently in the model. The results show that the inclusion of the ph excitation strongly affects the transfer mode giving rise to a drift of the charge centroid towards charge asymmetry. The model predicts a roughly equal excitation energy for the two fragments rather than one proportional to their masses. (orig.)

  15. Relaxation of electron excitations in beryllium oxide. Auto localized excitons

    International Nuclear Information System (INIS)

    Combined luminescent-optical investigations within 80-600 K temperature range and 5-36 eV energy range is conducted for BeO nominally pure crystals. Analysis of selective excitation spectra of luminescence, kinetic parameters and temperature dependences of the selected luminosity, as well as, of spectra of transit optical absorption induced by electron beam, is presented. Models of auto localized excitons differing in configuration of hole component are suggested and fact of coexistence of high and low radii excitons is determined on the basis of the analysis with regard to peculiarities of BeO crystalline structure. 40 refs.; 8 figs

  16. Education and solar conversion. Demonstrating electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Smestad, Greg P. [Institute of Physical Chemistry, ICP-2, Swiss Federal Institute of Technology, EPFL, CH-1015 Lausanne (Switzerland)

    1998-07-23

    A simplified solar cell fabrication procedure is presented that uses natural anthocyanin or chlorophyll dyes extracted from plants. This procedure illustrates how interdisciplinary science can be taught at lower division university and upper division high school levels for an understanding of renewable energy as well as basic science concepts. Electron transfer occurs on the Earth in the mitochondrial membranes found in living cells, and in the thylakoid membranes found in the photosynthetic cells of green plants. Since we depend on the results of this electron and energy transfer, e.g. in our use of petroleum and agricultural products, it is desirable to understand and communicate how the electron transfer works. The simplified solar cell fabrication procedure, based on nanocrystalline dye-sensitized solar cells, has therefore been developed so that it can be inexpensively reproduced and utilized in the teaching of basic principles in biology, chemistry, physics, and environmental science. A water-based solution of commercial nanocrystalline titanium dioxide (TiO{sub 2}) powder is used to deposit a highly porous semiconductor electron acceptor. This acceptor couples the light-driven processes occurring at an organic dye to the macroscopic world and an external electrical circuit. Materials science and semiconductor physics are emphasized during the deposition of the sintered TiO{sub 2} nanocrystalline ceramic film. Chelation, complexation and molecular self-assembly are demonstrated during the attachment of the dye molecule to the surface of the TiO{sub 2} semiconductor particles. Environmental chemistry and energy conversion can be linked to these concepts via the regenerative oxidation and reduction cycle found in the cell. The resulting device, made in under 3 h, can be used as a light detector or power generator that produces 0.4-0.5 V at open circuit, and 1-2 mA per square cm under solar illumination

  17. The Particle-Hole Map: A Computational Tool To Visualize Electronic Excitations.

    Science.gov (United States)

    Li, Yonghui; Ullrich, Carsten A

    2015-12-01

    We introduce the particle-hole map (PHM), which is a visualization tool to analyze electronic excitations in molecules in the time or frequency domain, to be used in conjunction with time-dependent density-functional theory (TDDFT) or other ab initio methods. The purpose of the PHM is to give detailed insight into electronic excitation processes that is not obtainable from local visualization methods, such as transition densities, density differences, or natural transition orbitals. The PHM is defined as a nonlocal function of two spatial variables and provides information about the origins, destinations, and connections of charge fluctuations during an excitation process; it is particularly valuable to analyze charge-transfer excitonic processes. In contrast with the transition density matrix, the PHM has a statistical interpretation involving joint probabilities of individual states and their transitions; it satisfies several sum rules and exact conditions, and it is easier to read and interpret. We discuss and illustrate the properties of the PHM and give several examples and applications to excitations in one-dimensional model systems, in a hydrogen chain, and in a benzothiadiazole (BT)-based molecule. PMID:26609707

  18. Dynamics of Electron Transfer Processes at the Surface of Dye-Sensitized Mesoporous Semiconductor Films

    OpenAIRE

    Teuscher, Joël

    2010-01-01

    Electron transfer reactions taking place at the surface of dye-sensitized semiconductors are key processes in dye-sensitized solar cells (DSSCs). After light absorption, the excited state of a dye injects an electron into a wide-bandgap semiconductor, usually titanium dioxyde, TiO2. The formed oxidized dye can then be intercepted by a redox mediator, typically iodide, before charge recombination between the injected electron and the oxidized dye...

  19. Vibrational and Electronic Energy Transfer and Dissociation of Diatomic Molecules by Electron Collisions

    Science.gov (United States)

    Huo, Winifred M.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also, the average electron temperature is expected to be between 10,000 and 20,000 K. Thus only data for low energy electrons are relevant to the model.

  20. Ultrafast Spectroscopy of Delocalized Excited States of the Hydrated Electron

    International Nuclear Information System (INIS)

    Research under support of this grant has been focused on the understanding of highly delocalized ''conduction-band-like'' excited states of solvated electrons in bulk water, in water trapped in the core of reverse micelles, and in alkane solvents. We have strived in this work to probe conduction-band-like states by a variety of ultrafast spectroscopy techniques. (Most of which were developed under DOE support in a previous funding cycle.) We have recorded the optical spectrum of the hydrated electron for the first time. This was accomplished by applying a photo-detrapping technique that we had developed in a previous funding cycle, but had not yet been applied to characterize the actual spectrum. In the cases of reverse micelles, we have been investigating the potential role of conduction bands in the electron attachment process and the photoinduced detrapping, and have published two papers on this topic. Finally, we have been exploring solvated electrons in isooctane from various perspectives. All of these results strongly support the conclusion that optically accessible, highly delocalized electronic states exist in these various media

  1. Electronically excited states and photochemical reaction mechanisms of ?-glucose.

    Science.gov (United States)

    Tuna, Deniz; Sobolewski, Andrzej L; Domcke, Wolfgang

    2014-01-01

    Carbohydrates are important molecular components of living matter. While spectroscopic and computational studies have been performed on carbohydrates in the electronic ground state, the lack of a chromophore complicates the elucidation of the excited-state properties and the photochemistry of this class of compounds. Herein, we report on the first computational investigation of the singlet photochemistry of ?-glucose. It is shown that low-lying singlet excited states are of n?* nature. Our computations of the singlet vertical excitation energies predict absorption from 6.0 eV onward. Owing to a dense manifold of weakly-absorbing states, a sizable and broad absorption in the ultraviolet-C range arises. We have explored two types of photochemical reaction mechanisms: hydrogen-detachment processes for each of the five O-H groups and a C-O ring-opening process. Both types of reactions are driven by repulsive n?* states that are readily accessible from the Franck-Condon region and lead to conical intersections in a barrierless fashion. We have optimized the geometries of the conical intersections involved in these photochemical processes and found that these intersections are located around 5.0 eV for the O-H hydrogen-detachment reactions and around 4.0 eV for the C-O ring-opening reaction. The energies of all conical intersections are well below the computed absorption edge. The calculations were performed using linear-response methods for the computation of the vertical excitation energies and multiconfigurational methods for the optimization of conical intersections and the computation of energy profiles. PMID:23959595

  2. Vibrational excitation in adsorbed acetylene by electron impact

    International Nuclear Information System (INIS)

    The authors have studied the vibrational spectra of acytylene adsorbed on Ni(111) at 150 K by electron energy loss spectroscopy. They observe both dipole scattering and vibrational excitation by electron impact via a broad resonance around 5 eV. The adsorbed acetylene is characterized by C-C and C-H stretching modes at 1200 and 2920 cm-1, respectively. This indicates a rehybridization of the molecule between sp2 and sp3 and a lowering of the C-C bond order down to approximately 1.5. This suggests that the acetylene is predominantly di-sigma-bonded to the surface and the structure resembles that of ethylene. (Auth.)

  3. Large radius new etching system using electron beam excited plasma

    International Nuclear Information System (INIS)

    A new electron beam excited plasma (EBEP) etching system has been developed. This EBEP system can efficiently generate a high density and uniform plasma by introducing a high current low-energy electron beam into an etching gas chamber. The uniformity of the Cl plasma density is within ±2.5% over an 8 in. wafer and the uniformity of the plasma and floating potential across the wafer is within ±2 V. This ultrahigh uniformity of the potentials overcomes the problem of the breakdown of thin gate insulators during etching that originate from the nonuniformity of the potential at the substrate. The selectivity of etching obtained is 40:1 for poly-Si/resist and more than 100:1 for poly-Si/SiO2. The etch rate is 3600 A/min. 4 refs., 9 figs

  4. Influence of multiphonon excitations and transfer on the fusion of Ca+Zr

    CERN Document Server

    Esbensen, H

    2014-01-01

    Fusion data for $^{48}$Ca+$^{90,96}$Zr are analyzed by coupled-channels calculations that are based on the M3Y+repulsion, double-folding potential. By applying a previously determined nuclear density of $^{48}$Ca, the neutron densities of the zirconium isotopes are adjusted to optimize the fit to the fusion data, whereas the proton densities are determined by electron scattering experiments. It is shown that the fusion data can be explained fairly well by including couplings to one- and two-phonon excitations of the reacting nuclei and to one- and two-nucleon transfer reactions but there is also some sensitivity to multiphonon excitations. The neutron skin thicknesses extracted for the two zirconium isotopes are consistent with anti-proton measurements. The densities of the zirconium isotopes are used together with the previously determined nuclear density of $^{40}$Ca to calculate the M3Y+repulsion potentials and predict the fusion cross sections of $^{40}$Ca+$^{90,96}$Zr. The predicted cross sections for $^...

  5. Consequences of strong coupling between solvation and electronic structure in the excited state of a betaine dye.

    Science.gov (United States)

    Ishida, Tateki; Rossky, Peter J

    2008-09-11

    The electronic ground and excited-state structures of the betaine dye molecule pyridinium- N-phenoxide [4-(1-pyridinio)phenolate] are investigated both in the gas phase and in aqueous solution, using the reference interaction site model self-consistent-field (RISM-SCF) procedure within a CASSCF framework. We obtain the total free energy profiles in both the ground and excited states with respect to variation in the torsion angle between the phenoxide and pyridinium rings. We analyze the effect of solvent on the variation of the solute dipole moment and on the charge transfer character in the excited state. In the gas phase, it is shown that the potential energy profile in the excited-state decreases monotonically toward a perpendicular ring orientation and the dipole moment decreases along with decreasing charge localization. In water, the free energy surface for twisting is better characterized as nearly flat along the same coordinate for sterically accessible angles. These results are analyzed in terms of contributions of the solvation free energy, the solute electronic energy, and their coupling. Correspondingly, the dependence of the charge transfer character on solute geometry and solvation are analyzed, and the important roles in the excitation and subsequent relaxation processes for the betaine dye are discussed. It is found that there is considerable solute electronic reorganization associated with the evolution of solvation in the excited state, and it is suggested that this reorganization may contribute significantly to the early time evolution of transient spectra following photoexcitation. PMID:18707072

  6. Linker proteins enable ultrafast excitation energy transfer in the phycobilisome antenna system of Thermosynechococcus vulcanus.

    Science.gov (United States)

    Nganou, C; David, L; Adir, N; Mkandawire, M

    2016-01-01

    We applied a femtosecond flash method, using induced transient absorption changes, to obtain a time-resolved view of excitation energy transfer in intact phycobilisomes of Thermosynechococcus vulcanus at room temperature. Our measurement of an excitation energy transfer rate of 888 fs in phycobilisomes shows the existence of ultrafast kinetics along the phycocyanin rod subcomplex to the allophycocyanin core that is faster than expected for previous excitation energy transfer based on Förster theory in phycobilisomes. Allophycocyanin in the core further transfers energy to the terminal emitter(s) in 17 ps. In the phycobilisome, rod doublets composed of hexameric phycocyanin discs and internal linker proteins are arranged in a parallel fashion, facilitating direct rod-rod interactions. Excitonic splitting likely drives rod absorption at 635 nm as a result of strong coupling between ?84 chromophores (20 ± 1 Å) in adjacent hexamers. In comparison to the absorbance of the phycobilisome antenna system of the cyanobacterium Acaryochloris marina, which possesses a single rod structure, the linkers in T. vulcanus rods induce a 17 nm red shift in the absorbance spectrum. Furthermore, the kinetics of 888 fs indicates that the presence of the linker protein induces ultrafast excitation energy transfer between phycocyanin and allophycocyanin inside the phycobilisome, which is faster than all previous excitation energy transfer in phycobilisome subunits or sub-complexes reported to date. PMID:26537632

  7. Electron impact excitation of resonance transitions in atomic potassium

    International Nuclear Information System (INIS)

    Cross sections for electron impact excitation of the 4 s2S - 4p 2Po and 4s 2S - 5p 2Po transitions in atomic potassium are calculated in the low-energy region from 1.5 to 30 eV using the R-matrix method. We included eight target states (4s 2S, 4p 2Po, 5s 2S, 3d 2D, 5p 2Po, 4d 2D, 6S 2S, and 4f 2Fo) in the close-coupling expansion. These states are represented by extensive configuration- interaction wavefunctions constructed from the orthogonal one-electron orbitals: 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, and 6s. The calculated results are compared with the available experiments and other calculations. The present calculation shows a resonance structure in the cross section for the excitation of the resonance 4s 2S - 4p 2Po transition around 2.5 eV

  8. Inelastic electron and light scattering from the elementary electronic excitations in quantum wells: Zero magnetic field

    Directory of Open Access Journals (Sweden)

    Manvir S. Kushwaha

    2012-09-01

    Full Text Available The most fundamental approach to an understanding of electronic, optical, and transport phenomena which the condensed matter physics (of conventional as well as nonconventional systems offers is generally founded on two experiments: the inelastic electron scattering and the inelastic light scattering. This work embarks on providing a systematic framework for the theory of inelastic electron scattering and of inelastic light scattering from the electronic excitations in GaAs/Ga1?xAlxAs quantum wells. To this end, we start with the Kubo's correlation function to derive the generalized nonlocal, dynamic dielectric function, and the inverse dielectric function within the framework of Bohm-Pines’ random-phase approximation. This is followed by a thorough development of the theory of inelastic electron scattering and of inelastic light scattering. The methodological part is then subjected to the analytical diagnoses which allow us to sense the subtlety of the analytical results and the importance of their applications. The general analytical results, which know no bounds regarding, e.g., the subband occupancy, are then specified so as to make them applicable to practicality. After trying and testing the eigenfunctions, we compute the density of states, the Fermi energy, the full excitation spectrum made up of intrasubband and intersubband – single-particle and collective (plasmon – excitations, the loss functions for all the principal geometries envisioned for the inelastic electron scattering, and the Raman intensity, which provides a measure of the real transitions induced by the (laser probe, for the inelastic light scattering. It is found that the dominant contribution to both the loss peaks and the Raman peaks comes from the collective (plasmon excitations. As to the single-particle peaks, the analysis indicates a long-lasting lack of quantitative comparison between theory and experiments. It is inferred that the inelastic electron scattering can be a potential alternative of the inelastic light scattering for investigating elementary electronic excitations in quantum wells.

  9. How coherence help excitation energy transfer between chromophres of photosynthesis systems

    CERN Document Server

    Liang, Xian-Ting

    2010-01-01

    In this paper, we investigate the excited energy transfer (EET) between chromophres by using a dynamical model of EET in photosynthesis systems. The numerical path integral method is used. This method includes the non-Markovian effects of the environmental affects and it does not need the perturbation approximation in solving the dynamics of systems of interest. We obtained that coherence help EET between molecules is because it increases the transfer time rather than enhances the transfer rate of energy.

  10. Electronic Energy Transfer in Polarizable Heterogeneous Environments

    DEFF Research Database (Denmark)

    Svendsen, Casper Steinmann; Kongsted, Jacob

    2015-01-01

    Theoretical prediction of transport and optical properties of protein-pigment complexes is of significant importance when aiming at understanding the structure versus function relationship in such systems. Electronic energy transfer (EET) couplings represent a key property in this respect since...... embedding model has been suggested (C. Curutchet, A. Muñoz-Losa, S. Monti, J. Kongsted, G. D. Scholes, and B. Mennucci, J. Chem. Theory Comput., 2009 5 (7), 1838-1848). In this work, we further develop this computational model by extending it with an ab initio derived polarizable force field including...

  11. Direct heterogeneous electron transfer of theophylline oxidase

    OpenAIRE

    Christenson, Andreas; Dock, Eva; Gorton, Lo; Ruzgas, Tautgirdas

    2004-01-01

    Direct electron transfer (DET) was shown between the heme containing enzyme theophylline oxidase (ThO) and the surface of both graphite and gold electrodes. As proof on graphite a steady state current for theophylline was recorded using the electrode modified with adsorbed ThO. The electrode showed a Michaelis–Menten-like response to theophylline with a detection limit of 0.2 mM and a Michaelis–Menten constant equal to 3.2 mM. These initial results open up a possibility for the development of...

  12. Double electron transfer in H- + H+ collisions

    International Nuclear Information System (INIS)

    Absolute cross sections for double electron transfer in H- + H+ collisions have been measured for center-of-mass energies from 0.5 keV to 12 keV. Clear oscillations in the cross section are observed which are in excellent agreement with earlier measurements at lower energies by Brouillard et al (1979) as well as Peart and Dolder (1979). After an oscillation maximum at 3 keV center-of-mass energy the cross section decreases for increasing energy with no indication of further oscillations

  13. Double electron transfer in H- + H+ collisions

    Science.gov (United States)

    Bräuning, H.; Helm, H.; Briggs, J. S.

    2007-11-01

    Absolute cross sections for double electron transfer in H- + H+ collisions have been measured for center-of-mass energies from 0.5 keV to 12 keV. Clear oscillations in the cross section are observed which are in excellent agreement with earlier measurements at lower energies by Brouillard et al (1979) as well as Peart and Dolder (1979). After an oscillation maximum at 3 keV center-of-mass energy the cross section decreases for increasing energy with no indication of further oscillations.

  14. Electronic excitation of atoms and molecules by electron impact in a linear algebraic, separable potential approach

    International Nuclear Information System (INIS)

    The linear algebraic, separable potential approach is applied to the electronic excitation of atoms and molecules by electron impact. By representing the exchange and off-diagonal direct terms on a basis, the standard set of coupled inelastic equations is reduced to a set of elastic inhomogeneous equations. The procedure greatly simplifies the formulation by allowing a large portion of the problem to be handled by standard bound-state techniques and by greatly reducing the order of the scattering equations that must be solved. Application is made to the excitation of atomic hydrogen in the three-state close-coupling (1s, 2s, 2p) approximation. (author)

  15. Excitation of solid electron by proton and hydrogen molecular ions

    International Nuclear Information System (INIS)

    An electric stopping power of solid for hydrogen molecular ion (H2+, H3+) and ion cluster (2H+, 3H+) which lost the bounded electron from the former, were estimated and compared with the value of proton. The spacial distribution of the bounded electron of hydrogen molecular ions such as H2+ and H3+ was assumed by the molecular orbital on the basis of gauss function. In calculating the electric stopping power, a conduction electron is modelled on the free electron gas model and an exitation of bounded electron on the wave packet model. In any cases, the excitation of electron is described by the dielectric function. An effective charge Zeff, the index of the amount of stopping power S, is defined as Zeff = (s/sp)2/1 where Sp represents the stopping power for proton running with the same velocity in the same solid. This effective charge is a useful physical parameter to arrange the stopping power data, because it shows the practical charge number of the injection ion with bounded electron to be reduced to the point charge. The effective charges of H2+ and He+ in low energy field are different depend on the orientations when they transmitted through the carbon film. The effective charge of H2+ was less than 1 if the molecular axis was parallel to the running direction. In high energy field, the dependence of orientation was not observed. The differences of effective charges of H3+ passing through the carbon, aluminium and krypton gas were about 0.2, the small value indicating the small dependence of value on the materials. (S.Y.)

  16. Excitation of kinetic Alfvén waves by fast electron beams

    Energy Technology Data Exchange (ETDEWEB)

    Chen, L.; Wu, D. J.; Zhao, G. Q. [Purple Mountain Observatory, CAS, Nanjing (China); Tang, J. F. [Xinjiang Astronomical Observatory, CAS, Urumqi 830011 (China); Huang, J., E-mail: clvslc214@pmo.ac.cn, E-mail: djwu@pmo.ac.cn, E-mail: gqzhao@pmo.ac.cn, E-mail: jftang@xao.ac.cn, E-mail: huangj@bao.ac.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing (China)

    2014-09-20

    Energetic electron beams, which are ubiquitous in a large variety of active phenomena in space and astrophysical plasmas, are one of the most important sources that drive plasma instabilities. In this paper, taking account of the return-current effect of fast electron beams, kinetic Alfvén wave (KAW) instability driven by a fast electron beam is investigated in a finite-? plasma of Q < ? < 1 (where ? is the kinetic-to-magnetic pressure ratio and Q ? m{sub e} /m{sub i} is the mass ratio of electrons to ions). The results show that the kinetic resonant interaction of beam electrons is the driving source for KAW instability, unlike the case driven by a fast ion beam, where both the kinetic resonant interaction of beam ions and the return-current are the driving source for the KAW instability. KAW instability has a nonzero growth rate in the range of the perpendicular wave number, 0electron beam v{sub b} , and the most favorable beam velocity occurs between 8v{sub A} < v{sub b} < 10v{sub A} . On the other hand, the excited KAWs are weakly dispersive with k ? {sub i} < 1 and have the maximum growth rate at relatively low perpendicular wave numbers in the range 0.3electron beams in the terrestrial magnetosphere is briefly discussed.

  17. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov’yov, Ilia A.

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome–a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor. PMID:26689792

  18. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov’Yov, Ilia A.

    2015-12-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome–a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  19. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor. PMID:26689792

  20. Effect of electronic excitation on high-temperature flows behind strong shock waves

    International Nuclear Information System (INIS)

    In the present paper, a strongly non-equilibrium one-dimensional steady-state flow behind the plane shock wave is studied. We consider a high-temperature chemically reacting five-component ionized mixture of nitrogen species (N2/N22/N/N+/e?) taking into account electronic degrees of freedom in N and N+ (170 and 625 electronic energy levels respectively), and electronic-rotational-vibrational modes in N2 and N2+ (5 and 7 electronic terms). Non-equilibrium reactions of ionization, dissociation, recombination and charge-transfer are included to the kinetic scheme. The system of governing equations is written under the assumption that translation and internal energy relaxation is fast whereas chemical reactions and ionization proceed on the macroscopic gas-dynamics time-scale. The developed model is applied to simulate the flow behind a plane shock wave under initial conditions characteristic for the spacecraft re-entry from an interplanetary flight (Hermes and Fire II experiments). Fluid-dynamic parameters behind the shock wave as well as transport coefficients and the heat flux are calculated for the (N2/N2+/N/N+/e?) mixture. The effect of electronic excitation on kinetics, dynamics and heat transfer is analyzed. Whereas the contribution of electronic degrees of freedom to the flow macroparameters is negligible, their influence on the heat flux is found to be important under conditions of Hermes re-entry

  1. Characteristics of Response of Piezoelectric Actuators in Electron Flux Excitation

    Directory of Open Access Journals (Sweden)

    Philip C. Hadinata

    2003-11-01

    Full Text Available In this paper the working parameters of non-contact strain control for piezoelectric ceramics are evaluated. The piezoelectric material functions as an actuator that transforms electrical into mechanical energy, and the electrical input is carried out by electron flux on the positive surface. The sample is exposed to some quasi-static inputs, and its responses are recorded using strain gages. The data shows faster and more stable response in the positive regime, but significantly slower response with drift in the negative regime. An electron collector is introduced on the positive surface to enhance the response in the negative regime. Theoretical analyses of energy transfer and electron movements is discussed, and a string of working conditions for controlling the surface strain of piezoelectric material are given as conclusions.

  2. Electron hole pair mediated vibrational excitation in CO scattering from Au(111): Incidence energy and surface temperature dependence

    Energy Technology Data Exchange (ETDEWEB)

    Shirhatti, Pranav R.; Werdecker, Jörn; Golibrzuch, Kai; Wodtke, Alec M.; Bartels, Christof, E-mail: cbartel@gwdg.de [Institute for Physical Chemistry, Georg August University of Göttingen, 37077 Göttingen (Germany); Max Planck Institute for Biophysical Chemistry, 37077 Göttingen (Germany)

    2014-09-28

    We investigated the translational incidence energy (E{sub i}) and surface temperature (T{sub s}) dependence of CO vibrational excitation upon scattering from a clean Au(111) surface. We report absolute v = 0 ? 1 excitation probabilities for E{sub i} between 0.16 and 0.84 eV and T{sub s} between 473 and 973 K. This is now only the second collision system where such comprehensive measurements are available – the first is NO on Au(111). For CO on Au(111), vibrational excitation occurs via direct inelastic scattering through electron hole pair mediated energy transfer – it is enhanced by incidence translation and the electronically non-adiabatic coupling is about 5 times weaker than in NO scattering from Au(111). Vibrational excitation via the trapping desorption channel dominates at E{sub i} = 0.16 eV and quickly disappears at higher E{sub i}.

  3. Excitation of Lanthanum and Lutetium Double-Charged Ions in Electron-Atom Collisions

    OpenAIRE

    Yuriy Mikhailovich Smirnov

    2015-01-01

    Excitation of LaIII and LuIII in collisions of slow electrons with La and Lu atoms (excitation with simultaneous double ionization) have been studied in experiment. At exciting electron energy of 50 eV at 19 excitation cross-sections for each of LaIII and LuIII were measured. At two optical excitation functions for both of ions were recorded, in the electron energy range of 0–200 eV for LaIII and in the range of 0–250 eV for LuIII. Absolute values of excitation cross-sections for similar leve...

  4. Surface nanostructuring of LiNbO3 by high-density electronic excitations

    International Nuclear Information System (INIS)

    Lithium niobate (LiNbO3) single crystals were irradiated with high energy gold ions (0.5–2.2 GeV) at the UNILAC (GSI) and with 150-keV highly charged xenon ions from an EBIT (Electron Beam Ion Trap, HZDR). The surfaces of the irradiated crystals were analyzed by scanning force microscopy showing very similar topographic changes. Swift heavy ions and slow highly charged ions produce hillock-like nanostructures on the surface. In both cases, the energy deposition of the ions is characterized by dense localized electronic excitations and efficient transfer to the lattice. Furthermore, the irradiation results in a shift in the band gap energy as evidenced by UV–Vis absorption spectroscopy. Specific modifications (e.g. hillock size, energy loss threshold) induced by slow highly charged ions are discussed in comparison with effects due to the electronic energy loss by swift heavy ions

  5. Surface nanostructuring of LiNbO{sub 3} by high-density electronic excitations

    Energy Technology Data Exchange (ETDEWEB)

    El-Said, A.S., E-mail: elsaid@kfupm.edu.sa [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328 Dresden (Germany); Physics Department, King Fahd University of Petroleum and Minerals, Dhahran 31261 (Saudi Arabia); Nuclear and Radiation Physics Lab, Physics Department, Faculty of Science, Mansoura University, 35516 Mansoura (Egypt); Wilhelm, R.A. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328 Dresden (Germany); Technische Universität Dresden, 01062 Dresden (Germany); Facsko, S. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328 Dresden (Germany); Trautmann, C. [GSI Helmholtz Centre for Heavy Ion Research, 64291 Darmstadt (Germany); Technische Universität Darmstadt, 64289 Darmstadt (Germany)

    2013-11-15

    Lithium niobate (LiNbO{sub 3}) single crystals were irradiated with high energy gold ions (0.5–2.2 GeV) at the UNILAC (GSI) and with 150-keV highly charged xenon ions from an EBIT (Electron Beam Ion Trap, HZDR). The surfaces of the irradiated crystals were analyzed by scanning force microscopy showing very similar topographic changes. Swift heavy ions and slow highly charged ions produce hillock-like nanostructures on the surface. In both cases, the energy deposition of the ions is characterized by dense localized electronic excitations and efficient transfer to the lattice. Furthermore, the irradiation results in a shift in the band gap energy as evidenced by UV–Vis absorption spectroscopy. Specific modifications (e.g. hillock size, energy loss threshold) induced by slow highly charged ions are discussed in comparison with effects due to the electronic energy loss by swift heavy ions.

  6. Surface nanostructuring of LiNbO3 by high-density electronic excitations

    Science.gov (United States)

    El-Said, A. S.; Wilhelm, R. A.; Facsko, S.; Trautmann, C.

    2013-11-01

    Lithium niobate (LiNbO3) single crystals were irradiated with high energy gold ions (0.5-2.2 GeV) at the UNILAC (GSI) and with 150-keV highly charged xenon ions from an EBIT (Electron Beam Ion Trap, HZDR). The surfaces of the irradiated crystals were analyzed by scanning force microscopy showing very similar topographic changes. Swift heavy ions and slow highly charged ions produce hillock-like nanostructures on the surface. In both cases, the energy deposition of the ions is characterized by dense localized electronic excitations and efficient transfer to the lattice. Furthermore, the irradiation results in a shift in the band gap energy as evidenced by UV-Vis absorption spectroscopy. Specific modifications (e.g. hillock size, energy loss threshold) induced by slow highly charged ions are discussed in comparison with effects due to the electronic energy loss by swift heavy ions.

  7. Electron scattering by magnesium: excitation of the 3s3p 1P1 state

    International Nuclear Information System (INIS)

    Differential cross sections (DCS) for electron-impact excitation of the 3s3p 1P1 state in magnesium at incident electron energies E0 = 10, 15, 20, 40, 60, 80 and 100 eV have been measured and corresponding calculations carried out. Scattered-electron intensities were measured over a wide range of scattering angles (100-1500) and normalized to the DCSs at 100 experimentally obtained by Filipovic et al (2006 Int. J. Mass Spectrom. 251 66). Corresponding calculations have been conducted in the relativistic distorted-wave approximation. Integrated (integral, momentum transfer and viscosity) cross sections are determined by numerical integration of our DCSs. The results are analysed and compared with previous experimental data and theoretical calculations

  8. Direct electron transfer from photosystem II to hematite in a hybrid photoelectrochemical cell.

    Science.gov (United States)

    Wang, Wangyin; Wang, Zhiliang; Zhu, Qingjun; Han, Guangye; Ding, Chunmei; Chen, Jun; Shen, Jian-Ren; Li, Can

    2015-11-17

    A hybrid photoanode integrating the cyanobacterial photosystem II (PSII) with a hematite film for water oxidation is constructed. Direct electron transfer from PSII to the excited Ti/Fe2O3 electrode occurs under light irradiation, resulting in a significant improvement of the photocurrent. PMID:26443427

  9. Mediated Electron Transfer at Redox Active Monolayers

    Directory of Open Access Journals (Sweden)

    Michael E.G. Lyons

    2001-12-01

    Full Text Available A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. Although the analysis presented has quite general applicability, a specific focus of the paper is concerned with the idea that redox active monolayers can be used to model an ensemble of individual molecular nanoelectrodes. Three possible rate determining steps are considered: heterogeneous electron transfer between immobilized mediator and support electrode ; bimolecular chemical reaction between redox mediator and reactant species in the solution phase, and diffusional mass transport of reactant in solution. A general expression for the steady state reaction flux is derived which is valid for any degree of reversibility of both the heterogeneous electron transfer reaction involving immobilized mediator species and of the bimolecular cross exchange reaction between immobilized mediator and solution phase reactant. The influence of reactant transport in solution is also specifically considered. Simplified analytical expressions for the net reaction flux are derived for experimentally reasonable situations and a kinetic case diagram is constructed outlining the relationships between the various approximate solutions. The theory enables simple diagnostic plots to be constructed which can be used to analyse experimental data.

  10. Electron transfer pathways in microbial oxygen biocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Freguia, Stefano, E-mail: stefano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Tsujimura, Seiya, E-mail: seiya@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Kano, Kenji, E-mail: kkano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan)

    2010-01-01

    The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O{sub 2} reduction by heme compounds. Here we showed that 1 muM of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O{sub 2} reduction to H{sub 2}O{sub 2} with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

  11. Surface excitations in the modelling of electron transport for electron- beam-induced deposition experiments

    OpenAIRE

    Salvat-Pujol, Francesc; Valenti, Roser; Werner, Wolfgang S.

    2015-01-01

    The aim of the present overview article is to raise awareness of an essential aspect that is usually not accounted for in the modelling of electron transport for focused-electron-beam-induced deposition (FEBID) of nanostructures: surface excitations are on the one hand responsible for a sizeable fraction of the intensity in reflection-electron-energy-loss spectra for primary electron energies of up to a few keV and, on the other hand, they play a key role in the emission of ...

  12. Integral cross sections for electron impact excitation of vibrational and electronic states in phenol

    Energy Technology Data Exchange (ETDEWEB)

    Neves, R. F. C. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Instituto Federal do Sul de Minas Gerais, Campus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Lopes, M. C. A. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Blanco, F. [Departamento de Física Atómica, Molecular y Nuclear, Universidad Complutense de Madrid, 28040 Madrid (Spain); García, G. [Instituto de Física Fundamental, CSIC, Serrano 113-bis, 28006 Madrid (Spain); Ratnavelu, K. [Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Brunger, M. J., E-mail: Michael.Brunger@flinders.edu.au [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2015-05-21

    We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15–250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties.

  13. Total Electron Scattering and Electronic State Excitations Cross Sections for O_2, CO, and CH_4

    Science.gov (United States)

    Kanik, I.; Trajmar, S.; Nickel, J. C.

    1993-01-01

    Available electron collision cross section data concerning total and elastic scattering, vibrationalexcitation, and ionization for O_2, CO, and CH_4 have been critically reviewed, and a set of crosssections for modeling of planetary atmospheric behavior is recommended. Utilizing theserecommended cross sections, we derived total electronic state excitation cross sections and upperlimits for dissociation cross sections, which in the case of CH_4 should very closely equal the actualdissociation cross section.

  14. Selection rules for transport excitation spectroscopy of few-electron quantum dots

    CERN Document Server

    Pfannkuche, D; Pfannkuche, Daniela; Ulloa, Sergio E

    1995-01-01

    Tunneling of electrons traversing a few-electron quantum dot is strongly influenced by the Coulomb interaction leading to Coulomb blockade effects and single-electron tunneling. We present calculations which demonstrate that correlations between the electrons cause a strong suppression of most of the energetically allowed tunneling processes involving excited dot states. The excitation of center-of-mass modes, in contrast, is unaffected by the Coulomb interaction. Therefore, channels connected to these modes dominate the excitation spectra in transport measurements.

  15. Electron Spin Excited States Spectroscopy in a Quantum Dot Probed by QPC Back-action

    OpenAIRE

    Li, HaiOu; Xiao, Ming; Cao, Gang; Zhou, Cheng; Shang, RuNan; Tu, Tao; Guo, GuangCan; Jiang, Hongwen; Guo, Guoping

    2011-01-01

    The quantum point contact (QPC) back-action has been found to cause non-thermal-equilibrium excitations to the electron spin states in a quantum dot (QD). Here we use back-action as an excitation source to probe the spin excited states spectroscopy for both the odd and even electron numbers under a varying parallel magnetic field. For a single electron, we observed the Zeeman splitting. For two electrons, we observed the splitting of the spin triplet states $|T^{+}>$ and $|T...

  16. Enhanced formation of negative ions by electron attachment to highly excited molecules in a flowing afterglow plasma

    International Nuclear Information System (INIS)

    Preliminary evidence for efficient negative-ion formation using a plasma mixing scheme was reported in a recent letter [L. A. Pinnaduwage, W. Ding, and D. L. McCorkle, Appl. Phys. Lett. 71, 3634 (1997)]. In the present article we confirm the negative ion formation using a probe-assisted photodetachment technique and estimate rate constants for electron attachment to electronically excited CH4 and NO in a flowing afterglow plasma. It is shown that enhanced electron attachment to molecules in highly excited states populated via excitation transfer from rare gas metastables is responsible for the observed negative ion formation. Implications for plasma processing and plasma remediation discharges are also discussed. copyright 1998 American Institute of Physics

  17. A stochastic reorganizational bath model for electronic energy transfer

    International Nuclear Information System (INIS)

    Environmentally induced fluctuations of the optical gap play a crucial role in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker (HSR) model, in which the energy-gap fluctuation is approximated as white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to account for excitation energies’ thermal fluctuations. On the other hand, since the original work of HSR, many groups have employed stochastic models to simulate the same transfer dynamics. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equations via the generalized Langevin approach. Based on this connection, we propose a novel scheme to take account of reorganization effects within the framework of stochastic models. The proposed scheme provides a better description of the population dynamics especially in the regime of strong exciton-phonon coupling. Finally, we discuss the effect of the bath reorganization in the absorption and fluorescence spectra of ideal J-aggregates in terms of the Stokes shifts. We find a simple expression that relates the reorganization contribution to the Stokes shifts – the reorganization shift – to the ideal or non-ideal exciton delocalization in a J-aggregate. The reorganization shift can be described by three parameters: the monomer reorganization energy, the relaxation time of the optical gap, and the exciton delocalization length. This simple relationship allows one to understand the physical origin of the Stokes shifts in molecular aggregates

  18. Transfer of excitation between 2p levels of neon induced by collisions with neutral neon atoms

    International Nuclear Information System (INIS)

    The reaction coefficients for transfer of excitation between 2p atoms of neon induced by collisions with neutral neon atoms have been determined for nine 2p states. By means of a continuous dye laser 1s atoms of neon in a plasma generated by a 20-MeV proton beam in 110 torr neon, were excited to a specific 2p state. The relative population density of 2p states produced via collisional transfer of excitation was determined from the spectrum of the induced fluorescence light. This has been carried out for laser excitation to eight 2p levels. The reaction coefficients were calculated after inserting the observed population densities in a set of balance equations. The ratios of the experimental values of the reaction coefficients for collisional coupling between each two 2p states appeared to be consistent with a relation following from the principle of detailed balancing. (Auth.)

  19. 77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...

    Science.gov (United States)

    2012-06-08

    ...Collection of Information: Electronic Transfer Account...on a continuing information collection. By...FMS-111, ``Electronic Transfer Account...collection of information described below: Title: Electronic Transfer...

  20. Vibrational and electronic excitation of hexatriacontane thin films by low energy electron impact

    International Nuclear Information System (INIS)

    Thin polycrystalline films of hexatriacontane (HTC) were irradiated with low energy (E=0.5--15 eV) electrons, and off-specular backscattered electron spectra were measured. Below E?7 eV, single and multiple vibrational excitations only are observed, which relax the electrons down to the bottom of the HTC conduction band. Due to the negative electron affinity of HTC, thermal electrons are emitted into vacuum. Structure in the backscattered electron current at kinetic energies about 1.5 and 4 eV are associated to conduction band density of states. Above E?7 eV, the dominant losses correspond to electronic excitations, excitons, or above a threshold (energy of the electron inside the HTC film) at 9.2±0.1 eV, electron--hole pair generation. The latter process is very efficient and reaches a yield of the order of one ?11 eV. Evidence for chemical reaction above E?4 eV is observed

  1. Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy

    Science.gov (United States)

    Milot, Rebecca Lee

    Terahertz spectroscopy is distinguished from other far infrared and millimeter wave spectroscopies by its inherent phase sensitivity and sub-picosecond time resolution making it a versatile technique to study a wide range of physical phenomena. As THz spectroscopy is still a relatively new field, many aspects of THz generation mechanisms have not been fully examined. Using terahertz emission spectroscopy (TES), THz emission from ZnTe(110) was analyzed and found to be limited by two-photon absorption and free-carrier generation at high excitation fluences. Due to concerns about the continued use of fossil fuels, solar energy has been widely investigated as a promising source of renewable energy. Dye-sensitized solar cells (DSSCs) have been developed as a low-cost alternative to conventional photovoltaic solar cells. To solve the issues of the intermittency and inefficient transport associated with solar energy, researchers are attempting to adapt DSSCs for water oxidation and chemical fuel production. Both device designs incorporate sensitizer molecules covalently bound to metal oxide nanoparticles. The sensitizer, which is comprised of a chromophore and anchoring group, absorbs light and transfers an electron from its excited state to the conduction band of the metal oxide, producing an electric current. Using time-resolved THz spectroscopy (TRTS), an optical pump/THz probe technique, the efficiency and dynamics of electron injection from sensitizers to metal oxides was evaluated as a function of the chromophore, its anchoring group, and the metal oxide identity. Experiments for studying fully functioning DSSCs and water oxidation devices are also described. Bio-inspired pentafluorophenyl porphyrin chromophores have been designed and synthesized for use in photoelectrochemical water oxidation cells. Influences on the efficiency and dynamics of electron injection from the chromophores into TiO2 and SnO2 nanoparticles due to changes in both the central substituent to the porphyrin ring and degree of fluorination of ring substituents were analyzed. Due to the high reduction potentials of these sensitizers, injection into TiO2 was generally not observed. Injection timescales from the porphyrins into SnO2 depended strongly on the identity of the central substituent and were affected by competition with excited-state deactivation processes. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but is typically not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency and water stability of several alternative anchoring groups, including phosphonic acid, hydroxamic acid, acerylacetone, and boronic acid, were evaluated. While all of the anchoring groups exhibited water stability superior to carboxylate, the hydroxamate anchor had the best combination of ease of handling and electron injection efficiency. The effects on photoconductivity due to metal oxide morphology and the addition of dopants were also analyzed. Mixtures of anatase and rutile TiO 2 nanoparticles are known to exhibit cooperative effects which increase the efficiency of DSSCs and photocatalysis relative to the pure-phase materials. Through analysis of TRTS measurements, the mechanism of this synergistic effect was found to involve electron transfer from the lower-mobility, higher surface area rutile nanoparticles to anatase particles, resulting in a higher charge collection efficiency. In addition to morphology, doping has been investigated as a means of expanding the spectral range of visible absorption of photocatalysts. Doping ZnO nanowires with manganese(II) was found to significantly decrease the electron mobility, and doping with cobalt(II) increased the timescale for electron trapping. These differences can be understood by considering the changes to the band structure of ZnO effected by the dopants. Preliminary analyses of the solvent and electrolyte dependence on the electron injection rate and efficiency suggest that electron injection can be affected by

  2. Vibrational excitations in molecular layers probed by ballistic electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kajen, Rasanayagam Sivasayan; Chandrasekhar, Natarajan [Institute of Materials Research and Engineering, 3 Research Link, 117602 (Singapore); Feng Xinliang; Muellen, Klaus [Max-Planck-Institut fuer Polymerforschung, Postfach 3148, D-55021 Mainz (Germany); Su Haibin, E-mail: n-chandra@imre.a-star.edu.sg, E-mail: muellen@mpip-mainz.mpg.de, E-mail: hbsu@ntu.edu.sg [Division of Materials Science, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore)

    2011-10-28

    We demonstrate the information on molecular vibrational modes via the second derivative (d{sup 2}I{sub B}/dV{sup 2}) of the ballistic electron emission spectroscopy (BEES) current. The proposed method does not create huge fields as in the case of conventional derivative spectroscopy and maintains a zero bias across the device. BEES studies carried out on three different types of large polycyclic aromatic hydrocarbon (PAH) molecular layers show that the d{sup 2}I{sub B}/dV{sup 2} spectra consist of uniformly spaced peaks corresponding to vibronic excitations. The peak spacing is found to be identical for molecules within the same PAH family though the BEES onset voltage varies for different molecules. In addition, injection into a particular orbital appears to correspond to a specific vibrational mode as the manifestation of the symmetry principle.

  3. Electron impact excitation of carbon and oxygen ions

    International Nuclear Information System (INIS)

    This report is an attempt at a comprehensive compilation of currently available theoretical data on electron impact excitation of carbon and oxygen ions. It is designed to be of use primarily to theoretical atomic physicists, allowing them a broader than usual view of how various approximations compare. We do not attempt to place an estimate on the accuracy to which any of the collision strengths are known. The reader may obtain some idea of the accuracy from the spread in the calculations. Further, we do not evaluate rate coefficients or make any comparison with observed results. We do provide simple analytic fits to the data, where possible, thus allowing the reader to make comparison with observation or evaluate rate coefficients if he desires. The present data contains little about resonance effects, due to the difficulty of their presentation. It is possible that resonances could make a considerable change in the average collision strength near threshold, and this topic requires further study

  4. Solvent effects on electron-driven proton-transfer processes: adenine-thymine base pairs.

    Science.gov (United States)

    Dargiewicz, Monika; Biczysko, Malgorzata; Improta, Roberto; Barone, Vincenzo

    2012-07-01

    Time-Dependent Density Functional Theory (TD-DFT) computations, with M05-2X and PBE0 functionals, have been employed for a detailed study of the Electron-Driven Proton-Transfer (PT) processes in an Adenine-Thymine Watson-Crick Base Pair in the gas phase and in solution, with the bulk solvent described by the polarizable continuum model. In the gas phase, TD-DFT computations predict that the Adenine ? Thymine Charge Transfer (CT) excited state undergoes a barrierless PT reaction, in agreement with CC2 computations (S. Perun, A. Sobolewski, W. Domcke, J. Phys. Chem. A, 2006, 110, 9031.). The good agreement between the TD-DFT approach and CC2 results validates the former for the studies of excited state properties, excited state proton transfer reaction, and deactivation mechanisms in the DNA base pairs. Next, it is shown that inclusion of solvent effects significantly influences the possibility of both barrier-less excited state proton transfer and radiation-less deactivation through conical intersection with the ground state, affecting the energy of the CT excited state in the Franck-Condon region, the energy barrier associated to the PT process and the energy gap with the ground electronic state. These findings clearly indicate that environmental effects, with a special attention to proper treatment of dynamical solvation effects, have to be included for reliable computational analysis of photophysical and photochemical processes occurring in condensed phases. PMID:22398748

  5. Decision making based on optical excitation transfer via near-field interactions between quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Naruse, Makoto, E-mail: naruse@nict.go.jp [Photonic Network Research Institute, National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795 (Japan); Nomura, Wataru; Ohtsu, Motoichi [Department of Electrical Engineering and Information Systems, Graduate School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Aono, Masashi [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguru-ku, Tokyo 152-8550 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012 (Japan); Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge [Université Grenoble Alpes, Inst. NEEL, F-38000 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Kim, Song-Ju [WPI Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

    2014-10-21

    Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

  6. Decision making based on optical excitation transfer via near-field interactions between quantum dots

    CERN Document Server

    Naruse, Makoto; Aono, Masashi; Ohtsu, Motoichi; Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge; Kim, Song-Ju

    2014-01-01

    Optical near-field interactions between nanostructured matter, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

  7. Decision making based on optical excitation transfer via near-field interactions between quantum dots

    Science.gov (United States)

    Naruse, Makoto; Nomura, Wataru; Aono, Masashi; Ohtsu, Motoichi; Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge; Kim, Song-Ju

    2014-10-01

    Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

  8. Decision making based on optical excitation transfer via near-field interactions between quantum dots

    International Nuclear Information System (INIS)

    Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

  9. Rhodamine-6G can photosensitize folic acid decomposition through electron transfer

    Science.gov (United States)

    Hirakawa, Kazutaka; Ito, Hiroki

    2015-05-01

    Rhodamine-6G photosensitized folic acid decomposition in aqueous solution, and its quantum yield in the presence of 10 ?M folic acid was 9.9 × 10-6. A possible mechanism of this photodecomposition is direct oxidation through an electron transfer from folic acid to rhodamine-6G. The fluorescence lifetime of rhodamine-6G was slightly decreased by folic acid, suggesting electron transfer in the excited singlet state of rhodamine-6G. The quenching rate coefficient estimated from the Stern-Volmer plot of the fluorescence quenching supported that this electron transfer proceeds as a diffusion-controlled reaction. The quantum yields of the electron transfer and the following reaction could be determined.

  10. Time-resolved spectroscopy of energy and electron transfer processes in the photosynthetic bacterium Heliobacillus mobilis.

    Science.gov (United States)

    Lin, S; Chiou, H C; Kleinherenbrink, F A; Blankenship, R E

    1994-02-01

    The kinetics of excitation energy transfer and electron transfer processes within the membrane of Heliobacillus mobilis were investigated using femtosecond transient absorption difference spectroscopy at room temperature. The kinetics in the 725- to 865-nm region, upon excitation at 590 and 670 nm, were fit using global analysis. The fits returned three kinetic components with lifetimes of 1-2 ps and 27-30 ps, and a component that does not decay within several nanoseconds. The 1- to 2-ps component is attributed to excitation equilibration to form a thermally relaxed excited state. The 27- to 30-ps phase corresponds to the decay of the relaxed excited state to form a charge-separated state. The intrinsic energy and electron transfer rates were estimated using the experimental results and theoretical models for excitation migration and trapping dynamics. Taking into account the number of antenna pigments and their spectral distribution, an upper limit of 1.2 ps for the intrinsic time constant for charge separation in the reaction center is calculated. This upper limit corresponds with the trapping-limited case for excitation migration and trapping. Reduction of the primary electron acceptor A0 was observed in the 640 to 700 nm region using excitation at 780 nm. An instantaneous absorbance increase followed by a decay of about 30 ps was observed over a broad wavelength region due to the excited state absorption and decay of BChl g molecules in the antenna. In addition, a narrow bleaching band centered at 670 nm grows in with an apparent time constant of about 1.0 ps, superimposed on the 30-ps absorbance increase due to excited state absorption. Measurements on a longer time scale showed that besides the 670 nm pigment a BChl g molecule absorbing near 785 nm may be involved in the primary charge separation, and that this pigment may be in equilibrium with the 670 nm pigment. The bleaching bands at 670 nm and 785nm recovered with a time constant of about 600 ps, due to forward electron transport to a secondary electron acceptor. Energy and electron transfer properties of H. mobilis membranes are compared with Photosystem 1, to which the heliobacteria bear an evolutionary relationship. PMID:8161697

  11. Application of Degenerately Doped Metal Oxides in the Study of Photoinduced Interfacial Electron Transfer.

    Science.gov (United States)

    Farnum, Byron H; Morseth, Zachary A; Brennaman, M Kyle; Papanikolas, John M; Meyer, Thomas J

    2015-06-18

    Degenerately doped In2O3:Sn semiconductor nanoparticles (nanoITO) have been used to study the photoinduced interfacial electron-transfer reactivity of surface-bound [Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+) (RuP(2+)) molecules as a function of driving force over a range of 1.8 eV. The metallic properties of the ITO nanoparticles, present within an interconnected mesoporous film, allowed for the driving force to be tuned by controlling their Fermi level with an external bias while their optical transparency allowed for transient absorption spectroscopy to be used to monitor electron-transfer kinetics. Photoinduced electron transfer from excited-state -RuP(2+*) molecules to nanoITO was found to be dependent on applied bias and competitive with nonradiative energy transfer to nanoITO. Back electron transfer from nanoITO to oxidized -RuP(3+) was also dependent on the applied bias but without complication from inter- or intraparticle electron diffusion in the oxide nanoparticles. Analysis of the electron injection kinetics as a function of driving force using Marcus-Gerischer theory resulted in an experimental estimate of the reorganization energy for the excited-state -RuP(3+/2+*) redox couple of ?* = 0.83 eV and an electronic coupling matrix element, arising from electronic wave function overlap between the donor orbital in the molecule and the acceptor orbital(s) in the nanoITO electrode, of Hab = 20-45 cm(-1). Similar analysis of the back electron-transfer kinetics yielded ? = 0.56 eV for the ground-state -RuP(3+/2+) redox couple and Hab = 2-4 cm(-1). The use of these wide band gap, degenerately doped materials provides a unique experimental approach for investigating single-site electron transfer at the surface of oxide nanoparticles. PMID:25668488

  12. Coupling of radiation, excited states and electron energy distribution function in non equilibrium hydrogen plasmas

    International Nuclear Information System (INIS)

    Some of the recent efforts in the state-to-state modeling of H/H2-based plasma are considered, with particular concern to the aspects of self-consistent coupling between the chemical kinetics, electron kinetics and radiation. These aspects are first illustrated in the case of a 0-dimensional model considering both optically thin and optically thick cases in recombining and ionizing regimes. In the second part of the paper, a 1-dimensional extension of the model is applied to study a steady normal shock generated in an H2/He plasma of interest in atmospheric entry problems. A radiation transfer equation is coupled to the model as well, to analyze the effect of radiation transfer on chemical kinetics and compare to the commonly used thin and thick plasma approximations. The most significant result is the influence of reabsorption on the concentration of excited states, which in turn creates additional structure on the electron energy distribution function through second kind collisions. - Highlights: • We review our recent efforts in modeling of H2/H plasmas. • We stress the couplings between state-to-state chemical kinetics, electron kinetics and radiation. • These issues are illustrated using a 0-d and 1-d models. • The effect of radiation transfer on chemical kinetics is considered

  13. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    International Nuclear Information System (INIS)

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed

  14. Activation entropy of electron transfer reactions

    CERN Document Server

    Milischuk, A A; Newton, M D; Milischuk, Anatoli A.; Matyushov, Dmitry V.; Newton, Marshall D.

    2005-01-01

    We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by conti...

  15. Direct electron transfer based enzymatic fuel cells

    International Nuclear Information System (INIS)

    In this mini-review we briefly describe some historical developments made in the field of enzymatic fuel cells (FCs), discussing important design considerations taken when constructing mediator-, cofactor-, and membrane-less biological FCs (BFCs). Since the topic is rather extensive, only BFCs utilizing direct electron transfer (DET) reactions on both the anodic and cathodic sides are considered. Moreover, the performance of mostly glucose/oxygen biodevices is analyzed and compared. We also present some unpublished results on mediator-, cofactor-, and membrane-less glucose/oxygen BFCs recently designed in our group and tested in different human physiological fluids, such as blood, plasma, saliva, and tears. Finally, further perspectives for BFC applications are highlighted.

  16. Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

    OpenAIRE

    Vauthey, Eric

    2006-01-01

    Several controversial questions in the field of bimolecular photoinduced electron transfer reactions in polar solvents are first briefly reviewed. Results obtained in our group using ultrafast spectroscopy and giving a new insight into these problems will then be described. They concern the driving force dependence of the charge separation distance, the formation of the reaction product in an electronic excited state, the absence of normal region for weakly exergonic charge recombination proc...

  17. Experimental study on the kinetically induced electronic excitation in atomic collisional cascades

    International Nuclear Information System (INIS)

    the present thesis deals with the ion-collision-induced electronic excitation of metallic solids. For this for the first time metal-insulator-metal layer systems are used for the detection of this electronic excitation. The here applied aluminium/aluminium oxide/silver layer sytems have barrier heights of 2.4 eV on the aluminium respectively 3.3 eV on the silver side. With the results it could uniquely be shown that the electronic excitation is generated by kinetic processes, this excitation dependenc on the kinetic energy of the colliding particles, and the excitation dependes on the charge state of the projectile

  18. Rate of Excitation Energy Transfer between Fluorescent Dyes and Nanoparticles

    CERN Document Server

    Saini, S; Shenoy, V B; Bagchi, B; Saini, Sangeeta; Bhowmick, Somnath; Shenoy, Vijay B.; Bagchi, Biman

    2006-01-01

    Long range resonance energy transfer (RET) between a donor and an acceptor molecule is increasingly being used in many areas of biological and material science. The phenomenon is used to monitor the in vivo separation between different (bio) polymers/units of (bio) polymers and hence the dynamics of various biomolecular processes. Because of the sensitivity of the rate on to the distance between the donor (D) and the acceptor (A), the technique is popularly termed as "spectroscopic ruler". In this work we examine the distance and orientation dependence of RET in three different systems: (i) between a conjugated polymer and a fluorescent dye, (ii) between a nanometal particle (NMP) and a fluorescent dye and (iii) between two NMP. We show that in all the three cases, the rate of RET follows a distance dependence of d^(- sigma) where exponent sigma approaches 6 at large d (F"orster type dependence) but has a value varying from 3-4 at short to intermediate distance. At short separation, the amplitude of rate is c...

  19. Valence-Shell Excitations of Nitrous Oxide Studied by Fast Electron Impact

    Science.gov (United States)

    Liu, Ya-Wei; Wang, You-Yan; Zhu, Lin-Fan

    2012-04-01

    The valence-shell excitations of nitrous oxide are studied by fast electron energy loss spectroscopy. From the spectra measured at 2.5 keV and scattering angles of 3.5°-8.5°, it is found that the asymmetric peak of the transition B1? can be well fitted by Haarhoff-Van der Linde function, while the symmetric peaks of the transitions of C1? and D1?+ can be well fitted by the Voigt function. The parameters of the peak profiles of B1?, C1? and D1?+, i.e., their energy level positions and linewidths, are determined. With the aid of these parameters, the overlapping spectra measured at the low-energy electron impact can be deconvolved, which provides the possibility to determine the quantitative differential cross sections. The present results also show that the peak profiles of the transitions of B1?, C1? and D1?+, are independent of the momentum transfer.

  20. The Polarisation of radiation emitted from molecular states excited by polarised electrons and polarised synchrotron radiation

    International Nuclear Information System (INIS)

    Full text: Recent experiments have investigated the transfer of spin angular momentum into molecular systems, using spin-polarised electrons and observing the circular polarisation of the emitted radiation. The results have been interesting since circular polarization has been observed in fluorescence from molecular hydrogen and from atomic fragments created in the photo-dissociation of molecular hydrogen but not in the fluorescence from molecular nitrogen. This paper discusses the way in which angular momentum is shared in molecular systems and compares the results obtained in electron scattering experiments with measurements of the circular polarization obtained from various molecular states in H2 and N2 excited with circularly-polarised synchrotron radiation. Copyright (2005) Australian Institute of Physics

  1. An efficient implementation of the localized operator partitioning method for electronic energy transfer

    CERN Document Server

    Nagesh, Jayashree; Brumer, Paul

    2014-01-01

    The localized operator partitioning method [Y. Khan and P. Brumer, J. Chem. Phys. 137, 194112 (2012)] rigorously defines the electronic energy on any subsystem within a molecule and gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. However, an efficient implementation of this approach has been hindered by complicated one- and two-electron integrals arising in its formulation. Using a resolution of the identity in the definition of partitioning we reformulate the method in a computationally e?cient manner that involves standard one- and two-electron integrals. We apply the developed algorithm to the 9-((1-naphthyl)-methyl)-anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH2-naphthyl groups as subsystems, and examine their electronic energies and populations for several excited states using Configuration Interaction Singles method. The implemented approach shows a wide variety o...

  2. The population transfer of high excited states of Rydberg lithium atoms in a microwave field

    International Nuclear Information System (INIS)

    Using the time-dependent multilevel approach (TDMA), the properties of high excited Rydberg lithium atom have been obtained in the microwave field. The population transfer of lithium atom are studied on numerical calculation, quantum states are controlled and manipulated by microwave field. It shows that the population can be completely transferred to the target state by changing the chirped rate and field amplitude. (authors)

  3. Excited-state proton transfer from pyranine to acetate in methanol

    Indian Academy of Sciences (India)

    Sudip Kumar Mondal; Subhadip Ghosh; Kalyanasis Sahu; Pratik Sen; Kankan Bhattacharyya

    2007-03-01

    Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (1) is calculated to be ∼ 1 × 109 M-1 s-1. This is slower by about two orders of magnitude than that in bulk water (8 × 1010 M-1 s-1) at 4 M acetate.

  4. Analytical model for rates of electron attachment and intramolecular electron transfer in electron transfer dissociation mass spectrometry.

    Science.gov (United States)

    Simons, Jack

    2010-05-26

    A new physical model is put forth to allow the prediction of electron transfer rates and distances for (i) intramolecular transfer from an n > or = 3 Rydberg orbital on a positive site to a disulfide or amide bond site and (ii) intermolecular transfer from an anion donor to an n > or = 3 Rydberg orbital of a positively charged polypeptide. Although ab initio methods have proven capable of handling such electron transfer events when the Rydberg orbital has principal quantum number n = 3, they have proven to be incapable of handling Rydberg states having quantum number n > 3, so having a new tool capable of handling n > 3 Rydberg states is important. The model (i) focuses on each Rydberg orbital's large peak of high amplitude, (ii) approximates the electron density within this peak as constant within a radial shell characterized by a radius and thickness T both of which depend on the quantum number n, and (iii) assumes that strong coupling (either with an orbital of an anion donor or to a disulfide sigma* or a backbone amide pi* orbital) occurs when the valence orbital penetrates fully within the radial shell of the Rydberg orbital. These assumptions permit a derivation of the ratios of rates of electron transfer for n > 3 to those for n = 3. Combining these ratios with ab initio rates for n = 3 allows one to make rate predictions for inter- and intramolecular electron transfer involving Rydberg orbitals appropriate to the electron transfer dissociation process. One important prediction of this model is that the combination of large-penetration and Landau-Zener surface-crossing conditions places very severe limitations on which Rydberg levels can initially be populated in electron transfer dissociation. Another prediction is that a Rydberg orbital of a given principal quantum number n has a limited range of distances over which it can transfer an electron; sigma* or pi* orbitals either too far from or too close to a given Rydberg orbital cannot accept an electron from that orbital. PMID:20438123

  5. Electron transfer processes in photosynthetics biological systems

    International Nuclear Information System (INIS)

    This seminar presents a conceptual model of the sequence of primary light induced electron transfer (ET) steps in photosynthetic bacteria. The temperature dependence of some of these redox reactions, like ET process between cytochrome and bacteriochlorophyll in Chromatium, is characterized by a temperature-independent rate at low temperatures and exhibits the Arrhenius-type dependence at high temperatures. The other primary ET processes, like an ET reaction between bacteriopheophytin and Fe-quinone complex in Rps. spheroides, are temperature-independent in the broad range of 4-300K. The third type of ET processes, exemplified by back ET reactions between Fe-quinone and bacteriochlorophyll in Rhs. rubrum, exhibits negative activation energy at high temperatures. The theoretical approach, describing the primary ET processes in photosynthesis, is based on the non-adiabatic multiphonon ET theory, which incorporates both a continuous distribution of optical phonons in a polar solvent and discrete intramolecular vibrational modes. The last two types of the redox reactions are attributed to activationless ET processes which play an essential role in highly efficient charge separation in primary photosynthetic processes. The transition temperature, separating the tunneling region from the activated region indicates the range of phonon frequencies involved in the ET process. Comparing the low-temperature rates with calculated Franck-Condon factors one can determine the value of the electron-exchange matrix element, which in turn provides a rough estimate of the distance scale between a donor and an acceptor in the primary ET events

  6. Soliton-like Solutions and Electron Transfer in DNA

    OpenAIRE

    Lakhno, V. D.

    2000-01-01

    We consider various mechanisms of long-range electron transfer in DNAwhich enable us to explain recent controversial experiments. We show thatcontinuous super-exchange theory can explain the values of electron rateconstants in short fragments of DNA. The soliton-type electron transfer inlong segments of DNA is also dealt with.

  7. Photoreduction of polyhalogenated anthraquinones by direct electron transfer from alcohol

    Science.gov (United States)

    Inoue, Haruo; Ikeda, Kenji; Mihara, Hayao; Hida, Mitsuhiko

    1983-02-01

    Polyhalogenated anthraquinones such as perfluoroanthraquinone, 1,2,3,4-tetrafluoroanthraquinone, and 1,2,3,4-tetrachloroanthraquinone are photoreduced in ethanol via direct electron transfer from ethanol. A dramatic switch-over from hydrogen-atom abstraction to electron transfer is induced by mixing of?? with n? * states in their T 1 state and the enhanced electron-accepting character of polyhalogenated anthraquinones.

  8. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive...

  9. Electron degradation and yields of initial products. I. Excited species generated by electrons in binary mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, M.; Inokuti, M.

    1987-10-01

    Initial yields of excited species resulting from electron degradation in Ar+H/sub 2/ mixtures have been calculated using the Fowler equation. Following up the previous study of yields of ions by Eggarter (J. Chem. Physl 84, 6123 (1986)) and by Inokuti and Eggarter (J. Chem. Phys. 86, 3870 (1987)), the present work treats initial yields of excited species over the entire range of the composition of Ar+H/sub 2/ mixtures. The variation of the yield with the composition depends on the kind of excited species. The most noteworthy of the results obtained concerns the Ar metastable-state yield, which shows peculiar behavior when a small amount of H/sub 2/ is introduced in the media.

  10. Electron transfer and ionization in collisions of highly stripped ions with neutral targets at intermediate velocities

    International Nuclear Information System (INIS)

    A highly-charged ion impinging upon a neutral target atom will capture electrons into excited states of the projectile. If the velocity is much less than that of the target electrons, little direct ionization is expected, although appreciable target ionization has been reported for very highly charged ions. Recent studies on both transfer and ionization for Arq+ (6?q?17) and O+8,7 on Ar and He target shave been performed for projectile velocities between 0.2 and 1.7 a.u. The measured quantities include charge-state-correlated differential cross sections, K-x-ray emission, and longitudinal recoil- ion momentum transfer, from which Q values can be deduced. Non-negligible direct ionization is observed. Information is extracted on both the primary transfer process and the decay of the multiply excited projectile states formed. Comparisons with model predictions will be made

  11. Electron-hole plasma excitations in single-walled carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Afshin [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of)], E-mail: afshin551@gmail.com

    2008-08-18

    We study theoretically the {pi}-electron-hole plasma excitations in single-walled metallic carbon nanotubes within the framework of the classical electrodynamics. The {pi}-electrons and holes of the nanotubes are described by means of the two-fluid hydrodynamic theory. Numerical results show that the low-energy excitations are in qualitative agreement with low-frequency excitations ({pi} plasmon) in experimental observations in the case where the {pi}-electron and hole effective masses are nearly equal.

  12. Electronic excitations by chemical reactions on metal surfaces

    Science.gov (United States)

    Nienhaus, Hermann

    2002-01-01

    Dissipation of chemical energy released in exothermic reactions at metal surfaces may happen adiabatically by creation of phonons or non-adiabatically by excitation of the electronic system of the metal or the reactants. In the past decades, the only direct experimental evidence for such non-adiabatic reactions has been exoelectron emission into vacuum and surface chemiluminescence which are observed in a special class of very exothermic reactions. The creation of e-h pairs in the metal has been discussed in many theoretical models but it was only recently that a novel experimental approach using Schottky diodes with ultrathin metal films makes direct measurement of reaction-induced hot electrons and holes possible. The chemical reaction creates hot charge carriers which travel ballistically from the metal film surface toward the Schottky interface and are detected as a chemicurrent in the diode. By now, such currents have been observed during adsorption of atomic hydrogen and deuterium on Ag, Cu and Fe surfaces as well as chemisorption of atomic and molecular oxygen, of NO and NO 2 molecules and of certain hydrocarbons on Ag. This paper reviews briefly exoelectron and chemiluminescence experiments and the concept of the Nørskov-Newns-Lundqvist model. The major part is devoted to the detection of chemically induced e-h pairs with thin metal film Si Schottky diodes by discussing the different influences on the chemicurrent magnitude and presenting experimental results predominantly with hydrogen and deuterium atoms. The experiments introduce a new method to investigate surface reaction kinetics and dynamics by use of an electronic device. In addition, the diodes may be used as selective reactive gas sensors.

  13. Excitation of heavy hydrogen-like ions by light atoms in relativistic collisions with large momentum transfers

    OpenAIRE

    Najjari, B; Voitkiv, A. B.

    2012-01-01

    We present a theory for excitation of heavy hydrogen-like projectile-ions by light target-atoms in collisions where the momentum transfers to the atom are very large on the atomic scale. It is shown that in this process the electrons and the nucleus of the atom behave as (quasi-) free particles with respect to each other and that their motion is governed by the field of the nucleus of the ion. The effect of this field on the atomic particles can be crucial for the contribution to the excitati...

  14. Excited-State Proton Transfer in Resveratrol and Proposed Mechanism for Plant Resistance to Fungal Infection.

    Science.gov (United States)

    Simkovitch, Ron; Huppert, Dan

    2015-09-01

    Steady-state and time-resolved fluorescence techniques were employed to study the photophysics and photochemistry of trans-resveratrol. trans-Resveratrol is found in large quantities in fungi-infected grapevine-leaf tissue and plays a direct role in the resistance to plant disease. We found that trans-resveratrol in liquid solution undergoes a trans-cis isomerization process in the excited state at a rate that depends partially on the solvent viscosity, as was found in previous studies on trans-stilbene. The hydroxyl groups of the phenol moieties in resveratrol are weak photoacids. In water and methanol solutions containing weak bases such as acetate, a proton is transferred to the base within the lifetime of the excited state. When resveratrol is adsorbed on cellulose (also a component of the plant's cell wall), the cis-trans process is slow and the lifetime of the excited state increases from several tens of picoseconds in ethanol to about 1.5 ns. Excited-state proton transfer occurs when resveratrol is adsorbed on cellulose and acetate ions are in close proximity to the phenol moieties. We propose that proton transfer from excited resveratrol to the fungus acid-sensing chemoreceptor is one of the plant's resistance mechanisms to fungal infection. PMID:26247232

  15. Proton transfer in phenol-amine complexes: phenol electronic effects on free energy profile in solution.

    Science.gov (United States)

    Aono, Shinji; Kato, Shigeki

    2010-12-01

    Free energy profiles for the proton transfer reactions in hydrogen-bonded complex of phenol with trimethylamine in methyl chloride solvent are studied with the reference interaction site model self-consistent field method. The reactions in both the electronic ground and excited states are considered. The second-order Møller-Plesset perturbation (MP) theory or the second-order multireference MP theory is used to evaluate the effect of the dynamical electron correlation on the free energy profiles. The free energy surface in the ground state shows a discrepancy with the experimental results for the related hydrogen-bonded complexes. To resolve this discrepancy, the effects of chloro-substitutions in phenol are examined, and its importance in stabilizing the ionic form is discussed. The temperature effect is also studied. In contrast to the ground state, the ??* excited state of phenol-trimethylamine complex exhibits the proton transfer reaction with a low barrier. The reaction is almost thermoneutral. This is attributed to the reduction of proton affinity of phenol by the ??* electronic excitation. We further examine the possibility of the electron-proton-coupled transfer in the ??* state through the surface crossing with the charge transfer type ??* state. PMID:20602442

  16. Electron transfer reaction in the Marcus inverted region: Role of high frequency vibrational modes

    International Nuclear Information System (INIS)

    A theoretical study of the dynamics of photo-electron transfer reactions in the Marcus inverted regime is presented. This study is motivated partly by the recent proposal of Barbara et al. (J. Phys. Chem. 96, 3728, 1991) that a minimal model of an electron transfer reaction should consist of a polar solvent mode (X), a low frequency vibrational mode (Q) and one high frequency mode (q). Interplay between these modes may be responsible for the crossover observed in the dynamics from a solvent controlled to a vibrational controlled electron transfer. The following results have been obtained. (i) In the case of slowly relaxing solvents, the proximity of the point of excitation to an effective sink on the excited surface is critical in determining the decay of the reactant population. This is because the Franck-Condon overlap between the reactant ground and the product excited states decreases rapidly with increase in the quantum number of the product vibrational state. (ii) Non-exponential solvation dynamics has an important effect in determining the rates of electron transfer. Especially, a biphasic solvation and a large coupling between the reactant and the product states both may be needed to explain the experimental results

  17. Analytic approximations for integrated electron-atom excitations

    International Nuclear Information System (INIS)

    Accurate calculations of atomic excitations require estimates of the effect of higher excitations on the effective (optical) potential coupling various reaction channels. The total cross section for a particular excitation is proportional to the maximum contribution of that excitation to the imaginary part of the elastic momentum-space optical potential, and is typical of the contribution to the potential in general. Analytic expressions relevant to the calculation of optical potentials are given. Their validity is estimated by comparison with more-accurate calculations and with experimental excitation cross sections

  18. Interfacial Electron Transfer in TiO2 Surfaces Sensitized with Ru(II)-Polypyridine Complexes

    Science.gov (United States)

    Jakubikova, Elena; Snoeberger, Robert C., III; Batista, Victor S.; Martin, Richard L.; Batista, Enrique R.

    2009-07-01

    Studies of interfacial electron transfer (IET) in TiO2 surfaces functionalized with (1) pyridine-4-phosphonic acid, (2) [Ru(tpy)(tpy(PO3H2))]2+, and (3) [Ru(tpy)(bpy)(H2O)-Ru(tpy)(tpy(PO3H2))]4+ (tpy = 2,2':6,2''-terpyridine; bpy = 2,2'-bipyridine) are reported. We characterize the electronic excitations, electron injection time scales, and interfacial electron transfer (IET) mechanisms through phosphonate anchoring groups. These are promising alternatives to the classic carboxylates of conventional dye-sensitized solar cells since they bind more strongly to TiO2 surfaces and form stable covalent bonds that are unaffected by humidity. Density functional theory calculations and quantum dynamics simulations of IET indicate that electron injection in 1-TiO2 can be up to 1 order of magnitude faster when 1 is attached to TiO2 in a bidentate mode (? ˜ 60 fs) than when attached in a monodentate motif (? ˜ 460 fs). The IET time scale also depends strongly on the properties of the sensitizer as well as on the nature of the electronic excitation initially localized in the adsorbate molecule. We show that IET triggered by the visible light excitation of 2-TiO2 takes 1-10 ps when 2 is attached in a bidentate mode, a time comparable to the lifetime of the excited electronic state. IET due to visible-light photoexcitation of 3-TiO2 is slower, since the resulting electronic excitation remains localized in the tpy-tpy bridge that is weakly coupled to the electronic states of the conduction band of TiO2. These results are particularly valuable to elucidate the possible origin of IET efficiency drops during photoconversion in solar cells based on Ru(II)-polypyridine complexes covalently attached to TiO2 thin films with phosphonate linkers.

  19. Systematic trends in electron–hole pair trapping efficiency of rare earth doped YBO3 under vacuum ultraviolet excitation

    International Nuclear Information System (INIS)

    Host-to-activator energy transfer efficiencies in rare-earth doped YBO3 under vacuum ultraviolet excitation have been estimated using excitation and reflectance spectroscopy. From these data, relative electron–hole pair (e–h) trapping rate constants have been calculated for seven different lanthanide dopants. In addition, the energies of activator electronic states relative to YBO3 band states were estimated using published empirical methods. From this, we find a correlation between e–h trapping efficiency and the energy of activator electronic states relative to YBO3 conduction and valence band energies. - Highlights: • Relative e–h trapping rate constants are calculated for lanthanide dopants in YBO3. • Dopant energy levels are estimated relative to the valence and conduction bands of YBO3. • Dopants are classified as hole traps or electron traps. • A correlation between trapping efficiency and the energy of dopant trap is observed

  20. Mechanism for Highly Efficient Non-Radiative Deactivation of Electronic Excitation in Rutin

    Science.gov (United States)

    Bondarev, S. L.; Knyukshto, V. N.; Tikhomirov, S. A.; Buganov, O. V.

    2016-01-01

    Steady-state and pulsed spectroscopic methods are used to study the spectroscopic and photophysical properties of the biologically important plant pigment rutin at room temperature and 77 K in organic solvents and a buffer solution at pH 7.0. The large dipole moment ?e = 13.3 D of the rutin molecule in a Franck-Condon excited state indicates that rutin is dipolar in this excited state. The nonstationary S1 ? Sn induced absorption spectra are characterized by a short-wavelength band at ?abs max = 460 nm and low-intensity absorption in the 500-750 range which clearly belongs to associates of rutin. No residual induced absorption which might be related to triplet-triplet T1?Tk transitions in rutin was observed over the entire spectral range for times >50 ns. S1 ? S0 fluorescence with a quantum yield ?fl ~ 10-4 was also observed at room temperature. The fluorescence and fluorescence excitation spectra manifest a weak dependence on the excitation and detection wavelengths, which may be related to the presence of conformers in the solution owing to rotation of the phenol B ring around a single 1'-2 bond. Lowering the temperature of a glassy frozen solution of rutin in ethanol to 77 K raises ?fl by a factor of 750. A rate constant kic = 3.7·1011 s-1 for internal conversion from the S1 state at room temperature is calculated from the spectral-luminescence data. It is found that the main channel for exchange of electronic excitation energy in the rutin molecule at room temperature is S1(?,?*) ~~> S0-internal conversion induced by the charge-transfer state.

  1. Sequential energy and electron transfer in a three-component system aligned on a clay nanosheet.

    Science.gov (United States)

    Fujimura, Takuya; Ramasamy, Elamparuthi; Ishida, Yohei; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, Vaidhyanathan

    2016-02-10

    To achieve the goal of energy transfer and subsequent electron transfer across three molecules, a phenomenon often utilized in artificial light harvesting systems, we have assembled a light absorber (that also serves as an energy donor), an energy acceptor (that also serves as an electron donor) and an electron acceptor on the surface of an anionic clay nanosheet. Since neutral organic molecules have no tendency to adsorb onto the anionic surface of clay, a positively charged water-soluble organic capsule was used to hold neutral light absorbers on the above surface. A three-component assembly was prepared by the co-adsorption of a cationic bipyridinium derivative, cationic zinc porphyrin and cationic octaamine encapsulated 2-acetylanthracene on an exfoliated anionic clay surface in water. Energy and electron transfer phenomena were monitored by steady state fluorescence and picosecond time resolved fluorescence decay. The excitation of 2-acetylanthracene in the three-component system resulted in energy transfer from 2-acetylanthracene to zinc porphyrin with 71% efficiency. Very little loss due to electron transfer from 2-acetylanthracene in the cavitand to the bipyridinium derivative was noticed. Energy transfer was followed by electron transfer from the zinc porphyrin to the cationic bipyridinium derivative with 81% efficiency. Analyses of fluorescence decay profiles confirmed the occurrence of energy transfer and subsequent electron transfer. Merging the concepts of supramolecular chemistry and surface chemistry we realized sequential energy and electron transfer between three hydrophobic molecules in water. Exfoliated transparent saponite clay served as a matrix to align the three photoactive molecules at a close distance in aqueous solutions. PMID:26820105

  2. Computer modelling of coherence effects in excitation transfer in hexagonal PSU

    International Nuclear Information System (INIS)

    The time development of the site occupation probabilities in the hexagonal model of photosynthetic units is investigated. The method based on Stochastic Liouville Equations allows us to describe the excitation transfer with a trap (reaction center) in coherent, quasicoherent and incoherent regimes. (author). 26 refs, 9 figs

  3. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

    KAUST Repository

    Whited, Matthew T.

    2012-01-01

    We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9?-bianthryl.

  4. On the rate of triplet excitation transfer in the diffuse limit

    International Nuclear Information System (INIS)

    The usefulness of spectral data in estimating intermolecular triplet excitation transfer rates in found to be rather limited and to depend explicitly on the mechaisms which allow the optical transitions. Necessary conditions for the validity of such use of spectra are given, and the otherwise required correction factors are discussed and estimated. (Author)

  5. Elastic, excitation, ionization and charge transfer cross sections of current interest in fusion energy research

    International Nuclear Information System (INIS)

    Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low- to intermediate-energy regime. We summarize here some of our recent work

  6. Elastic, excitation, ionization and charge transfer cross sections of current interest in fusion energy research

    Energy Technology Data Exchange (ETDEWEB)

    Schultz, D.R.; Krstic, P.S. [Oak Ridge National Lab. TN (United States). Physics Div.

    1997-01-01

    Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low-to intermediate-energy regime. We summarize here some of our recent work. (author)

  7. I. Concepts of Highly Excited Electronic Systems / II. Electronic Correlation Mapping from Finite to Extended Systems

    Science.gov (United States)

    Berakdar, Jamal

    2006-02-01

    Knowledge of the excitation characteristics of matter is decisive for the descriptions of a variety of dynamical processes, which are of significant technological interest. E.g. transport properties and the optical response are controlled by the excitation spectrum. This self-contained work is a coherent presentation of the quantum theory of correlated few-particle excitations in electronic systems. It begins with a compact resume of the quantum mechanics of single particle excitations. Particular emphasis is put on Green function methods, which offer a natural tool to unravel the relations between the physics of small and large electronic systems. The book contains explicit expressions for the Coulomb Green function of two charge particles and a generalization to three-body systems. Techniques for the many-body Green function of finite systems are introduced and some explicit calculations of the Green functions are given. Concrete examples are provided and the theories are contrasted with experimental data, when available. A complimentary volume presents an up-to-date selection of applications of the developed concepts and a comparison with available experiments is made

  8. Excitation and ionization of highly charged ions by electron impact

    International Nuclear Information System (INIS)

    Two approaches for very rapid calculation of atomic data for high temperature plasma modeling have been developed. The first uses hydrogenic basis states and has been developed and applied in many papers discussed in previous progress reports. Hence, it is only briefly discussed here. The second is a very rapid, yet accurate, fully relativistic approach that has been developed over the past two or three years. It is described in more detail. Recently it has been applied to large scale production of atomic data. Specifically, it has been used to calculate relativistic distorted wave collision strengths and oscillator strengths for the following: all transitions from the ground level to the n=3 and 4 excited levels in the 71 Neon-like ions with nuclear charge number Z in the range 22 ? Z ? 92; all transitions among the 2s1/2, 2p1/2 and 2p3/2 levels and from them to all nlj levels with n=3,4 and 5 in the 85 Li-like ions with 8 ? Z ? 92; all transitions among the 3s1/2, 3p3/2, 3d3/2 and 3d5/2 levels and from them to all nlj levels with n=4 and 5 in the 71 Na-like ions with 22 ? Z ? 92; and all transitions among 4s1/2, 4p1/2, 4p3/2, 4d3/2, 4d5/2, 4f5/2 and 4f7/2 levels and from them to all nlj levels with n=5 in the 33 Cu-like ions with 60 ? Z ? 92. Also the program has been extended to give cross-sections for excitation to specific magnetic sublevels of the target ion by an electron beam and very recently it has been extended to give relativistic distorted wave cross sections for ionization of highly charged ions by electron impact

  9. Plugging in or going wireless: strategies for interspecies electron transfer

    OpenAIRE

    PravinMallaShrestha; Amelia-ElenaRotaru

    2014-01-01

    Interspecies exchange of electrons enables a diversity of microbial communities to gain energy from reactions that no one microbe can catalyze. The first recognized strategies for interspecies electron transfer were those that relied on chemical intermediates that are recycled through oxidized and reduced forms. Well-studied examples are interspecies H2 transfer and the cycling of sulfur intermediates in anaerobic photosynthetic communities. Direct interspecies electron transfer (DIET) in whi...

  10. Nonlocality in the excitation energy transfer in the Fenna-Matthews-Olson complex

    CERN Document Server

    Bengtson, Charlotta; Sjöqvist, Erik

    2015-01-01

    Pigment protein complexes involved in photosynthesis are remarkably efficient in transferring excitation energy from light harvesting antenna molecules to a reaction centre where it is converted to and stored as chemical energy. Recent experimental and theoretical studies suggest that quantum coherence and correlations may play a role in explaining this efficiency. We examine whether bipartite nonlocality, a property that verifies a strong correlation between two quantum systems, exists between different pairs of chromophore states in the Fenna-Matthews-Olson (FMO) complex and how this is connected to the amount of bipartite entanglement. In particular, it is tested in what way these correlation properties are affected by different initial conditions (i.e., which chromophore is initially excited). When modeling the excitation energy transfer (EET) in the FMO complex with the hierarchically coupled equations of motions (HEOM), it is found that bipartite nonlocality indeed exists for some pairs of chromophore s...

  11. Integral cross sections for electron impact excitation of electronic states of N2

    International Nuclear Information System (INIS)

    We report integral cross sections (ICSs) for electron impact excitation of the A 3?u+, B 3?g, W 3?u, B' 3?y-, a' 1?u-, a 1?g, ? 1?u, C 3?u, E 3?g+ and a'' 1?g+ electronic states of N2. The present data, for each state, were derived at five incident electron energies in the range 15-50 eV, from the earlier crossed-beam differential cross section (DCS) measurements of our group. This was facilitated by using a molecular phase shift analysis technique to extrapolate the measured DCSs to 0 deg. and 180 deg., before performing the integration. A comprehensive comparison of the present ICSs with the results of earlier experimental studies, both crossed beam and electron swarm, and theoretical calculations is provided. This comparison clearly indicates that some of the previous estimates for these excited electronic-state cross sections need to be reassessed. In addition, we have used the present ICSs in a Monte Carlo simulation for modelling the behaviour of an electron swarm in the bulk of a low current N2 discharge. The macroscopic transport parameters determined from this simulation are compared against those measured from independent swarm-based experiments and the self-consistency of our ICSs evaluated. (author)

  12. Tuning the reorganization energy of electron transfer in supramolecular ensembles - metalloporphyrin, oligophenylenevinylenes, and fullerene - and the impact on electron transfer kinetics

    Science.gov (United States)

    Stangel, Christina; Schubert, Christina; Kuhri, Susanne; Rotas, Georgios; Margraf, Johannes T.; Regulska, Elzbieta; Clark, Timothy; Torres, Tomás; Tagmatarchis, Nikos; Coutsolelos, Athanassios G.; Guldi, Dirk M.

    2015-01-01

    Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions between electron donors and acceptors in the ground and excited states. No appreciable electron interactions were noted in the ground state, which was being probed by electrochemistry, absorption spectroscopy, etc.; the electron acceptors are sufficiently decoupled from the electron donors. In the excited state, a different picture evolved. In particular, steady-state and time-resolved fluorescence and transient absorption measurements revealed substantial electron donor-acceptor interactions. These led, upon photoexcitation of the porphyrins, to tunable intramolecular electron-transfer processes, that is, the oxidation of porphyrin and the reduction of C60. In this regard, the largest impact stems from a rather strong distance dependence of the total reorganization energy in stark contrast to the distance independence seen for covalently linked conjugates.Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions between electron donors and acceptors in the ground and excited states. No appreciable electron interactions were noted in the ground state, which was being probed by electrochemistry, absorption spectroscopy, etc.; the electron acceptors are sufficiently decoupled from the electron donors. In the excited state, a different picture evolved. In particular, steady-state and time-resolved fluorescence and transient absorption measurements revealed substantial electron donor-acceptor interactions. These led, upon photoexcitation of the porphyrins, to tunable intramolecular electron-transfer processes, that is, the oxidation of porphyrin and the reduction of C60. In this regard, the largest impact stems from a rather strong distance dependence of the total reorganization energy in stark contrast to the distance independence seen for covalently linked conjugates. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05165c

  13. Fast-electron-impact study on excitations of 4d electron of xenon

    Science.gov (United States)

    Zhang, Xin; Liu, Ya-Wei; Peng, Yi-Geng; Xu, Long-Quan; Ni, Dong-Dong; Kang, Xu; Wang, Yang-Yang; Qi, Yue-Ying; Zhu, Lin-Fan

    2015-12-01

    The electron energy loss spectrum of the 4d excitations of xenon was measured at an incident electron energy of 1500 eV and a scattering angle of 6°. Besides the optically allowed transitions of and the optically forbidden transitions of and were observed. The measured features are assigned with the help of the calculation by the Cowan Code. The line profile parameters of both optically allowed transitions and optically forbidden ones were determined and compared with the previous available data. It is found that the natural widths of both dipole-allowed and dipole-forbidden excitations are approximately identical, which means the spectator transitions dominate the resonant Auger effect for both dipole-allowed and dipole-forbidden transitions. Project supported by the National Natural Science Foundation of China (Grant Nos. U1332204, 11274291, 11504361, and 11320101003).

  14. Chemically intuitive indices for charge-transfer excitation based on SAC-CI and TD-DFT calculations.

    Science.gov (United States)

    Ehara, Masahiro; Fukuda, Ryoichi; Adamo, Carlo; Ciofini, Ilaria

    2013-11-01

    A recently proposed charge-transfer (CT) index and some related quantities aimed to the description of CT excitations in push-pull donor-acceptor model systems were computed in vacuum and in ethanol by the direct symmetry-adapted cluster-configuration interaction (SAC-CI) method including solvent effects by means of the nonequilibrium state-specific approach. The effects of both solvation and electron correlations on these quantities were found to be significant. The present results are also in line with previous time-dependent (TD) density functional theory calculations and they demonstrate that SAC-CI provides a description of the excitation character close to that of TD-PBE0. Indeed, CT indices evaluated by the SAC-CI and TD-PBE0 would be useful in the field of materials chemistry, for the design and development of novel molecular materials. PMID:24037799

  15. Ultrafast static and diffusion-controlled electron transfer at Ag29 nanocluster/molecular acceptor interfaces

    Science.gov (United States)

    Aly, Shawkat M.; Abdulhalim, Lina G.; Besong, Tabot M. D.; Soldan, Giada; Bakr, Osman M.; Mohammed, Omar F.

    2016-03-01

    Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV2+) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs.Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV2+) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05328e

  16. Electron transfer reactions of metal complexes in solution

    International Nuclear Information System (INIS)

    A few representative electron-transfer reactions are selected and their kinetic parameters compared with the predictions of activated complex models. Since Taube has presented an elegant treatment of intramolecular electron-transfer reactions, emphasis is on bimolecular reactions. The latter electron-transfer reactions are more complicated to treat theoretically since the geometries of their activated complexes are not as well known as for the intramolecular case. In addition in biomolecular reactions, the work required to bring the two reactants together needs to be calculated. Since both reactants generally carry charges this presents a non-trivial problem at the ionic strengths usually used to study bimolecular electron transfer

  17. Spin-transfer torque based damping control of parametrically excited spin waves in a magnetic insulator

    Science.gov (United States)

    Lauer, V.; Bozhko, D. A.; Brächer, T.; Pirro, P.; Vasyuchka, V. I.; Serga, A. A.; Jungfleisch, M. B.; Agrawal, M.; Kobljanskyj, Yu. V.; Melkov, G. A.; Dubs, C.; Hillebrands, B.; Chumak, A. V.

    2016-01-01

    The damping of spin waves parametrically excited in the magnetic insulator Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an adjacent normal-metal film. The experiment is performed on a macroscopically sized YIG(100 nm)/Pt(10 nm) bilayer of 4 × 2 mm2 lateral dimensions. The spin-wave relaxation frequency is determined via the threshold of the parametric instability measured by Brillouin light scattering spectroscopy. The application of a dc current to the Pt film leads to the formation of a spin-polarized electron current normal to the film plane due to the spin Hall effect. This spin current exerts a spin transfer torque in the YIG film and, thus, changes the spin-wave damping. Depending on the polarity of the applied dc current with respect to the magnetization direction, the damping can be increased or decreased. The magnitude of its variation is proportional to the applied current. A variation in the relaxation frequency of ± 7.5 % is achieved for an applied dc current density of 5 × 1010 A/m2.

  18. Study of excitation transfer in fluid molecular media: I theoretical description

    International Nuclear Information System (INIS)

    The kinetics of excitation transfer between moving donors and acceptors in fluid solution is studied with a particular emphasis to the respective influence of the diffusive motion of the particules and of the mechanism of the reactive step. Our results show that all the microscopic properties of the transfer interaction (range and intensity) are included in the observable expressions of the transfer kinetics, in contrast to the conclusions of the widely used diffusion-limited reaction theory where the reactive interaction is represented by a more or less absorbing sink of arbitrary radius

  19. Development of an electron-temperature-dependent interatomic potential for molecular dynamics simulation of tungsten under electronic excitation

    International Nuclear Information System (INIS)

    Irradiation of a metal by lasers or swift heavy ions causes the electrons to become excited. In the vicinity of the excitation, an electronic temperature is established within a thermalization time of 10-100 fs, as a result of electron-electron collisions. For short times, corresponding to less than 1 ps after excitation, the resulting electronic temperature may be orders of magnitude higher than the lattice temperature. During this short time, atoms in the metal experience modified interatomic forces as a result of the excited electrons. These forces can lead to ultrafast nonthermal phenomena such as melting, ablation, laser-induced phase transitions, and modified vibrational properties. We develop an electron-temperature-dependent empirical interatomic potential for tungsten that can be used to model such phenomena using classical molecular dynamics simulations. Finite-temperature density functional theory calculations at high electronic temperatures are used to parametrize the model potential

  20. Investigation of the charge-transfer in photo-excited nanoparticles for CO2 reduction in non-aqueous media

    Directory of Open Access Journals (Sweden)

    Dimitrijevi? Nada M.

    2013-01-01

    Full Text Available Photoinduced charge separation in TiO2 and Cu2O semiconductor nanoparticles was examined using Electron Paramagnetic Resonance spectroscopy in order to get insight into the photocatalytic reduction of CO2 in nonaqueous media. For dissolution/grafting of CO2 we have used carboxy-PEG4-amine, and as a solvent poly(ethylene glycol 200. We have found that, in this system, reduction of CO2 starts at potential of -0.5 V vs Ag/AgCl, which is significantly more positive than the potential for electrochemical reduction of CO2 in most organic solvents and water (-2.0 V vs. Ag/AgCl. The electron transfer from excited nanoparticles to CO2 is governed both by thermodynamic and kinetic parameters, namely by the redox potential of conduction band electrons and adsorption/binding of CO2 on the surface of nanoparticles.