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Sample records for electronic excitation transfer

  1. Electronic structure charge transfer excitations, and high temperature superconductivity

    International Nuclear Information System (INIS)

    The high precision local density electronic band structure results (for YBa2Cu3O7, YBa2Cu3O6, and GdBa2Cu3O7) lead to the possibly important role of charge transfer excitations as the mechanism of high Tc superconductivity. They explain the coexistence of magnetism and superconductivity in the high Tc rare-earth superconductors

  2. 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

  3. Rate coefficients and inelastic momentum transfer cross sections for electronic excitation of N2 by electrons

    International Nuclear Information System (INIS)

    Rate coefficients, as a function of the electron temperature, have been determined from the integral cross sections for excitation of the 19 singlet and triplet electronic states of N2 within 14.2 eV of the ground state. For electron temperatures less than 10 eV, the rates for excitation of the A 3?+/sub u/, B 3Pi/sub g/, W 3?/sub u/, and a 1Pi/sub g/ are all greater than that for excitation of the C 3Pi/sub u/ state. The differential cross sections for excitation of these same electronic states were also used to calculate the inelastic momentum transfer associated with the excitation of these states. The total momentum transfer cross section for electrons in N2, as a function of the electron energy, was obtained by adding the inelastic momentum transfer to that associated with elastic scattering. Inelastic momentum transfer accounts for about 25% of the total momentum transfer above 15 eV. Over the energy range 20--60 eV, inelastic scattering contributes 20--25% to the total N2 electron scattering cross section. The total scattering cross section obtained here is in good agreement with a recent direct measurement of this cross section

  4. Electronic excitation transfer in clustered chromophore systems: Calculation of time-resolved observables for intercluster transfer

    Science.gov (United States)

    Marcus, A. H.; Fayer, M. D.

    1991-04-01

    A theoretical description is given for electronic excitation transport among interacting clusters of chromophores. Each cluster is a finite volume system with a limited number of chromophores. At high cluster concentration, intercluster transfer will become significant. The theory is based on a first-order cumulant approximation of the solution to the transport master equation. Gs(t) the probability of finding the excitation on the initially excited chromophore is calculated. The problem is first solved for two clusters at fixed separations. This result is extended to many clusters and then to the thermodynamic limit of an infinite number of clusters in an infinite volume. An example calculation is performed of excitation transport among chromophores on the surfaces of interacting micelles. For realistic parameters characterizing the system octadecylrhodamine B (chromophores) in Triton X-100 micelles, it is found that intermicelle excitation transfer can compete with intramicelle transfer. For an isolated micelle-chromophore system (chromophores on the surface of a sphere), a new time domain expression for Gs(t) is obtained.

  5. 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.

  6. Coherence, energy and charge transfers in de-excitation pathways of electronic excited state of biomolecules in photosynthesis

    DEFF Research Database (Denmark)

    Bohr, Henrik; Malik, F. Bary

    2013-01-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin–chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used F¨orster–Dexter theory, which does not allow for charge transfer, is a special case of B-A theory. The latter could, under appropriate circumstances, lead to excimers.

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

    Science.gov (United States)

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-01

    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.

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

    Science.gov (United States)

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    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. PMID:25978880

  9. 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

  10. 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

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

    Science.gov (United States)

    Tong, Jing; Li, Xiang-Yuan

    2002-11-01

    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 N 3rad 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.

  12. The Golden Rule. Application for fun and profit in electron transfer, energy transfer, and excited-state decay.

    Science.gov (United States)

    Ito, Akitaka; Meyer, Thomas J

    2012-10-28

    Time-dependent perturbation theory and application of the Golden Rule have been shown to be quantitatively applicable to electron transfer in the inverted region, energy transfer, and excited-state decay based on spectroscopic measurements on d?(6) polypyridyl complexes of Ru(II), Os(II), and Re(I). PMID:22842806

  13. 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.

  14. Electron transfer and aqua cation-cation complex formation in the excited state of the uranyl ion

    International Nuclear Information System (INIS)

    Excited-state mechanistic aspects of electron transfer between two aqua-cationic species are investigated and discussed in the case of excites UO2+2sub(()sub(a)sub(q)sub()) as acceptor and Ag+sub(()sub(a)sub(q)sub()) as donor. It is shown that excited-state electron transfer leads to an inner-sphere non-radiative complex of appreciable binding energy. (orig.)

  15. Electron transfer dynamics and excited state branching in a charge-transfer platinum(II) donor-bridge-acceptor assembly.

    Science.gov (United States)

    Scattergood, Paul A; Delor, Milan; Sazanovich, Igor V; Bouganov, Oleg V; Tikhomirov, Sergei A; Stasheuski, Alexander S; Parker, Anthony W; Greetham, Gregory M; Towrie, Michael; Davies, E Stephen; Meijer, Anthony J H M; Weinstein, Julia A

    2014-12-21

    A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAP[triple bond, length as m-dash]Pt(PBu3)2[triple bond, length as m-dash]Ph-CH2-PTZ (), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ?50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet (3)NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state (3)CSS ((3)[PTZ(+)-NAP(-)]) with 10% yield as determined by target analysis. The (3)CSS decays by charge-recombination to the ground state with ?1 ns lifetime. The lowest excited state is (3)NAP, which possesses a long lifetime of 190 ?s and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state. PMID:25361227

  16. 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

  17. Probing electron transfer processes in YPO(4):Ce, Sm by combined synchrotron-laser excitation spectroscopy.

    Science.gov (United States)

    Poolton, N R J; Bos, A J J; Jones, G O; Dorenbos, P

    2010-05-12

    Yttrium phosphate co-doped with cerium and samarium acts as a charge storage phosphor, but in highly doped material (0.5% co-doping levels), the proximity of defects leads to the uncontrolled non-radiative loss of stored charge through tunnelling. In order to characterize these defects, their mutual interactions and intra-pair charge transfer routes, experiments have been undertaken in which a laser probe is deployed during luminescence excitation using a synchrotron. Two modes of operation are described; in each case, the laser (2.8 eV) probes only Sm(2+) ions, and the detection is set to monitor exclusively Ce(3+) 5d-4f emission. Mode 1: the sample is pumped with monochromatic synchrotron photons in the range 4.5-12 eV, and the resultant charge populations probed with the laser 30 s later; this has the effect of sampling electrons trapped at Sm(2+) that are in quasi-equilibrium. Here, a clear transition between a sub-bandgap Urbach tail region and excitations above the mobility edge is especially apparent, enabling an accurate value of the conduction band energy of YPO(4) to be determined, 9.20 eV. Furthermore, the Sm(2+) and Ce(3+) ground state energies can be positioned within the bandgap (6.8 eV and 3.85 eV above the top of the valence band, respectively). Mode 2: the sample is pumped with monochromatic synchrotron photons in the range 4.5-12 eV and, during this pumping process, the laser probe is activated. This more dynamic process probes direct electron transfer excitation processes between spatially correlated Sm-Ce defect pairs, via their excited states; the laser probe enhances the Ce(3+) emission if direct electron transfer from the Ce(3+) ground state to the excited states of Sm(2+) is being pumped, or quenches the luminescence if the Ce(3+) excited states are pumped. The experiments allow for a precise measure of the difference in energy between the Sm(2+) and Ce(3+) ground states (2.98 eV). PMID:21393684

  18. 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)

  19. Electron transfer, ionization, and excitation in atomic collisions. Progress report, June 15, 1992--June 14, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Winter, T.G.; Alston, S.G.

    1995-08-01

    The research program of Winter and Alston addresses the fundamental processes of electron transfer, ionization, and excitation in ion-atom, ion-ion, and ion-molecule collisions. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-core interaction can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. Winter has focussed on intermediate collision energies (e.g., proton energies for p-He{sup +} collisions on the order of 100 kilo-electron volts), in which many electron states are strongly coupled during the collision and a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. Alston has concentrated on higher collision energies (million electron-volt energies), or asymmetric collision systems, for which the coupling of the projectile is weaker with, however, many more target states being coupled together so that high-order perturbation theory is essential. Several calculations by Winter and Alston are described, as set forth in the original proposal.

  20. Ultrafast interfacial electron transfer from the excited state of anchored molecules into a semiconductor

    Science.gov (United States)

    Gundlach, L.; Ernstorfer, R.; Willig, F.

    Ultrafast heterogeneous electron transfer (HET) from the excited singlet state of the large organic chromophore perylene into the inorganic semiconductor rutile TiO 2 was investigated with femtosecond time-resolved two-photon photoemission (TR-2PPE). The strength of the electronic interaction between the chromophore and the semiconductor was varied by inserting different anchor/bridge groups that functioned either as electronic wire or electronic tunnelling barrier. Both anchor groups, i.e. carboxylic and phosphonic acid, formed strong chemical bonds at the TiO 2 surface. The perylene chromophore with the different anchor/bridge groups was adsorbed from solution in a dedicated ultra-high-vacuum (UHV) chamber. The adsorption geometry of the chromophore perylene was determined from angle and polarization dependent two-photon photoemission (2PPE) signals and was found to be very different for the two different anchor/bridge groups. The measured adsorption geometries are compatible with recent DFT (density functional theory) calculations by P. Persson and co-workers [M. Nilsing, S. Lunell, P. Persson, L. Ojamäe, Phosphonic acid adsorption at the TiO 2 anatase (1 0 1) surface investigated by periodic hybrid HF-DFT computations, Surf. Sci. 582 (2005) 49-60]. Two different processes contributed to the TR-2PPE transients, firstly electron transfer from the chromophore to the electronic acceptor states on the surface and secondly escape of the electrons from the surface into the bulk of the semiconductor. The latter escape process was measured separately by making the interfacial electron injection process instantaneous when the chromophore catechol was employed in place of the perylene compounds. The thus measured electron escape behavior was governed by the same time constants that have recently been predicted by Prezhdo and coworkers from time dependent DFT calculations [W.R. Duncan, W.M. Stier, O.V. Prezhdo, Ab initio nonadiabatic molecular dynamics of the ultrafast electron injection across the Alizarin-TiO 2 interface, J. Am. Chem. Soc. 127 (2005) 7941-7951]. The HET times derived from the 2PPE transients showed very good agreement with HET times measured via transient absorption (TA) on anatase TiO 2 layers. The measured energy distribution of the 2PPE signals for the injected electrons suggests that a high density of electronic acceptor states is operative in both systems and is spread over an at least 1 eV wide energy range. The acceptor states are tentatively identified with surface states created through the formation of chemical bonds between the anchor groups of the organic molecules and surface atoms of the semiconductor.

  1. Fluorescence and dissociative energy transfer in high pressure Ar--HCN mixtures excited by relativistic electrons

    International Nuclear Information System (INIS)

    Studies of the radiation from Ar--HCN and Ar--H2O mixtures, excited by relativistic electrons from a Febetron 706 electron gun, are presented. The energy deposited by the electrons channels rapidly into the Ar* and Ar2* states; then by dissociative collisions with HCN it is transferred partly into the CN(B) state and partly into a reservoir state [most probably the CN(A) state] with near unit efficiency. Fluorescence emission from the electronic states A (2Pi/sub i/) and B (2?+) of the CN radical, as well as the emission from the Ar2* excimer state, were measured for an Ar pressure range of 750--9000 torr [15--180 psi (absolute)], and an HCN pressure range of 0.2--13 torr. The quenching rates of Ar* metastable and the Ar2* excimer states, by collision with HCN molecules, were measured to be 6 x 10-10 and 1 x 10-9 cm3 sec-1, respectively. Our results suggest that population inversion can be achieved by collisional dissociation of simple molecules with excited rare gas atoms and excimers. Indeed the peak CN(B) population density was found to be 1.5 x 1015 cm-3, which corresponds to an optical gain for the B--X transition of 0.4 cm-1 if the ground state is empty. A computer kinetic model is presented that explains the time dependence and intensity of the CN(B) emission. In Ar--H2O mixtures the reaction rate 2O mixtures the reaction rate for quenching of Ar2* excimer by H2O molecules is extremely high; however, the yield into the OH(A 2?+) is only 3%

  2. Electronic excitation transfer and lasing characteristics of mixed dye solutions under conditions of inhomogeneous broadening of their molecular spectra

    Energy Technology Data Exchange (ETDEWEB)

    Akimov, A.; Levshin, L.; Saletskii, A.; Yuzhakov, V.

    1981-11-01

    An investigation was made of the influence of processes of excitation energy transfer from rhodamine 6G (donor) to cresyl violet (acceptor) during lasing in their binary solutions under conditions of inhomogeneous broadening of the electronic spectra of both components. It was found that an increase in the lasing power of the acceptor on increase in the inhomogeneous spectral broadening was due to both radiative and nonradiative energy transfer from the donor to the acceptor.

  3. Electronic excitation transfer and lasing characteristics of mixed dye solutions under conditions of inhomogeneous broadening of their molecular spectra

    Science.gov (United States)

    Akimov, A. I.; Levshin, L. V.; Saletskii, A. M.; Iuzhakov, V. I.

    1981-11-01

    The effect of excitation energy transfer from rhodamine 6G (donor) to cresyl violet (acceptor) during lasing in their binary solutions under conditions of the inhomogeneous broadening of the electronic spectra of both components was investigated. The inhomogeneous spectral broadening was found to increase the lasing power of the acceptor dye. The lasing power of cresyl violet in a mixed solution increased both as a result of nonradiative energy transfer (about 20%) and by a radiative mechanism (about 80%).

  4. Excited hydrogen atom formed by non-adiabatic electron transfer from metal surfaces

    International Nuclear Information System (INIS)

    Formation of excited hydrogen atoms at a tungsten surface is explained by the non-adiabatic single electron capture by protons. Occupation probabilities of the excited levels are calculated using a one-dimensional mixed quantum-classical model for proton velocities of 0.1 - 1.0 a.u. The non-adiabatic evolution of electronic states is attributed to wave functions astride of the potential ridge. (author)

  5. 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

  6. Predicting Accurate Electronic Excitation Transfer Rates via Marcus Theory with Boys or Edmiston-Ruedenberg Localized Diabatization

    OpenAIRE

    Subotnik, Joseph E.; Vura-Weis, Josh; Sodt, Alex J.; Ratner, Mark A.

    2010-01-01

    We model the triplet-triplet energy transfer experiments from the Closs group [G. L. Closs et al, JACS, 110, p. 2652 (1988)] using a combination of Marcus theory and either Boys or Edmiston-Ruedenberg localized diabatization. We show that relative and absolute rates of electronic excitation transfer may be computed successfully, as we find ?calc = 2.8 per C-C bond, compared with the experimental value ?exp = 2.6, for the case where both donor and acceptor occupy equatorial positions on a rigi...

  7. Predicting Accurate Electronic Excitation Transfer Rates via Marcus Theory with Boys or Edmiston-Ruedenberg Localized Diabatization

    Science.gov (United States)

    Sodt, Alex J.; Ratner, Mark A.

    2010-01-01

    We model the triplet-triplet energy transfer experiments from the Closs group [G. L. Closs et al, JACS, 110, p. 2652 (1988)] using a combination of Marcus theory and either Boys or Edmiston-Ruedenberg localized diabatization. We show that relative and absolute rates of electronic excitation transfer may be computed successfully, as we find ?calc = 2.8 per C-C bond, compared with the experimental value ?exp = 2.6, for the case where both donor and acceptor occupy equatorial positions on a rigid cyclohexane bridge. This work highlights the power of using localized diabatization methods as a tool for modeling non-equilibrium processes. PMID:20446743

  8. Polarisation effects in electron transfer reactions with laser excited Na(3P) at medium energies

    International Nuclear Information System (INIS)

    We report new experimental data for the investigation of the role of electronic orbital alignment and orientation in charge transfer processes, in the medium energy range where the collision velocity vc and the velocity of the active electron ve are of the same order of magnitude. The results obtained for the H2+-Na(3p) and He+-Na(3p) collisions are discussed in comparison with the experimental and theoretical findings obtained for the H+-Na(3p) system. Recent time-of-flight measurements for charge transfer in Li+-Na (3s and 3p) collisions are also presented. (orig.)

  9. Electron transfer from laser excited Rydberg atoms to molecules. Absolute rate constants at low and intermediate principal quantum numbers

    International Nuclear Information System (INIS)

    Using mass spectrometric detection of positive and negative ions, we have investigated ionizing reactions of Ne(ns,nd) Rydberg atoms, efficiently excited by resonant two-photon excitation of metastable Ne(3s3P2) atoms, with electron attaching molecules BC (BC=SF6, CCl4, CS2, O2) at thermal collision energies. Absolute rate constants have been determined in the range of low and intermediate principal quantum numbers n(5?n3P2) atoms, associated with the laser excitation. Substantially different n-dependences of the electron transfer cross section have been found for the larger molecules (BC=SF6, CCl4) and the smaller molecules (BC=CS2, O2). Simple model calculations have been performed to gain new insight into the dynamics of the electron transfer process; for BC=SF6, our results at low n(5?n?10) suggest that internal energy conversion in the Coulombic complex Ne+-SF6- is important for the formation of the detected ions. (orig.)

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

    International Nuclear Information System (INIS)

    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 (?,?*) 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? position and a pyrimidine in the 3? 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?-purine-pyrimidine-3? sequence favors the formation of charge transfer excited states

  11. Ultrafast Excited State Dynamics of the Perylene Radical Cation Generated upon Bimolecular Photoinduced Electron Transfer Reaction

    OpenAIRE

    Pages, Ste?phane; Lang, Bernhard Felix; Vauthey, Eric

    2006-01-01

    The ultrafast ground state recovery (GSR) dynamics of the radical cation of perylene, Pe•+, generated upon bimolecular photoinduced electron transfer in acetonitrile, has been investigated using pump?pump?probe spectroscopy. With 1,4-dicyanobenzene as electron acceptor, the free ion yield is substantial and the GSR dynamics of Pe•+ was found to depend on the time delay between the first and second pump pulses, ?t12, i.e., on the "age" of the ion. At short ?t12, the GSR dynamics is b...

  12. [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

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

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-12-31

    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{sup +}, Li{sup 2+}, Be{sup 3+}, B{sup 4+}, C{sup 5+}, and the H{sup +} + Na system.

  14. Probing electron transfer processes in Y PO4:Ce, Sm by combined synchrotron-laser excitation spectroscopy

    Science.gov (United States)

    Poolton, N. R. J.; Bos, A. J. J.; Jones, G. O.; Dorenbos, P.

    2010-05-01

    Yttrium phosphate co-doped with cerium and samarium acts as a charge storage phosphor, but in highly doped material (0.5% co-doping levels), the proximity of defects leads to the uncontrolled non-radiative loss of stored charge through tunnelling. In order to characterize these defects, their mutual interactions and intra-pair charge transfer routes, experiments have been undertaken in which a laser probe is deployed during luminescence excitation using a synchrotron. Two modes of operation are described; in each case, the laser (2.8 eV) probes only Sm2 + ions, and the detection is set to monitor exclusively Ce3 + 5d-4f emission. Mode 1: the sample is pumped with monochromatic synchrotron photons in the range 4.5-12 eV, and the resultant charge populations probed with the laser 30 s later; this has the effect of sampling electrons trapped at Sm2 + that are in quasi-equilibrium. Here, a clear transition between a sub-bandgap Urbach tail region and excitations above the mobility edge is especially apparent, enabling an accurate value of the conduction band energy of Y PO4 to be determined, 9.20 eV. Furthermore, the Sm2 + and Ce3 + ground state energies can be positioned within the bandgap (6.8 eV and 3.85 eV above the top of the valence band, respectively). Mode 2: the sample is pumped with monochromatic synchrotron photons in the range 4.5-12 eV and, during this pumping process, the laser probe is activated. This more dynamic process probes direct electron transfer excitation processes between spatially correlated Sm-Ce defect pairs, via their excited states; the laser probe enhances the Ce3 + emission if direct electron transfer from the Ce3 + ground state to the excited states of Sm2 + is being pumped, or quenches the luminescence if the Ce3 + excited states are pumped. The experiments allow for a precise measure of the difference in energy between the Sm2 + and Ce3 + ground states (2.98 eV).

  15. Role of thermal excitation in ultrafast energy transfer in chlorosomes revealed by two-dimensional electronic spectroscopy.

    Science.gov (United States)

    Jun, Sunhong; Yang, Cheolhee; Kim, Tae Wu; Isaji, Megumi; Tamiaki, Hitoshi; Ihee, Hyotcherl; Kim, Jeongho

    2015-07-21

    Chlorosomes are the largest light harvesting complexes in nature and consist of many bacteriochlorophyll pigments forming self-assembled J-aggregates. In this work, we use two-dimensional electronic spectroscopy (2D-ES) to investigate ultrafast dynamics of excitation energy transfer (EET) in chlorosomes and their temperature dependence. From time evolution of the measured 2D electronic spectra of chlorosomes, we directly map out the distribution of the EET rate among the manifold of exciton states in a 2D energy space. In particular, it is found that the EET rate varies gradually depending on the energies of energy-donor and energy-acceptor states. In addition, from comparative 2D-ES measurements at 77 K and room temperature, we show that the EET rate exhibits subtle dependence on both the exciton energy and temperature, demonstrating the effect of thermal excitation on the EET rate. This observation suggests that active thermal excitation at room temperature prevents the excitation trapping at low-energy states and thus promotes efficient exciton diffusion in chlorosomes at ambient temperature. PMID:26095203

  16. Plasmon induced electron transfer at gold-TiO2 interface under femtosecond near-IR two-photon excitation

    International Nuclear Information System (INIS)

    Charge-transfer process from photoexcited gold nanoparticles to TiO2 is significant due to the very strong surface plasmon absorption band of gold nanoparticles and the very high photocatalytic activity of TiO2. Bioapplication of gold-TiO2 systems utilizing near-infrared (NIR) light based on the two photon excitation of the surface plasmon band will be interesting. In this study, TiO2 particles with a 30 nm average diameter loaded with 10 nm gold spherical nanoparticles were used to explore the electron injection kinetics by observing electrons in TiO2 using femtosecond IR-probe transient absorption (TA) spectroscopy. Optical excitation of the gold-TiO2 system using ? 150 fs light at 1200 nm led to very fast (2. Excitation intensity dependence of the initial TA signals gave a second order nonlinear relation, confirming the occurrence of two photon induced electron injection. Two photon absorption cross section of gold nanoparticle at 1200 nm was estimated to be very high, around 108 GM (1 GM = 10-50 cm4 s photon-1 molecule-1).

  17. 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

  18. Short-lived charge-transfer-to-solvent-states and multiple electronic relaxations following femtosecond excitation of aqueous chloride ion

    Science.gov (United States)

    Gauduel, Y.; Gelabert, H.; Ashokkumar, M.

    1995-08-01

    Early charge transfer processes triggered by the photoexcitation of an aqueous sodium chloride solution (molar ratio H 2O/NaCl = 55) at 294 K have been investigated by using femtosecond absorption UV-IR spectroscopy. The initial UV energy deposition proceeding by one- (4 eV) and/or two-photon (2 × 4 eV) absorption results in the formation of multiple short-lived electronic states which have been discriminated within the spectral range 360-1250 nm (3.44-0.99 eV). Two well-separated spectral signatures involving UV and infrared transitions have been discriminated and assigned to different excited CTTS states (charge transfer to solvent) as recently suggested by quantum simulations of an aqueous halide I - [Sheu and Rossky, Chem. Phys. Letters 202 (1993) 186; 213 (1993) 233]. A short-lived ultraviolet component appearing within the UV pump pulse and exhibiting a monoexponential relaxation time of 190 ± 20 fs would correspond to a lo excited CTTS state of the chloride ion (CTTS ?). The other ultrashort-lived band peaking above 0.99 eV (1250 nm) and characterized by a high deactivation rate (?2 × 10 13s -1) is tentatively assigned to a high excited CTTS state (CTTS ??) triggered by a two-photon absorption process (8 eV). This transient state precedes the ap pearance of a well-defined infrared component peaking around 1250 nm and due to the (p-like) excited hydrated electron (e prehyd-). The relaxation of this infrared electron occurs with a time constant of 300 fs and leads to the formation of the ground state of the hydrated electron (e hyd-). Near-infrared spectroscopic investigations performed in the energy range 1.51-1.24 eV (820-1000 nm) have permitted to clearly identify the existence of additional absorption bands peaking around 880 nm. It is the first time that near-infrared bands are directly observed in an aqueous solution of halide ions. These spectral contributions are assigned to inhomogeneous populations of electron-atom pairs ({e -:Cl nH 2O A,B}). The involved photochemical channel can compete wit electron hydration channel for which a pre-hydrated state (e prehyd-) has been identified. The existence of these near-infrared states would be due to local solvent effects which assist or impede an electron localization outside the first hydration shells of the atomic core (Cl). The electronic population absorbing in the near infrared exhibits a dual behavior whose characteristic times are 330 fs ({e -:Cl nH 2O A}) and 750 fs (e -: Cl nH 2O B) respectivley. The faster relaxation channel due to contribute to the early geminate recombination between the ground state of the hydrated electron and the chlorine atom. The slower deactivation channel (1.29 × 10 12s -1) would be due to an electronic state ({e -:Cl nH f2 0 B}) whose interconversion with a ground state of a hydrated electron has been identified in the present study. This electron photodetachment pathway leads to a delayed formation of hydrated electrons (e hyd-') and can be seen as a specific solvent cage effect in the vicinity of the counterion (Na +). The direct characterization of short-lived semi-ionized states by near-infrared spectroscopy provides new informations on solvent cage effects during ultrafast electron transfer reactions in ionic solutions. These complex photochemical data obtained with aqueous sodium chloride are discussed at the microscopic level considering recent quantum theories on semi-ionized or metastable states in ionic solutions.

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

    KAUST Repository

    Alsulami, Qana A.

    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.

  20. 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.

  1. Charge Transfer Mechanism and Spatial Density Correlation of Electronic States of Excited Zinc (3d9 Films

    Directory of Open Access Journals (Sweden)

    Li Chen

    2014-04-01

    Full Text Available In material science, half filled 3d orbital of transition metals is essentially an important factor controlling characteristics of alloys and compounds. This paper presents a result of the challenge of excitation of inner-core electron system with long lifetime of zinc films. The advanced zinc films with excited inner-core electron, 3dn (n = 9, 8. We report experimental results of XPS measurements of 9 points in the sample along vertical direction, respectively. The most pronounced futures are existence of satellites, which are about 4 eV higher than the main lines. According to the charge transfer mechanism proposed by A. Kotani and K. Okada, it was clarified that the origins of these peaks are c3d9L for the main peak and c3d9 for the satellite, respectively. From the energy difference, ?EB, and peak intensity ratio, I+/I-, between c3d9 and c3d10L, the energy for charge transfer, ?, and mixing energy, T, were estimated. In the region where the intensity of c3d10L becomes large, ? becomes small, 1.2 ?dc = 5.5 eV and Udd = 5.5 eV. In the analysis along vertical direction, intensity profile of Zn3d9 showed odd functional symmetry and that of Zn3d10L showed even functional symmetry. Only the intensity profile of C1s (288 eV showed the same spatial correlation with Zn3d9. In our experiment, the sample also showed high mobility of the constituting elements. These suggest that charge conservation in excited zinc atom suggests combination between Zn3d9 and C2-.

  2. 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

  3. 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.

  4. Nonlocal thermodynamic equilibrium effects in stratospheric HF by collisional energy transfer from electronically excited O2 and implications for infrared remote sensing

    Science.gov (United States)

    Kaye, Jack A.

    1989-01-01

    A possible nonlocal thermodynamic equilibrium (non-LTE) effect involving stratospheric HF arising from the direct photochemical excitation of vibrationally excited HF by collisional energy transfer from electronically excited O2 is presented. Although this non-LTE effect is smaller that one associated with the direct solar excitation of both HF(nv = 1) and HF(nv = 2), calculations show that inclusion of the mechanism into retrieval algorithms is necessary if correct daytime upper stratosphere HF profiles are to be inferred in future IR thermal emission measurements.

  5. Monte Carlo simulations of excitation and electron transfer in grana membranes.

    Science.gov (United States)

    Gibasiewicz, Krzysztof; Adamiec, Ma?gorzata; Luci?ski, Robert; Giera, Wojciech; Che?miniak, Przemys?aw; Szewczyk, Sebastian; Sipi?ska, Weronika; G?ów, Edyta; Karolczak, Jerzy; van Grondelle, Rienk; Jackowski, Grzegorz

    2015-03-01

    Time-resolved fluorescence measurements on grana membranes with instrumental response function of 3ps reveal faster excitation dynamics (120ps) than those reported previously. A possible reason for the faster decay may be a relatively low amount of "extra" LHCII trimers per reaction center of Photosystem II. Monte Carlo modeling of excitation dynamics in C2S2M2 form of PSII-LHCII supercomplexes has been performed using a coarse grained model of this complex, constituting a large majority of proteins in grana membranes. The main factor responsible for the fast fluorescence decay reported in this work was the deep trap constituted by the primary charge separated state in the reaction center (950-1090cm(-1)). This value is critical for a good fit, whereas typical hopping times between antenna polypeptides (from ~4.5 to ~10.5ps) and reversible primary charge separation times (from ~4 to ~1.5ps, respectively) are less critical. Consequently, respective mean migration times of excitation from anywhere in the PSII-LHCII supercomplexes to reaction center range from ~30 to ~80ps. Thus 1/4-2/3 of the ~120-ps average excitation lifetime is necessary for the diffusion of excitation to reaction center, whereas the remaining time is due to the bottle-neck effect of the trap. Removal of 27% of the Lhcb6 apoprotein pool by mutagenesis of DEG5 gene caused the acceleration of the excitation decay from ~120 to ~100ps. This effect may be due to the detachment of LHCII-M trimers from PSII-LHCII supercomplexes, accompanied by deepening of the reaction center trap. PMID:25524819

  6. 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.

    1800-18-01

    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 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.

  7. 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)

  8. Transfer of electronic excitation in collisions of metastable argon atoms with nitrogen molecules

    International Nuclear Information System (INIS)

    Measurements have been made of the product vibrational and rotational state distributions for the process Ar/sup asterisk/(3P/sub 2,0/)+N2(X) ?Ar(1S0)+N2/sup asterisk/(C,3Pi/sub u/) by spectrometric observation of the C?B fluorescence at the intersection of supersonic beams of the reactant species over the relative kinetic energy range 0.06--0.41 eV. The results are compared with the predictions of a ''golden rule'' model which gives the transition probabilities in the highly impulsive limit as the product of Franck--Condon and density of states factors. Below 0.17 eV, the model fits the experimentally determined v'=0/v'=1 population ratio reasonably well. At higher energies the experimental ratio rises, however, and reaches a maximum at 0.3 eV. A statistical population of rotational levels for v'=0 corresponding to rotational temperatures of 1300 0K and 1100 0K at 0.161 and 0.089 eV relative energy, respectively, is observed, while the ''golden rule'' predicts considerably higher rotational excitation in each case

  9. 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

  10. Electron-impact ionization-excitation dynamics at large momentum transfer: (e,2e) studies on He and H2

    International Nuclear Information System (INIS)

    We report an (e,2e) study on simultaneous ionization-excitation processes of He and H2 at large momentum transfer. The symmetric noncoplanar (e,2e) cross sections have been measured for transitions to excited ion states. It has been found that noticeable higher-order effects are involved even at the rather high impact energies employed, which ranged between 1.2 and 4.3 keV. Second Born approximation calculations satisfactorily account for the experimental results, indicating that the second-order two-step mechanisms serve as a key to understanding the ionization-excitation dynamics. Roles of the two-step mechanisms will be fully discussed.

  11. Fission-fragment excitation of metal electrons

    International Nuclear Information System (INIS)

    The authors mathematically formulate the formation and relaxation of excited-electron regions along the paths of fission fragments under conditions of first wall sputtering and ionization and fission fragment transport into the wall. Their model incorporates all collisional and absorptional aspects of energy transfer between fragments and electrons and includes thermal diffusion and heat transfer between electrons and the metal lattice. Interactions with quasi particles in the solid-state regime are also given consideration

  12. Excited-state intramolecular proton transfer reaction modulated by low-frequency vibrations: An effect of an electron-donating substituent on the dually fluorescent bis-benzoxazole

    Science.gov (United States)

    Sepio?, J.; Grabowska, A.; Borowicz, P.; Kijak, M.; Broquier, M.; Jouvet, Ch.; Dedonder-Lardeux, C.; Zehnacker-Rentien, A.

    2011-07-01

    Excited-state intramolecular proton transfer (ESIPT) reaction has been studied in a molecule showing dual fluorescence, the 2,5-bis(2-benzoxazolyl)-4-methoxyphenol (BBMP), and its isotopomers, where the methoxy, and alternatively, the OH group has been deuterated. Attention is focused on the influence of electron donating OCH3 substituent on fast excited state reaction. Comparison between the resonance-enhanced multiphoton ionization spectrum and the laser-induced excitation of the primary and phototautomeric emissions has been done. The geometry, electron density distribution, vibrational structure as well as the potential energy profiles in the S0 and S1 states of four possible rotameric forms of BBMP were calculated with application of the density functional theory (DFT). It allowed identifying the most probable conformer and assessing the role of low-frequency motions for the ESIPT efficiency.

  13. 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

  14. The electronic structure and charge transfer excited states of the endohedral trimetallic nitride C80 (I(h)) fullerenes-Zn-tetraphenyl porphyrin dyads.

    Science.gov (United States)

    Basurto, Luis; Amerikheirabadi, Fatemeh; Zope, Rajendra; Baruah, Tunna

    2015-02-28

    Endohedral fullerenes offer the possibility of tuning their properties through a choice of the endohedral unit. The Sc3N@C80 fullerene is the most abundant fullerene after C60 and C70. Recently, Sc3N@C80 has been tested for light harvesting properties with encouraging results. In this work, we study the electronic structure of three endohedral fullerene-Zn tetraphenyl porphyrin complexes using density functional theory. The binding between the components in these complexes arises due to van der Waals interaction. A fragment orbital analysis is carried out to examine the interaction between the two components which shows that a small charge transfer occurs in the ground state from the ZnTPP to the fullerenes and that the orientation of the Sc3N plane affects the ground state charge transfer. The charge transfer excited state energies are calculated using our perturbative delta-SCF method. A comparison with earlier calculations shows that the charge transfer excitation energy increases as C60-ZnTPP < C70-ZnTPP < Sc3N@C80-ZnTPP < Y3N@C80-ZnTPP. The orientation of the endohedral unit does not influence the excitation energy in the donor-acceptor complexes. PMID:25631359

  15. Momentum-Transfer-Resolved Electron Energy Loss Spectroscopy of BaBiO3: Anisotropic Dispersion of Threshold Excitation and Optically Forbidden Transition

    Science.gov (United States)

    Wang, Y. Y.; Dravid, V. P.; Bulut, N.; Han, P. D.; Klein, M. V.; Schnatterly, S. E.; Zhang, F. C.

    1995-09-01

    Momentum-transfer-resolved electron energy loss spectroscopy of the valence band transitions in BaBiO3 has revealed for the first time that dispersion of the excitation at the optical gap \\(~2 eV\\) and an optically forbidden transition at 4.5 eV are all anisotropic along [100] and [110]. The anisotropic dispersion of the threshold excitation cannot be described by a simple charge density wave picture but can be explained by a small exciton model proposed in this paper. The optically forbidden transition is found to agree well with a proposed molecular orbital model, where the transition is assigned as the excitation from the O 2p? nonbonding states to the empty Bi 6s state.

  16. Kinetic parameters for the electron-transfer quenching of the luminescent excited state of ruthenium(II)-polypyridine complexes by aromatic amines in acetonitrile solution

    International Nuclear Information System (INIS)

    Rate constants are reported for the reductive electron-transfer quenching of the luminescent excited state of four Ru(II)-polypyridine complexes by seven aromatic amines in acetonitrile solution. The log k/sub q/ vs. ?G plots obtained have been analyzed on the basis of the current theories for electron-transfer processes. The quenching constants for Ru(bpy)32+, Ru(bpy)2(biq)2+, and Ru(bpy)2(DMCH)2+, where bpy is 2,2'-bipyridine, biq is 2,2'-biquinoline, and DMCH is a 2,2'-biquinoline derivative, lie on the same log k/sub q/ vs. ?G curve whose best-fitting analysis yields the following values for the intrinsic barrier and electronic transmission coefficient of the *RuL32+/RuL3+ self-exchange electron-transfer reactions: ?G/sup double dagger/(0) = 3.1 kcal/mol, K = 1 x 10-2. The quenching constants concerning Ru(DTB-bpy)32+, where DTB-bpy is 4,4'-di-tert-butyl-2,2'-bipyridine, are rather scattered and lie clearly below the curve which fits the quenching constants of the other complexes, showing that substitution of the hydrogen atoms in the 4 and 4' positions of the bpy ring by bulky tert-butyl groups lowers the electronic transmission coefficient K to values of the order of 10-5. The kinetic parameters obtained for self-exchange electron transfer of the Ru complexes are compared with those previously obtained for sed with those previously obtained for self-exchange energy transfer. 52 references, 5 figures, 1 table

  17. 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.

  18. Electron shuttling in electron transfer dissociation

    Science.gov (United States)

    Neff, Diane; Smuczynska, Sylwia; Simons, Jack

    2009-06-01

    Ab initio electronic structure calculations have been performed on two model systems containing a disulfide linkage and one or two positively charged sites, aimed at gaining further insight into how and where electrons attach to positively charged peptides under electron capture (ECD) and electron transfer dissociation (ETD) mass spectroscopy conditions. Couplings among electronic states involving (i) an entrance-channel with the excess electron residing on a donor anion interacting with the positively charged peptide, (ii) a state in which the electron has been transferred to the SS [sigma]* orbital to cause bond cleavage, and (iii) a manifold of states in which the electron has been transferred to a ground- or excited-Rydberg orbital on a positive site. The results of this study suggest that specific excited Rydberg states play a key role in effecting electron shuttling to the SS [sigma]* orbital. The excited-Rydberg orbitals close in energy to the SS [sigma]* orbital and with sufficient radial extent to span the distance between the positive site and the SS [sigma]* orbital play the key role. Then, when the anion donor, excited-Rydberg, and SS [sigma]* orbitals achieve spatial proximity and similarity in energies, one can have what is termed here a shuttle of an electron from the donor to the SS [sigma]* orbital, which results in SS bond cleavage. For the singly and doubly charged systems studied here, it was the 3p and 3d Rydberg orbitals, respectively, that met these criteria of spatial and energetic proximity. For other peptides having different charge states, it will be other Rydberg orbitals that meet these criteria because the relative energies of the SS [sigma]* and Rydberg orbitals are governed by the (different) Coulomb stabilizations these orbitals experience. However, the evidence suggests that it is not very high-energy Rydberg states but states with 3 ETD, and ECID experiments.

  19. 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

  20. 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 ...

  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. 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

    2014-10-21

    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. PMID:25338878

  3. ELECTRON TRANSFER AND K-SHELL EXCITATION IN SINGLE COLLISIONS OF 47-365 MeV Ca17+ WITH Ne, Ar, AND Kr

    OpenAIRE

    Clark, M.; Tanis, J.; Berkner, K.; Bernstein, E.; Dubois, R.; Graham, W.; Mcfarland, R.; Morgan, T.; Mueller, D.; Schlachter, A.; Stalder, K.; Stearns, J.; Stockli, M.

    1987-01-01

    The occurance of electron capture and projectile K-shell excitation in singlecollision events has been investigated by measuring K-x-ray emission coincident with single-electron capture for 47-365 MeV Ca17+ ions colliding with Ne, Ar, and Kr. The results indicate that this two-electron process takes place primarily due to independent capture and excitation events, in contrast to previous measurements for He targets which show that the capture and excitation arise from the electron-electron in...

  4. Charge transfer and excitation in high-energy ion-atom collisions

    International Nuclear Information System (INIS)

    Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K-shell of Ca ions and the L-shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture. (orig.)

  5. Charge transfer and excitation in high-energy ion-atom collisions

    International Nuclear Information System (INIS)

    Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K shell of Ca ions and the L shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture

  6. 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

  7. Two-Electron Transfer Pathways.

    Science.gov (United States)

    Lin, Jiaxing; Balamurugan, D; Zhang, Peng; Skourtis, Spiros S; Beratan, David N

    2015-06-18

    The frontiers of electron-transfer chemistry demand that we develop theoretical frameworks to describe the delivery of multiple electrons, atoms, and ions in molecular systems. When electrons move over long distances through high barriers, where the probability for thermal population of oxidized or reduced bridge-localized states is very small, the electrons will tunnel from the donor (D) to acceptor (A), facilitated by bridge-mediated superexchange interactions. If the stable donor and acceptor redox states on D and A differ by two electrons, it is possible that the electrons will propagate coherently from D to A. While structure-function relations for single-electron superexchange in molecules are well established, strategies to manipulate the coherent flow of multiple electrons are largely unknown. In contrast to one-electron superexchange, two-electron superexchange involves both one- and two-electron virtual intermediate states, the number of virtual intermediates increases very rapidly with system size, and multiple classes of pathways interfere with one another. In the study described here, we developed simple superexchange models for two-electron transfer. We explored how the bridge structure and energetics influence multielectron superexchange, and we compared two-electron superexchange interactions to single-electron superexchange. Multielectron superexchange introduces interference between singly and doubly oxidized (or reduced) bridge virtual states, so that even simple linear donor-bridge-acceptor systems have pathway topologies that resemble those seen for one-electron superexchange through bridges with multiple parallel pathways. The simple model systems studied here exhibit a richness that is amenable to experimental exploration by manipulating the multiple pathways, pathway crosstalk, and changes in the number of donor and acceptor species. The features that emerge from these studies may assist in developing new strategies to deliver multiple electrons in condensed-phase redox systems, including multiple-electron redox species, multimetallic/multielectron redox catalysts, and multiexciton excited states. PMID:25583181

  8. 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.

  9. 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

  10. 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...

  11. 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.

  12. On the suppression of quantum oscillations and the choice of site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer

    CERN Document Server

    Ritschel, G; Strunz, W T; Aspuru-Guzik, A; Eisfeld, A

    2011-01-01

    Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. We find that in all considered cases there is very little transfer between the monomers. Since it is believed that the eighth BChl is located near the main light harvesting antenna we look at the differences in transfer between the situation when BChl 8 is initially excited and the usually considered case when BChl 1 or 6 is initially excited. We find strong differences in the transfer dynamics, both qualitatively and quantitatively. When the excited state dynamics is initialized at site eight of the FMO complex, we see a slow exponential-like decay of the excitation. This is in contrast to the oscillations and a relatively fast transfer that occurs when only seven sites or initialization at sites 1 and 6 is considered. Additionall...

  13. 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

  14. Electron Capture Into Excited States in H + Ar18+, Kr36+ and Xe54+ Charge Transfer Collisions

    Science.gov (United States)

    Jane, R. K.; Belic, D. S.

    1983-01-01

    Partial cross-sections for electron capture into specific final state principal shells in H + Ar18+, Kr36+ and Xe54+ collisions are calculated. A multichannel Landau-Zener model, which includes also the rotational transitions in the ionic channels, is employed. The calculations are performed in the energy range from 10-2 to 102 keV amu-1.

  15. UV Resonance Raman Investigation of the Conformations and Lowest Energy Allowed Electronic Excited States of Tri- and Tetraalanine: Charge Transfer Transitions

    OpenAIRE

    Sharma, Bhavya; Asher, Sanford A

    2010-01-01

    UV resonance Raman excitation profiles and Raman depolarization ratios were measured for trialanine and tetraalanine between 198 and 210 nm. Excitation within the ???* electronic transitions of the peptide bond results in UVRR spectra dominated by amide peptide bond vibrations. In addition to the resonance enhancement of the normal amide vibrations, we find enhancement of the symmetric terminal COO? vibration. The Ala3 UVRR AmIII3 band frequencies indicate that poly-proline II and 2.51 ...

  16. 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 1s2s2p2 3D 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

  17. Electron transfer to sulfides:

    International Nuclear Information System (INIS)

    The problem of characterizing the steps associated with the dissociative reduction of sulfides has been addressed. The electrochemical reduction of diphenylmethyl para-methoxyphenyl sulfide in N,N-dimethylformamide, on both glassy carbon and mercury electrodes, was chosen as a test system. The electrode process involves the slow heterogeneous outer-sphere electron transfer to the sulfide, the fast cleavage of the C-S bond, the reduction of the ensuing carbon radical, and the self-protonation triggered by the generation of the strong base Ph2CH-. The latter reaction is rather slow, in agreement with the large intrinsic barriers characterizing proton transfers between CH-acids and carbon bases. The dissociative reduction was studied in the presence of an exogenous acid. The results, obtained by convolution analysis, point to a stepwise DET mechanism in which the ET step is accompanied by rather large reorganization energy. Similar results were obtained on both electrode materials. Analysis of the heterogeneous electron transfer and associated C-S bond cleavage indicate that the reduction of this and other sulfides lies between the stepwise dissociative electron transfers leading to the formation of stiff ?* radical anions and those going through the intermediacy of loose ?* radical anions

  18. Nonadiabatic anharmonic electron transfer

    International Nuclear Information System (INIS)

    The effect of an inner sphere, local mode vibration on an electron transfer is modeled using the nonadiabatic transition probability (rate) expression together with both the anharmonic Morse and the harmonic oscillator potential. For an anharmonic inner sphere mode, a variational analysis uses harmonic oscillator basis functions to overcome the difficulties evaluating Morse-model Franck-Condon overlap factors. Individual matrix elements are computed with the use of new, fast, robust, and flexible recurrence relations. The analysis therefore readily addresses changes in frequency and/or displacement of oscillator minimums in the different electron transfer states. Direct summation of the individual Boltzmann weighted Franck-Condon contributions avoids the limitations inherent in the use of the familiar high-temperature, Gaussian form of the rate constant. The effect of harmonic versus anharmonic inner sphere modes on the electron transfer is readily seen, especially in the exoergic, inverted region. The behavior of the transition probability can also be displayed as a surface for all temperatures and values of the driving force/exoergicity ?=??G. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy (?=?s) along a maximum ln (w) vs. ? ridge of the surface. The surface also reveals additional regions for ? where ln (w) appears to be insensitive to temperature, or effectivelyive to temperature, or effectively activationless, for some kinds of inner sphere contributions.

  19. Vibrational Dependence of Excited State Intramolecular Proton Transfer in 2-(2'-PYRIDYL)PYRROLE in the Gas Phase via High Resolution Electronic Spectroscopy.

    Science.gov (United States)

    Morgan, Philip J.; Fleisher, Adam J.; Pratt, David W.; Kijak, Michal; Waluk, Jacek

    2010-06-01

    {Rotationally resolved fluorescence excitation spectra of the S_1?S_0 origin band and +144 cm^{-1} vibrational band transitions of 2-(2^'-Pyridyl)pyrrole (2PP) have been recorded in the collision free environment of a molecular beam. Analyses of these data provide new information about the changes in geometry that occur when 2PP absorbs light. Additionally, significant line broadening is observed in both spectra, which we attribute to an excited state intramolecular proton transfer (ESIPT) reaction. The dynamics and vibrational mode dependence of ESIPT in 2PP will be discussed.}

  20. 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.

  1. Electron paramagnetic resonance of photocatalytic reaction which involve electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Kaise, M. [National Institute of Materials and Chemical Research, Tsukuba (Japan)

    1995-10-13

    Transient radicals generated under photocatalytic reactions in a polar solvent and their electronically spinned polarization were discussed under UV irradiation by using EPR and N2 gas pulse laser time-divided EPR. The reaction is a reaction of electron transfer from such amines as DABCO or electron donor molecules of SO3{sup -} to such electron accepting compounds as 1,4-benzoquinone and maleic anhydride under the presence of photocatalysts (triple photosensitizers) such as benzophenone and xanthone (XT). Spin polarized cation radicals of DABCO and radical anions of XT were detected in association with one electron transfer. A triple mechanism lies in the spinned polarization of both radicals, and transient XT in the triple state begin the electron transfer reaction. Photo-excited XT acts as a photocatalyst in one electron transfer reaction, the triple XT turns into an electron accepting body, and the transient anion radicals of XT become the electron donor. The XT(S) acts as a photocatalyst in the inter-molecular electron transfer from amine (D) to quinone (A). Its reaction is expressed by the following formula: D + S{sup *} + A{yields}D{sup dot +}+S+A{sup dot -} (where S{sup *} denotes a photo-excited state). 53 refs., 21 figs., 3 tabs.

  2. 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

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

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

    Theophilou, Iris; Tassi, M.; Thanos, S.

    2014-04-01

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for 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.

  5. Theory of electron transfer reactions

    Science.gov (United States)

    Marcus, Rudolph A.

    1994-06-01

    An objective of the research performed on this grant is the understanding of the detailed behavior of a variety of electron transfer processes. Theories were developed for (1) the rate of electron transfer between a reagent in one liquid phase and another in a second (immiscible) liquid or polymer, (2) the rate of long distance electron transfer in proteins, (3) charge transfers spectra in frozen media, (d) scanning tunneling microscopy (stm) of molecular adsorbates, and (4) analysis of models of solvents used in computer simulations of electron transfer, particularly examining the error incurred by their common neglect of the electronic and vibrational contributions of the solvent's dielectric response.

  6. Electron impact excitations of S2 molecules

    CERN Document Server

    Tashiro, Motomichi

    2007-01-01

    Low-energy electron impact excitations of S_2 molecules are studied using the fixed-bond R-matrix method based on state-averaged complete active space SCF orbitals. Integral cross sections are calculated for elastic electron collision as well as impact excitation of the 7 lowest excited electronic states. Also, differential cross sections are obtained for elastic collision and excitation of the a^1 Delta_g, b^1 Sigma_g^+ and B^3 Sigma_u^- states. The integrated cross section of optically allowed excitation of the B^3 Sigma_u^- state agrees reasonably well with the available theoretical result.

  7. Nuclear reorganization barriers to electron transfer

    International Nuclear Information System (INIS)

    The nuclear barrier to electron transfer arises from the need for reorganization of intramolecular and solvent internuclear distances prior to electron transfer. For reactions with relatively small driving force (''normal'' free-energy region) the nuclear factors and rates increase as intrinsic inner-shell and outer-shell barriers decrease; this is illustrated by data for transition metal complexes in their ground electronic states. By contrast, in the inverted free-energy region, rates and nuclear factors decrease with decreasing ''intrinsic'' barriers; this is illustrated by data for the decay of charge-transfer excited states. Several approaches to the evaluation of the outer-shell barrier are explored in an investigation of the distance dependence of the nuclear factor in intramolecular electron-transfer processes. 39 refs., 14 figs., 3 tabs

  8. Photocontrol on ultrafast excited state transfer processes

    International Nuclear Information System (INIS)

    Our studies on photo-switching of intramolecular charge transfer in our newly designed anthracene (donor)/pyridinium (acceptor) substituted bistable dithienylethene supermolecule (J. Am. Chem. Soc. 122 (2000) 3037) are extended by applying fs transient-absorption spectroscopy. For the open-ring isomer of the dithienylethene switching unit, the transient-absorption spectra of the supermolecule evolve from the locally-excited to the radical-cation state of the donor anthracene, indicating a two-step photoinduced charge-transfer process with a time-constant of ?CT?1.7 ps. In contrast, after photocyclisation to the closed-ring isomer, no radical-cation signal is detected, while it reappears upon re-opening. Comparison is made with a molecular system without a switching subunit. In a polymer environment the charge transfer is inhibited

  9. Photoinduced electron transfer in a tris(2,2'-bipyridine)-C60-ruthenium(II) dyad: evidence of charge recombination to a fullerene excited state

    International Nuclear Information System (INIS)

    A novel fulleropyrrolidine covalently linked to a tris(2,2'-bipyridine)-ruthenium(II) complex is presented. While electrochemical investigations suggest the absence of any ground-state interaction between ruthenium and fullerence chromophores, photoinduced optical absorption studies clearly show that electron transfer occurs to afford the Ru3+-C60.- pair with characteristic fullerene radical anion band at ?max=1040 nm. (orig.)

  10. Electron impact excitations of S2 molecules

    OpenAIRE

    Tashiro, Motomichi

    2007-01-01

    Low-energy electron impact excitations of S_2 molecules are studied using the fixed-bond R-matrix method based on state-averaged complete active space SCF orbitals. Integral cross sections are calculated for elastic electron collision as well as impact excitation of the 7 lowest excited electronic states. Also, differential cross sections are obtained for elastic collision and excitation of the a^1 Delta_g, b^1 Sigma_g^+ and B^3 Sigma_u^- states. The integrated cross section...

  11. Electron transfer, target excitation, and ionization in H++Na(3s) and H++Na(3p) collisions in the coupled-Sturmian-pseudostate approach

    International Nuclear Information System (INIS)

    For all the above quantities, when a comparison is made between theory and measurement, our results are equally good or better than the earlier calculations employing different theoretical approaches. We still find a persistent discrepancy between theory (present as well as previous calculations) and measurements for the electron transfer cross sections into the metastable state of the H atom (?capH(2s)). Our results for the orientation and alignment effects in the electron transfer process of H++Na(3p) collisions are in good qualitative accord with recent observations and previous theoretical studies. In particular, we see a strong enhancement for the H(n?3) capture cross sections in the H++Na(3p) collisions. The H(n=2) production cross sections in the H++Na(3p) collisons follow a roughly similar trend, as observed experimentally when plotted against the impact energy

  12. 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.

  13. 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

  14. Electronic excitation and charge transfer processes in collisions of H+, H2+, and H3+ ions with carbon monoxide at typical solar-wind velocities

    International Nuclear Information System (INIS)

    Luminescence in the 200-580 nm spectral region was observed in the collisions of H+, H2+, and H3+ 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+(A-X) comet-tail system, CO+(B-X) first negative system, CO+(B-A) Baldet-Johnson system, and CO(b-a) third positive system. Also, an emission from atomic hydrogen (H? 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+(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+(B-X) emission to the sum of two main emissions (CO+(A-X)+CO+(B-X)) is velocity dependent and does not depend on the projectile ion type. For small velocities (below 100 km s–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 max(1 – v th/v), (where R max = 33%, v th = 87 km s–1). This could be used to infer the velocity of ions producing the observed emission of CO+ products.

  15. Excitation energy transfer in a non-markovian dynamical disordered environment: localization, narrowing, and transfer efficiency.

    Science.gov (United States)

    Chen, Xin; Silbey, Robert J

    2011-05-12

    The non-markovian effect of a fluctuating environment plays an important role in electronic excitation transfer in organic disordered media, such as light-harvesting systems and conjugated polymers. Stochastic Liouville equations (SLE) are used to study the interaction between excitons and the environment. We model the non-markovian environment phenomenologically with a dichotomic process. An exact approach to solve the SLE based on Shapiro and Loginov's differentiation formulas allows us to rigorously study the effect of the non-markovian environment on excitation energy transfer, such as coherence conservation and its implication for transfer efficiency. This simple SLE model goes beyond the perturbative second-order master equation valid for both the weak coupling and short time correlation conditions. In addition, we discuss why our non-markovian model is a good approximation to the SLE model driven by the stationary Gauss-Markov process (Ornstein-Uhlenbeck process) over a broad range of fluctuation strengths and correlation times. Numerical results based on our SLE model for dimeric aggregates and the Fenna-Matthews-Olson (FMO) complex reveal the important interplay of intermolecular coupling, correlation time, and fluctuation strength, and their effects on the exciton relaxation process due to the environmental phonon. The results also uncover the connection between localization and motional narrowing, and the efficiency of electronic excitation transfer, demonstrating that the non-markovian environment is critical for chromophore aggregates to achieve an optimal transfer rate in a noisy environment and to contribute to the robustness of the FMO excitation energy transfer network. PMID:21384851

  16. 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.

  17. Excitation energy transfer in chromophore aggregates within a dissipative medium

    International Nuclear Information System (INIS)

    The Redfield theory-based model of excitation energy transfer in chromophore ensembles within dissipative environment is proposed. Application of the multipole expansion to an operator of interaction between the chromophore molecules and the environment together with some assumptions about the latter led to the closed-form expressions for the elements of the dissipation tensor. These expressions relate the rates of transition between eigenstates of a chromophore ensemble with the spectral and electronic properties of an environment and the chromophore molecules. For several model cases the exact solution of the Redfield equations was obtained. -- Highlights: ? A model for electronic relaxation dynamics in supramolecular ensembles is proposed. ? Closed-form expressions for relaxation rates are derived. ? Redfield equations are solved in closed form for several model systems. ? The effect of structural and electronic parameters on relaxation rates is discussed.

  18. Heterogeneous chamiluminescence investigation of generation and transfer of electron excitation energy on Y2O3-, CaO-, CaSO4 surface during simple heterogeneous reactions

    International Nuclear Information System (INIS)

    Measurements of spectra of radical-recombination luminescence and photoluminescence (RRL and PL) of Y2O3-Eu3+, Y2O3-Tb3+ samples has been carried out. The dependence of PL and RRL intensity on the concentration of activator introduced has been measured. Concentration quenching of RRL is manifested at considerably lower activator concentrations than that of PL. Results of comparative investigation of adsorption luminescence (AL) and (PL) of CaO oxyl, activated by Bi3+, are presented. Parameters of the surface centers - electron transition energies, dynamic characteristics and the Stokes losses - differ from parameters of luminescence centers in the volume. In the spectra of the Y2O3-Tb3+, CaO-Mn2+, CaSO4-Mn2+ excited by hydrogen atoms local vibrations of a hydrogen molecule adsorbed on a luminescence centre are manifested, which results in broadening of luminescence spectral lines

  19. 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.

  20. Resonant electron transfer between quantum dots

    CERN Document Server

    Openov, L 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 states in different quantum dots is viewed as the superposition of bits 0 and 1.

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

    Energy Technology Data Exchange (ETDEWEB)

    Loong, C.K.

    1984-01-01

    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 PrO/sub 2/, UO/sub 2/, BaPrO/sub 3/ and CeB/sub 6/ 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 /sub 74/Th /sub 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.

  2. 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.)

  3. Electronic excitation spectrum of metallic carbon nanotubes

    CERN Document Server

    Sapmaz, S; Kong, J; Dekker, C; Kouwenhoven, L P; Van der Zant, H S J

    2005-01-01

    We have studied the discrete electronic spectrum of closed metallic nanotube quantum dots. At low temperatures, the stability diagrams show a very regular four-fold pattern that allows for the determination of the electron addition and excitation energies. The measured nanotube spectra are in excellent agreement with theoretical predictions based on the nanotube band structure. Our results permit the complete identification of the electron quantum states in nanotube quantum dots.

  4. Electronic energy transfer in benzophenone adlayer.

    Science.gov (United States)

    Bresenden, D; Carlson, A S; Partain, P J; Reynoso, G; Oudinarath, B; Martin, K A; Nishimura, A M

    1995-12-01

    The extent to which energy transfer occurs in electronically excited organic adlayer films on dielectric surfaces is investigated. Migration and subsequent trapping of the energy in the film are observed by pumping the singlet state of an organic adlayer of benzophenone and by monitoring the phosphorescence and fluorescence lifetimes. To observe the effects of adsorption, benzophenone was chosen as the adlayer because the energies of its well characterizedn,? carbonyl states are remarkably sensitive to solvent interactions. Upon excitation with a nitrogen laser, the perturbation on the electronic states of benzophenone by the substrate caused the emergence of the normally absent fluorescence from the adlayer traps at the interface between the surface of the dielectric substrate and the adlayer. Energy transfer to this interface was observed as a function of film thickness. On the surface of a single crystal of an organic crystal, naphthalene, energy transfer from the adlayer to the substrate was observed, whereas such transfer was not energetically possible with the other dielectric surfaces. PMID:24226914

  5. Electron impact double excitation in heliumlike ions

    International Nuclear Information System (INIS)

    Calculation of cross sections for the electron impact double excitation of heliumlike ions in the framework of Coulomb-Born-Oppenheimer approximation is presented. Closed form expressions for both the differential and the total cross sections have been obtained without the use of partial wave analysis. The total cross section for excitation of Li+ from the ground state to each of the excited states 2s2 sup(1)Ssub(g), 2s2p 1, sup(3)pu, 2p2 sup(1)Ssub(g), sup(3)Psub(g) and sup(1)Dsub(g) is computed. (author)

  6. 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.

  7. 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.

  8. 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

  9. Vanadium atom level excitation by slow electrons

    International Nuclear Information System (INIS)

    The excitation of the vanadium atom 4G0-, 4H0- and 4I0-levels by electron-atom collisions is studied through the methods of extended crossing beams and optical spectroscopy. The complete excitation cross sections for these levels by the electron energy of 30 eV are determined. The highest values of the cross sections (about 2 x 10 -16 cm2) correspond to the 4F(1P)x 4Gj0 levels. The experimental values of the cross sections for all the quartet and sextet levels systematically exceed by 1.5-2 times the theoretical ones

  10. Coherence in electron transfer pathways.

    Science.gov (United States)

    Skourtis, Spiros S; Beratan, David N; Waldeck, David H

    2011-01-01

    Central to the view of electron-transfer reactions is the idea that nuclear motion generates a transition state geometry at which the electron/hole amplitude propagates coherently from the electron donor to the electron acceptor. In the weakly coupled or nonadiabatic regime, the electron amplitude tunnels through an electronic barrier between the donor and acceptor. The structure of the barrier is determined by the covalent and noncovalent interactions of the bridge. Because the tunneling barrier depends on the nuclear coordinates of the reactants (and on the surrounding medium), the tunneling barrier is highly anisotropic, and it is useful to identify particular routes, or pathways, along which the transmission amplitude propagates. Moreover, when more than one such pathway exists, and the paths give rise to comparable transmission amplitude magnitudes, one may expect to observe quantum interferences among pathways if the propagation remains coherent. Given that the effective tunneling barrier height and width are affected by the nuclear positions, the modulation of the nuclear coordinates will lead to a modulation of the tunneling barrier and hence of the electron flow. For long distance electron transfer in biological and biomimetic systems, nuclear fluctuations, arising from flexible protein moieties and mobile water bridges, can become quite significant. We discuss experimental and theoretical results that explore the quantum interferences among coupling pathways in electron-transfer kinetics; we emphasize recent data and theories associated with the signatures of chirality and inelastic processes, which are manifested in the tunneling pathway coherence (or absence of coherence). PMID:23833692

  11. Vibronic effects on the low-lying electronic excitations in CO2 induced by electron impact

    Science.gov (United States)

    Watanabe, Noboru; Hirayama, Tsukasa; Suzuki, Daisuke; Takahashi, Masahiko

    2013-05-01

    We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations of CO2. Experimentally, momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations have been derived from EELS spectra measured at incident electron energy of 3 keV. Theoretically, we have calculated GOS profiles using wave functions at the equation-of-motion coupled-cluster singles and doubles level. In the calculation, vibronic effects are taken into account by evaluating the electronic transition amplitudes along the individual normal coordinates. The calculation satisfactorily reproduces the experiment for the 1?g and 1?u transitions and reveals prominent roles of strong coupling between the associated mixed-Rydberg-valence and valence excited states through the bending vibration of CO2. Vibronic effects on GOS profiles have also been examined for the 1?u+, 1?u, and 21?g transitions.

  12. Vibronic effects on the low-lying electronic excitations in CO2 induced by electron impact.

    Science.gov (United States)

    Watanabe, Noboru; Hirayama, Tsukasa; Suzuki, Daisuke; Takahashi, Masahiko

    2013-05-14

    We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations of CO2. Experimentally, momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations have been derived from EELS spectra measured at incident electron energy of 3 keV. Theoretically, we have calculated GOS profiles using wave functions at the equation-of-motion coupled-cluster singles and doubles level. In the calculation, vibronic effects are taken into account by evaluating the electronic transition amplitudes along the individual normal coordinates. The calculation satisfactorily reproduces the experiment for the (1)?g and (1)?u transitions and reveals prominent roles of strong coupling between the associated mixed-Rydberg-valence and valence excited states through the bending vibration of CO2. Vibronic effects on GOS profiles have also been examined for the (1)?u (+), (1)?u, and 2(1)?g transitions. PMID:23676048

  13. Photoinduced electron transfer between the dendritic zinc phthalocyanines and anthraquinone

    Science.gov (United States)

    Chen, Kuizhi; Wen, Junri; Liu, Jiangsheng; Chen, Zhenzhen; Pan, Sujuan; Huang, Zheng; Peng, Yiru

    2015-03-01

    The intermolecular electron transfer between the novel dendritic zinc (II) phthalocyanines (G1-DPcB and G2-DPcB) and anthraquinone (AQ) was studied by steady-state fluorescence and UV/Vis absorption spectroscopic methods. The effect of dendron generation on intermolecular electron transfer was investigated. The results showed that the fluorescence emission of these dendritic phthalocyanines could be greatly quenched by AQ upon excitation at 610 nm. The Stern- Volmer constant (KSV) of electron transfer was decreased with increasing the dendron generations. Our study suggested that these novel dendritic phthalocyanines were effective new electron donors and transmission complexes and could be used as a potential artifical photosysthesis system.

  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. Light-driven microbial dissimilatory electron transfer to hematite.

    Science.gov (United States)

    Li, Dao-Bo; Cheng, Yuan-Yuan; Li, Ling-Li; Li, Wen-Wei; Huang, Yu-Xi; Pei, Dan-Ni; Tong, Zhong-Hua; Mu, Yang; Yu, Han-Qing

    2014-11-14

    The ability of dissimilatory metal-reducing microorganisms (DMRM) to conduct extracellular electron transfer with conductive cellular components grants them great potential for bioenergy and environmental applications. Crystalline Fe(III) oxide, a type of widespread electron acceptor for DMRM in nature, can be excited by light for photocatalysis and microbial culture-mediated photocurrent production. However, the feasibility of direct electron transfer from living cells to light-excited Fe(III) oxides has not been well documented and the cellular physiology in this process has not been clarified. To resolve these problems, an electrochemical system composed of Geobacter sulfurreducens and hematite (?-Fe2O3) was constructed, and direct electron transfer from G. sulfurreducens cells to the light-excited ?-Fe2O3 in the absence of soluble electron shuttles was observed. Further studies evidenced the efficient excitation of ?-Fe2O3 and the dependence of photocurrent production on the biocatalytic activity. Light-induced electron transfer on the cell-?-Fe2O3 interface correlated linearly with the rates of microbial respiration and substrate consumption. In addition, the G. sulfurreducens cells were found to survive on light-excited ?-Fe2O3. These results prove a direct mechanism behind the DMRM respiration driven by photo-induced charge separation in semiconductive acceptors and also imply new opportunities to design photo-bioelectronic devices with living cells as a catalyst. PMID:25238285

  17. Dissociation mechanisms of excited CH3X (X = Cl, Br, and I) formed via high-energy electron transfer using alkali metal targets

    Science.gov (United States)

    Hayakawa, Shigeo; Tsujinaka, Taiga; Fujihara, Akimasa

    2012-11-01

    High-energy electron transfer dissociation (HE-ETD) on collisions with alkali metal targets (Cs, K, and Na) was investigated for CH3X+ (X = Cl, Br, and I) ions by a charge inversion mass spectrometry. Relative peak intensities of the negative ions formed via HE-ETD strongly depend on the precursor ions and the target alkali metals. The dependency is explained by the exothermicities of the respective dissociation processes. Peak shapes of the negative ions, especially of the X- ions, which comprise a triangle and a trapezoid, also strongly depend on the precursor ions and the target alkali metals. The trapezoidal part of the I- peak observed with the Na target is more dominant and much broader than that with the Cs target. This dependence on the targets shows an inverse relation between the peak width and the available energy, which corresponds to the exothermicity assuming formation of fragment pair in their ground internal states. From a comparison of the kinetic energy release value calculated from the trapezoidal shape of I- with the available energy of the near-resonant level on the CH3I potential energy curve reported by ab initio calculations, the trapezoidal part is attributed to the dissociation to CH3 + I(2P3/2) via the repulsive 3Q1 state of CH3I, which is not dominant in the photo-dissociation of CH3I. The observation of trapezoid shape of the CH2I- peak with the Cs target indicates spontaneous dissociation via repulsive potential from the 3R2 Rydberg state, although the correlation between the 3R2 Rydberg state and relevant repulsive states has not been reported by any theoretical calculation.

  18. Quasiparticle theory of electron excitations in solids

    International Nuclear Information System (INIS)

    A first-principles quasiparticle approach to electron excitation energies in solids is reviewed. The theory has been applied to explain and predict the spectroscopic properties of a variety of systems including bulk crystals, surfaces, interfaces, clusters, defects, and materials under pressure. Several illustrative applications are presented and some recent theoretical developments discussed

  19. Control excitation and coherent transfer in a dimer

    OpenAIRE

    Li, Hong-rong; Zhang, Pei; Liu, Yingjun; Li, Fu-li; Zhu, Shi-Yao

    2013-01-01

    In this article, the processes of energy absorption and coherent transfer in a dimer is studied. The dimer includes two two-level pigments --- donor and acceptor, where donor is assumed being excited by a control pulse in the time domain. We investigate the dynamics of probability that the acceptor is in the excited state and the total efficiency of energy absorption and transfer under different temporal shape of control pulse. Quantum concurrence of the dimer is also discus...

  20. Suppression of quantum oscillations and the dependence on site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer

    OpenAIRE

    Ritschel, G.; Roden, J.; Strunz, W. T.; Aspuru-guzik, A.; Eisfeld, A.

    2011-01-01

    Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. We find that in all considered cases there is very little transfer between the monomers. Since it is believed that the eighth BChl is located near the main light harvesting antenna we look at the ...

  1. Efficient and coherent excitation transfer across disordered molecular networks

    OpenAIRE

    Scholak, Torsten; Melo, Fernando; Wellens, Thomas; Mintert, Florian; Buchleitner, Andreas

    2009-01-01

    We show that finite-size, disordered molecular networks can mediate highly efficient, coherent excitation transfer which is robust against ambient dephasing and associated with strong multi-site entanglement. Such optimal, random molecular conformations may explain efficient energy transfer in the photosynthetic FMO complex.

  2. 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.

  3. Electron transfer reactions in microporous solids

    Energy Technology Data Exchange (ETDEWEB)

    Mallouk, T.E.

    1992-05-01

    We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

  4. 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.

  5. 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

  6. Observation of electronically excited states of tetraoxygen

    Science.gov (United States)

    Helm, H.; Walter, C. W.

    1993-04-01

    We have investigated electron transfer to O4(+) in reactions with O2, NO, and Cs. We observe formation of O4 molecules that decay by predissociation and by direct dissociation. The kinetic energy release in dissociation as well as the nature of the dissociation products are determined. Evidence for three short-lived electronic states of tetraoxygen at energies near 2 eV above O2 + O2 is obtained in electron transfer from O2 and NO. In the experiment with cesium we find evidence for longer-lived electronic states at 9.4 and 10.5 eV. The energy release and symmetry of the dissociation pattern suggests that the high-lying states are symmetric molecular configurations at extended bond lengths.

  7. 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

  8. Kinetic ion thermometers for electron transfer dissociation.

    Science.gov (United States)

    Pepin, Robert; Ture?ek, František

    2015-02-19

    Peptide fragment ions of the z-type were used as kinetic ion thermometers to gauge the internal energy of peptide cation-radicals produced by electron transfer in the gas-phase. Electron transfer dissociation (ETD)-produced z2 ions containing the leucine residue, z2(Leu-Lys) and z2(Leu-Arg), were found to undergo spontaneous dissociation by loss of C3H7 that was monitored by time-resolved kinetic measurements on the time scale of the linear ion trap mass spectrometer. Kinetic modeling of the dissociations, including collisional cooling and product loss by neutralization, provided unimolecular rate constants for dissociation that were converted to the z ion internal energies using RRKM theory. The internal energy of z2(Leu-Lys) and z2(Leu-Arg) fragment ions was found to decrease with the increasing size of the precursor peptide ion, indicating vibrational energy partitioning between the ion and neutral fragments and ergodic behavior. The experimentally determined excitation in the peptide cation-radicals upon electron transfer (285-327 kJ mol(-1)) was found to be lower than that theoretically calculated from the reaction exothermicity. The reasons for this missing energy are discussed. PMID:25594857

  9. Intrinsic and dynamical reaction pathways of an excited state proton transfer.

    Science.gov (United States)

    Raucci, Umberto; Savarese, Marika; Adamo, Carlo; Ciofini, Ilaria; Rega, Nadia

    2015-02-12

    The detailed knowledge of excited state proton transfer mechanisms in complex environments is of paramount importance in chemistry. However, the definition of an effective reaction coordinate and the understanding of the driving force of the reaction can be difficult from both the experimental and the theoretical points of view. Here we analyzed by theoretical approaches the mechanism and the driving forces of the excited state proton transfer reaction occurring between the 7-hydroxy-4-(trifluoromethyl)coumarin photoacid and the 1-methylimidazole base molecules in toluene solution. In particular, we compared the intrinsic and the dynamical reaction pathways, obtained by integrating the reaction coordinate, and by performing ab initio simulations of molecular dynamics, respectively. Time-dependent density functional theory and polarizable solvation continuum models were adopted to define the excited state potential energy surface. Results were analyzed by means of the D(CT) electronic density based index. Our findings suggest that the reaction coordinate is mainly composed of several intra- and intermolecular modes of the reactants. An analysis of both the intrinsic coordinate and the dynamical results shows that the charge transfer induced by electronic excitation of the coumarin molecule is the main proton transfer driving force. With regards to the methodological validation, the combination of ab initio molecular dynamics with time-dependent density functional theory appears to be feasible and reliable to study excited state proton transfer reactions in the condensed phase. PMID:25517266

  10. Probing electronic excitations in molecular conduction

    CERN Document Server

    Muralidharan, B; Pati, S K; Datta, S

    2005-01-01

    We identify experimental signatures in the current-voltage (I-V) characteristics of weakly contacted molecules directly arising from excitations in their many electron spectrum. We calculate transport properties using a multielectron master equation in the Fock space of an exact diagonalized model many-body Hamiltonian benchmarked for a prototypical molecule (benzene). Using this approach, we quantitatively explain various unique features of molecular conduction that are difficult to capture even qualitatively using standard one-electron self-consistent field (SCF) approaches.

  11. 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; Ha?ttig, 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 result...

  12. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation

    International Nuclear Information System (INIS)

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations

  13. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Yang [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States); Aggelen, Helen van [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States); Department of Inorganic and Physical Chemistry, Ghent University, 9000 Ghent (Belgium); Yang, Weitao, E-mail: weitao.yang@duke.edu [Department of Chemistry and Department of Physics, Duke University, Durham, North Carolina 27708 (United States)

    2013-12-14

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  14. Excitation of local magnetic moments by tunneling electrons

    Science.gov (United States)

    Gauyacq, Jean-Pierre; Lorente, Nicolás; Novaes, Frederico Dutilh

    2012-05-01

    The advent of milli-kelvin scanning tunneling microscopes (STM) with inbuilt magnetic fields has opened access to the study of magnetic phenomena with atomic resolution at surfaces. In the case of single atoms adsorbed on a surface, the existence of different magnetic energy levels localized on the adsorbate is due to the breaking of the rotational invariance of the adsorbate spin by the interaction with its environment, leading to energy terms in the meV range. These structures were revealed by STM experiments in IBM Almaden in the early 2000s for atomic adsorbates on CuN surfaces. The experiments consisted in the study of the changes in conductance caused by inelastic tunneling of electrons (IETS, inelastic electron tunneling spectroscopy). Manganese and Iron adatoms were shown to have different magnetic anisotropies induced by the substrate. More experiments by other groups followed up, showing that magnetic excitations could be detected in a variety of systems: e.g. complex organic molecules showed that their magnetic anisotropy was dependent on the molecular environment, piles of magnetic molecules showed that they interact via intermolecular exchange interaction, spin waves were excited on ferromagnetic surfaces and in Mn chains, and magnetic impurities have been analyzed on semiconductors. These experiments brought up some intriguing questions: the efficiency of magnetic excitations was very high, the excitations could or could not involve spin flip of the exciting electron and singular-like behavior was sometimes found at the excitation thresholds. These facts called for extended theoretical analysis; perturbation theories, sudden-approximation approaches and a strong coupling scheme successfully explained most of the magnetic inelastic processes. In addition, many-body approaches were also used to decipher the interplay between inelastic processes and the Kondo effect. Spin torque transfer has been shown to be effective in changing spin orientations of an adsorbate in theoretical works, and soon after it was shown experimentally. More recently, the previously mentioned strong coupling approach was extended to treat the excitation of spin waves in atomic chains and the ubiquitous role of electron-hole pair creation in de-exciting spins on surfaces has been analyzed. This review article expounds these works, presenting the theoretical approach by the authors while trying to thoroughly review parallel theoretical and experimental works.

  15. Electron Collisional Excitation of S II

    Science.gov (United States)

    Tayal, Swaraj

    1997-10-01

    Electron collisional excitation strengths for inelastic transitions are calculated using the R-matrix method in a 19-state (3s^23p^3 ^4S^o, ^2D^o, ^2P^o, 3s3p^4 ^4P, ^2D, ^2S, 3s^23p^23d ^2P, ^4F, ^4D, ^2F, ^4P, 3s^23p^24s ^4P, ^2P, 3s^23p^24p, ^2S^o, ^4D^o, ^4P^o, ^2D^o, ^4S^o, and ^2P^o) close-coupling approximation. These target states are represented by extensive configuration-interaction wave functions that give excitation energies and oscillator strengths that are usually in good agreement with the experimental values and the available accurate calculations. Rydberg series of resonances converging to the excited state thresholds are explicitly included in the scattering calculation. The effective collision strengths are determined assuming a Maxweelian distribution of electron energies. The results for collision strengths will be compared with the recent merged beams energy loss measurements and other calculations.

  16. Electron impact excitation of Si X

    International Nuclear Information System (INIS)

    Excitation cross sections of Si9+ by electron impact have been computed, in different approximations and in different target descriptions. Collision strengths have been calculated for fine-structure transitions between the ground configuration term 2s22p 2P0 and the excited configurations 2s2p24P, 2D, 2S, 2P and 2p34S0, 2D0, 2P0 of Si9+ using the eight-state close-coupling approximation and distorted-wave approximation for the energy range 6.0 to 70.0 Ryd. The results indicate that the use of an elaborate target description and a more accurate treatment of the collision problem may change some cross sections by more than 25%. Results are compared with earlier work. This problem has important applications in plasma diagnostics and in the interpretation of the extreme ultraviolet solar emission spectrum. (author)

  17. Excitation transfer and luminescence in porphyrin-carbon nanotube complexes

    CERN Document Server

    Magadur, G; Alain-Rizzo, V; Voisin, C; Roussignol, Ph; Deleporte, E; Delaire, J A

    2007-01-01

    Functionalization of carbon nanotubes with hydrosoluble porphyrins (TPPS) is achieved by "$\\pi$-stacking". The porphyrin/nanotube interaction is studied by means of optical absorption, photoluminescence and photoluminescence excitation spectroscopies. The main absorption line of the porphyrins adsorbed on nanotubes exhibits a 120 meV red shift, which we ascribe to a flattening of the molecule in order to optimize $\\pi-\\pi$ interactions. The porphyrin-nanotube complex shows a strong quenching of the TPPS emission while the photoluminescence intensity of the nanotubes is enhanced when the excitation laser is in resonance with the porphyrin absorption band. This reveals an efficient excitation transfer from the TPPS to the carbon nanotube.

  18. Electron excitations in two-dimensional buckled honeycomb lattices

    Science.gov (United States)

    Shih, Po-Hsin; Chiu, Yu-Huang; Lin, Min-Fa

    2015-03-01

    The two-dimensional buckled honeycomb lattices system exhibits the rich Coulomb excitation spectra, being dominated by the free carrier density, band structure, and transferred momentum (q). There are two kinds of plasmon peaks in the energy loss spectra, calculated from the random phase approximation. They are, respectively, revealed at low and middle frequencies. The former, which arises from the free carriers, belongs to acoustic mode. It's frequency depends on ?{ q} at long wavelength limit. On the other hand, the latter is due to all the ?-electronic collective excitations is an optical mode. Whether such plasmon can service is mainly determined by q. The frequencies and intensities of plasmon modes are very different among graphene, silicene, germanene, and Tin. Thanks the Ministry of Science and Technology of Taiwan (ROC) for funding support.

  19. Semiclassical approximation for electron impact excitation of hydrogenic ions

    Science.gov (United States)

    Jung, Young-Dae

    1993-01-01

    The threshold behavior of the electron impact excitation cross sections for hydrogenic ions is investigated using the semiclassical approximation with the hyperbolic orbit for the projectile path, rather than the straight line path. The symmetric approximation is applied to modify the ordinary hyperbolic orbit. The modification factor due to the hyperbolic orbit approximation produces the correct energy dependence of the cross section near the excitation threshold. This result is very similar to that of the quantum mechanical case. The semiclassical enhancement factor due to this simple modification corresponds to the Coulomb focusing factor in the Born-Bethe approximation. In the high-energy limit, the semiclassical cross sections approach the Born-Bethe cross sections, with a finite cutoff in the momentum transfer for dipole transitions.

  20. Excited State Dynamics of Protonated Phenylalanine and Tyrosine: Photo-Induced Reactions Following Electronic Excitation.

    Science.gov (United States)

    Féraud, Géraldine; Broquier, Michel; Dedonder, Claude; Jouvet, Christophe; Grégoire, Gilles; Soorkia, Satchin

    2015-06-11

    The electronic spectroscopy and the electronic excited state properties of cold protonated phenylalanine and protonated tyrosine have been revisited on a large spectral domain and interpreted by comparison with ab initio calculations. The protonated species are stored in a cryogenically cooled Paul trap, maintained at ?10 K, and the parent and all the photofragment ions are mass-analyzed in a time-of-flight mass spectrometer, which allows detecting the ionic species with an improved mass resolution compared to what is routinely achieved with a quadrupole mass spectrometer. These new results emphasize the competition around the band origin between two proton transfer reactions from the ammonium group toward either the aromatic chromophore or the carboxylic acid group. These reactions are initiated by the coupling of the locally excited ??* state with higher charge transfer states, the positions and coupling of which depend on the conformation of the protonated molecules. Each of these reaction processes gives rise to specific fragmentation channels that supports the conformer selectivity observed in the photofragmentation spectra of protonated tyrosine and phenylalanine. PMID:25248102

  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. 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. Electron transfer in helical polyaromatics.

    Czech Academy of Sciences Publication Activity Database

    Pospíšil, Lubomír; Gál, Miroslav; Horá?ek, Michal; Teplý, Filip; Adriaenssens, Louis; Severa, Lukáš

    Xi´an : International Society of Electrochemistry, 2009. O06-O06. [International Symposium on Frontiers of Electrochemical Science and Technology. 12.08.2009-15.08.2009, Xi´an] R&D Projects: GA ?R GA203/08/1157; GA MŠk OC 140; GA ?R GA203/09/0705; GA ?R GP203/09/P502; GA MŠk ME09114 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506 Keywords : electron transfer * helical polyaromatics Subject RIV: CG - Electrochemistry

  4. The effect of atoms excited by electron beam on metal evaporation

    CERN Document Server

    Xie Guo Feng; Ying Chun Tong

    2002-01-01

    In atomic vapor laser isotope separation (AVLIS), the metal is heated to melt by electron beams. The vapor atoms may be excited by electrons when flying through the electron beam. The excited atoms may be deexcited by inelastic collision during expansion. The electronic energy transfers translational energy. In order to analyse the effect of reaction between atoms and electron beams on vapor physical parameters, such as density, velocity and temperature, direct-simulation Monte Carlo method (DSMC) is used to simulate the 2-D gadolinium evaporation from long and narrow crucible. The simulation results show that the velocity and temperature of vapor increase, and the density decreases

  5. Collisionally excited few-electron systems: theoretical introduction and survey

    International Nuclear Information System (INIS)

    We consider excitation, ionization, and charge transfer in collisions of protons (and antiprotons) with the single-electron targets H, He+, and Li2+. These collisions are first compared to other types of ion-atom collisions. A brief review of our own theoretical method is given; in particular we describe how we allow for both large charge transfer and ionization probabilities while retaining the computational efficiency that allows us to consider a variety of collision partners and collision energies. We comment on the comparison of our results to other theoretical work and to experiment. The qualitative features of the various inelastic cross sections are discussed, in particular how they scale with collision energy, target nuclear charge, and the sign of the projectile charge. 15 references, 6 figures

  6. Collisionally excited few-electron systems: theoretical introduction and survey

    International Nuclear Information System (INIS)

    Excitation, ionization, and charge transfer in collisions of protons (and antiprotons) with the single-electron targets H, He+, and Li2+ are considered. These collisions are fist compared to other types of ion-atom collisions. A brief review of the authors' theoretical method is given; in particular a description is given of how the authors allow for both large charge transfer and ionization probabilities while retaining the computational efficiency that allows them to consider a variety of collision partners and collision energies. The comparison of the results to other theoretical work and to experiment is commented on. The qualitative features of the various inelastic cross sections are discussed, in particular how they scale with collision energy, target nuclear charge, and the sign of the projectile charge. 15 references, 6 figures

  7. Damage generation by electronic excitations in crystalline metals

    International Nuclear Information System (INIS)

    This paper will give a rapid overview of the main experimental results concerning the effects of high electronic energy deposition in metallic targets and present a tentative model based on the Coulomb explosion mechanism. More detailed reviews have been made recently concerning both the experiments and the theoretical model. High levels of localized energy deposition in electronic excitation are easily obtained using GeV heavy ions which during their slowing-down typically transfer a few keV/A to the electronic system of the target and a few eV/A in elastic collisions with target nuclei. In insulators and organic materials, it is well-known that both slowing-down processes contribute to damage creation, whereas in metals it has been claimed for a long time that the sole nuclear collisions are involved in damage processes. Although this last assertion remains true for some metals such as Cu, Ag, W, Cu3 Au...[2], high levels of electronic excitation can induce a partial annealing of the defects resulting from nuclear collisions in Fe, Ni, Nb, Pt..., lead to additional defect creation in Fe, Co, Zr, Ti...[2] or even to phase transformations in NiZr2 [5], Ni3B [6], NiTi [7], Ti [8]... In the following, we shall only focus on the last two effects. (author). 15 refs

  8. 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...

  9. Laser-assisted nuclear ? excitation by the inverse electronic-bridge process

    International Nuclear Information System (INIS)

    A method to generate low-energy and high-multipolarity nuclear transitions through a laser-assisted, resonant, inverse electronic-bridge process is presented. The cross section of the suggested nuclear-excitation process is calculated in a simple model. The yield is compared with the yields of ordinary ?-ray absorption and Coulomb excitation. The excitation of the 235mU isomeric state of energy 73.5 eV by an E3 transition is traced numerically. The excitation of an electron from the O4 (5d3/2) electronic shell of binding energy 105 eV can be followed by a P3 (6p3/2)?O4 transition, which can be tuned by the laser to resonance with the nuclear transition. In case of resonance, the electronic excitation energy is transferred to the nucleus with a high efficiency

  10. 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.

  11. Resonant optical electron transfer in one-dimensional multiwell structures

    OpenAIRE

    Tsukanov, A. V.

    2008-01-01

    We consider coherent single-electron dynamics in the one-dimensional nanostructure under resonant electromagnetic pulse. The structure is composed of two deep quantum wells positioned at the edges of structure and separated by a sequence of shallow internal wells. We show that complete electron transfer between the states localized in the edge wells through one of excited delocalized states can take place at discrete set of times provided that the pulse frequency matches one...

  12. 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

  13. Autoionizing resonances in electron-impact excitation of oxygenlike selenium

    International Nuclear Information System (INIS)

    We have investigated the contributions of doubly excited, autoionizing resonances to the rate coefficients for electron-impact excitation of the n = 2 to n = 2 transitions in oxygenlike selenium. The cross sections for direct excitation were calculated using a relativistic distorted-wave approximation. The detailed Auger and radiative rates required for evaluating the resonance contributions were calculated using a multiconfigurational Dirac-Fock model. The largest effect is on the electric-dipole-forbidden transitions. For some J = 0 to J = 0 transitions involving two-electron excitations, the resonances enhance the collisional excitation rates by factors up to 104 at electron temperatures relevant for laboratory plasmas

  14. Kinklike excitations as an energy-transfer mechanism in microtubules

    Science.gov (United States)

    Satari?, M. V.; Tuszy?ski, J. A.; Žakula, R. B.

    1993-07-01

    A model is presented that is intended to provide a realistic physical picture of the energy-transfer mechanism in cell microtubules. A classical ?4 model in the presence of a constant electric field is used as a conceptual basis. It is demonstrated that kinklike excitations arise as a result of the guanosine 5'-triphosphate (GTP) hydrolysis and that an intrinsic electrical force may cause them to propagate along a microtubule. A discussion is given on the possible effects of these excitations on the dynamics of microtubules.

  15. 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

  16. Electron impact excitation of Si X

    Energy Technology Data Exchange (ETDEWEB)

    Saha, H.P.; Trefftz, E. (Max-Planck-Institut fuer Physik und Astrophysik, Garching (Germany, F.R.). Inst. fuer Astrophysik)

    1982-04-14

    Excitation cross sections of Si/sup 9 +/ by electron impact have been computed, in different approximations and in different target descriptions. Collision strengths have been calculated for fine-structure transitions between the ground configuration term 2s/sup 2/2p /sup 2/P/sup 0/ and the excited configurations 2s2p/sup 2/ /sup 4/P, /sup 2/D, /sup 2/S, /sup 2/P and 2p/sup 3/ /sup 4/S/sup 0/, /sup 2/D/sup 0/, /sup 2/P/sup 0/ of Si/sup 9 +/ using the eight-state close-coupling approximation and distorted-wave approximation for the energy range 6.0 to 70.0 Ryd. The results indicate that the use of an elaborate target description and a more accurate treatment of the collision problem may change some cross sections by more than 25%. Results are compared with earlier work. This problem has important applications in plasma diagnostics and in the interpretation of the extreme ultraviolet solar emission spectrum.

  17. Electronic excitations in metallic systems: from defect annihilation to track formation

    International Nuclear Information System (INIS)

    This paper presents an overview of the effects of high electronic energy deposition in metallic targets irradiated with GeV heavy ions. The main result of these investigations is that high electronic excitations lead to various and sometimes conflicting effects according to the nature of the target: - partial annealing of the defects induced by elastic collisions, - creation of additional disorder, - phase transformation (tracks formation and amorphization), - anisotropic growth. These different effects of high electronic energy deposition in metallic targets are probably manifestations at various degrees of the same basic energy transfer process between the excited electrons and the target atoms. Up to now no theoretical model explains these effects. 24 refs

  18. Distance dependence of excitation energy transfer between spacer-separated conjugated polymer films

    Science.gov (United States)

    Shaw, Paul E.; Ruseckas, Arvydas; Samuel, Ifor D. W.

    2008-12-01

    We report a systematic study of the scaling with distance of electronic energy transfer between thin films of conjugated polymers separated by a silica spacer. The energy-transfer kinetics were obtained directly from time-resolved photoluminescence measurements and show a 1/z3 distance dependence of the transfer rate between the excited donor and the acceptor film for z?8nm . This is consistent with Förster theory; but at shorter separations the energy transfer is slower than predicted and can be explained by the breakdown of the point-dipole approximation at ztilde 5nm . The results are relevant for organic photovoltaics and light-emitting devices, where energy transfer can provide a means of increasing performance.

  19. 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.)

  20. Anisotropic excitation transfer to acceptors randomly distributed on surfaces.

    OpenAIRE

    Kellerer, H; BLUMEN, A

    1984-01-01

    We presented exact expressions for the ensemble averaged decay of the excitation of a donor molecule due to the energy transfer via anisotropic dipolar interactions to acceptors distributed randomly on a surface. The disorder extended both over the positions of the acceptors and over the orientations of their transition dipoles with respect to that of the donor molecule. Several cases were considered explicitly (a) random orientations of the acceptors in space, with the donor being (a1) perpe...

  1. 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.

  2. 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

  3. 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.

  4. Vibronic effects on the low-lying electronic excitations in N2O induced by electron impact

    Science.gov (United States)

    Watanabe, Noboru; Takahashi, Masahiko

    2014-08-01

    We report a theoretical study on the valence-shell electronic excitations of N2O induced by electron impact. Momentum transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles have been calculated for the low-lying electronic excitations using theoretical wave functions at the equation-of-motion coupled-cluster singles and doubles level. In the calculation, Herzberg-Teller vibronic effects are taken into account. The computed results are in overall agreement with experimental GOS profiles reported in the literature and reveal prominent roles of the bending vibration of N2O in the B1? and C1? transitions.

  5. Vibronic effects on the low-lying electronic excitations in N2O induced by electron impact

    International Nuclear Information System (INIS)

    We report a theoretical study on the valence-shell electronic excitations of N2O induced by electron impact. Momentum transfer–dependent generalized oscillator strengths (GOSs) or GOS profiles have been calculated for the low-lying electronic excitations using theoretical wave functions at the equation-of-motion coupled-cluster singles and doubles level. In the calculation, Herzberg–Teller vibronic effects are taken into account. The computed results are in overall agreement with experimental GOS profiles reported in the literature and reveal prominent roles of the bending vibration of N2O in the B1? and C1? transitions. (paper)

  6. 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.

  7. Multiple Excitation of Confined Graphene Plasmons by Single Free Electrons

    OpenAIRE

    de Abajo, F. Javier Garcia

    2013-01-01

    We show that free electrons can efficiently excite plasmons in doped graphene with probabilities of order one per electron. More precisely, we predict multiple excitations of a single confined plasmon mode in graphene nanostructures. These unprecedentedly large electron-plasmon couplings are explained using a simple scaling law and further investigated through a general quantum description of the electron-plasmon interaction. From a fundamental viewpoint, multiple plasmon ex...

  8. 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

  9. Exocellular electron transfer in anaerobic microbial communities

    OpenAIRE

    Stams, A. J. M.; Bok, F.A.M. de; Plugge, C. M.; Eekert van, M.H.A.; Dolfing, J.; Schraa, G.

    2006-01-01

    Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory syntrophic consortia of proton-reducing acetogenic bacteria and hydrogen-consuming methanogenic archaea. Anaerobic microorganisms that use insoluble electron acceptors for growth, such as iron- an...

  10. Electron transfer reactions in microporous solids

    Science.gov (United States)

    Mallouk, T. E.

    1991-05-01

    We are studying the synthesis of light-induced electron transfer reactions which occur within microporous materials. Some highlights of our progress in the last year are in the fields of (1) electron transfer reactions of donor/acceptor molecules at the zeolite/solution interface; (2) photochemistry of zeolite/TiO2 composites; and (3) photochemistry of layered oxide semiconductors.

  11. 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

  12. 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.

  13. 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}\

  14. 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

  15. 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...

  16. Reduced radiation losses in electron beam excited propagating plasmons

    OpenAIRE

    Lei WANG; Cai, Wei; Xiang, Yinxiao; Zhang, Xinzheng; Xu, Jingjun; García de Abajo, F Javier

    2011-01-01

    Except for heating losses in metal, propagating plasmons also suffer a lot from radiation losses. In this paper, electron beams are proposed as a way to excite higher-order, multipolar plasmons, which would otherwise not be excited by light, as a way to reduce radiation losses. Specifically, electron excited guided plasmons in a coupled nanoparticle chain and a symmetrical four-wire waveguide are separately discussed. In the coupled nanoparticle chain, the plasmon mode formed by quadrupolar p...

  17. 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.

  18. Electron tunneling from electronically excited states of isolated bisdisulizole-derived trianion chromophores following UV absorption.

    Science.gov (United States)

    Winghart, Marc-Oliver; Yang, Ji-Ping; Kühn, Michael; Unterreiner, Andreas-Neil; Wolf, Thomas J A; Dau, Phuong D; Liu, Hong-Tao; Huang, Dao-Ling; Klopper, Wim; Wang, Lai-Sheng; Kappes, Manfred M

    2013-05-14

    Photoelectron spectra of isolated [M-BDSZ](3-) (BDSZ = bisdisulizole, M = H, Li, Na, K, Cs) triply charged anions exhibit a dominant constant electron kinetic energy (KE) detachment feature, independent of detachment wavelengths over a wide UV range. Photoelectron imaging spectroscopy shows that this constant KE feature displays an angular distribution consistent with delayed rather than direct electron emission. Time-resolved pump-probe (388 nm/775 nm) two-colour photoelectron spectroscopy reveals that the constant KE feature results from two simultaneously populated excited states, which decay at different rates. The faster of the two rates is essentially the same for all the [M-BDSZ](3-) species, regardless of M. The slower process is associated with lifetimes ranging from several picoseconds to tens of picoseconds. The lighter the alkali cation is, the longer the lifetime of this state. Quantum chemical calculations indicate that the two decaying states are in fact the two lowest singlet excited states of the trianions. Each of the two corresponding photoexcitations is associated with significant charge transfer. However, electron density is transferred from different ends of the roughly chain-like molecule to its aromatic center. The energy (and therefore the decay rate) of the longer-lived excited state is found to be influenced by polarization effects due to the proximal alkali cation complexed to that end of the molecule. Systematic M-dependent geometry changes, mainly due to the size of the alkali cation, lead to M-dependent shifts in transition energies. At the constant pump wavelength this leads to different amounts of vibrational energy in the respective excited state, contributing to the variations in decay rates. The current experiments and calculations confirm excited state electron tunneling detachment (ESETD) to be the mechanism responsible for the observed constant KE feature. The ESETD phenomenon may be quite common for isolated multiply charged anions, which are strong fluorophores in the condensed phase - making ESETD useful for studies of the transient response of such species after electronic excitation. PMID:23549163

  19. Nonequilibrium electron–phonon coupling after ultrashort laser excitation of gold

    International Nuclear Information System (INIS)

    Exciting a metal by an ultrashort laser pulse, the electrons are driven out of thermal equilibrium, while the phonon system remains almost unaffected. During and after the irradiation, the electrons thermalize and transfer energy to the phonons. In this work, we investigate the electron–phonon coupling in gold. The dependence of the coupling strength on the phonon properties as well as the nonequilibrium electrons has been taken into account. For the phonon system, we utilize several phonon temperatures. For the electrons we apply different excitation scenarios depending on the laser fluence and the photon energy. We observe that for gold at electron temperatures below 2000 K, the phonon distribution may affect the coupling slightly. However, the electron distribution, especially under nonequilibrium conditions, governs the electron–phonon coupling factor significantly.

  20. Electron-impact excitation of Fe II

    International Nuclear Information System (INIS)

    We report in this paper the computation of accurate total collision strengths and effective collision strengths for electron-impact excitation of FeII, using the parallel R-matrix program PRMAT. Target states corresponding to the 3d64s, 3d7, 3d64p and 3d54s4s basis configurations were included in the calculations giving rise to a 113 LS state 354 coupled channel problem. Following a detailed systematic study of correlation effects in both the target state and collision wavefunctions, it was found that an additional 21 configuration functions needed to be included in the Configuration Interaction expansion to obtain significantly more accurate target states and collision wavefunctions. This much improved 26-configuration model has been used to calculate converged total effective collision strengths for all sextet to quartet transitions among these levels with total spin S = 2, giving a total of 1785 lines. These calculations have laid the foundation for an approach which may be adopted in the study of electron collisions with the low ionization stages of other iron peak elements. The work has been further extended with the commencement of a Breit-Pauli relativistic calculation for one of the smaller models and includes 262 fine-structure levels and over 1800 coupled channels. At the same time the PRMAT parallel R-matrix package is being extended to include relativistic effects which will allow us to attempt the more sophisticill allow us to attempt the more sophisticated 26-configuration model and produce for the first time the amount and quality of atomic data required to perform a meaningful synthesis of the Fe II spectrum

  1. Computer simulation of electron transfer in molecular electronic devices

    OpenAIRE

    Correia, Helena M. G.; Ramos, Marta M. D.

    2005-01-01

    The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-Bis((2???-para-mercaptophen...

  2. Kinetics of excitation and charge transfer reactions in nonpolar media

    International Nuclear Information System (INIS)

    On the basis of rate constants determined by electron pulse radiolysis and laser flash photolysis the kinetics of energy transfer processes in nonpolar media was analyzed. The rate constants k of charge, singlet-singlet and triplet-triplet transfer show a marked dependence on the free energy of the reaction in such a way that at low energy differences ?E, k increases with increasing exothermicity, reaching a plateau-like limit (diffusion control) at higher ?E. This k v.s. ?E behaviour can be attributed to the FRANCK-CONDON barrier of the high-frequency reactant modes in a transfer step as could be shown by a theoretical model taking a transfer reaction as radiationless transition in the system reactants/environment. (author)

  3. 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.)

  4. Photoinduced electron transfer from chloropromazine and promethazine to chloroalkanes accompanied by cleavage of C Cl bond

    Science.gov (United States)

    Nath, Sukhendu; Sapre, Avinash V.

    2001-08-01

    Electron transfer from two phenothiazine derivatives namely promethazine and chloropromazine to chloroalkanes namely carbontetrachloride and chloroform has been studied by steady state fluorescence and transient absorption techniques. These phenothiazine derivatives also form weak charge transfer complexes with the above two chloroalkanes. Picosecond transient absorption studies provide direct evidence for two processes: (1) charge separation in the charge transfer complex and (2) electron transfer from the excited state of phenothiazines to chloroalkanes. A modified Marcus electron transfer theory proposed by Saveant [J. Am. Chem. Soc. 109 (1987) 6788], which incorporates the bond cleavage, has been used to explain the observed experimental results.

  5. Ultrafast Electron Dynamics Theory of Photo-excited Ruthenium Complexes

    CERN Document Server

    Chang, Jun; van Veenendaal, Michel

    2010-01-01

    An explanation is provided for the ultrafast photo-excited electron dynamics in low-spin Ruthenium (II) organic complexes. The experimentally-observed singlet to triplet decay in the metal-to-ligand charge-transfer (MLCT) states contradicts the expectation that the system should oscillate between the singlet and triplet states in the presence of a large spin-orbit coupling and the absence of a significance change in metal-ligand bond length. This dilemma is solved with a novel quantum decay mechanism that causes a singlet to triplet decay in about 300 femtoseconds. The decay is mediated by the triplet metal-centered state ($^3$MC) state even though there is no direct coupling between the $^1$MLCT and $^3$MC states. The coupling between the $^3$MLCT and $^3$MC via excited phonon states leads to vibrational cooling that allows the local system to dissipate the excess energy. In the relaxed state, the population of the $^3$MC state is low and the metal-ligand bond length is almost unchanged with respect to the i...

  6. Transfer excitation reactions in fast proton-helium collisions

    CERN Document Server

    Schöffler, M S; Chuluunbaatar, O; Houamer, S; Galstyan, A G; Titze, J N; Jahnke, T; Schmidt, L Ph H; Schmidt-B"ocking, H; D"orner, R; Popov, Yu V; Bulychev, A A

    2013-01-01

    Continuing previous work, we have measured the projectile scattering-angle dependency for transfer excitation of fast protons (300-1200 keV/u) colliding with helium (p+He $\\rightarrow$ H + He$^{+ *}$). Our high-resolution fully differential data are accompanied by calculations, performed in the plane wave first Born approximation and the eikonal wave Born approximation. Experimentally we find a deep minimum in the differential cross section around 0.5 $mrad$. The comparison with our calculations shows that describing the scattering angle dependence of transfer exitation in fast collisions requires to go beyond the first Born approximation and in addition to use initial state wave function, which contains some degree of angular correlations.

  7. Vibrational excitation induced proton transfer in hydrated Nafion membranes.

    Science.gov (United States)

    Liu, Liyuan; Bakker, Huib J

    2015-02-12

    We study the energy relaxation and structural relaxation dynamics of hydrated protons in Nafion membranes at different hydration levels using femtosecond infrared transient absorption spectroscopy. At low hydration levels we observe that the excitation of the proton vibration of an Eigen-like proton hydration structure leads to a structural relaxation process in which the Eigen-like structure evolves to a Zundel-like proton hydration structure. This reorganization leads to a transfer of the proton charge and closely follows the mechanism of infrared-induced adiabatic proton transfer that has been proposed by S. Hammes-Schiffer, J. T. Hynes, and others. At high hydration levels, the spectral dynamics are dominated by vibrational energy relaxation and subsequent cooling of the proton hydration structures and the surrounding water molecules. Using a kinetic analysis of the transient spectral data, we determine the rates of proton transfer, vibrational energy relaxation, and cooling as a function of hydration level. We find that infrared-induced proton transfer occurs at all hydration levels but becomes less observable at high hydration levels due to the increasingly dominant influence of the vibrational energy relaxation. PMID:25506744

  8. 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.

  9. Coupled electron transfers in artificial photosynthesis

    OpenAIRE

    Hammarström, Leif; Styring, Stenbjörn

    2007-01-01

    Light-induced charge separation in molecular assemblies has been widely investigated in the context of artificial photosynthesis. Important progress has been made in the fundamental understanding of electron and energy transfer and in stabilizing charge separation by multi-step electron transfer. In the Swedish Consortium for Artificial Photosynthesis, we build on principles from the natural enzyme photosystem II and Fe-hydrogenases. An important theme in this biomimetic effort is that of cou...

  10. Electron Transfer for Large Molecules through Delocalization

    Energy Technology Data Exchange (ETDEWEB)

    Neuhauser, D.; Reslan, R.; Hernandez, S.; Arnsen, C.; Lopata, K.; Govind, N.; Gao, Y.; Tolbert, S.; Schwartz, B.; Rubin, Y.; Nardes, A.; Kopidakis, N.

    2012-01-01

    Electron transfer for large molecules lies in between a Marcus-Theory two-state transfer and a Landauer description. We discuss a delocalization formalism which,through the introduction of artificial electric fields which emulate bulk dipole fields, allows calculation between a pair of identical molecules (A+A- (R)A-+A) with several open states. Dynamical electron polarization effects can be inserted with TDDFT and are crucial for large separations.

  11. 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...

  12. 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 Projects: GA MŠk LH12186 Institutional support: RVO:68378271 Keywords : quantum dots * nanoparticles * electron-phonon interaction * energy transfer Subject RIV: BM - Solid Matter Physics ; Magnetism

  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. 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.

  15. Site specific photochemical reaction of PMMA by core electron excitation

    International Nuclear Information System (INIS)

    The photon energy dependence of photoion emission from solid films of poly (methyl methacrylate) was measured to investigate the primary steps in radiation induced decomposition following carbon and oxygen 1s electron excitations using monochromatic pulsed-synchrotron radiation. Various ions including the monomer ion were observed. Further it was clearly found that the decomposition depends on the nature of the electronic states created in the excitation process. Excitations of carbon 1s electrons to ?* and ?* resonance states at 287.9 eV show remarkable enhancement of the ion emission for CH+ and CH2+. In the energy region of oxygen 1s electron excitation, the increase of COOCH3+ ion was not observed due to a fragmentation of the side chain by creating oxygen 1s hole. (author)

  16. Density functional theory based analysis of photoinduced electron transfer in a triazacryptand based K? sensor.

    Science.gov (United States)

    Briggs, Edward A; Besley, Nicholas A

    2015-03-26

    The electronic structure and photoinduced electron transfer processes in a K(+) fluorescent sensor that comprises a 4-amino-naphthalimide derived fluorophore with a triazacryptand ligand is investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) in order to rationalize the function of the sensor. The absorption and emission energies of the intense electronic excitation localized on the fluorophore are accurately described using a ?SCF Kohn-Sham DFT approach, which gives excitation energies closer to experiment than TDDFT. Analysis of the molecular orbital diagram arising from DFT calculations for the isolated molecule or with implicit solvent cannot account for the function of the sensor, and it is necessary to consider the relative energies of the electronic states formed from the local excitation on the fluorophore and the lowest fluorophore ? chelator charge transfer state. The inclusion of solvent in these calculations is critical since the strong interaction of the charge transfer state with the solvent lowers its energy below the local fluorophore excited state making a reductive photoinduced electron transfer possible in the absence of K(+), while no such process is possible when the sensor is bound to K(+). The rate of electron transfer is quantified using Marcus theory, which gives a rate of electron transfer of k(ET) = 5.98 × 10(6) s(-1). PMID:25734899

  17. Beyond the Förster theory of excitation energy transfer: importance of higher-order processes in supramolecular antenna systems.

    Science.gov (United States)

    May, Volkhard

    2009-12-01

    Electronic excitation energy transfer in molecular systems is connected with the de-excitation of one molecule and the excitation of the other. Mostly, it can be understood in terms of Förster (or fluorescence) resonance energy transfer. An increasing interest in the optimization of artificial light harvesting systems, however, requires a more detailed study going beyond the standard Förster scheme. There are two main routes to do this. Considering a Coulombic less-strongly coupled system first, coherences among different chromophores may be considered in the framework of perturbation theory with higher-order mechanisms correcting the standard second-order description. Secondly, if inter-chromophore coherences are dominant and delocalized Frenkel-exciton states are formed, it becomes of some importance to study their decay due to the coupling to vibrational degrees of freedom. While we will also comment on this latter mechanism, the first description based on localized excitations will be the main focus. A general higher-order theory resulting in respective transition rates and rate equations is utilized. Its capability is demonstrated when presenting a systematic description of short-range and long-range corrections to the basic Förster mechanism. Accordingly, a unique description of bridge-mediated and photon-mediated long-range electronic excitation energy transfer is offered. Moreover, short-range excitation energy transfer appearing as a two electron exchange is also discussed. And, the exciton-exciton annihilation process present at higher optical excitation intensities is described as a direct higher-order transition. The related higher-order vibrational correlation functions are presented and estimated for the reference case where the coupling to vibrational degrees of freedom either of intra-molecular or inter-molecular type is reduced to a simple electronic state dephasing process. PMID:19904437

  18. Elementary Electronic Excitations in Graphene Nanoribbons

    CERN Document Server

    Brey, L

    2007-01-01

    We analyze the collective mode spectrum of graphene nanoribbons within the random phase approximation. In the undoped case, only metallic armchair nanoribbons support a propagating plasmon mode. Landau damping of this mode is shown to be suppressed through the chirality of the single particle wavefunctions. We argue that undoped zigzag nanoribbons should not support plasmon excitations because of a broad continuum of particle-hole excitations associated with surface states, into which collective modes may decay. Doped nanoribbons have properties similar to those of semiconductor nanowires, including a plasmon mode dispersing as $q\\sqrt{-\\ln qW}$ and a static dielectric response that is divergent at $q=2k_F$.

  19. Angular anisotropy of autoionization electrons from sodium atoms simultaneously excited by laser and electron beams

    International Nuclear Information System (INIS)

    First measurements of the angular distributions of autoionization electrons from 2p53s3p2D5/2 state of Na atom excited by electron impact from the ground and laser excited 3p 2P3/2 state are reported. Strong anisotropy of the angular distribution is revealed, which has different signs for the excitation from the ground and excited states. Theoretical analysis based on the Born approximation is given. (Author)

  20. Saturn spectrum in the EUV-electron excited hydrogen

    International Nuclear Information System (INIS)

    Recent laboratory observations of electron excited H2 in the EUV have brought about the realization that higher Rydberg series band systems make a significant contribution to the emission spectrum. Theoretical cross section estimates for the excitation of the D, D', B', B'' states agree with these results. Model calculations for particle excitation of the Saturn atmosphere, including the higher states, now show excellent agreement with Voyager auroral and dayside equatorial spectra. The model data also confirm the relative spectral response calibration of the Voyager instruments, providing a basis for accurate analysis of the excitation processes on both Jupiter and Saturn

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

    OpenAIRE

    Abramavicius, Vytautas; Abramavicius, Darius

    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...

  2. Effects of oxidants and reductants on the efficiency of excitation transfer in green photosynthetic bacteria

    Science.gov (United States)

    Wang, J.; Brune, D. C.; Blankenship, R. E.

    1990-01-01

    The efficiency of energy transfer in chlorosome antennas in the green sulfur bacteria Chlorobium vibrioforme and Chlorobium limicola was found to be highly sensitive to the redox potential of the suspension. Energy transfer efficiencies were measured by comparing the absorption spectrum of the bacteriochlorophyll c or d pigments in the chlorosome to the excitation spectrum for fluorescence arising from the chlorosome baseplate and membrane-bound antenna complexes. The efficiency of energy transfer approaches 100% at low redox potentials induced by addition of sodium dithionite or other strong reductants, and is lowered to 10-20% under aerobic conditions or after addition of a variety of membrane-permeable oxidizing agents. The redox effect on energy transfer is observed in whole cells, isolated membranes and purified chlorosomes, indicating that the modulation of energy transfer efficiency arises within the antenna complexes and is not directly mediated by the redox state of the reaction center. It is proposed that chlorosomes contain a component that acts as a highly quenching center in its oxidized state, but is an inefficient quencher when reduced by endogenous or exogenous reductants. This effect may be a control mechanism that prevents cellular damage resulting from reaction of oxygen with reduced low-potential electron acceptors found in the green sulfur bacteria. The redox modulation effect is not observed in the green gliding bacterium Chloroflexus aurantiacus, which contains chlorosomes but does not contain low-potential electron acceptors.

  3. Recent advances in studies of the electronic decay of core excited states in small molecules

    International Nuclear Information System (INIS)

    Electronic decay spectra of neutral core excited states give new insight into charge transfer, screening and electron correlation effects in atoms, molecules and solids. The basic decay mechanism is an Auger decay but the transition occurs in a neutral rather than in a core ionized system. The study of the electronic decay of neutral core excited states yields information that is complementary to that obtained in both photoemission and Auger spectroscopy. Using synchrotron radiation as the excitation source, deexcitation spectroscopy has been developed over the past decade. Here, these developments are briefly reviewed and new prospects, opened up by the availability of high resolution, high intensity undulator radiation, are highlighted using spectra for N2 as an example. (orig.)

  4. 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

  5. Electron transfer exchange in viologen systems

    International Nuclear Information System (INIS)

    Pulse radiolysis has been utilized to generate viologen radicals and to study the electron transfer rates and equilibria among a variety of such viologen systems as well as the electron transfer reactions between the viologens and other systems (quinones, nitrobenzene, Ru(NH/sub 3/)/sub 6//sup 3+/). The viologen systems include polystyrene viologens, surfactant viologens and zwitterionic viologens. The electron transfer reactions were studied both in homogeneous and micellar systems. The rate of the reaction of the polymeric viologen radicals with Ru(NH/sub 3/)/sub 6//sup 3+/ is slower by three orders of magnitudes than that of the zwitterionic viologen radical. This large difference in rates provides a route to determine equilibria constants for electron exchange between the viologen systems. Complex formation between semiquinones and the viologens is indicated. Implications of the thermodynamic and kinetic parameters to photochemical energy conversion schemes is discussed

  6. Reduced radiation losses in electron beam excited propagating plasmons.

    Science.gov (United States)

    Wang, Lei; Cai, Wei; Xiang, Yinxiao; Zhang, Xinzheng; Xu, Jingjun; García de Abajo, F Javier

    2011-09-12

    Except for heating losses in metal, propagating plasmons also suffer a lot from radiation losses. In this paper, electron beams are proposed as a way to excite higher-order, multipolar plasmons, which would otherwise not be excited by light, as a way to reduce radiation losses. Specifically, electron excited guided plasmons in a coupled nanoparticle chain and a symmetrical four-wire waveguide are separately discussed. In the coupled nanoparticle chain, the plasmon mode formed by quadrupolar polarized particles with low radiation is efficiently coupled by electron beams. Meanwhile, in the four-wire waveguide, the excited plasmons with zero momentum in the cross-section of each wire possess longer propagating distance than other higher-order plasmons. PMID:21935241

  7. 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.

  8. Transverse electron guns for plasma excitation

    International Nuclear Information System (INIS)

    We report a plasma gun, which generates on a continuous basis, kilowatt electron beam discharges (e.g., 0.4 A at 4 kV) in an ambient pressure 0.1--1 Torr without differential pumping. Gun design characteristics, operating parameters, and measured beam profiles are given. Electron beam generation on a pulsed basis has also been studied. More than 100 A of beam current has been measured with a Faraday cup biased to -100V. A trapped electron beam scheme for achieving efficient deposition of the electron beam energy in a gas medium is described

  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. Energy transfer of a relativistic electron beam to a plasma

    International Nuclear Information System (INIS)

    The energy loss of a relativistic electron beam and the accompanying plasma heating have been measured in an experiment injecting and electron beam of 500 keV, 0.5 kA and 20 ns pulse duration into a plasma of density between 1011 cm-3 and 1012 cm-3 confined in a magnetic mirror trap with 0.2T in the homogeneous middle section of 2 m length. The diamagnetic loop measurements show plasma perpendicular energies corresponding to heating efficiencies up to 10%. Results with an energy analyser show that the beam loses about 10% of its energy. Beam energy spectrum and loss as a function of time are shown. Energy losses and plasma electron heating agree within a factor two with theoretical calculations for energy transfer due to the beam excited instability at the electron plasma frequency. (author)

  11. Protein electron transfer: Dynamics and statistics

    Science.gov (United States)

    Matyushov, Dmitry V.

    2013-07-01

    Electron transfer between redox proteins participating in energy chains of biology is required to proceed with high energetic efficiency, minimizing losses of redox energy to heat. Within the standard models of electron transfer, this requirement, combined with the need for unidirectional (preferably activationless) transitions, is translated into the need to minimize the reorganization energy of electron transfer. This design program is, however, unrealistic for proteins whose active sites are typically positioned close to the polar and flexible protein-water interface to allow inter-protein electron tunneling. The high flexibility of the interfacial region makes both the hydration water and the surface protein layer act as highly polar solvents. The reorganization energy, as measured by fluctuations, is not minimized, but rather maximized in this region. Natural systems in fact utilize the broad breadth of interfacial electrostatic fluctuations, but in the ways not anticipated by the standard models based on equilibrium thermodynamics. The combination of the broad spectrum of static fluctuations with their dispersive dynamics offers the mechanism of dynamical freezing (ergodicity breaking) of subsets of nuclear modes on the time of reaction/residence of the electron at a redox cofactor. The separation of time-scales of nuclear modes coupled to electron transfer allows dynamical freezing. In particular, the separation between the relaxation time of electro-elastic fluctuations of the interface and the time of conformational transitions of the protein caused by changing redox state results in dynamical freezing of the latter for sufficiently fast electron transfer. The observable consequence of this dynamical freezing is significantly different reorganization energies describing the curvature at the bottom of electron-transfer free energy surfaces (large) and the distance between their minima (Stokes shift, small). The ratio of the two reorganization energies establishes the parameter by which the energetic efficiency of protein electron transfer is increased relative to the standard expectations, thus minimizing losses of energy to heat. Energetically efficient electron transfer occurs in a chain of conformationally quenched cofactors and is characterized by flattened free energy surfaces, reminiscent of the flat and rugged landscape at the stability basin of a folded protein.

  12. Marcus theory for outer-sphere heterogeneous electron transfer: Predicting electron-transfer rates for quinones

    OpenAIRE

    Rees, Nv; Clegg, Ad; Klymenko, Ov; Coles, Ba; Compton, Rg

    2004-01-01

    Steady-state voltammetry is used to measure the heterogeneous electron-transfer rates for the reduction of quinones to determine the dependence of k0 on molecular size, according to Marcus theory. This dependence is then used to predict the electron-transfer rate constants of related quinones, and the predictions are compared to experimental measurements.

  13. Transfer matrices and excitations with matrix product states

    Science.gov (United States)

    Zauner, V.; Draxler, D.; Vanderstraeten, L.; Degroote, M.; Haegeman, J.; Rams, M. M.; Stojevic, V.; Schuch, N.; Verstraete, F.

    2015-05-01

    We use the formalism of tensor network states to investigate the relation between static correlation functions in the ground state of local quantum many-body Hamiltonians and the dispersion relations of the corresponding low-energy excitations. In particular, we show that the matrix product state transfer matrix (MPS-TM)—a central object in the computation of static correlation functions—provides important information about the location and magnitude of the minima of the low-energy dispersion relation(s), and we present supporting numerical data for one-dimensional lattice and continuum models as well as two-dimensional lattice models on a cylinder. We elaborate on the peculiar structure of the MPS-TM’s eigenspectrum and give several arguments for the close relation between the structure of the low-energy spectrum of the system and the form of the static correlation functions. Finally, we discuss how the MPS-TM connects to the exact quantum transfer matrix of the model at zero temperature. We present a renormalization group argument for obtaining finite bond dimension approximations of the MPS, which allows one to reinterpret variational MPS techniques (such as the density matrix renormalization group) as an application of Wilson’s numerical renormalization group along the virtual (imaginary time) dimension of the system.

  14. Electron emission from 57Fe nuclei excited with synchrotron radiation

    International Nuclear Information System (INIS)

    Time-dependent electron emission from iron foils excited by synchrotron radiation at the 14.4-keV nuclear resonance of 57Fe was observed. The measured time spectra are explained as the sum of three contributions, the emission of conversion electrons with and without creating or annihilating phonons during absorption and the emission of photoelectrons. copyright 1996 The American Physical Society

  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. 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.)

  17. 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.

  18. Excited state proton transfer in ionic liquid mixed micelles.

    Science.gov (United States)

    Mondal, Tridib; Das, Atanu Kumar; Sasmal, Dibyendu Kumar; Bhattacharyya, Kankan

    2010-10-21

    Excited state proton transfer (ESPT) of pyranine (8-hydroxypyranine-1,3,6-trisulfonate, HPTS) in room temperature ionic liquid (RTIL) mixed micelles is studied by femtosecond up-conversion. The mixed micelle consists of a triblock copolymer, (PEO)(20)-(PPO)(70)-(PEO)(20) (Pluronic P123), and one of the two RTILs, 1-pentyl-3-methyl-imidazolium bromide ([pmim][Br]) and 1-pentyl-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF(4)]). The size and structure of the mixed micelle vary with the relative amount of the RTIL. For [pmim][Br], the hydrodynamic diameter of the mixed micelle is 26 nm in 0.3 M RTIL and 3500 nm in 3.0 M RTIL. The time constant of initial proton transfer (?(PT)) in P123 micelle (65 ps) is 10 times slower than that (5 ps) in water, while the time constants of recombination (?(rec)) and dissociation (?(diss)) are 2-3 times slower in P123 micelle. On addition of the RTIL, the rate of ESPT is markedly modified. In 0.3 M RTIL-P123 mixed micelle, ?(PT) is shorter than that in P123 micelle. In the mixed micelle, ?(PT) increases with an increase in the concentration of the RTIL (230 ps in 3 M [pmim][Br] and 55 ps in 0.9 M [pmim][BF(4)]). This is attributed to large scale penetration of the P123 micelle by RTIL replacing water molecules. The time constants of proton transfer (?(PT), ?(rec), and ?(diss)) are faster than the slowest component (200-500 ps) of solvation dynamics. It seems that the ultrafast component of solvation (<0.3 ps and <5 ps) is enough for inducing proton transfer. The time constant of the proton transfer (?(PT)) in [pmim][BF(4)]-P123 mixed micelle is longer (?20%) than that in [pmim][Br]-P123 mixed micelle for the same concentration of RTIL. The counterion dependence of ESPT is attributed to the difference in the structure and greater hydrophobicity of the [pmim][BF(4)]. PMID:20863113

  19. Energy and electron transfer processes in polymethine dyes

    International Nuclear Information System (INIS)

    Polymethine dyes and its derivatives are attractive for their interesting optical and photo-electric properties. They are used as very efficient spectral sensitizers and laser dyes. Due to the high rate constant of deactivation channels of such dyes the primary processes of bimolecular processes as energy or electron transfer proceed within not more than some picoseconds or even shorter. In the case of a polymethine which does not isomerize we were able to show by means of time-resolved absorption spectroscopy that the singlet state photoelectron transfer to methyl- and benzylviologen had an efficiency of 0.15 with rate constants of 6.7·109 and 4.6·109 l/mole·s, respectively, yielding the polymethine dication radical. The photoreduction with tetraphenylborate and potassium rhodanide is also very efficient with an efficiency of about 0.10 with rate constants of 2.4·1010 and 1.6·1010 l/mole·s, respectively, yielding the polymethine neutral radical. The spectral differences of the observed radical spectra are small. The investigation of the temperature dependence of the photo induced electron transfer of the investigated polymethine to methylviologen results in an activation energy ?G*=24 kJ/mole and a value of the frequency factor of A=4.7·1014 l/mole·s. Strong deviation from a linear Arrhenius plot was observed at low temperatures which can be explained by solvent-solute interaction decreasing the electronteraction decreasing the electron transfer rate constant at lower temperatures. The calculated electron transfer rate constants agree with the assumption of the investigated process as a diffusion-controlled one. Energy transfer occurs as a efficient competitive deactivation channel from photo excited polymethine dyes to other chromophore systems with a strong overlapping of the fluorescence and the absorption bands of the donor and the acceptor, respectively. We have investigated the time and spectral evolution of the energy transfer process from a polymethine dye to different energy acceptor dyes in solution. The general question within this respect was the involvement of an intermediate electron transfer as competitive process in the energy transfer process. Whereas the Foerster energy transfer radius calculated from the time-resolved data exceeds the value received from the overlap integral by 15%, indicating deviation from a normal Foerster decay type the semilogarithmic plot of the ground state recovery kinetics vs. square root of time results in an ideal straight line dependence. No intermediate spectra as well as intermediate time behaviour was found in these complexes

  20. Rate coefficients for electron impact excitation of CO

    International Nuclear Information System (INIS)

    Highlights: • Rate coefficients for electron impact excitation of CO have been calculated. • All relevant non-elastic processes have been included in calculations. • Equilibrium and non-equilibrium conditions have been considered. • Electron energy distribution functions were determined by a Monte Carlo simulation. • Rate coefficients have also been determined in the presence of magnetic field. - Abstract: Rate coefficients for electron impact excitation of the CO molecule have been calculated both for equilibrium and non-equilibrium conditions in the presence of electric and magnetic fields. The rate coefficients have been determined for all relevant non-elastic processes: rotational excitation, vibrational excitation, electronic excitation into singlet and triplet states and particularly for ionization. In the case of non-equilibrium conditions, we had to determine electron energy distribution functions needed for rate coefficients calculations. The distribution functions were obtained by employing a Monte Carlo simulation developed in our laboratory. The simulations were performed for moderate values of electric field over gas number density ratios, E/N, from 0 to 1000 Td. Also, the rate coefficients have been determined in presence of magnetic field for typical values of magnetic field over gas number density ratios, B/N, from 500 to 3000 Hx. The results of equilibrium rate coefficients along with non-equilibrium ones have been shown

  1. Excited Spectator Electron Effects on Spectral Line Shapes

    Energy Technology Data Exchange (ETDEWEB)

    Iglesias, C A

    2009-10-12

    Excited spectator electron effects on Stark broadened spectral line shapes of transitions involving tightly bound electrons are investigated. It is shown that the interference terms in the electron impact broadening are essential to describe the overlapping lines generated by these configurations (e.g.; dielectronic satellite lines). The main impact is narrower spectral features and reduced far wing intensities compared to calculations neglecting the interference terms.

  2. Electron-impact resonant vibrational excitation and dissociation processes involving vibrationally excited N2 molecules

    International Nuclear Information System (INIS)

    Resonant vibrational excitation cross sections and the corresponding rate coefficients for electron–N2 collisions occurring through the N2?(X 2?g) resonant state are reviewed. New calculations are performed using accurate potential energy curves for the N2 electronic ground state, taken from the literature, and for the N2? resonant state, obtained from R-matrix calculations. The calculations are extended to resonant excitation processes involving the N2 ground state vibrational continuum, leading to dissociation. Electron-impact dissociation is found to be significant from higher vibrational levels. Accurate analytical fits for the complete set of the rate coefficients are provided. The behavior of the dissociative cross sections is investigated for rotationally excited N2 molecules, with J = 50, 100 and 150, and for different vibrational levels. (paper)

  3. ATOMIC AND MOLECULAR PHYSICS: Integral Reduction Arising in Double Transfer and Excitation Amplitude

    Science.gov (United States)

    Zerarka, A.; Soukeur, A.; Bensalah, N.

    2010-03-01

    The purpose of this article is to develop an integral derived from the double transfer and excitation theory. The reduced form of this integral, so obtained, can serve in the computation of the transition amplitude which is from numerical point of view difficult to implement. This amplitude is of great interest in the resonant and non resonant transfer and excitation (RTE and NTE) processes.

  4. 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.

  5. Enhancement of molecular modes by electronically resonant multipulse excitation: further progress towards mode selective chemistry.

    Science.gov (United States)

    Hauer, Jürgen; Buckup, Tiago; Motzkus, Marcus

    2006-08-14

    We show that molecular vibrations induced by resonant excitation pulses can be enhanced by pulse trains, compared to Fourier-limited pulses of equal pulse energy. As a proof-of-principle, a low frequency mode of Nile Blue at 600 cm(-1) is observed and amplified in a pump and probe experiment. In addition to previous experiments in our group, an increased population transfer to the excited electronic state is identified as an important element of the underlying physical mechanism. These results suggest an enhancement on the level of individual molecules rather than a macroscopic effect. PMID:16942265

  6. Electron-impact excitation of Rb+

    International Nuclear Information System (INIS)

    We carry out R-matrix calculations for excitations of 4p55s 1P1o, 3P1o states and 4p54d 1P1o, 3P1o, 3D1o states from the ground 4p6 1S0e state of Rb+. The R-matrix method with 35, 61 and 73 target state is used for these transitions in the low incident energy. We compare our results with experimental measurements. The energy dependence of present cross sections for the 4p6 1S0e ? 4p55s 1P1o and 3P1o transitions are in agreement with the experimental results. (author)

  7. NEGATIVE ELECTRON TRANSFER DISSOCIATION OF GLYCOSAMINOGLYCANS

    OpenAIRE

    Wolff, Jeremy J.; Leach, Franklin E.; Laremore, Tatiana N.; Kaplan, Desmond A.; Easterling, Michael L.; Linhardt, Robert J.; Amster, I. Jonathan

    2010-01-01

    Structural characterization of glycosaminoglycans (GAGs) has been a challenge in the field of mass spectrometry, and the application of electron detachment dissociation (EDD) Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has shown great promise to GAG oligosaccharide characterization in a single tandem mass spectrometry experiment. In this work, we apply the technique of negative electron transfer dissociation (NETD) to GAGs on a commercial ion trap mass spectrometer....

  8. 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

  9. 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.

  10. Electron transfer in dinucleoside phosphate anions

    International Nuclear Information System (INIS)

    The electron transfer reaction within various dinucleoside phosphate radical anions has been investigated by ESR spectroscopy and pulse radiolysis. In the ESR work electrons are produced by photolysis of K4Fe(CN)6 in a 12 M LiCl glass at 770K. Upon photobleaching the electrons react with the dinucleoside phosphate to form the anion radical. The anions of the four DNA nucleosides were also produced and their ESR spectra were appropriately weighted and summed by computer to simulate the spectra found for the dinucleoside phosphate anions. From the analysis the relative amounts of each of the nucleoside anions in the dinucleoside phosphate anion were determined. Evidence suggests the electron affinity of the pyrimidine bases are greater than the purine bases; however, the results are not sufficient to distinguish between the individual purine or pyrimidine. When dinucleoside phosphate anions containing thymidine are warmed, protonation occurs only on thymine to produce the well known ''thymyl'' spectrum. Pulse radiolysis experiments on individual nucleotides (TMP, dAMP), mixtures of these nucleotides and the dinucleoside phosphate, TdA, in aqueous solution at room temperature show that in the TdA anion electron transfer occurs from adenine to thymine, whereas no electron transfer is found for mixtures of individual nucleotides. Protonation is found to occur only on thymine in the TdA anion in agreement with the ESR resultsement with the ESR results

  11. The electron transfer flavoprotein: ubiquinone oxidoreductases.

    Science.gov (United States)

    Watmough, Nicholas J; Frerman, Frank E

    2010-12-01

    Electron transfer flavoprotein: ubiqionone oxidoreductase (ETF-QO) is a component of the mitochondrial respiratory chain that together with electron transfer flavoprotein (ETF) forms a short pathway that transfers electrons from 11 different mitochondrial flavoprotein dehydrogenases to the ubiquinone pool. The X-ray structure of the pig liver enzyme has been solved in the presence and absence of a bound ubiquinone. This structure reveals ETF-QO to be a monotopic membrane protein with the cofactors, FAD and a [4Fe-4S](+1+2) cluster, organised to suggests that it is the flavin that serves as the immediate reductant of ubiquinone. ETF-QO is very highly conserved in evolution and the recombinant enzyme from the bacterium Rhodobacter sphaeroides has allowed the mutational analysis of a number of residues that the structure suggested are involved in modulating the reduction potential of the cofactors. These experiments, together with the spectroscopic measurement of the distances between the cofactors in solution have confirmed the intramolecular pathway of electron transfer from ETF to ubiquinone. This approach can be extended as the R. sphaeroides ETF-QO provides a template for investigating the mechanistic consequences of single amino acid substitutions of conserved residues that are associated with a mild and late onset variant of the metabolic disease multiple acyl-CoA dehydrogenase deficiency (MADD). PMID:20937244

  12. 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

  13. 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

  14. Electron collisional excitation of S XII

    International Nuclear Information System (INIS)

    Atomic data have been obtained for the coronal ion S XII using the UCL program codes. Energy levels and radiative transition probabilities have been computed with different target descriptions allowing for configuration interaction and relativistic effects. Multi-configuration Hartree-Fock method is used to calculate the target wave functions. Collisional excitation cross sections between the 2s22p 2P0, 2s2p24P, 2D, 2S, 2P and 2p34S0, 2D0, 2P0 eigenstates of S XII have been calculated using eight-state close coupling and distorted wave approximations with a target description employing a anti 3anti d pseudo orbital. Collision strengths between the lowest five eigenstates of S XII have also been computed in five-state close coupling and distorted wave approximations for comparison. The results are compared with available theoretical work. It is found that the use of elaborate target wave functions and the choice of a more accurate scattering approximation may change the cross section by more than 25% in some of the transitions. (orig.)

  15. Electron collisional excitation of S XII

    Energy Technology Data Exchange (ETDEWEB)

    Saha, H.P.; Trefftz, E.

    1982-08-01

    Atomic data have been obtained for the coronal ion S XII using the UCL program codes. Energy levels and radiative transition probabilities have been computed with different target descriptions allowing for configuration interaction and relativistic effects. Multi-configuration Hartree-Fock method is used to calculate the target wave functions. Collisional excitation cross sections between the 2s/sup 2/2p /sup 2/P/sup 0/, 2s2p/sup 2/4P, /sup 2/D, /sup 2/S, /sup 2/P and 2p/sup 3/ /sup 4/S/sup 0/, 2D/sup 0/, 2P/sup 0/ eigenstates of S XII have been calculated using eight-state close coupling and distorted wave approximations with a target description employing a anti 3anti d pseudo orbital. Collision strengths between the lowest five eigenstates of S XII have also been computed in five-state close coupling and distorted wave approximations for comparison. The results are compared with available theoretical work. It is found that the use of elaborate target wave functions and the choice of a more accurate scattering approximation may change the cross section by more than 25% in some of the transitions.

  16. 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

  17. Study of excitation transfer in laser dye mixtures by direct measurement of fluorescence lifetime

    Science.gov (United States)

    Lin, C.; Dienes, A.

    1973-01-01

    By directly measuring the donor fluorescence lifetime as a function of acceptor concentration in the laser dye mixture Rhodamine 6G-Cresyl violet, we found that the Stern-Volmer relation is obeyed, from which the rate of excitation transfer is determined. The experimental results indicate that the dominant mechanism responsible for the efficient excitation transfer is that of resonance transfer due to long range dipole-dipole interaction.

  18. Electron-phonon coupling in laser excited metals

    Energy Technology Data Exchange (ETDEWEB)

    Klett, Isabel; Mueller, Benedikt; Rethfeld, Baerbel [TU Kaiserslautern (Germany)

    2011-07-01

    Irradiation of metals with an ultrashort laser pulse leads to a hot electron gas while the lattice stays cold. The corresponding electron-phonon coupling has been calculated using a thermalized Fermi distribution function. However, after laser excitation, the electrons cannot be assumed in equilibrium, due to their relaxation time of tens of femtoseconds. In order to allow a nonequilibrium distribution function, the Boltzmann equation is applied. This model is extended by implementing the density of states of real metals into the Boltzmann collision terms. From the solution we extract the electron-phonon coupling in thermal nonequilibrium.

  19. Electron impact excitation cross sections in F-like selenium

    International Nuclear Information System (INIS)

    Cross sections for excitation induced by electron collision between low-lying 1s22s22p5 and 1s22s2p6 states of f-like selenium and from these states to singly excited states with the excited electron occupying the M shell have been calculated by relativistic distorted-wave Born procedures. The GRASP2 code was used for the atomic structure calculations. The continuum orbitals for the construction of continuum states were computed in the distorted-wave approximation, in which the distorted-wave potential used was the spherically averaged potential of the nucleus plus the potential of the bound electrons of the bound state. The cross sections for excitations were computed first by a 233-level multiconfiguration Dirac-Fock (MCDF) configuration expansion and then by a 279-level MCDF configuration expansion. The latter procedure, which also took into account contributions from all the participating singly excited N-shell states, was found to be necessary for improved accuracy. The cross section data should be a useful reference in the development of x-ray lasers and other related fields involving highly stripped ions

  20. Ultrafast nonradiative dynamics in electronically excited hexafluorobenzene by femtosecond time-resolved mass spectrometry

    Science.gov (United States)

    Studzinski, Harald; Zhang, Song; Wang, Yanmei; Temps, Friedrich

    2008-04-01

    The fast nonradiative decay dynamics of the lowest two excited ?? * electronic states (S2 and S3) of hexafluorobenzene have been investigated by using femtosecond time-resolved time-of-flight mass spectrometry. The molecules were excited at wavelengths between 265nm??pump?217nm and probed by four- and three-photon ionization at ?probe=775nm. The observed temporal profiles exhibit two exponential decay times (?1=0.54-0.1ps and ?2=493-4.67ps, depending on the excitation wavelength) and a superimposed coherent oscillation with vibrational frequency ?osc=97cm-1 and damping time ?D that is two to three times longer than the respective ?1. The first decay component (?1) is assigned to rapid radiationless transfer from the excited optically bright ?? * electronic state (S2 or S3, respectively) through a conical intersection (CI) to the lower-lying optically dark ?? * state (S1) of the molecule; the second component (?2) is attributed to the subsequent slower relaxation from the S1 state back to the electronic ground state (S0). ?2 dramatically decreases with increasing vibronic excitation energy up to the CI connecting the ?? * with the S0 state. The coherent oscillation is identified as nuclear motion along the out-of-plane vibration ?16a (notation as for benzene), which has e2u symmetry and acts as coupling mode between the ?? * and ?? * states.

  1. 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)

  2. 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...

  3. Electron beam exciter for optical emission spectroscopy and optical excitation cross section analysis in processing systems

    Science.gov (United States)

    Padron Wells, Gabriel

    Plasma processing technology is indispensable for manufacturing the very large scale integrated circuits (ICs) used by the electronics industry. 48 Generally, the precise control and characterization of the plasma processing medium becomes pivotal to develop a successful product. At present, a variety of complementary characterization techniques are providing precise and detailed information on a variety of processing plasmas. However, newer generations of plasma processing techniques are becoming far too complex and their operating conditions impose great limitations on the operability and functionality of many important diagnostics. To adapt to these new set of constraints, the present work focuses on the development of a new Electron Beam Exciter device designed to conduct quantitative optical measurements in processing systems. This newly developed Exciter prototype employs a highly controllable electron beam of controlled energy level (Ee = 1/2 mv2) and density (n e) to cause light emission from electron-impact excitation events with gas particles that are part of the chemical makeup characterizing the processing environment. As such, the current design utilizes an inductively coupled plasma (ICP) source (RF coil antenna, 29 MHz) to generate a continuous cloud of electrons that can be extracted to an excitation region where optical and electrical measurements are collected. This variable plasma source, or electron bottle, is made out of a quartz or sapphire tube and is positioned opposite to an electron extraction assembly (or accelerator assembly), so that plasma electrons are extracted from the source via controlled dc electric potentials. The electron extraction assembly is composed of three distinct electrodes, namely the nozzle extractor, an extractor plate and a Faraday cup electrode, and is protected by a Tin doped Indium Oxide (ITO) interface that allows device operability in harsh halide enriched environments. Furthermore, the ability to successfully control the electron energy distribution function (EEDF) and energy level (Ee) characterizing the extracted electron beams allows the measurement of optical excitation cross-section from several reactive plasma effluents, some of which have not been measured before. The distinctiveness of the system with such a measurement capability to real time diagnostics, and its usefulness to measure cross sections of molecular species from plasmas are discussed.

  4. Minimal-excitation states for electron quantum optics using levitons.

    Science.gov (United States)

    Dubois, J; Jullien, T; Portier, F; Roche, P; Cavanna, A; Jin, Y; Wegscheider, W; Roulleau, P; Glattli, D C

    2013-10-31

    The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the time domain. Finally, the generation technique could be applied to cold atomic gases, leading to the possibility of atomic levitons. PMID:24153178

  5. Electron-impact excitation of gas-phase uracil

    International Nuclear Information System (INIS)

    The low lying excited states of uracil have been studied using electron energy-loss spectroscopy. In addition to the dipole allowed transitions to the singlet states, the two lowest triplet states are also observed. In the uracil molecule, the singlet electronic states have been found, being blue-shifted by about 0.5 eV as compared to the UV-absorption results.

  6. 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...

  7. The coupling of condensed matter excitations to electron probes

    International Nuclear Information System (INIS)

    Aspects of coupling of a classical electron with bulk and surface excitations in condensed matter have been sketched. Some considerations of a self-energy approach to the complete quantal treatment of this coupling have been given. 19 refs., 3 figs

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

    Science.gov (United States)

    Bocan, G.; Miraglia, J. E.

    2003-03-01

    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, Rösler 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.

  9. Spin-Forster transfer in optically excited quantum dots

    CERN Document Server

    Govorov, A O

    2005-01-01

    The mechanisms of energy and spin transfer in quantum dot pairs coupled via the Coulomb interaction are studied. Exciton transfer can be resonant or phonon-assisted. In both cases, the transfer rates strongly depend on the resonance conditions. The spin selection rules in the transfer process come from the exchange and spin-orbit interactions. The character of energy dissipation in spin transfer is different than that in the traditional spin currents. The spin-dependent photon cross-correlation functions reflect the exciton transfer process. In addition, a mathematical method to calculate F\\"orster transfer in crystalline nanostructures beyond the dipole-dipole approximation is described.

  10. 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.

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

    International Nuclear Information System (INIS)

    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

  12. 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.

  13. Heavy-ion versus electron-beam excitation of an excimer laser

    Science.gov (United States)

    Moratz, Thomas J.; Saunders, Todd D.; Kushner, Mark J.

    1988-10-01

    A model is described for the heavy-ion pumping of an XeF(B) laser by uranium fission fragments (FF).The model is a self-consistent accounting of the generation and transport of the FF's through the fission foils, slowing of the fragments in the gas, evolution of the secondary-electron-source function and distribution, and the XeF laser plasma kinetics. By simulating the same quantities for an e-beam-pumped plasma, direct comparisons can be made for laser performance. We found that the secondary-electron source generated by the e-beam is more energetic than that for direct ionization by FF's due to a more favorable mass ratio for momentum transfer collisions with orbital electrons. This difference in the electron-source functions significantly affects W values and excitation fractions. The impact on laser performance, though, is not large due to the high efficiency of channeling deposited energy to the upper laser level in XeF lasers. For conditions typical of FF excitation (power deposition 1-3 kW cm-3, pulse length ?200 ?s), e-beam excitation results in 10%-15% higher gain than heavy-ion excitation.

  14. Dynamics of the excited state intramolecular charge transfer

    International Nuclear Information System (INIS)

    The 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan), a derivative of 6-propanoyl- 2-dimethylaminonaphthalene (prodan), has been used as a fluorescent probe in cell imaging, especially in visualizing the lipid rafts by the generalized polarization (GP) images, where GP=(I440-I490)/(I440+I490) with I being the fluorescence intensity. The fluorescence spectrum of laurdan is sensitive to its dipolar environment due to the intramolecular charge transfer (ICT) process in S1 state, which results in a dual emission from the locally excited (LE) and the ICT states. The ICT process and the solvation of the ICT state are very sensitive to the dipolar nature of the environment. In this work, the ICT of laurdan in ethanol has been studied by femtosecond time resolved fluorescence (TRF), especially TRF spectra measurement without the conventional spectral reconstruction method. TRF probes the excited states exclusively, a unique advantage over the pump/probe transient absorption technique, although time resolution of the TRF is generally lower than transient absorption and the TRF spectra measurement was possible only though the spectral reconstruction. Over the years, critical advances in TRF technique have been made in our group to achieve <50 fs time resolution with direct full spectra measurement capability. Detailed ICT and the subsequent solvation processes can be visualized unambiguously from the TRF spectra. Fig. 1 shobiguously from the TRF spectra. Fig. 1 shows the TRF spectra of laurdan in ethanol at several time delays. Surprisingly, two bands at 433 and 476 nm are clearly visible in the TRF spectra of laurdan even at T = 0 fs. As time increases, the band at 476 nm shifts to the red while its intensity increases. The band at 433 nm also shifts slightly to the red, but loses intensity as time increases. The intensity of the 476 nm band reaches maximum at around 5 ps, where it is roughly twice as intense as that at 0 fs, and stays constant until lifetime decay is noticeable. The spectra were fit by two log-normal functions, each corresponding to the fluorescence from the LE state and ICT state. Relative populations and the average frequency of the ICT state are shown in Fig.2 and Fig.3, which represents the ICT dynamics and the subsequent solvation process, respectively. The TRF spectra illustrate unambiguously how the ICT and the solvation processes take place for laurdan dissolved in ethanol. First of all, the ICT and the solvation occur in serial. Second, the ICT proceeds in several time scales exhibiting heterogeneity of the molecular conformation in liquid. About one third of the laurdan molecules undergoes ICT immediately in much less than <50 fs time scale. Rest of them undergoes ICT by two time constants, 6.4 ps and 28 ps. The ICT state then undergoes solvation process by 47 ps time constants. Because the molecule is large and flexible, fast inertial component was not observed. In conclusion, TRF spectra in femtosecond resolution reveal detailed intramolecular charge transfer process of laurdan. The ICT process shows a series of time scales due to the conformational heterogeneity in solution. (authors)

  15. Electron transfer from CO2lg-bullet- to perylene in cyclohexane

    International Nuclear Information System (INIS)

    CO2lg-bullet- formed by the reactions of the electron with CO2 in cyclohexane transfers an electron to perylene with a rate constant of 2.9 x 1010 M-1s-1. G?580nm for the perylene radical anion is 9 x 103 molecules (100 eV)-1 M -1 cm-1. The transfer of an electron from CO2lg-bullet+ to an aromatic molecule is a significant process when CO2 is used as an electron scavenger in solution where the production of excited states of the aromatic molecule is studied. 24 refs., 6 figs

  16. Spin-Forster transfer in optically excited quantum dots

    OpenAIRE

    Govorov, Alexander O

    2005-01-01

    The mechanisms of energy and spin transfer in quantum dot pairs coupled via the Coulomb interaction are studied. Exciton transfer can be resonant or phonon-assisted. In both cases, the transfer rates strongly depend on the resonance conditions. The spin selection rules in the transfer process come from the exchange and spin-orbit interactions. The character of energy dissipation in spin transfer is different than that in the traditional spin currents. The spin-dependent phot...

  17. A questionable excited-state double-proton transfer mechanism for 3-hydroxyisoquinoline.

    Science.gov (United States)

    Zhao, Jinfeng; Chen, Junsheng; Cui, Yanling; Wang, Jing; Xia, Lixin; Dai, Yumei; Song, Peng; Ma, Fengcai

    2015-01-14

    Two excited state proton transfer mechanisms of 3-hydroxyisoquinoline (3HIQ) in cyclohexane and acetic acid (ACID) were investigated based on the time-dependent density functional theory (TDDFT), suggesting a different double-proton transfer mechanism from the one proposed previously (J. Phys. Chem. B, 1998, 102, 1053). Instead of the formation of keto-enol complexes for 3HIQ self-association in cyclohexane, our theoretical results predicted that 3HIQ self-association exists in two forms: the normal form (enol/enol) and the tautomer form (keto/keto) in cyclohexane. A high barrier (37.023 kcal mol(-1)) between the 3HIQ enol monomer and 3HIQ keto monomer form indicated that the 3HIQ keto monomer in the ground state should not exist. In addition, the constructed potential energy surfaces of the ground state and excited state have been used to explain the proton transfer process. Upon optical excitation, the enol/enol form is excited to the first excited state, then transfers one proton, in turn, transition to the ground state to transfer another proton. A relatively low barrier (8.98 kcal mol(-1)) demonstrates two stable structures in the ground state. In view of the acetic acid solvent effect, two protons of 3HIQ/ACID transfer along the dihydrogen bonds in the first excited state, which is a different transfer mechanism to 3HIQ self-association. In addition, the proton transfer process provides a possible explanation for the fluorescence quenching observed. PMID:25418334

  18. Excited state Intramolecular Proton Transfer in Anthralin : Quantum Chemical Calculations and Fluorescence Spectra

    DEFF Research Database (Denmark)

    MØller, SØren; Andersen, Kristine B.

    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 results are interpreted as an indication of a large equilibrium geometry change upon excitation, associated with an excited-state intramolecular proton transfer process.

  19. Cross sections for resonant transfer and excitation in Feq++H2 collisions

    International Nuclear Information System (INIS)

    Resonant transfer and excitation (RTE) is investigated for Feq+ ions (q=23, 24, and 25) colliding with H2. For each charge state, cross sections for RTE were obtained from measurements of K x rays, emitted from the doubly excited intermediate state, coincident with single-electron capture by the incident ion. Additionally, for Fe25+ cross sections were obtained from measurements of coincidences between the two K x rays emitted from the intermediate state. These latter measurements provide information on the lifetimes of intermediate metastable states formed in the RTE process. In all cases, measured cross sections are in good agreement with calculations based on theoretical cross sections for dielectronic recombination (DR). Since RTE closely approximates DR, the results indicate that dielectronic-recombination cross sections involving K-shell excitation can be accurately predicted for highly charged iron ions. The results for Fe25+ show that metastable states are sufficiently short lived to be observable in the RTE (or DR) process for these hydrogenlike ions

  20. Constrained dynamics of excitation transfer due to a structured nano system

    International Nuclear Information System (INIS)

    Optical near-field phenomena observed in nanoscale systems were recently proposed to be applied to nanofabrication and nanophotonic devices. One of the elementary near-field processes is excitation transfer that originates from near-field photons localized in nanoscale space, which are different from propagating far-field photons. In recent experiments, excitation transfer has been controlled by semiconductor nanostructures under external fields. In this paper, we present a full-quantum-mechanical theory of near-field excitation transfer, and clarify the mechanism of effective interaction between matter and near-field photons.

  1. Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline

    DEFF Research Database (Denmark)

    Eriksen, Janus J.; Sauer, Stephan P. A.

    2013-01-01

    We investigate the failure of Time{Dependent Density Functional Theory (TDDFT) with the CAM{B3LYP exchange{correlation (xc) functional coupled to the Polarizable Embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge{transfer excitation in para{nitroaniline (pNA) in water by comparing with results obtained with the Coupled Cluster Singles and Doubles (CCSD) model also coupled to the Polarizable Embedding scheme (PE-CCSD). We determine the amount of charge separation in the ground and excited charge{transfer state with both methods by calculating the electric dipole moments in the gas phase and for 100 solvent congurations. We find that CAM-B3LYP overestimates the amount of charge separation inherent in the ground state and TDDFT/CAM-B3LYP drastically underestimates this amount in the excited charge-transfer state. As the errors in the solvatochromatic shift are found to be inverse proportional to thechange in dipole moment upon excitation, we conclude that the flaws in the description of the solvatochromic shift of this excitation are related to TDDFT itself and how it responds to the solvent e¿ects modelled by the PE scheme. We recommend therefore to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge{transfer excitations in molecular systems similar to pNA against higher{level ab initio wave function methods, like, e.g., CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a measure for charge{transfer character, we furthermore conrm that the di¿erence between excitation energies calculated with TDDFT and with the Tamm-Danco¿ approximation (TDA) to TDDFT is indeed correlated with the charge-transfer character of a given electronic transition both in vacuo and in solution. This is supported by a corresponding correlation between the change in dipole moment and the size of the index diagnostic for the investigated CT excitation.

  2. 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.

  3. Reaction coordinates for electron transfer reactions

    International Nuclear Information System (INIS)

    The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

  4. 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.

  5. Computational study of the electronic excitations of some anthocyanidins

    Science.gov (United States)

    Pereira, Grace K.; Galembeck, Sérgio E.

    1998-02-01

    Electronic excitations among the singlet states and those among the triplet states were studied for the flavylium cation as well as for some anthocianidins, that is, cations: apigeninidin, pelargonidin, luteolidinin, cyanidin and delphinidin. In order to carry out the calculations, the INDO 1/S and AM1 methods were used. The absorption spectra are reproduced in a general fashion. The progressive hydroxylation in the B-ring causes shift of the maximum absorption band to greater wavelengths due to a resonance increase in the fundamental state. The electronic excitations cause practically the same polarity variations in various compounds in both methods. For the triplet states, polarity increases only in the oxygen atoms. Practically, the same transitions also occur in the various states of the studied compounds. The INDO 1/S method provides results that are more coherent as to the electronic transitions of organic compounds than the AM1 method.

  6. 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

  7. Electron Transfer Dissociation of Milk Oligosaccharides

    OpenAIRE

    Han, Liang; Catherine E. Costello

    2011-01-01

    For structural identification of glycans, the classic collision-induced dissociation (CID) spectra are dominated by product ions that derived from glycosidic cleavages, which provide only sequence information. The peaks from cross-ring fragmentation are often absent or have very low abundances in such spectra. Electron transfer dissociation (ETD) is being applied to structural identification of carbohydrates for the first time, and results in some new and detailed information for glycan struc...

  8. Electron Transfer Dissociation Mass Spectrometry in Proteomics

    OpenAIRE

    Kim, Min-Sik; Pandey, Akhilesh

    2012-01-01

    Mass spectrometry has rapidly evolved to become the platform of choice for proteomic analysis. While CID remains the major fragmentation method for peptide sequencing, electron transfer dissociation (ETD) is emerging as a complementary method for characterization of peptides and post-translational modifications (PTMs). Here, we review the evolution of ETD and some of its newer applications including characterization of PTMs, non-tryptic peptides and intact proteins. We will also discuss some ...

  9. Promoting Interspecies Electron Transfer with Biochar

    OpenAIRE

    Shanshan Chen; Amelia-Elena Rotaru; Pravin Malla Shrestha; Malvankar, Nikhil S.; Fanghua Liu; Wei Fan; 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...

  10. Electron transfer in branched expanded pyridinium molecules.

    Czech Academy of Sciences Publication Activity Database

    Hromadová, Magdaléna; Lachmanová, Št?pánka; Pospíšil, Lubomír; Fortage, J.; Dupeyre, G.; Perruchot, Ch.; Lainé, P. P.

    Aveiro : DEMAC - Universidade de Aveiro, 2014. s. 99-99. [Meeting of the Portuguese Electrochemical Society /19./. Iberian Meeting of Electrochemistry /16./. 30.06.2014-02.07.2014, Aveiro] R&D Projects: GA ?R(CZ) GA14-05180S Grant ostatní: Rada Programu interní porpory projekt? mezinárodní spolupráce AV ?R M200401202 Institutional support: RVO:61388955 Keywords : electron transfer * electrochemistry * pyridinium Subject RIV: CG - Electrochemistry

  11. 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.)

  12. 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.)

  13. Electron-impact excitation for F-like selenium

    International Nuclear Information System (INIS)

    Electron-impact excitation cross sections from the low-lying 1s22s22p5 state of F-like selenium to singly excited states have been calculated. Our relativistic distorted-wave Born procedures have been used for the present calculations. Instead of atomic structure code GRASP, the latest version GRASP2 code is used as multiconfiguration Dirac-Fock atomic structure calculations. The present results have been comprehensively compared with earlier calculations. One of the motivations for the present work is that there are some discrepancies between our results and those of others. copyright 1997 The American Physical Society

  14. Distorted-wave theory of electron-ion collisions. I. Direct excitation and ionization

    International Nuclear Information System (INIS)

    A simple modification of the Bethe approximation for high-energy electron-atom collisions is considered for the purpose of analyzing the medium-energy scattering by highly stripped ionic targets. The effect of amplitude and phase distortions of the projectile-electron wave function on the excitation and ionization cross sections is approximately taken into account using the Elwert factor and the eikonal procedure, respectively. To facilitate the cross-section calculation further, the momentum-transfer-dependent part in the excitation matrix element is factored out in terms of an average transfer. The energy dependence of the various modification factors is studied in detail, showing that the distortion effect is large for ionic targets and decays only slowly with the scattering energy, as E/sup -1/2/. For a neutral target, however, the distortion effects roughly cancel with each other, thus resulting in the effectiveness of the unmodified Bethe cross section at much lower energies than one usually expects. The improved formalism is applied to estimate the total cross sections for the direct excitation and ionization of outer-shell electrons of the ionic target. The results are drastically changed from the unmodified Bethe approximation, and are generally in fair agreement with experimental data for all energies except in the threshold region

  15. Transfer coating by electron initiated polymerization

    International Nuclear Information System (INIS)

    The high speed and depth of cure possible with electron initiated monomer/oligomer coating systems provide many new opportunities for approaches to product finishing. Moreover, the use of transfer or cast coating using films or metallic surfaces offers the ability to precisely control the surface topology of liquid film surfaces during polymerization. Transfer coating such as with textiles has been a commercial process for many years and the synergistic addition of EB technology permits the manufacture of unusual new products. One of these, the casting paper used in the manufacture of vinyl and urethane fabrics, is the first EB application to use a drum surface for pattern replication in the coating. In this case the coated paper is cured against, and then released from, an engraved drum surface. Recent developments in the use of plastic films for transfer have been applied to the manufacture of transfer metallized and coated paper and paperboard products for packaging. Details of these and related processes are presented as well as a discussion of the typical product areas (e.g. photographic papers, release papers, magnetic media) using this high speed transfer technology

  16. Transfer coating by electron initiated polymerization

    International Nuclear Information System (INIS)

    The high speed and depth of cure possible with electron initiated monomer/oligomer coating systems provide many new opportunities for approaches to product finishing. Moreover, the use of transfer or cast coating using films or metallic surfaces offers the ability to precisely control the surface topology of liquid film surfaces during polymerization. Transfer coating such as with textiles has been a commercial process for many years and the synergistic addition of EB technology permits the manufacture of unusual new products. One of these, the casting paper used in the manufacture of vinyl and urethane fabrics, is the first EB application to use a drum surface for pattern replication in the coating. In this case the coated paper is cured against, and then released from, an engraved drum surface. Recent developments in the use of plastic films for transfer have been applied to the manufacture of transfer metallized and coated paper and paperboard products for packaging. Details of these and related processes will be presented as well as a discussion of the typical product areas using this high speed transfer technology. (author)

  17. TD-DFT assessment of the excited state intramolecular proton transfer in hydroxyphenylbenzimidazole (HBI) dyes.

    Science.gov (United States)

    Houari, Ymène; Chibani, Siwar; Jacquemin, Denis; Laurent, Adèle D

    2015-02-12

    Dyes undergoing excited state intramolecular proton transfer (ESIPT) received increasing attention during the last decades. If their unusual large Stokes shifts and sometimes dual-fluorescence signatures have paved the way toward new applications, the rapidity of ESIPT often prevents its investigation with sole experimental approaches, and theoretical simulations are often welcome, if necessary, to obtain a full rationalization of the observations. In the present paper, we evaluate both the absorption and the fluorescence spectra of, respectively, the enol and keto forms of a series of hydroxyphenylbenzimidazole (HBI) using a robust protocol based on Time-Dependent Density Functional Theory (TD-DFT). Optical spectra were obtained accounting for both vibronic and environmental effects. The aim of this work is therefore not to evaluate the radiationless pathway going through the twisted ESIPT structures, though excited-state reaction paths between enol and keto forms have been rationalized. First we have compared three dyes differing by the strength of the donor groups, and we have quantified the impact of the flexible butyl chain substituting the imidazole side. In accordance with experiments, we show that the presence of a dialkylamino auxochrome allows to tune the excited-state potential energy surface leading to a weaker tendency to ESIPT. This trend is rationalized in terms of both structural and electronic effects. Next, larger hydroxyphenyl-phenanthroimidazole (HPI) were considered to assess the impact of a stronger ?-delocalization. 0-0 energies and vibrationally resolved spectra of the corresponding fluoroborate derivatives were studied as well. The dialkylamino auxochrome significantly decreases the 0-0 energies due to the presence of an important charge transfer character, while the addition of a BODIPY moiety induces a change of the emission signature now localized on the BODIPY side rather than on the NBO core. PMID:25426781

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

    Science.gov (United States)

    Duque, H. V.; Do, T. P. T.; Lopes, M. C. A.; Konovalov, D. A.; White, R. D.; Brunger, M. J.; Jones, D. B.

    2015-03-01

    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.

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

    Science.gov (United States)

    Duque, H V; Do, T P T; Lopes, M C A; Konovalov, D A; White, R D; Brunger, M J; Jones, D B

    2015-03-28

    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. PMID:25833579

  20. Study of localised electronic excitations by neutron scattering

    International Nuclear Information System (INIS)

    Neutron scattering allows the spectroscopic study of the energy levels associated with both nuclear and electronic motion. With the advent of neutron sources with higher incident energy the upper limit of the range covered will be extended from say 0.1 eV to perhaps 1 eV. It is therefore appropriate to consider what types of experiment will be profitable in this area. The brief for these lectures is to consider localised electronic excitations. The first part of the lectures is concerned with the theory of such transitions between electronic energy levels, assuming fixed nuclei. Such transitions can be observed in principle at all Q, but the form factors cause the cross sections to fall off rapidly at large Q. In addition to strictly localised levels a brief discussion of possible transitions to exciton states is given. These are co-operative excitations with well defined momentum q which must be conserved in the transition, but are not being considered elsewhere in this meeting, although co-operative magnetic excitations (spin waves) are discussed by Lindgard, while electronic band states are considered by Cooke

  1. Monitoring molecule dynamics by free electron transfer

    International Nuclear Information System (INIS)

    Complete text of publication follows. Phenol radical cations and phenoxyl radicals were observed as direct products of free electron transfer from phenol-type solute molecules to solvent parent radical cations generated by ionizing irradiation. The finding of the two species in comparable amounts is attributed to the dynamics of the phenol molecule oscillating in the femtosecond range by vibration, rotation and other motions. Analyzing the hetero group rotation around the C-OH bond, two border line conformer structures can be distinguished such as the plane molecule and a rotated one where the substituent is twisted by 90 deg. Assuming a promt free electron transfer (FET) in each encounter, ionization of all rotation-caused conformer states should happen, resulting in different products. This seem reasonable under the aspect that accompanied with the rotation also electron distribution should change. Quantum-chemical calculations indicate that for phenol as solute primarily its conformers with perpendicular C-OH axis orientation to the aromatic ring tend to deprotonate after ionization. A quite similar behavior could be predicted for the heteroanalogous thio- and selenophenols. Quite generally considerable changes in the electron distribution of the ground state molecules with the twisting angle of the -OH, -SH and -SeH groups could be calculated, with the greatest differences between 'parallel' and 'perpendicular' conformations. On the assumption that FET projects the equilibrium solute conformer distribution onto the solute cation conformer one it is demonstrated that the experimental findings are compatible with a simple solute-cation internal relaxation model

  2. 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.

  3. Optogalvanic monitoring of collisional transfer of laser excitation energy in a neon RF plasma

    International Nuclear Information System (INIS)

    The optogalvanic signals produced by pulsed laser excitation of 1s5--2p8 and 1s5-2p9 (Paschen notation) transition by a ?29 MHz radiofrequency (rf) discharge at ?5 torr have been investigated. The optogalvanic signal produced by 1s5-2p9 excitations indicates that there is transfer of energy from the 2p9 state to some other state. The state to which this energy is transferred is believed to be mainly the 2p8 state because of the very small energy gap between the 2p9 and 2p8 states. To verify this transfer, the 1s5-2p8 transition was investigated. The similarity of the temporal profiles of the optogalvanic signals in both excitations confirms the collisional transfer of laser excitation energy from 2p9 to 2p8

  4. 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.

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

    DEFF Research Database (Denmark)

    Olsen, Thomas; Gavnholt, Jeppe

    2009-01-01

    We present a model for desorption induced 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 regimes 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.

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

    Science.gov (United States)

    Sedelnikova, O. V.; Bulusheva, L. G.; Asanov, I. P.; Yushina, I. V.; Okotrub, A. V.

    2014-04-01

    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.

  7. 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.

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

    International Nuclear Information System (INIS)

    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 S2?S1 internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S1 state to the keto isomer in S2 state

  9. Promoting Interspecies Electron Transfer with Biochar

    Science.gov (United States)

    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 biochar may enhance methane production from organic wastes under anaerobic conditions. PMID:24846283

  10. 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.

  11. Electron-impact excitation of complex atoms and ions

    International Nuclear Information System (INIS)

    A new R-matrix approach for calculating cross sections and rate coefficients for electron-impact excitation of complex atoms and ions is described. This approach, based on an expansion of the total wavefunction in target configurations rather than in individual target states and taking advantage of the special status of the scattered electron in the collisional wavefunction, enables the angular integrals to be performed very much more efficiently than hitherto. It also enables electron correlation effects in the target and in the electron-target collision complex to be treated consistently, eliminating pseudo-resonances which have caused serious difficulties in some earlier work. A major new program package RMATRIX II has been written that implements this approach and, as an example, electron-impact excitation of Fe2+ is considered where the four target configurations 3d6, 3d54s, 3d54p and 3d54d are retained in the expansion of the total wavefunction. RMATRIX II is compared with the standard R-matrix program package and is found to be much more efficient showing that accurate electron scattering calculations involving complex targets, such as the astrophysically important low ionization stages of iron-peak elements, are now possible. (author)

  12. Dynamics and mechanisms of photoinduced electron transfer and related phenomena

    International Nuclear Information System (INIS)

    This book contains papers which examine the fundamental aspects of photoinduced electron transfer reactions, an area in which a number of breakthroughs have recently occurred. This book is divided into four parts. Parts I and II are mainly concerned with the fundamental aspects of the inter- and intra-molecular charge transfer, electron transfer and related phenomena such as solvents effect, and solvation dynamics. Part III is concerned with electron transfer and energy transfer phenomena in polymers, films, crystals, and other confined systems. In Part IV, the mechanisms of the energy and electron transfer in biological photosynthetic systems, proteins and reaction center systems are discussed. (author). refs., figs

  13. Motion-enhanced quantum entanglement in the dynamics of excitation transfer

    CERN Document Server

    Song, Wei; Yang, Ming; Cao, Zhuo-Liang

    2014-01-01

    We investigate the dynamics of entanglement in the excitation transfer through a chain of interacting molecules. In the case of two-molecule coupled to noisy environments we show that entanglement can be further enhanced if the distance between the molecules is oscillating. Our results demonstrate that motional effect plays a constructive role on quantum entanglement in the dynamics of excitation transfer. This mechanism might provide useful guideline for designing artificial systems to battle against decoherence.

  14. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Ryosuke [JST-CREST, Venture Business Laboratory, Center for Advanced Science and Innovation, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871 (Japan)]. E-mail: ryo@mls.eng.osaka-u.ac.jp; Wang, Peng [Faculty of Science and Technology, Kwansei Gakuin University, Gakuen, Sanda, Hyogo 669-1337 (Japan); Fujii, Ritsuko [Department of Physics, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan); Koyama, Yasushi [Faculty of Science and Technology, Kwansei Gakuin University, Gakuen, Sanda, Hyogo 669-1337 (Japan); Hashimoto, Hideki [Department of Physics, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan); PRESTO-JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan); Kanematsu, Yasuo [JST-CREST, Venture Business Laboratory, Center for Advanced Science and Innovation, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871 (Japan)

    2006-07-15

    The intra- and inter-molecular vibrational relaxation in the electronic excited state (1B{sub u}{sup +}) 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 1B{sub u}{sup +}(v=1) or 1B{sub u}{sup +}(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 1B{sub u}{sup +}(v=2) state hot luminescence from the 1B{sub u}{sup +}(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 1B{sub u}{sup +}(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.

  16. 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

  17. Excitation transfer from a donor to acceptors in condensed media: a unified approach

    International Nuclear Information System (INIS)

    The paper reports a study of the direct energy transfer from an excited donor molecule to acceptors randomly embedded in a host matrix or immersed in a fluid. From the exact, closed-form expressions for the ensemble-averaged decay of the donor excitation, the approximate forms valid for low acceptor concentrations are determined

  18. Zeeman deceleration of electron-impact-excited metastable helium atoms

    Science.gov (United States)

    Dulitz, Katrin; Tauschinsky, Atreju; Softley, Timothy P.

    2015-03-01

    We present experimental results that demonstrate—for the first time—the Zeeman deceleration of helium atoms in the metastable 23S1 state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m s?1 to a final velocity of 370 m s?1. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Metastable helium is efficiently generated even in a mixture of other noble gases that have much lower excitation energies. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.

  19. High resolution IR diode laser study of collisional energy transfer between highly vibrationally excited monofluorobenzene and CO2: The effect of donor fluorination on strong collision energy transfer

    Science.gov (United States)

    Kim, Kilyoung; Johnson, Alan M.; Powell, Amber L.; Mitchell, Deborah G.; Sevy, Eric T.

    2014-12-01

    Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm-1) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ˜41 000 cm-1 was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1?S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ?E region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ?E region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency.

  20. Electronic Excited States in Bilayer Graphene Double Quantum Dots

    OpenAIRE

    Volk, Christian; Fringes, Stefan; Terrés, Bernat; Dauber, Jan; Engels, Stephan; Trellenkamp, Stefan; Stampfer, Christoph

    2011-01-01

    We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features addition energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states ...

  1. Electronic Excitations from a Perturbative LDA+GdW Approach

    OpenAIRE

    Rohlfing, Michael

    2010-01-01

    We discuss an efficient approach to excited electronic states within ab-initio many-body perturbation theory (MBPT). Quasiparticle corrections to density-functional theory result from the difference between metallic and non-metallic dielectric screening. They are evaluated as a small perturbation to the DFT-LDA band structure, rather than fully calculating the self energy and evaluating its difference from the exchange-correlation potential. The dielectric screening is desri...

  2. 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.)

  3. 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.)

  4. 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.

  5. Resonant excitation of plasma wakefields using multiple electron bunches

    International Nuclear Information System (INIS)

    We plan to resonantly excite plasma wakefields using a train of electron bunches separated by an integer number of plasma wavelengths. The multiple electron bunches are generated by a photocathode based RF gun by splitting the laser beam into temporally separated pulses. The amplitude of the wakefields generated by the sequence of bunches is expected to be higher than that generated if all charge had been in only one bunch, because this single bunch would be considerably longer than the individual sub-bunches due to space charge effects in our gun

  6. Electron-transfer acceleration investigated by time resolved infrared spectroscopy.

    Science.gov (United States)

    Vl?ek, Antonín; Kvapilová, Hana; Towrie, Michael; Záliš, Stanislav

    2015-03-17

    Ultrafast electron transfer (ET) processes are important primary steps in natural and artificial photosynthesis, as well as in molecular electronic/photonic devices. In biological systems, ET often occurs surprisingly fast over long distances of several tens of angströms. Laser-pulse irradiation is conveniently used to generate strongly oxidizing (or reducing) excited states whose reactions are then studied by time-resolved spectroscopic techniques. While photoluminescence decay and UV-vis absorption supply precise kinetics data, time-resolved infrared absorption (TRIR) and Raman-based spectroscopies have the advantage of providing additional structural information and monitoring vibrational energy flows and dissipation, as well as medium relaxation, that accompany ultrafast ET. We will discuss three cases of photoinduced ET involving the Re(I)(CO)3(N,N) moiety (N,N = polypyridine) that occur much faster than would be expected from ET theories. [Re(4-N-methylpyridinium-pyridine)(CO)3(N,N)](2+) represents a case of excited-state picosecond ET between two different ligands that remains ultrafast even in slow-relaxing solvents, beating the adiabatic limit. This is caused by vibrational/solvational excitation of the precursor state and participation of high-frequency quantum modes in barrier crossing. The case of Re-tryptophan assemblies demonstrates that excited-state Trp ? *Re(II) ET is accelerated from nanoseconds to picoseconds when the Re(I)(CO)3(N,N) chromophore is appended to a protein, close to a tryptophan residue. TRIR in combination with DFT calculations and structural studies reveals an interaction between the N,N ligand and the tryptophan indole. It results in partial electronic delocalization in the precursor excited state and likely contributes to the ultrafast ET rate. Long-lived vibrational/solvational excitation of the protein Re(I)(CO)3(N,N)···Trp moiety, documented by dynamic IR band shifts, could be another accelerating factor. The last discussed process, back-ET in a porphyrin-Re(I)(CO)3(N,N) dyad, demonstrates that formation of a hot product accelerates highly exergonic ET in the Marcus inverted region. Overall, it follows that ET can be accelerated by enhancing the electronic interaction and by vibrational excitation of the reacting system and its medium, stressing the importance of quantum nuclear dynamics in ET reactivity. These effects are experimentally accessible by time-resolved vibrational spectroscopies (IR, Raman) in combination with quantum chemical calculations. It is suggested that structural dynamics play different mechanistic roles in light-triggered ET involving electronically excited donors or acceptors than in ground-state processes. While TRIR spectroscopy is well suitable to elucidate ET processes on a molecular-level, transient 2D-IR techniques combining optical and two IR (or terahertz) laser pulses present future opportunities for investigating, driving, and controlling ET. PMID:25699661

  7. 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...

  8. 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.

  9. Muon transfer induced by collisional excitation of helium muonide He?+ after muon catalyzed fusion

    International Nuclear Information System (INIS)

    Possibility of negative muon transfer from helium muonide He?+ to T (or D) through collisional excitation after muon catalyzed fusion has been pointed out. The transfer process depends on the efficiency of collisional excitation of He?+ in the medium of tritium or deuterium. It is argued that tritium has larger nuclear stopping power and better excitation efficiency than deuterium. This effect is in the same direction as the tritium concentration dependence of muon loss probability in recent experimental work. (author) 9 refs.; 3 figs

  10. Fast photoinduced electron transfer through DNA intercalation.

    OpenAIRE

    Murphy, C. J.; Arkin, M. R.; Ghatlia, N. D.; Bossmann, S.; Turro, N. J.; Barton, J. K.

    1994-01-01

    We report evidence for fast photoinduced electron transfer mediated by the DNA helix that requires metal complexes that are avid intercalators of DNA. Here the donor bis(phenanthroline)(dipyridophenazine)ruthenium(II) [Ru(phen)2dppz2+] and acceptor bis(9,10-phenanthrenequinone diimine)(phenanthroline)rhodium(III) [Rh(phi)2phen3+] intercalate into DNA with Kb > 10(6) M-1. Luminescence quenching experiments in the presence of two different lengths of DNA yield upward-curving Stern-Volmer plots ...

  11. Self-regulation of photoinduced electron transfer by a molecular nonlinear transducer.

    Science.gov (United States)

    Straight, Stephen D; Kodis, Gerdenis; Terazono, Yuichi; Hambourger, Michael; Moore, Thomas A; Moore, Ana L; Gust, Devens

    2008-05-01

    Organisms must adapt to survive, necessitating regulation of molecular and subcellular processes. Green plant photosynthesis responds to potentially damaging light levels by downregulating the fraction of excitation energy that drives electron transfer. Achieving adaptive, self-regulating behaviour in synthetic molecules is a critical challenge that must be met if the promises of nanotechnology are to be realized. Here we report a molecular pentad consisting of two light-gathering antennas, a porphyrin electron donor, a fullerene electron acceptor and a photochromic control moiety. At low white-light levels, the molecule undergoes photoinduced electron transfer with a quantum yield of 82%. As the light intensity increases, photoisomerization of the photochrome leads to quenching of the porphyrin excited state, reducing the quantum yield to as low as 27%. This self-regulating molecule modifies its function according to the level of environmental light, mimicking the non-photochemical quenching mechanism for photoprotection found in plants. PMID:18654524

  12. Electron Transfer in Myoglobin-based Single-Electron Transistors

    Science.gov (United States)

    Li, Debin; Gannett, Peter; Lederman, David

    2009-03-01

    The mechanism of electron transfer by myoglobin was investigated using nanometer-gap platinum electrodes fabricated by breaking a small junction by electromigration at cryogenic temperatures. The experimental results suggest single electron transport behavior is mediated by resonance of the electronic levels of the heme group in a single myoglobin protein. Evidence for a two-step electron tunneling process, resulting from the structural relaxation of the protein with the addition of a single electron, was observed. Our experimental results show that the slow protein relaxation may result in resonant tunneling and the fast protein relaxation is the condition of two-step resonant tunneling behavior. The conformation and orientation of myoglobin in the gap of electrodes may significantly affect the conductance of these devices. The calculation for the conductance graph as a function of gate voltage and bias voltage was performed with the rate equations for electron tunneling via discrete quantum states and considering the two-step process. The results of calculation match those of our experiment.

  13. Absolute cross sections for electronic excitation of furan by electron impact

    Science.gov (United States)

    Regeta, Khrystyna; Allan, Michael

    2015-01-01

    We measured differential cross sections for exciting the three lowest electronically excited states in furan, as functions both of electron energy and of scattering angle. Emphasis of the present work is on recording detailed excitation functions, revealing resonances in the excitation process. The cross section for the first triplet state has a shoulder in the first 2 eV above threshold, assigned to the high-energy tails of the shape resonances, followed by two peaks at 6.5 and 8.0 eV, assigned to two 2(? ,?*2) core-excited shape resonances with substantial configuration mixing. The excitation mechanism thus closely follows that of the prototype case of ethene, except that as the number of double bonds doubles, the numbers of both shape and core-excited resonances also double. The cross section for the singlet states around 6 eV (primarily the S21B2 state) rises linearly with energy and attains very high values in the forward direction as expected for a dipole-allowed transition, but has a vertical onset at higher scattering angles, possibly due to a threshold core-excited 2(? ,?*3 s ¯) resonance responsible also for dissociative attachment. Elastic cross sections are also presented. Both elastic and inelastic absolute values compare favorably with existing measurements where available, except very near threshold. The results are compared to existing calculations.

  14. 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 $^...

  15. Disturbed excitation energy transfer in Arabidopsis thaliana mutants lacking minor antenna complexes of photosystem II.

    Science.gov (United States)

    Dall'Osto, Luca; Ünlü, Caner; Cazzaniga, Stefano; van Amerongen, Herbert

    2014-12-01

    Minor light-harvesting complexes (Lhcs) CP24, CP26 and CP29 occupy a position in photosystem II (PSII c' plants between the major light-harvesting complexes LHCII and the PSII core subunits. Lack of minor Lhcs in vivo causes impairment of PSII organization, and negatively affects electron transport rates anc photoprotection capacity. Here we used picosecond-fluorescence spectroscopy to study excitation-energy transfer (EET) in thylakoid membranes isolated from Arabidopsis thaliana wild-type plants and knockout lines depleted of either two (koCP26/24 and koCP29/24) or all minor Lhcs (NoM). In the absence of all minor Lhcs. the functional connection ofLHCII to the PSII cores appears to be seriously impaired whereas the "disconnected" LHCII is substantially quenched. For both double knock-out mutants, excitation trapping in PSII is faster than in NoM thylakoids but slower than in WT thylakoids. In NoM thylakoids, the loss of all minor Lhcs is accompanied by an over-accumulation ofLHCII, suggesting a compensating response to the reduced trapping efficiency in limiting light, which leads to a photosynthetic phenotype resembling that of low-light-acclimated plants. Finally. fluorescence kinetics and biochemical results show that the missing minor complexes are not replaced by other Lhcs, implying that they are unique among the antenna subunits and crucial for the functioning and macroorganization of PSII. PMID:25291424

  16. Electronic excited States of polynucleotides: a study by electroabsorption spectroscopy.

    Science.gov (United States)

    Krawczyk, Stanislaw; Luchowski, Rafal

    2007-02-01

    Electroabsorption spectra were obtained for single-stranded polynucleotides poly(U), poly(C), poly(A), and poly(G) in glycerol/water glass at low temperature, and the differences in permanent dipole moment (Deltamu) and polarizability (Deltaalpha) were estimated for several spectral ranges covering the lowest energy absorption band around 260 nm. In each spectral range, the electrooptical parameters associated with apparent features in the absorption spectrum exhibit distinct values representing either a dominant single transition or the resultant value for a group of a relatively narrow cluster of overlapping transitions. The estimated spacing in energy between electronic origins of these transitions is larger than the electronic coupling within the Coulombic interaction model which is usually adopted in computational studies. The electroabsorption data allow us to distinguish a weak electronic transition associated with a wing in polynucleotide absorption spectra, at an energy below the electronic origin in absorption spectra of monomeric nucleobases. In poly(C) and poly(G), these low-energy transitions are related to increased values of Deltamu and Deltaalpha, possibly indicating a weak involvement of charge resonance in the respective excited states. A model capable of explaining the origin of low-energy excited states, based on the interaction of pipi* and npi* transitions in neighboring bases, is introduced and briefly discussed on the grounds of point dipole interaction. PMID:17266277

  17. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    Science.gov (United States)

    Hong, Woo-Pyo; Jung, Young-Dae

    2014-08-01

    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.

  18. 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

  19. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

    2014-08-15

    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.

  20. Effect of electron flux on electronic-excitation-induced phase separation in GaSb nanoparticles

    Science.gov (United States)

    Yasuda, H.; Tanaka, A.; Usui, H.; Mori, H.; Lee, J. G.

    2006-02-01

    We studied the effect of electron flux on phase separation induced by electronic excitation in GaSb nanoparticles, in order to see whether the phase separation is characterized as a cooperative phenomenon, in which a nonlinear relation may be found between density of excited states introduced and the efficiency of the phase separation or not. The phase separation to two phases consisting of an antimony core and a gallium shell proceeds abruptly after incubation time with increasing electron dose and does only at the flux above a threshold value. It is suggested that such nonlinear behaviors take place as a cooperative phenomenon among electronic-excitation effect, nano-size effect and temperature.

  1. 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

  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. 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.

  4. Electron transfer pathways in microbial oxygen biocathodes

    International Nuclear Information System (INIS)

    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 O2 reduction by heme compounds. Here we showed that 1 ?M 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 O2 reduction to H2O2 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.

  5. Tracking the charge and spin dynamics of electronic excited states in inorganic complexes

    Science.gov (United States)

    Gaffney, Kelly

    2015-03-01

    Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications. These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes. Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2'-bipyridine)N]2 N - 4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations. Work supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  6. Electron impact excitation of zinc atoms studied by the electron-photon polarization correlation method

    International Nuclear Information System (INIS)

    Full text: A high resolution electron impact spectrometer incorporating both the unpolarised and polarized electron beams is developed to study excitation of multi-electron metal atoms, initially zinc. Choice of electron polarization (zero, 28 or 75%) will highlight the spin-dependent effects. Detection of the scattered electron and polarized decay photon will be used to measure differential Stokes parameters and spin up-down asymmetries. Symmetry-and spin-forbidden excitation of the 41D and 43D states of zinc is expected to show a full range of many-electron effects which need to be adequately modelled. Details of experiment and preliminary results will be presented at the Congress. Copyright (2005) Australian Institute of Physics

  7. Electrostatic mode coupling of beat-excited electron plasma waves

    International Nuclear Information System (INIS)

    The process of beat excitation of electron plasma waves in a plasma containing a density ripple is studied theoretically, experimentally, and computationally. A single theoretical model has been developed which, for modest experimental parameters, predicts a new beat wave saturation mechanism. This mechanism involves the excitation of a spectrum of secondary electrostatic modes which divert pump energy from the beat wave and can lead to saturation of the beat wave at an amplitude well below that expected for relativistic detuning. Experiments designed to study the coupled mode spectrum were performed. The measured properties of the electrostatic spectrum are in reasonable agreement with the theory. To bridge the gap between the idealized model and the experiment, computer simulations were performed for a variety of parameters

  8. Mechanistic studies of photoinduced spin crossover and electron transfer in inorganic complexes.

    Science.gov (United States)

    Zhang, Wenkai; Gaffney, Kelly J

    2015-04-21

    Electronic excited-state phenomena provide a compelling intersection of fundamental and applied research interests in the chemical sciences. This holds true for coordination chemistry, where harnessing the strong optical absorption and photocatalytic activity of compounds depends on our ability to control fundamental physical and chemical phenomena associated with the nonadiabatic dynamics of electronic excited states. The central events of excited-state chemistry can critically influence the dynamics of electronic excited states, including internal conversion (transitions between distinct electronic states) and intersystem crossing (transitions between electronic states with different spin multiplicities), events governed by nonadiabatic interactions between electronic states in close proximity to conical intersections, as well as solvation and electron transfer. The diversity of electronic and nuclear dynamics also makes the robust interpretation of experimental measurements challenging. Developments in theory, simulation, and experiment can all help address the interpretation and understanding of chemical dynamics in organometallic and coordination chemistry. Synthesis presents the opportunity to chemically engineer the strength and symmetry of the metal-ligand interactions. This chemical control can be exploited to understand the influence of electronic ground state properties on electronic excited-state dynamics. New time-resolved experimental methods and the insightful exploitation of established methods have an important role in understanding, and ideally controlling, the photophysics and photochemistry of transition metal complexes. Techniques that can disentangle the coupled motion of electrons and nuclear dynamics warrant emphasis. We present a review of electron localization dynamics in charge transfer excited states and the dynamics of photoinitiated spin crossover dynamics. Both electron localization and spin crossover have been investigated by numerous research groups with femtosecond resolution spectroscopy, but challenges in experimental interpretation have left significant uncertainty about the molecular properties that control these phenomena. Our Account will emphasize how tailoring the experimental probe, femtosecond resolution vibrational anisotropy for electron localization, and femtosecond resolution hard X-ray fluorescence for spin crossover can make a significant impact on the interpretability of experimental measurements. The emphasis on thorough and robust interpretation has also led to an emphasis on simpler molecular systems. This enables iteration between experiment and theory, a requirement for the development of a more predictive understanding of electronic excited-state phenomena and an essential step to the development of design rules for solar materials. PMID:25789406

  9. Fermi surface fluctuations and single electron excitations near Pomeranchuk instability in two dimensions

    CERN Document Server

    Dell'Anna, L; Anna, Luca Dell'; Metzner, Walter

    2005-01-01

    A metallic electron system near an orientational symmetry breaking Pomeranchuk instability is characterized by a ''soft'' Fermi surface with enhanced collective fluctuations. We analyze fluctuation effects in a two-dimensional electron system on a square lattice in the vicinity of a Pomeranchuk instability with d-wave symmetry, using a phenomenological model which includes interactions with a small momentum transfer only. We compute the dynamical density correlations with a d-wave form factor for small momenta and frequencies, the dynamical effective interaction due to fluctuation exchange, and the electron self-energy. At the quantum critical point the density correlations and the dynamical forward scattering interaction diverge with a dynamical exponent z=3. The singular forward scattering leads to large self-energy corrections, which destroy Fermi liquid behavior over the whole Fermi surface except near the Brillouin zone diagonal. The decay rate of single-particle excitations, which is related to the widt...

  10. 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

  11. Electron-electron interaction effects on optical excitations in semiconducting single-walled carbon nanotubes

    OpenAIRE

    Zhao, Hongbo; Mazumdar, Sumit

    2004-01-01

    We report correlated-electron calculations of optically excited states in ten semiconducting single-walled carbon nanotubes with a wide range of diameters. Optical excitation occurs to excitons whose binding energies decrease with the increasing nanotube diameter, and are smaller than the binding energy of an isolated strand of poly-(paraphenylene vinylene). The ratio of the energy of the second optical exciton polarized along the nanotube axis to that of the lowest exciton ...

  12. 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.)

  13. 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.)

  14. 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.

  15. 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)

  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. Role of 3,5-dimethyl anisole (DMA) as an electron donor in photoinduced electron transfer (ET) reactions

    Science.gov (United States)

    Sinha, S.; De, R.; Ganguly, T.

    1997-01-01

    The present investigation was carried out to reveal the nature of photoinduced bimolecular quenching reactions, e.g. electron transfer (ET) and energy transfer processes within the donor DMA and acceptor 2-nitrofluorene (2NF) molecules in polar acetonitrile (ACN) fluid solution at the ambient temperature. From the observed large negative values of ?G (the energy gap between the locally excited, LE and radical ion pair or RIP states) when one of the chromorphores was excited along with large R0 ( ˜27 Å), Förster critical transfer distance between the donor and acceptor measured from the considerable overlapping region of donor DMA emission with acceptor absorption and nearly 100% theoretical transfer efficiency ( T) value of the Förster type energy transfer the concurrent occurrences of the two processes, photoinduced ET and excitational energy transfer, were inferred. Moreover it was suggested that ET reaction within the present donor and acceptor systems is of outersphere type as evidenced from the large negative value of ?G (˜ -2.3 eV).

  18. Excitation transfer and luminescence in porphyrin-carbon nanotube complexes

    OpenAIRE

    Magadur, Gurvan; Lauret, Jean-Sébastien; Alain-Rizzo, Valérie; Voisin, C; Roussignol, Ph.; Deleporte, Emmanuelle; Delaire, Jacques

    2007-01-01

    Functionalization of carbon nanotubes with hydrosoluble porphyrins (TPPS) is achieved by "$\\pi$-stacking". The porphyrin/nanotube interaction is studied by means of optical absorption, photoluminescence and photoluminescence excitation spectroscopies. The main absorption line of the porphyrins adsorbed on nanotubes exhibits a 120 meV red shift, which we ascribe to a flattening of the molecule in order to optimize $\\pi-\\pi$ interactions. The porphyrin-nanotube complex shows a...

  19. Directed excitation transfer in vibrating chains by external fields

    CERN Document Server

    Muelken, Oliver

    2010-01-01

    We study the coherent dynamics of excitations on vibrating chains. By applying an external field and matching the field strength with the oscillation frequency of the chain it is possible to obtain an (average) transport of an initial Gaussian wave packet. We distinguish between a uniform oscillation of all nodes of the chain and the chain being in its lowest eigenmode. Both cases can lead to directed transport.

  20. Electron transfer in gas surface collisions

    International Nuclear Information System (INIS)

    In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

  1. Defect nucleation and transformation at electron excitation relaxation in solids

    International Nuclear Information System (INIS)

    Basic theoretical notions concerned with defect nucleation and transformation mechanisms at electron excitation relaxation in solids are delivered. Classification of such mechanisms according to the type of previous instability of local atomic configuration is presented, and basic characteristics of these mechanisms are described. A review on the theory of elctrostatic mechanisms being decisive in defect nucleation in semiconductors is presented. Models of the mechanisms with vibrational instability in ionic crystals and semiconductors are described. Specific features of defect formation in amorphous semiconductors under visible and other radiations both in vitreous semiconductors and in materials like hydrogenized amorphous silicon are considered

  2. 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

  3. Magic Angle Electron Energy Loss Spectroscopy (MAEELS) of core electron excitation in anisotropic systems

    CERN Document Server

    Sun, Y K

    2004-01-01

    A general theory for the core-level electron excitation of anisotropic systems using angular integrated electron energy-loss spectroscopy has been derived. We show that it is possible to define a magic angle condition at which the specimen orientation has no effect on the electron energy-loss spectra. We have not only resolved the existing discrepancy between different studies of the magic angle condition, but also extended its applicability to all anisotropic systems. We have demonstrated that magic angle electron energy loss spectroscopy is equivalent to the orientation averaged EELS, although the specimen remains stationary. Our analysis provides the theoretical framework for the comparison between theoretical calculation and experimental measurement of core-level electron excitation spectra in anisotropic systems. In addition to MAEELS, we have also discovered a magic orientation condition which will also give rise to orientationally averaged spectra. It's relation with the magic angle X-ray absorption sp...

  4. 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.

  5. The Liability of banks in electronic fund transfer transaction

    OpenAIRE

    Algudah, Fayyad

    1993-01-01

    The liability of banks in electronic fund transfer (EFT) transactions is discussed in this thesis under the British and the United States law. The thesis covers banks’ liability in electronic credit and debit transfers. It covers banks’ liability in Electronic Fund Transfer at the Point Of Sale (EFTPOS), Automatic Teller Machines (ATM) and home and office banking. Liability of banks in credit card transactions and cheque truncation falls outside the scope of this thesis. In ...

  6. 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...

  7. Excitation cross sections for electron scattering from K+ ions

    Science.gov (United States)

    Tayal, S. S.; Zatsarinny, O.

    2008-07-01

    The B -spline Breit-Pauli R -matrix method is used to investigate electron scattering from singly ionized potassium in the energy range from threshold to 400eV . The primary aim of the present work is to resolve discrepancies between the available experimental and theoretical cross sections for excitation of the K+ resonance lines. The multiconfiguration Hartree-Fock method with term-dependent nonorthogonal orbitals is employed for an accurate representation of the target wavefunctions. The close-coupling expansion includes 43 bound levels of K+ covering all possible terms of the lowest configurations 3p6 , 3p54s , 3p53d , 3p54p , 3p55s , and 3p54d . Our results confirm that the apparent cross section for the (60.1+60.8+61.3)nm emission line from the 3p5(4s+3d) levels in the crossed-beams experiment of Zapesochny {Zh. Eksp. Teor. Fiz. 90, 1972 (1986) [Sov. Phys. JETP 63, 1155 (1986)]} was normalized with an error of about a factor of 4. We also present the cross sections for excitation of the 3p54p , 3p55s , and 3p54d levels and discuss the cascade contribution from higher excited levels to the 3p54s and 3p53d levels.

  8. Zeeman deceleration of electron-impact-excited metastable helium atoms

    CERN Document Server

    Dulitz, Katrin; Softley, Timothy P

    2015-01-01

    We present experimental results that demonstrate - for the first time - the Zeeman deceleration of helium atoms in the metastable 2^3S_1state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m/s to a final velocity of 370 m/s. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.

  9. Analysis of Atomic Electronic Excitation in Nonequilibrium Air Plasmas

    Science.gov (United States)

    He, Xin; Dang, Wei-Hua; Jia, Hong-Hui; Yin, Hong-Wei; Zhang, Hai-Liang; Chang, Sheng-Li; Yang, Jun-Cai

    2014-09-01

    Electronic excitation of atoms is studied in nonequilibrium air plasmas with the electronic temperature between 8000 K and 20000 K. By using the modified Saha—Boltzmann equation, our simplified method takes into account significant radiative processes and strong self-absorption of the vacuum ultraviolet lines. Calculations are carried out at three trajectory points of the Fire II flight experiment. Good agreement with the detailed collisional-radiative model is obtained, and the performance of this method in applications to highly nonequilibrium conditions is better than Park's quasi-steady-state model and Spradian-9.0. A short discussion on the influence of optical thickness of the vacuum ultraviolet radiation is also given. It costs about 2.9 ms on the average to solve one cell of the shock layer on a low cost computer, which shows that the present method is fast and efficient.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. Excitation mechanism of Er in Si studied with a free-electron laser

    International Nuclear Information System (INIS)

    We investigate the influence of infrared illumination using a free-electron laser on the photoluminescence of erbium-implanted silicon material. In addition to the earlier reported quenching of the Er-related photoluminescence due to dissociation of the intermediate excitation stage, two more features of the energy transfer mechanism are revealed. In the wavelength dependence of the quenching effect a local extreme is detected for a beam energy of approximately 100 meV. A possible origin of this effect is discussed. Further, the current experiment revealed the presence of non-radiative recombination centers which could transfer their energy to Er ions under the influence of the infrared beam. The centers were found to be characterized by extremely slow generation and decay kinetics. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

  17. Interligand Electron Transfer in Heteroleptic Ruthenium(II) Complexes Occurs on Multiple Time Scales.

    Science.gov (United States)

    Stark, Charles W; Schreier, Wolfgang J; Lucon, Janice; Edwards, Ethan; Douglas, Trevor; Kohler, Bern

    2015-05-21

    The time-dependent localization of the metal-to-ligand charge transfer (MLCT) excited states of ruthenium(II) complexes containing 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) ligands was studied by femtosecond transient absorption spectroscopy. Time-resolved anisotropy measurements indicate that the excited state hops randomly among the three ligands of each complex by subpicosecond interligand electron transfer (ILET). Although the bpy- and phen-localized (3)MLCT states have similar energies and steady-state emission spectra, pronounced differences in their excited-state absorption spectra make it possible to observe changes in excited state populations using magic angle transient absorption measurements. Analysis of the magic angle signals shows that the excited electron is equally likely to be found on any of the three ligands approximately 1 ps after excitation, but this statistical distribution subsequently evolves to a Boltzmann distribution with a time constant of approximately 10 ps. The apparent contradiction between ultrafast ILET revealed by time-dependent anisotropy measurements and the slower ILET seen in magic angle measurements on the tens of picoseconds time scale is explained by a model in which the underlying rates depend dynamically on excess vibrational energy. The insight that ILET can occur over multiple time scales reconciles contradictory literature observations and may lead to improved photosensitizer performance. PMID:25896139

  18. Experimental and theoretical study on generalized oscillator strengths of the valence-shell electronic excitations in CF4

    Science.gov (United States)

    Watanabe, Noboru; Suzuki, Daisuke; Takahashi, Masahiko

    2011-02-01

    We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations in CF4. Experimentally momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations at 12.6, 13.8, and 14.8 eV are derived from EELS spectra measured at an incident electron energy of 3 keV. We also calculate GOS profiles using theoretical wave functions at the equation-of-motion coupled cluster singles and doubles level. There are good agreements between experiment and theory except for a significant discrepancy at small momentum transfer for the 1tl ? 3s Rydberg excitation at 12.6 eV. The experimental GOS profile for 1tl ? 3s exhibits a shape that is typical of a dipole allowed transition, while the excitation is formally dipole forbidden. This symmetry breaking behavior is rationally accounted for by qualitatively analyzing the nature of vibronic coupling effects. For the excitation band at 13.8 eV, a shoulder and extrema are observed in the GOS profile and are then found to be mainly due to the 21T2 transition. Furthermore, the theoretical GOS profile for the 21T2 transition exhibits a remarkable oscillatory pattern; its origin is discussed by considering multicenter interference effects. For the 14.8 eV excitation band, the predominant nondipole nature of the underlying transitions are revealed and comparisons with the theoretical calculations show that major contributions to this band come from the 4t2 ? 3p excitation.

  19. Experimental and theoretical study on generalized oscillator strengths of the valence-shell electronic excitations in CF4.

    Science.gov (United States)

    Watanabe, Noboru; Suzuki, Daisuke; Takahashi, Masahiko

    2011-02-14

    We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations in CF(4). Experimentally momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations at 12.6, 13.8, and 14.8 eV are derived from EELS spectra measured at an incident electron energy of 3 keV. We also calculate GOS profiles using theoretical wave functions at the equation-of-motion coupled cluster singles and doubles level. There are good agreements between experiment and theory except for a significant discrepancy at small momentum transfer for the 1t(l) ? 3s Rydberg excitation at 12.6 eV. The experimental GOS profile for 1t(l) ? 3s exhibits a shape that is typical of a dipole allowed transition, while the excitation is formally dipole forbidden. This symmetry breaking behavior is rationally accounted for by qualitatively analyzing the nature of vibronic coupling effects. For the excitation band at 13.8 eV, a shoulder and extrema are observed in the GOS profile and are then found to be mainly due to the 2(1)T(2) transition. Furthermore, the theoretical GOS profile for the 2(1)T(2) transition exhibits a remarkable oscillatory pattern; its origin is discussed by considering multicenter interference effects. For the 14.8 eV excitation band, the predominant nondipole nature of the underlying transitions are revealed and comparisons with the theoretical calculations show that major contributions to this band come from the 4t(2) ? 3p excitation. PMID:21322680

  20. Cold chemistry with electronically excited Ca+ Coulomb crystals

    International Nuclear Information System (INIS)

    Rate constants for chemical reactions of laser-cooled Ca+ ions and neutral polar molecules (CH3F, CH2F2, or CH3Cl) have been measured at low collision energies (coll>/kB=5-243 K). Low kinetic energy ensembles of 40Ca+ ions are prepared through Doppler laser cooling to form ''Coulomb crystals'' in which the ions form a latticelike arrangement in the trapping potential. The trapped ions react with translationally cold beams of polar molecules produced by a quadrupole guide velocity selector or with room-temperature gas admitted into the vacuum chamber. Imaging of the Ca+ ion fluorescence allows the progress of the reaction to be monitored. Product ions are sympathetically cooled into the crystal structure and are unambiguously identified through resonance-excitation mass spectrometry using just two trapped ions. Variations of the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of 40Ca+ involved in the laser-cooling cycle, and these are modeled by solving the optical Bloch equations for the eight-level system. Systematic variation of the steady-state populations over a series of reaction experiments allows the extraction of bimolecular rate constants for reactions of the ground state (2S1/2) and the combined excited states (2D3/2 and 2D3/2 and 2P1/2) of 40Ca+. These results are analyzed in the context of capture theories and ab initio electronic structure calculations of the reaction profiles. In each case, suppression of the ground state rate constant is explained by the presence of a submerged or real barrier on the ground state potential surface. Rate constants for the excited states are generally found to be in line with capture theories.

  1. Cold chemistry with electronically excited Ca+ Coulomb crystals.

    Science.gov (United States)

    Gingell, Alexander D; Bell, Martin T; Oldham, James M; Softley, Timothy P; Harvey, Jeremy N

    2010-11-21

    Rate constants for chemical reactions of laser-cooled Ca(+) ions and neutral polar molecules (CH(3)F, CH(2)F(2), or CH(3)Cl) have been measured at low collision energies (/k(B)=5-243 K). Low kinetic energy ensembles of (40)Ca(+) ions are prepared through Doppler laser cooling to form "Coulomb crystals" in which the ions form a latticelike arrangement in the trapping potential. The trapped ions react with translationally cold beams of polar molecules produced by a quadrupole guide velocity selector or with room-temperature gas admitted into the vacuum chamber. Imaging of the Ca(+) ion fluorescence allows the progress of the reaction to be monitored. Product ions are sympathetically cooled into the crystal structure and are unambiguously identified through resonance-excitation mass spectrometry using just two trapped ions. Variations of the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of (40)Ca(+) involved in the laser-cooling cycle, and these are modeled by solving the optical Bloch equations for the eight-level system. Systematic variation of the steady-state populations over a series of reaction experiments allows the extraction of bimolecular rate constants for reactions of the ground state ((2)S(1/2)) and the combined excited states ((2)D(3/2) and (2)P(1/2)) of (40)Ca(+). These results are analyzed in the context of capture theories and ab initio electronic structure calculations of the reaction profiles. In each case, suppression of the ground state rate constant is explained by the presence of a submerged or real barrier on the ground state potential surface. Rate constants for the excited states are generally found to be in line with capture theories. PMID:21090857

  2. Revisiting the Excitation Energy Transfer in the Fenna-Matthews-Olson Complex

    CERN Document Server

    Yi, X X; Oh, C H

    2012-01-01

    It is believed that the quantum coherence itself cannot explain the very high excitation energy transfer (EET) efficiency in the Fenna-Matthews-Olson (FMO) complex. In this paper, we show that this is not the case if the inter-site couplings take complex values. By phenomenologically introducing phases into the inter-site couplings, we obtain the EET efficiency as high as 0.8972 in contrast to 0.6781 with real inter-site couplings. Dependence of the excitation energy transfer efficiency on the initial states is elaborated. Effects of fluctuations in the site energies and inter-site couplings are also examined.

  3. 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 contributi...

  4. Angular correlations between electrons and photons in the electron excitation of helium and neon

    International Nuclear Information System (INIS)

    Angular correlations have been measured between the electrons exciting the 21P state in helium and the photons arising from the decay of this state to the ground state. Analysis of these angular correlations yield the ratio ? of the differential cross sections for the excitation of the m=1 and m=0 magnetic substates, and the relative phase chi of the scattering amplitudes for the excitation of these substates. The parameters ? and chi have been measured at 80 eV and 120 eV and scattering angles between 100 and 160. The data are compared with the predictions of the first Born approximation and the Glauber approximation which show relatively good agreement for ? but poor agreement for the relative phase chi. Where the present data overlap with previous measurements excellent agreement is found. Data are presented for the parameters ? and chi for the excitation of the resonant 31P1 state in neon. (author)

  5. Study of fluorescence probe transfer mechanism based on a new type of excited-state intramolecular proton transfer

    Science.gov (United States)

    Dai, Yumei; Zhao, Jinfeng; Cui, Yanling; Wang, Qianyu; Song, Peng; Ma, Fengcai; Zhao, Yangyang

    2015-06-01

    3-Hydroxyflavone (3-HF) is a typical representative of a new type of fluorescent molecular probe. The intramolecular proton transfer mechanisms of 3-HF and its derivatives have been studied theoretically based on detailed density functional theory. An optical physical cycle diagram of intramolecular proton transfer of 3-HF and its derivatives has been found based on the optimal configuration before and after proton transfer. An analysis of the absorption and fluorescence spectra of these probes explains their optical physical mechanism, which agrees well with experimental results. This correlation indicates that the adopted theory is reasonable and effective. The primary bond lengths, angles and infrared vibrational spectra indicate that the intramolecular hydrogen bonds were strengthened, which is an indication of the excited-state intramolecular proton transfer (ESIPT) processes. The constructed potential energy curves of the ground and first excited state based on these three chromophores provide the ESIPT mechanism, which demonstrates that potential barriers lower than the 6 kcal/mol and justifies the ESIPT processes occur in the first excited state. The fluorescence quenching phenomenon has been explained based on the ESIPT mechanism.

  6. Influence of excited electron lifetimes on the electronic structure of carbon nanotubes

    OpenAIRE

    Hertel, Tobias; Moos, Gunnar

    1999-01-01

    We have studied the dynamics of electrons in single wall carbon nanotubes using femtosecond time-resolved photoemission. The lifetime of electrons excited to the pi* bands is found to decrease continuously from 130 fs at 0.2 eV down to less than 20 fs at energies above 1.5 eV with respect to the Fermi level. This should lead to a significant lifetime--induced broadening of the characteristic van Hove singularities in the nanotube DOS.

  7. Charge transfer from core-excited argon adsorbed on clean and hydrogenated Si(100): ultrashort timescales and energetic structure

    International Nuclear Information System (INIS)

    Using the well-established core hole-clock method under resonant Auger Raman conditions we have measured the charge transfer (CT) times for the 4s electron on 2p3/2 core excited Ar atoms adsorbed on Si(100). The influences of the doping (p- or n-type), surface condition (clean or covered with monohydride) and varied excitation energy have been examined. The data for the Si-H surfaces are most extensive and distinct and undisturbed by background or losses. The CT times, which are identical for n- and p-type materials, are found to be about 2 fs at resonance. They show a distinct energy dependence when broadly tuning the excitation energy through the Ar core resonance. The CT times on clean Si(100), for which the data are not as extensive, are shorter by a factor of ?2 compared to the Si-H surfaces and again about the same for n- and p-type Si(100). The unexpectedly short CT times found, as well as the energetic structure seen, are discussed in terms of possible influences of the projected surface electronic structure of Si(100) in the energy range of the Ar 4s electron, and of other explanations. Theoretical modeling would be highly desirable.

  8. Decision Maker based on Nanoscale Photo-excitation Transfer

    Science.gov (United States)

    Kim, Song-Ju; Naruse, Makoto; Aono, Masashi; Ohtsu, Motoichi; Hara, Masahiko

    2013-08-01

    Decision-making is one of the most important intellectual abilities of the human brain. Here we propose an efficient decision-making system which uses optical energy transfer between quantum dots (QDs) mediated by optical near-field interactions occurring at scales far below the wavelength of light. The simulation results indicate that our system outperforms the softmax rule, which is known as the best-fitting algorithm for human decision-making behaviour. This suggests that we can produce a nano-system which makes decisions efficiently and adaptively by exploiting the intrinsic spatiotemporal dynamics involving QDs mediated by optical near-field interactions.

  9. Collision rates for electron excitation of Mg V lines

    Science.gov (United States)

    Tayal, S. S.; Sossah, A. M.

    2015-02-01

    Aims: Transition probabilities and electron impact excitation collision strengths and rates for astrophysically important lines in Mg V are reported. The 86 fine-structure levels of the 2s22p4, 2s2p5, 2p6, 2s22p33s, 2s22p33p and 2s22p33d configurations are included in our calculations. The effective collision strengths are presented as a function of electron temperature for solar and other astrophysical applications. Methods: The collision strengths have been calculated using the B-splineBreit-Pauli R-matrixmethod for all fine-structure transitions among the 86 levels. The one-body mass, Darwin and spin-orbit relativistic effects are included in the Breit-Pauli Hamiltonian in the scattering calculations. The one-body and two-body relativistic operators are included in the multiconfiguration Hartree-Fock calculations of transition probabilities. Several sets of non-orthogonal spectroscopic and correlation radial orbitals are used to obtain accurate description of Mg V 86 levels and to represent the scattering functions. Results: The calculated excitation energies are in very good agreement with experiment and represents an improvement over the previous calculations. The present collision strengths show good agreement with the previously available R-matrix and distorted-wave calculations. The oscillator strengths for E1 transitions normally compare very well with previous calculations. The thermally averaged collision strengths are obtained by integrating total resonant and non-resonant collision strengths over a Maxwellian distribution of electron energies and these are presented over the temperature range log 10Te = 3.2-6.0 K. Tables 1-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A87

  10. Electron capture into excited states of multi-charged ions

    International Nuclear Information System (INIS)

    This thesis deals with charge exchange reactions in slow collisions of multi-charged ions with neutral atoms or molecules. These reactions proceed very efficiently via a curve crossing mechanism, which leads to preferential population of excited states of the ion. The subsequent decay of these states leads to the emission of characteristic radiation. From wavelength resolved measurements of the absolute intensity of this radiation, cross sections for selective population of the excited (n,l-) states of the ion were determined. In addition, for some systems the total capture cross section was measured directly by means of charge state analysis of the secondary projectile ions. The role of charge exchange processes in fusion plasmas and in astrophysical plasmas is indicated. An experimental set-up is described with emphasis on the Electron Cyclotron Resonance Ion Source that was used in the experiments. Results for collisions of C6+, N6+, O6+ and Ne6+ with He, H2 and Ar are presented as well as for electron capture from Li atoms by C4+ and He2+. The interaction of the iso-electronic sequence C4+, N5+, O6+ with atomic hydrogen, molecular hydrogen and helium is studied. First results for partial and total cross sections in collisions of fully stripped carbon, nitrogen and oxygen ions with atomic hydrogen are presented. These data are of particular importance for applications in fusion diagnostics. The data indicate that calculations of both molecular and atomic orbital type yield correct results, if an extended basis set is used. (Auth.)

  11. Interfacial electron transfer dynamics of ru(II)-polypy6ridine sensitized TiO2

    Energy Technology Data Exchange (ETDEWEB)

    Jakubikova, Elena [Los Alamos National Laboratory; Martin, Richard L [Los Alamos National Laboratory; Batista, Enrique R [Los Alamos National Laboratory; Snoeberger, Robert C [YALE UNIV.; Batista, Victor S [YALE UNIV.

    2009-01-01

    Quantum dynamics simulations combined with density functional theory calculations are applied to study interfacial electron transfer (IET) from pyridine-4-phosphonic acid, [Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 2+} and [Ru(tpy)(bpy)(H{sub 2}O)-Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 4+} into the (101) surface of anatase TiO{sub 2}. IET rate from pyridine-4-phosphonic acid attached to the nanoparticle in bidentate mode ({tau} {approx} 100 fs) is an order of magnitude faster than the IET rate of the adsorbate attached in the monodentate mode ({tau} {approx} 1 ps). Upon excitation with visible light, [Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 2+} attached to TiO{sub 2} in bidentate binding mode will undergo IET with the rate of {approx} 1-10 ps, which is competitive with the excited state decay into the ground state. The probability of electron injection from [Ru(tpy)(bpy)(H{sub 2}O)-Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 4+} is rather low, as the excitation with visible light localizes the excited electron in the tpy-tpy bridge, which does not have favorable coupling with the TiO{sub 2} nanoparticle. The results are relevant to better understanding of the adsorbate features important for promoting efficient interfacial electron transfer into the semiconductor.

  12. 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.

  13. Mechanisms of interchromophore interactions and relaxation of electron excitation energy in covalently bound porphyrin dimers

    Energy Technology Data Exchange (ETDEWEB)

    Gurinovich, G.P.; Zen`kevich, E.I.; Sagun, E.I.; Shul`ga, A.M. [Academy of Sciences of Belarus (Russian Federation)

    1995-11-01

    The results presented in the work and the conclusions made on their basis show that the directed synthesis of covalently bound dimers of porphyrins and chlorins with required structural and energy properties of their components allows determination and investigation of real concrete mechanisms determining deactivation of electron excitation energy in these systems and, consequently, control of the interaction of this kind of object with molecular oxygen. The results obtained can be used in practice for seeking effective quenchers (as well as sensitizers) of singlet oxygen for inhibition of its destructive role in biological systems and for protecting materials from oxidation. Finally, the authors have shown recently that a combination of the methods of chemical synthesis with the principles of supermolecular chemistry is promising in forming self-organizing trimer and pentamer complexes with effective energy and electron transfer in solutions.

  14. Coherent electron impact excitation of the n = 2 states of atomic hydrogen at intermediate energies

    International Nuclear Information System (INIS)

    A theoretical analysis is given of the parameters M1 + M3, M2 and cos delta which describe the coherent excitation of the n=2 states of atomic hydrogen by intermediate-energy electrons. At small momentum transfers, the parameters M1 + M3 and M2 are dominated by first Born s-p amplitudes, but outside the small-angle region higher-order effects are shown to be very important. The parameter cos delta is also very sensitive to higher-order effects. Unitarised eikonal-Born series results are presented for M1 + M3, M2 and cos delta at incident electron energies of 100, 300 and 350 eV. (author)

  15. Vibronic effects on the 1t(1) ? 3s Rydberg excitation in CF4 induced by electron impact.

    Science.gov (United States)

    Watanabe, Noboru; Suzuki, Daisuke; Takahashi, Masahiko

    2011-06-21

    We report a theoretical study of vibronic effects on the 1t(1) ? 3s Rydberg excitation in CF(4) induced by electron impact. The generalized oscillator strength for the excitation has been calculated using theoretical wave functions at the equation-of-motion coupled cluster singles and doubles level. In the calculation vibronic effects have been taken into account by evaluating the electronic transition moment along the individual normal coordinates. The present calculation successfully reproduces our recent experimental result [N. Watanabe, D. Suzuki, and M. Takahashi, J. Chem. Phys. 134, 064307 (2011)] over the full momentum transfer region studied. By examining contributions from individual normal modes, the asymmetric stretching mode is found to play a leading role in the 1t(1) ? 3s transition at small momentum transfer. PMID:21702558

  16. Modeling time-coincident ultrafast electron transfer and solvation processes at molecule-semiconductor interfaces

    Science.gov (United States)

    Li, Lesheng; Giokas, Paul G.; Kanai, Yosuke; Moran, Andrew M.

    2014-06-01

    Kinetic models based on Fermi's Golden Rule are commonly employed to understand photoinduced electron transfer dynamics at molecule-semiconductor interfaces. Implicit in such second-order perturbative descriptions is the assumption that nuclear relaxation of the photoexcited electron donor is fast compared to electron injection into the semiconductor. This approximation breaks down in systems where electron transfer transitions occur on 100-fs time scale. Here, we present a fourth-order perturbative model that captures the interplay between time-coincident electron transfer and nuclear relaxation processes initiated by light absorption. The model consists of a fairly small number of parameters, which can be derived from standard spectroscopic measurements (e.g., linear absorbance, fluorescence) and/or first-principles electronic structure calculations. Insights provided by the model are illustrated for a two-level donor molecule coupled to both (i) a single acceptor level and (ii) a density of states (DOS) calculated for TiO2 using a first-principles electronic structure theory. These numerical calculations show that second-order kinetic theories fail to capture basic physical effects when the DOS exhibits narrow maxima near the energy of the molecular excited state. Overall, we conclude that the present fourth-order rate formula constitutes a rigorous and intuitive framework for understanding photoinduced electron transfer dynamics that occur on the 100-fs time scale.

  17. Photoinduced Electron-transfer Reaction of Pentafluoroiodobenzene with Alkenes

    OpenAIRE

    Qing-Yun Chen; Zheng-Yu Long; Ping Cao

    1997-01-01

    Irradiation of pentafluoroiodobenzene and alkenes gave the corresponding adducts. The presence of single electron-transfer scavengers, (p-dinitrobenzene and t-Bu2NO) and the free radical inhibitor (hydroquinone) suppressed the reaction. A photoinduced electron-transfer mechanism is proposed.

  18. Excited-state proton and charge transfer in protonated amino and methylated derivatives of 2-(2'-hydroxyphenyl)benzimidazole.

    Science.gov (United States)

    Ríos Vázquez, Sonia; Pérez Lustres, J Luis; Rodríguez-Prieto, Flor; Mosquera, Manuel; Ríos Rodríguez, M Carmen

    2015-02-12

    We studied the excited-state behavior of a family of mono- and diprotonated derivatives of 2-phenylbenzimidazole in different solvents, using steady-state and time-resolved fluorescence spectroscopy. The species investigated were 2-(4'-amino-2'-hydroxyphenyl)benzimidazole (1), the diethylamino analogue 2-(4'-N,N-diethylamino-2'-hydroxyphenyl)benzimidazole (2) and its N-methylated derivative 1-methyl-2-(4'-N,N-diethylamino-2'-hydroxyphenyl)benzimidazole (3). The O-methoxy derivatives of 2 and 3 (2-OMe and 3-OMe), and the simpler models 2-phenylbenzimidazole (4) and its 4'-amino (5) and 4'-dimethylamino (6) derivatives were also studied. We found that the dications of 1, 2, and 3 (protonated at the benzimidazole N3 and at the amino group) were strong photoacids, which were deprotonated at the hydroxyl group upon excitation in aqueous solution (totally for 2 and 3) to give a tautomer of the ground-state monocation. In contrast, no photodissociation was observed for the monocations of these species. Instead, some of the monocations studied behaved as molecular rotors, for which electronic excitation led to a twisted intramolecular charge transfer (TICT) state. The monocations of 2, 3, 2-OMe, 3-OMe, and 6, protonated at the benzimidazole N3, experienced a polarity- and viscosity-dependent radiationless deactivation associated with a large-amplitude rotational motion. We propose that this process is connected to an intramolecular charge transfer from the dimethylaminophenyl or diethylaminophenyl moiety (donor) to the protonated benzimidazole group (acceptor) of the excited monocation, which yields a twisted charge-transfer species. No fluorescence from this species was detected except for 3 and 3-OMe in low-viscosity solvents. PMID:25226567

  19. 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

  20. Electron Transfer in Porphyrin Complexes in Different Solvents

    CERN Document Server

    Kilin, D S; Schreiber, M

    2000-01-01

    The electron transfer in different solvents is investigated for systems consisting of donor, bridge and acceptor. It is assumed that vibrational relaxation is much faster than the electron transfer. Electron transfer rates and final populations of the acceptor state are calculated numerically and in an approximate fashion analytically. In wide parameter regimes these solutions are in very good agreement. The theory is applied to the electron transfer in ${\\rm H_2P-ZnP-Q}$ with free-base porphyrin (${\\rm H_2P}$) being the donor, zinc porphyrin (${\\rm ZnP}$) the bridge, and quinone (${\\rm Q}$) the acceptor. It is shown that the electron transfer rates can be controlled efficiently by changing the energy of the bridging level which can be done by changing the solvent. The effect of the solvent is determined for different models.

  1. Ultrafast electron and energy transfer in dye-sensitized iron oxide and oxyhydroxide nanoparticles

    DEFF Research Database (Denmark)

    Gilbert, Benjamin; Katz, Jordan E.

    2013-01-01

    An emerging area in chemical science is the study of solid-phase redox reactions using ultrafast time-resolved spectroscopy. We have used molecules of the photoactive dye 2?,7?-dichlorofluorescein (DCF) anchored to the surface of iron(iii) oxide nanoparticles to create iron(ii) surface atoms via photo-initiated interfacial electron transfer. This approach enables time-resolved study of the fate and mobility of electrons within the solid phase. However, complete analysis of the ultrafast processes following dye photoexcitation of the sensitized iron(iii) oxide nanoparticles has not been reported. We addressed this topic by performing femtosecond transient absorption (TA) measurements of aqueous suspensions of uncoated and DCF-sensitized iron oxide and oxyhydroxide nanoparticles, and an aqueous iron(iii)–dye complex. Following light absorption, excited state relaxation times of the dye of 115–310 fs were found for all samples. Comparison between TA dynamics on uncoated and dye-sensitized hematite nanoparticles revealed the dye de-excitation pathway to consist of a competition between electron and energy transfer to the nanoparticles. We analyzed the TA data for hematite nanoparticles using a four-state model of the dye-sensitized system, finding electron and energy transfer to occur on the same ultrafast timescale. The interfacial electron transfer rates for iron oxides are very close to those previously reported for DCF-sensitized titanium dioxide (for which dye–oxide energy transfer is energetically forbidden) even though the acceptor states are different. Comparison of the alignment of the excited states of the dye and the unoccupied states of these oxides showed that the dye injects into acceptor states of different symmetry (Ti t2g vs. Fe eg).

  2. Oxide/Electrolyte interface: Electron transfer phenomena

    Directory of Open Access Journals (Sweden)

    Fernández-Ibáñez, P.

    2000-08-01

    Full Text Available Electron transfer on a titanium dioxide/electrolyte solution interface has been studied. As observed by other researchers on similar interfaces (TiO2- and ZnO- electrolyte solution, slow consumption of OH- ions was found. A theoretical model has been developed for calculating the change in Fermi energy levels of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by a decreased difference in their Fermi energies. A kinetic constant (? is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion.

    En este trabajo se ha estudiado un proceso de transferencia de electrones en la interfase dióxido de titanio/electrolito acuoso. Tal y como han observado otros investigadores en interfases similares (TiO2- y ZnO- electrolito, se ha detectado un consumo lento de iones OH-. Para dar explicación a este proceso, se ha desarrollado un modelo teórico basado en el cálculo de las energías de Fermi en el semiconductor y en el electrolito. De este modo, se demuestra que dicho consumo de iones está favorecido por una disminución de la diferencia entre ambos niveles de Fermi. Para caracterizar el proceso de consumo lento de OH- se define una constante cinética (?, cuyo valor aumenta a medida que crece la concentración másica de semiconductor y de electrolito en la suspensión. Adicionalmente, este fenómeno proporciona una herramienta para determinar experimentalmente el punto de carga nula de la suspensión de dióxido de titanio en el medio acuoso.

  3. Collision Strengths for Electron Collisional Excitation of S II

    Science.gov (United States)

    Tayal, S. S.

    1997-08-01

    Electron collisional excitation strengths for inelastic transitions in S II are calculated using the R-matrix method in a 19-state (3s23p3 4So, 2Do, 2Po, 3s3p4 4P, 2D, 2S, 3s23p23d 2P, 4F, 4D, 2F, 4P, 3s23p24s 4P, 2P, 3s23p24p 2So, 4Do, 4Po, 2Do, 4So, 2Po) close-coupling approximation. These target states are represented by extensive configuration-interaction wave functions that give excitation energies and oscillator strengths that are usually in good agreement with the experimental values and the available accurate calculations. The present results for collision strengths are in very good agreement with the recent merged beams energy loss measurement of Liao et al. and agree reasonably well with the 18-state R-matrix calculation of Ramsbottom, Bell, & Stafford, but show significant differences from the 12-state R-matrix calculation of Cai & Pradhan.

  4. Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene

    International Nuclear Information System (INIS)

    Photochemical properties of pyrene and fluorene appended fulleropyrrolidine triads (AH1-C60-AH2; AH1=pyrene and fluorene; AH2=naphthalene and phenyl) are reported. Electrochemical studies using cyclic voltammetry technique and DFT calculations at B3LYP/3-21G(*) method revealed that the charge-separated states in pyrene and fluorene appended triads are pyrenedot+-C60dot-AH2 and fluorenedot+-C60dot-AH2, respectively; however, no such charge-separated states could be established for naphthalene and phenyl appended triads. As demonstrated from the time resolved fluorescence, upon excitation of AH moiety in nonpolar solvents, energy transfer predominantly occurred from the singlet excited fluorophore to the C60 moiety, whereas in polar DMF charge-separation also contributed to the fluorescence quenching. Additionally, charge separation also occurred from the singlet excited C60 to the pyrene or fluorene entities of the triads in DMF. The rates and quantum yields of charge separation obtained by time-resolved emission studies were around 109s-1 and 0.9-0.6 for pyrene-C60-AH2 and fluorene-C60-AH2 triads. Nanosecond transient absorption spectral studies performed by using 355nm laser light on the triads, exhibited transient bands corresponding to thibited transient bands corresponding to the C60dot- and pyrenedot+ or fluorenedot+, thus establishing the occurrence of electron transfer in these triads in DMF. The rates of charge recombination obtained by monitoring the decay of the C60dot- were found to be around 106s-1 in DMF which resulted in the lifetimes of the radical ion pairs up to 1000ns indicating charge stabilization in pyrene-C60-AH2 and fluorene-C60-AH2 triads. The formations of long-lived charge-separated states, pyrenedot+-C60d'ot-AH2 and fluorenedot+-C60dot-AH2 in DMF, were rationalized by evaluating the Marcus parameters from the temperature dependence of the charge-recombination rate constants

  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. Generating Excitement: Build Your Own Generator to Study the Transfer of Energy

    Science.gov (United States)

    Fletcher, Kurt; Rommel-Esham, Katie; Farthing, Dori; Sheldon, Amy

    2011-01-01

    The transfer of energy from one form to another can be difficult to understand. The electrical energy that turns on a lamp may come from the burning of coal, water falling at a hydroelectric plant, nuclear reactions, or gusts of wind caused by the uneven heating of the Earth. The authors have developed and tested an exciting hands-on activity to…

  7. 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.

  8. The excitation of Li(3s) by electron impact

    International Nuclear Information System (INIS)

    A comparative study of the excitation of Li(3s) by electron impact in several distorted-wave approximations is made. These include the distorted-wave first and second Born approximations with both first- and second-order distortion in initial and final states. Second-order effects representing both target and projectile distortion are found to give a large correction to the first-order DWBA results. The predictions of the present full second-order model are compared with absolute measurements of the differential cross section in the energy range 10-60 eV. Calculations have also been made in the plane-wave second Born approximation, and the results show the failure of a perturbative approach based on the plane-wave Born series at intermediate energies. (author)

  9. Excitation of Li(3s) by electron impact

    Energy Technology Data Exchange (ETDEWEB)

    Winters, K.H. (UKAEA Atomic Energy Research Establishment, Harwell. Theoretical Physics Div.); Vanderpoorten, R. (Mons Univ. (Belgium))

    1982-11-14

    A comparative study of the excitation of Li(3s) by electron impact in several distorted-wave approximations is made. These include the distorted-wave first and second Born approximations with both first- and second-order distortion in initial and final states. Second-order effects representing both target and projectile distortion are found to give a large correction to the first-order DWBA results. The predictions of the present full second-order model are compared with absolute measurements of the differential cross section in the energy range 10-60 eV. Calculations have also been made in the plane-wave second Born approximation, and the results show the failure of a perturbative approach based on the plane-wave Born series at intermediate energies.

  10. Development of Neutral Beam Source Using Electron Beam Excited Plasma

    Science.gov (United States)

    Hara, Yasuhiro; Hamagaki, Manabu; Mise, Takaya; Hara, Tamio

    2011-10-01

    A low-energy neutral beam (NB) source, which consists of an electron-beam-excited plasma (EBEP) source and two carbon electrodes, has been developed for damageless etching of ultra-large-scale integrated (ULSI) devices. It has been confirmed that the Ar ion beam energy was controlled by the acceleration voltage and the beam profile had good uniformity over the diameter of 80 mm. Dry etching of a Si wafer at the floating potential has been carried out by Ar NB. Si sputtering yield by an Ar NB clearly depends on the acceleration voltage. This result shows that the NB has been generated through the charge exchange reaction from the ion beam in the process chamber.

  11. 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

  12. Excited State Intramolecular Proton Transfer and Photophysics of a New Fluorenyl Two-Photon Fluorescent Probe

    Science.gov (United States)

    Morales, Alma R.; Schafer-Hales, Katherine J.; Yanez, Ciceron O.; Bondar, Mykhailo V.; Przhonska, Olga V.; Marcus, Adam I.; Belfield, Kevin D.

    2009-01-01

    The steady-state photophysical, NMR, and two-photon absorption (2PA) properties of a new fluorene derivative (1) containing the 2-(2?-hydroxyphenyl) benzothiazole (HBT) terminal construct was investigated for use as a fluorescence probe in bioimaging. A comprehensive analysis of the linear spectral properties revealed inter- and intramolecular hydrogen bonding and excited state intramolecular proton transfer (ESIPT) processes in the HBT substituent. A specific electronic model with a double minimum potential energy surface was consistent with the observed spectral properties. The 2PA spectra were obtained using a standard two-photon induced fluorescence method with femtosecond kHz laser system, affording a maximum 2PA cross section of ~600 GM, a sufficiently high value for two-photon fluorescence imaging. No dependence of two-photon absorption efficiency on solvent properties and hydrogen bonding in the HBT substituent was observed. The potential use of this fluorenyl probe in bioimaging was demonstrated via one- and two-photon fluorescence imaging of COS-7 cells. PMID:19449363

  13. 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

  14. Quantum coherent contributions in biological electron transfer

    CERN Document Server

    Dorner, Ross; Heaney, Libby; Farrow, Tristan; Roberts, Philippa G; Hirst, Judy; Vedral, Vlatko

    2011-01-01

    Many biological electron transfer (ET) reactions are mediated by metal centres in proteins. NADH:ubiquinone oxidoreductase (complex I) contains an intramolecular chain of seven iron-sulphur (FeS) clusters, one of the longest chains of metal centres in biology and a test case for physical models of intramolecular ET. In biology, intramolecular ET is commonly described as a diffusive hopping process, according to the semi-classical theories of Marcus and Hopfield. However, recent studies have raised the possibility that non-trivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we extend the semi-classical model for biological ET to incorporate both semi-classical and coherent quantum phenomena using a quantum master equation based on the Holstein Hamiltonian. We test our model on the structurally-defined chain of FeS clusters in complex I. By exploring a wide range of realistic parameters we and that, when the energy profile for ET along the chain is relatively at, ...

  15. Electron Transfer Dissociation of Milk Oligosaccharides

    Science.gov (United States)

    Han, Liang; Costello, Catherine E.

    2011-06-01

    For structural identification of glycans, the classic collision-induced dissociation (CID) spectra are dominated by product ions that derived from glycosidic cleavages, which provide only sequence information. The peaks from cross-ring fragmentation are often absent or have very low abundances in such spectra. Electron transfer dissociation (ETD) is being applied to structural identification of carbohydrates for the first time, and results in some new and detailed information for glycan structural studies. A series of linear milk sugars was analyzed by a variety of fragmentation techniques such as MS/MS by CID and ETD, and MS3 by sequential CID/CID, CID/ETD, and ETD/CID. In CID spectra, the detected peaks were mainly generated via glycosidic cleavages. By comparison, ETD generated various types of abundant cross-ring cleavage ions. These complementary cross-ring cleavages clarified the different linkage types and branching patterns of the representative milk sugar samples. The utilization of different MS3 techniques made it possible to verify initial assignments and to detect the presence of multiple components in isobaric peaks. Fragment ion structures and pathways could be proposed to facilitate the interpretation of carbohydrate ETD spectra, and the main mechanisms were investigated. ETD should contribute substantially to confident structural analysis of a wide variety of oligosaccharides.

  16. Electronic transfer of sensitive patient data.

    Science.gov (United States)

    Detterbeck, A M W; Kaiser, J; Hirschfelder, U

    2015-01-01

    The purpose of this study was to develop decision-making aids and recommendations for dental practitioners regarding the utilization and sharing of sensitive digital patient data. In the current environment of growing digitization, healthcare professionals need detailed knowledge of secure data management to maximize confidentiality and minimize the risks involved in both archiving patient data and sharing it through electronic channels. Despite well-defined legal requirements, an all-inclusive technological solution does not currently exist. The need for a preliminary review and critical appraisal of common practices of data transfer prompted a search of the literature and the Web to identify viable methods of secure data exchange and to develop a flowchart. A strong focus was placed on the transmission of datasets both smaller than and larger than 10 MB, and on secure communication by smartphone. Although encryption of patient-related data should be routine, it is often difficult to implement. Pretty Good Privacy (PGP) and Secure/Multipurpose Internet Mail Extensions (S/MIME) are viable standards for secure e-mail encryption. Sharing of high-volume data should be accomplished with the help of file encryption. Careful handling of sensitive patient data is mandatory, and it is the end-user's responsibility to meet any requirements for encryption, preferably by using free, open-source (and hence transparent) software. PMID:25911828

  17. Vectorial electron transfer on designed surfaces

    Science.gov (United States)

    Bard, A. J.; Campion, A.; Fox, M. A.; Mallouk, T. E.; Webber, S. E.

    Bipolar CdSe/CoS semiconductor photoelectrode panels, capable of vectorial electron transfer, were used in series arrays to photodecompose water to yield hydrogen and oxygen in stoichiometric ratio with a maximum solar efficiency of about 1 precent. An analytical model was developed for these arrays which addresses the question of watersplitting and electrical power generation efficiencies as functions of the number of panels, the overpotential of the gas generating electrodes, incident light intensity, and the concentrations of the redox couples. Hydrogen production using a self-assembling zeolite system was discovered. Sensitized anatase TiO2 electrodes were used in photoelectrochemical cells employing variety of solution redox couples. The photoassisted production of hydrogen from methanol-water solutions containing mixtures of small particles of CdS/SiO2 and a wide bandgap semiconductor (TiO, ZnO, SnO2, or WO3), supported on silica and platinized was studied. The phenomenon of interparticle charge separation for Cds/SiO2 was found to be operative for CdS/SiO2 with WS sub 2/SiO2.

  18. 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...

  19. Reduction of aryl halides by consecutive visible light-induced electron transfer processes.

    Science.gov (United States)

    Ghosh, Indrajit; Ghosh, Tamal; Bardagi, Javier I; König, Burkhard

    2014-11-01

    Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis. PMID:25378618

  20. Electron-electron interaction effects on optical excitations in semiconducting single-walled carbon nanotubes

    CERN Document Server

    Zhao, H; Zhao, Hongbo; Mazumdar, Sumit

    2004-01-01

    We report correlated-electron calculations of optically excited states in ten semiconducting single-walled carbon nanotubes with a wide range of diameters. Optical excitation occurs to excitons whose binding energies decrease with the increasing nanotube diameter, and are smaller than the binding energy of an isolated strand of poly-(paraphenylene vinylene). The ratio of the energy of the second optical exciton polarized along the nanotube axis to that of the lowest exciton is smaller than the value predicted within single-particle theory. The experimentally observed weak photoluminescence is an intrinsic feature of semiconducting nanotubes, and is consequence of dipole-forbidden excitons occurring below the optical exciton.

  1. The distance and temperature dependence of electron-transfer rates

    International Nuclear Information System (INIS)

    Electron transfer occurs over relatively long distances in a variety of systems. In interpreting the measured electron-transfer rates it is usually assumed that the rate constants depend exponentially on the distance separating the two redox sites and that this distance dependence arises from the decrease in the electronic coupling of the redox sites with increasing separation. Although the electronic coupling is an important factor determining the distance dependence of the rate, theoretical considerations suggest that the nuclear factors are also important. The various factors determining long-range electron-transfer rates are discussed and it is shown that very different distance dependences are predicted for reactions in the normal and inverted free-energy regions. The effect of the enthalpy change on the electron-transfer rate is also considered; three enthalpy regions are identified depending on the overall free energy and entropy changes for the reaction

  2. High-energy spin and charge excitations in electron-doped copper oxide superconductors

    Science.gov (United States)

    Ishii, K.; Fujita, M.; Sasaki, T.; Minola, M.; Dellea, G.; Mazzoli, C.; Kummer, K.; Ghiringhelli, G.; Braicovich, L.; Tohyama, T.; Tsutsumi, K.; Sato, K.; Kajimoto, R.; Ikeuchi, K.; Yamada, K.; Yoshida, M.; Kurooka, M.; Mizuki, J.

    2014-04-01

    The evolution of electronic (spin and charge) excitations upon carrier doping is an extremely important issue in superconducting layered cuprates and the knowledge of its asymmetry between electron- and hole-dopings is still fragmentary. Here we combine X-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper L3 resonant inelastic X-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone centre and they deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the ?-point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin excitations (paramagnons) recently observed in hole-doped compounds even at high doping levels.

  3. Electronic energy transfer between coumarin 460 and Eu3+ in thorium phosphate xerogel

    International Nuclear Information System (INIS)

    Optical spectroscopy experiments performed on thorium phosphate xerogels, doped with both a laser dye (coumarin 460) and europium, have pointed out the existence of an electronic energy transfer from coumarin 460 to the 5D3 level of Eu3+. Indeed, the excitation spectrum of the red fluorescence of Eu3+ in thorium phosphate xerogel doped simultaneously with coumarin 460 exhibits a broad band corresponding to the absorption of coumarin 460 in this optical region

  4. Picosecond time-resolved fluorescence studies on excitation energy transfer in a histidine 117 mutant of the D2 protein of photosystem II in Synechocystis 6803.

    Science.gov (United States)

    Vasil'ev, S; Bruce, D

    2000-11-21

    The role of the peripheral reaction center chlorophyll a molecule associated with His117 of the D2 polypeptide in photosystem II was investigated in Synechocystis sp. PCC 6803 using a combination of steady state, pump-probe, and picosecond time-resolved fluorescence spectroscopy. Data were obtained from intact cells and isolated thylakoid membranes of a control mutant and a D2-H117T mutant, both of which lacked photosystem I. Excitation energy transfer and trapping were investigated by analyzing the data with a kinetic model that used an exact numerical solution of the Pauli master equation, taking into account available photosystem II spectral and structural information. The results of our kinetic analysis revealed the observed difference in excited-state dynamics between the H117T mutant and the control to be consistent with a retardation of the rate of excitation energy transfer from the peripheral chlorophyll of D2 (Chl at His117) to the electron-transfer pigments and an increase of the rate constant for charge recombination in the H117T mutant. The kinetic model was able to account for the experimentally observed changes in absorption cross section and fluorescence decay kinetics between the control and mutant by invoking changes in only these two rate constants. The results rule out quenching of excitation by a chlorophyll cation radical as a mechanism responsible for the lower efficiency of excitation energy utilization in the H117T mutant. Our work also demonstrates the importance of the chlorophyll associated with His117 of the D2 protein for excitation energy transfer to the PSII electron-transfer pigments and for the effective stabilization of the primary radical pair. PMID:11087370

  5. Electron Transfer Dissociation of iTRAQ Labeled Peptide Ions

    OpenAIRE

    Han, Hongling; Pappin, Darryl J.; Ross, Philip L.; McLuckey, Scott A.

    2008-01-01

    Triply and doubly charged iTRAQ (isobaric tagging for relative and absolute quantitation) labeled peptide cations from a tryptic peptide mixture of bovine carbonic anhydrase II were subjected to electron transfer ion/ion reactions to investigate the effect of charge bearing modifications associated with iTRAQ on the fragmentation pattern. It was noted that electron transfer dissociation (ETD) of triply charged or activated ETD (ETD + supplemental collisional activation of intact electron tran...

  6. Excited state proton transfer dynamics of thioacetamide in S2(??*) state: resonance Raman spectroscopic and quantum mechanical calculations study.

    Science.gov (United States)

    Chen, Xiao; Zhao, Yanying; Zhang, Haibo; Xue, Jiadan; Zheng, Xuming

    2015-02-01

    The photophysics and photochemistry of thioacetamide (CH3CSNH2) after excitation to the S2 electronic state were investigated by using resonance Raman spectroscopy in conjunction with the complete active space self-consistent field (CASSCF) method and density functional theory (DFT) calculations. The A-band resonance Raman spectra in acetonitrile, methanol, and water were obtained at 299.1, 282.4, 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of thioacetamide in the S2 state. CASSCF calculations were done to determine the transition energies and structures of the lower-lying excited states, the conical intersection points CI(S2/S1) and CI(S1/S0), and intersystem crossing points. The structural dynamics of thioacetamide in the S2 state was revealed to be along eight Franck-Condon active vibrational modes ?15, ?11, ?14, ?10, ?8, ?12, ?18, and ?19, mostly in the CC/CS/CN stretches and the CNH8,9/CCH5,6,7/CCN/CCS in-plane bends as indicated by the corresponding normal mode descriptions. The S2 ? S1 decay process via the S2/S1 conical intersection point as the major channel were excluded. The thione-thiol photoisomerization reaction mechanism of thioacetamide via the S2,FC ? S'1,min excited state proton transfer (ESPT) reaction channel was proposed. PMID:25559740

  7. Investigations of excitation energy transfer and intramolecular interactions in a nitrogen corded distrylbenzene dendrimer system

    Science.gov (United States)

    Varnavski, O.; Samuel, I. D. W.; Pâlsson, L.-O.; Beavington, R.; Burn, P. L.; Goodson, T.

    2002-05-01

    The photophysics of an amino-styrylbenzene dendrimer (A-DSB) system is probed by time-resolved and steady state luminescence spectroscopy. For two different generations of this dendrimer, steady state absorption, emission, and photoluminescence excitation spectra are reported and show that the efficiency of energy transfer from the dendrons to the core is very close to 100%. Ultrafast time-resolved fluorescence measurements at a range of excitation and detection wavelengths suggest rapid (and hence efficient) energy transfer from the dendron to the core. Ultrafast fluorescence anisotropy decay for different dendrimer generations is described in order to probe the energy migration processes. A femtosecond time-scale fluorescence depolarization was observed with the zero and second generation dendrimers. Energy transfer process from the dendrons to the core can be described by a Förster mechanism (hopping dynamics) while the interbranch interaction in A-DSB core was found to be very strong indicating the crossover to exciton dynamics.

  8. Simulations of fluorescence quenching using theoretical models of energy and electron transfer in random arrays

    Science.gov (United States)

    Boulu, Laurent G.; Kozak, John J.

    A master equation is solved numerically for investigating energy transfer and trapping in two-dimensional disordered systems of chlorophylls and quinones. Quenching of the excitation occurs both by electron transfer from a chlorophyll to a neighbouring quinone and by energy transfer to self-quenching traps consisting of statistical pairs of chlorophyll molecules closer than a critical distance. The quinone concentration dependence of the average lifetime of the calculated fluorescence decay is determined for different values of the Förster transfer radius 0 and A, the microscopic electron transfer rate at 'zero distance'. Quasi-Stern-Volmer behaviour is obtained. The half-quenching concentration and the quenching rate kQ depend strongly on A; they increase little with faster energy transfer because of competing self-quenching and slow electron transfer. Our results are compared to recent fluorescence quenching data that Chauvet and Patterson obtained from real-time measurements in monolayers of chlorophyll a and vitamin K1 diluted in dioleylphosphatidylcholine (DOL). Our convoluted decays fit the experimental data if A = 50-100 ns-1 and tMPH0193_images = 60-70 Å. Accordingly, kQ = 3-5 × 10-5 cm2/molecules·s. These values are in close agreement with those reported in the literature.

  9. Golden rule partitioning of vibronic energy: excitation transfer in collisions of metastable argon atoms with nitrogen

    International Nuclear Information System (INIS)

    Optical emission from N2* formed in electronic energy transfer collisions between metastable argon atoms and groundstate nitrogen molecules has been measured in the spectral range 300-870 nm using a beam plus scattering gas arrangement. A resonance decay model of energy transfer successfully predicts the dependence of product vibronic state distributions on the relative kinetic energy of collision. (Auth.)

  10. Dielectronic recombination and resonant transfer excitation processes for helium-like krypton

    International Nuclear Information System (INIS)

    The relativistic configuration interaction method is employed to calculate the dielectronic recombination (DR) cross sections of helium-like krypton via the 1s2lnl' (n = 2, 3, ..., 15) resonances. Then, the resonant transfer excitation (RTE) processes of Kr34+ colliding with H, He, H2, and CHx (x = 0?4) targets are investigated under the impulse approximation. The needed Compton profiles of targets are obtained from the Hartree—Fock wave functions. The RTE cross sections are strongly dependent on DR resonant energies and strengths, and the electron momentum distributions of the target. For H2 and H targets, the ratio of their RTE cross sections changes from 1.85 for the 1s2l2l' to 1.88 for other resonances, which demonstrates the weak molecular effects on the Compton profiles of H2. For CHx (x = 0?4) targets, the main contribution to the RTE cross section comes from the carbon atom since carbon carries 6 electrons; as the number of hydrogen increases in CHx, the RTE cross section almost increases by the same value, displaying the strong separate atom character for the hydrogen. However, further comparison of the individual orbital contributions of C(2p, 2s, 1s) and CH4(1t2, 2a1, 1a1) to the RTE cross sections shows that the molecular effects induce differences of about 25.1%, 19.9%, and 0.2% between 2p?1t2, 2s?2a1, and 1s?1a1 orbitals, respectively

  11. Transient behavior of cavity excitation driven by a modulated electron beam

    International Nuclear Information System (INIS)

    A theoretical model of cavity excitation driven by a modulated electron beam is developed in connection with application to relativistic klystron amplifiers. Based on an equivalent circuit representation of a cavity impedance, the equations which govern the phase and amplitude of the excitation voltage appearing on the cavity opening are obtained in terms of time t and current modulation strength. Several points are noteworthy from the theoretical analysis. First, amplitude and phase shift of the induced voltage indicate a damping oscillation, whose frequency is proportional to the mismatch |??| between the modulation frequency ? and the cavity resonance frequency ?0. Second, rise time of the cavity excitation amplitude decreases as the value of the frequency mismatch increases. Third, for a large value of the frequency mismatch |??|, the power transfer from the modulated beam to the cavity occurs at the beginning of the beam pulse. Finally, it is observed that the absolute amount of energy delivered from the beam to the cavity decreases drastically as the frequency mismatch increases

  12. Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot

    International Nuclear Information System (INIS)

    This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket

  13. Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Rasmussen, Andrew M., E-mail: andyras@gmail.com; Ramakrishna, S.; Weiss, Emily A.; Seideman, Tamar, E-mail: t-seideman@northwestern.edu [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113 (United States)

    2014-04-14

    This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket.

  14. Excitation of helium atoms in collisions with plasma electrons in an electric field

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, B. M., E-mail: bmsmirnov@gmail.com [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

    2013-01-15

    The rate constants are evaluated for excitation of helium atoms in metastable states by electron impact if ionized helium is located in an external electric field and is supported by it, such that a typical electron energy is small compared to the atomic excitation energy. Under these conditions, atomic excitation is determined both by the electron traveling in the space of electron energies toward the excitation threshold and by the subsequent atomic excitation, which is a self-consistent process because it leads to a sharp decrease in the energy distribution function of electrons, which in turn determines the excitation rate. The excitation rate constant is calculated for the regimes of low and high electron densities, and in the last case, it is small compared to the equilibrium rate constant where the Maxwell distribution function is realized including its tail. Quenching of metastable atomic states by electron impact results in excitation of higher excited states, rather than transition to the ground electron state for the electric field strengths under consideration. Therefore, at restricted electron number densities, the rate of emission of resonant photons of the wavelength 58 nm, which results from the transition from the 2{sup 1}P state of the helium atom to the ground state, is close to the excitation rate of metastable atomic states. The efficiency of atomic excitation in ionized helium, i.e., the part of energy of an electric field injected in ionized helium that is spent on atomic excitation, is evaluated. The results exhibit the importance of electron kinetics for an ionized gas located in an electric field.

  15. Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.

    Science.gov (United States)

    Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

    2015-04-21

    The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and vibrational movement are coupled in a donor-bridge-acceptor complex based on a Pt(II) trans-acetylide design motif. Time-resolved IR (TRIR) spectroscopy reveals that the rate of electron transfer (ET) is highly dependent on the amount of excess energy localized on the bridge following electronic excitation. Using an adaptation of T-2DIR, we are able to selectively perturb bridge-localized vibrational modes during charge separation, resulting in the donor-acceptor charge separation pathway being completely switched off, with all excess energy redirected toward the formation of a long-lived intraligand triplet state. A series of control experiments reveal that this effect is mode specific: it is only when the high-frequency bridging C?C stretching mode is pumped that radical changes in photoproduct yields are observed. These experiments therefore suggest that one may perturb electronic movement by stimulating structural motion along the reaction coordinate using IR light. These studies add to a growing body of evidence suggesting that controlling the pathways and efficiency of charge transfer may be achieved through synthetic and perturbative approaches aiming to modulate vibronic coupling. Achieving such control would represent a breakthrough for charge transfer-based applications such as solar energy conversion and molecular electronics. PMID:25789559

  16. Modulating the electronic structure of chromophores by chemical substituents for efficient energy transfer: application to fluorone.

    Science.gov (United States)

    Sand, Andrew M; Liu, Claire; Valentine, Andrew J S; Mazziotti, David A

    2014-08-01

    Strong electron correlation within a quasi-spin model of chromophores was recently shown to enhance exciton energy transfer significantly. Here we investigate how the modulation of the electronic structure of the chromophores by chemical substitution can enhance energy-transfer efficiency. Unlike previous work that does not consider the direct effect of the electronic structure on exciton dynamics, we add chemical substituents to the fluorone dimer to study the effect of electron-donating and electron-withdrawing substituents on exciton energy transfer. The exciton dynamics are studied from the solution of a quantum Liouville equation for an open system whose model Hamiltonian is derived from excited-state electronic structure calculations. Both van der Waals energies and coupling energies, arising from the Hellmann-Feynman force generated upon transferring the dimers from infinity to a finite separation, are built into the model Hamiltonian. Though these two effects are implicitly treated in dipole-based models, their explicit and separate treatment as discussed here is critical to forging the correct connection with the electronic structure calculations. We find that the addition of electron-donating substituents to the fluorone system results in an increase in exciton-transfer rates by factors ranging from 1.3-1.9. The computed oscillator strength is consistent with the recent experimental results on a larger heterodimer system containing fluorone. The oscillator strength increases with the addition of electron-donating substituents. Our results indicate that the study of chromophore networks via electronic structure will help in the future design of efficient synthetic light-harvesting systems. PMID:25062094

  17. Efficient Plasmon-Induced Hot Electron Transfer and Photochemistry in Semiconductor-Au Nanorod Heterostructures

    Science.gov (United States)

    Lian, Tianquan

    2014-03-01

    In recent years, it has been shown that excitation of plasmons in metal nanostructures can lead to the injection of hot electrons into semiconductors and enhanced photochemistry. This novel plasmon-exciton interaction mechanism suggests that plasmonic nanostructures can potentially function as a new class of widely tunable and robust light harvesting materials for photo-detection or solar energy conversion. However, plasmon-induced hot electron injections from metal to semiconductor or molecules are still inefficient because of the competing ultrafast hot electron relaxation (via ultrafast electron-electron and electron-phonon scattering) processes within the metallic domain. In this paper we discuss a recent study on the plasmon-exciton interaction mechanisms in colloidal quantum-confined epitaxially-grown semiconductor-gold plexcitonic nanorod heterostructures. Using transient absorption spectroscopy, we show that optical excitation of plasmons in the Au tip leads to efficient hot electron injection into the semiconductor nanorod. In the presence of sacrificial electron donors, this plasmon induced hot electron transfer process can be utilized to drive photoreduction reactions under continuous illumination. Ongoing studies are examining how to further improve the plasmon induced hot electron injection efficiency through controlling the size and shape of the plasmonic and excitonic domains.

  18. Ultrafast excited-state charge-transfer dynamics in laccase type I copper site.

    Science.gov (United States)

    Delfino, Ines; Viola, Daniele; Cerullo, Giulio; Lepore, Maria

    2015-01-01

    Femtosecond pump-probe spectroscopy was used to investigate the excited state dynamics of the T1 copper site of laccase from Pleurotus ostreatus, by exciting its 600nm charge transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching occurs in a single step and is modulated by clearly visible oscillations. Global analysis of the two-dimensional differential transmission map shows that the excited state exponentially decays with a time constant of 375fs, thus featuring a decay rate slower than those occurring in quite all the investigated T1 copper site proteins. The ultrashort pump pulse induces a vibrational coherence in the protein, which is mainly assigned to ground state activity, as expected in a system with fast excited state decay. Vibrational features are discussed also in comparison with the traditional resonance Raman spectrum of the enzyme. The results indicate that both excited state dynamics and vibrational modes associated with the T1 Cu laccase charge transfer have main characteristics similar to those of all the T1 copper site-containing proteins. On the other hand, the differences observed for laccase from P. ostreatus further confirm the peculiar hypothesized trigonal T1 Cu site geometry. PMID:25819432

  19. Electron impact investigation of electronic excitations in furan, thiophene, and pyrrole

    International Nuclear Information System (INIS)

    The electronically excited states of furan, thiophene, and pyrrole have been studied by electron impact at scattering angles from 0degree to 80degree, and impact energies of 30 and 50 eV. Low-lying features at 3.99 and 5.22 eV in furan, 3.75 and 4.62 eV in thiophene, and 4.21 eV in pyrrole are identified as singlet ? triplet transitions. The locations and, for furan and thiophene, the energy splittings of these excitations suggest that they are analogous to the lowest ? ? ?* singlet ? triplet transitions in benzene, and that these heterocycles have appreciable aromatic character. A weak feature observed in pyrrole at 5.22 eV is attributed to an optically forbidden singlet ? singlet transition. In all three molecules, transitions to several superexcited states are observed

  20. Absolute cross sections for electron collisions with diacetylene: Elastic scattering, vibrational excitation and dissociative attachment

    International Nuclear Information System (INIS)

    We present absolute experimental cross sections for elastic scattering, vibrational excitation by electron impact and for dissociative electron attachment to 1,3-butadiyne, as well as calculations of the elastic cross sections.

  1. Heat Transfer Augmentation for Electronic Cooling

    OpenAIRE

    Suabsakul Gururatana

    2012-01-01

    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,...

  2. Photoinduced electron and energy transfer in a new porphyrin-phthalocyanine triad

    International Nuclear Information System (INIS)

    Complexes of porphyrins, phthalocyanines, and chlorophylls are well suited for modelling both the electron and energy transfer processes in photosynthetic reaction centers and natural chlorophyll complexes. In the present paper, we report the synthesis and photophysical characterization of a novel tetraphenylporphyrin-silicon(IV) phthalocyanine triad, where two porphyrins are linked to the central silicon atom of a phthalocyanine moiety. It has been found that the photophysical properties of the triad (Tr) are strongly affected by two different types of interactions between the porphyrin (P) and the phthalocyanine (Pc) parts of Tr, namely excitation energy transfer (EET) and photoinduced electron transfer (ET). The first one results in appearance of the Pc fluorescence when the P-part was initially excited and plays dominant role in fast depopulation of the first excited singlet state of the P moiety. Another competitive process in quenching of P-part fluorescence is electron transfer, but the probability of it is six times less compared to that of EET. If the first excited singlet state of the Pc-part is populated (directly or via EET), it undergoes fast depopulation via ET to the charge-separated state. As a result, the fluorescence quantum yield of the Pc-part of Tr is approximately three orders of magnitude less compared to that of silicon(IV) phthalocyanine with two axial poly(ethylene glycol) chains (SiPc) used as a reference. Analysis of transient absorption darence. Analysis of transient absorption data has shown that charge-recombination occurs with a decay time of 30 ps directly to the ground state

  3. 76 FR 29901 - Electronic Fund Transfers

    Science.gov (United States)

    2011-05-23

    ...when the government of a foreign country sets the exchange rate after a transfer has...the central bank of the foreign country sets the exchange rate after the transfer has...not set or disclose a foreign exchange rate to the sender. It...

  4. 77 FR 71035 - Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT...

    Science.gov (United States)

    2012-11-28

    ...Electronic Funds Transfer (EFT) Market Research Study AGENCY: Financial Management...Electronic Funds Transfer (EFT) Market Research Study.'' DATES: Written comments...Electronic Funds Transfer (EFT) Market Research Study. OMB Number:...

  5. Down-converted luminescence and energy transfer of ?-KGd1?xEuxF4 nanophosphors with selective excitation

    International Nuclear Information System (INIS)

    A series of KGd1?xEuxF4 (x=1, 5, 10, 15, 20, 40, 60, 80 and 100 mol%) nanophosphors were prepared by a simple and reproducible hydrothermal route. The structural and morphological properties of the samples were studied by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing uniform nano-sized particles with cubic phase. The excitation spectra disclosed the intrinsic absorption bands of Eu3+5L6 state at 393 nm and of Gd3+6IJ state at 272.4 nm. From the downconversion (DC) emission spectra, it was found that the optimal Eu3+ concentration was 20 mol% and 15 mol% under 393 nm and 272.4 nm excitation, respectively. The nonradiative energy transfer (ET) mechanism is discussed and it turns out that ET of Eu3+–Eu3+ couple and Gd3+–Eu3+ couple occurs mainly via electric dipole–dipole and electric dipole–quadrupole interactions, respectively. From luminescence decay curves, the lifetimes of KGd1?xEuxF4 nanophosphors are seen to decrease with the increase of Eu3+ concentration. Both the emission spectra and luminescence decay curves show that downconversion ET between Gd3+ and Eu3+ ions is more efficient than that between Eu3+ and Eu3+ ions, thus suggesting potential applications in mercury-free fluorescence lamp and plasma display panel under vacuum ultraviolet (VUV) radiation. -- Highlights: • We prepare a series of KGd1?xEuxF4 nanocrystals with a simple hydrothermal route. • Concentration quenching phenomenon is observed under selective excitations. • The energy transfer mechanism with selective excitations is explored. • KGd1?xEuxF4 phosphors show excellent emissions under VUV excitaion

  6. REFLECTIONS ON THE TWO-STATE ELECTRON TRANSFER MODEL.

    Energy Technology Data Exchange (ETDEWEB)

    Brunschwig, B.S.

    2000-01-12

    There is general agreement that the two most important factors determining electron transfer rates in solution are the degree of electronic interaction between the donor and acceptor sites, and the changes in the nuclear configurations of the donor, acceptor, and surrounding medium that occur upon the gain or loss of an electron Ll-51. The electronic interaction of the sites will be very weak, and the electron transfer slow, when the sites are far apart or their interaction is symmetry or spin forbidden. Since electron motion is much faster than nuclear motion, energy conservation requires that, prior to the actual electron transfer, the nuclear configurations of the reactants and the surrounding medium adjust from their equilibrium values to a configuration (generally) intermediate between that of the reactants and products. In the case of electron transfer between , two metal complexes in a polar solvent, the nuclear configuration changes involve adjustments in the metal-ligand and intraligand bond lengths and angles, and changes in the orientations of the surrounding solvent molecules. In common with ordinary chemical reactions, an electron transfer reaction can then be described in terms of the motion of the system on an energy surface from the reactant equilibrium configuration (initial state) to the product equilibrium configuration (final state) via the activated complex (transition state) configuration.

  7. 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

  8. Measured multipole moments of continuum electron transfer angular distributions

    International Nuclear Information System (INIS)

    The velocity space distribution of electrons emitted near the forward direction from collisions involving fast, highly stripped oxygen ions with gaseous and solid targets is presented and described in terms of multipole moments of the ejected charge distribution, which permits direct comparison with recent theory. The measurements are produced by employing position-sensitive electron detection to combine emission angle definition with conventional electrostatic spectrometry. Agreement obtained between theory and distributions observed for binary continuum electron loss processes coupled with a similar multipole content observed with solid targets suggests a model of convoy electron production dominated by electron loss from the projectile within the bulk of the target. Further, the connection between multipoles of the projectile electron emission distribution in single collisions and the state of excitation of that projectile excited states may provide the basis for a probe of the state of ions traversing bulk solid matter. 14 refs., 3 figs., 1 tab

  9. Highly Oxidizing Excited States of One-Electron Oxidized Guanine in DNA: Wavelength and pH Dependence

    OpenAIRE

    Khanduri, Deepti; Adhikary, Amitava; Sevilla, Michael D.

    2011-01-01

    Excited states of one-electron oxidized guanine in DNA are known to induce hole transfer to the sugar moiety and on deprotonation result in neutral sugar radicals that are precursors of DNA-strand breaks. This work carried out in homogeneous aqueous glass (7.5 M LiCl) at low temperatures (77 to 175 K) shows the extent of photoconversion of one-electron oxidized guanine and the associated yields of individual sugar radicals and are crucially controlled by photon energy, protonation state, and ...

  10. Differential cross sections for electron impact excitation of the electronic bands of phenol

    Science.gov (United States)

    Neves, R. F. C.; Jones, D. B.; Lopes, M. C. A.; Nixon, K. L.; da Silva, G. B.; Duque, H. V.; de Oliveira, E. M.; da Costa, R. F.; Varella, M. T. do N.; Bettega, M. H. F.; Lima, M. A. P.; Ratnavelu, K.; García, G.; Brunger, M. J.

    2015-03-01

    We report results from a joint theoretical and experimental investigation into electron scattering from the important organic species phenol (C6H5OH). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C6H5OH. The measurements were carried out at energies in the range 15-40 eV, and for scattered-electron angles between 10? and 90?. The energy resolution of those experiments was typically ˜80 meV. Corresponding Schwinger multichannel method with pseudo-potentials calculations, with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were conducted at the static exchange plus polarisation (SEP)-level using a minimum orbital basis for single configuration interaction (MOBSCI) approach. Agreement between the measured and calculated DCSs was typically fair, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOBSCI.

  11. 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

  12. Electron scattering at high momentum transfer and small excitation energy

    International Nuclear Information System (INIS)

    A brief report on the experimental knowledge of the form factors of deuterium, tritium and helium-3 is presented. I also present the projects which are being carried out at Saclay by our group. The existing results are compared to theoretical predictions, without presenting again the theoretical frameworks

  13. Solar energy conversion dynamics of interfacial electron and excitation transfer

    CERN Document Server

    Piotrowiak, Piotr

    2013-01-01

    The importance of developing new, clean and renewable sources of energy will continue to grow in the foreseeable future and so will the need for the education of researchers in this field of research. The interest and challenges of the field continue to shift from simple homogeneous solutions to increasingly more complex heterogeneous systems and interfaces. Over the past decade there have been numerous theoretical and experimental breakthroughs many of which still exist only in the primary literature. The aim of this book is to gather in one volume the description of modern, sometimes explora

  14. DOUBLE-ELECTRON EXCITATION AT THE Si K-EDGE OF AMORPHOUS SILICON

    OpenAIRE

    Filipponi, A.; Evangelisti, F.; Bernieri, E.; Mobilio, S.

    1987-01-01

    In this paper we report the experimental evidence of a double-electron excitation involving two deep core states in the X-ray absorption coefficient of a solid amorphous system. For the first time a fine structure (EXAFS) in a double-electron excitation cross section has been identified. Such feature has unambiguously allowed us to assign the dominant excitation channel to a (1s,2p) ? (3p,?p) shake-up transition.

  15. Electron-Transfer Acceleration Investigated by Time Resolved Infrared Spectroscopy.

    Czech Academy of Sciences Publication Activity Database

    Vl?ek Jr., Antonín; Kvapilová, Hana; Towrie, M.; Záliš, Stanislav

    2015-01-01

    Ro?. 48, ?. 3 (2015), s. 868-876. ISSN 0001-4842 Institutional support: RVO:61388955 Keywords : electron transfer * infrared spectroscopy Subject RIV: CG - Electrochemistry Impact factor: 22.323, year: 2014

  16. Combining UV photodissociation with electron transfer for peptide structure analysis.

    Science.gov (United States)

    Shaffer, Christopher J; Marek, Ales; Pepin, Robert; Slovakova, Kristina; Turecek, Frantisek

    2015-03-01

    The combination of near-UV photodissociation with electron transfer and collisional activation provides a new tool for structure investigation of isolated peptide ions and reactive intermediates. Two new types of pulse experiments are reported. In the first one called UV/Vis photodissociation-electron transfer dissociation (UVPD-ETD), diazirine-labeled peptide ions are shown to undergo photodissociation in the gas phase to form new covalent bonds, guided by the ion conformation, and the products are analyzed by electron transfer dissociation. In the second experiment, called ETD-UVPD wherein synthetic labels are not necessary, electron transfer forms new cation-peptide radical chromophores that absorb at 355?nm and undergo specific backbone photodissociation reactions. The new method is applied to distinguish isomeric ions produced by ETD of arginine containing peptides. PMID:25800183

  17. Combining UV photodissociation with electron transfer for peptide structure analysis.

    Czech Academy of Sciences Publication Activity Database

    Shaffer, C. J.; Marek, Aleš; Pepin, R.; Slováková, K.; Ture?ek, F.

    2015-01-01

    Ro?. 50, ?. 3 (2015), s. 470-475. ISSN 1076-5174 Institutional support: RVO:61388963 Keywords : electron transfer dissociation * laser photodissociation * peptide ions * cation radical * chromophores * isomer distinction Subject RIV: CE - Biochemistry Impact factor: 2.709, year: 2013

  18. 76 FR 81019 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2011-12-27

    ...relating to electronic fund transfers, or dormancy, inactivity, or service fees, or expiration...the card, code, or other device. (5) Dormancy or inactivity fee. The terms ``dormancy fee'' and ``inactivity fee'' mean...

  19. Prototropic studies in vitreous and in solid phases: Pyranine and 2-naphthol excited state proton transfer

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Fátima Aparecida das Chagas [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Rezende, Eduardo Triboni [Universidade Nove de Julho, São Paulo, SP (Brazil); Filho, Décio Briotto [Departamento de Bioquímica Instituto de Química, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Brito Rezende, Daisy de [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Cuccovia, Iolanda Midea [Departamento de Bioquímica Instituto de Química, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Gome, Ligia Ferreira [Departamento de Análises Clínicas, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Silva, Mauro Francisco Pinheiro da [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); and others

    2014-02-15

    Excited state proton transfer processes in vitreous glasses and in solid mixtures are investigated by steady state fluorimetry and laser flash photolysis kinetic studies with the photoacids pyranine and 2-naphthol. Glasses were derived from TEOS by the sol–gel condensation process and hydrated solid mixtures from NaCl or KH{sub 2}PO{sub 4}/K{sub 2}HPO{sub 4} crystals. The extent of the water content necessary for the reaction is determined. Shrinkage of TEOS derived monoliths from water loss leads to an increase in proton transfer extent due to the increase in local concentrations of accepting and donor buffer species, but the concomitant increase in the ionic strength actuates in an opposite direction. Furthermore, water losses by aging of air-exposed gel goes to a critical 20% weight fraction, beyond it proton transfer reactions are hindered. Similar studies with solid NaCl or solid phosphate buffer mixtures demonstrated the same critical water level indicating that free water molecules are crucial for the proton to escape from the original cage where the geminate ion pair [–||RO{sup ??}H{sup +}||–] is formed and can undergo coupled proton transfer reactions. -- Highlights: • Pyranine and 2-naphthol excited state proton transfer in SiO{sub 2} gel, solid phosphate buffer and NaCl. • Sol–gel formation leads to contraction and concentration of donor and accepting species. • 20% weight fraction water is required for the ESPT to go forward.

  20. Photoinduced electron transfer and persistent spectral hole-burning in natural emerald.

    Science.gov (United States)

    Riesen, Hans

    2011-06-01

    Wavelength-selective excited-state lifetime measurements and absorption, luminescence, and hole-burning spectra of a natural African emerald crystal are reported. The (2)E excited-state lifetime displays an extreme wavelength dependence, varying from 190 to 37 ?s within 1.8 nm of the R(1)-line. Overall, the excited state is strongly quenched, in comparison to laboratory-created emerald (?=1.3 ms), with an average quenching rate of ?6 × 10(3) s(-1) at 2.5 K. This quenching is attributed to photoinduced electron transfer caused by a relatively high concentration of Fe(2+) ions. The forward electron-transfer rate, k(f), from the nearest possible Fe(2+) sites at around 5 Å is estimated to be ?20 × 10(3) s(-1) at 2.5 K. The photoreductive quenching of the excited Cr(3+) ions by Fe(2+) is followed by rapid electron back-transfer in the ground state upon deactivation. The exchange interaction based quenching can be modeled by assuming a random quencher distribution within the possible Fe(2+) sites with the forward electron-transfer rate, k(f), given as a function of acceptor-donor separation R by exp[(R(f)-R)/a(f)]; R(f) and a(f) values of 13.5 and 2.7 Å are obtained at 2.5 K. The electron transfer/back-transfer reorganizes the local crystal lattice, occasionally leading to a minor variation of the short-range structure around the Cr(3+) ions. This provides a mechanism for spectral hole-burning for which a moderately high quantum efficiency of about ?0.005% is observed. Spectral holes are subject to spontaneous hole-filling and spectral diffusion, and both effects can be quantified within the standard two-level systems for non-photochemical hole-burning. Importantly, the absorbance increases on both sides of broad spectral holes, and isosbestic points are observed, in accord with the expected distribution of the "photoproduct" in a non-photochemical hole-burning process. PMID:21548614

  1. Electron impact excitation of Si II and Fe XIV

    Science.gov (United States)

    Aggarwal, K. M.; Keenan, F. P.

    2015-01-01

    Energy levels, radiative rates, lifetimes, collision strengths and effective collision strengths are calculated for two important Al-like ions, namely Si II and Fe XIV. For Si II, the lowest 56 levels of the 3s23p, 3s3p2 3p3 3s23d, 3s3p3d, 3s24l and 3s25l configurations are included, whereas for Fe XIV additional 80 levels of 3p23d, 3s3d2 and 3p3d2 are considered, but not of 3s2 5l. For the determination of atomic structure GRASP has been adopted and radiative rates are calculated for all E1, E2, Ml and M2 transitions. Electron impact excitation collision strengths are calculated with the DARC code, over a wide energy range, and resonances are resolved in a fine energy mesh to determine effective collision strengths over a wide range of temperatures. Extensive comparisons are made for all atomic parameters with available theoretical and experimental data, and the accuracy of the present results is assessed. Energy levels are estimated to be accurate to ~1% and all other parameters to be better than 20%.

  2. Detailed glycan structural characterization by electronic excitation dissociation.

    Science.gov (United States)

    Yu, Xiang; Jiang, Yan; Chen, Yajie; Huang, Yiqun; Costello, Catherine E; Lin, Cheng

    2013-11-01

    The structural complexity and diversity of glycans parallel their multilateral functions in living systems. To better understand the vital roles glycans play in biological processes, it is imperative to develop analytical tools that can provide detailed glycan structural information. This was conventionally achieved by multistage tandem mass spectrometry (MS(n)) analysis using collision-induced dissociation (CID) as the fragmentation method. However, the MS(n) approach lacks the sensitivity and throughput needed to analyze complex glycan mixtures from biological sources, often available in limited quantities. We define herein the critical parameters for a recently developed fragmentation technique, electronic excitation dissociation (EED), which can yield rich structurally informative fragment ions during liquid chromatographic (LC)-MS/MS analysis of glycans. We further demonstrate that permethylation, reducing end labeling and judicious selection of the metal charge carrier, can greatly facilitate spectral interpretation. With its high sensitivity, throughput, and compatibility with online chromatographic separation techniques, EED appears to hold great promise for large-scale glycomics studies. PMID:24080071

  3. Primary electron transfer processes in photosynthetic reaction centers from oxygenic organisms.

    Science.gov (United States)

    Mamedov, Mahir; Govindjee; Nadtochenko, Victor; Semenov, Alexey

    2015-08-01

    This minireview is written in honor of Vladimir A. Shuvalov, a pioneer in the area of primary photochemistry of both oxygenic and anoxygenic photosyntheses (See a News Report: Allakhverdiev et al. 2014). In the present paper, we describe the current state of the formation of the primary and secondary ion-radical pairs within photosystems (PS) II and I in oxygenic organisms. Spectral-kinetic studies of primary events in PS II and PS I, upon excitation by ~20 fs laser pulses, are now available and reviewed here; for PS II, excitation was centered at 710 nm, and for PS I, it was at 720 nm. In PS I, conditions were chosen to maximally increase the relative contribution of the direct excitation of the reaction center (RC) in order to separate the kinetics of the primary steps of charge separation in the RC from that of the excitation energy transfer in the antenna. Our results suggest that the sequence of the primary electron transfer reactions is P680 ? ChlD1 ? PheD1 ? QA (PS II) and P700 ? A 0A/A 0B ? A 1A/A 1B (PS I). However, alternate routes of charge separation in PS II, under different excitation conditions, are not ruled out. PMID:25648636

  4. Study of the Ne(^3P_2) + CH_3F Electron Transfer Reaction below 1 Kelvin

    OpenAIRE

    Jankunas, Justin; Bertsche, Benjamin; Osterwalder, Andreas

    2014-01-01

    Relatively little is known about the dynamics of electron transfer reactions at low collision energy. We present a study of Penning ionization of ground state methyl fluoride molecules by electronically excited neon atoms in the 13 $\\mu$eV--4.8 meV (150 mK--56 K) collision energy range, using a neutral-neutral merged beam setup. Relative cross sections have been measured for three Ne($^3P_2$)+ CH$_3$F reaction channels by counting the number of CH$_3$F$^+$, CH$_2$F$^+$, and ...

  5. Theory of electron transfer and ionization

    International Nuclear Information System (INIS)

    The main effort reported is directed toward charge transfer and ionization in high energy atomic collisions. The research may be divided into classical trajectory calculations, quantum - mechanical collision theory, and phenomenological treatments of quantal interference effects in heavy ion collisions

  6. Love at first fright: partner salience moderates roller-coaster-induced excitation transfer.

    Science.gov (United States)

    Meston, Cindy M; Frohlich, Penny F

    2003-12-01

    This study examined the effects of residual nervous system arousal on perceptions of sexual attraction. Researchers approached individuals (males, n = 165; females, n = 135) at amusement parks as they were either waiting to begin or as they had just gotten off a roller-coaster ride. Participants were shown a photograph of an average attractive, opposite-gendered individual and asked to rate the individual on attractiveness and dating desirability. Participants were also asked to rate their seatmates' levels of attractiveness. Consistent with the predictions of excitation transfer theory, for males and females riding with a nonromantic partner, ratings of attractiveness and dating desirability toward the photographed individual were higher among persons exiting than entering the ride. Among persons riding with a romantic partner, there were no significant differences in attractiveness or dating desirability ratings between persons entering and exiting the ride. The findings are discussed in terms of the potential moderator effects of a salient romantic partner on excitation transfer. PMID:14574097

  7. Reactant-Product Quantum Coherence in Electron Transfer Reactions

    OpenAIRE

    Kominis, I. K.

    2012-01-01

    We investigate the physical meaning of quantum superposition states between reactants and products in electron transfer reactions. We show that such superpositions are strongly suppressed and to leading orders of perturbation theory do not pertain in electron transfer reactions. This is because of the intermediate manifold of states separating the reactants from the products. We provide an intuitive description of these considerations with Feynman diagrams. We also discuss t...

  8. Interfacial Electron Transfer into Functionalized Crystalline Polyoxotitanate Nanoclusters

    OpenAIRE

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

    2012-01-01

    Interfacial electron transfer (IET) between a chromophore and a semi-conductor nanoparticle is one of the key processes in a dye sensitized solar cell. Theoretical simulations of the electron transfer in polyoxotitanate nanoclusters Ti17O24(OPri)20 (Ti17) functionalized with four para-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 bee...

  9. Multiple-state interfacial electron injection competes with excited state relaxation and de-excitation to determine external quantum efficiencies of organic dye-sensitized solar cells.

    Science.gov (United States)

    Zhang, Min; Yang, Lin; Yan, Cancan; Ma, Wentao; Wang, Peng

    2014-10-14

    A comprehensive description of the complicated dynamics of excited state evolution and charge transfer at the photochemical interface in dye-sensitized solar cells is crucial to understand the mechanism of converting solar photons to clean electricity, providing an informative basis for the future development of advanced organic materials. By selecting two triarylamine-based organic donor-acceptor dyes characteristic of the respective benzoic acid and cyanoacrylic acid anchors, in this paper we reveal stepwise excited state relaxations and multiple-state electron injections at a realistic titania/dye/electrolyte interface based upon ultrafast spectroscopic measurements and theoretical simulations. Density functional theory (DFT) and time-dependent DFT calculations show that the optically generated "hot" excited state of the dye molecules can undergo a significant conformational relaxation via multistage torsional motions, and thereby transform into an equilibrium quinonoid structure characteristic of a more planar conjugated backbone. A set of kinetic parameters derived from the target analysis of femtosecond transient absorption spectra have been utilized to estimate the electron injection yield, which is in good accord with the maximum of external quantum efficiencies. PMID:25156537

  10. Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

    Science.gov (United States)

    Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

    2001-01-01

    The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

  11. Collisional energy transfer from excited polyatomic molecules produced by infrared multiple photon absorption

    Science.gov (United States)

    Baldwin, Alan C.; van den Bergh, Hubert

    1981-01-01

    A simple energy-grained master equation is used to model data on the multiphoton dissociation of CF2HCl as a function of laser fluence and argon bath-gas pressure. Information on energy transfer from vibrationally excited CF2HCl is obtained from an analysis of the competition between laser pumping and collisional energy removal using suitable parametrizations of the laser intensity and the collision process.

  12. Evidence of additional excitation energy transfer pathways in the phycobiliprotein antenna system of Acaryochloris marina.

    Science.gov (United States)

    Nganou, A C; David, L; Adir, N; Pouhe, D; Deen, M J; Mkandawire, M

    2015-02-01

    To improve the energy conversion efficiency of solar organic cells, the clue may lie in the development of devices inspired by an efficient light harvesting mechanism of some aquatic photosynthetic microorganisms that are adapted to low light intensity. Consequently, we investigated the pathways of excitation energy transfer (EET) from successive light harvesting pigments to the low energy level inside the phycobiliprotein antenna system of Acaryochloris marina, a cyanobacterium, using a time resolved absorption difference spectroscopy with a resolution time of 200 fs. The objective was to understand the actual biochemical process and pathways that determine the EET mechanism. Anisotropy of the EET pathway was calculated from the absorption change trace in order to determine the contribution of excitonic coupling. The results reveal a new electron energy relaxation pathway of 14 ps inside the phycocyanin component, which runs from phycocyanin to the terminal emitter. The bleaching of the 660 nm band suggests a broader absorption of the terminal emitter between 660 nm and 675 nm. Further, there are trimer depolarization kinetics of 450 fs and 500 fs in high and low ionic strength, respectively, which arise from the relaxation of the ?84 and ?84 in adjacent monomers of phycocyanin. Under conditions of low ionic strength buffer solution, the evolution of the kinetic amplitude during the depolarization of the trimer is suggestive of trimer conservation within the phycocyanin hexamer. The anisotropy values were 0.38 and 0.40 in high and in low ionic strength, respectively, indicating that there is no excitonic delocalization in the high energy level of phycocyanin hexamers. PMID:25470281

  13. Observation of excited state charge transfer with fs/ps-CARS

    Energy Technology Data Exchange (ETDEWEB)

    Blom, Alex Jason

    2009-08-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4{prime}-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  14. Observation of excited state charge transfer with fs/ps-CARS

    International Nuclear Information System (INIS)

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4(prime)-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4(prime)-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles

  15. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin

    2006-09-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  16. Excitation of Lanthanum and Lutetium Double-Charged Ions in Electron-Atom Collisions

    Directory of Open Access Journals (Sweden)

    Yuriy Mikhailovich Smirnov

    2015-04-01

    Full Text Available 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 levels of LaIII and LuIII are compared.

  17. Electronic reorganization triggered by electron transfer: the intervalence charge transfer of a Fe³?/Fe²? bimetallic complex.

    Science.gov (United States)

    Domingo, Alex; Angeli, Celestino; de Graaf, Coen; Robert, Vincent

    2015-04-30

    The key role of the molecular orbitals in describing electron transfer processes is put in evidence for the intervalence charge transfer (IVCT) of a synthetic nonheme binuclear mixed-valence Fe(3+)/Fe(2+) compound. The electronic reorganization induced by the IVCT can be quantified by controlling the adaptation of the molecular orbitals to the charge transfer process. We evaluate the transition energy and its polarization effects on the molecular orbitals by means of ab initio calculations. The resulting energetic profile of the IVCT shows strong similarities to the Marcus' model, suggesting a response behaviour of the ensemble of electrons analogue to that of the solvent. We quantify the extent of the electronic reorganization induced by the IVCT process to be 11.74 eV, a very large effect that induces the crossing of states reducing the total energy of the transfer to 0.89 eV. PMID:25739890

  18. Sub-excitation electron interactions in rare gases: I, Evidence for the time evolution of the sub-excitation spectrum

    International Nuclear Information System (INIS)

    The production of the '2p' electronic excited states of the rare gases neon, argon, krypton and xenon has been studied using picosecond pulse radiolysis techniques. At pressures below about 5 torr, the emission from these excited states shows a pressure dependent growth-decay pattern. Kinetic analysis of the growth-decay curves reveal formation rate constants which are all greater than 1012M/sup /minus/1/sec/sup /minus/1/. These observations preclude atom-atom collisional processes and support an excitation mechanism involving collisional energy loss from electrons. It is thus concluded that the secondary electron spectrum in pure rare gases at pressures below a few torr takes a few nanoseconds to degrade to energies below that of the lowest excited state. This time scale therefore (by definition) corresponds to the time needed to form subexcitation electrons. In 1 atmosphere of rare gas the time taken would be of the order of 20--30 picoseconds. 5 refs., 4 figs., 1 tab

  19. Electron Transfer in Ferritin as Probed by Muon Spin Relaxation

    Science.gov (United States)

    Telling, Mark T. F.; Kilcoyne, Susan H.

    Electron-transfer processes play a vital role in many biological phenomena, from energy storage to photosynthesis. Positive muons allow such transfer processes in macromolecules, such as proteins, to be probed on a microscopic level. We have used this probe via muon spin relaxation (?SR) to investigate electron-transfer processes in ferritin; the normal iron storage protein. Data collected at finite fields is well described using the Risch-Kehr model at all measured temperatures with inter and intra-chain diffusion rates of 109 and 1011 rad s-1 being determined respectively. The results are compared to similar measurements on other proteins.

  20. Double-hybrid density functional theory for excited electronic states of molecules

    Science.gov (United States)

    Grimme, Stefan; Neese, Frank

    2007-10-01

    Double-hybrid density functionals are based on a mixing of standard generalized gradient approximations (GGAs) for exchange and correlation with Hartree-Fock (HF) exchange and a perturbative second-order correlation part (PT2) that is obtained from the Kohn-Sham (GGA) orbitals and eigenvalues. This virtual orbital-dependent functional (dubbed B2PLYP) contains only two empirical parameters that describe the mixture of HF and GGA exchange (ax) and of the PT2 and GGA correlation (ac), respectively. Extensive testing has recently demonstrated the outstanding accuracy of this approach for various ground state problems in general chemistry applications. The method is extended here without any further empirical adjustments to electronically excited states in the framework of time-dependent density functional theory (TD-DFT) or the closely related Tamm-Dancoff approximation (TDA-DFT). In complete analogy to the ground state treatment, a scaled second-order perturbation correction to configuration interaction with singles (CIS(D)) wave functions developed some years ago by Head-Gordon et al. [Chem. Phys. Lett. 219, 21 (1994)] is computed on the basis of density functional data and added to the TD(A)-DFT/GGA excitation energy. The method is implemented by applying the resolution of the identity approximation and the efficiency of the code is discussed. Extensive tests for a wide variety of molecules and excited states (of singlet, triplet, and doublet multiplicities) including electronic spectra are presented. In general, rather accurate excitation energies (deviations from reference data typically <0.2eV) are obtained that are mostly better than those from standard functionals. Still, systematic errors are obtained for Rydberg (too low on average by about 0.3eV) and charge-transfer transitions but due to the relatively large ax parameter (0.53), B2PLYP outperforms most other functionals in this respect. Compared to conventional HF-based CIS(D), the method is more robust in electronically complex situations due to the implicit account of static correlation effects by the GGA parts. The (D) correction often works in the right direction and compensates for the overestimation of the transition energy at the TD level due to the elevated fraction of HF exchange in the hybrid GGA part. Finally, the limitations of the method are discussed for challenging systems such as transition metal complexes, cyanine dyes, and multireference cases.

  1. On the validity of the electron transfer model in photon emission from ion bombarded vanadium surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Ait El Fqih, M.; El Boujlaidi, A.; Jourdani, R.; Kaddouri, A. [Equipe de Spectroscopie and Imagerie Atomiques des Materiaux, Universite Cadi Ayyad, Marrakech (Morocco); Ait El Fqih, M. [Faculte Polydisciplinaire, Universite Chouaib Doukkali, B.P. 2390 El Jadida (Morocco)

    2011-06-15

    The spectral structure of the radiation (250-500 nm) emitted during sputtering of clean and oxygen-covered polycrystalline vanadium and V{sub 2}O{sub 5} by 5 keV Kr{sup +} ions is presented. The optical spectra obtained by bombarding the vanadium target consist of series of sharp lines, which are attributed to neutral and ionic excited V. The same lines are observed in the spectra of V{sub 2}O{sub 5} and vanadium when oxygen is present. The absolute intensities of VI and VII lines are measured under similar conditions for all spectra. The difference in photon yield from the clean and oxide vanadium targets is discussed in terms of the electron-transfer processes between the excited sputtered and electronic levels of the two types of surfaces. We have examined the existing models of ionisation, excitation, neutralisation and de-excitation of atomic particles in the vicinity of solid surfaces. Continuum radiation was also observed and interpreted as a result of the emission of excited molecules of the metal-oxide. (authors)

  2. On the validity of the electron transfer model in photon emission from ion bombarded vanadium surfaces

    International Nuclear Information System (INIS)

    The spectral structure of the radiation (250-500 nm) emitted during sputtering of clean and oxygen-covered polycrystalline vanadium and V2O5 by 5 keV Kr+ ions is presented. The optical spectra obtained by bombarding the vanadium target consist of series of sharp lines, which are attributed to neutral and ionic excited V. The same lines are observed in the spectra of V2O5 and vanadium when oxygen is present. The absolute intensities of VI and VII lines are measured under similar conditions for all spectra. The difference in photon yield from the clean and oxide vanadium targets is discussed in terms of the electron-transfer processes between the excited sputtered and electronic levels of the two types of surfaces. We have examined the existing models of ionisation, excitation, neutralisation and de-excitation of atomic particles in the vicinity of solid surfaces. Continuum radiation was also observed and interpreted as a result of the emission of excited molecules of the metal-oxide. (authors)

  3. Electron-impact excitation of low-lying preionization-edge electronic and Rydberg transitions of fluoroform and chloroform: Bethe surfaces and absolute generalized oscillator strengths

    International Nuclear Information System (INIS)

    Absolute generalized oscillator strengths (GOSs) of valence-shell electronic transitions of CHF3 and CHCl3 as functions of energy loss (0 endash 150 eV) and momentum transfer (i.e., the Bethe surfaces) have been determined using angle-resolved electron energy-loss spectroscopy at an impact energy of 2.5 keV. The assignments for the prominent low-lying preionization-edge energy-loss features of CHF3 and CHCl3 were inferred from the term values reported previously and from their characteristic experimental GOS profiles. In particular, the GOS profiles of the low-lying Rydberg transitions (which originated from the nonbonding highest occupied molecular orbitals) below the ionization edge at 11.1, 11.9, 12.7, and 13.7 eV in CHF3 and at 8.5, 9.6, and 10.6 eV in CHCl3 were determined. These GOS profiles were found to be dominated by a strong maximum at zero-momentum transfer, which is characteristic of dipole interaction. Weak secondary maxima (and minima) were also observed and could be interpreted qualitatively in terms of the spatial overlaps between the initial-state and final-state orbital wave functions. In addition, the low-lying feature at 7.2 eV in CHCl3 could be attributed predominantly to electronic excitations from the Cl 3p nonbonding (n) orbitals (2a2, 9e, 9a1, and 8e) to a C-Cl ?* antibonding orbital (10a1), according to a single-excitation configuraccording to a single-excitation configuration-interaction (CI) excited-state calculation. The experimental GOS profile of this low-lying feature was found to have a shape that is characteristic of a mixture of dipole-allowed and nondipole interactions, with maxima at momentum transfers of 0 and ?0.9 a.u., respectively. (Abstract Truncated)

  4. Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors

    OpenAIRE

    Kittilstved, Kevin R.; Liu, William K.; Gamelin, Daniel R.

    2005-01-01

    A close link between the charge transfer electronic structures and polarity dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs predicted from their charge transfer energies reproduce experimental trends well. These results provide a unified basis for understanding both n- and p-type ferromagnetic oxide DMSs.

  5. High-energy spin and charge excitations in electron-doped copper oxide superconductors

    OpenAIRE

    Ishii, K.; Fujita, M.; Sasaki, T; Minola, M.; Dellea, G.; Mazzoli, C.; Kummer, K.; Ghiringhelli, G.; Braicovich, L.; Tohyama, T.; Tsutsumi, K; Sato, K.; Kajimoto, R.; Ikeuchi, K.; Yamada, K.

    2014-01-01

    The evolution of electronic (spin and charge) excitations upon carrier doping is an extremely important issue in superconducting layered cuprates and the knowledge of its asymmetry between electron- and hole-dopings is still fragmentary. Here we combine x-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper L3 resonant inelastic x-ray scattering spectra show that magnetic exci...

  6. Methods, algorithms and computer codes for calculation of electron-impact excitation parameters

    OpenAIRE

    Bogdanovich, P.; Kisielius, R.; Stonys, D.

    2015-01-01

    We describe the computer codes, developed at Vilnius University, for the calculation of electron-impact excitation cross sections, collision strengths, and excitation rates in the plane-wave Born approximation. These codes utilize the multireference atomic wavefunctions which are also adopted to calculate radiative transition parameters of complex many-electron ions. This leads to consistent data sets suitable in plasma modelling codes. Two versions of electron scattering co...

  7. Observation of strong electronic correlation for highly excited double Rydberg states of ytterbium

    Science.gov (United States)

    Huang, W.; Xu, X. Y.; Xu, C. B.; Xue, M.; Li, L. Q.; Chen, D. Y.

    1994-02-01

    Using five-laser resonance excitation in combination with a method of sequential ionization by a pulsed and a constant electric field, we have observed the nearly pure spectra (the ion resonance background was greatly suppressed) for the highly excited double Rydberg states NLn'l (N>~40, N/n'>~0.5 and L,lAnalysis of the spectra (relative cross section for different L states) has revealed the importance of the ``hybridization'' in the excited electron orbits which arises from the correlation of the two electrons in such highly excited states.

  8. Scanning electron microscopy of Rydberg-excited Bose-Einstein condensates

    CERN Document Server

    Manthey, T; Niederpruem, T; Langer, P; Guarrera, V; Barontini, G; Ott, H

    2014-01-01

    We report on the realization of high resolution electron microscopy of Rydberg-excited ultracold atomic samples. The implementation of an ultraviolet laser system allows us to excite the atom, with a single-photon transition, to Rydberg states. By using the electron microscopy technique during the Rydberg excitation of the atoms, we observe a giant enhancement in the production of ions. This is due to $l$-changing collisions, which broaden the Rydberg level and therefore increase the excitation rate of Rydberg atoms. Our results pave the way for the high resolution spatial detection of Rydberg atoms in an atomic sample.

  9. Single Production of Excited Neutrino at Clic based Electron Photon Colliders

    International Nuclear Information System (INIS)

    The discovery of excited quarks and leptons, as predicted by composite models, would supply convincing evidence for substructure of fermions. Electron-photon interactions at very high energies provide ideal conditions to look for excited states of first generations offermions. In particular, in magnetic- transition coupling the electron to a gauge bo son would allow for single production of excited neutrinos (?*) through t-channel W boson exchange. In this work, (?*) production followed by the electroweak radiative decays ?*???, ?* ?eW, ?* ??Z is presented. The production cross sections and PT distributions of excited neutrino are studied for CLlC

  10. Electron-helium S-wave model benchmark calculations. II. Double ionization, single ionization with excitation, and double excitation

    International Nuclear Information System (INIS)

    The propagating exterior complex scaling (PECS) method is extended to all four-body processes in electron impact on helium in an S-wave model. Total and energy-differential cross sections are presented with benchmark accuracy for double ionization, single ionization with excitation, and double excitation (to autoionizing states) for incident-electron energies from threshold to 500 eV. While the PECS three-body cross sections for this model given in the preceding article [Phys. Rev. A 81, 022715 (2010)] are in good agreement with other methods, there are considerable discrepancies for these four-body processes. With this model we demonstrate the suitability of the PECS method for the complete solution of the electron-helium system.

  11. Electron transfer in self-assembled orthogonal structures.

    Science.gov (United States)

    Harriman, Anthony; Rostron, James P; Cesario, Michèle; Ulrich, Gilles; Ziessel, Raymond

    2006-07-01

    Two new molecular dyads, comprising pyrromethene (bodipy) and 2,2':6',2"-terpyridine (terpy) subunits, have been synthesized and fully characterized. Absorption and fluorescence spectral profiles are dominated by contributions from the bodipy unit. Zinc(II) cations bind to the vacant terpy ligand to form both 1:1 and 1:2 (cation:ligand) complexes, as evidenced by X-ray structural data, NMR and spectrophotometric titrations. Attachment of the cations is accompanied by a substantial decrease in fluorescence from the bodipy chromophore due to intramolecular electron transfer across the orthogonal structure. At low temperature, nuclear tunneling occurs and the rate of electron transfer is essentially activationless. However, activated electron transfer is seen at higher temperatures and allows calculation of the corresponding reorganization energy and electronic coupling matrix element. In both cases, charge recombination is faster than charge separation. PMID:16805483

  12. Peroxyacetyl radical: electronic excitation energies, fundamental vibrational frequencies, and symmetry breaking in the first excited state.

    Science.gov (United States)

    Copan, Andreas V; Wiens, Avery E; Nowara, Ewa M; Schaefer, Henry F; Agarwal, Jay

    2015-02-01

    Peroxyacetyl radical [CH3C(O)O2] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X?) and first (A?) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals. PMID:25662641

  13. Contribution of electronically excited states to the radiation chemistry of organic systems. Progress report, December 1, 1981-November 30, 1984

    International Nuclear Information System (INIS)

    The fluorescence of saturated hydrocarbon liquids excited by 85Kr beta particles has been studied as a function of the concentration of electron scavenger. It has been possible to extract the probability, p+, that the scavengers attach a geminate electron. The effect of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) to scavenge geminate positive ions in irradiated hydrocarbon liquids has been studied via examination of the recombination fluorescence of TMPD+ + e- as a function of TMPD concentration. The scavenging probability p+ is found to be simply proportional to c. An effect of electron scavengers to reduce the photocurrent from TMPD excited optically above its ionization threshold in nonpolar liquids has been observed and explained in terms of interaction of the scavenger with epithermal electrons. The field and temperature dependences of the photocurrent has been studied in the presence and absence of electron scavengers and the results support the epithermal model. The fractional reduction in TMPD fluorescence in liquid tetramethylsilane caused by imposition of an electric field has been studied as a function of excitation energy (above the photoionization threshold) and as a function of field strength. It has been possible to extract the photoionization quantum yield and the electron thermalization range from approx. = 5.5 eV to 7.5 eV. From an absolute measurement of the yield of excited solute states in irradiated benzene and comparison with optical measurements, it is concluded that the energy transfer efficiency is representable by a Stern-Volmer function that extrapolates to unity at infinite solute concentration. The excimer to monomer ratio in photoexcited polystyrene in solution is found not to depend on polystyrene concentration

  14. Excitation-energy transfer between carotenoid and chlorophyll a in cytochrome b6f complex from bryopsis corticulans

    International Nuclear Information System (INIS)

    The physiological functions of Car and chlorophyll a (Chl a) molecules in the cytochrome b6f (Cyt b6f) complex have attracted considerable research interest. A number of recent findings point to the photo-protective role of Car, although detailed mechanisms remain to be clarified. The Car-to-Chl singlet energy transfer in the Cyt b6f complex seems to be species-dependent, which is probably due to a structural difference in the pigment-protein assembly of Cyt b6f complexes from different species. Our recent work has confirmed the light-harvesting function of ?-carotene in the Cyt b6f complex from Bryopsis corticulans (B. corticulans). Ultrafast Car-to-Chl singlet-energy transfer in the Cyt b6f complex from B. corticulans was investigated by means of femtosecond time-resolved absorption spectroscopy. For all-trans-?-carotene free in n-hexane, the lifetimes of two low-lying singlet excited states, S1(2Ag-) and S2(1Bu+), were determined to be 14.3±0.4 ps and 230±10 fs, respectively. For 9-cis-?-carotene bound to the Cyt b6f complex, the lifetime of S1(2Ag-) state remained unchanged (14.7±0.9 ps), while that of the S2(1Bu+) state was significantly reduced (110±30 fs). In addition, a correlation between the decay of the 1Bu+ state of ?-caru+ state of ?-carotene and the rise of the singlet state of Chla was clearly observed. This spectroscopic evidence shows that the S2(1Bu+) state is able to transfer electronic excitation to the Qx state of Chl a whereas the S1(2Ag-) state remains inactive. The time constant and efficiency of energy transfer via the 1Bu+ state were determined to be 240±40 fs and (49±4)%, respectively; the latter value supports the overall energy-transfer efficiency of 24% that was determined by steady-state fluorescence spectroscopy, the apparent discrepancy in efficiency may be due to competing deactivation of the 1Bu+ state. The efficient ? -carotene-to-Chl a singlet energy-transfer in the Cyt b6f complex from B. corticulans may originate from the unique protein structure that is adapted to the harsh condition of light exposure in the tidal zone. B. corticulans is considered as a unique sample for studying possible light-assisted roles of Car and Chl a molecules in the Cyt b6f complex. (authors)

  15. Nonlinear responses of electronic-excitation-induced phase transformations in GaSb nanoparticles

    International Nuclear Information System (INIS)

    We studied electronic-excitation-induced phase transformations in nanoparticles using transmission electron microscopy. GaSb particles excited by 75 keV electrons transform to two phases consisting of an antimony core and a gallium shell or an amorphous phase, or remain in the original crystalline phase, depending on particle size and/or temperature. It is suggested that such nonlinear responses of the phase transformations may arise from synergistic effects of bond instability, localized excitations, enhanced diffusivity, or thermal equilibrium in reactions

  16. Nonlinear Responses of Electronic-Excitation-Induced Phase Transformations in GaSb Nanoparticles

    Science.gov (United States)

    Yasuda, H.; Mori, H.; Lee, J. G.

    2004-03-01

    We studied electronic-excitation-induced phase transformations in nanoparticles using transmission electron microscopy. GaSb particles excited by 75keV electrons transform to two phases consisting of an antimony core and a gallium shell or an amorphous phase, or remain in the original crystalline phase, depending on particle size and/or temperature. It is suggested that such nonlinear responses of the phase transformations may arise from synergistic effects of bond instability, localized excitations, enhanced diffusivity, or thermal equilibrium in reactions.

  17. Ultrafast electronic dynamics in laser-excited crystalline bismuth

    OpenAIRE

    Chekalin S.; Misochko O.; Melnikov A.

    2013-01-01

    Femtosecond spectroscopy was applied to capture complex dynamics of non equilibrium electrons in bismuth. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along the ?-T direction of the Brillouin zone

  18. Direct spectroscopic evidence of energy transfer from photo-excited semiconducting polymers to single-walled carbon nanotubes

    International Nuclear Information System (INIS)

    Single-walled carbon nanotubes have been efficiently dispersed in an organic solvent using the semiconducting polymers MEHPPV and PFO. It has been found that energy is transferred to the carbon nanotubes when the polymer is photo-excited across its minimum energy gap. This is shown using photoluminescence excitation mapping in the range of both the polymer's and the nanotube's optical absorbance. Possible mechanisms for the energy transfer are discussed

  19. Direct spectroscopic evidence of energy transfer from photo-excited semiconducting polymers to single-walled carbon nanotubes.

    OpenAIRE

    Nish, A; Hwang, JY; Doig, J.; Nicholas, RJ

    2008-01-01

    Single-walled carbon nanotubes have been efficiently dispersed in an organic solvent using the semiconducting polymers MEHPPV and PFO. It has been found that energy is transferred to the carbon nanotubes when the polymer is photo-excited across its minimum energy gap. This is shown using photoluminescence excitation mapping in the range of both the polymer's and the nanotube's optical absorbance. Possible mechanisms for the energy transfer are discussed.

  20. ATOMIC AND MOLECULAR PHYSICS: Theoretical Study on Inner Shell Electron Impact Excitation of Lithium

    Science.gov (United States)

    Yang, Ning-Xuan; Dong, Chen-Zhong; Jiang, Jun

    2009-06-01

    Cross sections for electron impact excitation of lithium from the ground state 1s22s to the excited states 1s2s2, 1s2p2, 1s2snp (n = 2-5), 1s2sns (n = 3-5), 1s2pns (n = 3-5), and 1s2pnp (n = 3-5) are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25(2008)3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57eV show two-peak structures.

  1. Effect of proton transfer on the electronic coupling in DNA

    Energy Technology Data Exchange (ETDEWEB)

    Rak, Janusz [Faculty of Chemistry, University of Gdansk, Sobieskiego 18, 80-353 Gdansk (Poland)], E-mail: janusz@raptor.chem.univ.gda.pl; Makowska, Joanna [Faculty of Chemistry, University of Gdansk, Sobieskiego 18, 80-353 Gdansk (Poland); Voityuk, Alexander A. [Institucio Catalana de Recerca i Estudis Avancats (ICREA), Institute of Computational Chemistry, Universitat de Girona, 17071 Girona (Spain)], E-mail: alexander.voityuk@icrea.es

    2006-06-20

    The effects of single and double proton transfer within Watson-Crick base pairs on donor-acceptor electronic couplings, V {sub da}, in DNA are studied on the bases of quantum chemical calculations. Four dimers [AT,AT], [GC,GC], [GC,AT] and [GC,TA)] are considered. Three techniques - the generalized Mulliken-Hush scheme, the fragment charge method and the diabatic states method - are employed to estimate V {sub da} for hole transfer between base pairs. We show that both single- and double proton transfer (PT) reactions may substantially affect the electronic coupling in DNA. The electronic coupling in [AT,AT] is predicted to be most sensitive to PT. Single PT within the first base pair in the dimer leads to increase in the hole transfer efficiency by a factor of 4, while proton transfer within the second pair should substantially, by 2.7 times, decrease the rate of charge transfer. Thus, directional asymmetry of the PT effects on the electronic coupling is predicted. The changes in the V {sub da} matrix elements correlate with the topological properties of orbitals of donor and acceptor and can be qualitatively rationalized in terms of resonance structures of donor and acceptor. Atomic pair contributions to the V {sub da} matrix elements are also analyzed.

  2. Effect of proton transfer on the electronic coupling in DNA

    International Nuclear Information System (INIS)

    The effects of single and double proton transfer within Watson-Crick base pairs on donor-acceptor electronic couplings, V da, in DNA are studied on the bases of quantum chemical calculations. Four dimers [AT,AT], [GC,GC], [GC,AT] and [GC,TA)] are considered. Three techniques - the generalized Mulliken-Hush scheme, the fragment charge method and the diabatic states method - are employed to estimate V da for hole transfer between base pairs. We show that both single- and double proton transfer (PT) reactions may substantially affect the electronic coupling in DNA. The electronic coupling in [AT,AT] is predicted to be most sensitive to PT. Single PT within the first base pair in the dimer leads to increase in the hole transfer efficiency by a factor of 4, while proton transfer within the second pair should substantially, by 2.7 times, decrease the rate of charge transfer. Thus, directional asymmetry of the PT effects on the electronic coupling is predicted. The changes in the V da matrix elements correlate with the topological properties of orbitals of donor and acceptor and can be qualitatively rationalized in terms of resonance structures of donor and acceptor. Atomic pair contributions to the V da matrix elements are also analyzed

  3. Differential cross section measurements for electron impact on barium in ground and laser excited states

    International Nuclear Information System (INIS)

    Absolute differential cross section measurements were made for electron scattering by atomic barium in ground and laser-excited states. A crossed electron-atom-laser beam geometry was employed, and a new electron impact spectrometer was developed. Differential cross section (DCS) measurements for electron scattering by the ground 6s2 1S level of barium included elastic and inelastic (excitation of the 6s6p 1P and 6s5d 1D levels) processes. Measurements were made for scattering angles ranging from 30 to 1300 for incident electron energies of 20, 30, 40, 60, 80, and 100 eV. All of the DCS were extremely forward peaked, with the 1P DCS often exceeding the elastic DCS for scattering angles less than 100. The excited 6s6p 1P level of barium was optically pumped by a tunable, single-frequency dye laser. Through cascade processes, the lower-lying 6s6p 3P, 6s5d 1D, and 6s5d 3D levels were also populated. DCS measurements for electron scattering from these excited states were made for an angular range from 30 to 200 at 30 eV electron impact energy. A total of 6 superelastic and 18 inelastic transitions from these excited states were observed. Absolute DCS were measured for electron scattering by the excited 6s6p 1P and 6s5d 1D levels, while relative DCS were measured for scattering by the 6s6p 33P and 6s5d 3D levels. For these excited states, inelastic electronscattering dominated over superelastic electron scattering. The excited 6s6p 1P level was prepared as a specific, known combination of magnetic sublevels. Electron scattering from this polarized atomic beam provided information on the scattering amplitudes and their relative phase

  4. Sodium 3P fine-structure excitation transfer induced by collisions with rubidium and caesium atoms

    International Nuclear Information System (INIS)

    The cross sections for the excitation energy transfer in the collisional processes Na*(3P1/2)+M(nS1/2)?Na*(3P3/2)+M(nS1/2), M being ground-state Rb (n=5) or Cs (n=6) atom, have been measured by laser fluorescence method. With either of the two sodium 3P fine-structure states optically excited, the intensity ratio of the sensitized to direct fluorescence was measured. The polarization effects due to partially polarized and anisotropic direct fluorescence were investigated. The measured cross sections (T=530 K) for the sodium 3P fine-structure excitation transfer induced by collisions with Rb are: ?(1/2?3/2)=170 A2 and ?(3/2?1/2)=94 A2, with an overall accuracy of 20%. The corresponding values in the Cs case are: ? (1/2?3/2)=140 A2, ?(3/2?1/2)=83 A2. The theoretical calculations reveal the decisive role of the dipole-quadrupole interaction. The obtained values are in satisfactory agreement with the experiment only if both the dipole-dipole and dipole-quadrupole interactions are taken into account, while the calculations involving the dipole-dipole term alone yield the cross section values which are as much as one order magnitude lower than the experimentally observed ones. (Author)

  5. Excitation transfer in two two-level systems coupled to an oscillator

    International Nuclear Information System (INIS)

    We consider a generalization of the spin-boson model in which two different two-level systems are coupled to an oscillator, under conditions where the oscillator energy is much less than the two-level system energies, and where the oscillator is highly excited. We find that the two-level system transition energy is shifted, producing a Bloch-Siegert shift in each two-level system similar to what would be obtained if the other were absent. At resonances associated with energy exchange between a two-level system and the oscillator, the level splitting is about the same as would be obtained in the spin-boson model at a Bloch-Siegert resonance. However, there occur resonances associated with the transfer of excitation between one two-level system and the other, an effect not present in the spin-boson model. We use a unitary transformation leading to a rotated system in which terms responsible for the shift and splittings can be identified. The level splittings at the anticrossings associated with both energy exchange and excitation transfer resonances are accounted for with simple two-state models and degenerate perturbation theory using operators that appear in the rotated Hamiltonian

  6. Plugging in or going wireless: strategies for interspecies electron transfer

    Science.gov (United States)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena

    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 which two species establish electrical contact is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions. PMID:24904551

  7. Plugging in or Going Wireless: Strategies for Interspecies Electron Transfer

    Directory of Open Access Journals (Sweden)

    PravinMallaShrestha

    2014-05-01

    Full Text Available 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 which two species establish electrical contacts is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. It seems likely that there are additional alternative strategies for interspecies electrical connections that have yet to be discovered. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions.

  8. Plugging in or Going Wireless : Strategies for Interspecies Electron Transfer

    DEFF Research Database (Denmark)

    Shrestha, Pravin; Rotaru, Amelia-Elena

    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 which two species establish electrical contact is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions.

  9. Electrochemical proton-coupled electron transfer: Beyond the golden rule

    International Nuclear Information System (INIS)

    Electrochemical proton-coupled electron transfer rate constant expressions that interpolate between the golden rule and solvent-controlled limits are derived. These expressions include the effects of solvent dynamics and thus are applicable for a wide range of vibronic couplings and solvent relaxation times. The golden rule limit is defined in terms of weak vibronic coupling and fast solvent relaxation, and the solvent-controlled limit is defined in terms of strong vibronic coupling and slow solvent relaxation. In the golden rule limit, the rate constant is proportional to the square of the vibronic coupling and is independent of the solvent relaxation time. In the solvent-controlled limit, the rate constant is independent of the vibronic coupling and increases as the solvent relaxation time decreases. The interconversion between the solvent-controlled and golden rule limits can be induced by altering the proton donor-acceptor mode frequency and the overlap between the reactant and product proton vibrational wave functions, as well as the electronic coupling, the solvent relaxation time, and the overpotential. The kinetic isotope effect behaves differently in the solvent-controlled and golden rule limits and thus provides a unique probe for characterizing electrochemical proton-coupled electron transfer processes. The analogous rate constant expressions for electrochemical electron transfer and homogeneous proton-coupled electron transfer are also presented. The impacron transfer are also presented. The impact of electrode overpotential, solvent relaxation time, and proton donor-acceptor mode frequency on the rate constants are analyzed for model systems.

  10. Dissociative electron attachment and electron-impact resonant dissociation of vibrationally excited O2 molecules

    CERN Document Server

    Laporta, V; Tennyson, J

    2015-01-01

    State-by-state cross sections for dissociative electron attachment and electron-impact dissociation for molecular oxygen are computed using ab initio resonance curves calculated with the R-matrix method. When O2 is in its vibrational ground state, the main contribution for both processes comes from the $^2\\Pi_u$ resonance state of $O_2^-$ but with a significant contribution from the $^4\\Sigma$ resonant state. Vibrational excitation leads to an increased contribution from the low-lying $^2\\Pi_{g}$ resonance, greatly increased cross sections for both processes, and the threshold moving to lower energies. These results provide important input for models of O2-containing plasmas in nonequilibrium conditions.

  11. Performance of the M11 and M11-L density functionals for calculations of electronic excitation energies by adiabatic time-dependent density functional theory.

    Science.gov (United States)

    Peverati, Roberto; Truhlar, Donald G

    2012-08-28

    Adiabatic time-dependent density functional theory is a powerful method for calculating electronic excitation energies of complex systems, but the quality of the results depends on the choice of approximate density functional. In this article we test two promising new density functionals, M11 and M11-L, against databases of 214 diverse electronic excitation energies, and we compare the results to those for 16 other density functionals of various kinds and to time-dependent Hartree-Fock. Charge transfer excitations are well known to be the hardest challenge for TDDFT. M11 is a long-range-corrected hybrid meta-GGA, and it shows better performance for charge transfer excitations than any of the other functionals except M06-HF, which is a specialized functional that does not do well for valence excitations. Several other long-range-corrected hybrid functionals also do well, and we especially recommend M11, ?B97X, and M06-2X for general spectroscopic applications because they do exceptionally well on ground-state properties as well as excitation energies. Local functionals are preferred for many applications to extended systems because of their significant cost advantage for large systems. M11-L is a dual-range local functional and-unlike all previous local functionals-it has good performance for Rydberg states as well as for valence states. Thus it is highly recommended for excitation energy calculations on extended systems. PMID:22801459

  12. Control of electron localization in highly excited states with two ultraviolet laser pulses

    International Nuclear Information System (INIS)

    We propose and demonstrate a scheme for controlling the electron localization in the dissociating H2+ in highly excited states. The control is achieved through two steps: the excitation and the coupling of the electronic wavepackets. Firstly, the excitation is triggered by an ultraviolet laser pulse with a critical wavelength, in which the wavepackets can be launched to the highly excited state (2s?g) efficiently from the ground state (1s?g). Then, we utilize a second time-delayed ultraviolet laser pulse to manipulate the population of the degenerate state (3p?u) around the one-photon coupling region. Our results show that, by adjusting the time delay between the two pulses and the carrier–envelope phase of the second pulse, the control of electron localization of H2+ in highly excited states can be achieved. (paper)

  13. Photoinduced electron transfer in arylacridinium conjugates in a solid glass matrix.

    Science.gov (United States)

    Jones, Guilford; Yan, Dingxue; Hu, Jingqiu; Wan, Jiandi; Xia, Bing; Vullev, Valentine I

    2007-06-21

    The photophysical properties of a series of 9-arylacridinium conjugates in solid glass matrices composed of sucrose octaacetate have been determined. The fluorescence of the charge-shift states is significantly enhanced because of the retardation of nonradiative pathways for back-electron transfer. Changes of more than 3 orders of magnitude in back-electron-transfer rates (sucrose octaacetate glass vs conventional solvents at room temperature) were observed. Transient spectra displayed long-lived charge-shift species in the microsecond time regime for thianthrene acridinium conjugates. The rate retardation is associated with slow solvation times for surrounding solvent layers in the solid matrix. The red-edge effect (excitation wavelength-dependent fluorescence) for the arylacridinium ions in solid glass confirms the microheterogeneity of the sucrose octaacetate medium. PMID:17539680

  14. Electron Transport, Energy Transfer, and Optical Response in Single Molecule Junctions

    Science.gov (United States)

    White, Alexander

    2015-03-01

    The field of molecular electronics has grown significantly since the first measurements of single molecule conductance. The single molecule junction, a device in which two conducting leads are spanned by a single molecule, has become a powerful tool for studying charge transfer at the molecular level. While early experiments were focused on elastic electron conductance, today measurements of vibronic effects, molecular optical response, spintronics, thermal conductance, and quantum interference and decoherence effects are prominent areas of research. These new experimental advancements demand improved theoretical treatments which properly account for the interactions between different degrees of freedom: charge, electronic, vibrational, spin, etc.; all in physically relevant parameter ranges. This talk focuses on using a many-body states based approach to investigate the regime of strong interaction between these degrees of freedom, with relatively weak coupling between the molecule and the electric reservoirs created by the conducting leads. We focused on three related processes, electron transfer, electronic energy transfer and molecular excitation. In collaboraton with Boris Fainberg, Faculty of Sciences, Holon Institute of Technology; Sergei Tretiak, Theoretical Division, Center for Integrated Nanotechnologies, Los Alamos National Laboratory; and Michael Galperin, Department of Chemistry and Biochemistry, University of California San Diego.

  15. Peculiar effects from number theory for doubly excited Rydberg states of two-electron ions

    International Nuclear Information System (INIS)

    Without electron repulsion there were accidental degeneracies between some of the excited states of two- (or more-) electron atoms among themselves and also with ionization threshold. The effects of these degeneracies on resonances of highly ionized atoms decaying by the Auger effect of autoionization, are investigated by treating the repulsion between the electrons as a perturbation. (author)

  16. Excitation and dissociation of molecules by low-energy (0-15 eV) electrons

    International Nuclear Information System (INIS)

    The author deals with excitation and dissociation processes which result from the interaction between low-energy (0.15 eV) electrons and molecules. Low-energy electron-impact spectroscopy is used to gain a better knowledge of the electronic structure of halomethanes, ethylene and some of its halogen substituted derivatives, and some more complex organic molecules. (Auth.)

  17. Ultrafast intermolecular vibrational excitation transfer from solute to solvent: Observation of intermediate states

    Science.gov (United States)

    Son, Hyewon; Park, Kwang-Hee; Kwak, Kyung-Won; Park, Sungnam; Cho, Minhaeng

    2013-08-01

    Ultrafast two-dimensional infrared (2DIR) and IR pump-probe (PP) spectroscopy was used to study the intermolecular vibrational energy transfer process from the excited state of asymmetric stretching vibration of HN3 to the overtone band of C-O stretching vibration of solvent methanol. A series of time-resolved 2DIR spectra indicate an intermolecular vibrational excitation transfer between the two modes, since the corresponding cross peaks appear at longer waiting times (>20 ps). However, detailed analyses of temperature-dependent FTIR, dispersed IR PP, and 2DIR spectra showed that the vibrational relaxation of the azido stretch mode and its energy transfer to solvent methanol C-O stretch overtone mode involve not only heat dissipation directly to the solvent bath modes but also production of transient intermediate states. The present experimental work demonstrates that ultrafast nonlinear IR spectroscopy is quite useful to shed light into the complicated vibrational relaxation dynamics of H-bonded solute-solvent systems.

  18. Direct Interspecies Electron Transfer between Geobacter metallireducens and Methanosarcina barkeri

    Science.gov (United States)

    Shrestha, Pravin Malla; Liu, Fanghua; Markovaite, Beatrice; Chen, Shanshan; Nevin, Kelly P.; Lovley, Derek R.

    2014-01-01

    Direct interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability of Methanosarcina barkeri to participate in DIET was evaluated in coculture with Geobacter metallireducens. Cocultures formed aggregates that shared electrons via DIET during the stoichiometric conversion of ethanol to methane. Cocultures could not be initiated with a pilin-deficient G. metallireducens strain, suggesting that long-range electron transfer along pili was important for DIET. Amendments of granular activated carbon permitted the pilin-deficient G. metallireducens isolates to share electrons with M. barkeri, demonstrating that this conductive material could substitute for pili in promoting DIET. When M. barkeri was grown in coculture with the H2-producing Pelobacter carbinolicus, incapable of DIET, M. barkeri utilized H2 as an electron donor but metabolized little of the acetate that P. carbinolicus produced. This suggested that H2, but not electrons derived from DIET, inhibited acetate metabolism. P. carbinolicus-M. barkeri cocultures did not aggregate, demonstrating that, unlike DIET, close physical contact was not necessary for interspecies H2 transfer. M. barkeri is the second methanogen found to accept electrons via DIET and the first methanogen known to be capable of using either H2 or electrons derived from DIET for CO2 reduction. Furthermore, M. barkeri is genetically tractable, making it a model organism for elucidating mechanisms by which methanogens make biological electrical connections with other cells. PMID:24837373

  19. First-principles calculations of heat capacities of ultrafast laser-excited electrons in metals

    Science.gov (United States)

    Bévillon, E.; Colombier, J. P.; Recoules, V.; Stoian, R.

    2015-05-01

    Ultrafast laser excitation can induce fast increases of the electronic subsystem temperature. The subsequent electronic evolutions in terms of band structure and energy distribution can determine the change of several thermodynamic properties, including one essential for energy deposition; the electronic heat capacity. Using density functional calculations performed at finite electronic temperatures, the electronic heat capacities dependent on electronic temperatures are obtained for a series of metals, including free electron like, transition and noble metals. The effect of exchange and correlation functionals and the presence of semicore electrons on electronic heat capacities are first evaluated and found to be negligible in most cases. Then, we tested the validity of the free electron approaches, varying the number of free electrons per atom. This shows that only simple metals can be correctly fitted with these approaches. For transition metals, the presence of localized d electrons produces a strong deviation toward high energies of the electronic heat capacities, implying that more energy is needed to thermally excite them, compared to free sp electrons. This is attributed to collective excitation effects strengthened by a change of the electronic screening at high temperature.

  20. DFT and time-resolved IR investigation of electron transfer between photogenerated 17- and 19-electron organometallic radicals

    Energy Technology Data Exchange (ETDEWEB)

    Cahoon, James B.; Kling, Matthias F.; Sawyer, Karma R.; Andersen, Lars K.; Harris, Charles B.

    2008-04-30

    The photochemical disproportionation mechanism of [CpW(CO){sub 3}]{sub 2} in the presence of Lewis bases PR{sub 3} was investigated on the nano- and microsecond time-scales with Step-Scan FTIR time-resolved infrared spectroscopy. 532 nm laser excitation was used to homolytically cleave the W-W bond, forming the 17-electron radicals CpW(CO){sub 3} and initiating the reaction. With the Lewis base PPh{sub 3}, disproportionation to form the ionic products CpW(CO){sub 3}PPh{sub 3}{sup +} and CpW(CO){sub 3}{sup -} was directly monitored on the microsecond time-scale. Detailed examination of the kinetics and concentration dependence of this reaction indicates that disproportionation proceeds by electron transfer from the 19-electron species CpW(CO){sub 3}PPh{sub 3} to the 17-electron species CpW(CO){sub 3}. This result is contrary to the currently accepted disproportionation mechanism which predicts electron transfer from the 19-electron species to the dimer [CpW(CO){sub 3}]{sub 2}. With the Lewis base P(OMe){sub 3} on the other hand, ligand substitution to form the product [CpW(CO){sub 2}P(OMe){sub 3}]{sub 2} is the primary reaction on the microsecond time-scale. Density Functional Theory (DFT) calculations support the experimental results and suggest that the differences in the reactivity between P(OMe){sub 3} and PPh{sub 3} are due to steric effects. The results indicate that radical-to-radical electron transfer is a previously unknown but important process for the formation of ionic products with the organometallic dimer [CpW(CO){sub 3}]{sub 2} and may also be applicable to the entire class of organometallic dimers containing a single metal-metal bond.