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1

Electron-transfer reactions of excited states  

Energy Technology Data Exchange (ETDEWEB)

Powerful models exist for the prediction and analysis of excited state outer-sphere electron transfer reactivity. Important parameters in these models are the driving force for the electron transfer and the electron exchange rate of the excited state couple. The driving force for excited state electron transfer is determined by the reduction potentials of the excited state and of its reaction partner, and the reduction potential of the excited state can be estimated from its excitation energy and the corresponding ground state reduction potential or from the free energy dependence of its reactions with characterized couples. The electron exchange rate of the excited state couple can be estimated from analogies with ground state exchanges or from the rates of its reactions with characterized reaction partners. The free energy dependences of quenching and back reactions are determined by the competition of elementary electron transfer steps and diffusional processes. Detailed analyses of these dependences can provide nearly unique information about the individual electron transfer steps - information that is crucial to the understanding of the factors determining quenching rates in particular systems and to the manipulation of photochemical yields. The relations between ground state and excited state electron transfer reactions of transition metal complexes, particularly of the polypyridine complexes, are discussed.

Sutin, N.; Creutz, C.

1983-10-01

2

Radiationsless transfer of electron excitation during vibrational relaxation  

International Nuclear Information System (INIS)

[en] The hot transfer of electronic excitation during the vibrarional relaxation in the excited electronic state of the donor is studied theoretically for strong vibronic interactions. The theory is applied to inter- and intra-centre transfer. The Weber effect is explained. The role of hot transfer in photosynthesis, in intra-centre luminescence depolarisation and in oher processes is discussed

1974-01-01

3

Electronic and Nuclear Factors in Charge and Excitation Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Piotr Piotrowiak

2004-09-28

4

Studies of impulsive vibrational influence on ultrafast electronic excitation transfer.  

Science.gov (United States)

We investigated electronic energy-transfer dynamics in three model dimers within which coherent intramonomer nuclear motion had been induced by impulsive Raman excitation using an optimized, electronically preresonant control pulse. Calculations of the donor-survival probability, the ultrafast pump-probe signal, and the pump-probe difference signal are presented for dithia-anthracenophane and homodimers of 2-difluoromethylanthracene and 2-trifluoromethylanthracene. Survival probabilities and signals, along with phase-space analyses, elucidated the mechanisms, extent, and spectroscopic manifestations of external vibrational or torsional control over electronic excitation transfer. PMID:22236325

Biggs, Jason D; Cina, Jeffrey A

2012-02-10

5

Electron energy transfer rates for vibrational excitation of N2.  

Energy Technology Data Exchange (ETDEWEB)

The calculation of the electron density and electron temperature distribution in our ionosphere (from {approx} 150-600 km) requires a knowledge of the various heating, cooling and energy flow processes that occur. The energy transfer from electrons to neutral gases and ions is one of the dominant electron cooling processes in the ionosphere, and the role of vibrationally excited N2 in this is particularly significant.

Campbell, L. (Laurence); Cartwright, D. C. (David C.); Tuebner, P. J. O.; Brunger, M. J. (Michael J.)

2003-01-01

6

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

International Nuclear Information System (INIS)

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

1987-01-01

7

Electronic structure charge transfer excitations, and high temperature superconductivity  

International Nuclear Information System (INIS)

[en] 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

1988-01-01

8

Importance of Charge Transfer Excitations in DNA Electron Spectrum:  

Science.gov (United States)

Electron spectra of DNA model compounds, adenosine-thymidine and guanosine-cytidine nucleoside base pairs, as well as the relevant homogeneous stacked base pair steps in A-DNA and B-DNA conformations, were investigated using ZINDO semiempirical quantum-chemical method. This work confirms that, in DNA with intact Watson-Crick hydrogen bonding and base stacking, the highest occupied molecular orbitals (HOMO) are residing on purine base residues, whereas the lowest unoccupied molecular orbitals (LUMO) — on pyrimidine base residues. In general, the present results are satisfactorily comparable with the available experimental data. The role of charge transfer excitations in the polymer DNA 260 nm spectral band is discussed.

Starikov, E. B.

9

Electron transfer, ionization, and excitation in atomic collisions  

International Nuclear Information System (INIS)

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

1992-01-01

10

Electron transfer by excited benzoquinone anions: slow rates for two-electron transitions.  

UK PubMed Central (United Kingdom)

Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ?G°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -?G° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-?G°) can restore fast rates of electron transfer.

Zamadar M; Cook AR; Lewandowska-Andralojc A; Holroyd R; Jiang Y; Bikalis J; Miller JR

2013-09-01

11

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1984-01-01

12

Search for resonant electron transfer and double excitation in Kr(sup 34+) + H2 collisions  

Science.gov (United States)

Resonant electron transfer and double excitation (RME) is a correlated electron process which is expected to occur in an ion-atom collision when electron capture is accompanied by the simultaneous excitation of two inner-shell electrons. RT2 is similar to resonant transfer excitation (RTE) in which only a single electron is excited. RT2E was investigated experimentally for 38-42 MeV/u Kr34 + H2 collisions by observing x-ray emission associated with single-electron capture. No events associated with Kr K x rays (near 13 keV) were observed; however, events do occur at about twice (greater than 22 keV) the Kr K x-ray energy. Several possible sources of these latter x rays have been considered.

Zaharakis, K. E.; Haar, R. R.; Tanis, J. A.; Clark, M. W.; Plano, V. L.

13

Using Wave-Packet Interferometry to Monitor the External Vibrational Control of Electronic Excitation Transfer  

CERN Multimedia

We investigate the control of electronic energy transfer in molecular dimers through the preparation of specific vibrational coherences prior to electronic excitation, and its observation by nonlinear wave-packet interferometry. Laser-driven coherent nuclear motion can affect the instantaneous resonance between site-excited electronic states and thereby influence short-time electronic excitation transfer (EET). We first illustrate this control mechanism with calculations on a dimer whose constituent monomers undergo harmonic vibrations. We then consider the use of nonlinear wave-packet interferometry (nl-WPI) experiments to monitor the nuclear dynamics accompanying EET in general dimer complexes following impulsive vibrational excitation by a sub-resonant control pulse (or control pulse sequence). In measurements of this kind, two pairs of polarized phase-related femtosecond pulses following the control pulse generate superpositions of coherent nuclear wave packets in optically accessible electronic states. I...

Biggs, Jason D

2009-01-01

14

Study of intermediates from transition metal excited-state electron- transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

Progress on 6 projects is reported: excited state absorption spectrum of Ru(bpy)[sub 3][sup 2+], solvent cage model for electron transfer quenching, reductive quenching of [sup *]Cr(III) complexes, solution medium effects in oxidative quenching of [sup *]Ru(II) complexes, photosensitized oxidation of phenol in aqueous solution, and quenching of Ru(II) complexes by oxygen.

Hoffman, M.Z.

1993-03-31

15

Quenching of the excited state of hydrated Europium(III) ions by electron transfer  

Energy Technology Data Exchange (ETDEWEB)

This thesis explores the oxidation-reduction chemistry of the excited state of Eu(III) ions, *Eu{sub aq}{sup 3+}, in aqueous solutions. Evidence is presented for the quenching of *Eu{sup 3+} by reductive electron transfer. It is concluded that *Eu{sup 3+} is not a strong energy transfer reagent. The reactivity of *Eu{sub aq}{sup 3+} is compared with that of *UO{sub 2}{sup 2+}.

Christensen, K.

1993-08-01

16

Search for resonant electron transfer and double excitation in Kr(sup 34+) + H(sub 2) collisions.  

Science.gov (United States)

Resonant electron transfer and double excitation (RME) is a correlated electron process which is expected to occur in an ion-atom collision when electron capture is accompanied by the simultaneous excitation of two inner-shell electrons. RT2 is similar to...

K. E. Zaharakis R. R. Haar J. A. Tanis M. W. Clark V. L. Plano

1992-01-01

17

Electron transfer of carbonylmetalate radical pairs: femtosecond visible spectroscopy of optically excited ion pairs  

Energy Technology Data Exchange (ETDEWEB)

Charge transfer excitation at 640 nm of the cobaltocenium tetracarbonylcobaltate ion pair, [Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup -}], was monitored in 1,2- dichloroethane solution by femtosecond transient visible absorption spectroscopy. The absorption prepares a neutral radical pair that can undergo spontaneous back electron transfer, and which shows a double peaked spectrum with features at 760 and 815 nm at 3 ps delay time. Transient decay times of 5.8{+-}0.5 ps were measured by monitoring the decay of Co(CO){sub 4} at 757 nm and 780 nm, and these are assigned to the back electron transfer step. The ET kinetics are consistent with the previously reported rates of electron transfer that were measured for specific vibrational states by picosecond transient IR.

Wen, X.; Spears, K.G. [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Wiederrecht, G.P.; Wasielewski, M.R. [Argonne National Lab., IL (United States)

1997-02-01

18

Quantum mechanical methods applied to excitation energy transfer: A comparative analysis on excitation energies and electronic couplings  

International Nuclear Information System (INIS)

We present a comparative study on the influence of the quantum mechanical (QM) method (including basis set) on the evaluation of transition energies, transition densities and dipoles, and excitation energy transfer (EET) electronic couplings for a series of chromophores (and the corresponding pairs) typically found in organic electro-optical devices and photosynthetic systems. On these systems we have applied five different QM levels of description of increasing accuracy (ZINDO, CIS, TD-DFT, CASSCF, and SAC-CI). In addition, we have tested the effects of a surrounding environment (either mimicking a solvent or a protein matrix) on excitation energies, transition dipoles, and electronic couplings through the polarizable continuum model (PCM) description. Overall, the results obtained suggest that the choice of the QM level of theory affects the electronic couplings much less than it affects excitation energies. We conclude that reasonable estimates can be obtained using moderate basis sets and inexpensive methods such as configuration interaction of single excitations or time-dependent density functional theory when appropriately coupled to realistic solvation models such as PCM.

2008-07-21

19

Ground vs. excited state electron transfer: adsorbed monolayers and trimers in solution.  

UK PubMed Central (United Kingdom)

Transient emission spectroscopy has been used to probe the rate of photoinduced electron transfer between metal centres within a novel trimeric complex [[Os(bpy)2(bpe)2][Os(bpy)2Cl]2]4+, where bpy is 2,2'-bipyridyl and bpe is trans-1,2-bis-(4-pyridyl)ethylene. Transient emission experiments on the trimer, and on [Os(bpy)2 (bpe)2]2+ in which the [Os(bpy)2 Cl]+ quenching moieties are absent, reveal that the rate of photoinduced electron transfer (PET) across the bpe bridge is 1.3 +/- 0.1 x 10(8) s(-1). Investigations into the driving forces for oxidation and reduction of the electronically excited state within the trimer indicate that quenching of the [Os(bpy)2 (bpe)2]2+ centre within the trimer involves electron transfer from the [bpe Os(bpy)2 Cl]+ centres to the electronically excited state with a driving force of -0.3 eV. Monolayers of the complex, [Os(bpy)2 bpe pyridine]2+, have been formed by spontaneous adsorption onto platinum microelectrodes and used to probe the dynamics of electron transfer across the trans-1,2-bis-(4-pyridyl)ethylene bridge in the ground state. These monolayers are stable and exhibit well defined voltammetric responses for the Os2+/3+ redox reaction. Cyclic voltammograms recorded at high scan rates can be accurately modelled according to a non-adiabatic electron transfer model based on the Marcus theory using a standard heterogeneous electron transfer rate constant, k(o), of 3.1 +/- 0.2 x 10(4) s(-1) and a reorganization energy of 0.4 +/- 0.1 eV. This rate constant is a factor of approximately two orders of magnitude smaller than that found for photoinduced electron transfer across the same bpe bridge for identical driving forces. This significant difference is interpreted in terms of both the nature of the orbitals involved in electrochemically and optically driven electron transfer, as well as the strength of electronic coupling between two molecular components as opposed to a molecular component and a metal electrode.

Brennan JL; Howlett M; Forster RJ

2002-01-01

20

Using wave-packet interferometry to monitor the external vibrational control of electronic excitation transfer  

Science.gov (United States)

We investigate the control of electronic energy transfer in molecular dimers through the preparation of specific vibrational coherences prior to electronic excitation, and its observation by nonlinear wave-packet interferometry (nl-WPI). Laser-driven coherent nuclear motion can affect the instantaneous resonance between site-excited electronic states and thereby influence short-time electronic excitation transfer (EET). We first illustrate this control mechanism with calculations on a dimer whose constituent monomers undergo harmonic vibrations. We then consider the use of nl-WPI experiments to monitor the nuclear dynamics accompanying EET in general dimer complexes following impulsive vibrational excitation by a subresonant control pulse (or control pulse sequence). In measurements of this kind, two pairs of polarized phase-related femtosecond pulses following the control pulse generate superpositions of coherent nuclear wave packets in optically accessible electronic states. Interference contributions to the time- and frequency-integrated fluorescence signals due to overlaps among the superposed wave packets provide amplitude-level information on the nuclear and electronic dynamics. We derive the basic expression for a control-pulse-dependent nl-WPI signal. The electronic transition moments of the constituent monomers are assumed to have a fixed relative orientation, while the overall orientation of the complex is distributed isotropically. We include the limiting case of coincident arrival by pulses within each phase-related pair in which control-influenced nl-WPI reduces to a fluorescence-detected pump-probe difference experiment. Numerical calculations of pump-probe signals based on these theoretical expressions are presented in the following paper [J. D. Biggs and J. A. Cina, J. Chem. Phys. 131, 224302 (2009)].

Biggs, Jason D.; Cina, Jeffrey A.

2009-12-01

 
 
 
 
21

Using wave-packet interferometry to monitor the external vibrational control of electronic excitation transfer.  

UK PubMed Central (United Kingdom)

We investigate the control of electronic energy transfer in molecular dimers through the preparation of specific vibrational coherences prior to electronic excitation, and its observation by nonlinear wave-packet interferometry (nl-WPI). Laser-driven coherent nuclear motion can affect the instantaneous resonance between site-excited electronic states and thereby influence short-time electronic excitation transfer (EET). We first illustrate this control mechanism with calculations on a dimer whose constituent monomers undergo harmonic vibrations. We then consider the use of nl-WPI experiments to monitor the nuclear dynamics accompanying EET in general dimer complexes following impulsive vibrational excitation by a subresonant control pulse (or control pulse sequence). In measurements of this kind, two pairs of polarized phase-related femtosecond pulses following the control pulse generate superpositions of coherent nuclear wave packets in optically accessible electronic states. Interference contributions to the time- and frequency-integrated fluorescence signals due to overlaps among the superposed wave packets provide amplitude-level information on the nuclear and electronic dynamics. We derive the basic expression for a control-pulse-dependent nl-WPI signal. The electronic transition moments of the constituent monomers are assumed to have a fixed relative orientation, while the overall orientation of the complex is distributed isotropically. We include the limiting case of coincident arrival by pulses within each phase-related pair in which control-influenced nl-WPI reduces to a fluorescence-detected pump-probe difference experiment. Numerical calculations of pump-probe signals based on these theoretical expressions are presented in the following paper [J. D. Biggs and J. A. Cina, J. Chem. Phys. 131, 224302 (2009)].

Biggs JD; Cina JA

2009-12-01

22

Laser-excited electronic-to-electronic energy transfer in sodium  

International Nuclear Information System (INIS)

[en] Energy-transfer rates for the E ? E process Na(2P/sub 3/2/) + Na (2S/sub 1/2/) reversible Na (2P/sub 1/2/) + Na (2S/sub 1/2/) + ?E = 17.2 cm-1 have been measured following direct excitation of specific 2P levels with a pulsed tunable dye laser of 10-2-A linewidth and 5-ns duration. The cross sections for the forward and backward reactions at 2720C have been found by Pitre and Krause to be 250 +- 40 and 480 +-- 80 A, respectively

1975-01-01

23

Search for resonant electron transfer and double excitation in Kr{sup 34+} + H{sub 2} collisions  

Energy Technology Data Exchange (ETDEWEB)

Resonant electron transfer and double excitation (RME) is a correlated electron process which is expected to occur in an ion-atom collision when electron capture is accompanied by the simultaneous excitation of two inner-shell electrons. RT2 is similar to resonant transfer excitation (RTE) in which only a single electron is excited. RT2E was investigated experimentally for 38--42 MeV/u Kr{sup 34} + H{sub 2} collisions by observing x-ray emission associated with single-electron capture. No events associated with Kr K x rays (near 13 keV were observed; however, events do occur at about twice (> 22 keV) the Kr K x-ray energy. Several possible sources of these latter x rays have been considered.

Zaharakis, K.E.; Haar, R.R.; Tanis, J.A. [Western Michigan Univ., Kalamazoo, MI (United States); Clark, M.W. [Lawrence Livermore National Lab., CA (United States); Plano, V.L. [Michigan State Univ., East Lansing, MI (United States)

1992-12-31

24

High temperature superconductivity in transition metal oxides: electronic structure and charge transfer excitations  

International Nuclear Information System (INIS)

The discovery of superconductivity above 90 K by Chu and collaborators in Y-Ba-Cu-O compounds has generated experimental and theoretical excitement on an unprecedented scale. A key ingredient to the high TC appears to be the degree of oxygen vacancies (?) in the YBa2Cu3O7-? structure. Thus, as with other materials discussed at this Symposium, defects play an important role in the structure, physics and chemistry of these materials. This paper discusses some important contributions made by highly precise local density energy band studies of the electronic structure and properties for (1) superconducting YBa2Cu3O7-? and (2) non-superconducting YBa2Cu3O6, and the possible role of charge transfer excitations as the mechanism of high TC superconductivity. (author) 21 refs., 4 figs.

1989-01-01

25

Monte Carlo simulations of electronic excitation transfer in polymer composites and comparison to theory  

Energy Technology Data Exchange (ETDEWEB)

Monte Carlo (MC) simulations of electronic excitation transfer (EET) among a small number of chromophores covalently incorporated into copolymer molecules are presented and used to test the results of previously developed analytical EET theories that are useful for the study of polymer chain structure [K. A. Peterson and M. D. Fayer, J. Chem. Phys. {bold 85}, 4702 (1986)] and phase separation in polymer blends [A. H. Marcus and M. D. Fayer, J. Chem. Phys. {bold 94}, 5622 (1991)]. The simulations and theory account for EET among chromophores bound to a single chain and among chromophores attached to different chains. The calculated quantity, {l_angle}G{sup s}(t){r_angle}, which is the probability that an initially excited chromophore is still excited at time {ital t}, is related to time-resolved fluorescence depolarization experiments. The theories, particularly the treatment of interchain EET, depend on a series of approximations whose efficacy has not been determined. Close agreement between the MC simulations and the analytical theory are found for a variety of situations, including those that mimic real polymer systems. The limits beyond which agreement is weakened provide specific guidelines for the design of polymer structure and phase-separation experiments. {copyright} {ital 1998 American Institute of Physics.}

Hussey, D.M.; Matzinger, S.; Fayer, M.D. [Department of Chemistry, Stanford University, Stanford, California 94305-5080 (United States)

1998-11-01

26

Calculations of electronic excitation transfer: Applications to ordered phases in polymeric materials  

Energy Technology Data Exchange (ETDEWEB)

A general treatment of electronic excitation transfer (EET) for any random or nonrandom chromophore distribution is applied to finite-volume systems which can be modeled as spherical shells of finite thickness, cylinders, and lamellae. These geometries were chosen because they occur in a wide variety of materials of interest in synthetic polymer research, as well as in biological systems. The EET dynamics are described by the function , the probability of finding the excitation on the originally excited chromophore. is directly related to the observables in fluorescence anisotropy and lifetime experiments, for donor-donor and donor-trap EET, respectively. The method is shown to be accurate in the limits for which analytical expressions in closed form are available. The model`s usefulness in experimental design is demonstrated for the case of coronal swelling in spherical micelles of diblock copolymers. It was found that random labeling of the blocks which form coronae is the preferred method for observation of this effect and that the sensitivity can be enhanced by selectively tagging the junction of the two blocks with trap chromophores. The influence of the shape of the chromophore distribution function on was also investigated, to test the sensitivity of EET observables to the shape of the chromophore distribution at the A-B interface of a diblock copolymer material. 14 refs., 5 figs.

Keller, L.; Hussey, D.M.; Fayer, M.D. [Stanford Univ., CA (United States)

1996-06-13

27

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 for quenching of Ar2* excimer by H2O molecules is extremely high; however, the yield into the OH(A 2?+) is only 3%

1976-12-01

28

Resonant transfer excitation: Interference effects  

International Nuclear Information System (INIS)

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

1991-01-01

29

Excited electron transfer between a core-excited Ar* (2 p -1 3/2 4s) atom and the metal substratein the Ar/Cu (111) system  

Science.gov (United States)

The transfer of the excited electron from the core-excited Ar* (2 p -1 3/2 4s) atom to a metal substrate is studied theoretically in the case of Ar atoms physisorbed on Cu(111). The study is based on a wave packet propagation (WPP) approach associated with a model representation of the system. The L band gap of Cu is shown to lead to a drastic decrease of the resonant charge transfer rate in the case of a Cu(111) surface, as compared to the case of a free-electron metal surface. Comparison between the present results and earlier results for the charge transfer rates in alkali/Cu(111) systems allows a discussion of the validity of the so-called Z+1 approximation for core-excited states. The cases of a single Ar atom and of 1, 2, and 3 monolayers of Ar on the surface are investigated. The dynamics of the excited electron transfer is shown to be strongly influenced by neighboring Ar atoms, through polarization and confinement effects associated with the insulating properties of solid Ar. The present theoretical results are discussed in connection with recent experimental results on the Ar* -metal charge transfer problem.

Gauyacq, J. P.; Borisov, A. G.

2004-06-01

30

Study of intermediates from transition metal excited-state electron- transfer reactions. Progress report, January 1, 1992--March 31, 1993  

Energy Technology Data Exchange (ETDEWEB)

Progress on 6 projects is reported: excited state absorption spectrum of Ru(bpy){sub 3}{sup 2+}, solvent cage model for electron transfer quenching, reductive quenching of {sup *}Cr(III) complexes, solution medium effects in oxidative quenching of {sup *}Ru(II) complexes, photosensitized oxidation of phenol in aqueous solution, and quenching of Ru(II) complexes by oxygen.

Hoffman, M.Z.

1993-03-31

31

Excitation-wavelength-dependent, ultrafast photoinduced electron transfer in bisferrocene/BF2-chelated-azadipyrromethene/fullerene tetrads.  

Science.gov (United States)

Donor-acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron-transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor-acceptor dyads, revealing excitation-wavelength-dependent photochemical properties demands multimodular, photosynthetic-reaction-center model compounds. Here, we successfully demonstrate donor- acceptor excitation-wavelength-dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF2 -chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured "closely" and "distantly" positioned donor-acceptor systems. The near-IR-emitting BF2-chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation-wavelength-dependent, photoinduced, electron-transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc(+)-ADP-C60(.-) charge-separated state upon C60 excitation, and Fc(+)-ADP(.-)-C60 formation upon ADP excitation is demonstrated. PMID:23554157

Bandi, Venugopal; El-Khouly, Mohamed E; Ohkubo, Kei; Nesterov, Vladimir N; Zandler, Melvin E; Fukuzumi, Shunichi; D'Souza, Francis

2013-03-28

32

Excitation-wavelength-dependent, ultrafast photoinduced electron transfer in bisferrocene/BF2-chelated-azadipyrromethene/fullerene tetrads.  

UK PubMed Central (United Kingdom)

Donor-acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron-transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor-acceptor dyads, revealing excitation-wavelength-dependent photochemical properties demands multimodular, photosynthetic-reaction-center model compounds. Here, we successfully demonstrate donor- acceptor excitation-wavelength-dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF2 -chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured "closely" and "distantly" positioned donor-acceptor systems. The near-IR-emitting BF2-chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation-wavelength-dependent, photoinduced, electron-transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc(+)-ADP-C60(.-) charge-separated state upon C60 excitation, and Fc(+)-ADP(.-)-C60 formation upon ADP excitation is demonstrated.

Bandi V; El-Khouly ME; Ohkubo K; Nesterov VN; Zandler ME; Fukuzumi S; D'Souza F

2013-05-01

33

Mixed quantum classical simulations of electronic excitation energy transfer: The pheophorbide-a DAB dendrimer P4 in solution  

International Nuclear Information System (INIS)

Photoinduced electronic excitation energy transfer in chromophore complexes is studied by utilizing a mixed quantum classical methodology. Electronic excitations are characterized by a Frenkel-exciton model and treated quantum mechanically while all nuclear coordinates are described classically finally by carrying out room-temperature MD simulations. The theory is applied to the chromophore complex P4 dissolved in ethanol. P4 is formed by a butanediamine dendrimer to which four pheophorbide-a molecules have been covalently linked. The P4 excited electronic states have to be described in an improved exciton model which accounts for charge distributions in the chromophores electronic ground and excited state. It also includes a correct description of the excitonic coupling among different chromophores based on the introduction of atomic centered transition charges. Excitation energy transfer is discussed in using adiabatic exciton states as well as a full solution of the time-dependent Schroedinger equation. To underline the effect of strong excitonic coupling emphasis is also placed on MD runs where two chromophores are positioned close together. Relations are discussed to the standard treatment of exciton dynamics in using the density matrix theory as well as by introducing rate equations based on rate expressions according to Foerster

2008-07-03

34

Electron Transfer, Ionization, and Excitation in Collisions between ? Particles and H(1s) Atoms.  

Science.gov (United States)

At the last DAMOP meeting, the author reported Sturmian calculations on electron transfer in 8-200 keV ?-H collisions, both checking numerically and extending to somewhat lower energies and substantially larger bases the calculations carried out a quarter of a century ago, which were limited to 19-24 states. The importance of revisiting earlier coupled-state calculations- --limited by the computers then available---was pointed out in a recent review. Present larger basis calculations should be able to extend the range of energies while treating ionization as well as capture and excitation to lower individual states up to n=3, albeit with much less accuracy than the summed cross section. Further, rough error bars may be placed on the cross sections by comparing values with different bases. The present calculations are with up to about 80 states on a 3.3 GHz IBM ThinkPad, taking on the order of one hour per integrated cross section. T. G. Winter, Bull. Am. Phys. Soc. 50, 82 (2005). T. G. Winter, Phys. Rev. A 25, 697 (1982). T. G. Winter, Adv. At. Mol. Opt. Phys. 52, 391 (2005).

Winter, Thomas

2006-05-01

35

Excitation of Li(2p) by electron transfer in slow Li-metal surface collisions  

Energy Technology Data Exchange (ETDEWEB)

The reflection of Li atoms from oxygen and alkali covered polycrystalline tungsten surfaces is studied at impact energies between 100 and 1000 eV for incidence angles between 87/sup 0/ and 75/sup 0/ with respect to the surface normal. The efficiency for formation of Li/sup +/, Li(2s) and Li(2p) depends strongly on the work function of the metal surfaces. For oxygen covered tungsten the fraction of Li/sup +/ ions is > 0.9, while for alkali-covered surfaces with a work function > 2.1 eV the fraction of neutral scattered atoms is > 0.5. A significant fraction of these Li atoms is in the Li(2p) state. About 3% Li(2p) atoms have been obtained from alkali covered surface having a photoelectrically determined work function of 2.1 and 1.5 eV for K and Cs, respectively. We show that the existing theories for resonant electron transfer must be modified in order to explain the formation of excited Li-atoms: the band structure of the alkali-covered metal surface must be considered, and the Hartree-Fock approximation usually made when treating surface neutralization must be abandoned at large atom-surface distances.

Hermann, J.; Welle, B.; Gehring, J.; Schall, H.; Kempter, V.

1984-03-01

36

Influence of environment induced correlated fluctuations in electronic coupling on coherent excitation energy transfer dynamics in model photosynthetic systems.  

UK PubMed Central (United Kingdom)

Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light harvesting complex, we explore the influence of including correlations in inter-chromophore couplings between different chromophore dimers that share a common chromophore. We find that the relative sign of the different correlations can have profound influence on decoherence time and energy transfer rate and can provide sensitive control of relaxation in these complex quantum dynamical open systems.

Huo P; Coker DF

2012-03-01

37

A TDDFT study on the excited-state intramolecular proton transfer (ESIPT): excited-state equilibrium induced by electron density swing.  

UK PubMed Central (United Kingdom)

One important issue of current interest is the excited-state equilibrium for some ESITP dyes. However, so far, the information about the driving forces for excited-state equilibrium is very limited. In this work, the time-dependent density functional theory (TDDFT) method was employed to investigate the nature of the excited-state intramolecular proton transfer (ESIPT). The geometric structures, vibrational frequencies, frontier molecular orbitals (MOs) and the potential-energy curves for 1-hydroxy-11H-benzo[b]fluoren-11-one (HHBF) in the ground and the first singlet excited state were calculated. Analysis of the results shows that the intramolecular hydrogen bond of HHBF is strengthened from E to E*. Moreover, it is found that electron density swing between the proton acceptor and donor provides the driving forces for the forward and backward ESIPT, enabling the excited-state equilibrium to be established. Furthermore, we proposed that the photoexcitation and the interchange of position for electron-donating and electron-withdrawing groups are the main reasons for the electron density swing. The potential-energy curves suggest that the forward ESIPT and backward ESIPT may happen on the similar timescale, which is faster than the fluorescence decay of both E* and K* forms.

Zhang M; Yang D; Ren B; Wang D

2013-07-01

38

Enhanced charge transfer to molecular ions by electronic excitation of the target  

Energy Technology Data Exchange (ETDEWEB)

A beam of molecular ions (ArH{sup +}, ArD{sup +}, or D{sub 3}{sup +}) was neutralized by passage through an excited cesium vapor; two single-mode diode lasers were used to populate the 6 {sup 2}{ital P}{sub 3/2} state of the cesium atoms. The charge-transfer cross section could be increased by laser excitation of the Cs target, in some cases by orders of magnitude. This was established by observing the intensity of the luminescence from the neutralized molecules, which was enhanced by a factor of up to 10. The enhancement factors are in qualitative agreement with results of computations that follow the theoretical treatment for atoms introduced by Rapp and Francis [J. Chem. Phys. 37, 2631 (1962)]. This experimental technique is a generally applicable method for any molecular-beam technique that relies on charge transfer.

Bruckmeier, R.; Wunderlich, C.; Figger, H. [Max-Planck-Institut fuer Quantenoptik, 85748 Garching (Germany)

1995-07-01

39

Electron transfer triggered by optical excitation of phenothiazine-tris(meta-phenylene-ethynylene)-(tricarbonyl)(bpy)(py)rhenium(I).  

Science.gov (United States)

We have investigated excited-state electron transfer in a donor-bridge-acceptor complex containing phenothiazine (PTZ) linked via tris(meta-phenylene-ethynylene) to a tricarbonyl(bipyridine)(pyridine)Re(I) unit. Time-resolved luminescence experiments reveal two excited-state (*Re) decay regimes, a multiexponential component with a mean lifetime of 2.7 ns and a longer monoexponential component of 530 ns in dichloromethane solution. The faster decay is attributed to PTZ ? *Re electron transfer in a C-shaped PTZ-bridge-Re conformer (PTZ-Re ? 7.5 Å). We assign the longer lifetime, which is virtually identical to that of free *Re, to an extended conformer (PTZ-Re > 20 Å). The observed biexponential *Re decay requires that interconversion of PTZ-bridge-Re conformers be slower than 10(6) s(-1). PMID:22533820

Bingöl, Bahar; Durrell, Alec C; Keller, Gretchen E; Palmer, Joshua H; Grubbs, Robert H; Gray, Harry B

2012-05-03

40

Cross-sections for excited state nonadiabatic ionospheric reactions involving charge transfer and collision induced electronic transitions  

Science.gov (United States)

New methods for treating nonadiabatic excited state reactions are tested using accurate ab initio potentials and nonadiabatic couplings in studies of excited state atom quenching reactions including N(2D) + O(3P) ? N(4S) + O(3P) and O(1D) + O(3P) ? O(3P) + O(3P). Energy dependent cross-sections for these processes which involve collision induced electronic transitions (CIET) obtained from a nonadiabatic mixed quantum-classical surface hopping approach, a nonadiabatic extension to quasiclassical methods, as well as a semiclassical mapping Hamiltonian approach will be compared with the results of exact full quantum close coupled calculations, to develop an understanding of the conditions under which these approximate methods can be reliable. These CIET processes play a crucial role in quenching excited atoms produced in ionospheric reactions such as dissociative recombination which are initiated by nonadiabatic charge transfer reactions like O2 + O+(D,P) ? O2+(v) + O or N2 + O+(D,P) ? N2+(v) + O. Potential surfaces and non-adiabatic couplings for these processes computed using the MOLPRO package will be presented. Subsequent electron capture by the vibrationally excited molecular ions produced in the above processes results in their dissociation into excited atomic fragments which can initiate the CIET processes described earlier. The approximate nonadiabatic trajectory based dynamics methods will be employed in studies of these charge transfer reactions to compute molecular ion vibrational distributions from which cross sections and rates of these more complex molecular reactions can be computed.

Coker, D. F.; Dothe, H.; Chen, L.; Tambouret, Y.; Duff, J. W.

 
 
 
 
41

Large momentum transfer excitation of He(31P) by electron impact at 81.2 eV incident energy  

International Nuclear Information System (INIS)

This paper reports measurements of helium lambda and chi parameters for electron impact excitation of the 31P state of helium at an incident energy of 81.2 eV and at large momentum transfers. Comparison is made with previous 21P results and both sets of results show very similar trends. The data are also compared with a number of theoretical calculations but the agreement is not good

1982-01-01

42

Electron-impact excitation of He and H{sub 2} in the doubly excited state energy region observed using a momentum transfer technique  

Energy Technology Data Exchange (ETDEWEB)

We report evidence for the electron-impact excitation of doubly excited states in helium and H{sub 2} which are stable against autoionization. By detecting only long-lived (metastable) excited neutral states created by near-threshold electron scattering our technique discriminates against directly excited metastable states and is highly sensitive.

Harries, J R [Photon Factory, IMSS, KEK, 1-1 Oho, Tsukuba-shi, Ibaraki-ken 305-0081 (Japan); Hammond, P [University of Western Australia, Crawley, Perth, WA 6009 (Australia); Murray, A J [Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom)

2003-06-28

43

Electron-impact excitation of He and H2 in the doubly excited state energy region observed using a momentum transfer technique  

International Nuclear Information System (INIS)

We report evidence for the electron-impact excitation of doubly excited states in helium and H2 which are stable against autoionization. By detecting only long-lived (metastable) excited neutral states created by near-threshold electron scattering our technique discriminates against directly excited metastable states and is highly sensitive.

2003-06-28

44

TDDFT calculations of electronic spectra of benzoxazoles undergoing excited state proton transfer.  

Science.gov (United States)

Energies and oscillator strengths of vertical transitions for various rotameric and tautomeric species of 2-(2'-hydroxyphenyl)benzoxazole (HBO), 2,5-bis(2-benzoxazolyl)phenol (DBP) and 2,5-bis(2-benzoxazolyl)hydroquinone (BBHQ) have been calculated in the ground and first excited states with the use of TDDFT methods. The TDDFT results demonstrate good correspondence to the frequencies of absorption and fluorescence bands of the benzoxazoles reported for measurements in supersonic jets and solution, but fail to predict relative energies of the enol and keto tautomers of DBP and BBHQ in the excited state. Low intensity of the fluorescence bands attributed to the conformations of HBO and DBP that do not undergo excited state proton transfer is shown to be caused by low concentrations of the conformations in the ground state. For the three compounds large-amplitude twisting of the keto tautomer is found to be one of radiationless processes resulting in decrease of the fluorescence with a large Stokes shift. PMID:23475275

Syetov, Y

2013-03-09

45

Study of intermediates from transition metal excited-state electron-transfer reactions  

International Nuclear Information System (INIS)

This is the progress report for the period of January 1989 to March 1990 and contains brief summaries for the undertaken projects. The projects discussed are: cage escape yields in the quenching of Ru(II) photosensitizers, characterization of one-electron reduced Ru(II) complexes; application of Marcus theory to electron-transfer processes in Ru(II) complexes; synthesis and characterization of new Ru(II) photosensitizers; NMR study of ion-pairing in aqueous solutions containing Ru(bpy)32+; and reductive quenching of Ru(II) and Cr(III) complexes

1990-01-01

46

Ruthenium-manganese complexes for artificial photosynthesis: factors controlling intramolecular electron transfer and excited-state quenching reactions.  

Science.gov (United States)

Continuing our work toward a system mimicking the electron-transfer steps from manganese to P(680)(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 x 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximately 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium(III) electron-transfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties. PMID:11896722

Abrahamsson, Malin L A; Baudin, Helena Berglund; Tran, Anh; Philouze, Christian; Berg, Katja E; Raymond-Johansson, Mary Katherine; Sun, Licheng; Akermark, Bjorn; Styring, Stenbjorn; Hammarstrom, Leif

2002-03-25

47

[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

1998-01-01

48

Transfer and excitation in high-energy He+-He collisions: V. Electronic continuum influence on ejected electron distributions and TE cross sections  

International Nuclear Information System (INIS)

[en] Compared to experimental data based on 0 deg. electron spectroscopy, previous theoretical predictions related to simultaneous transfer and excitation (TE) processes occurring in collisions between fast He+ projectiles and helium targets are not fully satisfactory. In fact, peaks in energy distributions of forward-emitted electrons have always been considered as the result of the production of (bound) doubly excited states followed by post-collisional Auger decay. However, two indistinguishable collision channels, hereafter referred to as TI, can also produce forward-ejected electrons: (a) direct target ionization and (b) simultaneous electron transfer and projectile ionization. They are ignored in these first studies, although experimental electron spectra show asymmetrical profiles. Here the TE process is re-examined within the framework of the continuum distorted wave with four-body (CDW-4B) formalism. Our approach sticks to Fano's description of a resonance, i.e. the adjacent electronic continuum of a doubly excited state produced during the collision is included. Very good agreement is found between the present predictions and the experimental data both for energy distributions of ejected electrons and for so-called total TE cross sections. Further, it is shown that TE cross sections, which are extracted directly from lineshapes, always contain non-separable contributions from the two above-mentioned TI channels. (author)

1999-05-14

49

Chemical Physics Electrons and Excitations  

CERN Multimedia

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

Larsson, Sven

2012-01-01

50

Ultrafast pump-probe spectroscopy of electronic excitation transfer in random molecular systems and in photosynthetic antennae  

Energy Technology Data Exchange (ETDEWEB)

Optical pump-probe (transient absorption) spectroscopy was used to study excitation energy transfer (EET) in random molecular systems and in antenna complexes of photosynthetic organisms. Energy transfer was first studied for Rhodamine 640 adsorbed on ZnO and fused silica surfaces at submonolayer coverage. Ground state recovery on fused silica was coverage-dependent due to excitation trapping by dye aggregates; on ZnO recovery was fast and independent of coverage. This can be explained by energy transfer into semiconductor surface states. Also, EET experiments were performed on solutions of Rhodamine 640 in glycerol using both absorption depolarization and the well-known technique of fluorescence depolarization using time-correlated single photon counting. Data from both techniques match within experimental error theoretical predictions, showing the validity of pump-probe techniques in studying EET. The absorption depolarization of the Q{sub x} electronic transition in BChl a-protein from P. aestuarii was monitored, and the anisotropy was found to decay to a constant, nonzero value due to nonrandom chromophore orientations. The timescale of depolarization was found to be consistent with transfer between delocalized exciton states. Results of experiments on the core antenna complex of photosystem I were remarkably similar, showing that local ordering exists in PS I. This also suggests that EET occurs between groups of chromophores in PS I similar to those in the BChl a-protein.

Causgrove, T.P.

1988-01-01

51

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

International Nuclear Information System (INIS)

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

2013-01-01

52

Probing charge transfer in benzodifuran-c60 dumbbell-type electron donor-acceptor conjugates: ground- and excited-state assays.  

UK PubMed Central (United Kingdom)

Rigid electron donor-acceptor conjugates (1-3) that combine ?-extended benzodifurans as electron donors and C60 molecules as electron acceptors with different linkers have been synthesized and investigated with respect to intramolecular charge-transfer events. Electrochemistry, fluorescence, and transient absorption measurements revealed tunable and structure-dependent charge-transfer processes in the ground and excited states. Our experimental findings are underpinned by density-functional theory calculations.

Li H; Schubert C; Dral PO; Costa RD; La Rosa A; Thüring J; Liu SX; Yi C; Filippone S; Martín N; Decurtins S; Clark T; Guldi DM

2013-09-01

53

Probing charge transfer in benzodifuran-c60 dumbbell-type electron donor-acceptor conjugates: ground- and excited-state assays.  

Science.gov (United States)

Rigid electron donor-acceptor conjugates (1-3) that combine ?-extended benzodifurans as electron donors and C60 molecules as electron acceptors with different linkers have been synthesized and investigated with respect to intramolecular charge-transfer events. Electrochemistry, fluorescence, and transient absorption measurements revealed tunable and structure-dependent charge-transfer processes in the ground and excited states. Our experimental findings are underpinned by density-functional theory calculations. PMID:23918655

Li, Hui; Schubert, Christina; Dral, Pavlo O; Costa, Rubén D; La Rosa, Andrea; Thüring, Jürg; Liu, Shi-Xia; Yi, Chenyi; Filippone, Salvatore; Martín, Nazario; Decurtins, Silvio; Clark, Timothy; Guldi, Dirk M

2013-08-05

54

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

UK PubMed Central (United Kingdom)

In the photosynthetic green filamentous bacterium Chloroflexus aurantiacus, excitation energy is transferred from a large bacteriochlorophyll (BChl) c antenna via smaller BChl a antennas to the reaction center. The effects of substituted 1,4-naphthoquinones on BChl c and BChl a fluorescence and on flash-induced cytochrome c oxidation were studied in whole cells under aerobic conditions. BChl c fluorescence in a cell suspension with 5.4 microM BChl c was quenched to 50% by addition of 0.6 microM shikonin ((R)-2-(1-hydroxy-4-methyl-3-pentenyl)-5,8-dihydroxy-1, 4-naphthoquinone), 0.9 microM 5-hydroxy-1,4-naphthoquinone, or 4 microM 2-acetyl-3-methyl-1,4-naphthoquinone. Between 25 and 100 times higher quinone concentrations were needed to quench BChl a fluorescence to a similar extent. These quinones also efficiently inhibited flash-induced cytochrome c oxidation when BChl c was excited, but not when BChl a was excited. The quenching of BChl c fluorescence induced by these quinones correlated with the inhibition of flash-induced cytochrome c oxidation. We concluded that the quinones inhibited electron transfer in the reaction center by specifically quenching the excitation energy in the BChl c antenna. Our results provide a model system for studying the redox-dependent antenna quenching in green sulfur bacteria because the antennas in these bacteria inherently exhibit a sensitivity to O(2) similar to the quinone-supplemented cells of Cfx. aurantiacus.

Frigaard N; Tokita S; Matsuura K

1999-11-01

55

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

Directory of Open Access Journals (Sweden)

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.

Maryam Dehestani; Somaie Shojaei; Azita Khosravan

2012-01-01

56

Thermal conductivity and the electron-ion heat transfer coefficient in condensed media with a strongly excited electron subsystem  

Science.gov (United States)

The two-temperature ( T e > T i ) thermal conductivity coefficient ?2 T and electron-ion heat transfer coefficient ?, which are necessary for the quantitative description of the processes initiated by ultrashort laser pulse, have been calculated using a kinetic equation, the matrix element for the scattering probability, and a screened Coulomb potential describing the interaction between charged particles. Quantitative information has been obtained for coefficients ?2 T and ? values for noble and transition metals, where the d-band electrons play a significant role.

Petrov, Yu. V.; Inogamov, N. A.; Migdal, K. P.

2013-03-01

57

Ultrafast pump-probe spectroscopy of electronic excitation transfer in random molecular systems and in photosynthetic antennae  

Energy Technology Data Exchange (ETDEWEB)

Optical pump-probe (transient absorption) spectroscopy was used to study excitation energy transfer (EET) in random molecular systems and in antenna complexes of photosynthetic organisms. Energy transfer was first studied for Rhodamine 640 adsorbed on ZnO and fused silica surfaces at submonolayer coverage. Also, EET experiments were performed on solutions of Rhodamine 640 in glycerol using both absorption depolarization and the well-known technique of fluorescence depolarization using time-correlated single photon counting. Data from both techniques match within experimental error theoretical predictions, showing the validity of pump-probe techniques in studying EET. The absorption depolarization of the Q/sub x/ electronic transitions in BChl a-protein from P. aestuarii was monitored, and the anisotropy was found to decay to a constant, nonzero value due to nonrandom chromophore orientations. The timescale of depolarization was found to be consistent with transfer between delocalized exciton states. Results of experiments on the core antenna complex of photosystem I were remarkably similar. 279 refs., 52 figs., 9 tabs.

Causgrove, T.P.

1989-02-01

58

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

Scientific Electronic Library Online (English)

Full Text Available Abstract in english 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.

Dehestani, Maryam; Shojaei, Somaie; Khosravan, Azita

2012-01-01

59

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

Science.gov (United States)

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

Skryshevski, Yu. A.

2013-05-01

60

Study of intermediates from transition metal excited-state electron-transfer reactions  

International Nuclear Information System (INIS)

This report contains sections entitled: (1) Cage escape yields in the quenching of Ru(II) photosensitizers; (2) Characterization of one-electron reduced Ru(II) complexes; (3) Synthesis and characterization of new Ru(II) photosensitizers; (4) Reductive quenching of Ru(II) and Cr(III) complexes; and (5) Photosensitized initiation of polymerization. 11 refs

1991-01-01

 
 
 
 
61

Electronic and nuclear factors in intramolecular charge and excitation transfer processes. [Annual report], October 1992--September 1993  

Energy Technology Data Exchange (ETDEWEB)

A qualitative discussion is given of initial work on the following topics: intramolecular triplet excitation transfer bands, donor-- bridge--acceptor systems with a tethered ion, and depolarization of transient microwave conductivity. A number of special compounds were synthesized, such as spiranes, 2,6-diamino-dihydroanthracene precursor, and para-amino-nitro-biphenyl and -terphenyl.

Piotrowiak, P.

1993-12-31

62

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

CERN Multimedia

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

Biggs, Jason D

2009-01-01

63

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

UK PubMed Central (United Kingdom)

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

Biggs JD; Cina JA

2009-12-01

64

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

Science.gov (United States)

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

Biggs, Jason D.; Cina, Jeffrey A.

2009-12-01

65

Addition of ketene silyl acetals to the triplet excited state of C{sub 60} via photoinduced electron transfer leading to the fullereneacetates  

Energy Technology Data Exchange (ETDEWEB)

The photochemical carbon-carbon bond formation of C{sub 60} with ketene silyl acetals is described to give a new way for fullerene functionalization chemistry. The photoaddition of ketene silyl acetals to C{sub 60} occurs efficiently under irradiation of the visible light in benzene as well as benzonitrile to yield the fullereneacetates. The comparison of the observed rate constants determined from the dependence of the quantum yields on the concentrations of ketene silyl acetals as well as the quenching of triplet excited state of C{sub 60} by ketene silyl acetals with those predicted for the electron transfer processes indicates that the photoaddition proceeds via photoinduced electron transfer from ketene silyl acetals to the triplet excited state of C{sub 60}. The negative shift in the one-electron reduction potentials by the adduct formation of C{sub 60} is examined by the cyclic voltammetry measurements. The factors to control the formation of mono- and bisadducts of C{sub 60} are clarified based on the rates of photoinduced electron transfer from ketene silyl acetals to the triplet excited states of C{sub 60} and the adducts. 40 refs., 7 figs., 2 tabs.

Mikami, Koichi; Matsumoto, Shoji [Tokyo Inst. of Technology (Japan); Ishida, Akito; Takamuku, Setsue; Suenobu, Tomoyoshi; Fukuzumi, Shunichi [Osaka Univ. (Japan)

1995-11-15

66

Study of intermediates from transition metal excited-state electron-transfer reactions. Progress report, April 1, 1984-March 31, 1985. [EDTA-radicals  

Energy Technology Data Exchange (ETDEWEB)

Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of most photochemical solar energy conversion schemes. Our research, which utilizes 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: (1) the effect of solution medium on the properties and quenching of the excited states; (2) the control of the quantum yield of formation of redox products; and (3) the mechanisms by which reduced species interact with water to yield H/sub 2/ homogeneously and heterogeneously. Research activities are summarized for the following: (1) reaction of methyl viologen with EDTA-radicals; (2) solution medium control of photoredox yields; (3) photochemistry of methyl viologen charge-transfer complexes; (4) thermal reduction of methyl viologen in alkaline solution; (5) formation of dihydrogen from reduced methyl viologen; and (6) photophysics of Cr(III)-polypyridyl complexes.

Hoffman, M.Z.

1985-03-31

67

Re-evaluation of the side effects of cytochrome b(6)f inhibitor dibromothymoquinone on photosystem II excitation and electron transfer.  

UK PubMed Central (United Kingdom)

Dibromothymoquinone (DBMIB) has been used as a specific inhibitor of plastoquinol oxidation at the Q(0) binding site of the cytochrome b(6)f complex for 40 years. It is thought to suppress electron transfer between photosystem (PS) II and I, as well as cyclic electron transfer around PSI. However, DBMIB has also been reported to act as a quencher of chlorophyll excited states. In this study, we have re-evaluated the effects of DBMIB on chlorophyll excited states and PSII photochemistry. The results show that DBMIB significantly quenches the chlorophyll excited states of PSII antenna even at low concentration (from 0.1 ?M), lowering the effective excitation rate of the actinic light. It also acts as a potent PSII electron acceptor retarding the reduction of the plastoquinone pool with almost maximal potency at 2 ?M. Altogether, these results suggest that experiments using DBMIB can easily be misinterpreted and stress on the importance of taking into account all these side effects that occur in the same range of DBMIB concentration used for inhibition of plastoquinol oxidation (1 ?M).

Belatik A; Joly D; Hotchandani S; Carpentier R

2013-02-01

68

Formation of electronically excited products in electron-transfer reactions: reaction of polypyridine complexes of cobalt(I) and ruthenium(III) in acetonitrile  

Energy Technology Data Exchange (ETDEWEB)

The yields of the metal-to-ligand charge-transfer excited state of poly(pyridine)ruthenium(II) complexes (*RuL/sub 3//sup 2 +/) produced in the reaction of RuL/sub 3//sup 3 +/ with poly(pyridine)cobalt(I) complexes in acetonitrile have been measured by use of a combination of continuous flow methods and chemical actinometry. The *RuL/sub 3//sup 2 +/ yields are high, ranging from 0.31 +/- 0.04 for the most exergonic system (Ru(bpy)/sub 3//sup 3 +/ and Co(4,4'-(CH/sub 3/)/sub 2/bpy)/sub 3//sup +/) to 0.07 +/- 0.02 for the least exergonic system studied (Ru(4,7-(CH/sub 3/)/sub 2/phen)/sub 3//sup 3 +/ and Co(bpy)/sub 3//sup +/. The results are interpreted in terms of competing electron-transfer channels yielding primarily *RuL/sub 3//sup 2 +/ + CoL/sub 3//sup 2 +/ and RuL/sub 3//sup 2 +/ + *CoL/sub 3//sup 2 +/(/sup 2/T), with the formation of entirely ground-state products being negligible. A new actinometer consisting of Os(terpy)/sub 2//sup 2 +/ and Co(NH/sub 3/)/sub 5/Cl/sup 2 +/, for use at wavelengths up to approx.720 nm, is described.

Liu, D.K.; Brunschwig, B.S.; Creutz, C.; Sutin, N.

1986-04-16

69

Environmental Effects on Photoinduced Electron Transfer Reactions.  

Science.gov (United States)

Photoinduced electron transfer reactions between an electronically excited photosensitizer molecule and a reversible electron acceptor capable of hydrogen production were studied to determine the possible utility of these reactions in solar energy convers...

T. E. Casti

1985-01-01

70

Ground- and excited-state electron-transfer reactions: photoinduced redox reactions of poly(pyridine)ruthenium(II) complexes and cobalt(III) cage compounds  

Energy Technology Data Exchange (ETDEWEB)

Rate constants for the quenching of poly(pyridine)ruthenium(II) (RuL/sub 3//sup 2 +/) excited states by caged cobalt(III) amine complexes (Co(cage)/sup 3 +/) range from 2 x 10/sup 8/ to 1 x 10/sup 9/ M/sup -1/ s/sup -1/ at 25/sup 0/C. The quenching process involves parallel energy transfer (k/sub en/ approx. 1 x 10/sup 8/ M/sup -1/ s/sup -1/) and electron transfer (k/sub el/ = (0.1-1) x 10/sup 9/ M/sup -1/ s/sup -1/) from RuL/sub 3//sup 2 +/ to Co(cage)/sup 3 +/. The rate constants for electron-transfer quenching are consistent with expectations based on an adiabatic semiclassical model. The yields of electron-transfer products range from 0.3 to 1.0, increasing as the rate constants for the back-reaction of RuL/sub 3//sup 3 +/ with Co(cage)/sup 2 +/ diminish. The relatively low magnitudes of the back-reaction rate constants, (0.08-8) x 10/sup 8/ M/sup -1/ s/sup -1/, are consistent with the high yields of electron-transfer products and derive from poor coupling of the RuL/sub 3//sup 3 +/ and Co(cage)/sup 2 +/ orbitals. 30 references, 3 figures, 4 tables.

Mok, C.Y.; Zanella, A.W.; Creutz, C.; Sutin, N.

1984-08-29

71

Resonant transfer and excitation by crystal channeling  

International Nuclear Information System (INIS)

A transition amplitude for resonant transfer and excitation (RTE) in a crystal channel is derived and compared with observations of Belkacem et al. [Phys. Rev. Lett. 64, 380 (1990)] of titanium ions channeled in a thin gold crystal. Using a one-dimensional tight-binding model of the gold lattice, the RTE cross section is shown to be proportional to the Compton profile of atomic gold multiplied by a crystal-structure factor, analogous to multislit interference of light with diffraction. It is suggested that Belkacem et al. observed a single (principal) maximum with a very narrow width determined by the crystal's Fermi energy. It is found that the observed shift in the RTE peak, relative to that expected for a quasifree crystal electron, can be accounted for by a change in the Coulomb energy of the transferred electron caused by the highly charged ''impurity'' ion prior to transfer.

1991-01-01

72

Electron-excited molecule interactions  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1991-01-01

73

Study of intermediates from transition metal excited-state electron-transfer reactions. Progress report, April 1, 1983-March 31, 1984. [Methyl viologen radical cation  

Energy Technology Data Exchange (ETDEWEB)

In our study of intermediates from excited-state electron-transfer reactions, we have focused our attention during the past year on MV/sup +/., the reduced methyl viologen radical cation, which is a precursor to the formation of H/sub 2/ in the photosensitized reduction of water. Through the use of photochemical and radiation chemical techniques, we have examined the efficiency of interaction of MV/sup +/. with colloidal Pt, the stability of MV/sup +/. as a function of pH, the quantum yield of formation of MV/sup +/. in the Ru(bpy)/sub 3//sup 2 +//MV/sup 2 +//EDTA system, and the formation of photoactive charge-transfer complexes between MV/sup 2 +/ and sacrificial electron donors.

Hoffman, M.Z.

1984-03-31

74

Formalism of collective electron excitations in fullerenes  

CERN Multimedia

We present a detailed formalism for the description of collective electron excitations in fullerenes in the process of the electron inelastic scattering. Considering the system as a spherical shell of a finite width, we show that the differential cross section is defined by three plasmon excitations, namely two coupled modes of the surface plasmon and the volume plasmon. The interplay of the three plasmons appears due to the electron diffraction of the fullerene shell. Plasmon modes of different angular momenta provide dominating contributions to the differential cross section depending on the transferred momentum.

Verkhovtsev, Alexey V; Solov'yov, Andrey V

2012-01-01

75

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

International Nuclear Information System (INIS)

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

1986-01-01

76

Electron attachment to excited molecules  

Energy Technology Data Exchange (ETDEWEB)

Studies on electron attachment to molecules rotationally/vibrationally excited thermally or via infrared-laser excitation showed that the effect of internal energy of a molecule on its electron attachment properties depends on the mode--dissociative or nondissociative--of electron attachment. They quantified the effect of the internal energy of the molecule on the rate of destruction (by autodissociation or by autodetachment) of its parent transient anion. Generally, increases in ro-vibrational molecular energy increase the cross section for dissociative electron attachment and decrease the effective cross section for parent anion formation due mainly to increased autodetachment. These findings and their understanding are discussed. A discussion is given, also, of recent investigations of electron attachment to electronically excited molecules, especially photoenhanced dissociative electron attachment to long- and short-lived excited electronic states of molecules produced directly or indirectly by laser irradiation. These studies showed that the cross sections for dissociative electron attachment to electronically excited molecules usually are many orders of magnitude larger than those for the ground-state molecules. The new techniques that have been developed for such studies are briefly described also.

Christophorou, L.G.; Pinnaduwage, L.A. [Oak Ridge National Lab., TN (United States). Atomic, Molecular, and High Voltage Physics Group; Datskos, P.G. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics

1993-12-31

77

Observation of resonant transfer and excitation in O/sup 5 +/ + He collisions through high resolution O/sup 0/ Auger electron spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

In this paper we present new evidence that (resonant transfer and excitation) RTE is an important mechanism for the production of Be-like doubly excited states in energetic collisions of Li-like O/sup 5 +/ ions incident on He. We have measured the cross sections for the production of Auger electrons from the decay of the (1s2s2p/sup 2/)/sup 3/D and the (1s2s2p/sup 2/)/sup 1/D states in O/sup 4 +/ in high resolution at O/sup 0/, as a function of the incident ion energy. We observe a resonant increase in the Auger cross section with a maximum at approx.13 MeV and full-width-at-half-maximum of approx.7 MeV. This feature is seen to sit on a non-resonant NTE background, which populates the same intermediate states through a two step capture and excitation process governed by the electron-nucleus Coulomb interaction. 13 ref., 3 figs.

Swenson, J.K.; Stolterfoht, N.; Yamasaki, Y.; Miller, P.D.; Krause, H.; Dittner, P.F.; Pepmiller, P.L.; Datz, S.

1986-01-01

78

Nuclear Excitation involving Inner-Shell Electrons  

International Nuclear Information System (INIS)

[en] The experimental and theoretical studies on nuclear excitation involving atomic electrons are described. Several processes, such as nuclear excitation by electron transition, nuclear excitation by free-electron capture, nuclear excitation by target electron capture in ion-atom collisions, nonresonant photoexcitation, and nuclear excitation by positron annihilation, are discussed

2003-01-24

79

Triplet Excitation Energy Transfer with Constrained Density Functional Theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the electronic coupling matrix element for triplet excitation energy-transfer processes with a number of different computational methods. For the first time, constrained density functional theory (CDFT) is applied to the problem of energy transfer, and results are compared with direct coupl...

Yeganeh, Sina; Van Voorhis, Troy

80

X-ray absorption spectroscopy of ground and excited rhenium-carbonyl-diimine complexes: evidence for a two-center electron transfer.  

UK PubMed Central (United Kingdom)

Steady-state and picosecond time-resolved X-ray absorption spectroscopy is used to study the ground and lowest triplet states of [ReX(CO)(3)(bpy)](n+), X = Etpy (n = 1), Cl, or Br (n = 0). We demonstrate that the transient spectra at both the Re L(3)- and Br K-edges show the emergence of a pre-edge feature, absent in the ground-state spectrum, which is associated with the electron hole created in the highest occupied molecular orbital following photoexcitation. Importantly, these features have the same dynamics, confirming previous predictions that the low-lying excited states of these complexes involve a two-center charge transfer from both the Re and the ligand, X. We also demonstrate that the DFT optimized ground and excited structures allow us to reproduce the experimental XANES and EXAFS spectra. The ground-state structural refinement shows that the Br atom contributes very little to the latter, whereas the Re-C-O scattering paths are dominant due to the so-called focusing effect. For the excited-state spectrum, the Re-X bond undergoes one of the largest changes but still remains a weak contribution to the photoinduced changes of the EXAFS spectrum.

El Nahhas A; van der Veen RM; Penfold TJ; Pham VT; Lima FA; Abela R; Blanco-Rodriguez AM; Záliš S; Vl?ek A; Tavernelli I; Rothlisberger U; Milne CJ; Chergui M

2013-01-01

 
 
 
 
81

Photochemical transformations. 37. Electron-transfer requirements for photosolvolysis and photo-Wagner-Meerwein reactions of some dichlorodibenzobicyclo(2. 2. 2)octadienes in singlet and triplet excited states  

Energy Technology Data Exchange (ETDEWEB)

Substituted trans-7,8-dichloro-10-X-2,3:5,6-dibenzobicyclo(2.2.2)octa-2,5-dienes (X = COCH/sub 3/, CN, and NO/sub 2/) and corresponding dinitro-substituted compounds (10,15-dinitro) were solvolyzed with silver acetate in acetic acid and were irradiated in glacial acetic acid or acetonitrile with 254- and 300-nm light. The structures of the monoring-substituted diastereoisomeric dichlorides were demonstrated by proof of structures of the daughter solvolysis products. Unlike compounds previously studied, these compounds were either photochemically inert or photoinactive with respect to Wagner-Meerwein rearrangement or to solvolysis. These results have been rationalized in terms of the inability of the excited states of the light-absorbing chromophores in these compounds to transfer electrons to the carbon-chlorine bonds remote from these chromophores. While triplet states of a variety of cis- and trans-7,8-dichloro-2,3:5,6-dibenzobicyclo(2.2.2)octa-2,5-dienes are reported to be similarly inert, the 10,11-dimethoxy derivatives all were photoactive with acetone sensitization. The migration stereochemistries of the sensitized reactions were quite different from those of direct irradiations or of ground-state reactions. Estimations of the free energies of electron transfer were consistent with these and previously reported results. 26 references, 1 table.

Cristol, S.J.; Bindel, T.H.; Hoffmann, D.; Aeling, E.O.

1984-06-29

82

Impulse approximation treatment of electron-electron excitation and ionization in energetic ion-atom collisions  

International Nuclear Information System (INIS)

[en] The effect of electron-electron interactions between projectile and target electrons observed in recent measurements of projectile K-shell excitation and ionization using 0 projectile Auger electron spectroscopy are analysed within the framework of the impulse approximation (IA). The IA formulation is seen to give a good account of the threshold behavior of both ionization and excitation, while providing a remarkably simple intuitive picture of such electron-electron interactions in ion-atom collisions in general. Thus, the applicability of the IA treatment is extended to cover most known processes involving such interactions including resonance transfer excitation, binary encounter electron production, electron-electron excitation and ionization. (orig.)

1993-01-01

83

Electron-impact excitation of krypton  

International Nuclear Information System (INIS)

First-order many-body theory has been used to calculate the differential, integrated, and momentum-transfer cross sections for the electron-impact excitation of the 5s'[(1/2)]10( 1P1 ), 5s[(3/2)]10( 3P1), 5s'[(1/2)]00( 3P0), and 5s[(3/2)]20( 3P2)= states of krypton for the incident energies of 20, 30, 50, 60, and 100 eV. Electron-photon coincidence parameters for the optically allowed states have been obtained. The results are compared to available experimental results

1985-01-01

84

Vibronic coupling in dicyano-complex-bridged mixed-valence complexes. Relaxation of vibronic constraints in systems with degenerate bridging-ligand and electron-transfer excited states  

Energy Technology Data Exchange (ETDEWEB)

Intense near-infrared (NIR) absorption bands have been found in mixed-valence Ru(NH{sub 3}){sub 5}{sup 2+,3+} complexes bridged by trans-Ru(py){sub 4}(CN){sub 2} and cis-Os(bpy){sub 2}(CN){sub 2}, {epsilon}{sub max {approximately}} 1.5 x 10{sup 3} cm{sup {minus}1} and {Delta}{nu}{sub 1/2} {approximately} 5 x 10{sup 3} cm{sup {minus}1} for bands at 1000 and 1300 nm, respectively. The NIR transitions implicate substantial comproportionation constants (64 and 175, respectively) characteristic of moderately strong electronic coupling in the mixed-valence complexes. This stands in contrast to the weakly forbidden electronic coupling of Ru(NH {sub 3}){sub 5}{sup 2+,3+} couples bridged by M(MCL)-(CN){sub 2}{sup +} complexes (MCL = a tetraazamacrocyclic ligand). A straightforward perturbation theory argument is used to account for t his contrasting behavior. The electronic coupling between a cyanide-bridged, donor-acceptor pair, D-(CN{sup {minus}})-A, alters the properties of the bridging ligand. Such systems are described by a vibronic model in which the electronic matrix element, H{sub DA}, is a function of the nuclear coordinates, Q{sub N}, of the bridging ligand: H{sub DA} = H{sub DA}{degree} + b!{sub N}. Electronic coupling in the dicyano-complex-bridged, D-[(NC)M(CN)]-A, systems is treated as the consequence of the perturbational mixing of the local, D(NC)M and M(CN)A, vibronic interactions. If M is an electron-transfer acceptor, then the nuclear coordinates are assumed to be configured so that bQ{sub N} is larger for D(NC)M but very small (bQ{sub N}{approximately}0) for M(CN)A. When the vertical energies of the corresponding charge-transfer transitions, E{sub DM} and E{sub DA}, differ significantly, a perturbation theory treatment results in H{sub DA}= H{sub DA}H{sub AM}/E{sub ave} independent of M and consistent with the earlier report. When E{sub DM} {approx{underscore}equal} E{sub DA}, configurational mixing of the excited states leads to H{sub DA} proportional to H{sub DM}, consistent with the relatively intense intervalence bands reported in this paper. Some implications of the model are discussed.

Macatangay, A.V.; Endicott, J.F.

2000-02-07

85

Light induced electron transfer of metal complexes  

International Nuclear Information System (INIS)

Light induced electron transfer of metal complexes has been studied extensively during the last decade. This interest was stimulated by attempts to develop an artificial photosynthesis for the conversion and chemical storage of solar energy. Even if this goal has not yet been achieved photochemical redox processes of coordination compounds are now much better understood. In this review the various possibilities of photoinduced electron transfer are discussed and illustrated by selected samples. A distinction is made between intra- and intermolecular electron transfer which may occur as a direct optical transition or by an excited state electron transfer mechanism. (author). 52 refs.; 1 fig.

1992-01-01

86

Dynamics of electron transfer in amine photooxidation  

Energy Technology Data Exchange (ETDEWEB)

Studies were initiated utilizing picosecond (ps) absorption spectroscopy, to directly monitor the dynamics of electron transfer from 1,4-diazabicyclo(2.2.2)octane (Dabco) to the excited states of benzophenone and fluorenone. These two systems were chosen because of their contrasting photochemistry. The quantum yield for photoreduction of benzophenone in polar solvents is generally greater than 0.1, while that of fluorenone is zero. In polar solvents, the proposed mechanism dictates that an electron is transferred to the excited singlet state fluorenone, which then back-transfers the electron, regenerating ground-state fluorenone and amine. Photolysis of benzophenone in the presence of an amine transfers an electron to an excited triplet state, forming an ion pair that is stable relative to diffusional separation. The results of this study verify this proposal.

Peters, K.S.; Freilich, S.C.; Schaeffer, C.G.

1980-08-13

87

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1983-06-01

88

Problems of back electron transfer in electron transfer sensitization  

Energy Technology Data Exchange (ETDEWEB)

The problems of back electron transfer in electron transfer sensitization were discussed and methods of preventing back electron transfer to improve the quantum efficiency of charge separation in homogeneous systems were proposed. Although complete quenching of an excited sensitizer by an electron donor or acceptor is not difficult, chemical yields of oxidized or reduced species are in general low. The importance of the coulombic effect was demonstrated for benzophenone/leuco crystal violet, pyrene/methylviologen (MV/sup 2 +/)/ethylenediaminetetraacetic acid and phenothiazine/viologen analogue systems. Then the discussion was extended to the quenching of Ru(bpy)/sub 3/sup(2+*) (bpy=2,2'-bipyridine) by organic acceptors and donors in acetonitrile. The magnitude of the quenching constant ksub(q) as a function of exoergicity could be explainable by the Rehm-Weller equation in both cases: ..delta..H/sup + +/ is apparently negative for oxidative quenching (RuL/sub 3/sup(2+*)+A->RuL/sub 3//sup 3 +/+A/sup -/); in contrast, for reductive quenching (RuL/sub 3/sup(2+*)+D->RuL/sub 3//sup +/+D/sup +/) ..delta..H/sup + +/ is normal and controls ksub(q). A detailed kinetic mechanistic study leads to the conclusion that the attraction between RuL/sub 3//sup 3 +/ and A/sup -/ in oxidative quenching brings about back electron transfer to the excited state, and the charge separation yield is found to be lower than that for reductive quenching as would be expected.

Tazuke, Shigeo; Kitamura, Noboru; Kawanishi, Yuji

1985-05-01

89

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.

1989-01-01

90

Molecular transport junctions: Current from electronic excitations in the leads  

CERN Multimedia

Using a model comprising a 2-level bridge connecting free electron reservoirs we show that coupling of a molecular bridge to electron-hole excitations in the leads can markedly effect the source-drain current through a molecular junction.In some cases, e.g. molecules that exhibit strong charge transfer transitions, the contribution from electron-hole excitations can exceed the Landauer elastic current and dominate the observed conduction.

Galperin, M; Ratner, M A; Galperin, Michael; Nitzan, Abraham; Ratner, Mark A.

2006-01-01

91

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

Energy Technology Data Exchange (ETDEWEB)

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

Pinnaduwage, L.A. [Oak Ridge National Lab., TN (United States). Health Sciences Research Div.]|[Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics

1995-12-31

92

Correlations of two excited electrons  

Energy Technology Data Exchange (ETDEWEB)

Advances over the last twenty years are reported, with the emphasis on describing correlations through the distribution of an electron pair's wavefunction in its configuration space. The symmetry of the Schroedinger equation and its eigenfunctions are thus viewed and found to be important. The radial correlations are more significant for the mechanics of the pair than the angular correlations. Connections with other approaches to the subject are described. Earlier studies concerning doubly excited helium and the hydrogen negative ion are related to Wannier's threshold law for ionization by electron collision, but these two subjects are not yet fully connected. Recent studies on the alkaline earths and helium negative ion are described and viewed as a prelude to a renewed analysis and interpretation of the optical spectra and electron collisions for atoms with partially filled valence shells, which afford ample opportunity for the manifestation of strong correlations.

Fano, U. (Chicago Univ., IL (USA). Dept. of Physics)

1983-02-01

93

Electron-beam excitation of gas lasers  

International Nuclear Information System (INIS)

[en] Gas-laser-excitation with intense relativistic electron beams has gained popularity through many successful demonstrations of efficient conversion of electron-beam energy to laser energy. In some instances, electron-beam excitation of gas lasers has resulted in record laser energy and/or power, in higher efficiencies than has ever been obtained with any other excitation scheme, and in the discovery of lasers that have not been produced by any other excitation schemes. The feature of electron beams that make this laser excitation scheme so promising for use in high-power lasers is the high-power capability of electron beams. Three electron-beam geometrical configurations have been applied to gas-laser-excitation; electron-beam coaxial with the laser axis, electron-beam perpendicular to the laser axis, and radial convergent electron-beams. Measurements and comparisons with theory for these three geometries are given

1975-11-03

94

A study of electron transfer in Ru(dcbpy)2(NCS)2 sensitized nanocrystalline TiO2 and SnO2 films induced by red-wing excitation.  

Science.gov (United States)

Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a distribution of triplet states with energies below the semiconductor conduction band edge. PMID:18259639

Myllyperkiö, Pasi; Benko, Gábor; Korppi-Tommola, Jouko; Yartsev, Arkady P; Sundström, Villy

2007-12-10

95

Electronic excitation in bulk and nanocrystalline alkali halides.  

UK PubMed Central (United Kingdom)

The lowest energy excitations in bulk alkali halides are investigated by considering five different excited state descriptions. It is concluded that excitation transfers one outermost halide electron in the fully ionic ground state to the lowest energy vacant s orbital of one closest cation neighbour to produce the excited state termed dipolar. The excitation energies of seven salts were computed using shell model description of the lattice polarization produced by the effective dipole moment of the excited state neutral halogen-neutral metal pair. Ab initio uncorrelated short-range inter-ionic interactions computed from anion wavefunctions adapted to the in-crystal environment were augmented by short-range electron correlation contributions derived from uniform electron-gas density functional theory. Dispersive attractions including wavefunction overlap damping were introduced using reliable semi-empirical dispersion coefficients. The good agreement between the predicted excitation energies and experiment provides strong evidence that the excited state is dipolar. In alkali halide nanocrystals in which each ionic plane contains only four ions, the Madelung energies are significantly reduced compared with the bulk. This predicts that the corresponding intra-crystal excitation energies in the nanocrystals, where there are two excited states depending on whether the halide electron is transferred to a cation in the same or in the neighbouring plane, will be reduced by almost 2 eV. For such an encapsulated KI crystal, it has been shown that the greater polarization in the excited state of the bulk crystal causes these reductions to be lowered to a 1.1 eV-1.5 eV range for the case of charge transfer to a neighbouring plane. For intra-plane charge transfer the magnitude of the polarization energy is further reduced thus causing the excitation in these encapsulated materials to be only 0.2 eV less than in the bulk crystal.

Bichoutskaia E; Pyper NC

2012-11-01

96

Nonadiabatic anharmonic electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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 {Delta}=-{Delta}G. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy ({Delta}={Lambda}{sub s}) along a maximum ln (w) vs. {Delta} ridge of the surface. The surface also reveals additional regions for {Delta} where ln (w) appears to be insensitive to temperature, or effectively activationless, for some kinds of inner sphere contributions.

Schmidt, P. P. [Molecular Physics Research, 6547 Kristina Ursula Court, Falls Church, Virginia 22044 (United States)

2013-03-28

97

Nonadiabatic anharmonic electron transfer  

Science.gov (United States)

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 effectively activationless, for some kinds of inner sphere contributions.

Schmidt, P. P.

2013-03-01

98

Electron distribution function in electron-beam-excited plasmas  

International Nuclear Information System (INIS)

[en] In monatomic plasmas excited by high-intensity relativistic electron beams, the electron secondary distribution function is dominated by elastic electron-electron collisions at low electron energies and by inelastic electron-atom collisions at high electron energies (above the excitation threshold). Under these conditions, the total rate of excitation by inelastic collisions is limited by the rate at which electron-electron collisions relax the distribution function in the neighborhood of the excitation threshold. To describe this effect quantitatively, an approximate analytic solution of the electron Boltzmann equation is obtained, including both electron-electron and inelastic collisions. The result provides a simple formula for the total rate of excitation

1976-07-01

99

Two-electron excitation of an interacting cold Rydberg gas  

CERN Multimedia

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

Millen, J; Jones, M P A

2010-01-01

100

General considerations for the Symposium on correlated transfer/excitation and autoionization''  

Energy Technology Data Exchange (ETDEWEB)

This paper discusses the general aspects of correlated transfer/excitation and autoionization. The close relatioship between dielectronic recombination (DR) and resonant transfer and excitation (RTE) is reviewed and competing processes are considered. Several electron-ion like'' aspects of ion-atom collisions are identified and their significance discussed.

Tanis, J.A. (Department of Physics, Western Michigan University, Kalamazoo, MI (USA))

1990-06-01

 
 
 
 
101

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.)

1998-01-01

102

Ferroelectrics with Low-energy Electronic Excitations  

CERN Multimedia

We formulate a general theory of the dielectric response of a lattice with a structural transition and a polarization instability due to a soft-optic mode coupled to low energy electronic excitations by the electromagnetic fields. the electronic excitations considered are in two-limits; those of a low density of free-electrons or those of a low density of strongly localized electrons in the Coulomb-glass phase. The ferroelectric transition in the absence of the electronic-excitations and the low energy dielectric properties are shown to be strongly modified.

Ng, T K

2001-01-01

103

Nuclear reorganization barriers to electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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.

Sutin, N.; Brunschwig, B.S.; Creutz, C.; Winkler, J.R.

1988-01-01

104

Evidence for interference between resonant and nonresonant transfer and excitation  

International Nuclear Information System (INIS)

The first angular distribution measurements of Auger electrons arising from transfer and excitation Auger (TE) processes were performed at O5+ projective energies of 8 MeV, where the resonant (RTE) and the nonresonant (NTE) transfer and excitation have equal contributions in populating the (1s2s2p2)3D state, and at 13 MeV where RTE is predominant and at 6 MeV where NTE is more significant. The TE angular distributions are strongly forward peaked along the beam direction. The data were fitted to w(?p)=C[1+a2P2(cos?p)+a4P4(cos?p)] and the magnetic substate population probabilities were inferred

1991-01-01

105

Photoreduction of indigo dyes by electron donors. One- and two-electron-transfer reactions as a consequence of excited-state quenching  

Energy Technology Data Exchange (ETDEWEB)

The indigoid dyes, thioindigo (TI), N,N'-diacetylindigo, (NDI) and oxalylindigo (OI), all undergo reduction upon irradiation of the dyes in the presence of electron donors such as triethylamine (TEA) or N-benzyl-1,4-dihydronicotinamide (BNAH). Product analysis by NMR and high-resolution mass spectrometry has shown that the products for TI and NDI are the formal H/sub 2/ adducts TIH/sub 2/ and NDIH/sub 2/; the product for OI has been shown to be the semireduced radical OIH which is readily detected by its characteristic ESR spectrum. Mechanistic studies have been carried out for the visible-light-induced reduction of the three dyes.

Schanze, K.S.; Lee, L.Y.C.; Giannotti, C.; Whitten, D.G.

1986-05-14

106

Lifetime of electronic excitations in metal nanoparticles  

International Nuclear Information System (INIS)

Electronic excitations in metal particles with sizes up to a few nanometers are shown to have a one-electron character when a laser pulse is applied off the plasmon resonance. The calculated lifetimes of these excitations are in the femtosecond timescale but their values are substantially different from those in bulk. This deviation can be explained from the large weight of the excitation wave function in the nanoparticle surface region, where dynamic screening is significantly reduced. The well-known quadratic dependence of the lifetime with the excitation energy in bulk breaks down in these finite-size systems.

2010-01-01

107

Integrated light in direct excitation and energy transfer luminescence  

CERN Multimedia

Integrated light in direct excitation and energy transfer luminescence has been investigated. In the investigations reported here, monomolecular centers were taken into account. It was found that the integrated light is equal to the product of generation rate and time of duration of excitation pulse for both direct excitation and energy transfer luminescence.

Chimczak, Eugeniusz

2007-01-01

108

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

International Nuclear Information System (INIS)

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

1995-01-01

109

Excitation transfer, charge transfer and hydrogen abstraction reaction, kinetic studies of modification of DNA components  

International Nuclear Information System (INIS)

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

1994-01-01

110

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

Energy Technology Data Exchange (ETDEWEB)

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

Lin, Nianyun [Academia Sinica, Shanghai, SH (China). Shanghai Inst. of Nuclear Research

1995-03-01

111

Excitation transfer, charge transfer and hydrogen abstraction reaction, kinetic studies of modification of DNA components  

Science.gov (United States)

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

Y. Lin, N.

1996-02-01

112

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

International Nuclear Information System (INIS)

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

2008-06-23

113

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

114

Electron-impact excitation of holmium atoms  

International Nuclear Information System (INIS)

The electron-impact excitation of holmium atoms was studied by the method of extended crossing beams. The cross sections and the optical excitation functions were obtained for odd levels of Ho I, including the 22014 cm-1 laser level. Over 99% of the atoms were shown to reside in the ground level prior to collisions with electrons. Also measured were the excitation cross sections for six even levels, which presumably participate in the formation of inversion population in a gas-discharge holmium vapour laser. (laser applications and other topics in quantum electronics)

2000-06-30

115

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

1984-01-01

116

Nuclear excitation by electronic transition (NEET).  

Energy Technology Data Exchange (ETDEWEB)

We present a report on recent measurements using the Advanced Photon Source at Argonne National Laboratory to explore the phenomenon of Nuclear Excitation by Electronic Transition (NEET) in the {sup 189}Os atomic/nuclear system.

Ahmad, I.; Dunford, R. W.; Esbensen, H.; Gemmell, D. S.; Kanter, E. P.; Kraessig, B.; Ruett, U.; Southworth, S. H.

1999-04-28

117

Dynamics of solvent controlled excited state intramolecular proton transfer coupled charge transfer reactions.  

UK PubMed Central (United Kingdom)

Coupled intramolecular proton and charge transfer reactions play an important role in many biological and chemical reactions. In this article, we report the relaxation dynamics of the excited states of a donor substituted 1,3-diketone (DMADK, ) using steady state and ultrafast transient absorption and fluorescence spectroscopic techniques. Dramatic dependence of the fluorescence quantum yield, nonradiative rate as well as the excited state relaxation pathways on solvent polarity reveals the solvent controlled excited state intramolecular proton transfer (ESIPT) directed intramolecular charge transfer (ICT) dynamics. The molecules in the ground state coexist in two possible cis-enol (Enol-A and Enol-B) forms. Time-dependent density functional theory (TDDFT) calculations reveal solvent polarity controlled thermodynamic stabilization of one of the tautomeric structures in the S1 state, dictating the direction of proton transfer and subsequent structural relaxation. In low and medium polarity solvents, the S1 state of Enol-B (Enol-B*) undergoes ultrafast ESIPT leading to the population of Enol-A*, followed by the ICT process. In polar solvents, the ESIPT process is reversed to populate Enol-B*, which undergoes a twisted intramolecular charge transfer (TICT) process via twisting of the N,N-dimethylaniline group. This work demonstrates that the strength of electronic coupling between the donor and acceptor group determines the structure of the ICT state.

Ghosh R; Palit DK

2013-06-01

118

Transfer excitation in F6+ and Ne7+ ions colliding with He and Ne targets  

International Nuclear Information System (INIS)

An experimental study is presented, using coincident energy gain spectroscopy, of transfer excitation processes in the low keV energy range, for lithium-like F6+ and Ne7+ ions colliding with He and Ne atoms. A theoretical model is developed in a quasimolecular framework, implying the same basic interactions as invoked in non-resonant transfer excitation (NTE), a mechanism well established at large collision velocity. This model describes transfer excitation as a two-step process essentially governed by the electron-nucleus interactions. (Author).

1994-01-01

119

Inner-shell excitation by channeled electrons  

International Nuclear Information System (INIS)

An interesting situation occurs when inner shell electrons in crystalline materials are excited by electron beams of kilovolt energies in a transmission electron microscope. For many years the subsequent x-ray emission has been used as the basis of an analytical technique, giving compositional information at high spatial resolution. Recently this technique has been extended to provide information on impurity lattice site location, the basis of the technique being to take two fluorescence spectra, one under channeling conditions and one ''random'' spectrum with the crystal oriented away from strongly channeling planes or axes. Since electrons channel along the positive potential wells of the atomic planes or strings, a higher yield of characteristic x-ray emission is expected from the channeled case, for the same incident beam current. This channeling effect can be defined as the relative increase in x-ray yield. This paper discusses using channeled electron to excited inner-shell electrons. 4 refs., 3 figs

1988-01-01

120

Electronic excitation spectrum of metallic carbon nanotubes  

CERN Multimedia

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.

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

2005-01-01

 
 
 
 
121

Vibrational promotion of electron transfer.  

UK PubMed Central (United Kingdom)

By using laser methods to prepare specific quantum states of gas-phase nitric oxide molecules, we examined the role of vibrational motion in electron transfer to a molecule from a metal surface free from the complicating influence of solvation effects. The signature of the electron transfer process is a highly efficient multiquantum vibrational relaxation event, where the nitrogen oxide loses hundreds of kilojoules per mole of energy on a subpicosecond time scale. These results cannot be explained simply on the basis of Franck-Condon factors. The large-amplitude vibrational motion associated with molecules in high vibrational states strongly modulates the energetic driving force of the electron transfer reaction. These results show the importance of molecular vibration in promoting electron transfer reactions, a class of chemistry important to molecular electronics devices, solar energy conversion, and many biological processes.

Huang Y; Rettner CT; Auerbach DJ; Wodtke AM

2000-10-01

122

Fishbone instability excited by circulating electrons  

International Nuclear Information System (INIS)

Fishbone instability excited by the supra-thermal circulating electrons in tokamaks is investigated. It is found for the first time that the precession of all the circulating electrons is in the ion diamagnetic drift direction if magnetic shear is neglected. The circulating electrons, which experience both the high field side and the low field side, play a bigger role on the modes than the barely trapped electrons. The analyses show that the mode frequency is close to the precession frequency of circulating electrons comparable with experiment observations. The correlation of the theory with experiments is discussed.

2007-01-01

123

Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.

Bixner O.; Christensson N.; Hauer J.; Milota F.; Man?al T.; Lukeš V.; Kauffmann H. F.

2013-01-01

124

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 th/sup>D 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.

1991-01-01

125

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

2001-01-01

126

Theory of parametric excitation of electron plasma  

Energy Technology Data Exchange (ETDEWEB)

The possibility of parametric excitation of longitudinal and transverse oscillations of pure cold electron plasma in high-frequency electric fields, when the relativistic oscillatory motion of the plasma electrons is taken into account, is studied. It is shown that the longitudinal and transverse oscillations are parametrically excited. Two equations describing the growth-rate of longitudinal and transverse oscillations and the parametric resonance conditions are obtained. It is also shown that due to the decrease of the proper plasma frequency, the penetration depth of electromagnetic fields in plasma is increased.

El-Ashry, M.Y. (Suez Canal Univ., Ismailia (Egypt). Physics Dept.)

1985-03-01

127

Bioinspired electron-transfer systems and applications  

International Nuclear Information System (INIS)

Bioinspired electron-transfer systems including artificial photosynthesis and respiration are presented herein together with some of their applications. First, multi-step electron-transfer systems composed of electron donor-acceptor ensembles have been developed, mimicking functions of the photosynthetic reaction center. However, a significant amount of energy is lost during the multi-step electron-transfer processes. Then, as an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer within redox cascades, simple donor-acceptor dyads have been developed to attain along-lived and high energy charge-separated state without significant loss of excitation energy, by fine control of the redox potentials and of the geometry of donor-acceptor dyads that have small reorganization energies of electron transfer. Such simple molecular dyads, capable of fast charge separation but extremely slow charge recombination, have significant advantages with regard to synthetic feasibility, providing a variety of applications including construction of organic solar cells and development of efficient photo-catalytic systems for the solar energy conversion. An efficient four-electron reduction of dioxygen to water by one-electron reductants such as ferrocene derivatives as well as by an NADH analog has also been achieved as a respiration model by using a cofacial dicobalt porphyrin that can form the ?-peroxo Co(III)-O2Co(III) complex. The catalytic mechanism of the four-electron reduction of dioxygen has been clarified based on the detailed kinetic study and the detection of the intermediate. (author)

2006-01-01

128

Excited states in electronic structure calculations  

Energy Technology Data Exchange (ETDEWEB)

A first-principles quasiparticle approach to the electronic excitation energies in crystals and at surfaces is described. The quasiparticle energies are calculated within the GW approximation for comparison with photoemission and other spectroscopic experiments. Applications of the method to bulk semiconductors and the Si(111)2[times]l, Ge(111)2[times]l. and H/Si(III) surfaces are presented. In both cases, significant self-energy corrections arising from many-electron effects to the excitation energies are found. Using atomic positions from total energy minimization, the calculated excitation energies explain quantitatively the experimental spectra. This approach thus provides an ab initio means for analyzing and predicting results from spectroscopic probes.

Louie, S.G.

1992-07-01

129

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.

1994-08-13

130

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

UK PubMed Central (United Kingdom)

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.

Watanabe N; Hirayama T; Suzuki D; Takahashi M

2013-05-01

131

Ultrafast excitation energy transfer in small semiconducting carbon nanotube aggregates.  

Science.gov (United States)

We study excitation energy transfer in small aggregates of chirality enriched carbon nanotubes by transient absorption spectroscopy. Ground state photobleaching is used to monitor exciton population dynamics with sub-10 fs time resolution. Upon resonant excitation of the first exciton transition in (6,5) tubes, we find evidence for energy transfer to (7,5) tubes within our time resolution (<10 fs). Excitation in the visible spectral range, where the second excitonic transitions occur, is followed by fast intratube relaxation and subsequent energy transfer, in particular from the (8,4) tube toward other tubes, the latter process occurring in less than 10 fs. PMID:20518568

Lüer, Larry; Crochet, Jared; Hertel, Tobias; Cerullo, Giulio; Lanzani, Guglielmo

2010-07-27

132

Ultrafast excitation energy transfer in small semiconducting carbon nanotube aggregates.  

UK PubMed Central (United Kingdom)

We study excitation energy transfer in small aggregates of chirality enriched carbon nanotubes by transient absorption spectroscopy. Ground state photobleaching is used to monitor exciton population dynamics with sub-10 fs time resolution. Upon resonant excitation of the first exciton transition in (6,5) tubes, we find evidence for energy transfer to (7,5) tubes within our time resolution (<10 fs). Excitation in the visible spectral range, where the second excitonic transitions occur, is followed by fast intratube relaxation and subsequent energy transfer, in particular from the (8,4) tube toward other tubes, the latter process occurring in less than 10 fs.

Lüer L; Crochet J; Hertel T; Cerullo G; Lanzani G

2010-07-01

133

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

Science.gov (United States)

High-energy electron transfer dissociation (HE-ETD) on collisions with alkali metal targets (Cs, K, and Na) was investigated for CH(3)X(+) (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 CH(3)I potential energy curve reported by ab initio calculations, the trapezoidal part is attributed to the dissociation to CH(3) + I((2)P(3/2)) via the repulsive (3)Q(1) state of CH(3)I, which is not dominant in the photo-dissociation of CH(3)I. The observation of trapezoid shape of the CH(2)I(-) peak with the Cs target indicates spontaneous dissociation via repulsive potential from the (3)R(2) Rydberg state, although the correlation between the (3)R(2) Rydberg state and relevant repulsive states has not been reported by any theoretical calculation. PMID:23163372

Hayakawa, Shigeo; Tsujinaka, Taiga; Fujihara, Akimasa

2012-11-14

134

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

UK PubMed Central (United Kingdom)

High-energy electron transfer dissociation (HE-ETD) on collisions with alkali metal targets (Cs, K, and Na) was investigated for CH(3)X(+) (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 CH(3)I potential energy curve reported by ab initio calculations, the trapezoidal part is attributed to the dissociation to CH(3) + I((2)P(3/2)) via the repulsive (3)Q(1) state of CH(3)I, which is not dominant in the photo-dissociation of CH(3)I. The observation of trapezoid shape of the CH(2)I(-) peak with the Cs target indicates spontaneous dissociation via repulsive potential from the (3)R(2) Rydberg state, although the correlation between the (3)R(2) Rydberg state and relevant repulsive states has not been reported by any theoretical calculation.

Hayakawa S; Tsujinaka T; Fujihara A

2012-11-01

135

Model studies of the kinetics of collisional population transfer between dark and radiating excited electronic states: CaO(A' 1Pi)+N2Oarrow-right-leftCaO(A 1?+)+N2O  

International Nuclear Information System (INIS)

In a previous article [J. Chem. Phys. 76, 429 (1982)] we presented a model for collisional energy transfer between dark (A' 1Pi, a 3Pi) and radiating (A 1?+) excited electronic states of the alkaline earth oxides. The inelastic transitions result from coupling between the electric dipole of the collision partner and a transition dipole in the alkaline earth oxide, which arises from the non-Born--Oppenheimer coupling between the rovibronic manifolds of two different electronic states. Here we use the rate constants reported in the previous article to investigate population flow from the nominally v = 6 manifold of the A' 1Pi state of CaO into the nominally v = 0 manifold of the A 1?+ state, induced by collisions with N2O. The master equation is solved in the steady state limit. The resulting populations are then used to simulate the pressure dependence of the (0--0) band of the CaO A 1?+?X 1?+ spectrum, and investigate the variation of the predicted spectral features with respect to changing the conditions which characterize both the rate of formation of the excited states as well as the rate of translational loss out of the zone of observation. At low to moderate target gas pressure the major effect of collisions is A'?A population transfer in the region of the largest coupling between the two rotational manifolds. The concomitant intensity increase and the spectral variation in the A state emission are qualitatively similar to features seen in experimental spectra of Irvin and Dagdigian, which we present here. The pressure dependent changes in the emission spectra are extremely sensitive to the assumed rate of translational loss, which must be taken into account in any comparison between experiments carried out under flame and molecular beam conditions.

1982-01-01

136

Electronic excitation of methane molecule by electron impact  

International Nuclear Information System (INIS)

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

1988-01-01

137

Electron transfer and decay processes of highly charged iodine ions  

International Nuclear Information System (INIS)

In the present experimental work we have investigated multi-electron transfer processes in Iq+ (q=10, 15, 20 and 25) + Ne, Ar, Kr and Xe collisions at 1.5q keV energy. The branching ratios between Auger and radiative decay channels have been measured in decay processes of multiply excited states formed by multi-electron transfer collisions. It has been shown that, in all the multi-electron transfer processes investigated, the Auger decays are far dominant over the radiative decay processes and the branching ratios are clearly characterized by the average principal quantum number of the initial excited states of projectile ions. We could express the branching ratios in high Rydberg states formed in multi-electron transfer processes by using the decay probability of one Auger electron emission. (author)

2005-01-01

138

Chlorophyll a Franck-Condon factors and excitation energy transfer  

Energy Technology Data Exchange (ETDEWEB)

The Franck-Condon factors for the S{sub 1}(Q{sub y}) {leftrightarrow} S{sub 0} electronic transition of chlorophyll (Chl) molecules are important for understanding excitation energy transfer in photosynthetic complexes. Currently, there are two sets of Chl a Frank-Condon factors for over 40 modes, one determined by spectral hole burning and the other by fluorescence line narrowing. Those obtained by the latter spectroscopy are, on average, a factor of 30 times smaller than the hole burning values. Nonline-narrowed fluorescence results for the light-harvesting complex 2 of photosystem 2 at 4.2 K are presented that agree quite well with the hole burning but not the fluorescence line narrowing values.

Pieper, J. [Humboldt Univ., Berlin (Germany). Inst. of Physics]|[Ames Lab., IA (United States)]|[Iowa State Univ., Ames, IA (United States). Dept. of Chemistry; Voigt, J. [Humboldt Univ., Berlin (Germany). Inst. of Physics; Small, G.J. [Ames Lab., IA (United States)]|[Iowa State Univ., Ames, IA (United States). Dept. of Chemistry

1999-04-01

139

Ultrafast excitation transfer and trapping in a thin polymer film  

Science.gov (United States)

Transient absorption anisotropy of a polythiophene polymer in a thin film was studied on a femtosecond time scale. The anisotropy has a non-exponential decay on the sub-picosecond time scale, with a fastest component characterized by an ˜40 fs time constant. To simulate the anisotropy decay an incoherent energy migration model has been used. Comparison between the simulated and experimental kinetics enabled us to estimate the nearest-neighbor pair wise hopping time (?h=1±0.1 ps), the fraction of the interchain aggregates (˜10%) and the structural disorder of the polymer. The initial ˜30 fs anisotropy decay does not originate from incoherent hopping energy transfer but from some other relaxation among electronic excited states within a spectroscopic unit.

Grage, Mette M.-L.; Zaushitsyn, Yuri; Yartsev, Arkady; Chachisvilis, Mirianas; Sundström, Villy; Pullerits, Tõnu

2003-05-01

140

Excited electronic states of AuF.  

UK PubMed Central (United Kingdom)

We have recorded laser excitation spectra of transitions from the ground X(1)Sigma(+) state of gaseous gold fluoride (AuF) into three excited electronic states in the visible region. We prepared the sample in a dc electric discharge by flowing a dilute mixture of SF(6) in argon through a hollow gold cathode. Two of these electronic states give rise to the previously reported yellow bands of the molecule, for which a rotational analysis is given here for the first time. We have analyzed the (0,0), (1,1), (0,1), and (1,2) bands of these two transitions, which we identify as [17.8]0(+)-X(1)Sigma(+) and [17.7]1-X(1)Sigma(+); their red-degraded (0,0) band heads lie at 563.0 and 566.2 nm, respectively. The (0,0) band of a new, red-degraded [14.0]1-X(1)Sigma(+) transition at 715.1 nm has also been recorded and analyzed. An accurate set of molecular constants of the three excited states as well as the ground state has been determined by least-squares fitting all of the optical data together with measurements made by other workers of the pure rotational spectrum of AuF in its ground state. These constants include the electronic term energies, vibrational frequencies, rotational constants, and Omega-doubling constants. We discuss the nature of these three excited electronic states in terms of the ionic Au(+)F(-) electronic configurations from which they are derived.

Butler EK; Knurr BJ; Manke KJ; Vervoort TR; Varberg TD

2010-04-01

 
 
 
 
141

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.

1987-01-01

142

Effect resonance radiation transfer of excitation porous silicon to I sub 2 molecules sorbed in pores  

CERN Multimedia

One studies the effect of resonance radiation-free transfer of electronic excitation between silicon nanocrystals and iodine molecules sorbed in pores. The experiment procedure includes laser-induced luminescence and laser desorption mass spectrometry. One analyzes photoluminescence spectra prior to and upon iodine sorption. Excitation of iodine through the mechanism of resonance transfer is determined to result in desorption of the iodine sorbed molecules with relatively high kinetic energies (3-1 eV). One evaluated the peculiar distance of resonance transfer the approximate value of which was equal to 2 nm

Zakharchenko, K V; Kuznetsov, M B; Chistyakov, A A; Karavanskij, V A

2001-01-01

143

Orthogonality constrained density functional theory for electronic excited States.  

Science.gov (United States)

We report a novel scheme for computing electronic excitation energies within the framework of density functional theory (DFT) based on a time-independent variational formulation of DFT. The excited state density functional is recast as a Kohn-Sham functional, which is further simplified by an adiabatic approximation of the exchange-correlation functional. Under the adiabatic approximation, the minimization of the excited state Kohn-Sham functional is shown to be equivalent to a ground state DFT computation augmented with orthogonality constraints with respect to the ground state Kohn-Sham determinant. An algorithm for the optimization of the energy subject to orthogonality constraints, which does not suffer from variational collapse, is described and implemented. A benchmark test set containing 28 organic molecules ( Schreiber , M. J. Chem. Phys. 2008 , 128 , 134110 ) was used to assess the quality of the excitation energies obtained. Two novel approaches to spin-adapt the resulting excitation energies are discussed and found to provide results with error metrics similar to those of time-dependent DFT. Similarities and differences with respect to other time-independent DFT approaches are highlighted and some of the advantages of our scheme-including the ability to correctly describe charge-transfer excitations-are critically assessed. PMID:23590595

Evangelista, Francesco A; Shushkov, Philip; Tully, John C

2013-05-28

144

Orthogonality constrained density functional theory for electronic excited States.  

UK PubMed Central (United Kingdom)

We report a novel scheme for computing electronic excitation energies within the framework of density functional theory (DFT) based on a time-independent variational formulation of DFT. The excited state density functional is recast as a Kohn-Sham functional, which is further simplified by an adiabatic approximation of the exchange-correlation functional. Under the adiabatic approximation, the minimization of the excited state Kohn-Sham functional is shown to be equivalent to a ground state DFT computation augmented with orthogonality constraints with respect to the ground state Kohn-Sham determinant. An algorithm for the optimization of the energy subject to orthogonality constraints, which does not suffer from variational collapse, is described and implemented. A benchmark test set containing 28 organic molecules ( Schreiber , M. J. Chem. Phys. 2008 , 128 , 134110 ) was used to assess the quality of the excitation energies obtained. Two novel approaches to spin-adapt the resulting excitation energies are discussed and found to provide results with error metrics similar to those of time-dependent DFT. Similarities and differences with respect to other time-independent DFT approaches are highlighted and some of the advantages of our scheme-including the ability to correctly describe charge-transfer excitations-are critically assessed.

Evangelista FA; Shushkov P; Tully JC

2013-08-01

145

Description of electronic excited states using electron correlation operator  

Science.gov (United States)

The electron correlation energy in a chemical system is defined as a difference between the energy of an exact energy for a given Hamiltonian, and a mean-field, or single determinant, approximation to it. A promising way to model electron correlation is through the expectation value of a linear two-electron operator for the Kohn-Sham single determinant wavefunction. For practical reasons, it is desirable for such an operator to be universal, i.e., independent of the positions and types of nuclei in a molecule. The correlation operator models the effect of electron correlation on the interaction energy in a electron pair. We choose an operator expanded in a small number of Gaussians as a model for electron correlation, and test it by computing atomic and molecular adiabatic excited states. The computations are performed within the ? Self-Consistent Field (?SCF) formalism, and are compared to the time-dependent density functional theory model with popular density functionals. The simplest form of the correlation operator contains only one parameter derived from the helium atom ground state correlation energy. The correlation operator approach significantly outperforms other methods in computation of atomic excitation energies. The accuracy of molecular excitation energies computed with the correlation operator is limited by the shortcomings of the ?SCF methodology in describing excited states.

Nichols, Bryan; Rassolov, Vitaly A.

2013-09-01

146

Description of electronic excited states using electron correlation operator.  

UK PubMed Central (United Kingdom)

The electron correlation energy in a chemical system is defined as a difference between the energy of an exact energy for a given Hamiltonian, and a mean-field, or single determinant, approximation to it. A promising way to model electron correlation is through the expectation value of a linear two-electron operator for the Kohn-Sham single determinant wavefunction. For practical reasons, it is desirable for such an operator to be universal, i.e., independent of the positions and types of nuclei in a molecule. The correlation operator models the effect of electron correlation on the interaction energy in a electron pair. We choose an operator expanded in a small number of Gaussians as a model for electron correlation, and test it by computing atomic and molecular adiabatic excited states. The computations are performed within the ? Self-Consistent Field (?SCF) formalism, and are compared to the time-dependent density functional theory model with popular density functionals. The simplest form of the correlation operator contains only one parameter derived from the helium atom ground state correlation energy. The correlation operator approach significantly outperforms other methods in computation of atomic excitation energies. The accuracy of molecular excitation energies computed with the correlation operator is limited by the shortcomings of the ?SCF methodology in describing excited states.

Nichols B; Rassolov VA

2013-09-01

147

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

UK PubMed Central (United Kingdom)

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

Toppari JJ; Wirth J; Garwe F; Stranik O; Csaki A; Bergmann J; Paa W; Fritzsche W

2013-02-01

148

Collapse of an orbit of excited electron  

Energy Technology Data Exchange (ETDEWEB)

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

Kuchas, S.A.; Karosene, A.V.; Karaziya, R.I. (AN Litovskoj SSR, Vilnyus. Inst. Fiziki)

1981-12-01

149

Vibrational excitation of water by electron impact  

Science.gov (United States)

Experimental and calculated differential cross sections (DCSs) for electron-impact excitation of the (010) bending mode and unresolved (100) symmetric and (001) antisymmetric stretching modes of water are presented. Measurements are reported at incident energies of 1-100 eV and scattering angles of 10°-130° and are normalized to the elastic-scattering DCSs for water determined earlier by our group. The calculated cross sections are obtained in the adiabatic approximation from fixed-nuclei, electronically elastic scattering calculations using the Schwinger multichannel method. The present results are compared to available experimental and theoretical data.

Khakoo, M. A.; Winstead, C.; McKoy, V.

2009-05-01

150

Vibrational excitation of water by electron impact  

International Nuclear Information System (INIS)

Experimental and calculated differential cross sections (DCSs) for electron-impact excitation of the (010) bending mode and unresolved (100) symmetric and (001) antisymmetric stretching modes of water are presented. Measurements are reported at incident energies of 1-100 eV and scattering angles of 10 deg. - 130 deg. and are normalized to the elastic-scattering DCSs for water determined earlier by our group. The calculated cross sections are obtained in the adiabatic approximation from fixed-nuclei, electronically elastic scattering calculations using the Schwinger multichannel method. The present results are compared to available experimental and theoretical data.

2009-01-01

151

Erbium emission in MOS light emitting devices: from energy transfer to direct impact excitation  

International Nuclear Information System (INIS)

The electroluminescence (EL) at 1.54 µm of metal–oxide–semiconductor (MOS) devices with Er3+ ions embedded in the silicon-rich silicon oxide (SRSO) layer has been investigated under different polarization conditions and compared with that of erbium doped SiO2 layers. EL time-resolved measurements allowed us to distinguish between two different excitation mechanisms responsible for the Er3+ emission under an alternate pulsed voltage signal (APV). Energy transfer from silicon nanoclusters (Si-ncs) to Er3+ is clearly observed at low-field APV excitation. We demonstrate that sequential electron and hole injection at the edges of the pulses creates excited states in Si-ncs which upon recombination transfer their energy to Er3+ ions. On the contrary, direct impact excitation of Er3+ by hot injected carriers starts at the Fowler–Nordheim injection threshold (above 5 MV cm?1) and dominates for high-field APV excitation. (paper)

2012-03-30

152

Polar solvation and electron transfer  

Energy Technology Data Exchange (ETDEWEB)

The report is divided into the following sections: completion of previous studies on solvation dynamics, dipole lattice studies, inertial components of solvation response, simple models of solvation dynamics, rotational dynamics and dielectric friction, intramolecular electron transfer reactions, and intermolecular donor-acceptor complexes.

1993-04-13

153

CN excitation and electron densities in diffuse molecular clouds  

Science.gov (United States)

Utilizing previous work by the authors on the spin-coupled rotational cross-sections for electron-CN collisions, data for the associated rate coefficients are presented. Data on rotational, fine-structure and hyperfine-structure transition involving rotational levels up to N = 20 are computed for temperatures in the range 10-1000 K. Rates are calculated by combining Born-corrected R-matrix calculations with the infinite-order-sudden approximation. The dominant hyperfine transitions are those with ?N = ?j = ?F = 1. For dipole-allowed transitions, electron-impact rates are shown to exceed those for excitation of CN by para-H2(j = 0) by five orders of magnitude. The role of electron collisions in the excitation of CN in diffuse clouds, where local excitation competes with the cosmic microwave background photons, is considered. Radiative transfer calculations are performed and the results compared to observations. These comparisons suggest that electron density lies in the range n(e) ˜ 0.01-0.06 cm-3 for typical physical conditions present in diffuse clouds.

Harrison, Stephen; Faure, Alexandre; Tennyson, Jonathan

2013-11-01

154

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads. Technical progress report, 1989  

Energy Technology Data Exchange (ETDEWEB)

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

1989-04-12

155

Environmental effects on photoinduced electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

Photoinduced electron transfer reactions between an electronically excited photosensitizer molecule and a reversible electron acceptor capable of hydrogen production were studied to determine the possible utility of these reactions in solar energy conversion systems. The influence of charged macromolecules on the forward and back electron-transfer reaction between oppositely charged initial photoproducts, the photosensitizer zinc tetra(4-N-methyl pyridinium) porphyrin (ZnP/sup +4/) and the neutral electron acceptor, propyl viologen sulfonate (PVS/sup 0/), has been investigated using continuous photolysis and flash photolysis techniques. Flash photolysis experiments have been performed to study the effect of anionic polyelectrolyte poly(styrene sulfonate) (PSS) on the photoreaction between ZnP/sup +4/ and PVS/sup 0/. These experiments show that all bimolecular rate constants involving PSS-bound ZnP/sup +4/ are decreased by a factor for 40-100. A kinetic model has been developed that describes the transient absorbance behavior of ZnP/sup +4//PVS/sup 0//colloidal silica photolysis systems in which scavenging of PVS/sup -/ by residual O/sub 2/ occurs. Flash photolysis experiments confirmed that alumina-modified silica particles are significantly more effective than unmodified silica sols in neutral pH media at decreasing the rate of back-reaction between ZnP/sup +4/ and PVS/sup -/. 25 refs., 32 figs., 5 tabs.

Casti, T.E.

1985-12-01

156

Excitation of He+ by electron impact  

International Nuclear Information System (INIS)

A five-state close-coupling approximation in which 1s, 2s, and 2p eigenstates and 3s-bart-baru-barv-barw-barx-bary-barz-barI and 3p-barq-barr-bars-bart-baru-barv-barw-barx-bary-barz-barI pseudostates of He+ are included in the expansion, is used to calculate 1s ? 2s and 1s ? 2p excitation of He+ by electron impact in the intermediate energy range up to about three times ionization threshold energy. Pseudostates are chosen to maximize their overlap with bound states and low-lying continuum states of the same symmetry. Present results for 1s ? 2s excitation provide a link between accurate low- and high-energy results and agree with experiment above 70 eV

1976-01-01

157

Coherence in electron-impact excitation of helium  

Energy Technology Data Exchange (ETDEWEB)

This thesis describes an experimental study into the electron-impact excitation to the 3{sup 3}P, 3{sup 1}D and 3{sup 3}D 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 {gamma}. It is shown that results of measurements on 3{sup 1}D 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 3{sup 3}P excitation the predicted large value of {gamma} is indeed found experimentally. This supports the suggestion that exchange scattering is underestimated in model calculations for {sup 1}P excitation. Another result is that for {sup 1}P and {sup 3}P 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 3{sup 3}D 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 3{sup 3}D state. It is shown that the coincident measurement gives an unique opportunity to determine the excited 3{sup 3}D state completely. Results of measurements with photon detection in the scattering plane are given. They supplement previous 3{sup 1}D and 3{sup 3}D results and allow physical parameters, such as L perpendicular and {gamma}, to be obtained. (H.W.). 132 refs.; 20 figs.; 18 tabs.

Batelaan, Hermanus

1991-06-10

158

Motional effects on the efficiency of excitation transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-15

159

Motional effects on the efficiency of excitation transfer  

CERN Document Server

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

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

2010-01-01

160

Excitation of Be+ by electron impact  

International Nuclear Information System (INIS)

Calculations of the collision strength for excitation of the 2p state of Be+ are performed at incident energies of 2, 5, and 8 Ry. A modified five state close coupling expansion is used in which three pseudo-states anti 3s, anti 3p, and anti 3d are retained in addition to target states 2s and 2p. Pseudostates are chosen so that, for a given incident electron energy, there is a minimum in the dominant partial wave collision strength with respect to variation of the range parameter. Collision strengths are obtained which lie between five state calculations of Hayes et al. and measurements of Taylor et al

1977-01-01

 
 
 
 
161

Electron impact excitation for Ar VI  

Science.gov (United States)

Radiative atomic and electron impact excitation data for Ar VI ion have been calculated using the AUTOSTRUCTURE code. The two-body non-fine structure operators of the Breit-Pauli Hamiltonian have been incorporated in AUTOSTRUCTURE, and for the collisional problem, we use the distorted wave approximation. We compare our radiative atomic results with the few available ones. To our best knowledge, there are no distorted wave collision strengths for Ar VI. Some discrepancies have been reported between our oscillator strengths and the only calculated ones using the MCHF method. We perform the same calculations with the UCL codes SST/DW/JAJOM and we compare with the present AUTOSTRUCTURE results.

Elabidi, Haykel

2012-12-01

162

Reactive scattering of electronically excited alkali atoms with molecules  

International Nuclear Information System (INIS)

Representative families of excited alkali atom reactions have been studied using a crossed beam apparatus. For those alkali-molecule systems in which reactions are also known for ground state alkali and involve an early electron transfer step, no large differences are observed in the reactivity as Na is excited. More interesting are the reactions with hydrogen halides (HCl): it was found that adding electronic energy into Na changes the reaction mechanism. Early electron transfer is responsible of Na(5S, 4D) reactions, but not of Na(3P) reactions. Moreover, the NaCl product scattering is dominated by the HCl- repulsion in Na(5S, 4D) reactions, and by the NaCl-H repulsion in the case of Na(3P). The reaction of Na with O2 is of particular interest since it was found to be state specific. Only Na(4D) reacts, and the reaction requires restrictive constraints on the impact parameter and the reactants' relative orientation. The reaction with NO2 is even more complex since Na(4D) leads to the formation of NaO by two different pathways. It must be mentioned however, that the identification of NaO as product in these reactions has yet to be confirmed.

1987-01-01

163

Excitation energy transfer between closely spaced multichromophoric systems: Effects of band mixing and intraband relaxation  

CERN Multimedia

We theoretically analyze the excitation energy transfer between two closely spaced linear molecular J-aggregates, whose excited states are Frenkel excitons. The aggregate with the higher (lower) exciton band edge energy is considered as the donor (acceptor). The celebrated theory of F\\"orster resonance energy transfer (FRET), which relates the transfer rate to the overlap integral of optical spectra, fails in this situation. We point out that in addition to the well-known fact that the point-dipole approximation breaks down (enabling energy transfer between optically forbidden states), also the perturbative treatment of the electronic interactions between donor and acceptor system, which underlies the F\\"orster approach, in general loses its validity due to overlap of the exciton bands. We therefore propose a nonperturbative method, in which donor and acceptor bands are mixed and the energy transfer is described in terms of a phonon-assisted energy relaxation process between the two new (renormalized) bands. ...

Didraga, C; Knöster, J

2006-01-01

164

Excitation transfer and luminescence in porphyrin-carbon nanotube complexes  

CERN Multimedia

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.

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

2007-01-01

165

Ultrafast excited-state intramolecular proton transfer of aloesaponarin I.  

Science.gov (United States)

Time-resolved emission of aloesaponarin I was studied with the fluorescence up-conversion and time-correlated single-photon-counting techniques. The rates of the excited-state intramolecular proton transfer, of the solvent and molecular rearrangements, and of the decay from the excited proton-transferred species were determined and interpreted in the light of time-dependent density functional calculations. These results were discussed in conjunction with UV protection and singlet-oxygen quenching activity of aloe. PMID:23153299

Nagaoka, Shin-ichi; Uno, Hidemitsu; Huppert, Dan

2012-11-26

166

Electron impact excitation of copper atoms  

International Nuclear Information System (INIS)

The optical excitation function method has been used in a crossed atom and electron beam arrangement to measure the electron impact cross section of the copper 42P ? 42S resonance lines (324.8, 327.4 nm) from threshold (3.8 eV) to 8 eV. Relative experimental cross section data are normalized at an energy of 1000 eV with respect to first Born theory that includes the 42S ? 42P resonance transition with an oscillator strength of 0.652 and cascading from the (3d10nd)2D states with n = 4, hor-ellipsis 10. The measured Cu 42S4 ? 42P cross section is compared with recent theoretical calculations in close-coupling approximation. Very good agreement is found with the ten-state close-coupling theory of Scheibner.

1993-01-01

167

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

CERN Document Server

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

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

2013-01-01

168

Electronic excitations and the tunneling spectra of metallic nanograins  

CERN Document Server

Tunneling-induced electronic excitations in a metallic nanograin are classified in terms of {em generations}: subspaces of excitations containing a specific number of electron-hole pairs. This yields a hierarchy of populated excited states of the nanograin that strongly depends on (a) the available electronic energy levels; and (b) the ratio between the electronic relaxation rate within the nano-grain and the bottleneck rate for tunneling transitions. To study the response of the electronic energy level structure of the nanograin to the excitations, and its signature in the tunneling spectrum, we propose a microscopic mean-field theory. Two main features emerge when considering an Al nanograin coated with Al oxide: (i) The electronic energy response fluctuates strongly in the presence of disorder, from level to level and excitation to excitation. Such fluctuations produce a dramatic sample dependence of the tunneling spectra. On the other hand, for excitations that are energetically accessible at low applied ...

Narvaez, G A; Kirczenow, George; Narvaez, Gustavo A.

2003-01-01

169

Proton-coupled electron transfer with photoexcited metal complexes.  

UK PubMed Central (United Kingdom)

Proton-coupled electron transfer (PCET) plays a crucial role in many enzymatic reactions and is relevant for a variety of processes including water oxidation, nitrogen fixation, and carbon dioxide reduction. Much of the research on PCET has focused on transfers between molecules in their electronic ground states, but increasingly researchers are investigating PCET between photoexcited reactants. This Account describes recent studies of excited-state PCET with d(6) metal complexes emphasizing work performed in my laboratory. Upon photoexcitation, some complexes release an electron and a proton to benzoquinone reaction partners. Others act as combined electron-proton acceptors in the presence of phenols. As a result, we can investigate photoinduced PCET involving electron and proton transfer in a given direction, a process that resembles hydrogen-atom transfer (HAT). In other studies, the photoexcited metal complexes merely serve as electron donors or electron acceptors because the proton donating and accepting sites are located on other parts of the molecular PCET ensemble. We and others have used this multisite design to explore so-called bidirectional PCET which occurs in many enzymes. A central question in all of these studies is whether concerted proton-electron transfer (CPET) can compete kinetically with sequential electron and proton transfer steps. Short laser pulses can trigger excited-state PCET, making it possible to investigate rapid reactions. Luminescence spectroscopy is a convenient tool for monitoring PCET, but unambiguous identification of reaction products can require a combination of luminescence spectroscopy and transient absorption spectroscopy. Nevertheless, in some cases, distinguishing between PCET photoproducts and reaction products formed by simple photoinduced electron transfer (ET) (reactions that don't include proton transfer) is tricky. Some of the studies presented here deal directly with this important problem. In one case study we employed a cyclometalated iridium(III) complex. Our other studies with ruthenium(II) complexes and phenols focused on systematic variations of the reaction free energies for the CPET, ET, and proton transfer (PT) steps to explore their influence on the overall PCET reaction. Still other work with rhenium(I) complexes concentrated on the question of how the electronic structure of the metal-to-ligand charge transfer (MLCT) excited states affects PCET. We used covalent rhenium(I)-phenol dyads to explore the influence of the electron donor-electron acceptor distance on bidirectional PCET. In covalent triarylamine-Ru(bpy)?²?/Os(bpy)?²?-anthraquinone triads (bpy = 2,2'-bipyridine), hydrogen-bond donating solvents significantly lengthened the lifetimes of photogenerated electron/hole pairs because of hydrogen-bonding to the quinone radical anion. Until now, comparatively few researchers have investigated this variation of PCET: the strengthening of H-bonds upon photoreduction.

Wenger OS

2013-07-01

170

Proton-coupled electron transfer with photoexcited metal complexes.  

Science.gov (United States)

Proton-coupled electron transfer (PCET) plays a crucial role in many enzymatic reactions and is relevant for a variety of processes including water oxidation, nitrogen fixation, and carbon dioxide reduction. Much of the research on PCET has focused on transfers between molecules in their electronic ground states, but increasingly researchers are investigating PCET between photoexcited reactants. This Account describes recent studies of excited-state PCET with d(6) metal complexes emphasizing work performed in my laboratory. Upon photoexcitation, some complexes release an electron and a proton to benzoquinone reaction partners. Others act as combined electron-proton acceptors in the presence of phenols. As a result, we can investigate photoinduced PCET involving electron and proton transfer in a given direction, a process that resembles hydrogen-atom transfer (HAT). In other studies, the photoexcited metal complexes merely serve as electron donors or electron acceptors because the proton donating and accepting sites are located on other parts of the molecular PCET ensemble. We and others have used this multisite design to explore so-called bidirectional PCET which occurs in many enzymes. A central question in all of these studies is whether concerted proton-electron transfer (CPET) can compete kinetically with sequential electron and proton transfer steps. Short laser pulses can trigger excited-state PCET, making it possible to investigate rapid reactions. Luminescence spectroscopy is a convenient tool for monitoring PCET, but unambiguous identification of reaction products can require a combination of luminescence spectroscopy and transient absorption spectroscopy. Nevertheless, in some cases, distinguishing between PCET photoproducts and reaction products formed by simple photoinduced electron transfer (ET) (reactions that don't include proton transfer) is tricky. Some of the studies presented here deal directly with this important problem. In one case study we employed a cyclometalated iridium(III) complex. Our other studies with ruthenium(II) complexes and phenols focused on systematic variations of the reaction free energies for the CPET, ET, and proton transfer (PT) steps to explore their influence on the overall PCET reaction. Still other work with rhenium(I) complexes concentrated on the question of how the electronic structure of the metal-to-ligand charge transfer (MLCT) excited states affects PCET. We used covalent rhenium(I)-phenol dyads to explore the influence of the electron donor-electron acceptor distance on bidirectional PCET. In covalent triarylamine-Ru(bpy)?²?/Os(bpy)?²?-anthraquinone triads (bpy = 2,2'-bipyridine), hydrogen-bond donating solvents significantly lengthened the lifetimes of photogenerated electron/hole pairs because of hydrogen-bonding to the quinone radical anion. Until now, comparatively few researchers have investigated this variation of PCET: the strengthening of H-bonds upon photoreduction. PMID:23402212

Wenger, Oliver S

2013-02-13

171

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

International Nuclear Information System (INIS)

[en] K-shell excitation of F6+(1s22s) projectile ions in collisions with H2 targets has been studied by measuring 0 degree state-resolved Auger electron production cross sections in the projectile energy range of 0.25 to 2 MeV/u. Projectile 1s?2p excitation due to the interaction with a ''target electron'' (electron-electron Excitation1 [eeE]) has been observed in the production of the 1s(2s2p3P)2P- and 1s(2s2p1P)2P+ states as well as 1s2s2p4P state above the electron impact threshold. Projectile excitation is also produced by the target nucleus (electron-nucleus Excitation [enE]) for the 2P± states. The eeE and enE cross sections were evaluated by Impulse Approximation (IA) and PWBA, respectively. The total KLL Auger electron production cross sections were also determined and exhibited the overall electron-electron interaction effects of eeE and Resonant-Transfer Excitation (RTE) which, in particular, is the 1s?2p excitation with 2p capture to result in 1s2s2p2 3,1D states

1197-01-00

172

Hydrogen transfer in excited pyrrole–ammonia clusters  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The excited state hydrogen atom transfer reaction (ESHT) has been studied in pyrrole–ammonia clusters [PyH–(NH3)n+h??Py'+'NH4(NH3)n-1]. The reaction is clearly evidenced through two-color R2P1 experiments using delayed ionization and presents a threshold around 235 nm (5.3 eV). The cluster dynamics ...

David, O.; Dedonder-Lardeux, C.; Jouvet, C.; Kang, H.; Martrenchard, S.; Ebata, Takayuki; Sobolewski, A.L.; ???, ????

173

Harvesting singlet fission for solar energy conversion: one versus two-electron transfer electron transfer from the quantum superposition state  

Science.gov (United States)

Singlet fission (SF) is being explored to increase the efficiency of organic photovoltaics. A key question is how to effectively extract multiple electron-hole pairs from multiple excitons with the presence of other competing channels such as electron transfer from the singlet state. Recent experiments on the pentacene and tetracene show that a quantum superposition of the singlet (S1) and multiexciton (ME) state is formed during SF. However, little is known about the kinetics of electron transfer from this quantum superposition. Here, we apply time-resolved photoemission spectroscopy to the tetracene/C60 interface to probe one and two electron transfer from S1 and ME states, respectively. Because of the relatively slow ( 7 ps) SF in tetracene, both one- and two-electron transfer are allowed. We show evidence for the formation of two distinct charge transfer states due to electron transfer from photo-excited tetracene to the lowest unoccupied molecular orbital (LUMO) and the LUMO+1 levels in C60. Kinetic analysis shows that 60% of the quantum superposition transfers one electron through the S1 state to C60 while 40% undergoes two-electron transfer through the ME state.

Chan, Wai-Lun; Tritsch, John; Zhu, Xiaoyang

2013-03-01

174

Energy and photoinduced electron transfer in porphyrin-fullerene dyads  

Energy Technology Data Exchange (ETDEWEB)

Time-resolved fluorescence and absorption techniques have been used to investigate energy and photoinduced electron transfer in a covalently linked free-base porphyrin-fullerene dyad and its zinc analogue. In toluene, the porphyrin first excited singlet states decay in about 20 ps by singlet-singlet energy transfer to the fullerene. The fullerene first excited singlet state is not quenched and undergoes intersystem crossing to the triplet, which exists in equilibrium with the porphyrin triplet state. In benzonitrile, photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene competes with energy transfer. The fullerene excited singlet state is also quenched by electron transfer from the porphyrin. Overall, the charge-separated state is produced with a quantum yield approaching unity. This state lives for 290 ps in the free-base dyad and 50 ps in the zinc analog. These long lifetimes suggest that such dyads may be useful as components of more complex light-harvesting systems. 32 refs., 12 figs., 1 tab.

Kuciauskas, D.; Lin, S.; Seely, G.R.; Moore, A.L.; Moore, T.A.; Gust, D. [Arizona State Univ., Tempe, AZ (United States); Drovetskaya, T.; Reed, C.A. [Univ. of Southern California, Los Angeles, CA (United States); Boyd, P.D.W. [Univ. of Auckland (New Zealand)

1996-09-26

175

The effect of atoms excited by electron beam on metal evaporation  

CERN Multimedia

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

Xie Guo Feng; Ying Chun Tong

2002-01-01

176

Excitation energy transfer: Study with non-Markovian dynamics  

Science.gov (United States)

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

Liang, Xian-Ting

2010-11-01

177

Excitation energy transfer: Study with non-Markovian dynamics  

International Nuclear Information System (INIS)

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

2010-01-01

178

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

Energy Technology Data Exchange (ETDEWEB)

The focus of the work described in this report is on single electron transfer reactions of excited states which culminate in the formation of stable or metastable even electron species. For the most part the studies have involved even electron organic substrates which are thus converted photochemically to odd electron species and then at some stage reconvert to even electron products. These reactions generally fall into two rather different categories. In one set of studies we have examined reactions in which the metastable reagents generated by single electron transfer quenching of an excited state undergo novel fragmentation reactions, chiefly involving C-C bond cleavage. These reactions often culminate in novel and potentially useful chemical reactions and frequently have the potential for leading to new chemical products otherwise unaffordable by conventional reaction paths. In a rather different investigation we have also studied reactions in which single electron transfer quenching of an excited state is followed by subsequent reactions which lead reversibly to metastable two electron products which, often stable in themselves, can nonetheless be reacted with each other or with other reagents to regenerate the starting materials with release of energy. 66 refs., 9 figs., 1 tab.

Whitten, D.G.

1991-10-01

179

Photochemical electron transfer in liquid/liquid solvent systems  

Energy Technology Data Exchange (ETDEWEB)

A photoinduced charge transfer at the water/1,2-dichloroethane and water/benzonitrile interfaces was studied, using the photoredox couple ruthenium-trisbipyridine complex, Ru(byp){sub 3}{sup 2+}, dissolved in the organic phase and methyl viologen, MV{sup 2+}, in the aqueous phase. It was concluded that the photocurrent observed can be ascribed to an electron transfer between the excited ruthenium complex and methyl viologen.

Marecek, V.; De Armond, A.H.; De Armond, M.K. (New Mexico State Univ., Las Cruces (USA))

1989-03-29

180

Excitation of Be+ by electron impact  

International Nuclear Information System (INIS)

Calculations of the collision strength for excitation of the 2p state of Be+ are performed at incident energies of 2, 5, and 8 Ry. A modified five-state close-coupling expansion is used in which three pseudostates 3s, 3p, and 3d are retained in addition to target states 2s and 2p. Pseudostates are chosen so that, for a given incident electron energy, there is a minimum in the dominant partial-wave collision strength with respect to variation of the range parameter. Collision strengths are obtained which lie a few percent closer to the measurements of Taylor, Phaneuf, and Dunn than do the five-state calculations of Hayes et al

1978-01-01

 
 
 
 
181

Patterning of insulating surfaces by electronic excitation  

International Nuclear Information System (INIS)

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

2009-05-01

182

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

CERN Multimedia

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...

Pavanello, Michele; Visscher, Lucas; Neugebauer, Johannes

2012-01-01

183

Theoretical study of excited electronic states at surfaces, link with photo-emission and photo-desorption experiments  

International Nuclear Information System (INIS)

[en] Excited electronic states at surfaces play a very important role in a variety of surface processes. These excited states have a finite lifetime due to electron-transfer processes and their efficiency as reaction intermediates depends crucially on their lifetime. A review of several physical situations, where an excited electronic state localized on an atom interacting with a metal surface intervenes in a surface process, is presented with an emphasis on the way the metal electronic structure influences the excited state dynamics. Examples are chosen among the alkali/metal systems, stressing how the same transient electronic state can influence different dynamical processes.

2008-10-01

184

Light induced electron transfer reactions of metal complexes  

International Nuclear Information System (INIS)

[en] 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

1980-07-19

185

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

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 induced decomposition of water into hydrogen and oxygen is reviewed.

Sutin, N.; Creutz, C.

1980-01-01

186

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

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.

Sutin, N; Creutz, C

1980-01-01

187

Regulating energy transfer of excited carriers and the case for excitation-induced hydrogen dissociation on hydrogenated graphene.  

UK PubMed Central (United Kingdom)

Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD that predict H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations.

Bang J; Meng S; Sun YY; West D; Wang Z; Gao F; Zhang SB

2013-01-01

188

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads. Technical progress report  

Energy Technology Data Exchange (ETDEWEB)

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind`s energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

Gust, J.D. Jr.; Moore, T.A.

1988-04-12

189

Collective electronic excitation modes in a superlattice  

International Nuclear Information System (INIS)

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

1985-01-01

190

Collective electronic excitation modes in a superlattice  

Energy Technology Data Exchange (ETDEWEB)

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

Lee, Y.I.

1985-01-01

191

Electronic Excitations and Correlation Effects in Metals  

CERN Multimedia

Theoretical descriptions of the spectrum of electronic excitations in real metals have not yet reached a fully predictive, "first-principles" stage. In this paper we begin by presenting brief highlights of recent progress made in the evaluation of dynamical electronic response in metals. A comparison between calculated and measured spectra - we use the loss spectra of Al and Cs as test cases - leads us to the conclusion that, even in "weakly-correlated" metals, correlation effects beyond mean-field theory play an important role. Furthermore, the effects of the underlying band structure turn out to be significant. Calculations which incorporate the effects of both dynamical correlations and band structure from first principles are not yet available. As a first step towards such goal, we outline a numerical algorithm for the self-consistent solution of the Dyson equation for the one-particle Green's function. The self-energy is evaluated within the shielded-interaction approximation of Baym and Kadanoff. Our me...

Eguiluz, A G; Eguiluz, Adolfo G.; Schoene, Wolf-Dieter

1997-01-01

192

Electron-impact excitation of Fe7+  

Science.gov (United States)

Electron-impact excitation cross sections for Fe7+ are calculated using R-matrix close-coupling theory. The calculation includes 33 LS terms of the seven configurations: 3p63d, 3p53d2, 3p53d4s, 3p64s, 3p64p, 3p64d, and 3p64f. Following an intermediate-coupling frame transformation of the LS K-matrices, cross sections and effective collision strengths are obtained for 2926 transitions among 77 LSJ levels of the original seven configurations. After the solution of the corresponding collisional-radiative equations, the emission line ratio involving a blend of the 3p64f 2F -> 3p63d 2D transitions at around 131 A and another blend of the 3p53d2 2P -> 3p63d 2D and 3p53d2 2D -> 3p63d 2D transitions at around 168 A is found to provide a very useful electron-temperature diagnostic.

Griffin, D. C.; Pindzola, M. S.; Badnell, N. R.

2000-03-01

193

The rate of the electron-ion heat transfer in swift heavy particle tracks in metals  

Energy Technology Data Exchange (ETDEWEB)

A model of the heat transfer from the excited electron gas to the ionic framework in tracks formed by swift heavy particles in metals is discussed. The model allows to predict the rate of the electron-to-ion heat transfer in tracks in the broad range of electron temperatures, both above and below the Fermi energy. (orig.).

Volkov, A.E. [Kurchatov Inst. (RKI), Moscow (Russian Federation); Borodin, V.A. [Kurchatov Inst. (RKI), Moscow (Russian Federation)

1996-02-01

194

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

1991-01-01

195

Charge-Transfer Excitations in the Model Superconductor HgBa2CuO4+?  

Science.gov (United States)

We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa2CuO4+? at optimal doping (Tc=96.5K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly dispersive (<0.5eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a remnant charge-transfer gap deep in the superconducting phase. Quite generally, our results, which include additional data for the Mott insulator La2CuO4, demonstrate the importance of exploring the incident photon-energy dependence of the RIXS cross section.

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

2005-11-01

196

"Inverted" Solvent Effect on Charge Transfer in the Excited State.  

UK PubMed Central (United Kingdom)

Faster in cyclohexane than in acetonitrile is the fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by amines and sulfides. Although this photoreaction is induced by charge transfer (CT; see picture) and exciplexes are formed, the increase in the dipole moment of the exciplex is not large enough to offset the solvent stabilization of the excited reactants, and an "inverted" solvent effect results.

Nau WM; Pischel U

1999-10-01

197

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.

2006-01-01

198

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

2001-01-01

199

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 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

2007-03-01

200

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.

1990-01-01

 
 
 
 
201

Electronic and structural properties of low-lying excited states of vitamin B12.  

UK PubMed Central (United Kingdom)

Time-dependent density functional theory (TD-DFT) has been applied to explore electronically excited states of vitamin B(12) (cyanocobalamin or CNCbl). To explain why the Co-C bond in CNCbl does not undergo photodissociation under conditions of simple photon excitation, electronically excited states have been computed along the Co-C(CN) stretched coordinate. It was found that the repulsive (3)(?(Co-C) ? ?*(Co-C)) triplet state drops in energy as the Co-C(CN) bond lengthens, but it does not become dissociative. Low-lying excited states were also computed as function of two axial bond lengths. Two energy minima have been located on the S(1)/CNCbl, as well as T(1)/CNCbl, surfaces. The full geometry optimization was carried out for each minimum and electronic properties associated with each optimized structure were analyzed in details. One minimum was described as excitation having mixed ??*/MLCT (metal-to-ligand charge transfer) character, while the second as ligand-to-metal charge transfer (LMCT) transition. Neither of them, however, can be viewed as pure MLCT or LMCT transitions since additional excitation to or from ?-bonds (SB) of N-Co-C unit have also noticeable contributions. Inclusion of solvent altered the character of one of the excitations from ??*/MLCT/SBLCT to ??*/LMCT/LSBCT-type, and therefore, both of them gained significant contribution from LMCT/LSBCT transition. Finally, the nature of S(1) electronic state has been comparatively analyzed in CNCbl and MeCbl cobalamins.

Lodowski P; Jaworska M; Kornobis K; Andruniów T; Kozlowski PM

2011-11-01

202

Electronic excitations induced by hydrogen surface chemical reactions on gold.  

UK PubMed Central (United Kingdom)

Associated with chemical reactions at surfaces energy may be dissipated exciting surface electronic degrees of freedom. These excitations are detected using metal-insulator-metal (MIM) heterostructures (Ta-TaOx-Au) and the reactions of H with and on a Au surface are probed. A current corresponding to 5×10(-5) electrons per adsorbing H atom and a marked isotope effect are observed under steady-state conditions. Analysis of the current trace when the H atom flux is intermitted suggests that predominantly the recombination reaction creates electronic excitations. Biasing the front versus the back electrode of the MIM structure provides insights into the spectrum of electronic excitations. The observed spectra differ for the two isotopes H and D and are asymmetric when comparing negative and positive bias voltages. Modeling indicates that the excited electrons and the concurrently created holes differ in their energy distributions.

Schindler B; Diesing D; Hasselbrink E

2011-01-01

203

Electronic energy transfer: vibrational control and nonlinear wavepacket interferometry  

CERN Multimedia

The time-development of photoexcitations in molecular aggregates exhibits specific dynamics of electronic states and vibrational wavefunction. We discuss the dynamical formation of entanglement between electronic and vibrational degrees of freedom in molecular aggregates with theory of electronic energy transfer and the method of vibronic 2D wavepackets [Cina, Kilin, Humble, J. Chem. Phys. 118, 46 (2003)]. The vibronic dynamics is also described by applying Jaynes-Cummings model to the electronic energy transfer [Kilin, Pereverzev, Prezhdo, J. Chem. Phys. 120, 11209 (2004);math-ph/0403023]. Following the ultrafast excitation of donor[chem-ph/9411004] the population of acceptor rises by small portions per each vibrational period, oscillates force and back between donor and acceptor with later damping and partial revivals of this oscillation. The transfer rate gets larger as donor wavepacket approaches the acceptor equilibrium configuration, which is possible at specific energy differences of donor and acceptor...

Kilin, D S; Prezhdo, O V; Kilin, Dmitri S.; Cina, Jeffrey A.; Prezhdo, Oleg V.

2004-01-01

204

Spin-Transfer Torque and Electron-Magnon Scattering  

CERN Multimedia

According to the spin-torque model, current-driven magnetic dynamics in ferromagnetic multilayers is determined by the transfer of electron spin perpendicular to the layers' magnetizations. By separating the largest contributions to the magnetic dynamics, we demonstrate that the dominant effect of spin-torque is rather due to the electron spin parallel to the field. We show that this effect can be equivalently described as stimulated current-driven excitation of spin-waves, and discuss four specifically quantum-mechanical aspects of spin-transfer, not described by the spin-torque.

Urazhdin, S

2004-01-01

205

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

DEFF Research Database (Denmark)

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.

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

2013-01-01

206

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.

1990-01-01

207

Rotationally resolved electron-photon coincidence study of H2(d3IIsub(u)) excitation  

International Nuclear Information System (INIS)

The three normalised Stokes' parameters characterising the decay of the electron impact excited d 3IIsub(u) rotational level of H2 were determined in an electron-photon coincidence experiment at 25 eV impact energy and 600 scattering angle. The low degree of polarisation which was observed could be caused by both the averaging over the magnetic sublevels of the ground state of the target and the fine and hyperfine relaxation process. The average angular momentum transfer perpendicular to the scattering plane from the electrons to the molecules was found to be near zero in this excitation process. (author)

1985-04-14

208

Dual fluorescence of ellipticine: excited state proton transfer from solvent versus solvent mediated intramolecular proton transfer.  

UK PubMed Central (United Kingdom)

Photophysical properties of a natural plant alkaloid, ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), which comprises both proton donating and accepting sites, have been studied in different solvents using steady state and time-resolved fluorescence techniques primarily to understand the origin of dual fluorescence that this molecule exhibits in some specific alcoholic solvents. Ground and excited state calculations based on density functional theory have also been carried out to help interpretation of the experimental data. It is shown that the long-wavelength emission of the molecule is dependent on the hydrogen bond donating ability of the solvent, and in methanol, this emission band arises solely from an excited state reaction. However, in ethylene glycol, both ground and excited state reactions contribute to the long wavelength emission. The time-resolved fluorescence data of the system in methanol and ethylene glycol indicates the presence of two different hydrogen bonded species of ellipticine of which only one participates in the excited state reaction. The rate constant of the excited state reaction in these solvents is estimated to be around 4.2-8.0 × 10(8) s(-1). It appears that the present results are better understood in terms of solvent-mediated excited state intramolecular proton transfer reaction from the pyrrole nitrogen to the pyridine nitrogen leading to the formation of the tautomeric form of the molecule rather than excited state proton transfer from the solvents leading to the formation of the protonated form of ellipticine.

Banerjee S; Pabbathi A; Sekhar MC; Samanta A

2011-08-01

209

Energy-transfer processes from the excited singlet manifold of chlorophyll  

Energy Technology Data Exchange (ETDEWEB)

The observation of fluorescence from S/sub N/ states produced by photon absorption in S/sub 1/ states of chlorophyll species is presented. Electronic energy transfer (EET) from the highly excited states of chlorophyll a or the covalently linked chlorophyllide a pair in pyridine to an acceptor molecule, F555, has been studied. Energy up-conversion that involves energy transfer from the chlorophyll triplet to the ground state of the rubrene molecule followed by a collisional interaction of two rubrene triplets to yield a ground-state and singlet rubrene is reported.

Hunt, J.E.; Katz, J.J.; Svirmickas, A.; Hindman, J.C.

1983-01-01

210

Excitation curve for auger decay of the (1S2S2P2)3D state of C4+ formed through RTE [Resonant Transfer and Excitation  

International Nuclear Information System (INIS)

The ORNL EN tandem supplied beams of 3.5--9 MeV C3+ ions which were incident on a differentially pumped He target. Auger electrons emitted by fast C4+ ions emerged at 10 deg(lab)w.r.t. the incident ion beam. They were detected using a two stage spectrometer with kinematic refocusing. An excitation curve was obtained for the (1s2s2p)3D state Auger decay to the ground state of C3+. The excitation curve peaks at ?6 MeV, which strongly supports the notion that the state is formed through Resonant Transfer and Excitation. 10 refs., 2 figs

1990-01-01

211

Photonic modulation of electron transfer with switchable phase inversion.  

Science.gov (United States)

Photochromes may be reversibly photoisomerized between two metastable states and their properties can influence, and be influenced by, other chromophores in the same molecule through energy or electron transfer. In the photochemically active molecular tetrad described here, a porphyrin has been covalently linked to a fullerene electron acceptor, a quinoline-derived dihydroindolizine photochrome, and a dithienylethene photochrome. The porphyrin first excited singlet state undergoes photoinduced electron transfer to the fullerene to generate a charge-separated state. The quantum yield of charge separation is modulated by the two photochromes: one isomer of each quenches the porphyrin excited state, reducing the quantum yield of electron transfer to near zero. Interestingly, when the molecule is illuminated with white light, the quantum yield decreases as the white light intensity is increased, generating an out-of-phase response of the quantum yield to white light. However, when the same experiment is performed in the presence of additional, steady-state UV illumination, a phase inversion occurs. The quantum yield of electron transfer now increases with increasing white light intensity. Such effects illustrate emergent complexity in a relatively simple system and could find applications in molecular logic, photochemical labeling and drug delivery, and photoprotection for artificial photosynthetic molecules. The photochemistry leading to this behavior is discussed. PMID:23259536

Frey, Julien; Kodis, Gerdenis; Straight, Stephen D; Moore, Thomas A; Moore, Ana L; Gust, Devens

2013-01-09

212

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.)

1993-01-01

213

Photoinitiated electron transfer in multi-chromophoric species: Synthetic tetrads and pentads. Technical progress report, 1987--1990  

Energy Technology Data Exchange (ETDEWEB)

This research project involves the design, synthesis and study of the molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

1990-02-14

214

Processes of dissipation and sensitization of electron excitation energy in erbium laser glasses/sup 1/)  

Energy Technology Data Exchange (ETDEWEB)

An experimental investigation was made of the laws governing nonradiative transfer of electron excitation energy in a system comprising Yb/sup 3 +/, Er/sup 3 +/, and Nd/sup 3 +/ rare-earth ions. Dependences of the parameters of elementary donor--acceptor interactions on the glass composition, and on the types of vitrifier and modifier were obtained.

Gapontsev, V.P.; Gromov, A.K.; Kravchenko, V.B.; Kozyukov, V.M.; Matytsin, S.M.; Sverchkov, Y.E.; Sedmalis, U.Y.

1981-08-01

215

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

International Nuclear Information System (INIS)

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

1994-01-01

216

Coupled electron transfers in artificial photosynthesis.  

Science.gov (United States)

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 coupled electron-transfer reactions, which have so far received only little attention. (i) Each absorbed photon leads to charge separation on a single-electron level only, while catalytic water splitting and hydrogen production are multi-electron processes; thus there is the need for controlling accumulative electron transfer on molecular components. (ii) Water splitting and proton reduction at the potential catalysts necessarily require the management of proton release and/or uptake. Far from being just a stoichiometric requirement, this controls the electron transfer processes by proton-coupled electron transfer (PCET). (iii) Redox-active links between the photosensitizers and the catalysts are required to rectify the accumulative electron-transfer reactions, and will often be the starting points of PCET. PMID:17954432

Hammarström, Leif; Styring, Stenbjörn

2008-03-27

217

Angular momentum transfer and polarization degree of ions with one-valence electron by electron impact  

International Nuclear Information System (INIS)

We carry out the R-matrix calculations for electron-impact excitations of ions with one valence electron. The integral cross sections and polarization degree are obtained for the excitation process from the ground state to the first 2P0 state of Li2+, B2+ and Al2+ as functions of electron incident energy. The differential cross sections and angular momentum transfer are also shown at non-resonant low-energy points. As for the angular momentum transfer (Lperpendicular) at small scattering angles, they are negative for B2+ and Al2+, while it is positive for Li2+. Thus Lperpendicular of doubly charged ions with one-valence electron is not simple.

2009-04-01

218

Vibration-assisted resonance in photosynthetic excitation energy transfer  

CERN Multimedia

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

Irish, E K; Lovett, B W

2013-01-01

219

Electron transfer reactions in condensed phases  

Energy Technology Data Exchange (ETDEWEB)

Despite the multitude of formalisms, there is general agreement that the crux of the electron transfer problem is the change in equilibrium nuclear configurations that occurs when a molecule or ion gains or loses an electron. In recent developments attention has been focused on the dynamics of these nuclear configuration changes, and, in addition, on the electronic factors, determining the electron transfer rate. In parallel with these theoretical developments there have been a large number of experimental studies. These studies have not only elucidated the factors determining electron transfer rates, but have in many cases directly tested the theories and suggested modifications to the theories where appropriate. It is impossible in an article such as this to cover the entire area of electron transfer reactions. Instead the authors shall concentrate on those aspects of the problem in which they are particularly interested. Steady-state schemes for the diffusion, activation, and electron transfer steps in bimolecular reactions are discussed first. This is followed by a description in terms of Born-Oppenheimer states and surfaces and a discussion of the classical, semiclassical, and quantum mechanical formalisms. Recent experimental studies bearing on the questions raised are presented in the final section. Throughout the discussion to localized or trapped systems is restricted, specifically to systems in which the electronic interaction of the initial and final states is sufficiently small so that the electron transfer can be described in terms of the electronic properties of the unperturbed reactants and products.

Newton, M.D.; Sutin, N.

1984-01-01

220

Energy transfer from excited N2 and 02 as a source of 0(1S) in the aurora  

International Nuclear Information System (INIS)

[en] It is proposed that energy transfer from excited 02 contributes to the production of 0(1S) in aurora. An analysis is presented of the 01 5577 A emission in an IBC II+ aurora between 90 and 130 km. The volume emission rate of the emission at these altitudes is consistent with the production rate of 0(1S) by energy transfer to 0(3P) from N2 in the A3?sub(u)+ state and 02 in the A3?sub(u)+, C3?sub(u) and c1?sub(u)- states, the N2A state being populated by direct electron impact excitation and B ? A cascade and the excited 02 states by direct excitation above the peak emission altitude (approximately 105 km), energy transfer from N2A is the predominant production mechanism for 0(1S). Below it, contribution from quenching of the 02 states becomes significant. (author)

1979-01-01

 
 
 
 
221

Electron excitation of electric giant multiple resonance in 65Cu  

International Nuclear Information System (INIS)

Electric transitions of various multipolarities in 65Cu have been investigated by means of electron inelastic scattering in the excitation-energy region from 1 to 37 MeV. Reduced transition probabilities obtained from the experimental data give concentrations in excitation energy in the form of individual branches of giant multipole resonances

1987-01-01

222

Search for excited electrons in ep collisions at HERA  

Energy Technology Data Exchange (ETDEWEB)

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

Aaron, F.D. [National Inst. for Physics and Nuclear Engineering (NIPNE), Bucharest (Romania)]|[Bucharest Univ. (Romania). Faculty of Physics; Alexa, C. [National Inst. for Physics and Nuclear Engineering (NIPNE), Bucharest (Romania); Andreev, V. [Lebedev Physical Inst., Moscow (RU)] (and others)

2008-05-15

223

Search for excited electrons in ep collisions at HERA  

International Nuclear Information System (INIS)

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

2008-05-29

224

The role of interfacial charge transfer-type interactions in the decay of plasmon excitations in metal nanoparticles.  

UK PubMed Central (United Kingdom)

This perspective describes the influence of interfacial charge transfer-type interactions on the optical spectra and hot electron cooling processes in plasmonic nanoparticles (NPs), and ongoing work to optimize these interactions for charge extraction from the plasmon or hot electron state. The manuscript focuses on interfaces of metal NPs with organic molecules and with semiconductors. Charge extraction from multi-electron excited states has applications in photodetection, sensing, and conversion of solar energy to electricity and fuels.

Aruda KO; Tagliazucchi M; Sweeney CM; Hannah DC; Weiss EA

2013-05-01

225

Energy spectra of electronic excitations in collision cascades  

Energy Technology Data Exchange (ETDEWEB)

The energy distribution of excited electrons and the electronic energy density produced by collision cascades in metals is discussed. The value of the excitation energy density at the surface of aluminium are numerically estimated. It is shown that the energy density at the Fermi surface can reach fairly high values above 10{sup 20} eV/cm{sup 3} which correspond to temperatures above 10{sup 3} K when thermalized. (author).

Falcone, G.; Sroubek, Z. (Calabria Univ., Cosenza (Italy). Dip. di Fisica)

1989-01-01

226

Theoretical investigation of excited state proton transfer process in the N-salicylidene-2-bromoethylamine.  

UK PubMed Central (United Kingdom)

Excited state reaction coordinate and the consequent energy profiles of a new Schiff base, N-salicylidene-2-bromoethylamine, have been investigated at the CC2 level of theory. The electron-driven proton transfer and torsional deformation have been identified as the most important photochemical reaction coordinates. In contrast to the ground state, the excited state potential energy profile shows a barrierless dissociation pattern along the O-H stretching coordinate, which verifies the proton transfer reaction along the O-H coordinate at the S(1) state. The calculations showed that the PT is electron driven and that the S(1) transition has charge transfer character. The keto-type S(1) state attained by barrierless proton transfer is found to be unstable via a torsional motion, which provides fast access to a S(1)-S(0) conical intersection. From the conical intersection, a barrierless reaction path directs the system back to the enol-type minimum of the S(0) potential energy surface, thus closing the photocycle.

Moghadam AJ; Omidyan R; Mirkhani V; Azimi G

2013-01-01

227

Theoretical investigation of excited state proton transfer process in the N-salicylidene-2-bromoethylamine.  

Science.gov (United States)

Excited state reaction coordinate and the consequent energy profiles of a new Schiff base, N-salicylidene-2-bromoethylamine, have been investigated at the CC2 level of theory. The electron-driven proton transfer and torsional deformation have been identified as the most important photochemical reaction coordinates. In contrast to the ground state, the excited state potential energy profile shows a barrierless dissociation pattern along the O-H stretching coordinate, which verifies the proton transfer reaction along the O-H coordinate at the S(1) state. The calculations showed that the PT is electron driven and that the S(1) transition has charge transfer character. The keto-type S(1) state attained by barrierless proton transfer is found to be unstable via a torsional motion, which provides fast access to a S(1)-S(0) conical intersection. From the conical intersection, a barrierless reaction path directs the system back to the enol-type minimum of the S(0) potential energy surface, thus closing the photocycle. PMID:23312032

Moghadam, Ahmad J; Omidyan, Reza; Mirkhani, Valiollah; Azimi, Gholamhasan

2013-01-22

228

Excitation of Be exp + by Electron Impact.  

Science.gov (United States)

Calculations of the collision strength for excitation of the 2p state of Be exp + are performed at incident energies of 2, 5, and 8 Ry. A modified five state close coupling expansion is used in which three pseudo-states anti 3s, anti 3p, and anti 3d are r...

R. J. W. Henry W. L. van Wyngaarden J. J. Matese

1977-01-01

229

Saturn spectrum in the EUV-electron excited hydrogen  

Energy Technology Data Exchange (ETDEWEB)

Recent laboratory observations of electron excited H/sub 2/ 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.

Shemansky, D.E.; Ajello, J.M.

1983-01-01

230

Electron beam excited mixtures of O/sub 2/ in argon. II. Electron distributions and excitation rates  

Energy Technology Data Exchange (ETDEWEB)

We calculate the effect on the electron energy distribution of small partial fractions of oxygen in electron beam excited argon discharges. We find the calculated dissociation rates of O/sub 2/ by electrons do not explain experimentally observed dissociation rates if we include only the 8.4 eV energy loss peak as dissociation.

Keto, J.W.

1981-04-15

231

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)

1994-08-28

232

Water Reduction with Visible Light: Synergy between Optical Transitions and Electron Transfer in Au-TiO2 Catalysts Visualized by In situ EPR Spectroscopy.  

UK PubMed Central (United Kingdom)

Golden electrons: Visible light excites conduction electron transfer from gold particles to support vacancies where they are taken up by protons to produce hydrogen. This transfer process was visualized by in situ EPR spectroscopy.

Priebe JB; Karnahl M; Junge H; Beller M; Hollmann D; Brückner A

2013-09-01

233

Double-electron excitation above Xe K-edge  

International Nuclear Information System (INIS)

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

2000-01-01

234

Electron transfer rates for asymmetric reactions  

CERN Document Server

We use a numerically exact real-time path integral Monte Carlo scheme to compute electron transfer dynamics between two redox sites within a spin-boson approach. The case of asymmetric reactions is studied in detail in the least understood crossover region between nonadiabatic and adiabatic electron transfer. At intermediate-to-high temperature, we find good agreement with standard Marcus theory, provided dynamical recrossing effects are captured. The agreement with our data is practically perfect when temperature renormalization is allowed. At low temperature we find peculiar electron transfer kinetics in strongly asymmetric systems, characterized by rapid transient dynamics and backflow to the donor.

Mühlbacher, L

2004-01-01

235

Electronic excited state of protonated aromatic molecules: protonated Fluorene  

CERN Multimedia

The photo-fragmentation spectrum of protonated fluorene has been recorded in the visible spectral region, largely red shifted as compared to the first excited state absorption of neutral fluorene. The spectrum shows two different vibrational progressions, separated by 0.19 eV that are assigned to the absorption of two isomers. As in protonated linear PAHs, comparison with ab-initio calculations indicates that the red shift is due to the charge transfer character of the excited state.

Alata, Ivan; Dedonder, Claude; Jouvet, Christophe; Marceca, Ernesto

2011-01-01

236

Reaction dynamics of electronically excited alkali atoms with simpler molecules  

International Nuclear Information System (INIS)

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

1985-01-01

237

Computing electronic structures: A new multiconfiguration approach for excited states  

International Nuclear Information System (INIS)

We present a new method for the computation of electronic excited states of molecular systems. This method is based upon a recent theoretical definition of multiconfiguration excited states [due to one of us, see M. Lewin, Solutions of the multiconfiguration equations in quantum chemistry, Arch. Rat. Mech. Anal. 171 (2004) 83-114]. Our algorithm, dedicated to the computation of the first excited state, always converges to a stationary state of the multiconfiguration model, which can be interpreted as an approximate excited state of the molecule. The definition of this approximate excited state is variational. An interesting feature is that it satisfies a non-linear Hylleraas-Undheim-MacDonald type principle: the energy of the approximate excited state is an upper bound to the true excited state energy of the N-body Hamiltonian. To compute the first excited state, one has to deform paths on a manifold, like this is usually done in the search for transition states between reactants and products on potential energy surfaces. We propose here a general method for the deformation of paths which could also be useful in other settings. We also compare our method to other approaches used in Quantum Chemistry and give some explanation of the unsatisfactory behaviours which are sometimes observed when using the latter. Numerical results for the special case of two-electron systems are provided: we compute the first singlet excited state potential energy surface of the H 2 molecule.

2006-02-10

238

Transfer and excitation processes studied in H-like S and Li-like and H-like F colliding with H/sub 2/  

Energy Technology Data Exchange (ETDEWEB)

We have studied transfer and simultaneous excitation by three different experimental techniques. Coincidences between two K x rays were measured for S/sup 15 +/, coincidences between one K x ray and the charge exchanged projectile for Li-like F and projectile Auger electrons for H-like F in each case colliding with H/sub 2/. For all three collision systems, the measured cross sections are dominated by Resonant Transfer and Excitation (RTE). Also, for the F projectiles, strong contributions from Two Electron Transfer and Excitation (2eTE) were found. 9 refs., 3 figs.

Schulz, M.; Datz, S.; Dittner, P.F.; Giese, J.P.; Krause, H.F.; Miller, P.D.; Schoene, H.; Swenson, J.K.; Vane, C.R.; Schuch, R.; Justiniano, E.; Benhenni, M.; Shafroth, S.M.; Mokler, P.H.; Reusch, S.

1988-01-01

239

Dual fluorescence of ellipticine: excited state proton transfer from solvent versus solvent mediated intramolecular proton transfer.  

Science.gov (United States)

Photophysical properties of a natural plant alkaloid, ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), which comprises both proton donating and accepting sites, have been studied in different solvents using steady state and time-resolved fluorescence techniques primarily to understand the origin of dual fluorescence that this molecule exhibits in some specific alcoholic solvents. Ground and excited state calculations based on density functional theory have also been carried out to help interpretation of the experimental data. It is shown that the long-wavelength emission of the molecule is dependent on the hydrogen bond donating ability of the solvent, and in methanol, this emission band arises solely from an excited state reaction. However, in ethylene glycol, both ground and excited state reactions contribute to the long wavelength emission. The time-resolved fluorescence data of the system in methanol and ethylene glycol indicates the presence of two different hydrogen bonded species of ellipticine of which only one participates in the excited state reaction. The rate constant of the excited state reaction in these solvents is estimated to be around 4.2-8.0 × 10(8) s(-1). It appears that the present results are better understood in terms of solvent-mediated excited state intramolecular proton transfer reaction from the pyrrole nitrogen to the pyridine nitrogen leading to the formation of the tautomeric form of the molecule rather than excited state proton transfer from the solvents leading to the formation of the protonated form of ellipticine. PMID:21812494

Banerjee, Sanghamitra; Pabbathi, Ashok; Sekhar, M Chandra; Samanta, Anunay

2011-08-04

240

Plasmon excitations in photo- and electron impact ionization of fullerenes  

Science.gov (United States)

We study collective electron excitations (also referred to as plasmons) in the C60 fullerene in the processes of photoionization and electron inelastic scattering. To reveal the contribution of collective electron excitations, we utilize the plasmon resonance approximation. It is shown that within this framework the photoionization cross section is described as a sum of two contributions, which represent two coupled modes of the surface plasmon. The electron energy loss spectra of C60 are described by three contributions, namely by the two modes of the surface plasmon and the volume plasmon. The results of calculations are in good agreement with experimental data on photoionization and electron inelastic scattering of C60. We show that the collective excitations play a significant role in the ionization process and provide a dominant contribution to the spectra.

Verkhovtsev, A. V.; Korol, A. V.; Solov'yov, A. V.

2013-06-01

 
 
 
 
241

Electron-pair excitations and the molecular Coulomb continuum  

International Nuclear Information System (INIS)

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about by the pair's relative momentum. A helium-like description of the molecular pi.Joto double ionization is thus extended to higher angular momenta of the electron pair. A simple three-state superposition is found to account surprisingly well for recent observations of noncoplanar electron-pair, molecular-axis angular distributions.

2009-01-01

242

Vibrational excitation coefficients for electrons in HBr  

International Nuclear Information System (INIS)

Rate coefficients were calculated for the first time for vibrational excitation in pure HBr in both DC and RF, E and in ExB fields. We have studied the effect of the amplitude and frequency of applied fields. The calculation was based on a Monte Carlo technique. It was found that a complex behavior may develop due to sharp and very large vibrational cross sections and modulation of the energy distribution function by time-dependent fields and by magnetic field.

2005-09-02

243

Vibrational excitation coefficients for electrons in HBr  

Energy Technology Data Exchange (ETDEWEB)

Rate coefficients were calculated for the first time for vibrational excitation in pure HBr in both DC and RF, E and in ExB fields. We have studied the effect of the amplitude and frequency of applied fields. The calculation was based on a Monte Carlo technique. It was found that a complex behavior may develop due to sharp and very large vibrational cross sections and modulation of the energy distribution function by time-dependent fields and by magnetic field.

Sasic, Olivera [Institute of Physics, POB 68, 11080 Belgrade (Serbia and Montenegro); Petrovic, Zoran Lj. [Institute of Physics, POB 68, 11080 Belgrade (Serbia and Montenegro)]. E-mail: zoran@phy.bg.ac.yu

2007-03-15

244

Isomer triggering via nuclear excitation by electron capture  

CERN Multimedia

Triggering of nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in bare or highly-charged ions can excite the nucleus from the isomeric state to a triggering level that subsequently decays directly or in cascades to the ground state. We present total cross sections for NEEC followed by the decay of the isomeric state considering experimentally confirmed low-lying triggering levels. Reaction rates of NEEC isomer triggering are calculated assuming realistic experimental parameters for ion beams and electron targets in storage rings. A comparison with other isomer triggering mechanisms such as bremsstrahlung photons and nuclear excitation by electron transition shows that, among these, NEEC is the most efficient nuclear excitation mechanisms of the isomeric state.

Pálffy, Adriana; Keitel, Christoph H

2007-01-01

245

Angular momentum transfer and polarization degree of ions with two-valence electrons by electron impact  

Energy Technology Data Exchange (ETDEWEB)

We study for electron-impact excitation of ions with two valence electrons (Be{sup 2+}, C{sup 2+} and Si{sup 2+}) from the ground state to the first {sup 1}P{sup 0} state using the R-matrix method. The integral cross sections and polarization degree for this transition of each ion are obtained. The differential cross sections and angular momentum transfer are also shown at a few energies in the non-resonant region. The present angular momentum transfer for Be{sup 2+} and C{sup 2+} at small scattering angles has positive values, while it is negative for Si{sup 2+}.

Akita, Kenichi; Nakazaki, Shinobu; Igarashi, Akinori [Department of Applied Physics, Faculty of Engineering, University of Miyazaki, Miyazaki 889-2192 (Japan); Kai, Takeshi, E-mail: akita@phys.miyazaki-u.ac.j [Quantum Beam Science Directorate, Japan Atomic Energy Agency 8-1 Umemidai Kizugawa-city Kyoto 619-0215 (Japan)

2009-04-01

246

Angular momentum transfer and polarization degree of ions with two-valence electrons by electron impact  

International Nuclear Information System (INIS)

We study for electron-impact excitation of ions with two valence electrons (Be2+, C2+ and Si2+) from the ground state to the first 1P0 state using the R-matrix method. The integral cross sections and polarization degree for this transition of each ion are obtained. The differential cross sections and angular momentum transfer are also shown at a few energies in the non-resonant region. The present angular momentum transfer for Be2+ and C2+ at small scattering angles has positive values, while it is negative for Si2+.

2009-04-01

247

The electronically excited states of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine): Vertical excitations  

Science.gov (United States)

The RDX molecule, hexahydro-1,3,5-trinitro-1,3,5-triazine, is a key component for several energetic materials, which have important practical applications as explosives. A systematic study of the electronic excited states of RDX in gas phase using time-dependent density functional theory (TDDFT), algebraic diagrammatic construction through second order method [ADC (2)], and resolution of the identity coupled-cluster singles and doubles method (RI-CC2) was carried out. Transition energies and optical oscillator strengths were computed for a maximum of 40 transitions. RI-CC2 and ADC (2) predict a spectrum shaped by three intense ?-?* transitions, two with charge transfer and one with localized character. TDDFT fails in the description of the charge transfer states. The low-energy band of the experimental UV spectrum of RDX is assigned to the first charge transfer state. Two alternative assignments of the high-energy band are proposed.

Borges, Itamar; Aquino, Adélia J. A.; Barbatti, Mario; Lischka, Hans

248

Electronic energy transfer: vibrational control and nonlinear wavepacket interferometry  

Science.gov (United States)

The time-development of photoexcitations in molecular aggregates exhibits specific dynamics of electronic states and vibrational wavefunction. We discuss the dynamical formation of entanglement between electronic and vibrational degrees of freedom in molecular aggregates with theory of electronic energy transfer and the method of vibronic 2D wavepackets [ J. Chem. Phys. 118, 46 (2003); quant-ph/0412219]. The vibronic dynamics is also described by applying Jaynes-Cummings model to the electronic energy transfer [J. Chem. Phys. 120, 11209 (2004); math-ph/0403023]. Following the ultrafast excitation of donor [ J. Phys. Chem 99, 2568 (1995); chem-ph/9411004] the population of acceptor rises by small portions per each vibrational period, oscillates force and back between donor and acceptor with later damping and partial revivals of this oscillation. The transfer rate gets larger as donor wavepacket approaches the acceptor equilibrium configuration, which is possible at specific energy differences of donor and acceptor and at maximal amount of the vibrational motion along the line that links donor and acceptor equilibria positions. The four-pulse phase-locked nonlinear wavepacket 2D interferograms reflect the shape of the relevant 2D vibronic wavepackets and have maxima at longer delay between excitation pulses for dimers with equal donor-acceptor energy difference compare to dimers with activationless energy configuration [Cina, Fleming, J. Phys. Chem. A. 108, 11196 (2004)].

Prezhdo, Oleg V.; Cina, Jeffrey A.; Kilin, Dmitri S.

2005-04-01

249

Vectorial electron transfer in spatially ordered arrays  

Energy Technology Data Exchange (ETDEWEB)

Progress was made on synthesis of new materials for directional electron transfer (block copolymers and helical oligopeptides), preparation and characterization of anisotropic composites bearing organics and inorganics, electrocatalysis (redox-activated catalysts), and surface modifications of metals and semiconductors.

Fox, M.A.

1993-02-01

250

Hierarchical control of electron-transfer  

DEFF Research Database (Denmark)

In this chapter the role of electron transfer in determining the behaviour of the ATP synthesising enzyme in E. coli is analysed. It is concluded that the latter enzyme lacks control because of special properties of the electron transfer components. These properties range from absence of a strong back pressure by the protonmotive force on the rate of electron transfer to hierarchical regulation of the expression of the gens that encode the electron transfer proteins as a response to changes in the bioenergetic properties of the cell.The discussion uses Hierarchical Control Analysis as a paradigm. This allows one to analyse a complex system of regulatory interactions in terms of the importance of the contributing factors.

Westerhoff, Hans V.; Jensen, Peter Ruhdal

1997-01-01

251

Photoinduced electron transfer reactions through dendrimer architecture  

Energy Technology Data Exchange (ETDEWEB)

Herein we report the first photoreactive dendritic metalloporphyrin having noncovalently assembled electron-acceptor molecules on the exterior surface and describe a long-range photoinduced electron transfer through dendrimer architecture. Here, water-soluble dendritic zinc porphyrins with two different numbers of generations ([KO{sub 2}C]{sub 2(n+1)}LnPZn, n = 2, 4) were newly synthesized. In conclusion the long-range photoinduced electron transfer through an aryl ether dendrimer framework was demonstrated for a water-soluble dendritic zinc porphyrin bearing noncovalently assembled electron-acceptor molecules on the exterior surface. 14 refs., 2 figs., 1 tab.

Sadamoto, Reiko; Tomioka, Nobuyuki; Aida, Takuzo [Univ. of Tokyo (Japan)

1996-04-24

252

Ion induced electronic excitations in a spin-polarized electron gas  

CERN Multimedia

We calculate both the stopping power of a H atom and the number of electrons it excites, when it moves slowly in a spin-polarized electron gas. The potential induced by the projectile in which the medium electrons scatter off is obtained self-consistently within density functional theory, in the local spin density approximation. We show that both the stopping power and the number of excited electrons decrease slightly when increasing the polarization of the electron gas. Furthermore, the spin-polarization of the excited electrons increases with the projectile velocity and remains in all the cases lower than the polarization of the medium.

Alducin, M; Juaristi, J I

2003-01-01

253

Ultrafast electron diffraction studies of optically excited thin bismuth films  

Energy Technology Data Exchange (ETDEWEB)

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.)

Rajkovic, Ivan

2008-10-21

254

Pressure-induced effect on electronic excitations in osmium  

International Nuclear Information System (INIS)

Electronic Raman scattering has been studied in single crystals of 5d transition metal osmium under pressures up to 60 GPa in the temperature range of 10-300K. With the use of green and blue excitation wavelengths we observe an appearance of well-defined electronic peaks at ? 580 cm-1 for wave vector direction q parallel [0001

2008-01-01

255

Electronic excitations, spectroscopy and quantum transport from ab initio theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Spectroscopy and quantum transport constitute powerful ways to study the physics of matter and to access the electronic and atomic structure. Excitations, in turn determined by the electronic and atomic structure, lie at the origin of spectroscopy and quantum transport. Ab initio calculation of exci...

Olevano, Valerio

256

Dynamics of charge-transfer excited states relevant to photochemical energy conversion  

Energy Technology Data Exchange (ETDEWEB)

The primary objective of the research program is to gain a fundamental understanding of the factors governing the efficiency of excited-state charge transfer CT interactions between two chromophores that are brought together in close proximity, either by a very short covalent linkage or by ground-state complex formation. CT and van der Walls (vdW), interactions in covalently bonded bichromophoric compounds in condensed phase, as well as those in vdW complexes in supersonic jets, are being investigated using laser-based techniques under a variety of experimental conditions. This progress report is divided into three parts, according to the class of molecular systems and the phase (liquid vs. gas) in which the excited-state interactions are probed. The first is concerned with the excited states of bridged diaryl compounds in the condensed phase. The second involves the excited states of vdW complexes in supersonic jets. Finally, the third, is concerned with the excited states of electron donor-acceptor (EDA) systems in both the condensed phase and supersonic jets. In each of these studies, we are concerned with the interchromophore interactions ranging from weak vdW forces to strong CT forces, and the factors determining whether the interaction forces are weak or strong in related molecules.

Lim, E.C.

1991-11-01

257

Energy transfer from the host excitations to Ce3+ ions in scandium borate  

International Nuclear Information System (INIS)

Efficient energy transfer from the host excitations (self-trapped excitons, STE) excited at ??160 nm to Ce3+ impurity ions was observed in scandium borate (ScBO3). The luminescence and excitation spectra as well as time-resolved emission data were obtained. Energy transfer rates from the STE to Ce3+ of about 108 s-1 are observed and these are within an order of magnitude of estimates based on dipole-dipole energy transfer.

2007-01-01

258

Long-range electron transfer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent investigations have shed much light on the nuclear and electronic factors that control the rates of long-range electron tunneling through molecules in aqueous and organic glasses as well as through bonds in donor–bridge–acceptor complexes. Couplings through covalent and hydrogen bonds are muc...

Gray, Harry B.; Winkler, Jay R.

259

Peculiarities of electron decay excitation in ionic-molecular crystals  

International Nuclear Information System (INIS)

Peculiarities of chemical and energetic structure of ionic-molecular crystals (IMC) are causing by number of electron excitation decay features in compare with alkali halogen crystals. These features are as follows: both the electrons and the holes simultaneously can been captured and localized on anion and cation complexes; intramolecular forces arising in the result of charge capture can conduct to decay of anion and cation complexes; products of anion and cation complexes decay could participating in following reactions for new products formation. All these processes and products of electron excitation decay exert strong influence on optical, magnetic and electrical performances of IMC. Knowledge of ways and mechanisms of electron excitation in IMC can allow to radiation stability control of crystals with help of impurities, participating in different channels of solid state reactions

1999-01-01

260

Heat Transfer Augmentation for Electronic Cooling  

Directory of Open Access Journals (Sweden)

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.

Suabsakul Gururatana

2012-01-01

 
 
 
 
261

Electron-impact excitation of ions  

Energy Technology Data Exchange (ETDEWEB)

A review of electron-ion beam experiments is given. Techniques, difficulties, and present trends in this area are discussed. Measured cross sections are compared with theoretical results and the current level of agreement is assessed. 74 references. (WHK)

Crandall, D.H.

1981-01-01

262

Electron-impact excitation of ions  

International Nuclear Information System (INIS)

A review of electron-ion beam experiments is given. Techniques, difficulties, and present trends in this area are discussed. Measured cross sections are compared with theoretical results and the current level of agreement is assessed. 74 references

1981-09-26

263

Dynamics of the excited state intramolecular charge transfer  

International Nuclear Information System (INIS)

[en] 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

2006-01-01

264

Effect of long-distance electron transfer on chemiluminescence efficiencies  

Energy Technology Data Exchange (ETDEWEB)

The electrogenerated chemiluminescence (ecl) of Mo/sub 6/Cl/sub 14//sup 2 -/ with three series of structurally and electronically related electroactive organic compounds in acetonitrile has been investigated. The yields for the formation of the electronically excited Mo/sub 6/Cl/sub 14//sup -/ ion produced by the electron-transfer reaction of Mo/sub 6/Cl/sub 14//sup 3 -/ with aromatic amine radical cations (A+) and by the reaction of Mo/sub 6/Cl/sub 14//sup -/ with nitroaromatic radical anions (D/sup -/) and pyridinium radicals (D) have been measured over a wide potential range by simply varying the reduction potential of the electroactive organic reagent. The dependence of the formation yield of Mo/sub 6/Cl/sub 14//sup 2 -/*, phi/sub es/, on the driving force of the annihilation reaction is similar for the three series, phi/sub es/ is immeasurable (< 10/sup -6/) for reactions with free energies positive of a threshold value. Over a narrow free energy range just negative of threshold, phi/sub es/ rapidly increases. And with increasing exergonicity of the electron-transfer reaction, phi/sub es/ asymptotically approaches a limiting value less than unity (phi/sub es//sup lim/(Mo/sub 6/Cl/sub 14//sup -//D/sup -/) = 0.013 +/- 0.001; phi/sub es//sup lim/(Mo/sub 6/Cl/sub 14//sup -//D) = 0.079 +/- 0.008; phi/sub es//sup lim/(Mo/sub 6/Cl/sub 14//sup 3 -//A/sup +/) = 0.132 +/- 0.006). Analysis of these excited-state production yields by Marcus theory suggests that unit efficiencies for excited-state production are circumvented by long-distance electron transfer.

Mussell, R.D.; Nocera, D.G.

1988-04-27

265

Excited state intramolecular charge transfer suppressed proton transfer process in 4-(diethylamino)-2-hydroxybenzaldehyde.  

UK PubMed Central (United Kingdom)

In this work, we report intramolecular charge transfer (ICT) suppressed excited state intramolecular proton transfer (ESIPT) process in 4-(diethylamino)-2-hydroxybenzaldehyde (DEAHB). Photophysical properties of DEAHB have been extensively studied in different solvents with varying pH, polarity, and hydrogen bonding capability of the solvent using steady state and time-resolved spectroscopy. To establish the competition between the ICT and ESIPT processes in DEAHB, we have synthesized and studied the photophysical properties of 4-(diethylamino)-2-methoxybenzaldehyde (DEAMB) molecule where only the charge transfer process has been observed. Recently, we have reported simple Schiff base molecules (J. Phys. Chem. A 2012, 116, 10948) formed by condensation of DEAHB and hydrazine (5-(diethylamino)-2-[(4-(diethylamino)benzylidene)hydrazonomethyl]phenol (DDBHP) and N,N'-bis(4-N,N-(diethylamino)salisalidene)hydrazine (DEASH)), where charge transfer is assisted by the proton transfer process. In the present case, the DEAHB molecule shows the reverse phenomenon; i.e., charge transfer is suppressed by the proton transfer process. Comparing the photophysical properties of DEAHB with DEAMB it is also found that ICT process in DEAHB is suppressed by the ESIPT process.

Jana S; Dalapati S; Guchhait N

2013-05-01

266

Resonant excitation of molecules by low-energy electrons  

Directory of Open Access Journals (Sweden)

Full Text Available Low-energy electron impact vibrational and electronic excitation cross sections of the CO, N2 and CO2 molecules are measured by use of a high resolution crossed-beams double trochoidal electron spectrometer. The spectrometer is designed to work in standard and time-of-flight regimes. The energy dependences of the resonant vibrational excitation of the first several vibrational levels of the N2, CO, and CO2 molecules, have been measured. Characteristic substructures in energy excitation spectra in the cases of N2 and CO have been obtained and discussed for some vibrational channels for the first time. The ratio of forward-to-backward scattered electrons from the 2? resonance in CO is found to be equal to 1, and thus the angular distribution of scattered electrons to be symmetric relative to 90°. This conclusion supports the fact that the contribution of the p? partial wave is dominant in the energy region of the 2? resonance in CO. The energy dependences of the near threshold resonant excitation of the valence and Rydberg states of the N2 and CO molecules have been measured. The cross sections of the near threshold resonant excitation of the C 3?u valence state, and the E 3?+ g and a'' 1?+ g Rydberg states of the N2 molecule have been measured. In the case of the CO molecule, the cross sections of the near threshold resonant excitation of the a 3? valence state, and the b 3?+ and B 1?+ Rydberg states have been measured. Resonant structures in excitation functions of all measured electronic states are observed and their locations are compared with resonances obtained in different decay channels.

Popari? Goran B.

2008-01-01

267

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

UK PubMed Central (United Kingdom)

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.

Wang J; Brune DC; Blankenship RE

1990-02-01

268

Mean excitation energy and electronic stopping power of solids  

International Nuclear Information System (INIS)

The mean excitation energy, I, of some solid materials has been studied. An examination for the local-plasma approximation and a discussion about theoretical connections for I between solid and gaseous materials have been made. This examination led to the development of a combined model which utilized the local-plasma approximation for inner-shell electrons and the dielectric response function for valence electrons. In the local-plasma approximation, we have used electron density distribution obtained from the Hartree-Fock model with the Wigner-Seitz boundary condition for solid atoms. A Drude-type dielectric function for multi-group valence electrons was applied to the valence band. From first principles, we have calculated the mean excitation energy as varying with the energy of incident electrons. Applying these data to the Bethe stopping power formula, we were able to extend successfully this formula to lower electron energies. (author).

1985-01-01

269

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

Energy Technology Data Exchange (ETDEWEB)

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

Grimes, R.M.

1986-11-01

270

Electron emission from metal surfaces excited by intense femtosecond pulses  

International Nuclear Information System (INIS)

[en] Electron emission from a metal surface excited by an intense femtosecond laser pulse can be dominated by thermionic emission due to highly non-equilibrium electron heating process because of the small electronic heat capacity and brief uncoupling between the electron and lattice. Experimental observations of such transient thermionic emission could potentially serve as a diagnostic of peak electron temperature Te. However, their interpretation is difficult because the large electron emission rate introduces tremendous space-charge fields at the surface, which substantially suppress the electron yield and simultaneously distorting the detected electron energy distribution from the initial distribution. In order to understand quantitatively the electron yield and energy distribution and to develop a useful diagnostic technique, the authors present a combined experimental, analytical theory and particle simulation investigation of femtosecond pulse induced electron emission from Al, Ag and W surfaces

1993-01-01

271

Review of biorthogonal coupled cluster representations for electronic excitation  

CERN Document Server

Single reference coupled-cluster (CC) methods for electronic excitation are based on a biorthogonal representation (bCC) of the (shifted) Hamiltonian in terms of excited CC states, also referred to as correlated excited (CE) states, and an associated set of states biorthogonal to the CE states, the latter being essentially configuration interaction (CI) configurations. The bCC representation generates a non-hermitian secular matrix, the eigenvalues representing excitation energies, while the corresponding spectral intensities are to be derived from both the left and right eigenvectors. Using the perspective of the bCC representation, a systematic and comprehensive analysis of the excited-state CC methods is given, extending and generalizing previous such studies. Here, the essential topics are the truncation error characteristics and the separability properties, the latter being crucial for designing size-consistent approximation schemes. Based on the general order relations for the bCC secular matrix and the...

Schirmer, J

2009-01-01

272

Collisional electron transfer to photoexcited acceptor radical anions  

DEFF Research Database (Denmark)

In this article, we show that photoexcitation of radical anions facilitates electron transfer from sodium atoms in femtosecond encounters. Thus, excitation of 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and fluorinated TCNQ (TCNQ-F(4)) anions to the second optically active state at 478 nm led to increases in the yields of dianions of about 20% and 10%, respectively. Photoexcitation with a nanosecond-long laser pulse was done a few microseconds before the ions entered the sodium collision cell so that none of the ions would be in any of the initially reached doublet-excited states. We suggest an explanation for the higher electron capture cross section based on the formation of long-lived quartet state anions. Excitation of TCNQ anions within the lowest-energy absorption band, where there are no accessible quartet states, led instead to a lower yield of dianions. There are at least three explanations for the lower dianion yields: (1) Depletion of the monoanion beam due to photodetachment after the absorption ofminimum two photons; (2) Formation of short-lived vibrationally excited dianions that decay by electron autodetachment prior to identification; and (3) Lower electron capture cross sections of vibrationally excited monoanions. Similar losses in dianion signal can occur at 478 nm so the actual yield of dianions at this wavelength due to the population of quartet states is therefore greater than that observed. Our methodology devises a more efficient route for the production of molecular dianions, and at the same time it may provide information on long-lived electronic states.

Wyer, Jean Ann; StØchkel, Kristian

2012-01-01

273

Coherent versus incoherent excitation energy transfer in molecular systems  

Science.gov (United States)

We investigate the Markovian limit of a polaronic quantum master equation for coherent resonance energy transfer proposed recently by Jang et al. [J. Chem. Phys. 129, 101104 (2008)]. An expression for the rate of excitation energy transfer (EET) is derived and shown to exhibit both coherent and incoherent contributions. We then apply this theory to calculated EET rates for model dimer systems, and demonstrate that the small-polaron approach predicts a variety of dynamical behaviors. Notably, the results indicate that the EET dynamical behaviors can be understood by the interplay between noise-assisted EET and dynamical localization, while both are well captured by the polaron theory. Finally, we investigate bath correlation effects on the rate of EET and show that bath correlations (or anti-correlations) can either enhance or suppress EET rate depending on the strength of individual system-bath couplings. In summary, we introduce the small-polaron approach as an intuitive physical framework to consolidate our understanding of EET dynamics in the condensed phase.

Chang, Hung-Tzu; Cheng, Yuan-Chung

2012-10-01

274

Coherent versus incoherent excitation energy transfer in molecular systems.  

UK PubMed Central (United Kingdom)

We investigate the Markovian limit of a polaronic quantum master equation for coherent resonance energy transfer proposed recently by Jang et al. [J. Chem. Phys. 129, 101104 (2008)]. An expression for the rate of excitation energy transfer (EET) is derived and shown to exhibit both coherent and incoherent contributions. We then apply this theory to calculated EET rates for model dimer systems, and demonstrate that the small-polaron approach predicts a variety of dynamical behaviors. Notably, the results indicate that the EET dynamical behaviors can be understood by the interplay between noise-assisted EET and dynamical localization, while both are well captured by the polaron theory. Finally, we investigate bath correlation effects on the rate of EET and show that bath correlations (or anti-correlations) can either enhance or suppress EET rate depending on the strength of individual system-bath couplings. In summary, we introduce the small-polaron approach as an intuitive physical framework to consolidate our understanding of EET dynamics in the condensed phase.

Chang HT; Cheng YC

2012-10-01

275

Analyses of donor-acceptor distance-dependent rates of photo-induced electron transfer in flavoproteins with three kinds of electron transfer theories  

International Nuclear Information System (INIS)

Reported donor-acceptor distance-dependent rates of photo-induced electron transfer from tryptophan (Trp), tyrosine (Tyr), and benzoate (Bz) to the excited isoalloxazine in ten flavoprotein systems were analyzed with three kinds of electron transfer theories by Marcus, by Bixon and Jortner, and also by Kakitani, Yoshimori, and Mataga. Average donor-acceptor distances that were obtained from X-ray structures of flavoproteins were used for the analysis, rather than the edge-to-edge distance. The observed photo-induced electron transfer rates were best reproduced by the Kakitani, Yoshimori, and Mataga theory.

2008-06-02

276

Excited Spectator Electron Effects on Spectral Line Shapes  

Energy Technology Data Exchange (ETDEWEB)

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.

Iglesias, C A

2009-10-12

277

Electron-impact excitation of [1.1.1] propellane  

International Nuclear Information System (INIS)

We have calculated cross sections for low-energy electron impact excitation of the first triplet state (5a1'?3a2double-prime) of [1.1.1] propellane. Our results support the assignment of a recently observed [O. Schafer, M. Allan, G. Szeimies, and M. Sanktjohansen, J. Am. Chem. Soc. (submitted)] near-threshold peak as a (5a1')(3a2double-prime)2 core-excited shape resonance.

1992-01-01

278

Electron-impact excitation of metastable argon and krypton  

International Nuclear Information System (INIS)

[en] Born cross sections have been calculated for electron-impact excitation of metastable levels of argon and krypton to higher-lying excited states. It is shown that the intermediate-coupling representation must be used to obtain reliable results. An approximate treatment of strong-coupling effects is included for the dominant ns-np transitions, and the applicable range and validity of the Born calculations are considered

1978-01-01

279

Electron-impact excitation cross sections for neon  

International Nuclear Information System (INIS)

[en] An analytic atomic independent particle model adjusted to experimental single-particle energy levels is used to generate wavefunctions for the excited states of neon. Using these wavefunctions in conjunction with the Born approximation and the Russell-Saunders LS-coupling scheme, a calculation is presented of generalized oscillator strengths and cross sections for electron-impact excitation of neon from the 2p6(1S0) ground state. (author)

1979-01-01

280

Elementary excitations in double electron layers with tunnel coupling  

International Nuclear Information System (INIS)

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

2003-01-01

 
 
 
 
281

Accumulative electron transfer: multiple charge separation in artificial photosynthesis.  

UK PubMed Central (United Kingdom)

To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme.

Karlsson S; Boixel J; Pellegrin Y; Blart E; Becker HC; Odobel F; Hammarström L

2012-01-01

282

Accumulative electron transfer: multiple charge separation in artificial photosynthesis.  

Science.gov (United States)

To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme. PMID:22470977

Karlsson, Susanne; Boixel, Julien; Pellegrin, Yann; Blart, Errol; Becker, Hans-Christian; Odobel, Fabrice; Hammarström, Leif

2012-01-01

283

Magnetic resonance studies of photo-induced electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ([pi]/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser excitation. Investigations of electron transfer reactions focused on porphyrin (donor) - quinone (acceptor) systems. First, two hydrogen abstraction reactions were studied with FT EPR: photoreduction of acetone with 2-propanol, yielding the acetone ketyl radical, and the reaction of 2-propanol with t-butoxy radicals. Then, the FT EPR study of benzoquinone or duroquinone anion radicals generated by pulsed-laser induced electron transfer from zinc tetraphenylporphyrin (ZnTPP) or tetrasulfonated Zn(TPP), was carried out in homogeneous solution, micellar solutions, and silica gel. Finally, FT EPR was used to study electron transfer quenching of triplet C[sub 60] by electron donors.

van Willigen, H.

1992-11-01

284

Electron-impact excitation of the lowest four excited states of argon  

International Nuclear Information System (INIS)

First-order many-body theory has been used to calculate the differential and integral cross sections for electron-impact excitation of the argon atom to the 4 3P0, 4 3P2, 4 3P1, and 4 1P1 electronic states, for incident electron energies of 16, 20, 30, 50, and 80.4 eV. The resulting cross sections are in good agreement with recent results extracted from electron energy-loss measurements on argon. Detailed calculations show that spin-orbit coupling must be included in the 3P1 wave function in order to describe the electron-impact excitation of the state properly

1981-01-01

285

An Exciting Aspect of Nanotechnology: Unimolecular Electronics  

Directory of Open Access Journals (Sweden)

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.

Metzger R. M.

2013-01-01

286

Nuclear interlevel transfer driven by electronic transitions  

International Nuclear Information System (INIS)

[en] 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

1985-01-01

287

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

Energy Technology Data Exchange (ETDEWEB)

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

Bauer, H.

1998-12-31

288

Single Molecule Spectroscopy of Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

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.

Michael Holman; Ling Zang; Ruchuan Liu; David M. Adams

2009-10-20

289

Ro-vibrational excitation of HCl by electron impact  

International Nuclear Information System (INIS)

Ab initio calculations of cross sections for simultaneous rotational and vibrational excitation of HCl by low-energy electrons have been made in the multipole-extracted adiabatic-nuclei approximation. These calculations employed a free-electron-gas model of the exchange interaction, and represent the first application of a new parameter-free model of the correlation-polarization interaction to vibrational excitation. The cross sections increase by an order of magnitude with the inclusion of this interaction, which is much more important for vibrationally inelastic than elastic collisions. 22 references

1984-01-01

290

Ro-vibrational excitation of HCl by electron impact  

International Nuclear Information System (INIS)

Ab initio calculations of cross sections for simultaneous rotational and vibrational excitation of HCl by low-energy electrons have been made in the multipole-extracted adiabatic-nuclei (MEAN) approximation. These calculations employed a free-electron-gas model of the exchange interaction, and represent the first application of a new parameter-free model of the correlation-polarization interaction to vibrational excitation. The cross sections increase by an order of magnitude with the inclusion of this interaction, which is much more important for vibrationally inelastic than elastic collisions

1984-01-01

291

Protein electron transfer: Dynamics and statistics.  

UK PubMed Central (United Kingdom)

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.

Matyushov DV

2013-07-01

292

Exothermic rate restrictions on electron transfer in a rigid medium  

International Nuclear Information System (INIS)

Many highly exothermic (2--3 eV) electron transfer reactions are shown to be slower than moderately exothermic reactions by factors as large as 105. The decrease occurs in a regular way with increasing exothermicity, tending to confirm theoretical predictions of Franck--Condon restrictions on strongly exothermic electron transfer reactions. Deviations from the above trends occur if the reaction product, a molecular anion, has a low-lying electronic excited state into which the reaction may occur with more moderate vibrational exothermicity. Then greatly enhanced rates are found. The rates are enhanced to a lesser extent for acceptors likely to undergo configurational changes upon accepting an electron. These effects are found in measurements of rates of electron tunneling reactions between trapped electrons and 48 organic electron acceptors in rigid 2-methyltetrahydrofuran glass at 77 K. Electron tunneling rates were observed from 10-6 to 102 s. Measured tunneling distances were 15--40 A. In most cases the observed kinetic decay curves are well simulated by a theory in which the only variable parameter is the effective Franck--Condon factor (F), which is a constant characteristic of the acceptor. For the various acceptors F ranges from 1 to 10-5, and scales the reaction rate at each distance. However in reactions of small vibration exothermicity, the Franck--Condon factors are expected to be very sensitive to small changes in reaction exothermicity caused by relaxations of trapped electrons, which deepen their trap depths with time and, possibly, a dispersion of trap depths. These effects cause F to change with time leading to changes in the shapes of the decay curves. The relationship between the shapes of the decay curves, Franck--Condon factors, and exothermicity allows a semiquantitative interpretation of the present results and much of the earlier tunneling data on electron transfer

1979-12-01

293

Distance dependence of photochemical electron transfer across peptide spacers  

Energy Technology Data Exchange (ETDEWEB)

The distance dependence of the rate and activation parameters for photoinduced electron transfer (ET) across a series of L-proline peptide spacers has been determined in compounds 0-2. In 0-2, the d{pi}(Re){yields}{pi}{sup *}(bpy) metal-to-ligand charge-transfer (MLCT) excited state is quenched by intramolecular ET from the aromatic amine. The rate for ET (k{sub et}) was determined by comparing the MLCT emission lifetimes of 0-2 with the lifetimes of appropriate model complexes. The kinetic results are consistent with a nonadiabatic mechanism for ET in which the variation of k{sub et} with distance results mainly from a decrease in electronic coupling with increased donor-acceptor separation.

Schanze, K.S.; Cabana, L.A. (Univ. of Florida, Gainesville (USA))

1990-04-05

294

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

Long range photoinduced electron transfer between electron donor and acceptor groups is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. As part of an extensive study of long range electron transfer involving biopolymers, we have carried out this year investigations of the assembly of electron transfer agents in a system of model short peptides. Also studied is a polyelectrolyte that can adopt a helical conformation when electrostatically complexed with organic dye counter-ions. The principal interest in these systems has to do with the well ordered secondary structures adopted by peptide polymers, and the capabilities for synthetic modification of peptide side chains and end groups with chromophores or electroactive substituents. The present report gives a brief account of the following elements of work related to photochemical electron transfer themes: (1) the synthesis and photochemical characterization of chromophore-bound peptides and amino acid model compounds based on the amino acids, tryptophan and the spacer residue, alanine (Ala); (2) the study of binding of the cationic organic dye to a peptide electrolyte, for which cooperative dye loading and helix formation is important; and (3) completion of the synthesis of a new series of acridinium chromophores that have rod-like'' arrangements of inked aryl rings for assembly of electron donor-acceptor systems that will exhibit especially long lived charge separation.

Jones, G. II.

1991-12-01

295

Ultrafast interatomic electronic decay in multiply excited clusters  

CERN Multimedia

An ultrafast mechanism belonging to the family of interatomic Coulombic decay (ICD) phenomena is proposed. When two excited species are present, an ultrafast energy transfer can take place bringing one of them to its ground state and ionizing the other one. It is shown that if large homoatomic clusters are exposed to an ultrashort and intense laser pulse whose photon energy is in resonance with an excitation transition of the cluster constituents, the large majority of ions will be produced by this ICD mechanism rather than by two-photon ionization. A related collective-ICD process that is operative in heteroatomic systems is also discussed.

Kuleff, Alexander I; Kopelke, Soeren; Cederbaum, Lorenz S

2010-01-01

296

Dissociation of benzene and methylene chloride based on enhanced dissociative electron attachment to highly excited molecules  

Science.gov (United States)

We present preliminary results on a low-pressure glow-discharge-based process for the destruction of dilute concentrations of volatile organic compounds. Methylene chloride and benzene were studied in dilute mixtures with Ar, Ne and He rare gases. The destruction efficiency was observed to increase with increasing pressure. This and other observations are compatible with molecular dissociation by dissociative electron attachment to high-lying Rydberg states of molecules produced via excitation transfer from the metastable states of the rare gases.

McCorkle, Dennis L.; Ding, Weixing; Ma, Cheng-Yu; Pinnaduwage, Lal A.

1999-01-01

297

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.

1998-01-01

298

Differential electron scattering from acetylene - elastic scattering and vibrational excitation  

International Nuclear Information System (INIS)

[en] Absolute differential cross sections for elastic scattering of electrons from acetylene are reported. The relative flow method was applied to normalize these cross sections, using helium as a standard. The measurements were made at incident electron energies from 5 eV to 100 eV for electron scattering angles in the range of 10o to 125o. In addition, we report differential cross sections for excitation of vibrational modes of acetylene at 5 eV and 10 eV incident electron energies for scattering angles in the range of 20o to 120o. (author)

1993-12-28

299

Enhanced electron transfer in Penning gases  

Energy Technology Data Exchange (ETDEWEB)

We present the discovery of the enhanced transfer of electrons produced in avalanches through metal grids in Penning gas mixtures. Measurements are presented showing the enhancement which is particularly dramatic at very low transfer fields. With electric fields on either side of the grid in the ratio of 0.015 the transfer ratio is 0.11, representing an increase of a factor of 7 over that predicted and observed in a conventional gas by Bunemann et al. (1949). We propose a model for this phenomenon and we show that both a uniform electric field and the Penning effect are necessary for this transfer to occur. We also identify a possible reason why other workers have not obtained similar results in Penning mixtures. The application of this 'Penning transfer' to a position sensitive X-ray detector (the Penning Gas Imager or PGI) is discussed.

Schwarz, H.E.; Thornton, J.; Mason, I.M. (University Coll., London (UK). Mullard Space Science Lab.)

1984-08-15

300

Enhanced electron transfer in Penning gases  

International Nuclear Information System (INIS)

We present the discovery of the enhanced transfer of electrons produced in avalanches through metal grids in Penning gas mixtures. Measurements are presented showing the enhancement which is particularly dramatic at very low transfer fields. With electric fields on either side of the grid in the ratio of 0.015 the transfer ratio is 0.11, representing an increase of a factor of 7 over that predicted and observed in a conventional gas by Bunemann et al. (1949). We propose a model for this phenomenon and we show that both a uniform electric field and the Penning effect are necessary for this transfer to occur. We also identify a possible reason why other workers have not obtained similar results in Penning mixtures. The application of this 'Penning transfer' to a position sensitive X-ray detector (the Penning Gas Imager or PGI) is discussed. (orig.).

1984-01-01

 
 
 
 
301

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

International Nuclear Information System (INIS)

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

1981-01-01

302

Low-energy charge transfer excitations in NiO  

International Nuclear Information System (INIS)

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

2012-08-20

303

Electronically excited states of protonated aromatic hydrocarbons: phenanthrene and pyrene.  

Science.gov (United States)

The first and second electronic excited states (S1 and S2) of protonated phenanthrene and protonated pyrene, having the ??* nature, are strongly red-shifted compared to corresponding electronic transitions in neutral homologues. The CC2 calculations identify an out-of-plane deformation as the most important photochemical reaction coordinate in protonated phenanthrene as well as protonated benzene. It was shown that the excited S1 states of protonated phenanthrene and protonated benzene are unstable via a torsional motion, which provides a fast access to a S1-S0 conical intersection. From the conical intersection, a barrier-less reaction path directs the system back to the minimum of the S0 potential-energy surface. In contrast to the most stable isomer of protonated phenanthrene, the most stable structure of protonated pyrene shows planar structure in both the S1 and S2 excited states, without considerable geometry deformations. PMID:23441848

Saed, Behnaz; Omidyan, Reza

2013-03-15

304

Exciting the Nucleus by Target Electron Capture into Atomic Orbitals  

Energy Technology Data Exchange (ETDEWEB)

A new mechanism by which the resonant capture of a target electron by a swiftly moving heavy ion is translated in one step into nuclear excitation is identified. It is in fact the inverse of internal conversion. Predicted resonances have energies E greater than or equal to 10 MeV/u, widths specified by the target electrons' momentum distribution, and cross-sections approaching tens of millibarns for some, and appear to be observable under channelling condition.

Cue, N.; Poizat, J.C.; Remillieux, J.

1989-01-01

305

Exciting the Nucleus by Target Electron Capture into Atomic Orbitals  

International Nuclear Information System (INIS)

[en] A new mechanism by which the resonant capture of a target electron by a swiftly moving heavy ion is translated in one step into nuclear excitation is identified. It is in fact the inverse of internal conversion. Predicted resonances have energies E ? 10 MeV/u, widths specified by the target electrons' momentum distribution, and cross-sections approaching tens of millibarns for some, and appear to be observable under channelling condition

1989-01-01

306

Electron-impact excitation and dissociation processes in H2  

International Nuclear Information System (INIS)

The electron-impact excitation and dissociation cross sections for the C1Pi/sub u/, c 3Pi/sub u/, B' 1?/sub u/+, and EF 1?/sub g/+ states of H2 have been calculated within the distorted-wave approximation. The distorted waves are obtained as solutions of the static-exchange potential field of the ground electronic state. Both differential and integral inelastic cross sections are reported and compared with other calculated results and available experimental data

1982-01-01

307

Role of vibrationally excited NO in promoting electron emission when colliding with a metal surface: a nonadiabatic dynamic model.  

UK PubMed Central (United Kingdom)

A nonadiabatic quantum dynamic model has been developed to study the process of electron emission from a low-work-function metal surface. The process is initiated by scattering a highly vibrationally excited NO molecule from a surface composed of a Cs layer covering a Ru crystal. The model addresses the increasing quantum yield of the electron emission as a function of the molecular vibrational excitation and incident kinetic energy. The reaction mechanism is identified as a long-range harpooning electron transfer to a molecular ion which is then accelerated toward the surface. Upon impact, the molecular ion emits its excess electron.

Katz G; Zeiri Y; Kosloff R

2005-10-01

308

Electronic excitation processes in rare gas clusters studied by electron energy loss spectroscopy  

International Nuclear Information System (INIS)

We present the electron energy loss spectra for Ar clusters as a function of incident electron energy and of cluster size. In spectra measured with 100 eV incident electron energy the bulk excitation peak becomes visible for a mean cluster size above 170 atoms per cluster. For 250 eV incident electron energy the bulk excitation peak is clearly observable even for a mean cluster size of 120 atoms per cluster. These experimental results are qualitatively reproduced by a simple calculation that accounts for the mean free path of electrons in Ar clusters; i.e., the penetration depth of incident electrons into the cluster.

2009-11-30

309

Molecular dynamics simulation of electronically excited polyatomic molecules  

International Nuclear Information System (INIS)

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

1993-01-01

310

Investigations of ultrafast dynamics in electronically excited alkylbenzenes  

Science.gov (United States)

We investigate ultrafast dynamics in electronically excited states of some typical alkylbenzenes by time-resolved two-colour four wave mixing and velocity map imaging as complementary methods. In this context an upgraded double-sided time-resolved velocity map imaging setup is also proposed.

Liu, Y.; Gerber, T.; Radi, P.; Sych, Y.; Maksyutenko, P.; Knopp, G.

2013-03-01

311

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

Energy Technology Data Exchange (ETDEWEB)

First measurements of the angular distributions of autoionization electrons from 2p[sup 5]3s3p[sup 2]D[sub 5/2] state of Na atom excited by electron impact from the ground and laser excited 3p [sup 2]P[sub 3/2] 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).

Dorn, A.; Nienhaus, J.; Wetzstein, M.; Winnewisser, C.; Mehlhorn, W.; Grum-Grzhimailo, A.N.; Kabachnik, N.M. (Freiburg Univ. (Germany). Fakultaet fuer Physik); Balashov, V.V. (Moskovskij Gosudarstvennyj Univ., Moscow (Russian Federation). Nauchno-Issledovatel' skij Inst. Yadernoj Fiziki); Zatsarinny, O.I. (Institute of Electron Physics, Uzhgorod (Ukraine))

1994-08-28

312

Electron transfer in weakly interacting systems  

International Nuclear Information System (INIS)

[en] A recently proposed semiclassical model, in which an electronic transmission coefficient and a nuclear tunneling factor are introduced as corrections to the classical activated-complex expression, is described. The nuclear tunneling corrections are shown to be important only at low temperatures or when the electron transfer is very exothermic. By contrast, corrections for nonadiabaticity may be significant for most outer-sphere reactions of metal complexes. The rate constants for the Fe(H2O)62+-Fe(H2O)63+, Ru(NH3)62+-Ru(NH3)63+ and Ru(bpy)32+-Ru(bpy)33+ electron exchange reactions predicted by the semiclassical model are in very good agreement with the observed values. The implications of the model for optically-induced electron transfer in mixed-valence systems are noted

1981-06-12

313

Electron transfer in weakly interacting systems  

Energy Technology Data Exchange (ETDEWEB)

A recently proposed semiclassical model, in which an electronic transmission coefficient and a nuclear tunneling factor are introduced as corrections to the classical activated-complex expression, is described. The nuclear tunneling corrections are shown to be important only at low temperatures or when the electron transfer is very exothermic. By contrast, corrections for nonadiabaticity may be significant for most outer-sphere reactions of metal complexes. The rate constants for the Fe(H/sub 2/O)/sub 6//sup 2 +/-Fe(H/sub 2/O)/sub 6//sup 3 +/, Ru(NH/sub 3/)/sub 6//sup 2 +/-Ru(NH/sub 3/)/sub 6//sup 3 +/ and Ru(bpy)/sub 3//sup 2 +/-Ru(bpy)/sub 3//sup 3 +/ electron exchange reactions predicted by the semiclassical model are in very good agreement with the observed values. The implications of the model for optically-induced electron transfer in mixed-valence systems are noted.

Sutin, N.; Brunschwig, B.S.

1981-01-01

314

Energy transfer between electrons and ions in dense displacement cascades  

International Nuclear Information System (INIS)

A theory of the energy exchange between valence electrons and ions in the dense displacement cascades in metals is proposed. It is shown that the theory based on the relaxation of the nonequilibrium electron-ion system gives a common basis for the electronic stopping power of slow ions due to valence electrons and for the energy transfer via an electron-phonon interaction. It is found that the energy loss owing to the electron-phonon interaction bears a close relationship to the electronic stopping power, but it is greatly enhanced because of the emergence of phonon excitations and band structure. The corresponding cooling rates of the thermalizing cascade are several times greater in metals with a strong electron-ion interaction than in metals with a weak interaction. A similar conclusion holds in the intermediate region, where the ions in the thermalizing cascade are essentially free to move but band-structure effects persist. However, conduction electrons play a role in the cooling of the cascade only if the dynamics of the ions gives rise to phonons.

1993-01-01

315

Energy transfer between electrons and ions in dense displacement cascades  

Energy Technology Data Exchange (ETDEWEB)

A theory of the energy exchange between valence electrons and ions in the dense displacement cascades in metals is proposed. It is shown that the theory based on the relaxation of the nonequilibrium electron-ion system gives a common basis for the electronic stopping power of slow ions due to valence electrons and for the energy transfer via an electron-phonon interaction. It is found that the energy loss owing to the electron-phonon interaction bears a close relationship to the electronic stopping power, but it is greatly enhanced because of the emergence of phonon excitations and band structure. The corresponding cooling rates of the thermalizing cascade are several times greater in metals with a strong electron-ion interaction than in metals with a weak interaction. A similar conclusion holds in the intermediate region, where the ions in the thermalizing cascade are essentially free to move but band-structure effects persist. However, conduction electrons play a role in the cooling of the cascade only if the dynamics of the ions gives rise to phonons.

Koponen, I. (Department of Physics, University of Helsinki, Siltavuorenpenger 20 D, SF-00170 Helsinki (Finland))

1993-06-01

316

Collective electronic excitation coupling between planar optical lattices using Ewald's method  

Science.gov (United States)

Using Ewald's summation method, we investigate collective electronic excitations (excitons) of ultracold atoms in parallel planar optical lattices including long-range interactions. The exciton dispersion relation can then be suitably rewritten and efficiently calculated for long-range resonance dipole-dipole interactions. Such in-plane excitons resonantly couple for two identical optical lattices, with an energy transfer strength decreasing exponentially with the distance between the lattices. This allows a restriction of the transfer to neighbouring planes and gives rise to excitons delocalized between the lattices. In general, equivalent results will hold for any planar system containing lattice layers of optically active and dipolar materials.

Zoubi, Hashem; Ritsch, Helmut

2011-10-01

317

Collective Electronic Excitation Coupling between Planar Optical Lattices using Ewald's Method  

CERN Document Server

Using Ewald's summation method we investigate collective electronic excitations (excitons) of ultracold atoms in parallel planar optical lattices including long range interactions. The exciton dispersion relation can then be suitably rewritten and efficiently calculated for long range resonance dipole-dipole interactions. Such in-plane excitons resonantly couple for two identical optical lattices, with an energy transfer strength decreasing exponentially with the distance between the lattices. This allows a restriction of the transfer to neighboring planes and gives rise to excitons delocalized between the lattices. In general equivalent results will hold for any planar system containing lattice layers of optically active and dipolar materials.

Zoubi, Hashem

2011-01-01

318

Collective electronic excitation coupling between planar optical lattices using Ewald's method  

Energy Technology Data Exchange (ETDEWEB)

Using Ewald's summation method, we investigate collective electronic excitations (excitons) of ultracold atoms in parallel planar optical lattices including long-range interactions. The exciton dispersion relation can then be suitably rewritten and efficiently calculated for long-range resonance dipole-dipole interactions. Such in-plane excitons resonantly couple for two identical optical lattices, with an energy transfer strength decreasing exponentially with the distance between the lattices. This allows a restriction of the transfer to neighbouring planes and gives rise to excitons delocalized between the lattices. In general, equivalent results will hold for any planar system containing lattice layers of optically active and dipolar materials.

Zoubi, Hashem; Ritsch, Helmut, E-mail: hashem.zoubi@uibk.ac.at [Institut fur Theoretische Physik, Universitat Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)

2011-10-28

319

Collective electronic excitation coupling between planar optical lattices using Ewald's method  

International Nuclear Information System (INIS)

Using Ewald's summation method, we investigate collective electronic excitations (excitons) of ultracold atoms in parallel planar optical lattices including long-range interactions. The exciton dispersion relation can then be suitably rewritten and efficiently calculated for long-range resonance dipole-dipole interactions. Such in-plane excitons resonantly couple for two identical optical lattices, with an energy transfer strength decreasing exponentially with the distance between the lattices. This allows a restriction of the transfer to neighbouring planes and gives rise to excitons delocalized between the lattices. In general, equivalent results will hold for any planar system containing lattice layers of optically active and dipolar materials.

2011-10-28

320

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 Multimedia

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...

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

2002-01-01

 
 
 
 
321

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

Energy Technology Data Exchange (ETDEWEB)

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)

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

1997-03-01

322

Electron emission from materials at low excitation energies  

Energy Technology Data Exchange (ETDEWEB)

Full text: An experimental system has been designed and developed with the purpose of measuring the total electron emission yield from materials at low energy excitation. In the first instance the reliability of the system was checked by measuring the total electron emission yield for a well defined surface (aluminium 99.45%). The obtained data was in the expected range given by the literature, and consequently the system will be used further for measuring the total electron yield for a range of materials with interest in the instrumentation industry. We intend to measure the total electron emission yield under electron bombardment as a function of incident electron energy up to 1200 eV, angle of incidence, state of the surface and environment to which the surface has been exposed. Dependence of emission on total electron irradiated dose is also of interest. For many practical application of the `Secondary Electron Emission`, the total electron yield is desired to be as large as possible. The above phenomenon has practical applicability in electron multiplier tube and Scanning electron microscopy - when by means of the variation of the yield of the emitted electrons one may produce visible images of small sample areas. The electron multiplier tube, is a device which utilises the above effect to detect and amplify both single particles and low currents streams of charged particles. The majority of electron tubes use electrons with low energy, hundreds of eV. Not a lot has been published in the literature about this regime and also about the emission when the impinging electrons have small energy, up to 1 KeV. The information obtained from the experimental measurements concerning the total electron emission yield is used to asses the investigated materials as a potential electron emitting surfaces or dynodes in an electron multiplier tube

Urma, N.; Kijek, M.; Millar, J.J. [RMIT, Melbourne, VIC (Australia). Department of Applied Physics

1996-12-31

323

Dissociative electron attachment to laser-excited benzene  

Energy Technology Data Exchange (ETDEWEB)

We have conducted comprehensive measurements on enhanced electron attachment to ArF and KrF laser-excited benzene in the presence of Ar and N{sub 2} buffer gases. At both these laser lines, two-photon absorption leads to excitation of benzene to energies above its ionization potential. Such excitations have been shown to lead to a population of long-lived, core-excited high-Rydberg states in addition to the ionization of the molecule. Present measurements on the dependence of negative ion yield on laser fluence, benzene pressure, and applied electric field verify that the observed negative ion formation is due to the attachment of the photoelectrons to the concomitantly produced high-Rydberg states. Using a rate equation analysis, the electron attachment rate constant for the core-excited Rydberg states was estimated to be of the order of 10{sup -4}-10{sup -3} cm{sup 3} s{sup -1}. Laser photoionization cross sections were also estimated, and the cross section at the KrF laser line is in agreement (author)

Tav, C. [Department of Physics, University of Tennessee, Knoxville, TN (United States); Pinnaduwage, L.A. [Department of Physics, University of Tennessee, Knoxville, TN (United States) and Oak Ridge National Laboratory, Oak Ridge, TN (United States)]. E-mail: llp@ornl.gov

2000-10-07

324

Electron transfer experiments and atomic magnetism values. Progress report, February 1, 1975--September 30, 1975  

International Nuclear Information System (INIS)

Progress in the first seven months of this new research is described. A new apparatus was constructed, tested and moved to Oak Ridge National Laboratory for studies using the Penning ion source test facility. Preliminary electron transfer cross section results for N4+, N5+, He2+ and C5+ ions on gases were obtained. Energy loss measurements made to date support expectations that single electron transfer for multiply-charged ions colliding with gas atoms produces excited final state ions

1975-01-01

325

Controlling Optimal Excitation Wavelength of Energy Transfer from Photo-Excited Polymers to Single-Walled Carbon Nanotubes.  

Science.gov (United States)

The optimal excitation wavelength for the energy transfer from aromatic polymers poly(9,9-dioctylfluoreny- 2,7-diyl) (PFO) to single-walled carbon nanotubes (SWNTs) is tunable in a wide wavelength range (from 388 to 480 nm) depending on the concentration of excess PFO polymers. The concentration governs the aggregation state and chain conformation of the polymers proximate to SWNT surfaces, which in turn alters the optimal excitation wavelength. This study suggests an exciting and convenient method of adjusting the desired optical wavelengths for the energy conversion, useful for polymer-SWNT composites in optoelectronic applications.

Li, Lain-Jong; Chen, Fuming; Jia, Mingli; Wei, Li; Chen, Yuan; Chan-Park, M. B.; Xia, Andong

2009-03-01

326

Dynamics of two-electron excitations in helium  

Energy Technology Data Exchange (ETDEWEB)

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.

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

1997-04-01

327

Solvent gating of intramolecular electron transfer  

Energy Technology Data Exchange (ETDEWEB)

The rates for ionic photodissociation of malachite green leucocyanide to form cyanide ion and a malachite green carbonium ion were measured as a function of solvent and temperature. The observed rates in mixtures of polar and nonpolar solvents all had an activation energy of about 1 kcal/mol for a wide range of dielectric constants. This dissociative intramolecular electron transfer (DIET) is unusual because it is the first example where solvent configurational entropy changes are required to enable a large amplitude molecular distortion leading to a nonadiabatic electron transfer and ionic dissociation. This solvent gated intramolecular electron-transfer mechanism is supported by analysis of the preexponential and activation energy trends in dipolar aprotic solven mixtures and alcohol solvents. The large amplitude motion is not separately measurable due to the slow gating rates, but viscosity effects on both the preexponential and the activation energy are analyzed to demonstrate consistency with a barrierless diffusion model having a structural dependence on electron-transfer rate. The rate has an inverse dependence on viscosity raised to the 0.53 power. 36 refs., 6 figs., 4 tabs.

Miller, R.M. (California State Univ., Chico, CA (United States)); Spears, K.G.; Gong, J.H.; Wach, M. (Northwestern Univ., Evanston, IL (United States))

1994-02-03

328

Photoinduced electron transfer reaction in zeolite cages  

Energy Technology Data Exchange (ETDEWEB)

Research continued on photochemically induced electron transfer in zeolites. Reactions and synthesis of Ru(bpy){sub 3}{sup 2+} are discussed. Also, the intercalation properties of LiAl{sub 2}(OH){sub 6}{sup +}-X{sup {minus}} are being pursued. 5 figs. (CBS)

Dutta, P.K.

1990-01-01

329

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

Photochemical studies on organic polymers or biopolymers (particularly synthetic peptides) that have been modified by covalent attachment (or other means of binding) of organic chromophores and electron transfer agents are described. Specific projects involve are: peptide conjugates bearing electroactive residues such as tryptophan and specifically labeled at the N- or C-terminus of peptide chains; the electrostatic binding of organic dyes to poly-electrolytes (polyacrylates) for which the formation of dimeric aggregates of bound dye that display unusual photophysical and electron transfer properties is important; a study of the binding of dyes and electron transfer agents to the protein mimic,'' polyvinyl-2-pyrrolidinone (PVP), in hydrophobic domains that depend on specific H-bond interaction; and completion of an earlier study having to do with the triplet state properties of charge-transfer (CT) complexes of a high potential quinone and various electron donors (investigation of the properties of triplet (contact) radical-ion pairs). 13 refs., 5 figs., 2 tabs.

Jones, G. II.

1990-10-20

330

A Study Looking the Electronic Funds Transfer  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this paper is to present the characteristics of the most important electronic funds transfer in the world, both interperson and interbank. We identified the following informations: location, type, owner, operator, number of transactions, transsactions value, clients, financial scheme and the message format.

Codruta POENAR

2008-01-01

331

Electron transfer between cytochrome c and porphyrins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electron transfer between cytochrome c and several water-soluble porphyrins (ZnTPPS, ZnTMPyP, ZnTPPC, H2TPPS, and H2TMPyP where TPPS is tetrakis(sulfonatophenyl)porphyrin, TMPyP is tetrakis(N-methylpyridyl)porphyrin, and TPPC is tetrakis(carboxyphenyl)porphyrin) has been studied by the method of...

Cho, KC; Che, CM; Ng, KM; Choy, CL

332

Electron transfer between azurin and metalloporphyrins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electron-transfer reactions between azurin and the triplet as well as the radicals of several water-soluble metalloporphyrins (ZnTPPS, ZnTPPC, and ZnTMPyP where TPPS is tetrakis(sulfonatophenyl)porphyrin, TPPC is tetrakis(carboxyphenyl)porphyrin, and TMPyP is tetrakis(N-methylpyridyl)porphyrin) ...

Cho, KC; Che, CM; Ng, KM; Choy, CL

333

Electron collisions and internal excitation in stored molecular ion beams  

Energy Technology Data Exchange (ETDEWEB)

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.)

Buhr, H.

2006-07-26

334

Probing excited electronic states and ionisation mechanisms of fullerenes.  

UK PubMed Central (United Kingdom)

Fullerenes are interesting model systems for probing the complex, fundamental electron dynamics and ionisation mechanisms of large molecules and nanoparticles. In this Tutorial Review we explain how recent experimental and theoretical advances are providing insight into the interesting phenomenon of thermal electron emission from molecular systems and the properties of hydrogenic, diffuse, excited electronic states, known as superatom molecular orbitals, which are responsible for relatively simple, well-resolved structure in fs laser photoelectron spectra of fullerenes. We focus on the application of velocity map imaging combined with fs laser photoionisation to study angular-resolved photoelectron emission.

Johansson JO; Campbell EE

2013-07-01

335

Total electron impact excitation cross sections of Ar and Kr  

International Nuclear Information System (INIS)

[en] A simple accurate method for normalizing the absolute magnitude of measured relative rare-gas excitation cross-section data to published measurements of the first Townsend coefficient is presented. Using a code which solved the Boltzmann equation we have determined that the predicted first Townsend coefficient is a very sensitive function of the electron impact excitation cross section. In Ar and Kr we have found that a 10% change in the cross section results in a 30% change in the first Townsend coefficient

1976-10-15

336

Correlations in highly excited two-electron atoms - planetary behavior  

International Nuclear Information System (INIS)

[en] The onset of strong mixing of atomic configurations in core/excited autoionization states of Ba has been observed using multiphoton isolated core excitation (ICE). The behavior of the different atomic configurations is categorized into two groups: states where n is much greater than m; and states where n is approximately equal to m. The spectral characteristics of 6s15 to 10sn-prime s transitions is in the case of n is much greater than m described within the framework of the independent electron model of Percival (1977). Estimates of the relative autoionization rates corresponding to the different atomic configurations are given in an appendix. 10 references

1984-01-01

337

Excitement tem-horn antenna by impulsive relativistic electron beam  

International Nuclear Information System (INIS)

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

2000-01-01

338

Electronic excitations and chemistry in Nitromethane and HMX  

Energy Technology Data Exchange (ETDEWEB)

The nature of electronic excitations in crystalline solid nitromethane under conditions of shock loading and static compression are examined. Density functional theory calculations are used to determine the crystal bandgap under hydrostatic stress, uniaxial strain, and shear strain. Bandgap lowering under uniaxial strain due to molecular defects and vacancies is considered. In all cases, the bandgap is not lowered enough to produce a significant population of excited states in the crystal. Preliminary simulations on the formation of detonation product molecules from HMX are discussed.

Reed, E J; Manaa, M R; Joannopoulos, J D; Fried, L E

2001-06-19

339

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

1997-01-01

340

Quantum dynamics of electron-nuclear correlations in photo-excited molecular dimers  

Science.gov (United States)

Ultrafast photoinduced dynamics of electronic excitation in molecular dimers is affected by the dynamic reorganization of inter- and intra- molecular nuclear configuration modeled by quantized nuclear degree of freedom [Cina et. al, J. Chem Phys. 118, 46 (2003)]. The quantum dynamics of electronic-nuclear excitation in a model dimer is analyzed in the limit of small nuclear reorganization for excited electronic states. The relaxational behavior of mean coordinate, population inversion, electronic-vibrational correlation etc. are obtained by means of the reduced description [Prezhdo, J. Chem. Phys. 117, 2995 (2002)], that is potentially applicable to large biological systems. Despite of absence of the heat bath the system is approaching the quasi-equilibrium state, due to the destructive interference of the wavefunction coefficients. The correlation between electronic and vibrational subsystems rises, oscillates, and relaxes similar to the population inversion. The averages and dispersions of electronic and vibrational operators oscillate in a complementary fashion. This work is being developing towards description of the exciton transfer and femtosecond optical experiments in molecular systems.

Kilin, Dmitri S.; Pereverzev, Yuri V.; Prezhdo, Oleg V.

2003-05-01

 
 
 
 
341

Electron reactions and electron transfer reactions catalyzed by micellar systems  

International Nuclear Information System (INIS)

[en] The kinetics of the reaction of hydrated electrons with pyrene, pyrene butyric acid, and pyrene sulfonic acid (PSA) have been investigated in aqueous solutions of cetyltrimethylammonium bromide (CTAB). With all three solubilizates the formation of the electron adduct (P-) occurs very rapidly with rate constants greater than 1011 M-1.sec-1. These abnormally high rate constants are shown to be due to fast trapping of e-/sub aq/ in the positive potential field of the middle and subsequent efficient penetration of electrons into the micellar interior. A similar enhancement was observed for electron transfer reactions between CO2- and solutes solubilized in or on the micelle. For example CO2- readily transfers an electron to pyrene sulfonic acid on the surface of the micelle. This reaction does not occur in homogeneous solution but is catalyzed by the positive electrostatic surface potential. Addition of electrolyte drastically reduces the rate of e-/sub aq/ and CO2- with solubilizates. The Debye-Hueckel theory of electrolytes was invoked to elucidate the role of the charged micellar interface in facilitating the penetration of the electron into the micelle and promoting the electron transfer reaction on the surface. Ion distributions were calculated via solution of a Poisson--Boltzmann equation, generalized to take into account the probable change of the microscopic dielectric constant in the vicinity of the micellar interface

1975-03-01

342

Search for nuclear excitation by electronic transition in 235U  

International Nuclear Information System (INIS)

We have searched for the nuclear excitation by electronic transition (NEET) of the isomeric level at 76 eV in 235U in a plasma induced by a YAG laser with an energy of 1 Joule and a full width at half maximum time distribution of 5 ns, operating at an intensity of 1013 W cm-2. We present a thorough description of the experimental conditions and analysis of our data. In this experimental situation we do not detect any excitation of the isomeric level, a result that is at variance with a previously reported one. An upper limit of 6x10-6 per atom and per second averaged over the laser-pulse width has been set on the nuclear excitation rate. This value is compared with results obtained in previous experimental and theoretical works

2004-01-01

343

Excited electronic states and photophysics of uracil-water complexes  

International Nuclear Information System (INIS)

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

2008-05-23

344

Electronic excitation and dynamic promotion of a surface reaction.  

UK PubMed Central (United Kingdom)

The mechanism of recombinative desorption of hydrogen from a Ru(0001) surface induced by femtosecond-laser excitation has been investigated and compared to thermally initiated desorption. For the laser-driven process, it is shown that hot substrate electrons mediate the reaction within a few hundred femtoseconds resulting in a huge isotope effect between H2 and D2 in the desorption yield. In mixed saturation coverages, this ratio crucially depends on the proportions of H and D. Deviations from second order desorption kinetics demonstrate that the recombination is dynamically promoted by excitation of neighboring, but nonreacting adatoms. A concentration dependent rate constant which accounts for the faster excitation of H versus D is proposed.

Denzler DN; Frischkorn C; Hess C; Wolf M; Ertl G

2003-11-01

345

Excited electronic states and photophysics of uracil-water complexes  

Energy Technology Data Exchange (ETDEWEB)

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

Yoshikawa, Akihiko [Department of Chemistry, Temple University, Philadelphia, PA 19122 (United States); Matsika, Spiridoula [Department of Chemistry, Temple University, Philadelphia, PA 19122 (United States)], E-mail: smatsika@temple.edu

2008-05-23

346

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

CERN Multimedia

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

Najjari, B

2012-01-01

347

K-shell resonant-transfer-excitation cross sections for S/sup 13+/ and Ca/sup 17+/  

Energy Technology Data Exchange (ETDEWEB)

Resonant-transfer-excitation (RTE) cross sections are calculated for K-shell excitation in Ca/sup 17+/+He, Ca/sup 17+/+H/sub 2/, and S/sup 13+/+He collision systems, and the results are compared with experiments. The RTE cross sections are obtained in the impulse approximation by averaging the corresponding dielectronic-recombination cross sections over the momentum distribution of the target electrons. Agreement is excellent for S/sup 13+/, but there are discrepancies in the Ca/sup 17+/ case.

McLaughlin, D.J.; Hahn, Y.

1988-05-01

348

Excited state proton transfer reactions of acridine studied by nanosecond fluorometry  

International Nuclear Information System (INIS)

Rate constants for excited state protonation reactions of acridine in aqueous solution have been determined using fluorescence decay measurements. The value of the excited state pK derived from the rate constants is in full agreement with the one obtained from steady state fluorescence measurements. It is concluded that acridine follows a two states reaction scheme in its electronically excited state. (Auth.).

1978-01-01

349

Chlorophyll-quinone photochemical electron transfer in liposomes  

Energy Technology Data Exchange (ETDEWEB)

The study described involves the reduction of electron acceptors (quinones) by photoexcited Chloroplasts (Chl). Chl a (from spinach) is incorporated into phosphatidylcholine (either synthetic or from hen egg yolks) liposomes suspended in 10 mM phosphate buffer (pH 7.0). The quinones are either present during liposome formation or added later, depending upon their water solubility. The measurement technique employed is laser flash photolysis. A pulsed nitrogen laser pumps a dye laser, which delivers a short light flash (10 ns) to the sample at a wavelength (655-660 nm) within an absorption band of Chl. This raises Chl to an excited singlet level, which can rapidly cross to the lowest excited triple level (/sup 3/Chl). From this state Chl can transfer an electron to acceptors such as quinones, resulting in the formation of the Chl cation radical (Chl./sup +/) and the semiquinone anion radical (Q./sup +/). Transient absorbance changes ocurring within the sample cell are monitored and can be attributed to processes such as excited state quenching (of /sup 3/Chl by Q) and radical product formation and decay. (JMT)

Hurley, J.K.; Castelli, F.; Tollin, G.

1981-09-01

350

Efficiencies of photoinduced electron-transfer reactions: Role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs  

Energy Technology Data Exchange (ETDEWEB)

In photoinduced electron-transfer processes the primary step is conversion of the electronic energy of an excited state into chemical energy retained in the form of a redox (geminate radical-ion) pair (A + D {sup hv}{yields} A{sup {sm bullet}{minus}}/D{sup {sm bullet}+}). In polar solvents, separation of the geminate pair occurs with formation of free radical ions in solution. The quantum yields of product formation, from reactions of either the free ions, or of the geminate pair, are often low, however, due to the return electron transfer reaction (A{sup {sm bullet}{minus}}/D{sup {sm bullet}+} {yields} A + D), an energy-wasting step that competes with the useful reactions of the ion pair. The present study was undertaken to investigate the parameters controlling the rates of these return electron transfer reactions. Quantum yields of free radical ion formation were measured for ion pairs formed upon electron-transfer quenching of the first excited singlet states of cyanoanthracenes by simple aromatic hydrocarbon donors in aceonitrile at room temperature. The free-ion yields are determined by the competition between the rates of separation and return electron transfer.

Gould, I.R.; Ege, D.; Moser, J.E.; Farid, S. (Eastman Kodak Company, Rochester, NY (USA))

1990-05-23

351

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

DEFF Research Database (Denmark)

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.

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

2013-01-01

352

Charge-transfer interactions in 1-cyanonaphthalene van der Waals complexes with aliphatic amines: Dependence of excited-state dynamics on donor ionization potential  

Energy Technology Data Exchange (ETDEWEB)

The exciplex formation reaction that occurs within the initially excited van der Waals complexes of 1-cyanonaphthalene with a variety of aliphatic amines has been studied as a function of the ionization potential (IP) of the amines and the excess vibrational energy of the electronically excited complexes. In all cases, the fluorescence excitation spectra are composed of only narrow-band features originating from local excitations of the acceptor chromophore. While complexes involving amines of high IP are inefficient in producing exciplexes, those with amines of low IP give rise to exciplex fluorescence from the charge-transfer state. The tributylamine complex, unlike the others, undergoes the exciplex formation upon excitation into its S{sub 1} origin. These results are interpreted in terms of the crossing of the initially excited van der Waals state and the charge-transfer state.

Saigusa, Hiroyuki; Lim, E.C. (Univ. of Akron, OH (United States))

1991-10-03

353

Electronic excited states at ultrathin dielectric-metal interfaces  

Science.gov (United States)

Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ultrathin (1–2 monolayers) LiF epitaxial films, are investigated via many-body perturbation theory calculations achieving an atomistic level of detail. The full self-consistent solution of the GW equations is used to account for correlation effects and to properly describe the screened potential in the vacuum. In addition to the correct prediction of image-potential states, we find that the mixing between resonances and image states and the charge compression due to the dielectric ultrathin overlayer give rise to excitations with a hybrid localized but low-lying character whose accurate description cannot intrinsically be achieved via simple models or low-level calculations, but which are expected to play a crucial role in determining the electronic response and transport properties of these systems.

Sementa, L.; Marini, A.; Barcaro, G.; Negreiros, F. R.; Fortunelli, A.

2013-09-01

354

Threshold electron excitation of Auger-electron and x-ray emissions in La  

International Nuclear Information System (INIS)

The intensities of the M5O3 and M5N3 characteristic x-ray lines and the M5N/sub 4,5/N/sub 4,5/ Auger-electron line from La were measured as functions of the electron excitation energy near the M5 ionization energy. The excitation curve of each of these emissions contains a linelike structure a few eV above the threshold. The full width at half maximum (3.0 +- 0.2 eV) and relative height (4 x ) of this structure are the same in these three excitation curves; however, they are different than the respective values (2.3 +- 0.2 eV and 200 x ) we previously measured for a resonant bremsstrahlung emission observed when the electron excitation energy was near the M5 ionization energy. These results support our earlier proposal that two distinct states are excited for near threshold, electron excitation of the La M5 level: the 3d94f 0 state which decays via the M5 series characteristic x-ray and Auger-electron emissions, and the 3d 94f 2 intermediate bound state which appears to decay by only a single channel: the emission of a resonant x ray with a photon energy of 832 +- 1 eV. These results may be evidence of a closed channel resonance in the electron scattering cross section in solid La, similar to resonances found in Ne gas.

1984-01-01

355

Nuclear, electronic, and frequency factors in electron-transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

The crux of the problem is the fact that the equilibrium configuration of a species changes when it loses an electron. Configuration changes of organometallic metal complexes involve the metal-ligand and intra-ligand bond lengths and angles as well as changes in vibrations and rotation of surrounding solvent dipoles. Discussion indicates that rate constants can be expressed as a product of a nuclear, an electronic, and a frequency factor. Good agreement with measured rate constants is obtained in the normal free-energy region. Understanding of electron transfer rates in highly exothermic regions remains uncertain. 75 references, 2 figures, 2 tables.

Sutin, N.

1982-09-01

356

Nuclear, electronic, and frequency factors in electron-transfer reactions  

International Nuclear Information System (INIS)

The crux of the problem is the fact that the equilibrium configuration of a species changes when it loses an electron. Configuration changes of organometallic metal complexes involve the metal-ligand and intra-ligand bond lengths and angles as well as changes in vibrations and rotation of surrounding solvent dipoles. Discussion indicates that rate constants can be expressed as a product of a nuclear, an electronic, and a frequency factor. Good agreement with measured rate constants is obtained in the normal free-energy region. Understanding of electron transfer rates in highly exothermic regions remains uncertain. 75 references, 2 figures, 2 tables

1982-01-01

357

Search for excited electrons through $\\gamma\\gamma$ scattering  

CERN Multimedia

We study the potential of $\\gamma \\gamma$ option of future high energy linear $e^{+}e^{-}$ colliders to search for excited electrons with spin-1/2. We calculate single production cross sections, give the angular distributions and $f-m^*$ contour plots for $\\sqrt{s}=0.5$ TeV and $\\sqrt{s}=3$ TeV both using the standard (tree level) couplings and anomal couplings.

Ozansoy, A

2012-01-01

358

Raman scattering by electron-hole excitations in silver nanocrystals  

International Nuclear Information System (INIS)

Raman scattering experiments from silver nanocrystals embedded in films of amorphous silica are reported. In addition to the low-frequency peak due to vibrational quadrupolar modes, a broadband is observed in the high-frequency range, with a maximum at about 1000 cm-1. The linear dependence of the position of this maximum on the inverse cluster radius is in agreement with Raman scattering by single or collective electron-hole excitations

2001-06-15

359

Raman scattering by electron-hole excitations in silver nanocrystals  

CERN Multimedia

Raman scattering experiments from silver nanocrystals embedded in films of amorphous silica are reported. In addition to the low-frequency peak due to vibrational quadrupolar modes, a broadband is observed in the high-frequency range, with a maximum at about 1000 $cm^{-1}$. The linear dependence of the position of this maximum on the inverse cluster radius is in agreement with the Raman scattering by single or collective electron-hole excitations.

Portales, H; Saviot, L; Fujii, M; Sumitomo, M; Hayashi, S

2001-01-01

360

Raman scattering by electron-hole excitations in silver nanocrystals  

Energy Technology Data Exchange (ETDEWEB)

Raman scattering experiments from silver nanocrystals embedded in films of amorphous silica are reported. In addition to the low-frequency peak due to vibrational quadrupolar modes, a broadband is observed in the high-frequency range, with a maximum at about 1000 cm{sup {minus}1}. The linear dependence of the position of this maximum on the inverse cluster radius is in agreement with Raman scattering by single or collective electron-hole excitations.

Portales, H.; Duval, E.; Saviot, L.; Fujii, M.; Sumitomo, M.; Hayashi, S.

2001-06-15

 
 
 
 
361

Intense electron-beam excitation of organic dye vapors  

Energy Technology Data Exchange (ETDEWEB)

Experimental studies of electron-beam excitation of organic dye vapors of p-phenylene-bis-(5-phenyl-2-oxazole) POPOP and p-quaterphenyl have demonstrated short-duration high-gain and super-radiant laser behavior accompanied by severe fluorescence quenching due to dye fragmentation. This has been analyzed quantitatively by evaluation of the nitrogen fluorescence, originating from the complete breakdown of the POPOP structure.

Marowsky, G.; Tittel, F.K.; Wilson, W.L.

1981-01-01

362

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

DEFF Research Database (Denmark)

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.

Olsen, Thomas; Gavnholt, Jeppe

2009-01-01

363

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

CERN Multimedia

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.

Olsen, Thomas; Schiøtz, Jakob

2008-01-01

364

Electron transfer reactions in microporous solids  

Science.gov (United States)

The research program involves the use of microporous solids (zeolites, clays, layered, and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. The purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H2 and I3(-), or H2 and O2) from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

Mallouk, T. E.

1993-01-01

365

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.)

2006-01-01

366

Theory of nuclear excitation by electron capture for heavy ions  

Energy Technology Data Exchange (ETDEWEB)

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.)

Gagyi-Palffy, A.

2006-07-01

367

Electron and energy transfer in artificial photosynthesis supermolecules  

Science.gov (United States)

Photophysical properties of a variety of organic supermolecules were studied in order to elucidate structural and thermodynamic criteria pertinent to the design of artificial photosynthetic structures and molecular electronic devices. These supermolecules were designed using covalently linked porphyrins, carotenoids, C60 fullerenes, quinones, and aromatic imide chromophores. Time-resolved absorption and fluorescence spectroscopy on a femtosecond to millisecond time scale was used to investigate mechanisms of photoinduced electron transfer, singlet and triplet energy transfer, and radical pair dynamics. Several photophysical processes, previously found only in photosynthetic reaction centers, were observed and characterized for the first time in these artificial systems. Molecular dyads, triads, and a hexad were shown to form long-lived charge separated states with high quantum yields, thus efficiently converting electronic excited state energy into (electro) chemical energy. These systems demonstrate that favorable photophysical properties can be conveniently (and predictably) controlled by changes in the molecular structure and the physical characteristics of the medium, such as the solvent polarity or temperature. Molecules studied in this work could be utilized as components of functional supramolecular assemblies. C60 fullerenes were shown to be preferable electron acceptors in molecular structures intended to function in a non-polar media or at low temperatures. This was attributed to the low intramolecular and solvent reorganization energies for C60 fullerenes. The magnetic field dependence of charge recombination in linked organic biradicals was studied. This effect can be used as the basis for a magnetically controlled molecular optical or optoelectronic switch (AND gate).

Kuciauskas, Darius

1999-12-01

368

Nanosecond length electron pulses from a laser-excited photocathode  

Energy Technology Data Exchange (ETDEWEB)

A photocathode made from polycrystalline lanthanum hexaboride (LaB{sub 6}) has produced nanosecond length electron pulses when excited by an excimer laser at 308nm. Peak currents in excess of 1A have been observed, with quantum yields of 4 {times} 10{sup {minus}5} being measured. A method for extracting the electrons from an emission-limited cathode, plasma extraction, has been demonstrated. This technique uses a low power continuous discharge to provide the electric field needed to extract the photoelectrons. This technique may be useful in producing high repetition rate short pulse ion sources. 10 refs., 4 figs.

Young, A.T.; D' Etat, B.; Stutzin, G.C.; Leung, K.N.; Kunkel, W.B.

1989-06-01

369

Nanosecond length electron pulses from a laser-excited photocathode  

International Nuclear Information System (INIS)

[en] A photocathode made from polycrystalline lanthanum hexaboride (LaB6) has produced nanosecond length electron pulses when excited by an excimer laser at 308nm. Peak currents in excess of 1A have been observed, with quantum yields of 4 x 10-5 being measured. A method for extracting the electrons from an emission-limited cathode, plasma extraction, has been demonstrated. This technique uses a low power continuous discharge to provide the electric field needed to extract the photoelectrons. This technique may be useful in producing high repetition rate short pulse ion sources. 10 refs., 4 figs

1989-01-01

370

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

1998-01-01

371

Resonant excitation of plasma wakefields using multiple electron bunches.  

Energy Technology Data Exchange (ETDEWEB)

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.

Conde, M. E.

1998-09-25

372

Dissociative attachment of electrons to vibronically excited SO2  

International Nuclear Information System (INIS)

[en] Dissociative electron attachment (DEA) to vibronically excited SO2 in the Clements' band in the 288 to 298 nm region has been studied. The O- ion yield, to a first approximation, follows the photo absorption spectrum in this range indicating the DEA process to be independent of the vibrational levels in this band. This is in contrast to what is generally observed for vibrational level dependence from the electronic ground state. The current measurements also do not show any qualitative change in the dissociative attachment process due to change of symmetry as one moves from the peaks to the valleys of the Clements band

2004-01-01

373

Imidazole facilitates electron transfer from organic reductants.  

UK PubMed Central (United Kingdom)

In cyclic voltammetry studies at pH 8, imidazole facilitates oxidation of organic compounds that normally lose hydrogen atoms. High concentrations of imidazole shift the oxidizing wave of ascorbic acid, 2,3-dimethoxy-5-methyl-1,4-hydroquinone, and the vitamin E analogue Trolox toward lower potentials. By contrast, imidazole has no effect on the cyclic voltammogram of methyl viologen, which undergoes electron rather than hydrogen-atom transfer. The effect of imidazole is observed at pH 8.0 but only to a lesser extent at pH 5.5 indicating that imidazole must be unprotonated to facilitate oxidation. Digital simulation shows that these results are consistent with a mechanism in which imidazole acts as a proton acceptor permitting concerted proton/electron transfer by the organic reductant.

Kipp BH; Faraj C; Li G; Njus D

2004-08-01

374

Imidazole facilitates electron transfer from organic reductants.  

Science.gov (United States)

In cyclic voltammetry studies at pH 8, imidazole facilitates oxidation of organic compounds that normally lose hydrogen atoms. High concentrations of imidazole shift the oxidizing wave of ascorbic acid, 2,3-dimethoxy-5-methyl-1,4-hydroquinone, and the vitamin E analogue Trolox toward lower potentials. By contrast, imidazole has no effect on the cyclic voltammogram of methyl viologen, which undergoes electron rather than hydrogen-atom transfer. The effect of imidazole is observed at pH 8.0 but only to a lesser extent at pH 5.5 indicating that imidazole must be unprotonated to facilitate oxidation. Digital simulation shows that these results are consistent with a mechanism in which imidazole acts as a proton acceptor permitting concerted proton/electron transfer by the organic reductant. PMID:15219240

Kipp, Brian H; Faraj, Chadi; Li, Guoliang; Njus, David

2004-08-01

375

Highly selective excited state intramolecular proton transfer (ESIPT)-based superoxide probing.  

UK PubMed Central (United Kingdom)

Two novel fluorescent probe conjugates of 2-(benzothiazol-2-yl)-phenol (HBT) enable ratiometric and selective superoxide detection by an established excited state intramolecular proton transfer (ESIPT) mechanism giving a 60-fold intensity increase.

Murale DP; Kim H; Choi WS; Churchill DG

2013-08-01

376

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

1994-01-01

377

Resonant transfer excitation in collisions of F6+ and Mg9+ with H2  

International Nuclear Information System (INIS)

[en] Experimental and theoretical investigations of resonant transfer excitation (RTE) for F6++H2 and Mg9++H2 collisions have been made. For both collision systems good agreement is obtained between the measured cross sections for K-shell x-ray emission coincident with electron-capture and theoretical RTE calculations. For F6+ the present calculations are about 10% lower than previous results of Bhalla and Karim [Phys. Rev. A 39, 6060 (1989); 41, 4097(E) (1990)]; the measured cross sections are a factor of 2.3 larger than earlier measurements of Schulz et al. [Phys. Rev. A 38, 5454 (1988)]. The previous disagreement between experiment and theory for F6+ is removed

1991-10-01

378

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.

1984-01-01

379

Electronic excitations from a linear-response range-separated hybrid scheme  

CERN Document Server

We study linear-response time-dependent density-functional theory (DFT) based on the single-determinant range-separated hybrid (RSH) scheme, i.e. combining a long-range Hartree-Fock exchange kernel with a short-range DFT exchange-correlation kernel, for calculating electronic excitation energies of molecular systems. It is an alternative to the long-range correction (LC) scheme which has a standard full-range DFT correlation kernel instead of only a short-range one. We discuss the local-density approximation (LDA) to the short-range exchange-correlation kernel, and assess the performance of the linear-response RSH scheme for singlet-singlet and singlet-triplet valence and Rydberg excitations in the N2, CO, H2CO, C2H4, and C6H6 molecules, and for the first charge-transfer excitation in the C2H4-C2F4 dimer. The introduction of long-range HF exchange corrects the underestimation of charge-transfer and high-lying Rydberg excitation energies obtained with standard (semi)local density-functional approximations, but...

Rebolini, Elisa; Toulouse, Julien

2013-01-01

380

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  

Directory of Open Access Journals (Sweden)

Full Text Available 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 was 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.

João Batista Marques Novo; Lauro Camargo Dias Júnior

2011-01-01

 
 
 
 
381

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)

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 was 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 si (more) mulations and the expected theoretical results shows that it can be used for the luminescence and excited states decay kinetic teaching.

Novo, João Batista Marques; Dias Júnior, Lauro Camargo

2011-01-01

382

Influence of donor-donor transport on excitation energy transfer  

International Nuclear Information System (INIS)

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

1989-01-01

383

Integral cross sections for electron-impact ionization-excitation of laser-excited barium  

International Nuclear Information System (INIS)

We have measured electron-impact ionization-excitation (IE) cross sections for the Ba+ (...6p 2P) level out of the excited (...6s5d 1, 3D1, 2) and (...6s6p 1P1) levels of the neutral Ba atom in the energy range of 20-50 eV. Cross sections for IE out of the (...6s6p 1P1) level are approximately 50% larger than those from the (...6s2 1S0) ground state, while cross sections for IE out of the D levels are approximately 50% that of IE out of the ground state. The dependence of these cross sections on the initial P state alignment has been found to be small.

2010-09-28

384

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

Energy Technology Data Exchange (ETDEWEB)

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

Hou, H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1995-12-01

385

Electron transfer dissociation of peptide anions.  

Science.gov (United States)

Ion/ion reactions of multiply deprotonated peptide anions with xenon radical cations result in electron abstraction to generate charge-reduced peptide anions containing a free-radical site. Peptide backbone cleavage then occurs by hydrogen radical abstraction from a backbone amide N to facilitate cleavage of the adjacent C-C bond, thereby producing a- and x-type product ions. Introduction of free-radical sites to multiply charged peptides allows access to new fragmentation pathways that are otherwise too costly (e.g., lowers activation energies). Further, ion/ion chemistry, namely electron transfer reactions, presents a rapid and efficient means of generating odd-electron multiply charged peptides; these reactions can be used for studying gas-phase chemistries and for peptide sequence analysis. PMID:15907703

Coon, Joshua J; Shabanowitz, Jeffrey; Hunt, Donald F; Syka, John E P

2005-04-14

386

Electron transfer dissociation of peptide anions.  

UK PubMed Central (United Kingdom)

Ion/ion reactions of multiply deprotonated peptide anions with xenon radical cations result in electron abstraction to generate charge-reduced peptide anions containing a free-radical site. Peptide backbone cleavage then occurs by hydrogen radical abstraction from a backbone amide N to facilitate cleavage of the adjacent C-C bond, thereby producing a- and x-type product ions. Introduction of free-radical sites to multiply charged peptides allows access to new fragmentation pathways that are otherwise too costly (e.g., lowers activation energies). Further, ion/ion chemistry, namely electron transfer reactions, presents a rapid and efficient means of generating odd-electron multiply charged peptides; these reactions can be used for studying gas-phase chemistries and for peptide sequence analysis.

Coon JJ; Shabanowitz J; Hunt DF; Syka JE

2005-06-01

387

Electronic excitation of carbon monoxide by low-energy electron impact  

International Nuclear Information System (INIS)

Studies of the cross sections for electron-impact excitation of the valence states of carbon monoxide, i.e., the a 3?, 1?, a' 3?+, 3?-, d 3?, I 1?-, and D 1? states, have been carried out using the Schwinger multichannel variational method. Both differential and integral cross sections are obtained and compared with available experimental data. Reasonable agreement between the present results and experiment is seen for most of the states, and some differences are discussed. Estimates of the total cross section for electronic excitation of CO by low-energy electrons are provided.

1992-01-01

388

Contact and solvent-separated geminate radical ion pairs in electron-transfer photochemistry  

Energy Technology Data Exchange (ETDEWEB)

The two primary intermediates that play a major role in determining the efficiencies of bimolecular photoinduced electron-transfer reactions are the contact (A{sup {sm bullet}{minus}}D{sup {sm bullet}+}) and the solvent-separated (A{sup {sm bullet}{minus}}(S)D{sup {sm bullet}+}) radical ion pairs, CRIP and SSRIP, respectively. These two species are distinguished by differences in electronic coupling, which is much smaller for the SSRIP compared to the CRIP, and solvation, which is much larger for the SSRIP compared to the CRIP. The present work addresses the quantitative aspects of these and other factors that influence the rates of energy-wasting return electron transfer within the ion-pair intermediates. The electron acceptor tetracyanoanthracene (TCA) forms ground-state charge-transfer complexes with alkyl-substituted benzene donors. By a change of the excitation wavelength and/or donor concentration, either the free TCA or the CT complex can be excited. Quenching of free {sup 1}TCA{sup *} by the alkylbenzene donors that have low oxidation potentials, such as pentamethylbenzene and hexamethylbenzene, in acetonitrile solution leads to the direct formation of geminate SSRIP. Excitation of the corresponding charge-transfer complexes leads to the formation of geminate CRIP. Rates of return electron transfer within the two types of ion pair are determined from quantum yields for formation of free radical ions pairs depend upon the reaction exothermicity in a manner consistent with the Marcus inverted region.

Gould, I.R.; Young, R.H.; Moody, R.E.; Farid, S. (Eastman Kodak Company, Rochester, NY (USA))

1991-03-07

389

Theoretical study of photoinduced electron transfer from tetramethylethylene to tetracyanoethylene  

Science.gov (United States)

Using ab initio and density functional calculations, we studied photoexcitation of a charge-balanced electron donor-acceptor (DA) complex comprised of tetracyanoethylene (TCE) and tetramethylethylene (TME). We considered both the TCE-TME stacked conformer and a possible conformer with a solvent molecule (dichloromethane) inserted between TCE and TME. The photoexcitation of the DA complex can directly form a charge transfer (CT) state. Our theoretical investigations show that the CT state can also be produced from the decay of higher excited states. Using the continuum model, we investigated the solvent effects on CT absorption, local excitation, and CT emission in the polar solvent. The equilibrium solvation energies of the ground and excited states of the DA complex were calculated using the self-consistent reaction field method, and then the correction of nonequilibrium solvation energies for the vertical transitions was made. The transition energies (i.e., CT absorption for the DA complexes and CT emission for the contact ion pair complexes) in the polar solvent show redshifts relative to those in the gas phase.

Yi, Hai-Bo; Duan, Xiao-Hui; Lee, Jin Yong; Lee, Han Myoung; Li, Xiang-Yuan; Kim, Kwang S.

2003-11-01

390

Near-threshold electron-impact excitation of xenon  

Science.gov (United States)

Near-threshold electron-impact excitation is often dominated by contributions from one or just a few partial-wave symmetries. Consequently, negative-ion resonances may become the prominent features. Following up on previous R-matrix (close-coupling) calculations for the angle-integrated excitation cross sections and the Stokes parameters of the light emitted from the np^5(n+1)s states in noble gases [1,2], we have performed new calculations for e--Xe collisions [3]. We extend the discussion from angle-integrated to angle-differential cross sections and investigate the effect of near-threshold resonance structures for selected scattering angles. The results will be compared with the available experimental data. [1] V. Zeman and K. Bartschat (1997), J. Phys. B 30, 4609. [2] V. Zeman et al. (1998), Phys. Rev. A 58, 1275. [3] A.N. Grum-Grzhimailo and K. Bartschat (2002), submitted to J. Phys. B.

Grum-Grzhimailo, A. N.; Bartschat, K.

2002-10-01

391

Electron-impact excitation for F-like selenium  

Energy Technology Data Exchange (ETDEWEB)

Electron-impact excitation cross sections from the low-lying 1s{sup 2}2s{sup 2}2p{sup 5} 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 GRASP{sup 2} 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} {ital 1997} {ital The American Physical Society}

Guo-xin, C.; Yu-bo, Q. [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009-57, Beijing 100088 (China)

1997-11-01

392

Substituent effects on twisted internal charge transfer excited states of N-borylated carbazoles and (diphenylamino)boranes.  

UK PubMed Central (United Kingdom)

N-Boryl-substituted carbazoles (carBR(2)) and (diphenylamino)boranes (Ph(2)NBR(2)) with R = Mes (mesityl) and FMes [tris(trifluoromethyl)phenyl] substituents on boron exhibit large UV/vis Stokes shifts. To investigate the substituent effect on the magnitude of the Stokes shifts, we studied the electronic structure and spectroscopic properties of carBR(2) and Ph(2)NBR(2) with R = H, Mes, and FMes using hybrid density functional theory (B3LYP) and time-dependent density functional theory (TD-B3LYP) for ground and low-lying excited states. The lowest lying excited state with a nonvanishing oscillator strength is a twisted internal charge transfer (TICT) (1)A state in the C(2) point group, owing to a single-electron excitation from the nitrogen lone pair to the unoccupied boron p(z) AO, Nlp ? Bp(z). Emission from these (1)A excited states are predicted to be much brighter than from the energetically close (1)B excited states that are not directly related to CT excitation from N to B, due to symmetry. An analysis of geometrical relaxations in the excited state and the state energies relative to the ground state energy of the equilibrium geometry reveals that (a) the carbazole skeleton induces a general red shift in UV/vis spectra, (b) bulky boryl substituents reduce the predicted Stokes shifts of TICT states, and (c) the presence of electron-withdrawing functional groups induces a further general red shift in UV/vis spectra but does not significantly alter Stokes shifts.

Wang J; Wang Y; Taniguchi T; Yamaguchi S; Irle S

2012-02-01

393

Light-induced electron transfer in a cryptochrome blue-light photoreceptor.  

Science.gov (United States)

Cryptochromes are flavoproteins implicated in multiple blue light-dependent signaling pathways regulating, for example, photomorphogenesis in plants or circadian clocks in animals. Using transient absorption spectroscopy, it is demonstrated that the primary light reactions in isolated Arabidopsis thaliana cryptochrome-1 involve intraprotein electron transfer from tryptophan and tyrosine residues to the excited flavin adenine dinucleotide cofactor. PMID:12730688

Giovani, Baldissera; Byrdin, Martin; Ahmad, Margaret; Brettel, Klaus

2003-06-01

394

Light-induced electron transfer in a cryptochrome blue-light photoreceptor.  

UK PubMed Central (United Kingdom)

Cryptochromes are flavoproteins implicated in multiple blue light-dependent signaling pathways regulating, for example, photomorphogenesis in plants or circadian clocks in animals. Using transient absorption spectroscopy, it is demonstrated that the primary light reactions in isolated Arabidopsis thaliana cryptochrome-1 involve intraprotein electron transfer from tryptophan and tyrosine residues to the excited flavin adenine dinucleotide cofactor.

Giovani B; Byrdin M; Ahmad M; Brettel K

2003-06-01

395

Enhanced energy transfer in respiratory-deficient endothelial cells probed by microscopic fluorescence excitation spectroscopy  

Science.gov (United States)

Mitochondrial malfunction may be concomitant with changes of the redox states of the coenzymes nicotinamide adenine dinucleotide (NAD+/NADH), as well as flavin.mononucleotide or dinucleotide. The intrinsic fluorescence of these coenzymes was therefore proposed to be a measure of malfunction. Since mitochondrial fluorescence is strongly superposed by autofluorescence from various cytoplasmatic fluorophores, cultivated endothelial cells were incubated with the mitochondrial marker rhodamine 123 (R123), and after excitation of flavin molecules, energy transfer to R123 was investigated. Due to spectral overlap of flavin and R123 fluorescence, energy transfer flavin yields R123 could not be detected from their emission spectra. Therefore, the method of microscopic fluorescence excitation spectroscopy was established. When detecting R123 fluorescence, excitation maxima at 370 - 390 nm and 420-460 nm were assigned to flavins, whereas a pronounced excitation band at 465 - 490 nm was attributed to R123. Therefore, excitation at 475 nm reflected the intracellular concentration of R123, whereas excitation at 385 nm reflected flavin excitation with a subsequent energy transfer to R123 molecules. An enhanced energy transfer after inhibition of specific enzyme complexes of the respiratory chain is discussed in the present article.

Schneckenburger, Herbert; Gschwend, Michael H.; Bauer, Manfred; Strauss, Wolfgang S.; Steiner, Rudolf W.

1996-12-01

396

Theoretical study on water-mediated excited-state multiple proton transfer in 7-azaindole: significance of hydrogen bond rearrangement.  

Science.gov (United States)

Excited-state multiple proton transfer (ESMPT) in the cluster of 7-azaindole with three water molecules [7-azaindole(H(2)O)(3)] is theoretically investigated by the TDDFT, CASPT2, and CC2 methods. Examination of the potential energy surface in the first excited state indicates that ESMPT in 7-azaindole(H(2)O)(3) proceeds initially with the rearrangement of hydrogen bond structure of water molecules from a bridged-planar isomer to a cyclic-nonplanar isomer, followed by triple proton transfer in the latter. This reaction is found to be energetically more favorable than quadruple proton transfer in the bridged-planar isomer without hydrogen bond reorganization. It is also shown that all proton-transfer processes follow a concerted mechanism rather than a stepwise mechanism. The computational results show good consistency with the unexpected experimental observations as to the electronic spectra and excited-state lifetime. In particular, the barrier of the hydrogen bond rearrangement is found to be less than 1 kcal/mol, consistent with the missing vibronic bands for 7-azaindole(H(2)O)(3) with an excess energy of more than 200 cm(-1) in the S(1) state. PMID:23043464

Yu, Xue-fang; Yamazaki, Shohei; Taketsugu, Tetsuya

2012-10-18

397

Theoretical study on water-mediated excited-state multiple proton transfer in 7-azaindole: significance of hydrogen bond rearrangement.  

UK PubMed Central (United Kingdom)

Excited-state multiple proton transfer (ESMPT) in the cluster of 7-azaindole with three water molecules [7-azaindole(H(2)O)(3)] is theoretically investigated by the TDDFT, CASPT2, and CC2 methods. Examination of the potential energy surface in the first excited state indicates that ESMPT in 7-azaindole(H(2)O)(3) proceeds initially with the rearrangement of hydrogen bond structure of water molecules from a bridged-planar isomer to a cyclic-nonplanar isomer, followed by triple proton transfer in the latter. This reaction is found to be energetically more favorable than quadruple proton transfer in the bridged-planar isomer without hydrogen bond reorganization. It is also shown that all proton-transfer processes follow a concerted mechanism rather than a stepwise mechanism. The computational results show good consistency with the unexpected experimental observations as to the electronic spectra and excited-state lifetime. In particular, the barrier of the hydrogen bond rearrangement is found to be less than 1 kcal/mol, consistent with the missing vibronic bands for 7-azaindole(H(2)O)(3) with an excess energy of more than 200 cm(-1) in the S(1) state.

Yu XF; Yamazaki S; Taketsugu T

2012-11-01

398

Computer simulation of electronic excitation in atomic collision cascades  

Energy Technology Data Exchange (ETDEWEB)

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.)

Duvenbeck, A.

2007-04-05

399

Theoretical study of excitation-energy transfer in a diarylethyne-linked porphyrin array  

International Nuclear Information System (INIS)

Carrying out quantum chemical calculations, we examined the excitation-energy transfer (EET) in a diphenylethyne-linked porphyrin array. The calculations showed that this transfer is caused by nonadiabatic interaction induced by the rotation around the porphyrin-diphenylethyne bond. This result is consistent with our theory that regards, in contrast to Foerster's theory, the EET as a nonadiabatic transition.

2003-08-22

400

Theoretical study of excitation-energy transfer in a diarylethyne-linked porphyrin array  

Energy Technology Data Exchange (ETDEWEB)

Carrying out quantum chemical calculations, we examined the excitation-energy transfer (EET) in a diphenylethyne-linked porphyrin array. The calculations showed that this transfer is caused by nonadiabatic interaction induced by the rotation around the porphyrin-diphenylethyne bond. This result is consistent with our theory that regards, in contrast to Foerster's theory, the EET as a nonadiabatic transition.

Okuno, Yoshishige; Mashiko, Shinro

2003-08-22

 
 
 
 
401

Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation II: non-Maxwellian electron distributions  

CERN Multimedia

In solar EUV spectra the He I and He II resonance lines show unusual behaviour and have anomalously high intensities compared with other transition region lines. The formation of the helium resonance lines is investigated through extensive non-LTE radiative transfer calculations. The model atmospheres of Vernazza, Avrett & Loeser are found to provide reasonable matches to the helium resonance line intensities but significantly over-estimate the intensities of other transition region lines. New model atmospheres have been developed from emission measure distributions derived by Macpherson & Jordan, which are consistent with SOHO observations of transition region lines other than those of helium. These models fail to reproduce the observed helium resonance line intensities by significant factors. The possibility that non-Maxwellian electron distributions in the transition region might lead to increased collisional excitation rates in the helium lines is studied. Collisional excitation and ionization rat...

Smith, G R

2003-01-01

402

Compilation of electron collision excitation cross sections for neutral argon  

International Nuclear Information System (INIS)

[en] 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 3p5 ns (n=4to 12), np(n=4to8) and nd(n=3to8)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 3p5 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) 35 refs

1993-01-01

403

Effect of Electronic Excitation on Thin Film Growth  

Energy Technology Data Exchange (ETDEWEB)

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.

Elsayed-Ali, Hani E. [Old Dominion University

2011-01-31

404

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).

1993-01-01

405

Variable electron transfer pathways in an amphibian cryptochrome: tryptophan versus tyrosine-based radical pairs.  

Science.gov (United States)

Electron transfer reactions play vital roles in many biological processes. Very often the transfer of charge(s) proceeds stepwise over large distances involving several amino acid residues. By using time-resolved electron paramagnetic resonance and optical spectroscopy, we have studied the mechanism of light-induced reduction of the FAD cofactor of cryptochrome/photolyase family proteins. In this study, we demonstrate that electron abstraction from a nearby amino acid by the excited FAD triggers further electron transfer steps even if the conserved chain of three tryptophans, known to be an effective electron transfer pathway in these proteins, is blocked. Furthermore, we were able to characterize this secondary electron transfer pathway and identify the amino acid partner of the resulting flavin-amino acid radical pair as a tyrosine located at the protein surface. This alternative electron transfer pathway could explain why interrupting the conserved tryptophan triad does not necessarily alter photoreactions of cryptochromes in vivo. Taken together, our results demonstrate that light-induced electron transfer is a robust property of cryptochromes and more intricate than commonly anticipated. PMID:23430261

Biskup, Till; Paulus, Bernd; Okafuji, Asako; Hitomi, Kenichi; Getzoff, Elizabeth D; Weber, Stefan; Schleicher, Erik

2013-02-19

406

Subpicosecond time-resolved intramolecular electronic energy transfer in flexible bichromophoric Coumarin molecules  

Energy Technology Data Exchange (ETDEWEB)

By excite-and-probe spectroscopy with subpicosecond time resolution, the authors have measured the intramolecular electronic energy transfer in bichromophoric coumarins linked by a flexible polymethylene chain. The transfer proceeds on a time scale between 1 and 20 ps depending on the polymethylene chain length. The results can be well described by a dipole-dipole interaction model that takes into account the statistical distribution of intramolecular distances between the two chromophores.

Kaschke, M.; Ernsting, N.P. (Max-Planck-Institut fuer Biophysikalische Chemie, Goettingen (West Germany)); Valeur, B.; Bourson, J. (CNRS, Paris (France))

1990-07-26

407

Impact Excitation and Electron-Hole Multiplication in Graphene and Carbon Nanotubes.  

Science.gov (United States)

In semiconductor photovoltaics, photoconversion efficiency is governed by a simple competition: the incident photon energy is either transferred to the crystal lattice (heat) or transferred to electrons. In conventional materials, energy loss to the lattice is more efficient than energy transferred to electrons, thus limiting the power conversion efficiency. Quantum electronic systems, such as quantum dots, nanowires, and two-dimensional electronic membranes, promise to tip the balance in this competition by simultaneously limiting energy transfer to the lattice and enhancing energy transfer to electrons. By exploring the optical, thermal, and electronic properties of quantum materials, we may perhaps find an ideal optoelectronic material that provides low cost fabrication, facile systems integration, and a means to surpass the standard limit for photoconversion efficiency. Nanoscale carbon materials, such as graphene and carbon nanotubes, provide ideal experimental quantum systems in which to explore optoelectronic behavior for applications in solar energy harvesting. Within essentially the same material, researchers can achieve a broad spectrum of energetic configurations, from a gapless semimetal to a large band-gap semiconducting nanowire. Owing to their nanoscale dimensions, graphene and carbon nanotubes exhibit electronic and optical properties that reflect strong electron-electron interactions. Such strong interactions may lead to exotic low-energy electron transport behavior and high-energy electron scattering processes such as impact excitation and the inverse process of Auger recombination. High-energy processes, which become very important under photoexcitation, may be particularly efficient in nanoscale carbon materials due to the relativistic-like, charged particle band structure and sensitivity to the dielectric environment. In addition, due to the covalently bonded carbon framework that makes up these materials, electron-phonon coupling is very weak. In carbon nanomaterials, strong electron-electron interactions combined with weak electron-phonon interactions results in excellent optical, thermal and electronic properties, the exploration of which promises to reveal fundamentally new physical processes and deliver advanced nanotechnologies. In this Account, we review the results of novel optoelectronic experiments that explore the intrinsic photoresponse of carbon nanomaterials integrated into nanoscale devices. By fabricating gate voltage-controlled photodetectors composed of atomically thin sheets of graphene and individual carbon nanotubes, we are able to fully explore electron transport in these systems under optical illumination. We find that strong electron-electron interactions play a key role in the intrinsic photoresponse of both materials, as evidenced by hot carrier transport in graphene and highly efficient multiple electron-hole pair generation in nanotubes. In both of these quantum systems, photoexcitation leads to high-energy electron-hole pairs that relax energy predominantly into the electronic system, rather than heating the lattice. Due to highly efficient energy transfer from photons into electrons, graphene and carbon nanotubes may be ideal materials for solar energy harvesting devices with efficiencies that could exceed the Shockley-Queisser limit. PMID:23369453

Gabor, Nathaniel M

2013-01-31

408

Vibrational Excitation of Water by Low-Energy Electrons  

Science.gov (United States)

Experimental and calculated differential and integral cross-sections for electron-impact excitation of the unresolved stretching modes (100+001) and the bending mode (010) of water will be presented. The experimental DCSs are taken over an extensive range of incident energies (1eV to 100eV) and scattering angles (10 to 130 degrees) and are normalized to the recently measured elastic DCSs.ootnotetextKhakoo et al., Phys. Rev. A 78, 052710 (2008). The calculations are carried out in the adiabatic approximation using the Schwinger multichannel method. The present results are compared to previous theoretical and experimental results in the literature.

Khakoo, Murtadha A.; Muse, John H.; Winstead, Carl; McKoy, Vincent

2009-05-01

409

Relaxation of electron excitations in beryllium oxide. Auto localized excitons  

International Nuclear Information System (INIS)

[en] 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

1994-01-01

410

Nonideal fishbone instability excited by trapped energetic electrons  

Energy Technology Data Exchange (ETDEWEB)

It is shown that trapped energetic electrons can resonate with the collisionless m = 1 nonideal kink mode, therefore exciting the nonideal e-fishbone, which would often lead to a drop in soft x-ray emissivity and frequency chirping. The theory predictions agree well with the experimental observations of e-fishbone on HL-2A. It is also found that the effects of MHD energy of background plasma might be the reason for the observed phenomena: frequency chirping up and down, and V-font-style sweeping.

Liu, Y.; Tang, C. J. [College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China); Wang, Z. T.; Long, Y. X.; Dong, J. Q. [Southwestern Institute of Physics, Chengdu, Sichuan 610041 (China)

2013-03-15

411

Quenching of electronically excited UF6 by selected inorganics  

International Nuclear Information System (INIS)

[en] Rate constants at 250C have been evaluated for the quenching of electronically-excited UF6 by selected inorganic molecules. Values for the rate constants at 250C (units of 1011 l/mole s) for O2, N2, and Ar are 1.0, 0.025, and 0.0097, respectively, N2 and Ar quenching exhibit a saturation effect at high pressures and their rate constants were evaluated from low-pressure data where the quenching follows a linear Stern-Volmer relationship. (Auth.)

1978-03-15

412

Photoinduced electron transfer reactions in zeolite cages  

Energy Technology Data Exchange (ETDEWEB)

This report summarizes work in the two areas of zeolites and layered double hydroxides. Results of studies on structural aspects of Ru(bpy)[sub 3][sup 2+]-zeolite Y are summarized. Photoinduced electron transfer between entrapped Ru(bpy)[sub 3][sup 2+] and methylviologen (MV) in neighboring supercages was examined. Benzylviologen was also used. Since molecules larger than 13 [angstrom] cannot be accomodated in zeolite cages, the layered double metal hydroxides (LDH) LiAl[sub 2](OH)[sub 6][sup +]X[sup [minus

Dutta, P.K.

1992-01-01

413

Mixed Valent Sites in Biological Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

Many of the active sites involved in electron transfer (ET) in biology have more than one metal and are mixed valent in at least one redox state. These include Cu(A), and the polynuclear Fe-S clusters which vary in their extent of delocalization. In this tutorial review the relative contributions to delocalization are evaluated using S K-edge X-ray absorption, magnetic circular dichroism and other spectroscopic methods. The role of intra-site delocalization in ET is considered.

Solomon, E.I.; Xie, X.; Dey, A.

2009-05-26

414