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1

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

2

Electron transfer reactions between excited atoms and molecules  

International Nuclear Information System (INIS)

Electron transfer reactions have been extensively studied for atoms in ground state colliding with molecules. On the contrary, few experiments have been performed for atoms excited above the first resonance states and it has been supposed by some authors that above a given degree of excitation, electron transfer becomes negligeable. By using a simple Landau-Zener model and a LCAO calculation of the coupling matrix element between ionic and covalent states for excited atoms and molecules with small electron affinities, we conclude that there is no limit to the electron transfer, in agreement with the experimental observation of ion pair formation for Rydberg atoms colliding with given molecules such as SF6

1984-01-01

3

Long-distance electron transfer from a triplet excited state  

Science.gov (United States)

Electron transfer from the triplet excited state of N,N,N',N'-tetramethylphenylene diamine to phthalic anhydride has been monitored by phosphorescence emission decay. The kinetics of the transfer process were observed directly and the rate constant depends exponentially on the reacting distance, k(r) = 1 × 10 4 exp(-0.58 r) s -1. The electron transfer rate has been found to be invariant over the temperature interval 77-143 K.

Murtagh, James; Thomas, J. Kerry

4

Electron transfer reactions between excited atoms and molecules  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer reactions have been extensively studied for atoms in ground state colliding with molecules. On the contrary, few experiments have been performed for atoms excited above the first resonance states and it has been supposed by some authors that above a given degree of excitation, electron transfer becomes negligeable. By using a simple Landau-Zener model and a LCAO calculation of the coupling matrix element between ionic and covalent states for excited atoms and molecules with small electron affinities, we conclude that there is no limit to the electron transfer, in agreement with the experimental observation of ion pair formation for Rydberg atoms colliding with given molecules such as SF/sub 6/.

Astruc, J.P.; Barbe, R.; Schermann, J.P. (Laboratoire de Physique des Lasers, 93 - Villetaneuse (France))

1984-01-01

5

Electronic structure charge transfer excitations, and high temperature superconductivity  

International Nuclear Information System (INIS)

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

1988-01-01

6

Electronic Structure, Charge Transfer Excitations and High Temperature Superconductivity.  

Science.gov (United States)

High precision local density electronic band structure results (for YBa sub 2 Cu sub 3 O sub 7 , YBa sub 2 Cu sub 3 O sub 6 and GdBa sub 2 Cu sub 3 O sub 7 ) lead to the possibly important role of charge transfer excitations as the mechanism of high T/sub...

A. J. Freeman J. Yu S. Massidda D. D. Koelling

1987-01-01

7

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

Energy Technology Data Exchange (ETDEWEB)

Fundamental processes of electron transfer, ionization, and excitation in ion-atom and ion-ion collisions are studied. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-ion core can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. At intermediate collision energies (e.g., proton energies for p-He{sup +} collisions on the order of 100 kilo-electron volts), many electronic states are strongly coupled during the collision, a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. At higher collision energies (million electron-volt energies) the coupling is weaker with, however, many more states being coupled together, so that high-order perturbation theory is essential.

1992-12-31

8

[Electron transfer, ionization, and excitation in atomic collisions  

International Nuclear Information System (INIS)

Fundamental processes of electron transfer, ionization, and excitation in ion-atom and ion-ion collisions are studied. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-ion core can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. At intermediate collision energies (e.g., proton energies for p-He"+ collisions on the order of 100 kilo-electron volts), many electronic states are strongly coupled during the collision, a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. At higher collision energies (million electron-volt energies) the coupling is weaker with, however, many more states being coupled together, so that high-order perturbation theory is essential

1992-01-01

9

Ultrafast spectroscopy of electron transfer dynamics in liquids; excitation transfer studies of phase transitions  

Science.gov (United States)

The transfer of an electron from a donor to an acceptor is the fundamental step in a wide range of chemical and biological processes. As a result, electron-transfer reactions have been the focus of numerous theoretical and experimental efforts aimed at understanding the kinetics and mechanism of the transfer event. Liquid solvents are an important medium for electron-transfer processes. The influences of the distance dependence, diffusion, the radial distribution function, and the hydrodynamic effect have been incorporated into the theory of electron transfer in solution, as well as into the theory of electron transfer between donors and acceptors in the head group regions of micelles. The development of new laser system with a pulse duration of tens of femtoseconds, with tunable wavelength allowed us to study these processes on a considerably shorter time scale than previous studies. This allowed us to observe not only the diffusion controlled but also the kinetics of electron transfer for donor/acceptor pairs that are in close proximity. In one set of experiments we have studied the kinetics of electron transfer in electron accepting molecule (rhodamine 3B) dissolved in electron donating solvent (N,N-dimethylaniline). The data for the forward electron transfer and geminate recombination are approximated by the statistical theory of the electron transfer. Optical anisotropy observed in the experiment demonstrates the orientation dependence of the electron transfer rate. In further experiments we investigated the electron transfer in non-hydrogen bonding liquids of increasing viscosity. The effective value of the donor/acceptor electronic coupling was found to decrease with viscosity. Electron transfer experiments were also carried out on the surface of micelles. The systems studied are the hole donor octadecyl-rhodamine B (ODRB) and the hole acceptor N,N-dimethyl-aniline (DMA) in micelles made of dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB). It was found that the effective coupling is reduced compared to donor/acceptor pairs dissolved in simple liquids. In the 2nd half of thesis we have addressed the question of the dynamics of phase transitions. We have demonstrated the ability to use the fluorescent excitation-transfer technique to study the demixing of liquids specifically, kinetics of demixing water and 2,6-dimethylpyridine. These two liquids possess a low critical temperature point, which allowed us to use a temperature jump from a laser pulse to initiate the process of phase separation. It was found that Coumarin480 laser dye and HPTS (8-Hydroxypyrene-1,3,6-trisulfonic acid) fluorescent dye have significantly different solubilities in the components of the mixture. These dyes undergo excitation transfer from Coumarin480 to HPTS in the uniform state, but not in the phase-separated state. A system with a temperature jump pump and an excitation transfer probe measured the time scale of the initial step of the phase separation.

Goun, Alexei A.

10

Electron transfer mechanism and photochemistry of ferrioxalate induced by excitation in the charge transfer band.  

Science.gov (United States)

The photoredox reaction of ferrioxalate after 266/267 nm excitation in the charge transfer band has been studied by means of ultrafast extended X-ray absorption fine structure (EXAFS) analysis, optical transient spectroscopy, and quantum chemistry calculations. The Fe-O bond length changes combined with the transient spectra and kinetics have been measured and in combination with ultrahigh frequency density functional theory (UHF/DFT) calculations are used to determine the photochemical mechanism for the Fe(III) to Fe(II) redox reaction. The present data and the results obtained with 266/267 nm excitations strongly suggest that the primary reaction is the dissociation of the Fe-O bond before intramolecular electron transfer occurs. Low quantum yield electron photodetachment from ferrioxalate has also been observed. PMID:18284192

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

2008-03-17

11

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

Directory of Open Access Journals (Sweden)

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

Brunger Michael

2009-01-01

12

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

DEFF Research Database (Denmark)

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

Bohr, Henrik; Malik, F. Bary

2013-01-01

13

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

Science.gov (United States)

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 efficiency 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, Boris M.

1984-01-01

14

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

Energy Technology Data Exchange (ETDEWEB)

Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

Hoffman, M.Z.

1992-07-31

15

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

Science.gov (United States)

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

Ito, Akitaka; Meyer, Thomas J

2012-10-28

16

Theoretical study on the electronic structure of triphenyl sulfonium salts: Electronic excitation and electron transfer processes  

Science.gov (United States)

Density functional theory (DFT) and Time Dependent DFT calculations on triphenyl sulfonium cation (TPS) and the salts of TPS with triflate, nonaflate, perfluoro-1-octanesulfonate and hexafluoro antimonate anions are presented. These systems are widely used as cationic photoinitiators and as electron ejection layer for polymer light-emitting diodes. While some differences exist in the electronic structure of the different salts, their lowest energy intense absorption maxima are calculated at nearly the same energy for all systems. The first excited state of TPS and of the TPS salts is dissociating. Electron addition to the TPS salts lowers their energy by 1.0-1.33 eV.

Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula; Lathiotakis, Nektarios N.; Georgiadou, Dimitra G.; Vasilopoulou, Maria; Argitis, Panagiotis

2014-05-01

17

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

Energy Technology Data Exchange (ETDEWEB)

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

Giribabu, Lingamallu, E-mail: giribabu@iict.res.in; Kandhadi, Jaipal; Kanaparthi, Ravi Kumar; Reeta, P. Silviya

2014-01-15

18

Sensitization of ultra-long-range excited-state electron transfer by energy transfer in a polymerized film  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, to Acr-An triplet energy transfer occurs followed by long-range, Acr-3An—Acr-An ? Acr-An—Acr-3An, energy migration. With methyl viologen dication (MV2+) added as a trap, Acr-3An + MV2+ ? Acr-An+ + MV+ electron...

Ito, Akitaka; Stewart, David J.; Fang, Zhen; Brennaman, M. Kyle; Meyer, Thomas J.

2012-01-01

19

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

Energy Technology Data Exchange (ETDEWEB)

During this period, conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used for the characterization of the intermediates that are involved in transition metal excited-state electron-transfer reactions. The intermediates of interest were the excited states of Ru(II) and Cr(III) photosensitizers, their reduced forms, and the species formed in the reactions of redox quenchers and electron-transfer agents. Of particular concern has been the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes.

Hoffman, M.Z.

1991-12-31

20

Electron-electron interactions in transfer and excitation in F/sup 8 +//r arrow/H/sub 2/ collisions  

Energy Technology Data Exchange (ETDEWEB)

We have measured projectile Auger electrons emitted after collisions ofH-like F with H/sub 2/. The cross sections for emission of /ital KLL/,/ital KLM/, /ital KLN/, and /ital KLO/ Auger electrons show maxima as a functionof the projectile energy. One maximum in the /ital KLL/ emission cross sectionis due to resonant transfer and excitation. A second maximum in the crosssection for /ital KLL/ emission as well as the maxima in the emission crosssection for the higher-/ital n/ Auger electrons are attributed to a new transferand excitation process. This involves excitation of a projectile electron byone target electron accompanied by the capture of a second target electron.

Schulz, M.; Giese, J. P.; Swenson, J. K.; Datz, S.; Dittner, P. F.; Krause, H. F.; Schone, H.; Vane, C. R.; Benhenni, M.; Shafroth, S. M.; and others

1989-04-10

 
 
 
 
21

[Electron transfer, ionization, and excitation in atomic collisions]. [Pennsylvania State Univ  

Energy Technology Data Exchange (ETDEWEB)

Fundamental processes of electron transfer, ionization, and excitation in ion-atom and ion-ion collisions are studied. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-ion core can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. At intermediate collision energies (e.g., proton energies for p-He[sup +] collisions on the order of 100 kilo-electron volts), many electronic states are strongly coupled during the collision, a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. At higher collision energies (million electron-volt energies) the coupling is weaker with, however, many more states being coupled together, so that high-order perturbation theory is essential.

1992-01-01

22

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

Science.gov (United States)

The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co-O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal-oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism. PMID:18832175

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

2008-10-01

23

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

Science.gov (United States)

The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co–O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal–oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism.

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

2008-01-01

24

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

International Nuclear Information System (INIS)

Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of the most photochemical solar energy conversion schemes. The authors research, which has utilized the techniques of continuous and pulsed photolysis and radiolysis, has focused on three general aspects of these reactions involving transition metal coordination complexes and electron donor-acceptor complexes: i) the effect of solution medium on the properties and quenching of the excited states; ii) the control of the quantum yields of formation of redox products; iii) the mechanism by which reduced species interact with water to yield H_2 homogeneously and heterogeneously. EDTA is among the most popular sacrificial electron donors used in model systems. Its role is to scavenge the oxidized form of the photosensitizer in order to prevent its rapid reaction with the reduced form of the electron relay species that results from the electron-transfer quenching of the excited photosensitizer. In systems involving MV"2"+, the radicals resulting from the oxidation of EDTA can eventually lead to the generation of a second equivalent of MV"+; the reducing agent is believed to be a radical localized on the carbon atom alpha to the carboxylate group. The reaction of radiolytically-generated OH/H with EDTA produces this radical directly via H-abstraction or indirectly via deprotonation of the carbon atom adjacent to the nitrogen radical site in the oxidized amine moiety; it reduces MV"2"+ with rate constants of 2.8 x 10"9, 7.6 x 10"9, and 8.5 x 10"6M"-"1s"-"1 at pH 12.5, 8.3, and 4.7, respectively. Degradative decarboxylation of EDTA-radicals and their back electron-transfer reactions are enhanced in acidic solution causing the yield of MV"+ to be severely diminished

1985-06-02

25

Resonant Transfer Excitation Followed by Auger-Electron Emission for Ne-like Ions  

International Nuclear Information System (INIS)

In ion-atom (I/A) collision, resonant transfer excitation followed by Auger emission (RTEA) is a complementary process to resonant transfer excitation followed by X-rays (RTEX). In both processes positive ions are assumed to collide with molecular H2-target or atomic He-targets. RTEA and RTEX are related to the resonance excitation (RE) and dielectronic recombination (DR) in electron-ion collisions. The cross sections of RTEA and RE are related under the validity of the conditions of impulse approximation, in which the ionic projectiles must move with very high velocity. RTEA are calculated for Ne-like ions with L-shell excitation. The database generated for Auger and radiative decay rates in LS coupling scheme. RTEA processes proceed through formation of resonance R states. These R-states have a general form 2p5n1 l 1n2 l 2 ; n1 = 3, 4 and n2 ? 4. It is found that RTEA cross sections exhibit a one-peak behavior with a peak value 1.6 x 10-18 cm2 when it collides with H2 as a target. This peak value decreases to 0.488x10-18 cm2 in case of Se24+

2005-03-17

26

Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the distance dependence of the rate of electronic excitation energy transfer from a dye molecule to a metal nanoparticle. Using the spherical jellium model, we evaluate the rates corresponding to the excitation of l = 1, 2, and 3 modes of the nanoparticle. Our calculation takes into account both the electron-hole pair and the plasmon excitations of the nanoparticle. The rate follows conventional R^-6 dependence at large distances while small deviations from this beh...

Swathi, R. S.; Sebastian, K. L.

2007-01-01

27

Excited states in electron-transfer reaction products: ultrafast relaxation dynamics of an isolated acceptor radical anion.  

Science.gov (United States)

The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the lower energy state relaxing within 200 fs and a near-threshold valence-excited state relaxing on a 60 fs time scale. These excited states, and in particular the valence-excited state, present efficient pathways for electron-transfer reactions in the highly exergonic inverted region which commonly displays rates exceeding predictions from electron-transfer theory. PMID:21682320

Horke, Daniel A; Roberts, Gareth M; Verlet, Jan R R

2011-08-01

28

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-08-01

29

Electronic structure, charge transfer excitations, and high-temperature superconducting oxides (invited)  

International Nuclear Information System (INIS)

We present high-precision results on the electronic band structure and properties of YBa2Cu3O/sub 7-//sub ?/, YB2Cu3O6, GdBa2Cu3O/sub 7-//sub ?/, and La/sub 2-//sub x/M/sub x/CuO4 as obtained from highly precise state-of-the-art local density calculations. The results obtained demonstrate the close relation of the band structure to the structural arrangements of the constituent atoms and provide an integrated chemical and physical picture of the interactions and their possible relation to superconductivity. The ionic character of the Y is proven by similar detailed highly precise local density calculations for high T/sub C/ GdBa2Cu3O7, and explains the coexistence of magnetism and superconductivity in the high T/sub C/ rare-earth superconductors. Surprising features are the low density of states (DOS) at E/sub F/, especially for ??0.1 which is lower per Cu atom than that in La/sub 2-//sub x/Sr/sub x/CuO4: in agreement with experiment and a relatively large magnetic Stoner factor. Strong indications are demonstrated for the inadequacy of a conventional phonon mechanism for obtaining the higher T/sub C/. Charge transfer excitations of occupied Cu1-O dp? antibonding orbitals into their empty Cu1-O dp? antibonding orbital partners, result in poorly screened ''Cu3+-Cu4+'' -like charge fluctuations. These charge transfer excitations (excitons) thus lead to strong polarization effects in these poorly screened (highly ionic) materials and induce attractive interactions among the 2D electrons

1988-04-15

30

Electronic structure, charge transfer excitations, and high-temperature superconducting oxides (invited)  

Energy Technology Data Exchange (ETDEWEB)

We present high-precision results on the electronic band structure and properties of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/, YB/sub 2/Cu/sub 3/O/sub 6/, GdBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/, and La/sub 2-//sub x/M/sub x/CuO/sub 4/ as obtained from highly precise state-of-the-art local density calculations. The results obtained demonstrate the close relation of the band structure to the structural arrangements of the constituent atoms and provide an integrated chemical and physical picture of the interactions and their possible relation to superconductivity. The ionic character of the Y is proven by similar detailed highly precise local density calculations for high T/sub C/ GdBa/sub 2/Cu/sub 3/O/sub 7/, and explains the coexistence of magnetism and superconductivity in the high T/sub C/ rare-earth superconductors. Surprising features are the low density of states (DOS) at E/sub F/, especially for deltagreater than or equal to0.1 which is lower per Cu atom than that in La/sub 2-//sub x/Sr/sub x/CuO/sub 4/: in agreement with experiment and a relatively large magnetic Stoner factor. Strong indications are demonstrated for the inadequacy of a conventional phonon mechanism for obtaining the higher T/sub C/. Charge transfer excitations of occupied Cu1-O dp..pi.. antibonding orbitals into their empty Cu1-O dpsigma antibonding orbital partners, result in poorly screened ''Cu/sup 3 +/-Cu/sup 4 +/'' -like charge fluctuations. These charge transfer excitations (excitons) thus lead to strong polarization effects in these poorly screened (highly ionic) materials and induce attractive interactions among the 2D electrons.

Freeman, A.J.; Yu, J.; Massidda, S.; Fu, C.L.; Xu, J.

1988-04-15

31

Increasing the efficiency of oxazine 17 lasing by transferring electron energy from excited molecules of rhodamine dyes  

Energy Technology Data Exchange (ETDEWEB)

The possibility of increasing the efficiency of oxazine 17 lasing by transferring the electron energy from molecules of Rhodamine dyes with coherent and lamp pumping is demonstrated. The optimum conditions for obtaining dual-band lasing are determined and the possibility of significantly broadening the spectral region of lasing is shown. The lifetimes of the excited donor molecules (Rhodamine 6zh) do not depend on the acceptor concentration (axazine 17), which reflects a radiactive mechanism of energy transfer. The energy transfer during the excitation of lasing also takes place by radiative means.

Reva, M.G.; Akimov, A.I.; Denisov, L.K.; Uzhinov, B.N.

1981-01-01

32

Quantum yield and electron-transfer reaction of the lowest excited state of uranyl ion  

International Nuclear Information System (INIS)

The pulsed photoreduction (using N2 laser photolysis technique) of uranyl ion, UO22+, both in its ground state and in the lowest excited state (at pH 2 and in 2 M H3PO4 aqueous solutions) has been studied. We found that *UO22+ is quenched by ruthenium tris (bipyridine) ions, Ru(bpy)32+, and Ru(bpy)33+ is formed; namely, *UO22+ is an electron-acceptor species. It is shown here that the rate of decay of *UO22+ in the presence of Ru(byp)32+ exactly corresponds to the formation rate of Ru(bpy)33+, as measured by the bleaching of the Ru(bpy)32+ ground-state absorption. The excited state of Ru(bpy)32+ is found to be quenched by UO22+, and again Ru(bpy)33 is formed, UO22+ being an electron acceptor in its ground state. The quantum yield of the formation of the lowest excited state of UO22+, multiplied by the yield of electron transfer, between *UO22 and Ru(bpy)32 is found to be 0.5 at pH 2 and unity in 2 M H3PO4 solution. In the presence of a negatively charged polyelectrolyte, such as poly(vinyl sulfate), PVS, the value of this product is reduced to an upper limit of 0.1. It is shown that the lowest excited state of UO22 is unaffected by the presence of PVS. The back reaction, UO2 + Ru(bpy)33 ? UO22 + Ru(bpy)32+, is a second-order reaction, k/epsilon wave length = 450 nm) = 1.05 x 105 s-1 cm at pH 2 and 1.78 x 102 s/sup -1/ cm in 2 M H3PO4 solution. This reaction is accelerated in the presence of O2 or PVS. The yields and rates of formations and reactions of the photochemical products are discussed

1980-10-30

33

The influence of the molecular charge on potential energy curves for the proton transfer in electronic ground and excited states  

Science.gov (United States)

The potential energy curves were studied for the proton transfer in the electronic ground and excited states for the model systems H3O2-, H4O2, and H5O2+. The complete active space self-consistent-field calculations were performed for the ground state optimized structures. The potential energy curves for the proton transfer in the excited states undergo a dramatic change due to the different electronic density distribution as an effect of electronic excitations. In all cases of the studied excited states, the electron population on the transferred proton is higher compared to that in the ground state. The total charge of the system greatly influences the potential curves. Energy separation between ground and excited states is decreased due to the negative charge of the system and is increased when the studied species are positively charged. The vertical excitations of the complex are similar to those in the monomers, but the proton relaxation leads to significant energetical (energy barriers) and structural (H+ position) changes.

Kowal, Marek; Roszak, Szczepan; Leszczynski, Jerzy

2001-05-01

34

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

Science.gov (United States)

Following earlier coupled-Sturmian calculations by ShakeshaftootnotetextR. Shakeshaft, Phys. Rev. A 14, 1626 (1976). on p-H collisions, the author reported Sturmian calculations on electron transfer in 20-200 keV ?-H collisions.ootnotetextT. G. Winter, Phys. Rev. A 25, 697 (1982). These calculations, carried out 24 years ago on Penn State's IBM 3033 mainframe computer, took 2-4 cpu hours per total cross section per ? energy. Now, using a very similar Fortran program, they have been repeated with the same 19- to 24-state bases and numerical parameters on a 3.32 GHz IBM ThinkPad in about 1/300th the cpu time, reproducing the transition probabilities at each impact parameter to at least five digits and the integrated capture cross sections to the full published three digits. The cross sections have also now been confirmed stable to three digits with respect to the choice of the numerical parameters. These calculations can now much more readily be extended to larger bases and a wider range of energies. Direct excitation and ionization will also be considered.

Winter, Thomas

2005-05-01

35

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

International Nuclear Information System (INIS)

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

2001-01-01

36

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

Science.gov (United States)

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. PMID:23494167

Zhang, Mingzhen; Yang, Dapeng; Ren, Baiping; Wang, Dandan

2013-07-01

37

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

International Nuclear Information System (INIS)

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

2003-10-01

38

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

Science.gov (United States)

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

Sobolewski, Andrzej L.; Domcke, Wolfgang

2003-10-01

39

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

International Nuclear Information System (INIS)

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

1994-06-01

40

Structural and photoluminescence properties of excited state intramolecular proton transfer capable compounds-potential emissive and electron transport materials.  

Science.gov (United States)

Electronic factors influencing the photoluminescence properties and rates of excited state intramolecular proton transfer (ESIPT) reaction of o-hydroxy derivatives of 2,5-diphenyl-1,3,4-oxadiazole have been studied. The potential of these molecules as emissive and electron transport materials in designing improved organic light emitting diodes (OLEDs) has been studied by analyzing possible reasons for the unusually high Stokes shifts and ESIPT reaction rates. Time-dependent density functional theory (TDDFT) methods have been used to calculate the ground and excited state properties of the phototautomers that are the ESIPT reaction products. We study the relative effect of electron-withdrawing substituents on the proton-acceptor moiety and predict that the lowest ESIPT rate (1.9 x 10(11) s(-1)) is achieved with a dimethylamino substituent and that the Stokes shifts are around 11 000 cm(-1) for all three derivatives. PMID:16789783

Gaenko, Alexander V; Devarajan, Ajitha; Tselinskii, Igor V; Ryde, Ulf

2006-06-29

 
 
 
 
41

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

2013-07-01

42

Phase-sensitive detection in modulation excitation spectroscopy applied to potential induced electron transfer in cytochrome c oxidase.  

Science.gov (United States)

Cytochrome c oxidase (CcO) from Rhodobacter sphaeroides was investigated by modulated excitation surface-enhanced infrared-absorption spectroscopy (SEIRAS). Sequential electron transfer (ET) within CcO was initiated by electrochemical excitation. During modulated excitation by periodic potential pulses with frequencies between 20 and 500 Hz, time-resolved infrared spectra were measured by the step-scan technique, with time resolution in the millisecond range. Conformational changes of the protein structure as a result of ET lead to rather complex SEIRA spectra with many overlapping bands embedded in a broad background signal. Phase-sensitive detection (PSD) was used to separate single components within the broad band of overlapping structural bands in the amide I region. PSD is able to extract the periodic response of single components with the same frequency as the excitation from noise or from static background and therefore enhances the signal-to-noise ratio. Moreover, PSD enables validation of the fit model used for the deconvolution of overlapping bands by analyzing phase lags of single components acquired at different stimulation frequencies. Phase lags between the evaluated vibrational components and the modulated excitation increase with increasing excitation frequencies, an inherent prerequisite of this evaluation method. PMID:24405948

Schwaighofer, Andreas; Ferguson-Miller, Shelagh; Naumann, Renate L C; Knoll, Wolfgang; Nowak, Christoph

2014-01-01

43

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)_3"2"+; and reductive quenching of Ru(II) and Cr(III) complexes

1990-01-01

44

A new transferable method to calculate electronic excitations in adsorption on metal surfaces  

Energy Technology Data Exchange (ETDEWEB)

Non-adiabatic effects in adsorption on metal surfaces include the excitation of electrons and holes, which can be observed as chemicurrents. We present a new quantitative method on the basis of ground-state density-functional theory (DFT) to calculate these excitation probabilities. The method uses first-order time-dependent perturbation theory, which is implemented using the evaluation of matrix elements between Kohn-Sham states of the rate of change of the Kohn-Sham potential between subsequent static DFT calculations. We can access the excitation spectra directly. The method is applied to adsorption of atomic hydrogen isotopes on-top the Al(111) surface. Results can explain the experimental data for noble metal surfaces; in particular the observed isotope effect in H versus D adsorption is described. Moreover, the results are in quantitative agreement with computationally expensive calculations of the full dynamics within time-dependent DFT, with the notable exception of effects due to spin dynamics. The method presented is simple enough to be applied to a wide class of adsorbates and surfaces, while at the same time allowing us to extract system-specific information. It can be implemented with reasonable effort within existing DFT codes.

Timmer, Matthias; Kratzer, Peter [Fachbereich Physik - Theoretische Physik, Centre for Nanointegration (CeNIDE), Universitaet Duisburg-Essen, Lotharstr. 1, 47048 Duisburg (Germany)

2009-07-01

45

Visible-light-induced electron transfer between alternating stacked layers of tungstate and titanate mediated by excitation of intercalated dye molecules.  

Science.gov (United States)

Visible-light-induced electron transfer from a tungstate to a titanate layer was demonstrated to be mediated by excited rhodamine B (RhB) intercalated by ion exchange between the two layers. The distance of only 1 nm between the layers provides a large contact area that enables the efficient mediation of electron transfer by RhB. PMID:24276153

Kishimoto, Fuminao; Mochizuki, Dai; Kumagai, Kozue; Maitani, Masato M; Suzuki, Eiichi; Wada, Yuji

2014-01-21

46

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

Energy Technology Data Exchange (ETDEWEB)

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.

Vitukhnovskii, A. G., E-mail: alexei@sci.lebedev.ru; Vashchenko, A. A.; Lebedev, V. S. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Vasiliev, R. B. [Moscow State University (Department of Materials Science) (Russian Federation); Brunkov, P. N. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Bychkovskii, D. N. [Optogan-OLS (Russian Federation)

2013-07-15

47

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

2013-07-01

48

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

Energy Technology Data Exchange (ETDEWEB)

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

Hoffman, M.Z.

1997-12-31

49

Chemical Physics Electrons and Excitations  

CERN Document Server

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

Study of intermediates from transition metal excited-state electron-transfer reactions. [Annual] progress report, August 1, 1989--July 31, 1992  

Energy Technology Data Exchange (ETDEWEB)

Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

Hoffman, M.Z.

1992-07-31

51

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

Energy Technology Data Exchange (ETDEWEB)

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

Sobolewski, Andrzej L.; Domcke, Wolfgang

2003-10-01

52

Excited singlet (S1) state interactions of calixarenes with chloroalkanes: A combination of concerted and stepwise dissociative electron transfer mechanism  

Science.gov (United States)

Both steady-state and time-resolved studies in acetonitrile (ACN) solutions show that the excited singlet (S1) states of calixarenes (CX) undergo quenching by chloroalkanes (CA). It has been revealed by characterizing the Cl ions in the photolyzed CX-CA systems in ACN solutions that the quenching occurs due to dissociative electron transfer (DET) mechanism, whereby a C-Cl bond of the CAs undergoes dissociation on acceptance of an electron from excited CX. The bimolecular quenching constants (kq) in the present systems were correlated with the free energy changes for the concerted DET reactions based on a suitable DET theory. Such a correlation results in the recovery of an intramolecular reorganization energy, which is substantially lower to account for the C-Cl bond dissociation energy of the CAs. Comparing present results with those of an another donor-acceptor system (e.g., biphenyldiol-CA systems) where a concerted DET mechanism is applicable, it is inferred that in CX-CA systems both concerted and stepwise DET mechanisms operate simultaneously. It is proposed that the interaction of excited CXs with encaged CAs follows the stepwise mechanism whereas that with the out of cage CAs follows the concerted mechanism.

Mohanty, J.; Pal, H.; Nayak, S. K.; Chattopadhyay, S.; Sapre, A. V.

2002-12-01

53

Electron Excitation and Dissociation  

International Nuclear Information System (INIS)

There is a long standing controversy about the electronic excitation of nitrogen - with an unresolved disagreement between theory and experiment (and between different experiments) both for integral and differential cross sections for most of the energy range studied. The disagreement is both qualitative and quantitative and is attributable to the complexities of performing both the experiments and calculations. The main experimental difficulty lies in deconvoluting the contribution to the excitation cross section from each electronic state

2014-02-01

54

Quenching reactions of electronically excited atoms  

Energy Technology Data Exchange (ETDEWEB)

The two-body, thermal quenching reactions of electronically excited atoms are reviewed using excited states of Ar, Kr, and Xe atoms as examples. State-specific interstate relaxation and excitation-transfer reactions with atomic colliders are discussed first. These results then are used to discuss quenching reactions of excited-state atoms with diatomic and polyatomic molecules, the latter have large cross sections, and the reactions can proceed by excitation transfer and by reactive quenching. Excited states of molecules are not considered; however, a table of quenching rate constants is given for six excited-state molecules in an appendix.

Setser, D.W. [Kansas State Univ., Manhattan, KS (United States). Dept. of Chemistry

2001-07-01

55

Electron-electron interaction in strong central fields studied by resonant transfer and excitation with two-photon processes in U91+ - H2 collisions  

International Nuclear Information System (INIS)

We studied the angular distribution of the X-ray emission associated with KLL-RTE for H-like U91+ ions colliding with quasi-free electrons from an H2 target. In this resonant transfer and excitation process an intermediate doubly excited He-like U90+** with two electrons in the L-shell is produced by electron-electron interaction; this exotic state decays by the emission of two photons, a K?-hypersatellite and a K?-satellite X-ray. According to the different j values (1/2 and 3/2) for the L-shell electrons three different KLL-RTE resonance groups can be distinguished by the corresponding ion energies. At the three resonance energies and one off-resonance energy (116.6, 124.9, 133.1 and 102.0 MeV/u, respectively) X-ray spectra were taken simultaneously at seven different observation angles. The K?2 satellite lines (j=1/2-j=1/2 transitions) are isotropic, whereas the K?1 hypersatellite lines (3/2-1/2 transitions) for the second resonance display a pronounced anisotropy pointing to a strong alignment of the involved doubly excited states. Our data agree with full relativistic theory in its general features

2003-05-01

56

Electron-electron interaction in strong central fields studied by resonant transfer and excitation with two-photon processes in U 91+ - H 2 collisions  

Science.gov (United States)

We studied the angular distribution of the X-ray emission associated with KLL-RTE for H-like U 91+ ions colliding with quasi-free electrons from an H 2 target. In this resonant transfer and excitation process an intermediate doubly excited He-like U 90+** with two electrons in the L-shell is produced by electron-electron interaction; this exotic state decays by the emission of two photons, a K?-hypersatellite and a K?-satellite X-ray. According to the different j values (1/2 and 3/2) for the L-shell electrons three different KLL-RTE resonance groups can be distinguished by the corresponding ion energies. At the three resonance energies and one off-resonance energy (116.6, 124.9, 133.1 and 102.0 MeV/u, respectively) X-ray spectra were taken simultaneously at seven different observation angles. The K?2 satellite lines ( j=1/2- j=1/2 transitions) are isotropic, whereas the K?1 hypersatellite lines (3/2-1/2 transitions) for the second resonance display a pronounced anisotropy pointing to a strong alignment of the involved doubly excited states. Our data agree with full relativistic theory in its general features.

Ma, X.; Mokler, P. H.; Bednarz, G.; Bosch, F.; Gumberidze, A.; Kozhuharov, C.; Liesen, D.; Sierpowski, D.; Stachura, Z.; Stöhlker, Th.; Warczak, A.

2003-05-01

57

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 SciELO Brazil | Language: English 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 mak [...] e the connection between excitation energy transfers using quantum Fourier transform, where n is the number of qubits required for simulation of transfers and N is the number of chlorophylls in the antenna complexes.

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

58

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

International Nuclear Information System (INIS)

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

2013-01-01

59

Nonlocal thermodynamic equilibrium effects in strato- spheric HF by collisional energy transfer from electronically excited O sub 2 and implications for infrared remote sensing  

Energy Technology Data Exchange (ETDEWEB)

A possible nonlocal thermodynamic equilibrium (non-LTE) effect involving stratospheric HF arising from the direct photochemical excitation of vibrationally excited HF by collisional energy transfer from electronically excited O{sub 2} (O{sub 2}({sup 1}{Delta}), O{sub 2}({sup 1}{Sigma})) is presented. Although this non-LTE effect is smaller than one associated with the direct solar excitation of both HF({ital v} = 1) and HF({ital v} = 2), calculations show that inclusion of the mechanism proposed here into retrieval algorithms is necessary if correct daytime upper stratosphere HF profiles are to be inferred in future infrared thermal emission measurements. Accurate determinations of the state-to-state rate constants of the reactions involved in these excitation processes and of the quenching rates of vibrationally excited HF are needed if IR thermal emission techniques are to be accurately employed in the measurement of stratosphere HF.

Kaye, J.A. (NASA Goddard Space Flight Center, Atmospheric Chemistry Dynamics Branch, Greenbelt, Maryland 20771 (US))

1989-10-01

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

Study of intermediates from transition metal excited-state electron-transfer reactions. Progress report, August 1, 1989--December 31, 1991  

Energy Technology Data Exchange (ETDEWEB)

During this period, conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used for the characterization of the intermediates that are involved in transition metal excited-state electron-transfer reactions. The intermediates of interest were the excited states of Ru(II) and Cr(III) photosensitizers, their reduced forms, and the species formed in the reactions of redox quenchers and electron-transfer agents. Of particular concern has been the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes.

Hoffman, M.Z.

1991-12-31

62

Enhanced electronic excitation energy transfer between dye molecules incorporated in nano-scale media with apparent fractal dimensionality  

Science.gov (United States)

In the present study, we analyze the efficiency of Electronic Excitation Energy Transfer (EEET) between two dyes, an energy donor (D) and acceptor (A), concentrated in structurally heterogeneous media (surfactant micelles, liposomes, and porous SiO2 matrices). In all three cases, highly effective EEET in pairs of dyes has been found and cannot be explained by Standard Förster-type theory for homogeneous solutions. Two independent approaches based on the analysis of either the D relative quantum yield ( F_{{DA}} /F_{{D}} ) or the D fluorescence decay have been used to study the deviation of experimental results from the theoretical description of EEET process. The observed deviation is quantified by the apparent fractal distribution of molecules parameter d . We conclude that the highly effective EEET observed in the nano-scale media under study can be explained by both forced concentration of the hydrophobic dyes within nano-volumes and non-uniform cluster-like character of the distribution of D and A dye molecules within nano-volumes.

Yefimova, Svetlana L.; Rekalo, Andrey M.; Gnap, Bogdan A.; Viagin, Oleg G.; Sorokin, Alexander V.; Malyukin, Yuri V.

2014-04-01

63

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

Science.gov (United States)

We combine ultrafast electronic and vibrational spectroscopy and computational modeling to investigate the photoinduced excited-state intramolecular hydrogen-transfer dynamics in 1,8-dihydroxy-9,10-anthraquinone (DHAQ) in tetrachloroethene, acetonitrile, dimethyl sulfoxide, and methanol. We analyze the electronic excited states of DHAQ with various possible hydrogen-bonding schemes and provide a general description of the electronic excited-state dynamics based on a systematic analysis of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S1 state where DHAQ exhibits ESIHT dynamics. In this equilibration process, the excited-state population is distributed between the 9,10-quinone (S2) and 1,10-quinone (S1) states while undergoing vibrational energy redistribution, vibrational cooling, and solvation dynamics on the 0.1-50 ps time scale. Transient UV/vis pump-probe data in methanol also suggest additional relaxation dynamics on the subnanosecond time scale, which we tentatively ascribe to hydrogen bond dynamics of DHAQ with the protic solvent, affecting the equilibrium population dynamics within the S2 and S1 electronic excited states. Ultimately, the two excited singlet states decay with a solvent-dependent time constant ranging from 139 to 210 ps. The concomitant electronic ground-state recovery is, however, only partial because a large fraction of the population relaxes to the first triplet state. From the similarity of the time scales involved, we conjecture that the solvent plays a crucial role in breaking the intramolecular hydrogen bond of DHAQ during the S2/S1 relaxation to either the ground or triplet state. PMID:24684387

Mohammed, Omar F; Xiao, Dequan; Batista, Victor S; Nibbering, Erik T J

2014-05-01

64

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

Science.gov (United States)

The techniques of continuous photolysis and pulsed laser flash photolysis, continuous and pulse radiolysis, fast-scan cyclic voltammetry, and time-resolved fluorimetry have been used to examine intramolecular electron transfer within the solvent quenching...

M. Z. Hoffman

1997-01-01

65

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

CERN Document Server

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

66

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

International Nuclear Information System (INIS)

In our study of intermediates from excited-state electron-transfer reactions, we have focused our attention during the past year on MV"+., the reduced methyl viologen radical cation, which is a precursor to the formation of H_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"+. with colloidal Pt, the stability of MV"+. as a function of pH, the quantum yield of formation of MV"+. in the Ru(bpy)_3"2"+/MV"2"+/EDTA system, and the formation of photoactive charge-transfer complexes between MV"2"+ and sacrificial electron donors

1984-01-01

67

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

68

Absence of Quantum Oscillations and Dependence on Site Energies in Electronic Excitation Transfer in the Fenna–Matthews–Olson Trimer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Energy transfer in the photosynthetic Fenna–Matthews–Olson (FMO) complex of green sulfur bacteria is studied numerically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. The coupling to the non-Markovian environment is treated with a master equation derived from non-Markovian quantum state diffusion. When the excited-state dynamics is initialized at site eight, which is believed to play an important role...

Ritschel, Gerhard; Roden, Jan; Strunz, Walter T.; Aspuru-guzik, Ala?n; Eisfeld, Alexander Jurgen

2011-01-01

69

Comment on quantum yield and electron-transfer reaction of the lowest excited state of the uranyl ion  

International Nuclear Information System (INIS)

When experiments were conducted with aqueous solutions (pH_2) of uranyl nitrate and tris (1,10-phenanthroline) ruthenium (II) perchlorate using steady-state fluorescence quenching, quenching of *Ru(phen)_3"2"+ by UO_2"2"+ followed Stern-Volmer kinetics, with K/sub sv/ = (1.89 +- 0.20) x 10"2m"-"1. Using this and the known lifetime of *Ru(phen)_3"2"+ under these conditions (after correcting for quenching by dissolved oxygen), a rate constant of 1.2 x 10"9M"-"1s"-"1 was obtained for the quenching process. This is close to the rate of quenching of *Ru(phen)_3"2"+ by Fe"3"+ "2 is slightly higher than the rate of quenching of *Ru(bpy)_3"2"+ by UO_2"2"2 "1 and is consistent with the same mechanism as in these two cases, i.e., electron transfer. As observed with the Ru(bpy)_3"2"+/UO_2"2"+ system, prolonged photolysis did not result in any permanent change in the absorption spectrum of the system, demonstrating a high overall photostability. Because of the intense absorption of the Ru(phen)_3"2"+ species, the steady-state experiments do not permit demonstration of the reverse quenching of *UO_2"2"+ by Ru(phen)_3"2"+. However, studies on the fluorescence excitation spectra are consistent with the occurrence of such a process

1982-03-18

70

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

Science.gov (United States)

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

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

2011-07-01

71

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

International Nuclear Information System (INIS)

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

1988-01-01

72

Theoretical studies of the external vibrational control of electronic excitation transfer and its observation using polarization- and optical phase-sensitive ultrafast spectroscopy  

Science.gov (United States)

Our theoretical studies involve the control of electronic energy transfer in molecular dimers through the preparation of specific vibrational coherences prior to electronic excitation. Our control strategy is based upon the fact that, following impulsive electronic excitation, nuclear motion acts to change the instantaneous energy difference between site-excited electronic states and thereby influences short-time electronic excitation transfer (EET). By inducing coherent intramolecular vibration in one of the chromophores prior to short-pulse electronic excitation, we exert external control over electronic dynamics. As a means to monitor this coherent control over EET, we propose using multidimensional wave-packet interferometry (md-WPI). Two pairs of polarized phase-related femtosecond pulses following the control pulse would generate superpositions of coherent nuclear wave packets in optically accessible electronic states. Interference contributions to the time- and frequency-integrated fluorescence signal due to overlaps among the superposed wave packets provide amplitude-level information on the nuclear and electronic dynamics. We test both the control strategy and its spectroscopic investigation by calculating pump-probe difference signals for various combinations of pulse polarizations. That signal is the limiting case of the control-influenced md-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 a variety of systems including a simplified model of the covalent dimer dithia-anthracenophane (DTA) in which we treat only the weakly Franck-Condon active nu12 anthracene vibration at 385 cm-1. We further present calculated nl-WPI difference signals for an oriented DTA complex, which reveal amplitude-level dynamical information about the interaction of nuclear motion and electronic energy transfer. We also present pump-probe difference signals from a model system in which a CF3 group, whose torsional angle is strongly Franck-Condon active, has been added to the anthracene monomers which make up DTA. We make use of electronic structure calculations to find the torsional potential of the monomer, from which we calculate the spectroscopic signals of the dimer. We show that a significant measure of control over short-time EET is achievable in this system. This dissertation includes previously published coauthored material.

Biggs, Jason Daniel

73

Maximizing singlet fission in organic dimers: theoretical investigation of triplet yield in the regime of localized excitation and fast coherent electron transfer.  

Science.gov (United States)

In traditional solar cells one photon absorbed can lead to at most one electron of current. Singlet fission, a process in which one singlet exciton is converted to two triplet excitons, provides a potential improvement by producing two electrons from each photon of sufficient energy. The literature contains several reports of singlet fission in various systems, but the mechanism of this process is poorly understood. In this paper we examine a two-step mechanism with a charge transfer state intermediate, applicable when the initial excited state is localized. Density matrix theory is used to examine how various molecular properties such as orbital energies and electronic couplings affect singlet fission yield in the regime of fast, coherent electron transfer. Several promising chromophores are discussed and density functional theory is used to predict fission yield for each in the context of this mechanism. Finally, implications for chromophore design are discussed, and future experiments are suggested. PMID:20184354

Greyson, Eric C; Vura-Weis, Josh; Michl, Josef; Ratner, Mark A

2010-11-18

74

Solvent evaporation versus proton transfer in nucleobase-Pt(CN)4,6(2-) dianion clusters: a collisional excitation and electronic laser photodissociation spectroscopy study.  

Science.gov (United States)

Isolated molecular clusters of adenine, cytosine, thymine and uracil with Pt(CN)6(2-) and Pt(CN)4(2-) were studied for the first time to characterize the binding and reactivity of isolated transition metal complex ions with nucleobases. These clusters represent model systems for understanding metal complex-DNA adducts, as a function of individual nucleobases. Collisional excitation revealed that the clusters decay on the ground electronic surface by either solvent evaporation (i.e. loss of a nucleobase unit from the cluster) or via proton transfer from the nucleobase to the dianion. The Pt(CN)6(2-)-nucleobase clusters decay only by solvent evaporation, while the Pt(CN)4(2-) clusters fragment by both pathways. The enhanced proton-transfer reactivity of Pt(CN)4(2-) is attributed to the higher charge-density of the ligands in this transition metal anion. % fragmentation curves of the clusters reveal that the adenine clusters display distinctively higher fragmentation onsets, which are traced to the propensity of adenine to form the shortest intercluster H-bond. We also present laser electronic photodissociation measurements for the Pt(CN)6(2-)·Ur, Pt(CN)4(2-)·Ur and Pt(CN)4(2-)·Ur2 clusters to illustrate the potential of exploring metal complex DNA photophysics as a function of nucleobase within well-defined gaseous clusters. The spectra reported herein represent the first such measurements. We find that the electronic excited states decay with production of the same fragments (associated with solvent evaporation and proton transfer) observed upon collisional excitation of the electronic ground state, indicating ultrafast deactivation of the excited-state uracil-localized chromophore followed by vibrational predissociation. PMID:24949578

Sen, Ananya; Luxford, Thomas F M; Yoshikawa, Naruo; Dessent, Caroline E H

2014-07-01

75

Multistate CASPT2 study of native iron(III)-dependent catechol dioxygenase and its functional models: electronic structure and ligand-to-metal charge-transfer excitation.  

Science.gov (United States)

We theoretically investigated the ligand-to-metal charge-transfer (LMCT) excitation of the native iron(III)-dependent catechol dioxygenase and its functional model complexes with multistate complete active space second-order perturbation theory (MS-CASPT2) because the LMCT (catecholate-to-iron(III) charge-transfer) excitation energy is believed to relate to the reactivity of the native enzyme and its functional model complexes. The ground state calculated by the MS-CASPT2 method mainly consists of the iron(III)-catecholate electron configuration and moderately of the iron(II)-semiquinonate electron configuration for both of the enzyme active centers and the model complexes when the active center exists in the protein environment and the model complexes exist in the solution. However, the ground-state wave function mainly consists of the iron(II)-semiquinonate electron configuration for both the enzyme active site without a protein environment and the model complexes in vacuo. These results clearly show that the protein environment and solvent play important roles to determine the electronic structure of the catecholatoiron(III) complex. The LMCT excitation energy clearly relates to the weight of the iron(III)-catecholate configuration in the ground state. The reactivity and the LMCT excitation energy directly relate to the ionization potential of the catecholate (IP(CAT)) in the model complex. This is because the charge transfer from the catecholate moiety to the dioxygen molecule plays a key role to activate the dioxygen molecule. However, the reactivity of the native catechol dioxygenase is much larger than those of the model complexes, despite the similar IP(CAT) values, suggesting that other factors such as the coordinatively unsaturated iron(III) center of the native enzyme play a crucial role in the reactivity. PMID:21462943

Nakatani, Naoki; Hitomi, Yutaka; Sakaki, Shigeyoshi

2011-04-28

76

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

77

Does bimolecular charge recombination in highly exergonic electron transfer afford the triplet excited state or the ground state of a photosensitizer?  

Science.gov (United States)

The investigations were made on photoinduced electron transfer (ET) from the singlet excited state of rubrene (1RU*) to p-benzoquinone derivatives (duroquinone, 2,5-dimethyl-p-benzoquinone, p-benzoquinone, 2,5-dichloro-p-benzoquinone, and p-chloranil) in benzonitrile (PhCN) by using the steady state and time-resolved spectroscopies. The photoinduced ET produces solvent-separated type charge-separated (CS) species and the charge-recombination (CR) process between RU radical cation and semiquinone radical anions obeys second-order kinetics. Not only the CS species but also the triplet excited state of RU (3RU*) is seen in the transient absorption spectra upon laser excitation of a PhCN solution of RU and p-benzoquinone derivatives. The comparison of their time profiles clearly suggests that the CR process between RU radical cation and semiquinone radical anions to the ground state is independent from the deactivation of 3RU*. This indicates that the CR in a highly exergonic ET occurs at a longer distance with a large solvent reorganization energy, which results in faster ET to the ground state than to the triplet excited state that is lower in energy than the CS state. Photoinduced ET from 3RU* in addition from 1RU* also occurs when p-benzoquinone derivatives with electron-withdrawing substituents were employed as electron acceptors. PMID:18173251

Murakami, Motonobu; Ohkubo, Kei; Mandal, Paulami; Ganguly, Tapan; Fukuzumi, Shunichi

2008-01-31

78

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

CERN Multimedia

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

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

2003-01-01

79

Electron spin polarization transfer to the charge-separated state from locally excited triplet configuration: theory and its application to characterization of geometry and electronic coupling in the electron donor-acceptor system.  

Science.gov (United States)

We present a theoretical model of analysis of the time-resolved electron paramagnetic resonance (TREPR) spectrum of the charge-separated (CS) state generated by the photoinduced electron transfer (ET) reaction via the locally excited triplet state in an electron donor-acceptor (D-A) system with a fixed molecular orientation. We show, by the stochastic-Liouville equation, that chemically induced dynamic electron polarization (CIDEP) of the triplet mechanism is explained by lack of transfer of quantum coherence terms in the primary triplet spin state, resulting in net emissive or absorptive electron spin polarization (ESP) which is dependent on anisotropy of the singlet-triplet intersystem crossing in the precursor excited state. This disappearance of the coherence is clearly shown to occur when the photoinduced ET rate is smaller than the angular frequency of the Zeeman splitting: the transferred coherence terms are averaged to be zero due to effective quantum oscillations during the time that the chemical reaction proceeds. The above theory has been applied to elucidate the molecular geometries and spin-spin exchange interactions (2J) of the CS states for both folded and extended conformers by computer simulations of TREPR spectra of the zinc porphyrin-fullerene dyad (ZnP-C(60)) bridged by diphenyldisilane. On the extended conformation, the electronic coupling is estimated from the 2J value. It has been revealed that the coupling term is smaller than the reported electronic interactions of the porphyrin-C(60) systems bridged by diphenylamide spacers. The difference in the electronic couplings has been explained by the difference in the LUMO levels of the bridge moieties that mediate the superexchange coupling for the long-range ET reaction. PMID:20509645

Kobori, Yasuhiro; Fuki, Masaaki; Murai, Hisao

2010-11-18

80

Electron excitation rates for helium  

International Nuclear Information System (INIS)

Electron excitation cross-sections between 1"1s, 2"3s, 2"1s, 2"3p and 2"1p states of helium have been calculated recently using the R-matrix method. These cross-sections have been integrated over a Maxwellian distribution to give electron excitation rates. (author)

1982-01-01

 
 
 
 
81

Theoretical study of intermolecular energy transfer involving electronically excited molecules: He("1S) + H_2(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 + H_2(B "1?/sub u/"+) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H_2(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 + H_2(E,F "1?/sub g/"+) and with He + H_2(X "1?/sub g/"+) and cause a local maximum and a deep minimum in the He + H_2(B "1?/sub u/"+) PES, respectively. The crossing with He + H_2(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 H_2(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

82

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

83

Intramolecular electron transfer rates  

Science.gov (United States)

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

Hupp, Joseph T.

84

Electronically excited cold ion crystals  

CERN Document Server

The laser excitation of an ion crystal to high lying and long-lived electronic states is a genuine many-body process even if in fact only a single ion is excited. This is a direct manifestation of the strong coupling between internal and external dynamics and becomes most apparent in the vicinity of a structural phase transition. Here we show that utilizing highly excited states offers a new approach to the coherent manipulation of ion crystals. This permits the study of phenomena which rely on a strong coupling between electronic and vibrational dynamics and opens up a route towards the quantum simulation of molecular processes in a Paul trap.

Li, Weibin

2011-01-01

85

Optical excitations in electron microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This review discusses how low-energy valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resolution. Electron microscopes are capable of focusing electron beams on subnanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theoretical frameworks suited to calculate the probability of energy loss and light emission cathod...

Garci?a Abajo, F. Javier

2010-01-01

86

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

CERN Document Server

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

Theophilou, Iris; Thanos, S

2014-01-01

87

Electron impact excitation of K shell electrons  

Energy Technology Data Exchange (ETDEWEB)

Recently, Botero and Macek developed a new perturbation theory for electron atom scattering with arbitrary boundary conditions, resulting in a modified effective charge Coulomb-Born series, and applied it to the electron impact ionization of the K shell of light neutral atoms. We examine the utility of this approach in the case of electron impact excitation. We calculate the first term of this perturbation series (including exchange) and apply it to the excitation of K shell electrons to the L shell. We compare our results with data from scattering experiments on light elements.

Bergstrom, P.M. Jr.; Macek, J.H. [Univ. of Tennessee, Knoxville, TN (United States)]|[Oak Ridge National Laboratory, TN (United States)

1993-05-01

88

Electron impact excitation of K shell electrons  

International Nuclear Information System (INIS)

Recently, Botero and Macek developed a new perturbation theory for electron atom scattering with arbitrary boundary conditions, resulting in a modified effective charge Coulomb-Born series, and applied it to the electron impact ionization of the K shell of light neutral atoms. We examine the utility of this approach in the case of electron impact excitation. We calculate the first term of this perturbation series (including exchange) and apply it to the excitation of K shell electrons to the L shell. We compare our results with data from scattering experiments on light elements

1993-05-01

89

Electron transfer kinetics in purified reaction centers from the green sulfur bacterium Chlorobium tepidum studied by multiple-flash excitation.  

Science.gov (United States)

Reaction center preparations from the green sulfur bacterium Chlorobium tepidum, which contain monoheme cytochrome c, were studied by flash-absorption spectroscopy in the near-UV, visible, and near-infrared regions. The decay kinetics of the photooxidized primary donor P840(+), together with the amount of photooxidized cytochrome c, were analyzed along a series of four flashes spaced by 1 ms: 95% of the P840(+) was reduced by cytochrome c with a t(1/2) of approximately 65 micros after the first flash, 80% with a t(1/2) of approximately 100 micros after the second flash, and 23% with a t(1/2) of approximately 100 micros after the third flash; after the fourth flash, almost no cytochrome c oxidation occurred. The observed rates, the establishment of redox equilibrium after each flash, and the total amount of photooxidizable cytochrome c are consistent with the presence of two equivalent cytochrome c molecules per photooxidizable P840. The data are well fitted assuming a standard free energy change DeltaG degrees of -53 meV for electron transfer from one cytochrome c to P840(+), DeltaG degrees being independent of the oxidation state of the other cytochrome c. These observations support a model with two monoheme cytochromes c which are symmetrically arranged around the reaction center core. From the ratio of menaquinone-7 to the bacteriochlorophyll pigment absorbing at 663 nm, it was estimated that our preparations contain 0.6-1.2 menaquinone-7 molecules per reaction center. However, no transient signal due to menaquinone could be observed between 360 and 450 nm in the time window from 10 ns to 4 micros. No recombination reaction between the primary partners P840(+) and A(0)(-) could be detected under normal conditions. Such a recombination was observed (t(1/2) approximately 19 ns) under highly reducing conditions or after accumulation of three electrons on the acceptor side during a series of flashes, showing that the secondary acceptors can stabilize three electrons. From our data, there is no evidence for involvement of menaquinone in charge separation in the reaction center of green sulfur bacteria. PMID:10508417

Kusumoto, N; Sétif, P; Brettel, K; Seo, D; Sakurai, H

1999-09-14

90

Electron impact excitation of coronene  

Energy Technology Data Exchange (ETDEWEB)

A preliminary study of the electron-impact excitation of thermally evaporated coronene at 550{degree} C was carried out using electron-energy-loss spectroscopy. Measurements of the energy-loss spectra of coronene at high (100 eV) and low (5--20 eV) impact energies are presented. One of the high-energy spectra was converted to an apparent generalized oscillator strength spectrum and compared to the photoabsorption spectrum of coronene. Observations concerning vibrational excitation of coronene by electron impact are also presented and discussed.

Khakoo, M.A.; Ratliff, J.M.; Trajmar, S. (Jet Propulsion Laboratory, Pasadena, CA 91109 (USA))

1990-12-15

91

Electron impact excitation of coronene  

Science.gov (United States)

A preliminary study of the electron-impact excitation of thermally evaporated coronene at 550 C was carried out using electron-energy-loss spectroscopy. Measurements of the energy-loss spectra of coronene at high (100 eV) and low (5-20 eV) impact energies are presented. One of the high-energy spectra was converted to an apparent generalized oscillator strength spectrum and compared to the photoabsorption spectrum of coronene. Observations concerning vibrational excitation of coronene by electron impact are also presented and discussed.

Khakoo, M. A.; Ratliff, J. M.; Trajmar, S.

1990-01-01

92

Electron impact excitation of coronene  

International Nuclear Information System (INIS)

A preliminary study of the electron-impact excitation of thermally evaporated coronene at 550 degree C was carried out using electron-energy-loss spectroscopy. Measurements of the energy-loss spectra of coronene at high (100 eV) and low (5--20 eV) impact energies are presented. One of the high-energy spectra was converted to an apparent generalized oscillator strength spectrum and compared to the photoabsorption spectrum of coronene. Observations concerning vibrational excitation of coronene by electron impact are also presented and discussed

1990-12-15

93

Electron-transfer reaction from sodium benzenethiolate to acceptors assisted by photo-excited tris(2,2'-bipyridine)ruthenium(II)  

International Nuclear Information System (INIS)

The photo-excited tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+*) was effectively quenched by sodium benzenethiolate in acetonitrile (Stern-Volmer constant = 4860 dm3 mol-1). The flash photolysis of a solution containing Ru(bpy)32+ and benzenethiolate (excitation wavelength (lambda) > 480 nm) produced transient species absorbing ca. 510 nm; this species was identified as Ru(bpy)3+ and decayed with first-order kinetics with k = 3.0 s-1. This slow decay of Ru(bpy)3+ implies that the back-electron-transfer reaction was suppressed. The decay of Ru(bpy)3+ was accelerated by the addition of water, suggesting the possibility of the reaction between Ru(bpy)3+ and water, though no H2 was detected. The steady irradiation of a solution containing Ru(bpy)32+, benzenethiolate, and an electron-acceptor produced the radical anion of the added acceptor, which was detected with ESR spectroscopy. (author)

1981-01-01

94

Proton-Coupled Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

Proton-Coupled Electron Transfer (PCET) describes reactions in which there is a change in both electron and proton content between reactants and products. It originates from the influence of changes in electron content on acid?base properties and provides a molecular-level basis for energy transduction between proton transfer and electron transfer. Coupled electron?proton transfer or EPT is defined as an elementary step in which electrons and protons transfer from different orbitals on the donor to different orbitals on the acceptor. There is (usually) a clear distinction between EPT and H-atom transfer (HAT) or hydride transfer, in which the transferring electrons and proton come from the same bond. Hybrid mechanisms exist in which the elementary steps are different for the reaction partners. EPT pathways such as PhO•/PhOH exchange have much in common with HAT pathways in that electronic coupling is significant, comparable to the reorganization energy with H{sub DA} ~ ?. Multiple-Site Electron?Proton Transfer (MS-EPT) is an elementary step in which an electron?proton donor transfers electrons and protons to different acceptors, or an electron?proton acceptor accepts electrons and protons from different donors. It exploits the long-range nature of electron transfer while providing for the short-range nature of proton transfer. A variety of EPT pathways exist, creating a taxonomy based on what is transferred, e.g., 1e{sup -}/2H{sup +} MS-EPT. PCET achieves “redox potential leveling” between sequential couples and the buildup of multiple redox equivalents, which is of importance in multielectron catalysis. There are many examples of PCET and pH-dependent redox behavior in metal complexes, in organic and biological molecules, in excited states, and on surfaces. Changes in pH can be used to induce electron transfer through films and over long distances in molecules. Changes in pH, induced by local electron transfer, create pH gradients and a driving force for long-range proton transfer in Photosysem II and through other biological membranes. In EPT, simultaneous transfer of electrons and protons occurs on time scales short compared to the periods of coupled vibrations and solvent modes. A theory for EPT has been developed which rationalizes rate constants and activation barriers, includes temperature- and driving force (?G)-dependences implicitly, and explains kinetic isotope effects. The distance-dependence of EPT is dominated by the short-range nature of proton transfer, with electron transfer being far less demanding.Changes in external pH do not affect an EPT elementary step. Solvent molecules or buffer components can act as proton donor acceptors, but individual H2O molecules are neither good bases (pK{sub a}(H{sub 3}O{sup +}) = ?1.74) nor good acids (pK{sub a}(H{sub 2}O) = 15.7). There are many examples of mechanisms in chemistry, in biology, on surfaces, and in the gas phase which utilize EPT. PCET and EPT play critical roles in the oxygen evolving complex (OEC) of Photosystem II and other biological reactions by decreasing driving force and avoiding high-energy intermediates.

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

2012-01-01

95

Manifestations of sequential electron transfer  

Energy Technology Data Exchange (ETDEWEB)

An essential feature of efficient photo-initiated charge separation is sequential electron transfer. Charge separation is initiated by photoexcitation of an electron donor followed by rapid electron transfer steps from the excited donor through a series of electron acceptors, so that, after one or two successive steps, charge separation is stabilized by the physical separation between the oxidized donor and reduced acceptor. The prime example of this process is the sequential electron transfer that takes place in the purple photosynthetic bacterial reaction center, resulting in the charge separation between P{sup +} and Q{sub A}{sup -} across a biological membrane. We have developed magnetic resonance tools to monitor sequential electron transfer. We are applying these techniques to study charge separation in natural photo-synthetic systems in order to gain insights into the features of the reaction center proteins that promote efficient charge separation. As we establish what some of these factors are, we are beginning to design artificial photosynthetic systems that undergo photoinduced sequential electron transfer steps.

Thurnauer, M.C.; Tang, J.

1996-05-01

96

Electronic excitations and energy transfer in A2SiO5-Ce (A=Y, Lu, Gd) and Sc2SiO5 single crystals  

International Nuclear Information System (INIS)

The time-resolved emission spectra (2-6 eV), reflection and luminescence excitation spectra (4.5-35 eV) as well as the kinetics of luminescence have been studied for single crystals of silicates A2SiO5-Ce (A=Y, Gd, Lu) and Sc2SiO5 at 5.8 and 300 K using synchrotron radiation of X-ray (storage ring VEPP-3) or selective vacuum ultraviolet (storage ring DORIS) range. The spectral and decay parameters of the impurity and intrinsic luminescence are determined. The photon multiplication effect was found for all compounds for energy E>15 eV (E>2.5Eg). The role of electron-hole and exciton mechanisms of energy transfer in the silicates and their dependence on temperature are discussed

2001-09-01

97

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

International Nuclear Information System (INIS)

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

1986-01-01

98

Excited State Intramolecular Proton Transfer in Polymers.  

Science.gov (United States)

Excited state intramolecular proton transfer (ESIPT) has been demonstrated in new intramoleculary hydrogen bonded (IHB) polymers of interest as photostabilizers, triplet quenchers, photochromic materials, laser dyes and electroluminescent materials. The n...

R. M. Tarkka S. A. Jenekhe

1996-01-01

99

Electronically Excited Cold Ion Crystals  

Science.gov (United States)

The laser excitation of an ion crystal to high-lying and long-lived electronic states is a genuine many-body process even if in fact only a single ion is excited. This is a direct manifestation of the strong coupling between internal and external dynamics and becomes most apparent in the vicinity of a structural phase transition. Here we show that utilizing highly excited states offers a new approach to the coherent manipulation of ion crystals. This opens up a new route towards the creation of nonclassical motional states in a Paul trap and permits the study of quantum phenomena that rely on a strong coupling between electronic and vibrational dynamics.

Li, Weibin; Lesanovsky, Igor

2012-01-01

100

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

International Nuclear Information System (INIS)

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.)

1993-06-01

 
 
 
 
101

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

International Nuclear Information System (INIS)

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

1986-11-06

102

Excitation transfer in ion--Rydberg-atom collisions  

International Nuclear Information System (INIS)

Recently, electron-loss cross sections were presented by Kim and Meyer [Phys. Rev. Lett. 44, 1047 (1980)] for 40 keV/amu N"3"++H**(n) collisions which scaled as n/sup 3.12/, where n is the principal quantum number of the excited H"0. Such results are in contrast to an n"2 scaling predicted by classical and first Born theoretical methods. Our calculations indicate that a major component of the experimentally observed ion signal was due to Stark ionization by deflector grids of highly excited H"0 produced in excitation-transfer collisions. Inclusion of the excitation process in a theoretical interpretation reveals qualitative agreement between theory and experiment and stresses the importance of excitation transfer in ion--Rydberg-atom collisions

1981-01-01

103

Electron excitation of Ca XVII  

Energy Technology Data Exchange (ETDEWEB)

Calculations are made of the electron-excitation collision strengths for transitions between the ten lowest levels of Ca XVII. At high impact energies, where all the channels are open, the calculation is made in the LS-coupling approximation by means of the R-matrix method. Transitions between the fine structure levels are then determined by applying a unitary transformation to the LS-coupled K matrices. At low impact energies, where some of the channels may be closed, an extension of the R-matrix method is used to allow for relativistic effects directly in the scattering equations. The results are found to be generally in good agreement with recent distorted-wave calculations. Electron-excitation rates for a range of electron temperatures are presented. 25 references.

Dufton, P.L.; Kingston, A.E.; Scott, N.S.

1983-08-28

104

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

105

UV and 532 nm Photo-Dissociation of 2-Nitrotoluene: Observation of Electronically-Excited NO; Emission from Carbon (I); N2-NO Energy Transfer; and Stabilization of 2-Nitrotoluene-Ar Clusters  

Science.gov (United States)

2-nitrotoluene is a taggant used in explosive compounds and also often used as a simulant for nitro-based high explosives. Various spectroscopic techniques focus on the detection of vibrationally excited NO as an indicator for the presence of explosives. We report on the photo-dissociation of 2-nitrotoluene using UV and 532 nm wavelengths. We not only observe vibrationally excited NO in its electronic ground state, but also vibrationally excited NO in its electronic excited state. The photo-dissociation of 2-nitrotoluene leads to the formation of atomic carbon and its emission, overlapping the NO emission, is observed. Energy transfer from laser-excited nitrogen to NO leads to NO emission with long lifetimes. Argon atoms stabilize 2-nitrotoluene molecules and delay their photo-dissociation.

Diez-y-Riega, H.; Eilers, H.

2012-07-01

106

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

107

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

108

Electron-phonon coupling and charge-transfer excitations in organic systems from many-body perturbation theory  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We review in this article recent developments within the framework of ab initio many-body perturbation theory aiming at providing an accurate description of the electronic and excitonic properties of ?-conjugated organic systems currently used in organic photovoltaic cells. In particular, techniques such as the GW and Bethe-Salpeter formalisms are being benchmarked for acenes, fullerenes, porphyrins, phthalocyanines, and other molecules of interest for solar energy applications. It is shown ...

Faber, Carina; Duchemin, Ivan; Deutsch, Thierry; Attaccalite, Claudio; Olevano, Valerio; Blase, Xavier

2012-01-01

109

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

CERN Multimedia

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

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

2011-01-01

110

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

1989-07-04

111

The momentum transfer dependence of double excitations of helium  

International Nuclear Information System (INIS)

The momentum transfer dependence of fundamental double excitation processes of helium is studied with high resolution and fast electron impact. It elucidates the dynamical correlations, in terms of internal correlation quantum numbers, K, T and A. The Fano profile parameters q, f_a, ?"2, f and S of doubly excited states _2(1,0)_2"+"1"s"e, _2(0,1)_2"+"1"p"0 and _2(1,0)_2"+"1"D"e are determined as functions of momentum transfer K"2. (author)

2005-02-01

112

Experimental evidence of the target excitation in transfer ionization of He2+ on argon collisions  

Science.gov (United States)

We have investigated the dependence of electron capture to the continuum (ECC) on the longitudinal momentum of recoil ions in the transfer ionization of 120 and 300 keV He2+ on argon collisions. Compared with theoretical lines predicted by the kinematical relationship between longitudinal momentum of recoil ions and ECC electrons, it is shown that the electron is mainly transferred to the first excited state of He+ ions. The experimental data also show that the electron capture to the ground state of He+ is accompanied by target excitation, where the target excitation results from direct excitation in the transfer ionization processes.

Zhang, Ruitian; Ma, Xinwen; Zhang, Shaofeng; Zhu, Xiaolong; Chen, Ximeng

2013-09-01

113

Collision dynamic in transfer excitation processes revisited  

International Nuclear Information System (INIS)

We have measured the projectile scattering angle dependency for different final states for single electron capture in proton-helium collisions at an incident energy of 300 keV. With this fully differential data set we are able to get new insights in the dynamics of electron capture processes in combination with target or projectile excitation

2008-03-10

114

Collision dynamic in transfer excitation processes revisited  

Energy Technology Data Exchange (ETDEWEB)

We have measured the projectile scattering angle dependency for different final states for single electron capture in proton-helium collisions at an incident energy of 300 keV. With this fully differential data set we are able to get new insights in the dynamics of electron capture processes in combination with target or projectile excitation.

Schoeffler, Markus; Titze, Jasmin; Kim, Hong-Keun; Schmidt, Lothar; Jagutzki, Ottmar; Schmidt-Boecking, Horst; Doerner, Reinard [Johann Wolfgang Goethe-Universitaet, Frankfurt (Germany)

2008-07-01

115

Correlations of two excited electrons  

International Nuclear Information System (INIS)

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 ionisation 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. (author)

1983-01-01

116

Two-Electron Excitation of an Interacting Cold Rydberg Gas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 b...

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

2010-01-01

117

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

Science.gov (United States)

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

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

2010-06-01

118

Ultrafast electron transfer, recombination and spin dynamics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The quenching of excited singlet methylene blue (1MB+*) by N,N-dimethylaminomethylferrocene (FcN) in acetonitrile at room temperature has been studied using femtosecond pump-probe absorption spectroscopy. At high FcN concentration static quenching via an intermolecular electron transfer mechanism constitutes the predominating decay channel for 1MB+*. The time constants of the large amplitude components for the forward electron transfer from FcN donor to 1MB+* and the subsequent recombination ...

Gilch, Peter; Po?llinger-dammer, Florian; Steiner, Ulrich; Michel-beyerle, Maria Elisabeth

1997-01-01

119

Photophysical studies of chromium sensitizers designed for excited state hole transfer to semiconductors and sequential hole/electron transfers from photoexcited cadmium sulfide nanorods to mononuclear ruthenium water-oxidation catalysts  

Science.gov (United States)

This dissertation describes three research projects related to solar cells and solar water splitting with a goal of utilizing solar energy, a renewable energy source. The first project is focused on photophysical studies of four newly-synthesized Cr(III) tris-bipyridyl complexes featuring the 4-dmcbpy (dimethyl 2,2'-bipyridine-4,4'-dicarboxylate) ligand. Static and time-resolved emission results suggest that the complexes store ˜1.7 eV of energy for multiple microseconds. Using cyclic voltammetry, it is found that the inclusion of 4-dmcbpy shifts the E1/2 of CrIII/II by +0.2 V from the homoleptic parent complexes without 4-dmcbpy. All four complexes have excited state potentials of CrIII*/II between +1.8 and +2.0 V vs. NHE, placing them among the most powerful photooxidants reported and making them candidates for hole-injection sensitizers. The second project continues with Cr(III) complexes, but using iminopyridine Schiff base ligands. Two complexes feature hexadentate ligands and the other two are their tris-bidentate analogues. One of each pair contains methyl ester groups for attachment to semiconductors. Cyclic voltammograms show that the hexadentate and tris-bidentate analogues have almost identical reduction potentials, but the addition of ester substituents shifts the reduction potentials by +0.2 V. The absorption spectra of the hexadentate complexes show improved absorption of visible light compared to the tris-bidentate analogues. For freshly prepared sample solutions in CH3CN, time-resolved emission and transient absorption measurements for the Cr(III) tris-bidentate ester complex show a doublet excited state with a 17-19 microsecond lifetime at room temperature, while no emission or transient absorption signals from the doublet states are observed for the hexadentate analogue under the same conditions. The dramatic difference is due to the presence of a nonligated bridgehead nitrogen atom. The third project features charge transfer interactions between a photoexcited cadmium sulfide nanorod and [Ru(diethyl 2,2'-bipyridine-4,4'-dicarboxylate)(2,2':6',2"-terpyridine)Cl] +, a mononuclear water-oxidation catalyst. Upon photoexcitation, hole transfer from the cadmium sulfide nanorod oxidizes the catalyst (Ru 2+ ? Ru3+) on a 100 ps to 1 ns timescale. This is followed by electron transfer (10-100 ns) from the nanorod to reduce the Ru3+ center. The relatively slow electron transfer dynamics may provide opportunities for the accumulation of multiple holes at the catalyst, which is required for water oxidation.

Tseng, Huan-Wei

120

On the role of pigment-pigment and pigment-protein interaction in regulating excitation energy and electron transfer in photosynthesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The pathways of excitation energy transfer (EET) to photosynthetic reaction centres inside phycobiliprotein antenna system of Acaryochloris Marina (A. marina) were studied using time resolved absorption difference spectroscopy with a resolution time of 200 fs. The results revealed a new pathway of 14 ps inside the phycocyanin spectral band in addition to the previously known EET-equilibration pathway of all phycocyanins to allophycocyanin. This EET funnelling is faster than the previous kinet...

Nganou Assonkeng, Albert Collins

2012-01-01

 
 
 
 
121

Excitation transfer from porous silicon to polymer  

International Nuclear Information System (INIS)

The optical properties of porous silicon (PS) and poly[2-methoxy-5(2'-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) polymer composites were investigated. The experiment results showed that the luminescence intensity of the composites was enhanced and the PL peak position was found red shift. The pore structure of PS decreased the collision and increased conjugation of MEH-PPV molecules, which caused the enhanced luminescence of the composites. Also, the reaction between the surface states of PS and MEH-PPV molecules provided a route of non-radiation recombination that then transferred a part of excitation energy of PS to MEH-PPV. And the excitation transfer caused the enhanced luminescence and red shift

2005-08-15

122

L-shell resonant transfer and excitation for NE-like niobium ions  

International Nuclear Information System (INIS)

Projectile excitation and charge transfer (capture) can occur simultaneously in a single encounter with a target atom through the electron-electron interaction between a projectile electron and a weakly bound target electron. This process is referred to as resonant transfer and excitation (RTE). L-shell RTE has been investigated for 230 to 610 MeV Nb"3"1"+ (neonlike) ions incident on H_2. 11 refs., 1 fig

1986-09-17

123

Reactions of Electronically Excited Oxygen Molecules.  

Science.gov (United States)

A method of obtaining measurable concentrations of excited oxygen for kinetic studies has been developed, and a number of reactions of these excited molecules are described. Evidence is presented for simultaneous electronic transitions in a weakly bound c...

L. W. Bader E. A. Ogryzlo

1964-01-01

124

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

International Nuclear Information System (INIS)

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

2014-04-28

125

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

Science.gov (United States)

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

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

2014-04-01

126

Electron impact excitations of S2 molecules  

CERN Multimedia

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

Tashiro, Motomichi

2007-01-01

127

Electronic excitation in electron bombardment enhancement of chemical reactions  

International Nuclear Information System (INIS)

The role of electronic excitation in the electron bombardment enhancement of surface reactivity of graphite with hydrogen has been identified. The correlation between the electron and photon enhanced reactivities of a graphite surface is consistent with electrons exciting the 4.8-eV Pi-valence to Pi-conduction transition responsible for photoenhanced reactivity. An electron impact study has shown that low-energy electrons excite the same low-energy transitions observed in optical studies. Secondary electrons produced by electron bombardment are of appropriate energies to excite these transitions. Similar processes are expected to be operative in other chemical systems exhibiting photoenhanced reactivity

1983-09-15

128

Electron paramagnetic resonance of photocatalytic reaction which involve electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-10-13

129

Frontier orbital symmetry control of intermolecular electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Research continued on the study of intermolecular electron transfer. This report discusses the following topics: fluorescence quenching by electron transfer and the modification of quenching dynamics by solvent properties and net free energy change; transient absorption measurements following selective excitation of 1:1 EDA complex isomers; selective quenching of dual fluorescence from linked EDA systems; electron-transfer sensitized cycloreversion of rubrene endoperoxide; and vibronic modification of adiabatic requirements for intermolecular electron transfer. (CBS)

Stevens, B.

1990-11-01

130

Modifying excitation transfer cross sections with an ac Stark effect  

Energy Technology Data Exchange (ETDEWEB)

We show that it is possible to manipulate electronic energy transfer collision cross sections between different atomic species by using a strong electromagnetic field close to resonance with a transition between two excited states to modify the energy levels (i.e., to create dressed states), which may be placed in or out of resonance with populated states (forming a population reservoir) in one of the species. We outline an estimate for a transfer cross section for a demonstration scheme and show that cross-section enhancements of the order of 10/sup 3/ are possible.

Coutts, J.; Cooper, J.; Burnett, K.

1988-05-01

131

Modifying excitation transfer cross sections with an ac Stark effect.  

Science.gov (United States)

We show that it is possible to manipulate electronic energy transfer collision cross sections between different atomic species by using a strong electromagnetic field close to resonance with a transition between two excited states to modify the energy levels (i.e., to create dressed states), which may be placed in or out of resonance with populated states (forming a population reservoir) in one of the species. We outline an estimate for a transfer cross section for a demonstration scheme and show that cross-section enhancements up to the order of 10(3) are possible. PMID:19745896

Coutts, J; Cooper, J; Burnett, K

1988-05-01

132

Modifying excitation transfer cross sections with an ac Stark effect  

Energy Technology Data Exchange (ETDEWEB)

It is possible to manipulate electronic energy-transfer collision cross sections between different atomic species by using a strong electromagnetic field close to resonance with a transition between two excited states to modify the energy levels (i.e., to create dressed states), which may be placed in or out of resonance with populated states (forming a population reservoir) in one of the species. The authors outline an estimate for a transfer cross section for a demonstration scheme and show that cross-section enhancements up to the order of 1000 are possible.

Coutts, J.; Cooper, J.; Burnett, K.

1988-05-01

133

Two-electron excitation of an interacting cold Rydberg gas  

CERN Document Server

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

134

Electron Transfer at Sensitized Semiconductor Electrodes.  

Science.gov (United States)

Electron transfer from the excited state of sensitizing dyes to the conduction band of semiconductors has been studied through photoelectrochemical techniques. Two systems were analyzed in detail: rhodamine B on ZnO and rose bengal on TiO sub 2 . Prior to...

M. T. Spitler

1977-01-01

135

A time-resolved study of electron transfer mechanisms: Beyond outer-sphere electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Of the primary objectives of our research has been to understand some of the fundamental mechanistic issues underlying electron transfer reactions. We have designed molecular systems to provide information on several aspects of charge transfer reactions, including the role of protons in long-distance electron transfer, bimolecular donor-acceptor pair reactivity at high driving forces, and excited state multielectron transformations. In our systems a photon can initiate the reaction by placing the molecules in an excited electronic state, which permits the reactant and product concentrations to be monitored as a function of time. These dynamic measurements are conducted by exciting the molecules with a short light pulse, and following the progress of the reaction by optical methods, such as transient absorption spectroscopy and emission lifetime. Electron transfer reactions through a proton interface have been conducted by the design of hydrogen-bonded donor-acceptor pairs, where the donor, a carboxylic acid derivative of a Zn-substituted porphyrin, transfer an electron to several aromatic acceptors from its excited state. The charge separation and subsequent charge recombination rates have been determined utilizing picosecond transient absorption spectroscopy, for protiated and deuterated donors and acceptors. A slight attenuation in the rates is observed. The transient absorption technique has also been utilized to characterize the excited states that lead to two-electron reactivity in quadrupoly-bonded inorganic complexes of the type M{sub 2}Cl{sub 4}(L){sub n}, where M = molybdenum or tungsten and L = monodentate or bidentate phosphine ligands. It was observed that the reactions do not proceed directly from an excited electronic state, but from a conformationally-distorted intermediate formed following light excitation. The distorted intermediate is believed to possess favorable characteristics that permit the observed two-electron oxidative-addition reactions.

Turro, C.

1992-12-31

136

Chemical Bonding in Excited Electronic States.  

Science.gov (United States)

The electronic and vibrational spectra of the series of compounds fluorene, dibenzofuran (diphenylene oxide) and carbazole were examined for the purpose of studying chemical bonding in electronically excited molecules. Assignments of the ground state vibr...

S. C. Wait

1969-01-01

137

Integral encounter theory of strong electron transfer  

International Nuclear Information System (INIS)

The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong

2005-03-22

138

A simplified approach for the coupling of excitation energy transfer  

International Nuclear Information System (INIS)

Highlights: ? We propose a simple method to calculate the coupling of singlet-to-singlet and triplet-to-triplet energy transfer. ? Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer. ? Effect from the intermolecular charge-transfer states dorminates in triplet-to-triplet energy transfer. ? This method can be expanded by including correlated wavefunctions. - Abstract: A simplified approach for computing the electronic coupling of nonradiative excitation-energy transfer is proposed by following Scholes et al.’s construction on the initial and final states [G.D. Scholes, R.D. Harcourt, K.P. Ghiggino, J. Chem. Phys. 102 (1995) 9574]. The simplification is realized through defining a set of orthogonalized localized MOs, which include the polarization effect of the charge densities. The method allows calculating the coupling of both the singlet-to-singlet and triplet-to-triplet energy transfer. Numerical tests are performed for a few of dimers with different intermolecular orientations, and the results demonstrate that Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer whereas in the case of triplet-to-triplet energy transfer, the dominant effect is arisen from the intermolecular charge-transfer states. The present application is on the Hartree–Fock level. However, the correlated wavefunctions which are normally expanded in terms of the determinant wavefunctions can be employed in the similar way.

2012-02-06

139

Nuclear reorganization barriers to electron transfer  

International Nuclear Information System (INIS)

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

1988-08-15

140

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

 
 
 
 
141

Electron transfer from excited F centres to F/sup +/, F/sup +/sub(A) and F/sup +/sub(AA) centres in CaO studied by optically detected magnetic resonance (ODMR)  

Energy Technology Data Exchange (ETDEWEB)

ODMR measurements via the magnetic circular polarization of the emission (MCPE) of Fsub(A)(Mg) centres in CaO at 1.6K showed besides the known Fsub(A)-ODMR lines a non zero MCPE, which vanishes at g approximately equal to 2. From the dynamical behaviour of this MCPE and the Fsub(A) luminescence is shown that an electron tunneling takes place from the excited Tsub(lu)F centre state to F/sup +/sub(A) centres forming excited Fsub(A) centres. The ground state back tunneling rate is 10/sup 7/ times smaller and cannot explain the observed electron transfer cycle. The back tunneling is also going via excited states. The results can be understood assuming a random centre distribution. A new luminescence band at 785nm could be identified by ODMR as being due to tetragonal Fsub(AA) centres. The electron transfer is also observed between F and F/sup +/ and F/sup +/sub(AA) centres.

Ahlers, F.J.; Lohse, F.; Spaeth, J.M. (Fachbereich Naturwissenschaften I, Experimentalphysik Universitaet-Gesamthochschule, Paderborn, W. Germany)

1982-08-01

142

Electron transfer from excited F centres to F"+, F"+sub(A) and F"+sub(AA) centres in CaO studied by optically detected magnetic resonance (ODMR)  

International Nuclear Information System (INIS)

ODMR measurements via the magnetic circular polarization of the emission (MCPE) of Fsub(A)(Mg) centres in CaO at 1.6K showed besides the known Fsub(A)-ODMR lines a non zero MCPE, which vanishes at g approximately equal to 2. From the dynamical behaviour of this MCPE and the Fsub(A) luminescence is shown that an electron tunneling takes place from the excited Tsub(lu)F centre state to F"+sub(A) centres forming excited Fsub(A) centres. The ground state back tunneling rate is 10"7 times smaller and cannot explain the observed electron transfer cycle. The back tunneling is also going via excited states. The results can be understood assuming a random centre distribution. A new luminescence band at 785nm could be identified by ODMR as being due to tetragonal Fsub(AA) centres. The electron transfer is also observed between F and F"+ and F"+sub(AA) centres. (author)

1982-01-01

143

Recoil-charge-state--target-K-Auger-electron coincidences: A technique to study excitation patterns in K-K charge transfer  

International Nuclear Information System (INIS)

We have measured coincidences between Ne K Auger electrons emitted after impact excitation by hydrogenlike F/sup 8+/ and bare F/sup 9+/ projectiles at 0.53 and 0.23 MeV/u collision energies and the recoiling Ne target ion in a well-defined charge state. The quasiresonant K-K charge-tgas-atom pairs to calculate adiabatic potentials for some low-lying states. Using the calculated potentials, broadening and shift rates of resonance lines of Sr"+, Ca"+, and Mg"+ perturbed by Ar and He have been calculated and compared with experiments. The overall agreement is good

1986-01-01

144

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)

1995-03-01

145

Electron transfer at nickel electrode  

International Nuclear Information System (INIS)

There is considerable contemporary interest in the electron transfer reaction. at active (transition) metal electrodes. this work reports the electrochemical behavior of potassium ferrocyanide at nickel electrode in aqueous potassium nitrate solution. Potassium ferrocyanide is frequently employed to probe one-electron transfer reactions at solid, electrodes. It was found that the voltammetric oxidation of ferrocyanide at nickel is a simple electron transfer reaction. Normal pulse voltammetry revealed similar behavior. (author)

2009-01-01

146

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

147

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

International Nuclear Information System (INIS)

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

2008-06-23

148

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

Science.gov (United States)

The time evolution of electronically excited vitamin B 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; Poisson, Lionel; Soep, Beno?ˆt

2008-06-01

149

Electronic structure, charge transfer excitations and high temperature superconductivity. [La/sub 2-x/M/sub x/CuO/sub 4/ and YBa/sub 2/Cu/sub 3/O/sub 7-delta/  

Energy Technology Data Exchange (ETDEWEB)

High precision local density electronic band structure results (for YBa/sub 2/Cu/sub 3/O/sub 7/, YBa/sub 2/Cu/sub 3/O/sub 6/ and GdBa/sub 2/Cu/sub 3/O/sub 7/) lead to the possibly important role of charge transfer excitations as the mechanism of high T/sub c/ superconductivity, and explain the coexistence of magnetism and superconductivity in the high T/sub c/ rare-earth superconductors. 21 refs., 3 figs.

Freeman, A.J.; Yu, Jaejun; Massidda, S.; Koelling, D.D.

1987-09-01

150

Photoinduced electron transfer from a conducting polymer to buckminsterfullerene  

Energy Technology Data Exchange (ETDEWEB)

Evidence for photoinduced electron transfer form the excited state of a conducting polymer onto buckminsterfullerene, C{sub 60}, is reported. After photo-excitation of the conjugated polymer with light of energy greater than the {pi}-{pi} gap, an electron transfer to the C{sub 60} molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components, consistent with photo-excited charge transfer. A photoinduced electron spin resonance signal exhibits signatures of both the conducting polymer cation and the C{sub 60} anion. Because the photoluminescence in the conducting polymer is quenched by interaction with C{sub 60}, the data imply that charge transfer form the excited state occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures. 34 refs., 4 figs.

Sarciftci, N.S.; Smilowitz, L.; Heeger, A.J. [Univ. of California, Santa Barbara, CA (United States)] [and others

1992-11-27

151

Femtosecond excitation transfer processes in biliprotein trimers  

Science.gov (United States)

Femtosecond processes in allophycocyanin, C-phycocyanin and phycoerythrocyanin trimers and monomers have been examined by means of polarization pump-probe technique. No femtosecond kinetics were observed in monomeric preparations. The isotropic absorption recovery kinetics with (tau) equals 440 +/- 50 fs which is not accompanied by anisotropy decay kinetics was obtained in allophycocyanin trimers at 612 nm. The conclusion about energy transfer between neighboring (alpha) 84 and (beta) 84 chromophores with different absorption spectra was made. The proposed model takes into account a stabilizing role of the linker peptide. Spectral and kinetic measurements were made in the 635 - 690 nm spectral region where the proposed acceptor should absorb. The bleaching of the 650-nm band occurs with a delay relative to the bleaching at 615 nm. Only a rise term was observed at 658 nm in consistence with the proposed model. Anisotropy values calculated around 650 nm at 3 ps after excitation are in the range 0.1 - 0.25 corresponding to an angle of 30 degree(s) - 45 degree(s) between the donor and acceptor transition dipole moments. A 500-fs absorption recovery and anisotropy decay process was obtained for C-phycocyanin trimers and explained by Forster energy transfer over 20.8 angstroms between neighboring (alpha) 84 and (beta) 84 chromophores of different monomeric subunits having similar absorption spectra and with a 65 degree(s) angle between their orientations. Energy transfer between violobilin ((alpha) 84) and phycocyanobilin ((beta) 84) chromophores was examined in donor and acceptor spectral regions of phycoerythrocyanin trimers, and was found to take 400 fs.

Sharkov, A. V.; Khoroshilov, E. V.; Kryukov, I. V.; Palsson, Lars-Olof; Kryukov, P. G.; Fischer, R.; Scheer, Hella-C.; Gillbro, Tomas

1993-06-01

152

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

Science.gov (United States)

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. PMID:23503708

Ghosh, Rajib; Palit, Dipak K

2013-06-01

153

Medium effects in photoinduced electron transfer reactions  

International Nuclear Information System (INIS)

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

1988-01-01

154

Excitation of aluminium atoms by electron impact  

International Nuclear Information System (INIS)

The electron impact excitation cross sections of aluminium 4s and 4p levels are calculated at incident electron energies from the threshold up to 1 Ryd. The calculations take into account close coupling of the 3s23p2P-4s2S-4p2P states with exchange. Semiempirical atomic single electron orbitals are used. Partial and total excitation cross sections of the 4s and 4p levels are shown. The agreement with experimental data is discussed for the 4s level. The experimental values seem to be too small, but they show the structure similar to that of the theoretical curve

1980-01-01

155

Dynamics of solvent-mediated electron localization in electronically excited hexacyanoferrate(III).  

Science.gov (United States)

We have used polarization-resolved UV pump-mid-IR probe spectroscopy to investigate the dynamics of electron hole localization for excited-state ligand-to-metal charge-transfer (LMCT) excitation in Fe(CN)(6)(3-). The initially generated LMCT excited state has a single CN-stretch absorption band with no anisotropy. This provides strong evidence that this initial excited state preserves the octahedral symmetry of the electronic ground state by delocalizing the ligand hole in the LMCT excited state on all six cyanide ligands. This delocalized LMCT excited state decays to a second excited state with two CN-stretch absorption bands. We attribute both peaks to a single excited state because the formation time for both peaks matches the decay time for the delocalized LMCT excited state. The presence of two CN-stretch absorption bands demonstrates that this secondary excited state has lower symmetry. This observation, in conjunction with the solvent-dependent time constant for the formation of the secondary excited state, leads us to conclude that the secondary excited state corresponds to a LMCT state with a localized ligand hole. PMID:22233125

Zhang, Wenkai; Ji, Minbiao; Sun, Zheng; Gaffney, Kelly J

2012-02-01

156

Coherent electron transfer in polyacetylene  

Science.gov (United States)

We examine, using mixed classical-quantum electron-ion dynamics, electron transfer in a donor-acceptor-like molecular junction system based on polyacetylene. We identify two qualitatively-different transfer regimes: hopping and tunnelling. We discuss the criteria for achieving each one and for minimising inelastic scattering and decoherence arising from the coupling to the ions, and we connect our main results to quantities derived from electron dynamics involving simpler, three-state model systems. We identify the requirements to have near-ballistic transfer.

Psiachos, D.

2014-06-01

157

Electronic excitation transport, diffusion and trapping  

Science.gov (United States)

Excitation energy transfer between donor (trypaflavine) and acceptor (rhodamine B, rhodamine 6G and cresyl violet) molecules randomly distributed in condensed phases is investigated using a time correlated single photon counting technique. The influence of excitation migration and translational diffusion is experimentally observed. The donor decay data demonstrate that fast diffusion/migration governs the decay kinetics in low viscosity solutions — the donor fluorescence decay being single exponential. The value of the diffusion coefficient calculated from decay curve analysis is almost a factor of five larger than the spatial diffusion constant and two orders of magnitude faster than the excitation migration transport constant. In high viscosity solvents efficient energy transfer follows the Förster dipole—dipole model.

Pandey, K. K.

1992-09-01

158

Electron-beam-excited gas laser research  

International Nuclear Information System (INIS)

Net energy gain in laser fusion places requirements on the laser that are not realized by any existing laser. Utilization of relativistic electron beams (REB's), a relatively new source for the excitation of gas laser media, may lead to new lasers that could satisfy these requirements. Already REB's have been utilized to excite gas laser media and produce gas lasers that have not been produced as successfully any other way. Electron-beam-excitation has produced electronic-transition dimer lasers that have not yet been produced by any other excitation scheme (for example, Xe_2/ sup *(1)/, Kr:O(2"1S)/sup 2/, KrF/sup *(3)/). In addition, REB's have initiated chemical reactions to produce HF laser radiation with unique and promising results. Relativistic-electron-beam gas-laser research is continuing to lead to new lasers with unique properties. Results of work carried out at Sandia Laboratories in this pioneering effort of electron-beam-excited-gas lasers are reviewed. (U.S.)

1975-06-01

159

Electronic band structure in porous silicon studied by photoluminescence and photoluminescence excitation spectroscopy  

International Nuclear Information System (INIS)

In this research, we used photoluminescence (PL) and photoluminescence excitation (PLE) to visualize the electronic band structure in porous silicon (PS). From the combined results of the PLE measurements at various PL emission energies and the PL measurements under excitation at various PLE absorption energies, we infer that three different electronic band structures, originating from different luminescent origins, give rise to the PL spectrum. Through either thermal activation or diffusive transfer, excited carriers are moved to each of the electronic band structures.

2004-10-01

160

Computer simulation of cluster impact induced electronic excitation of solids  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-05-15

 
 
 
 
161

Superexchange coupling mechanisms for electron transfer processes  

Science.gov (United States)

Electron transfer matrix elements for electron exchange between various pairs of transition metal complexes in close contact have been calculated and analyzed for a variety of approach geometries for the two reactants. The coupling between the nominal metal ion donor/acceptor sites is achieved by superexchange of the hole type arising from ligand-to-metal charge transfer (LMCT), the dominant ligand-field interaction for the electron-donor ligands considered (H sub 2 O, NH sub 3, the cyclopentadienide anion). The pronounced variations of H sub if with geometry are not correlated with the separation distance of the metal ions (between which the direct overlap is negligible) and span the range from non-adiabatic to strongly adiabatic electronic coupling. The values for metallocene/metallocinium redox pairs bracket recently reported experimental values. Analysis of the results using the method of corresponding orbitals demonstrates the validity of an effective 1-electron model for the electron transfer process to within about 10 percent for the class of systems considered. A higher-order superexchange mechanism was encountered for the Co(NH sub 3) sub 6 (2+/3+) exchange process, in which the LMCT-driven hole-transport mechanism couples excited local states of the metal ions, which in turn are connected to the corresponding ground states by spin-orbit mixing. This mechanism yields on electronic transmission factor within two orders of magnitude of unity.

Newton, M. D.

162

Ultrafast Electron Dynamics Theory of Photo-excited Ruthenium Complexes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An explanation is provided for the ultrafast photo-excited electron dynamics in low-spin Ruthenium (II) organic complexes. The experimentally-observed singlet to triplet decay in the metal-to-ligand charge-transfer (MLCT) states contradicts the expectation that the system should oscillate between the singlet and triplet states in the presence of a large spin-orbit coupling and the absence of a significance change in metal-ligand bond length. This dilemma is solved with a nov...

Chang, Jun; Fedro, A. J.; Veenendaal, Michel

2010-01-01

163

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

164

Electroluminescence from graphene excited by electron tunneling.  

Science.gov (United States)

We use low-energy electron tunneling to excite electroluminescence in single layer graphene. Electrons are injected locally using a scanning tunneling microscope and the luminescence is analyzed using a wide-angle optical imaging system. The luminescence can be switched on and off by inverting the tip-sample bias voltage. The observed luminescence is explained in terms of a hot luminescence mechanism. PMID:24407020

Beams, Ryan; Bharadwaj, Palash; Novotny, Lukas

2014-02-01

165

Core excitation of Li by electron impact  

International Nuclear Information System (INIS)

Cross sections for the excitation of a core electron, which leads to autoionization, in lithium (Li) atomic system by electron impact have been calculated with use of the single-configuration Hartree-Fock wave function within the asymptotic Green's-function approximation (AGFA) in the low-bombarding-energy region. Comparison is made with available results. Our investigation demonstrates that the AGFA supports the R-matrix as well as the distorted-wave Born-approximation behavior

1985-01-01

166

Laser Emission from Electron Beam Excited Znte.  

Science.gov (United States)

Laser emission was obtained from ZnTe excited by an electron beam. A peak output power of 90W with 8 percent overall power efficiency at a wavelength of 5280A was measured at liquid helium temperature. Lasers at liquid nitrogen temperature with an emissio...

C. E. Hurwitz

1967-01-01

167

Intermultiplet and angular momentum transfers of excited sodium atoms in collisions with molecules. II. Models  

Energy Technology Data Exchange (ETDEWEB)

The use of ionic intermediate models for the description of collisions involving excited alkali atoms and molecules is discussed. It is shown that the multiple curve crossing and the quasifree electron models can be expressed with the same formalism. The results of these models are compared to experimental electronic to electronic transfer cross sections in the case of oxygen and nitrogen molecules for which detailed informations upon the resonant free electron--molecule scattering data are available.

Desfrancois, C.; Astruc, J.P.; Barbe, R.; Schermann, J.P.

1988-03-01

168

Excited-state hydrogen-atom transfer along solvent wires: water molecules stop the transfer.  

Science.gov (United States)

Excited-state hydrogen-atom transfer (ESHAT) along a hydrogen-bonded solvent wire occurs for the supersonically cooled n = 3 ammonia-wire cluster attached to the scaffold molecule 7-hydroxyquinoline (7HQ) [Tanner, C.; et al. Science 2003, 302, 1736]. Here, we study the analogous three-membered solvent-wire clusters 7HQ.(NH3)n.(H2O)m, n + m = 3, using resonant two-photon ionization (R2PI) and UV-UV hole-burning spectroscopies. Substitution of H2O for NH3 has a dramatic effect on the excited-state H-atom transfer: The threshold for the ESHAT reaction is approximately 200 cm(-1) for 7HQ.(NH3)3, approximately 350 cm(-1) for both isomers of the 7HQ.(NH3)2.H2O cluster, and approximately 600 cm(-1) for 7HQ.NH3.(H2O)2 but increases to approximately 2000 cm(-1) for the pure 7HQ.(H2O)3 water-wire cluster. To understand the effect of the chemical composition of the solvent wire on the H-atom transfer, the reaction profiles of the low-lying electronic excited states of the n = 3 pure and mixed solvent-wire clusters are calculated with the configuration interaction singles (CIS) method. For those solvent wires with an NH3 molecule at the first position, injection of the H atom into the wire can occur by tunneling. However, further H-atom transfer is blocked by a high barrier at the first (and second) H2O molecule along the solvent wire. H-atom transfer along the entire length of the solvent wire, leading to formation of the 7-ketoquinoline (7KQ) tautomer, cannot occur for any of the H2O-containing clusters, in agreement with experimentally observed absence of 7KQ fluorescence. PMID:16451005

Tanner, Christian; Thut, Markus; Steinlin, Andreas; Manca, Carine; Leutwyler, Samuel

2006-02-01

169

Perfect transfer of multiple excitations in quantum networks  

CERN Document Server

We present a general formalism to the problem of perfect state-transfer (PST), where the state involves multiple excitations of the quantum network. A key feature of our formalism is that it allows for inclusion of nontrivial interactions between the excitations. Hence, it is perfectly suited to addressing the problem of PST in the context of various types of physical realizations. The general formalism is also flexible enough to account for situations where multiple excitations are "focused" onto the same site.

Brougham, T; Jex, I; 10.1103/PhysRevA.83.022323

2011-01-01

170

Electronic excited states of CO2: An electron impact investigation  

International Nuclear Information System (INIS)

The electronic excited states of CO2 were restudied by variable incident energy, variable angle electron impact spectroscopy. In this study, valence states of mixed configurations were distinguished from pure Rydberg states. Our results are incompatible with the theoretical description of CO2, in which only two valence singlet states are located

1984-01-15

171

Electron transfer to continuum states  

Energy Technology Data Exchange (ETDEWEB)

Gene Rudd`s analysis of doubly differential cross sections for the ionization of He atoms by proton impact suggested that electrons were being carried along by the proton for a short period of time after being ejected from the target region. Normally, this would represent an electron capture event in which an excited state of atomic hydrogen is formed. Because the electron ends up ionized it was recognized that these states of the proton must be continuum states. This insight was confirmed by observations of the continuum electron capture (CEC) cusp when the electron velocity equals the proton velocity in the final state. The impact of this idea upon the theory of ionization at high energies is reviewed.

Macek, J.H. [Univ. of Tenenssee, Knoxville, TN (United States)]|[Oak Ridge National Lab., TN (United States)

1994-12-31

172

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

173

Al double core electron excitation in asymmetric collisions  

Science.gov (United States)

We report a detailed Auger study on the double 2p electron excitation in Al by bombarding polycrystalline Al with 5-15 keV noble gas ions (Ne +, Ar +, Kr +, and Xe +) and Mg xAl 1 - x alloys ( x = 0, 0.25, 0.50, and 0.75) with Ar + ions. Fo resolved spectra show three well distinct narrow atomic L 2-Auger peaks at ~ 76, ~ 82, and ~ 85.5 eV which exhibit clear Doppler shifts. These doubly excited Al Auger lines are detectable only for heavy noble gas ion (Ar +, Kr +, and Xe +) impact along off-normal incidence directions suggesting that the excitation occurs in the primary asymmetric collisions. However, for Mg xAl 1 - x alloys such atomic L 2-Auger peaks are clearly present even for normal Ar + ion incidence, unambiguously indicating that the Al double core electron excitation may also occur in collisions with lighter partners. Based on the linear dependence of the intensity of the prominent Al L 2MM peak normalized to its surface concentration on the surface Mg concentration we suggest that it is due to transfer of double L-shell vacancies from one Mg atom excited in the primary Ar +?Mg collision to an Al atom in a subsequent Mg?Al encounter through, for example, 4f?-3d? radial coupling.

Xu, F.; Camarca, M.; Oliva, A.; Mandarino, N.; Zoccali, P.; Bonanno, A.

1991-05-01

174

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photoinduced charge transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for accurate and computationally inexpensive treatment of charge transfer excitations is a topic that attracts nowadays a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations (M. Tassi, I. Theophilou and S. Thanos, Int. J. Quantum Chem., {...

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

2014-01-01

175

Time-resolved photoelectron imaging of the chloranil radical anion: ultrafast relaxation of electronically excited electron acceptor states.  

Science.gov (United States)

The spectroscopy and dynamics of near-threshold excited states of the isolated chloranil radical anion are investigated using photoelectron imaging. The photoelectron images taken at 480 nm clearly indicate resonance-enhanced photodetachment via a bound electronic excited state. Time-resolved photoelectron imaging reveals that the excited state rapidly decays on a timescale of 130 fs via internal conversion. The ultrafast relaxation dynamics of excited states near threshold are pertinent to common electron acceptor molecules based on the quinone moiety and may serve as doorway states that enable efficient electron transfer in the highly exergonic inverted regime, despite the presence of large free energy barriers. PMID:21971531

Horke, Daniel A; Verlet, Jan R R

2011-11-21

176

Nonresonant excitation transfer in the He (21S, 23S) + Ne reactions  

International Nuclear Information System (INIS)

The terms of the He-Ne (n, s) quasimolecules with n=4.5 are calculated by a method based on the characteristics of electron-atomic scattering and by using the experimental data on He-Ne+ interaction. The calculated terms are supplemented by those derived from experiments on differential scattering. In this way it has been possible to determine the coordinates of the nonadiabaticity region and to elucidate the mechanisms of nonresonant excitation transfer involving the population of various states of Ne*. The temperature dependences of the rate constants K(T) of the excitation energy transfer reactions are related by single integration to the transition probabilities between quasi-intersecting terms. The matrix interaction elements are determined by comparing the caicuiated and experimental dependences K(T). Energy dependences of the excitation cross sections for various neon states during excitation transfer are calculated

1984-06-01

177

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

CERN Document Server

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

Nalbach, P; Thorwart, M

2013-01-01

178

L-shell alignment observed after resonant transfer and excitation in U90+ ? C collisions  

Science.gov (United States)

With heavy, highly-charged ions the electron-electron correlation is probed in the relativistic domain by Resonant Transfer and Excitation, RTE. For the studied case of initially He-like U90+ ions the KLL-RTE splits into three resonance groups according to the j values of the electrons involved in the doubly-excited intermediate states. For a K to L excitation into a j = ½ state with a simultaneous capture also to a j' = ½ state, relativistic effects yield a strong cross section enhancement. The doubly excited states with jj' = 1/2-3/2 show a strong anistropy for the radiative ground state transition of the j' = 3/2 electron manifesting a pronounced non-isotropic population of the magnetic substates.

Mokler, P. H.; Kandler, T.; Stöhlker, Th; Geissel, H.; Kozhuharov, C.; Rymuza, P.; Scheidenberger, C.; Stachura, Z.; Warczak, A.; Dunford, R. W.

1997-01-01

179

Electron-impact vibrational excitation of furan  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-12-15

180

Electron-impact vibrational excitation of furan  

International Nuclear Information System (INIS)

We report measurements of differential cross sections for the vibrational excitation of furan (C4H4O), obtaining results for nine features spanning the electron energy loss range from 0 to 0.8 eV, at electron-impact energies of 5, 6, 7.5, 10, and 15 eV and for scattering angles ranging from 10o to 130o. The normalization of the differential cross sections was done using elastic differential cross sections for furan determined earlier by our group [Khakoo et al., Phys. Rev A 81, 062716 (2010)].

2011-12-01

 
 
 
 
181

Experimental station for inelastic scattering spectroscopy of electronic excitations  

International Nuclear Information System (INIS)

An experimental station for inelastic x-ray scattering spectroscopy (IXSS) of phonons and electronic excitation is being built on the undulator beamline of Sector 3 at the Advanced Photon Source. The subject of the present article is a description of the instrumentation for the spectroscopy of electronic excitations. The goal of this program is to provide users with the possibility to study IXSS in low- and middle-Z materials with an energy resolution from 1 eV (with a beam coming directly from the high-heat-load monochromator to the specimen) to 100 meV (with a second channel-cut monochromator) in the energy transfer range of 200 eV. The optical scheme of the station is described, and status of the station is reported. copyright 1996 American Institute of Physics

1996-09-01

182

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-15

183

Motional effects on the efficiency of excitation transfer  

CERN Multimedia

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

184

Combustion enhancement through electronically excited oxygen  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-07-01

185

Photoinitiated electron transfer in multi-chromophoric species: Synthetic tetrads and pentads  

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

186

Electron Transfer to Vinylaromatic Polymers  

International Nuclear Information System (INIS)

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

1965-10-01

187

Efficiency of excitation transfer in photosynthesis under quantum coherence  

CERN Document Server

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

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

2007-01-01

188

Electron Beam Excitation of Zn2 Excimer  

Science.gov (United States)

Bound-free emission of the Zn2 excimer, which was predicted as a possible long-lived excimer system, has been observed in dense Zn vapor with helium or argon buffer gas by means of electron beam excitation. A continuum emission band at 431 408 nm was assigned to Zn2 13?+ u?11?+ g excimer transition. In addition, a strong diffuse emission at 427.6 nm was observed in He/Zn mixtures, which overlapped to the Zn2 continuum. We suggest that this emission band is attributed to the ZnHe excimer.

Xing, Da; Ueda, Ken-ichi; Takuma, Hiroshi

1994-12-01

189

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

1987-09-14

190

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

Science.gov (United States)

Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations. PMID:24329054

Yang, Yang; van Aggelen, Helen; Yang, Weitao

2013-12-14

191

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

Science.gov (United States)

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

Yang, Yang; van Aggelen, Helen; Yang, Weitao

2013-12-01

192

Positron impact electronic excitation of N2  

International Nuclear Information System (INIS)

We present the results of scattering cross sections for positron impact excitation of electronic states of nitrogen molecule (N2) using the Schwinger multichannel method (SMC). All calculated cross sections took three collision channels into account (X1?g and degenerate a1?g states). Present theoretical results for excitation to the a1?g states failed to reproduce the near-threshold structure observed in the recent and the only available experimental data [Sullivan et al., Phys. Rev. Lett. 87 (2001) 073201-1]. Scattering calculations from the a1?g states (elastic and superelastic) are also reported. A spurious resonant structure found in the excitation to the a1?g states was detected in a square integrable basis set calculation designed to reproduce the first Born approximation (FBA). Such spurious structure was removed by taking out the trial configuration state functions in which the positron was weakly coupled to the target. This may be a promising technique to separate unphysical resonances from the physical ones. We also observe that a combination between SMC scattering amplitudes (l?2) with FBA ones (l?3) significantly improved the cross sections at higher energies

2004-07-01

193

Electron excitation of hydrogen using an extended Glauber approximation  

International Nuclear Information System (INIS)

Elastic and inelastic electron-hydrogen scattering is considered using an unrestricted version of the Glauber approximation. The integral expressions that are derived are shown to reduce to those of the restricted Glauber approximation when q ? 0 for 1s ? ns excitation and to give the same divergent behavior as the conventional restricted Glauber approximation when q, the momentum transfer, approaches zero. The integrals for the electron-electron and the electron-nucleus interactions can be separated and evaluated analytically in the asymptotic limit of large q. The electron-nucleus term is shown to be dominant and to have Rutherford-like dependence on q for fixed energy at large q. Cross sections and Fano--Macek alignment and orientation parameters have been computed numerically for various scattering angles and incident energies. The total cross sections and polarization fraction of Ly-? radiation agree closely with Byron's Monte-Carlo integrations of the generalized Glauber transition matrix. The states excited as a function of scattering angle are found to be elliptically polarized in our calculations in contrast to the predictions of the Born and conventional eikonal-type approximations

1975-01-01

194

Efficient Deactivation of a Model Base Pair via Excited-State Hydrogen Transfer  

Science.gov (United States)

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

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

2004-12-01

195

Calculation of nuclear excitation in an electron transition  

Energy Technology Data Exchange (ETDEWEB)

We have made a theoretical investigation of nuclear excitation during an electron transition (NEET). Our approach allows us to express the NEET probabilities in terms of the excited nuclear level width, the energy difference between the nuclear and electron transition, the Coulomb interaction between the initial electron states, and the electron level width. A comparison is made with the available experimental results. (orig.).

Pisk, K. (Institut Rudjer Boskovic, Zagreb (Yugoslavia)); Kaliman, Z. (Rijeka Univ. (Yugoslavia). Faculty of Pedagogics); Logan, B.A. (Ottawa Univ., ON (Canada). Ottawa-Carleton Centre for Physics)

1989-11-06

196

Resonant transfer of excitation between two molecules using Maxwell fields.  

Science.gov (United States)

The matrix element for the resonant transfer of excitation between two molecules possessing electric and magnetic multipole moments of arbitrary order is calculated using quantum electrodynamical response theory. A prerequisite of the method is the functional form for the lth order linear electric and magnetic multipole dependent electric displacement and magnetic field operators in the neighborhood of a molecule, whose derivation is also given. The initially unexcited species is viewed as a test body accepting energy resonantly via coupling to the Maxwell fields of the excited multipole source molecule. The generalized electric-electric multipole contribution to the matrix element is shown to agree with an earlier calculation using time-dependent perturbation theory. As an application involving both electric and magnetic terms, the rate of excitation transfer between two chiral molecules is computed and found to depend on the handedness of each species. PMID:15740241

Salam, A

2005-01-22

197

SNMS by electron beam excited plasma  

International Nuclear Information System (INIS)

SIMS is one of the major techniques that apply sputtering to analysis of the elementary composition in the depth direction. With the aim of resolving major problems with SIMS, SNART (sputtered neutral analysis-Riken type), a sputtered neutral particle mass analysis method, is developed which uses electron beam excited plasma to perform low-energy sputtering and postionization of sputtered neutron particles. Low energy sputtering serves to minimize surface roughness due to ion induction of knock-on mixing. SNART employs high-density plasma produced by electron beam, resulting in easy reduction in the ion energy down to below 100eV while achieving an ion current of several tens mA/cm2 at the surface of a target sample. Such an electron density achieves a very high sputtering rate in spite of low energy sputtering. Measurements demonstrate that the use of such high density plasma permits 80eV Ar+ ion sputtering while maintaining a high etching rate of 0.9 nm/sec and achieving a depth resolution of 1.4 nm (in Cr-Ni multilayer film). It is also shown that a postionization efficiency of greater than 20 percent is attained by using high-energy, high-current electron beam. (N.K.)

1989-01-01

198

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

199

Near-threshold rovibrational excitation of HF by electron impact  

International Nuclear Information System (INIS)

The pronounced threshold peaks found in cross sections for electron-impact excitation of the vibrational levels of HF have been studied using an R-matrix method, in which electron exchange, correlation effects and polarization are included. Vibration is modelled inside the R-matrix sphere using the energy-modified adiabatic phase matrix method (EMAP). Rotation of the target molecule is treated outside the R-matrix sphere, using the frame transformation method. The external rovibronic close-coupling equations are solved by analytic methods. Analysis of the multichannel threshold structures indicates that the peaks found for rovibrational excitation of v = 1 can interpreted as virtual states while those for v = 2 correspond to nuclear-excited Feshbach resonances. These two different results correspond simply to a change of sign of a small parameter that is determined by the threshold analysis. Whereas the overall shapes of the excitation peaks agree with earlier theoretical results, we have found detailed rotational fine structures for scattering energies on the order of the rotational constant above and below the opening of the vibrational channels. The partial and total cross sections for rovibrational state-to-state transitions in the energy region of the peaks are analysed. Characteristic cusp structures and excitation peaks are found at the rovibrational thresholds for transitions with small angular momentum transfer ?j =0, 1 and 2. Differential cross sections are similar to recent measurements. These experimental data do not show the relatively sharp rise at the vibrational thresholds indicated by theory. Theory and experiment are in good agreement for the shape and magnitude of the angular dependence of cross sections for rovibrational state-to-state transitions, especially at larger energies. (Author)

1993-03-28

200

Near-Threshold Rovibrational Excitation of HF by Electron Impact  

Science.gov (United States)

The pronounced threshold peaks found in cross sections for electron-impact excitation of the vibrational levels of HF have been studied using an R-matrix method, in which electron exchange, correlation effects and polarization are included. Vibration is modelled inside the R-matrix sphere using the energy-modified adiabatic phase matrix method (EMAP). Rotation of the target molecule is treated outside the R-matrix sphere, using the frame transformation method. The external rovibronic close-coupling equations are solved by analytic methods. Analysis of the multichannel threshold structures indicates that the peaks found for rovibrational excitation of nu = 1 can be interpreted as virtual states while those for nu = 2 correspond to nuclear-excited Feshbach resonances. These two different results correspond simply to a change of sign of a small parameter that is determined by the threshold analysis. Whereas the overall shapes of the excitation peaks agree with earlier theoretical results, we have found detailed rotational fine structures for scattering energies on the order of the rotational constant above and below the opening of the vibrational channels. The partial and total cross sections for rovibrational state-to-state transitions in the energy region of the peaks are analysed. Characteristic cusp structures and excitation peaks are found at the rovibrational thresholds for transitions with small angular momentum transfer (Delta)j =0, 1 and 2. Differential cross sections are similar to recent measurements. These experimental data do not show the relatively sharp rise at the vibrational thresholds indicated by theory. Theory and experiment are in good agreement for the shape and magnitude of the angular dependence of cross sections for rovibrational state-to-state transitions, especially at larger energies.

Thummel, Helmar T.; Nesbet, Robert K.; Peyerimhoff, Sigrid D.

1993-01-01

 
 
 
 
201

Rerouting Excitation Transfer in the Fenna-Matthews-Olson Complex  

CERN Document Server

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

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

2013-01-01

202

Selective-excitation study of collisional excitation transfer for helium 3sup(1,3)P and D states  

International Nuclear Information System (INIS)

By observing the time-resolved fluorescence following the laser excitation of a helium level in a discharge plasma, the authors have determined the excitation transfer rate coefficients among the n = 3 levels due to atomic and electronic collisions. The result in the form of the thermally averaged cross section is: for 31P ? 31D = (1.9 +- 0.4) x 10-15 cm2 and = (2.4 +- 1.2) x 10-13 cm2; for 33D ? 33P = (5.3 +- 1.2) x 10-17 cm2 and = (0.9 +- 0.4) x 10-13 cm2. The cross sections for atomic collisions are in reasonably good agreement with other experimental and theoretical data, but the cross sections for electronic collisions are larger than the earlier experimental data by two orders and are in extremely good agreement with the recent calculations. (author)

1980-01-01

203

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

International Nuclear Information System (INIS)

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

1993-06-05

204

Double electron excitation and the Glauber theory  

Energy Technology Data Exchange (ETDEWEB)

The electron excitation cross sections for He (1s/sup 2/ /sup 1/S..-->..2p/sup 2/ /sup 3/P), Mg (3s/sup 2/ /sup 1/S..-->..3p/sup 2/ /sup 1/P), and Ca (4s/sup 2/ /sup 1/S..-->..4p/sup 2/ /sup 3/P) have been calculated with the use of the Ochkur, Glauber, and a simplified Glauber approximation. The results are compared with the Born-Oppenheimer approximation and, in the case of helium, with available experimental data. The Glauber and simplified Glauber approximations are found to differ significantly from the Born-Oppenheimer approximation, especially in the high-energy limit.

Williamson, W. Jr.; Ellis, D.G.; Ramanujam, P.S.

1982-12-01

205

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

206

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

207

Light induced electron transfer reactions of metal complexes  

International Nuclear Information System (INIS)

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

1980-07-19

208

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

209

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

Energy Technology Data Exchange (ETDEWEB)

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 which predicts 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, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, Shengbai

2013-01-15

210

CdJ2 dissociative excitation by electron impact  

International Nuclear Information System (INIS)

Effective cross sections of dissociative excitation of CdJ2 molecules by an electron impact in the energy range from the excitation threshold up to 100 eV were firstly measured. It follows from the results obtained that the process of dissociative excitation B2?1/2+ of CdJ* state by the electron impact has high intensity and its absolute value of the cross section is maximum in the region of low energies of electrons

1989-11-26

211

Electronic Excitations and Correlation Effects in Metals  

CERN Document Server

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

212

Resonant optical electron transfer in one-dimensional multiwell structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Tsukanov, A. V.

2008-01-01

213

Electron excitation of H_2(v'') levels to yield vibrationally excited H_2 molecules  

International Nuclear Information System (INIS)

Electron excitation cross sections to produce vibrationally excited H_2 molecules are calculated for molecules initially in the first and second vibrational levels. The pattern of excitation cross sections as a function of final vibrational level v'' differs from that found in previous calculations initiated from the ground vibrational level. 2 refs., 3 figs

1986-10-27

214

Energy transfer and excitation migration in organic semiconductors  

Science.gov (United States)

Energy transfer plays a key role in various applications of organic semiconductors such as electroluminescence, photovoltaics, and sensors. We have carried out a study combining transient and continuous wave (CW) optical spectroscopy with modeling. The fluorescence spectra and dynamics of a functionalized pentacene doped into a fluorescent host (Alq3) were measured and simulated by a Monte Carlo model incorporating distributed dopants and exciton migration. For nonluminescent materials, transient absorption spectroscopy provides insight into excitation migration. Singlet diffusion rates in C60 were determined by probing delayed charge transfer to ZnPc in films with a layered nanostructure.

Lane, Paul A.; Wolak, Mason A.; Cunningham, Paul D.; Melinger, Joseph S.

2012-09-01

215

Excitation transfer in th case of three interacting terms  

International Nuclear Information System (INIS)

Expressions are obtained for the cross section and rate constant in the case of three interacting terms. The results are used to study the excitation transfer during He(23S)+Ne collisions, with account of both a reduction in the potential barrier in adiabatic motion and multiple passage through non-adiabatic regions during vibrational motion in potential pits. The interaction parameters are determined from comparison of the calculated rate constants with experimental data on He(23S)+Ne quenching. Partial rate constants and excitation transfer cross sections for the Ne(4s1P1), Ne(4s3P0) and Ne(3d, 4p) level are calculated in wide ranges. It is established, that the population of Ne(4s1P1) levels is 2 times as high as that of Ne(4s3P0) levels

1985-01-01

216

Intramolecular Electron Scattering and Electron Transfer Following Autoionization in Dissociating Molecules  

Science.gov (United States)

Resonant Auger decay of core-excited molecules during ultrafast dissociation leads to a Doppler shift of the emitted electrons depending on the direction of the electron emission relative to the dissociation axis. We have investigated this process by angle-resolved electron-fragment ion coincidence spectroscopy. Electron energy spectra for selected emission angles for the electron relative to the molecular axis reveal the occurrence of intermolecular electron scattering and electron transfer following the primary emission. These processes amount to approximately 25% of the resonant atomic Auger intensity emitted in the studied transition.

Kugeler, O.; Prümper, G.; Hentges, R.; Viefhaus, J.; Rolles, D.; Becker, U.; Marburger, S.; Hergenhahn, U.

2004-07-01

217

Small reorganization energies of photoinduced electron transfer between spherical fullerenes.  

Science.gov (United States)

Rate constants of photoinduced electron transfer between spherical fullerenes were determined using triscandium nitride encapsulated C80 fullerene (Sc3N@C80) as an electron donor and the triplet excited state of lithium ion-encapsulated C60 fullerene (Li(+)@C60) as an electron acceptor in polar and less polar solvents by laser flash photolysis measurements. Upon nanosecond laser excitation at 355 nm of a benzonitrile (PhCN) solution of Li(+)@C60 and Sc3N@C80, electron transfer from Sc3N@C80 to the triplet excited state [(3)(Li(+)@C60)*] occurred to produce Sc3N@C80(•+) and Li(+)@C60(•-) (?(max) = 1035 nm). The rates of the photoinduced electron transfer were monitored by the decay of absorption at ?(max) = 750 nm due to (3)(Li(+)@C60)*. The second-order rate constant of electron transfer from Sc3N@C80 to (3)(Li(+)@C60)* was determined to be k(et) = 1.5 × 10(9) M(-1) s(-1) from dependence of decay rate constant of (3)(Li(+)@C60)* on the Sc3N@C80 concentration. The rate constant of back electron transfer from Li(+)@C60(•-) to Sc3N@C80(•+) was also determined to be k(bet) = 1.9 × 10(9) M(-1) s(-1), which is close to be the diffusion limited value in PhCN. Similarly, the rate constants of photoinduced electron transfer from C60 to (3)(Li(+)@C60)* and from Sc3N@C80 to (3)C60* were determined together with the back electron-transfer reactions. The driving force dependence of log k(et) and log k(bet) was well fitted by using the Marcus theory of outer-sphere electron transfer, in which the internal (bond) reorganization energy (?i) was estimated by DFT calculations and the solvent reorganization energy (?s) was calculated by the Marcus equation. When PhCN was replaced by o-dichlorobenzene (o-DCB), the ? value was decreased because of the smaller solvation changes of highly spherical fullerenes upon electron transfer in a less polar solvent. PMID:23862971

Kawashima, Yuki; Ohkubo, Kei; Fukuzumi, Shunichi

2013-08-01

218

One-phonon excitations of 92Zr from electron scattering  

International Nuclear Information System (INIS)

Low-lying collective vibrational excitations in 94Mo have previously been investigated with electron scattering experiments at the 130 MeV superconducting electron accelerator S-DALINAC. The evaluation of the measured form factors as a function of momentum transfer had supported the one-phonon interpretation of symmetric and mixed-symmetric states (MSSs) which have been defined in the framework of IBM-2. In the neighbouring even-even isotone 92Zr formed by N=52 neutrons with two valence neutrons and Z=40 with no protons occupying the ?(g9/2) sub-shell a stronger configurational isospin polarization of the one-phonon states than in 94Mo is expected. In order to verify this expectation, a new electron scattering experiment at the S-DALINAC has been performed. Our data and a comparison to the momentum-transfer dependence of the form factor of the 2+ states are presented. The E2 transition strength of the one-quadrupole phonon states and the E3 transition strength of the one-octupole phonon state have been extracted and are compared to previously derived spectroscopic data on MSSs of 92Zr.

2009-03-16

219

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

220

Electronic excited states of protonated aromatic molecules: Protonated Fluorene  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-01-17

 
 
 
 
221

Electron transfer at sensitized semiconductor electrodes  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer from the excited state of sensitizing dyes to the conduction band of semiconductors has been studied through photoelectrochemical techniques. Two systems were analyzed in detail: rhodamine B on ZnO and rose bengal on TiO/sub 2/. Prior to electrochemical experimentation, the adsorption characteristics of these dyes were investigated using ZnO, ZnS, and TiO/sub 2/ single crystals as substrates. Absorbance measurements of the adsorbed dye were taken as a function of the solution concentration of the dye. Adsorption isotherms heats of adsorption were also established; they were similar to literature data reported for adsorption of these dyes on powdered substrates. Using the absorbance data, the quantum efficiency for photoinjection of electrons from rhodamine B into a ZnO electrode was determined to be 2.7 x 10/sup -2/. This value was independent of the dye surface concentration down to 50% coverage of the electrode. With the assumption that not all of the rhodamine B adsorbed on the electrode has the same rate of electron injection, a kinetic model for the time decay of the photocurrent was developed; data were analyzed according to this theory. A rate constant for photoreduction of the adsorbed dye was determined for the reducing agents. 86 references.

Spitler, M.T.

1977-03-01

222

Measuring electron and hole transfer in core/shell nanoheterostructures.  

Science.gov (United States)

Using femtosecond transient absorption and time-resolved photoluminescence spectroscopy, we studied the electron versus hole dynamics in photoexcited quasi-type-II heterostructured nanocrystals with fixed CdTe core radii and varying CdSe shell coverage. By choosing the pump wavelength in resonance with the core or the shell states, respectively, we were able to measure the excited electron and hole dynamics selectively. Both, the core- and the shell-excited CdTe/CdSe nanocrystals showed the same spectral emission and photoluminescence lifetimes, indicating that ultrafast electron and hole transfer across the core/shell interface resulted in the identical long-lived charge transfer state. Both charge carriers have subpicosecond transfer rates through the interface, but the subsequent relaxation rates of the hole (?(dec) ? 800 ps) and electron (?(avg) ? 8 ps) are extremely different. On the basis of the presented transient absorption measurements and fitting of the steady-state spectra, we find that the electron transfer occurs in the Marcus inverted region and mixing between the CdTe exciton and charge transfer states takes place and therefore needs to be considered in the analysis. PMID:21671650

Chuang, Chi-Hung; Doane, Tennyson L; Lo, Shun S; Scholes, Gregory D; Burda, Clemens

2011-07-26

223

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

CERN Document Server

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

Nagesh, Jayashree; Brumer, Paul

2013-01-01

224

Multiphoton excitation of doubly excited states of two-electron atoms  

International Nuclear Information System (INIS)

One of the outstanding problems in atomic physics is to better understand the dynamics of highly excited two-electron systems. On the experimental side, single photon excitation studies have been limited to relatively low-lying states in He, while electron scattering experiments do not adequately resolve individual states. This paucity of experimental data is due to three general characteristics of these highly excited double electron states: (1) they have high energies usually greater than 1 Ryd; (2) they have little overlap with the ground state; (3) single photon excitation will not efficiently excite these states. It is the purpose of this paper to discuss the multiphoton excitation of these sperial states in two-electron systems. 12 references, 4 figures

1984-09-04

225

Chirped pulse control of long range electron transfer  

International Nuclear Information System (INIS)

We have studied the capabilities of intense ultrashort chirped pulses for controlling the long range electron transfer in systems strongly coupled to a polar medium. We considered a two state electronic donor/acceptor system, possessing a large difference of permanent dipole moments between donor and acceptor states, with relaxation treated as a diffusion on electronic potential energy surfaces. This relaxation model has enabled us to trace continuously the transition from a coherent population transfer to incoherent one. In addition to the field controlled electron transfer, we take into account a possibility of the direct optical transition between electronic states under study as well. We have introduced the generalized Rabi frequency that enabled us to extend the concepts and ideas of population transfer, developed for optical transitions, to the electron transfer (radiationless process) controlled with strong electromagnetic field. We have shown that it is possible to realize the 'radiationless' analogies to ?-pulse excitation, adiabatic rapid passage and pump-dump process. We have obtained a physically clear picture of the analogy to the adiabatic rapid passage for the chirped controlled long-range electron transfer by studying vibrationally non-equilibrium populations behavior and careful examination of all the conditions needed for adiabatic rapid passage

2004-12-06

226

Chirped pulse control of long range electron transfer  

Energy Technology Data Exchange (ETDEWEB)

We have studied the capabilities of intense ultrashort chirped pulses for controlling the long range electron transfer in systems strongly coupled to a polar medium. We considered a two state electronic donor/acceptor system, possessing a large difference of permanent dipole moments between donor and acceptor states, with relaxation treated as a diffusion on electronic potential energy surfaces. This relaxation model has enabled us to trace continuously the transition from a coherent population transfer to incoherent one. In addition to the field controlled electron transfer, we take into account a possibility of the direct optical transition between electronic states under study as well. We have introduced the generalized Rabi frequency that enabled us to extend the concepts and ideas of population transfer, developed for optical transitions, to the electron transfer (radiationless process) controlled with strong electromagnetic field. We have shown that it is possible to realize the 'radiationless' analogies to {pi}-pulse excitation, adiabatic rapid passage and pump-dump process. We have obtained a physically clear picture of the analogy to the adiabatic rapid passage for the chirped controlled long-range electron transfer by studying vibrationally non-equilibrium populations behavior and careful examination of all the conditions needed for adiabatic rapid passage.

Fainberg, B.D. [Department of Exact Sciences, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102 (Israel) and Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel-Aviv University, Tel-Aviv 69978 (Israel)]. E-mail: fainberg@hait.ac.il; Gorbunov, V.A. [Department of Exact Sciences, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102 (Israel); Lin, S.H. [Institute of Atomic and Molecular Science, Academia Sinica, P.O. Box 23-166, Taipei 106, Taiwan ROC (China)

2004-12-06

227

Molecular Basis for Directional Electron Transfer*  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of electron tunneling with distance. In this work intermolecular electron transfer was studied in kinetic experiments performed with the small tetraheme cytochrome from Shewanella oneidensis MR-1 and fro...

Paquete, Catarina M.; Saraiva, Ivo H.; Calc?ada, Eduardo; Louro, Ricardo O.

2010-01-01

228

Intramolecular shielding of charge-transfer excited states of surfactant-active rhenium(I) photosensitizers  

Energy Technology Data Exchange (ETDEWEB)

Excited-state electron-transfer processes involving organized assemblies are currently under active study. Such systems show promise for increasing the efficiency of energy-storage reactions. In particular, surfactant-active analogues of Ru(bpy)/sub 3//sup 2 +/ (bpy = 2,2'-bipyridine) with long hydrophobic alkyl chains have been used to modify sensitizer chemistry and photophysics. Reported here is an investigation of a new series of surfactant-active Re(I) photosensitizers: fac-((bpy)Re/sup 1/(CO)/sub 3/L)/sup +/ (L = NC(CH/sub 2/)/sub n/CH/sub 3/, n = 0,2,5,6,7,9,10,13,17). These systems exhibit intense d-..pi..* metal to ligand charge-transfer (MLCT) emissions in fluid solutions similar to the parent acetonitrile complex (n = 0). A dramatic example of an intramolecular perturbation of CT excited-state properties by the electronically passive alkyl chain is examined.

Reitz, G.A.; Dressick, W.J.; Demas, J.N.; DeGraff, B.A.

1986-08-20

229

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

International Nuclear Information System (INIS)

Recent experimental studies of resonant transfer and excitation (RTE) in ion-atom collisions are reviewed. In the RTE process correlated electron capture and projectile excitation occur together in a single encounter with a target atom. Measurements of Ca"q"+ + H_2 (q=10-19) from 100 to 370 MeV establish the projectile charge-state dependence of K-shell RTE and provide a detailed collision system. A comparison of the Ca"1"7"+ + H_2 data with previous results for Ca"1"7"+ + He demonstrates the effect of the target-electron momentum distribution on the RTE process. Studies of 230-610 MeV Nb"3"1"+ + H_2 provide information about RTE involing projectile L-shell excitation. All the measurements are in reasonable agreement wit theoretical calculations. (orig.)

1987-04-01

230

Dissociative excitation of carbon disulfide by electron impact  

International Nuclear Information System (INIS)

Dissociative excitation of carbon disulfide (CS2) producing CS fragments in the A1? excited state has been studied by optical excitation method in the electron energy range from threshold to 30 eV. The threshold energy for the dissociative excitation has been determined to be 9.33±0.06 eV. It has been also verified that the vibrational population of the CS radicals is inverted for v=0 and 1 levels

2003-09-01

231

Excitation transfer through open quantum networks: a few basic mechanisms  

CERN Multimedia

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

Venuti, Lorenzo Campos

2011-01-01

232

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

233

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

1990-09-17

234

Theory of nuclear excitation by electron capture for heavy ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2006-01-01

235

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

International Nuclear Information System (INIS)

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

1985-07-24

236

One-phonon excitations in 92Zr from electron scattering  

International Nuclear Information System (INIS)

Low-lying collective vibrational excitations of 92Zr have been investigated with electron scattering at the S-DALINAC. The form factors of isospin polarized one-quadrupole phonon states of 92Zr at the Z = 40 proton subshell closure have been measured and the momentum-transfer dependence of the form factors for the one-quadrupole phonon states have been compared to the prediction of the Quasiparticle Phonon Model. The E2 transition strengths of the one-quadrupole phonon states and the E3 transition strength of the one-octupole phonon state have been extracted. A comparison to the data on 94Mo and previous spectroscopic information on mixed-symmetric states (MSSs) of 92Zr will be given.

2010-01-01

237

Multiple excitation of confined graphene plasmons by single free electrons.  

Science.gov (United States)

We show that free electrons can efficiently excite plasmons in doped graphene with probabilities in the order of one per electron. More precisely, we predict multiple excitations of a single confined plasmon mode in graphene nanostructures. These unprecedentedly large electron-plasmon couplings are explained using a simple scaling law and further investigated through a general quantum description of the electron-plasmon interaction. From a fundamental viewpoint, multiple plasmon excitations by a single electron provide a unique platform for exploring the bosonic quantum nature of these collective modes. Not only does our study open a viable path toward multiple excitation of a single plasmon mode by a single electron, but it also reveals electron probes as ideal tools for producing, detecting, and manipulating plasmons in graphene nanostructures. PMID:24219514

Garc?ía de Abajo, F Javier

2013-12-23

238

Primary reactions in photosynthetic reaction centers of Rhodobacter sphaeroides - Time constants of the initial electron transfer  

Science.gov (United States)

The primary dynamics of reaction centers from Rhodobacter sphaeroides at room temperature are studied at low excitation intensities and low excitation rates. Analysis based on singular value decomposition yields three time constants in the picosecond range (ca. 1.2 ps, 3.5 ps and 220 ps). The spectral and temporal signatures are fully consistent with the step-wise electron transfer model published previously, with a first electron transfer to the bacteriochlorophyll with a time constant of 3.5 ps and a second 1.2 ps transfer to the bacteriopheophytin. No indications for adiabatic electron transfer are found in the time range >0.5 ps.

Dominguez, Pablo Nahuel; Himmelstoss, Matthias; Michelmann, Jeff; Lehner, Florian Thomas; Gardiner, Alastair T.; Cogdell, Richard J.; Zinth, Wolfgang

2014-05-01

239

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

Science.gov (United States)

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

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

2013-05-14

240

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

Energy Technology Data Exchange (ETDEWEB)

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.

Laursen, S.L.

1990-01-01

 
 
 
 
241

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

242

Low-energy electron attachment and detachment in vibrationally excited oxygen  

International Nuclear Information System (INIS)

Three-body electron attachment to O2 molecules and electron detachment from O2- ions have been theoretically studied in vibrationally excited oxygen and O2-containing mixtures. Assuming that electron attachment and detachment proceed via the formation of vibrationally excited temporary O2- ions, the rates of these processes were determined on the basis of the statistical approach for the vibrational transfer and relaxation in collisions between O2- ions and O2 molecules. The calculated attachment and detachment rate constants turned out to agree well with available measurements in unexcited oxygen. This method was extended to calculate attachment and detachment rates in vibrationally excited oxygen. It was shown that the effect of vibrational excitation on electron detachment is profound, whereas attachment of low-energy electrons to vibrationally excited O2 is inefficient. The calculated vibrational distribution of stable O2- ions turned out to be non-equilibrium in an excited gas and the effective vibrational temperature of the ions was much lower than the vibrational temperature of molecules. An analytical method was suggested to determine this distribution and the effective vibrational temperature. The calculated rate constants were used to simulate the formation and decay of an electron-beam-generated plasma in N2 : O2 mixtures at elevated vibrational temperatures. The calculations showed that vibrational excitation of molecules leads to orders of magnitude increase in the plasma density and in the plasma lifetime, in agreement with available observations.

2009-11-21

243

Exocellular electron transfer in anaerobic microbial communities  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2006-01-01

244

Electron excitation and capture in F"8"+ plus Ne collisions  

International Nuclear Information System (INIS)

K x-ray spectra from the nearly symmetric collision system F"8"+ plus Ne were obtained over the bombarding energy range from 10 to 40 MeV with sufficient spectral resolution to observe separately the K x-ray transitions from states formed by K-shell electron excitation and electron capture to excited states of fluorine. The cross sections for the two processes were obtained by normalization to total K x-ray production cross sections. The K x-ray production cross section for electron capture to excited states falls off by a factor of 40 over the energy range of 10 to 40 MeV, and the K-shell electron excitation cross section increases by a factor of 4 over the energy range 20 to 40 MeV. The K-shell excitation cross section has an energy dependence quite different from that observed for the asymmetric systems

1982-01-01

245

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

246

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

247

Noisy Quantum Cellular Automata for Quantum versus Classical Excitation Transfer  

Science.gov (United States)

We introduce a class of noisy quantum cellular automata on a qubit lattice that includes all classical Markov chains, as well as maps where quantum coherence between sites is allowed to build up over time. We apply such a construction to the problem of excitation transfer through 1D lattices, and compare the performance of classical and quantum dynamics with equal local transition probabilities. Our discrete approach has the merits of stripping down the complications of the open system dynamics, of clearly isolating coherent effects, and of allowing for an exact treatment of conditional dynamics, all while capturing a rich variety of dynamical behaviors.

Avalle, Michele; Serafini, Alessio

2014-05-01

248

Excitation energy transfer in novel acetylenic perylene diimide scaffolds  

DEFF Research Database (Denmark)

New perylene diimide (PDI) dimers (bis(PDI)s) with either tetraethynylethene (TEE) or 2,4-hexadiyne as the bridging unit were synthesized and the degree of intramolecular communication between the two PDI units was investigated as a function of the spacer unit and solvent polarity by absorption and emission spectroscopies, electrochemistry, and by atomic force microscopy (AFM). The experiments reveal that energy transfer occurs between TEE and PDI, and between PDI units. In the bis(PDI)-TEE system, flexible linkers allowed for intramolecular pi-pi stacking of the PDI chromophores in solution. The degree of stacking is solvent dependent, being more pronounced in non-polar solvents. The molecules were also found to self-assemble at a mica surface by intermolecular pi-pi interactions and to form fibrilar structures. Intermolecular excitation energy transfer was observed at the surface.

Shanks, David Euan; Preus, Søren

2010-01-01

249

High density electronic excitation under heavy ion bombardment  

International Nuclear Information System (INIS)

Upon the interaction of heavy ions with a solid, the energy possessed by the impinging ions is imparted to the solid in the form of the kinetic energy of nuclei and the electronic excitation energy. In this paper, the atomic displacement induced by electronic excitation is discussed. Since the energy imparted to electronic excitation by energetic ions is about 10"3 times as much as that imparted to the kinetic energy of nuclei, the atomic displacement induced by electronic excitation dominates in the materials in which this process is effective. The atomic displacement induced by electronic excitation has been well known, but recently, it has attracted attention anew because the recombination-induced defects in semiconductors arise from the same origin. In this review, the general concept of the atomic displacement induced by electronic excitation is first discussed. Then, the experimental results on its process in the tracks of energetic heavy ions and in laser-irradiated surface layers are presented. Finally, its possible mechanism is surveyed. The present state of the understanding of the phenomena of atomic displacement induced by high density electronic excitation is shown. (Kako, I.)

1985-08-01

250

Resonant transfer and excitation (RTE) in ion-atom collisions and dielectronic recombination in plasmas  

International Nuclear Information System (INIS)

In the resonant (charge) transfer and excitation (RTE) process, resonance states in the charge changed projectile are formed due to Coulomb-interaction with the target electrons. The calculated RTE cross section is proportional to the cross section for dielectronic recombination and its projectile energy dependence reflects the momentum distribution of the target electrons. Sample calculations for K x-ray production in S_1_3"+ + Ar collisions are discussed. An estimate of the experimental background indicates that RTE is more pronounced for heavy projectiles and light targets

1983-01-01

251

Electron-impact excitation of forbidden transitions in bismuth  

International Nuclear Information System (INIS)

The excitation of forbidden transitions of bismuth atoms and ions was investigated by the method of intersecting extended electron and atomic beams. The atomic beam was produced by evaporating bismuth from a tantalum crucible heated up by an electron beam. The electron beam was formed by a special low-voltage electron gun with an oxide cathode of the indirect chan-- nel with emitting surface 13x190 mm"2; energy distribution width for 90% of beam electrons about 0.9 eV. The excitation of bismuth spectral lines was studied in 190-850 nm range. The excitation of five forbidden bismuth cross sections was inves-- tigated. Excitation cross sections for bismuth forbidden transitions and forbidden transition radiation probabilities were calculated

1985-06-01

252

Excited electronic states and Raman spectra of 2-benzoylpyridine.  

Science.gov (United States)

Raman excitation profiles of several normal modes of 2-benzoylpyridine were measured, and the structural changes encountered on excitations, excited state symmetries, and vibronic couplings among various excited electronic states of the molecule were investigated. Vibrational spectroscopic studies of the molecule were done in detail, and critical investigation on the electronic spectra of the molecule was also carried out. It is shown that the experimentally allowed transitions, corresponding to the band around 262 and 238 nm, occur to the excited states, where the major geometry changes involve both ring CC/CN and CO stretching vibrations. An excited state lying around 185 nm above the ground state was also found to play an important role in the scattering process. All necessary and valuable quantum chemical calculations accompany the presented spectral studies. PMID:24359660

Datta, Shirsendu; Sett, Pinaky; Chowdhury, Joydeep; Ghosh, Manash; Mallick, Prabal Kumar

2013-12-01

253

Molecular dynamics simulations of the interactions of excited electrons  

International Nuclear Information System (INIS)

In this paper the processes of electron-electron interaction taking place in a highly excited electron gas are analyzed on the basis of molecular dynamics simulations. The time evolution of the system is described by using either classic mechanics or a quantum mechanical representation. New aspects of the collective behavior of the particles are born out by the simulations

1989-12-02

254

Theoretical Studies of Chemical Reactions following Electronic Excitation  

Science.gov (United States)

The use of multi-configurational wave functions is demonstrated for several processes: tautomerization reactions in the ground and excited states of the DNA base adenine, dissociation of glycine molecule after electronic excitation, and decomposition/deformation of novel rare gas molecules HRgF. These processes involve bond brealung/formation and require multi-configurational approaches that include dynamic correlation.

Chaban, Galina M.

2003-01-01

255

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

256

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

2008-08-14

257

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*{yields}e{gamma}, e*{yields}eZ and e*{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* 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* production via contact interactions is also addressed for the first time in ep collisions.

Aaron, F.D.; Alexa, C. [National Institute for Physics and Nuclear Engineering (NIPNE), Bucharest (Romania); Andreev, V. [Lebedev Physical Institute, Moscow (Russian Federation); Antunovic, B.; Aplin, S. [DESY, Hamburg (Germany); Asmone, A. [Dipartimento di Fisica, Universita di Roma Tre and INFN Roma 3, Roma (Italy); Astvatsatourov, A. [Inter-University Institute for High Energies ULB-VUB, Universiteit Antwerpen, Antwerpen (Belgium); Bacchetta, A. [DESY, Hamburg (Germany); Backovic, S. [Faculty of Science, University of Montenegro, Podgorica (Montenegro); Baghdasaryan, A. [Yerevan Physics Institute, Yerevan (Armenia); Baranov, P. [Lebedev Physical Institute, Moscow (Russian Federation); Barrelet, E. [LPNHE, Universites Paris VI and VII, IN2P3-CNRS, Paris (France); Bartel, W.; Beckingham, M. [DESY, Hamburg (Germany); Begzsuren, K. [Institute of Physics and Technology of the Mongolian Academy of Sciences, Ulaanbaatar (Mongolia); Behnke, O. [Physikalisches Institut, Universitaet Heidelberg, Heidelberg (Germany); Belousov, A. [Lebedev Physical Institute, Moscow (Russian Federation); Berger, N. [Institut fuer Teilchenphysik, ETH, Zuerich (Switzerland); Bizot, J.C. [LAL, Universite Paris-Sud, CNRS/IN2P3, Orsay (France); Boenig, M.-O. [Institut fuer Physik, TU Dortmund, Dortmund (Germany)] (and others)

2008-08-14

258

Electron impact excitation rate coefficients of N II ion  

International Nuclear Information System (INIS)

This paper calculates the electron impact excitation rate coefficients from the ground term 2s22p23P to the excited terms of the 2s22p2, 2s2p3, 2s22p3s, 2s22p3p, and 2s22p3d configurations of N II. In the calculations, multiconfiguration Dirac–Fork wave functions have been applied to describe the target-ion states and relativistic distorted-wave calculation has been performed to generate fine-structure collision strengths. The collision strengths are then averaged over a Maxwellian distribution of electron velocities in order to generate the effective collision strengths. The calculated rate coefficients are compared with available experimental and theoretical data, and some good agreements are found for the outer shell electron excitations. But for the inner shell electron excitations there are still some differences between the present calculations and available experiments. (atomic and molecular physics)

2010-09-01

259

Transport coefficients in nonequilibrium gas-mixture flows with electronic excitation  

International Nuclear Information System (INIS)

In the present paper, a one-temperature model of transport properties in chemically nonequilibrium neutral gas-mixture flows with electronic excitation is developed. The closed set of governing equations for the macroscopic parameters taking into account electronic degrees of freedom of both molecules and atoms is derived using the generalized Chapman-Enskog method. The transport algorithms for the calculation of the thermal-conductivity, diffusion, and viscosity coefficients are proposed. The developed theoretical model is applied for the calculation of the transport coefficients in the electronically excited N/N2 mixture. The specific heats and transport coefficients are calculated in the temperature range 50-50 000 K. Two sets of data for the collision integrals are applied for the calculations. An important contribution of the excited electronic states to the heat transfer is shown. The Prandtl number of atomic species is found to be substantially nonconstant.

2009-10-01

260

Transport coefficients in nonequilibrium gas-mixture flows with electronic excitation.  

Science.gov (United States)

In the present paper, a one-temperature model of transport properties in chemically nonequilibrium neutral gas-mixture flows with electronic excitation is developed. The closed set of governing equations for the macroscopic parameters taking into account electronic degrees of freedom of both molecules and atoms is derived using the generalized Chapman-Enskog method. The transport algorithms for the calculation of the thermal-conductivity, diffusion, and viscosity coefficients are proposed. The developed theoretical model is applied for the calculation of the transport coefficients in the electronically excited N/N(2) mixture. The specific heats and transport coefficients are calculated in the temperature range 50-50,000 K. Two sets of data for the collision integrals are applied for the calculations. An important contribution of the excited electronic states to the heat transfer is shown. The Prandtl number of atomic species is found to be substantially nonconstant. PMID:19905461

Kustova, E V; Puzyreva, L A

2009-10-01

 
 
 
 
261

Investigation of the strong electronic excitation effect in fullerite films induced by swift ions  

Energy Technology Data Exchange (ETDEWEB)

In order to investigate the strong electronic excitation effect, mainly including transformation from crystalline into amorphous state, of thin fullerite films in more detail, C{sub 60} films were irradiated by 171.2 MeV S{sup 9+} and 120 keV H ions. The irradiated samples were analysed by means of Raman scattering and X-ray photoelectron spectroscopy (XPS) techniques. The analysis results indicated that the amorphization process of C{sub 60} films irradiated by both ions is fully dominated by electronic energy transfer. An annealing effect of strong electronic excitation, which induced the intermediate graphitization process before amorphization in the case of H ion irradiation, was found for the first time. But in the case of S{sup 9+} ion irradiation, the destructive action of the strong electronic excitation exceeds the annealing effect, and therefore there is no intermediate graphitization process.

Jin Yunfan E-mail: hiam@ns.lzb.ac.cn; Yang Ru; Wang Yanbin; Liu Changlong; Liu Jie; Hou Mingdong; Yao Jianghong

2000-04-01

262

Collisional excitation of electron Landau levels in strong magnetic fields  

Science.gov (United States)

The cross sections for the excitation and deexcitation of the quantized transverse energy levels of an electron in a magnetic field are calculated for electron-proton and electron-electron collisions in light of the importance of the cross sections for studies of X-ray pulsar emission. First-order matrix elements are calculated using the Dirac theory of the electron, thus taking into account relativistic effects, which are believed to be important in accreting neutron stars. Results for the collisional excitation of ground state electrons by protons are presented which demonstrate the importance of proton recoil and relativistic effects, and it is shown that electron-electron excitations may contribute 10 to 20% of the excitation rate from electron-proton scattering in a Maxwellian plasma. Finally, calculations of the cross section for electron-proton small-angle scattering are presented which lead to relaxation rates for the electron velocity distribution which are modified by the magnetic field, and to a possible increase in the value of the Coulomb logarithm.

Langer, S. H.

1981-01-01

263

Simultaneous excitation and ionization of Ar by electron impact  

Energy Technology Data Exchange (ETDEWEB)

Absolute cross sections for the simultaneous excitation and ionization of Ar by electron impact have been measured by the optical method. In particular we report the measurements of eighteen levels belonging to the 3p/sup 4/ 4p and 3d/sup 4/ 4d configurations of Ar II. The dependence on electron energy of the excitation functions of some 3p/sup 4/ 4p levels was studied in the range 0-6000 eV. (orig.).

Sanchez, J.A.; Blanco, F.; Campos, J.; Garcia, G.

1989-02-01

264

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 excited states requires to go beyond ground-state density-functional theory (DFT). In this work we review three theoretical frameworks beyond DFT: the first is time-dependent density-functional theory ...

Olevano, Valerio

2009-01-01

265

Electronic Funds Transfer and Monetary Policy.  

Science.gov (United States)

A comprehensive analysis of the institutions, the instruments, and the channels of influence of monetary policy in the national economy is presented. It includes an examination of major points of impact of electronic funds transfer on monetary policy base...

1976-01-01

266

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)

2000-06-05

267

Electron impact excitation of argon in the extreme vacuum ultraviolet  

International Nuclear Information System (INIS)

Polarization-free excitation cross sections in the extreme vacuum ultraviolet have been measured for electron impact on Ar. Observed spectral features were those lines of Ar I and Ar II which lie between 700 and 1100 A. Excitation functions were measured for the Ar I resonance line at 1048 A and the Ar II resonance line at 920 A. Peak cross sections for these two lines were found to be (39.4 +- 7.9) x 10/sup -18/ and (6.9 +- 1.4) x 10/sup -18/ cm2, respectively. At low energies, excitation of the Ar II resonance line is dominated by an electron exchange transition

1976-01-01

268

Nuclear excitation by electronic transition - NEET  

International Nuclear Information System (INIS)

Experiments seeking to demonstrate nuclear excitation induced by synchrotron radiation have been enabled by the development of intense synchrotron radiation. The phenomena has been demonstrated in 197Au, while realistic upper limits for 189Os have been established. These new experiments report probabilities for NEET which are orders of magnitude below earlier experiments. A new experiment to measure atomic-nuclear mixing in 189Os is described. The experimental claim of NEET in isomeric 178Hf is not credible

2002-11-06

269

Electron Transfer for Large Molecules through Delocalization  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-01-01

270

Chemical generation of electronically excited nitrogen N2(A3 epsilon+ mu) and lasers on electronic transitions  

Science.gov (United States)

A numerical modeling of H2-F-HN3 and H2-F-NF2 flames was done in order to investigate the use of these flames as a pumping source for a N2(A)-IF electronic energy transfer (EET) laser. Equations for concentrations of different chemical species, populations of the ground and excited states of molecules, and energy-exchange processes were included in the model. The main processes determining the kinetics of electronically excited particles in H2-F-NF2 and H2-F-NH3 flames leading to the formation of N2(A) are listed. Results indicate the possibility of high concentrations of NA2(A) generation in these media. Electronically excited NA2(A) may be used as an energy donor to pump acceptors radiating in the visible region and the media considered appear to be promising sources for optical pumping.

Dvoriankin, A. N.; Makarov, V. N.

271

Electron-pair excitations and the molecular coulomb continuum  

Energy Technology Data Exchange (ETDEWEB)

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about the pair's relative momentum. A helium-like description of the molecular photo 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.

Feagin, J M [Department of Physics, California State University-Fullerton, Fullerton, CA 92834 (United States); Colgan, J [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Reddish, T J [Department of Physics, University of Windsor, 401 Sunset Avenue, Ontario, N9B 3P4 (Canada); Huetz, A, E-mail: jfeagin@fullerton.ed

2009-11-01

272

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

273

Rate coefficients for electron impact excitation of CO  

Science.gov (United States)

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

Vojnovi?, M.; Popovi?, M.; Risti?, M. M.; Vi?i?, M. D.; Popari?, G. B.

2013-09-01

274

A stochastic reorganizational bath model for electronic energy transfer  

CERN Document Server

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

Fujita, Takatoshi; Aspuru-Guzik, Alan

2014-01-01

275

Dynamics Of Electronic Excitation Of Solids With Ultrashort Laser Pulse  

International Nuclear Information System (INIS)

When ultrashort laser pulses irradiate a solid, photoabsorption by electrons in conduction band produces nonequilibrium highly energetic free electrons gas. We study the ionization and excitation of the electronic subsystem in a semiconductor and a metal (solid silicon and aluminum, respectively). The irradiating femtosecond laser pulse has a duration of 10 fs and a photon energy of h-bar ? = 38 eV. The classical Monte Carlo method is extended to take into account the electronic band structure and Pauli's principle for electrons excited to the conduction band. In the case of semiconductors this applies to the holes as well. Conduction band electrons and valence band holes induce secondary excitation and ionization processes which we simulate event by event. We discuss the transient electron dynamics with respect to the differences between semiconductors and metals. For metals the electronic distribution is split up into two branches: a low energy distribution as a slightly distorted Fermi-distribution and a long high energy tail. For the case of semiconductors it is split into two parts by the band gap. To thermalize, these excited electronic subsystems need longer times than the characteristic pulse duration. Therefore, the analysis of experimental data with femtosecond lasers must be based on non-equilibrium concepts.

2010-10-08

276

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

2007-07-01

277

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

278

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

International Nuclear Information System (INIS)

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

1992-01-01

279

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

International Nuclear Information System (INIS)

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

1993-10-01

280

Electron transfer processes in disordered media  

Energy Technology Data Exchange (ETDEWEB)

The paper reviews a broad range of approaches to the chemical dynamics in condensed phase systems. We analyze the problem of thermal electron transfer in disordered media (proteins) and discuss the interplay of quantum tunneling effects, electronic non-adiabaticity, friction and conformational changes on kinetic rate of the process. (author). 113 refs, 8 figs.

Gudowska-Nowak, E. [Dept. of Statistical Physics, Inst. of Physics, Jagiellonian Univ., Cracow (Poland)

1995-09-01

 
 
 
 
281

Electron transfer induced fragmentation of acetic acid  

Science.gov (United States)

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

Ferreira da Silva, F.; Meneses, G.; Almeida, D.; Limão-Vieira, P.

2014-04-01

282

DFT based computational study on the excited state intramolecular proton transfer processes in o-hydroxybenzaldehyde  

Science.gov (United States)

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of o-hydroxybenzaldehyde (OHBA) were studied using DFT-B3LYP/6-31G(d) and TD-DFT-B3LYP/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer in this compound. Excited states PE calculations support the ESIPT process in OHBA. The contour PE diagram and the variation of oscillator strength along the proton transfer co-ordinate support the dual emission in OHBA. Our calculations also support the experimental observations of Nagaoka et al. [S. Nagaoka, U. Nagashima, N. Ohta, M. Fujita, T. Takemura, J. Phys. Chem. 92 (1988) 166], i.e. normal emission of the title compound comes from S 2 state and the red-shifted proton transfer band appears from the S state. ESIPT process has also been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of OHBA and from the potential energy surfaces.

De, Sankar Prasad; Ash, Sankarlal; Bhui, Dipak kumar; Bar, Harekrishna; Sarkar, Priyanka; Sahoo, Gobinda Prasad; Misra, Ajay

2009-01-01

283

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

284

Ultrafast electron diffraction studies of optically excited thin bismuth films  

International Nuclear Information System (INIS)

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

2008-01-01

285

Excited baryon program at the Bonn electron stretcher accelerator ELSA  

International Nuclear Information System (INIS)

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

1988-08-04

286

Double-electron excitation above Xe K-edge  

International Nuclear Information System (INIS)

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

2001-06-01

287

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

288

Electronic excitations of helium bilayers on a metal substrate  

Science.gov (United States)

Neutral one-hole, one-electron excitations converging to the He1s ionization limit of He bilayers on a metal surface are studied with linearly polarized synchrotron radiation and time-of-flight techniques. Comparing signals of emitted electrons, emitted He atoms in metastable excited states, and fluorescence photons as a function of photon energy and polarization with theoretical results, a detailed picture of the photoexcitation is obtained. We show that the width of the photoabsorption peaks is governed in an anisotropic way by the large zero point motion of the He atoms; broadening directly correlates with the shape of the electronic clouds of the absorbing states.

Kossler, S.; Feulner, P.; Gauyacq, J.-P.

2014-04-01

289

Peculiarities of electron excitations decay in ion-molecular crystals  

International Nuclear Information System (INIS)

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

1996-09-19

290

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

291

Nuclear interlevel transfer driven by electronic transitions  

International Nuclear Information System (INIS)

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

1985-05-21

292

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

293

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

294

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

Energy Technology Data Exchange (ETDEWEB)

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.

Tanaka, Fumio [SC1-413, Department of Chemistry, Faculty of Science, Mahasarakham University, Mahasarakham 44150 (Thailand)], E-mail: fukoh2003@yahoo.com; Rujkorakarn, Rong [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Chosrowjan, Haik; Taniguchi, Seiji; Mataga, Noboru [Institute for Laser Technology, Utsubo-Hommachi 1-8-4, Nishiku, Osaka 550-0004 (Japan)

2008-06-02

295

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

296

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

297

A non-adiabatic quantum-classical dynamics study of the intramolecular excited state hydrogen transfer in ortho-nitrobenzaldehyde.  

Science.gov (United States)

Ab initio surface-hopping dynamics calculations have been performed to simulate the intramolecular excited state hydrogen transfer dynamics of ortho-nitrobenzaldehyde (o-NBA) in the gas phase from the electronic S(1) excited state. Upon UV excitation, the hydrogen is transferred from the aldehyde substituent to the nitro group, generating o-nitrosobenzoic acid through a ketene intermediate. The semiclassical propagations show that the deactivation from the S(1) is ultrafast, in agreement with the experimental measurements, which detect the ketene in less than 400 fs. The trajectories show that the deactivation mechanism involves two different conical intersections. The first one, a planar configuration with the hydrogen partially transferred, is responsible for the branching between the formation of a biradical intermediate and the regeneration of the starting material. The conversion of the biradical to the ketene corresponds to the passage through a second intersection region in which the ketene group is formed. PMID:21734992

Leyva, Verónica; Corral, Inés; Feixas, Ferran; Migani, Annapaola; Blancafort, Lluís; González-Vázquez, Jesús; González, Leticia

2011-08-28

298

The electronically excited states of 2-phenylindole  

Science.gov (United States)

The light absorption of 2-pbenylindole (2PI) in the UV region (210-350 nm) is investigated by means of linear dichroism in stretched polyethylene film and fluorescence polarization anisotropy in a propylene glycol glass. Experimentally, 2PI is found to have five distinct electronic transitions located above 200 nm for which the transition moments are determined. The conclusions are supported by quantum chemical calculations and the origin of the so-called composite band is discussed. Comparison with the absorption spectrum of the fluorescent DNA binding probe DAPI is also made and 2PI is found to be an appropriate model system for the electronic transitions of DAPI.

Albinsson, Bo; Eriksson, Svante; Lyng, Reidar; Kubista, Mikael

1991-03-01

299

Electronically excited states of tryptamine and its microhydrated complex  

Science.gov (United States)

The lowest electronically excited singlet states of tryptamine and the tryptamine (H2O)1 cluster have been studied, using time dependent density functional theory for determination of the geometries and multireference configuration interaction for the vertical and adiabatic excitation energies, the permanent dipole moments, and the transition dipole moment orientations. All molecular properties of the seven experimentally observed conformers of tryptamine could be reproduced with high accuracy. A strong solvent reorientation has been found upon electronic excitation of the 1:1 water cluster of tryptamine to the La and Lb states. The adiabatically lowest excited singlet state in case of the tryptamine monomer is the Lb state, while for the 1:1 water complex, the La is calculated below the Lb state.

Schmitt, Michael; Brause, Robert; Marian, Christel M.; Salzmann, Susanne; Meerts, W. Leo

2006-09-01

300

Vibrational excitation in electron-DCl scattering  

International Nuclear Information System (INIS)

A preliminary report is given of the results of fixed-nuclei and adiabatic calculations of the e-HCl and e-DCl electron-molecule scattering systems. The calculations are performed in the rotational and vibrational adiabatic approximation, and the use of DCl rather than HCl allows calculation to substantially lower energy

1979-01-01

 
 
 
 
301

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

CERN Document Server

Resonant vibrational excitation cross sections and the corresponding rate coefficients for electron-N$_2$ collisions occurring through the N$_2^-(\\textrm{X}\\ ^2\\Pi_g)$ resonant state are reviewed. New calculations are performed using accurate potential energies curves for the N$_2$ electronic ground state, taken from literature, and for the N$_2^-$ resonant state, obtained from $R$-matrix calculations. The calculations are extended also to the resonant excitation processes involving the N$_2$ ground state vibrational continuum, leading to dissociation. Electron impact dissociation is found to be significant from higher vibrational levels. Accurate analytical fits for the complete set of the rate coefficients are provided. The behavior of the dissociative cross sections is investigated for rotationally excited N$_2$ molecules, with $J=50,100$ and 150 and for different vibrational levels.

Laporta, V; Celiberto, R; Tennyson, J

2014-01-01

302

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

Science.gov (United States)

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. PMID:21894986

Lodowski, Piotr; Jaworska, Maria; Kornobis, Karina; Andruniów, Tadeusz; Kozlowski, Pawel M

2011-11-17

303

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

Science.gov (United States)

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

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

2014-06-01

304

Computational Approach to Electron Charge Transfer Reactions  

DEFF Research Database (Denmark)

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

Jónsson, Elvar �rn

2013-01-01

305

Protein electron transfer: Dynamics and statistics.  

Science.gov (United States)

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. PMID:23862967

Matyushov, Dmitry V

2013-07-14

306

Protein electron transfer: Dynamics and statistics  

Science.gov (United States)

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, Dmitry V.

2013-07-01

307

Radiative electron transfer in planar donor acceptor quinoxaline derivatives  

Science.gov (United States)

Synthetic and spectral studies have been performed for a family of electron donor-acceptor (D-A) quinoxaline derivatives possessing an aromatic amine as an electron donor. A photophysical behaviour of the compounds with an internal degree of freedom for internal D-A rotation and their rigid analogues with a fixed planar conformation appears to be very similar. Electronic transition dipole moments related to the charge-transfer (CT) absorption and fluorescence are determined by both the direct interactions between the 1CT and ground states and by the contributions from the locally excited configurations. The radiative properties of the D-A systems under study can be explained in terms of the simple model which assumes that the electronic coupling elements are mainly determined by the interactions between the atoms forming the A-D bond.

Czerwieniec, Rafa?; Herbich, Jerzy; Kapturkiewicz, Andrzej; Nowacki, Jacek

2000-08-01

308

Titanium(III) chemistry: electron-transfer reactions with ground-state poly(pyridine)osmium(III) complexes, quenching reactions with excited-state poly(pyridine)ruthenium(II) complexes, and formal reduction potentials  

International Nuclear Information System (INIS)

Potentiometric titrations of aquotitanium(III) with ferric ions have been performed in hydrochloric acid solution. The potentiometric data are described by E (V vs. NHE) = 0.03 - 0.059 log ([Ti(III)]/[Ti(IV)][H+]2) at 250C and 3.0 M ionic strength and are consistent with the interpretation that Ti3+(aq) and TiO2+ are the principal titanium(III) and titanium(IV) species, respectively, present at acid concentrations of 0.1 - 3.0 M. Rate constants for the oxidation of titanium(III) by a series of osmium(III) complexes, OsL33+, where L is a bipyridine or phenanthroline derivative, have been determined at 250C and 3.0 M ionic strength. The rates are interpreted in terms of the reactions of Ti3+(aq) and TiOH2+. The rate constants are correlated with the Marcus theory, and the exchange rate constants for the Ti4+ 3+(aq) and TiOH3+ 2+ couples are estimated. The rate constants for the reaction of titanium(III) with the excited states of the ruthenium(II) complexes RuL32+ are insensitive to the reduction potentials of the ruthenium(II) complexes. Arguments are presented to show that the quenching reactions proceed predominatly by energy-transfer mechanisms. The implications of these results for the production of Ti2+(aq) in quenching reactions are discussed. 6 figures, 5 tables

1979-01-01

309

Sub-shell excitations of rare gas atoms by electron impact  

International Nuclear Information System (INIS)

The sub-shell excitations of rare gas atoms have been investigated by electron energy-loss spectroscopy at various impact energies. In energy-loss spectra, we have observed several structures involving ones by the optically forbidden transitions, which are embedded in a continuum. Besides, we have found new states formed by two-electron excitations. In this region, above the first ionization limit the rare gas atoms can be ionized either directly or via the other excited states like inner-shell excited states or doubly excited states, which are coupled to the ionization continuum. These resonance line profiles have been theoretically studied by Fano. We have found that the line profile depend on the incident electron energy and scattering angle. In particular, the line profile parameters q for each state of spectra of argon have been determined. Besides, for 3s ? 4p excitation it has been found that the q parameters which are described as a function of momentum transfer has fallen on the straight line. (author)

2008-03-01

310

The low-energy, charge-transfer excited states of 4-amino-4-prime-nitrodiphenyl sulfide  

Science.gov (United States)

Absorption and emission spectra of 4-amino-4-prime-nitrodiphenyl sulfide in polar and nonpolar solvents were used to characterize and assign the low-energy excited states of the molecule. Fluorescence-excitation anisotropy spectra and fluorescence quantum yields were also used to characterize the photophysics of these states. The lowest-energy fluorescent singlet state was determined to be an intramolecular charge transfer (ICT) state involving transfer of a full electron charge from the amino to the nitro group yielding a dipole moment of about 50 D. A low-energy, intense absorption band is assigned as a transition to a different ICT state involving a partial electron charge transfer from sulfur to the nitro group.

O'Connor, Donald B.; Scott, Gary W.; Tran, Kim; Coulter, Daniel R.; Miskowski, Vincent M.; Stiegman, Albert E.; Wnek, Gary E.

1992-01-01

311

Photo-induced nuclear excitation by electron transition  

Science.gov (United States)

The nuclear excitation at electron transition (NEET), induced by X rays, is described on the basis of strict collision theory. All stages of the process are considered, including formation of the hole in the electron K shell, its decay accompanied by excitation of the nucleus, filling of the M-vacancy and subsequent deexcitation of the nucleus. The cross sections for the NEET and photoabsorption of X rays near K-edge are calculated. The results agree with the data of Kishimoto et al.

Dzyublik, A. Ya.

2011-07-01

312

Excitation of symmetric surface waves by electron tubular beams  

International Nuclear Information System (INIS)

The nonlinear theory of symmetric surface wave excitation by a low-density electron tubular beam in a cylindrical plasma-vacuum-metal waveguide is presented. A set of nonlinear equations is derived that describes the time evolution of the plasma-beam interaction. The influence of the beam and waveguide structure parameters on the saturation amplitude and excitation efficiency of the surface wave is investigated both numerically and analytically. Thermalization of the electron beam in the wave-fields is studied as well

2006-08-01

313

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

314

Excitation of ytterbium(3) ion luminescence by intramolecular energy transfer  

International Nuclear Information System (INIS)

Itterbium ion ability to luminescence in the complexes with a number of organic ligands has been studied. Itterbium chloride solution with the final concentration 1x10-4 M is used, to which aqueous or alcoholic solutions of reagents to create their final concentration 2-4x10-4 M are added. The necessary pH values are attained by the addition of acetate or ammonia buffer solutions. The luminescence is excited by mercury lamp radiation with the wave length 313 and 546 nm. Luminescence spectra are recorded in the range 960-1O0a nm. It is established that in certain compounds, resulting in colour reactions with lanthanide ions, Yb(3) ion luminescence, is manifested corresponding to the transition sub(2)Fsub(5/2) ? sup(2)Fsub(7/2). The type of ytterbium ion luminescence spectrum for the majority of complexes is similar, the radiation maximum is at 980 nm. The highest luminescence intensity ytterbium manifests in the complexes with phthalexone, pyridylazonaphthol, pyridylazoresorcinol and xylenol orange. The observed luminescence of Yb3+ can be atrributed to intramolecular energy transfer from organic part of molecules through triplet state

1983-01-01

315

Electronic excitations of a magnetic impurity state in the diluted magnetic semiconductor (Ga,Mn)As.  

Science.gov (United States)

The electronic structure of doped Mn in (Ga,Mn)As is studied by resonant inelastic x-ray scattering. From configuration-interaction cluster-model calculations, the line shapes of the Mn L3 resonant inelastic x-ray scattering spectra can be explained by d-d excitations from the Mn ground state dominated by charge-transferred states, in which hole carriers are bound to the Mn impurities, rather than a pure acceptor Mn2+ ground state. Unlike archetypical d-d excitation, the peak widths are broader than the experimental energy resolution. We attribute the broadening to a finite lifetime of the d-d excitations, which decay rapidly to electron-hole pairs in the host valence and conduction bands through the hybridization of the Mn 3d orbital with the ligand band. PMID:24679325

Kobayashi, M; Niwa, H; Takeda, Y; Fujimori, A; Senba, Y; Ohashi, H; Tanaka, A; Ohya, S; Hai, P N; Tanaka, M; Harada, Y; Oshima, M

2014-03-14

316

Fluorescent excitation transfer as a tool for the phase transition studies  

Science.gov (United States)

The use of the fluorescent resonant excitation transfer technique (FRET) to study the phase transition kinetics is demonstrated. The laser temperature jump is applied to the water/2,6-lutidine mixture and causes the demixing. Coumarin 480 and hydroxypyrene laser dyes form excitation transfer that interrogates the spatial structure of the system. Due to the differential solubility of these dyes in the components of the mixture, the excitation transfer ceases once the phase separation occurs. The spatial resolution of the method is determined by the Forster distance of the excitation transfer pair, and in this case is equal to 3 nm. The phase separation is completed within 1 microsecond. The rising edge of the fluorescence is consistent with polynomial growth of the phase separated domains, and not with Cahn-Hilliard fixed length instability. The theoretical model for the excitation transfer in a variety of systems such as separation of binary mixture, phase reorganization of membranes, formation of lamellar structure is developed.

Goun, Alexei

2012-02-01

317

Energy and electron transfer processes in polymethine dyes  

Science.gov (United States)

Polymethine dyes and its derivatives are attractive for their interesting optical and photo-electric properties. They are used as very efficient spectral sensitizers and laser dyes. Due to the high rate constant of deactivation channels of such dyes the primary processes of bimolecular processes as energy or electron transfer proceed within not more than some picoseconds or even shorter. In the case of a polymethine which does not isomerize we were able to show by means of time-resolved absorption spectroscopy that the singlet state photoelectron transfer to methyl- and benzylviologen had an efficiency of 0.15 with rate constants of 6.7.109 and 4.6.109 l/mole.s, respectively, yielding the polymethine dication radical. The photoreduction with tetraphenylborate and potassium rhodanide is also very efficient with an efficiency of about 0.10 with rate constants of 2.4.1010 and 1.6.1010 l/mole.s, respectively, yielding the polymethine neutral radical. The spectral differences of the observed radical spectra are small. The investigation of the temperature dependence of the photo induced electron transfer of the investigated polymethine to methylviologen results in an activation energy ?G*=24 kJ/mole and a value of the frequency factor of A=4.7.1014 l/mole.s. Strong deviation from a linear Arrhenius plot was observed at low temperatures which can be explained by solvent-solute interaction decreasing the electron transfer rate constant at lower temperatures. The calculated electron transfer rate constants agree with the assumption of the investigated process as a diffusion-controlled one. Energy transfer occurs as a efficient competitive deactivation channel from photo excited polymethine dyes to other chromophore systems with a strong overlapping of the fluorescence and the absorption bands of the donor and the acceptor, respectively. We have investigated the time and spectral evolution of the energy transfer process from a polymethine dye to different energy acceptor dyes in solution. The general question within this respect was the involvement of an intermediate electron transfer as competitive process in the energy transfer process. Whereas the Förster energy transfer radius calculated from the time-resolved data exceeds the value received from the overlap integral by 15%, indicating deviation from a normal Förster decay type the semilogarithmic plot of the ground state recovery kinetics vs. square root of time results in an ideal straight line dependence. No intermediate spectra as well as intermediate time behaviour was found in these complexes.

Feller, Karl-Heinz; Gadonas, Roaldas

1996-04-01

318

Electron impact excitation of argon in the extreme vacuum ultraviolet. [excitation functions, resonances, cross sections  

Energy Technology Data Exchange (ETDEWEB)

Polarization-free excitation cross sections in the extreme vacuum ultraviolet have been measured for electron impact on Ar. Observed spectral features were those lines of Ar I and Ar II which lie between 700 and 1100 A. Excitation functions were measured for the Ar I resonance line at 1048 A and the Ar II resonance line at 920 A. Peak cross sections for these two lines were found to be (39.4 +- 7.9) x 10/sup -18/ and (6.9 +- 1.4) x 10/sup -18/ cm/sup 2/, respectively. At low energies, excitation of the Ar II resonance line is dominated by an electron exchange transition. (AIP)

Mentall, J.E.; Morgan, H.D.

1976-09-01

319

Electron transfer in weakly interacting systems  

International Nuclear Information System (INIS)

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

320

Excitation of helium Rydbeig states in electron-beam plasma. 4. Mathematical simulation of excitation processes  

International Nuclear Information System (INIS)

A nonstability problem of the formation of Rydberg level population distribution is solved under conditions of continuous selective excitation of np-levels and linearly growing concentration of slow electrons. The calculation data confirm the qualitative interpretation of the experimental results which was elaborated in the previous works

1993-09-01

 
 
 
 
321

Electron transfer in dinucleoside phosphate anions  

International Nuclear Information System (INIS)

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

1976-02-12

322

Direct conversion of graphite into diamond through electronic excited states  

International Nuclear Information System (INIS)

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

2003-06-25

323

Minimal-excitation states for electron quantum optics using levitons  

Science.gov (United States)

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

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

2013-10-01

324

P nonconservation in nuclear excitation in the electron bremsstrahlung  

Energy Technology Data Exchange (ETDEWEB)

The purpose of the paper is to study space odd circular polarization of photons under bremsstrahlung of non-polarized electrons with account of nucleus excitation: e/sup -/+Asub(i)..-->..e/sup -/+..gamma..+Asub(f). Different constituents of hadron weak neutral current (WNC) are investigated separately by chosing transitions of an excited nucleus with certain quantum numbers, Effects of mixing nuclear states opposite parity conditioned by weak NN-interaction are studied. Differential cross section of bremsstrahlung for circularly polarized photons and degree of circular polarization of bremsstrahlung photons are calculated. Angular dependence of the degree of circular polarization for bremsstrahlung photons in /sup 12/C nucleus excitation (O/sup +/O..-->..1/sup +/1) by electrons with the energy E=30, 100, 300 and 500 MeV calculated in the Glashow-Salam-Weinberg model is presented. It is concluded that at high energies P-odd circular polarization of photons is conditioned exclusively by electroweak interference.

Kerimov, B.K.; Ganiev, A.G.; Ehl' gavkhari, A.I.; Safin, M.Ya. (Moskovskij Gosudarstvennyj Univ. (USSR))

1984-01-01

325

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 dynamic...

Bang, Junhyeok; Meng, Sheng; Sun, Yi-yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, S. B.

2013-01-01

326

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

CERN Document Server

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

327

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

328

Excitation of He (11S ? 33D) by electron impact  

International Nuclear Information System (INIS)

The total cross section Q(11S?33D) for electron impact excitation of helium have been recalculated using the Oppenheimer approximation. The present results, which differ considerably from an earlier calculation by Massey and Mohr (Proc. R. Soc.; A140:613 (1933)) are in much better agreement with experiment than the Ochkur approximation. (author)

1980-12-28

329

23P excitation of helium by electron impact  

International Nuclear Information System (INIS)

We present highly accurate relative measurements of 23P excitation of helium by electron impact at 30, 40 and 50 eV. These, when normalised to the convergent close-coupling (CCC) theory at one angle, yield excellent agreement at the remaining angles. This resolves some of the outstanding discrepancies between the CCC theory and earlier measurements. (authors). 14 refs., 3 figs

1996-01-01

330

Nanosecond Length Electron Pulses from a Laser-Excited Photocathode.  

Science.gov (United States)

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 ...

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

1989-01-01

331

Investigations of ultrafast dynamics in electronically excited alkylbenzenes  

Directory of Open Access Journals (Sweden)

Full Text Available 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.

Maksyutenko P.

2013-03-01

332

Energy transfer and photoluminescence quenching by benzophenones in some liquid scintillator solutions under gamma excitation  

International Nuclear Information System (INIS)

The rate parameter K3 of solvent-solute energy transfer and the rate parameter K7b of solvent-quencher energy transfer are determined under gamma excitation, for the system 2,5-diphenyloxazole in toluene using benzophenone, 4-bromobenzophenone and 4-nitrobenzophenone as external quenchers at 30degC. The relative contributions of diffusion, solvent excitation migration and dipole interaction to energy transfer and to quenching are estimated using different theoretical models. (author). 11 refs., 1 fig., 1 tab

1992-01-01

333

Electronic energy transfer in actinyl crystals  

International Nuclear Information System (INIS)

Time-resolved luminescence and excitation spectra of single crystals of caesium uranyl chloride containing a wide range of concentrations of bromide ion impurity have been studied between 4.2 K and room temperature. There is no evidence that the trapping process is diffusion controlled even in crystals containing one trap centre in 104. It follows that a lower limit on the resonant transfer rate at 4.2 K is 1010 s-1. The observation of distinct spectroscopic features characterizing sites adjacent to the trap site enables the anisotropy of the trapping rate to be demonstrated. (author)

1982-10-10

334

Electron transfer with TD-Split, a linear response time-dependent method  

International Nuclear Information System (INIS)

Graphical abstract: A simple method, time-dependent split (TD-Split) is developed for electron transfer through a TD evaluation of the lowest excitation energy from the ground state of the combined charged system. As an example, we study transfer between substituted fullerenes, primarily PCBM. Numerical linearization reduces the number of required iterations, and trends similar to experiment are found. Highlights: ? Electron transmission from charged-dimer transition-state excitation. ? Starting point: extended dimer charged (above-gap) homo, which is then excited. ? Excitation by real-time and linear response TD propagation. ? Analogous to two level system, but with full polarization included. ? TD-Split much larger than from static LUMO + 1–LUMO splitting for fullerene dimers. - Abstract: We present a simple method, time-dependent split (TD-Split) for A ? B electron transfer by a TD evaluation of the lowest excitation energy from the ground state of the combined (AB)? system. As an example, we study transfer between substituted fullerenes, primarily PCBM. Electron transfer in such fullerene systems is important as it is often the bottleneck in organic solar cells. The TD-Split method is described in detail, including numerical linearization which reduces the number of required iterations, and comparison to other possible approaches. We also compare to other molecules such as C60Me5H, and find similar trends as experiment.

2011-11-24

335

Quinone methide generation via photoinduced electron transfer.  

Science.gov (United States)

Photochemical activation of water-soluble 1,8-naphthalimide derivatives (NIs) as alkylating agents has been achieved by irradiation at 310 and 355 nm in aqueous acetonitrile. Reactivity in aqueous and neat acetonitrile has been extensively investigated by laser flash photolysis (LFP) at 355 nm, as well as by steady-state preparative irradiation at 310 nm in the presence of water, amines, thiols, and ethyl vinyl ether. Product distribution analysis revealed fairly efficient benzylation of the amines, hydration reaction, and 2-ethoxychromane generation, in the presence of ethyl vinyl ether, resulting from a [4 + 2] cycloaddition onto a transient quinone methide. Remarkably, we found that the reactivity was dramatically suppressed under the presence of oxygen and radical scavengers, such as thiols, which was usually associated with side product formation. In order to unravel the mechanism responsible for the photoreactivity of these NI-based molecules, a detailed LFP study has been carried out with the aim to characterize the transient species involved. LFP data suggest a photoinduced electron transfer (PET) involving the NI triplet excited state (?(max) 470 nm) of the NI core and the tethered quinone methide precursor (QMP) generating a radical ions pair NI(•-) (?(max) 410 nm) and QMP(•+). The latter underwent fast deprotonation to generate a detectable phenoxyl radical (?(max) 390 and 700 nm), which was efficiently reduced by the radical anion NI(•-), generating detectable QM. The mechanism proposed has been validated through a LFP investigation at 355 nm exploiting an intermolecular reaction between the photo-oxidant N-pentylnaphthalimide (NI-P) and a quaternary ammonium salt of a Mannich base as QMP (2a), in both neat and aqueous acetonitrile. Remarkably, these experiments revealed the generation of the model o-QM (?(max) 400 nm) as a long living transient mediated by the same reactivity pathway. Negligible QM generation has been observed under the very same conditions by irradiation of the QMP in the absence of the NI. Owing to the NIs redox and recognition properties, these results represent the first step toward new molecular devices capable of both biological target recognition and photoreleasing of QMs as alkylating species, under physiological conditions. PMID:21425810

Percivalle, Claudia; La Rosa, Andrea; Verga, Daniela; Doria, Filippo; Mella, Mariella; Palumbo, Manlio; Di Antonio, Marco; Freccero, Mauro

2011-05-01

336

Influence of multiphonon excitations and transfer on the fusion of Ca+Zr  

Science.gov (United States)

Fusion data for 48Ca+90,96Zr are analyzed by coupled-channels calculations that are based on the M3Y +repulsion, double-folding potential. By applying a previously determined nuclear density of Ca48, the neutron densities of the zirconium isotopes are adjusted to optimize the fit to the fusion data, whereas the proton densities are determined by electron-scattering experiments. It is shown that the fusion data can be explained fairly well by including couplings to one- and two-phonon excitations of the reacting nuclei and to one- and two-nucleon transfer reactions but there is also some sensitivity to multiphonon excitations. The neutron skin thicknesses extracted for the two zirconium isotopes are consistent with antiproton measurements. The densities of the zirconium isotopes are used together with the previously determined nuclear density of Ca40 to calculate the M3Y +repulsion potentials and predict the fusion cross sections of 40Ca+90,96Zr. The predicted cross sections for 40Ca+90Zr are in reasonable agreement with the data when the influence of multiphonon excitations and a modest transfer is considered. The prediction of the 40Ca+96Zr fusion cross section, on the other hand, is poor and underpredicts the data by 30% to 40%. Although couplings to transfer channels with positive Q values were expected to play an important role, they are not able to explain the data, primarily because the predicted Coulomb barrier is about 1.5 MeV too high. Possible reasons for this failure are discussed.

Esbensen, H.; Stefanini, A. M.

2014-04-01

337

Vibrational energy transfer in selectively excited diatomic molecules  

International Nuclear Information System (INIS)

Single rovibrational states of HCl(v=2), HBr(v=2), DCl(v=2), and CO(v=2) were excited with a pulsed optical parametric oscillator (OPO). Total vibrational relaxation rates near - resonance quenchers were measured at 295"0K using time resolved infrared fluorescence. These rates are attributed primarily to V - V energy transfer, and they generally conform to a simple energy gap law. A small deviation was found for the CO(v) + DCl(v') relaxation rates. Upper limits for the self relaxation by V - R,T of HCl(v=2) and HBr(v=2) and for the two quantum exchange between HCl and HBr were determined. The HF dimer was detected at 295"0K and 30 torr HF pressure with an optoacoustic spectrometer using the OPO. Pulsed and chopped, resonant and non-resonant spectrophones are analyzed in detail. From experiments and first order perturbation theory, these V - V exchange rates appear to behave as a first order perturbation in the vibrational coordinates. The rotational dynamics are known to be complicated however, and the coupled rotational - vibrational dynamics were investigated theoreticaly in infinite order by the Dillon and Stephenson and the first Magnus approximations. Large ?J transitions appear to be important, but these calculations differ by orders of magnitude on specific rovibrational transition rates. Integration of the time dependent semiclassical equations by a modified Gordon method and a rotationally distorted wave approximation are discussed as methods which would treat the rotational motion more accurately. 225 references

1978-01-01

338

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

339

Excitation and ionization of 4He clusters by electrons  

International Nuclear Information System (INIS)

Clusters are produced by expanding high pressure (P0?20 bar), low temperature (T0?5 K) helium gas through a 5 ?m nozzle into a vacuum. The neutral beam time-of-flight distribution has three peaks which we associate with distinct groups of large and small clusters, and atoms. The beam is ionized by electron impact and the resulting time resolved charged fragment mass distribution reveals in addition to previously observed anomalies (''magic numbers'') a new strong He+4 signal at high source pressures and low temperatures. The dependence of the various charged and neutral metastable fragment currents on the bombarding electron energy reveals that each has a unique appearance potential. A comparison with the calculated energy required for an electron to create various electronic excitations in the interior of a large cluster indicates that the production and dynamical evolution of metastable 3S1 atomic and a 3?+u molecular excitations plays a significant role in the formation of charged fragments from large clusters, but that the production of detectable metastable cluster fragments apparently proceeds via decay of high lying excitonic states. The strong He+4 signal does not appear until the incident electron has about enough energy to create two metastable 3S1 excitations in a cluster. Thus we propose that this ion signal results from the recombination of a pair of a 3?+u molecular excitons in or on a large cluster, or possibly from the dynamical evolution of a metastable spin quartet bound hole-exciton pair

1991-12-01

340

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

 
 
 
 
341

Spodumene and garnet luminescence excited by subnanosecond electron beams  

Science.gov (United States)

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

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

2011-11-01

342

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

343

Electron collisions and internal excitation in stored molecular ion beams  

International Nuclear Information System (INIS)

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

2006-01-01

344

Ultrashort electron beam generation from resonantly excited nonlinear laser wakefield  

Science.gov (United States)

A method for generating an ultrashort electron beam from a resonantly excited nonlinear wake field is proposed using a short laser pulse with a relativistic intensity. The considerable amount of electrons up to 10 C/m2 are extracted from an appropriate thin plasma layer. When the laser intensity is highly relativistic, the electron beam is singly bunched and has a pulse length less than the laser wavelength and a large energy spread with a maximum energy of tens of MeV.

Nagashima, K.; Kishimoto, Y.; Takuma, H.

1999-01-01

345

Excitation of low-frequency waves by auroral electron beams  

Science.gov (United States)

The electron distribution functions measured by the Dynamics Explorer 1 satellite during an auroral pass in 1981 are used in a linear instability analysis of low-frequency electromagnetic and electrostatic waves near and below the hydrogen gyrofrequency. It is suggested that the low-frequency electric and magnetic noise in the auroral zone might be explained by O and H electromagnetic ion cyclotron waves excited by energetic electron beams. An instability analysis suggests that upward and downward streaming electrons throughout the central plasma sheet region provide the free energy for heating oxygen ion through oxygen electrostatic ion cyclotron waves.

Lin, C. S.; Wong, H. K.; Koga, J.; Burch, J. L.

1989-01-01

346

Calculations of electron impact excitation cross sections related with plasmas  

International Nuclear Information System (INIS)

Fully relativistic distorted-wave (RDW) calculations of electron impact excitation (EIE) cross sections for Ne-like iron and neutral xenon have been performed. In the present method, Multi-configuration Dirac-Fock wavefunctions are used to describe the target-ion states, and the relativistic continuum wavefunctions are calculated in the frozen orbital self-consistent-field (SCF) approach with inclusion of exchange effects between the continuum electron and the target-ion. And in the calculations, the effects of electron correlation, Breit interaction and high partial wave contributions on EIE cross sections are considered systematically. The results are compared with previous calculations and experiments, good agreement is obtained. (author)

2008-03-01

347

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

Science.gov (United States)

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

Abramavicius, Vytautas; Abramavicius, Darius

2014-02-01

348

Electron impact excitation cross section studies of methane and acetylene  

Science.gov (United States)

The 40-200-nm emission features of electron-impact-excited CH4 and C2H2 are investigated experimentally using the crossed-beam apparatus and VUV calibration techniques described by Ajello et al. (1982 and 1985). The results are presented in extensive tables and graphs and characterized in detail. All of the features are attributed to the atomic dissociation fragments C I, C II, and H, and the long lifetimes and high kinetic energies of the excited H fragments are shown to truncate the H Lyman series near principal quantum number n = 10.

Pang, K. D.; Ajello, J. M.; Franklin, B.; Shemansky, D. E.

1987-01-01

349

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

350

Correlations in highly excited two-electron atoms - planetary behavior  

International Nuclear Information System (INIS)

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

351

Excitation of He(21,3S) by electron impact  

International Nuclear Information System (INIS)

Theoretical data for electron impact excitation of neutral helium in the He (21,3S) states are reviewed and a preferred data set is established for excitation to the He (n1,3L) states with n=2-4. Such a set of data was presented in a FOM report. The present work is an improvement made possible by new theoretical data, in particular the convergent close coupling data of Bray and Fursa, valid for the entire impact energy range of interest. (author). 29 refs, figs

1995-01-01

352

Isomer triggering via nuclear excitation by electron capture.  

Science.gov (United States)

Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient. PMID:17995323

Pálffy, Adriana; Evers, Jörg; Keitel, Christoph H

2007-10-26

353

Eucken correction in high-temperature gases with electronic excitation.  

Science.gov (United States)

In the present paper, thermal conductivity coefficient of high-temperature molecular and atomic gases with excited electronic states is studied using both the kinetic theory algorithm developed by authors earlier and the well known simple expression for the thermal conductivity coefficient proposed by Eucken and generalized by Hirschfelder. The influence of large collision diameters of excited states on the thermal conductivity is discussed. The limit of validity of the Eucken correction is evaluated on the basis of the kinetic theory calculations; an improved model suitable for air species under high-temperature conditions is proposed. PMID:24832274

Istomin, V A; Kustova, E V; Mekhonoshina, M A

2014-05-14

354

Electron impact excitation of atomic hydrogen and hydrogenic ions  

International Nuclear Information System (INIS)

The second-order potential model of Bransden and Coleman is used to calculate total cross-sections for the excitation of the n = 2 levels of one-electron ions in the energy interval 25Z"2 to 250Z"2 eV, enabling the range of validity of the Coulomb-Born approximation to be assessed. Previously reported work on the excitation of hydrogen is corrected and extended by the inclusion of exchange effects. Good agreement is obtained with the available experimental data. (author)

1975-01-01

355

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

DEFF Research Database (Denmark)

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

Møller, Søren; Andersen, Kristine B.

1998-01-01

356

Transient Raman spectroscopic studies on the excited-state intramolecular reverse proton transfer in 1-hydroxyanthraquinone  

Science.gov (United States)

We carried out the transient Raman spectroscopic studies to investigate the relaxation process of the excited-state intramolecular reverse proton transfer (r-ESIPT) in 1-hydroxyanthraquinone. To assign the observed excited-state vibrational modes, we carried out the mode analysis through the ab initio calculation with HF/4-31G(d) and CIS/4-31G(d) methods. The frequency changes of the proton-transfer-related Raman modes provide more quantitative feature on the r-ESIPT process in the excited triplet-state. Especially, the solvent natures affect the relaxation process of the excited keto-tautomer.

Cho, Dae Won; Kim, Seung Hoon; Yoon, Minjoong; Jeoung, Sae Chae

2004-06-01

357

Steric effects in photoinduced electron transfer reactions of ruthenium(II) complexes with aromatic amines  

International Nuclear Information System (INIS)

The rate constants (kq) of excited state electron transfer reactions of RuL32+ complexes (L is 4-alkyl-4'-methyl-2, 2'-bipyridyl) with several aromatic amines are sensitive to the size of the ligand and nature of the amine. The variation of kq with the size of the ligand is explained in terms of the change of electron transfer distance and steric effect. The importance of back electron transfer to form *RuL32+ in the endoergic and slightly exoergic regions has been realised. (author). 1 tab., 4 figs., 19 refs

1991-01-01

358

Energy transfer from the host excitations to Ce{sup 3+} ions in scandium borate  

Energy Technology Data Exchange (ETDEWEB)

Efficient energy transfer from the host excitations (self-trapped excitons, STE) excited at {lambda}{approx}160 nm to Ce{sup 3+} impurity ions was observed in scandium borate (ScBO{sub 3}). The luminescence and excitation spectra as well as time-resolved emission data were obtained. Energy transfer rates from the STE to Ce{sup 3+} of about 10{sup 8} s{sup -1} are observed and these are within an order of magnitude of estimates based on dipole-dipole energy transfer.

Feofilov, S.P. [Ioffe Physical-Technical Institute, St. Petersburg (Russian Federation)]. E-mail: Sergey.Feofilov@pop.ioffe.rssi.ru; Zhou, Y. [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States); Jeong, J.Y. [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States); Keszler, D.A. [Department of Chemistry, Oregon State University, Corvallis, OR 97331 (United States); Meltzer, R.S. [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2007-07-15

359

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

Science.gov (United States)

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

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

2011-11-01

360

Synthesis and characterization of C70-corrole--a new electron transfer dyad.  

Science.gov (United States)

A new electron transfer dyad, covalently linked C70-corrole, was prepared via C70 and 10-(4-Formylaryl)-5,15-bis(pentafluorophenyl). The structures and the properties of the new material were investigated by HPLC, MALDI-TOF-MS, UV-Vis-NIR spectroscopy, NMR, fluorescence analysis and CV/DPV. The free-energy of C70-corrole calculated by employing the redox potentials and singlet excited-state energy suggested the possibility of electron transfer from the excited singlet state of corrole to the fullerene entity, which agreed with the results of the theoretical calculation. PMID:24758033

Wang, Youde; Wang, Zhenzhen; Guo, Xihong; Cui, Rongli; Gao, Xingfa; Yang, Shangyuan; Chang, Fei; Dong, Jinquan; Sun, Baoyun

2014-07-01

 
 
 
 
361

A study on the rate constant of excited energy transfer from cyclohexane excited state to trioctyl phosphine oxide  

International Nuclear Information System (INIS)

The rate constant of excited energy transfer in the ? radiolysis of CH-TOPO system was studied by final product analysis. The results showed that the rate constant for the system was 1.9 x 1010L·mol·s-1, which was a little larger than that of an ordinary diffusion-controlled process

2001-02-01

362

Calculation of electron impact excitation and ionization of Be+  

International Nuclear Information System (INIS)

We present results from R-matrix with pseudo-states (RMPS) and convergent close-coupling (CCC) calculations for electron-impact excitation from and direct ionization of the ground state of the Be+ ion. The CCC and RMPS results are in very good agreement with each other. The long-standing discrepancy between theory and experiment for the total ionization cross section is unresolved, with the RMPS calculations supporting the present and earlier CCC results of Bray. The present 2P excitation results are in good accord with those of Mitroy and coworkers, but the values for the 3S, 3P and 3D cross sections are substantially different. In our view, the excitation cross sections for the n = 3 and n = 4 states have been predicted accurately from threshold to 1 keV for the first time. (Author)

1997-02-14

363

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

364

Study of localised electronic excitations by neutron scattering  

International Nuclear Information System (INIS)

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

1984-01-01

365

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

366

Coincidence study of excitation of cadmium atoms by electron impact  

Energy Technology Data Exchange (ETDEWEB)

We present experimental values of the electron impact coherence parameters (EICP) and reduced Stokes parameters for excitation of 5{sup 1}P{sub 1} state of cadmium atoms. The results have been obtained using electron-photon coincidence technique for incident electron energies 80 eV and 60 eV and electron scattering angles in the range of 5 deg. to 50 deg. We also present an additional set of data for electron energy 100 eV and scattering angle 50 deg. which complements our previous results. All the experimental values are compared with theoretical relativistic distorted-wave approximation (RDWA) calculations. The first Born approximation (FBA) predictions of the alignment angle are also presented. The theoretical results are in good qualitative agreement with the experimental data.

Piwinski, M [Institute of Physics, Nicholas Copernicus University, ul. Grudziadzka 5-7, PL 87-100 Torun (Poland); Dziczek, D [Institute of Physics, Nicholas Copernicus University, ul. Grudziadzka 5-7, PL 87-100 Torun (Poland); Klosowski, L [Institute of Physics, Nicholas Copernicus University, ul. Grudziadzka 5-7, PL 87-100 Torun (Poland); Srivastava, R [Department of Physics, Indian Institute of Technology, Roorkee 247 667, Uttranchal (India); Chwirot, S [Institute of Physics, Nicholas Copernicus University, ul. Grudziadzka 5-7, PL 87-100 Torun (Poland)

2006-04-28

367

Theoretical studies on the reaction pathways of electronically excited DAAF  

Energy Technology Data Exchange (ETDEWEB)

The use of temporally and spectrally shaped ultrafast laser pulses to initiate, as well as detect, high explosives is being explored at Los Alamos. High level ab initio calculations, presented here, are employed to help guide and interpret the experiments. The ground and first excited electronic states of 3,3{prime}-diamino-4,4{prime}-azoxyfurazan (DAAF) are investigated using complete active space self-consistent field (CASSCF) and time-dependent density functional theory (TD-DFT). The geometrical and energetic character of the excited state minima, conical intersections and reaction pathways of DAAF are described. Two radiative and two non-radiative excited state population quenching mechanisms are outlined, and possible pathways for photochemical and spectroscopic control are discussed. The use of laser light to control chemical reactions has many applications. The initiation and the detection of explosives are two such applications currently under development at Los Alamos. Though inherently experimental, the project can be aided by theory through both prediction and interpretation. When the laser light is in the UV/visible region of the electromagnetic spectrum, the absorbing molecule is excited electronically and excitation decay may occur either radiatively (fluorescence or phosphorescence) or non-radiatively (through internal conversion). In many cases decay of the excitation occurs through a mixture of processes, and maximizing the desired result requires sophisticated laser pulses whose amplitude has been optimally modulated in time and/or frequency space. Control of cis-stilbene photochemistry was recently demonstrated in our group, and we aim to extend this work to high explosive compounds. Maximizing radiative decay leads to increased fluorescence quantum yields and enhances the possibility of spectral detection of the absorbing molecule. Maximizing non-radiative decay can lead to chemistry, heating of the sample and possibly detonation initiation in an explosive compound. Here we describe high level quantum chemistry calculations aimed at mapping the electronic states involved in excitation of 3,3{prime}-Diamino-4,4{prime}-azoxyfurazan (DAAF) with 400-nm light. DAAF is a high-nitrogen high explosive that is of interest for its relative insensitivity to shock compression. The goal of the theoretical work described here is to determine the competing pathways for radiative and non-radiative electronic state quenching in an effort to help guide spectroscopic experiments being conducted in tandem.

Quenneville, Jason M [Los Alamos National Laboratory; Moore, David S [Los Alamos National Laboratory

2009-01-01

368

Reaction coordinates for electron transfer reactions  

International Nuclear Information System (INIS)

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

2008-12-07

369

Electron transfer in silver telluride melt  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer in silver telluride melt was studied experimentally at different temperatures. The method used to study electron transfer and thermodiffusion is based on Onsager's theory and consists of measuring the electrodiffusion potential which varies as a function of time in the system formed by the liquid semiconductor and the neutral metallic electrodes. The effective charges and the average coefficients of diffusion of silver ions were calculated and the ionic component of the total electrical conductivity of Ag/sub 2/Te melt was evaluated. It was observed that the indicated characteristics vary systematically in the series of silver chalcogenides with anionic substitution. The negative temperature coefficient of electrical conductivity in silver sulfide and silver selenide melts was explained.

Glazov, V.M.; Burkhanov, A.S.

1987-06-01

370

Custody transfer enhanced by electronic billing system  

Energy Technology Data Exchange (ETDEWEB)

Transcontinental Gas Pipe Line (TGPL) Corp. engineers have developed an electronic billing system for custody transfer that can reduce the cost of doing business and improve the accuracy of transfer measurements. The system accurately measures gas flow and quality, transmits gas data to a central facility, provides a capability to review the collected data, prepares bills based upon these data, and reduces staffing associated with the data collection and billing process. On-line flow computers are keys to this electronic billing system. These computers, referred to as remote terminal units (RTU's), are currently in service at TGPL at more than 30 locations with 30 more locations due to be on-line within 6 months and an additional 40 locations due within 15 months. These RTU's will be obtaining gas data from metering stations located in New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, Georgia, Louisiana, and Texas.

Knox, R.M.

1986-10-20

371

Imaging Excited State Dynamics with 2d Electronic Spectroscopy  

Science.gov (United States)

Excited states in the condensed phase have extremely high chemical potentials making them highly reactive and difficult to control. Yet in biology, excited state dynamics operate with exquisite precision driving solar light harvesting in photosynthetic complexes though excitonic transport and photochemistry through non-radiative relaxation to photochemical products. Optimized by evolution, these biological systems display manifestly quantum mechanical behaviors including coherent energy transfer, steering wavepacket trajectories through conical intersections and protection of long-lived quantum coherence. To image the underlying excited state dynamics, we have developed a new spectroscopic method allowing us to capture excitonic structure in real time. Through this method and other ultrafast multidimensional spectroscopies, we have captured coherent dynamics within photosynthetic antenna complexes. The data not only reveal how biological systems operate, but these same spectral signatures can be exploited to create new spectroscopic tools to elucidate the underlying Hamiltonian. New data on the role of the protein in photosynthetic systems indicates that the chromophores mix strongly with some bath modes within the system. The implications of this mixing for excitonic transport will be discussed along with prospects for transferring underlying design principles to synthetic systems.

Engel, Gregory S.

2012-06-01

372

Hydrogen and surface excitation in electron spectra of polyethylene  

Science.gov (United States)

The inelastic mean free path (IMFP) of electrons of polyethylene was determined by elastic peak electron spectroscopy (EPES). Hydrogen cannot be detected directly by conventional electron spectroscopies, such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), reflection electron energy loss spectroscopy (REELS) and EPES. The evaluation of electron spectra on polyethylene (PE) and other polymers needs corrections for hydrogen and surface excitation. Electron elastic backscattering on H atoms appears in the splitting of the elastic peak, shifting and Doppler broadening of the H peak produced by recoil effect. This shift is 0.34-3.8 eV for E=0.2-2.0 keV. Experiments resulted in separating the very low H elastic signal from the background. Surface excitation is characterised by the parameter Pse( E) which was described by formulae of Tanuma, Werner and Chen, using different definitions. The Pse( E) of PE was determined by our new procedure. Si and Ag were used as reference samples for its determination by EPES experiments. Experiments were made with a HSA spectrometer of high energy resolution. Their Monte Carlo evaluation was based on the NIST 64 database and IMFP of Tanuma et al., Gries and Cumpson. Pse( E) of PE was determined by best fit of experimental parameters, comparing the different IMFPs and surface excitation correction factors of Chen and Werner et al. The criteria of best fit are the RMS deviations from the different corrections. The total backscattering spectra (elastic and inelastic) of PE, C and Cu resulted in indirect observation of H.

Orosz, G. T.; Gergely, G.; Menyhard, M.; Tóth, J.; Varga, D.; Lesiak, B.; Jablonski, A.

2004-09-01

373

Activation entropy of electron transfer reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are...

Milischuk, Anatoli A.; Matyushov, Dmitry V.; Newton, Marshall D.

2005-01-01

374

Photonically excited electron emission from modified graphitic nanopetal arrays  

Energy Technology Data Exchange (ETDEWEB)

Efficient electron emission for energy conversion requires a low work function and a stable emitter material. The work function of graphene-based carbon materials can decrease significantly by intercalation with alkali metals, thus increasing their emission current. In this work, electron emission from potassium-intercalated carbon nanosheet extensions grown on electrode graphite is investigated. These petal-like structures, composed of 5-25 layers of graphene, are synthesized using microwave plasma chemical vapor deposition. Samples are intercalated with potassium, and a hemispherical energy analyzer is used to measure the emission intensity caused by both thermal and photonic excitation. The emission from the potassium-intercalated structures is found to consistently decrease the work function by 2.4 to 2.8 eV relative to non-intercalated samples. High emission intensity induced by photonic excitation from a solar simulator, with a narrow electron energy distribution relative to established theory, suggests that electron scattering decreases emitted electron energy as compared to surface photoemission. A modified photoemission theory is applied to account for electron scattering, and the sample work function and mean number of scattering events are used as parameters to fit theory to experimental data. The thermal stability of the intercalated nanopetals is investigated, and after an initial heating and cooling cycle, the samples are stable at low temperatures.

McCarthy, Patrick T.; Fisher, Timothy S. [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Vander Laan, Scott J.; Janes, David B. [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

2013-05-21

375

Extremely confined gap surface-plasmon modes excited by electrons.  

DEFF Research Database (Denmark)

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

Raza, Søren; Stenger, Nicolas

2014-01-01

376

Extremely confined gap surface-plasmon modes excited by electrons.  

Science.gov (United States)

High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5?nm. We argue that excitation of this mode, featuring very strong absorption, has a crucial role in experimental realizations of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. The occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices. PMID:24939641

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

2014-01-01

377

Excitation characteristics of different energy transfer in nanotube-perylene complexes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report the properties of perylene-nanotube complexes that form efficient energy transfer systems. Most perylene-derivatives yield similar ratios between transfer and direct luminescence (0.66 +/- 0.04). The photoluminescence spectra of the free compounds and the transfer complex are similar indicating that perylene and nanotubes act as separate systems. A further increase in interaction yields 40% higher transfer rates and luminescence excitation spectra that indicate a change in stacking ...

Ernst, Friederike; Heek, Timm; Setaro, Antonio; Haag, Rainer; Reich, Stephanie

2013-01-01

378

General theory of nuclear excitation by electron transitions  

Science.gov (United States)

We described the nuclear excitation by electron transition (NEET) by using strict collision theory combined with quantum electrodynamics. All stages of the process are considered, which include ionization of the atom by an x-ray photon with the formation of the hole in an inner electronic shell, its decay accompanied by the excitation of the nucleus, and the subsequent deexcitation of the nucleus. The cross sections for the NEET and photoabsorption of x rays are calculated near the threshold. We also analyzed the fine structure of the NEET curve analogous to the extended x-ray-absorption fine structure, well known in x-ray optics. The results agree with the findings of Kishimoto [Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.74.031301 74, 031301(R) (2006)].

Dzyublik, A. Ya.

2013-11-01

379

Study of excitation transfer in fluid molecular media: 2. Experimental aspects  

International Nuclear Information System (INIS)

The validity of our kinetic theory of excitation transfer between moving donors and acceptors is examined from donor fluorescence decay measurements performed in solutions with various acceptors. The experimental existence of specific fast and slow diffusion regimes has been made conspicuous. Experimentally deduced transfer lengths are discussed as a function of the viscosity of the solvent and of the reactive interaction responsible for excitation transfer. The characteristic parameters of the naphthalene-anthracene exchange interaction-cooperating in conjunction with a long-range dipole-dipole mechanism - could be deduced from transfer rate measurements in solvents of different viscosities

1986-01-01

380

The first observation of emission of electronically-excited states of the divalent Eu2+? ion in the new chemiluminescent system EuCl3·6H2O–Bui2AlH–O2 and the energy transfer from Eu2+? ion to the trivalent ion, Tb3+  

International Nuclear Information System (INIS)

We have discovered a new bright blue chemiluminescence (CL) in the title system, visible to the naked eye, caused by broadband fd emission of electronically-excited divalent europium ion, Eu2+? (?max=465 nm). This is the first example in which a divalent lanthanide ion acts as a emitter and enhancer of liquid-phase CL. The CL was produced by adding the diisobutylaluminum hydride Bui2AlH to a suspension of EuCl3·6H2O crystalline hydrate in THF. Bui2AlH removes water molecules from the coordination sphere of Eu3+, and reduces Eu3+ to Eu2+. As a result, aluminoxane, isobutane, hydrogen and the complex EuCl2·(THF)x, where x?2, are formed. And simultaneously excess of Bui2AlH is oxidized by oxygen traces generating a primary emitter, triplet-excited molecule, isobutyric aldehyde. The energy of the latter is transferred to the europium complex, EuCl2·(THF)x (x?2), which emits blue light. The divalent Eu2+ ion is a much more efficient enhancer of CL in oxidation of Bui2AlH than the trivalent lanthanide ion Tb3+. -- Highlights: ? The first chemiluminescence of divalent lanthanide Eu2+ in liquid-phase reaction was found. ? Eu2+? is generated and emitted at ?max=465 nm in EuCl3·6H2O–THF–Bui2AlH–O2 the system. ? Eu2+? is formed during energy transfer from triplet C3H7S(H)O? generated in Bui2AlH oxidation by O2. ? For the first time was established of energy transfer from Eu2+? to Tb3+ in solution was established

2013-04-01

 
 
 
 
381

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

382

Initial stage of the phase separation, observed with fluorescent excitation transfer technique  

Science.gov (United States)

The use of the fluorescent resonant excitation transfer (FRET) to study the phase transition kinetics is demonstrated. The laser temperature jump is applied to the water/2,6-lutidine mixture and causes the demixing of the mixture components. Coumarin 480 and hydroxypyrene laser dyes form excitation transfer pair once they are in the uniform phase of the mixture. Due to the differential solubility of these dyes in the componens of the mixture, the excitation transfer ceases once the phase separation occurs. The increase of the donor fluorescence indicates the extent of the phase separation. The spatial resolution of the method is determined by the Forster distance of the excitation transfer pair, and in this case is equal to 3 nm. The phase separation is completed within 1 microsecond. The rising edge of the fluorescence is consistent with polynomial growth of the phase separated domains, and not with Cahn-Hilliard fixed length instability.

Goun, Alexei; Fayer, Michael

2010-03-01

383

Rabi oscillations of 2D electrons under ultrafast intersubband excitation  

CERN Multimedia

We investigate coherent nonlinear dynamics of 2D electrons under ultrafast intersubband excitation by mid-IR pulses. We include the effects of relaxation and dephasing, both homogeneous and inhomogeneous, as well as detuning within a non-Markovian equation to obtain temporal population redistributions. We show how, using a cross-correlation method, the effects of Rabi oscillations may be detected in this system, and briefly discuss other detection methods.

McPeake, D; O'Reilly, E P

2003-01-01

384

Vibrational excitation of H2O by electron impact  

International Nuclear Information System (INIS)

We present results for the vibrational excitation of H2O by low-energy electrons (3) is made using a closure approximation. The results are consistent with other theoretical treatments. For the bending mode there is agreement with two older experiments but disagreement with a more recent experiment at 7.5 eV. However, the present results for the stretch modes are less than the experimental values. (author)

2001-10-14

385

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

International Nuclear Information System (INIS)

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

2009-02-01

386

Electron-impact excitation of argon at intermediate energies  

Science.gov (United States)

Large-scale R-matrix-with-pseudostates calculations for electron collisions with argon atoms, using a recently developed parallel version of our B-spline R-matrix code, are reported. The calculations were carried out in the semirelativistic jK-coupling scheme. They are intended to provide converged (with respect to the number of coupled states) results for electron-impact excitation of individual target states with dominant configurations 3p54s,3p54p, 3p53d, and 3p55s for incident electron energies from threshold to 300 eV. The close-coupling expansion includes 500 target states, with the lowest 78 states representing the bound spectrum and the remaining 422 the ionization continuum. The results reveal dramatic reductions of the predicted excitation cross sections at intermediate energies due to a strong influence of coupling to the target continuum and the higher-lying Rydberg states. Comparison with available experimental data for excitation raises questions about the absolute normalization in the measurements.

Zatsarinny, Oleg; Wang, Yang; Bartschat, Klaus

2014-02-01

387

75 FR 51707 - Electronic Funds Transfer of Depository Taxes  

Science.gov (United States)

...Electronic Funds Transfer of Depository Taxes AGENCY: Internal Revenue Service (IRS...proposed regulations relating to Federal tax deposits (FTDs) by Electronic Funds Transfer...contains proposed amendments to the Income Tax Regulations (26 CFR part 1), the...

2010-08-23

388

76 FR 709 - Electronic Funds Transfer of Depository Taxes; Correction  

Science.gov (United States)

...Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue...providing guidance relating to Federal tax deposits (FTDs) by Electronic Funds Transfer...List of Subjects 26 CFR Part 40 Excise taxes, Reporting and recordkeeping...

2011-01-06

389

Collision frequency of electrons in laser excited small clusters  

Energy Technology Data Exchange (ETDEWEB)

Laser excited small metallic clusters are simulated using classical pseudo potential molecular dynamics simulations. Time-dependent distribution functions are obtained from the electron and ion trajectories in order to investigate plasma properties. The question of local thermodynamic equilibrium is addressed, and size effects are considered. Results for the electron distribution in phase space are given, which are interpreted within equilibrium statistical physics. Momentum autocorrelation functions were calculated for different cluster sizes and for different expansion states from the expanding system after the laser-cluster interaction. A resonance behaviour of the autocorrelation function in finite systems was observed. First, results concerning collision frequencies in small clusters are given.

Raitza, Thomas; Reinholz, Heidi; Roepke, Gerd [Institut fuer Physik, Universitaet Rostock, 18055 Rostock (Germany); Morozov, Igor [Joint Institute for High Temperatures of RAS, Izhorskaya, 13, Building 2, Moscow 125412 (Russian Federation)], E-mail: thomas.raitza@uni-rostock.de

2009-05-29

390

Indistinguishability in electron-impact excitation-ionization of helium  

Energy Technology Data Exchange (ETDEWEB)

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

Harris, A. L.; Milum, B. [Physics Department, Henderson State University, 1100 Henderson St., Arkadelphia, Arkansas 71999 (United States); Madison, D. H. [Physics Department, Missouri University of Science and Technology, 1315 N. Pine Street, Rolla, Missouri 65409 (United States)

2011-11-15

391

Collisions of excited alkali atoms with O_2. I. Intermultiplet transfer  

International Nuclear Information System (INIS)

The cross sections for the Rb(7S?5D), Rb(5D?7S), and Na(4D?5S) collisional transfers induced by O_2 have been measured in absolute values as a function of the collision energy using a crossed beam apparatus. The experimental data have been compared with the predictions given by a multiple curve-crossing model where the symmetries of the states formed by the colliding alkali-metal atom--O_2 system as well as the molecular orientation are considered. Good agreement is observed between experimental and calculated cross sections. This tends to show that in spite of its approximations, a multiple curve-crossing model would be useful to obtain fairly accurate informations about collisional processes involving alkali atoms with as much as 4 eV electronic excitation

1987-08-15

392

Motion-enhanced quantum entanglement in the dynamics of excitation transfer  

CERN Document Server

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

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

2014-01-01

393

Excited State Proton Transfer of Carbazole. A Convenient Way to Study Microheterogeneous Environments  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract: Excited state proton transfer of carbazole gives rise to dual fluorescence from the two prototropic species. Simultaneous consideration of the two emissions takes care of many of the instrumental artifacts. The relative intensity of the two emissions of carbazole is sensitive not only to the pH of the bulk medium but also the microenvironment around the probe. Hence, excited state proton transfer of carbazole has been well studied and exploited extensively to study the detail of mic...

Nitin Chattopadhyay

2003-01-01

394

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

International Nuclear Information System (INIS)

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

1983-01-01

395

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

Science.gov (United States)

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

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

2014-04-01

396

Dynamics of Electron Transfer Processes at the Surface of Dye-Sensitized Mesoporous Semiconductor Films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron transfer reactions taking place at the surface of dye-sensitized semiconductors are key processes in dye-sensitized solar cells (DSSCs). After light absorption, the excited state of a dye injects an electron into a wide-bandgap semiconductor, usually titanium dioxyde, TiO2. The formed oxidized dye can then be intercepted by a redox mediator, typically iodide, before charge recombination between the injected electron and the oxidized dye...

Teuscher, Joe?l

2010-01-01

397

Oligo(phenylenevinylene) hybrids and self-assemblies: versatile materials for excitation energy transfer.  

Science.gov (United States)

Oligo(phenylenevinylene)s (OPVs) are extensively investigated ?-conjugated molecules that exhibit absorption and fluorescence in the UV-Vis spectral region, which can be widely tuned by chemical functionalisation and external control (e.g. solvent, temperature, pH). Further modulation of the optoelectronic properties of OPVs is possible by supramolecular aggregation, primarily driven by hydrogen bonding or ?-stacking interactions. In recent years, extensive research work has been accomplished in exploiting the unique combination of the structural and electronic properties of OPVs, most of which has been targeted at the preparation of molecules and materials featuring photoinduced energy transfer. This review intends to offer an overview of the multicomponent arrays and self-assembled materials based on OPV which have been designed to undergo energy transfer by means of a thorough choice of excitation donor-acceptor partners. We present a few selected examples of photoactive dyads and triads containing organic moieties (e.g. fullerene, phenanthroline) as well as coordination compounds (Cu(I) complexes). We then focus more extensively on self-assembled materials containing suitably functionalised OPVs that lead to hydrogen bonded aggregates, helical structures, gels, nanoparticles, vesicles, mesostructured organic-inorganic hybrid films, functionalised nanoparticles and quantum dots. In most cases, these materials exhibit luminescence whose colour and intensity is related to the efficiency and direction of the energy transfer processes. PMID:24553456

Praveen, Vakayil K; Ranjith, Choorikkat; Bandini, Elisa; Ajayaghosh, Ayyappanpillai; Armaroli, Nicola

2014-06-21

398

Charge transfer, vibrational excitation, and dissociative adsorption in molecule--surface collisions: Classical trajectory theory  

International Nuclear Information System (INIS)

The consequences of charge transfer processes occurring when a molecular beam of diatomic molecules is directed upon a solid surface are here considered. In analogy with resonance electron scattering from molecules or harpooning processes in atom--diatom collisions, the incident beam could either be scattered into a highly vibrationally excited molecular state, dissociatively scattered, or dissociatively adsorbed due to formation of temporary negative molecular ions which enable redistribution of the incident translation energy of the beam into intramolecular degrees of freedom. In this work, the exact classical trajectories for the diatomic molecule, including internal vibrational motion, are calculated for motion over model diabatic potential surfaces in which surface hopping due to charge transfer/harpooning is accounted for. Connections between classes of trajectories and topological features of the potential energy surfaces (PES) are illustrated. The model is used to study the average translational to vibrational energy transfer as a function of incident kinetic energy and of PES parameters. Branching ratios between scattered and dissociatively adsorbed molecules are obtained as a function of both incident translational and total energy and the role of the intermediate negative ion resonance in influencing the dynamics of molecular processes at surfaces is illustrated. Comparison with quantum mechanical theories is given in a subsequent paper

1985-06-01

399

Promoting interspecies electron transfer with biochar  

DEFF Research Database (Denmark)

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

Chen, Shanshan; Rotaru, Amelia-Elena

2014-01-01

400

Promoting interspecies electron transfer with biochar.  

Science.gov (United States)

Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why biochar may enhance methane production from organic wastes under anaerobic conditions. PMID:24846283

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

2014-01-01

 
 
 
 
401

Electronic excitations in magnesium epitaxy: Experiment and theory  

Science.gov (United States)

The nonadiabatic response of the electronic system during growth of Mg films is investigated both experimentally by measuring chemicurrents in Mg/p-Si(001) Schottky diodes, and theoretically by time-dependent perturbation theory applied to first-principles electronic-structure calculations. Reverse currents are detected in the diodes when they are exposed to thermally evaporated Mg atoms. Dissipation of condensation energy to the electronic system as well as absorption of infrared photons due to heat radiation are the current-generating mechanisms. They can be distinguished by studying the dependence of the currents on the evaporator temperature and on the Mg film thickness. In contrast to the photocurrents, the chemicurrent is proportional to the Mg atom flux as it reproduces the enthalpy of Mg sublimation in an Arrhenius diagram. Independent measurements of photocurrents by use of an empty evaporator as a source of heat radiation provide further evidence for a chemicurrent contribution to the overall signal. The presence of chemicurrents in Mg epitaxy is further supported by simulations of monolayer growth and calculations of the pertinent rates for nonadiabatic electronic transitions in Mg adsorption. The simulations show that the grown surface is atomically rough with many step and kink sites. Adsorption at these sites is sufficiently exothermic to induce energetic electron-hole pairs that give rise to a detectable current across the Schottky barrier of the diode. The calculated spectra of the excited electrons and holes are found to display high-energy tails above 0.4 eV. While the contribution of the electronic channel to the dissipation of condensation energy is very small (less than 1%), the calculated probability for high-energy electronic excitations in Mg epitaxy is compatible with the chemicurrent contribution extracted from the experimental data.

Hagemann, Ulrich; Timmer, Matthias; Krix, David; Kratzer, Peter; Nienhaus, Hermann

2010-10-01

402

Photon-to-electron quantum information transfer  

Science.gov (United States)

Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly readout the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and nonprecessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.

Kosaka, Hideo

2011-05-01

403

Marcus' contributions to electron-transfer theory  

Energy Technology Data Exchange (ETDEWEB)

The contributions of R.A. Marcus to the development of electron-transfer theory are reviewed. Marcus was one of the first to postulate that electron transfer depended upon nuclear configuration changes. He later developed a parallel formalism for electron-transfer and redox reactions at an electrode.

Sutin, N.

1986-07-31

404

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

405

Electronically Excited C2 from Laser Photodissociated C60  

Science.gov (United States)

Spectral and transient emission measurements are made of radiation from products of laser excitation of buckminsterfullerene (C60) vapor diluted in argon at 973 K. The principal radiation is from the Swan band system of C2 and, at early times, also from a black body continuum. The C2 radiation is observed only when C60 is excited by green (532 nm) and not with IR (1064 nm) laser radiation at energy densities of about 1.5 J/square cm. Transient measurements indicate that there are two characteristic periods of decay of radiation. The first period, lasting about 2 micro seconds, has a characteristic decay time of about 0.3 micro seconds. The second period, lasting at least 50 micro seconds, has a characteristic decay time of about 5 micro seconds. These characteristic times are thought to be associated with cooling of C60 molecules or nanosized carbon particles during the early period; and with electronically excited C2 that is a decomposition product of laser excited C60, C58, ... molecules during the later period.

Arepalli, Sivaram; Scott, Carl D.; Nikolaev, Pavel; Smalley, Richard E.

1999-01-01

406

Dynamic nuclear polarization with simultaneous excitation of electronic and nuclear transitions  

CERN Document Server

Dynamic nuclear polarization transfers spin polarization from electrons to nuclei. We have achieved this by a new method, simultaneously exciting transitions of electronic and nuclear spins. The efficiency of this technique improves with increasing magnetic field. Experimental results are shown for N@C60 with continuous-wave microwaves, which can be expected to produce even higher polarization than the corresponding pulsed techniques for electron spins greater than 1/2. The degree of nuclear polarization in this case can be easily monitored through the intensities of the well resolved hyperfine components in the EPR spectrum. The nuclear spin-lattice relaxation time is orders of magnitude longer than that of the electrons.

Morley, G W; Ardavan, A; van Tol, J

2008-01-01

407

Energy transfer in aminonaphthalimide-boron-dipyrromethene (BODIPY) dyads upon one- and two-photon excitation: applications for cellular imaging.  

Science.gov (United States)

Aminonaphthalimide-BODIPY energy transfer cassettes were found to show very fast (kEET ? 10(10)-10(11) s(-1) and efficient BODIPY fluorescence sensitization. This was observed upon one- and two-photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison with the direct excitation of the BODIPY chromophore, the two-photon absorption cross-section ? of the dyads is significantly incremented by the presence of the aminonaphthalimide donor [? ? 10 GM for the BODIPY versus 19-26 GM in the dyad at ?(exc)=840 nm; 1 GM (Goeppert-Mayer unit)=10(-50) cm(4) smolecule(-1) photon-(1)]. The electronic decoupling of the donor and acceptor, which is a precondition for the energy transfercassette concept, was demonstrated by time-dependent density functional theory calculations. The applicability of the new probes in the one- and twophoton excitation mode was demonstrated in a proof-of-principle approach in the fluorescence imaging of HeLa cells. To the best of our knowledge, this is the first demonstration of the merging of multiphoton excitation with the energy transfer cassette concept for a BODIPY-containing dyad. PMID:24730057

Collado, Daniel; Remón, Patricia; Vida, Yolanda; Najera, Francisco; Sen, Pratik; Pischel, Uwe; Perez-Inestrosa, Ezequiel

2014-03-01

408

Uv and 532 NM Photodissociation of O-Nitrotoluene Detection of Electronically Excited Nitric Oxide in Nitrogen and Argon  

Science.gov (United States)

It is well known that NO is one of the main fragments produced by photodissociation of o-nitrotoluene. We detected vibrationally-excited NO in ground and electronically excited states using LIF. We also observed emission due to the formation of C(I) which is overlapping with NO emission. In the presence of N_2, longer lifetime of the NO emission is observed showing evidence of energy transfer from highly excited N_2. In the presence of Ar, evidence of o-nitrotoluene-Ar cluster formation was observed.

Diez-y-Riega, Helena; Eilers, Hergen

2012-06-01

409

Remote interfacial electron transfer from supramolecular sensitizers  

Energy Technology Data Exchange (ETDEWEB)

There has been intense research in light-to-electrical energy conversion with ruthenium(II) polypyridyl charge transfer sensitizers anchored to wide bandgap semiconductors such as TiO{sub 2}. In an effort to achieve improved molecular control of sensitizer orientation the authors turned to bimetallic coordination compounds based on rhenium and ruthenium where the facial geometry of the Re center holds a Ru sensitizer proximate to the TiO{sub 2} surface. In this communication, the authors report the photophysical and photoelectrochemical properties of two Re-Ru linkage isomers in solution and the same isomers anchored to nanostructured TiO{sub 2} films. The results demonstrate rapid efficient interfacial electron transfer and a remarkably high light-to-electrical energy conversion even though the sensitizer is remote to the semiconductor-bound ligand.

Argazzi, R.; Bignozzi, C.A. [Dipartimento di Chimica dell`Universita, Ferrara (Italy); Heimer, T.A.; Meyer, G.J. [Johns Hopkins Univ., Baltimore, MD (United States)

1997-01-01

410

Progress and challenges in the calculation of electronic excited states.  

Science.gov (United States)

A detailed understanding of the properties of electronic excited states and the reaction mechanisms that molecules undergo after light irradiation is a fundamental ingredient for following light-driven natural processes and for designing novel photonic materials. The aim of this review is to present an overview of the ab initio quantum chemical and time-dependent density functional theory methods that can be used to model spectroscopy and photochemistry in molecular systems. The applicability and limitations of the different methods as well as the main frontiers are discussed. To illustrate the progress achieved by excited-state chemistry in the recent years as well as the main challenges facing computational chemistry, three main applications that reflect the authors' experience are addressed: the UV/Vis spectroscopy of organic molecules, the assignment of absorption and emission bands of organometallic complexes, and finally, the obtainment of non-adiabatic photoinduced pathways mediated by conical intersections. In the latter case, special emphasis is put on the photochemistry of DNA. These applications show that the description of electronically excited states is a rewarding but challenging area of research. PMID:21922624

González, Leticia; Escudero, Daniel; Serrano-Andrés, Luis

2012-01-16

411

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