WorldWideScience
1

Electron transfer, ionization, and excitation atomic collisions  

International Nuclear Information System (INIS)

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

2

Electron transfer and projectile excitation in single collisions  

International Nuclear Information System (INIS)

Studies of electron transfer (capture) and projectile excitation together in a single encounter are reviewed. This combined capture and excitation can result from either a correlated or an uncorrelated interaction. The correlated process is referred to as resonant transfer and excitation (RTE), while the uncorrelated process is called nonresonant transfer and excitation (NTE). RTE is analogous to dielectronic recombination (DR) which occurs in the interaction between an ion and a free electron. Experimental and theoretical works leading to establishing the existence of RTE are reviewed as well as considerations relevant to distinguishing RTE from NTE. The dependences of RTE on projectile atomic number (14 ? Z ? 23) for Li-like ions, and on projectile charge state for H-like to Ne-like ions have been measured and compared with theory. The effect of the target electron momentum distribution on RTE has been demonstrated by comparing measurements for H2 and He targets. Measurements of RTE involving L-shell excitation have been conducted and compared with K-shell results. All of the measured RTE cross sections to date for H2 and He targets are in reasonable agreement with calculations based on theoretical DR cross sections averaged over the target electron momentum distribution; however, systematic discrepancies between experiment and theory exist. Additionally, is has been found that RTE can contribute considerably to total single-electron capturerably to total single-electron capture cross sections in the region where RTE is important, accounting for nearly half of the total capture events for calcium ions colliding with H2. (orig.)

3

[Electron transfer, ionization and excitation in atomic collisions  

International Nuclear Information System (INIS)

The research being carried out at Penn State by Winter and Alston addresses the fundamental atomic-collision processes of electron transfer, ionization, and excitation. Winter has focussed attention on intermediate and, more recently, higher collision energies -- proton energies of at least about 50 keV -- for which coupled-state approaches are appropriate. Alston has concentrated on perturbative approaches to symmetric ion-ion/atom collisions at high energies and to asymmetric collisions at intermediate to high energies

4

Electron transfer, ionization, and excitation in atomic collisions  

Energy Technology Data Exchange (ETDEWEB)

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

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

1992-01-01

5

Energy transfer between electronically excited zinc and calcium atoms  

International Nuclear Information System (INIS)

A series of experiments have been performed in which zinc atoms carried in a flowing stream of helium are excited to the 4(3P1) state by optical pumping with a XeCl excimer laser. Addition of calcium atoms to the flow results in quenching of the excited zinc atoms. The cross section for this energy transfer process is sigma> or =3 x 10-16 cm2, corresponding to Zn(4 3P/sub J/) quenching in fewer than 10 collisons with calcium atoms. Subsequent to optical excitation of the zinc atoms, emission was observed from both the 4 1P1 and 5 3S1 excited states of calcium. Integration of the intensities of the calcium emissions indicated that excitation of the singlet and triplet manifolds in calcium occurs with comparable probability, suggesting that spin conservation is not a strong constraint in the energy transfer process. Summation of the intensities indicate that the E--E transfer process accounts for most of the quenching of the excited zinc atoms

6

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.

7

Linear energy relationships in ground state proton transfer and excited state proton-coupled electron transfer.  

Science.gov (United States)

Proton-coupled electron transfer (PCET) processes are elementary chemical reactions involved in a broad range of radical and redox reactions. Elucidating fundamental PCET reaction mechanisms are thus of central importance for chemical and biochemical research. Here we use quantum chemical density functional theory (DFT), time-dependent density functional theory (TDDFT), and the algebraic diagrammatic-construction through second-order (ADC(2)) to study the mechanism, thermodynamic driving force effects, and reaction barriers of both ground state proton transfer (pT) and photoinduced proton-coupled electron transfer (PCET) between nitrosylated phenyl-phenol compounds and hydrogen-bonded t-butylamine as an external base. We show that the obtained reaction barriers for the ground state pT reactions depend linearly on the thermodynamic driving force, with a Brønsted slope of 1 or 0. Photoexcitation leads to a PCET reaction, for which we find that the excited state reaction barrier depends on the thermodynamic driving force with a Brønsted slope of 1/2. To support the mechanistic picture arising from the static potential energy surfaces, we perform additional molecular dynamics simulations on the excited state energy surface, in which we observe a spontaneous PCET between the donor and the acceptor groups. Our findings suggest that a Brønsted analysis may distinguish the ground state pT and excited state PCET processes. PMID:25485993

Gamiz-Hernandez, Ana P; Magomedov, Artiom; Hummer, Gerhard; Kaila, Ville R I

2015-02-12

8

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

Czech Academy of Sciences Publication Activity Database

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

Král, Karel; Menšík, Miroslav

9

Energy transfer mechanism of electron excitation from UO22+ to Eu3+ in phosphate glasses  

International Nuclear Information System (INIS)

The concentration dependence of luminescent-kinetic properties of the Eu3+-activated cesium uranyl-phosphate glasses is investigated. It is concluded that the energy transfer mechanism of electron excitation may be explained from the viewpoint of exchange interactions

10

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

Bohr, Henrik; Malik, F. Bary

2013-01-01

11

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

Science.gov (United States)

The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4?-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H+ is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated +H?B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state. PMID:21555541

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

2011-01-01

12

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1984-01-01

13

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

14

Search for resonant electron transfer and double excitation in Kr34+ + H2 collisions  

International Nuclear Information System (INIS)

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

15

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

Czech Academy of Sciences Publication Activity Database

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

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

16

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-03-03

17

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

International Nuclear Information System (INIS)

Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 105?s?1. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices

18

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

19

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

20

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

Energy Technology Data Exchange (ETDEWEB)

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

Hoffman, M.Z.

1993-03-31

21

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

22

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

Energy Technology Data Exchange (ETDEWEB)

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

Christensen, K.

1993-08-01

23

Fragment transition density method to calculate electronic coupling for excitation energy transfer  

Energy Technology Data Exchange (ETDEWEB)

A general approach, the Fragment Transition Density (FTD) scheme, is introduced to estimate electronic coupling for excitation energy transfer in a molecular system. Within this method, the excitation energies and transition densities of the system are used to derive the coupling matrix element. The scheme allows one to treat systems where exciton donor and acceptor are close together and their exchange interaction and orbital overlap are significant. The FTD method can be applied in combination with any quantum mechanical approach to treat excited states of general nature including single-, double-, and higher excitations. Using FTD approach, we derive excitonic couplings for several systems computed with the CIS, TD DFT and MS-CASPT2 methods. In particular, it is shown that the estimated coupling values in DNA ?-stacks are strongly affected by the short-range electronic interaction of adjacent nucleobases.

Voityuk, Alexander A., E-mail: alexander.voityuk@icrea.cat [Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain and Institut de Química Computacional i Catàlisi (IQCC), Universitat de Girona 17071 Girona (Spain)

2014-06-28

24

Resonant transfer and excitation (RTE) and nonresonant electron transfer and excitation (NTE) in Si11+ on He collisions  

International Nuclear Information System (INIS)

Recently, crossed electron-ion beam experiments, involving 2s-2p or 3s-3p excitations designed to measure the scale for dielectronic recombination (DR) cross sections have been reported. Si11+ ion beams with energies varying from 15-100 MeV are incident on He and Si K X-rays in coincidence with Si10+ ions are recorded so that cross sections can be extracted. At 85 MeV, RTE is the dominant process. Impact parameters dependent models of capture and excitation describe the shape of the NTE feature quite well. The energy dependence of Si K X-ray excitation cross sections is reasonably well described by a semiclassical calculation with a straight line trajectory and screened hydrogenic wavefunctions. The capture cross sections are compared with an impact parameter dependent Bohr-Lindhard model, scaled OBK, and empirical scaling rules. (orig./HSI)

25

Proton transfer between phenol and ammonia in ground and excited electronic states  

Science.gov (United States)

Ab initio calculations consider the H-bonded complex between phenol and ammonia. The transfer of a proton in the ground electronic state, which would form PhO - … +HNH 3, is highly disfavored. However, the situation changes dramatically in the first excited singlet state where the proton transfer potential develops a second minimum, competitive in energy with the neutral pair PhOH … NH 3. Following electron ejection, the radical cation complex, PhOH + … NH 3, contains a very flat proton transfer potential connecting PhOH ·+ … NH 3 with PhO · … H +NH 3. Addition of more ammonia molecules further stabilizes the proton-transfered PhO · … H +NH 3 configuration.

Yi, Manyin; Scheiner, Steve

1996-11-01

26

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

Science.gov (United States)

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

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

2014-12-21

27

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

International Nuclear Information System (INIS)

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

28

Electron transfer, ionization, and excitation in atomic collisions. Progress report, June 15, 1989--June 14, 1992  

Energy Technology Data Exchange (ETDEWEB)

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

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

1992-08-01

29

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

International Nuclear Information System (INIS)

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

30

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

31

Influence of electronic delocalization in metal-to-ligand charge transfer excited states  

Energy Technology Data Exchange (ETDEWEB)

In the metal-to-ligand-charge transfer (MLCT) excited states of the ligand-bridged complexes [(dmb){sub 2}Ru({mu}-bbpe)-Ru(dmb){sub 2}](PF{sub 6}){sub 4} and [(bpy){sub 2}Os({mu}-bbpe)Os(bpy){sub 2}](PF{sub 6}){sub 4} (bpy is 2,2{prime}-bipyridine, dmb is 4,4{prime}-dimethyl-2,2{prime}-bipyridine, bbpe is trans-1,2-bis-(4-(4{prime}-methyl)-2,2{prime}bipyridyl)ethene) bbpe acts as the acceptor ligand. This conclusion is based on transient UV-visible and resonance Raman measurements, which also reveal that the excited electron in the Ru complex is localized over the bbpe ligand. Compared to related complexes having comparable energy gaps, the lifetimes of [(dmb){sub 2}Ru({mu}-bbpe)Ru(dmb){sub 2}]{sup 4+*} ({tau} = 1.31 {mu}s in CH{sub 3}CN at 298 K) and [(dmb){sub 2}Ru(bbpe)]{sup 2+*} ({tau} = 1.15 {mu}s in CH{sub 3}CN at 298 K) are unusually long. The extended lifetimes are a delocalization effect caused by decreased bond displacement changes in the excited state. This decreases vibrational overlap between states, and the rate constant for nonradiative decay. Delocalization disperses the excited electron over the molecular framework of the acceptor ligand, decreasing changes in local bond displacements compared to bpy. These results have important implications for the design of complexes which are broad visible light absorbers and yet retain accessible excited state lifetimes.

Strouse, G.F.; Schoonover, J.R.; Boyde, S.; Jones, W.E. Jr.; Meyer, T.J.; Duesing, R. [Univ. of North Carolina, Chapel Hill, NC (United States)

1995-01-18

32

Antenna excited state decay kinetics establish primary electron transfer in reaction centers as heterogeneous.  

Science.gov (United States)

The decay of the excited primary electron donor P* in bacterial photosynthetic reaction centers (both membrane-bound and detergent-isolated) has been observed to be nonexponential on a time scale of some tens of picoseconds. Although the multipicosecond nonexponentiality of P* has been ascribed to heterogeneity in teh rate of primary electron transfer (PET), the decay kinetics can be interpreted equally well using homogeneous models. To address this ambiguity, we studied the decay of excited bacteriochlorophyll (Bchl) in the membrane-bound core antenna/reaction center complexes of wild-type and mutant reaction center strains of Rhodobacter capsulatus. Reaction centers isolated from these same strains display a range of multiexponentiality in primary charge separation. The mutant strains carry substitutions of amino acids residing near the monomeric Bchl on the active and/or inactive sides of the reaction center. Transient absorption measurements monitoring the Qy bleach of antenna Bchls require at least two exponential components to fit all decays. The wild type was fitted with equal-amplitude components whose lifetimes are 24 and 65 ps. The shortest-lived component is relatively insensitive to mutation, in contrast to the longer-lived component(s) whose amplitude and magnitude were dramatically perturbed by amino acid substitutions. Unlike the situation with isolated reaction centers, here the only kinetic models consistent with the data are those in which the primary electron-transfer rate constant is heterogeneous, suggesting at least two structural populations of RCs. PET in the population with the shortest-lived antenna decay causes the kinetics to be transfer-to-trap-limited, whereas the kinetics in the other population(s)--having longer-lived antenna decays--are limited by the rate of PET. Observation of both types of kinetic limitation within a single light-harvesting system is unexpected and complicates any discussion of the rate-limiting step of light energy utilization in photosynthesis. PMID:9289013

Laible, P D; Greenfield, S R; Wasielewski, M R; Hansen, D K; Pearlstein, R M

1997-07-22

33

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

Science.gov (United States)

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

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

34

Mode-specific vibrational excitation and energy redistribution after ultrafast intramolecular electron transfer  

Science.gov (United States)

Vibrational relaxation in the electronic ground state initiated by intramolecular back-electron transfer (b-ET) of betaine-30 (B-30) is studied by picosecond time-resolved anti-Stokes Raman spectroscopy. Measurements were carried out with B-30 dissolved in slowly as well as in rapidly relaxing solvents. We observed a risetime of the Raman band with the highest frequency near 1600 cm-1 which is close to the b-ET time ?b-ET of B-30. For B-30 dissolved in propylene carbonate (?b-ET˜1 ps), the population of this mode exhibits a rise time of 1 ps whereas vibrational populations between 400 and 1400 cm-1 increase substantially slower. In contrast, in glycerol triacetin (?b-ET˜3.5 ps) and in ethanol (?b-ET˜6 ps) rise times of all modes are close to the respective b-ET times. Within the first few picoseconds, direct vibrational excitation through b-ET is favored for modes with the highest frequencies and high Franck-Condon factors. Later on, indirect channels of population due to vibrational energy redistribution (IVR) become effective. Thermal equilibrium populations of the Raman active modes are established within 10 to 15 ps after optical excitation.

Hogiu, S.; Werncke, W.; Pfeiffer, M.; Dreyer, J.; Elsaesser, T.

2000-07-01

35

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

Energy Technology Data Exchange (ETDEWEB)

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

Hoffman, M.Z.

1993-03-31

36

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

International Nuclear Information System (INIS)

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

37

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

Science.gov (United States)

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

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

1981-11-01

38

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

International Nuclear Information System (INIS)

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

39

Hierarchical coarse-graining model for photosystem II including electron and excitation-energy transfer processes.  

Science.gov (United States)

We propose a hierarchical reduction scheme to cope with coupled rate equations that describe the dynamics of multi-time-scale photosynthetic reactions. To numerically solve nonlinear dynamical equations containing a wide temporal range of rate constants, we first study a prototypical three-variable model. Using a separation of the time scale of rate constants combined with identified slow variables as (quasi-)conserved quantities in the fast process, we achieve a coarse-graining of the dynamical equations reduced to those at a slower time scale. By iteratively employing this reduction method, the coarse-graining of broadly multi-scale dynamical equations can be performed in a hierarchical manner. We then apply this scheme to the reaction dynamics analysis of a simplified model for an illuminated photosystem II, which involves many processes of electron and excitation-energy transfers with a wide range of rate constants. We thus confirm a good agreement between the coarse-grained and fully (finely) integrated results for the population dynamics. PMID:24418347

Matsuoka, Takeshi; Tanaka, Shigenori; Ebina, Kuniyoshi

2014-03-01

40

Exploring photoinduced electron transfer and excited-state proton transfer reactions involving 9-aminoacridine hydrochloride hydrate and methyl viologen using laser flash photolysis  

Science.gov (United States)

In this letter photoinduced interactions of methyl viologen (MV2+) with 9-aminoacridine hydrochloride hydrate (9AA-HCl) have been studied. In homogeneous medium, both photoinduced electron transfer (PET) and excited-state proton transfer (ESPT) are occurring whereas in micellar medium only PET is prevalent. Magnetic field effect confirms that the PET takes place primarily in the triplet state. Discrepancy in theoretically calculated and experimentally obtained B1/2 values indicates the presence of electron hopping mechanism. Amalgamation of this letter with our previous report indicates that 9AA-HCl may either act as an electron donor or acceptor in PET reactions under suitable condition of redox potentials.

Mitra, Piyali; Chakraborty, Brotati; Basu, Samita

2014-08-01

41

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

42

Charge transfer and electronic excitation in collisions of protons with water molecules below 10keV  

Science.gov (United States)

Charge transfer and electronic excitation processes for H++H2O collisions are investigated theoretically below 10keV . Molecular-orbital close-coupling approach is employed for scattering dynamics, while an ab initio multireference single- and double-configuration interaction method is used for the determination of molecular states. The present results for charge transfer show rather weak energy dependence in the energy range from 10keV down to a few tens of eV with very slowly varying cross-section value of 4-13×10-16cm2 , and are found to be in excellent agreement with experimental measurements by Lindsay [Phys. Rev. A 55, 3945 (1997)] where the energy in the experiment and theory overlaps. The electronic-excitation cross sections are found to be much smaller than those for the charge transfer, but increase rapidly and become comparable to charge transfer at a few keV. Most of the water molecular ions and excited species produced in the collision are unstable and soon undergo dissociation; some insight into the fragmentation process and the fragmented species is given.

Mada, Shogo; Hida, Ken-Nosuke; Kimura, Mineo; Pichl, Lukáš; Liebermann, Heinz-Peter; Li, Yan; Buenker, Robert J.

2007-02-01

43

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

Science.gov (United States)

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

Sodt, Alex J.; Ratner, Mark A.

2010-01-01

44

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

45

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

Energy Technology Data Exchange (ETDEWEB)

The research on theoretical atomic collisions that was funded at The Pennsylvania State University`s Wilkes-Barre Campus by DOE from 1986 to 1998 was carried out by Winger from 1986 to 1989 and by Winter and Alston from 1989 to 1998. The fundamental processes of electron transfer, ionization, and excitation in ion-ion, ion-atom, and, more recently, ion-molecule collisions were addressed. These collision processes were treated in the context of simple one-electron, quasi-one-electron, or two-electron systems in order to provide unambiguous results and reveal more clearly the collisional mechanisms. Winter`s work generally focused on the intermediate projectile-energy range corresponding to proton energies from about ten to a few hundred keV. In this velocity-matching energy range, the electron-transfer cross section reaches a peak, and many states, including electron-transfer and ionization states, contribute to the overall electron-cloud distribution and transition probabilities; a large number of states are coupled, and therefore perturbative approaches are generally inappropriate. These coupled-state calculations were sometimes also extended to higher energies to join with perturbative results. Alston concentrated on intermediate-energy asymmetric collision systems, for which coupling with the projectile is weaker, but many target states are included, and on high energies (MeV energies). Thus, while perturbation theory for electron transfer is valid, it is not adequate to first order. The studies by Winter and Alston described were often done in parallel. Alston also developed formal perturbative approaches not tied to any particular system. Materials studied included He{sup +}, Li{sup 2+}, Be{sup 3+}, B{sup 4+}, C{sup 5+}, and the H{sup +} + Na system.

NONE

1998-12-31

46

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

International Nuclear Information System (INIS)

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

47

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

48

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

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

Excited state electron transfer precedes proton transfer following irradiation of the hydrogen-bonded single water complex of 7-azaindole with UV light  

Science.gov (United States)

High resolution electronic spectra of the single water complex of 7-azaindole (7AIW) and of a deuterated analog (7AIW-d3) have been recorded in a molecular beam, both in the absence and presence of an applied electric field. The obtained data include the rotational constants of both complexes in their ground (S0) and first excited (S1) electronic states, their S1- S0 electronic transition moment and axis-tilting angles, and their permanent electric dipole moments (EDM's) in both electronic states. Analyses of these data show that the water molecule forms two hydrogen bonds with 7AI, a donor O-H...N7 bond and an acceptor O...H-N1 bond. The resulting structure has a small EDM in the S0 state (? = 0.54 D) but a greatly enhanced EDM in the S1 state (? = 3.97 D). We deduce from the EDM's of the component parts that 0.281 e- of charge is transferred from the acidic N1-H site to the basic N7 site upon UV excitation of 7AIW, but that water-assisted proton transfer from N1 to N7 does not occur. A model of the resulting electrostatic interactions in the solute-solvent pair predicts a solvent-induced red-shift of 1260 cm-1 which compares favorably to the experimental value of 1290 cm-1.

Young, Justin W.; Pratt, David W.

2011-08-01

51

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

Directory of Open Access Journals (Sweden)

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

Maryam Dehestani

2012-01-01

52

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

Directory of Open Access Journals (Sweden)

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

Li Chen

2014-04-01

53

Quenching reactions of electronically excited atoms  

International Nuclear Information System (INIS)

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

54

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-09-28

55

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

International Nuclear Information System (INIS)

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

56

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

Science.gov (United States)

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

Kaye, Jack A.

1989-01-01

57

Excitation energy transfer in the photosystem I  

Energy Technology Data Exchange (ETDEWEB)

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

Webber, Andrew N

2012-09-25

58

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 (pH2) of uranyl nitrate and tris (1,10-phenanthroline) ruthenium (II) perchlorate using steady-state fluorescence quenching, quenching of *Ru(phen)32+ by UO22+ followed Stern-Volmer kinetics, with K/sub sv/ = (1.89 +- 0.20) x 102m-1. Using this and the known lifetime of *Ru(phen)32+ under these conditions (after correcting for quenching by dissolved oxygen), a rate constant of 1.2 x 109M-1s-1 was obtained for the quenching process. This is close to the rate of quenching of *Ru(phen)32+ by Fe3+2 is slightly higher than the rate of quenching of *Ru(bpy)32+ by UO2221 and is consistent with the same mechanism as in these two cases, i.e., electron transfer. As observed with the Ru(bpy)32+/UO22+ 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)32+ species, the steady-state experiments do not permit demonstration of the reverse quenching of *UO22+ by Ru(phen)32+. However, studies on the fluorescence excitation spectra are consistent wscence excitation spectra are consistent with the occurrence of such a process

59

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.

1800-18-01

60

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

International Nuclear Information System (INIS)

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

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

Photogalvanic cells driven by electron transfer quenching of excited singlet states  

Science.gov (United States)

Photoreduction of oxonine by iron(II) sulfate in dilute acid is produced by quenching of the excited signlet state (S1). No induced intersystem crossing to the tripolet (T1) is observed by nanosecond flash photolysis. The photoreduction of oxonine (S1) by iron(II) was used in a totally illuminated thin layer photogalvanic cell. Power conversion efficiencies are, however, very low. The fluorescence of oxonine and thiazine dyes such as thionine is quenched by acids. Oxonine fluorescence is also quenched by hydroquinone and catechol sulfonates and related compounds. Eleven new thiazine dyes were synthesized. A few photogalvanic experiments were carried out using high concentrations of the water miscible dye and iron(II) in a TI/TL cell. Ferrophos, an iron phosphorus alloy, can be substituted for platinum or gold as a cathode in photogalvanic cells.

Creed, D.; Fawcett, N. C.

63

Photogalvanic cells driven by electron transfer quenching of excited singlet states. Final technical report  

Energy Technology Data Exchange (ETDEWEB)

Photoreduction of oxonine by iron(II) sulfate in dilute acid is produced by quenching of the excited singlet state (S/sub 1/). No induced intersystem crossing to the tripolet (T/sub 1/) can be observed by nanosecond flash photolysis. The photoreduction of oxonine (S/sub 1/) by iron(II) has been used in a totally illuminated thin layer photogalvanic cell. Power conversion efficiencies are, however, very low. The fluorescence of oxonine and thiazine dyes such as thionine is quenched by acids. Oxonine fluorescence is also quenched by hydroquinone and catechol sulfonates and related compounds. Eleven new thiazine dyes have been synthesized. A few photogalvanic experiments have been carried out using high concentrations (> 10/sup -2/N) of the water miscible dye and iron(II) in a TI/TL cell. Ferrophos, an iron-phosphorus alloy, can be substituted for platinum or gold as a cathode in photogalvanic cells.

Creed, D.; Fawcett, N.C.

1983-01-01

64

A combined IR/IR and IR/UV spectroscopy study on the proton transfer coordinate of isolated 3-hydroxychromone in the electronic ground and excited state.  

Science.gov (United States)

In this paper the excited state proton transfer (ESPT) of isolated 3-hydroxychromone (3-HC), the prototype of the flavonols, is investigated for the first time by combined IR/UV spectroscopy in molecular beam experiments. The IR/UV investigations are performed both for the electronically excited and electronic ground state indicating a spectral overlap of transitions of the 3-HC monomer and clusters with water in the electronic ground state, whereas in the excited state only the IR frequencies of the proton-transferred monomer structure are observed. Due to the loss of isomer and species selectivity with respect to the UV excitations IR/IR techniques are applied in order to figure out the assignment of the vibrational transitions in the S0 state. In this context the quadruple resonance IR/UV/IR/UV technique (originally developed to distinguish different isomers in the electronically excited state) could be applied to identify the OH stretching vibration of the monomer in the electronic ground state. In agreement with calculations the OH stretching frequency differs significantly from the corresponding values of substituted hydroxychromones. PMID:25200683

Stamm, A; Weiler, M; Brächer, A; Schwing, K; Gerhards, M

2014-10-21

65

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

OpenAIRE

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) e...

Biggs, Jason D.; Cina, Jeffrey A.

2009-01-01

66

Laser induced picosecond electron transfer with participation of excited states for porphyrins covalently linked with electron acceptor  

Science.gov (United States)

The dynamics and pathways of relaxation processes in meso-ortho-nitrophenyl substituted octaethylporphyrins OEP-OEPPh(o-NO II) and PdOEP-Ph(o-NO II) occurring with the participation of the S I and T I states was studied in polar Ph((dimethylformamide) and nonpolar (toluene) solvents at 295 and 77 K using pico- and nanosecond laser kinetic spectroscopy. At 295 K, steric interactions between bulky ?-alkyl substituents and ortho-nitro groups of meso-phenyl in these compounds create optimal conditions for overlapping of molecular orbitals of the porphyrin macrocycle (donor) and NO II-group (acceptor), thus leading to an efficient photoinduced electron transfer (PET). For free-base OEP-Ph(o-NO II), PET occurs only via the porphyrin S I state within 40 ps (dimethylformamide) and 125 ps (toluene), whereas the competing intersystem crossing S I ~~>T I is low probable. For metallocomplex PdOEP-Ph(o-NO II), PET involves both S I and T I states. In the last case, the direct PET from the T I state to CT state also occurs within picosecond range (20 and 46 ps for dimethylformamide and toluene, respectively, at 295 K). Rate constants for PET with participation of T1 states are by 3-5 times smaller with respect to those found for PET occurring via the S I state. For both compounds, the observed long-lived component (250-700 ns) in decays of the transient T I-T n absorption is due to the recombination processes of radical-ion pairs whose lifetime decreases with an increase of the surrounding polarity and is hardly dependent on the presence of molecular oxygen in the solution. For both compounds, PET is completely absent in rigid solutions at 77 K.

Sagun, Evgenii I.; Zenkevich, Eduard I.; Knyukshto, Valentin N.; Shulga, Alexander M.; Tikhomirov, Sergei A.

2007-06-01

67

Optimal initiation of electronic excited state mediated intramolecular H-transfer in malonaldehyde by UV-laser pulses  

Science.gov (United States)

Optimally controlled initiation of intramolecular H-transfer in malonaldehyde is accomplished by designing a sequence of ultrashort (~80 fs) down-chirped pump-dump ultra violet (UV)-laser pulses through an optically bright electronic excited [ S 2 ( ? ? ?)] state as a mediator. The sequence of such laser pulses is theoretically synthesized within the framework of optimal control theory (OCT) and employing the well-known pump-dump scheme of Tannor and Rice [D.J. Tannor, S.A. Rice, J. Chem. Phys. 83, 5013 (1985)]. In the OCT, the control task is framed as the maximization of cost functional defined in terms of an objective function along with the constraints on the field intensity and system dynamics. The latter is monitored by solving the time-dependent Schrödinger equation. The initial guess, laser driven dynamics and the optimized pulse structure (i.e., the spectral content and temporal profile) followed by associated mechanism involved in fulfilling the control task are examined in detail and discussed. A comparative account of the dynamical outcomes within the Condon approximation for the transition dipole moment versus its more realistic value calculated ab initio is also presented.

Nandipati, K. R.; Singh, H.; Nagaprasad Reddy, S.; Kumar, K. A.; Mahapatra, S.

2014-12-01

68

Multiple-electron excitation, ionization, and transfer in high-velocity atomic and molecular collisions  

International Nuclear Information System (INIS)

This paper reports that the many-body and many-electron problem is common in various areas of physics as well as in chemistry and biology. Basic understanding of phenomena ranging from the nature of matter at the creation of time to the properties of useful materials in the human environment is limited by the boundaries of our knowledge of the many-body problem. There is an advantage in studying the many-body problem in atomic physics since the two-body and parts of the three-body problem are understood. Furthermore, both the mystery of the meanings of quantum mechanics and the mystery of the transition from microscopic time-reversible atomic processes to the dynamics of macroscopic time-irreversible aggregates of atomic particles is inherent in the many-body problems of atomic interactions. Thus, by studying the many-body problem in atomic physics we are able to develop effective tools to discover insights that provide both meaning and utility in our lives

69

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

Science.gov (United States)

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

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

2005-01-01

70

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

71

Zinc porphyrin-Re(I) bipyridyl-fullerene triad: synthesis, characterization, and kinetics of the stepwise electron-transfer processes initiated by visible excitation.  

Science.gov (United States)

A new triad system featuring one zinc porphyrin and one fullerene moieties attached to a central redox-active Re(I) connector was obtained in remarkable yield by cleverly exploiting a facile two-step synthesis. Detailed description and discussion on the characterization of this multicomponent system and of its parent free-base analogue are presented, along with a kinetic study of the stepwise electron-transfer processes occurring upon visible excitation. PMID:25523017

Cavigli, Paolo; Da Ros, Tatiana; Kahnt, Axel; Gamberoni, Marta; Indelli, Maria Teresa; Iengo, Elisabetta

2015-01-01

72

Excited nanoscale-TiO{sub 2} induced interfacial electron transfer reaction of redox active cobalt(III)-alkyl amine complex and the solid surface  

Energy Technology Data Exchange (ETDEWEB)

Interfacial electron transfer reaction mechanism has been probed using {lambda} = 254 nm excited TiO{sub 2} nanoparticles and cis-[Co{sup III}(en){sub 2}(RNH{sub 2})Cl]Cl{sub 2} adsorbates (where RNH{sub 2} = MeNH{sub 2}, EtNH{sub 2}, Pr{sup n}NH{sub 2,} Bu{sup n}NH{sub 2,} Bu{sup i}NH{sub 2,} Pen{sup n}NH{sub 2}, Hex{sup n}NH{sub 2}, Bz{sup n}NH{sub 2}) in aqueous 2-propanol. These tailor made complexes differing in coordination environment due to RNH{sub 2} adhere onto TiO{sub 2} surface producing compact nano-TiO{sub 2}//cobalt(III)-(RNH{sub 2}) surface compound. The surface of the anatase under UV irradiation is uniquely powerful as adsorbent due to inherent hydrophobic/hydrophilic properties. Therefore, the compact structure facilitates an efficient electron transfer to the Co(III) center resulting a high photoefficiency of formation of Co(II). A model for the electron transfer is arrived by considering: (i) the overlap of conduction band of TiO{sub 2} with the acceptor level (Co center): (e{sup -}, CB)/(e{sup -}, tr) + (Co{sup III}, ad) {yields} Co{sup II} and (ii) electronic coupling of donor level (localized on Ti center) with acceptor level (Co center): Ti (center) + (Co{sup III}, ad) {yields} Co{sup II}. These pathways indicate accumulation of electron and appropriately available for reduction of the adhered complex ion. Significant insights were gained on the role of RNH{sub 2} moiety in modifying compact structure of TiO{sub 2}-cobalt(III)-RNH{sub 2} compound, redox power of semiconductor surface, and the proposed mechanism of interfacial electron transfer reactions. Highlights: Black-Right-Pointing-Pointer Interfacial electron transfer reactions can be probed with tailor made complexes. Black-Right-Pointing-Pointer Excited anatase surface acts as a uniquely powerful adsorbent. Black-Right-Pointing-Pointer Structurally integrated cobalt(III) complexes adhere to form surface compounds. Black-Right-Pointing-Pointer Compact surface compound can facilitate electron transfer.

Anbalagan, K., E-mail: kanuniv@gmail.com [Department of Chemistry, Pondicherry University, Kalapet, Pondicherry 605 014 (India); Ganeshraja, A.S.; Maharaja Mahalakshmi, C. [Department of Chemistry, Pondicherry University, Kalapet, Pondicherry 605 014 (India)

2012-06-15

73

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

International Nuclear Information System (INIS)

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

74

Advances in electron transfer chemistry  

CERN Document Server

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

Mariano, Patrick S

1995-01-01

75

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

International Nuclear Information System (INIS)

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

76

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, fa, ?2, f and S of doubly excited states 2(1,0)2+1se, 2(0,1)2+1p0 and 2(1,0)2+1De are determined as functions of momentum transfer K2. (author)

77

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

78

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

International Nuclear Information System (INIS)

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

79

Faster photoinduced electron transfer in a diluted mixture than in a neat donor solvent: effect of excited-state H-bonding.  

Science.gov (United States)

In a neat electron-donating solvent (in this case aniline), photoinduced electron transfer (PET) from the solvent to an excited acceptor (e.g. a coumarin fluorophore) may be anticipated to be the most efficient because of the close contact of the acceptor with many donors. Addition of an inert component would most likely retard the PET process by replacing some donors from the neighbourhood of the acceptors. Surprisingly, we found dramatic acceleration of PET (6-10 fold enhancement compared to neat aniline), for coumarin 102 (C102) dissolved in a binary mixture of aniline and an inert solvent (cyclohexane or toluene). The PET induced fluorescence follows an anomalous trend against the mole fraction of aniline (XAN); first quenches up to certain XAN (0.075 for cyclohexane; 0.13 for toluene), thereafter, enhances with increase in XAN. Although the non-interacting component cannot directly participate in the PET process, it may modulate C102-aniline H-bonding association by changing the polarity of the medium or by disrupting the aniline-aniline H-bond. The study clearly illustrates the dominant role of hydrogen bonding in activating the electron transfer rate where standard thermodynamics predicts very weak donor-acceptor interaction. PMID:24562294

Barman, Nabajeet; Singha, Debabrata; Sahu, Kalyanasis

2014-04-01

80

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

Science.gov (United States)

Steady-state and picosecond time-resolved X-ray absorption spectroscopy is used to study the ground and lowest triplet states of [ReX(CO)(3)(bpy)](n+), X = Etpy (n = 1), Cl, or Br (n = 0). We demonstrate that the transient spectra at both the Re L(3)- and Br K-edges show the emergence of a pre-edge feature, absent in the ground-state spectrum, which is associated with the electron hole created in the highest occupied molecular orbital following photoexcitation. Importantly, these features have the same dynamics, confirming previous predictions that the low-lying excited states of these complexes involve a two-center charge transfer from both the Re and the ligand, X. We also demonstrate that the DFT optimized ground and excited structures allow us to reproduce the experimental XANES and EXAFS spectra. The ground-state structural refinement shows that the Br atom contributes very little to the latter, whereas the Re-C-O scattering paths are dominant due to the so-called focusing effect. For the excited-state spectrum, the Re-X bond undergoes one of the largest changes but still remains a weak contribution to the photoinduced changes of the EXAFS spectrum. PMID:23249289

El Nahhas, A; van der Veen, R M; Penfold, T J; Pham, V T; Lima, F A; Abela, R; Blanco-Rodriguez, A M; Záliš, S; Vl?ek, A; Tavernelli, I; Rothlisberger, U; Milne, C J; Chergui, M

2013-01-17

81

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

82

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

Science.gov (United States)

Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2'-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy. PMID:25338878

Fukuda, Ryoichi; Ehara, Masahiro

2014-10-21

83

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.)

84

Electron-excited molecules in nonequilibrium plasma  

International Nuclear Information System (INIS)

This book focuses on electron-excited molecules in nonequilibrium Plasma. Topics covered include: Distributions of electron-excited molecules over vibrational-rotational levels in gas discharge: Formation mechanisms; Electron-impact excitation levels of molecules electron states in gas discharge; and Doppler spectral line broadening and the velocity distributions of excited atoms and molecules in nonequilibrium plasma

85

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

86

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

Science.gov (United States)

Intense near-infrared (NIR) absorption bands have been found in mixed-valence Ru(NH3)5(2+,3+) complexes bridged by trans-Ru(py)4(CN)2 and cis-Os(bpy)2(CN)2, epsilonmax approximately 1.5 x 10(3) cm(-1) and deltav1/2 approximately 5 x 10(3) cm(-1) for bands at 1,000 and 1,300 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(NH3)5(2+,3+) couples bridged by M(MCL)(CN)2+ complexes (MCL = a tetraazamacrocyclic ligand) (Macatangay; et al. J. Phys. Chem. 1998, 102, 7537). A straightforward perturbation theory argument is used to account for this contrasting behavior. The electronic coupling between a cyanide-bridged, donor-acceptor pair, D-(CN-)-A, alters the properties of the bridging ligand. Such systems are described by a "vibronic" model in which the electronic matrix element, HDA, is a function of the nuclear coordinates, QN, of the bridging ligand: HDA = HDA degrees + bQN. 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 bQN is larger for D(NC)M but very small (bQN approximately 0) for M(CN)A. When the vertical energies of the corresponding charge-transfer transitions, EDM and EDA, differ significantly, a perturbation theory treatment results in HDA = HDAHAM/Eave independent of M and consistent with the earlier report. When EDM approximately equals EDA, configurational mixing of the excited states leads to HDA proportional to HDM, consistent with the relatively intense intervalence bands reported in this paper. Some implications of the model are discussed. PMID:11229560

Macatangay, A V; Endicott, J F

2000-02-01

87

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

88

Phonons and charge-transfer excitations in HTS superconductors  

Energy Technology Data Exchange (ETDEWEB)

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.

Bishop, A.R.

1989-01-01

89

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

CERN Document Server

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

90

Relations among theories of excitation transfer  

International Nuclear Information System (INIS)

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

91

Intramolecular electron transfer in the inverted region  

Energy Technology Data Exchange (ETDEWEB)

In 1960 Marcus predicted that rate constants for electron transfer should decrease with -{Delta}G in the inverted region. In the inverted region, -{Delta}G > {lambda}, where {lambda} is the reorganization energy and {Delta}G the free energy loss associated with the electron transfer. Experimental verification of this prediction has been difficult to obtain but has been found by pulse radiolysis in rigid organic glasses, by Closs, Miller, and co-workers in unsymmetrical, linked organics, in accounting for separation yields in photoinduced electron transfer, and by light-induced electron transfer in linked porphyrin-quinone systems. The authors report here the first examples based on transition-metal complexes and, as predicted theoretically, that there is a clear relationship between electron transfer in the inverted region and nonradiative decay in a closely related family of excited states.

Chen, Pingyun; Duesing, R.; Tapolsky, G.; Meyer, T.J. (Univ. of North Carolina, Chapel Hill (USA))

1989-10-11

92

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 Nb31+ (neonlike) ions incident on H2. 11 refs., 1 fig

93

Cross sections for electron impact excitation of molecules  

International Nuclear Information System (INIS)

The discussion in this chapter is restricted to elastic scattering, rotational, vibrational, and electronic excitation and total scattering cross sections in electron molecule collisions. Experimental data on differential, integral and momentum transfer cross sections are surveyed and short remarks are made on experimental techniques and theoretical approaches used for generating cross section data. 11 references, 3 figures

94

Electron transfer in biology  

Science.gov (United States)

Electron transfer is one of the key reactions of biology not just in catalysis of oxidation/reduction reactions but in the conversion of sources of energy such as light to usable form for chemical transformations. There are then two intriguing problems. What is the nature of the matrix in which electrons flow in a biological cell after the initial charge separation due for example to the absorption of light. Here we are examining biological structures similar to man's electronic wires and the construction must be of low resistance in what are apparently insulators - organic polymers. It has been found that the electronic conduction system is largely made from metallo-proteins associated with lipid membranes. We understand much about these biological wires today. The second problem concerns the conversion of the energy captured from the light into usable chemical form. The major synthetic step in the production of biological polymers, including proteins, DNA, RNA, polysaccharides and fats, is condensation, i.e. the removal of water in the formation of amides, esters and so on. Now these condensation reactions are driven in biology by using a drying agent in water, namely the anhydride, pyrophosphate, in a special compound ATP, adenosine triphosphate. The central problem is to discover exactly how the flow of electrons can be related to the synthesis of (bound) pyrophosphate. (In a thermodynamic sense pyrophosphate is a water soluble kinetically stable drying agent comparable with solid P2O5.) In the biological systems the connection between these different classes of reaction, electron transfer and condensation, is known to be via the production of an energized gradient of protons across the biological membrane which arises from the flow of electrons across the same membrane in the electron transport wires of biology. However we do not understand thoroughly the steps which lead from electron flow in a membrane to proton gradients in that membrane, i.e. electron/proton coupling. Again we do not understand thoroughly how subsequently the proton gradient across a membrane makes ATP, pyrophosphate. Today there is good experimental evidence as to the likely answers in principle. These analyse the coupling devices in mechanical terms. In this article I describe at first the 'wires' of biology, uncoupled simple electron flow, and then go on to the ways in which electron flow could be transduced by mechanical devices, also proteins, into proton gradients and then ATP. This will be termed coupled electron flow. The objective of the article is to stimulate participation by physical chemists in the further description of biological energy capture from light or the oxidation of hydrocarbons to a form suitable for driving chemical syntheses in a controlled manner.

Williams, R. J. P.

95

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. PMID:24784248

Theophilou, Iris; Tassi, M; Thanos, S

2014-04-28

96

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

97

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-04-28

98

Advances in electron transfer chemistry  

CERN Document Server

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

Mariano, Patrick S

1993-01-01

99

Two-Electron Excitation of an Interacting Cold Rydberg Gas  

International Nuclear Information System (INIS)

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.

100

Quantum Plasmonics: Electron transfer processes  

Science.gov (United States)

Plasmon energies can be tuned across the spectrum by simply changing the geometrical shape of a nanostructure. Plasmons can efficiently capture incident light and focus it to nanometer sized hotspots which can enhance electronic and vibrational excitations in nearby structures.[1] Another important but still relatively unexplored property of plasmons, is that they can be efficient sources of hot energetic electrons which can transfer into nearby structures and induce a variety of processes. This process is a quantum mechanical effect: the decay of plasmon quanta into electron-hole pairs. I will discuss how plasmon induced hot electrons can be used in various applications: such as to induce chemical reactions in molecules physisorbed on a nanoparticle surface;[2] to inject electrons directly into the conduction band of a nearby substrate;[3] and to induce local doping of a nearby graphene sheet.[4] References [1] N.J. Halas et al., Adv. Mat. 24(2012)4842 [2] R. Huschka et al., JACS 133(2011)12247; S. Mukherjee et al. TBP 2012 [3] M. W. Knight et al., Science 332(2011)702, Z.Y. Fang et al., NL 12(2012)3808 [4] Z.Y. Fang et al., ACS Nano 6(2012)10.1021/nn304028b

Nordlander, Peter

2013-03-01

101

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

102

Evidence for interference between resonant and nonresonant transfer and excitation  

International Nuclear Information System (INIS)

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

103

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

International Nuclear Information System (INIS)

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

104

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

Science.gov (United States)

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

Lin, N. Y.

1996-02-01

105

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

International Nuclear Information System (INIS)

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

106

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)

107

Energy transfer from PO excited states to alkali metal atoms in the phosphorus chemiluminescence flame  

OpenAIRE

Phosphorus chemiluminescence under ambient conditions of a phosphorus oxidation flame is found to offer an efficient electronic energy transferring system to alkali metal atoms. The lowest resonance lines, 2P3 / 2,½?2S½, of potassium and sodium are excited by energy transfer when an argon stream at 80°C carrying potassium or sodium atoms intersects a phosphorus vapor stream, either at the flame or in the postflame region. The lowest electronically excited metastable 4IIi state of PO or t...

Khan, Ahsan U.

1980-01-01

108

Photochemistry on surfaces. Intermolecular energy electron transfer processes between excited Ru(bpy){sub 3}{sup 2+} and H-aggregates of cresyl violet on SiO{sub 2} and SnO{sub 2} colloids  

Energy Technology Data Exchange (ETDEWEB)

Cresyl violet, a cationic dye (CV{sup +}), forms H-aggregates on the negatively charged SiO{sub 2} and SnO{sub 2} colloids. These aggregates exhibit broad absorbance around 520 nm. By coadsorbing a sensitizer, Ru(bpy){sub 3}{sup 2+}, we are able to characterize the triplet excited state and reduced form of dye-aggregates on the colloidal SiO{sub 2} and SnO{sub 2} suspensions. On SiO{sub 2} surfaces, the excited state quenching of Ru(bpy){sub 3}{sup 2+} by dye-aggregates proceeds via an energy transfer mechanism. Picosecond laser flash photolysis experiments indicate that such a surface-promoted energy transfer is completed within 20 ps. On the other hand dye-aggregates adsorbed onto SnO{sub 2} colloids undergo photosensitized reduction since the excited sensitizer, Ru(bpy){sub 3} {sup 2+}, is efficiently quenched by the semiconductor support. The role of support material in promoting energy and electron transfer processes is described. 87 refs., 11 figs.

Liu, D.; Hug, G.L.; Kamat, P.V. [Univ. of Notre Dame, IN (United States)

1995-11-09

109

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

Energy Technology Data Exchange (ETDEWEB)

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

Lichtin, N.N.

1979-03-15

110

Symmetry characterization of electrons and lattice excitations  

Directory of Open Access Journals (Sweden)

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

Schober H.

2012-03-01

111

Spin-orbit coupling induced magnetic field effects in electron-transfer reactions with excited triplets : the role of triplet exciplexes and radical pairs in geminate recombination  

OpenAIRE

The magnetic field dependence of free-radical yield in the electron-transfer quenching of methylene blue triplet by p-iodoaniline has been determined between 0.00 and 3.30 T in methanol/ethylene glycol mixtures of various viscosities by using laser flash spectroscopy and a photostationary flow technique. The observed decrease of the free-radical yield with the magnetic field is interpreted by heavy-atom-induced spin-orbit coupling causing magnetic field sensitivity according to the triplet me...

Steiner, Ulrich; Haas, Werner

1991-01-01

112

Nuclear excitation by electronic transition (NEET).  

Energy Technology Data Exchange (ETDEWEB)

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

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

1999-04-28

113

Resonant electron transfer between quantum dots  

OpenAIRE

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

Openov, Leonid A.

1999-01-01

114

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

International Nuclear Information System (INIS)

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

115

Enhanced electron attachment to vibrationally and electronically excited molecules  

Science.gov (United States)

Electron attachment studies on vibrationally and electronically excited states have been measured. The attachment of electrons to vibrationally excited states of the ground electronic state populated via temperature increase was measured in the mean electron energy range, (?), 0.04 to 4.8 eV, over the temperature range, T, 300 to 700 K and over the total gas number density, Nt, 2.25 to 15.5 × 1019 molecules/cm3. These studies are presented in Part 1 for three technologically important molecules: Methylene Chloride (C2H2Cl2), Boron Trichloride (BCl3), and Trichlorotrifluoroethane (1,1,2-C 2Cl3F3). Electron attachment rate constants, k a((?),T), was measured as a function of mean electron energy in Ar and N2 gases at different temperatures. Using swarm unfolding technique, electron attachment cross sections, ?a(?,T), was measured as a function of electron energy by unfolding ka((?),T) at each temperature. The results of these measurements show that the dissociative electron attachment cross sections increase with the increase of vibrational energies. In the studies an electronically-excited states, the attaching electrons and the excited states of molecules were produced with a single excimer-laser pulse. The excitation of molecules to energies above the ionization potential (IP) caused the population of core-excited Rydberg states (HR). The electrons produced via photoionization were attached to the concomitantly produced highly-excited molecules leading to negative ion formation under the high-pressure environment provided by Ar or N2 gases. In these experiments two different experimental techniques were used: two- electrode arrangement and three-electrode arrangement. The two-electrode arrangement techniques provided information on the lifetimes of the excited molecules as well as estimates of various experimental parameters including the electron attachment rate constant of excited molecules. The other technique, the three- electrode arrangement, provided information about the density of charged species including electrons and negative ions and the estimation of electron attachment rate constant. These results are presented in Part II for three molecules: Benzene (C6H 6), Oxygen (O2), and Dichlorodifluoromethane (CCl2,F2). It was shown that the electron attachment to highly-excited molecules was extremely efficient process leading to enormous electron attachment cross sections, ?a, ~ 10-10 cm2, which were many orders of magnitude larger compared to the cross sections for corresponding ground electronic states.

Tav, Cumali

116

Collective Excitations of Dirac Electrons in Graphene  

CERN Document Server

Two-dimensional electrons in graphene are known to behave as massless fermions with Dirac-Weyl type linear dispersion near the Dirac crossing points. We have investigated the collective excitations of this system in the presence or absence of an external magnetic field. Unlike in the conventional two-dimensional electron system, the $\

Apalkov, V; Chakraborty, T; Apalkov, Vadim; Wang, Xue-Feng; Chakraborty, Tapash

2006-01-01

117

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

International Nuclear Information System (INIS)

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

118

75 FR 31665 - Electronic Fund Transfers  

Science.gov (United States)

...responsibilities of participants in electronic fund transfer systems. An...one consent form (or in the course of obtaining opt-ins through...205 Consumer protection, Electronic fund transfers, Federal Reserve...as follows: PART 205--ELECTRONIC FUND TRANSFERS...

2010-06-04

119

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

120

Spin-orbit coupling induced magnetic field effects in electron-transfer reactions with excited triplets: The role of triplet exciplexes and radical pairs in geminate recombination  

Energy Technology Data Exchange (ETDEWEB)

The magnetic field dependence of free-radical yield in the electron-transfer quenching of methylene blue triplet by p-iodoaniline has been determined between 0.00 and 3.30 T in methanol/ethylene glycol mixtures of various viscosities by using laser flash spectroscopy and a photostationary flow technique. The observed decrease of the free-radical yield with the magnetic field is interpreted by heavy-atom-induced spin-orbit coupling causing magnetic field sensitivity according to the triplet mechanism (TM) in intermediate triplet exciplexes and to the {Delta}g type radical pair mechanism (RPM) in germinate triplet radical pairs originating from dissociation of the triplet exciplexes. Analytical expressions are provided for a treatment of a combination of both mechanisms including the case of reversible formation of the triplet exciplex from the geminate radical pair. The formalism of Pedersen developed for the high field radical pair mechanism and modified by Vollenweider and Fischer to account for effects of exchange interaction is generalized to include various boundary conditions for the electron spin density matrix suggested in the literature to describe the effects of encounters and chemical reaction. With a physically consistent choice of TM and RPM parameters model calculations provide a very good quantitative fit of the observed magnetic field and viscosity dependence of the yield of free radicals.

Steiner, U.E.; Haas, W. (Universitaet Konstanz (West Germany))

1991-03-07

121

Electron-beam-excited gas laser research  

International Nuclear Information System (INIS)

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

122

Bioinspired electron-transfer systems and applications  

International Nuclear Information System (INIS)

Bioinspired electron-transfer systems including artificial photosynthesis and respiration are presented herein together with some of their applications. First, multi-step electron-transfer systems composed of electron donor-acceptor ensembles have been developed, mimicking functions of the photosynthetic reaction center. However, a significant amount of energy is lost during the multi-step electron-transfer processes. Then, as an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer within redox cascades, simple donor-acceptor dyads have been developed to attain along-lived and high energy charge-separated state without significant loss of excitation energy, by fine control of the redox potentials and of the geometry of donor-acceptor dyads that have small reorganization energies of electron transfer. Such simple molecular dyads, capable of fast charge separation but extremely slow charge recombination, have significant advantages with regard to synthetic feasibility, providing a variety of applications including construction of organic solar cells and development of efficient photo-catalytic systems for the solar energy conversion. An efficient four-electron reduction of dioxygen to water by one-electron reductants such as ferrocene derivatives as well as by an NADH analog has also been achieved as a respiration model by using a cofacial dicobalt porphyrin that can form the ?-peroxo Co(III)-O2hat can form the ?-peroxo Co(III)-O2Co(III) complex. The catalytic mechanism of the four-electron reduction of dioxygen has been clarified based on the detailed kinetic study and the detection of the intermediate. (author)

123

Electronic excitation spectrum of metallic carbon nanotubes  

CERN Document Server

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

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

2005-01-01

124

Electronic excitation and Auger spectroscopy of hexamethyldissilane  

International Nuclear Information System (INIS)

In this work, it is presented an spectroscopic study of Si2 (CH3)6 which presents interesting characteristics in the Si - Si bond. Electron energy loss technique was used in the energy range of 500 - 200 eV for the electron beam. Electronic excitation spectra were obtained for the energy loss range from 5 to 30 eV, and also Auger spectra. (A.C.A.S.)

125

Electron impact excitation of helium atoms  

International Nuclear Information System (INIS)

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

126

Coherence in electron-impact excitation of helium  

International Nuclear Information System (INIS)

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

127

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

128

Vibrational and electronic excitations in gold nanocrystals  

Science.gov (United States)

An experimental analysis of all elementary excitations - phonons and electron-holes - in gold nanocrystals has been performed using plasmon resonance Raman scattering. Assemblies of monodisperse, single-crystalline gold nanoparticles, specific substrates and specific experimental configurations have been used. Three types of excitations are successively analyzed: collective quasi-acoustical vibrations of the particles (Lamb's modes), electron-hole excitations (creating the so-called ``background'' in surface-enhanced Raman scattering) and ensembles of atomic vibrations (``bulk'' phonons). The experimental vibrational density of states extracted from the latter contribution is successfully compared with theoretical estimations performed using atomic simulations. The dominant role of surface atoms over the core ones on lattice dynamics is clearly demonstrated. Consequences on the thermodynamic properties of nanocrystals such as the decrease of the characteristic Debye temperature are also considered.

Bayle, Maxime; Combe, Nicolas; Sangeetha, Neralagatta M.; Viau, Guillaume; Carles, Robert

2014-07-01

129

Quasiparticle theory of electron excitations in solids  

International Nuclear Information System (INIS)

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

130

Electronic energy transfer on a vibronically coupled quantum aggregate  

Science.gov (United States)

We examine the transfer of electronic excitation (an exciton) along a chain of electronically coupled monomers possessing internal vibronic structure and which also interact with degrees of freedom of the surrounding environment. Using a combination of analytical and numerical methods, we calculate the time evolution operator or time-dependent Green's function of the system and thereby isolate the physical parameters influencing the electronic excitation transport. Quite generally, we show that coupling to vibrations slows down and inhibits migration of electronic excitation due to dephasing effects on the coherent transfer present without vibrations. In particular, coupling to a continuous spectrum of environment states leads to a complete halting of transfer, i.e., a trapping of the exciton.

Roden, Jan; Schulz, Georg; Eisfeld, Alexander; Briggs, John

2009-07-01

131

Ultrafast excitation energy transfer in small semiconducting carbon nanotube aggregates.  

Science.gov (United States)

We study excitation energy transfer in small aggregates of chirality enriched carbon nanotubes by transient absorption spectroscopy. Ground state photobleaching is used to monitor exciton population dynamics with sub-10 fs time resolution. Upon resonant excitation of the first exciton transition in (6,5) tubes, we find evidence for energy transfer to (7,5) tubes within our time resolution (tube toward other tubes, the latter process occurring in less than 10 fs. PMID:20518568

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

2010-07-27

132

Excitation of nonlinear electron acoustic waves  

International Nuclear Information System (INIS)

A particle in cell (PIC) simulation is used to investigate the excitation of electron acoustic waves (EAWs) and the stability of the EAWs against decay. An EAW is a nonlinear wave with a carefully tailored trapped particle population, and the excitation process must create the trapped particle population. For a collisionless plasma, successful excitation occurs when a relatively low amplitude driver that is spatially and temporally resonant with the EAW is applied for a sufficiently long time (many trapping periods). The excited EAW rings at a nearly constant amplitude long after the driver is turned off, provided the EAW has the largest wavelength that fits in the simulation domain. Otherwise, the excited EAW decays to a longer wavelength EAW. In phase space, this decay to longer wavelength appears as a tendency of the vortex-like trapped particle populations to merge. In a collisional plasma, successful excitation of an EAW requires the driver amplitude to exceed a threshold value. The period for a trapped particle oscillation must be short compared to the time for collisions to smooth out the trapped particle plateau

133

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

CERN Document Server

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

134

Effect resonance radiation transfer of excitation porous silicon to I2 molecules sorbed in pores  

International Nuclear Information System (INIS)

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

135

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

136

Light-driven microbial dissimilatory electron transfer to hematite.  

Science.gov (United States)

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

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

2014-11-14

137

Fluorescent probes as indicators of sub-excitation electrons  

International Nuclear Information System (INIS)

In this study, the integrated emission has been monitored from the pulse radiolysis of gaseous rare gases containing traces of anthracene, terphenyl or tetracene. The emission from the lowest singlet states of these molecules has been studied using picosecond pulse radiolysis techniques. Pulses of approximately 30 psec, 20 MeV electrons from a linac have been used to excite gaseous systems containing up to 1 atm of bulk gas with a trace (approximately 1 mm) of fluorescent probe. The decay of the 'S emission was monitored for each probe as a function of the pressure of a bulk gas. The emission yields for anthracene and terphenyl were determined in the presence of neon, argon, krypton, xenon and nitrogen. The decay or the emission was complete (under the conditions used) before any collisional energy transfer processes from rare gas to probe could occur. The yields, when expressed in terms of the yield per ionising event in the bulk gas, indicate that the processes responsible for excitation are (1) not due to a direct excitation by the primary beam and (2) dependent, linearly, on the lowest energy level of the bulk medium. The conclusions to be drawn are that the majority of the yield of excited states is from excitation processes involving low energy electrons. (author)

138

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

139

Polar solvation and electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

1993-04-13

140

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

International Nuclear Information System (INIS)

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

141

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

International Nuclear Information System (INIS)

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

142

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

Science.gov (United States)

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

Rajeev, R.; Rishad, K. P. M.; Madhu Trivikram, T.; Krishnamurthy, M.

2013-12-01

143

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

144

Theory of plasmon enhanced interfacial electron transfer  

Science.gov (United States)

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

Wang, Luxia; May, Volkhard

2015-04-01

145

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

146

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)].

147

A study of transfer excitation in F8+ + He, Ne and Ar collision  

International Nuclear Information System (INIS)

High resolution x-ray spectroscopy has been used to measure F K x rays resulting from the decay of doubly excited two electron states formed during F8+ + He, Ne, or Ar collisions. The energy range spanned by the spectrometer includes the 2s2p(3P) ? 1s2s(3S), 2s2p(1P) ? 1s2s(1S), 2p2(1D) ? 1s2p(1P), 2p23P) ? 1s2p(3P) and the 2p2(1S) ? 1s2p(1P) transitions. These states may be formed by nonresonant transfer excitation, in which electron excitation is coupled with electron capture to an excited state, or by resonant transfer excitation, a process related to dielectronic recombination, in which the capture of a loosely bound target electron results in projectile electron excitation. Calculations have been performed to estimate the contribution of each process to the total measured cross section

148

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

International Nuclear Information System (INIS)

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

149

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

Science.gov (United States)

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

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

2015-02-12

150

Kinetic ion thermometers for electron transfer dissociation.  

Science.gov (United States)

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

Pepin, Robert; Ture?ek, František

2015-02-19

151

Experimental study of electron impact excitation of multiply charged ions  

International Nuclear Information System (INIS)

We report on measurements of angular differential cross sections for the excitation of multiply charged ions by electron impact. An ion beam is crossed by an electron beam; electrons which are inelastically scattered at different angles are identified by their energy loss due to the excitation process. Absolute excitation cross sections are obtained by comparing the signals of the elastic and the inelastic electron-ion scattering. Results obtained from the 3s?3p excitation of Ar7+ are discussed. (orig.)

152

Motional effects on the efficiency of excitation transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-15

153

Neutron scattering investigation of magnetic excitations at high energy transfers  

International Nuclear Information System (INIS)

The authors have measured, using chopper spectrometers and time-of-flight techniques, the magnetic response functions of a series of d and f transition metals and compounds over a wide range of energy and momentum transfer. In PrO2, UO2, BaPrO3, and CeB6 the authors observed crystal-field transitions between the magnetic ground state and the excited levels in the energy range from 40 to 260 meV. In materials exhibiting spin-fluctuation or mixed-valent character such as Ce/sub 0.74/Th/sub 0.26/, on the other hand, no sharp crystal-field lines but a broadened quasielastic magnetic peak was observed. The line width of the quasielastic component is thought to be connected to the spin-fluctuation energy of the 4f electrons. The significance of the neutron scattering results in relation to the ground state level structure of the magnetic ions and the spin dynamics of the f electrons is discussed. 26 references, 7 figures

154

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

155

Electron excitation of alkali atoms. [EACLOC computer code for excitation of alkali atoms by electron collisions  

Energy Technology Data Exchange (ETDEWEB)

The development and testing of a synthesized close-coupling effective model potential ten-channel electron-atom scattering code and some preliminary calculations of resonances in cross sections for the excitation of excited states of potassium by low energy electrons are described. The main results obtained are: identification of /sup 1/S and /sup 1/D structures in excitation cross sections below the 5/sup 2/S threshold of neutral potassium; indications of additional structures - /sup 1/P and /sup 1/D between the 5/sup 2/S and 5/sup 2/D thresholds; and a suggested explanation of anomalously high interstate-electron impact excitation cross sections inferred from experiments on potassium-seeded plasmas. The effective potential model imbedded in the code can be used to simulate any atomic system that can be approximated by a single bound electron outside an ionic core. All that is needed is a set of effective potential parameters--experimental or theoretical. With minor modifications the code could be adapted to calculations of electron scattering by two-electron systems.

Ormonde, S.

1979-02-01

156

Single-molecule kinetics of interfacial electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Measurements of single-molecule chemical reaction kinetics are demonstrated for interfacial electron transfer from excited cresyl violet molecules to the conduction band of indium tin oxide (ITO) or energetically accessible surface electronic states under ambient conditions by using a far-field fluorescence microscope. In this system, each single molecule exhibits a single-exponential electron transfer kinetics. A wide distribution of site-specific electron transfer rates is observed for many single cresyl violet molecules examined. This work reveals that the physical origin of multiexponential kinetics of electron transfer in this system is the inhomogeneity of molecular interactions on the semiconductor surface of ITO. We illustrate that the single-molecule experiments provide detailed information not obtainable from experiments conducted on large ensembles of molecules. Single-molecule kinetics is particularly useful in understanding multiexponential behavior of chemical reactions in heterogeneous systems. 42 refs., 4 figs.

Lu, H.P.; Xie, X.S. [Pacific Northwest National Lab., Richland, WA (United States)

1997-04-10

157

Electron-transfer organic and bioorganic photochemistry  

International Nuclear Information System (INIS)

A review is given of the literature on electron transfer in organic and bioorganic photochemistry mainly from 1985 to April 1988. Topics covered include the theory and kinetics of electron transfer, the dynamic and chemical behaviour of the geminate ion-radical pair, the effects of salts on photoinduced electron-transfer reactions, the photorepair of UV-damaged DNA and cyclobutane-ring splitting by photoinduced electron transfer, model compounds of NAD(P)+/NAD(P)H, deazoflavin and flavin and two-electron photoredox reactions and the application of photoinduced electron transfer reactions to organic synthesis. (U.K.)

158

Electron dynamics and energy dissipation in highly excited dielectrics  

International Nuclear Information System (INIS)

When dielectrics are irradiated with an ultrashort laser pulse or a swift heavy ion, the transient density of electrons in the conduction band increases considerably. This density is a crucial parameter for the subsequent behavior of the material: After ion irradiation, it influences energy dissipation to the lattice as well as the energy transport to the outer track. For the case of laser irradiation on a timescale of about hundred femtoseconds, the free-electron density increase due to irradiation also determines the further absorption of the pulse energy. Additionally, the distribution function of the excited electrons may influence energy absorption and dissipation. We study the evolution of the free-electron density and energy in laser-irradiated solids on ultrashort timescales. Our calculations also give insights to the case of irradiation with a swift heavy ion. Various theoretical approaches are applied to trace the non-equilibrium distribution function of the highly excited electronic system as well as the energy transfer to the lattice and the transport of heat and carriers to the depth of the irradiated material

159

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

Science.gov (United States)

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

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

2014-12-01

160

Double electron excitation and the Glauber theory  

International Nuclear Information System (INIS)

The electron excitation cross sections for He (1s21S?2p23P), Mg (3s21S?3p21P), and Ca (4s21S?4p23P) 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

161

Excitation of Be+ by electron impact  

International Nuclear Information System (INIS)

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

162

Double Resonance Studies of Electronically Excited Acetylene.  

Science.gov (United States)

The double resonance techniques of Ultraviolet ^{-}Ultraviolet Double Resonance (UVUVDR), Ultraviolet-Optical Double Resonance (UVODR), and Stimulated Emission Pumping (SEP) have been used to investigate electronically excited states of acetylene. Electronically excited states of acetylene have stable structures in the linear (D_{infty h}), cis-bent (C_sp{2v}{b}) , trans-bent (C_sp{2h} {c}), vinylidene (C_sp {2v}{a}), and nonplanar (C _sp{2}{b} and C _sp{2}{c}) configurations, all of which might appear in the spectrum. The Complete Nuclear Permutation Inversion-Molecular Symmetry (CNPI -MS) group theoretical treatment was utilized (Chapter 2) to provide a consistent and point group independent framework with which to classify the overall rovibronic wavefunctions connected with these different structures. Knowing the unique patterns of rotational energy levels presented by the different isomeric structures of acetylene is instrumental in determining the electronic symmetry and molecular structure of the states appearing in the spectrum. Although the excited states in the 60,000-78,000 cm^{-1} energy region are strongly predissociated, the UVUVDR and UVODR double resonance techniques permit the recording the rotationally resolved spectra. The rotationally resolved spectra allow the complete characterization of these states, which in a one-photon absorption spectrum can only be classified as diffuse. The most important result of these double resonance studies is the structural and electronic symmetry characterization of two predissociated electronic states (Chapters 3 and 4), most notably the nonplanar ~ E -state. Confirmation of this nonplanar gauche structure relies heavily on the observation of an unprecedented K_{a} dependent pattern of rotational selection rules. The rotational energy level pattern exhibited by the ~ E -state is consistent with that expected (Chapter 2) for a nonplanar near cis-bent (C_sp{2} {b}) state of ^1 A electronic symmetry. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Lundberg, James Kenneth

1992-01-01

163

Excited state intramolecular proton transfer in Schiff bases. Decay of the locally excited enol state observed by femtosecond resolved fluorescence.  

Science.gov (United States)

Although the late (t>1 ps) photoisomerization steps in Schiff bases have been described in good detail, some aspects of the ultrafast (sub-100 fs) proton transfer process, including the possible existence of an energy barrier, still require experimental assessment. In this contribution we present femtosecond fluorescence up-conversion studies to characterize the excited state enol to cis-keto tautomerization through measurements of the transient molecular emission. Salicylideneaniline and salicylidene-1-naphthylamine were examined in acetonitrile solutions. We have resolved sub-100 fs and sub-0.5 ps emission components which are attributed to the decay of the locally excited enol form and to vibrationally excited states as they transit to the relaxed cis-keto species in the first electronically excited state. From the early spectral evolution, the lack of a deuterium isotope effect, and the kinetics measured with different amounts of excess vibrational energy, it is concluded that the intramolecular proton transfer in the S1 surface occurs as a barrierless process where the initial wave packet evolves in a repulsive potential toward the cis-keto form in a time scale of about 50 fs. The absence of an energy barrier suggests the participation of normal modes which modulate the donor to acceptor distance, thus reducing the potential energy during the intramolecular proton transfer. PMID:17583330

Rodríguez-Córdoba, William; Zugazagoitia, Jimena S; Collado-Fregoso, Elisa; Peon, Jorge

2007-07-19

164

Proton-coupled electron transfer with photoexcited metal complexes.  

Science.gov (United States)

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

Wenger, Oliver S

2013-07-16

165

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

CERN Document Server

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

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

2013-01-01

166

Electron excitation relaxation in wide-gap single crystal insulators under swift heavy-ion irradiation  

Science.gov (United States)

A heavy, multicharged ion moving in a solid interacts with nuclei and electrons of the matter atoms. If the projectile velocity exceeds the typical orbital velocity of the target electrons, the main process is excitation of the electronic subsystem, i.e., excitation and ionization of bound electrons. Initially, relaxation of the electron excitations results from electronic processes alone, and energy transfer from electrons to lattice happens later. Since free charge carriers are absent in insulators before irradiation, the motion of the excited electrons is possible only together with holes. Due to inner pressure of the electron-hole plasma the expansion takes place. The velocity of the expansion is determined by the heat velocity of electron-hole pairs. As the excitation region expands, the density of the electron-hole pairs decreases, the average distance between pairs increases, and excitons are produced. The expansion can be terminated in the time t?10-13 s, when, due to the electron-phonon interaction, self-trapped holes (and excitons) are formed. The annihilation of the trapped excitons gives rise to Frenkel defects. The set of equations comprising the continuity equation, the Euler equation and energy conservation is considered. The analytic dependence on time of the electron temperature and the radius of the excitation region is derived. The observation of projectile traces in a target is discussed in the single projectile regime.

Yavlinskii, Yu. N.

2000-05-01

167

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

Science.gov (United States)

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

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

2014-09-23

168

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

Energy Technology Data Exchange (ETDEWEB)

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

Whitten, D.G.

1991-10-01

169

Impact Excitation of 4 2P-Potassium by Polarized Electrons  

Science.gov (United States)

The present work investigates the 42 P impact excitation of potassium by longitudinally polarized electrons. Exchange scattering causes a polarization transfer from the primary electron beam to the ensemble of excited atoms which results in a non zero circular polarization of the fluorescence light emitted in foreward direction. The experimental values of light polarization agree well with values calculated using close coupling data of Moores.

Ludwig, N.; Bauch, A.; Naß, P.; Reichert, E.; Welker, W.

1986-06-01

170

Electron capture into excited states of low-energy Krq+(q = 8-7) ions  

International Nuclear Information System (INIS)

The low-energy charge exchange collision between Kr8+ and Kr7+ projectiles and He or H2 targets have been studied by vacuum ultraviolet spectroscopy. New lines are identified. Emission cross sections of the observed transitions have been measured. Absolute cross sections of the n and l projectile excited states formed by single electron capture have been deduced. The double electron capture and transfer ionisation processes have also been observed and measured. Excitation of the He target has been observed. (author)

171

Excitation energy transfer processes in condensed matter theory and applications  

CERN Document Server

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

Singh, Jai

1994-01-01

172

Transfer and excitations in grazing heavy ion reactions  

International Nuclear Information System (INIS)

Expanding the determinant state of the TDHF theory in terms of basis functions involving the single particle states of separate nuclei and introducing certain statistical assumptions we derive closed formulas for the transfer and excitation probabilities. They depend on two parameters: the mean excitation energy z and the ratio q of the one nucleon transfer probability and the probability of a 1p-1h excitation. We obtain q and z by a fit to the experimental mass distribution and to the slope of the quasi-elastic cross section (at given scattering angle) in the inelastic channels .q is found to be close to 1. With these values of q and z, the calculated cross section exhibits resonance-like structures which are similar to the ones found experimentally. Preliminary calculations within TDHF also lead to large values of q

173

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

174

Photoinduced Magnetism Caused by Charge-Transfer Excitations in Tetracyanoethylene-Based Organic Magnets  

Science.gov (United States)

The photoinduced magnetism in Mn-tetracyanoethylene (TCNE) molecule-based magnets is ascribed to charge-transfer excitations from manganese to TCNE. Charge-transfer energies are calculated using density functional theory; photoinduced magnetization is described using a model Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from the manganese core spins into the lowest unoccupied orbital of TCNE with photon energies around 3 eV increase the magnetization through a reduction of the canting angle of the manganese core spins for an average electron density on TCNE less than one. When photoexciting with a smaller energy, divalent TCNE molecules are formed. The delocalization of the excited electron causes a local spin flip of a manganese core spin.

Erdin, Serkan; van Veenendaal, Michel

2006-12-01

175

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

CERN Document Server

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

176

Excited-state intramolecular H-atom transfer in nearly symmetrical perylene quinones  

Science.gov (United States)

H-atom transfer and proton transfer reactions, like electron transfer reactions, are of fundamental importance in both the physical and biological sciences. Hatom transfer and proton transfer reactions lie at the heart of acid-base chemistry and of a wide range of catalytic reactions in biological systems. Although much progress has been made in understanding electron transfer reactions through the combination of experimental and theoretical work, many aspects of excited-state H-atom and proton transfer reactions are poorly understood, in particular, the way in which the solvent or the intramolecular modes of the solute couple to the reaction. We argue that hypericin and the hypocrellins undergo excited-state intramolecular H-atom transfer reactions. The hypericin and hypocrellin reactions are, relatively speaking, very slow, occurring in about 10 ps for hypericin and from 10-250 ps for hypocrellin A and may be explained in terms of a reaction coordinate that is dominated by intramolecular motions of the aromatic skeleton and the side chains. The observation of a 10 ps transient in hypocrellin A (which, like its analogue in hypericin, lacks a deuterium isotope effect) is essential in attaining a unified understanding of the hypericin and hypocrellin photophysics. Without this common 10 ps component, the photophysics of these two systems bear no similarities and are seemingly unrelated. Our assignment of intramolecular H-atom transfer to the excited-state kinetics has at times been controversial, owing largely to the mirror image symmetry between the absorption and emission spectra and to the absence of deuterium isotope effects. These topics are discussed in detail and we conclude that neither the absence of mirror image symmetry nor the presence of an isotope effect is a conditio sine qua non for a H-atom transfer reaction.

Petrich, J. W.

177

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

178

Electron-shock excitation cross sections of lutetium atom  

Energy Technology Data Exchange (ETDEWEB)

The cross sections of electron shock excitations for 55 transitions of LUI in the spectrum region of 250-660 nm have been measured. For all the cross sections measured, the optical exctation functions are recorded with the energy of the exciting electrons changing from the excitation threshold up to 250 eV. Using the measurements of the threshold excitation energy, the upper lower levels for 8 earlier unclassified transitions have been determined.

Krasavin, A.Yu.; Smirnov, Yu.M.

1984-10-01

179

Electron-hole plasma excitation spectra of cadmium sulfide crystals  

International Nuclear Information System (INIS)

Electron-hole plasma (EHP) emission and excitation spectra were investigated in pure and impurity cadmium sulfide samples different in thickness providing helium temperature and high excited levels. In pure sample excitation spectra maxima related to EHP and free exciton resonance excitation are determined. EHP excitation spectra in thin and impurity cadmium sulfide samples testify to Coulomb interaction screening in EHP and permit to estimate EHP binding energy (about 12-13 MeV) relatively free exciton decay

180

Cross sections of excitations of silicon atoms by electron impact  

International Nuclear Information System (INIS)

The excitation of spectra lines of the silicon atom has been investiaated by the method of crossing beams. The absolute values of excitation cross-sections of 14 ultraviolet lines of the silicon atom have been measured, with the energy of the exciting electrons changing from 250 eV up to the excitation threshold. For four lines, the optical excitation functions have been detected

181

Cross sections of excitations of silicon atoms by electron impact  

Energy Technology Data Exchange (ETDEWEB)

The excitation of spectra lines of the silicon atom has been investigated by the method of crossing beams. The absolute values of excitation cross-sections of 14 ultraviolet lines of the silicon atom have been measured, with the energy of the exciting electrons changing from 250 eV up to the excitation threshold. For four lines, the optical excitation functions have been detected.

Kolosov, P.A.; Krasavin, A.Yu.; Smirnov, Yu.M. (Moskovskij Ehnergeticheskij Inst. (USSR))

182

Resonant optical electron transfer in one-dimensional multiwell structures  

OpenAIRE

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

183

Electron transfer in pendant-group and molecularly doped polymers  

Science.gov (United States)

Utilizing the molecular-ion model previously constructed to describe photoemission and ultraviolet absorption in pendant-group polymers, we derive an expression for the probability of electron transfer between a molecular ion and a neutral molecular species embedded in a frequency-dependent dielectric medium described by the (nonlocal) longitudinal dielectric response function ?(q-->,?). The medium is taken to exhibit three branches of its longitudinal polarization excitation spectrum defined by ?(q-->,?(q-->))=0: a low-frequency branch corresponding to intermolecular motions, an infrared branch corresponding to molecular vibrational modes, and a high-frequency branch corresponding to valence-electron excitations. In addition, the linear coupling of the electron to the intramolecular modes of the initial and final molecular ions is incorporated into the model. The electron-transfer probability is evaluated as a function of the spacing, R, between the molecular-ion sites and the energy difference between the intitial and final molecular-ion states. Utilizing parameters in ?(q-->,?) typical of pendant-group polymers (e.g., polystyrene, polyvinylpyridine) or the matrices utilized in molecularly doped polymers films (e.g., polycarbonates), we find that the electron-transfer process is activated and that the low-frequency dielectric relaxations characteristic of these polymers create this activation. Explicit expressions for the activation energies are derived and evaluated numerically for poly(2-vinylypyridine): a material for which a model of ?(q-->,?) is available in the literature. The valence-electron excitations do not influence the electron-transfer activation energies, but both the intramolecular and longitudinal-polarization vibrational modes increase these activation energies above the values predicted using the low-frequency relaxations alone. The energies, ??n, of many of these vibrational modes are, however, larger than thermal energies, kT. Consequently, the predicted electron-transfer activation energies are smaller than those given by traditional semiclassical models of electron transfer. Moreover, these activation energies also depend explicitly on the spacing, R, between the two sites. This R dependence is evaluated for both classical and quantum-mechanical models of the change densities on the molecular ions. Our analysis predicts, therefore, the complete spacing and temperature dependence of the electron-transfer probabilities as functions of the intramolecular molecular-ion vibrational frequencies and electron-vibration coupling constants, and of the frequency and spatial dependence of the dielectric response of the medium in which these ions are embedded. This prediction permits the identification of scaling laws relating both the activation energies and electron-transfer prefactors to molecular and dielectric observables: an identification which provides valuable guidance in the molecular design of efficient electronic transport media.

Duke, C. B.; Meyer, R. J.

1981-03-01

184

Picosecond Raman investigation of interligand electron transfer in Ruthenium(II) complexes  

Energy Technology Data Exchange (ETDEWEB)

Interligand electron transfer has been investigated in the excited MLCT electronic states of mixed ligand ruthenium(II) polypyridine complexes containing bipyridine, bipyrimidine, and carboxybipyridine. Two-color picosecond Raman spectroscopy has been used to unambiguously establish the vibrational spectrum corresponding to the ligand-localized MLCT states. With these data direct measurements of electron-transfer dynamics are obtained. It is found that interligand electron transfer is complete on a time scale significantly faster than the 30-ps experimental time resolution.

Yabe, T.; Orman, L.K.; Anderson, D.R.; Yu, Soochang; Xu, Xiaobing; Hopkins, J.B. (Louisiana State Univ., Baton Rouge (USA))

1990-09-06

185

Resonant excitation of molecules by low-energy electrons  

OpenAIRE

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 spectr...

Popari? Goran B.

2008-01-01

186

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

Scientific Electronic Library Online (English)

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

Marinônio Lopes, CORNÉLIO.

187

Excited State Muon Transfer in Hydrogen/Deuterium Mixtures  

CERN Document Server

We report the first direct observation of excited state muon transfer in hydrogen/deuterium mixtures by direct measurement of q_1s, the probability that a mu-p atom, which is initially formed in an excited state, reaches the 1s ground state. The dependence of q_1s on deuterium concentration c_d was measured for two different densities at cryogenic temperatures using charge coupled devices (CCDs) to detect the muonic X rays. First results based on the analysis of the K_alpha-lines of the two isotopes are presented.

Lauss, B; Breunlich, W H; Gartner, B; Jeitler, Manfred; Kammel, P; Marton, J; Prymas, W; Zmeskal, J; Chatellard, D; Egger, J P; Jeannet, E; Daniel, H; Hartmann, F J; Kosak, A; Petitjean, C

1996-01-01

188

Experimental study of electron impact excitation of multiply charged ions  

Energy Technology Data Exchange (ETDEWEB)

We report on measurements of angular differential cross sections for the excitation of multiply charged ions by electron impact. An ion beam is crossed by an electron beam; electrons which are inelastically scattered at different angles are identified by their energy loss due to the excitation process. Absolute excitation cross sections are obtained by comparing the signals of the elastic and the inelastic electron-ion scattering. Results obtained from the 3s{yields}3p excitation of Ar{sup 7+} are discussed. (orig.).

Ristori, C.; Hervieux, P.A.; Maurel, M.; Perrin, P.; Rocco, J.C.; Zadworny, F.; Huber, B.A. (CEA Centre d' Etudes Nucleaires de Grenoble, 38 (France). Service de Physique Atomique); Andrae, H.J.; Brenac, A.; Lamboley, G.; Lamy, T. (CEA Centre d' Etudes Nucleaires de Grenoble, 38 (France). LAGRIPPA); Crancon, J. (CEA Centre d' Etudes Nucleaires de Grenoble, 38 (France). DRFMC)

1991-11-01

189

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

International Nuclear Information System (INIS)

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

190

Collective electronic excitation modes in a superlattice  

International Nuclear Information System (INIS)

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

191

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

192

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

193

Excited-state energy transfer pathways in photosynthetic reaction centers: 5. Oxidized and triplet excited special pairs as energy acceptors  

International Nuclear Information System (INIS)

In bacterial photosynthetic reaction centers, ultrafast singlet excited-state energy transfer occurs from the monomeric bacteriochlorophylls, B, and bacteriopheophytins, H, to the homodimer special pair, P, a pair of strongly interacting bacteriochlorophylls. Using fluorescence upconversion spectroscopy, energy transfer to the special pair can be monitored by observing the decay of 1B emission and/or the rise of 1P. We report 1B decay kinetics following excitation in the H band in reaction centers where the homodimer and heterodimer (M202HL) special pairs are oxidized, P+ and D+, respectively, and when the homodimer special pair is in the triplet state, 3P. In wild type and the M71GL mutant (a carotenoid-less reaction center), the rates of 1B decay when P+ and 3P are present (?260 fs)-1 and (?235 fs)-1, respectively, are similar to that for energy transfer to 1P (?190 fs)-1 in wild type measured by either the fluorescence decay of 1B or the rise of 1P. In contrast to the homodimer special pair in wild type where the energy transfer rates along the two branches are very similar, singlet energy transfer from the monomeric chromophores along the L and M branches to the heterodimer special pair is asymmetric and is slower along the L side. The 1B decay in wild type is well described by a singlld type is well described by a single rate constant of (?190 fs)-1 and in M202HL exhibits two components with rate constants (?780 fs)-1 and (?250 fs)-1. In M202HL reaction centers containing D+, 1B decays with a single rate constant of (?343 fs)-1; hence, the energy transfer rates along the two branches become similar. Thus, while conversion of the special pair homodimer to a heterodimer breaks the symmetry of ultrafast energy transfer along the two branches of chromophores, symmetry can be restored by oxidizing the heterodimer special pair. To our knowledge, this is the first report of such dramatic alteration of energy transfer within a single reaction center protein. These findings bear on the mechanism of energy transfer in the reaction center and may provide insight into the differences in the electronic interactions on the L vs. M sides of the RC that are relevant to unidirectional electron transfer

194

Molecular Basis for Directional Electron Transfer*  

OpenAIRE

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

195

Excitation of resonators by electron beams  

OpenAIRE

In this paper the main consequences of the vector theory of excitation of resonators by particle beams are presented. Some features of excitation of broadband radiation in longitudinal modes of the enclosed and open resonators are discussed.

Shibata, Yukio; Sasaki, Satoshi; Ishi, Kimihiro; Ikezawa, Mikihiko; Bessonov, E. G.

2000-01-01

196

Primary step in the bacteriorhodopsin photocycle: photochemistry or excitation transfer?  

OpenAIRE

The absorption polarization of the first intermediate (K610) formed at room temperature in the proton-pumping photochemical cycle of bacteriorhodopsin (bR) shows a strong correlation with the polarization direction of the photolyzed parent molecule. The results suggest that, unlike other photosynthetic systems, excitation transfer does not take place prior to the primary photochemical change in bR. These observations together with the previously observed circular dichroism and the polarizatio...

El-sayed, M. A.; Karvaly, B.; Fukumoto, J. M.

1981-01-01

197

Hydrogen-bonded Intramolecular Charge Transfer Excited State of Dimethylaminobenzophenone using Time Dependent Density Functional Theory  

Science.gov (United States)

Density functional theory and time-dependent density-functional theory have been used to investigate the photophysical properties and relaxation dynamics of dimethylaminobenzophenone (DMABP) and its hydrogen-bonded DMABP-MeOH dimer. It is found that, in non-polar aprotic solvent, the transitions from S0 to S1 and S2 states of DMABP have both n??* and ???* characters, with the locally excited feature mainly located on the C=O group and the partial CT one characterized by electron transfer mainly from the dimethylaminophenyl group to the C=O group. But when the intermolecular hydrogen bond C=O···H—O is formed, the highly polar intramolecular charge transfer character switches over to the first excited state of DMABP-MeOH dimer and the energy difference between the two low-lying electronically excited states increases. To gain insight into the relaxation dynamics of DMABP and DMABP-MeOH dimer in the excited state, the potential energy curves for conformational relaxation are calculated. The formation of twisted intramolecular charge transfer state via diffusive twisting motion of the dimethylamino/dimethylaminophenyl groups is found to be the major relaxation process. In addition, the decay of the S1 state of DMABP-MeOH dimer to the ground state, through nonradiative intermolecular hydrogen bond stretching vibrations, is facilitated by the formation of the hydrogen bond between DMABP and alcohols.

Chu, Yu-ling; Yang, Zhong; Pan, Zhe-feng; Liu, Jing; Han, Yue-yi; Ding, Yong; Song, Peng

2012-12-01

198

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

199

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

200

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. (Auth.)

201

Final Report: Vibrational Dynamics in Photoinduced Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

The objective of this grant was to understand how molecular vibrational states (geometry distortions) are involved in photoinduced electron transfer rates of molecules. This subject is an important component of understanding how molecular absorbers of light convert that energy into charge separation. This is important because the absorption usually excites molecular vibrations in a new electronic state prior to electron transfer to other molecules or semiconductor nanoparticles, as in some types of solar cells. The speeds of charge separation and charge recombination are key parameters that require experiments such as those in this work to test the rules governing electron transfer rates. Major progress was made on this goal. Some of the molecular structures selected for developing experimental data were bimolecular charge transfer complexes that contained metals of cobalt or vanadium. The experiments used the absorption of an ultrafast pulse of light to directly separate charges onto the two different molecular parts of the complex. The charge recombination then proceeds naturally, and one goal was to measure the speed of this recombination for different types of molecular vibrations. We used picosecond and femtosecond duration pulses with tunable colors at infrared wavelengths to directly observe vibrational states and their different rates of charge recombination (also called electron transfer). We discovered that different contact geometries in the complexes had very different electron transfer rates, and that one geometry had a significant dependence on the amount of vibration in the complex. This is the first and only measurement of such rates, and it allowed us to confirm our interpretation with a number of molecular models and test the sensitivity of electron transfer to vibrational states. This led us to develop a general theory, where we point out how molecular distortions can change the electron transfer rates to be much faster than prior theories predict. This provides a new method to predict electron transfer rates for particular conditions, and it will be important in designing new types of solar cells. A related set of studies were also done to understand how much the environment around the active charge transfer molecules can control the speed of charge transfer. We studied different complexes with femtosecond transient absorption spectroscopy to show that solvent or components of a matrix environment can directly control ultrafast electron transfer when the environmental relaxation time response is on a similar time-scale as the natural electron transfer. Understanding such processes in both liquids and in a matrix is essential for designing new types of solar cells.

Kenneth G. Spears

2006-04-19

202

Search for Excited Electrons in ep Collisions at HERA  

CERN Document Server

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

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

2008-01-01

203

Effect of electronic correlation on atomic excitation probability accompanying ? decay  

International Nuclear Information System (INIS)

The probability of atomic excitation for K-shell electron during nuclear ? decay has been calculated on the basis of the sudden approximation. Calculations were made with the variational wave functions for the ground states of helium isoelectronic sequence. The effect of electronic correlation on atomic excitation probability is discussed. (author)

204

Theory of nuclear excitation by electron capture for heavy ions  

OpenAIRE

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...

Gagyi-palffy, Adriana

2006-01-01

205

Photonic modulation of electron transfer with switchable phase inversion.  

Science.gov (United States)

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

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

2013-01-24

206

Long-distance photoinitiated electron transfer through polyene molecular wires  

International Nuclear Information System (INIS)

Long-chain polyenes can be used as molecular wires to facilitate electron transfer between a photo-excited donor and an acceptor in an artificial photosynthetic system. The authors present data here on two Zn-porphyrin-polyene-anthraquinone molecules possessing either 5 or 9 all trans double bonds between the donor and acceptor, 1 and 2. The center-to-center distances between the porphyrin and the quinone in these relatively rigid molecules are 25 angstrom for 1 and 35 angstrom for 2. Selective picosecond laser excitation of the Zn-porphyrin and 1 and 2 results in the very rapid transfer of an electron to the anthraquinone in <2 ps and 10 ps, respectively. The resultant radical ion pairs recombine with ? = 10 ps for 1 and ? = 25 ps for 2. The electron transfer rates remain remarkably rapid over these long distances. The involvement of polyene radical cations in the mechanism of the radical ion pair recombination reaction is clear from the transient absorption spectra of 1 and 2, which show strong absorbances in the near-infrared. The strong electronic coupling between the Zn-porphyrin n the anthraquinone provided by low-lying states of the polyene make it possible to transfer an electron rapidly over very long distances

207

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

208

Slow-ion-induced single excitations in an electron gas  

International Nuclear Information System (INIS)

We evaluate electron excitation spectra generated by slow ions in an electron gas. Energy and angular spectra, and total excitation rates, are given. Non-linear screening effects on the intruding charge Z result in Z oscillations in the spectra of electron excitations and in the total excitation rate. Predictions are given, for different electron gas densities, using phase shifts obtained from numerical self-consistent solutions, of the Kohn-Sham density-functional formalism. The results are compared with those obtained in the linear dielectric response, and with the pseudopotential model of target response. The connection between electron excitation spectra and ion energy loss parameters (stopping power and straggling) is discussed. (Author)

209

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

International Nuclear Information System (INIS)

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

210

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.)

211

Electronic excitation of furan molecules by low energy electron impact  

Science.gov (United States)

Absolute differential and integral cross sections are presented for electron impact excitation of the ^3B2 and ^3A1 states of furan. The energy range of the present data set was 5-15eV. The measurements were normalized relative to the elastic cross section data of [1] and are compared to new calculations employing a multi-state Schwinger Multichannel approach with pseudopotentials [2]. The differential cross sections are peaked in the backwards direction, which is characteristic for optically forbidden transitions. Agreement between experiment and theory is good in some cases, although discrepancies remain, particularly above the ionization threshold. These differences are currently being investigated. The influence of polarization and multichannel coupling effects is also examined. [4pt] [1] M.A. Khakoo et al., Phys Rev A, 81, 062716 (2010)[0pt] [2] M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)

Serna, Gabriela; Hargreaves, Leigh; Khakoo, Murtadha A.; Lopes, Maria Christina A.; da Costa, Romarly; Bettega, Marcio H. F.; Lima, Marco A. P.

2012-06-01

212

Nuclear excitation by electronic processes: NEEC and NEET effects  

Energy Technology Data Exchange (ETDEWEB)

The nuclear excitation by electron capture (NEEC) and nuclear excitation by electronic transition (NEET), and related de-excitation, are two important electromagnetic processes to modify the nuclear state populations. In this paper, we present, on one hand, an experiment, accepted at GANIL (France) in September 2004, to measure the NEEC effect with a fully stripped {sup 57}Fe ion beam and, on the other hand, a complete calculation leading to the NEET rate of the first excited state of the {sup 235}U in a local thermodynamic equilibrium (LTE) plasma.

Morel, P. [Commissariat a l' Energie Atomique, Service de Physique Nucleaire, Boite Postale 12, 91680 Bruyeres-le-Chatel (France); Daugas, J.M. [Commissariat a l' Energie Atomique, Service de Physique Nucleaire, Boite Postale 12, 91680 Bruyeres-le-Chatel (France); Gosselin, G. [Commissariat a l' Energie Atomique, Service de Physique Nucleaire, Boite Postale 12, 91680 Bruyeres-le-Chatel (France); Meot, V. [Commissariat a l' Energie Atomique, Service de Physique Nucleaire, Boite Postale 12, 91680 Bruyeres-le-Chatel (France); Gogny, D. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

2004-12-27

213

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

OpenAIRE

Smell is a vital sense for animals. The mainstream explanation of smell is based on recognition of the odorant molecules through characteristics of their surface, e.g., shape, but certain experiments suggest that such recognition is complemented by recognition of vibrational modes. According to this suggestion an olfactory receptor is activated by electron transfer assisted through odorant vibrational excitation. The hundreds to thousands of different olfactory receptors in an animal recogniz...

Solov’yov, Ilia A.; Chang, Po-yao; Schulten, Klaus

2012-01-01

214

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 S13+ + Ar collisions are discussed. An estimate of the experimental background indicates that RTE is more pronounced for heavy projectiles and light targets

215

Kinetics of excitation and charge transfer reactions in nonpolar media  

International Nuclear Information System (INIS)

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

216

Vibration-assisted resonance in photosynthetic excitation energy transfer  

CERN Document Server

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

Irish, E K; Lovett, B W

2013-01-01

217

Ultrafast Electron Dynamics Theory of Photo-excited Ruthenium Complexes  

CERN Document Server

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

Chang, Jun; van Veenendaal, Michel

2010-01-01

218

Primary step in the bacteriorhodopsin photocycle: photochemistry or excitation transfer  

Energy Technology Data Exchange (ETDEWEB)

The absorption polarization of the first intermediate (K/sub 610/) formed at room temperature in the proton-pumping photochemical cycle of bacteriorhodopsin (bR) shows a strong correlation with the polarization direction of the photolyzed parent molecule. The results suggest that, unlike other photosynthetic systems, excitation transfer does not take place prior to the primary photochemical change in bR. These observations together with the previously observed circular dichroism and the polarization temperature dependence are discussed in terms of the exciton structure and the nature of the absorption bandwidths (i.e., homogeneous vs. inhomogeneous) of the bR monomers within the trimer structure.

El-Sayed, M.A.; Karvaly, B.; Fukumoto, J.M.

1981-12-01

219

Primary step in the bacteriorhodopsin photocycle: photochemistry or excitation transfer?  

Science.gov (United States)

The absorption polarization of the first intermediate (K610) formed at room temperature in the proton-pumping photochemical cycle of bacteriorhodopsin (bR) shows a strong correlation with the polarization direction of the photolyzed parent molecule. The results suggest that, unlike other photosynthetic systems, excitation transfer does not take place prior to the primary photochemical change in bR. These observations together with the previously observed circular dichroism and the polarization temperature dependence are discussed in terms of the exciton structure and the nature of the absorption bandwidths (i.e., homogeneous vs. inhomogeneous) of the bR monomers within the trimer structure. PMID:6278477

El-Sayed, M A; Karvaly, B; Fukumoto, J M

1981-12-01

220

Heat transfer between adsorbate and laser-heated hot electrons  

Energy Technology Data Exchange (ETDEWEB)

Strong short laser pulses can give rise to a strong increase in the electronic temperature at metal surfaces. Energy transfer from the hot electrons to adsorbed molecules may result in adsorbate reactions, e.g. desorption or diffusion. We point out the limitations of an often used equation to describe the heat transfer process in terms of a friction coupling. We propose a simple theory for the energy transfer between the adsorbate and hot electrons using a newly introduced heat transfer coefficient, which depends on the adsorbate temperature. We calculate the transient adsorbate temperature and the reaction yield for a Morse potential as a function of the laser fluency. The results are compared to those obtained using a conventional heat transfer equation with temperature-independent friction. It is found that our equation of energy (heat) transfer gives a significantly lower adsorbate peak temperature, which results in a large modification of the reaction yield. We also consider the heat transfer between different vibrational modes excited by hot electrons. This mode coupling provides indirect heating of the vibrational temperature in addition to the direct heating by hot electrons. The formula of heat transfer through linear mode-mode coupling of two harmonic oscillators is applied to the recent time-resolved study of carbon monoxide and atomic oxygen hopping on an ultrafast laser-heated Pt(111) surface. It is found that the maximum temperature of the frustrated translation mode can reach high temperatures for hopping, even when direct friction coupling to the hot electrons is not strong enough.

Ueba, H [Graduate School of Science and Engineering, University of Toyama, Toyama (Japan); Persson, B N J [IFF, FZ-Juelich, Postfach 1913, 52425 Juelich (Germany)], E-mail: ueba@eng.u-toyama.ac.jp

2008-06-04

221

Transfer excitation reactions in fast proton-helium collisions  

CERN Document Server

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

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

2013-01-01

222

Plasmoelectronics: coupling plasmonic excitation with electron flow.  

Science.gov (United States)

Explorations of the coupling of light and charge via localized surface plasmons have led to the discovery that plasmonic excitation can influence macroscopic flows of charge and, conversely, that charging events can change the plasmonic excitation. We discuss recent theory and experiments in the emerging field of plasmoelectronics, with particular emphasis on the application of these materials to challenges in nanotechnology, energy use, and sensing. PMID:22385329

Warren, Scott C; Walker, David A; Grzybowski, Bartosz A

2012-06-19

223

Multiply excited molecules produced by photon and electron interactions  

International Nuclear Information System (INIS)

The photon and electron interactions with molecules resulting in the formation of multiply excited molecules and the subsequent decay are subjects of great interest because the independent electron model and Born-Oppenheimer approximation are much less reliable for the multiply excited states of molecules than for the ground and lower excited electronic states. We have three methods to observe and investigate multiply excited molecules: 1) Measurements of the cross sections for the emission of fluorescence emitted by neutral fragments in the photoexcitation of molecules as a function of incident photon energy [1-3], 2) Measurements of the electron energy-loss spectra tagged with the fluorescence photons emitted by neutral fragments [4], 3) Measurements of the cross sections for generating a pair of photons in absorption of a single photon by a molecule as a function of incident photon energy [5-7]. Multiply excited states degenerate with ionization continua, which make a large contribution in the cross section curve involving ionization processes. The key point of our methods is hence that we measure cross sections free from ionization. The feature of multiply excited states is noticeable in such a cross section curve. Recently we have measured: i) the cross sections for the emission of the Lyman- fluorescence in the photoexcitation of CH4 as a function of incident photon energy in the range 18-51 eV, ii) the electron energy-loss spectrum of CH4 on energy-loss spectrum of CH4 tagged with the Lyman-photons at 80 eV incident electron energy and 10 electron scattering angle in the range of the energy loss 20-45 eV, in order to understand the formation and decay of the doubly excited methane in photon and electron interactions. [8] The results are summarized in this paper and the simultaneous excitation of two electrons by electron interaction is compared with that by photon interaction in terms of the oscillator strength. (authors)

224

Vibrational excitation induced proton transfer in hydrated nafion membranes.  

Science.gov (United States)

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

Liu, Liyuan; Bakker, Huib J

2015-02-12

225

Relaxation of electronic excitations in YAG and YAP crystals  

Energy Technology Data Exchange (ETDEWEB)

One- and two-photon spectroscopy is used for the investigation of the nature of the lowest electronic excitations and their relaxation in YAG and YAP crystals. The coexistence of two types of electronic states (the metastable excitons and the electron-hole continuum) having different relaxation ways has been observed in the exciton absorption region. The peculiarities of the electronic state spectrum observed are supposed to be connected with the complexity of the electron structure of the oxides investigated. ((orig.))

Muerk, V. (Institute of Physics, Riia 142, EE2400 Tartu (Estonia)); Kuznetsov, A. (Institute of Physics, Riia 142, EE2400 Tartu (Estonia)); Namozov, B. (Institute of Physics, Riia 142, EE2400 Tartu (Estonia)); Ismailov, K. (Institute of Physics, Riia 142, EE2400 Tartu (Estonia))

1994-06-01

226

Energy transfer from excited nitrenes at high density  

Science.gov (United States)

This report describes the results of a sixteen month program which supplemented a broader effort dealing with reactions and energy transfer processes of excited nitrenes (AFOSR grant no. F4962O-92-J-027O). This supplemental program was directed specifically toward the generation of NCl(a(1)delta) at high densities, and its energy transfer process with iodine atoms. In one task, NCl(a(1)delta) was created by pulsed photolysis of ClN3. This effort was quite successful in that high densities of both NCl(a(1)delta) and excited l(5()2P) were generated. A second task involved continuous generation of NCl(a(1)delta) by the H + NCl3 reaction in a fast discharge-flow reactor. Although high densities of reagents were achieved, the yield of NCl(a)1)delta) was small. Extensive modeling indicated that the low yield was likely caused by loss of NCl(a(1)delta), NCl3, or NCl2 at the reactor walls.

Coombe, Robert D.

1994-11-01

227

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

OpenAIRE

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 i...

Laporta, V.; Little, D. A.; Celiberto, R.; Tennyson, J.

2014-01-01

228

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

229

Ultrafast tryptophan-to-heme electron transfer in myoglobins revealed by UV 2D spectroscopy.  

Science.gov (United States)

Tryptophan is commonly used to study protein structure and dynamics, such as protein folding, as a donor in fluorescence resonant energy transfer (FRET) studies. By using ultra-broadband ultrafast two-dimensional (2D) spectroscopy in the ultraviolet (UV) and transient absorption in the visible range, we have disentangled the excited state decay pathways of the tryptophan amino acid residues in ferric myoglobins (MbCN and metMb). Whereas the more distant tryptophan (Trp(7)) relaxes by energy transfer to the heme, Trp(14) excitation predominantly decays by electron transfer to the heme. The excited Trp(14)?heme electron transfer occurs in <40 picoseconds with a quantum yield of more than 60%, over an edge-to-edge distance below ~10 angstroms, outcompeting the FRET process. Our results raise the question of whether such electron transfer pathways occur in a larger class of proteins. PMID:23393092

Consani, Cristina; Auböck, Gerald; van Mourik, Frank; Chergui, Majed

2013-03-29

230

Transfer and excitation processes studied in H-like S and Li-like and H-like F colliding with H2  

International Nuclear Information System (INIS)

We have studied transfer and simultaneous excitation by three different experimental techniques. Coincidences between two K x rays were measured for S15+, coincidences between one K x ray and the charge exchanged projectile for Li-like F and projectile Auger electrons for H-like F in each case colliding with H2. For all three collision systems, the measured cross sections are dominated by Resonant Transfer and Excitation (RTE). Also, for the F projectiles, strong contributions from Two Electron Transfer and Excitation (2eTE) were found. 9 refs., 3 figs

231

Electron transfer: classical approaches and new frontiers  

Science.gov (United States)

Electron transfer, under conditions of weak interaction and a medium acting as a passive thermal bath, is very well understood. When electron transfer is accompanied by transient chemical bonding, such as in interfacial coordination electrochemical mechanisms, strong interaction and molecular selectivity are involved. These mechanisms, which take advantage of "passive self-organization," cannot yet be properly described theoretically, but they show substantial experimental promise for energy conversion and catalysis. The biggest challenge for the future, however, may be dynamic, self-organized electron transfer. As with other energy fluxes, a suitable positive feedback mechanism, through an active molecular environment, can lead to a (transient) decrease of entropy equivalent to an increase of molecular electronic order for the activated complex. A resulting substantial increase in the rate of electron transfer and the possibility of cooperative transfer of several electrons (without intermediates) can be deduced from phenomenological theory. The need to extend our present knowledge may be derived from the observation that chemical syntheses and fuel utilization in industry typically require high temperatures (where catalysis is less relevant), whereas corresponding processes in biological systems are catalyzed at environmental conditions. This article therefore focuses on interfacial or membrane-bound electron transfer and investigates an aspect that nature has developed to a high degree of perfection: self-organization. PMID:9506932

Tributsch; Pohlmann

1998-03-20

232

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.)

233

Coherent excitation of autoionizing resonances by electron impact  

International Nuclear Information System (INIS)

Interference effects caused by coherent population by electron impact, of cadmium autoionizing levels and continua of differing total angular momentum and parity. The work provides information both the excitation mechanism by charged particle impact and the spectroscopy of autoionizing levels

234

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

International Nuclear Information System (INIS)

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

235

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

Energy Technology Data Exchange (ETDEWEB)

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

Mineo, H. [Institute of Applied Mechanics, National Taiwan University, Taipei 106, Taiwan (China); Kanno, M.; Kono, H. [Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan); Chao, S.D. [Institute of Applied Mechanics, National Taiwan University, Taipei 106, Taiwan (China); Lin, S.H. [Institute of Atomic and Molecular Science, Academia Sinica, Taipei 106, Taiwan (China); Department of Applied Chemistry, Chiao-Tung University, Hsin-Chu 300, Taiwan (China); Fujimura, Y., E-mail: fujimurayuichi@m.tohoku.ac.jp [Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan); Department of Applied Chemistry, Chiao-Tung University, Hsin-Chu 300, Taiwan (China)

2012-01-02

236

Magnesium atom singlet levels excitation by electron impact  

International Nuclear Information System (INIS)

The aim of the paper is experimental study of magnesium atom singlet levels excitation by electron impact by the intersecting beam method. Data on the cross sections and optical excitation functions (OEF) of magnesium atoms are presented in dependence on the electrons energy in the range of 0-200 eV. The OEF dependences of the magnesium atom singlet spectral series on the main quantum number are presented too

237

Anomalous temperature dependence of excitation transfer betweenquantum dots.  

Czech Academy of Sciences Publication Activity Database

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

Král, Karel; Menšík, Miroslav

238

Microscopic solvation dynamics and solvent-controlled electron transfer  

Energy Technology Data Exchange (ETDEWEB)

In this paper the authors investigate solvent size effects on solvent-controlled electron transfer (ET) in polar liquids. An interrelationship was established between the solvation time correlation function and the ET rate, which was presented within the first passage time approximation. For the case of activationless ET the ET rate, which is equal to the initial solvation rate, was expressed within the framework of the mean spherical approximation. The theory predicts that the activationless ET times are shorter than the average dipole solvation times, in accord with experimental data for intramolecular ET in electronically excited bianthryl in nonassociated polar solvents.

Rips, I.; Klafter, J.; Jortner, J. (Tel Aviv Univ. (Israel))

1990-11-15

239

Advances in electron transfer chemistry, v.6  

CERN Document Server

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

Mariano, PS

1999-01-01

240

Nuclear Excitation by Electronic Transition - NEET  

Energy Technology Data Exchange (ETDEWEB)

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 {sup 197}Au, while realistic upper limits for {sup 189}Os have been established. A new experiment in {sup 189}Os is described. The experimental claim of NEET in isomeric {sup 178}Hf is not credible.

Becker, J.A.

2002-06-10

241

Inelastic electron scattering at low momentum transfer  

International Nuclear Information System (INIS)

Recent advances of high energy resolution (?E approx. 30 keV FWHM) inelastic electron scattering at low momentum transfer (q -1) using selected experimental data from the Darmstadt electron linear accelerator are discussed. Strong emphasis is given to a comparison of the data with theoretical nuclear model predictions. Of the low multipolarity electric transitions investigated, as examples only E1 transitions to unnatural parity states in 11B and E2 transitions of the very fragmented isoscalar quadrupole giant resonance in 208Pb are considered. In 11B the role of the Os hole in the configuration of the 1/2+, 3/2+ and 5/2+ states is quantitatively determined via an interference mechanism in the transition probability. By comparison of the high resolution data with RPA calculations the E2 EWSR in 208Pb is found to be much less exhausted than anticipated from previous medium energy resolution (e,e) and hadron scattering experiments. In the case of M1 transitions it is shown that the simplest idealized independent particle shell-model prediction breaks down badly. In 28Si, ground-state correlations influence largely the detected M1 strength and such ground-state correlations are also responsible for the occurence of a strong M1 transition to a state at Ex = 10.319 MeV in 40Ca. In 90Zr only about 10% of the theoretically expected M1 strength is he theoretically expected M1 strength is seen in (e,e) and in 140Ce and 208Pb none (detection limit 1-2 ?2K). In the case of 208Pb high resolution spectra exist now up to an excitation energy of Ex = approx. 12MeV. The continuous decrease of the M1 strength with mass number is corroborated by the behaviour of strong but very fragmented M2 transitions which are detected in 28Si, 90Zr, 140Ce and 208Pb concentrated at an excitation energy E x approx. 44A-1/3MeV. In 90Zr, the distribution of spacings and widths of the many J? = 2 states are consistent with a Wigner and Porter-Thomas distribution, respectively. (orig.) 891 KBE/orig. 892 ARA

242

Photorelaxation induced by water-chromophore electron transfer.  

Science.gov (United States)

Relaxation of photoexcited chromophores is a key factor determining diverse molecular properties, from luminescence to photostability. Radiationless relaxation usually occurs through state intersections caused by distortions in the nuclear geometry of the chromophore. Using excited-state nonadiabatic dynamics simulations based on algebraic diagrammatic construction, it is shown that this is the case of 9H-adenine in water cluster, but not of 7H-adenine in water cluster. 7H-adenine in water cluster relaxes via a state intersection induced by electron transfer from water to the chromophore. This result reveals an unknown reaction pathway, with implications for the assignment of relaxation mechanisms of exciton relaxation in organic electronics. The observation of photorelaxation of 7H-adenine induced by water-chromophore electron transfer is a proof of principle calling for further computational and experimental investigations to determine how common this effect is. PMID:25010652

Barbatti, Mario

2014-07-23

243

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

International Nuclear Information System (INIS)

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

244

Electronic excited state of protonated aromatic molecules: protonated Fluorene  

CERN Document Server

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

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

2011-01-01

245

Electron impact excitation of the gas-phase tellurium  

International Nuclear Information System (INIS)

The excitation processes of vapor tellurium by low energy electron impact (0-50 eV) were studied. The emission spectra in the wavelength range from 200 to 525 nm for electron-impact energies of 10, 15, 20, 30 eV were investigated. The optical excitation functions of the most intense atomic lines and molecular bands were measured. It was found that in the temperature range of 270-320°C a lot of diatomic molecules of Te2 along with polyatomic tellurium molecules were in the vapor. Atomic lines of Te* formed through dissociative excitation of tellurium molecules. (authors)

246

Reaction dynamics of electronically excited alkali atoms with simpler molecules  

International Nuclear Information System (INIS)

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

247

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

248

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

Science.gov (United States)

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

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

2015-02-12

249

Excited state distortions in a charge transfer state of a donor-acceptor [2]rotaxane.  

Science.gov (United States)

The charge transfer excited state of a mechanically interlocked [2]rotaxane (R(4+)) with a donor 1,5-dioxynaphthalene (DNP) unit in the rod and the acceptor cyclobis(paraquat-p-phenylene) (CBPQT(4+)) ring component, along with the analogous non-interlocked [2]pseudorotaxane (P(4+)), is studied by resonance Raman spectroscopy and electronic absorption spectroscopy. Resonance Raman excitation profiles are obtained, calculated quantitatively using time-dependent theoretical methods, and interpreted with the assistance of DFT calculations. The active vibrational modes are consistent with an electron transfer from the HOMO centered on the DNP unit to the LUMO on the CBPQT(4+) ring. Displacement vectors of highly distorted modes agree with the bonding changes predicted from the MO nodal pattern. Subtle changes in the frequency of some modes in the free components compared with those in R(4+) are observed. The largest distortions are found for modes involving ring breathing in the DNP unit of the rod and the paraquat units of the CBPQT(4+) ring. The individual mode contributions to the vibrational reorganization energy, as well as the total vibrational reorganization energy, are calculated. Very similar values of ?(v) for R(4+) and P(4+) are calculated (?2910 cm(-1)), indicating that the mechanical stoppers in the interlocked system do not significantly affect the excited state properties of R(4+) compared with P(4+). PMID:20871904

Stephenson, Rachel M; Wang, Xianghuai; Coskun, Ali; Stoddart, J Fraser; Zink, Jeffrey I

2010-11-14

250

Direct conversion of graphite into diamond through electronic excited states  

CERN Document Server

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

Nakayama, H

2003-01-01

251

Selective excitation in charge-transfer collisions with Ne2  

International Nuclear Information System (INIS)

The possible advantages of employing neon-dominated gas mixtures in e-beam laser cavities are discussed, and cross sections for selective excitation of N2+, CO+, and CO2+ in charge-transfer collisions between Ne2+ and N2, CO and CO2 are reported. The magnitudes of these cross sections (measured using beam techniques) compare favorably with analogous measurements involving He2+ reactant ions, suggesting that laser action in neon-dominated mixtures might be achieved. The addition of helium to the ion source was observed to increase the Ne2+ beam current; however, the accompanying increased photon yield was greater than the percentage increase in the beam current, indicating that vibrationally relaxed Ne2+ is preferred. It is suggested that ''seeding'' a neon-filled e-beam laser cavity with helium could increase the over-all efficiency of such a device

252

Accumulative electron transfer: multiple charge separation in artificial photosynthesis.  

Science.gov (United States)

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

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

2012-01-01

253

Low Temperature Electronic Transport and Electron Transfer through Organic Macromolecules  

OpenAIRE

It is shown that at low temperatures and moderate electron dephasing the electron transmission function reveales a structure containing information about donor/acceptor sites effectively participating in the electron transfer (ET) processes and primary pathways of electrons tunneling through molecular bridges in macromolecules. This important information can be obtained as a result of analysis of experimental low temperature current-voltage characteristics for chosen molecules.

Zimbovskaya, Natalya A.

2002-01-01

254

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

Science.gov (United States)

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

Olsen, Seth

2015-02-12

255

Real-time simulations of photoinduced coherent charge transfer and proton-coupled electron transfer.  

Science.gov (United States)

Photoinduced electron transfer (ET) and proton-coupled electron transfer (PCET) are fundamental processes in natural phenomena, most noticeably in photosynthesis. Time-resolved spectroscopic evidence of coherent oscillatory behavior associated with these processes has been reported both in complex biological environments, as well as in biomimetic models for artificial photosynthesis. Here, we consider a few biomimetic models to investigate these processes in real-time simulations based on ab initio molecular dynamics and Ehrenfest dynamics. This allows for a detailed analysis on how photon-to-charge conversion is promoted by a coupling of the electronic excitation with specific vibrational modes and with proton displacements. The ET process shows a characteristic coherence that is linked to the nuclear motion at the interface between donor and acceptor. We also show real-time evidence of PCET in a benzimidazole-phenol redox relay. PMID:25224924

Eisenmayer, Thomas J; Buda, Francesco

2014-10-20

256

Excitation functions of slow proton transfer reactions involving negative ions  

International Nuclear Information System (INIS)

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

257

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

258

Pressure-induced effect on electronic excitations in osmium  

International Nuclear Information System (INIS)

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

259

Pseudospin Transfer Torques in Semiconductor Electron Bilayers  

OpenAIRE

We use self-consistent quantum transport theory to investigate the influence of electron-electron interactions on interlayer transport in semiconductor electron bilayers in the absence of an external magnetic field. We conclude that, even though spontaneous pseudospin order does not occur at zero field, interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer torques do alter tunneling I-V characteristics, and can lead to time-dependent response to a d...

Kim, Youngseok; Macdonald, Allan H.; Gilbert, Matthew J.

2012-01-01

260

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

261

Ground- and excited-state dipole moments of some nitroaromatics: Evidence for extensive charge transfer in twisted nitrobenzene systems  

Science.gov (United States)

Electro-optical absorption measurements have been made on four model nitroaromatics to determine the effect of twisting of the donor-acceptor single bond on the charge-transfer characteristics in the Franck-Condon excited states. Observed ground- and excited-state dipole moments of nitromesitylene, which has been treated experimentally as the nonplanar analogue of planar nitrobenzene, indicate that electronic excitation of twisted nitrobenzene results in a nearly full unit charge transfer from donor (benzene) to the acceptor (nitro) group (??=18.3 D). On the other hand, in planar nitrobenzene and nitronaphthalene the charge transfer is more delocalized over the whole molecular skeleton, resulting in normal changes in dipole moment (??=5-10 D). In the analogous anthracene system, i.e., 9-nitroanthracene, the charge transfer upon electronic excitation is extremely low (??=1.7 D), which is reflected by its very small change in the dipole moment. Therefore, it is evident that the charge-transfer processes in the twisted molecules are quite different for different aromatic ring systems. Simple molecular-orbital calculations satisfactorily explain the reason for such differences on the basis of their highest occupied molecular-orbital (HOMO) and lowest unoccupied molecular-orbital (LUMO) characteristics. Transition moment directions have also been obtained experimentally and compared with the theoretically predicted directions based on the symmetry properties of the HOMO and LUMO. Agreement is found in all cases studied.

Sinha, Hemant K.; Yates, Keith

1990-11-01

262

Single Molecule Spectroscopy of Electron Transfer  

International Nuclear Information System (INIS)

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

263

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

264

Excitation transfer reactions in neon afterglows at 1500K, 3000K and 4000K  

International Nuclear Information System (INIS)

The results of an experimental study of excitation transfer reactions in the afterglow period of pulsed discharges in pure neon are presented. The temporal decay of excited atom populations were monitored using the technique of resonance absorption, and absolute excited state populations were determined for the lowest lying manifold of excited states (3P2, 3P1, 3P0, 1P1). The density range 5 x 1017 - 1019 cm-3 was examined and rate data determined at operating temperatures of 1500K, 3000K and 4000K through analysis of the individual excited state decay profiles. In agreement with results of previous experimental studies, collisions with ground state neon atoms were found to play the dominant role in quenching individual excited state populations. A matrix of rate constants for neutral induced two-body mixing between the triplet states and three-body quenching of the excited states were determined at each of the operating temperatures. Additionally, rate data was determined for two-body processes involving electrons and for the decay of imprisoned radiation of the resonant state 3P1. The temperature dependences of the measured rate coefficients indicate a need for refinement of the theoretical potential curves presently available. For example, the temperature variation of both the two-the temperature variation of both the two-body and three-body rate coefficients for the 3P2 state warrant a less repulsive long-range potential for the potential curves than currently allowed. Additionally, the large two-body rates found for the 3P0 state suggest the need for addiational coupling mechanisms in the theoretical calculations of mixing rate constants

265

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

266

Directed emission of fast electrons from excited metal nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Experimental studies on laser excited silver particles reveal a strong asymmetric electron emission characteristic giving electron kinetic energies of up to 1.3 keV in the direction of the laser polarization axis. It could be shown that in a dual pulse experiment the evolution of the plasmon frequency following the pump pulse enables resonant excitation by the probe pulse. The resulting electron energies, gained in the nanometer scaled microplasma, as well as the spatial asymmetry in emission direction cannot be explained by a conventional hydrodynamical or a purely coulomb driven expansion process. We present a novel acceleration mechanism through plasmon assisted, phase-matched electron-cluster rescattering, which is capable to explain the generation of a directed emission of high energy electrons obtained in the experiment. Moreover, Vlasov simulations show that an attosecond electron pulse train is generated.

Passig, Johannes; Fennel, Thomas; Truong, Nguyen Xuan; Tiggesbaeumker, Josef; Meiwes-Broer, Karl-Heinz [Universitaet Rostock (Germany). Institut fuer Physik

2008-07-01

267

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

268

Rate coefficients for electron impact excitation of CO  

International Nuclear Information System (INIS)

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

269

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

270

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

271

Dissociation of vibrationally excited D2+ by electrons  

OpenAIRE

Abstract We have investigated the electron impact dissociation of the deuterium molecular cation assuming a Franck-Condon distribution of the initial vibrational states given by electron impact ionization of D2. The electron energy range 1-12 eV has been considered. The relative contributions of the initial vibrational states to the total cross sections of the D2+ dissociative recombination and excitation have been determined.

Fifirig, Magda; Stroe, Marius

2011-01-01

272

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 Örn

2013-01-01

273

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

274

Spectroelectrochemical identification of charge-transfer excited states in transition metal-based polypyridyl complexes.  

Science.gov (United States)

Identification of transient species is a necessary part of delineating the kinetics and mechanisms associated with chemical dynamics; when dealing with photo-induced processes, this can be an exceptionally challenging task due to the fact that spectra associated with excited state(s) sampled over the course of a photochemical event often cannot be uniquely identified nor readily calculated. Using Group 8 complexes of the general form [M(terpy)2](2+) and [M(bpy)3](2+) as a platform (where terpy is 2,2':6',2''-terpyridine and bpy is 2,2'-bipyridine), we demonstrate how spectroelectrochemical measurements can serve as an effective tool for identifying spectroscopic signatures of charge-transfer excited states of transition metal-based chromophores. Formulating the metal-to-ligand charge-transfer (MLCT) excited state(s) as M(3+)-L(-), the extent to which a linear combination of the spectra of the oxidized and reduced forms of the parent complexes can be used to simulate the characteristic absorptions of MLCT-based transient species is examined. Quantitative agreement is determined to be essentially unachievable due to the fact that certain transitions associated with the optically prepared excited states are either overcompensated for in the spectroelectrochemical data, or simply cannot be replicated through electrochemical means. Despite this limitation, it is shown through several illustrative examples that this approach can still be extremely useful as a qualitative if not semi-quantitative guide for interpreting time-resolved electronic absorption data of charge-transfer compounds, particularly in the ultrafast time domain. PMID:25321952

Brown, Allison M; McCusker, Catherine E; McCusker, James K

2014-12-21

275

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

276

An Exciting Aspect of Nanotechnology: Unimolecular Electronics  

Directory of Open Access Journals (Sweden)

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

Metzger R. M.

2013-08-01

277

Collective two-particle excitations in cuprates and manganites: Resonant inelastic x-ray scattering and electron energy loss spectroscopy  

International Nuclear Information System (INIS)

The two-particle charge excitations of Sr2CuO3, which contains one-dimensional corner-sharing CuO2-chains, were studied by Resonant Inelastic X-ray Scattering (RIXS) at the Cu K-edge. At the center of the Brillouin zone, the dependence of the various charge-transfer excitations on the incident photon energy Ei was studied in detail. The different charge transfer excitations resonate for different intermediate states, i.e., different Ei, which allows to draw conclusions about the symmetry of the created excitations. Further, the RIXS results are discussed in comparison to previous Electron Energy Loss Spectroscopy (EELS) studies. A similar approach was then used to investigate the two-particle excitations (La,Sr)2MnO4. Surprisingly, the excitations observed for the doped manganite materials share similar traits with the ones observed for the doped cuprates.

278

Electron-collision excitation cross section of the silver atom  

International Nuclear Information System (INIS)

The cross sections for direct excitation by electron collision were measured for fifteen transitions of the silver atom. For thirteen of these transitions the optical excitation functions were recorded, varying the energy of the exciting electrons from the threshold energy to 250 eV. The operating region of the spectrum was 2000--5500 A. The excitation cross sections of the two principal lines exceeded the excitation cross sections of all the remaining lines by more than an order of magnitude. Reabsorption of the resonance lines was detected from the change in the ratio of intensities of the lines at 3280.68 and 3382.89 A, and so their intensity has been corrected relative to the intensities of the nonreabsorbed lines. All radiative transitions, with the exception of resonance transitions, participate in cascade population of the lowest resonance levels, making it possible to determine the resulting direct excitation cross sections of the 5p2P/sub 1/2/ and 5p2P/sub 3/2/ levels from the ground state of the silver atom. The part played by cascade population of the resonance levels is not large and is 2P/sub 3/2/ level, and 10% for the 5p2P/sub 1/2/ level, of the excitation cross sections of the corresponding resonance transitions

279

Electron-collision excitation cross section of the silver atom  

Energy Technology Data Exchange (ETDEWEB)

The cross sections for direct excitation by electron collision were measured for fifteen transitions of the silver atom. For thirteen of these transitions the optical excitation functions were recorded, varying the energy of the exciting electrons from the threshold energy to 250 eV. The operating region of the spectrum was 2000--5500 A. The excitation cross sections of the two principal lines exceeded the excitation cross sections of all the remaining lines by more than an order of magnitude. Reabsorption of the resonance lines was detected from the change in the ratio of intensities of the lines at 3280.68 and 3382.89 A, and so their intensity has been corrected relative to the intensities of the nonreabsorbed lines. All radiative transitions, with the exception of resonance transitions, participate in cascade population of the lowest resonance levels, making it possible to determine the resulting direct excitation cross sections of the 5p/sup 2/P/sub 1/2/ and 5p/sup 2/P/sub 3/2/ levels from the ground state of the silver atom. The part played by cascade population of the resonance levels is not large and is <8% for the 5p/sup 2/P/sub 3/2/ level, and 10% for the 5p/sup 2/P/sub 1/2/ level, of the excitation cross sections of the corresponding resonance transitions.

Krasavin, A.Y.; Kuchenev, A.N.; Smirnov, Y.M.

1983-01-01

280

Electron transfer at sensitized TiO/sub 2/ electrodes  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer from the excited state of tetra-iodo, tetra-chloro fluorescein (rose bengal) to the conduction band of TiO/sub 2/ has been studied through photoelectrochemical techniques. The measured transfer rate was correlated with information from absorbance and adsorption measurements of this dye molecule on the (001) surface of the single crystals used as electrodes. The quantum efficiency for the photoinjection of electrons was determined to be 4.0 x 10/sup -3/ independent of the pH of the electrolyte and the dye surface concentration. With these data, an argument is given supporting the existence of excitation transfer among the dye molecules on the surface. A temperature study of the electron transfer efficiency yielded an activation enthalpy of 3.2 +- 0.3 kcal/mole with a pre-exponential factor of 1.0. A heat of adsorption of 7.6 +- 0.5 kcal/mole for this dye on TiO/sub 2/ single crystals was derived from analysis of adsorption isotherms measured at 21.5 and 36.5degreeC. In addition to the photo-oxidation process, a photoreduction was also observed upon cathodic polarization of the semiconductor. Action spectra revealed participation of solution dye molecules in this reaction; the reduction rate is dependent upon oxygen concentration in solution. It was concluded that the oxidized dye in solution accepts an electron from the TiO/sub 2/ to generate this current. This photoreduction was found with triphenylmethane and thiazine dyes as well as with other fluorescein derivatives.

Spitler, M.T.; Calvin, M.

1977-05-15

281

Enhancement of molecular modes by electronically resonant multipulse excitation: Further progress towards mode selective chemistry  

Science.gov (United States)

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

Hauer, Jürgen; Buckup, Tiago; Motzkus, Marcus

2006-08-01

282

Infrared multiphoton excitation and inverse electronic relaxation in SO2  

International Nuclear Information System (INIS)

Visible luminescence (lambda=270--470 nm) has been observed from S16O2 and S18O2 at pressures of 0.2 to 20 Torr following irradiation by an intense infrared laser (lambda=9.3 ?m). Our experiments show that the luminescence is not due to dielectric breakdown or recombination of dissociation fragments, but rather is fluorescence from the first excited singlet states of SO2 following inverse electronic relaxation from highly excited vibrational levels of the ground electronic state. Crossover from the ground to excited electronic states may also be collisionally assisted. Spectroscopic and kinetic measurements are consistent with previous studies on 1B1 emission from SO2. The pressure dependence of the fluorescence yield exhibits two distinct pressure regimes, while the dependence of visible emission on laser pump wavelength follows the small signal infrared absorption spectrum. The threshold for detection of fluorescence is 17--20 J/cm2 with 9.3 ?m radiation as the excitation source. These observations are discussed in terms of recently proposed theories which describe the photophysics of vibrationally excited states coupled to a radiative continuum through higher electronic states

283

Vibrational excitation of molecules by resonant electron scattering  

International Nuclear Information System (INIS)

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

284

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

DEFF Research Database (Denmark)

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

Solov'yov, Ilia; Chang, Po-Yao

2012-01-01

285

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

286

Ultrafast interatomic electronic decay in multiply excited clusters  

CERN Document Server

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

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

2010-01-01

287

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

OpenAIRE

The localized operator partitioning method [Y. Khan and P. Brumer, J. Chem. Phys. 137, 194112 (2012)] rigorously defines the electronic energy on any subsystem within a molecule and gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. However, an efficient implementation of this approach has been hindered by complicated one- and two-electron integrals arising in i...

Nagesh, Jayashree; Izmaylov, Artur F.; Brumer, Paul

2014-01-01

288

Theoretical study of ultrafast heterogeneous electron transfer reactions at dye-semiconductor interfaces  

International Nuclear Information System (INIS)

A detailed study of photoinduced electron transfer reactions from an electronically excited state of a dye molecule to the conduction band of a semiconductor substrate is presented. Adopting a generic model for electronic-vibrational coupling in heterogeneous electron transfer reactions, the quantum dynamics of the electron injection process is simulated employing the recently proposed self-consistent hybrid method. The results reveal the influence of coherent and dissipative vibrational motion on the electron transfer dynamics. Furthermore, the dependence of the injection dynamics on various electron transfer parameters, such as the energetic position of the donor state, the coupling strength between the dye molecule and the semiconductor substrate, the characteristic timescale of the nuclear degrees of freedom and the temperature, is discussed in some detail

289

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

Energy Technology Data Exchange (ETDEWEB)

Ytterbium ion ability to luminescence in the complexes with a number of organic ligands has been studied. Ytterbium chloride solution with the final concentration 1x10/sup -4/ M is used, to which aqueous or alcoholic solutions of reagents to create their final concentration 2-4x10/sup -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 Yb/sup 3 +/ can be atrributed to intramolecular energy transfer from organic part of molecules through triplet state.

Poluehktov, N.S.; Meshkova, S.B.; Korovin, Yu.V. (AN Ukrainskoj SSR, Odessa. Fiziko-Khimicheskij Inst.)

1983-01-01

290

Vibrational energy transfer in selectively excited diatomic molecules  

International Nuclear Information System (INIS)

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

291

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.

292

Excited-state proton transfer of photoacids adsorbed on biomaterials.  

Science.gov (United States)

The interaction between a photoacid (8-hydroxy-1,3,6-pyrenetrisulfonate, HPTS) and the surfaces of biomaterials and the diffusion of protons along the biomaterial surfaces were examined by following the excited-state proton transfer (ESPT) from the photoacid, adsorbed on the surfaces, to water molecules next to it. We chose two different types of biomaterial surfaces, hydrophobic insulin amyloid fibrils and hydrophilic cellulose surfaces. With the help of steady-state and time-resolved fluorescence techniques, we found that the rate of ESPT from HPTS on insulin fibrils to adjacent water molecules is about 1/10 that in bulk water. However, the proton geminate recombination takes place with an efficiency similar to that in bulk water. ESPT from HPTS in wet cellulose to water depends on the weight percentage of water adsorbed by the cellulose. In a semidry sample (interaction with water molecules, while obtaining important information regarding the hydration state of the surface that otherwise could not have been obtained. The model that we propose here for the use of photoacids to follow the hydrated state of a given surface is a promising new method of examining the interaction of water molecules with biological surfaces. PMID:25380297

Amdursky, Nadav; Simkovitch, Ron; Huppert, Dan

2014-12-01

293

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

International Nuclear Information System (INIS)

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

294

Promoting Knowledge Transfer with Electronic Note Taking  

Science.gov (United States)

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

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

2005-01-01

295

Quantum effects in biological electron transfer.  

Czech Academy of Sciences Publication Activity Database

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

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

2012-01-01

296

Femtosecond events in the free electron transfer  

Energy Technology Data Exchange (ETDEWEB)

The ion-molecule reaction between solvent parent radical cations and hetero group-substituted aromatics in non-polar media shows a characteristic product distribution, which depends strongly on the mobility of the substituent. This electron transfer phenomenon seems to reflect femtodynamics of the donor molecule, which is appearing in the nanosecond time range.

Brede, Ortwin [Interdisciplinary Group Time-Resolved Spectroscopy, University of Leipzig (Germany)]. E-mail: brede@mpgag.uni-leipzig.de; Naumov, Sergej [Institute of Surface Modification, Leipzig (Germany)

2007-08-15

297

Extremely confined gap surface plasmon modes excited by electrons  

CERN Document Server

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

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

2013-01-01

298

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

CERN Document Server

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

Zoubi, Hashem

2011-01-01

299

An excitable electronic circuit as a sensory neuron model  

OpenAIRE

An electronic circuit device, inspired on the FitzHugh-Nagumo model of neuronal excitability, was constructed and shown to operate with characteristics compatible with those of biological sensory neurons. The nonlinear dynamical model of the electronics quantitatively reproduces the experimental observations on the circuit, including the Hopf bifurcation at the onset of tonic spiking. Moreover, we have implemented an analog noise generator as a source to study the variabilit...

Medeiros, Bruno N. S.; Minces, Victor; Mindlin, Gabriel B.; Copelli, Mauro; Leite, Jose? R. Rios

2011-01-01

300

Characterization of charge transfer excitations in hexacyanomanganate(III) with Mn K-edge resonant inelastic x-ray scattering  

International Nuclear Information System (INIS)

We use hard x-ray resonant inelastic x-ray scattering (RIXS) and density functional theory (DFT) calculations to characterize charge transfer excitations in K3Mn(CN)6. The combination of RIXS measurements and DFT calculations allows us to characterize the strength of the ligand-metal electronic interaction and assign the Raman resonances in the RIXS spectra to charge transfer excitations. With x-ray excitation energies resonant with the T2g and Eg pre-edge peaks derived predominantly from the Mn 3d orbitals, we observe Raman resonances in the energy transfer range from 2 to 12 eV, which results from the filling of the 1s core-hole from T1u-symmetry occupied orbitals. DFT calculations indicate that these orbitals exhibit primarily ligand character, supporting the assignment of the energy transfer resonances to ligand-to-metal charge transfer excitations. Our RIXS measurements and DFT calculations also indicate that the Eg-orbital spin-splits by roughly 0.8 eV, though we do not cleanly resolve the two absorption peaks in the RIXS spectra. We also see evidence for a metal-to-ligand charge transfer (MLCT) excitation when exciting with a 6545.0 eV incident photon, roughly 4 eV above the Eg absorption peaks. The 6545.0 eV resonant emission spectrum shows a 6.0 eV energy transfer resonance, which corresponds to a final state hole in the T2g partially occupied orbital. DFT calculations indlly occupied orbital. DFT calculations indicate that excitation at 6545.0 eV populates an unoccupied T1u-symmetry orbital of primarily ligand character. Given the predominantly metal character of the final state hole, we assign the 6.0 eV Raman resonance to a MLCT excitation. These measurements demonstrate the ability of hard x-ray RIXS to characterize the valence electronic structure of coordination compounds.

301

Monitoring molecule dynamics by free electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Molecular oscillations take place in the time range of some 10-100 fs. In asymmetric molecules, accompanied with rotation and necking motions of molecule parts changes of the electron distribution of the molecular orbitals occur. In phenols the rotation motion of the C-OH bond with a frequency around 10{sup 13} Hz causes dramatical electron motions in the molecule. These motions could be monitored with an extremely rapid chemical reaction (free electron transfer) which results in product characteristics for the assumed different borderline structures of the phenol molecule.

Brede, O. E-mail: brede@mpgag.uni-leipzig.de; Naumov, S.; Hermann, R

2003-06-01

302

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

Science.gov (United States)

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

Lin, C.; Dienes, A.

1973-01-01

303

Molecular dynamics simulation of electronically excited polyatomic molecules  

International Nuclear Information System (INIS)

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

304

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

305

Electron impact excitation processes for carbon-containing molecules  

International Nuclear Information System (INIS)

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

306

Excitation of electron Langmuir frequency harmonics in the solar atmosphere  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-05-15

307

Electron transfer in keV-energy 4He++ atomic collisions. I. Single and double electron transfer with He, Ar, H2, and N2  

International Nuclear Information System (INIS)

Single- and double-electron-transfer cross sections have been measured for a 4He++ beam incident on thin He, Ar, H2, and N2 gas targets over the energy range 15--125 keV. Comparison with previous 3He++ experimental results is made at the same incident particle velocity. For He++ collisions with He, we find good agreement with the theory for double electron transfer, but conclude that the single-electron-transfer cross section is far from being understood. Interpretation of the data in terms of simple theoretical ideas indicates that capture into excited states of the He+ ion can be the dominant single-electron-transfer process in some keV-energy He++ atomic collisions

308

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

Science.gov (United States)

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

Nagesh, Jayashree; Izmaylov, Artur F.; Brumer, Paul

2015-02-01

309

A reversible photoredox reaction: Electron-transfer photoreduction of. beta. -lapachone by triethylamine  

Energy Technology Data Exchange (ETDEWEB)

Light-induced electron-transfer reactions are being studied as possible energy conversion or storage processes. One such reaction of a light-induced electron-transfer reaction and subsequent electron- and atom-transfer processes, which are at least partially reversible, is reported herein. The specific reaction studied was the photooxidation of triethylamine by excited state o-quinones. The energy stored in the overall process is modest, and the degree of reversibility is limited by the reactivity of the amine oxidation products. 33 refs.

Ci, Xiaohong; Goodman, J.L.; Whitten, D.G. (Univ. of Rochester, NY (USA)); da Silva, R.S.; Nicodem, D.E. (Univ. of Rio de Janeiro (Brazil))

1988-12-07

310

Electronic and vibrational excitations in adsorbed metalorganic molecules  

International Nuclear Information System (INIS)

HREELS has been used to probe the vibrational and electronic properties of metalorganic molecules adsorbed on III-V semiconductor surfaces. Following adsorbate characterisation, the HREELS electron beam is used to investigate possible resonant vibrational excitation for a range of alkyl-based molecules adsorbed on GaAs(100) and InSb(100). By varying the electron beam energy of the HREEL spectrometer, resonant vibrational excitation is demonstrated at discrete energies in all the molecules studied. This excitation mechanism is confirmed by obtaining adsorbate excitation functions, the observation of enhanced overtone and combination bands at the resonant energies, the measurement of angular distributions that are not consistent with dipole scattering, and by comparison of reflectivity measurements from both the clean and adsorbate covered surfaces. Resonant vibrational excitation is strong in the methyl-based molecules studied (Me3Al and Me3In), but even higher resonant cross-sections are evident in the larger alkyl-based metalorganics (Et3Ga and Np3Ga). The resonant behaviour is generally independent of substrate, although electronic excitation of the InSb(100) surface appears to prevent higher energy resonances (>10 eV) being observed for the methyl-based molecules. The incident HREELS electron beam causes dissociation of Me3Al and Me3In adsorbed on either surface, with a threshold energy of ? 10 eV;ace, with a threshold energy of ? 10 eV; an energy close to the ionisation potential of the molecules. An electron impact ionisation dissociation mechanism is inferred, with chemisorbed Me groups decomposing to surface CH2 species. Electron induced dissociation rarely occurs for molecules chemisorbed on metal surfaces due to the efficient quenching of the excited states on these substrates. No dissociation is observed for Et3Ga or NP3Ga, even above their ionisation potential. It is suggested that the time taken to form stable species in these larger compounds following ionisation is much longer than the quenching time and decomposition cannot occur. (author)

311

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

312

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

313

IR spectroscopy applied subsequent to a proton transfer reaction in the excited state of isolated 3-hydroxyflavone and 2-(2-naphthyl)-3-hydroxychromone.  

Science.gov (United States)

IR/R2PI-spectroscopy has been applied to the electronic ground and electronically excited states of 3-hydroxyflavone (3-HF) and 2-(2-naphthyl)-3-hydroxychromone (2-NHC) in a supersonic jet yielding direct structural information on the educt and product of a proton transfer reaction. We show that IR spectra of the electronically excited states can be recorded subsequent to a photoinduced chemical reaction, in this case a proton transfer. In combination with DFT and TDDFT calculations structural assignments are performed. PMID:19209360

Bartl, K; Funk, A; Schwing, K; Fricke, H; Kock, G; Martin, H-D; Gerhards, M

2009-02-28

314

Bimolecular processes on silica gel surfaces: energetic factors in determining electron-transfer rates.  

Science.gov (United States)

Triplet state and radical cation formation is observed following laser excitation of anthracene, phenanthrene and naphthalene (and their derivatives) adsorbed on silica gel. Energy- and electron-transfer reactions of these compounds with co-adsorbed azulene have been studied using a time-resolved diffuse reflectance laser flash photolysis technique. Triplet energy transfer from the arene derivative to azulene and electron transfer from azulene to the arene radical cation have been investigated in order to distinguish between diffusional and energetic control in these systems. Energy and electron transfer can be studied independently due to differing absorption properties and energy dependencies of production of the triplet states and radical cations. Transient decay kinetics for both electron and energy transfer have been modelled using two different rate constant distributions: a log Gaussian and a symmetrical Levy stable distribution. The latter model has also been demonstrated to be applicable to the decay of radical cations in the absence of an electron donor, which cannot be adequately described by the Gaussian model. Energy-transfer rates between the arene derivatives and azulene have been found to be close to the diffusion-controlled limit; however, in most cases, the rate of electron transfer is considerably lower. A correlation between the bimolecular rate constant and free energy of electron transfer has been found, indicating a Marcus inverted region. Compounds with bulky substituents show a further reduction in the rate of electron transfer, suggesting that an additional steric factor is involved in this process. PMID:14743281

Worrall, David R; Kirkpatrick, Iain; Williams, Sian L

2004-01-01

315

Linear free-enthalpy relation for radical yield in fluorescence quenching by electron transfer  

OpenAIRE

The rate constant (kq) and net electron-transfer yield (?r) in the quenching of an excited oxonine singlet by 24 aromatic amines and methoxy compounds were determined in methanol from stationary fluorescence measurements and flash spectroscopy. The systems investigated correspond to a variation of ?Get°, the standard free reaction enthalpy of the electron transfer from the quencher to excited singlet oxonine, between -0.12 and -1.56 eV. Whereas the kq values observed are all close to the d...

Iwa, Peter; Steiner, Ulrich; Vogelmann, Ekehardt; Kramer, Horst E. A.

1982-01-01

316

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

317

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

318

Estimates of electronic coupling for excess electron transfer in DNA  

Science.gov (United States)

Electronic coupling Vda is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of Vda for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an efficient strategy is established for calculating the ET matrix elements between base pairs in a ? stack. Two approaches are considered. First, we employ the diabatic-state (DS) method in which donor and acceptor are represented with radical anions of the canonical base pairs adenine-thymine (AT) and guanine-cytosine (GC). In this approach, similar values of Vda are obtained with the standard 6-31G* and extended 6-31++G** basis sets. Second, the electronic couplings are derived from lowest unoccupied molecular orbitals (LUMOs) of neutral systems by using the generalized Mulliken-Hush or fragment charge methods. Because the radical-anion states of AT and GC are well reproduced by LUMOs of the neutral base pairs calculated without diffuse functions, the estimated values of Vda are in good agreement with the couplings obtained for radical-anion states using the DS method. However, when the calculation of a neutral stack is carried out with diffuse functions, LUMOs of the system exhibit the dipole-bound character and cannot be used for estimating electronic couplings. Our calculations suggest that the ET matrix elements Vda for models containing intrastrand thymine and cytosine bases are essentially larger than the couplings in complexes with interstrand pyrimidine bases. The matrix elements for excess electron transfer are found to be considerably smaller than the corresponding values for hole transfer and to be very responsive to structural changes in a DNA stack.

Voityuk, Alexander A.

2005-07-01

319

Dynamics of the excited state intramolecular charge transfer  

International Nuclear Information System (INIS)

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

320

Excited electronic state of a cluster formed from self-trapped electrons  

Energy Technology Data Exchange (ETDEWEB)

The possibility of spontaneous clustering of self-trapped electrons in an excited electronic state is discussed. The pair interaction potential corresponds to the excited terms {sup 1}{Sigma}{sub g}(1s2s) in the single spin state and {sup 3}{Sigma}{sub u}(1s2s) in the triplet spin state. The energy interval corresponding to a pair of excited quasi-particles is calculated. Quantitative calculations are presented for electrons solvated in ammonia. 9 refs., 4 figs.

Mukhomorov, V.K. [Agrophysical Institute, St. Petersburg (Russian Federation)

1995-12-01

321

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

322

Dynamics of two-electron excitations in helium  

International Nuclear Information System (INIS)

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 (?), 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 ?n, and photoelectron angular distributions ?n were measured for all possible final ionic states He+(n) in the region of the double excitations N(K,T)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

323

Polarized Fluorescence from Nitrogen Molecules Excited by Polarized Electron Impact  

Science.gov (United States)

We have measured the optical excitation function and relative Stokes parameters for 388±5 nm fluorescence from spin-polarized electron impact excitation of molecular N2. Specifically, the circular polarization fraction normalized to the incident electron spin, P3/Pe, was found to be +1(5)% at an electron energy of 30eV. This result, even though it contains contributions from 6 different triplet spectral lines, is consistent with the data of the Münster group [1] who measured the N2 337 nm C3?u - B3?g (?'=0, ?=0) transition and found P3 DPG (VI) 29, 462 (1994). [2] A.S. Green et al., Phys. Rev. Lett. 92, 093201 (2004).

Maseberg, J. W.; Furst, J. E.; Gay, T. J.

2005-05-01

324

Quantum mechanical study of the coupling of plasmon excitations to atomic-scale electron transport  

International Nuclear Information System (INIS)

The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics.

325

Quantum mechanical study of the coupling of plasmon excitations to atomic-scale electron transport.  

Science.gov (United States)

The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics. PMID:21341863

Song, Peng; Nordlander, Peter; Gao, Shiwu

2011-02-21

326

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

327

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.)

328

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

CERN Document Server

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

Najjari, B

2012-01-01

329

Vibrational excitation of CO molecules by infrared free electron laser  

International Nuclear Information System (INIS)

This paper describes the vibrational excitation of CO molecules by FEL-SUT (Free Electron Laser at Tokyo University of Science). FEL is tuned to 4.67 ?m, corresponding to the X1?+(v''=1)1?+ Rydberg state. We find that ?10% of the population in v''=0 is excited to v''=1. In spite of the existence of the resonant vibrational ladder climbing channels via specific rotational levels, no signal originating from v''=2 is detectable. The predissociation in the B1?+(v'=2) state is believed to be responsible for the absence of CO+ signals

330

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

331

Quantum Monte Carlo approach to electronically excited molecules  

International Nuclear Information System (INIS)

Quantum Monte Carlo (QMC) is used to compute the electronic energies of H2(B 1?+/sub u/) and H2(E 1?+/sub g/). The E state calculation represents the first application of QMC to a molecular excited state with the same symmetry as a lower state. In this QMC approach a trial function specifies the nodes of the QMC distribution. The role of these nodes in excited state calculations is discussed. QMC energies that contain over 95% of the correlation energy are computed using MCSCF wave functions as trial functions

332

Electron excitations and sum rules for multipole transitions  

International Nuclear Information System (INIS)

Form factors and charge densities of the hydrodynamical model of the nucleus used in electron excitation are obtained from the multipole sum rules by assuming the partial exhaustion of the sum rules by one single state. Corrections are indicated. Simple relations are obtained for the transition radii Rsub(tr)(E1), resulting in a model-independent ratio of Rsub(tr)(E2)/Rsub(tr)(E0)=0.84. The static quadrupole moments of the giant resonances are shown to increase with multipolarity and to decrease with excitation energy

333

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 25Z2 to 250Z2 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)

334

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

335

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

336

Electronic excitation of the lB2 state of furan by electron impact  

Science.gov (United States)

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

da Costa, Romarly F.; Bettega, Márcio H. F.; Varella, Márcio T. do N.; Lima, Marco A. P.

2012-11-01

337

Electronic excitation of the lB2 state of furan by electron impact  

International Nuclear Information System (INIS)

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

338

Constrained dynamics of excitation transfer due to a structured nano system  

International Nuclear Information System (INIS)

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

339

Electron and energy transfer in artificial photosynthesis supermolecules  

Science.gov (United States)

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

Kuciauskas, Darius

1999-12-01

340

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

341

Electron transfer reactions in microporous solids  

Science.gov (United States)

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

Mallouk, T. E.

1993-01-01

342

Excited state proton transfer reactions of acridine studied by nanosecond fluorometry  

International Nuclear Information System (INIS)

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

343

Electron impact ionization and excitation of uracil molecules  

International Nuclear Information System (INIS)

The cross-sections of the formation of positive and negative ions of uracil, a nitrogenous base of nucleic acids, are obtained experimentally. The values for negative ions were shown to reach their maximum of 5.0x10-18 cm2 at an energy of bombarding electrons of 1.1 eV. The magnitudes and the energy dependence were determined for the cross-section of formation of positive uracil ions in the electron energy interval from the formation threshold to 200 eV. The ionization cross-section peak of (1.0±0:1)x10-15 cm2 was found at an energy of 95 eV. The luminescence spectrum for isolated uracil molecules consisting of about 20 spectral bands and lines emitted under the action of slow electrons was obtained in the wavelength range 200-500 nm. The uracil radiation spectrum was shown to be driven by the processes of molecular dissociative excitation, dissociative excitation with ionization, and excitation of electron levels in the initial molecule and the molecular ion. The biophysical consequences of the results obtained are discussed.

344

Nuclear excitation by electronic transition (NEET) in {sup 189}Os.  

Energy Technology Data Exchange (ETDEWEB)

Monochromatic x rays have been used to explore the phenomenon of nuclear excitation by electronic transition (NEET) in the {sup 189}Os atomic/nuclear system. A new theoretical approach to calculating this process has also been developed and predicts a value for the 'NEET probability,' PNEET, of 1.3 x 10{sup -10}. PNEET is the probability that a given atomic excitation (in this case a K vacancy), will result in the excitation of a specific nuclear state (in this case the 69.5-keV level in {sup 189}Os). This value is much lower than most of the calculated values given in the literature for this system. Our measurement gives the result PNEET <9 x 10{sup -10}, an upper limit which is several orders of magnitude lower than the values found in previous measurements, but which is consistent with the new calculation.

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

2000-05-01

345

Electron transfer in branched expanded pyridinium molecules.  

Czech Academy of Sciences Publication Activity Database

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

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

346

Promoting Interspecies Electron Transfer with Biochar  

OpenAIRE

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...

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

2014-01-01

347

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

348

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

Science.gov (United States)

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

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

1993-01-01

349

Multiplication Processes of Electronic Excitations in PbCl2 Crystals Excited by Vacuum Ultraviolet Radiation  

Science.gov (United States)

The excitation spectra for two intrinsic luminescence bands at 3.76 eV (UV) and 2.62 eV (BG) in PbCl2 have been measured using synchrotron radiation in the energy range up to 25 eV at 10 K. Since the UV and BG bands are connected to excitonic luminescence and electron-hole (e-h) recombination luminescence, respectively, an analysis of the difference in their excitation spectra allows us to separate excitonic and e-h mechanisms in the multiplication of electronic excitations. It is found that the intensity of the UV emission is sharply increased at 9.8 eV, which is higher than twice the band gap energy. Secondary excitons are formed by inelastic scattering of hot photoelectrons in the region above 9.8 eV. On the other hand, the BG emission is gradually enhanced in the range of 9-12.5 eV, and the intensity doubles at around 12.5 eV. This result indicates that the creation of two e-h pairs per photon predominantly causes in the region above 12.5 eV. The e-h multiplication originates not only in inelastic scattering of hot photoelectrons in the 12.5-25 eV range but also in interband Auger recombination of holes in the Cl- core levels with valence electrons in the 18-25 eV range.

Kitaura, Mamoru; Itoh, Minoru; Nakagawa, Hideyuki; Fujita, Masami

2003-03-01

350

Transfer coating by electron initiated polymerization  

International Nuclear Information System (INIS)

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

351

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.

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

2014-06-01

352

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-04-21

353

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

DEFF Research Database (Denmark)

We present a model for desorption induced by (multiple) electronic transitions [DIET (DIMET)] based on potential energy surfaces calculated with the delta self-consistent field extension of density-functional theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on various transition-metal surfaces and show that classical nuclear dynamics does not suffice for propagation in the excited state. We present a simple Hamiltonian describing the system with parameters obtained from the excited-state potential energy surface and show that this model can describe desorption dynamics in both the DIET and DIMET regimes and reproduce the power-law behavior observed experimentally. We observe that the internal stretch degree of freedom in the molecules is crucial for the energy transfer between the hot electrons and the molecule when the coupling to the surface is strong.

Olsen, Thomas; Gavnholt, Jeppe

2009-01-01

354

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

CERN Document Server

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

Olsen, Thomas; Schiøtz, Jakob

2008-01-01

355

Resonant structure in electron impact excitation of CO near threshold  

International Nuclear Information System (INIS)

Electron impact excitation functions of numerous states in CO have been measured at 45degree scattering angle with resolutions of 16--23 meV FWHM. The decay peak of the 10.04 eV resonance can be seen in the results for the a 3Pi, a' 3?+, and A 1Pi vibrational levels. There was no evidence of resonant excitation of the a' 3?+ state near 8 eV as suggested by Newton and Thomas. Excitation functions of the b 3?+, B 1?+, C 1?+, c 3Pi, and E 1Pi states, and a previously unobserved state at 11.26 eV show numerous sharp resonances in the first few eV above threshold. Energy loss spectra in the 8--14 eV loss region show peaks corresponding to known states as well as to unidentified states. No sign of the metastable state at about 9.5 eV seen by Wells, Borst, and Zipf could be detected in direct excitation, but an indirect excitation process involving the A 1Pi state is consistent with the data

356

TD-DFT Assessment of the Excited State Intramolecular Proton Transfer in Hydroxyphenylbenzimidazole (HBI) Dyes.  

Science.gov (United States)

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

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

2015-02-12

357

Zeeman deceleration of electron-impact-excited metastable helium atoms  

Science.gov (United States)

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

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

2015-03-01

358

Rotational excitation of molecular nitrogen by electron impact  

International Nuclear Information System (INIS)

Collision cross sections for rotational excitation processes of a molecular nitrogen by electron impact are calculated at the energy range of 0.01 to 3 eV. It is shown that integrated cross sections for rotationally inelastic scattering are noticeably enhanced by the short range interaction between the scattered electron and the target nitrogen molecule at the impact energy as low as 0.08 eV. At the energy region of the well-known ?g resonance, it is confirmed that the cross section for the rotational excitation of j = 0 to j' = 4 becomes larger than that for j = 0 to j' = 2 by more than the ratio of statistical weight (2j' + 1) of the final rotational state j'. An explanation to this fact is given by analysing the expression of the integrated cross section. (author)

359

Radiative lifetimes of excited electronic states in molecular ions  

International Nuclear Information System (INIS)

Radiative lifetimes of excited electronic states of several molecular ions have been measured using a technique which permits the mass selective storage of ions for periods of many ms. This technique is used to record radiative lifetimes ranging from 60 ns to approx. 10 ?s. The use of a radiofrequency quadrupole ion trap to confne the ions reduces the problem of space charge induced spatial dissipation of ions and permits the selective excitation of electronic states. Using this technique, careful measurements of the B2?+/sub u/ state of N+2 and the A2Pi states of N+2 and CO+ have been made. The results obtained are in good agreement with previous studies. The analysis of the radiative lifetime for the CH+ and CD+ A1Pi(?' = 0) state results in a value significantly larger than earlier determinations. The new results are used to make revised estimates of interstellar abundances of CH+

360

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

Science.gov (United States)

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

Lukas, Wolf-Dieter; Fulde, Peter

1984-07-01

361

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

362

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

363

Electronic Excitations from a Perturbative LDA+GdW Approach  

OpenAIRE

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

Rohlfing, Michael

2010-01-01

364

Decay Paths of Interfering Two-Electron Excitations in Helium  

International Nuclear Information System (INIS)

Partial photoionization cross sections and photoelectron angular distributions of He in the region of interfering Rydberg series below the n=5 threshold are measured and compared with theoretical results based on the hyperspherical close-coupling method. At a bandpass of 12 meV for the photon energy, this level of differentiation offers the most critical assessment of the dynamics of the two-electron excitations to date. A good understanding is achieved

365

Alignment effects in charge transfer and excitation for H+ and He2+ collisions with H2+  

International Nuclear Information System (INIS)

The excitation and charge transfer cross sections are calculated for the collision of H+ and He2+ with H2+ molecular ions. This is the simplest example of collisions between ions and molecules or molecular ions since it involves only one electron. The results in this paper emphasize effects due to the alignment of the axis of the H2+ molecular ion relative to the atomic ion velocity vector and due to the internuclear separation. The calculations show that the cross section versus the angle between the molecular ion axis and the ion velocity vector strongly depends on the ion velocity. Our results for He2+ collisions do not agree with the experiments and calculations of Reiser, Cocke, and Braeuning [Phys. Rev. A 67, 062718 (2003)] but are in qualitative agreement with the calculations of Cheng and Esry

366

Excitation energy transfer in ion pairs of polymethine cyanine dyes: efficiency and dynamics.  

Science.gov (United States)

The present work deals with singlet excitation energy transfer (EET) occurring in contact ion pairs (CIPs) of several anionic oxonol analogues (acting as EE donors) and cationic cyanines (acting as acceptors) characterized by off resonance individual transitions. Combining conductometric and spectroscopic measurements with decreasing solvent polarity, we were able to observe a progressive ion pairing leading first to solvent-separated ion pairs (SSIPs) and then to CIPs. Analysis of the absorption spectra of three selected salts (A2,C1, A2,C2, and A1,C4) in chloroform-toluene mixtures showed that the transformation of SSIP into CIP involves the appearance of a certain exciton coupling, the extent of which decreases regularly with increasing gap between the local excitation energies. Fluorescence excitation spectra showed that EET occurs in CIP, and EET efficiencies were evaluated with a procedure expressly devised for weakly emitting donors. These were between 0.2 and 0.65 for the examined ion pairs involving anions A1 and A2. The spectroscopic study was complemented by a theoretical investigation aimed at establishing the dynamic regime of the observed EET. From classical MD simulations and local full geometry optimizations, A2,C1 and A2,C2 were found to form rather stable sandwich-type CIP structures with interchromophore distances (R) of about 0.45-0.50 nm. The donor-acceptor electronic coupling was calculated in terms of Coulombic interactions between atomic transition charges. For CIP, the electronic coupling was decidedly beyond the limit of the weak coupling required for an incoherent Förster-type mechanism. Thus, we tried to arrange the EET dynamics within the theory developed by Kimura, Kakitani, and Yamato (J. Phys. Chem. B 2000, 104, 9276) for the intermediate coupling case, which provides analytical expressions of time-dependent occupation probability, EET rate, and coherency in terms of two basic quantities: the electronic coupling and a correlation time related to the Franck-Condon factor. The latter was shown to be primarily modulated by Förster's spectral overlap integral (related in turn to the excitation energy gap). Calculations were carried out for the three sample systems using three values of the electronic coupling roughly corresponding to CIP, 1.0, and 2.0 nm interchromophore distances. At the CIP distance, EET in both A2,C1 and A2,C2 was predicted to occur with a partial exciton mechanism, very short transfer times (about 10 fs), and high degree of coherence. In A1,C4 (having the largest energy gap), EET was found to occur with a hot-transfer mechanism. More or less hot-transfer dynamics appeared to be retained by all three systems at R = 1.0 nm. Fully incoherent EET appeared to become operative only at distances larger than 2.0 nm. PMID:16774193

Ponterini, G; Fiorini, M; Vanossi, D; Tatikolov, A S; Momicchioli, F

2006-06-22

367

Theory of nuclear excitation by electron capture for heavy ions  

Energy Technology Data Exchange (ETDEWEB)

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

Gagyi-Palffy, A.

2006-07-01

368

Ultrafast Structural Dynamics of Tertiary Amines upon Electronic Excitation  

Science.gov (United States)

The structural response of several tertiary amines to electronic excitation has been investigated using Rydberg Fingerprint Spectroscopy. The 3p Rydberg states are reached by excitation with a 5.93 eV photon while 3s states are populated by electronic relaxation from 3p state. We observe binding energy shifts on ultrafast time scales in all peaks that reflect the structural change of the molecular ion cores. The shifts are in the range of 15 meV to 30 meV, within time scales of less than 500 fs, depending on the specific molecular systems and the nature of the electronic state. In cases where the p states are spectrally separate, the trends of the energy shifts are different for the p_z and p_x_y Rydberg states whereas the p_z and s states are similar. This suggests that the response of the Rydberg states to structural displacements depends on the symmetry. Very fast binding energy shifts, observed on sub-picosecond time scales, are attributed to the structural adjustment from a pyramidal to a planar structure upon Rydberg excitation. The quantitative values of the binding energy shifts can also be affected by laser chirp, which we model using simulations.

Cheng, Xinxin; Minitti, Michael P.; Deb, Sanghamitra; Zhang, Yao; Budarz, James; Weber, Peter M.

2011-06-01

369

Electron plasma dynamics during autoresonant excitation of the diocotron mode  

Science.gov (United States)

Chirped-frequency autoresonant excitation of the diocotron mode is used to move electron plasmas confined in a Penning-Malmberg trap across the magnetic field for advanced plasma and antimatter applications. Plasmas of 108 electrons, with radii small compared to that of the confining electrodes, can be moved from the magnetic axis to ?90% of the electrode radius with near unit efficiency and reliable angular positioning. Translations of ?70% of the wall radius are possible for a wider range of plasma parameters. Details of this process, including phase and displacement oscillations in the plasma response and plasma expansion, are discussed, as well as possible extensions of the technique.

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

2015-02-01

370

Nanosecond length electron pulses from a laser-excited photocathode  

International Nuclear Information System (INIS)

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

371

Vibrational and Electronic Energy Transfer and Dissociation of Diatomic Molecules by Electron Collisions  

Science.gov (United States)

At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also, the average electron temperature is expected to be between 10,000 and 20,000 K. Thus only data for low energy electrons are relevant to the model.

Huo, Winifred M.; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

372

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

373

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

374

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

375

Many-body approach to electronic excitations concepts and applications  

CERN Document Server

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

Bechstedt, Friedhelm

2015-01-01

376

Red-edge excitation effect in intramolecular proton transfer in flavonols  

Science.gov (United States)

To investigate of 4'-diethylamino (FET) and 4'-(15-azacrown- 5) (FCR) derivatives of 3-hydroxyflavone in binary solvents and erythrocyte ghosts, we used the red-edge excitation spectroscopy. The results obtained prove the existence of spectral heterogeneity of flavonols in the studied systems. The effect manifests itself in the dependence of the efficiency of excited-state intramolecular proton transfer on the excitation frequency.

Kruchenok, Julia V.; Nemkovich, Nicolai A.; Sobchuk, A. N.; Petrov, E. P.; Rubinov, Anatoly N.; Pivovarenko, V. G.; Baumann, Wolfram

2002-05-01

377

Influence of donor-donor transport on excitation energy transfer  

International Nuclear Information System (INIS)

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

378

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

379

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 rus 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

380

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

Science.gov (United States)

Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm(-1)) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ?41,000 cm(-1) was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1?S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ?E region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ?E region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency. PMID:25527934

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

2014-12-21

381

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-12-01

382

Electron-transfer acceleration investigated by time resolved infrared spectroscopy.  

Science.gov (United States)

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

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

2015-03-17

383

Determination of differential cross sections for electron-impact excitation of electronic states of molecular oxygen  

Energy Technology Data Exchange (ETDEWEB)

The development and initial results of a method for the determination of differential cross sections for electron scattering by molecular oxygen are described. The method has been incorporated into an existing package of computer programs which, given spectroscopic factors, dissociation energies and an energy-loss spectrum for electron-impact excitation, determine the differential cross sections for each electronic state relative to that of the elastic peak. Enhancements of the original code were made to deal with particular aspects of electron scattering from O{sub 2}, such as the overlap of vibrational levels of the ground state with transitions to excited states, and transitions to levels close to and above the dissocation energy in the Herzberg and Schumann-Runge continua. The utility of the code is specifically demonstrated for the ''6-eV states'' of O{sub 2}, where we report absolute differential cross sections for their excitation by 15-eV electrons. In addition an integral cross section, derived from the differential cross section measurements, is also reported for this excitation process and compared against available theoretical results. The present differential and integral cross sections for excitation of the ''6-eV states'' of O{sub 2} are the first to be reported in the literature for electron-impact energies below 20 eV. (c) 2000 The American Physical Society.

Campbell, L. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Green, M. A. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Brunger, M. J. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Teubner, P. J. O. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Cartwright, D. C. [Theoretical Divisions, B285, Los Alamos National Laboratories, Los Alamos, New Mexico 87545 (United States)

2000-02-01

384

Absolute cross sections for electronic excitation of furan by electron impact  

Science.gov (United States)

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

Regeta, Khrystyna; Allan, Michael

2015-01-01

385

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

International Nuclear Information System (INIS)

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

386

Electronic excitations of potassium intercalated manganese phthalocyanine investigated by electron energy-loss spectroscopy  

OpenAIRE

The electronic excitations of manganese phthalocyanine (MnPc) films were studied as a function of potassium doping using electron energy-loss spectroscopy in transmission. Our data reveal doping induced changes in the excitation spectrum, and they provide evidence for the existence of three doped phases: K$_1$MnPc, K$_2$MnPc, and K$_4$MnPc. Furthermore, the addition of electrons first leads to a filling of orbitals with strong Mn 3d character, a situation which also affects ...

Mahns, Benjamin; Roth, Friedrich; Grobosch, Mandy; Zahn, Dietrich R. T.; Knupfer, Martin

2011-01-01

387

Intermediate state representation approach to physical properties of electronically excited molecules.  

Science.gov (United States)

Propagator methods provide a direct approach to energies and transition moments for (generalized) electronic excitations from the ground state, but they do not usually allow one to determine excited state wave functions and properties. Using a specific intermediate state representation (ISR) concept, we here show how this restriction can be overcome in the case of the algebraic-diagrammatic construction (ADC) propagator approach. In the ISR reformulation of the theory the basic ADC secular matrix is written as a representation of the Hamiltonian (or the shifted Hamiltonian) in terms of explicitly constructable states, referred to as intermediate (or ADC) states. Similar intermediate state representations can be derived for operators other than the Hamiltonian. Together with the ADC eigenvectors, the intermediate states give rise to an explicit formulation of the excited wave functions and allow one to calculate physical properties of excited states as well as transition moments for transitions between different excited states. As for the ground-state excitation energies and transition moments, the ADC excited state properties are size consistent so that the theory is suitable for applications to large systems. The established hierarchy of higher-order [ADC(n)] approximations, corresponding to systematic truncations of the IS configuration space and the perturbation-theoretical expansions of the ISR matrix elements, can readily be extended to the excited state properties. Explicit ISR matrix elements for arbitrary one-particle operators have been derived and coded at the second-order [ADC(2)] level of theory. As a first computational test of the method we have carried out ADC(2) calculations for singlet and triplet excited state dipole moments in H(2)O and HF, where comparison to full CI results can be made. The potential of the ADC(2) method is further demonstrated in an exploratory study of the excitation energies and dipole moments of the low-lying excited states of paranitroaniline. We find that four triplet states, T1-T4, and two singlet states, S1 and S2, lie (vertically) below the prominent charge transfer (CT) excitation, S3. The dipole moment of the S3 state (17.0D) is distinctly larger than that of the corresponding T3 triplet state (11.7D). PMID:15268179

Schirmer, J; Trofimov, A B

2004-06-22

388

Luminescence of Nd3+ ions under excitation of CdSe quantum dots in a glass system: energy transfer.  

Science.gov (United States)

We report rare evidence of energy transfer from CdSe quantum dots (QDs) to Nd3+ ions in a SNAB glass system using absorption electronic transitions of ion as a nonresonant excitation source. However, the luminescence band was observed at 880 nm (4F3/2?4I9/2 transition) under 409 nm excitation only when Nd3+ ions were embedded in the SNAB glass system with CdSe QDs. This happened because the Nd3+ ions absorbed the photons emitted by CdSe QDs with 409 nm excitation. Band overlap of the QD luminescence band and the ion optical absorption bands caused photon absorption and produced valleys in the QD luminescence spectrum. This overlap contributed to reduction in the lifetime 4F3/2 state. PMID:24365840

Serqueira, E O; Dantas, N O

2014-01-01

389

Excited electronic surfaces states of low index faces of copper  

International Nuclear Information System (INIS)

Full text: Excited surface states which are not occupied by electrons contained within a solid, are probed by k-resolved inverse photoemission spectroscopy (KRIPES) and two-photon photoemission (2PPE) and similar time-resolved techniques. By comparing these results to theoretical excited surface-state band structures which reproduce all the experimental details, one can obtain information concerning electron potentials at the surface. These potentials contain information about the geometric arrangement of surface atoms and molecules and the variation of the barrier potential from surface to vacuum. This information is needed in the analysis of many surface phenomena such as scanning-tunneling spectroscopy, ion-surface scattering and very low energy electron scattering and imaging. The copper surfaces have the most experimental data available and thus become the prototype for this type of analysis although semiconductor surfaces are more important for nanostructured device applications. Although the excited surface states and resonances of copper have been theoretically explored, at least in part, details of the features found experimentally have not been reproduced and conclusions about surface potentials and nanostructured surface arrangements have not been possible. In particular the lifetimes of energy bands for given momentum have not been explored. This is equivalent to finding the band structure of inelastic surface potentials and requires knowledge of the variantials and requires knowledge of the variation of the self-energy with momentum. In this work we use our calculations of the momentum dependence of the states and resonances to explore the effects of different bulk and surface electronic potentials, surface atomic reconstructions, and anisotropic inelastic potentials including bulk and surface phonon interactions. It is concluded that all these effects must be incorporated in such an analysis and we offer a surface potential for Cu (001) which is consistent with the large amount of experimental data available for that system

390

Transport of oxygen atoms mediated by electronic excitation  

International Nuclear Information System (INIS)

Diffusion of oxygen from substrate to the film was observed under the influence of large electronic excitation. CuO thin film ?210 nm on float glass was irradiated with 210 MeV I ions. We noticed the transport of oxygen from the substrate to the CuO film through the interface. The amount of oxygen transport from glass to the film was found to be fluence dependent. The loss of oxygen from the films was also observed. The erosion of Cu atoms was also observed beyond a fluence of 9.6x1013 ions/cm2. The measurements were performed by on-line elastic recoil detection using a large area position sensitive detector. Since the electronic energy loss dominates in the present case of 210 MeV I ions, the observed changes at the interface and surface are attributed to inelastic collisions of the incident ions with the atomic electrons in the sample

391

Electron correlations in a partially filled first excited Landau level  

CERN Document Server

The form of electron correlations in a partially filled degenerate Landau level (LL) is related to the behavior of the anharmonic part of the interaction pseudopotential. Unlike in the lowest LL, the pseudopotential in the first excited LL is harmonic at short range. As a result, the incompressible states in this LL have different correlations, occur at different filling factors nu, and cannot be described by a composite fermion model. The series of Laughlin-correlated states of electron pairs is proposed at nu=2+2/(q_2+2) with integer q_2. It includes Moore-Read nu=5/2 state and the nu=7/3 state. Despite coincidence of the values of nu, the latter state has different correlations than Laughlin state of single electrons at nu=1/3 and, in finite systems, occurs at a different LL degeneracy (flux).

Wójs, A; Wojs, Arkadiusz; Quinn, John J.

2002-01-01

392

Singly and doubly excited states in ejected electron spectra of neon at high incident electron energies  

Science.gov (United States)

Ejected electron spectroscopy has been used to study singly and doubly excited states of neon at constant incident electron energies between 505 and 2018 eV and ejection angles from 10° to 130° with high resolution in ejected energy range from 12 to 46 eV. The full ejected electron energy range has been studied at two extreme incidence energies and three ejected angles, namely 40°, 90° and 130°. The low energy region (12 to 21.5 eV) has been investigated at 505 eV over the full angular range and at 90° at six incident energies from 505 to 2018 eV. The features in the ejected electron spectra have been attributed to the autoionisation of Ne+ (2s2p6nl) excited states and Ne (2s2p5nln'l' and 2s22p4nln'l') double excited autionising states. Lower energy ejected electrons arise from simultaneous excitation of s and p electrons above the second ionisation potential (62.53 eV) while higher energy ejected electrons are coming from singly and doubly excited states. The high resolution and high sensitivity allowed us to see separated singlet from triplet states at high incident energies. Comparison with previous works gives a good agreement in energy positions of measured features. At the highest ejected electron energies only the features coming from double excitation are present, but with very low intensities in the spectra due to the small cross sections and high background. New resonances are found whose classification needs new experimental and theoretical investigations. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Stefan Matejcik, John Tanis and Kurt H. Becker.

Jureta, Jozo J.; Marinkovi?, Bratislav P.; Milosavljevi?, Aleksandar R.; Avaldi, Lorenzo

2015-03-01

393

Cross sections for electron capture and excitation in collisions of Liq+ (q=1, 2, 3) with atomic hydrogen  

International Nuclear Information System (INIS)

The two-center atomic orbital close-coupling method is employed to study electron capture and excitation reactions in collisions of Liq+ (q?=?1-3) ions with ground state atomic hydrogen in the ion energy range from 0.1?keV/u to 300?keV/u, where u is the atomic mass unit. The interaction of the active electron with the projectile ions (Li+, Li2+) is represented by a model potential. Total and state-selective cross sections for charge transfer and excitation processes are calculated and compared with data from other sources when available

394

Cross sections for electron capture and excitation in collisions of Liq+ (q=1, 2, 3) with atomic hydrogen  

Science.gov (United States)

The two-center atomic orbital close-coupling method is employed to study electron capture and excitation reactions in collisions of Liq+ (q = 1-3) ions with ground state atomic hydrogen in the ion energy range from 0.1 keV/u to 300 keV/u, where u is the atomic mass unit. The interaction of the active electron with the projectile ions (Li+, Li2+) is represented by a model potential. Total and state-selective cross sections for charge transfer and excitation processes are calculated and compared with data from other sources when available.

Liu, L.; Li, X. Y.; Wang, J. G.; Janev, R. K.

2014-06-01

395

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

CERN Document Server

Fusion data for $^{48}$Ca+$^{90,96}$Zr are analyzed by coupled-channels calculations that are based on the M3Y+repulsion, double-folding potential. By applying a previously determined nuclear density of $^{48}$Ca, the neutron densities of the zirconium isotopes are adjusted to optimize the fit to the fusion data, whereas the proton densities are determined by electron scattering experiments. It is shown that the fusion data can be explained fairly well by including couplings to one- and two-phonon excitations of the reacting nuclei and to one- and two-nucleon transfer reactions but there is also some sensitivity to multiphonon excitations. The neutron skin thicknesses extracted for the two zirconium isotopes are consistent with anti-proton measurements. The densities of the zirconium isotopes are used together with the previously determined nuclear density of $^{40}$Ca to calculate the M3Y+repulsion potentials and predict the fusion cross sections of $^{40}$Ca+$^{90,96}$Zr. The predicted cross sections for $^...

Esbensen, H

2014-01-01

396

Observation of nonradiative energy transfer in the excitation of Nd3+ in GaP  

OpenAIRE

We have carried out luminescence-excitation measurements on a Nd3+ complex in GaP in the range 1.5–2.2 eV to determine the mechanisms by which the internal Nd3+ luminescence is generated. At low temperatures we observe transitions into the 4S3/2 and 4F7/2 excited states of Nd3+ and two broad excitation bands whose integrated intensities are orders of magnitude greater than that of the Nd3+ excited states. These broadbands demonstrate for the first time that nonradiative energy transfer from...

Donegan, John Francis

1990-01-01

397

Electron-hydrogen excitation to the n=3 and n=4 levels in the Glauber approximation  

CERN Document Server

We have calculated the differential and integrated cross sections for excitation of atomic hydrogen to its n=3 and n=4 levels by electron impact using the Glauber approximation. Results are compared with measurements at 20, 30, 40, and 60 eV and also shown for 120 and 480 eV. At momentum transfers not too large at all energies considered, the calculated n=3 differential cross sections are qualitatively similar to but a factor of somewhat less than 3 larger than the calculated n=4 cross sections. The calculated integrated cross sections attain broad maxima near 41 eV.

Franco, V

2005-01-01

398

Nuclear Excited States in CALCIUM-48: AN Experimental Investigation of Nuclear Structure by Inelastic Electron Scattering.  

Science.gov (United States)

Electron scattering data in the momentum transfer region of 0.6 48)Ca is presented. Charge and current transition densities have been extracted for low lying 2('+), 4('+), 3('-) and 5('-) levels. Evidence for substantial quenching of the transverse current in both electric and magnetic single particle hole transitions is presented and discussed. Form factors for magnetic single particle hole 3('+) and 8(' -) states are extracted and reveal a 70% quenching of the transverse form factor. Analysis of the 5('-) level at 5.73 MeV excitation indicates the magnetization current is the source of the reduction. Form factors for a number of other levels are briefly presented and discussed.

Wise, John Edward, III

399

Electron capture in ground and excited states in proton-alkali-metal-atom collisions  

International Nuclear Information System (INIS)

The wave formulation of the impulse approximation has been applied to the case of electron capture into the ground, 2s and 2p excited states of hydrogen in collisions between protons and alkali-metal atoms sodium, potassium, rubidium and caesium. The transition matrix elements have been numerically calculated and used to determine the differential and integral cross sections for charge transfer for incident energy varying between 50 and 500 keV. Wherever possible our results have been compared with other available results. (author)

400

Dynamics of geminate recombination in excited state proton transfer reactions  

International Nuclear Information System (INIS)

Ion pairs are produced when aqueous solutions of certain hydroxy aromatic compounds are irradiated by light. The excited hydrated molecules dissociate in their first excited singlet state (illustrated). As a generation source for the ion pairs the authors used the 8-hydroxy 1,3,6 trisulfonate pyrene molecule (HPTS) which has a pK value of 0.5(4) - a 7 unit change from its ground state value. The concept of quasi equilibrium between dissociation and geminate recombination leads to a new description of the excited-states kinetic of molecules like HPTS. A model is presented which explains the very high yield of proton separation in the excited states, in spite of the geminate recombination, in terms of repetitive cycles of dissociation and association. The model accurately describes the nonexponential nature of the HPTS fluorescence decay and predicts that in many ionic dissociation reactions the apparent dissociation rates are considerably smaller than the molecular ones. The nonexponential decay is not unique to HPTS molecules but is observed in other HPTS-like molecules

401

Electron hole pair mediated vibrational excitation in CO scattering from Au(111): Incidence energy and surface temperature dependence  

Energy Technology Data Exchange (ETDEWEB)

We investigated the translational incidence energy (E{sub i}) and surface temperature (T{sub s}) dependence of CO vibrational excitation upon scattering from a clean Au(111) surface. We report absolute v = 0 ? 1 excitation probabilities for E{sub i} between 0.16 and 0.84 eV and T{sub s} between 473 and 973 K. This is now only the second collision system where such comprehensive measurements are available – the first is NO on Au(111). For CO on Au(111), vibrational excitation occurs via direct inelastic scattering through electron hole pair mediated energy transfer – it is enhanced by incidence translation and the electronically non-adiabatic coupling is about 5 times weaker than in NO scattering from Au(111). Vibrational excitation via the trapping desorption channel dominates at E{sub i} = 0.16 eV and quickly disappears at higher E{sub i}.

Shirhatti, Pranav R.; Werdecker, Jörn; Golibrzuch, Kai; Wodtke, Alec M.; Bartels, Christof, E-mail: cbartel@gwdg.de [Institute for Physical Chemistry, Georg August University of Göttingen, 37077 Göttingen (Germany); Max Planck Institute for Biophysical Chemistry, 37077 Göttingen (Germany)

2014-09-28

402

Electron hole pair mediated vibrational excitation in CO scattering from Au(111): Incidence energy and surface temperature dependence  

International Nuclear Information System (INIS)

We investigated the translational incidence energy (Ei) and surface temperature (Ts) dependence of CO vibrational excitation upon scattering from a clean Au(111) surface. We report absolute v = 0 ? 1 excitation probabilities for Ei between 0.16 and 0.84 eV and Ts between 473 and 973 K. This is now only the second collision system where such comprehensive measurements are available – the first is NO on Au(111). For CO on Au(111), vibrational excitation occurs via direct inelastic scattering through electron hole pair mediated energy transfer – it is enhanced by incidence translation and the electronically non-adiabatic coupling is about 5 times weaker than in NO scattering from Au(111). Vibrational excitation via the trapping desorption channel dominates at Ei = 0.16 eV and quickly disappears at higher Ei

403

Electronically driven adsorbate excitation mechanism in femtosecond-pulse laser desorption  

DEFF Research Database (Denmark)

Femtosecond-pulse laser desorption is a process in which desorption is driven by a subpicosecond temperature pulse of order 5000 K in the substrate-adsorbate electron system, whose energy is transferred into the adsorbate center-of-mass degrees of freedom by a direct coupling mechanism. We present a systematic theoretical treatment of this coupling process in the language of an electronic friction, which generates Langevin noise in the adsorbate center-of-mass degrees of freedom, while the electronic degrees of freedom are at a high temperature. Starting from an influence-functional path-integral description, a simple formula for the electronic friction is defined which is valid at all electronic temperatures. At low temperatures the formalism makes contact with the electronic friction appearing in the theory of adsorbate vibrational damping, whereas at high temperatures comparable with the adsorbate electronic excitation energies the friction becomes strongly temperature dependent due to dominance by virtualexcitations between different adsorbate potential energy surfaces. The former regime is related to the electronic friction model for the desorption process, and the latter to the desorption induced by multiple electronic transistions model for the process; the present formulation comprises both regimes. Desorption is calculated both by a simple quasianalytic Kramers rate approach, and by numerical solution to the Langevin equation. The magnitude of the desorbed fraction and the time scale for desorption are compared to experimental results.

Brandbyge, Mads; Hedegård, Per

1995-01-01

404

Lead-poisoned zinc fingers: quantum mechanical exploration of structure, coordination, and electronic excitations.  

Science.gov (United States)

Density functional theory (DFT) structure calculations and time-dependent DFT electronic excitation calculations on simple mononuclear lead structures confirm recent reports on the stabilization of tricoordinated structural domains in poisoned proteins. However, the possibility of the formation of tetracoordinated lead complexes should not be disregarded in studies on mechanisms of lead toxicity because structures with both coordination modes are plausible and might contribute to observed UV spectra. Reported calculations along with detailed molecular orbital analysis confirm that the intense UV signal at around 260 nm is an indicator of the ligand-to-metal charge transfer (LMCT) band where the electrons are transferred from the sulfur 3p orbital to the lead 6p orbital. The composition of the LMCT band reveals significant excitations not only from the Pb-S bonding orbitals but also from sulfur lone-pair orbitals to the Pb-S antibonding orbitals for which the electron density is largely localized on the Pb "6p-like" molecular orbitals. There is a solid indication that the stereochemically active pair orbital of lead is not strongly hybridized and remains largely of the 6s character in tricoordinated lead structures and is minimally hybridized in tetracoordinated lead structures. Computed UV spectra of lead model complexes are compared to experimental UV spectra of model lead peptides. The comparison shows a good agreement with the major spectral trends and changes observed in these experiments. PMID:17676837

Jarzecki, Andrzej A

2007-09-01

405

Collisional excitation transfer between Rb(5P) states in 50–3000 Torr of 4He  

International Nuclear Information System (INIS)

Measurements of the mixing rates and cross sections for collisional excitation transfer between the 5P1/2 and 5P3/2 states of rubidium (Rb) in the presence of 4He buffer gas are presented. Selected pulses from a high repetition rate, mode-locked femtosecond laser are used to excite either Rb state with the fluorescence due to collisional excitation transfer observed by time-correlated single-photon counting. The time dependence of this fluorescence is fitted to the solution of rate equations which include the mixing rate, atomic lifetimes and any quenching processes. The variation in the mixing rate over a large range of buffer gas densities allows the determination of both the binary collisional transfer cross section and a three-body collisional transfer rate. We do not observe any collisional quenching effects at 4He pressures up to 6 atm and discuss in detail other systematic effects considered in the experiment. (paper)

406

Production of excited electrons at TESLA and CLIC based e gamma colliders  

OpenAIRE

We analyze the potential of TESLA and CLIC based electron-photon colliders to search for excited spin-1/2 electrons. The production of excited electrons in the resonance channel through the electron-photon collision and their subsequent decays to leptons and electroweak gauge bosons are investigated. We study in detail the three signal channels of excited electrons and the corresponding backgrounds through the reactions e gamma --> e gamma, e gamma --> eZ and e gamma --> nu ...

Kirca, Z.; Cakir, O.; Aydin, Z. Z.

2002-01-01

407

Effect of Electronic Excitation on Thin Film Growth  

Energy Technology Data Exchange (ETDEWEB)

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

Elsayed-Ali, Hani E. [Old Dominion University

2011-01-31

408

Compilation of electron collision excitation cross sections for neutro argon  

International Nuclear Information System (INIS)

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

409

Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches  

Science.gov (United States)

We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual ?? molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

Ramakrishnan, Raghunathan; Nest, Mathias

2015-01-01

410

Electron transfer pathways in microbial oxygen biocathodes  

Energy Technology Data Exchange (ETDEWEB)

The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O{sub 2} reduction by heme compounds. Here we showed that 1 muM of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O{sub 2} reduction to H{sub 2}O{sub 2} with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

Freguia, Stefano, E-mail: stefano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Tsujimura, Seiya, E-mail: seiya@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Kano, Kenji, E-mail: kkano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan)

2010-01-01

411

Electron transfer pathways in microbial oxygen biocathodes  

International Nuclear Information System (INIS)

The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O2 reduction by heme compounds. Here we showed that 1 ?M of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O2 reduction to H2O2 with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

412

Mediated Electron Transfer at Redox Active Monolayers  

Directory of Open Access Journals (Sweden)

Full Text Available A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. Although the analysis presented has quite general applicability, a specific focus of the paper is concerned with the idea that redox active monolayers can be used to model an ensemble of individual molecular nanoelectrodes. Three possible rate determining steps are considered: heterogeneous electron transfer between immobilized mediator and support electrode ; bimolecular chemical reaction between redox mediator and reactant species in the solution phase, and diffusional mass transport of reactant in solution. A general expression for the steady state reaction flux is derived which is valid for any degree of reversibility of both the heterogeneous electron transfer reaction involving immobilized mediator species and of the bimolecular cross exchange reaction between immobilized mediator and solution phase reactant. The influence of reactant transport in solution is also specifically considered. Simplified analytical expressions for the net reaction flux are derived for experimentally reasonable situations and a kinetic case diagram is constructed outlining the relationships between the various approximate solutions. The theory enables simple diagnostic plots to be constructed which can be used to analyse experimental data.

Michael E.G. Lyons

2001-12-01

413

A stochastic reorganizational bath model for electronic energy transfer  

Energy Technology Data Exchange (ETDEWEB)

Environmentally induced fluctuations of the optical gap play a crucial role in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker (HSR) model, in which the energy-gap fluctuation is approximated as white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to account for excitation energies’ thermal fluctuations. On the other hand, since the original work of HSR, many groups have employed stochastic models to simulate the same transfer dynamics. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equations via the generalized Langevin approach. Based on this connection, we propose a novel scheme to take account of reorganization effects within the framework of stochastic models. The proposed scheme provides a better description of the population dynamics especially in the regime of strong exciton-phonon coupling. Finally, we discuss the effect of the bath reorganization in the absorption and fluorescence spectra of ideal J-aggregates in terms of the Stokes shifts. We find a simple expression that relates the reorganization contribution to the Stokes shifts – the reorganization shift – to the ideal or non-ideal exciton delocalization in a J-aggregate. The reorganization shift can be described by three parameters: the monomer reorganization energy, the relaxation time of the optical gap, and the exciton delocalization length. This simple relationship allows one to understand the physical origin of the Stokes shifts in molecular aggregates.

Fujita, Takatoshi, E-mail: tfujita@fas.harvard.edu, E-mail: aspuru@chemistry.harvard.edu; Huh, Joonsuk; Aspuru-Guzik, Alán, E-mail: tfujita@fas.harvard.edu, E-mail: aspuru@chemistry.harvard.edu [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States)

2014-06-28

414

A stochastic reorganizational bath model for electronic energy transfer  

International Nuclear Information System (INIS)

Environmentally induced fluctuations of the optical gap play a crucial role in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker (HSR) model, in which the energy-gap fluctuation is approximated as white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to account for excitation energies’ thermal fluctuations. On the other hand, since the original work of HSR, many groups have employed stochastic models to simulate the same transfer dynamics. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equations via the generalized Langevin approach. Based on this connection, we propose a novel scheme to take account of reorganization effects within the framework of stochastic models. The proposed scheme provides a better description of the population dynamics especially in the regime of strong exciton-phonon coupling. Finally, we discuss the effect of the bath reorganization in the absorption and fluorescence spectra of ideal J-aggregates in terms of the Stokes shifts. We find a simple expression that relates the reorganization contribution to the Stokes shifts – the reorganization shift – to the ideal or non-ideal exciton delocalization in a J-aggregate. The reorganization shift can be described by three parameters: the monomer reorganization energy, the relaxation time of the optical gap, and the exciton delocalization length. This simple relationship allows one to understand the physical origin of the Stokes shifts in molecular aggregates

415

Mimicking the electron transfer chain in photosystem II with a molecular triad thermodynamically capable of water oxidation.  

Science.gov (United States)

In the photosynthetic photosystem II, electrons are transferred from the manganese-containing oxygen evolving complex (OEC) to the oxidized primary electron-donor chlorophyll P680(•+) by a proton-coupled electron transfer process involving a tyrosine-histidine pair. Proton transfer from the tyrosine phenolic group to a histidine nitrogen positions the redox potential of the tyrosine between those of P680(•+) and the OEC. We report the synthesis and time-resolved spectroscopic study of a molecular triad that models this electron transfer. The triad consists of a high-potential porphyrin bearing two pentafluorophenyl groups (PF(10)), a tetracyanoporphyrin electron acceptor (TCNP), and a benzimidazole-phenol secondary electron-donor (Bi-PhOH). Excitation of PF(10) in benzonitrile is followed by singlet energy transfer to TCNP (? = 41 ps), whose excited state decays by photoinduced electron transfer (? = 830 ps) to yield Bi-PhOH-PF(10)(•+)-TCNP(•-). A second electron transfer reaction follows (? electron transfers involving the tyrosine-histidine pair in PSII. The final charge-separated state is thermodynamically capable of water oxidation, and its long lifetime suggests the possibility of coupling systems such as this system to water oxidation catalysts for use in artificial photosynthetic fuel production. PMID:22566659

Megiatto, Jackson D; Antoniuk-Pablant, Antaeres; Sherman, Benjamin D; Kodis, Gerdenis; Gervaldo, Miguel; Moore, Thomas A; Moore, Ana L; Gust, Devens

2012-09-25

416

Transfer line TT70 (electrons from PS to SPS)  

CERN Multimedia

As injectors for LEP, PS and SPS had to be converted to the acceleration of electrons and positrons. So far, only positively charged particles had been transferred from the PS to the SPS, for the negatively charged electrons a new transfer line, TT70, had to be built. Due to the difference in level of the two machines, the transfer line slopes and tilts.

1981-01-01

417

Negative Polarization through Photon to Electron Spin Polarization Transfer in GaAs Quantum Wells  

CERN Document Server

We demonstrate negative polarization created by light-hole exciton excitation in g-factor engineered GaAs quantum wells measured by time-resolved Kerr rotation and polarization-resolved photoluminescence. This negative polarization is a result of polarization transfer from a photon to an electron spin mediated by a light hole. This demonstration is an important step towards achieving quantum media conversion from a photonic qubit to an electron spin qubit required for building a quantum repeater.

Kosaka, H; Imamura, H; Mitsumori, Y; Rikitake, Y

2006-01-01

418

Negative Polarization through Photon to Electron Spin Polarization Transfer in GaAs Quantum Wells  

OpenAIRE

We demonstrate negative polarization created by light-hole exciton excitation in g-factor engineered GaAs quantum wells measured by time-resolved Kerr rotation and polarization-resolved photoluminescence. This negative polarization is a result of polarization transfer from a photon to an electron spin mediated by a light hole. This demonstration is an important step towards achieving quantum media conversion from a photonic qubit to an electron spin qubit required for buildi...

Kosaka, H.; Rikitake, Y.; Imamura, H.; Mitsumori, Y.; Edamatsu, K.

2006-01-01

419

Surface nanostructuring of LiNbO3 by high-density electronic excitations  

International Nuclear Information System (INIS)

Lithium niobate (LiNbO3) single crystals were irradiated with high energy gold ions (0.5–2.2 GeV) at the UNILAC (GSI) and with 150-keV highly charged xenon ions from an EBIT (Electron Beam Ion Trap, HZDR). The surfaces of the irradiated crystals were analyzed by scanning force microscopy showing very similar topographic changes. Swift heavy ions and slow highly charged ions produce hillock-like nanostructures on the surface. In both cases, the energy deposition of the ions is characterized by dense localized electronic excitations and efficient transfer to the lattice. Furthermore, the irradiation results in a shift in the band gap energy as evidenced by UV–Vis absorption spectroscopy. Specific modifications (e.g. hillock size, energy loss threshold) induced by slow highly charged ions are discussed in comparison with effects due to the electronic energy loss by swift heavy ions

420

Devices which transfer electrons one-by-one  

International Nuclear Information System (INIS)

An introduction is given to the field of single-electron devices, which are electronic circuits across which electrons may be transferred one by one. Experiments are described on the single-junction box and the four-junction box, devices in which electrons were transferred to a metallic island and their presence detected using a single-electron electrometer. The single-junction box