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1

The role of excited Rydberg States in electron transfer dissociation.  

Science.gov (United States)

Ab initio electronic structure methods are used to estimate the cross sections for electron transfer from donor anions having electron binding energies ranging from 0.001 to 0.6 eV to each of three sites in a model disulfide-linked molecular cation. The three sites are (1) the S-S sigma(*) orbital to which electron attachment is rendered exothermic by Coulomb stabilization from the nearby positive site, (2) the ground Rydberg orbital of the -NH(3)(+) site, and (3) excited Rydberg orbitals of the same -NH(3)(+) site. It is found that attachment to the ground Rydberg orbital has a somewhat higher cross section than attachment to either the sigma orbital or the excited Rydberg orbital. However, it is through attachment either to the sigma(*) orbital or to certain excited Rydberg orbitals that cleavage of the S-S bond is most likely to occur. Attachment to the sigma(*) orbital causes prompt cleavage because the sigma energy surface is repulsive (except at very long range). Attachment to the ground or excited Rydberg state causes the S-S bond to rupture only once a through-bond electron transfer from the Rydberg orbital to the S-S sigma(*) orbital takes place. For the ground Rydberg state, this transfer requires surmounting an approximately 0.4 eV barrier that renders the S-S bond cleavage rate slow. However, for the excited Rydberg state, the intramolecular electron transfer has a much smaller barrier and is prompt. PMID:16599533

Sobczyk, Monika; Simons, Jack

2006-04-13

2

Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies.  

Science.gov (United States)

Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Forster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Forster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene units placed between the chromophores. We find that the polarizability of the bridge significantly enhances the effective interaction. We compare our calculations to single molecule experiments on two types of dyads and find reasonable agreement between theory and experiment. PMID:18298155

Fückel, Burkhard; Köhn, Andreas; Harding, Michael E; Diezemann, Gregor; Hinze, Gerald; Basché, Thomas; Gauss, Jürgen

2008-02-21

3

Transfer excitation in slow collisions between ions of very high charge and two-electron targets  

International Nuclear Information System (INIS)

We argue that a three-step transfer-excitation (capture and target excitation) mechanism enhances (depletes) the cross section for one- (two-) electron removal from a two-electron target. This mechanism, which becomes very important at high projectile charge (q), is mediated through quasimolecular couplings between diabatic double-capture and transfer-excitation channels, in which the inner of two active electrons is transferred to an excited target state. The inclusion of this process in the extended classical over-barrier model gives excellent agreement with unexplained experimental cross sections for one- and two-electron removal from He in slow collisions with Xe ions of high charge (q?31)

4

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.

5

Coherence, Energy and Charge Transfers in De-Excitation Pathways of Electronic Excited State of Biomolecules in Photosynthesis  

Science.gov (United States)

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 Förster-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 G.; Malik, F. Bary

2013-11-01

6

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

2013-01-01

7

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

Directory of Open Access Journals (Sweden)

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

Brunger Michael

2009-01-01

8

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

2011-05-24

9

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

CERN Document Server

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

Biggs, Jason D

2009-01-01

10

Electron-impact vibrational excitation rates in the flow field of aeroassisted orbital transfer vehicles  

Science.gov (United States)

This paper examines the vibrational excitation rate processes expected in the flow field of aeroassisted orbital transfer vehicles (AOTVs). An analysis of the multiple-quantum vibrational excitation processes by electron impact is made to predict the vibrational excitation cross sections, rate coefficients, and relaxation times which control vibrational temperature. The expression for the rate of electron-vibration energy transfer is derived by solving the system of master equations which account for the multiple-level transitions. The vibrational excitation coefficients, which are the prerequisite physical quantities in solving the obtained vibrational equation, are calculated based on the theoretically predicted cross sections. These cross sections are obtained from quantum mechanical calculations, based on the concept that vibrational excitation of molecules by electron impact occurs through formation of an intermediate negative ion state. Finally, the modified Landau-Teller-type rate equation, which is suitable for the numerical calculations for the AOTV flow fields, is suggested.

Lee, J.-H.

1985-01-01

11

Electron impact excitation of SO2 - Differential, integral, and momentum transfer cross sections  

Science.gov (United States)

Electron impact excitation of the electronic states of SO2 was investigated. Differential, integral, and inelastic momentum transfer cross sections were obtained by normalizing the relative measurements to the elastic cross sections. The cross sections are given for seven spectral ranges of the energy-loss spectra extending from the lowest electronic state to near the first ionization limit. Most of the regions represent the overlap of several electronic transitions. No measurements for these cross sections have been reported previously.

Vuskovic, L.; Trajmar, S.

1982-01-01

12

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

13

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

International Nuclear Information System (INIS)

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

14

New electron energy transfer and cooling rates by excitation of O2  

Directory of Open Access Journals (Sweden)

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

A. V. Pavlov

15

Excited state electron transfer after visible light absorption by the Co(i) state of vitamin B12.  

Science.gov (United States)

The first example of excited state electron transfer from cob(i)alamin is reported herein. Vitamin B12 was anchored to a mesoporous TiO2 thin film and electrochemically reduced to the cob(i)alamin form. Pulsed laser excitation resulted in rapid excited state electron transfer, ket > 10(8) s(-1), followed by microsecond interfacial charge recombination to re-form cob(i)alamin. The supernucleophilic cob(i)alamin was found to be a potent photoreductant. The yield of excited state electron transfer was found to be excitation wavelength dependent. The implications of this dependence are discussed. PMID:25232558

Achey, Darren; Brigham, Erinn C; DiMarco, Brian N; Meyer, Gerald J

2014-10-01

16

Proton transfer from electronically excited alkane radical cations. effect of electronic excitation energy on proton-donor site selectivity: a study in ?-irradiated CCl3 F/heptane  

International Nuclear Information System (INIS)

Donor and acceptor site selectivity in the proton transfer from alkane radical cations to alkane molecules have been studied extensively in recent years, using ?-irradiated frozen CCl3F/alkane solutions to study symmetric proton transfer and ?-irradiated alkane mixed crystals for the study of asymmetric transfer. The purpose of the present study is the elucidation of the effect of electronic excitation energy on donor site selectivity in the proton-transfer process. To this effect, ?-irradiated cryogenic CCl3F/heptane systems containing heptane nanoparticles were investigated by EPR spectroscopy both before and after electronic excitation of the trapped heptane radical cations present (through illumination within their electronic absorption band). The electronic excitation results in a very substantial increase in the extent of proton transfer from heptane radical cations to heptane molecules. Also, the donor site selectivity typical for ground-state heptane radical cations vanishes completely, as the site of proton donation becomes instead related to the electronic structure of the electronically excited heptane radical cations. Thus, not the structure of the highest occupied molecular orbital (HOMO) in heptane but that of inner (more energetic) orbitals becomes decisive with respect to the site of proton donation from its radical cation. The study opens important new horizons for a detailed investigation of the electronic structure of the different electronically excited states of alkane radical cations, that are formed by removal of inner (non-HOMO) electrons. By combination with theoretical calculations, a detailed picture of the electronic structure of alkanes (not just from the HOMO) comes within reach

17

Absence of quantum oscillations in electronic excitation transfer in the Fenna-Matthews-Olson complex  

Science.gov (United States)

Energy transfer in the photosynthetic Fenna-Matthews-Olson (FMO) complex of the Green Sulfur Bacteria is studied theoretically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. For the calculations we use the efficient Non-Markovian Quantum State diffusion approach. 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. Additionally we show that differences in the values of the electronic transition energies found in the literature lead to a large difference in the transfer dynamics.

Eisfeld, Alexander; Ritschel, Gerhard; Roden, Jan; Strunz, Walter; Aspuru-Guzik, Alan

2012-02-01

18

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

International Nuclear Information System (INIS)

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

19

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

2014-11-12

20

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

 
 
 
 
21

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

22

Resonant transfer excitation: Interference effects  

International Nuclear Information System (INIS)

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

23

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

International Nuclear Information System (INIS)

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

24

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

International Nuclear Information System (INIS)

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

25

Two-photon fluorescence excitation spectrum of a naphthalene norbornylog: Implications for electron transfer  

Science.gov (United States)

Polarized two-photon fluorescence excitation spectra of 1,4-dimethoxy-2,3-dimethyl naphthalene and of a 1,4-dimethoxy-2,3-norbornolog naphthalene, in 0.002 M cyclohexane solution, are reported in the range 665-545 nm at 293 K. Intensity predictions for the 1L b and 1L a states based upon alternate hydrocarbon pseudoparity rules are confirmed: the weak 1L b origin is seen as is a strong 1L b vibronic origin attributed to the naphthalene 4b 2u vibration, but the 1L a origin is not identified. However, consideration of the one-photon absorption spectrum then reveals that the 1L a origin is higher in energy than is the 1L b origin, confirming that the fast through-bridge photoinduced electron transfer seen in naphthalene—dicyanoethylene norbornologs is an electronically forbidden but vibronically allowed process. As far as we are aware, these are the first examples of such processes.

Reimers, J. R.; Hush, N. S.; Sammeth, D. M.; Callis, P. R.

1990-06-01

26

Photoinduced electron transfer between excited Ru(bpy)32+ with some cobalt(III)-amine complexes in micelles  

International Nuclear Information System (INIS)

The excited state dynamics and electron transfer reactions of luminescent probes bound to hosts with different properties provide a means to compare the systems. Although photoinduced electron transfer reactions between photoexcited ruthenium(II)-poly pyridines and various acceptors have been known in the literature, relatively a few reports are available on reactions with cobalt(III) complexes as quenchers. The current interest in ruthenium-poly pyridines and micro heterogeneous systems such as micelles and DNA led us to study the effect of micelles on the quenching of the emission of *Ru(bpy)32+ by some cobalt(III) amine complexes. The results obtained on the photochemical electron transfer between excited Ru(bpy)32+ and several cobalt(III) amine complexes by emission quenching studies in ordinary aqueous solution as well as in micellar solutions have been presented in this report. (author)

27

Energy transfer as parametric excitation: an examination of nonlinearity in enzymatic reaction, nerve conduction, muscle contraction, electron tunneling, and electron transfer.  

Science.gov (United States)

Chemical parametric excitation is presented as the fundamental mechanism of energy transfer. Together with the Franck-Condon principle, it provides a mechanically sound explanation for enzymatic reaction, nerve excitation, muscle contraction, and electron transfer at a basic level. Intermediate between macroscopic models of membrane asymmetry and molecular models, the new model rests on a systematic approach, proposed here, to organizational aspects of the energy transfer processes. In support, a derivation is given of the chemical analog of the Manley-Rowe power conservation relations for parametrically excited electrical networks. This extension to chemical systems indicates for the first time an explanation of power flow directionality and delegates a pumping role to the enzyme. The generalized Manley-Rowe relations are suggested to be a universal law of nature. In such case, nonlinearity could be attributable to the coupling of three systems by these generalized Manley-Rowe conditions relating flows/reactions/oscillations--even though separately each system might be described by linear (Onsager) relations. PMID:7185062

Barrett, T W

1982-01-01

28

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

International Nuclear Information System (INIS)

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

29

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

30

Excited state electron transfer in systems with a well-defined geometry. [cyclophane  

Energy Technology Data Exchange (ETDEWEB)

The effect of temperature, dielectric strength and ligand on the structure of the mesopyropheophorbide cyclophanes will be studied. ESR, NMR, emission and absorption spectroscopy, as well as circular dichroism will be used. The changes in structure will be correlated with changes in the photochemical activity. Electron acceptors such as benzoquinone will be utilized to stabilize the charge separation. Charge separation in porphyrin quinone dimers will also be studied. It was found that electron transfer in the cyclophane system is relatively slow. This is presumably due to an orientation requirement for fast electron transfer. Solvent dielectric also is important in producing a charge separation. Decreasing the temperature effects the yield of charge transfer, but not the kinetics.

Kaufmann, K.J.

1980-12-01

31

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

International Nuclear Information System (INIS)

Charge transfer and electronic excitation processes for H++H2O collisions are investigated theoretically below 10 keV. 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 10 keV down to a few tens of eV with very slowly varying cross-section value of 4-13x10-16 cm2, and are found to be in excellent agreement with experimental measurements by Lindsay et al. [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

32

Excited state electron transfer in systems with a well-defined geometry. Progress report, May 1, 1979-April 30, 1980  

Energy Technology Data Exchange (ETDEWEB)

To determine what are the important criteria governing efficient light-induced electron transfer, we have been studying cyclophanes formed by joining two chlorophyll macrocycles together with two covalent linkages. The properties of the cofacial dimer can be altered by adding one or two magnesium atoms. When a cyclophane containing only one metal atom is excited electron transfer takes place in under ten picoseconds. Evidence for the formation of a state having a great deal of charge transfer interaction or perhaps even a radical pair is found in the time resolved difference spectrum which shows a contribution due to a cation of the magnesium containing macrocycle and an anion of the metal free portion of the molecule. The lifetime of the charge transfer state is 2.4 nsec. This would indicate that we have stabilized the charge separation for a relatively long time. The metal free dimer has an excited state product which does not appear to be a triplet state. The lifetime of this product is very long. The identity of the product has not as yet been obtained. It too could be a charge transfer state. If this is true, we have succeeded in stabilizing the charge separation for an extremely long time. Finally, we observed that the photophysical properties of the chlorophyll macrocycle are modified by reduction of the vinyl group on ring I.

Kaufmann, K.J.

1979-12-01

33

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

34

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

International Nuclear Information System (INIS)

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

35

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

Science.gov (United States)

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

Blancafort, Lluís; Voityuk, Alexander A.

2014-03-01

36

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-03-07

37

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

International Nuclear Information System (INIS)

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

38

[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

39

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

40

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

International Nuclear Information System (INIS)

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

 
 
 
 
41

Observation of resonant transfer and excitation in O5+ + He collisions through high resolution O0 Auger electron spectroscopy  

International Nuclear Information System (INIS)

In this paper we present new evidence that (resonant transfer and excitation) RTE is an important mechanism for the production of Be-like doubly excited states in energetic collisions of Li-like O5+ ions incident on He. We have measured the cross sections for the production of Auger electrons from the decay of the (1s2s2p2)3D and the (1s2s2p2)1D states in O4+ in high resolution at O0, as a function of the incident ion energy. We observe a resonant increase in the Auger cross section with a maximum at approx.13 MeV and full-width-at-half-maximum of approx.7 MeV. This feature is seen to sit on a non-resonant NTE background, which populates the same intermediate states through a two step capture and excitation process governed by the electron-nucleus Coulomb interaction. 13 ref., 3 figs

42

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

43

Electron Excitation and Dissociation  

International Nuclear Information System (INIS)

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

44

Electronic structure and charge transfer excited states of a Sc3N@C80-tetraphenyl porphyrin molecular conjugate  

Science.gov (United States)

Organic donor-acceptor molecular conjugates are often used as the basic component in organic solar cells. The photoexcited donor molecule donates one electron to the acceptor molecule creating a charge-transfer state. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. Such molecular conjugates are often large to describe using accurate quantum chemical methods. We have used our recently developed density functional theory based method to study the charge transfer excited states of a novel Sc3N@C80-tetraphenyl porphyrin complex. In this complex, the porphyrin is the donor and the endohedral Sc3N@C80 is the acceptor molecule. This endohedral fullerene is the third most abundant fullerene. There are few studies on such molecular complexes with endohedral fullerenes as compared to the C60 molecule. We study the role of Sc3N@C80 as acceptor compared to the widely used C60 molecule. Our results on the electronic structure of the complex, the Sc3N@C80 molecule in both isolation and in the complex, and the lowest charge separated states will be presented.

Amerikheirabadi, Fatemeh; Baruah, Tunna; Zope, Rajendra

2012-10-01

45

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

Science.gov (United States)

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.

Filatov, Michael

2014-09-01

46

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

47

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

48

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

International Nuclear Information System (INIS)

ct is reduced to an upper limit of 0.1. It is shown that the lowest excited state of UO22 is unaffected by the presence of PVS. The back reaction, UO2 + Ru(bpy)33 ? UO22 + Ru(bpy)32+, is a second-order reaction, k/epsilon wave length = 450 nm) = 1.05 x 105 s-1 cm at pH 2 and 1.78 x 102 s/sup -1/ cm in 2 M H3PO4 solution. This reaction is accelerated in the presence of O2 or PVS. The yields and rates of formations and reactions of the photochemical products are discussed

49

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.

50

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

International Nuclear Information System (INIS)

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

51

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

52

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 with the occurrence of such a process

53

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

Science.gov (United States)

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

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

2014-09-01

54

Involvement of triplet excited states in the electron transfer photodegradation of cinnamic acids using pyrylium and thiapyrylium salts as photocatalysts.  

Science.gov (United States)

The mechanistic pathway for degradation of cinnamic acids using 2,4,6-triphenylpyrylium as well as 2,4,6-triphenyl(thia)pyrylium salts (,) as solar photocatalysts has been unambiguously established. Results obtained in steady-state experiments have been correlated with time-resolved photophysical studies. High percentages of photodegradation (60-70%) were achieved when aqueous solutions of caffeic and ferulic acids (,) as model pollutants were submitted to irradiation in the presence of ,. Electron-transfer quenching of both the singlet and triplet excited states of , by , has been proved, and the quenching rate constants (close to diffusion control) have been determined. However, the percentages of singlet quenching by ,, even at relatively high concentrations of the model pollutants, is lower than 5%. In addition to this, growth of the signal corresponding to the pyranyl radical occurs in the microsecond timescale, incompatible with the singlet state as precursor. Thus, photodegradation of , mainly involves the triplet state of the photocatalysts. PMID:17668114

Marín, M Luisa; Miguel, Ana; Santos-Juanes, Lucas; Arques, Antonio; Amat, Ana M; Miranda, Miguel A

2007-08-01

55

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

CERN Document Server

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

Biggs, Jason D

2009-01-01

56

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

International Nuclear Information System (INIS)

In our study of intermediates from excited-state electron-transfer reactions, we have focused our attention during the past year on MV+., the reduced methyl viologen radical cation, which is a precursor to the formation of H2 in the photosensitized reduction of water. Through the use of photochemical and radiation chemical techniques, we have examined the efficiency of interaction of MV+. with colloidal Pt, the stability of MV+. as a function of pH, the quantum yield of formation of MV+. in the Ru(bpy)32+/MV2+/EDTA system, and the formation of photoactive charge-transfer complexes between MV2+ and sacrificial electron donors

57

Excited nanoscale-TiO2 induced interfacial electron transfer reaction of redox active cobalt(III)–alkyl amine complex and the solid surface  

International Nuclear Information System (INIS)

Interfacial electron transfer reaction mechanism has been probed using ? = 254 nm excited TiO2 nanoparticles and cis-[CoIII(en)2(RNH2)Cl]Cl2 adsorbates (where RNH2 = MeNH2, EtNH2, PrnNH2, BunNH2, BuiNH2, PennNH2, HexnNH2, BznNH2) in aqueous 2-propanol. These tailor made complexes differing in coordination environment due to RNH2 adhere onto TiO2 surface producing compact nano-TiO2//cobalt(III)–(RNH2) 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 TiO2 with the acceptor level (Co center): (e?, CB)/(e?, tr) + (CoIII, ad) ? CoII and (ii) electronic coupling of donor level (localized on Ti center) with acceptor level (Co center): Ti (center) + (CoIII, ad) ? CoII. These pathways indicate accumulation of electron and appropriately available for reduction of the adhered complex ion. Significant insights were gained on the role of RNH2 moiety in modifying compact structure of TiO2–cobalt(III)–RNH2 compound, redox power of semiconductor surface, and the proposed mechanism of interfacial electron transfer reactions. Highlights: ? Interfacial electron transfer reactions can be probed with tailor made complexes. ? Excited anatase surface acts as a uniquely powerful adsorbent. ? Structurally integrated cobalt(III) complexes adhere to form surface compounds. ? Compact surface compound can facilitate electron transfer.

58

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

Science.gov (United States)

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

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

2014-08-01

59

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

60

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

Science.gov (United States)

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

Kobori, Yasuhiro; Fuki, Masaaki; Murai, Hisao

2010-11-18

 
 
 
 
61

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 self-exchange energy transfer. 52 references, 5 figures, 1 table

62

Population transfer to the E 1?g excited electronic state of Li2 by femtosecond laser pulses with all possible interstate radiative couplings  

International Nuclear Information System (INIS)

Population transfer to the excited electronic state E 1?g of Li2 by transform limited delayed femtosecond pulses has been investigated. The validity of the usual neglect of some field-molecule coupling terms in such transfers, accomplished using counterintuitively ordered pulses through ''adiabatic passage on light-induced potentials,'' has been reexamined. It has been found that such an approximation cannot be justified in the case of the ladder system X 1?+g-A 1?+u-E 1?+g of Li2. However, the transfer can be successfully accomplished over a range of pulse parameters, which is more restricted than those obtained with the usual approximation. In this scheme, when two pulses with a small frequency difference between them are used, the lower-frequency pulse must precede the higher-frequency pulse for a successful transfer. We introduce an adiabatic representation, appropriate to this full coupling case, for examining the mechanism of transfer. In our representation the initial wave packet may be prepared on more than one adiabatic state, and at an early stage it is transferred to a single adiabatic surface after which the evolution mostly proceeds adiabatically. The vibrational analysis of the final wave packet shows that for short pulses high vibrational states are generally excited, while for pulses with larger width low-lyle for pulses with larger width low-lying vibrational states are preferred in cases where successful transfer occurs. These results can be understood in terms of the motion of the wave packet on the time-dependent adiabatic potentials.

63

Excited-state proton coupled electron transfer between photolyase and the damaged DNA through water wire: a photo-repair mechanism.  

Science.gov (United States)

The photolyase enzyme absorbs blue light to repair damaged DNA through a cyclic electron transfer reaction. A description of the underlying mechanism has proven to be a challenging issue for both experimental and theoretical studies. In the present work, combined CASPT2//CASSCF/AMBER (QM/MM) calculations have been performed for damaged DNA in photolyase. A proton-coupled electron transfer (PCET) mechanism has been determined for restoring cyclobutane pyrimidine dimer (CPD) to two normal thymine bases by irradiation of photolyase. A well-defined water wire between FADH(-) and CPD was determined as a bridge to assist the PCET process within FADH(-) and thereby trigger the forward electron transfer to CPD. The subsequent CPD splitting and the alternation of the H-bond pattern proceed in a concerted way, which makes the productive backward electron transfer occur on an ultrafast timescale. A local minimum of SCT((1)??*)-LMin was identified on the pathway of the futile backward electron transfer (BET), which is stabilized by the strong H-bond interaction between the water wire and CPD. As a result, the futile BET process is endothermic by ?18.0 kcal mol(-1), which is responsible for a 2.4 ns timescale inferred experimentally for the futile BET process. Besides the unbiased interpretation for the majority of the experimental findings, the present study provides a new excited-state PCET mechanism, which leads to a significant step toward a deeper understanding of the photo-repair process of damaged-DNA by the photolyase enzyme. PMID:25341360

Wang, Hongjuan; Chen, Xuebo; Fang, Weihai

2014-12-14

64

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

65

Electron attachment to excited molecules  

International Nuclear Information System (INIS)

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

66

Electron attachment to excited molecules  

Energy Technology Data Exchange (ETDEWEB)

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

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

1993-12-31

67

Bionano donor-acceptor hybrids of porphyrin, ssDNA, and semiconductive single-wall carbon nanotubes for electron transfer via porphyrin excitation.  

Science.gov (United States)

Photoinduced electron transfer in self-assemblies of porphyrins ion-paired with ssDNA wrapped around single-wall carbon nanotubes (SWCNTs) has been reported. To accomplish the three-component hybrids, two kinds of diameter-sorted semiconducting SWCNT(n,m)s of different diameter ((n,m) = (6,5) and (7,6)) and free-base or zinc porphyrin bearing peripheral positive charges ((TMPyP(+))M (tetrakis(4-N-methylpyridyl)porphyrin); M = Zn and H(2)) serving as light-absorbing photoactive materials are utilized. The donor-acceptor hybrids are held by ion-pairing between the negatively charged phosphate groups of ssDNA on the surface of the SWCNT and the positively charged at the ring periphery porphyrin macrocycle. The newly assembled bionano donor-acceptor hybrids have been characterized by transmission electron microscopy (TEM) and spectroscopic methods. Photoinduced electron transfer from the excited singlet porphyrin to the SWCNTs directly and/or via ssDNA as an electron mediator has been established by performing systematic studies involving the steady-state and time-resolved emission as well as the transient absorption studies. Higher charge-separation efficiency has been successfully demonstrated by the selection of the appropriate semiconductive SWCNTs with the right band gap, in addition to the aid of ssDNA as the electron mediator. PMID:22088093

D'Souza, Francis; Das, Sushanta K; Zandler, Melvin E; Sandanayaka, Atula S D; Ito, Osamu

2011-12-14

68

Electron impact excitation of rubidium  

Science.gov (United States)

The electron energy-loss spectrum of rubidium at 40 eV and scattering angle 8° has been recorded. The noticeable features are analysed. Differential cross sections for the resonance excitation are determined.

Predojevi?, B.; Pej?ev, V.; Ševi?, D.; Leki?, S.; Srivastava, R.; Stauffer, A.; Marinkovi?, B. P.

2012-11-01

69

State-selective electron transfer and ionization in collisions of highly charged ions with ground-state Na(3s) and laser-excited Na*(3p)  

Science.gov (United States)

Single electron transfer and ionization in collisions of N5+ and Ne8+ with ground state Na(3s) and laser excited Na*(3p) are investigated both experimentally and theoretically at collision energies from 1 to 10 keV/amu, which includes the classical orbital velocity of the valence electron. State-selective partial cross sections are obtained using recoil-ion momentum spectroscopy in combination with a magneto-optically cooled Na atom target. A strong dependence of the cross sections on the collision energy is observed. In general, both the relative magnitude and the energy dependence are found to be in good agreement with classical-trajectory Monte Carlo calculations.

Blank, I.; Otranto, S.; Meinema, C.; Olson, R. E.; Hoekstra, R.

2012-02-01

70

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.)

71

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

72

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

International Nuclear Information System (INIS)

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

73

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.)

74

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

International Nuclear Information System (INIS)

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

75

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 U{sup 91+} ions  

Energy Technology Data Exchange (ETDEWEB)

Electron-electron interaction is studied in the strongest possible atomic fields (Z.{alpha} => 1) in the presence of only two electrons. A quasi-free electron from a hydrogen gas target is resonantly captured into a L{sub j} subshell of a fast H-like U{sup 91+} ion by simultaneous excitation of the strongly bound K electron also into a L{sub j'} subshell of the projectile, with j and j' the total angular momenta of 1/2 or 3/2 for the electron of concern. This resonant capture and excitation process, KL{sub j}L{sub j'}-RTE, is mediated by electron-electron interaction. It is equivalent to dielectronic recombination (DR) in ion-electron collisions and leads to a doubly excited He-like U{sup 90+**} ion, which stabilizes - almost exclusively - via the emission of two successive K X-rays, first a K hypersatellite (K{alpha}i-H) and then a K satellite (K{alpha}i'-S) transition. The K X-ray emission characteristics associated with one-electron capture in collisions of U{sup 91+} ions with a hydrogen target is studied for the three resonance groups of the KL{sub j}L{sub j'}-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 KL{sub 1/2}L{sub 1/2} confirms the importance of the Breit contribution to the interaction. The angular distribution for the K{alpha}2-H transition (j=1/2) is isotropic in the projectile system whereas the K{alpha}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 KL{sub 1/2}L{sub 3/2}. The experimental results are in agreement with fully relativistic calculations including the generalized Breit interaction. (orig.)

Ma, X. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany)]|[Institute of Modern Physics, Lanzhou (China); Mokler, P.H.; Bosch, F.; Gumberidze, A.; Kozhuharov, C.; Liesen, D.; Stoehlker, T. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Sierpowski, D.; Warczak, A. [Jagellonian Univ., Inst. of Physics, Krakow (Poland); Stachura, Z. [Institute of Nuclear Physics, Krakow (Poland); Zakowicz, S.; Harman, Z.; Gruen, N.; Scheid, W. [Giessen Univ., Inst. fuer Theoretische Physik (Germany)

2003-08-01

76

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

Energy Technology Data Exchange (ETDEWEB)

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

Ma, X. E-mail: x.ma@impcas.ac.cn; Mokler, P.H.; Bednarz, G.; Bosch, F.; Gumberidze, A.; Kozhuharov, C.; Liesen, D.; Sierpowski, D.; Stachura, Z.; Stoehlker, Th.; Warczak, A

2003-05-01

77

Single electron transfer and target excitation in He{sup 2+} + Na (3s) collisions at 2-50 keV amu{sup -1} in the coupled-Sturmian-pseudostate approach  

Energy Technology Data Exchange (ETDEWEB)

A two-centre coupled-Sturmian-pseudostate approach is employed to calculate single electron transfer, target excitation and total ionization cross sections for the He{sup 2+} + Na (3s) collision system at 2-50 keV amu{sup -1} impact energies. The Sturmian basis set, together with an analytic Hartree-Fock potential for the Na core, are chosen carefully so that all three channels (transfer, excitation and ionization) are included in the coupled scheme. The present state-selective and total charge transfer cross sections compare fairly well with experimental data, as well as with previous theoretical results, particularly below 10 keV amu{sup -1}. The target excitation cross sections for the sodium 3p and 4d states are in very good agreement with the available measurements, while significant discrepancy exists between theory and experiment for the excitation of the Na (4p) state. (author).

Jain, A.; Winter, T.G. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Physics

1996-10-28

78

Energy transfer of highly vibrationally excited biphenyl  

Science.gov (United States)

The energy transfer between Kr atoms and highly vibrationally excited, rotationally cold biphenyl in the triplet state was investigated using crossed-beam/time-of-flight mass spectrometer/time-sliced velocity map ion imaging techniques. Compared to the energy transfer of naphthalene, energy transfer of biphenyl shows more forward scattering, less complex formation, larger cross section for vibrational to translational (V-->T) energy transfer, smaller cross section for translational to vibrational and rotational (T-->VR) energy transfer, larger total collisional cross section, and more energy transferred from vibration to translation. Significant increase in the large V-->T energy transfer probabilities, termed supercollisions, was observed. The difference in the energy transfer of highly vibrationally excited molecules between rotationally cold naphthalene and rotationally cold biphenyl is very similar to the difference in the energy transfer of highly vibrationally excited molecules between rotationally cold naphthalene and rotationally hot naphthalene. The low-frequency vibrational modes with out-of-plane motion and rotationlike wide-angle motion are attributed to make the energy transfer of biphenyl different from that of naphthalene.

Hsu, Hsu Chen; Dyakov, Yuri; Ni, Chi-Kung

2010-11-01

79

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

80

Charge transfer excitations in cofacial fullerene-porphyrin complexes  

Science.gov (United States)

Porphyrin and fullerene donor-acceptor complexes have been extensively studied for their photo-induced charge transfer characteristics. We present the electronic structure of ground states and a few charge transfer excited states of four cofacial porphyrin-fullerene molecular constructs studied using density functional theory at the all-electron level using large polarized basis sets. The donors are base and Zn-tetraphenyl porphyrins and the acceptor molecules are C60 and C70. The complexes reported here are non-bonded with a face-to-face distance between the porphyrin and the fullerene of 2.7 to 3.0 Å. The energies of the low lying excited states including charge transfer states calculated using our recent excited state method are in good agreement with available experimental values. We find that replacing C60 by C70 in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV. Variation of donor in these complexes has marginal effect on the lowest charge transfer excitation energy. The interfacial dipole moments and lowest charge transfer states are studied as a function of face-to-face distance.

Zope, Rajendra R.; Olguin, Marco; Baruah, Tunna

2012-08-01

 
 
 
 
81

Excitation of electron plasma waves  

International Nuclear Information System (INIS)

The excitation of electron plasma waves by interaction of two electromagnetic waves is examined. Analysis is based on Maxwell's equations and the electron-gas moment equations. Formulas are derived for power absorption densities. Effects of static magnetic fields and inhomogeneties on absorption efficiency are studied numerically. Stimulated Raman backscattering of electromagnetic waves from electron plasma waves in magnetized plasma is also investigated. Formulas are derived for the growth rate and threshold power associated with scattering from Langmuir and upper-hybrid waves in a homogeneous plasma. An analysis of spatial amplification of the decay waves in an inhomogeneous plasma is presented

82

Charge Transfer Excitations in Insulating Copper Oxides  

CERN Document Server

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

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

2005-01-01

83

Light induced electron transfer of metal complexes  

International Nuclear Information System (INIS)

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

84

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

85

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

86

Excited-state electronic coupling and photoinduced multiple electron transfer in two related ligand-bridged hexanuclear mixed-valence compounds.  

Science.gov (United States)

The synthesis, characterization, electrochemical, photophysical, and photochemical properties of two hexanuclear mixed-valence compounds are reported. Each supramolecular species consists of two cyano-bridged [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(3)L-NC-Fe(II)(CN)(5)] triads that are linked to each other through a Pt(IV)-L-Pt(IV) bridge, where L = 4,4'-dipyridyl (bpy) or 3,3'-dimethyl-4,4'-dipyridyl (dmb). The major difference between the two compounds is the electronic nature of the bridging ligand between the two Pt atoms. Both species exhibit a broad Fe(II) --> Pt(IV) intervalent (IT) absorption band at 421 nm with an oscillator strength that is approximately four times that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(5)] and twice that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) When L = bpy, the resonance Raman spectrum obtained by irradiating the IT band at 488 nm exhibits several dipyridyl ring modes at 1604, 1291, and 1234 cm(-1) which are not present in the spectrum when L = dmb. In addition, femtosecond pump-probe spectroscopy performed at 400 nm yields a transient bleach of the IT absorption band with a single exponential decay of 3.5 ps for L = bpy, compared with only 1.8 ps for L = dmb and 2.1 ps for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) Last, prolonged irradiation of the complexes at 488 nm leads to the formation of 4 equiv of ferricyanide with a quantum efficiency of 0.0014 for L = bpy and 0.0011 for L = dmb. The transient absorption, resonance Raman, and photochemical data suggest that the degree of excited electronic coupling in these compounds is tunable by changing the electronic nature of the Pt-L-Pt bridging ligand. PMID:12184755

Pfennig, Brian W; Mordas, Carolyn J; McCloskey, Alex; Lockard, Jenny V; Salmon, Patty M; Cohen, Jamie L; Watson, David F; Bocarsly, Andrew B

2002-08-26

87

Excited state proton-coupled electron transfer in 8-oxoG-C and 8-oxoG-A base pairs: a time dependent density functional theory (TD-DFT) study.  

Science.gov (United States)

In a recent experiment, the repair efficiency of DNA thymine cyclobutane dimers (TT) on UV excitation of 8-oxoG base paired either to C or A was reported. An electron transfer mechanism from an excited charge transfer state of 8-oxoG-C (or 8-oxoG-A) to TT was proposed and 8-oxoG-A was found to be 2-3 times more efficient than 8-oxoG-C in repair of TT. Intra base pair proton transfer (PT) in charge transfer (CT) excited states of the base pairs was proposed to quench the excited state and prevent TT repair. In this work, we investigate this process with TD-DFT calculations of the excited states of 8-oxoG-C and 8-oxoG-A base pairs in the Watson-Crick and Hoogsteen base pairs using long-range corrected density functional, ?B97XD/6-31G* method. Our gas phase calculations showed that CT excited state ((1)??*(CT)) of 8-oxoG-C appears at lower energy than the 8-oxoG-A. For 8-oxoG-C, TD-DFT calculations show the presence of a conical intersection (CI) between the lowest (1)??*(PT-CT) excited state and the ground state which likely deactivates the CT excited state via a proton-coupled electron transfer (PCET) mechanism. The (1)??*(PT-CT) excited state of 8-oxoG-A base pair lies at higher energy and its crossing with ground state is inhibited because of a high energy gap between (1)??*(PT-CT) excited state and ground state. Thus the gas phase calculations suggest the 8-oxoG-A would have longer excited state lifetimes. When the effect of solvation is included using the PCM model, both 8-oxoG-A and 8-oxoG-C show large energy gaps between the ground state and both the excited CT and PT-CT states and suggest little difference would be found between the two base pairs in repair of the TT lesion. However, in the FC region the solvent effect is greatly diminished owing to the slow dielectric response time and smaller gaps would be expected. PMID:23478652

Kumar, Anil; Sevilla, Michael D

2013-08-01

88

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

International Nuclear Information System (INIS)

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

89

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

Science.gov (United States)

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

Tseng, Huan-Wei

90

Nonadiabatic anharmonic electron transfer  

International Nuclear Information System (INIS)

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

91

Nonadiabatic anharmonic electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-03-28

92

Electron transfer to sulfides:  

International Nuclear Information System (INIS)

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

93

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

94

Momentum-Dependent Charge Transfer Excitations in Sr2CuO2Cl2 - Angle Resolved Electron Energy Loss Spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron-hole pair excitations in the insulating cuprates $Sr_2CuO_2Cl_2$ were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in $Cu-O_2$ plane. The former show a large energy dispersion $\\sim 1.5$eV along [110], and the latter appear at a higher energy position ($\\sim 4.5$eV) only along [100], but not along [110]. We interpret these results as transitions in...

Wang, Y. Y.; Zhang, F. C.; Dravid, V. P.; Ng, K. K.; Klein, M. V.; Schnatterly, S. E.; Miller, L. L.

1996-01-01

95

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

International Nuclear Information System (INIS)

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

96

A unified perspective on the hydrogen atom transfer and proton-coupled electron transfer mechanisms in terms of topographic features of the ground and excited potential energy surfaces as exemplified by the reaction between phenol and radicals.  

Science.gov (United States)

The relation between the hydrogen atom transfer (HAT) and proton-coupled electron transfer (PCET) mechanisms is discussed and is illustrated by multiconfigurational electronic structure calculations on the ArOH + R(*) --> ArO(*) + RH reactions. The key topographic features of the Born-Oppenheimer potential energy surfaces that determine the predominant reaction mechanism are the conical intersection seam of the two lowest states and reaction saddle points located on the shoulders of this seam. The saddle point corresponds to a crossing of two interacting valence bond states corresponding to the reactant and product bonding patterns, and the conical intersection corresponds to the noninteracting intersection of the same two diabatic states. The locations of mechanistically relevant conical intersection structures and relevant saddle point structures are presented for the reactions between phenol and the N- and O-centered radicals, (*)NH2 and (*)OOCH3. Points on the conical intersection of the ground doublet D0 and first excited doublet D1 states are found to be in close geometric and energetic proximity to the reaction saddle points. In such systems, either the HAT mechanism or both the HAT mechanism and the proton-coupled electron transfer (PCET) mechanism can take place, depending on the relative energetic accessibility of the reaction saddle points and the D0/D1 conical intersection seams. The discussion shows how the two mechanisms are related and how they blend into each other along intermediate reaction paths. The recognition that the saddle point governing the HAT mechanism is on the shoulder of the conical intersection governing the PCET mechanism is used to provide a unified view of the competition between the two mechanisms (and the blending of the two mechanisms) in terms of the prominent and connected features of the potential energy surface, namely the saddle point and the conical intersection. The character of the dual mechanism may be understood in terms of the dominant valence bond configurations of the intersecting states, which are zero-order approximations to the diabatic states. PMID:18465862

Tishchenko, Oksana; Truhlar, Donald G; Ceulemans, Arnout; Nguyen, Minh Tho

2008-06-01

97

Multiscale photosynthetic and biomimetic excitation energy transfer  

Science.gov (United States)

Recent evidence suggests that quantum coherence enhances excitation energy transfer (EET) through individual photosynthetic light-harvesting protein complexes (LHCs). Its role in vivo is unclear however, where transfer to chemical reaction centres (RCs) spans larger, multi-LHC/RC networks. Here we predict maximum coherence lengths possible in fully connected chromophore networks with the generic structural and energetic features of multi-LHC/RC networks. A renormalization analysis reveals the dependence of EET dynamics on multiscale, hierarchical network structure. Surprisingly, thermal decoherence rate declines at larger length scales for physiological parameters and coherence length is instead limited by localization due to static disorder. Physiological parameters support coherence lengths up to ~ 5nm, which is consistent with observations of solvated LHCs and invites experimental tests for intercomplex coherences in multi-LHC/RC networks. Results further suggest that a semiconductor quantum dot network engineered with hierarchically clustered structure and small static disorder may support coherent EET over larger length scales, at ambient temperatures.

Ringsmuth, A. K.; Milburn, G. J.; Stace, T. M.

2012-07-01

98

Collective excitations in electron-hole bilayers  

CERN Document Server

We report a combined analytic and Molecular Dynamics analysis of the collective mode spectrum of an electron-hole (bipolar) bilayer in the strong coupling quasi-classical limit. A robust, isotropic energy gap is identified in the out-of-phase spectra, generated by the combined effect of correlations and of the excitation of the bound dipoles; the in-phase spectra exhibit a correlation governed acoustic dispersion for the longitudinal and transverse modes. Strong nonlinear generation of higher harmonics of the fundamental dipole oscillation frequency and the transfer of harmonics between different modes is observed. The mode dispersions in the liquid state are compared with the phonon spectrum in the crystalline solid phase, reinforcing a coherent physical picture.

Kalman, G J; Donko, Z; Golden, K I; Kalman, Gabor J; Hartmann, Peter; Donko, Zoltan; Golden, Kenneth I

2006-01-01

99

Calculated electron excitation cross sections for excited state-excited state transitions in alkali atoms  

International Nuclear Information System (INIS)

Electron excitation cross sections for optically allowed excited state-excited state transitions in lithium, sodium, potassium, rubidium, and cesium have been calculated in the first Born approximation. An analytical Coulomb approximation is used to evaluate the transition matrix element of the valence electron. Cross sections are given for incident electron energies from 1.02 to 1,000 in threshold units. The accuracy of the calculation is tested by comparing oscillator strengths computed in the Coulomb approximation with other published values

100

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

 
 
 
 
101

Photoinduced electron transfer in a tris(2,2`-bipyridine)-C{sub 60}-ruthenium(II) dyad: evidence of charge recombination to a fullerene excited state  

Energy Technology Data Exchange (ETDEWEB)

A novel fulleropyrrolidine covalently linked to a tris(2,2`-bipyridine)-ruthenium(II) complex is presented. While electrochemical investigations suggest the absence of any ground-state interaction between ruthenium and fullerence chromophores, photoinduced optical absorption studies clearly show that electron transfer occurs to afford the Ru{sup 3+}-C{sub 60}{sup .-} pair with characteristic fullerene radical anion band at {lambda}{sub max}=1040 nm. (orig.)

Maggini, M.; Mondini, S.; Scorrano, G. [Centro Meccanismi Reazioni Organiche-CNR, Padova (Italy). Dipt. di Chimica Organica; Guldi, D.M. [Notre Dame Univ., IN (United States). Radiation Lab.; Paolucci, F.; Ceroni, P.; Roffia, S. [Bologna Univ. (Italy). Dipt. di Chimica G. Ciamician

1998-10-01

102

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)

103

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

104

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

International Nuclear Information System (INIS)

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

105

Neutron scattering investigation of magnetic excitations at high energy transfers  

International Nuclear Information System (INIS)

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

106

Electron transfer: Lower tunnel barriers  

Science.gov (United States)

A better understanding of electron transfer through molecules could provide the basis for many technological breakthroughs. Now, the rate of electron transfer has been enhanced in a family of molecules by making them more rigid, and this phenomenon may be explained by the loss of electronic energy to vibrations.

Miller, John R.

2014-10-01

107

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

108

Electron-impact vibrational excitation of tetrahydrofuran  

Science.gov (United States)

Low-energy differential and integral cross sections for the electron-impact vibrational excitation of tetrahydrofuran are presented. The data concern four features in the vibrational excitation electron energy-loss spectrum of tetrahydrofuran over the energy-loss range of 0-0.9 eV. The results show weak influence from long-range dipole interactions, being mainly isotropic. Comparison with earlier work is presented.

Khakoo, M. A.; Orton, D.; Hargreaves, L. R.; Meyer, N.

2013-07-01

109

Photochemistry of compounds in the constrained medium cellulose—part 8. Long-range electron transfer from excited pyrene to Cu(II) cation  

Science.gov (United States)

Steady state spectroscopic techniques and laser flash photolysis have been used to investigate the photo-induced electron transfer from pyrene to cupric ions in cellophane films. The data indicate that the rate constant k( r) as a function of reactant separation r is given by k( r)=5×10 11exp(-0.61r)s -1at 20° C. The rate constant decreases by a factor of 5 over the temperature range 20°C to -60°C which is attributed to a change of the adsorbed water in the cellophane; it then remains almost constant to 77 K.

Bitting, H.; Milosavljevic, B. H.; Thomas, J. K.

110

A simplified approach for the coupling of excitation energy transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Shi Bo [Hefei National Laboratory for Physical Science at Microscale, University of Science and Technology of China, Hefei 230026 (China); Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Gao Fang, E-mail: gaofang@iim.ac.cn [Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031 (China); State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016 (China); Liang Wanzhen [Hefei National Laboratory for Physical Science at Microscale, University of Science and Technology of China, Hefei 230026 (China); Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China)

2012-02-06

111

Electron excitation spectrum in complex oxides  

International Nuclear Information System (INIS)

Qualitative analysis of electron dielectric function is conducted using the strong coupling method. A special attention is paid to local field difference from the medium one. It is shown that the effect is very high in perovskite group lamellar oxides. Numeric evaluations of contributions to dielectic function of lamellar and cubical oxides from intraionic, interionic and intrazonal (plasma) electron excitations are conducted

112

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

113

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.)

114

Electronic excitations of poly(methylphenylsilane) films  

Science.gov (United States)

We report electroabsorption (EA), two-photon absorption (TPA), and the spectrum for charge-carrier generation in thin films of poly(methylphenylsilane) (PMPS). The one-photon absorption to a singlet exciton, which begins at Eg=3.5 eV, appears in EA and indicates a polarizability change of 1.8×10-22 cm3. The onset around 4.6 eV of direct generation of charge carriers by photons defines the interband gap Eb and correlates with an EA feature at 4.65 eV that we associate with charge transfer between polymer segments. The TPA around 4.4 eV is to the second 1Ag state and gives the alternation gap Ea, while the broad TPA above 5 eV is assigned to an even-parity state derived from exciting two electrons across Eg. A Pariser-Parr-Pople model for ? conjugation in polysilanes accounts for Eg, for polarizability changes, for TPA, and for the singlet-triplet gap Et in terms of correlated states. We contrast the spectra of amorphous PMPS with films of poly(di-n-hexylsilane), whose side groups are ordered at low temperature, and compare EA spectra in polysilanes with EA in crystalline organic solids and wideband semiconductors.

Kepler, R. G.; Soos, Z. G.

1991-05-01

115

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

116

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.)

117

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a theoretical study of excitation dynamics in the chlorosome antenna complex of green photosynthetic bacteria based on a recently proposed model for the molecular assembly. Our model for the excitation energy transfer (EET) throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of the supramolecular structure, and electronic structure calculations of the excited states. We characterized the optical properties...

Fujita, Takatoshi; Huh, Joonsuk; Saikin, Semion K.; Brookes, Jennifer Clare; Aspuru-guzik, Alan

2014-01-01

118

Enhanced electron attachment to highly excited molecules using a plasma mixing scheme  

International Nuclear Information System (INIS)

We present preliminary results on a glow discharge-based technique to populate highly excited states of molecules using a novel excitation transfer process, and to efficiently produce negative ions via electron attachment to those excited states. copyright 1997 American Institute of Physics

119

Vanadium atom level excitation by slow electrons  

International Nuclear Information System (INIS)

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

120

Electronic excitation of Na atom by electron impact  

International Nuclear Information System (INIS)

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

 
 
 
 
121

Computer simulation of cluster impact induced electronic excitation of solids  

International Nuclear Information System (INIS)

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

122

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

123

Electron transfer in pnicogen bonds.  

Science.gov (United States)

As a new type of noncovalent interactions, pnicogen bond between a VA group element (N, P, and As) and an electron donor (Lewis base) has grabbed attention in recent several years. Here we employ the block-localized wave function (BLW) based energy decomposition scheme to probe the bonding nature in a series of substituted phosphines X(n)PH(3-n) complexed with ammonia. As the BLW method can derive the optimal monomer orbitals in a complex with the electron transfer among monomers quenched, we can effectively examine the HOMO-LUMO interaction in these pnicogen bonding systems. Among various energy components, electron transfer energy together with the polarization energy dominates the pnicogen bonding energy. Although usually it is assumed that the electron transfer from ammonia to substituted phosphines occurs in the form of n ? ?*(XP) hyperconjugative interaction, we identify a kind of new pathway when X = NO2 and CN, i.e., n ? d?*, which results from the interaction between the ? orbital of cyano or nitro substituent and d orbitals on P. But still this picture of electron transfer using a single pair of orbitals is greatly simplified, as the electron density difference (EDD) maps corresponding to the overall electron transfer processes show the accumulation of electron density on the P side opposite to the X-P bond, with insignificant or even negligible gain of electron density on the substituent group side. Thus, the EDD maps tend to support the concept of ?-hole in pnicogen bonds. PMID:24588109

Guan, Liangyu; Mo, Yirong

2014-10-01

124

Excitations and benchmark ensemble density functional theory for two electrons  

CERN Document Server

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

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

2014-01-01

125

Excitations and benchmark ensemble density functional theory for two electrons  

International Nuclear Information System (INIS)

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

126

Excitations and benchmark ensemble density functional theory for two electrons  

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-05-14

127

Ab initio QM/MM study of excited state electron transfer between pyrene and 4,4'-bis(dimethylamino)-diphenylmethane with different solvent systems: Role of hydrogen bonding within solvent molecules  

Science.gov (United States)

The exciplex is a charge transfer species formed in the process of electron transfer between an electron donor and an electron acceptor and hence is very sensitive to solvent polarity. In order to understand the role of solvent in exciplex formation between pyrene (PY) and 4,4'-bis(dimethylamino)diphenylmethane (DMDPM), we used two types of solvent approximations: an implicit solvent model and an explicit solvent model. The difference in energies between the excited and the meta-stable Frank-Condon state (?E) of the structures were assumed to correspond to the emission maximum of the exciplex in different solvents. The ?E values show the trend of stabilization of the exciplex with an increase in solvent polarity. This trend in stabilization is substantially more prominent in the explicit solvent model than that with the implicit solvent model. The ?E value obtained in methanol reflects equal stabilization compared to that in a more polar solvent, N,N-dimethylformamide. This extra stabilization of the exciplex may be explained on the basis of the H-bonding capability of the protic solvent, methanol.

Sen, Kakali; Basu, Samita; Bhattacharyya, Dhananjay

128

Bioinspired electron-transfer systems and applications  

International Nuclear Information System (INIS)

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

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

Electron excitation of the liquid helium surface  

International Nuclear Information System (INIS)

A 25 keV electron beam incident on the surface of liquid helium has been used to excite metastable molecular states in the liquid. The dynamics of the metastables are monitored by detecting the ion pairs created by annihilation at the surface. (orig.)

131

A perspective of biological supramolecular electron transfer.  

Science.gov (United States)

Electron transfer is an essential activity in biological systems. The migrating electron originates from water-oxygen in photosynthesis and reverts to dioxygen in respiration. In this cycle two metal porphyrin complexes possessing circular conjugated system and macrocyclic pi-clouds, chlorophyll and heme, play a decisive role in mobilising electrons for travel over biological structures as extraneous electrons. Transport of electrons within proteins (as in cytochromes) and within DNA (during oxidative damage and repair) is known to occur. Initial evaluations did not favour formation of semiconducting pathways of delocalized electrons of the peptide bonds in proteins and of the bases in nucleic acids. Direct measurement of conductivity of bulk material and quantum chemical calculations of their polymeric structures also did not support electron transfer in both proteins and nucleic acids. New experimental approaches have revived interest in the process of charge transfer through DNA duplex. The fluorescence on photo-excitation of Ru-complex was found to be quenched by Rh-complex, when both were tethered to DNA and intercalated in the base stack. Similar experiments showed that damage to G-bases and repair of T-T dimers in DNA can occur by possible long range electron transfer through the base stack. The novelty of this phenomenon prompted the apt name, "chemistry at a distance". Based on experiments with ruthenium modified proteins, intramolecular electron transfer in proteins is now proposed to use pathways that include C-C sigma-bonds and surprisingly hydrogen bonds which remained out of favour for a long time. In support of this, some experimental evidence is now available showing that hydrogen bond-bridges facilitate transfer of electrons between metal-porphyrin complexes. By molecular orbital calculations over 20 years ago we found that "delocalization of an extraneous electron is pronounced when it enters low-lying virtual orbitals of the electronic structures of peptide units linked by hydrogen bonds". This review focuses on supramolecular electron transfer pathways that can emerge on interlinking by hydrogen bonds and metal coordination of some unnoticed structures with pi-clouds in proteins and nucleic acids, potentially useful in catalysis and energy missions. PMID:10844992

Ramasarma, T

1999-12-01

132

Energy transfer of highly vibrationally excited phenanthrene and diphenylacetylene.  

Science.gov (United States)

The energy transfer between Kr atoms and highly vibrationally excited, rotationally cold phenanthrene and diphenylacetylene in the triplet state was investigated using crossed-beam/time-of-flight mass spectrometer/time-sliced velocity map ion imaging techniques. Compared to the energy transfer between naphthalene and Kr, energy transfer between phenanthrene and Kr shows a larger cross-section for vibrational to translational (V ? T) energy transfer, a smaller cross-section for translational to vibrational and rotational (T ? VR) energy transfer, and more energy transferred from vibration to translation. These differences are further enlarged in the comparison between naphthalene and diphenylacetylene. In addition, less complex formation and significant increases in the large V ? T energy transfer probabilities, termed supercollisions in diphenylacetylene and Kr collisions were observed. The differences in the energy transfer between these highly vibrationally excited molecules are attributed to the low-frequency vibrational modes, especially those vibrations with rotation-like wide-angle motions. PMID:21298156

Hsu, Hsu Chen; Tsai, Ming-Tsang; Dyakov, Yuri; Ni, Chi-Kung

2011-05-14

133

Electronic excitation spectrum of calcium-doped picene: Electron energy-loss spectroscopy study  

Science.gov (United States)

The electronic excitations of Ca-doped picene films have been investigated using electron energy-loss spectroscopy in transmission. We demonstrate that a composition of Ca3picene can be achieved by evaporation of Ca onto pristine picene films under ultrahigh vacuum conditions. The core level excitations indicate a charge transfer of one electron per added Ca to the picene molecules and a hybridization of Ca and picene derived electronic states. Upon doping a new spectral feature is observed at about 2 eV in the electronic excitation spectrum. This new feature does not disperse which signals its localized character. The data analysis using a Kramers-Kronig transformation suggests that Ca3picene has a nonmetallic ground state.

Roth, Friedrich; Müller, Eric; Rellinghaus, Bernd; Büchner, Bernd; Knupfer, Martin

2013-11-01

134

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

Science.gov (United States)

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

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

2013-05-01

135

Electronic excitation and structural stability of solids  

International Nuclear Information System (INIS)

Passing through solid matter swift heavy ions generate a high density of electronic excitations. Thus a large fraction of the valence electrons are removed from valence band states of insulators or semiconductors and put into conduction band states. Typically, the valence band is of bonding character and the conduction band has antibonding character; then the electronic excitations weaken the covalent bonds and cause a repulsive force between the atoms. An instability of atomic structure thus arises, which occurs on a femtosecond timescale. The atoms reach high kinetic energies and the atomic structure is destroyed. This mechanism is distinct and complementary to the Coulomb explosion and thermal spike models for the damage done by swift heavy ions. It should be especially important for materials with a competing high pressure phase or where excitons induce lattice defects. (orig.)

136

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

International Nuclear Information System (INIS)

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

137

Electron-impact excitation of atmospheric gases  

Science.gov (United States)

Electron energy-loss and impact-induced emission techniques were used to investigate excitation of key features in molecular nitrogen and rare gases. Specifically, line and band emission intensities were investigated as a function of wavelength (at high resolution) and incident electron energy using various monochromator-detector combinations. In addition, electron energy-loss spectroscopy was utilized such that differential cross sections (DCSs) and integral cross sections (ICSs) were obtained. The emission cross sections, DCSs, and ICSs for these atmospheric species will be presented.

Malone, Charles P.; Young, Jason A.; Johnson, Paul V.; Liu, Xianming; Kanik, Isik; Ajdari, Bahar; Khakoo, Murtadha A.

2010-03-01

138

Electronic excitation of methane molecule by electron impact  

International Nuclear Information System (INIS)

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

139

Concepts of Highly Excited Electronic Systems  

Science.gov (United States)

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

Berakdar, Jamal

2003-05-01

140

Laser assisted excitation in electron-hydrogen-like ion collisions  

International Nuclear Information System (INIS)

An approach is developed for the study of the excitation of a ground-state hydrogenic ion under the simultaneous action of fast electron impact and a single mode, linearly polarized laser field in the framework of the Coulomb-Born approximation. The projectile-laser interaction is considered to all orders while the laser-ion interaction is considered to first order only. An elegant method is developed to construct the dressed excited states of a hydrogen-like ion target using the first-order perturbation theory in the parabolic coordinate representation which is the correct prescription for such laser assisted excitation processes. By virtue of this, the problem arising due to the l degeneracy of the excited states of a hydrogenic ion is overcome successfully. The differential (DCS) as well as total (TCS) cross sections are studied for the excitation to n = 2 level accompanied by the transfer of l photons with the field direction parallel to the incident momentum ?vector parallel kvectori. The variations of the cross sections with respect to the target charge number Z are also studied. The overall effect of the laser field is to suppress the field free cross sections. Some numerical results are also presented for the excitation of He+ ion to individual Stark manifolds for the n = 2 level

 
 
 
 
141

Collective excitations in electron-hole bilayers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report a combined analytic and Molecular Dynamics analysis of the collective mode spectrum of an electron-hole (bipolar) bilayer in the strong coupling quasi-classical limit. A robust, isotropic energy gap is identified in the out-of-phase spectra, generated by the combined effect of correlations and of the excitation of the bound dipoles; the in-phase spectra exhibit a correlation governed acoustic dispersion for the longitudinal and transverse modes. Strong nonlinear ge...

Kalman, Gabor J.; Hartmann, Peter; Donko, Zoltan; Golden, Kenneth I.

2006-01-01

142

An excitable electronic circuit as a sensory neuron model  

CERN Document Server

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

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

2011-01-01

143

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

144

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

2014-10-01

145

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

146

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

147

Electron-phonon relaxation and excited electron distribution in zinc oxide and anatase  

International Nuclear Information System (INIS)

We propose a first-principles method for evaluations of the time-dependent electron distribution function of excited electrons in the conduction band of semiconductors. The method takes into account the excitations of electrons by an external source and the relaxation to the bottom of the conduction band via electron-phonon coupling. The methods permit calculations of the non-equilibrium electron distribution function, the quasi-stationary distribution function with a steady-in-time source of light, the time of setting of the quasi-stationary distribution and the time of energy loss via relaxation to the bottom of the conduction band. The actual calculations have been performed for titanium dioxide in the anatase structure and zinc oxide in the wurtzite structure. We find that the quasi-stationary electron distribution function has a peak near the bottom of the conduction band and a tail whose maximum energy rises linearly with increasing energy of excitation. The calculations demonstrate that the relaxation of excited electrons and the setting of the quasi-stationary distribution occur within a time of no more than 500 fs for ZnO and 100 fs for anatase. We also discuss the applicability of the effective phonon model to energy-independent electron-phonon transition probability. We find that the model only reproduces the trends in the change of the characteristic times whereas the precision of such calculations is not high. The rate of energy transfer to phonons at the rate of energy transfer to phonons at the quasi-stationary electron distribution also have been evaluated and the effect of this transfer on the photocatalysis has been discussed. We found that for ZnO this rate is about five times less than in anatase.

148

CN excitation and electron densities in diffuse molecular clouds  

CERN Document Server

Utilising previous work by the authors on the spin-coupled rotational cross-sections for electron-CN collisions, data for the associated rate coefficients is presented. Data on rotational, fine-structure and hyperfine-structure transition involving rotational levels up to $N$=20 are computed for temperatures in the range 10 -- 1000~K. Rates are calculated by combining Born-corrected R-matrix calculations with the infinite-order-sudden (IOS) approximation. The dominant hyperfine transitions are those with $\\Delta N=\\Delta j= \\Delta F=1$. For dipole-allowed transitions, electron-impact rates are shown to exceed those for excitation of CN by para-H$_2$($j=0$) by five orders of magnitude. The role of electron collisions in the excitation of CN in diffuse clouds, where local excitation competes with the cosmic microwave background (CMB) photons, is considered. Radiative transfer calculations are performed and the results compared to observations. These comparisons suggest that electron density lies in the range $n...

Harrison, Stephen; Tennyson, Jonathan

2013-01-01

149

CN excitation and electron densities in diffuse molecular clouds  

Science.gov (United States)

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

Harrison, Stephen; Faure, Alexandre; Tennyson, Jonathan

2013-11-01

150

He2+-He collisions: one-electron capture versus electron removal and target-ion excitation  

International Nuclear Information System (INIS)

We have studied electronic redistribution processes, associated with production of excited He+ ions, in He2+-He collisions at energies ranging from 1 to 300 keV amu-1. Excited He+ ionic states can be formed (i) in the projectile by one-electron transfer, and (ii) in the target by removing one of the target electrons and simultaneously exciting the residual ion. At the highest energies the second process dominates over the first while at energies between ? 10 and 60 keV amu-1 the first process is the most important one. However, for low energies below 10 keV amu-1 we obtain the striking result that both processes are equally likely. (author)

151

Parameterized effective potential for excited electronic states  

Science.gov (United States)

The method of the parameterized effective potential (PEP) is developed for constructing the potential curves of excited electronic states of the same symmetry. Unlike the traditional methods of the density functional theory, the PEP is constructed as the direct mapping of an external potential. The PEP generates the one-particle orbitals such that the corresponding single-determinant Kohn-Sham function constructed on their basis is orthogonal to the determinant functions of lower-lying states. A comparison of the potential curves constructed for the HeH and H2 molecules by the PEP method with the precision data obtained based on the time-consuming configuration interaction methods shows that the PEP method can provide good accuracy for the geometry of an equilibrium configuration and the vertical excitation energies.

Fesenko, S. I.; Glushkov, V. N.; Mogilevskaya, N. V.

2011-07-01

152

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

International Nuclear Information System (INIS)

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

153

Coherence in electron-impact excitation of helium  

Energy Technology Data Exchange (ETDEWEB)

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

Batelaan, Hermanus

1991-06-10

154

Energy transfer of highly vibrationally excited naphthalene. III. Rotational effects  

Science.gov (United States)

The rotational effects in the energy transfer between Kr atoms and highly vibrationally excited naphthalene in the triplet state were investigated using crossed-beam/time-sliced velocity map ion imaging at various translational collision energies. As the initial rotational temperature changes from less than 10 to ~350 K, the ratio of vibrational to translational (V-->T) energy transfer cross section to translational to vibrational/rotational (T-->VR) energy transfer cross section increases, but the probability of forming a complex during the collisions decreases. Significant increases in the large V-->T energy transfer probabilities, termed supercollisions, at high initial rotational temperature were observed.

Liu, Chen-Lin; Hsu, Hsu Chen; Ni, Chi-Kung

2008-04-01

155

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

156

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

Energy Technology Data Exchange (ETDEWEB)

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

1990-02-14

157

Excitation transfer and luminescence in porphyrin-carbon nanotube complexes  

CERN Document Server

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

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

2007-01-01

158

Efficiency of excitation transfer in photosynthesis under quantum coherence  

CERN Document Server

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

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

2007-01-01

159

Convoy electrons emitted from resonant coherently excited ions  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate the use of selective excitation of fast ions by resonant coherent excitation as a new technique to study convoy electron production. It is shown that electron loss from excited states plays an important role in convoy electron production by fast-channeled ions. The absolute cross section for convoy production by hydrogenic ions in {ital n}=2 states is derived from the dtaa, as is an estimate of the absolute probability of resonant coherent excitation as a function of ion energy.

Kimura, K.; Gibbons, J.P.; Elston, S.B.; Biedermann, C.; DeSerio, R.; Keller, N.; Levin, J.C.; Breinig, M.; Burgdoerfer, J.; Sellin, I.A. (Department of Physics, University of Tennessee, Knoxville, Tennessee 37996-1200 an (US) Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6377)

1991-01-07

160

Mechanism of Foerster-type hopping of charge transfer and excitation energy transfer along blocked oligothiophenes by Si-atoms  

International Nuclear Information System (INIS)

The ground and excited-state properties of oligothiophenes connected by Si-atoms have been studied theoretically, based on recent experimental reports [M. Fujitsuka, D.W. Cho, J. Ohshita, A. Kunai, T. Majima, J. Phys. Chem. C 111 (2007) 1993]. Herein, we have employed a density-functional theory (DFT) approach toward examining the influence of the number of oligothiophenes on molecular ground-state properties, focusing on the density of state and the density distribution on the subunit of the oligothiophenes. Furthermore, we have investigated several excited-state properties of these oligothiophene. We discuss absorption with transition densities, which reveal the orientations and strengths of transition dipole moments, charge difference densities, which allow for the study of transition dipole moments and charge transfer in the absorption processes, and transition density matrices, which provide information about the electron-hole coherence and excitation delocalization. All of these properties were studied by employing time-dependent density functional theory (TD-DFT). Our theoretical results indicate that there are not only localized excited states, but also inter-branched charge transfer excited states in absorption for block copolymers of the oligothiophenes. In all, the theoretical analyses provide insight into the ground- and excited-state properties of the polymers, notably on the hopping mechanism of charge transfer in blocked oligothiophenes by Si atomsn blocked oligothiophenes by Si atoms

 
 
 
 
161

Transition-density-fragment interaction combined with transfer integral approach for excitation-energy transfer via charge-transfer states  

Science.gov (United States)

A transition-density-fragment interaction (TDFI) combined with a transfer integral (TI) method is proposed. The TDFI method was previously developed for describing electronic Coulomb interaction, which was applied to excitation-energy transfer (EET) [K. J. Fujimoto and S. Hayashi, J. Am. Chem. Soc. 131, 14152 (2009)] and exciton-coupled circular dichroism spectra [K. J. Fujimoto, J. Chem. Phys. 133, 124101 (2010)]. In the present study, the TDFI method is extended to the exchange interaction, and hence it is combined with the TI method for applying to the EET via charge-transfer (CT) states. In this scheme, the overlap correction is also taken into account. To check the TDFI-TI accuracy, several test calculations are performed to an ethylene dimer. As a result, the TDFI-TI method gives a much improved description of the electronic coupling, compared with the previous TDFI method. Based on the successful description of the electronic coupling, the decomposition analysis is also performed with the TDFI-TI method. The present analysis clearly shows a large contribution from the Coulomb interaction in most of the cases, and a significant influence of the CT states at the small separation. In addition, the exchange interaction is found to be small in this system. The present approach is useful for analyzing and understanding the mechanism of EET.

Fujimoto, Kazuhiro J.

2012-07-01

162

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-12-14

163

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

International Nuclear Information System (INIS)

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

164

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

Science.gov (United States)

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

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

2013-12-14

165

Energy transfer of highly vibrationally excited naphthalene. I. Translational collision energy dependence  

Science.gov (United States)

Energy transfer between highly vibrationally excited naphthalene and Kr atom in a series of translational collision energies (108-847cm-1) was studied separately using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. Highly vibrationally excited naphthalene in the triplet state (vibrational energy: 16194cm-1; electronic energy: 21400cm-1) was formed via the rapid intersystem crossing of naphthalene initially excited to the S2 state by 266nm photons. The collisional energy transfer probability density functions were measured directly from the scattering results of highly vibrationally excited naphthalene. At low collision energies a short-lived naphthalene-Kr complex was observed, resulting in small amounts of translational to vibrational-rotational (T?VR) energy transfer. The complex formation probability decreases as the collision energy increases. T ?VR energy transfer was found to be quite efficient at all collision energies. In some instances, nearly all of the translational energy is transferred to vibrational-rotational energy. On the other hand, only a small fraction of vibrational energy is converted to translational energy. The translational energy gained from vibrational energy extend to large energy transfer (up to 3000cm-1) as the collision energy increases to 847cm-1. Substantial amounts of large V?T energy transfer were observed in the forward and backward directions at large collision energies.

Liu, Chen-Lin; Hsu, Hsu Chen; Hsu, Yuan Chin; Ni, Chi-Kung

2007-09-01

166

Excitation energy transfer: Study with non-Markovian dynamics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Liang, Xian-ting

2010-01-01

167

Electron Transfer to Vinylaromatic Polymers  

International Nuclear Information System (INIS)

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

168

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

International Nuclear Information System (INIS)

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

169

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

170

COLTRIMS Study of Transfer-Excitation in Proton-Helium Collisions  

Science.gov (United States)

We have carried out a cold-target recoil-ion momentum spectroscopy (COLTRIMS) measurement for p + He collisions to study the capture of one and simultaneous excitation of the second target electron (transfer excitation, TE) as a function of the projectile scattering angle and velocity. The measurement was carried out at projectile energies of 25, 50, and 75 keV. The neutralized projectiles were measured in coincidence with the recoil ions. We obtained the energy loss of the projectile from the longitudinal component of the recoil-ion momentum and the scattering angle from its transverse component. The energy loss, in turn, was used to identify and distinguish TE from single capture. Absolute differential cross sections for TE as well as for state-selective single capture were obtained. Furthermore, cross section ratios of transfer excitation to single electron capture were analyzed. The role of correlated versus uncorrelated TE mechanisms will be discussed.

Hasan, A.; Tooke, B.; Schulz, M.

2006-05-01

171

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads  

Energy Technology Data Exchange (ETDEWEB)

This project involves the design, synthesis and study of molecules which mimic some of the important aspects of photosynthetic electron and energy transfer. This research project is leading to a better understanding of the energy conserving steps of photosynthesis via the study of synthetic model systems which abstract features of the natural photosynthetic apparatus. The knowledge gained from these studies will aid in the design of artificial photosynthetic reaction centers which employ the basic chemistry and physics of photosynthesis to help meet mankind`s energy needs. The approach to artificial photosynthesis employed in this project is to use synthetic pigments, electron donors, and electron acceptors similar to those found in biological reaction centers, but to replace the protein component with covalent bonds. These chemical linkages determine the electronic coupling between the various moieties by controlling separation, relative orientation, and overlap of electronic orbitals. The model systems are designed to mimic the following aspects of natural photosynthetic electron transfer: electron donation from a tetrapyrrole excited single state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they mimic carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

NONE

1993-03-01

172

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

173

Near-threshold rovibrational excitation of HF by electron impact  

International Nuclear Information System (INIS)

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

174

Excitation energy transfer: Study with non-Markovian dynamics  

Science.gov (United States)

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

Liang, Xian-Ting

2010-11-01

175

Excitation energy transfer: Study with non-Markovian dynamics  

International Nuclear Information System (INIS)

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

176

Collisionally excited few-electron systems: theoretical introduction and survey  

International Nuclear Information System (INIS)

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

177

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

178

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

179

Energy and photoinduced electron transfer in porphyrin-fullerene dyads  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-09-26

180

Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide  

International Nuclear Information System (INIS)

This paper studies the intramolecular photoinduced electron-transfer (PET) of covalent bonded azobenzene-perylene diimide (AZO-PDI) in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 1011 s?1 is found. This PET process is also consolidated by femtosecond transient absorption spectra

 
 
 
 
181

The effect of atoms excited by electron beam on metal evaporation  

CERN Document Server

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

Xie Guo Feng; Ying Chun Tong

2002-01-01

182

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

International Nuclear Information System (INIS)

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

183

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

184

Probing electron transfer dynamics of pyranine with reduced graphene oxide.  

Science.gov (United States)

A stable reduced graphene oxide (rGO) was prepared and characterized by X-ray diffraction (XRD) and laser Raman spectroscopy. Steady state and time-resolved fluorescence quenching studies have been carried out to elucidate the process of electron transfer from excited pyranine (POH) into the rGO dispersion. POH adsorbed strongly on rGO dispersion with an apparent association constant of 33.4 (mg ml)(-1), and its fluorescence emission was quenched with an apparent association constant of 33.7 (mg ml)(-1). Picosecond lifetime measurements gave the rate constant for the electron transfer process from the excited singlet state of POH into the rGO dispersion as 8.8 × 10(9) s(-1). Laser flash photolysis studies demonstrated the formation of radicals for the evidence of electron transfer between POH and rGO. PMID:25168852

Asha Jhonsi, M; Nithya, C; Kathiravan, A

2014-10-14

185

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

186

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

187

Energy traps of excited energy transfer processes in polymer solids  

International Nuclear Information System (INIS)

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

188

Separating annihilation and excitation energy transfer dynamics in light harvesting systems.  

Science.gov (United States)

The dependence of excitation energy transfer kinetics on the electronic state of the acceptor (ground vs excited) has been resolved with a novel multipulse prePump-Pump-Probe spectroscopy. The primary energy transfer and annihilation dynamics in two model light-harvesting systems were explored: an artificially synthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurring light-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as the primary excitation energy donor with porphyrin chromophores as the acceptor molecules. The prePump-Pump-Probe transient signals were analyzed with Monte Carlo modeling to explicitly address the underlying step-by-step kinetics involved in both excitation migration and annihilation processes. Both energy transfer and annihilation dynamics were demonstrated to occur with approximately the same rate in both systems, regardless of the excitation status of the acceptor pigments. The possible reasons for these observations are discussed in the framework of the Förster energy transfer model. PMID:23662680

Vengris, Mikas; Larsen, Delmar S; Valkunas, Leonas; Kodis, Gerdenis; Herrero, Christian; Gust, Devens; Moore, Thomas; Moore, Ana; van Grondelle, Rienk

2013-09-26

189

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

An efficient computational algorithm to implement a local operator approach to partitioning electronic energy in general molecular systems is presented. This approach, which rigorously defines the electronic energy on any subsystem within a molecule, gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. We apply the technique to the $9-$(($1-$naphthyl)$-$methyl)-an...

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

2013-01-01

190

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

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

Sutin, N; Creutz, C

1980-01-01

191

Estimates of electron capture cross sections for excited molecular states  

International Nuclear Information System (INIS)

The reciprocity between radiative electron attachment and photodetachment serves to justify the use of a one-electron theory of photodetachment to estimate the likelihood of interactions between a free electron and various excited molecular states. Results indicate a strong dependence of interaction likelihood on the electronic state of the molecule and imply that the electron capture cross sections for excited molecules could be significantly different than those for ground state molecules. 4 figs

192

Detection of ground state atoms by electron excitation to a metastable level  

International Nuclear Information System (INIS)

A method of detecting ground state atoms in a molecular beam, following electron excitation to a metastable state, is described. Using beams at right angles the momentum transfer and the spread in the momentum transfer are measured as functions of the electron energy. An experimental design for such an atom detector, for use with noble gases, is derived and the solid angle acceptance of the detector, which directly determines the amount of background suppression, is determined. (U.K.)

193

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.

194

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

195

The mechanism of electronic excitation in the bacterial bioluminescent reaction  

International Nuclear Information System (INIS)

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

196

Multiphoton excitation of doubly excited states of two-electron atoms  

International Nuclear Information System (INIS)

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

197

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

International Nuclear Information System (INIS)

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

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 o

199

VUV excitation and electronic decay of rubidium halide molecules  

International Nuclear Information System (INIS)

Previously we reported an interionic Auger decay following the VUV resonant excitations of the metal atom in the alkali halide molecules. Opening and closing of the spectator Auger decay channel was found to strongly influence the lineshape of the participator decay transitions, an effect attributed to the changes in the lifetime of the VUV-excited state. In this work, the VUV excitation and the following electronic decay of the resonant states of rubidium halides is studied. A series of electron spectra have been measured at photon energies around the 4p ? nl resonance excitation region. Experimental results and the theoretical modelling of the excitation and decay spectra are presented

200

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

 
 
 
 
201

Electronic excitation of methanol by low energy electrons  

Science.gov (United States)

Measurement of absolute differential and integral cross sections for the lowest lying electronically excited states of methanol will be presented. These cross sections were measured using a crossed electron gas beam spectrometer incorporating a moveable gas beam. The data were normalized against the elastic scattering signal, with the elastic cross sections previously determined in our laboratory [1] using the relative flow method with an aperture-type gas collimator [2]. These data are, to the best of the author's knowledge, the first reported study of these cross sections and have important implications for dosimetry modeling of radiation therapy. [4pt] [1] M.A. Khakoo et al., Phys. Rev. A, 77, 042705 (2008)[0pt] [2] M.A. Khakoo et al., J. Phys. B: At. Mol Phys., 40, 3601 (2007)

Tanner, Joshua; Hargreaves, Leigh; Khakoo, Murtadha

2012-10-01

202

Energy transfer of highly vibrationally excited 2-methylnaphthalene: Methylation effects  

Science.gov (United States)

The methylation effects in the energy transfer between Kr atoms and highly vibrationally excited 2-methylnaphthalene in the triplet state were investigated using crossed-beam/time-sliced velocity-map ion imaging at a translational collision energy of ~520 cm-1. Comparison of the energy transfer between naphthalene and 2-methylnaphthalene shows that the difference in total collisional cross section and the difference in energy transfer probability density functions are small. The ratio of the total cross sections is ?(naphthalene): ?(methylnaphthalene)=1.08+/-0.05:1. The energy transfer probability density function shows that naphthalene has a little larger probability at small T-->V/R energy transfer, ?EuT energy transfer, -800 cm-1transfer, such as supercollisions defined arbitrarily as ?Ed<-1500 cm-1, was observed. The possible methylation effects due to the subsequent successive collisions were discussed.

Hsu, Hsu Chen; Liu, Chen-Lin; Hsu, Yuan Chin; Ni, Chi-Kung

2008-07-01

203

Observation of site-specific electronic excitation in Li +-CO collisions near threshold  

Science.gov (United States)

The energy transfer spectra of Li + ions scattered from CO molecules were measured by a time-of-flight technique at laboratory collision energies 120 ? Elab ? 300 eV and scattering angles 5 ? ? ? 45 °. Electronic excitation of CO molecules was observed in the spectra measured at reduced scattering angles Elab ? ? 2.1 keV deg. Angular and energy dependence of the energy transfer spectra show that electronic excitation of the CO molecules by Li + impact near threshold on the C-atom side takes place with a probability much higher than that on the O-atom side.

Tanuma, H.; Kita, S.; Kusunoki, I.; Sato, Y.

1989-07-01

204

Electron-photon angular correlations from electron impact excitation of heavy rare-gas atoms  

International Nuclear Information System (INIS)

Electron-photon angular correlations have been measured for electron impact excitation of the first excited 1P and 3P states of krypton and of the first excited 3P state of xenon. In the case of these heavy atoms two independent measurements were necessary to determine the excitation parameters lambda and antichi for these states. (author)

205

Intramolecular Electron Scattering and Electron Transfer Following Autoionization in Dissociating Molecules  

Science.gov (United States)

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

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

2004-07-01

206

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

Science.gov (United States)

We present a theoretical study of excitation dynamics in the chlorosome antenna complex of green photosynthetic bacteria based on a recently proposed model for the molecular assembly. Our model for the excitation energy transfer (EET) throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of the supramolecular structure and electronic structure calculations of the excited states. We characterized the optical properties of the chlorosome with absorption, circular dichroism and fluorescence polarization anisotropy decay spectra. The simulation results for the excitation dynamics 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 several tens of ps. We assign the time scales of the EET to specific physical processes by comparing our results with the data obtained from time-resolved spectroscopy experiments. PMID:24504540

Fujita, Takatoshi; Huh, Joonsuk; Saikin, Semion K; Brookes, Jennifer C; Aspuru-Guzik, Alán

2014-06-01

207

Role of excited state intramolecular charge transfer in the photophysical properties of norfloxacin and its derivatives.  

Science.gov (United States)

The photophysical properties of 1-ethyl-6-fluoro-7-(1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid (norfloxacin, NFX) and some of its derivatives have been studied to evaluate the role of the free carboxylic acid and the nonprotonated piperazinyl group in the behavior of the 1,4-dihydro-4-oxoquinoline ring. Steady state and time-resolved fluorescence measurements at different pHs provide clear evidence in favor of singlet excited-state deactivation of NFX and its N(4')-methyl derivative pefloxacin (PFX) via intramolecular electron transfer from the N(4') atom of the piperazinyl ring to the fluoroquinolone (FQ) main system. This is a very efficient, energy-wasting pathway, which becomes dramatically enhanced in basic media. Acetylation at N(4') (as in ANFX) decreases the availability of the lone pair, making observable its fluorescence and the transient absorption spectrum of its triplet excited state even at high pH. It also reveals that the geometry of FQs changes from an almost sp3 hybridization of the N(1') of the piperazinyl substituent in the ground state to nearly sp2 in the singlet excited state (rehybridization accompanied by intramolecular charge transfer, RICT); accordingly, the singlet energy of ANFX is significantly lower than that of NFX and PFX. The fluorescence measurements using acetonitrile as a polar nonprotic organic solvent further support deactivation of the singlet excited state of nonacetylated NFX derivatives via intramolecular electron transfer from the N(4') atom. PMID:16494369

Cuquerella, M Consuelo; Miranda, Miguel A; Bosca, Francisco

2006-03-01

208

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

International Nuclear Information System (INIS)

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

209

Electronic excitations in fast ion-solid collisions  

Energy Technology Data Exchange (ETDEWEB)

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

Burgdoerfer, J. (Tennessee Univ., Knoxville, TN (USA). Dept. of Physics and Astronomy Oak Ridge National Lab., TN (USA))

1990-01-01

210

Theory of nuclear excitation by electron capture for heavy ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Gagyi-palffy, Adriana

2006-01-01

211

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, 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

212

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

CERN Document Server

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

Nagesh, Jayashree; Brumer, Paul

2013-01-01

213

Excitation transfer through open quantum networks: Three basic mechanisms  

Science.gov (United States)

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

Campos Venuti, Lorenzo; Zanardi, Paolo

2011-10-01

214

Excitation transfer through open quantum networks: a few basic mechanisms  

CERN Document Server

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

Venuti, Lorenzo Campos

2011-01-01

215

Inelastic light scattering by electronic excitations in artificial atoms  

CERN Document Server

In the paper, we present theoretical calculations of the cross section for inelastic light scattering by electronic excitations in a quantum dot charged with 42 electrons. The many-electron states involved in the computations are obtained in the framework of the Random Phase Approximation. The evaluation of energy-weighted sum rules allowed us to distinguish among single-particle (SPEs), collective charge (CDEs) and collective spin (SDEs) electronic excitations. Raman spectra in polarized and depolarized geometries are computed for a range of incident laser energies. The below-band-gap excitation regime reveals advantages for the identification of individual excited states contributing to the Raman spectra. The computed polarization ratios for Raman intensities show the breakdown of selection rules in the presence of a magnetic field. A new jump rule of Raman intensities at the band gap may help identifying the nature (charge or spin) of electronic excitations. Under extreme resonance (laser energy very close...

Delgado, A; Delgado, Alain; Gonzalez, Augusto

2005-01-01

216

Chirped pulse control of long range electron transfer  

International Nuclear Information System (INIS)

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

217

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

International Nuclear Information System (INIS)

Recent experimental studies of resonant transfer and excitation (RTE) in ion-atom collisions are reviewed. In the RTE process correlated electron capture and projectile excitation occur together in a single encounter with a target atom. Measurements of Ca/sup q+/ + H2 (q = 10 to 19) from 100 to 370 MeV establish the projectile charge-state dependence of K-shell RTE and provide a detailed test of the theory. Structure due to RTE is observed in the energy dependence of the total electron-capture cross sections for this collision system. A comparison of the Ca17+ + H2 data with previous results for Ca17+ + He demonstrates the effect of the target-electron momentum distribution on the RTE process. Studies of 230 to 610 MeV Nb31+ + H2 provide information about RTE involving agreement with theoretical calculations. 15 refs., 4 figs

218

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.)

219

Flavin Electron Shuttles Dominate Extracellular Electron Transfer by Shewanella oneidensis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Shewanella oneidensis strain MR-1 is widely studied for its ability to respire a diverse array of soluble and insoluble electron acceptors. The ability to breathe insoluble substrates is defined as extracellular electron transfer and can occur via direct contact or by electron shuttling in S. oneidensis. To determine the contribution of flavin electron shuttles in extracellular electron transfer, a transposon mutagenesis screen was performed with S. oneidensis to identify mutants unable to ...

Kotloski, Nicholas J.; Gralnick, Jeffrey A.

2013-01-01

220

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

Science.gov (United States)

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

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

2014-05-01

 
 
 
 
221

Concatenation of reversible electronic energy transfer and photoinduced electron transfer to control a molecular piston.  

Science.gov (United States)

Reversible electronic energy transfer and photoinduced electron transfer conspire in the light-driven dethreading of a molecular piston, showing the potential of combining these processes in supramolecular systems. PMID:22428161

Scarpantonio, Luca; Tron, Arnaud; Destribats, Carole; Godard, Pascale; McClenaghan, Nathan D

2012-04-25

222

Noisy Quantum Cellular Automata for Quantum versus Classical Excitation Transfer  

Science.gov (United States)

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

Avalle, Michele; Serafini, Alessio

2014-05-01

223

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

224

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

225

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

226

Topological Excitations of One-Dimensional Correlated Electron Systems  

CERN Document Server

Properties of low-energy excitations in one-dimensional superconductors and density-wave systems are examined by the bosonization technique. In addition to the usual spin and charge quantum numbers, a new, independently measurable attribute is introduced to describe elementary, low-energy excitations. It can be defined as a number w which determines, in multiple of $\\pi$, how many times the phase of the order parameter winds as an excitation is transposed from far left to far right. The winding number is zero for electrons and holes with conventional quantum numbers, but it acquires a nontrivial value w=1 for neutral spin-1/2 excitations and for spinless excitations with a unit electron charge. It may even be irrational, if the charge is irrational. Thus, these excitations are topological, and they can be viewed as composite particles made of spin or charge degrees of freedom and dressed by kinks in the order parameter.

Salkola, M I

1998-01-01

227

Theoretical study on a corrole-azafullerene dyad: Electronic structure, spectra and photoinduced electron transfer  

Science.gov (United States)

Density Functional Theory and Time-Dependent Density Functional Theory calculations have been carried out on a recently synthesized amino-corrole and a corrole-azafullerene dyad which exhibits photoinduced electron transfer (PET). Good agreement of the theoretical results with experiment is obtained regarding the absorption and emission spectra of the corrole, the absorption spectra of the corrole-azafullerene dyad and the transient anionic and cationic radicals of azafullerene and corrole respectively. Application of Mulliken's theory for charge-transfer states yields the excitation energy of the charge-separated state of the dyad very close to the S1 excitation of amino-corrole, consistent with a PET process.

Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula

2014-08-01

228

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

Energy Technology Data Exchange (ETDEWEB)

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

1990-02-14

229

Photoinduced electron transfer for complexes of methyl viologen: Wavelength effects on the yield of charge carriers  

Science.gov (United States)

Laser flash photolysis of charge-transfer (CT) complexes of methyl viologen (MV 2+) and electron donors which include aniline, aniline derivatives, and naphthalene results in net viologen reduction. Yields of electron transfer are sharply dependent on the excitation wavelength with enhanced quantum efficiences for irradiation at 355 versus 532 nm. This wavelength dependence is proposed to be a general phenomenon for ground-state CT systems in fluid solution, potentially involving preferential excitation of interchromophore vibrations or solvent phonons.

Jones, Guilford, II; Malba, Vincent

1985-08-01

230

Elementary Electronic Excitations in Graphene Nanoribbons  

CERN Document Server

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

Brey, L

2007-01-01

231

Relaxation of electronic excitations in YAG and YAP crystals  

International Nuclear Information System (INIS)

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.))

232

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

233

Electron Impact Excitation and Ionization of Neon  

Science.gov (United States)

We have further developed the B-Spline R-matrix (BSR) code [1] to allow for a large number of pseudo-states in the close-coupling expansion. In the present work, the BSRMPS approach [2] was employed to perform semi-relativistic (Breit-Pauli) close-coupling calculations for elastic scattering, excitation, and ionization of neon from both the ground state and the metastable excited states. Coupling to the ionization continuum through the pseudo-states is important for low-energy elastic scattering (to represent polarizability effects), for excitation in the ``intermediate'' energy regime of about 1-5 times the ionization potential, and to allow for the calculation of ionization processes by transforming the results obtained for excitation of the positive-energy pseudo-states. The current results represent a significant extension of our earlier near-threshold work [3] and previous non-relativistic RMPS calculations [4,5].[4pt] [1] O. Zatsarinny, Comp. Phys. Commun. 174 (2006) 273.[0pt] [2] O. Zatsarinny and K. Bartschat, Phys. Rev. Lett. 107 (2011) 023203.[0pt] [3] O. Zatsarinny and K. Bartschat, J. Phys. B 37 (2004) 2173.[0pt] [4] C. P. Ballance and D. C. Griffin, J. Phys. B 37 (2004) 2943.[0pt] [5] C. P. Ballance et al., J. Phys. B 37 (2004) 4779.

Zatsarinny, Oleg; Bartschat, Klaus

2012-10-01

234

Search for excited electrons in ep collisions at HERA  

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-05-15

235

Site specific photochemical reaction of PMMA by core electron excitation  

International Nuclear Information System (INIS)

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

236

Differential cross sections for the electron impact excitation of pyrimidine  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on differential cross section (DCS) measurements for the electron-impact excitation of the electronic states of pyrimidine. The energy range of the present measurements was 15-50 eV with the angular range of the measurements being 10°-90°. All measured DCSs displayed forward-peaked angular distributions, consistent with the relatively large magnitudes for the dipole moment and dipole polarizability of pyrimidine. Excitations to triplet states were found to be particularly importan...

Jones, D. B.; Bellm, S. M.; Blanco, F.; Fuss, Martina; Garci?a, G.; Lima?o-vieira, P.; Brunger, M. J.

2012-01-01

237

Theory of nuclear excitation by electron capture for heavy ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the resonant process of nuclear excitation by electron capture, in which a continuum electron is captured into a bound state of an ion with the simultaneous excitation of the nucleus. In order to derive the cross section a Feshbach projection operator formalism is introduced. Nuclear states and transitions are described by a nuclear collective model and making use of experimental data. Transition rates and total cross sections for NEEC followed by the radiativ...

Pa?lffy, Adriana; Harman, Zolta?n; Scheid, Werner

2007-01-01

238

Computer simulation of electron transfer in molecular electronic devices  

Energy Technology Data Exchange (ETDEWEB)

The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other, they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-bis((2'-para-mercaptophenyl)-ethinyl)-anthracene] and an asymmetric [1,4-bis((2'-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene] molecule bound to metal electrodes. Specifically addressed are the effects of voltage inversion on electron transfer between electrodes through both molecules. Our results show an electron transfer behaviour that reproduces the spatial symmetry of the molecules in agreement with experimental current-voltage data. The change in time of electron density and dimerisation at specific atomic sites is also discussed.

Correia, Helena M.G. [Departamento de Fisica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Ramos, Marta M.D. [Departamento de Fisica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal)]. E-mail: marta@fisica.uminho.pt

2005-12-15

239

Study of quasi one electron systems: excitation of the active electron to its first excited state  

International Nuclear Information System (INIS)

Experimental angular differential cross sections (ADCS) of four Quasi-One-Electron (QOE) scattering systems (Li+, Na+ + H, and Be+, Mg+ + He) are reported. These ADCS are determined for exciting the active electron to its first excited state. The angular range of the ACS is from 0 to ?3 mrad/sub lab/ with an angular resolution of ?120 ?rad/sub lab/. The energy range is from 19.4 to 150 keV with an energy-loss resolution of ?1 eV. The ADCS are compared to the available theories. The agreement between experiment and theory ranges from very poor to fair. No experiments exist which allow direct comparison to the present results. Integration of the present ADCS gives results which are compared to the experimental and theoretical total He targets cross section results. The agreement changes from energy to energy. Theoretical total cross section results exist in the cases involving H targets are in very poor to fair agreement with the present results. No experimental total cross sections exist in the H target case for comparison with the present results. The most striking feature occurs in the Na+ + H ADCS. Here the value of the ADCS at zero angle changes by 2 1/2 orders of magnitude from (3.96 +/- 2.00) x 10-15 cm2/sr at 35.9 keV (v = 1/4 a.u.) to (1.03 +/- 0.25) x 10-12 cm2/sr at 143.8 keV (v = 1/2 a.u.)

240

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

 
 
 
 
241

Computing electronic structures: A new multiconfiguration approach for excited states  

International Nuclear Information System (INIS)

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

242

Theory of nuclear excitation by electron capture for heavy ions  

CERN Document Server

We investigate the resonant process of nuclear excitation by electron capture, in which a continuum electron is captured into a bound state of an ion with the simultaneous excitation of the nucleus. In order to derive the cross section a Feshbach projection operator formalism is introduced. Nuclear states and transitions are described by a nuclear collective model and making use of experimental data. Transition rates and total cross sections for NEEC followed by the radiative decay of the excited nucleus are calculated for various heavy ion collision systems.

P'alffy, A; Scheid, W; P\\'alffy, Adriana; Harman, Zolt\\'an; Scheid, Werner

2006-01-01

243

Theory of nuclear excitation by electron capture for heavy ions  

International Nuclear Information System (INIS)

We investigate the resonant process of nuclear excitation by electron capture (NEEC), in which a continuum electron is captured into a bound state of an ion with the simultaneous excitation of the nucleus. In order to derive the cross section a Feshbach projection operator formalism is introduced. Nuclear states and transitions are described by a nuclear collective model and making use of experimental data. Transition rates and total cross sections for NEEC followed by the radiative decay of the excited nucleus are calculated for various heavy-ion collision systems

244

Single-centred calculations of excitation and electron removal in intermediate energy proton-hydrogen collisions  

International Nuclear Information System (INIS)

Single-centred expansion coupled states calculations are performed with basis sets large enough to achieve convergence. The particular collision system studied is p + H(1s) at energies of 15 keV and above. The results obtained establish the validity of this method for calculating excitation and electron removal cross sections even in situations where charge transfer is large. Cross sections for 1s ? 2l', 3l' and 4l' excitation and for electron removal are presented and compared to experiment and to other theoretical calculations. (author)

245

Electronic excitation in moderate-energy Li+-N2 and Li+-CO collisions  

Science.gov (United States)

By means of differential energy-transfer measurements, electronic excitation in Li+-N2 and Li+-CO collisions has been studied at the laboratory collision energies of 70~3 keV deg. An electronically inelastic peak in the spectra observed at lower collision energies is assigned to the 1?g<--X 1?+g transition of the N2 molecules. Analysis of the energy-transfer spectra suggests that anisotropy of the repulsive potential for the excited Li+-N2 (a 1?g) state is almost the same as that for the ground state. Predominant electronic excitation in the Li+-CO collisions is attributed to the 1X 1?+ transition of the CO molecules. The excitation signal begins to appear site specifically at Elab?~=2.1 and 4.2 keV deg in the collisions on the C-atom and O-atom sides, respectively. Regarding the specific molecular orientations ?=0° and 180° (linear configuration) at impact, electronic excitation takes place in the regions of the intermolecular distances R<=1.32 Å for the Li+-N2 collisions, and R<=1.47 and 1.22 Å for the Li+-CO collisions on the C-atom and O-atom sides, respectively. These critical distances, which correspond to the potential crossing points, can be adequately explained by assuming the binary ion-atom interactions.

Kita, S.; Tanuma, H.; Kusunoki, I.; Sato, Y.; Shimakura, N.

1990-07-01

246

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

247

Electron-pair excitations and the molecular Coulomb continuum  

Energy Technology Data Exchange (ETDEWEB)

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

Colgan, James [Los Alamos National Laboratory

2009-01-01

248

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

249

Nonlinear excitation of electron-acoustic waves  

International Nuclear Information System (INIS)

It is shown that for a plasma with ion temperature greater than electron temperature, an extraordinary electro-magnetic pump wave can parametrically decay into upper-hybrid and electron-acoustic oscillations. The threshold power flux and the growth rate of the instability are obtained. Comparison is made with earlier work and its possible application to a mirror machine is pointed out. (author)

250

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

Science.gov (United States)

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

Bricker, William P; Lo, Cynthia S

2014-08-01

251

Mechanism of electron transfer processes photoinduced by lumazine.  

Science.gov (United States)

UV-A (320-400 nm) and UV-B (280-320 nm) radiation causes damage to DNA and other biomolecules through reactions induced by different endogenous or exogenous photosensitizers. Lumazines are heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. The parent and unsubstituted compound called lumazine (pteridine-2,4(1,3H)-dione; Lum) is able to act as photosensitizer through electron transfer-initiated oxidations. To get further insight into the mechanisms involved, we have studied in detail the oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) photosensitized by Lum in aqueous solution. After UV-A or UV-B excitation of Lum and formation of its triplet excited state ((3)Lum*), three reaction pathways compete for the deactivation of the latter: intersystem crossing to singlet ground state, energy transfer to O(2), and electron transfer between dAMP and (3)Lum* yielding the corresponding pair of radical ions (Lum?(-) and dAMP?(+)). In the following step, the electron transfer from Lum?(-) to O(2) regenerates Lum and forms the superoxide anion (O(2)?(-)), which undergoes disproportionation into H(2)O(2) and O(2). Finally dAMP?(+) participates in subsequent reactions to yield products. PMID:22212735

Denofrio, M Paula; Dántola, M Laura; Vicendo, Patricia; Oliveros, Esther; Thomas, Andrés H; Lorente, Carolina

2012-02-01

252

Structure and Excitation Transfer Pathways in the Chlorophyll-Carotenoid Aggregate of the Photosynthetic Unit of Purple Bacteria  

Science.gov (United States)

The absorption of light by light harvesting complexes and transfer of electronic excitation to the photosynthetic reaction center (RC) has been investigated on the basis of an atomic level model of the so-called photosynthetic unit of the photosynthetic bacterium Rb. sphaeroides. The photosynthetic unit combines in the intracytoplasmic membrane a nanometric (20-100 nm) assembly of three protein complexes: (i) the photosynthetic reaction center, (ii) a ring-shaped light harvesting complex LH-I, and (iii) multiple copies of a similar complex, LH-II. The unit has been modeled using the known structure of LH-II of Rs. molischianum. The lecture describes in detail the organization of chromophores involved in primary light absorption and excitation transfer: a hierarchy of ring-shaped chlorophyl aggregates with attached carotenoids. A quantum-mechanical description of the entire light harvesting process is developed employing electron structure calculations of individual and aggregated chlorophylls and carotenoids and associated effective Hamiltonian descriptions. The transfer times calculated, ranging between 100 fs and 100 ps for various processes, are found in close agreement with measured transfer rates. The results suggest that excitons are the key carriers of the excitation transfered. The photoprotection of chlorophylls by chlorophylls through triplet excitation transfer is also described.

Schulten, Klaus

1998-03-01

253

How proteins trigger excitation energy transfer in the FMO complex of green sulfur bacteria.  

Science.gov (United States)

A simple electrostatic method for the calculation of optical transition energies of pigments in protein environments is presented and applied to the Fenna-Matthews-Olson (FMO) complex of Prosthecochloris aestuarii and Chlorobium tepidum. The method, for the first time, allows us to reach agreement between experimental optical spectra and calculations based on transition energies of pigments that are calculated in large part independently, rather than fitted to the spectra. In this way it becomes possible to understand the molecular mechanism allowing the protein to trigger excitation energy transfer reactions. The relative shift in excitation energies of the seven bacteriochlorophyll-a pigments of the FMO complex of P. aestuarii and C. tepidum are obtained from calculations of electrochromic shifts due to charged amino acids, assuming a standard protonation pattern of the protein, and by taking into account the three different ligand types of the pigments. The calculations provide an explanation of some of the earlier results for the transition energies obtained from fits of optical spectra. In addition, those earlier fits are verified here by using a more advanced theory of optical spectra, a genetic algorithm, and excitonic couplings obtained from electrostatic calculations that take into account the influence of the dielectric protein environment. The two independent calculations of site energies strongly favor one of the two possible orientations of the FMO trimer relative to the photosynthetic membrane, which were identified by electron microscopic studies and linear dichroism experiments. Efficient transfer of excitation energy to the reaction center requires bacteriochlorophylls 3 and 4 to be the linker pigments. The temporal and spatial transfer of excitation energy through the FMO complex is calculated to proceed along two branches, with transfer times that differ by an order of magnitude. PMID:16861264

Adolphs, Julia; Renger, Thomas

2006-10-15

254

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-04-01

255

Electron-impact excitation of ions  

International Nuclear Information System (INIS)

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

256

Electron-impact excitation of ions  

Energy Technology Data Exchange (ETDEWEB)

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

Crandall, D.H.

1981-01-01

257

Hierarchical control of electron-transfer  

DEFF Research Database (Denmark)

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

Jensen, Peter Ruhdal

1997-01-01

258

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

International Nuclear Information System (INIS)

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

259

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

260

Ultrafast electron diffraction studies of optically excited thin bismuth films  

Energy Technology Data Exchange (ETDEWEB)

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

Rajkovic, Ivan

2008-10-21

 
 
 
 
261

Photophysical and electron transfer studies of a stable carbocation  

Science.gov (United States)

Photophysical and electron transfer properties of the stable trioxatriangulenium carbocation ( 1) are reported. Photophysical studies include absorption, fluorescence and phosphorescence spectra, singlet and triplet state quantum yields and lifetimes. Both the singlet and triplet excited states of 1 can accept an electron from donor molecules leading to the formation of the donor radical cation and the radical of 1. In aqueous solution, 1 can photo-oxidize DNA nucleosides such as guanosine and adenosine indicating that 1 may have potential use as a DNA cleaving agent.

Dileesh, S.; Gopidas, K. R.

2000-11-01

262

Vibrational coherence in electron transfer: The tetracyanoethylene-pyrene complex  

Science.gov (United States)

Coherent vibrational wave packet motion is created in the excited charge-transfer state of the electron donor-acceptor complex between tetracyanoethylene (TCNE) and pyrene by an ultrashort (40 fs) 810 nm pump pulse. Observations of the dynamics of the TCNE-anion transient absorption and the disappearance of the bleach of the ground state absorption show that the electron-transfer reaction back to the ground state of the complex occurs on a 250 fs-1.5 ps time scale. The bleach recovery signal shows clear oscillations and both impulsive stimulated Raman scattering in the ground state and coherent repopulation of the ground state surface due to a vibrationally coherent electron transfer reaction were considered as the cause. Vibrational coherence has also been monitored by observing quantum beats in the stimulated emission from the charge transfer state back to the ground state in the near-ir. This observation strongly suggests that the electron transfer reaction is indeed vibrationally coherent and that the reaction rate is modulated by this coherence. This interpretation is corroborated by a classical Monte Carlo simulation of vibrationally coherent reactions in the inverted regime.

Wynne, Klaas; Reid, Gavin D.; Hochstrasser, Robin M.

1996-08-01

263

Auger-assisted electron transfer from photoexcited semiconductor quantum dots.  

Science.gov (United States)

Although quantum confined nanomaterials, such as quantum dots (QDs) have emerged as a new class of light harvesting and charge separation materials for solar energy conversion, theoretical models for describing photoinduced charge transfer from these materials remain unclear. In this paper, we show that the rate of photoinduced electron transfer from QDs (CdS, CdSe, and CdTe) to molecular acceptors (anthraquinone, methylviologen, and methylene blue) increases at decreasing QD size (and increasing driving force), showing a lack of Marcus inverted regime behavior over an apparent driving force range of ?0-1.3 V. We account for this unusual driving force dependence by proposing an Auger-assisted electron transfer model in which the transfer of the electron can be coupled to the excitation of the hole, circumventing the unfavorable Franck-Condon overlap in the Marcus inverted regime. This model is supported by computational studies of electron transfer and trapping processes in model QD-acceptor complexes. PMID:24359156

Zhu, Haiming; Yang, Ye; Hyeon-Deuk, Kim; Califano, Marco; Song, Nianhui; Wang, Youwei; Zhang, Wenqing; Prezhdo, Oleg V; Lian, Tianquan

2014-03-12

264

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

265

Coherent versus incoherent excitation energy transfer in molecular systems  

Science.gov (United States)

We investigate the Markovian limit of a polaronic quantum master equation for coherent resonance energy transfer proposed recently by Jang et al. [J. Chem. Phys. 129, 101104 (2008), 10.1063/1.2977974]. An expression for the rate of excitation energy transfer (EET) is derived and shown to exhibit both coherent and incoherent contributions. We then apply this theory to calculated EET rates for model dimer systems, and demonstrate that the small-polaron approach predicts a variety of dynamical behaviors. Notably, the results indicate that the EET dynamical behaviors can be understood by the interplay between noise-assisted EET and dynamical localization, while both are well captured by the polaron theory. Finally, we investigate bath correlation effects on the rate of EET and show that bath correlations (or anti-correlations) can either enhance or suppress EET rate depending on the strength of individual system-bath couplings. In summary, we introduce the small-polaron approach as an intuitive physical framework to consolidate our understanding of EET dynamics in the condensed phase.

Chang, Hung-Tzu; Cheng, Yuan-Chung

2012-10-01

266

Excitation energy transfer in covalently bonded porphyrin heterodimers  

Science.gov (United States)

We describe the photophysical properties of heterodimers that are formed by the free base 2-(2-carboxyvinyl)-5,10,15,20-tetraphenylporphyrin and the zinc complex of 5-( p-aminophenyl)-10,15,20-triphenylporphyrin and that are covalently bonded by the amide link. These dimers differ in the configuration of the double bond in the spacer group. We determine fluorescence quantum yields of heterodimers and their porphyrin components. The energy transfer rate constants have been estimated from the measured fluorescence lifetimes and fluorescence excitation spectra and, also, they have been calculated from the steady-state absorption and fluorescence spectra according to the Förster theory. We have found that the efficiency of the intramolecular energy transfer in heterodimers is 0.97-0.99, and the energy migration rate constants have been found to be (1.82-4.49) × 1010 s-1. The results of our investigation show that synthesized heterodimers can be used as efficient light-harvesting elements in solar energy conversion devices.

Paschenko, V. Z.; Konovalova, N. V.; Bagdashkin, A. L.; Gorokhov, V. V.; Tusov, V. B.; Yuzhakov, V. I.

2012-04-01

267

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

268

Electron-hydrogen excitation in the presence of laser field  

International Nuclear Information System (INIS)

The excitation of hydrogen atom in the presence of a non-resonant laser field with the transfer of 0, 1 and 2 photons between the field and the atomic system is considered by using the second order space translation method to study the modification of the target wave function by the laser field. (author). 15 re fs., 6 figs

269

Electron impact excitation cross sections of N2  

Science.gov (United States)

Differential cross sections (DCSs) are presented for electron impact excitation of the C3?u, E3?+g, and a'' 1?+g states in N2 from the ground state. Vibrationally-resolved DCSs are also presented for excitation of the C 3?? (?') state, where ?' = 0-4. The DCSs were obtained from measurements of energy-loss spectra in the region of 10.75 eV to 12.75 eV measured at numerous incident energies between 13 eV and 100 eV, and for scattering angles ranging from 5° to 130°. Relative excitation probabilities for the vibrational levels of the C 3?u state are shown to demonstrate non-Franck-Condon behavior for excitation energies less than approximately 50 eV. Integral cross sections are also presented for these excitation processes. These results are compared with existing measurements.

Malone, C. P.; Johnson, P. V.; Young, J. A.; Kanik, I.; Ajdari, B.; Khakoo, M. A.

2009-11-01

270

Review of biorthogonal coupled cluster representations for electronic excitation  

CERN Document Server

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

Schirmer, J

2009-01-01

271

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

272

Charge transfer and electron emission in ion-surface interactions  

International Nuclear Information System (INIS)

The formation and decay of multiply excited projectiles during collisions of slow highly charged ions with metal and insulator surfaces have been simulated based on a classical over-barrier model. Simulations including the full trajectory of the projectile have recently allowed the simultaneous evaluation of projectile kinetic energy gains, final charge-state distributions and emitted Auger electron yields in reasonable agreement with experiments. Due to the many-electron nature of these interactions, no detailed quantum mechanical calculations are available. In contrast, for low charge states of the incident ion, quantum mechanical close-coupling calculations have been performed that provide detailed information on resonance formation, hybridization, and electron transfer, including the effects of external electric fields. In this paper, some aspects of ion-surface collisions are reviewed within both (many-electron) over-barrier models and quantum mechanical single-electron expansion methods

273

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

Science.gov (United States)

Resonant vibrational excitation cross sections and the corresponding rate coefficients for electron-N2 collisions occurring through the N_2^-(X\\,{}^2\\Pi_g) resonant state are reviewed. New calculations are performed using accurate potential energy curves for the N2 electronic ground state, taken from the literature, and for the N_2^- resonant state, obtained from R-matrix calculations. The calculations are extended to resonant excitation processes involving the N2 ground state vibrational continuum, leading to dissociation. Electron-impact dissociation is found to be significant from higher vibrational levels. Accurate analytical fits for the complete set of the rate coefficients are provided. The behavior of the dissociative cross sections is investigated for rotationally excited N2 molecules, with J = 50, 100 and 150, and for different vibrational levels.

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

2014-12-01

274

Resonant Raman scattering by elementary electronic excitations in semiconductor structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We explain quantitatively why resonant Raman scattering spectroscopy, an extensively used experimental tool in studying elementary electronic excitations in doped low dimensional semiconductor nanostructures, always produces an observable peak at the so-called "single particle" excitation although the standard theory predicts that there should be no such single particle peak in the Raman spectra. We have thus resolved an experimental puzzle which dates back more than twenty-...

Sarma, S. Das; Wang, Daw-wei

1999-01-01

275

Excited Spectator Electron Effects on Spectral Line Shapes  

Energy Technology Data Exchange (ETDEWEB)

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

Iglesias, C A

2009-10-12

276

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

277

Electron transfer induced fragmentation of acetic acid  

Science.gov (United States)

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

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

2014-04-01

278

Excited state proton transfer of pyranine in octadecylamine Langmuir Blodgett films of different structures  

Science.gov (United States)

The structure and orientation of pyranine-adsorbed octadecylamine (ODA) LB films were investigated by several spectroscopic methods (UV-vis and fluorescence) and X-ray diffraction. Depending on preparation manners (deposition of a mixed monolayer of ODA and pyranine at the air/water interface or immersion of ODA LB films into a pyranine solution), pyranine-adsorbed films, respectively, exhibit unique structures and photo-excited relaxation processes. The excited state proton transfer (ESPT) in the pyranine-adsorbed ODA LB films was investigated by measurement of fluorescence lifetimes. From the results, the effect of ?- ? stacking interaction upon the ESPT in the LB films is considered to be similar to the one of the electron-withdrawing substitute in the bulk solution.

Tsukamoto, Osamu; Villeneuve, Masumi; Sakamoto, Akira; Nakahara, Hiroo

2008-03-01

279

LETTER TO THE EDITOR: Experimental evidence of transfer excitation in Ar6+-He collisions  

Science.gov (United States)

High-resolution cold-target recoil-ion momentum spectroscopy (COLTRIMS) has been used to study single-electron capture processes in collisions of Ar6+ ions with He at an impact energy of 9 keV and scattering angles between 0 and 3 mrad. The energy-gain spectra show that the capture occurs mainly into the 4s state with a significant contribution involving capture into the 4p state. Reaction channels associated with transfer excitation into the 3s3p3d states of Ar5+ are also observed for the first time, accounting for 6(±0.4)% of the total cross sections for single-electron capture. Experimental results are found to be in good agreement with the two-electron atomic orbital close-coupling calculations.

Kamber, E. Y.; Abdallah, M. A.; Cocke, C. L.; Stöckli, M.; Wang, J.; Hansen, J. P.

2000-03-01

280

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

 
 
 
 
281

Photon-induced electron transfer transitions of the solvated electrons  

Energy Technology Data Exchange (ETDEWEB)

The role of electron transfer transitions in the absorption spectrum of the solvated electron in liquid water is studied in terms of the generalized line shape function. When the density of trapping sites is greater than one third of the density of solvent molecules, the transition-dipole moment for photon-induced electron transfers was found to be greater than that of the single-site 1s..-->..2p transition. The solvated electron is assumed to be coupled with low-frequency solvent modes and a high-frequency molecular mode. The latter mode is responsible for a small isotope shift in the peak energy. The spectrum consists of contributions from short-distance transfers (''bound--bound'') and long-distance (''bound--free'') transfers, the latter being the minor component of the total spectrum.

Funabashi, K.; Carmichael, I.; Hamill, W.H.

1978-09-15

282

Magnetic resonance studies of photo-induced electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

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

van Willigen, H.

1992-11-01

283

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

284

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

International Nuclear Information System (INIS)

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

285

Structural Phase Transition of Aluminum Induced by Electronic Excitation  

International Nuclear Information System (INIS)

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

286

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

International Nuclear Information System (INIS)

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

287

Collective modes of laser excited electrons in clusters  

International Nuclear Information System (INIS)

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

288

Intramolecular electron transfer in bipyridinium disulfides.  

Science.gov (United States)

Reductive cleavage of disulfide bonds is an important step in many biological and chemical processes. Whether cleavage occurs stepwise or concertedly with electron transfer is of interest. Also of interest is whether the disulfide bond is reduced directly by intermolecular electron transfer from an external reducing agent or mediated intramolecularly by internal electron transfer from another redox-active moiety elsewhere within the molecule. The electrochemical reductions of 4,4'-bipyridyl-3,3'-disulfide (1) and the di-N-methylated derivative (2(2+)) have been studied in acetonitrile. Simulations of the cyclic voltammograms in combination with DFT (density functional theory) computations provide a consistent model of the reductive processes. Compound 1 undergoes reduction directly at the disulfide moiety with a substantially more negative potential for the first electron than for the second electron, resulting in an overall two-electron reduction and rapid cleavage of the S-S bond to form the dithiolate. In contrast, compound 2(2+) is reduced at less negative potential than 1 and at the dimethyl bipyridinium moiety rather than at the disulfide moiety. Most interesting, the second reduction of the bipyridinium moiety results in a fast and reversible intramolecular two-electron transfer to reduce the disulfide moiety and form the dithiolate. Thus, the redox-active bipyridinium moiety provides a low energy pathway for reductive cleavage of the S-S bond that avoids the highly negative potential for the first direct electron reduction. Following the intramolecular two-electron transfer and cleavage of the S-S bond the bipyridinium undergoes two additional reversible reductions at more negative potentials. PMID:24528295

Hall, Gabriel B; Kottani, Rudresha; Felton, Greg A N; Yamamoto, Takuhei; Evans, Dennis H; Glass, Richard S; Lichtenberger, Dennis L

2014-03-12

289

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

290

Ultrafast Interatomic Electronic Decay in Multiply Excited Clusters  

International Nuclear Information System (INIS)

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.

291

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

292

Electron-impact excitation in upper-atmosphere remote sensing  

International Nuclear Information System (INIS)

Full text: Electron-impact excitation plays a major role in emission from aurora and a minor role in the dayglow and nightglow. For some molecules, such as nitrogen and nitric oxide, electron-impact excitation can be followed by a radiative cascade through many different sets of energy levels, producing emission spectra with a large number of lines. We are investigating whether parts of this rich spectrum can be exploited for remote sensing of the atmosphere. We report on the ongoing development of a computer program which predicts the emission spectrum for nitrogen and nitric oxide in aurora and the ionosphere. This program includes the necessary atomic and molecular data such as electron-impact cross sections, Franck Condon factors, energy levels, transition probabilities, quenching rates and predissociation rates, as well as atmospheric data. The program performs a statistical equilibrium calculation to predict the spectrum of the radiation resulting from electron-impact excitation. We present sample results from this program and compare them against available measurements. The prospects for remote sensing by measurement of the spectrum of radiation resulting from electron-impact excitation are assessed

293

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

294

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

295

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1991-12-01

296

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

297

Direct conversion of graphite into diamond through electronic excited states  

International Nuclear Information System (INIS)

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

298

Minimal-excitation states for electron quantum optics using levitons  

Science.gov (United States)

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

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

2013-10-01

299

P nonconservation in nuclear excitation in the electron bremsstrahlung  

International Nuclear Information System (INIS)

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

300

Excited State Electronic Properties of Sodium Iodide and Cesium Iodide  

Energy Technology Data Exchange (ETDEWEB)

We compute from first principles the dielectric function, loss function, lifetime and scattering rate of quasiparticles due to electronic losses, and secondary particle spectrum due to plasmon decay in two scintillating alkali halides, sodium iodide and cesium iodide. Particular emphasis is placed on quasiparticles within several multiples of the band gap from the band edges. A theory for the decay spectra of plasmons and other electronic excitations in crystals is presented. Applications to Monte Carlo radiation transport codes are discussed.

Campbell, Luke W.; Gao, Fei

2013-05-01

 
 
 
 
301

Tuning ground states and excitations in complex electronic materials  

Energy Technology Data Exchange (ETDEWEB)

Modern electronic materials are characterized by a great variety of broken-symmetry ground states and excitations. Their control requires understanding and tuning underlying driving forces of spin-charge-lattice coupling, critical to macroscopic properties and applications. We report representative model calculations which demonstrate some of the richness of the phenomena and the challenges for successful microscopic modeling.

Bishop, A.R.

1996-09-01

302

Investigations of ultrafast dynamics in electronically excited alkylbenzenes  

Directory of Open Access Journals (Sweden)

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

Maksyutenko P.

2013-03-01

303

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

Science.gov (United States)

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

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

2009-03-14

304

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)

305

Electron excitation after plasmon decay in proton-aluminum collisions  

International Nuclear Information System (INIS)

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

306

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

307

Energy and electron transfer processes in polymethine dyes  

International Nuclear Information System (INIS)

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

308

Electron transfer in weakly interacting systems  

International Nuclear Information System (INIS)

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

309

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

International Nuclear Information System (INIS)

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

310

Cycloreversion of ?-lactams via photoinduced electron transfer.  

Science.gov (United States)

The radical anions of ?-lactams, photogenerated in the presence of DABCO as an electron donor, undergo cycloreversion via N-C4 bond cleavage, back electron transfer and final C2-C3 bond cleavage, leading to olefins. The involved intermediates are 1,4-radical anions and 1,4-biradicals. The experimental observations are consistent with the results of DFT calculations. PMID:25223340

Pérez-Ruiz, Raúl; Sáez, Jose A; Jiménez, M Consuelo; Miranda, Miguel A

2014-10-01

311

Electron excited M-region resonant x-ray excitation spectra from cerium and oxidized cerium  

International Nuclear Information System (INIS)

Electron excited M-region x-ray resonances in cerium and cerium oxide were investigated with an instrument which permits simultaneous recording of x-ray emissions and electron spectra from samples prepared in an ultrahigh vacuum. X-ray intensities were recorded as a function of incident electron energy from 850 to 930 eV. This range encompasses the binding energies of the M5 and M4 shell electrons in cerium and the associated x-ray continuum resonances. The x-ray excitation spectra obtained in this study show large resonances for incident electron energies near the M5 and M4 shell ionization energies, but the electron spectra show no corresponding features. The spectra of resonant x rays from cerium oxide show almost no ''chemical shift'' relative to those from the pure metal but exhibit large increases in the intensity of the resonances. No explanation as to why the oxidized sample x-ray yields are higher is offered. An estimate of the maximum x-ray photon yield per incident electron for cerium and cerium oxide via the resonance effect is 2x10-6 (M5 ) and 9x10-7 (M4 ) for cerium and 6x10-6 (M5 ) and 4x10-6 (M4 ) for cerium oxide

312

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-03-01

313

Low energy excitations in the low-carrier heavy-electron system Yb4As3  

International Nuclear Information System (INIS)

Detailed inelastic neutron scattering studies on the low-carrier heavy-electron system Yb4As3 reveals that the magnetic response from this material for the energy transfer above about 0.3 meV is due to the spin excitations in the one-dimensional Yb3+ chains caused by the charge ordering. The energy scale of the heavy-electron anomaly in the transport property of Yb4As3 must be very small, if its response is significant compared to that of the spin excitations. Inelastic neutron scattering from a polycrystalline sample of Yb4 (As0.6P0.4)3 suggests that the similar phenomenon seems to occur in this semi-conducting mixed compound which shows similar heavy-electron-like behaviours of susceptibility and specific heat. (author)

314

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

315

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

316

The DIET from semiconductor surfaces by excitation of valence electrons  

Science.gov (United States)

We discuss the desorption induced by electronic transitions (DIET) of constituent atoms from several types of non-metallic solids, particularly the DIET from semiconductors by valence electron excitations. We first classify the non-metallic solids into type A, in which no self-trapping of excitons occurs, and type B, in which self-trapping occurs. We argue that in type B solids the localization of electron-hole pairs or excitons through the self-trapping on the surfaces induces the Menzel-Gomer-Redhead-type anti-bonding state resulting in DIET. For the DIET from type A non-metals, typically semiconductors, in which the self-trapping is not induced, we derive two important characteristics: (1) the emission is related to defects on the surfaces and (2) single electronic excitation cannot induce the emissions. The recent experimental observations of laser-induced emissions satisfying these characteristics for the DIET from semiconductors are surveyed. Furthermore we present experimental evidence demonstrating that the observed emissions are of the electronic origin: the emission occurs dominantly when the excitation is localized on the surface. Finally, surface phenomena, such as laser ablation and dry etching, related to the DIET from semiconductors, and the applications of the DIET from semiconductors are discussed.

Kanasaki, Jun'ichi; Okano, Akiko; Ishikawa, Ken'ichi; Nakai, Yasuo; Itoh, Noriaki

1995-06-01

317

Computational study of the electronic excitations of some anthocyanidins  

Science.gov (United States)

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

Pereira, Grace K.; Galembeck, Sérgio E.

1998-02-01

318

Competition between radiative recombination and nuclear excitation by electron capture  

International Nuclear Information System (INIS)

The process of electron recombination is investigated considering the possible resonant channel of nuclear excitation by electron capture (NEEC), in which a continuum electron is captured into a bound state of an ion with the simultaneous excitation of the nucleus. Transition rates and total cross sections for NEEC followed by the radiative decay of the nucleus are presented for various heavy-ion collision systems. The role played by radiative recombination (RR) in the NEEC recombination mechanism is investigated and theoretical estimates of the magnitude of the interference between the two processes are presented. We discuss the experimental possibility of discerning NEEC from the RR background, studying the angular distribution of the radiation emitted in the two processes

319

Electron dynamics and intermolecular energy transfer in aqueous solutions studied by X-ray electron spectroscopy  

Science.gov (United States)

X-ray photoelectron spectroscopy measurements from a vacuum liquid microjet are performed to investigate the electronic structure of aqueous solutions. Here, focus is on the excited-state dynamics of chloride and hydroxide anions in water, following core-level excitation. A series of Cl^-(aq) charge-transfer-to-solvent (CTTS) states, and their ultrafast relaxation, on the time scale of the core hole, is identified from the occurrence of spectator Auger decay. Resonant oxygen 1s excitation of aqueous hydroxide, in contrast, leads to non-local decay, involving energy transfer into a neighboring water molecule. This channel is argued to arise from the weak hydrogen donor bond of OH^-(aq), and thus identifies a special transient hydration configuration, which can explain hydroxide's unusual and fast transport in water. Analogous measurements from pure water point to a similar relaxation channel, which is concluded from a strong isotope effect. The characteristic resonance spectral features are considerably stronger for H2O(aq) than for D2O(aq). As for OH^-(aq) the results can be understood in terms of energy transfer from the excited water molecule to a neighbor water molecule.

Winter, Bernd

2009-03-01

320

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

 
 
 
 
321

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.)

322

75 FR 51707 - Electronic Funds Transfer of Depository Taxes  

Science.gov (United States)

...impact on small business. Comments...copies) or electronic comments that...or place of business in the United...Deposits by electronic funds transfer...is made by electronic funds transfer by the next business day,...

2010-08-23

323

Itinerant Nature of Atom-Magnetization Excitation by Tunneling Electrons  

Science.gov (United States)

We have performed single-atom magnetization curve (SAMC) measurements and inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with 3.5?B being the mean value. ISTS reveals a magnetization excitation with a lifetime of 200 fsec which decreases by a factor of 2 upon application of a magnetic field of 12 T. The experimental observations are quantitatively explained by the decay of the magnetization excitation into Stoner modes of the itinerant electron system as shown by newly developed theoretical modeling.

Khajetoorians, A. A.; Lounis, S.; Chilian, B.; Costa, A. T.; Zhou, L.; Mills, D. L.; Wiebe, J.; Wiesendanger, R.

2011-01-01

324

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

325

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1990-10-20

326

A Study Looking the Electronic Funds Transfer  

Directory of Open Access Journals (Sweden)

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

Codruta POENAR

2008-01-01

327

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

328

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

Directory of Open Access Journals (Sweden)

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

Karen J. Brewer

2010-08-01

329

Electronic energy transfer in actinyl crystals  

International Nuclear Information System (INIS)

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

330

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-02-14

331

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

CERN Document Server

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

Abramavicius, Vytautas

2014-01-01

332

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

International Nuclear Information System (INIS)

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

333

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

Science.gov (United States)

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

Abramavicius, Vytautas; Abramavicius, Darius

2014-02-01

334

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

DEFF Research Database (Denmark)

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

MØller, SØren; Andersen, Kristine B.

1998-01-01

335

VUV spectroscopy and electronic excitations in nano-size alumina  

International Nuclear Information System (INIS)

Luminescence properties and electronic excitations of ?- and ?-phases of Al2O3 nano-powders, prepared by plasma processing technique, were studied using time-resolved luminescence spectroscopy under vacuum ultraviolet excitation. The fundamental absorption edge was found at 7.5 eV, which is 1.5 eV less than that of ?-Al2O3 in agreement with theoretical predictions for transition alumina. The broad-band emissions with maxima at 5.5 and 4.6 eV are assigned to radiative decay of the intrinsic excitations. Emission of transition metal impurities was found near 1.75 eV. The emission bands peaked at 3.1 and 2.6 eV are assigned to F+ and F centres, respectively.

336

Search for nuclear excitation by electronic transition in 235U  

International Nuclear Information System (INIS)

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

337

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.

Song, Peng; Nordlander, Peter; Gao, Shiwu

2011-02-01

338

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.

339

Luminescence spectral characteristics and excitation energy transfer in a POCl3-AlCl3-UO22+-Nd3+ solution  

International Nuclear Information System (INIS)

Nd3+ and UO22+ complexing and excitation energy transfer in the case of their mutual presence in mixed aproton solvent POCl3-AlCl3 are discussed taking into account data on electron absorption spectra, excitation spectra, luminescence and tautometry. It is established that in solutions POCl3-AlCl3-UO22+-Nd3+ luminescence of neodymium ions sensitized by uranyl ions is observed. And in this case sensitization coefficient turns to be higher than for solutions with other metal chlorides. It is connected with formation of more stable heterometallic complexes

340

Electronic excitation of ground state atoms by collision with heavy gas particles  

Science.gov (United States)

Most of the important chemical reactions which occur in the very high temperature air produced around space vehicles as they enter the atmosphere were investigated both experimentally and theoretically, to some extent at least. One remaining reaction about which little is known, and which could be quite important at the extremely high temperatures that will be produced by the class of space vehicles now contemplated - such as the AOTV - is the excitation of bound electron states due to collisions between heavy gas particles. Rates of electronic excitation due to free electron collisions are known to be very rapid, but because these collisions quickly equilibrate the free and bound electron energy, the approach to full equilibrium with the heavy particle kinetic energy will depend primarily on the much slower process of bound electron excitation in heavy particle collisions and the subsequent rapid transfer to free electron energy. This may be the dominant mechanism leading to full equilibrium in the gas once the dissociation process has depleted the molecular states so the transfer between molecular vibrational energy and free electron energy is no longer available as a channel for equilibration of free electron and heavy particle kinetic energies. Two mechanisms seem probable in electronic excitation by heavy particle impact. One of these is the collision excitation and deexcitation of higher electronic states which are Rydberg like. A report, entitled 'Semi-Classical Theory of Electronic Excitation Rates', was submitted previously. This presented analytic expressions for the transition probabilities, assuming that the interaction potential is an exponential repulsion with a perturbation ripple due to the dipole-induced dipole effect in the case of neutral-neutral collisions, and to the ion-dipole interaction in the case of ion-neutral collisions. However the above may be, there is little doubt that excitation of ground state species by collision occurs at the point where the initial and final potentials cross, or at least come very close. Therefore, this mechanism would be applicable to the case where a gas is initially at very low temperature suddenly subjected to high energy heavy particle bombardment. This situation would model the measurement of excitation cross section by molecular beam techniques, for example. The purpose is to report values of cross sections and rate coefficients for collision excitation of ground state atoms estimated with the Landau-Zener transition theory and to compare results with measurement of excitation cross sections for a beam of Hydrogen atoms impacting Argon atom targets. Some very dubious approximations are used, and the comparison with measurement is found less than ideal, but results are at least consistent within order of magnitude. The same model is then applied to the case of N-N atom collisions, even though the approximations then become even more doubtful. Still the rate coefficients obtained are at least plausible in both magnitude and functional form, and as far as I am aware these are the only estimates available for such rate coefficients.

Hansen, C. Frederick

1993-01-01

 
 
 
 
341

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

342

Vibrational relaxation pathways in the electronic excited state of carotenoid  

International Nuclear Information System (INIS)

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

343

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

344

Extremely confined gap surface-plasmon modes excited by electrons.  

Science.gov (United States)

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

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

2014-01-01

345

Extremely confined gap surface-plasmon modes excited by electrons.  

DEFF Research Database (Denmark)

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

Raza, SØren; Stenger, Nicolas

2014-01-01

346

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

347

Ru (bipy)/sub 2/ (Dipyridophenazine)/sup 2 +/: a complex with a long range directed charge transfer excited state  

Energy Technology Data Exchange (ETDEWEB)

Ru (bipy)/sub 2/ (dppz)/sup 2 +/ has been synthetized and studied; dppz (dipyridophenazine) consists of a bipy chelating subunit connected to a phenazine (pz) fragment, acting as an electron acceptor; electrochemical, optical and photophysical measurements show that the charge transfer excited state of Ru (bipy)/sub 2/ (dppz)/sup 2 +/ is directed from the ruthenium atom to the pz part of dppz.

Chambron, J.C.; Sauvage, J.P.; Amouyal, E.; Koffi, P. (Laboratoire de Chimie Organo-Minerale, U.A. 422 au C.N.R.S., Institut de Chimie, 67 - Strasbourg (France))

348

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

349

Electron densities and the excitation of CN in molecular clouds  

Science.gov (United States)

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

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

1991-01-01

350

The emission continuum of electron excited molecular hydrogen  

International Nuclear Information System (INIS)

Photo-excitation of hydrogen molecule from the X1?+g state to the B1?+u, C1?+u, and D1?u states and subsequent emission to the dissociation continuum is the primary destruction mechanism of H2 in interstellar clouds. The authors have recently calculated continuum emission profiles of B1?+u - X1?+g, C1?u - X1?+g, B' 1?+u - X1 ?+g, and D1?u - X1?+g transitions of H2. Synthetic spectra based on the calculated profiles are in excellent agreement with high-resolution electron-impact induced emission spectra obtained at 100 eV. An improved intensity calibration standard and dissociation yields of the Lyman and Werner continuua produced by both electron and photon impact excitation will be presented

351

High power electron beam accelerators for gas laser excitation  

International Nuclear Information System (INIS)

A preliminary parameter investigation has been used to determine a possible design of a high-power, relativistic electron beam, transversely excited laser. Based on considerations of present and developing pulsed power technology, broad area diode physics and projected laser requirements, an exciter is proposed consisting of a Marx generator, pulse shaping transmission lines, radially converging ring diodes and a laser chamber. The accelerator should be able to deliver approximately 20 kJ of electron energy at 1 MeV to the 104 cm2 cylindrical surface of a laser chamber 1 m long and 0.3 m in diameter in 24 ns with very small azimuthal asymmetry and uniform radial deposition

352

Electron-lattice Interaction and Nonlinear Excitations in Cuprate Structures  

International Nuclear Information System (INIS)

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

353

Local electron distributions and diffusion in anharmonic lattices mediated by thermally excited solitons  

Science.gov (United States)

We study the excitation of solitons in lattices with Morse interactions in a wide temperature range and their influence on (free) electrons moving in the lattice. The lattice units (considered as “atoms" or “screened ion cores") are treated by classical Langevin equations. For visualizations the densities of the core (valence) electrons are in a first estimate represented by Gaussian densities, thus permitting to visualize lattice compressions. The evolution of the (free) electrons is modelled in the tight binding approximation first using Schrödinger equation and, subsequently, a stochastic description of the evolution as a Markov process. We investigate electron transfer assisted by solitons and solitonic influences on macroscopic transport in particular on diffusion. Then we consider the electron-lattice interaction and obtain numerical solutions of the simultaneously evolving Langevin and Pauli master equations. We show that the proposed mechanism of riding on thermal solitons is relatively fast (of the order of the sound velocity).

Chetverikov, A. P.; Ebeling, W.; Velarde, M. G.

2009-07-01

354

A study of vibrational relaxation of electronically-excited molecules  

International Nuclear Information System (INIS)

The time kinetics of the vibrational relaxation of excimers is studied in the diffusional approximation. Simple formulae for functions of nonstationary vibrational distribution are found for the electronically excited molecules. Some spectral-kinetic dependencies of the excimer luminescence are explained in a new way. The possibilities of the determination of excimer parameters are discussed. The dependence of energetical characteristics of excimer lasers on these parameters is particularly emphasized. (author). 22 refs, 5 figs

355

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Ozansoy, A.; Billur, A. A.

2012-01-01

356

Photoinduced coupled twisted intramolecular charge transfer and excited-state proton transfer via intermolecular hydrogen bonding: A DFT/TD-DFT study  

Science.gov (United States)

We discuss theoretically the geometric and electronic structure properties of the thiazolidinedione derivative A and its hydrogen-bonded complex in dimethylformamide (DMF) solution in the S0 and S1 states. To gain insight into the photoinduced coupled excited-state proton transfer (ESPT) and twisted intramolecular charge transfer (TICT) associated with intermolecular hydrogen bonding, the potential energy profiles are provided along the Osbnd H bond and the twisted angle. It is predicted that TICT in S1 can facilitate ESPT initiated by intermolecular hydrogen-bond strengthening in the S1 state. The coupling of ESPT and TICT is energetically preferable.

Wang, Dandan; Lü, Rui; Yuan, Minghu; Chen, Junsheng; Feng, Liqiang; Fu, Aiping; Tian, Fenghui; Varandas, António J. C.; Chu, Tianshu

2014-08-01

357

Charge transfer excited state energies by perturbative delta self consistent field method  

Science.gov (United States)

We use our recently outlined perturbative approach to compute the lowest charge transfer excitation energies for a set of tetracynoehylene (TCNE)-hydrocarbon complexes, C2H4-C2F4, NH3-F2, pentacene-C60, and tetraphenyl porphyrin-C60 complexes. Results show that the method can provide a reliable description of charge transfer excitation energies, which are comparable to that obtained by time-dependent density functional theory using specially optimized range-corrected functionals. As the calculation cost of excited state is comparable to the ground state and the calculation of each excited state is independent of others, the method can be easily used to describe the charge transfer excited states of large donor-acceptor complexes containing 200 or more atoms.

Baruah, Tunna; Olguin, Marco; Zope, Rajendra R.

2012-08-01

358

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

359

Indistinguishability in electron-impact excitation-ionization of helium  

International Nuclear Information System (INIS)

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

360

Indistinguishability in electron-impact excitation-ionization of helium  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-11-15

 
 
 
 
361

Resonant excitation of plasma wakefields using multiple electron bunches  

International Nuclear Information System (INIS)

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

362

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

International Nuclear Information System (INIS)

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

363

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

364

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

International Nuclear Information System (INIS)

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

365

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

366

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

367

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

Science.gov (United States)

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

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

2014-04-01

368

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

369

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

International Nuclear Information System (INIS)

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

370

Polarisation effects in energy-transfer collisions between laser-excited atoms  

Energy Technology Data Exchange (ETDEWEB)

The analysis of energy-transfer collisions between laser-excited atoms in terms of rate constants for separate magnetic substates requires knowledge of the excited-state density matrix for each applied laser polarisation. We study the generalised rate equation for this density matrix. Then we describe the relation between the collision signals and the M-dependent collision amplitudes. The results are applied to our recent measurements of associative ionisation of laser-excited Na(3P) atoms.

Nienhuis, G. (Fysisch Laboratorium, Rijksuniversiteit Utrecht (Netherlands))

1985-01-01

371

Polarisation effects in energy-transfer collisions between laser-excited atoms  

International Nuclear Information System (INIS)

The analysis of energy-transfer collisions between laser-excited atoms in terms of rate constants for separate magnetic substates requires knowledge of the excited-state density matrix for each applied laser polarisation. We study the generalised rate equation for this density matrix. Then we describe the relation between the collision signals and the M-dependent collision amplitudes. The results are applied to our recent measurements of associative ionisation of laser-excited Na(3P) atoms

372

Motion-enhanced quantum entanglement in the dynamics of excitation transfer  

CERN Document Server

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

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

2014-01-01

373

Electron transfer theory revisit: Quantum solvation effect  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of solvation on the electron transfer (ET) rate processes is investigated on the basis of the exact theory constructed in J. Phys. Chem. B Vol. 110, (2006); quant-ph/0604071. The nature of solvation is studied in a close relation with the mechanism of ET processes. The resulting Kramers' turnover and Marcus' inversion characteristics are analyzed accordingly. The classical picture of solvation is found to be invalid when the solvent longitudinal relaxation time is...

Han, Ping; Xu, Rui-xue; Cui, Ping; Mo, Yan; He, Guozhong; Yan, Yijing

2006-01-01

374

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

Directory of Open Access Journals (Sweden)

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

João Batista Marques Novo

2011-01-01

375

Formation and quenching of NH fragments in excited states by high energy electron irradiation of helium-ammonia gas mixture  

International Nuclear Information System (INIS)

A gas mixture of helium and ammonia was irradiated with an electron beam from a Van de Graaff accelerator and emission intensities from excited NH fragments were measured as a function of pressure, concentration of ammonia, and the amounts of additives. The energy transfer process is discussed on the basis of the experimental results and kinetic analysis. (author)

376

Electron transfer control in soluble methane monooxygenase.  

Science.gov (United States)

The hydroxylation or epoxidation of hydrocarbons by bacterial multicomponent monooxygenases (BMMs) requires the interplay of three or four protein components. How component protein interactions control catalysis, however, is not well understood. In particular, the binding sites of the reductase components on the surface of their cognate hydroxylases and the role(s) that the regulatory proteins play during intermolecular electron transfer leading to the hydroxylase reduction have been enigmatic. Here we determine the reductase binding site on the hydroxylase of a BMM enzyme, soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath). We present evidence that the ferredoxin domain of the reductase binds to the canyon region of the hydroxylase, previously determined to be the regulatory protein binding site as well. The latter thus inhibits reductase binding to the hydroxylase and, consequently, intermolecular electron transfer from the reductase to the hydroxylase diiron active site. The binding competition between the regulatory protein and the reductase may serve as a control mechanism for regulating electron transfer, and other BMM enzymes are likely to adopt the same mechanism. PMID:24937475

Wang, Weixue; Iacob, Roxana E; Luoh, Rebecca P; Engen, John R; Lippard, Stephen J

2014-07-01

377

Isotope and substituent effects on the intramolecular proton transfer in the excited state of 6-(2-hydroxy-5-methylphenyl)-s-triazines  

International Nuclear Information System (INIS)

Isotope and substituent effects on the intramolecular proton transfer in the excited singlet state of the title compounds have been studied by means of picosecond and nanosecond time-resolved spectroscopy. The absolute rate constants k/sub PT/ for proton transfer were determined from the build up curve of the S/sub n/' ? S1' absorption to be 1.2 x 1010 s-1 [for (ON)/sub h/ and (ON)/sub d/] and 1.8 x 1010 s-1 for (NN)/sub h/ at 298 K. No isotope effect on proton transfer was observed, indicating that the intramolecular proton transfer in the excited state does not proceed via quantum mechanical tunneling but via a radiationless transition S1 ? S1' having no potential barrier. Substitution of electron-donating groups into the s-triazinyl moiety favors proton transfer in the excited state

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

Progress and challenges in the calculation of electronic excited states.  

Science.gov (United States)

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

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

2012-01-16

380

Monitoring molecule dynamics by free electron transfer  

International Nuclear Information System (INIS)

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

 
 
 
 
381

Critical binding of electron--dipole rotor systems; electronically excited states  

International Nuclear Information System (INIS)

Critical binding solutions for the electron--dipole rotor problem are extended to delineate the minimum dipole moments required to support the lowest two electronically excited dipole states. Such dipole states offer a source for threshold photodetachment resonances observed in recent studies involving polar anions

382

Electron spectra of autoionization states of strontium and calcium excited by low and intermediate energy electrons  

International Nuclear Information System (INIS)

The electron spectra of the auto-ionization states of strontium and calcium atoms are investigated by electron spectroscopy. Resonant excitation of auto ionization states and their subsequent multichannel decay are recoreed in the threshold collision energy region. The eneray dependences of the intensities for a number of spectrum lines are presented

383

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

Science.gov (United States)

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

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

2014-03-01

384

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

Science.gov (United States)

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: K1MnPc, K2MnPc, and K4MnPc. Furthermore, the addition of electrons first leads to a filling of orbitals with strong Mn 3d character, a situation which also affects the magnetic moment of the molecule.

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

2011-05-01

385

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

386

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

387

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

388

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

389

Optical and structural characterisation of low dimensional structures using electron beam excitation systems  

International Nuclear Information System (INIS)

This thesis presents studies on optical and structural characterisation of low dimensional structures that emit light within the visible region of the spectrum (ZnSe-based and GaN-based) using electron beam excitation systems. A guideline for theoretical design of strained and strain-free ZnCdSe/ZnSe quantum well (QW) structures with good carrier confinements has been provided. The emission energies of several QW structures have been estimated prior to the growth and are compared with the experimental results. The diffusion Monte Carlo technique that requires no trial wave function has been employed for the first time to calculate exciton binding energies in these structures. Characterisation of ZnCdSe/ZnSe single- and multi- QW structures by Cathodoluminescence (CL) and Photoluminescence (PL) techniques have revealed vertical carrier transport at low excitation energy and potential fluctuations and disorder in some structures. The temperature dependence of CL intensity of some ZnCdSe/ZnSe QW structures at low electron beam excitation energies have indicated a blue shift in emission energy with increasing temperature due to the presence of potential fluctuations. The luminescence thermal quenching process at high temperatures is found to be due to emission of carriers or excitons out of the confined QW states. The emitted carriers are subsequently captured by the wider neighbouring QW in good quality structures, in bad quality structures this carrier transfer is suppr structures this carrier transfer is suppressed by nonradiative recombination centres. The temperatures at which the QW luminescence starts to quench and the activation energies of luminescence quenching are found to depend on excitation conditions, sample quality and QW depth. The results of CL intensity dependence on the excitation intensity revealed that luminescence from good quality QW structures is dominated by radiative recombination processes even at high temperatures during thermal quenching. In contrast, in defected structures non-radiative recombination mechanisms dominate the luminescence properties at all temperatures. Secondary electron images of hexagonal growth hillocks of GaN obtained at a range of electron beam excitation energies vary because of the different signals involved in the imaging. Electron backscatter diffraction measurements have been used for phase identification and lattice constants determination in a strained GaN epilayer. (author)

390

Dissociative electron attachment and vibrational excitation of the chlorine molecule  

International Nuclear Information System (INIS)

This paper is aimed at the theoretical investigation of the inelastic processes taking place in resonant collisions of low-energy electrons with the chlorine molecule. Dissociative electron attachment and vibrational excitation of Cl2 by electron impact is investigated in the energy range 0-1.5 eV, where the 2?u+ resonance plays the central role. The calculations were carried out within the framework of the nonlocal resonance model. This approach makes it possible to calculate the integrated cross sections of the above-mentioned processes for a variety of initial and final rovibrational states of the target molecule. The present model is constructed on the basis of ab initio fixed-nuclei R-matrix calculations using the so-called Feshbach-Fano R-matrix method. The Schwinger-Lanczos algorithm was utilized to solve the Lippmann-Schwinger equation describing the motion of the nuclei

391

Dissociative attachment and vibrational excitation in low-energy electron collisions with chlorine molecules  

International Nuclear Information System (INIS)

In a combined experimental and theoretical effort, we have investigated dissociative attachment and vibrational excitation in low-energy electron collisions with chlorine molecules. Using the laser photoelectron attachment method, we have measured the energy dependence of the cross section ?DA(E) for dissociative electron attachment (Cl- formation) over the range 0 - 195 meV with an energy width of 1 - 3 meV and for Rydberg electron transfer at high principal quantum numbers (n>67). Near zero energy, the cross section shows a behaviour compatible with the threshold law for p-wave attachment via the 2?u+ resonance, reaches a maximum around 50 meV and declines towards higher energies. These findings are in good agreement with the results of semi-empirical R-matrix calculations. Measured rate coefficients knl for Cl- formation due to electron transfer from K**(nl) Rydberg atoms were found to be nearly constant for high principal quantum numbers (n>67) in contrast to the behaviour expected within the quasi-free electron model for p-wave attachment. The R-matrix calculations are extended to describe electron attachment through the 2?g and 2?u resonances, and recommended absolute cross sections for dissociative attachment to chlorine molecules at room temperature are provided over the energy range 0-9 eV. Furthermore, we predict cross sections for vibrationally inelastic electron scattering through the 2?u+, 2?g and 2?u resonances

392

Education and solar conversion. Demonstrating electron transfer  

Energy Technology Data Exchange (ETDEWEB)

A simplified solar cell fabrication procedure is presented that uses natural anthocyanin or chlorophyll dyes extracted from plants. This procedure illustrates how interdisciplinary science can be taught at lower division university and upper division high school levels for an understanding of renewable energy as well as basic science concepts. Electron transfer occurs on the Earth in the mitochondrial membranes found in living cells, and in the thylakoid membranes found in the photosynthetic cells of green plants. Since we depend on the results of this electron and energy transfer, e.g. in our use of petroleum and agricultural products, it is desirable to understand and communicate how the electron transfer works. The simplified solar cell fabrication procedure, based on nanocrystalline dye-sensitized solar cells, has therefore been developed so that it can be inexpensively reproduced and utilized in the teaching of basic principles in biology, chemistry, physics, and environmental science. A water-based solution of commercial nanocrystalline titanium dioxide (TiO{sub 2}) powder is used to deposit a highly porous semiconductor electron acceptor. This acceptor couples the light-driven processes occurring at an organic dye to the macroscopic world and an external electrical circuit. Materials science and semiconductor physics are emphasized during the deposition of the sintered TiO{sub 2} nanocrystalline ceramic film. Chelation, complexation and molecular self-assembly are demonstrated during the attachment of the dye molecule to the surface of the TiO{sub 2} semiconductor particles. Environmental chemistry and energy conversion can be linked to these concepts via the regenerative oxidation and reduction cycle found in the cell. The resulting device, made in under 3 h, can be used as a light detector or power generator that produces 0.4-0.5 V at open circuit, and 1-2 mA per square cm under solar illumination

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

1998-07-23

393

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

International Nuclear Information System (INIS)

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

394

Energy transfer of highly vibrationally excited naphthalene: Collisions with CHF3, CF4, and Kr  

Science.gov (United States)

Energy transfer of highly vibrationally excited naphthalene in the triplet state in collisions with CHF3, CF4, and Kr was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. Highly vibrationally excited naphthalene (2.0 eV vibrational energy) was formed via the rapid intersystem crossing of naphthalene initially excited to the S2 state by 266 nm photons. The shapes of the collisional energy-transfer probability density functions were measured directly from the scattering results of highly vibrationally excited naphthalene. In comparison to Kr atoms, the energy transfer in collisions between CHF3 and naphthalene shows more forward scatterings, larger cross section for vibrational to translational (V --> T) energy transfer, smaller cross section for translational to vibrational and rotational (T --> VR) energy transfer, and more energy transferred from vibration to translation, especially in the range -?Ed = -100 to -800 cm-1. On the other hand, the difference of energy transfer properties between collisional partners Kr and CF4 is small. The enhancement of the V --> T energy transfer in collisions with CHF3 is attributed to the large attractive interaction between naphthalene and CHF3 (1-3 kcal/mol).

Chen Hsu, Hsu; Tsai, Ming-Tsang; Dyakov, Yuri A.; Ni, Chi-Kung

2011-08-01

395

Electronic excitations and luminescence of SrMgF4 single crystals  

Science.gov (United States)

The electronic and crystal structures of SrMgF4 single crystals grown by the Bridgman method have been investigated. The undoped SrMgF4 single crystals have been studied using low-temperature ( T = 10 K) time-resolved fluorescence optical and vacuum ultraviolet spectroscopy under selective excitation by synchrotron radiation (3.7-36.0 eV). Based on the measured reflectivity spectra and calculated spectra of the optical constants, the following parameters of the electronic structure have been determined for the first time: the minimum energy of interband transitions E g = 12.55 eV, the position of the first exciton peak E n = 1 = 11.37 eV, the position of the maximum of the "exciton" luminescence excitation band at 10.7 eV, and the position of the fundamental absorption edge at 10.3 eV. It has been found that photoluminescence excitation occurs predominantly in the region of the low-energy fundamental absorption edge of the crystal and that, at energies above E g , the energy transfer from the matrix to luminescence centers is inefficient. The exciton migration is the main excitation channel of photoluminescence bands at 2.6-3.3 and 3.3-4.2 eV. The direct photoexcitation is characteristic of photoluminescence from defects at 1.8-2.6 and 4.2-5.5 eV.

Pustovarov, V. A.; Ogorodnikov, I. N.; Omelkov, S. I.; Isaenko, L. I.; Yelisseyev, A. P.; Goloshumova, A. A.; Lobanov, S. I.; Krinitsyn, P. G.

2014-03-01

396

Long-Range Electron Transfer and Electronic Transport Through Macromolecules  

CERN Document Server

A theory of electrical transport through molecular wires is used to estimate the electronic factor in the intramolecular electron transfer (ET) in porphyrin-nitrobenzene supermolecules, and to analyze its structure. The chosen molecules have complex donor and acceptor configurations, and relatively simple structure of the bridge, which enables us to concentrate our studies on the donor/acceptor coupling to the bridge. We present analytical and numerical results concerning the effect of donor/acceptor coupling to the bridge on the ET process in molecules with complex donor/acceptor subsystems. PACS 05.60.Gg, 36.20.-r

Zimbovskaya, N A; Zimbovskaya, Natalya; Gumbs, Godfrey

2002-01-01

397

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

International Nuclear Information System (INIS)

The intensities of the M5O3 characteristic x-ray line and the M5N/sub 4.5/N/sub 4.5/ Auger-electron line from metallic Ce were measured as a function of the electron excitation energy near the M5 ionization energy. The excitation curve of both emissions contained a peak about 3 eV above threshold. The full-width at half-maximum (3.3 +- 0.2 eV) and relative heigh