Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen

Science.gov (United States)

Barklem, P. S.

2018-02-01

Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000-20 000 K, and charge transfer and (de)excitation processes involving the first excited S-states, 4s.5So and 4s.3So, are found to have the highest rates. Data are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/vizbin/qcat?J/A+A/610/A57. The data are also available at http://https://github.com/barklem/public-data

Ultrafast Charge Photogeneration in MEH-PPV Charge-Transfer Complexes

NARCIS (Netherlands)

Bakulin, Artem A.; Paraschuk, Dmitry Yu; Pshenichnikov, Maxim S.; van Loosdrecht, Paul H. M.; Corkum, P; DeSilvestri, S; Nelson, KA; Riedle, E; Schoenlein, RW

2009-01-01

Visible-pump - IR-probe spectroscopy is used to study the ultrafast charge dynamics in MEH-PPV based charge-transfer complexes and donor-acceptor blends. Transient anisotropy of the polymer polaron band provides invaluable insights into excitation localisation and charge-transfer pathways.

State-selective charge transfer and excitation in ion-ion interactions at intermediate and high energies

International Nuclear Information System (INIS)

Samanta, R; Purkait, M

2012-01-01

Boundary Corrected Continuum Intermediate State (BCCIS) approximation and Classical Trajectory Monte Carlo (CTMC) methods are applied to calculate the charge transfer and excitation cross sections for ion-ion collisions.

An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings

Energy Technology Data Exchange (ETDEWEB)

Pavanello, Michele [Department of Chemistry, Rutgers University, Newark, New Jersey 07102-1811 (United States); Van Voorhis, Troy [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States); Visscher, Lucas [Amsterdam Center for Multiscale Modeling, VU University, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Neugebauer, Johannes [Theoretische Organische Chemie, Organisch-Chemisches Institut der Westfaelischen Wilhelms-Universitaet Muenster, Corrensstrasse 40, 48149 Muenster (Germany)

2013-02-07

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 for intermolecular separations ranging from hydrogen-bond distances to tens of Angstroms. Numerical examples are provided for molecular clusters comprised of up to 56 non-covalently bound molecules.

Charge transfer in low-energy collisions of H with He+ and H+ with He in excited states

Science.gov (United States)

Loreau, J.; Ryabchenko, S.; Muñoz Burgos, J. M.; Vaeck, N.

2018-04-01

The charge transfer process in collisions of excited (n = 2, 3) hydrogen atoms with He+ and in collisions of excited helium atoms with H+ is studied theoretically. A combination of a fully quantum-mechanical method and a semi-classical approach is employed to calculate the charge-exchange cross sections at collision energies from 0.1 eV u‑1 up to 1 keV u‑1. These methods are based on accurate ab initio potential energy curves and non-adiabatic couplings for the molecular ion HeH+. Charge transfer can occur either in singlet or in triplet states, and the differences between the singlet and triplet spin manifolds are discussed. The dependence of the cross section on the quantum numbers n and l of the initial state is demonstrated. The isotope effect on the charge transfer cross sections, arising at low collision energy when H is substituted by D or T, is investigated. Rate coefficients are calculated for all isotopes up to 106 K. Finally, the impact of the present calculations on models of laboratory plasmas is discussed.

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

Science.gov (United States)

Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

2015-10-01

Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

KAUST Repository

Whited, Matthew T.; Patel, Niral M.; Roberts, Sean T.; Allen, Kathryn; Djurovich, Peter I.; Bradforth, Stephen E.; Thompson, Mark E.

2012-01-01

We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9′-bianthryl.

Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.

Science.gov (United States)

Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo

2012-08-21

Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

Charge-Transfer Dynamics in the Lowest Excited State of a Pentacene–Fullerene Complex: Implications for Organic Solar Cells

KAUST Repository

Joseph, Saju

2017-10-02

We characterize the dynamic nature of the lowest excited state in a pentacene/C60 complex on the femtosecond time scale, via a combination of ab initio molecular dynamics and time-dependent density functional theory. We analyze the correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state, which point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state. We discuss the implications of our results on this model system for the exciton-dissociation process in organic solar cells.

Low-energy charge transfer excitations in NiO

International Nuclear Information System (INIS)

Sokolov, V I; Yermakov, A Ye; Uimin, M A; Gruzdev, N B; Pustovarov, V A; Churmanov, V N; Ivanov, V Yu; Sokolov, P S; Baranov, A N; Moskvin, A S

2012-01-01

Comparative analysis of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of NiO poly- and nanocrystals in the spectral range 2-5.5 eV reveals two PLE bands peaked near 3.7 and 4.6 eV with a dramatic rise in the low-temperature PLE spectral weight of the 3.7 eV PLE band in the nanocrystalline NiO as compared with its polycrystalline counterpart. In frames of a cluster model approach we assign the 3.7 eV PLE band to the low-energy bulk-forbidden p-d (t 1g (π)-e g ) charge transfer (CT) transition which becomes the allowed one in the nanocrystalline state while the 4.6 eV PLE band is related to a bulk allowed d-d (e g -e g ) CT transition scarcely susceptible to the nanocrystallization. The PLE spectroscopy of the nanocrystalline materials appears to be a novel informative technique for inspection of different CT transitions.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

Science.gov (United States)

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Elastic, excitation, ionization and charge transfer cross sections of current interest in fusion energy research

Energy Technology Data Exchange (ETDEWEB)

Schultz, D.R.; Krstic, P.S. [Oak Ridge National Lab. TN (United States). Physics Div.

1997-01-01

Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low-to intermediate-energy regime. We summarize here some of our recent work. (author)

An intramolecular charge transfer state of carbonyl carotenoids: implications for excited state dynamics of apo-carotenals and retinal

Czech Academy of Sciences Publication Activity Database

Polívka, Tomáš; Kaligotla, S.; Chábera, P.; Frank, H.A.

2011-01-01

Roč. 13, č. 22 (2011), s. 1463-9076 ISSN 1463-9076 Institutional research plan: CEZ:AV0Z50510513 Keywords : carotenoid * retinal * excited-state dynamics * charge-transfer state Subject RIV: BO - Biophysics Impact factor: 3.573, year: 2011

Efficient charge generation by relaxed charge-transfer states at organic interfaces

KAUST Repository

Vandewal, Koen

2013-11-17

Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy. © 2014 Macmillan Publishers Limited.

Efficient charge generation by relaxed charge-transfer states at organic interfaces

KAUST Repository

Vandewal, Koen; Albrecht, Steve N.; Hoke, Eric T.; Graham, Kenneth; Widmer, Johannes; Douglas, Jessica D.; Schubert, Marcel; Mateker, William R.; Bloking, Jason T.; Burkhard, George F.; Sellinger, Alan; Frechet, Jean; Amassian, Aram; Riede, Moritz Kilian; McGehee, Michael D.; Neher, Dieter; Salleo, Alberto

2013-01-01

Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy. © 2014 Macmillan Publishers Limited.

Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

International Nuclear Information System (INIS)

Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

2015-01-01

The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism

Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

Science.gov (United States)

Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

2015-06-01

The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

Energy Technology Data Exchange (ETDEWEB)

Elkins, Madeline H.; Williams, Holly L. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Neumark, Daniel M. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2015-06-21

The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

Modeling of charge-transfer transitions and excited states in d6 transition metal complexes by DFT techniques

Czech Academy of Sciences Publication Activity Database

Vlček, Antonín; Záliš, Stanislav

2007-01-01

Roč. 251, 3-4 (2007), s. 258-287 ISSN 0010-8545 R&D Projects: GA MŠk 1P05OC068; GA MŠk OC 139 Institutional research plan: CEZ:AV0Z40400503 Keywords : charge-transfer transition * DFT technique * excited states * spectroscopy Subject RIV: CG - Electrochemistry Impact factor: 8.568, year: 2007

Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

International Nuclear Information System (INIS)

Ye, ChuanXiang; Zhao, Yi; Liang, WanZhen

2015-01-01

The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT

Electronic structure and charge transfer excited states of endohedral fullerene containing electron donoracceptor complexes utilized in organic photovoltaics

Science.gov (United States)

Amerikheirabadi, Fatemeh

Organic Donor-Acceptor complexes form the main component of the organic photovoltaic devices (OPVs). The open circuit voltage of OPVs is directly related to the charge transfer excited state energies of these complexes. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. In this work, density functional theory as implemented in the NRLMOL code is used to investigate the electronic structure and related properties of these donor-acceptor complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group as the standard time dependent density functional approaches fail to accurately provide them. The model photovoltaics systems analyzed are as follows: Sc3N C 80--ZnTPP, Y3 N C80-- ZnTPP and Sc3 N C80-- ZnPc. In addition, a thorough analysis of the isolated donor and acceptor molecules is also provided. The studied acceptors are chosen from a class of fullerenes named trimetallic nitride endohedral fullerenes. These molecules have shown to possess advantages as acceptors such as long lifetimes of the charge-separated states.

Symmetric charge transfer cross section of uranium

International Nuclear Information System (INIS)

Shibata, Takemasa; Ogura, Koichi

1995-03-01

Symmetric charge transfer cross section of uranium was calculated under consideration of reaction paths. In the charge transfer reaction a d 3/2 electron in the U atom transfers into the d-electron site of U + ( 4 I 9/2 ) ion. The J value of the U atom produced after the reaction is 6, 5, 4 or 3, at impact energy below several tens eV, only resonant charge transfer in which the product atom is ground state (J=6) takes place. Therefore, the cross section is very small (4-5 x 10 -15 cm 2 ) compared with that considered so far. In the energy range of 100-1000eV the cross section increases with the impact energy because near resonant charge transfer in which an s-electron in the U atom transfers into the d-electron site of U + ion. Charge transfer cross section between U + in the first excited state (289 cm -1 ) and U in the ground state was also obtained. (author)

Charge-transfer channel in quantum dot-graphene hybrid materials

Science.gov (United States)

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-01

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd13Se13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine)₂(CN)₂

DEFF Research Database (Denmark)

Kjær, Kasper Skov; Zhang, Wenkai; Alonso-Mori, Roberto

2017-01-01

We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible...

Charge-transfer and Mott-Hubbard Excitations in FeBo3: Fe K-edge resonant Inelastic x-ray scattering study

International Nuclear Information System (INIS)

Kim, J.; Shvydko, Y.

2011-01-01

Momentum-resolved resonant inelastic x-ray scattering (RIXS) spectroscopy has been carried out successfully at the Fe K-edge for the first time. The RIXS spectra of a FeBO 3 single crystal reveal a wealth of information on ∼ 1-10 eV electronic excitations. The IXS signal resonates when the incident photon energy approaches the pre-edge (1s - -3d) and the main-edge (1s - -4p) of the Fe K-edge absorption spectrum. The RIXS spectra measured at the pre-edge and the main-edge show quantitatively different dependences on the incident photon energy, momentum transfer, photon polarization, and temperature. We present a multielectron analysis of the Mott-Hubbard (MH) and charge transfer (CT) excitations, and calculate their energies. Electronic excitations observed in the pre-edge and main-edge RIXS spectra are interpreted as MH and CT excitations, respectively. We propose the electronic structure around the chemical potential in FeBO 3 based on the experimental data.

Dynamics of the excited state intramolecular charge transfer

International Nuclear Information System (INIS)

Joo, T.; Kim, C.H.

2006-01-01

The 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan), a derivative of 6-propanoyl- 2-dimethylaminonaphthalene (prodan), has been used as a fluorescent probe in cell imaging, especially in visualizing the lipid rafts by the generalized polarization (GP) images, where GP=(I 440 -I 490 )/(I 440 +I 490 ) with I being the fluorescence intensity. The fluorescence spectrum of laurdan is sensitive to its dipolar environment due to the intramolecular charge transfer (ICT) process in S 1 state, which results in a dual emission from the locally excited (LE) and the ICT states. The ICT process and the solvation of the ICT state are very sensitive to the dipolar nature of the environment. In this work, the ICT of laurdan in ethanol has been studied by femtosecond time resolved fluorescence (TRF), especially TRF spectra measurement without the conventional spectral reconstruction method. TRF probes the excited states exclusively, a unique advantage over the pump/probe transient absorption technique, although time resolution of the TRF is generally lower than transient absorption and the TRF spectra measurement was possible only though the spectral reconstruction. Over the years, critical advances in TRF technique have been made in our group to achieve <50 fs time resolution with direct full spectra measurement capability. Detailed ICT and the subsequent solvation processes can be visualized unambiguously from the TRF spectra. Fig. 1 shows the TRF spectra of laurdan in ethanol at several time delays. Surprisingly, two bands at 433 and 476 nm are clearly visible in the TRF spectra of laurdan even at T = 0 fs. As time increases, the band at 476 nm shifts to the red while its intensity increases. The band at 433 nm also shifts slightly to the red, but loses intensity as time increases. The intensity of the 476 nm band reaches maximum at around 5 ps, where it is roughly twice as intense as that at 0 fs, and stays constant until lifetime decay is noticeable. The spectra were fit by

Charge-transfer state excitation as the main mechanism of the photodarkening process in ytterbium-doped aluminosilicate fibres

Energy Technology Data Exchange (ETDEWEB)

Bobkov, K K; Rybaltovsky, A A; Vel' miskin, V V; Likhachev, M E; Bubnov, M M; Dianov, E M [Fiber Optics Research Center, Russian Academy of Sciences, Moscow (Russian Federation); Umnikov, A A; Gur' yanov, A N; Vechkanov, N N [G.G.Devyatykh Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation); Shestakova, I A [Open Joint-Stock Company M.F. Stel' makh Polyus Research Institute, Moscow (Russian Federation)

2014-12-31

We have studied photodarkening in ytterbium-doped fibre preforms with an aluminosilicate glass core. Analysis of their absorption and luminescence spectra indicates the formation of stable Yb{sup 2+} ions in the glass network under IR laser pumping at a wavelength λ = 915 nm and under UV irradiation with an excimer laser (λ = 193 nm). We have performed comparative studies of the luminescence spectra of the preforms and crystals under excitation at a wavelength of 193 nm. The mechanism behind the formation of Yb{sup 2+} ions and aluminium – oxygen hole centres (Al-OHCs), common to ytterbium-doped YAG crystals and aluminosilicate glass, has been identified: photoinduced Yb{sup 3+} charge-transfer state excitation. (optical fibres)

Contribution of Jahn-Teller and charge transfer excitations to the photovoltaic effect of manganite/titanite heterojunctions

Science.gov (United States)

Ifland, Benedikt; Hoffmann, Joerg; Kressdorf, Birte; Roddatis, Vladimir; Seibt, Michael; Jooss, Christian

2017-06-01

The effect of correlation effects on photovoltaic energy conversion at manganite/titanite heterojunctions is investigated. As a model system we choose a heterostructure consisting of the small polaron absorber Pr0.66Ca0.34MnO3 (PCMO) epitaxially grown on single-crystalline Nb-doped SrTi0.998Nb0.002O3 (STNO) substrates. The high structural and chemical quality of the interfaces is proved by detailed characterization using high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) studies. Spectrally resolved and temperature-dependent photovoltaic measurements show pronounced contributions of both the Jahn-Teller (JT) excitations and the charge transfer (CT) transitions to the photovoltaic effect at different photon energies. A linear temperature dependence of the open-circuit voltage for an excitation in the PCMO manganite is only observed below the charge-ordering temperature, indicating that the diffusion length of the photocarrier exceeds the size of the space charge region. The photovoltaic response is compared to that of a heterojunction of lightly doped Pr0.05Ca0.95MnO3 (CMO)/STNO, where the JT transition is absent. Here, significant contributions of the CT transition to the photovoltaic effect set in below the Neel temperature. We conclude that polaronic correlations and ordering effects are essentials for photovoltaic energy conversion in manganites.

Comparative study on contribution of charge-transfer collision to excitations of iron ion between argon radio-frequency inductively-coupled plasma and nitrogen microwave induced plasma

Energy Technology Data Exchange (ETDEWEB)

Satoh, Kozue; Wagatsuma, Kazuaki, E-mail: wagatuma@imr.tohoku.ac.jp

2015-06-01

This paper describes an ionization/excitation phenomenon of singly-ionized iron occurring in an Okamoto-cavity microwave induced plasma (MIP) as well as an argon radio-frequency inductively-coupled plasma (ICP), by comparing the Boltzmann distribution among iron ionic lines (Fe II) having a wide range of the excitation energy from 4.76 to 9.01 eV. It indicated in both the plasmas that plots of Fe II lines having lower excitation energies (4.76 to 5.88 eV) were fitted on each linear relationship, implying that their excitations were caused by a dominant thermal process such as collision with energetic electron. However, Fe II lines having higher excitation energies (more than 7.55 eV) had a different behavior from each other. In the ICP, Boltzmann plots of Fe II lines assigned to the higher excited levels also followed the normal Boltzmann relationship among the low-lying excited levels, even including a deviation from it in particular excited levels having an excitation energy of ca. 7.8 eV. This deviation can be attributed to a charge-transfer collision with argon ion, which results in the overpopulation of these excited levels, but the contribution is small. On the other hand, the distribution of the high-lying excited levels was non-thermal in the Okamoto-cavity MIP, which did not follow the normal Boltzmann relationship among the low-lying excited levels. A probable reason for the non-thermal characteristics in the MIP is that a charge-transfer collision with nitrogen molecule ion having many vibrational/rotational levels could work for populating the 3d{sup 6}4p (3d{sup 5}4s4p) excited levels of iron ion broadly over an energy range of 7.6–9.0 eV, while collisional excitation by energetic electron would occur insufficiently to excite these high-energy levels. - Highlights: • This paper describes the excitation mechanism of iron ion in Okamoto-cavity MIP in comparison with conventional ICP. • Boltzmann distribution is studied among iron ionic lines of

Charge transfer in conjugated oligomers encapsulated into carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Almadori, Y.; Alvarez, L.; Michel, T.; Le Parc, R.; Bantignies, J.L.; Hermet, P.; Sauvajol, J.L. [Laboratoire Charles Coulomb UMR 5521, Universite Montpellier 2, 34095 Montpellier (France); Laboratoire Charles Coulomb UMR 5521, CNRS, 34095 Montpellier (France); Arenal, R. [Laboratoire d' Etude des Microstructures, CNRS-ONERA, 92322 Chatillon (France); Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, U. Zaragoza, 50018 Zaragoza (Spain); Babaa, R. [Laboratoire de Chimie des Surfaces et Interfaces, CEA, IRAMIS, SPCSI, 91191 Gif-sur-Yvette Cedex (France); Chemical Engineering Department, University of Technology PETRONAS, UTP, Ipoh-Perak (Malaysia); Jouselme, B.; Palacin, S. [Laboratoire de Chimie des Surfaces et Interfaces, CEA, IRAMIS, SPCSI, 91191 Gif-sur-Yvette Cedex (France)

2011-11-15

This study deals with a hybrid system consisting in quaterthiophene derivative encapsulated inside single-walled and multi-walled carbon nanotubes. Investigations of the encapsulation step are performed by transmission electron microscopy. Raman spectroscopy data point out different behaviors depending on the laser excitation energy with respect to the optical absorption of quaterthiophene. At low excitation energy (far from the oligomer resonance window) there is no significant modification of the Raman spectra before and after encapsulation. By contrast, at high excitation energy (close to the oligomer resonance window), Raman spectra exhibit a G-band shift together with an important RBM intensity loss, suggesting a significant charge transfer between the inserted molecule and the host nanotubes. Those results suggest a photo induced process leading to a significant charge transfer. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

A novel chalcone-analogue as an optical sensor based on ground and excited states intramolecular charge transfer: A combined experimental and theoretical study

International Nuclear Information System (INIS)

Fayed, Tarek A.

2006-01-01

Steady-state absorption and emission spectroscopic techniques as well as semiempirical quantum calculations at the AM1 and ZINDO/S levels have been used to investigate the intramolecular charge transfer (ICT) behaviour of a novel chalcone namely; 1-(2-pyridyl)-5-(4-dimethylaminophenyl)-penta-2,4-diene-1-one, DMAC. The ground state DMAC has a significant ICT character and a great sensitivity to the hydrogen bond donating ability of the medium as reflected from the change of the absorption spectra in pure and mixed organic solvents. On the other hand, its excited singlet state exhibits high ICT characters as manifested by the drastic solvatochromic effects. These results are consistent with the data of charge density calculations in both the ground and excited state, which indicates enhancement of the charge transfer from the dimethyl-amino group to the carbonyl oxygen upon excitation. Also, the dipole moment calculations indicates a highly dipolar excited singlet state (Δμ eg = 15.5 D). The solvent dependence of the fluorescence quantum yield of DMAC was interpreted on the basis of positive and negative solvatokinetic as well as the hydrogen bonding effects. Incorporation of the 2-pyridyl group in the chemical structure of the present DMAC led to design of a potential optical sensor for probing acidity of the medium and metal cations such as Zn 2+ , Cd 2+ and Hg 2+ . This was concluded from the high acidochromic and metallochromic behaviour of DMAC on adding such cations to its acetonitrile solutions

Charge exchange with ion excitation: asymptotic theory

International Nuclear Information System (INIS)

Ivakin, I.A.; Karbovanets, M.I.; Ostrovskii, V.N.

1987-01-01

There is developed an asymptotic (with respect to the large internuclear separation R) theory for computing the matrix element of the exchange interaction between states of quasimolecules, which is responsible for charge transfer with ion excitation: B + +A→B+A + *. A semiclassical approximation is used, which enables one to apply the theory to processes with the participation of multiply charged ions. The case of s--s transitions for excitation of the ion A + →A + *, where it is appropriate to take into account the distortion of the wave functions of the ion A + by the particle B, is treated separately. Calculations of cross sections and comparison with the results of experiments for He + --Cd and Ne + --Mg collisions at thermal energies are given. It is shown that it is impossible to explain the experimental data by the interaction of terms of the quasimolecules at large R only, and a possible mechanism for populating at small R is proposed

Pressure-induced emission band separation of the hybridized local and charge transfer excited state in a TPE-based crystal.

Science.gov (United States)

Liu, Xuedan; Li, Aisen; Xu, Weiqing; Ma, Zhiyong; Jia, Xinru

2018-05-08

We herein report a newly synthesized simple molecule, named TPE[double bond, length as m-dash]C4, with twisted D-A structure. TPE[double bond, length as m-dash]C4 showed two intrinsic emission bands ascribed to the locally excited (LE) state and the intramolecular charge transfer (ICT) state, respectively. In the crystal state, the LE emission band is usually observed. However, by applying hydrostatic pressure to the powder sample and the single crystal sample of TPE[double bond, length as m-dash]C4, dual-fluorescence (445 nm and 532 nm) was emerged under high pressure, owing to the pressure-induced emission band separation of the hybridized local and charge transfer excited state (HLCT). It is found that the emission of TPE[double bond, length as m-dash]C4 is generally determined by the ratio of the LE state to the ICT state. The ICT emission band is much more sensitive to the external pressure than the LE emission band. The HLCT state leads to a sample with different responsiveness to grinding and hydrostatic pressure. This study is of significance in the molecular design of such D-A type molecules and in the control of photoluminescence features by molecular structure. Such results are expected to pave a new way to further understand the relationship between the D-A molecular structure and stimuli-responsive properties.

Charge Transfer Channels in Formation of Exciplex in Polymer Blends

Science.gov (United States)

Dou, Fei; Zhang, Xin-Ping

2011-09-01

The strong dependence of photoluminescence of charge transfer excited states or exciplex in a blend film of poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4- phenylenediamine) (PFB) on the excitation wavelengths and morphology is investigated. The experimental results reveal that electron transfer in the LUMOs from PFB to F8BT is more efficient than hole transfer in the HOMOs from PFB to F8BT for the formation of exciplex at the interfacial junctions between these two types of molecules in the blend film. Furthermore, energy transfer from the blue-emitting PFB to the green-emitting F8BT at the interfaces introduces an additional two-step channel and thus enhances the formation of an exciplex. This is important for understanding of charge generation and separation in organic bulk heterojunctions and for design of optoelectronic devices.

Charge Transfer Channels in Formation of Exciplex in Polymer Blends

International Nuclear Information System (INIS)

Dou Fei; Zhang Xin-Ping

2011-01-01

The strong dependence of photoluminescence of charge transfer excited states or exciplex in a blend film of poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4- phenylenediamine) (PFB) on the excitation wavelengths and morphology is investigated. The experimental results reveal that electron transfer in the LUMOs from PFB to F8BT is more efficient than hole transfer in the HOMOs from PFB to F8BT for the formation of exciplex at the interfacial junctions between these two types of molecules in the blend film. Furthermore, energy transfer from the blue-emitting PFB to the green-emitting F8BT at the interfaces introduces an additional two-step channel and thus enhances the formation of an exciplex. This is important for understanding of charge generation and separation in organic bulk heterojunctions and for design of optoelectronic devices. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Resonance Raman and excitation energy dependent charge transfer mechanism in halide-substituted hybrid perovskite solar cells.

Science.gov (United States)

Park, Byung-wook; Jain, Sagar M; Zhang, Xiaoliang; Hagfeldt, Anders; Boschloo, Gerrit; Edvinsson, Tomas

2015-02-24

Organo-metal halide perovskites (OMHPs) are materials with attractive properties for optoelectronics. They made a recent introduction in the photovoltaics world by methylammonium (MA) lead triiodide and show remarkably improved charge separation capabilities when chloride and bromide are added. Here we show how halide substitution in OMHPs with the nominal composition CH3NH3PbI2X, where X is I, Br, or Cl, influences the morphology, charge quantum yield, and local interaction with the organic MA cation. X-ray diffraction and photoluminescence data demonstrate that halide substitution affects the local structure in the OMHPs with separate MAPbI3 and MAPbCl3 phases. Raman spectroscopies as well as theoretical vibration calculations reveal that this at the same time delocalizes the charge to the MA cation, which can liberate the vibrational movement of the MA cation, leading to a more adaptive organic phase. The resonance Raman effect together with quantum chemical calculations is utilized to analyze the change in charge transfer mechanism upon electronic excitation and gives important clues for the mechanism of the much improved photovoltage and photocurrent also seen in the solar cell performance for the materials when chloride compounds are included in the preparation.

Effects of Charge-Transfer Excitons on the Photophysics of Organic Semiconductors

Science.gov (United States)

Hestand, Nicholas J.

The field of organic electronics has received considerable attention over the past several years due to the promise of novel electronic materials that are cheap, flexible and light weight. While some devices based on organic materials have already emerged on the market (e.g. organic light emitting diodes), a deeper understanding of the excited states within the condensed phase is necessary both to improve current commercial products and to develop new materials for applications that are currently in the commercial pipeline (e.g. organic photovoltaics, wearable displays, and field effect transistors). To this end, a model for pi-conjugated molecular aggregates and crystals is developed and analyzed. The model considers two types of electronic excitations, namely Frenkel and charge-transfer excitons, both of which play a prominent role in determining the nature of the excited states within tightly-packed organic systems. The former consist of an electron-hole pair bound to the same molecule while in the later the electron and hole are located on different molecules. The model also considers the important nuclear reorganization that occurs when the system switches between electronic states. This is achieved using a Holstein-style Hamiltonian that includes linear vibronic coupling of the electronic states to the nuclear motion associated with the high frequency vinyl-stretching and ring-breathing modes. Analysis of the model reveals spectroscopic signatures of charge-transfer mediated J- and H-aggregation in systems where the photophysical properties are determined primarily by charge-transfer interactions. Importantly, such signatures are found to be sensitive to the relative phase of the intermolecular electron and hole transfer integrals, and the relative energy of the Frenkel and charge-transfer states. When the charge-transfer integrals are in phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits J

High Pressure Optical Studies of the Thallous Halides and of Charge-Transfer Complexes

Science.gov (United States)

Jurgensen, Charles Willard

High pressure was used to study the insulator -to-metal transition in sulfur and the thallous halides and to study the intermolecular interactions in charge -transfer complexes. The approach to the band overlap insulator -to-metal transition was studied in three thallous halides and sulfur by optical absorption measurements of the band gap as a function of pressure. The band gap of sulfur continuously decreases with pressure up to the insulator -to-metal transition which occurs between 450 and 485 kbars. The results on the thallous halides indicate that the indirect gap decreases more rapidly than the direct gap; the closing of the indirect gap is responsible for the observed insulator -to-metal transitions. High pressure electronic and vibrational spectroscopic measurements on the solid-state complexes of HMB-TCNE were used to study the intermolecular interactions of charge -transfer complexes. The vibrational frequency shifts indicate that the degree of charge transfer increases with pressure which is independently confirmed by an increase in the molar absorptivity of the electronic charge-transfer peak. Induction and dispersion forces contribute towards a red shift of the charge-transfer peak; however, charge-transfer resonance contributes toward a blue shift and this effect is dominant for the HMB-TCNE complexes. High pressure electronic spectra were used to study the effect of intermolecular interactions on the electronic states of TCNQ and its complexes. The red shifts with pressure of the electronic spectra of TCNQ and (TCNQ)(' -) in polymer media and of crystalline TCNQ can be understood in terms of Van der Waals interactions. None of the calculations which considered intradimer distance obtained the proper behavior for either the charge-transfer of the locally excited states of the complexes. The qualitative behavior of both states can be interpreted as the effect of increased mixing of the locally excited and charge transfer states.

Tracking excited-state charge and spin dynamics in iron coordination complexes

DEFF Research Database (Denmark)

Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe

2014-01-01

to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)(3)](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate......Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons(1-4). But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited...... states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics(5) and the flux limitations of ultrafast X-ray sources(6,7). Such a situation exists for archetypal poly-pyridyl iron complexes, such as [Fe(2...

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine2(CN2

Directory of Open Access Journals (Sweden)

Kasper S. Kjær

2017-07-01

Full Text Available We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy2(CN2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy2(CN2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy2(CN2] complement prior measurement performed on [Fe(bpy3]2+ and [Fe(bpy(CN4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpyN(CN6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.

A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence

DEFF Research Database (Denmark)

Chabera, Pavel; Liu, Yizhu; Prakash, Om

2017-01-01

Transition-metal complexes are used as photosensitizers(1), in light-emitting diodes, for biosensing and in photocatalysis(2). A key feature in these applications is excitation from the ground state to a charge-transfer state(3,4); the long charge-transfer-state lifetimes typical for complexes...

CoPc and CoPcF16 on gold: Site-specific charge-transfer processes

Directory of Open Access Journals (Sweden)

Fotini Petraki

2014-04-01

Full Text Available Interface properties of cobalt(II phthalocyanine (CoPc and cobalt(II hexadecafluoro-phthalocyanine (CoPcF16 to gold are investigated by photo-excited electron spectroscopies (X-ray photoemission spectroscopy (XPS, ultraviolet photoemission spectroscopy (UPS and X-ray excited Auger electron spectroscopy (XAES. It is shown that a bidirectional charge transfer determines the interface energetics for CoPc and CoPcF16 on Au. Combined XPS and XAES measurements allow for the separation of chemical shifts based on different local charges at the considered atom caused by polarization effects. This facilitates a detailed discussion of energetic shifts of core level spectra. The data allow the discussion of site-specific charge-transfer processes.

Evidence for excited state intramolecular charge transfer reaction in donor-acceptor molecule 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester: Experimental and quantum chemical approach

International Nuclear Information System (INIS)

Kumar Paul, Bijan; Samanta, Anuva; Kar, Samiran; Guchhait, Nikhil

2010-01-01

Intramolecular charge transfer (ICT) reaction has been investigated in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) using spectroscopic techniques. The molecule DPDAME shows local emission in non-polar solvent and dual emission in polar solvents. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the charge transfer character of the excited state. Quantum chemical calculations have been performed at Hartree-Fock (HF) and density functional theoretical (DFT) levels to correlate the experimental findings. Potential energy curves (PECs) for the ICT reaction have been evaluated along the donor twist angle at DFT and time dependent density functional theory (TDDFT) levels for the ground and excited states, respectively, using B3LYP hybrid functional and 6-31G** basis set. The solvent effects on the spectral properties have been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results are found to well substantiate the solvent polarity dependent Stokes shifted emission of DPDAME. Huge enhancement of dipole moment (Δμ=16.42 D) of the molecule following photoexcitation dictates the highly polar character of the excited state. Although elucidation of PECs does not exactly predict the operation of ICT according to twisted intramolecular charge transfer (TICT) model in DPDAME, lowering of vertical transition energy as a function of the donor twist coordinate scripts the occurrence of red shifted emission as observed experimentally.

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism.

Science.gov (United States)

Hu, Zhenming; Boyd, Russell J; Nakatsuji, Hiroshi

2002-03-20

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.

Charge transfer reactions in Xe plasma expansion

International Nuclear Information System (INIS)

Jiao, C. Q.; Garscadden, A.; Ganguly, B. N.

2007-01-01

Charge transfer reactions of fast Xe ions with hydrocarbons including methane (CH 4 ), ethene (C 2 H 4 ), and propane (C 3 H 8 ) are studied by adding these hydrocarbon gases into a cross flowing Xe plasma expansion. Branching ratios and relative reaction rates for the charge transfers of fast Xe + with each of the three hydrocarbon gases are measured under different rf powers of the inductively coupled Xe discharge. For CH 4 /Xe system, we find that fast Xe + reacts readily with CH 4 generating CH 4 + and CH 3 + in a ratio of 1:0.56, with an estimated rate coefficient of (2.3±0.3)x10 -10 cm 3 /s at 75 W rf power which slowly increases to (2.9±0.3)x10 -10 cm 3 /s at 250 W (error bars reflect only the uncertainties due to the unknown extent of the ion recombination that follows the charge transfer reaction). These observed charge transfer reactions are made possible by the kinetically excited Xe ions produced by free expansion of the plasma. For the C 2 H 4 /Xe system product ions C 2 H 4 + and C 2 H 2 + are observed, and for C 3 H 8 /Xe, C 2 H 4 + and C 2 H 5 + and minor product ions including C 2 H 2 + and C 3 H 7 + are observed

Charge transfer luminescence of Yb3+ ions in LiY1-xYbxP4O12 phosphates

International Nuclear Information System (INIS)

Stryganyuk, G; Zazubovich, S; Voloshinovskii, A; Pidzyrailo, M; Zimmerer, G; Peters, R; Petermann, K

2007-01-01

Spectral-kinetic studies have been performed for LiY 1-x Yb x P 4 O 12 (x = 0; 0.1; 0.9) phosphates at T = 8-320 K using synchrotron radiation for excitation within the 5-17 eV energy range. Mechanisms for the excitation of Yb 3+ charge transfer and f-f luminescence are discussed. The quasimolecular character of Yb 3+ charge transfer luminescence (CTL) is pointed out. The central Yb 2+ ion and hole delocalized over the surrounding ligands are proposed for consideration as a 'charge transfer cluster' (Yb 2+ CT cluster). Possible mechanisms of Yb 3+ CTL quenching are presumed

Excited state intramolecular charge transfer reaction in binary mixtures of water and tertiary butanol (TBA): alcohol mole fraction dependence.

Science.gov (United States)

Pradhan, Tuhin; Ghoshal, Piue; Biswas, Ranjit

2008-02-07

The excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) has been studied in water-tertiary butanol (TBA) mixtures at different alcohol mole fractions by using steady state and time-resolved fluorescence spectroscopy. The ratio between the areas under the locally excited (LE) and charge transferred (CT) emission bands is found to exhibit a sharp rise at alcohol mole fraction approximately 0.04, a value at which several thermodynamic properties of this mixture is known to show anomalous change due to the enhancement of H-bonding network. The radiative rate associated with the LE emission also shows a maximum at this TBA mole fraction. Although the structural transition from the water-like tetrahedral network to the alcohol-like chain is reflected in the red shift of the absorption spectrum up to TBA mole fraction approximately 0.10, the emission bands (both LE and CT) show the typical nonideal alcohol mole fraction dependence at all TBA mole fractions. Quantum yield, CT radiative rate as well as transition moments also exhibit a nonideal alcohol mole fraction dependence. The time-resolved emission decay of P4C has been found to be biexponential at all TBA mole fractions, regardless of emission collection around either the LE or the CT bands. The time constant associated with the slow component (tau(slow)) shows a minimum at TBA mole fraction approximately 0.04, whereas such a minimum for the fast time constant, tau(fast) (representing the rate of LE --> CT conversion reaction) is not observed. The nonobservation of the minimum in tau(fast) might be due to the limited time resolution employed in our experiments.

A simplified approach for the coupling of excitation energy transfer

Energy Technology Data Exchange (ETDEWEB)

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

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.

Detection of Intramolecular Charge Transfer and Dynamic Solvation in Eosin B by Femtosecond Two-Dimensional Electronic Spectroscopy

Science.gov (United States)

Ghosh, Soumen; Roscioli, Jerome D.; Beck, Warren F.

2014-06-01

We have employed 2D electronic photon echo spectroscopy to study intramolecular charge-transfer dynamics in eosin B. After preparation of the first excited singlet state (S_1) with 40-fs excitation pulses at 520 nm, the nitro group (--NO_2) in eosin B undergoes excited state torsional motion towards a twisted intramolecular charge transfer (TICT) state. As the viscosity of the surrounding solvent increases, the charge-transfer rate decreases because the twisting of the --NO_2 group is hindered. These conclusions are supported by the time evolution of the 2D spectrum, which provides a direct measure of the the ground-to-excited-state energy gap time-correlation function, M(t). In comparison to the inertial and diffusive solvation time scales exhibited by eosin Y, which lacks the nitro group, the M(t) function for eosin B exhibits under the same conditions an additional component on the 150-fs timescale that arises from quenching of the S_1 state by crossing to the TICT state. These results indicate that 2D electronic spectroscopy can be used as a sensitive probe of the rate of charge transfer in a molecular system and of the coupling to the motions of the surrounding solvent. (Supported by grant DE-SC0010847 from the Department of Energy, Office of Basic Energy Sciences, Photosynthetic Systems program.)

Excitation functions for quasielastic transfer reactions induced with heavy ions in bismuth

International Nuclear Information System (INIS)

Gardes, D.; Bimbot, R.; Maison, J.; de Reilhac, L.; Rivet, M.F.; Fleury, A.; Hubert, F.; Llabador, Y.

1978-01-01

The excitation functions for the production of 210 Bi, 210 Po, /sup 207-211/At, and 211 Rn through quasielastic transfer reactions induced with heavy ions in 209 Bi have been measured. The corresponding reactions involved the transfer of one neutron, one proton, two charges, and three charges from projectile to target. The projectiles used were 12 C, 14 N, 16 O, 19 F, 20 Ne, 40 Ar, 40 Ca, 56 Fe, and 63 Cu. The experimental techniques involved target irradiations and off-line α and γ activity measurements. Chemical separations were used to solve specific problems. Careful measuremnts of incident energies and cross sections were performed close to the reaction thresholds. All excitation functions exhibit the typical features of quasielastic transfer reactions: a sharp increase at low energy, and a constant value at high incident energy. The position of the thresholds are strongly influenced by the energetics of the reaction: High cross sections are observed under the strong interaction barrier if the energy balance at the minimum distance of approach is positive. This balance is equal to the difference between the interaction potentials in the entrance and exit channels, corrected for the mass balance. The constant cross sections observed for the high energy part of a given excitation function are consistent with the assumption that the curve P (R) which represents the transfer probability versus the distance between the nucleus centers does not vary with incident energy. This assumption implies the constancy of the optimum distance of approach R/sub opt/, of the R window ΔR for which P (R) is significant, and of the magnitude of P (R). Moreover the data show that the high energy cross sections for one-proton transfer are independent of the projectile, while odd-even effects of the projectile atomic number Z on the two-charge transfer cross sections are observed for the lightest incident ions 14 N to 20 Ne

Charge-transfer cross sections in collisions of ground-state Ca and H+

Science.gov (United States)

Dutta, C. M.; Oubre, C.; Nordlander, P.; Kimura, M.; Dalgarno, A.

2006-03-01

We have investigated collisions of Ca(4s2) with H+ in the energy range of 200eV/u-10keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states ( 11Σ+1 and seven Π+1 states) to determine charge-transfer cross sections. Except for the incoming channel 6Σ+1 , the molecular states all correspond to charge-transfer channels. Inclusion of Ca2+-H- is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca2+-H- creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6Σ+1 and the energetically close charge-transfer channel 7Σ+1 the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4×10-15cm2 at 200eV/u to 4.5×10-15cm2 at 10keV/u . Charge transfer occurs mostly to the excited Ca+(5p) state in the entire energy range, which is the sum of the charge transfer to 7Σ+1 and 4Π+1 . It accounts for ˜47% of the total charge transfer cross sections at 200eV/u . However, as the energy increases, transfer to Ca+(4d) increases, and at 10keV/u the charge-transfer cross sections for Ca+(5p) and Ca+(4d) become comparable, each giving ˜38% of the total cross section.

Charge-transfer cross sections in collisions of ground-state Ca and H+

International Nuclear Information System (INIS)

Dutta, C. M.; Oubre, C.; Nordlander, P.; Kimura, M.; Dalgarno, A.

2006-01-01

We have investigated collisions of Ca(4s 2 ) with H + in the energy range of 200 eV/u-10 keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states (11 1 Σ + and seven 1 Π + states) to determine charge-transfer cross sections. Except for the incoming channel 6 1 Σ + , the molecular states all correspond to charge-transfer channels. Inclusion of Ca 2+ -H - is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca 2+ -H - creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6 1 Σ + and the energetically close charge-transfer channel 7 1 Σ + the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4x10 -15 cm 2 at 200 eV/u to 4.5x10 -15 cm 2 at 10 keV/u. Charge transfer occurs mostly to the excited Ca + (5p) state in the entire energy range, which is the sum of the charge transfer to 7 1 Σ + and 4 1 Π + . It accounts for ∼47% of the total charge transfer cross sections at 200 eV/u. However, as the energy increases, transfer to Ca + (4d) increases, and at 10 keV/u the charge-transfer cross sections for Ca + (5p) and Ca + (4d) become comparable, each giving ∼38% of the total cross section

Dual structure in the charge excitation spectrum of electron-doped cuprates

Science.gov (United States)

Bejas, Matías; Yamase, Hiroyuki; Greco, Andrés

2017-12-01

Motivated by the recent resonant x-ray scattering (RXS) and resonant inelastic x-ray scattering (RIXS) experiments for electron-doped cuprates, we study the charge excitation spectrum in a layered t -J model with the long-range Coulomb interaction. We show that the spectrum is not dominated by a specific type of charge excitations, but by different kinds of charge fluctuations, and is characterized by a dual structure in the energy space. Low-energy charge excitations correspond to various types of bond-charge fluctuations driven by the exchange term (J term), whereas high-energy charge excitations are due to usual on-site charge fluctuations and correspond to plasmon excitations above the particle-hole continuum. The interlayer coupling, which is frequently neglected in many theoretical studies, is particularly important to the high-energy charge excitations.

Spectroscopy of nitrophenolates in vacuo: effect of spacer, configuration, and microsolvation on the charge-transfer excitation energy.

Science.gov (United States)

Brøndsted Nielsen, Steen; Brøndsted Nielsen, Mogens; Rubio, Angel

2014-04-15

In a charge-transfer (CT) transition, electron density moves from one end of the molecule (donor) to the other end (acceptor). This type of transition is of paramount importance in nature, for example, in photosynthesis, and it governs the excitation of several protein biochromophores and luminophores such as the oxyluciferin anion that accounts for light emission from fireflies. Both transition energy and oscillator strength are linked to the coupling between the donor and acceptor groups: The weaker the coupling, the smaller the excitation energy. But a weak coupling necessarily also causes a low oscillator strength possibly preventing direct excitation (basically zero probability in the noncoupling case). The coupling is determined by the actual spacer between the two groups, and whether the spacer acts as an insulator or a conductor. However, it can be difficult or even impossible to distinguish the effect of the spacer from that of local solvent molecules that often cause large solvent shifts due to different ground-state and excited-state stabilization. This calls for gas-phase spectroscopy experiments where absorption by the isolated molecule is identified to unequivocally establish the intrinsic molecular properties with no perturbations from a microenvironment. From such insight, the effect of a protein microenvironment on the CT excited state can be deduced. In this Account, we review our results over the last 5 years from mass spectroscopy experiments using specially designed apparatus on several charged donor-acceptor ions that are based on the nitrophenolate moiety and π-extended derivatives, which are textbook examples of donor-acceptor chromophores. The phenolate oxygen is the donor, and the nitro group is the acceptor. The choice of this system is also based on the fact that phenolate is a common structural motif of biochromophores and luminophores, for example, it is a constituent of the oxyluciferin anion. A presentation of the setups used for

Charge transfer in astrophysical nebulae

International Nuclear Information System (INIS)

Shields, G.A.

1990-01-01

Charge transfer has become a standard ingredient in models of ionized nebulae, supernovae remnants and active galactic nuclei. Charge transfer rate coefficients and the physics of ionized nebulae are considered. Charge transfer is applied to the ionization structure and line emission of ionized nebulae. Photoionized nebulae observations are used to test theoretical predictions of charge transfer rates. (author)

Charge migration and charge transfer in molecular systems

Directory of Open Access Journals (Sweden)

Hans Jakob Wörner

2017-11-01

Full Text Available The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review.

Through space and through bridge channels of charge transfer at p-n nano-junctions: A DFT study

Energy Technology Data Exchange (ETDEWEB)

Dandu, Naveen [Department of Chemistry and Biochemistry, NDSU, Fargo, ND 58108 (United States); Tretiak, Sergei [Theoretical Division, Center for Nonlinear Studies (CNLS) and Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, 57069, NM 87454 (United States); Kilina, Svetlana [Department of Chemistry and Biochemistry, NDSU, Fargo, ND 58108 (United States); Kilin, Dmitri, E-mail: Dmitri.Kilin@ndsu.edu [Department of Chemistry and Biochemistry, NDSU, Fargo, ND 58108 (United States)

2016-12-20

Highlights: • Properties of interacting QDs depend on the fashion of interaction: through-bond or through-space. • The disconnected and undoped dimer models shows FÓ§rster band formation. • Dimer models with some doping exhibit degenerate charge-transfer excitons. • p- and n-doped qds shows polarization at the interface. • A photoexcitation polarizes p-n interface, in relation to phototovoltaic effect. - Abstract: Details of charge density distribution at p-n nano interface are analyzed with density functional theory techniques using model system of dimers of doped silicon quantum dots interacting through bond and through space. Spatial distributions of transition densities between the ground and excited states suggest the character of essential electronic excitations, which have a FÓ§rster, bound, unbound, or charge transfer character. A redistribution of electronic density from n-impurities to p-impurities results in a ground state polarization and creates an offset of energies of the bands localized on p-doped quantum dot and the bands localized on n-doped quantum dot. Although impurities contribute very few orbitals to the total density, a ground state charge redistribution and polarization are both responsible for the presence of a large number of charge transfer excitations involving solely silicon orbitals.

Theory of Excitation Transfer between Two-Dimensional Semiconductor and Molecular Layers

Science.gov (United States)

Specht, Judith F.; Verdenhalven, Eike; Bieniek, Björn; Rinke, Patrick; Knorr, Andreas; Richter, Marten

2018-04-01

The geometry-dependent energy transfer rate from an electrically pumped inorganic semiconductor quantum well into an organic molecular layer is studied theoretically. We focus on Förster-type nonradiative excitation transfer between the organic and inorganic layers and include quasimomentum conservation and intermolecular coupling between the molecules in the organic film. (Transition) partial charges calculated from density-functional theory are used to calculate the coupling elements. The partial charges describe the spatial charge distribution and go beyond the common dipole-dipole interaction. We find that the transfer rates are highly sensitive to variations in the geometry of the hybrid inorganic-organic system. For instance, the transfer efficiency is improved by up to 2 orders of magnitude by tuning the spatial arrangement of the molecules on the surface: Parameters of importance are the molecular packing density along the effective molecular dipole axis and the distance between the molecules and the surface. We also observe that the device performance strongly depends on the orientation of the molecular dipole moments relative to the substrate dipole moments determined by the inorganic crystal structure. Moreover, the operating regime is identified where inscattering dominates over unwanted backscattering from the molecular layer into the substrate.

Excited state Intramolecular Proton Transfer in Anthralin

DEFF Research Database (Denmark)

Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens

1998-01-01

Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an unus......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......, associated with an excited-state intramolecular proton transfer process....

Charge-transfer excited state in pyrene-1-carboxylic acids adsorbed on titanium dioxide nanoparticles

Science.gov (United States)

Krawczyk, S.; Nawrocka, A.; Zdyb, A.

2018-06-01

The electronic structure of excited photosensitizer adsorbed at the surface of a solid is the key factor in the electron transfer processes that underlie the efficiency of dye-sensitized solar cells and photocatalysts. In this work, Stark effect (electroabsorption) spectroscopy has been used to measure the polarizability and dipole moment changes in electronic transitions of pyrene-1-carboxylic (PCA), -acetic (PAA) and -butyric (PBA) acids in ethanol, both free and adsorbed on colloidal TiO2, in glassy ethanol at low temperature. The lack of appreciable increase of dipole moment in the excited state of free and adsorbed PAA and PBA points that two or more single bonds completely prevent the expansion of π-electrons from the aromatic ring towards the carboxylic group, thus excluding the possibility of direct electron injection into TiO2. In free PCA, the pyrene's forbidden S0 → S1 transition has increased intensity, exhibits a long progression in 1400 cm-1 Ag mode and is associated with |Δμ| of 2 D. Adsorption of PCA on TiO2 causes a broadening and red shift of the S0 → S1 absorption band and an increase in dipole moment change on electronic excitation to |Δμ| = 6.5 D. This value increased further to about 15 D when the content of acetic acid in the colloid was changed from 0.2% to 2%, and this effect is ascribed to the surface electric field. The large increase of |Δμ| points that the electric field effect can not only change the energetics of electron transfer from the excited sensitizer into the solid, but can also shift the molecular electronic density, thus directly influencing the electronic coupling factor relevant for electron transfer at the molecule-solid interface.

Ion-atom charge-transfer system for a heavy-ion-beam pumped laser

International Nuclear Information System (INIS)

Ulrich, A.; Gernhaeuser, R.; Kroetz, W.; Wieser, J.; Murnick, D.E.

1994-01-01

An Ar target to which Cs vapor could be added, excited by a pulsed beam of 100-MeV 32 S ions, was studied as a prototype ion-atom charge-transfer system for pumping short-wavelength lasers. Low-velocity Ar 2+ ions were efficiently produced; a huge increase in the intensity of the Ar II 4d-4p spectral lines was observed when Cs vapor was added to the argon. This observation is explained by a selective charge transfer of the Cs 6s electron into the upper levels of the observed transitions. A rate constant of (1.4±0.2)x10 -9 cm 3 /s for the transfer process was determined

Evidence for charge exchange effects in electronic excitations in Al by slow singly charged He ions

Energy Technology Data Exchange (ETDEWEB)

Riccardi, P., E-mail: Pierfrancesco.riccardi@fis.unical.it [Dipartimento di Fisica, Università della Calabria and INFN Gruppo collegato di Cosenza, Via P. Bucci cubo 31C, 87036 – Arcavacata di Rende, Cosenza (Italy); Sindona, A. [Dipartimento di Fisica, Università della Calabria and INFN Gruppo collegato di Cosenza, Via P. Bucci cubo 31C, 87036 – Arcavacata di Rende, Cosenza (Italy); Dukes, C.A. [Laboratory for Astrophysics and Surface Physics, Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)

2016-09-01

We report on experiments of secondary electron emission in the interaction of helium ions with aluminum surfaces. Comparison between the electron emission induced by the impact of {sup 3}He{sup +} and {sup 4}He{sup +} on Al illustrates similarities and differences between the two projectiles. The intensity of emission shows the same dependence on velocity for the two isotopes, showing that KEE yields for helium ions impact on Al are dominated by direct excitation of valence electrons and not by electron promotion. Electron promotion and charge transfer processes are unambiguously identified by the observation of Auger electron emission from Al, at energies below the excitation threshold of Al–Al collisions, indicating energy losses for the projectiles higher than those commonly considered.

Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer.

Science.gov (United States)

Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A

2015-04-15

A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. Copyright © 2015 Elsevier Inc. All rights reserved.

Photoinduced charge and energy transfer in dye-doped conjugated polymers

International Nuclear Information System (INIS)

Veldman, Dirk; Bastiaansen, Jolanda J.A.M.; Langeveld-Voss, Bea M.W.; Sweelssen, Joergen; Koetse, Marc M.; Meskers, Stefan C.J.; Janssen, Rene A.J.

2006-01-01

Conjugated polymer-molecular dye blends of MDMO-PPV (poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene]) and PF1CVTP (poly[9,9-dioctylfluorene-2,7-diyl-alt-2,5-bis(2-thienyl-1-cyanovinyl) -1-(3',7= '-dimethyloctyloxy)-4-methoxybenzene-5'',5''-diyl]) with three dipyrrometheneboron difluoride (bodipy) dyes were studied by (time-resolved) fluorescence and photoinduced absorption spectroscopy to determine quantitatively the relation between the electronic HOMO and LUMO levels and the occurrence of energy or charge transfer after optical excitation. We find that for MDMO-PPV photoinduced charge transfer to the dyes occurs, while photoexcitation of PF1CVTP exclusively results in energy transfer. The differences can be rationalized by assuming that the energy of the charge separated state is 0.33-0.45 eV higher than the energy determined from oxidation and reduction potentials of donor and acceptor, respectively. This provides an important design rule to identify appropriate materials for polymer solar cells that can have a high open-circuit voltage

Investigation of the charge-transfer in photo-excited nanoparticles for CO2 reduction in non-aqueous media

Directory of Open Access Journals (Sweden)

Dimitrijević Nada M.

2013-01-01

Full Text Available Photoinduced charge separation in TiO2 and Cu2O semiconductor nanoparticles was examined using Electron Paramagnetic Resonance spectroscopy in order to get insight into the photocatalytic reduction of CO2 in nonaqueous media. For dissolution/grafting of CO2 we have used carboxy-PEG4-amine, and as a solvent poly(ethylene glycol 200. We have found that, in this system, reduction of CO2 starts at potential of -0.5 V vs Ag/AgCl, which is significantly more positive than the potential for electrochemical reduction of CO2 in most organic solvents and water (-2.0 V vs. Ag/AgCl. The electron transfer from excited nanoparticles to CO2 is governed both by thermodynamic and kinetic parameters, namely by the redox potential of conduction band electrons and adsorption/binding of CO2 on the surface of nanoparticles.

Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Zanni, Martin Thomas [Univ. of California, Berkeley, CA (United States)

1999-12-01

This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

International Nuclear Information System (INIS)

Zanni, Martin T.

1999-01-01

This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents

Charge transfer between O6+ and atomic hydrogen

Science.gov (United States)

Wu, Y.; Stancil, P. C.; Liebermann, H. P.; Buenker, R. J.; Schultz, D. R.; Hui, Y.

2011-05-01

The charge exchange process has been found to play a dominant role in the production of X-rays and/or EUV photons observed in cometary and planetary atmospheres and from the heliosphere. Charge transfer cross sections, especially state-selective cross sections, are necessary parameters in simulations of X-ray emission. In the present work, charge transfer due to collisions of ground state O6+(1s2 1 S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling method (QMOCC). The multi-reference single- and double-excitation configuration interaction approach (MRDCI) has been applied to compute the adiabatic potential and nonadiabatic couplings, and the atomic basis sets used have been optimized with the method proposed previously to obtain precise potential data. Total and state-selective cross sections are calculated for energies between 10 meV/u and 10 keV/u. The QMOCC results are compared to available experimental and theoretical data as well as to new atomic-orbital close-coupling (AOCC) and classical trajectory Monte Carlo (CTMC) calculations. A recommended set of cross sections, based on the MOCC, AOCC, and CTMC calculations, is deduced which should aid in X-ray modeling studies.

Selective Coherent Excitation of Charged Density Waves

NARCIS (Netherlands)

Tsvetkov, A.A.; Sagar, D.M.; Loosdrecht, P.H.M. van; Marel, D. van der

2003-01-01

Real time femtosecond pump-probe spectroscopy is used to study collective and single particle excitations in the charge density wave state of the quasi-1D metal, blue bronze. Along with the previously observed collective amplitudon excitation, the spectra show several additional coherent features.

Effect of charged and excited states on the decomposition of 1,1-diamino-2,2-dinitroethylene molecules

International Nuclear Information System (INIS)

Kimmel, Anna V.; Sushko, Peter V.; Shluger, Alexander L.; Kuklja, Maija M.

2007-01-01

The authors have calculated the electronic structure of individual 1,1-diamino-2,2-dinitroethylene molecules (FOX-7) in the gas phase by means of density functional theory with the hybrid B3LYP functional and 6-31+G(d,p) basis set and considered their dissociation pathways. Positively and negatively charged states as well as the lowest excited states of the molecule were simulated. They found that charging and excitation can not only reduce the activation barriers for decomposition reactions but also change the dominating chemistry from endo- to exothermic type. In particular, they found that there are two competing primary initiation mechanisms of FOX-7 decomposition: C-NO 2 bond fission and C-NO 2 to CONO isomerization. Electronic excitation or charging of FOX-7 disfavors CONO formation and, thus, terminates this channel of decomposition. However, if CONO is formed from the neutral FOX-7 molecule, charge trapping and/or excitation results in spontaneous splitting of an NO group accompanied by the energy release. Intramolecular hydrogen transfer is found to be a rare event in FOX-7 unless free electrons are available in the vicinity of the molecule, in which case HONO formation is a feasible exothermic reaction with a relatively low energy barrier. The effect of charged and excited states on other possible reactions is also studied. Implications of the obtained results to FOX-7 decomposition in condensed state are discussed

Construction of Vibronic Diabatic Hamiltonian for Excited-State Electron and Energy Transfer Processes.

Science.gov (United States)

Xie, Yu; Jiang, Shengshi; Zheng, Jie; Lan, Zhenggang

2017-12-21

Photoinduced excited-state electron and energy transfer processes are crucial in biological photoharvesting systems and organic photovoltaic devices. We discuss the construction of a diabatic vibronic Hamiltonian for the proper treatment of these processes involving the projection approach acting on both electronic wave functions and vibrational modes. In the electronic part, the wave function projection approach is used to construct the diabatic Hamiltonian in which both local excited states and charge-transfer states are included on the same footing. For the vibrational degrees of freedom, the vibronic couplings in the diabatic Hamiltonian are obtained in the basis of the pseudonormal modes localized on each monomer site by applying delocalized-to-localized mode projection. This systematic approach allows us to construct the vibronic diabatic Hamiltonian in molecular aggregates.

Dynamics of transfer of electron excitation in a donor-acceptor system with a carbon chain and ways of its relaxation

Directory of Open Access Journals (Sweden)

M.M. Sevryukova

2017-12-01

Full Text Available The optical properties and dynamics of transport of electron excitation and the ways of its relaxation in the supramolecular D–π–A complex on the basis of merocyanines have been investigated. There have been found two components in the transfer of charge: fast and slow, which correspond to different conformational states of the carbon chain in merocyanines. It was found that the main photoluminescence of the studied molecular solutions of merocyanines by its nature is similar to the exciplex luminescence, as a manifestation of resonant and charge transfer interaction in an excited state. The lifetime in this state is about 2000 ps.

Altering intra- to inter-molecular hydrogen bonding by dimethylsulfoxide: A TDDFT study of charge transfer for coumarin 343

Science.gov (United States)

Liu, Xiaochun; Yin, Hang; Li, Hui; Shi, Ying

2017-04-01

DFT and TDDFT methods were carried out to investigate the influences of intramolecular and intermolecular hydrogen bonding on excited state charge transfer for coumarin 343 (C343). Intramolecular hydrogen bonding is formed between carboxylic acid group and carbonyl group in C343 monomer. However, in dimethylsulfoxide (DMSO) solution, DMSO 'opens up' the intramolecular hydrogen bonding and forms solute-solvent intermolecular hydrogen bonded C343-DMSO complex. Analysis of frontier molecular orbitals reveals that intramolecular charge transfer (ICT) occurs in the first excited state both for C343 monomer and complex. The results of optimized geometric structures indicate that the intramolecular hydrogen bonding interaction is strengthened while the intermolecular hydrogen bonding is weakened in excited state, which is confirmed again by monitoring the shifts of characteristic peaks of infrared spectra. We demonstrated that DMSO solvent can not only break the intramolecular hydrogen bonding to form intermolecular hydrogen bonding with C343 but also alter the mechanism of excited state hydrogen bonding strengthening.

Search for excited charged leptons in electron positron collisions

CERN Document Server

Vachon, Brigitte Marie Christine; Sobie, Randall

2002-01-01

A search for evidence that fundamental particles are made of smaller subconstituents is performed. The existence of excited states of fundamental particles would be an unambiguous indication of their composite nature. Experimental signatures compatible with the production of excited states of charged leptons in electron-positron collisions are studied. The data analysed were collected by the OPAL detector at the LEP collider. No evidence for the existence of excited states of charged leptons was found. Upper limits on the product of the cross-section and the electromagnetic branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

Molecular-alignment dependence in the transfer excitation of H2

International Nuclear Information System (INIS)

Wang, Y.D.; McGuire, J.H.; Weaver, O.L.; Corchs, S.E.; Rivarola, R.D.

1993-01-01

Molecular-alignment effects in the transfer excitation of H 2 by high-velocity heavy ions are studied using a two-step mechanism with amplitudes evaluated from first-order perturbation theory. Two-electron transfer excitation is treated as a result of two independent collision processes (excitation and electron transfer). Cross sections for each one-electron subprocess as well as the combined two-electron process are calculated as functions of the molecular-alignment angle. Within the independent-electron approximation, the dynamic roles of electron excitation and transfer in conjunction with molecular alignment are explored. While both excitation and transfer cross sections may strongly depend on molecular alignment, it is electron transfer that is largely responsible for the molecular-alignment dependence in the transfer excitation process. Interpretation of some experimental observations based on this model will also be discussed

Self-excitation of space charge waves

DEFF Research Database (Denmark)

Lyuksyutov, Sergei; Buchhave, Preben; Vasnetsov, Mikhail

1997-01-01

We report a direct observation of space charge waves in photorefractive crystals with point group 23 (sillenites) based on their penetration into an area with uniform light illumination. It is shown experimentally that the quality factor of the waves increases substantially with respect to what c...... current theory predicts [B. Sturman el al., Appl. Phys. A 55, 235 (1992)]. This results in the appearance of strong spontaneous beams caused by space charge wave self-excitation....

Structural dynamics of a noncovalent charge transfer complex from femtosecond stimulated Raman spectroscopy.

Science.gov (United States)

Fujisawa, Tomotsumi; Creelman, Mark; Mathies, Richard A

2012-09-06

Femtosecond stimulated Raman spectroscopy is used to examine the structural dynamics of photoinduced charge transfer within a noncovalent electron acceptor/donor complex of pyromellitic dianhydride (PMDA, electron acceptor) and hexamethylbenzene (HMB, electron donor) in ethylacetate and acetonitrile. The evolution of the vibrational spectrum reveals the ultrafast structural changes that occur during the charge separation (Franck-Condon excited state complex → contact ion pair) and the subsequent charge recombination (contact ion pair → ground state complex). The Franck-Condon excited state is shown to have significant charge-separated character because its vibrational spectrum is similar to that of the ion pair. The charge separation rate (2.5 ps in ethylacetate and ∼0.5 ps in acetonitrile) is comparable to solvation dynamics and is unaffected by the perdeuteration of HMB, supporting the dominant role of solvent rearrangement in charge separation. On the other hand, the charge recombination slows by a factor of ∼1.4 when using perdeuterated HMB, indicating that methyl hydrogen motions of HMB mediate the charge recombination process. Resonance Raman enhancement of the HMB vibrations in the complex reveals that the ring stretches of HMB, and especially the C-CH(3) deformations are the primary acceptor modes promoting charge recombination.

Single-step electron transfer on the nanometer scale: ultra-fast charge shift in strongly coupled zinc porphyrin-gold porphyrin dyads.

Science.gov (United States)

Fortage, Jérôme; Boixel, Julien; Blart, Errol; Hammarström, Leif; Becker, Hans Christian; Odobel, Fabrice

2008-01-01

The synthesis, electrochemical properties, and photoinduced electron transfer processes of a series of three novel zinc(II)-gold(III) bisporphyrin dyads (ZnP--S--AuP(+)) are described. The systems studied consist of two trisaryl porphyrins connected directly in the meso position via an alkyne unit to tert-(phenylenethynylene) or penta(phenylenethynylene) spacers. In these dyads, the estimated center to center interporphyrin separation distance varies from 32 to 45 A. The absorption, emission, and electrochemical data indicate that there are strong electronic interactions between the linked elements, thanks to the direct attachment of the spacer on the porphyrin ring through the alkyne unit. At room temperature in toluene, light excitation of the zinc porphyrin results in almost quantitative formation of the charge shifted state (.+)ZnP--S--AuP(.), whose lifetime is in the order of hundreds of picoseconds. In this solvent, the charge-separated state decays to the ground state through the intermediate population of the zinc porphyrin triplet excited state. Excitation of the gold porphyrin leads instead to rapid energy transfer to the triplet ZnP. In dichloromethane the charge shift reactions are even faster, with time constants down to 2 ps, and may be induced also by excitation of the gold porphyrin. In this latter solvent, the longest charge-shifted lifetime (tau=2.3 ns) was obtained with the penta-(phenylenethynylene) spacer. The charge shift reactions are discussed in terms of bridge-mediated super-exchange mechanisms as electron or hole transfer. These new bis-porphyrin arrays, with strong electronic coupling, represent interesting molecular systems in which extremely fast and efficient long-range photoinduced charge shift occurs over a long distance. The rate constants are two to three orders of magnitude larger than for corresponding ZnP--AuP(+) dyads linked via meso-phenyl groups to oligo-phenyleneethynylene spacers. This study demonstrates the critical

Charge transfer in photorechargeable composite films of TiO2 and polyaniline

Science.gov (United States)

Nomiyama, Teruaki; Sasabe, Kenichi; Sakamoto, Kenta; Horie, Yuji

2015-07-01

A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2-polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness LS of the TiO2-PANi mixture. The quantum efficiency QEuv for UV photons had a maximum of ˜7% at LS ˜ 7 µm. The time constant τTP for the charge transfer was about 10-1 s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi.

A schematic model for energy and charge transfer in the chlorophyll complex

DEFF Research Database (Denmark)

Bohr, Henrik; Malik, F.B.

2011-01-01

A theory for simultaneous charge and energy transfer in the carotenoid-chlorophyll-a complex is presented here and discussed. The observed charge transfer process in these chloroplast complexes is reasonably explained in terms of this theory. In addition, the process leads to a mechanism to drive...... an electron in a lower to a higher-energy state, thus providing a mechanism for the ejection of the electron to a nearby molecule (chlorophyll) or into the environment. The observed lifetimes of the electronically excited states are in accord/agreement with the investigations of Sundström et al....... and are in the range of pico-seconds and less. The change in electronic charge distribution in internuclear space as the system undergoes an electronic transition to a higher-energy state could, under appropriate physical conditions, lead to oscillating dipoles capable of transmitting energy from the carotenoid-chlorophylls...

Cascading electron and hole transfer dynamics in a CdS/CdTe core-shell sensitized with bromo-pyrogallol red (Br-PGR): slow charge recombination in type II regime.

Science.gov (United States)

Maity, Partha; Debnath, Tushar; Chopra, Uday; Ghosh, Hirendra Nath

2015-02-14

Ultrafast cascading hole and electron transfer dynamics have been demonstrated in a CdS/CdTe type II core-shell sensitized with Br-PGR using transient absorption spectroscopy and the charge recombination dynamics have been compared with those of CdS/Br-PGR composite materials. Steady state optical absorption studies suggest that Br-PGR forms strong charge transfer (CT) complexes with both the CdS QD and CdS/CdTe core-shell. Hole transfer from the photo-excited QD and QD core-shell to Br-PGR was confirmed by both steady state and time-resolved emission spectroscopy. Charge separation was also confirmed by detecting electrons in the conduction band of the QD and the cation radical of Br-PGR as measured from femtosecond transient absorption spectroscopy. Charge separation in the CdS/Br-PGR composite materials was found to take place in three different pathways, by transferring the photo-excited hole of CdS to Br-PGR, electron injection from the photo-excited Br-PGR to the CdS QD, and direct electron transfer from the HOMO of Br-PGR to the conduction band of the CdS QD. However, in the CdS/CdTe/Br-PGR system hole transfer from the photo-excited CdS to Br-PGR and electron injection from the photo-excited Br-PGR to CdS take place after cascading through the CdTe shell QD. Charge separation also takes place via direct electron transfer from the Br-PGR HOMO to the conduction band of CdS/CdTe. Charge recombination (CR) dynamics between the electron in the conduction band of the CdS QD and the Br-PGR cation radical were determined by monitoring the bleach recovery kinetics. The CR dynamics were found to be much slower in the CdS/CdTe/Br-PGR system than in the CdS/Br-PGR system. The formation of the strong CT complex and the separation of charges cascading through the CdTe shell help to slow down charge recombination in the type II regime.

Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

Directory of Open Access Journals (Sweden)

Rebecca Boll

2016-07-01

Full Text Available Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse.

A new pathway for transmembrane electron transfer in photosynthetic reaction centers of Rhodobacter sphaeroides not involving the excited special pair.

NARCIS (Netherlands)

van Brederode, M.E.; Jones, M.R.; van Mourik, F.; van Stokkum, I.H.M.; van Grondelle, R.

1997-01-01

It is generally accepted that electron transfer in bacterial photosynthesis is driven by the first singlet excited state of a special pair of bacteriochlorophylls (P*). We have examined the first steps of electron transfer in a mutant of the Rhodobacter sphaeroides reaction center in which charge

A new pathway for transmembrane electron transfer in photosyntetic reaction centers of Rhodobacter sphaeroides not involving the excited special pair.

NARCIS (Netherlands)

van Brederode, M.E.; Jones, M.R.; van Mourik, F.; van Stokkum, I.H.M.; van Grondelle, R.

1997-01-01

It is generally accepted that electron transfer in bacterial photosynthesis is driven by the first singlet excited state of a special pair of bacteriochlorophylls (P*). We have examined the first steps of electron transfer in a mutant of the Rhodobacter sphaeroides reaction center in which charge

Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation

Science.gov (United States)

Delor, Milan; Archer, Stuart A.; Keane, Theo; Meijer, Anthony J. H. M.; Sazanovich, Igor V.; Greetham, Gregory M.; Towrie, Michael; Weinstein, Julia A.

2017-11-01

Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt(II)-acetylide charge-transfer donor-bridge-acceptor-bridge-donor 'fork' system: asymmetric 13C isotopic labelling of one of the two -C≡C- bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UVpump(excitation)-IRpump(perturbation)-IRprobe(monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices.

Synthetic system mimicking the energy transfer and charge separation of natural photosynthesis

Energy Technology Data Exchange (ETDEWEB)

Gust, D.; Moore, T.A.

1985-05-01

A synthetic molecular triad consisting of a porphyrin P linked to both a quinone Q and a carotenoid polyene C has been prepared as a mimic of natural photosynthesis for solar energy conversion purposes. Laser flash excitation of the porphyrin moiety yields a charge-separated state Csup(+.)-P-Qsup(-.) within 100 ps with a quantum yield of more than 0.25. This charge-separated state has a lifetime on the microsecond time scale in suitable solvents. The triad also models photosynthetic antenna function and photoprotection from singlet oxygen damge. The successful biomimicry of photosynthetic charge separation is in part the result of multistep electron transfers which rapidly separate the charges and leave the system at high potential, but with a considerable barrier to recombination.

An abnormally slow proton transfer reaction in a simple HBO derivative due to ultrafast intramolecular-charge transfer events.

Science.gov (United States)

Alarcos, Noemí; Gutierrez, Mario; Liras, Marta; Sánchez, Félix; Douhal, Abderrazzak

2015-07-07

We report on the steady-state, picosecond and femtosecond time-resolved studies of a charge and proton transfer dye 6-amino-2-(2'-hydroxyphenyl)benzoxazole (6A-HBO) and its methylated derivative 6-amino-2-(2'-methoxyphenyl)benzoxazole (6A-MBO), in different solvents. With femtosecond resolution and comparison with the photobehaviour of 6A-MBO, we demonstrate for 6A-HBO in solution, the photoproduction of an intramolecular charge-transfer (ICT) process at S1 taking place in ∼140 fs or shorter, followed by solvent relaxation in the charge transferred species. The generated structure (syn-enol charge transfer conformer) experiences an excited-state intramolecular proton-transfer (ESIPT) reaction to produce a keto-type tautomer. This subsequent proton motion occurs in 1.2 ps (n-heptane), 14 ps (DCM) and 35 ps (MeOH). In MeOH, it is assisted by the solvent molecules and occurs through tunneling for which we got a large kinetic isotope effect (KIE) of about 13. For the 6A-DBO (deuterated sample in CD3OD) the global proton-transfer reaction takes place in 200 ps, showing a remarkable slow KIE regime. The slow ESIPT reaction in DCM (14 ps), not through tunnelling as it is not sensitive to OH/OD exchange, has however to overcome an energy barrier using intramolecular as well as solvent coordinates. The rich ESIPT dynamics of 6A-HBO in the used solutions is governed by an ICT reaction, triggered by the amino group, and it is solvent dependent. Thus, the charge injection to a 6A-HBO molecular frame makes the ICT species more stable, and the phenol group less acidic, slowing down the subsequent ESIPT reaction. Our findings bring new insights into the coupling between ICT and ESIPT reactions on the potential-energy surfaces of several barriers.

The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C{sub 60} molecular triad

Energy Technology Data Exchange (ETDEWEB)

Olguin, Marco [Computational Science Program, University of Texas at El Paso, El Paso, Texas 79968 (United States); Basurto, Luis; Zope, Rajendra R. [Department of Physics, The University of Texas at El Paso, El Paso, Texas 79968 (United States); Baruah, Tunna, E-mail: tbaruah@utep.edu [Computational Science Program, University of Texas at El Paso, El Paso, Texas 79968 (United States); Department of Physics, The University of Texas at El Paso, El Paso, Texas 79968 (United States)

2014-05-28

We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C{sub 60} (CPC{sub 60}) molecular triad. The chain-like molecular triad undergoes photoinduced charge transfer process exhibiting a large excited state dipole moment, making it suitable for application to molecular-scale opto-electronic devices. An important consideration is that the structural flexibility of the CPC{sub 60} triad impacts its dynamics in solvents. Since experimentally measured dipole moments for the triad of ∼110 D and ∼160 D strongly indicate a range in structural variability in the excited state, studying the effect of structural changes on the CT excited state energetics furthers the understanding of its charge transfer states. We have calculated the variation in the lowest CT excited state energies by performing a scan of possible variation in the structure of the triad. Some of these configurations were generated by incrementally scanning a 360° torsional (dihedral) twist at the C{sub 60}-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC{sub 60} conformations were studied to determine the effect of pi-conjugation and particle-hole Coulombic attraction on the CT excitation energies. Our calculations show that configurational changes in the triad induces a variation of ∼0.6 eV in CT excited state energies in the gas-phase. The corresponding calculated excited state dipoles show a range of 47 D–188 D. The absorption spectra and density of states of these structures show little variation except for the structures where the porphyrin and aryl conjugation is changed.

Excited state populations and charge-exchange of fast ions in solids

International Nuclear Information System (INIS)

Miller, P.D.; Sofield, C.J.; Woods, C.J.

1984-01-01

Excited state populations and charge state fractions of 445 MeV Cl ions have been measured for a range of thicknesses of solid C targets. Cross sections for electron capture, loss, excitation and excited state quenching have been determined and these data are found to predict a quantitative difference between equilibrium charge state distributions from gases and solids for a special case of the Bohr-Lindhard density effect model. 8 references, 1 figure, 1 table

Integrated light in direct excitation and energy transfer luminescence

OpenAIRE

Chimczak, Eugeniusz

2007-01-01

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

Energy and charge transfer dynamics between Alq3 and CdSeS nanocrystals.

Science.gov (United States)

Zhang, Shuping; Liu, Yuqiang; Yang, Yanqiang

2010-03-01

The photoluminescence properties of the blend films consisting of organic small molecules and nanocrystals (NCs)--Alq3 and CdSeS NCs--were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy with different excited wavelengths. Both the fluorescence intensity and lifetime are intensively dependent on the NC concentration. The detailed analysis of experiment data proves that Forster energy transfer from the Alq3 to the NCs exists simultaneously with the charge transfer and both compete with each other in the blend films.

Unveiling the excited state energy transfer pathways in peridinin-chlorophyll a-protein by ultrafast multi-pulse transient absorption spectroscopy.

Science.gov (United States)

Redeckas, Kipras; Voiciuk, Vladislava; Zigmantas, Donatas; Hiller, Roger G; Vengris, Mikas

2017-04-01

Time-resolved multi-pulse methods were applied to investigate the excited state dynamics, the interstate couplings, and the excited state energy transfer pathways between the light-harvesting pigments in peridinin-chlorophyll a-protein (PCP). The utilized pump-dump-probe techniques are based on perturbation of the regular PCP energy transfer pathway. The PCP complexes were initially excited with an ultrashort pulse, resonant to the S 0 →S 2 transition of the carotenoid peridinin. A portion of the peridinin-based emissive intramolecular charge transfer (ICT) state was then depopulated by applying an ultrashort NIR pulse that perturbed the interaction between S 1 and ICT states and the energy flow from the carotenoids to the chlorophylls. The presented data indicate that the peridinin S 1 and ICT states are spectrally distinct and coexist in an excited state equilibrium in the PCP complex. Moreover, numeric analysis of the experimental data asserts ICT→Chl-a as the main energy transfer pathway in the photoexcited PCP systems. Copyright © 2017 Elsevier B.V. All rights reserved.

Differential charge-transfer cross sections for systems with energetically degenerate or near-degenerate channels

International Nuclear Information System (INIS)

Nguyen, H.; Bredy, R.; Camp, H.A.; DePaola, B.D.; Awata, T.

2004-01-01

Resolution plays a vital role in spectroscopic studies. In the usual recoil-ion momentum spectroscopy (RIMS), Q-value resolution is relied upon to distinguish between different collision channels: The better the Q-value resolution, the better one is able to resolve energetically similar channels. Although traditional COLTRIMS greatly improves Q-value resolution by cooling the target and thus greatly reducing the initial target momentum spread, the resolution of the technique is still limited by target temperature. However, with the recent development in RIMS, namely, magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) superior recoil ion momentum resolution as well as charge transfer measurements with laser excited targets have become possible. Through MOTRIMS, methods for the measurements of target excited state fraction and kinematically complete relative charge transfer cross sections have been developed, even for some systems having energetically degenerate or nearly degenerate channels. In the present work, the systems of interest having energy degeneracies or near degeneracies are Rb + , K + , and Li + colliding with trapped Rb(5l), where l=s and p

Lifetimes of partial charge transfer exciplexes of 9-cyanophenanthrene and 9-cyanoanthracene

OpenAIRE

Dolotova, Elena; Dogadkin, Denis; Soboleva, Irina; Kuzmin, Michael; Nicolet, Olivier; Vauthey, Eric

2003-01-01

The fluorescence decays of several exciplexes with partial charge transfer have been investigated in solvents of various polarity. The measured lifetimes are found to be in reasonable agreement with the activation enthalpy and entropy of exciplex decay obtained earlier from the temperature dependence of the exciplex emission quantum yields. For exciplexes with 9-cyanophenanthrene substantial contribution of the higher local excited state into the exciplex electronic structure is found and bor...

Effect of Viscosity and Polar Properties of Solvent on Dynamics of Photoinduced Charge Transfer in BTA-1 Cation — Derivative of Thioflavin T

Science.gov (United States)

Gogoleva, S. D.; Stsiapura, V. I.

2018-05-01

It was found that the spectral and fluorescent properties of BTA-1C cation in protic and aprotic solvents differ. It was shown that for solutions in long-chain alcohols viscosity is the main factor that determines the dynamics of intramolecular charge transfer in the excited state of the BTA-1C molecule. In the case of aprotic solvents a correlation was found between the rate constant of twisted intramolecular charge transfer (TICT) during rotation of fragments of the molecule in relation to each other in the excited state and the solvent relaxation rate: k TICT 1/τ S .

Excitation functions for quasi-elastic transfer reactions induced with heavy ions in bismuth

International Nuclear Information System (INIS)

Gardes, D.; Bimbot, R.; Maison, J.; Reilhac, L. de; Rivet, M.F.; Fleury, A.; Hubert, F.; Llabador, Y.

1977-01-01

The excitation functions for the production of 210 Bi, 210 Po, sup(207-211)At and 211 Rn through quasi-elastic transfer reactions induced with heavy ions in 209 Bi have been measured. The corresponding reactions involved the transfer of one neutron, one proton, two and three charges from projectile to target. The projectiles used were 12 C, 14 N, 16 O, 19 F, 20 Ne, 40 Ca, 56 Fe and 63 Cu. The experimental techniques involved target irradiations and off-line α and γ activity measurements. Chemical separations were used to solve specific problems. Careful measurements of incident energies and cross sections were performed close to the reaction thresholds

Charge Transfer in Collisions of S^4+ with H.

Science.gov (United States)

Stancil, P. C.; Turner, A. R.; Cooper, D. L.; Schultz, D. R.; Rakovic, M. J.; Fritsch, W.; Zygelman, B.

2001-05-01

Charge transfer processes due to collisions of ground state S^4+ ions with atomic hydrogen were investigated for energies between 1 meV/u and 10 MeV/u using the quantum-mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC), and continuum distorted wave methods. The MOCC calculations utilized ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. A number of variants of the CTMC approach were explored, including different momentum and radial distributions for the initial state, as well as effective charge and quantum-defect models to determine the corresponding quantum state after capture into final partially-stripped S^3+ excited classical states. Hydrogen target isotope effects were explored and rate coefficients for temperatures between 100 and 10^6 K will be presented

Spontaneous charged lipid transfer between lipid vesicles.

Science.gov (United States)

Richens, Joanna L; Tyler, Arwen I I; Barriga, Hanna M G; Bramble, Jonathan P; Law, Robert V; Brooks, Nicholas J; Seddon, John M; Ces, Oscar; O'Shea, Paul

2017-10-03

An assay to study the spontaneous charged lipid transfer between lipid vesicles is described. A donor/acceptor vesicle system is employed, where neutrally charged acceptor vesicles are fluorescently labelled with the electrostatic membrane probe Fluoresceinphosphatidylethanolamine (FPE). Upon addition of charged donor vesicles, transfer of negatively charged lipid occurs, resulting in a fluorescently detectable change in the membrane potential of the acceptor vesicles. Using this approach we have studied the transfer properties of a range of lipids, varying both the headgroup and the chain length. At the low vesicle concentrations chosen, the transfer follows a first-order process where lipid monomers are transferred presumably through the aqueous solution phase from donor to acceptor vesicle. The rate of transfer decreases with increasing chain length which is consistent with energy models previously reported for lipid monomer vesicle interactions. Our assay improves on existing methods allowing the study of a range of unmodified lipids, continuous monitoring of transfer and simplified experimental procedures.

Photoinduced Charge Shifts and Electron Transfer in Viologen-Tetraphenylborate Complexes: Push-Pull Character of the Exciplex.

Science.gov (United States)

Santos, Willy G; Budkina, Darya S; Deflon, Victor M; Tarnovsky, Alexander N; Cardoso, Daniel R; Forbes, Malcolm D E

2017-06-14

Viologen-tetraarylborate ion-pair complexes were prepared and investigated by steady-state and time-resolved spectroscopic techniques such as fluorescence and femtosecond transient absorption. The results highlight a charge transfer transition that leads to changes in the viologen structure in the excited singlet state. Femtosecond transient absorption reveals the formation of excited-state absorption and stimulated emission bands assigned to the planar (k obs < 10 12 s -1 ) and twisted (k obs ∼ 10 10 s -1 ) structures between two pyridinium groups in the viologen ion. An efficient photoinduced electron transfer from the tetraphenylborate anionic moiety to the viologen dication was observed less than 1 μs after excitation. This is a consequence of the push-pull character of the electron donor twisted viologen structure, which helps formation of the borate triplet state. The borate triplet state is deactivated further via a second electron transfer process, generating viologen cation radical (V •+ ).

Spectroscopic study of the charge-transfer complexes TiCl4/styrene and TiCl4/polystyrene

Science.gov (United States)

Gonçalves, Norberto S.; Noda, Lúcia. K.

2017-10-01

In this work, solutions of TiCl4/styrene and TiCl4/polystyrene charge-transfer complexes in CHCl3 or CDCl3 were investigated by UV-vis, resonance Raman and 1H NMR spectroscopies in order to study their molecular and electronic structures. Both show a yellow colour due to absorption in the 400 nm region, related to a charge-transfer transition. In Raman spectra, as the excitation approaches the resonance region, the primary enhancement of aromatic ring modes was mainly observed, rather than intensification of the vinylic double-bond stretch. Under the experimental conditions it was observed that formation of polystyrene takes place, as showed by 1H NMR spectra, and the most significant interaction occurs at the aromatic ring, as supported by the results from interaction of TiCl4 with polystyrene, as indicated by the charge-transfer band and resonant intensification of the aromatic ring modes.

Competitive photocyclization/rearrangement of 4-aryl-1,1-dicyanobutenes controlled by intramolecular charge-transfer interaction. Effect of medium polarity, temperature, pressure, excitation wavelength, and confinement.

Science.gov (United States)

Ito, Tadashi; Nishiuchi, Emi; Fukuhara, Gaku; Inoue, Yoshihisa; Mori, Tadashi

2011-09-01

A series of 4-aryl-1,1-dicyanobutenes (1a-1f) with different substituents were synthesized to control the intramolecular donor-acceptor or charge-transfer (C-T) interactions in the ground state. Photoexcitation of these C-T substrates led to competitive cyclization and rearrangement, the ratio being critically controlled by various environmental factors, such as solvent polarity, temperature and static pressure, and also by excitation wavelength and supramolecular confinement (polyethylene voids). In non-polar solvents, the rearrangement was dominant (>10 : 1) for all examined substrates, while the cyclization was favoured in polar solvents, in particular at low temperatures. Selective excitation at the C-T band further enhanced the cyclization up to >50 : 1 ratios. More importantly, the cyclization/rearrangement ratio was revealed to be a linear function of the C-T transition energy. However, the substrates with a sterically demanding or highly electron-donating substituent failed to give the cyclization product.

The simplest equivalent circuit of a pulsed dielectric barrier discharge and the determination of the gas gap charge transfer

Science.gov (United States)

Pipa, A. V.; Koskulics, J.; Brandenburg, R.; Hoder, T.

2012-11-01

The concept of the simplest equivalent circuit for a dielectric barrier discharge (DBD) is critically reviewed. It is shown that the approach is consistent with experimental data measured either in large-scale sinusoidal-voltage driven or miniature pulse-voltage driven DBDs. An expression for the charge transferred through the gas gap q(t) is obtained with an accurate account for the displacement current and the values of DBD reactor capacitance. This enables (i) the significant reduction of experimental error in the determination of q(t) in pulsed DBDs, (ii) the verification of the classical electrical theory of ozonizers about maximal transferred charge qmax, and (iii) the development of a graphical method for the determination of qmax from charge-voltage characteristics (Q-V plots, often referred as Lissajous figures) measured under pulsed excitation. The method of graphical presentation of qmax is demonstrated with an example of a Q-V plot measured under pulsed excitation. The relations between the discharge current jR(t), the transferred charge q(t), and the measurable parameters are presented in new forms, which enable the qualitative interpretation of the measured current and voltage waveforms without the knowledge about the value of the dielectric barrier capacitance Cd. Whereas for quantitative evaluation of electrical measurements, the accurate estimation of the Cd is important.

Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

KAUST Repository

Alsam, Amani Abdu; Aly, Shawkat Mohammede; Usman, Anwar; Parida, Manas R.; Del Gobbo, Silvano; Alarousu, Erkki; Mohammed, Omar F.

2015-01-01

We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

KAUST Repository

Alsam, Amani Abdu

2015-09-02

We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

Radioactive beam EXperiments at ISOLDE : Coulomb excitation and neutron transfer reactions of exotic nuclei.

CERN Multimedia

Kugler, E; Ratzinger, U; Wenander, F J C

2002-01-01

% IS347 \\\\ \\\\We propose to perform a pilot experiment to study very neutron rich (A<32) Na-Mg and (A<52) K-Ca isotopes in the region around the neutron shell closures of N=20 and N=28 after Coulomb excitation and neutron transfer, and to demonstrate highly efficient and cost-effective ways to bunch, charge-state breed and accelerate already existing mass-separated singly-charged radioactive ion beams. \\\\ \\\\To do this we plan to accelerate the ISOLDE beams up to 2~MeV/u by means of a novel acceleration scheme and to install an efficient $\\gamma$-ray array for low-multiplicity events around the target position.

Femtosecond stimulated Raman evidence for charge-transfer character in pentacene singlet fission.

Science.gov (United States)

Hart, Stephanie M; Silva, W Ruchira; Frontiera, Renee R

2018-02-07

Singlet fission is a spin-allowed process in which an excited singlet state evolves into two triplet states. We use femtosecond stimulated Raman spectroscopy, an ultrafast vibrational technique, to follow the molecular structural evolution during singlet fission in order to determine the mechanism of this process. In crystalline pentacene, we observe the formation of an intermediate characterized by pairs of excited state peaks that are red- and blue-shifted relative to the ground state features. We hypothesize that these features arise from the formation of cationic and anionic species due to partial transfer of electron density from one pentacene molecule to a neighboring molecule. These observations provide experimental evidence for the role of states with significant charge-transfer character which facilitate the singlet fission process in pentacene. Our work both provides new insight into the singlet fission mechanism in pentacene and demonstrates the utility of structurally-sensitive time-resolved spectroscopic techniques in monitoring ultrafast processes.

Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

Energy Technology Data Exchange (ETDEWEB)

Haverkate, Lucas A.; Mulder, Fokko M. [Reactor Institute Delft, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Zbiri, Mohamed, E-mail: zbiri@ill.fr; Johnson, Mark R. [Institut Laue Langevin, 38042 Grenoble Cedex 9 (France); Carter, Elizabeth [Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, NSW 2008 (Australia); Kotlewski, Arek; Picken, S. [ChemE-NSM, Faculty of Chemistry, Delft University of Technology, 2628BL/136 Delft (Netherlands); Kearley, Gordon J. [Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 (Australia)

2014-01-07

Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10{sup −2} electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

Discrete and continuum modeling of solvent effects in a twisted intramolecular charge transfer system: The 4-N,N-dimethylaminobenzonitrile (DMABN) molecule.

Science.gov (United States)

Modesto-Costa, Lucas; Borges, Itamar

2018-08-05

The 4-N,N-dimethylaminobenzonitrile (DMABN) molecule is a prototypical system displaying twisted intramolecular (TICT) charge transfer effects. The ground and the first four electronic excited states (S 1 -S 4 ) in gas phase and upon solvation were studied. Charge transfer values as function of the torsion angle between the donor group (dimethylamine) and the acceptor moiety (benzonitrile) were explicitly computed. Potential energy curves were also obtained. The algebraic diagrammatic construction method at the second-order [ADC(2)] ab initio wave function was employed. Three solvents of increased polarities (benzene, DMSO and water) were investigated using discrete (average solvent electrostatic configuration - ASEC) and continuum (conductor-like screening model - COSMO) models. The results for the S 3 and S 4 excited states and the S 1 -S 4 charge transfer curves were not previously available in the literature. Electronic gas phase and solvent vertical spectra are in good agreement with previous theoretical and experimental results. In the twisted (90°) geometry the optical oscillator strengths have negligible values even for the S 2 bright state. Potential energy curves show two distinct pairs of curves intersecting at decreasing angles or not crossing in the more polar solvents. Charge transfer and electric dipole values allowed the rationalization of these results. The former effects are mostly independent of the solvent model and polarity. Although COSMO and ASEC solvent models mostly lead to similar results, there is an important difference: some crossings of the excitation energy curves appear only in the ASEC solvation model, which has important implications to the photochemistry of DMABN. Copyright © 2018 Elsevier B.V. All rights reserved.

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

International Nuclear Information System (INIS)

Sobolewski, Andrzej L.; Domcke, Wolfgang

2003-01-01

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

The simplest equivalent circuit of a pulsed dielectric barrier discharge and the determination of the gas gap charge transfer

International Nuclear Information System (INIS)

Pipa, A. V.; Brandenburg, R.; Hoder, T.; Koskulics, J.

2012-01-01

The concept of the simplest equivalent circuit for a dielectric barrier discharge (DBD) is critically reviewed. It is shown that the approach is consistent with experimental data measured either in large-scale sinusoidal-voltage driven or miniature pulse-voltage driven DBDs. An expression for the charge transferred through the gas gap q(t) is obtained with an accurate account for the displacement current and the values of DBD reactor capacitance. This enables (i) the significant reduction of experimental error in the determination of q(t) in pulsed DBDs, (ii) the verification of the classical electrical theory of ozonizers about maximal transferred charge q max , and (iii) the development of a graphical method for the determination of q max from charge-voltage characteristics (Q-V plots, often referred as Lissajous figures) measured under pulsed excitation. The method of graphical presentation of q max is demonstrated with an example of a Q-V plot measured under pulsed excitation. The relations between the discharge current j R (t), the transferred charge q(t), and the measurable parameters are presented in new forms, which enable the qualitative interpretation of the measured current and voltage waveforms without the knowledge about the value of the dielectric barrier capacitance C d . Whereas for quantitative evaluation of electrical measurements, the accurate estimation of the C d is important.

Ultrafast Nonradiative Decay and Excitation Energy Transfer by Carotenoids in Photosynthetic Light-Harvesting Proteins

Science.gov (United States)

Ghosh, Soumen

This dissertation investigates the photophysical and structural dynamics that allow carotenoids to serve as efficient excitation energy transfer donor to chlorophyll acceptors in photosynthetic light harvesting proteins. Femtosecond transient grating spectroscopy with optical heterodyne detection has been employed to follow the nonradiative decay pathways of carotenoids and excitation energy transfer to chlorophylls. It was found that the optically prepared S2 (11Bu+) state of beta-carotene decays in 12 fs fs to populate an intermediate electronic state, Sx, which then decays nonradiatively to the S 1 state. The ultrafast rise of the dispersion component of the heterodyne transient grating signal reports the formation of Sx intermediate since the rise of the dispersion signal is controlled by the loss of stimulated emission from the S2 state. These findings were extended to studies of peridinin, a carbonyl substituted carotenoid that serves as a photosynthetic light-harvesting chromophore in dinoflagellates. Numerical simulations using nonlinear response formalism and the multimode Brownian oscillator model assigned the Sx intermediate to a torsionally distorted structure evolving on the S2 potential surface. The decay of the Sx state is promoted by large amplitude out-of-plane torsional motions and is significantly retarded by solvent friction owing to the development of an intramolecular charge transfer character in peridinin. The slowing of the nonradiative decay allows the Sx state to transfer significant portion of the excitation energy to chlorophyll a acceptors in the peridinin-chlorophyll a protein. The results of heterodyne transient grating study on peridinin-chlorophyll a protein suggests two distinct energy transfer channels from peridinin to chlorophyll a: a 30 fs process involving quantum coherence and delocalized peridinin-Chl states and an incoherent, 2.5 ps process involving the distorted S2 state of peridinin. The torsional evolution on the S2

Electronic-excitation energy transfer in heterogeneous dye solutions under laser excitation

International Nuclear Information System (INIS)

Levshin, L.V.; Mukushev, B.T.; Saletskii, A.M.

1995-01-01

An experimental study has been made of electronic-excitation energy transfer (EEET) among dye molecules of different types for different exciting-fight wavelengths and temperatures. Upon selective laser excitation of the donor, the inhomogeneous broadening of molecular levels increases the probability of EEET from the donor to acceptor molecules. The efficiency of this process is directly proportional to the acceptor molecule concentration and is temperature dependent. The EEET is accompanied by the spectral migration of energy among donor molecules, which reduces the fluorescence quantum efficiency of the donor. Increasing the frequency of the exciting light decreases in the donor fluorescence quantum efficiency. An increase in the acceptor molecule concentration results in a decrease of the spectral migration of excitation in the donor molecule system. 5 refs., 5 figs

State-selective charge transfer cross sections for light ion impact of atomic hydrogen

Energy Technology Data Exchange (ETDEWEB)

Schultz, D. R. [University of North Texas; Stancil, Phillip C. [University of Georgia, Athens; Havener, C. C. [Oak Ridge National Laboratory (ORNL)

2015-01-01

Owing to the utility of diagnosing plasma properties such as impurity concentration and spatial distribution, and plasma temperature and rotation, by detection of photon emission following capture of electrons from atomic hydrogen to excited states of multiply charged ions, new calculations of state-selective charge transfer involving light ions have been carried out using the atomic orbital close-coupling and the classical trajectory Monte Carlo methods. By comparing these with results of other approaches applicable in a lower impact energy regime, and by benchmarking them using key experimental data, knowledge of the cross sections can be made available across the range parameters needed by fusion plasma diagnostics.

Cross sections of electron excitation out of metastable helium levels with a fast metastable target product produced via charge exchange

International Nuclear Information System (INIS)

Lagus, M.E.; Boffard, J.B.; Anderson, L.W.; Lin, C.C.

1996-01-01

Absolute direct cross sections for electron excitation out of the 2 3 S level and into the 3 3 D, 4 3 D, and 3 3 S levels of the helium atom from threshold to 500 eV and into the 3 3 P level over a more limited energy range have been measured using a fast metastable atomic beam target. We produce the metastable atoms via near-resonant charge exchange between a 1.6-keV He + ion beam and Cs vapor. Because this reaction is highly nonresonant with the ground state of helium, the charge-transfer process yields a primarily metastable beam. We use a thermal detector which we calibrate with ions to measure absolutely the neutral beam flux. The atomic beam is crossed by an electron beam, and we collect the resulting fluorescence at right angles to both the electron and atomic beams. We obtain the cross sections for excitation out of the 2 3 S level into the various excited levels by monitoring the emission out of the excited level of interest. copyright 1996 The American Physical Society

Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy.

Science.gov (United States)

Akhtar, Parveen; Zhang, Cheng; Liu, Zhengtang; Tan, Howe-Siang; Lambrev, Petar H

2018-03-01

Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon's energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet-singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3-4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67-75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits-a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3-4 ps component is ascribed to equilibration with a "red" core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P 700 reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.

Charge Transfer into Aqueous Droplets via Kilovolt Potentials

Science.gov (United States)

Hamlin, B. S.; Rosenberg, E. R.; Ristenpart, W. D.

2012-11-01

When an aqueous droplet immersed in an insulating oil contacts an electrified surface, the droplet acquires net charge. For sufficiently large field strengths, the charged droplet is driven back and forth electrophoretically between the electrodes, in essence ``bouncing'' between them. Although it is clear that the droplet acquires charge, the underlying mechanism controlling the charge transfer process has been unclear. Here we demonstrate that the chemical species present in the droplet strongly affect the charge transfer process into the drop. Using two independent charge measurement techniques, high speed video velocimetry and direct current measurement, we show that the charge acquired during contact is strongly influenced by the droplet pH. We also provide physical evidence that the electrodes undergo electroplating or corrosion for droplets with appropriate chemical species present. Together, the observations strongly suggest that electrochemical reactions govern the charge transfer process into the droplet.

Multi-step intramolecular excitation energy transfer in dendritic pyrene-phosphorus(V)porphyrin heptads

Energy Technology Data Exchange (ETDEWEB)

Hirakawa, Kazutaka, E-mail: hirakawa.kazutaka@shizuoka.ac.jp [Applied Chemistry and Biochemical Engineering Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, Johoku 3-5-1, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Department of Optoelectronics and Nanostructure Science, Graduate School of Science and Technology, Shizuoka University, Johoku 3-5-1, Naka-ku, Hamamatsu, Shizuoka 432-8561 (Japan); Segawa, Hiroshi [Department of Multi-Disciplinary Science - General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8904 (Japan); Research Center for Advanced Science and Technology, The University of Tokyo, Komaba 4-6-1, Meguro-ku, Tokyo 153-8904 (Japan)

2016-11-15

Dendritic heptad molecules in which four pyrenyl groups are connected at the central phosphorus atom of the edge-porphyrins of the center-to-edge type porphyrin trimers were synthesized to investigate a multi-step excitation energy transfer. As the central energy acceptor, two types porphyrins which one was phosphorus(V)tetraphenylporphyrin (H2) and another was its derivative substituted by butoxy groups at four para-position of meso-phenyl groups (H1) were used. In the photoexcited state of the pyrene units, the excitation energy transfer to the central-porphyrin unit was observed in toluene. The excitation energy transfer is considered to be through two pathways; one is a stepwise pathway through the edge-porphyrin unit and another is a direct excitation energy transfer to the central porphyrin. The direct excitation energy transfer from pyrenes to the edge-porphyrin and central-porphyrin were observed in the case for H1. From the excited state of the edge-porphyrins, the excitation energy transfer to the central-porphyrin occurs in the H1 case. In the H2 case, the excitation energy of central-porphyrin is higher than that of H1, and the electron transfer from edge-porphyrin to the central-porphyrin become predominant process. - Highlights: • Dendritic pyrene-porphyrin heptads were synthesized. • Excitation energy transfer occurs from the pyrenyl moiety to the phosphorus(V)porphyrin. • The stepwise and direct energy transfer pathways were observed. • The quantum yields of these energy transfer pathways could be determined.

Multi-step intramolecular excitation energy transfer in dendritic pyrene-phosphorus(V)porphyrin heptads

International Nuclear Information System (INIS)

Hirakawa, Kazutaka; Segawa, Hiroshi

2016-01-01

Dendritic heptad molecules in which four pyrenyl groups are connected at the central phosphorus atom of the edge-porphyrins of the center-to-edge type porphyrin trimers were synthesized to investigate a multi-step excitation energy transfer. As the central energy acceptor, two types porphyrins which one was phosphorus(V)tetraphenylporphyrin (H2) and another was its derivative substituted by butoxy groups at four para-position of meso-phenyl groups (H1) were used. In the photoexcited state of the pyrene units, the excitation energy transfer to the central-porphyrin unit was observed in toluene. The excitation energy transfer is considered to be through two pathways; one is a stepwise pathway through the edge-porphyrin unit and another is a direct excitation energy transfer to the central porphyrin. The direct excitation energy transfer from pyrenes to the edge-porphyrin and central-porphyrin were observed in the case for H1. From the excited state of the edge-porphyrins, the excitation energy transfer to the central-porphyrin occurs in the H1 case. In the H2 case, the excitation energy of central-porphyrin is higher than that of H1, and the electron transfer from edge-porphyrin to the central-porphyrin become predominant process. - Highlights: • Dendritic pyrene-porphyrin heptads were synthesized. • Excitation energy transfer occurs from the pyrenyl moiety to the phosphorus(V)porphyrin. • The stepwise and direct energy transfer pathways were observed. • The quantum yields of these energy transfer pathways could be determined.

Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond

Indian Academy of Sciences (India)

Ultrafast Dynamics of Chemical Reactions in Condensed Phase: Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond · PowerPoint Presentation · Slide 3 · Slide 4 · Slide 5 · Slide 6 · Slide 7 · Slide 8 · Slide 9 · Slide 10 · Slide 11 · Slide 12 · Slide 13 · Slide 14 · Slide 15 · Slide 16 · Slide 17 · Slide 18 · Slide 19.

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

International Nuclear Information System (INIS)

Tanis, J.A.; Bernstein, E.M.; Clark, M.W.

1985-01-01

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

Excited state intramolecular charge transfer reaction in 4-(1 ...

Indian Academy of Sciences (India)

Administrator

cal reactions to the determination of paleotempera- tures from isotopic ... ordered liquid than H2O due to stronger H-bond in- teractions in the deuterated water ... layer chromatography and monitoring the excitation wavelength dependence of ...

Spectral Properties of Dyes with Interfragmental Charge Transfer: Solvatochromism and Solvatofluorochromism of 2-(3-Coumaroyl-benzopyrylium Perchlorates

Directory of Open Access Journals (Sweden)

Edward V. Sanin

2014-01-01

Full Text Available The paper deals with the spectral properties of dyes with interfragmental charge transfer, in particular, derivatives of 2-(3-coumaroylbenzopyrylium (CBP perchlorates. The positions of long-wavelength absorption and emission bands, quantum yields, and lifetimes of fluorescence were measured, mostly in aprotic solvents. Regression analysis of the relationship between the spectral characteristics of CBP and the main solvent parameters (polarity, polarisability, nucleophilicity, and electrophilicity was carried out. It was found that the characteristics of CBP depend mainly on two solvent parameters—polarity and/or nucleophilicity. An increase in these parameters results in a hypsochromic shift of absorption bands and a decrease of lifetimes and fluorescence intensity. The positions of the emission bands can demonstrate either hypsochromism or bathochromism, depending on the nature of the substituents. The solvatofluorochromic effects are not as strong as the solvatochromic ones. We believe that the spectral behaviour of CBP can be explained by cation depolarisation and by a decrease in the stability of nucleophilic complexes with solvent molecules that is associated with interfragmental charge transfer following excitation, relaxation, and radiative deactivation of the excited state.

Local charge exchange of He{sup +} ions at Aluminum surfaces

Energy Technology Data Exchange (ETDEWEB)

Riccardi, P., E-mail: pierfrancesco.riccardi@fis.unical.it [Dipartimento di Fisica, Università della Calabria and INFN – Gruppo collegato di Cosenza, Via P. Bucci cubo 33C, Arcavacata di Rende, Cosenza (Italy); Sindona, A. [Dipartimento di Fisica, Università della Calabria and INFN – Gruppo collegato di Cosenza, Via P. Bucci cubo 33C, Arcavacata di Rende, Cosenza (Italy); Dukes, C.A. [Laboratory for Astrophysics and Surface Physics, Materials Science and Engineering University of Virginia, Charlottesville, VA 22904 (United States)

2017-04-04

We report on experiments designed to observe the correlation between the autoionization of doubly excited helium atoms and the Auger decay of 2p vacancies in Al. The autoionizing states are formed when incident He{sup +*} and He{sup ++} are neutralized by resonant electron capture at the surface. 2p excitation in Al occurs in dielectronic charge transfer during the close encounter of an excited helium ion and an Al atom. These results clarify the mechanism for Al-2p excitation in the case of singly charged ground state He{sup +}(1s) ion impact, where the dielectronic transition occurs after promotion of the 1s electron of incoming ions. - Highlights: • We observe the correlation between autoionization of doubly excited helium atoms and the Auger decay of 2p vacancies in Al. • 2p excitation in Al occurs in dielectronic charge transfer during the close encounter of an excited helium ion and an Al atom. • These results clarify the mechanism for Al-2p excitation in the case of singly charged ground state He{sup +}(1s) ion impact.

Characterizing Plasmonic Excitations of Quasi-2D Chains

Science.gov (United States)

Townsend, Emily; Bryant, Garnett

A quantum description of the optical response of nanostructures and other atomic-scale systems is desirable for modeling systems that use plasmons for quantum information transfer, or coherent transport and interference of quantum states, as well as systems small enough for electron tunneling or quantum confinement to affect the electronic states of the system. Such a quantum description is complicated by the fact that collective and single-particle excitations can have similar energies and thus will mix. We seek to better understand the excitations of nanosystems to identify which characteristics of the excitations are most relevant to modeling their behavior. In this work we use a quasi 2-dimensional linear atomic chain as a model system, and exact diagonalization of the many-body Hamiltonian to obtain its excitations. We compare this to previous work in 1-d chains which used a combination of criteria involving a many-body state's transfer dipole moment, balance, transfer charge, dynamical response, and induced-charge distribution to identify which excitations are plasmonic in character.

Outer-shell excitation and capture processes: Alignment and orientation effects

International Nuclear Information System (INIS)

Andersen, N.; Dowek, D.; Dubois, A.; Hansen, J.P.; Nielsen, S.E.

1990-01-01

This contribution outlines some ongoing activities within a joint programme of experimental and theoretical studies of outer-shell excitation and charge transfer processes in atomic collisions. The main emphasis is presently on alignment and orientation phenomena. The aim is to reveal the shape and dynamics of the electronic charge cloud as it develops in time along the trajectory, and to understand these phenomena in terms of the underlying, basic mechanisms responsible for collisional excitation and transfer. (orig.)

Scientific Computation Application Partnerships in Materials and Chemical Sciences, Charge Transfer and Charge Transport in Photoactivated Systems, Developing Electron-Correlated Methods for Excited State Structure and Dynamics in the NWChem Software Suite

Energy Technology Data Exchange (ETDEWEB)

Cramer, Christopher J. [Univ. of Minnesota, Minneapolis, MN (United States)

2017-11-12

Charge transfer and charge transport in photoactivated systems are fundamental processes that underlie solar energy capture, solar energy conversion, and photoactivated catalysis, both organometallic and enzymatic. We developed methods, algorithms, and software tools needed for reliable treatment of the underlying physics for charge transfer and charge transport, an undertaking with broad applicability to the goals of the fundamental-interaction component of the Department of Energy Office of Basic Energy Sciences and the exascale initiative of the Office of Advanced Scientific Computing Research.

Excited state intramolecular charge transfer reaction in non-aqueous ...

Indian Academy of Sciences (India)

polar phase and thus leading to less swelling of reverse .... ues were restricted up to the limit at which no phase separation was ..... The lower panel of figure 1 also indicates that the slopes of ... probe in its ground and excited states.55.

Silver colloidal effects on excited-state structure and intramolecular charge transfer of p-N, N-dimethylaminobenzoic acid in aqueous cyclodextrin solutions

International Nuclear Information System (INIS)

Choi, Jung Kwon; Kim, Yang Hee; Yoon, Min Joong; Lee, Seung Joon; Kim, Kwan; Jeoung, Sae Chae

2001-01-01

The silver colloidal effects on the excited-state structure and intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABA) in aqueous cyclodextrin (CD) solutions have been investigated by UV-VIS absorption, steady-state and time-resolved fluorescence, and transient Raman spectroscopy. As the concentration of silver colloids increases, the ratio of the ICT emission to the normal emission (I a /I b ) of DMABA in the aqueous α-CD solutions are greatly decreased while the I a /I b values in the aqueous β-CD solutions are significantly enhanced. It is also noteworthy that the ICT emission maxima are red-shifted by 15-40 nm upon addition of silver colloids, implying that DMABA encapsulated in α-CD or β-CD cavity is exposed to more polar environment. The transient resonance Raman spectra of DMABA in silver colloidal solutions demonstrate that DMABA in the excited-state is desorbed from silver colloidal surfaces as demonstrated by the disappearance of v s (CO 2 - )(1380 cm -1 ) with appearance of v (C-OH)(1280 cm -1 ) band, respectively. Thus, in the aqueous β-CD solutions the carboxylic acid group of DMABA in the excited-state can be readily hydrogen bonded with the secondary hydroxyl group of β-CD while in aqueous and α-CD solutions the carboxylic acid group of DMABA has the hydrogen-bonding interaction with water. Consequently, in the aqueous β-CD solutions the enhancement of the I a /I b value arises from the intermolecular hydrogen-bonding interaction between DMABA and the secondary hydroxyl group of β-CD as well as the lower polarity of the rim of the β-CD cavity compared to bulk water. This is also supported by the increase of the association constant for DMABA/β-CD complex in the presence of silver colloids

Charge orders in organic charge-transfer salts

International Nuclear Information System (INIS)

Kaneko, Ryui; Valentí, Roser; Tocchio, Luca F; Becca, Federico

2017-01-01

Motivated by recent experimental suggestions of charge-order-driven ferroelectricity in organic charge-transfer salts, such as κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, we investigate magnetic and charge-ordered phases that emerge in an extended two-orbital Hubbard model on the anisotropic triangular lattice at 3/4 filling. This model takes into account the presence of two organic BEDT-TTF molecules, which form a dimer on each site of the lattice, and includes short-range intramolecular and intermolecular interactions and hoppings. By using variational wave functions and quantum Monte Carlo techniques, we find two polar states with charge disproportionation inside the dimer, hinting to ferroelectricity. These charge-ordered insulating phases are stabilized in the strongly correlated limit and their actual charge pattern is determined by the relative strength of intradimer to interdimer couplings. Our results suggest that ferroelectricity is not driven by magnetism, since these polar phases can be stabilized also without antiferromagnetic order and provide a possible microscopic explanation of the experimental observations. In addition, a conventional dimer-Mott state (with uniform density and antiferromagnetic order) and a nonpolar charge-ordered state (with charge-rich and charge-poor dimers forming a checkerboard pattern) can be stabilized in the strong-coupling regime. Finally, when electron–electron interactions are weak, metallic states appear, with either uniform charge distribution or a peculiar 12-site periodicity that generates honeycomb-like charge order. (paper)

Collective charge and mass transfer in heavy ion reactions

International Nuclear Information System (INIS)

Hahn, J.

1982-01-01

In this thesis the dynamics of the charge and mass asymmetry degree of freedom was studied in the framework of the fragmentation theory by means of a time-dependent Schroedinger equation. New is the introduction of a friction potential which describes the coupling of these collective degrees of freedom to the not explicitely treated other collective respectively internal degrees of freedom. Thereby it was shown that the measured widths of the isobaric charge distributions in the 86 Kr+sup(92,98)Mo reaction can be explained mainly by the quantum mechanical uncertainty in the charge asymmetry degree of freedom. The charge equilibration occurring at the begin of a deep inelastic collision can therefore by considered as a quantum mechanical, collective, damped motion which is connected with the excitation of the isovector giant dipole resonance of the nucleus-nucleus system. The study of the mass transfer in the reactions 132 Xe+ 120 Sn and 86 Kr+ 166 Er shows, how important at the begin of a deep inelastic collision shell structures and their conservation are for a large part of the reaction, even if the elemental distribution show no maxima in the region of magic shell closures. The experimental width are up to 10 MeV/A well described under conservation of the shell structure. (orig./HSI) [de

Bond charges and electronic charge transfer in ternary semiconductors

International Nuclear Information System (INIS)

Pietsch, U.

1986-01-01

By means of a simple molecule-theoretic model of 'linear superposition of two-electron molecules' the bond charges between nearest neighbours and the effective charges of ions are calculated for ternary zinc-blende structure alloys as well as chalcopyrite semiconductors. Taking into account both, the charge transfer among the ions caused by the differences of electronegativities of atoms used and between the bonds created by the internal stress of the lattice a nearly unvaried averaged bond charge amount of the alloy is found, but rather dramatically changed local bond charge parameters in comparison with the respective values of binary compounds used. This fact should influence the noncentral force interaction in such semiconductors. (author)

Four- and six-charge transfer reactions induced by 52Cr, 56Fe, 63Cu in rare-earths

International Nuclear Information System (INIS)

Mouchaty, G.

1977-01-01

The cross sections for transfer reactions in which 4 and 6 charges are gained by Sm and Nd targets have been measured, the projectiles being 52 Cr and 56 Fe at 343 and 377 MeV. These energies correspond to 1.5B, B being the interaction barrier. The results obtained indicate that the cross section increases when the number of charges transferred and the mass of the projectile are increased. The angular distributions and recoil ranges at each angle of 151 Dy produced through 52 Cr+ 148 Sm, 52 Cr+ 144 Nd, 56 Fe+ 144 Nd, 63 Cu+ 144 Nd reactions were determined for incident energies equivalent to 1.5B. After transformation into the c.m. system, the angular distributions exhibit a maximum close to 155 0 and a tail at small angles. The position of the maximum is independent of the incident ion and of the number of transferred charges. The analysis of the energy distributions indicate that the observed reactions can be explained by a two-step process: a transfer of nucleons followed by an evaporation step. The number of nucleons transferred in the 1st step and the associated excitation energies are higher for the events corresponding to the tail than for those corresponding to the maximum [fr

Effect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyads

KAUST Repository

Jiang, Junlin

2017-05-25

A series of -conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PEn-NDI, where n = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE NDI charge transfer dominates the deactivation of excited states of the PEn-NDI oligomers. Both charge separation (CS) and charge recombination (CR) are strongly exothermic (G0CS ~ -1.1 and G0CR ~ -2.0 eV), and the driving forces do not vary much across the series because the oxidation and reduction potentials and singlet energies of the OPEs do not vary much with their length. Bimolecular photoinduced charge transfer between model OPEs that do not contain the NDI acceptors with methyl viologen was studied, and the results reveal that the absorption of the cation radical state (OPE+•) remains approximately constant ( ~ 575 nm) regardless of oligomer length. This finding suggests that the cation radical (polaron) of the OPE is relatively localized, effectively occupying a confined segment of n 4 repeat units in the longer oligomers. Photoinduced intramolecular electron transfer dynamics in the PEn-NDI series was investigated by UV-visible femtosecond transient absorption spectroscopy with visible and mid-infrared probes. Charge separation occurs on the 1 – 10 ps timescale, with the rates decreasing slightly with increased oligomer length (βCS ~ 0.15 Å-1). The rate for charge-recombination decreases in the sequence PE4-NDI > PE6-NDI ~ PE8-NDI. The discontinuous distance dependence in the rate for charge recombination may be related to the spatial localization of the positive polaron state in the longer oligomers.

Effect of Conjugation Length on Photoinduced Charge-Transfer in π-Conjugated Oligomer-Acceptor Dyads

KAUST Repository

Jiang, Junlin; Alsam, Amani Abdu; Wang, Shanshan; Aly, Shawkat Mohammede; Pan, Zhenxing; Mohammed, Omar F.; Schanze, Kirk S.

2017-01-01

A series of -conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PEn-NDI, where n = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE NDI charge transfer dominates the deactivation of excited states of the PEn-NDI oligomers. Both charge separation (CS) and charge recombination (CR) are strongly exothermic (G0CS ~ -1.1 and G0CR ~ -2.0 eV), and the driving forces do not vary much across the series because the oxidation and reduction potentials and singlet energies of the OPEs do not vary much with their length. Bimolecular photoinduced charge transfer between model OPEs that do not contain the NDI acceptors with methyl viologen was studied, and the results reveal that the absorption of the cation radical state (OPE+•) remains approximately constant ( ~ 575 nm) regardless of oligomer length. This finding suggests that the cation radical (polaron) of the OPE is relatively localized, effectively occupying a confined segment of n 4 repeat units in the longer oligomers. Photoinduced intramolecular electron transfer dynamics in the PEn-NDI series was investigated by UV-visible femtosecond transient absorption spectroscopy with visible and mid-infrared probes. Charge separation occurs on the 1 – 10 ps timescale, with the rates decreasing slightly with increased oligomer length (βCS ~ 0.15 Å-1). The rate for charge-recombination decreases in the sequence PE4-NDI > PE6-NDI ~ PE8-NDI. The discontinuous distance dependence in the rate for charge recombination may be related to the spatial localization of the positive polaron state in the longer oligomers.

Charge-transfer complexes between p-toluidine and iodine in solution: a kinetic study

International Nuclear Information System (INIS)

Beggiato, G.; Casalbore, G.; Marconi, G.; Baraldi, C.

1985-01-01

The kinetics of charge-transfer interaction between p-toluidine and iodine in methylene chloride was investigated in depth. The thermal process of formation of the 'inner' complex was found to proceed to an equilibrium. The photochemical process follows a different reaction coordinate, going through the formation of an exciplex between the excited 'outer' complex and the amine ground state. In both cases the same ionic complex (Am 2 I + I - 3 , where Am stands for p-toluidine) was detected as the final product. (Author)

Scaling of the helium--nitrogen charge transfer laser

International Nuclear Information System (INIS)

Collins, C.B.; Cunningham, A.J.

1975-01-01

The scaling to high powers of the nitrogen ion laser pumped by charge transfer from He + 2 is reported. Intense emission has been found from three laser lines at 3914, 4278, and 4709 A upon discharge of a fast-pulsed electron beam gun, APEX-1, into several atmospheres of a mixture of helium and nitrogen. Excitation current densities were 1.3 kA/cm 2 at 1 MV over a 1times10-cm transverse geometry. The efficiency of the 4278-A laser emission was found to be proportional to the total pressure raised to the 1.2 power. Outputs of 36 mJ have been obtained from the 16-cm 3 working volume at 30-atm pressure and a peak efficiency of 1.6% relative to the energy lost by the electron beam in this radiating volume has been achieved

Impact of charge-transfer excitons in regioregular polythiophene on the charge separation at polythiophene-fullerene heterojunctions

Science.gov (United States)

Polkehn, M.; Tamura, H.; Burghardt, I.

2018-01-01

This study addresses the mechanism of ultrafast charge separation in regioregular oligothiophene-fullerene assemblies representative of poly-3-hexylthiophene (P3HT)-[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) heterojunctions, with special emphasis on the inclusion of charge transfer excitons in the oligothiophene phase. The formation of polaronic inter-chain charge separated species in highly ordered oligothiophene has been demonstrated in recent experiments and could have a significant impact on the net charge transfer to the fullerene acceptor. The present approach combines a first-principles parametrized multi-site Hamiltonian, based on time-dependent density functional theory calculations, with accurate quantum dynamics simulations using the multi-layer multi-configuration time-dependent Hartree method. Quantum dynamical studies are carried out for up to 182 electronic states and 112 phonon modes. The present analysis follows up on our previous study of (Huix-Rotllant et al 2015 J. Phys. Chem. Lett. 6 1702) and significantly expands the scope of this analysis by including the dynamical role of charge transfer excitons. Our investigation highlights the pronounced mixing of photogenerated Frenkel excitons with charge transfer excitons in the oligothiophene domain, and the opening of new transfer channels due the creation of such charge-separated species. As a result, it turns out that the interfacial donor/acceptor charge transfer state can be largely circumvented due to the presence of charge transfer excitons. However, the latter states in turn act as a trap, such that the free carrier yield observed on ultrafast time scales is tangibly reduced. The present analysis underscores the complexity of the transfer pathways at P3HT-PCBM type junctions.

The charge transfer structure and effective energy transfer in multiplayer assembly film

International Nuclear Information System (INIS)

Li Mingqiang; Jian Xigao

2005-01-01

Charge transfer multiplayer films have been prepared by layer-by-layer self-assembly technique. The films incorporate the rare-earth-containing polyoxometalate K 11 [Eu{PW 11 O 39 } 2 ].nH 2 O and the rich electron polyelectrolyte poly(3-viny-1-methyl-pyridine) quaternary ammonium and display a linear increase in the absorption and film thickness with the number of deposition cycles. Ultraviolet and visible absorption spectra, atomic force micrographs, small-angle X-ray reflectivity measurements, and photoluminescence spectra were used to determine the structure of films. Linear and regular multilayer growth was observed. We can observe the formation of charge transfer complex compound in multiplayer by layer-by-layer assembly method. Most importantly, the luminescence spectra show the charge transfer band in assembly films, which suggest that energy could be effectively transferred to rare earth ions in assembly multiplayer films

Transition rate diagrams and excitation of titanium in a glow discharge in argon and neon

Science.gov (United States)

Weiss, Zdeněk; Steers, Edward B. M.; Pickering, Juliet C.

2018-06-01

Emission spectra of titanium in a Grimm-type glow discharge in argon and neon were studied using the formalism of transition rate diagrams. Ti I spectra in argon and neon discharges are similar, without signs of selective excitation, and populations of Ti I levels exhibit a decreasing trend as function of energy, except for some scatter. A major excitation process of Ti II in argon discharge is charge transfer from argon ions to neutral titanium. In neon discharge, a strong selective excitation was observed of Ti II levels at ≈13.3-13.4 eV relative to the Ti I ground state. It was attributed to charge transfer from doubly charged titanium ions to neutral titanium, while the Ti++ ions are produced by charge transfer and ionization of neutral titanium by neon ions. Cascade excitation is important for Ti II levels up to an energy of ≈13 eV relative to the Ti I ground state, both in argon and neon discharges.

The momentum transfer dependence of double excitations of helium

International Nuclear Information System (INIS)

Zhu Lin-Fan; Liu Xiao-Jing; Yuan Zhen-Sheng; Xu Ke-Zun

2005-01-01

The momentum transfer dependence of fundamental double excitation processes of helium is studied with high resolution and fast electron impact. It elucidates the dynamical correlations, in terms of internal correlation quantum numbers, K, T and A. The Fano profile parameters q, f a , ρ 2 , f and S of doubly excited states 2 (1,0) 2 +1se , 2 (0,1) 2 +1p0 and 2 (1,0) 2 +1De are determined as functions of momentum transfer K 2 . (author)

Ultrafast excitation energy transfer from encapsulated quaterrylene to single-walled carbon nanotube

Energy Technology Data Exchange (ETDEWEB)

Koyama, Takeshi, E-mail: koyama@nuap.nagoya-u.ac.jp [Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603 (Japan); Tsunekawa, Takuya [Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603 (Japan); Saito, Takeshi [Research Center for Advanced Carbon Materials, AIST, Tsukuba, Ibaraki 305-8565 (Japan); Asaka, Koji; Saito, Yahachi [Department of Quantum Engineering, Nagoya University, Chikusa, Nagoya 464-8603 (Japan); Kishida, Hideo [Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603 (Japan); Nakamura, Arao [Department of Applied Physics, Nagoya University, Chikusa, Nagoya 464-8603 (Japan); Toyota Physical and Chemical Research Institute, Nagakute, Aichi 480-1192 (Japan)

2016-01-15

We investigate excitation energy transfer from an encapsulated quaterrylene molecule to a single-walled carbon nanotube by means of femtosecond pump-probe spectroscopy. The time constant of energy transfer becomes shorter with increasing average diameter of nanotube: 1.4±0.2 ps for 1.0 nm, 1.1±0.2 ps for 1.4 nm, and 0.4±0.1 ps for 1.8 nm. The observed behavior is discussed considering the distance of less than 1 nm between the molecule and the nanotube wall. - Highlights: • Dynamical properties of excited states in quaterrylene/SWNT composites were studied. • Excitation energy transfer occurs in the time range of 0.4-1.4 ps. • The transfer rate depends on the nanotube diameter, i.e. molecule-nanotube wall distance. • This dependence indicates the feature of excitation energy transfer on the nanoscale.

Two-Centre Close-Coupling method in charge transfer

Directory of Open Access Journals (Sweden)

Reza Bagheri

2017-09-01

Full Text Available In the present work, the transition matrix elements as well as differential and total scattering cross-sections for positronium formation in Positron-Hydrogen atom collision and hydrogen formation in Positronium-Hydrogen ion collision, through the charge transfer channel by Two-Centre Close-Coupling method up to a first order approximation have been calculated. The charge transfer collision is assumed to be a three-body reaction, while the projectile is a plane wave. Additionally, the hydrogen and positronium atoms are assumed, initially, to be in their ground states. For the case of charge transfer in the scattering of positron by hydrogen atoms, the differential cross sections are plotted for the energy range of 50eV to 10keV, where the Thomas peak is clearly observable. Finally, the total scattering cross-section for the charge transfer in the collision of Positron-Hydrogen and Positronium-Hydrogen ion are plotted as a function of projectile energies and compared with other methods in the literature.

Amino-Acid-Induced Preferential Orientation of Perovskite Crystals for Enhancing Interfacial Charge Transfer and Photovoltaic Performance.

Science.gov (United States)

Shih, Yen-Chen; Lan, Yu-Bing; Li, Chia-Shuo; Hsieh, Hsiao-Chi; Wang, Leeyih; Wu, Chih-I; Lin, King-Fu

2017-06-01

Interfacial engineering of perovskite solar cells (PSCs) is attracting intensive attention owing to the charge transfer efficiency at an interface, which greatly influences the photovoltaic performance. This study demonstrates the modification of a TiO 2 electron-transporting layer with various amino acids, which affects charge transfer efficiency at the TiO 2 /CH 3 NH 3 PbI 3 interface in PSC, among which the l-alanine-modified cell exhibits the best power conversion efficiency with 30% enhancement. This study also shows that the (110) plane of perovskite crystallites tends to align in the direction perpendicular to the amino-acid-modified TiO 2 as observed in grazing-incidence wide-angle X-ray scattering of thin CH 3 NH 3 PbI 3 perovskite film. Electrochemical impedance spectroscopy reveals less charge transfer resistance at the TiO 2 /CH 3 NH 3 PbI 3 interface after being modified with amino acids, which is also supported by the lower intensity of steady-state photoluminescence (PL) and the reduced PL lifetime of perovskite. In addition, based on the PL measurement with excitation from different side of the sample, amino-acid-modified samples show less surface trapping effect compared to the sample without modification, which may also facilitate charge transfer efficiency at the interface. The results suggest that appropriate orientation of perovskite crystallites at the interface and trap-passivation are the niche for better photovoltaic performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Positive photocatalysis of a Diels-Alder reaction by quenching of excited naphthalene-indole charge-transfer complex with cyclohexadiene.

Science.gov (United States)

Gonzalez-Béjar, María; Stiriba, Salah-Eddine; Miranda, Miguel A; Pérez-Prieto, Julia

2007-02-01

[reaction: see text] Naphthalene photo-catalyzes formation of cyclohexadiene-indole cycloadducts in a wavelength-dependent process. Steady-state irradiation and time-resolved fluorescence studies agree well with NP-InH ground-state charge transfer (CT) complexes as the key species responsible for the photo-catalyzed process.

Role of methylene spacer in the excitation energy transfer in europium 1- and 2- naphthylcarboxylates

Energy Technology Data Exchange (ETDEWEB)

Zhuravlev, K. [V.A. Kotelnikov Institute of Radioengineering and Electronics of RAS, 1 Vvedenskii sq., Fryazino Moscow reg. 141190 (Russian Federation); Tsaryuk, V., E-mail: vit225@ire216.msk.s [V.A. Kotelnikov Institute of Radioengineering and Electronics of RAS, 1 Vvedenskii sq., Fryazino Moscow reg. 141190 (Russian Federation); Kudryashova, V.; Pekareva, I. [V.A. Kotelnikov Institute of Radioengineering and Electronics of RAS, 1 Vvedenskii sq., Fryazino Moscow reg. 141190 (Russian Federation); Sokolnicki, J. [Faculty of Chemistry, University of WrocLaw, 14 F. Joliot-Curie str., WrocLaw 50-383 (Poland); Yakovlev, Yu. [V.A. Kotelnikov Institute of Radioengineering and Electronics of RAS, 1 Vvedenskii sq., Fryazino Moscow reg. 141190 (Russian Federation)

2010-08-15

A series of compounds Ln(RCOO){sub 3}.Phen (Ln=Eu, Gd, Tb; RCOO{sup -}-1- and 2-naphthoate, 1- and 2-naphthylacetate, 1- and 2-naphthoxyacetate anions, Phen-1,10-phenanthroline) was investigated by methods of optical spectroscopy. Compounds of composition Ln(RCOO){sub 3}.nH{sub 2}O with the same carboxylate ligands are also considered. Results of studies of the effects of methylene spacer decoupling the {pi}-{pi}- or p-{pi}-conjugation in the naphthylcarboxylate ligand on the structure of Eu{sup 3+} coordination centre, on the lifetime of {sup 5}D{sub 0} (Eu{sup 3+}) state, and on processes of the excitation energy transfer to Eu{sup 3+} or Tb{sup 3+} ions are presented. Introduction of the methylene bridge in the ligand weakens the influence of the steric hindrances in forming of a crystal lattice and results in lowering the distortion of the Eu{sup 3+} luminescence centre, and in elongation of the observed {sup 5}D{sub 0} lifetime {tau}{sub obs}. The latter is caused by decrease in contribution of the radiative processes rate 1/{tau}{sub r}. This is confirmed by the correlation between the lifetimes {tau}{sub obs} and the quantities '{tau}{sub r}.const' inversely proportional to the total integral intensities of Eu(RCOO){sub 3}.Phen luminescence spectra. The methylene spacer performs a role of regulator of sensitization of the Ln{sup 3+} luminescence efficiency by means of an influence on mutual location of lowest triplet states of the ligands, the ligand-metal charge transfer (LMCT) states, and the emitting states of Ln{sup 3+} ions. The lowest triplet state in lanthanide naphthylcarboxylate adducts with Phen is related to carboxylate anion. A presence of the methylene spacer in naphthylcarboxylate ligand increases the triplet state energy. At the same time, the energy of 'carboxylic group-Eu{sup 3+} ion' charge transfer states falls, which can promote the degradation of excitation energy. In naphthylcarboxylates investigated a range of the

Direct evidence for radiative charge transfer after inner-shell excitation and ionization of large clusters

Science.gov (United States)

Hans, Andreas; Stumpf, Vasili; Holzapfel, Xaver; Wiegandt, Florian; Schmidt, Philipp; Ozga, Christian; Reiß, Philipp; Ben Ltaief, Ltaief; Küstner-Wetekam, Catmarna; Jahnke, Till; Ehresmann, Arno; Demekhin, Philipp V.; Gokhberg, Kirill; Knie, André

2018-01-01

We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne2+-{{{N}}{{e}}}n-1 initial states of RCT are populated after resonant 1s-3p photoexcitation or 1s photoionization of Ne n clusters with ≈ 2800. These states relax further producing Ne+-Ne+-{{{N}}{{e}}}n-2 final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the{}{{{N}}{{e}}}2+(2{{{p}}}-2{[}1{{D}}]){--}{{{N}}{{e}}}n-1 initial state, while transitions from other possible initial states are proposed to be quenched by competing relaxation processes. The present results are in agreement with the commonly discussed scenario, where the doubly ionized atom in a noble gas cluster forms a dimer which dissipates its vibrational energy on a picosecond timescale. Our study complements the picture of the RCT process in weakly bound clusters, providing information which is inaccessible by charged particle detection techniques.

Charge exchange in a divertor plasma with excited particles

International Nuclear Information System (INIS)

Krasheninnikov, S.I.; Lisitsa, V.S.; Pigarov, A.Y.

1988-01-01

A model is constructed for the dynamics of neutral atoms and multicharged ions in a tokamak plasma. The influence of cascade excitation on charge exchange and ionization is taken into account. The effective rates of the resonant charge exchange of a proton with a hydrogen atom, the nonresonant charge exchange of a helium atom with a proton, and that of an α particle with atomic hydrogen are calculated as functions of the parameters of the divertor plasma in a tokamak. The charge exchange H + +He→H+He + can represent a significant fraction (∼30%) of the total helium ionization rate. Incorporating the charge exchange of He 2+ with atomic hydrogen under the conditions prevailing in the divertor plasma of the INTOR reactor can lead to substantial He 2+ →He + conversion and thereby reduce the sputtering of the divertor plates by helium ions

Crossed beam study of He+-O2 charge transfer reactions in the collision energy range 0.5-200 eV

International Nuclear Information System (INIS)

Bischof, G.; Linder, F.

1986-01-01

Energy spectra and angular distributions of the O + and O 2 + product ions resulting from the He + -O 2 charge transfer reaction have been measured in the collision energy range 0.5-200 eV using the crossed-beam method. The O 2 + ions represent only a minor fraction of the reaction products (0.2-0.6% over the energy range measured). In the dissociative charge transfer reaction, four main processes are identified leading to O+O + reaction products in different electronic states. Two different mechanisms can be distinguished, each being responsible for two of the observed processes: (i) a long-distance energy-resonant charge transfer process involving the c 4 Σsub(u) - (upsilon'=0) state of O 2 + and (ii) a slightly exothermic charge transfer process via the (III) 2 PIsub(u) state of O 2 + (with the exothermicity depending on the collision energy). Angle-integrated branching ratios and partial cross sections (in absolute units) have been determined. The branching ratios of the individual processes show a pronounced dependence on the collision energy. At low energies, the O + product ions are preferentially formed in the 2 P 0 and 2 D 0 excited states. The angular distributions of the O + product ions show an anisotropic behaviour indicating an orientation-dependent charge transfer probability in the He + -O 2 reaction. (orig.)

Nuclear charge-exchange excitations in a self-consistent covariant approach

International Nuclear Information System (INIS)

Liang, Haozhao

2010-01-01

Nowadays, charge-exchange excitations in nuclei become one of the central topics in nuclear physics and astrophysics. Basically, a systematic pattern of the energy and collectivity of these excitations could provide direct information on the spin and isospin properties of the in-medium nuclear interaction, and the equation of state of asymmetric nuclear matter. Furthermore, a basic and critical quantity in nuclear structure, neutron skin thickness, can be determined indirectly by the sum rule of spin-dipole resonances (SDR) or the excitation energy spacing between the isobaric analog states (IAS) and Gamow-Teller resonances (GTR). More generally, charge-exchange excitations allow one to attack other kinds of problems outside the realm of nuclear structure, like the description of neutron star and supernova evolutions, the β-decay of nuclei which lie on the r-process path of stellar nucleosynthesis, and the neutrino-nucleus cross sections. They also play an essential role in extracting the value of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element V ud via the nuclear 0 + → 0 + superallowed Fermi β decays. For all these reasons, it is important to develop the microscopic theories of charge-exchange excitations and it is the main motivation of the present work. In this work, a fully self-consistent charge-exchange relativistic random phase approximation (RPA) based on the relativistic Hartree-Fock (RHF) approach is established. Its self-consistency is verified by the so-called IAS check. This approach is then applied to investigate the nuclear spin-isospin resonances, isospin symmetry-breaking corrections for the superallowed β decays, and the charged-current neutrino-nucleus cross sections. For two important spin-isospin resonances, GTR and SDR, it is shown that a very satisfactory agreement with the experimental data can be obtained without any readjustment of the energy functional. Furthermore, the isoscalar mesons are found to play an essential role in spin

Photoinduced Charge Transfer from Titania to Surface Doping Site.

Science.gov (United States)

Inerbaev, Talgat; Hoefelmeyer, James D; Kilin, Dmitri S

2013-05-16

We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO 2 . Charge transfer from the photo-excited TiO 2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO 2 nanorod and catalytic site. A slab of TiO 2 represents a fragment of TiO 2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO 2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO 2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting.

Langevin description of fission fragment charge distribution from excited nuclei

CERN Document Server

Karpov, A V

2002-01-01

A stochastic approach to fission dynamics based on a set of three-dimensional Langevin equations was applied to calculate fission-fragment charge distribution of compound nucleus sup 2 sup 3 sup 6 U. The following collective coordinates have been chosen - elongation coordinate, neck-thickness coordinate, and charge-asymmetry coordinate. The friction coefficient of charge mode has been calculated in the framework of one-body and two-body dissipation mechanisms. Analysis of the results has shown that Langevin approach is appropriate for investigation of isobaric distribution. Moreover, the dependences of the variance of the charge distribution on excitation energy and on the two-body viscosity coefficient has been studied

Resonance charge exchange between excited states in slow proton-hydrogen collisions

International Nuclear Information System (INIS)

Tolstikhina, Inga Yu.; Kato, Daiji

2010-01-01

The theory of resonance charge exchange in slow collisions of a proton with a hydrogen atom in the excited state is developed. It extends the Firsov-Demkov theory of resonance charge exchange to the case of degenerate initial and final states. The theory is illustrated by semiclassical and quantum calculations of charge exchange cross sections between states with n=2 in parabolic and spherical coordinates. The results are compared with existing close-coupling calculations.

Charge transfer in graphene oxide-dye system for photonic applications

International Nuclear Information System (INIS)

Bongu, Sudhakara Reddy; Bisht, Prem B.; Thu, Tran V.; Sandhu, Adarsh

2014-01-01

The fluorescence of a standard dye Rhodamine 6G (R6G) in solution decreases on addition of reduced graphene oxide (rGO). The absorption spectra and lifetime measurements confirm that no excited-state but a ground-state complex formation is responsible for this effect. For silver decorated rGO (Ag-rGO), the quenching efficiency and ground state complex formation process is small. Z-scan measurements have been done to study the optical nonlinearity at 532 nm under ps time scale. Remarkable reduction in the saturable absorption (SA) effect of R6G indicates no nonlinear contribution from the ground state complex. The results have been explained with varying charge transfer rates and non-fluorescence nature of the complex

Charges and Electromagnetic Radiation as Topological Excitations

Directory of Open Access Journals (Sweden)

Manfried Faber

2017-01-01

Full Text Available We discuss a model with stable topological solitons in Minkowski space with only three degrees of freedom, the rotational angles of a spatial Dreibein. This model has four types of solitons differing in two topological quantum numbers which we identify with electric charge and spin. The vacuum has a two-dimensional degeneracy leading to two types of massless excitations, characterised by a topological quantum number which could have a physical equivalent in the photon number.

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

Energy Technology Data Exchange (ETDEWEB)

Ramakrishnan, Raghunathan, E-mail: r.ramakrishnan@unibas.ch [Institute of Physical Chemistry, National Center for Computational Design and Discovery of Novel Materials (MARVEL), Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel (Switzerland); Nest, Mathias [Theoretische Chemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching (Germany)

2015-01-13

Highlights: • We model electron dynamics across cyano alkanethiolates attached to gold cluster. • We present electron transfer time scales from TD-DFT and TD-CI based simulations. • Both DFT and CI methods qualitatively predict the trend in time scales. • TD-CI predicts the experimental relative time scale very accurately. - Abstract: We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual π{sup ∗} molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

Effect of vibrational excitation on the dynamics of ion-molecule reactions

International Nuclear Information System (INIS)

Anderson, S.L.

1981-11-01

A new experimental technique for the study of vibrational effects on ion-molecule reaction cross sections is described. Vibrational and collision energy dependent cross sections are presented for proton and H atom transfer, charge transfer and collision induced dissociation reactions in various isotopic H 2 + + H 2 systems. Charge and proton transfer cross sections are presented for the reactions of H 2 + and D 2 + with Ar, N 2 , CO, and O 2 . All the reactions are shown to be highly influenced by avoided crossings between the ground and first excited potential energy surfaces. Because of the nature of the crossings, vibrational motion of the systems can cause both adiabatic and non-adiabatic behavior of the system. This makes the vibrational dependences of the various cross sections a very sensitive probe of the dynamics of the collisions particularly, their behavior in the region of the crossings. Evidence is seen for charge transfer between reagents as they approach each other, transition to and in some cases reactions on excited potential energy surfaces, competition between different channels, and strong coupling of proton and charge transfer channels which occurs only for two of the systems studied (H 2 + + Ar, N 2 ). Oscillatory structure is observed in the collision energy dependence of the endoergic H 2 + (v = 0) + Ar charge transfer reaction for the first time, and a simple model which is commonly used for atom-atom charge transfer is used to fit the peaks. Finally a simple model is used to assess the importance of energy resonance and Franck-Condon effects on molecular charge transfer

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

KAUST Repository

Alsulami, Qana

2015-06-25

Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

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

KAUST Repository

Alsulami, Qana; Aly, Shawkat Mohammede; Goswami, Subhadip; Alarousu, Erkki; Usman, Anwar; Schanze, Kirk S.; Mohammed, Omar F.

2015-01-01

Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer

Science.gov (United States)

Lee, Victor; James, Nicole M.; Waitukaitis, Scott R.; Jaeger, Heinrich M.

2018-03-01

Electrostatic charging of insulating fine particles can be responsible for numerous phenomena ranging from lightning in volcanic plumes to dust explosions. However, even basic aspects of how fine particles become charged are still unclear. Studying particle charging is challenging because it usually involves the complexities associated with many-particle collisions. To address these issues, we introduce a method based on acoustic levitation, which makes it possible to initiate sequences of repeated collisions of a single submillimeter particle with a flat plate, and to precisely measure the particle charge in situ after each collision. We show that collisional charge transfer between insulators is dependent on the hydrophobicity of the contacting surfaces. We use glass, which we modify by attaching nonpolar molecules to the particle, the plate, or both. We find that hydrophilic surfaces develop significant positive charges after contacting hydrophobic surfaces. Moreover, we demonstrate that charging between a hydrophilic and a hydrophobic surface is suppressed in an acidic environment and enhanced in a basic one. Application of an electric field during each collision is found to modify the charge transfer, again depending on surface hydrophobicity. We discuss these results within the context of contact charging due to ion transfer, and we show that they lend strong support to O H- ions as the charge carriers.

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

International Nuclear Information System (INIS)

Goutte, Dominique.

1979-10-01

A determination was made of an angular distribution of the inelastic scattering cross-sections of electrons by the first excited state (Jsup(π)=3 - , E*=2.615 MeV) of 208 Pb. 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 -37 cm 2 /sr were determined whereas the limit reached before was 7x10 -35 cm 2 /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 [fr

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-02-14

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

Experimental determination of electron shock excitation cross sections for a singly charged gadolinium ion

International Nuclear Information System (INIS)

Smirnov, Yu.M.

1995-01-01

The trends observed in the processes of excitation with simultaneous ionization have received little study. This is particularly so for rare-earth elements having electron shells of complex structure and optical spectra very rich in lines. Among the basic factors responsible for such a situation, we should mention two: the difficulty presented by theoretical analysis of the processes discussed and the absence of factual information about the excitation cross sections with simultaneous ionization for the majority of rare-earth elements. The aim of the present work is to investigate the excitation of a singly charged gadolinium ion in the collisions of monokinetic electrons with gadolinium atoms. Up to the present time, only the excitation cross sections of a gadolinium atom have been measured, where investigation of the electron shock excitation of gadolinium atoms in their free state is associated with overcoming large experimental difficulties. About 160 crosss sections for the excitation of a singly charged gadolinium ion were measured and for a third of the cross sections; the energy dependences were recorded for the change in energy of the elecrons from the excitation threshold up to 200 eV. Included are tables of the wavelength, transistion, internal quantum number, the energy of the lowere and upper levels, and the values of cross sections for the charged gadolinium ion. Diagrams of the transistion energy states of Gd (II) and spectroscopy are presented and explained

Electron capture into excited states of multi-charged ions

International Nuclear Information System (INIS)

Dijkkamp, D.

1985-01-01

This thesis deals with charge exchange reactions in slow collisions of multi-charged ions with neutral atoms or molecules. These reactions proceed very efficiently via a curve crossing mechanism, which leads to preferential population of excited states of the ion. The subsequent decay of these states leads to the emission of characteristic radiation. From wavelength resolved measurements of the absolute intensity of this radiation, cross sections for selective population of the excited (n,l-) states of the ion were determined. In addition, for some systems the total capture cross section was measured directly by means of charge state analysis of the secondary projectile ions. The role of charge exchange processes in fusion plasmas and in astrophysical plasmas is indicated. An experimental set-up is described with emphasis on the Electron Cyclotron Resonance Ion Source that was used in the experiments. Results for collisions of C 6+ , N 6+ , O 6+ and Ne 6+ with He, H 2 and Ar are presented as well as for electron capture from Li atoms by C 4+ and He 2+ . The interaction of the iso-electronic sequence C 4+ , N 5+ , O 6+ with atomic hydrogen, molecular hydrogen and helium is studied. First results for partial and total cross sections in collisions of fully stripped carbon, nitrogen and oxygen ions with atomic hydrogen are presented. These data are of particular importance for applications in fusion diagnostics. The data indicate that calculations of both molecular and atomic orbital type yield correct results, if an extended basis set is used. (Auth.)

Watson-Crick base pairing controls excited-state decay in natural DNA.

Science.gov (United States)

Bucher, Dominik B; Schlueter, Alexander; Carell, Thomas; Zinth, Wolfgang

2014-10-13

Excited-state dynamics are essential to understanding the formation of DNA lesions induced by UV light. By using femtosecond IR spectroscopy, it was possible to determine the lifetimes of the excited states of all four bases in the double-stranded environment of natural DNA. After UV excitation of the DNA duplex, we detected a concerted decay of base pairs connected by Watson-Crick hydrogen bonds. A comparison of single- and double-stranded DNA showed that the reactive charge-transfer states formed in the single strands are suppressed by base pairing in the duplex. The strong influence of the Watson-Crick hydrogen bonds indicates that proton transfer opens an efficient decay path in the duplex that prohibits the formation or reduces the lifetime of reactive charge-transfer states. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Syntheses of planar 1,5,2,4,6,8-dithiotetrazocine derivatives and thermodynamic study on intermolecular charge transfer for developing efficient organic solar cell

Energy Technology Data Exchange (ETDEWEB)

Zhang, Chao-Zhi, E-mail: zhangchaozhi@nuist.edu.cn [Department of Chemistry, Nanjing University of Information Science & Technology, Nanjing 210044 (China); Shen, Dan [Department of Chemistry, Nanjing University of Information Science & Technology, Nanjing 210044 (China); Yuan, Yang [Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing University of Information Science & Technology, Nanjing 210044 (China); Song, Ming-Xia; Li, Shi-Juan [Department of Chemistry, Nanjing University of Information Science & Technology, Nanjing 210044 (China); Cao, Hui, E-mail: yccaoh@hotmail.com [Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Nanjing University of Information Science & Technology, Nanjing 210044 (China)

2016-07-01

A series of planar 1,5,2,4,6,8-dithiotetrazocine derivatives were synthesized for study on charge transfer at donor/acceptor interface. The fluorescence quenching spectra, and the highest occupied molecular orbital (−6.10 ∼ −6.25 eV) and the lowest unoccupied molecular orbital (−3.45 ∼ −3.58 eV) energy levels of these 1,5,2,4,6,8-dithiotetrazocine derivatives show that they would be potential acceptor materials. Based on theoretical calculations, thermodynamic study on charge transfer at donor/acceptor interface was carried out. The results of experiments and theoretical calculations show that the electrons could transfer spontaneously from poly(3-hexylthiophene) to these acceptors. The percentages of fluorescence quenching increase with negative Gibbs free energy values increasing in the charge transfer procedures. Therefore, short circuit current values of organic solar cells would increase with the Gibbs free energy values increasing. This paper suggests a useful way for developing efficient organic solar cells. - Highlights: • Syntheses of planar 1,5,2,4,6,8-dithiotetrazocine derivatives for develop effective acceptor. • Electrons at excited state in P3HT could transfer spontaneously to these acceptors. • Thermodynamic study on charge transfer at donor/acceptor interface. • Short circuit currents would be predicted by Gibbs free energy in procedure of charge transfer.

Theory of interfacial charge-transfer complex photophysics in π-conjugated polymer-fullerene blends

Science.gov (United States)

Aryanpour, K.; Psiachos, D.; Mazumdar, S.

2010-03-01

We present a theory of the electronic structure and photophysics of 1:1 blends of derivatives of polyparaphenylenevinylene and fullerenes [1]. Within the same Coulomb-correlated Hamiltonian applied previously to interacting chains of single-component π-conjugated polymers [2], we find an exciplex state that occurs below the polymer's optical exciton. Weak absorption from the ground state occurs to the exciplex. We explain transient photoinduced absorptions in the blend [3], observed for both above-gap and below-gap photoexcitations, within our theory. Photoinduced absorptions for above-gap photoexcitation are from the optical exciton as well as the exciplex, while for below-gap photoexcitation induced absorptions are from the exciplex alone. In neither case are free polarons generated in the time scale of the experiment. Importantly, the photophysics of films of single-component π-conjugated polymers and blends can both be understood by extending Mulliken's theory of ground state charge-transfer to the case of excited state charge-transfer. [1] K. Aryanpour, D. Psiachos, and S. Mazumdar, arXiv:0908.0366 [2] D. Psiachos and S. Mazumdar, Phys. Rev. B. 79 155106 (2009) [3] T. Drori et al., Phys. Rev. Lett. 101, 037402 (2008)

Quasi-resonant K-K charge transfer

International Nuclear Information System (INIS)

Hagmann, S.; Cocke, C.L.; Richard, P.; Skutlartz, A.; Kelbch, S.; Schmidt-Boecking, H.; Schuch, R.

1983-01-01

The impact parameter dependence, P(b), of single and double K to K charge transfer have been deduced from the coincidences between K-Auger electrons and scattered particles for F 9+ + Ne and F 9+ + Ne collisions at 10 MeV and 4.4 MeV. The 4.4 MeV single K-K transfer probability exhibits oscillations with b. The P(b) for delta-electron emission is also reported. To obtain more details on the mechanism, K-Auger electron-Ne recoil ion coincidences are measured for both F 8+ and F 9+ projectiles. The relative amounts of recoil ions and of satellite and hypersatellite Auger transitions vary substantially with projectile charge state. 11 references, 11 figures

Mass and charge transfer within a floating water bridge

Science.gov (United States)

Fuchs, Elmar C.; Agostinho, Luewton L. F.; Eisenhut, Mathias; Woisetschläger, Jakob

2010-11-01

When high voltage is applied to pure water filled into two beakers close to each other, a connection forms spontaneously, giving the impression of a floating water bridge 1-8. This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. In this work, the charge and mass transfer through the water bridge are investigated with schlieren visualization and laser interferometry. It can be shown that the addition of a pH dye increases the H+ and OH- production with subsequent electrolysis, whereas schlieren and interferometric methods reveal another mechanism where charge and mass transfer appear to be coupled. Whereas this mechanism seems to be responsible for the electrolysis-less charge and mass transfer in the water bridge, it is increasingly superseded by the electrochemical mechanism with rising conductivity. Thus it can be shown that a pH dye does only indirectly visualize the charge transfer in the water bridge since it is dragged along with the water flow like any other dye, and additionally promotes conventional electrochemical conduction mechanisms, thereby enhancing electrolysis and reducing the masscoupled charge transport and thus destabilizing the bridge.

Excitation of the Δ resonance in heavy ion charge exchange reactions

International Nuclear Information System (INIS)

Roy-Stephan, M.

1987-06-01

Results on the Δ excitation by heavy ion charge exchange are presented. 900 MeV per nucleon 12 C, 16 0, 20 Ne and 1100 MeV per nucleon 12 C have been used. The Δ excitation strength depends on the projectile - ejectile nature and on the incident energy. The role of the target mass is also discussed. The peak for the Δ in nuclei is energy shifted from the free Δ peak

Coupling of mass and charge distributions for low excited nuclear fission

International Nuclear Information System (INIS)

Salamatin, V.S.; )

2000-01-01

The simple model for calculation of charge distributions of fission fragments for low exited nuclear fission from experimental mass distributions is offered. The model contains two parameters, determining amplitude of even-odd effect of charge distributions and its dependence on excitation energy. Results for reactions 233 U(n th ,f), 235 U(n th ,f), 229 Th(n th ,f), 249 Cf(n th ,f) are spent [ru

Optical Switching Using Transition from Dipolar to Charge Transfer Plasmon Modes in Ge2Sb2Te5 Bridged Metallodielectric Dimers

Science.gov (United States)

Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih

2017-02-01

Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state.

Pressure dependence of excited-state charge-carrier dynamics in organolead tribromide perovskites

Science.gov (United States)

Liu, X. C.; Han, J. H.; Zhao, H. F.; Yan, H. C.; Shi, Y.; Jin, M. X.; Liu, C. L.; Ding, D. J.

2018-05-01

Excited-state charge-carrier dynamics governs the performance of organometal trihalide perovskites (OTPs) and is strongly influenced by the crystal structure. Characterizing the excited-state charge-carrier dynamics in OTPs under high pressure is imperative for providing crucial insights into structure-property relations. Here, we conduct in situ high-pressure femtosecond transient absorption spectroscopy experiments to study the excited-state carrier dynamics of CH3NH3PbBr3 (MAPbBr3) under hydrostatic pressure. The results indicate that compression is an effective approach to modulate the carrier dynamics of MAPbBr3. Across each pressure-induced phase, carrier relaxation, phonon scattering, and Auger recombination present different pressure-dependent properties under compression. Responsiveness is attributed to the pressure-induced variation in the lattice structure, which also changes the electronic band structure. Specifically, simultaneous prolongation of carrier relaxation and Auger recombination is achieved in the ambient phase, which is very valuable for excess energy harvesting. Our discussion provides clues for optimizing the photovoltaic performance of OTPs.

Mechanism for the Excited-State Multiple Proton Transfer Process of Dihydroxyanthraquinone Chromophores.

Science.gov (United States)

Zhou, Qiao; Du, Can; Yang, Li; Zhao, Meiyu; Dai, Yumei; Song, Peng

2017-06-22

The single and dual cooperated proton transfer dynamic process in the excited state of 1,5-dihydroxyanthraquinone (1,5-DHAQ) was theoretically investigated, taking solvent effects (ethanol) into account. The absorption and fluorescence spectra were simulated, and dual fluorescence exhibited, which is consistent with previous experiments. Analysis of the calculated IR and Raman vibration spectra reveals that the intramolecular hydrogen bonding interactions (O 20 -H 21 ···O 24 and O 22 -H 23 ···O 25 ) are strengthened following the excited proton transfer process. Finally, by constructing the potential energy surfaces of the ground state, first excited singlet state, and triplet state, the mechanism of the intramolecular proton transfer of 1,5-DHAQ can be revealed.

Charge and excitation dynamics in semiconducting polymer layers doped with emitters and charge carrier traps; Ladungstraeger- und Anregungsdynamik in halbleitenden Polymerschichten mit eingemischten Emittern und Ladungstraegerfallen

Energy Technology Data Exchange (ETDEWEB)

Jaiser, F

2006-06-15

blend, the nature of the excited states as well as the method of the charge transport through the layer are of great importance to the transfer. Again, the charge carrier balance influences the emission. To characterize the trapping of charges in trap states, a method based on the measurement of transient photocurrents is enhanced. The results show that models developed for ordered systems can not simply be transferred to polymer systems with a high degree of disorder. Finally, time-resolved measurements of the phosphorescence decay in blends of polymers with organo-metallic compounds are shown. Usually, these systems contain more components that facilitate charge transport. Thus, triplets may be transferred from the phosphorescent dye other components of the film. Knowing the underlying interactions, unwanted processes can be suppressed. (orig.)

Charge transfer cross sections for dysprosium and cerium

Energy Technology Data Exchange (ETDEWEB)

Adachi, Hajime; Tamura, Koji; Okazaki, Tetsuji; Shibata, Takemasa [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1998-06-01

Symmetric resonant charge transfer cross sections between singly ionized ions and the parent atoms were measured for dysprosium and cerium in the impact energy of 200-2000eV. The cross sections were determined from the ratio between the number of ions produced by charge transfer and those in primary ion beam. The primary ion beam was produced by a laser ion source in which their atoms were ionized by laser resonant photo-ionization. The slow ions produced by charge transfer and fast primary ions were detected with Faraday cups. The obtained cross sections were (1.82{+-}0.14) x 10{sup -14} cm{sup 2} for dysprosium and (0.88{+-}0.12) x 10{sup -14} cm{sup 2} for cerium in the above energy range. The difference of these values can mostly be explained by considering the electron configurations of these atoms and ions. (author)

Charge transfer cross sections for dysprosium and cerium

International Nuclear Information System (INIS)

Adachi, Hajime; Tamura, Koji; Okazaki, Tetsuji; Shibata, Takemasa

1998-06-01

Symmetric resonant charge transfer cross sections between singly ionized ions and the parent atoms were measured for dysprosium and cerium in the impact energy of 200-2000eV. The cross sections were determined from the ratio between the number of ions produced by charge transfer and those in primary ion beam. The primary ion beam was produced by a laser ion source in which their atoms were ionized by laser resonant photo-ionization. The slow ions produced by charge transfer and fast primary ions were detected with Faraday cups. The obtained cross sections were (1.82±0.14) x 10 -14 cm 2 for dysprosium and (0.88±0.12) x 10 -14 cm 2 for cerium in the above energy range. The difference of these values can mostly be explained by considering the electron configurations of these atoms and ions. (author)

Charge Transfer and Catalysis at the Metal Support Interface

Energy Technology Data Exchange (ETDEWEB)

Baker, Lawrence Robert [Univ. of California, Berkeley, CA (United States)

2012-07-31

Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalytic reaction kinetics.

Charge-transfer modified embedded atom method dynamic charge potential for Li-Co-O system.

Science.gov (United States)

Kong, Fantai; Longo, Roberto C; Liang, Chaoping; Nie, Yifan; Zheng, Yongping; Zhang, Chenxi; Cho, Kyeongjae

2017-11-29

To overcome the limitation of conventional fixed charge potential methods for the study of Li-ion battery cathode materials, a dynamic charge potential method, charge-transfer modified embedded atom method (CT-MEAM), has been developed and applied to the Li-Co-O ternary system. The accuracy of the potential has been tested and validated by reproducing a variety of structural and electrochemical properties of LiCoO 2 . A detailed analysis on the local charge distribution confirmed the capability of this potential for dynamic charge modeling. The transferability of the potential is also demonstrated by its reliability in describing Li-rich Li 2 CoO 2 and Li-deficient LiCo 2 O 4 compounds, including their phase stability, equilibrium volume, charge states and cathode voltages. These results demonstrate that the CT-MEAM dynamic charge potential could help to overcome the challenge of modeling complex ternary transition metal oxides. This work can promote molecular dynamics studies of Li ion cathode materials and other important transition metal oxides systems that involve complex electrochemical and catalytic reactions.

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

Science.gov (United States)

Zamadar, Matibur; Cook, Andrew R; Lewandowska-Andralojc, Anna; Holroyd, Richard; Jiang, Yan; Bikalis, Jin; Miller, John R

2013-09-05

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

Charge asymmetry in alignment of atoms excited by protons and antiprotons

International Nuclear Information System (INIS)

Balashov, V.V.; Sokolik, A.A.; Stysin, A.V.

2007-01-01

The multichannel diffraction approximation is used to consider excitation of lithium atom by proton and antiproton impact. Calculations are performed for the energy range 100 keV - 1 MeV of incoming proton and anti-proton which should be reliable enough due to the general requirements of the multichannel diffraction approximation. The sign-of-charge effect in the alignment of produced 1s 2 3d excited state and in the linear polarization of the subsequent spontaneous 1s 2 3d → 1s 2 2p radiation is expected to be considerable. The clear sign-of-charge effect in the polarization occurs for projectile energies below 1 MeV and become stronger when going to lower energies and the difference between the proton case and the anti-proton one looks considerable enough for experimental observation

Voltammetry for the charge transfer at two immiscible electrolyte solutions interface

International Nuclear Information System (INIS)

Kihara, S.; Suzuki, M.; Maeda, K.; Ogura, K.; Matsui, M.; Yoshida, Z.

1989-01-01

The voltammetry for the charge transfer (VCT) at the interface of immicible solutions is a very powerful method for understanding the dynamic features of the charge transfer because of its unmatched advantage that the transfer energy and the number of charges transferred can be measured simultaneously and in situ. In the present paper, several novel systems for electron transfer are outlined, and the following topics are discussed based on results obtained by the current scan polarography at the solution dropping electrode developed as a technique for VCT: the relation between the half-wave potential in VCT for ion transfer and the characteristics of the ion transferred; the relation between the half-wave potential in VCT for electron transfer and the electrochemical nature of a redox couple added in water and that added in organic solution; and the ion transfer through a liquid membrane promoted by electron transfer. Observations are presented and discussion is made on the characteristics of ion transfer polarograms, those of electron transfer polarograms, and ion transfer promoted by electron transfer at a liquid/membrane interface. (N.K.)

Charge-transfer spectra of tetravalent lanthanide ions in oxides

NARCIS (Netherlands)

Hoefdraad, H.E.

The charge-transfer spectra of Ce4+, Pr4+ and Tb4+ in a number of oxides are reported. It is noted that the position of the first charge-transfer band is fixed for the metal ion in an oxygen coordination of VI, but varies in VIII coordination as a function of the host lattice. It is argued that this

Excitation-energy influence at the scission configuration

Directory of Open Access Journals (Sweden)

Ramos D.

2017-01-01

Full Text Available Transfer- and fusion-induced fission in inverse kinematics was proven to be a powerful tool to investigate nuclear fission, widening the information of the fission fragments and the access to unstable fissioning systems with respect to other experimental approaches. An experimental campaign for fission investigation has being carried out at GANIL with this technique since 2008. In these experiments, a beam of 238U, accelerated to 6.1 MeV/u, impinges on a 12C target. Fissioning systems from U to Cf are populated through transfer and fusion reactions, with excitation energies that range from few MeV up to 46 MeV. The use of inverse kinematics, the SPIDER telescope, and the VAMOS spectrometer permitted the characterization of the fissioning system in terms of mass, nuclear charge, and excitation energy, and the isotopic identification of the full fragment distribution. The neutron excess, the total neutron multiplicity, and the even-odd staggering in the nuclear charge of fission fragments are presented as a function of the excitation energy of the fissioning system. Structure effects are observed at Z∼50 and Z∼55, where their impact evolves with the excitation energy.

Coherent excitation-energy transfer and quantum entanglement in a dimer

International Nuclear Information System (INIS)

Liao Jieqiao; Sun, C. P.; Huang Jinfeng; Kuang Leman

2010-01-01

We study coherent energy transfer of a single excitation and quantum entanglement in a dimer, which consists of a donor and an acceptor modeled by two two-level systems. Between the donor and the acceptor, there exists a dipole-dipole interaction, which provides the physical mechanism for coherent energy transfer and entanglement generation. The donor and the acceptor couple to two independent heat baths with diagonal couplings that do not dissipate the energy of the noncoupling dimer. Special attention is paid to the effect on single-excitation energy transfer and entanglement generation of the energy detuning between the donor and the acceptor and the temperatures of the two heat baths. It is found that, the probability for single-excitation energy transfer largely depends on the energy detuning in the low temperature limit. Concretely, the positive and negative energy detunings can increase and decrease the probability at steady state, respectively. In the high temperature limit, however, the effect of the energy detuning on the probability is negligibly small. We also find that the probability is negligibly dependent on the bath temperature difference of the two heat baths. In addition, it is found that quantum entanglement can be generated in the process of coherent energy transfer. As the bath temperature increases, the generated steady-state entanglement decreases. For a given bath temperature, the steady-state entanglement decreases with the increase of the absolute value of the energy detuning.

Transverse Schottky spectra and beam transfer functions of coasting ion beams with space charge

International Nuclear Information System (INIS)

Paret, Stefan

2010-01-01

A study of the transverse dynamics of coasting ion beams with moderate space charge is presented in this work. From the dispersion relation with linear space charge, an analytic model describing the impact of space charge on transverse beam transfer functions (BTFs) and the stability limits of a beam is derived. The dielectric function obtained in this way is employed to describe the transverse Schottky spectra with linear space charge as well. The difference between the action of space charge and impedances is highlighted. The setup and the results of an experiment performed in the heavy ion synchrotron SIS-18 at GSI to detect space-charge effects at different beam intensities are explicated. The measured transverse Schottky spectra and BTFs are compared with the linear space-charge model. The stability diagrams constructed from the BTFs are presented. The space-charge parameters evaluated from the Schottky and BTF measurements are compared with estimations based on measured beam parameters. The impact of collective effects on the Schottky and BTF diagnostics is also investigated through numerical simulations. For this purpose the self-field of beams with linear and non-linear transverse density-distributions is computed on a twodimensional grid. The noise of the random particle distribution causes fluctuations of the dipole moment of the beam which produce the Schottky spectrum. BTFs are simulated by exciting the beam with transverse kicks. The simulation results are used to verify the space-charge model. (orig.)

Transverse Schottky spectra and beam transfer functions of coasting ion beams with space charge

Energy Technology Data Exchange (ETDEWEB)

Paret, Stefan

2010-02-22

A study of the transverse dynamics of coasting ion beams with moderate space charge is presented in this work. From the dispersion relation with linear space charge, an analytic model describing the impact of space charge on transverse beam transfer functions (BTFs) and the stability limits of a beam is derived. The dielectric function obtained in this way is employed to describe the transverse Schottky spectra with linear space charge as well. The difference between the action of space charge and impedances is highlighted. The setup and the results of an experiment performed in the heavy ion synchrotron SIS-18 at GSI to detect space-charge effects at different beam intensities are explicated. The measured transverse Schottky spectra and BTFs are compared with the linear space-charge model. The stability diagrams constructed from the BTFs are presented. The space-charge parameters evaluated from the Schottky and BTF measurements are compared with estimations based on measured beam parameters. The impact of collective effects on the Schottky and BTF diagnostics is also investigated through numerical simulations. For this purpose the self-field of beams with linear and non-linear transverse density-distributions is computed on a twodimensional grid. The noise of the random particle distribution causes fluctuations of the dipole moment of the beam which produce the Schottky spectrum. BTFs are simulated by exciting the beam with transverse kicks. The simulation results are used to verify the space-charge model. (orig.)

Large impact of reorganization energy on photovoltaic conversion due to interfacial charge-transfer transitions.

Science.gov (United States)

Fujisawa, Jun-ichi

2015-05-14

Interfacial charge-transfer (ICT) transitions are expected to be a novel charge-separation mechanism for efficient photovoltaic conversion featuring one-step charge separation without energy loss. Photovoltaic conversion due to ICT transitions has been investigated using several TiO2-organic hybrid materials that show organic-to-inorganic ICT transitions in the visible region. In applications of ICT transitions to photovoltaic conversion, there is a significant problem that rapid carrier recombination is caused by organic-inorganic electronic coupling that is necessary for the ICT transitions. In order to solve this problem, in this work, I have theoretically studied light-to-current conversions due to the ICT transitions on the basis of the Marcus theory with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. An apparent correlation between the reported incident photon-to-current conversion efficiencies (IPCE) and calculated reorganization energies was clearly found, in which the IPCE increases with decreasing the reorganization energy consistent with the Marcus theory in the inverted region. This activation-energy dependence was systematically explained by the equation formulated by the Marcus theory based on a simple excited-state kinetic scheme. This result indicates that the reduction of the reorganization energy can suppress the carrier recombination and enhance the IPCE. The reorganization energy is predominantly governed by the structural change in the chemical-adsorption moiety between the ground and ICT excited states. This work provides crucial knowledge for efficient photovoltaic conversion due to ICT transitions.

Plasmon excitation in single wall carbon nanotubes by penetrating charged particles

International Nuclear Information System (INIS)

Segui, Silvina; Gervasoni, Juana L; Arista, Néstor R; Mowbray, Duncan J; Mišković, Zoran L

2012-01-01

In this work we study the excitation of plasmons due to the incidence of a charged particle passing through a single wall carbon nanotube. We use a quantized hydrodynamic, in which the σ and π electrons characteristic of these carbonaceous structures are depicted as two interacting 2-dimensional fluids, to calculate the average number of plasmons excited. We analyze the contribution of the different plasmon modes in a variety of configurations, and study the energy lost by the incident particle.

Theoretical Insights Into the Excited State Double Proton Transfer Mechanism of Deep Red Pigment Alkannin.

Science.gov (United States)

Zhao, Jinfeng; Dong, Hao; Zheng, Yujun

2018-02-08

As the most important component of deep red pigments, alkannin is investigated theoretically in detail based on time-dependent density functional theory (TDDFT) method. Exploring the dual intramolecular hydrogen bonds (O1-H2···O3 and O4-H5···O6) of alkannin, we confirm the O1-H2···O3 may play a more important role in the first excited state than the O4-H5···O6 one. Infrared (IR) vibrational analyses and subsequent charge redistribution also support this viewpoint. Via constructing the S 1 -state potential energy surface (PES) and searching transition state (TS) structures, we illuminate the excited state double proton transfer (ESDPT) mechanism of alkannin is the stepwise process that can be first launched by the O1-H2···O3 hydrogen bond wire in gas state, acetonitrile (CH 3 CN) and cyclohexane (CYH) solvents. We present a novel mechanism that polar aprotic solvents can contribute to the first-step proton transfer (PT) process in the S 1 state, and nonpolar solvents play important roles in lowering the potential energy barrier of the second-step PT reaction.

Charge-exchange processes in a divertor plasma with account for excited particles

International Nuclear Information System (INIS)

Krasheninnikov, S.I.; Lisitsa, V.S.; Pigarov, A.Yu.

1988-01-01

A model describing dynamics of neutral atoms and multicharge ions in tokamak plasma, taking account of cascade excitation effect on charge exchange and ionization processes, is constructed. Dependences of effective rate of processes of proton charge exchange on hydrogen atom and non-resonance helium atom charge exchange on proton and α-particle- on atomic hydrogen on tokamak divertor plasma parameters are calculated. It is shown that H + +He→H-He + charge exchange can make up a notable shave (∼30%) in full helium ionization rate. Accounting for Ge 2+ charge exchange on atomic hydrogen under INTOR reactor divertor plasma conditions can lead to substantial He 2+ →He + conversion and thus increase diverter plate sputtering by helium ions

Excitation of atomic nuclei and atoms by relativistic charge particles bound in a one-dimensional potential

International Nuclear Information System (INIS)

Almaliev, A.N.; Batkin, I.S.; Kopytin, I.V.

1987-01-01

The process of exciting atoms and atomic nuclei by relativistic electrons and positrons bound in a one-dimensional potential is investigated theoretically. It is shown that a pole corresponding to the emergence of a virtual photon on a bulk surface occurs in the matrix interaction element under definite kinematic relationships. It is obtained that the probability of the excitation process depends on the lifetime of the level being excited, the virtual photon, and the charged particle in a definite energetic state. An estimate of the magnitude of the excitation section of low-lying nuclear states yields a value exceeding by several orders the section obtained for charged particles in the absence of a binding potential

Charge transfer induced activity of graphene for oxygen reduction

International Nuclear Information System (INIS)

Shen, Anli; Xia, Weijun; Dou, Shuo; Wang, Shuangyin; Zhang, Lipeng; Xia, Zhenhai

2016-01-01

Tetracyanoethylene (TCNE), with its strong electron-accepting ability, was used to dope graphene as a metal-free electrocatalyst for the oxygen reduction reaction (ORR). The charge transfer process was observed from graphene to TCNE by x-ray photoelectron spectroscopy and Raman characterizations. Our density functional theory calculations found that the charge transfer behavior led to an enhancement of the electrocatalytic activity for the ORR. (paper)

Charge and energy dynamics in photo-excited poly(para-phenylenevinylene) systems

International Nuclear Information System (INIS)

Gisslen, L.; Johansson, A.; Stafstroem, S.

2004-01-01

We report results from simulations of charge and energy dynamics in poly(para-phenylenevinylene) (PPV) and PPV interacting with C 60 . The simulations were performed by solving the time-dependent Schroedinger equation and the lattice equation of motion simultaneously and nonadiabatically. The electronic system and the coupling of the electrons to the lattice were described by an extended three-dimensional version of the Su-Schrieffer-Heeger model, which also included an external electric field. Electron and lattice dynamics following electronic excitations at different energies have been simulated. The effect of additional lattice energy was also included in the simulations. Our results show that both exciton diffusion and transitions from high to lower lying excitations are stimulated by increasing the lattice energy. Also field induced charge separation occurs faster if the lattice energy is increased. This separation process is highly nonadiabatic and involves a significant rearrangement of the electron distribution. In the case of PPV coupled to C 60 , we observe a spontaneous charge separation. The separation time is in this case limited by the local concentration of C 60 molecules close to the PPV chain

Resonant and nonresonant transfer and excitation in Si11+ + He collisions

International Nuclear Information System (INIS)

Clark, M.W.

1988-01-01

For many years now, dielectronic recombination (DR) has been discussed as a possible energy loss mechanism in high temperature plasmas (e.g. stars). The process is basically the inverse Auger process and involves the capture of a free electron by an ion and the simultaneous excitation of an inner shell electron of the ion producing a doubly excited state. The DR process also includes the radiative deexcitation of the ion and hence represents an energy loss from the plasma since the plasma is essentially transparent to the photons. If, instead of a free electron, an electron that is weakly bound to an atom is captured and an inner shell electron of the ion is excited, the same excited states are produced as in DR. Because the bound electrons have a momentum distribution (Compton profile), individual doubly excited states cannot, in general, be observed in this case. This new process has been called Resonant Transfer and Excitation (RTE). There is also a competing mechanism for RTE in which excitation occurs via the interaction between a projectile ion electron and a target nucleus and the capture occurs because of the interaction of the projectile nucleus and a target electron. This competing mechanism has been termed Nonresonant Transfer and Excitation (NTE) Measurements have been performed to measure RTE and NTE cross sections. A discussion of the theory, methods, and results is included

Does charge transfer correlate with ignition probability?

International Nuclear Information System (INIS)

Holdstock, Paul

2008-01-01

Flammable or explosive atmospheres exist in many industrial environments. The risk of ignition caused by electrostatic discharges is very real and there has been extensive study of the incendiary nature of sparks and brush discharges. It is clear that in order to ignite a gas, an amount of energy needs to be delivered to a certain volume of gas within a comparatively short time. It is difficult to measure the energy released in an electrostatic discharge directly, but it is possible to approximate the energy in a spark generated from a well defined electrical circuit. The spark energy required to ignite a gas, vapour or dust cloud can be determined by passing such sparks through them. There is a relationship between energy and charge in a capacitive circuit and so it is possible to predict whether or not a spark discharge will cause an ignition by measuring the charge transferred in the spark. Brush discharges are in many ways less well defined than sparks. Nevertheless, some work has been done that has established a relationship between charge transferred in brush discharges and the probability of igniting a flammable atmosphere. The question posed by this paper concerns whether such a relationship holds true in all circumstances and if there is a universal correlation between charge transfer and ignition probability. Data is presented on discharges from textile materials that go some way to answering this question.

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

International Nuclear Information System (INIS)

Armstrong, T.D.

1994-01-01

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

Enhancing SERS by Means of Supramolecular Charge Transfer

Science.gov (United States)

Wong, Eric; Flood, Amar; Morales, Alfredo

2009-01-01

In a proposed method of sensing small quantities of molecules of interest, surface enhanced Raman scattering (SERS) spectroscopy would be further enhanced by means of intermolecular or supramolecular charge transfer. There is a very large potential market for sensors based on this method for rapid detection of chemical and biological hazards. In SERS, the Raman signals (vibrational spectra) of target molecules become enhanced by factors of the order of 108 when those molecules are in the vicinities of nanostructured substrate surfaces that have been engineered to have plasmon resonances that enhance local electric fields. SERS, as reported in several prior NASA Tech Briefs articles and elsewhere, has remained a research tool and has not yet been developed into a practical technique for sensing of target molecules: this is because the short range (5 to 20 nm) of the field enhancement necessitates engineering of receptor molecules to attract target molecules to the nanostructured substrate surfaces and to enable reliable identification of the target molecules in the presence of interferants. Intermolecular charge-transfer complexes have been used in fluorescence-, photoluminescence-, and electrochemistry-based techniques for sensing target molecules, but, until now, have not been considered for use in SERS-based sensing. The basic idea of the proposed method is to engineer receptor molecules that would be attached to nanostructured SERS substrates and that would interact with the target molecules to form receptor-target supramolecular charge-transfer complexes wherein the charge transfer could be photoexcited.

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

KAUST Repository

Gruenewald, Marco; Schirra, Laura K.; Winget, Paul; Kozlik, Michael; Ndione, Paul F.; Sigdel, Ajaya K.; Berry, Joseph J.; Forker, Roman; Bredas, Jean-Luc; Fritz, Torsten; Monti, Oliver L. A.

2015-01-01

with localized states (the shallow donors) in the substrate and charge back-donation, resulting in an effectively integer charge transfer across the interface. Charge transfer is thus not merely a question of locating the Fermi level above the PTCDA electron

Charge transfer devices and their application in physics

Energy Technology Data Exchange (ETDEWEB)

Soroko, L M [Joint Inst. for Nuclear Research, Dubna (USSR)

1979-01-01

Physical properties and technical specifications of charge transfer devices (CTD) are reviewed. The CTD are semiconductor devices based on silicon single crystals. The limiting charge density of the CTD, their efficiency of charge transfer, the background noise and radiation effects are considered. Fast response and low energy consumption are characteristic features of the devices. The application of the CTD in storage devices, real time spectral data processing systems and in streamer chambers is described. The algorithms of topological transformations in the stage of scanning particle track images, which can be realized with the help of the CTD are shortly considered. It is pointed out that applications of the CTD in different fields of science and technology are numerous and expanding.

Proton transfer to charged platinum electrodes. A molecular dynamics trajectory study.

Science.gov (United States)

Wilhelm, Florian; Schmickler, Wolfgang; Spohr, Eckhard

2010-05-05

A recently developed empirical valence bond (EVB) model for proton transfer on Pt(111) electrodes (Wilhelm et al 2008 J. Phys. Chem. C 112 10814) has been applied in molecular dynamics (MD) simulations of a water film in contact with a charged Pt surface. A total of seven negative surface charge densities σ between -7.5 and -18.9 µC cm(-2) were investigated. For each value of σ, between 30 and 84 initial conditions of a solvated proton within a water slab were sampled, and the trajectories were integrated until discharge of a proton occurred on the charged surfaces. We have calculated the mean rates for discharge and for adsorption of solvated protons within the adsorbed water layer in contact with the metal electrode as a function of surface charge density. For the less negative values of σ we observe a Tafel-like exponential increase of discharge rate with decreasing σ. At the more negative values this exponential increase levels off and the discharge process is apparently transport limited. Mechanistically, the Tafel regime corresponds to a stepwise proton transfer: first, a proton is transferred from the bulk into the contact water layer, which is followed by transfer of a proton to the charged surface and concomitant discharge. At the more negative surface charge densities the proton transfer into the contact water layer and the transfer of another proton to the surface and its discharge occur almost simultaneously.

Tribo-electric charging of dielectric solids of identical composition

Science.gov (United States)

Angus, John C.; Greber, Isaac

2018-05-01

Despite its long history and importance in many areas of science and technology, there is no agreement on the mechanisms responsible for tribo-electric charging, including especially the tribo-charging of chemically identical dielectric solids. Modeling of the excitation, diffusional transport, and de-excitation of electrons from hot spots shows that a difference in local surface roughness of otherwise identical solid dielectric objects leads to different transient excited electron concentrations during tribo-processes. The model predicts that excited electron concentrations are lower and concentration gradients higher in solids with rougher rather than smoother surfaces. Consequently, during contact, the flux of charge carriers (electrons or holes) from hot spots will be greater into the rougher solid than into the smoother solid. These predictions are in agreement with current and historical observations of tribo-electric charge transfer between solids of the same composition. This effect can take place in parallel with other processes and may also play a role in the charging of solids of different composition.

Ab initio study of H + + H 2 collisions: Elastic/inelastic and charge transfer processes

Science.gov (United States)

Saieswari, A.; Kumar, Sanjay

2007-12-01

An ab initio full configuration interaction study has been undertaken to obtain the global potential energy surfaces for the ground and the first excited electronic state of the H + + H 2 system employing Dunning's cc-pVQZ basis set. Using the ab initio approach the corresponding quasi-diabatic potential energy surfaces and coupling potentials have been obtained. A time-independent quantum mechanical study has been also undertaken for both the inelastic and charge transfer processes at the experimental collision energy Ec.m. = 20.0 eV and the preliminary results show better agreement with the experimental data as compared to the earlier available theoretical studies.

Formation of excited hydrogen atoms by charge transfer and dissociation. Progress report No. 11, December 1, 1974--November 1, 1975

International Nuclear Information System (INIS)

Thomas, E.W.; Zivitz, M.; Rausch, E.O.; Baird, W.E.; Harris, J.E.

1975-01-01

A study of the excited states of atoms backscattered from metal surfaces is presented. Incident ions were H + , H 2 + , and He + at energies of 10 to 30 keV. Preliminary data are presented for a study of the charge state distribution among atoms backscattered from surfaces. Results of a study of light emission from atoms sputtered off targets by 10 to 30 keV Ar + ions as a way to determine surface contamination are presented. Brief studies of radiation damage by 10 to 30 keV H + and He + ions are discussed. 5 figures

Photoinduced partial charge transfer between conjugated polymer and fullerene in solutions

International Nuclear Information System (INIS)

Lin Hongzhen; Weng Yufeng; Huang Hongmin; He Qingguo; Zheng Min; Bai Fenglian

2004-01-01

Photoinduced charge transfer between a conjugated polymer and C 60 and the related processes were investigated in dilute solutions. The substantial fluorescence quenching is correlated with the efficient exciton diffusion within the polymer chains, according to which a sphere-of-action mechanism is proposed. An emissive exciplex was found formed between the conjugated polymer and fullerene in a nonpolar solvent, indicating the occurrence of a photoinduced partial charge transfer process. The low-energy sites in the polymer are believed to play a crucial role in the partial charge transfer. The asymmetry of the exciplex provides a method for evaluating the tendency of photoinduced charge separation between the donor and the acceptor. This method allows screening candidates for photovoltaic applications

Electron transfer and decay processes of highly charged iodine ions

International Nuclear Information System (INIS)

Sakaue, Hiroyuki A.; Danjo, Atsunori; Hosaka, Kazumoto

2005-01-01

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

Complexes with charge transfer and ion-radical salts in catalysis

Energy Technology Data Exchange (ETDEWEB)

Krylov, O V [AN SSSR, Moscow. Inst. Khimicheskoj Fiziki

1978-01-01

Considered are the data experimentally proving formation of complexes with charge transfer as intermediate complexes in homogeneous and heterogeneous catalysis. Catalytic activity correlations with charge transfer energy (and in heterogeneous catalysis with width of semiconductor forbidden band can be useful while selection of catalysts (MoO/sub 3//MgO; V/sub 2/O/sub 5//MgO; MoO/sub 3//Al/sub 2/O/sub 3/; V/sub 2/O/sub 5//Al/sub 2/O/sub 3/). A review of papers on catalytic activity of the previously prepared complexes with charge transfer and ion-radical salts is given. The use of alkali metal complexes with aromatic compounds showed their high activity in hydrogenation reactions and proved principle possibility of activation of hydrogen and hydrocarbons by the systems which do not contain transfer metals.

Characterisation of a CMOS charge transfer device for TDI imaging

International Nuclear Information System (INIS)

Rushton, J.; Holland, A.; Stefanov, K.; Mayer, F.

2015-01-01

The performance of a prototype true charge transfer imaging sensor in CMOS is investigated. The finished device is destined for use in TDI applications, especially Earth-observation, and to this end radiation tolerance must be investigated. Before this, complete characterisation is required. This work starts by looking at charge transfer inefficiency and then investigates responsivity using mean-variance techniques

Ultrafast charge transfer and radiationless relaxations from higher excited state (S2) of directly linked Zn-porphyrin (ZP)-acceptor dyads: investigations into fundamental problems of exciplex chemistry

International Nuclear Information System (INIS)

Mataga, Noboru; Taniguchi, Seiji; Chosrowjan, Haik; Osuka, Atsuhiro; Yoshida, Naoya

2003-01-01

We have investigated photoinduced electron transfer and related processes from the higher excited electronic state (S 2 ) of Zn-porphyrin-imide acceptor directly linked supramolecular systems (ZP-I) designed especially for the critical studies of the energy gap law (EGL) of the charge separation (CS) from the S 2 state and solvent effects upon EGL. We have confirmed the modification of the EGL by change of solvent polarity from acetonitrile (ACN), tetrahydrofuran (THF) to toluene (Tol) and methyl-cyclohexane (MCH), from rather typical bell-shaped one in ACN to that with less prominent normal region and prominent inverted region with moderate slope extending over wider range of -ΔG CS values in nonpolar solvent MCH. We have demonstrated that these solvent effects upon EGL affect delicately various radiationless relaxation processes from S 2 state. We have examined also effects of the hydrogen bonding solvent ethanol (EtOH) on the EGL for CS and found very specific effect controlling the CS reaction and related processes

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

Science.gov (United States)

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

2012-02-01

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.

Red-excitation resonance Raman analysis of the nu(Fe=O) mode of ferryl-oxo hemoproteins.

Science.gov (United States)

Ikemura, Kenichiro; Mukai, Masahiro; Shimada, Hideo; Tsukihara, Tomitake; Yamaguchi, Satoru; Shinzawa-Itoh, Kyoko; Yoshikawa, Shinya; Ogura, Takashi

2008-11-05

The Raman excitation profile of the nuFe O mode of horseradish peroxidase compound II exhibits a maximum at 580 nm. This maximum is located within an absorption band with a shoulder assignable to an oxygen-to-iron charge transfer band on the longer wavelength side of the alpha-band. Resonance Raman bands of the nuFe O mode of various ferryl-oxo type hemoproteins measured at 590 nm excitation indicate that many hemoproteins in the ferryl-oxo state have an oxygen-to-iron charge transfer band in the visible region. Since this red-excited resonance Raman technique causes much less photochemical damage in the proteins relative to blue-excited resonance Raman spectroscopy, it produces a higher signal-to-noise ratio and thus represents a powerful tool for investigations of ferryl-oxo intermediates of hemoproteins.

On the use of analytical approximate expressions for the transfer rate in excitation transfer kinetics

International Nuclear Information System (INIS)

Kusba, J.; Sipp, B.

1985-01-01

We present a discussion about the range of validity of the usual approximate transfer rate expressions used in the description of the kinetics of diffusion-modulated excitation transfer, for a reactive interaction of exponential functional form. We simulate the features of energy transfer by a numerical inversion of the exact Laplace transform of the transfer rate. It is shown that for high diffusion coefficients of the order of 10 -5 cm 2 s -1 , the kinetics may be well reproduced, even at short times, by the asymptotic form of the transfer rate. For slow molecular displacements, the short time static regime is brought to direct observation, but the transfer rate approaches is asymptotic value at a much later time

A new technique for the study of charge transfer in multiply charged ion-ion collisions

International Nuclear Information System (INIS)

Shinpaugh, J.L.; Meyer, F.W.; Datz, S.

1994-01-01

While large cross sections (>10 -16 cm 2 ) have been predicted for resonant charge transfer in ion-ion collisions, no experimental data exist for multiply charged systems. A novel technique is being developed at the ORNL ECR facility to allow study of symmetric charge exchange in multiply charged ion-ion collisions using a single ion source. Specific intra-beam charge transfer collisions occurring in a well-defined interaction region labeled by negative high voltage are identified and analyzed by electrostatic analysis in combination with ion time-of-flight coincidence detection of the collision products. Center-of-mass collision energies from 400 to 1000 eV are obtained by varying source and labeling-cell voltages. In addition, by the introduction of a target gas into the high-voltage cell, this labeling-voltage method allows measurement of electron-capture and -loss cross sections for ion-atom collisions. Consequently, higher collision energies can be investigated without the requirement of placing the ECR source on a high-voltage platform

Ni-Ni ion pair excitation transfer in D sub(3h) symmetry

International Nuclear Information System (INIS)

Terrile, M.C.

1990-01-01

The mechanisms contributing to excitation transfer are examined for Ni-Ni ion pairs in order to explain the delocalized character of electronic excitations observed in CsNiF sub(3). Using both first-and second-order perturbation theory and from symmetry arguments, the kind of interactions giving matrix elements between states connecting different sites for the position of the excitation are discussed. (author)

Theoretical treatment of charge transfer processes of relevance to astrophysics

Energy Technology Data Exchange (ETDEWEB)

Krstic, P.S.; Stancil, P.C.; Schultz, D.R.

1997-12-01

Charge transfer is an important process in many astrophysical and atmospheric environments. While numerous experimental and theoretical studies exist for H and He targets, data on other targets, particularly metals and molecules, are sparse. Using a variety of theoretical methods and computational techniques the authors are developing methods to estimate the cross sections for electron capture (charge transfer) in slow collisions of low charge state ions with heavy (Mg, Ca, Fe, Co, Ni and Zn) neutrals. In this ongoing work particular attention is paid to ascertaining the importance of double electron capture.

Theoretical treatment of charge transfer processes of relevance to astrophysics

International Nuclear Information System (INIS)

Krstic, P.S.; Stancil, P.C.; Schultz, D.R.

1997-12-01

Charge transfer is an important process in many astrophysical and atmospheric environments. While numerous experimental and theoretical studies exist for H and He targets, data on other targets, particularly metals and molecules, are sparse. Using a variety of theoretical methods and computational techniques the authors are developing methods to estimate the cross sections for electron capture (charge transfer) in slow collisions of low charge state ions with heavy (Mg, Ca, Fe, Co, Ni and Zn) neutrals. In this ongoing work particular attention is paid to ascertaining the importance of double electron capture

Charge-transfer collisions for polarized ion sources

International Nuclear Information System (INIS)

Schlachter, A.S.

1983-06-01

Charge-transfer processes relevant to polarized ion sources are discussed and results are summarized. The primary atom discussed is hydrogen, with particulr emphasis on H - formation. Heavier negative ions are briefly discussed

Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

Science.gov (United States)

Sherman, David M.

1987-01-01

A molecular orbital description, based on Xα-Scattered wave calculations on a (FeTiO10)14− cluster, is given for Fe2+ → Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ → Ti4+ metal-metal charge transfer transition is 18040 cm−1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ → Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ → Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

Cold transfer between deformed, Coulomb excited nuclei

International Nuclear Information System (INIS)

Bauer, H.

1998-01-01

The scattering system 162 Dy → 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 γ-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 162 Dy has been analyzed. The gross properties of the measured population probabilities could be interpreted in a simple band mixing model. (orig.)

Low-Energy Charge Transfer in Multiply-Charged Ion-Atom Collisions Studied with the Combined SCVB-MOCC Approach

Directory of Open Access Journals (Sweden)

B. Zygelman

2002-03-01

Full Text Available A survey of theoretical studies of charge transfer involving collisions of multiply-charged ions with atomic neutrals (H and He is presented. The calculations utilized the quantum-mechanical molecular-orbital close-coupling (MOCC approach where the requisite potential curves and coupling matrix elements have been obtained with the spin-coupled valence bond (SCVB method. Comparison is made among various collision partners, for equicharged systems, where it is illustrated that even for total charge transfer cross sections, scaling-laws do not exist for low-energy collisions (i.e. < 1 keV/amu. While various empirical scaling-laws are well known in the intermediateand high-energy regimes, the multi-electron configurations of the projectile ions results in a rich and varied low-energy dependence, requiring an explicit calculation for each collision-partner pair. Future charge transfer problems to be addressed with the combined SCVB-MOCC approach are briefly discussed.

Quasi-elastic transfer and charge-exchange reactions in collisions of 48Ti on 42Ca and 26Mg

International Nuclear Information System (INIS)

Brendel, C.

1985-01-01

At the GSI magnetic spectrometer quasi-elastic transfer and charge-exchange reactions of the system 48 Ti + 42 Ca at incident energies E lab = 240, 300, and 385 MeV and additionally at the higher projectile energy the system 48 Ti + 26 Mg were studied each in the excitation energy range up to E x ≅ 80 MeV. The transition strength was for each particle-hole configuration of the final system calculated by means of the DWBA and subsequently folded with a Breit-Wigner distribution. The localization of the strength of the cross section and the specific structure of the energy spectra were at incident energies between 6 and 8 MeV/amu for all angles well reproduced. By an extension of the core-excitation model to many-stage reactions the charge-exchange reaction 48 Ti + 42 Ca → 48 Sc + 42 Sc could be described as sequential two-stage process. In the two-neutron stripping reaction 48 Ti + 42 Ca → 46 Ti + 44 Ca a surprisingly narrow line with a width of the experimental resolution and an excitation energy of E x = 17.8 MeV was measured at angles smaller than the grazing angle. In the 48 Ti + 26 Mg system the corresponding 46 Ti spectra show also under forward angles structures at excitation energies between 8 and 16 MeV. These lines can be explained as two-neutron states with high spin. (orig./HSI) [de

Graphene Charge Transfer, Spectroscopy, and Photochemical Reactions

Energy Technology Data Exchange (ETDEWEB)

Brus, Louis [Columbia Univ., New York, NY (United States)

2017-01-31

This project focused on the special electronic and optical properties of graphene and adsorbed molecular species. Graphene makes an excellent substrate for current collection in nanostructured photovoltaic designs. Graphene is almost transparent, and can be used as a solar cell window. It also has no surface states, and thus current is efficiently transported over long distances. Progress in graphene synthesis indicates that there will soon be practical methods for making large pieces of graphene for devices. We now need to understand exactly what happens to both ground state and electronically excited molecules and Qdots near graphene, if we are going to use them to absorb light in a nano-structured photovoltaic device using graphene to collect photocurrent. We also need to understand how to shift the graphene Fermi level, to optimize the kinetics of electron transfer to graphene. And we need to learn how to convert local graphene areas to semiconductor structure, to make useful spatially patterned graphenes. In this final report, we describe how we addressed these goals. We explored the question of possible Surface Enhanced Raman spectroscopy from molecular Charge Transfer onto Graphene substrates. We observed strong hole doping of graphene by adsorbed halogens as indicated by the shift of the graphene G Raman band. In the case of iodine adsorption, we also observed the anionic species made by hole doping. At low frequency in the Raman spectrum, we saw quite intense lines from I₃^- and I₅^- , suggesting possible SERS. We reported on Fresnel calculations on this thin film system, which did not show any net electromagnetic field enhancement.

The triplet excited state of Bodipy: formation, modulation and application.

Science.gov (United States)

Zhao, Jianzhang; Xu, Kejing; Yang, Wenbo; Wang, Zhijia; Zhong, Fangfang

2015-12-21

Boron dipyrromethene (Bodipy) is one of the most extensively investigated organic chromophores. Most of the investigations are focused on the singlet excited state of Bodipy, such as fluorescence. In stark contrast, the study of the triplet excited state of Bodipy is limited, but it is an emerging area, since the triplet state of Bodipy is tremendously important for several areas, such as the fundamental photochemistry study, photodynamic therapy (PDT), photocatalysis and triplet-triplet annihilation (TTA) upconversion. The recent developments in the study of the production, modulation and application of the triplet excited state of Bodipy are discussed in this review article. The formation of the triplet state of Bodipy upon photoexcitation, via the well known approach such as the heavy atom effect (including I, Br, Ru, Ir, etc.), and the new methods, such as using a spin converter (e.g. C60), charge recombination, exciton coupling and the doubly substituted excited state, are summarized. All the Bodipy-based triplet photosensitizers show strong absorption of visible or near IR light and the long-lived triplet excited state, which are important for the application of the triplet excited state in PDT or photocatalysis. Moreover, the methods for switching (or modulation) of the triplet excited state of Bodipy were discussed, such as those based on the photo-induced electron transfer (PET), by controlling the competing Förster-resonance-energy-transfer (FRET), or the intermolecular charge transfer (ICT). Controlling the triplet excited state will give functional molecules such as activatable PDT reagents or molecular devices. It is worth noting that switching of the singlet excited state and the triplet state of Bodipy may follow different principles. Application of the triplet excited state of Bodipy in PDT, hydrogen (H2) production, photoredox catalytic organic reactions and TTA upconversion were discussed. The challenges and the opportunities in these areas were

Charge transfer and ionization occurring in proton- and helium ion-atom collisions

International Nuclear Information System (INIS)

DuBois, R.D.

1985-12-01

Two examples are presented where specific channels have been identified that are responsible for single and double target ionization via direct coulomb ionization or charge transfer processes. Using ratios of absolute cross sections that have been measured for these processes it was shown that an independent electron model should be appropriate for calculating direct double target ionization but generally appears to be inadequate in calculating charge transfer plus ionization and double charge transfer cross sections. At present such detailed information can be obtained only in limited cases. However cross sections with detailed final charge state information should provide stringent tests for present and future theoretical work. 22 refs., 2 figs

Computational Approach to Electron Charge Transfer Reactions

DEFF Research Database (Denmark)

Jónsson, Elvar Örn

-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...... 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...

Charge transfer properties of pentacene adsorbed on silver: DFT study

Energy Technology Data Exchange (ETDEWEB)

N, Rekha T.; Rajkumar, Beulah J. M., E-mail: beulah-rajkumar@yahoo.co.in [PG & Research Department of Physics, Lady Doak College, Madurai 625002 (India)

2015-06-24

Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistribution of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.

Charge transfer processes in collisions of Si{sup 4+} ions with He atoms at intermediate energies

Energy Technology Data Exchange (ETDEWEB)

Suzuki, R. [Hitotsubashi Univ., Tokyo (Japan). Computer Center; Watanabe, A. [Dept. of Information Sciences, Ochanomizu Univ., Tokyo (Japan); Sato, H. [Graduate School of Humanities and Sciences, Ochanomizu Univ., Tokyo (Japan); Gu, J.P.; Hirsch, G.; Buenker, R.J. [Wuppertal Univ. (Gesamthochschule) (Germany). Lehrgebiet Theoretische Chemie; Kimura, M. [Graduate School of Science and Engineering, Yamaguchi Univ., Ube (Japan); Stancil, P.C. [Georgia Univ., Athens, GA (United States). Dept. of Physics

2001-07-01

Charge transfer in collisions of Si{sup 4+} ions with He atoms below 100 keV/u is studied by using a molecular orbital representation within both the semiclassical and quantal representations. Single transfer reaction Si{sup 4+} + He {yields} Si{sup 3+} + He{sup +} has been studied by a number of theoretical investigations. In addition to the reaction (1), the first semiclassical MOCC calculations are performed for the double transfer channel Si{sup 4+} + He {yields} Si{sup 2+} + He{sup 2+}. Nine molecular states that connect both with single and double electron transfer processes are considered in the present model. Electronic states and corresponding couplings are determined by the multireference single- and double- excitation configuration interaction method. The present cross sections tie well with the earlier calculations of Stancil et al., (1997) at lower energies, but show a rather different magnitude from those of Bacchus-Montabonel and Ceyzeriat, (1998). The present rate constant is found to be significantly different from the experimental finding of Fang and Kwong, (1996) at 4,600 K, and hence does not support the experiment. (orig.)

Formation of excited hydrogen atoms by charge transfer and dissociation. Progress report No. 12, December 1, 1975--November 1, 1976. [Summaries of research activities at Georgia Institute of Technology

Energy Technology Data Exchange (ETDEWEB)

Thomas, E.W.; Rausch, E.O.; Harriss, J.E.; Bell, J.T.

1976-11-01

The scattering of energetic hydrogenic ions from surfaces was investigated. Protons at energies 1 to 30 keV are incident on metal surfaces and studies made of the charge state and excited state fractions of the scattered particles; measurements are also made of angular distributions and velocity spectra. The excited state distribution of back-scattered atoms is found to be governed by Auger de-excitation at the surface. Molecular hydrogen ions (H/sup +//sub 2/ and H/sup +//sub 3/) incident on metal surfaces dissociate on impact and the subsequent behavior of the fragments is uncorrelated. Contamination of metal surfaces with oxygen causes an increase in the backscattered flux of excited particles related to changes in the Auger de-excitation rate. A study of charge state distributions and angular distribution of the backscattered flux has disclosed irregularities related to methods of surface preparation. Measured backscattering coefficients have been compared with theoretical calculations of McCracken and Freeman. A limited study was made of the Mossbauer spectra of Fe after H/sup +/ bombardment. Substantial (1 percent) changes to the hyperfine field occur and anneal out after a period of some days at room temperature. It is suggested that the changes to hyperfine field are related to vacancy formation. A list of publications is included.

Dynamical interaction of He atoms with metal surfaces: Charge transfer processes

International Nuclear Information System (INIS)

Flores, F.; Garcia Vidal, F.J.; Monreal, R.

1993-01-01

A self-consistent Kohn-Sham LCAO method is presented to calculate the charge transfer processes between a He * -atom and metal surfaces. Intra-atomic correlation effects are taken into account by considering independently each single He-orbital and by combining the different charge transfer processes into a set of dynamical rate equations for the different ion charge fractions. Our discussion reproduces qualitatively the experimental evidence and gives strong support to the method presented here. (author). 24 refs, 4 figs

Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

Energy Technology Data Exchange (ETDEWEB)

Pan, Shanlin [Univ. of Alabama, Tuscaloosa, AL (United States)

2014-11-16

Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an

Nuclear spin and isospin excitations

International Nuclear Information System (INIS)

Osterfeld, F.

1992-01-01

A review is given of our present knowledge of collective spin-isospin excitations in nuclei. Most of this knowledge comes from intermediate-energy charge-exchange reactions and from inelastic electron- and proton-scattering experiments. The nuclear-spin dynamics is governed by the spin-isospin-dependent two-nucleon interaction in the medium. This interaction gives rise to collective spin modes such as the giant Gamow-Teller resonances. An interesting phenomenon is that the measured total Gamow-Teller transition strength in the resonance region is much less than a model-independent sum rule predicts. Two physically different mechanisms have been discussed to explain this so-called quenching of the total Gamow-Teller strength: coupling to subnuclear degrees of freedom in the form of Δ-isobar excitation and ordinary nuclear configuration mixing. Both detailed nuclear structure calculations and extensive analyses of the scattering data suggest that the nuclear configuration mixing effect is the more important quenching mechanism, although subnuclear degrees of freedom cannot be ruled out. The quenching phenomenon occurs for nuclear-spin excitations at low excitation energies (ω∼10--20 MeV) and small-momentum transfers (q≤0.5 fm -1 ). A completely opposite effect is anticipated in the high (ω,q)-transfer region (0≤ω≤500 MeV, 0.5≤q≤3 fm -1 ). The nuclear spin-isospin response might be enhanced due to the attractive pion field inside the nucleus. Charge-exchange reactions at GeV incident energies have been used to study the quasifree peak region and the Δ-resonance region. An interesting result of these experiments is that the Δ excitation in the nucleus is shifted downwards in energy relative to the Δ excitation of the free proton

Non-Markovian reduced dynamics of ultrafast charge transfer at an oligothiophene–fullerene heterojunction

Energy Technology Data Exchange (ETDEWEB)

Hughes, Keith H., E-mail: keith.hughes@bangor.ac.uk [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Cahier, Benjamin [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Martinazzo, Rocco [Dipartimento di Chimica Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Tamura, Hiroyuki [WPI-Advanced Institute for Material Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main (Germany)

2014-10-17

Highlights: • Quantum dynamical study of exciton dissociation at a heterojunction interface. • The non-Markovian quantum dynamics involves a highly structured spectral density. • Spectral density is reconstructed from an effective mode transformation of the Hamiltonian. • The dynamics is studied using the hierarchical equations of motion approach. • It was found that the temperature has little effect on the charge transfer. - Abstract: We extend our recent quantum dynamical study of the exciton dissociation and charge transfer at an oligothiophene–fullerene heterojunction interface (Tamura et al., 2012) [6] by investigating the process using the non-perturbative hierarchical equations of motion (HEOM) approach. Based upon an effective mode reconstruction of the spectral density the effect of temperature on the charge transfer is studied using reduced density matrices. It was found that the temperature had little effect on the charge transfer and a coherent dynamics persists over the first few tens of femtoseconds, indicating that the primary charge transfer step proceeds by an activationless pathway.

Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

Energy Technology Data Exchange (ETDEWEB)

Morherr, Antonia, E-mail: morherr@stud.uni-frankfurt.de [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Witt, Sebastian [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Chernenkaya, Alisa [Graduate School Materials Science in Mainz, 55128 Mainz (Germany); Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz (Germany); Bäcker, Jan-Peter [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Schönhense, Gerd [Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz (Germany); Bolte, Michael [Institut für anorganische Chemie, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Krellner, Cornelius [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany)

2016-09-01

New charge transfer crystals of π-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure are reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-F{sub x}, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with π-conjugated donor molecules.

Collisionally excited few-electron systems: theoretical introduction and survey

International Nuclear Information System (INIS)

Ford, A.L.; Reading, J.F.; Becker, R.L.

1982-01-01

We consider excitation, ionization, and charge transfer in collisions of protons (and antiprotons) with the single-electron targets H, He + , and Li 2+ . 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

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

Energy Technology Data Exchange (ETDEWEB)

Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it [Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa (Italy); Koch, Henrik [Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Cappelli, Chiara [Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi, 3 I-56124 Pisa (Italy)

2014-12-14

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

Experimental evidence of state-selective charge transfer in inductively coupled plasma-atomic emission spectrometry

International Nuclear Information System (INIS)

Chan, George C.-Y.; Hieftje, Gary M.

2004-01-01

State-selective charge-transfer behavior was observed for Fe, Cr, Mn and Cu in inductively coupled plasma (ICP)-atomic emission spectrometry. Charge transfer from Ar + to Fe, Cr and Mn is state-selective because of inefficient collisional mixing of the quasiresonant charge-transfer energy levels with nearby levels. This low efficiency is the consequence of differences in electronic configuration of the core electrons. The reason for state-selective charge-transfer behavior to Cu is not clear, although a tentative explanation based on efficiency of intramultiplet and intermultiplet mixing for this special case is offered

Robust Stacking-Independent Ultrafast Charge Transfer in MoS2/WS2 Bilayers.

Science.gov (United States)

Ji, Ziheng; Hong, Hao; Zhang, Jin; Zhang, Qi; Huang, Wei; Cao, Ting; Qiao, Ruixi; Liu, Can; Liang, Jing; Jin, Chuanhong; Jiao, Liying; Shi, Kebin; Meng, Sheng; Liu, Kaihui

2017-12-26

Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attention recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behavior depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS 2 /WS 2 bilayer with various stacking configurations, by optical two-color ultrafast pump-probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ∼90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveals that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding, which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.

Reduced Charge Transfer Exciton Recombination in Organic Semiconductor Heterojunctions by Molecular Doping

Science.gov (United States)

Deschler, Felix; da Como, Enrico; Limmer, Thomas; Tautz, Raphael; Godde, Tillmann; Bayer, Manfred; von Hauff, Elizabeth; Yilmaz, Seyfullah; Allard, Sybille; Scherf, Ullrich; Feldmann, Jochen

2011-09-01

We investigate the effect of molecular doping on the recombination of electrons and holes localized at conjugated-polymer-fullerene interfaces. We demonstrate that a low concentration of p-type dopant molecules (<4% weight) reduces the interfacial recombination via charge transfer excitons and results in a favored formation of separated carriers. This is observed by the ultrafast quenching of photoluminescence from charge transfer excitons and the increase in photoinduced polaron density by ˜70%. The results are consistent with a reduced formation of emissive charge transfer excitons, induced by state filling of tail states.

An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

Science.gov (United States)

Hendrickson, Heidi Phillips

A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases.

Science.gov (United States)

Takaya, Tomohisa; Su, Charlene; de La Harpe, Kimberly; Crespo-Hernández, Carlos E; Kohler, Bern

2008-07-29

Excited electronic states created by UV excitation of the diribonucleoside monophosphates ApA, ApG, ApC, ApU, and CpG were studied by the femtosecond transient-absorption technique. Bleach recovery signals recorded at 252 nm show that long-lived excited states are formed in all five dinucleosides. The lifetimes of these states exceed those measured in equimolar mixtures of the constituent mononucleotides by one to two orders of magnitude, indicating that electronic coupling between proximal nucleobases dramatically slows the relaxation of excess electronic energy. The decay rates of the long-lived states decrease with increasing energy of the charge-transfer state produced by transferring an electron from one base to another. The charge-transfer character of the long-lived states revealed by this analysis supports their assignment to excimer or exciplex states. Identical bleach recovery signals were seen for ApA, (A)(4), and poly(A) at delay times >10 ps after photoexcitation. This indicates that excited states localized on a stack of just two bases are the common trap states independent of the number of stacked nucleotides. The fraction of initial excitations that decay to long-lived exciplex states is approximately equal to the fraction of stacked bases determined by NMR measurements. This supports a model in which excitations associated with two stacked bases decay to exciplex states, whereas excitations in unstacked bases decay via ultrafast internal conversion. These results establish the importance of charge transfer-quenching pathways for UV-irradiated RNA and DNA in room-temperature solution.

Trapping Dynamics in Photosystem I-Light Harvesting Complex I of Higher Plants Is Governed by the Competition Between Excited State Diffusion from Low Energy States and Photochemical Charge Separation.

Science.gov (United States)

Molotokaite, Egle; Remelli, William; Casazza, Anna Paola; Zucchelli, Giuseppe; Polli, Dario; Cerullo, Giulio; Santabarbara, Stefano

2017-10-26

The dynamics of excited state equilibration and primary photochemical trapping have been investigated in the photosystem I-light harvesting complex I isolated from spinach, by the complementary time-resolved fluorescence and transient absorption approaches. The combined analysis of the experimental data indicates that the excited state decay is described by lifetimes in the ranges of 12-16 ps, 32-36 ps, and 64-77 ps, for both detection methods, whereas faster components, having lifetimes of 550-780 fs and 4.2-5.2 ps, are resolved only by transient absorption. A unified model capable of describing both the fluorescence and the absorption dynamics has been developed. From this model it appears that the majority of excited state equilibration between the bulk of the antenna pigments and the reaction center occurs in less than 2 ps, that the primary charge separated state is populated in ∼4 ps, and that the charge stabilization by electron transfer is completed in ∼70 ps. Energy equilibration dynamics associated with the long wavelength absorbing/emitting forms harbored by the PSI external antenna are also characterized by a time mean lifetime of ∼75 ps, thus overlapping with radical pair charge stabilization reactions. Even in the presence of a kinetic bottleneck for energy equilibration, the excited state dynamics are shown to be principally trap-limited. However, direct excitation of the low energy chlorophyll forms is predicted to lengthen significantly (∼2-folds) the average trapping time.

Charge Transfer Processes in Collisions of Si4+ Ions with He Atoms at Intermediate Energies

Science.gov (United States)

Suzuki, R.; Watanabe, A.; Sato, H.; Gu, J. P.; Hirsch, G.; Buenker, R. J.; Kimura, M.; Stancil, P. C.

Charge transfer in collisions of Si4+ ions with He atoms below 100 keV/u is studied by using a molecular orbital representation within both the semiclassical and quantal representations. Single transfer reaction Si4++He →Si3++He+ has been studied by a number of theoretical investigations. In addition to the reaction (1), the first semiclassical MOCC calculations are performed for the double transfer channel Si4++HE→Si2++He2+ Nine molecular states that connect both with single and double electron transfer processes are considered in the present model. Electronic states and corresponding couplings are determined by the multireference single- and double- excitation configuration interaction method. The present cross sections tie well with the earlier calculations of Stancil et al., Phys. Rev. A 55, 1064 (1997) at lower energies, but show a rather different magnitude from those of Bacchus-Montabonel and Ceyzeriat, Phys. Rev. A 58, 1162 (1998). The present rate constant is found to be significantly different from the experimental finding of Fang and Kwong, Phys. Rev. A 59, 342 (1996) at 4,600 K, and hence does not support the experiment.

Excited state and charge-carrier dynamics in perovskite solar cell materials

Science.gov (United States)

Ponseca, Carlito S., Jr.; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G.

2016-02-01

Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.

Charge transfers in complex transition metal alloys (Ti2Fe)

International Nuclear Information System (INIS)

Abramovici, G.

1998-01-01

We introduce a new non-orthogonal tight-binding model, for complex alloys, in which electronic structure is characterized by charge transfers. We give the analytic calculation of a charge transfer, in which overlapping two-center terms are rigorously taken into account. Then, we apply numerically this result to an approximant phase of a quasicrystal of Ti 2 Fe alloy. This model is more particularly adapted to transition metals, and gives realistic densities of states. (orig.)

Polarized fine structure in the excitation spectrum of a negatively charged quantum dot

OpenAIRE

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Badescu, S. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-01-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of qua...

Femtosecond dynamics of electron transfer in a neutral organic mixed-valence compound

International Nuclear Information System (INIS)

Maksimenka, Raman; Margraf, Markus; Koehler, Juliane; Heckmann, Alexander; Lambert, Christoph; Fischer, Ingo

2008-01-01

In this article we report a femtosecond time-resolved transient absorption study of a neutral organic mixed-valence (MV) compound with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back-electron transfer was investigated in five different solvents, toluene, dibutyl ether, methyl-tert-butyl ether (MTBE), benzonitrile and n-hexane. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time constant. We assign one time constant to the rearrangement of solvent molecules in the charge-transfer state and the second time constant to back-electron transfer to the electronic ground state. Back-electron transfer rates range from 1.5 x 10 12 s -1 in benzonitrile through 8.3 x 10 11 s -1 in MTBE, around 1.6 x 10 11 s -1 in dibutylether and toluene and to 3.8 x 10 9 s -1 in n-hexane

Lifetime and g-factor measurements of excited states using Coulomb excitation and alpha transfer reactions

Energy Technology Data Exchange (ETDEWEB)

Guevara, Z. E., E-mail: zjguevaram@unal.edu.co; Torres, D. A., E-mail: datorresg@unal.edu.co [Physics Department, Universidad Nacional de Colombia, Bogotá D.C. (Colombia)

2016-07-07

In this contribution the challenges in the use of a setup to simultaneously measure lifetimes and g-factor values will be presented. The simultaneous use of the transient field technique and the Doppler Shift Attenuation Method, to measure magnetic moments and lifetimes respectively, allows to obtain a complete characterization of the currents of nucleons and the deformation in excited states close to the ground state. The technique is at the moment limited to Coulomb excitation and alpha-transfer reactions, what opens an interesting perspective to consider this type of experiments with radioactive beams. The use of deep-inelastic and fusion-evaporation reactions will be discussed. An example of a setup that makes use of a beam of {sup 106}Cd to study excited states of {sup 110}Sn and the beam nuclei itself will be presented.

Polyoxometalate active charge-transfer material for mediated redox flow battery

Energy Technology Data Exchange (ETDEWEB)

Anderson, Travis Mark; Hudak, Nicholas; Staiger, Chad; Pratt, Harry

2017-01-17

Redox flow batteries including a half-cell electrode chamber coupled to a current collecting electrode are disclosed herein. In a general embodiment, a separator is coupled to the half-cell electrode chamber. The half-cell electrode chamber comprises a first redox-active mediator and a second redox-active mediator. The first redox-active mediator and the second redox-active mediator are circulated through the half-cell electrode chamber into an external container. The container includes an active charge-transfer material. The active charge-transfer material has a redox potential between a redox potential of the first redox-active mediator and a redox potential of the second redox-active mediator. The active charge-transfer material is a polyoxometalate or derivative thereof. The redox flow battery may be particularly useful in energy storage solutions for renewable energy sources and for providing sustained power to an electrical grid.

Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Gross, Dieter Konrad Michael

2013-11-08

-quenching vanishes when this offset approaches 0.0 eV. The fact that PL-quenching and its correlation with the energetic offset was observed for both clustered and layered assembly provides a strong indirect indication of charge separation via electron transfer from CdTe to CdSe nanocrystals. The main result of this thesis is the direct proof of the charge separation on the type II interface of CdTe and CdSe nanocrystal layers. SPV-measurements as a direct measurement methode showed clearly the directionality of charge separation since the SPV measures the electric field of the separated charges. Electrons are collected on CdSe nanocrystal layers, holes on CdTe nanocrystal layers. A change in the order between CdSe and CdTe therefore leads to a change in the sign of the SPV-signal. Both SPVspectra and time-resolved SPV-measurements support this finding and showed that the charge selectivity of the CdTe-CdSe interface is unidirectional for the whole excitation spectrum and the entire investigated time range. This indicates that the directionality of the CdTe-CdSe interface is the only dominant charge separation mechanism that was observed. Hence, the type II alignment of the self-assembled nanocrystals used was clearly proven. Introducing an additional barrier between the nanocrystal layers doubled the barrier width so that the SPV-signal is quenched. This is consistent with tunneling transfer which is exponentially dependent on barrier width. Moreover, we learned that both absorption in CdTe and CdSe nanocrystals and the sample thickness contribute to the SPV-signal. Thus, we could observe electron diffusion in CdSe multilayers which was faster than the charge carrier diffusion dynamics in CdTe nanocrystal multilayers. Future research may address the combination of energy transfer dynamics with the charge separation processes presented in this thesis. On the one hand, this may provide a better understanding of their fundamental processes and differentiate between excitonic FRET and

Molecular approaches to solar energy conversion: the energetic cost of charge separation from molecular-excited states.

Science.gov (United States)

Durrant, James R

2013-08-13

This review starts with a brief overview of the technological potential of molecular-based solar cell technologies. It then goes on to focus on the core scientific challenge associated with using molecular light-absorbing materials for solar energy conversion, namely the separation of short-lived, molecular-excited states into sufficiently long-lived, energetic, separated charges capable of generating an external photocurrent. Comparisons are made between different molecular-based solar cell technologies, with particular focus on the function of dye-sensitized photoelectrochemical solar cells as well as parallels with the function of photosynthetic reaction centres. The core theme of this review is that generating charge carriers with sufficient lifetime and a high quantum yield from molecular-excited states comes at a significant energetic cost-such that the energy stored in these charge-separated states is typically substantially less than the energy of the initially generated excited state. The role of this energetic loss in limiting the efficiency of solar energy conversion by such devices is emphasized, and strategies to minimize this energy loss are compared and contrasted.

Resonant transfer excitation of fluorine-like Mo{sup 33+} ion

Energy Technology Data Exchange (ETDEWEB)

Ramadan, Hassan [Ain Shams Univ., Cairo (Egypt). Dept. of Basic Sciences; Elkilany, Sabbah [Kafr El-sheikh Univ. (Egypt). Dept. of Mathematics

2010-06-15

Dielectronic recombination (DR) cross sections (anti {sigma}{sup DR}) and rate coefficients ({alpha}{sup DR}) for Mo{sup 33+} are calculated using the angular momentum average scheme (AMA). Moreover, the resonant transfer excitation followed by X-ray emission (RTEX) cross sections ({sigma}{sup RTEX}) for the collision of Mo{sup 33+} with H{sub 2} and He targets are calculated and studied. The calculations of the cross sections are performed for both K- and L-shell excitations. A smooth change with the temperatures for {alpha}{sup DR} is found for all kinds of excitations. The rates for K-shell excitation are very small in comparison with the rates for L-shell excitation. The RTEX cross sections for Mo{sup 33+} ions are obtained from their corresponding DR cross sections by the method of folding in the impulse approximation (IMA). {sigma}{sup RTEX} for the K-shell excitation shows two overlapped peaks which may be attributed to the two groups in this excitation process. The present calculations are considered as a database for future comparison with theoretical and experimental data using other coupling schemes. Multiple Auger channels are complicating the dependence of the cross sections on principal quantum numbers. (orig.)

Charge transfer in chromium-transition metal alloys

International Nuclear Information System (INIS)

Kulakowski, K.; Maksymowicz, A.

1984-07-01

The average T-matrix approximation is applied for calculations of charge transfer of 3d-electrons in transition metal alloys. The role of concentration, long-range and short-range atomic order is investigated. The results are in reasonable agreement with experimental data. (author)

Systematics of excitation functions for (n, charged particle) reactions

International Nuclear Information System (INIS)

Zhao Zhixiang; Zhou Delin

1986-06-01

On the bases of evaporation model considering the preequilibrium emission under some approximations, the analytical expressions including two adjustable parameters have been derived for excitation functions of (n, charged particle) reactions. Fitting these expressions to the available measured data, these parameters have been extracted and the systematic behaviour of the parameters have been studied. More accurate predictions than before could be obtained by using these expressions and systematic parameters. In the present work the neutron energy is considered up to about 20 MeV and the target mass region is 23< A<197

ARCHITECTURE OF A CHARGE-TRANSFER STATE REGULATING LIGHT HARVESTING IN A PLANT ANTENNA PROTEIN

Energy Technology Data Exchange (ETDEWEB)

Fleming, Graham; Ahn, Tae Kyu; Avenson, Thomas J.; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K.; Bassi, Roberto; Fleming, Graham R.

2008-04-02

Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge-transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). In this work, we present evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a de-localized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can `tune? the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophylls-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

Excited state and charge-carrier dynamics in perovskite solar cell materials

International Nuclear Information System (INIS)

Ponseca, Carlito S Jr; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G

2016-01-01

Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research. (topical review)

Proton-coupled electron transfer versus hydrogen atom transfer: generation of charge-localized diabatic states.

Science.gov (United States)

Sirjoosingh, Andrew; Hammes-Schiffer, Sharon

2011-03-24

The distinction between proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms is important for the characterization of many chemical and biological processes. PCET and HAT mechanisms can be differentiated in terms of electronically nonadiabatic and adiabatic proton transfer, respectively. In this paper, quantitative diagnostics to evaluate the degree of electron-proton nonadiabaticity are presented. Moreover, the connection between the degree of electron-proton nonadiabaticity and the physical characteristics distinguishing PCET from HAT, namely, the extent of electronic charge redistribution, is clarified. In addition, a rigorous diabatization scheme for transforming the adiabatic electronic states into charge-localized diabatic states for PCET reactions is presented. These diabatic states are constructed to ensure that the first-order nonadiabatic couplings with respect to the one-dimensional transferring hydrogen coordinate vanish exactly. Application of these approaches to the phenoxyl-phenol and benzyl-toluene systems characterizes the former as PCET and the latter as HAT. The diabatic states generated for the phenoxyl-phenol system possess physically meaningful, localized electronic charge distributions that are relatively invariant along the hydrogen coordinate. These diabatic electronic states can be combined with the associated proton vibrational states to generate the reactant and product electron-proton vibronic states that form the basis of nonadiabatic PCET theories. Furthermore, these vibronic states and the corresponding vibronic couplings may be used to calculate rate constants and kinetic isotope effects of PCET reactions.

Optimization of excitation transfer in a spin chain

International Nuclear Information System (INIS)

Gurman, Vladimir I.; Guseva, Irina S.; Fesko, Oles V.

2016-01-01

A revised formulation of the problem of fastest transfer of the excitation in a spin chain is considered on the base of Shrödinger equation which Hamiltonian depends linearly on control. It is taken into account that the excitation of the first or last spin means that it has greatest amplitude equal to the chain invariant whereas its phase is undefined and can be considered as an additional control variable. The role of this additional control is analyzed via transformation of the original problem with unbounded linear control to the regular derived problem known from the theory of degenerate problems [1, 2], in the same way as in [2]. The overall procedure is demonstrated in computational experiments with the use of visual examples.

Phased Array Excitations For Efficient Near Field Wireless Power Transmission

Science.gov (United States)

2016-09-01

channeled to the battery or power plant. Figure 2. WPT System Block Diagram for Battery Charging. Source : [2]. Wireless power transfer has gained...EXCITATIONS FOR EFFICIENT NEAR-FIELD WIRELESS POWER TRANSMISSION by Sean X. Hong September 2016 Thesis Advisor: David Jenn Second Reader...TYPE AND DATES COVERED Master’s thesis 4. TITLE AND SUBTITLE PHASED ARRAY EXCITATIONS FOR EFFICIENT NEAR-FIELD WIRELESS POWER TRANSMISSION 5

Using metal complex-labeled peptides for charge transfer-based biosensing with semiconductor quantum dots

Science.gov (United States)

Medintz, Igor L.; Pons, Thomas; Trammell, Scott A.; Blanco-Canosa, Juan B.; Dawson, Philip E.; Mattoussi, Hedi

2009-02-01

Luminescent colloidal semiconductor quantum dots (QDs) have unique optical and photonic properties and are highly sensitive to charge transfer in their surrounding environment. In this study we used synthetic peptides as physical bridges between CdSe-ZnS core-shell QDs and some of the most common redox-active metal complexes to understand the charge transfer interactions between the metal complexes and QDs. We found that QD emission underwent quenching that was highly dependent on the choice of metal complex used. We also found that quenching traces the valence or number of metal complexes brought into close proximity of the nanocrystal surface. Monitoring of the QD absorption bleaching in the presence of the metal complex provided insight into the charge transfer mechanism. The data suggest that two distinct charge transfer mechanisms can take place. One directly to the QD core states for neutral capping ligands and a second to surface states for negatively charged capping ligands. A basic understanding of the proximity driven charge-transfer and quenching interactions allowed us to construct proteolytic enzyme sensing assemblies with the QD-peptide-metal complex conjugates.

Active pixel sensor with intra-pixel charge transfer

Science.gov (United States)

Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

2004-01-01

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

Electroluminescence from charge transfer states in Donor/Acceptor solar cells

DEFF Research Database (Denmark)

Sherafatipour, Golenaz; Madsen, Morten

Charge photocurrent generation is a key process in solar energy conversion systems. Effective dissociation of the photo-generated electron-hole pairs (excitons) has a strong influence on the efficiency of the organic solar cells. Charge dissociation takes place at the donor/acceptor interface via...... which the maximum open-circuit voltage can be estimated, and further can be used in the modeling and optimization of the OPV devices. [1] C. Deibe, T. Strobe, and V. Dyakonov, “Role of the charge transfer state in organic donor-acceptor solar cells,” Adv. Mater., vol. 22, pp. 4097–4111, 2010. [2] K...... charge transfer (CT) excitons, which is Coulombically bound interfacial electron- hole pairs residing at the donor/acceptor heterojunctions. The CT state represents an intermediate state between the exciton dissociation and recombination back to the ground state. Since the recombination of photo...

Electron Impact Excitation and Dielectronic Recombination of Highly Charged Tungsten Ions

Directory of Open Access Journals (Sweden)

Zhongwen Wu

2015-11-01

Full Text Available Electron impact excitation (EIE and dielectronic recombination (DR of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.

Anomalous temperature dependence of excitation transfer between quantum dots

Czech Academy of Sciences Publication Activity Database

Král, Karel; Menšík, Miroslav

2015-01-01

Roč. 7, č. 4 (2015), 325-330 ISSN 2164-6627 R&D Projects: GA MŠk(CZ) LD14011; GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : excitation transfer * quantum dots * temperature dependence * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

Determination of charge on vertically aligned particles in a complex plasma using laser excitations

CERN Document Server

Prior, N J; Samarian, A A

2003-01-01

Experimental studies on vertical oscillations of few particle vertical structures are described. One and two particle strings were subjected to two types of vertically driven oscillations. The first was electrode driven, which excites the structure as a whole, while the second was laser driven, which excites one particle in the structure only. The latter experiments are highly original, enabling us to excite two vertical resonances in our two particle structures. From the close agreement between our experimental data and theoretical model, several important physical parameters have been estimated, including the charge ratio and the Debye length.

Doping Phosphorene with Holes and Electrons through Molecular Charge Transfer.

Science.gov (United States)

Vishnoi, Pratap; Rajesh, S; Manjunatha, S; Bandyopadhyay, Arkamita; Barua, Manaswee; Pati, Swapan K; Rao, C N R

2017-11-03

An important aspect of phosphorene, the novel two-dimensional semiconductor, is whether holes and electrons can both be doped in this material. Some reports found that only electrons can be preferentially doped into phosphorene. There are some theoretical calculations showing charge-transfer interaction with both tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE). We have carried out an investigation of chemical doping of phosphorene by a variety of electron donor and acceptor molecules, employing both experiment and theory, Raman scattering being a crucial aspect of the study. We find that both electron acceptors and donors interact with phosphorene by charge-transfer, with the acceptors having more marked effects. All the three Raman bands of phosphorene soften and exhibit band broadening on interaction with both donor and acceptor molecules. First-principles calculations establish the occurrence of charge-transfer between phosphorene with donors as well as acceptors. The absence of electron-hole asymmetry is noteworthy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature-dependent kinetics of charge transfer, hydrogen-atom transfer, and hydrogen-atom expulsion in the reaction of CO+ with CH4 and CD4.

Science.gov (United States)

Melko, Joshua J; Ard, Shaun G; Johnson, Ryan S; Shuman, Nicholas S; Guo, Hua; Viggiano, Albert A

2014-09-18

We have determined the rate constants and branching ratios for the reactions of CO(+) with CH4 and CD4 in a variable-temperature selected ion flow tube. We find that the rate constants are collisional for all temperatures measured (193-700 K for CH4 and 193-500 K for CD4). For the CH4 reaction, three product channels are identified, which include charge transfer (CH4(+) + CO), H-atom transfer (HCO(+) + CH3), and H-atom expulsion (CH3CO(+) + H). H-atom transfer is slightly preferred to charge transfer at low temperature, with the charge-transfer product increasing in contribution as the temperature is increased (H-atom expulsion is a minor product for all temperatures). Analogous products are identified for the CD4 reaction. Density functional calculations on the CO(+) + CH4 reaction were also conducted, revealing that the relative temperature dependences of the charge-transfer and H-atom transfer pathways are consistent with an initial charge transfer followed by proton transfer.

Cu-O network dependence of optical charge-transfer gaps and spin-pair excitations in single-CuO2-layer compounds

International Nuclear Information System (INIS)

Tokura, Y.; Koshihara, S.; Arima, T.; Takagi, H.; Ishibashi, S.; Ido, T.; Uchida, S.

1990-01-01

Spectra of optical conductivity and magnon Raman scattering have been investigated in single crystals of a parent family of cuprate superconductors with various types of Cu-O single-layer networks. The analysis of the spectra shows the systematic dependence of the charge-transfer gaps and covalent character of Cu-O bonds on the pattern of the Cu-O network, while the spin-exchange energy is rather convergent for all the single-CuO 2 -sheet compounds

Charge-transfer properties in the gas electron multiplier

International Nuclear Information System (INIS)

Han, Sanghyo; Kim, Yongkyun; Cho, Hyosung

2004-01-01

The charge transfer properties of a gas electron multiplier (GEM) were systematically investigated over a broad range of electric field configurations. The electron collection efficiency and the charge sharing were found to depend on the external fields, as well as on the GEM voltage. The electron collection efficiency increased with the collection field up to 90%, but was essentially independent of the drift field strength. A double conical GEM has a 10% gain increase with time due to surface charging by avalanche ions whereas this effect was eliminated with the cylindrical GEM. The positive-ion feedback is also estimated. (author)

Process techniques of charge transfer time reduction for high speed CMOS image sensors

International Nuclear Information System (INIS)

Cao Zhongxiang; Li Quanliang; Han Ye; Qin Qi; Feng Peng; Liu Liyuan; Wu Nanjian

2014-01-01

This paper proposes pixel process techniques to reduce the charge transfer time in high speed CMOS image sensors. These techniques increase the lateral conductivity of the photo-generated carriers in a pinned photodiode (PPD) and the voltage difference between the PPD and the floating diffusion (FD) node by controlling and optimizing the N doping concentration in the PPD and the threshold voltage of the reset transistor, respectively. The techniques shorten the charge transfer time from the PPD diode to the FD node effectively. The proposed process techniques do not need extra masks and do not cause harm to the fill factor. A sub array of 32 × 64 pixels was designed and implemented in the 0.18 μm CIS process with five implantation conditions splitting the N region in the PPD. The simulation and measured results demonstrate that the charge transfer time can be decreased by using the proposed techniques. Comparing the charge transfer time of the pixel with the different implantation conditions of the N region, the charge transfer time of 0.32 μs is achieved and 31% of image lag was reduced by using the proposed process techniques. (semiconductor devices)

Bane of Hydrogen-Bond Formation on the Photoinduced Charge-Transfer Process in Donor–Acceptor Systems

KAUST Repository

Alsam, Amani Abdu

2017-03-14

Controlling the ultrafast dynamical process of photoinduced charge transfer at donor acceptor interfaces remains a major challenge for physical chemistry and solar cell communities. The process is complicated by the involvement of other complex dynamical processes, including hydrogen bond formation, energy transfer, and solvation dynamics occurring on similar time scales. In this study, we explore the remarkable impact of hydrogen-bond formation on the interfacial charge transfer between a negatively charged electron donating anionic porphyrin and a positively charged electron accepting pi-conjugated polymer, as a model system in solvents with different polarities and capabilities for hydiogen bonding using femtosecond transient absorption spectroscopy. Unlike the conventional understanding of the key role of hydrogen bonding in promoting the charge-transfer process, our steadystate and time-resolved results reveal that the intervening hydrogen-bonding environment and, consequently, the probable longer spacing between the donor and acceptor molecules significantly hinders the charge-transfer process between them. These results show that site-specific hydrogen bonding and geometric considerations between donor and acceptor can be exploited to control both the charge-transfer dynamics and its efficiency not only at donor acceptor interfaces but also in complex biological systems.

Theory and simulation of charge transfer through DNA - nanotube contacts

International Nuclear Information System (INIS)

Rink, Gunda; Kong Yong; Koslowski, Thorsten

2006-01-01

We address the problem of charge transfer between a single-stranded adenine oligomer and semiconducting boron nitride nanotubes from a theoretical and numerical perspective. The model structures have been motivated by computer simulations; sample geometries are used as the input of an electronic structure theory that is based upon an extended Su-Schrieffer-Heeger Hamiltonian. By analyzing the emerging potential energy surfaces, we obtain hole transfer rates via Marcus' theory of charge transfer. In the presence of nanotubes, these rates exceed those of isolated DNA single strands by a factor of up to 10 4 . This enhancement can be rationalized and quantified as a combination of a template effect and the participation of the tube within a superexchange mechanism

Positron Annihilation in Solid Charge-Transfer Complexes

DEFF Research Database (Denmark)

Lévay, B.; Jansen, P.

1979-01-01

Positron lifetime and angular correlation measurements have been carried out on 1:1 charge-transfer complexes, on their pure donor and acceptor components and on the 1:1 M mechanical mixtures of these components. Complex formation reduced the intensity of the long-lifetime component of the donor...

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)

Karen J. Brewer

2010-08-01

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.

Simulation of charge transfer and orbital rehybridization in molecular and condensed matter systems

Science.gov (United States)

Nistor, Razvan A.

The mixing and shifting of electronic orbitals in molecules, or between atoms in bulk systems, is crucially important to the overall structure and physical properties of materials. Understanding and accurately modeling these orbital interactions is of both scientific and industrial relevance. Electronic orbitals can be perturbed in several ways. Doping, adding or removing electrons from systems, can change the bond-order and the physical properties of certain materials. Orbital rehybridization, driven by either thermal or pressure excitation, alters the short-range structure of materials and changes their long-range transport properties. Macroscopically, during bond formation, the shifting of electronic orbitals can be interpreted as a charge transfer phenomenon, as electron density may pile up around, and hence, alter the effective charge of, a given atom in the changing chemical environment. Several levels of theory exist to elucidate the mechanisms behind these orbital interactions. Electronic structure calculations solve the time-independent Schrodinger equation to high chemical accuracy, but are computationally expensive and limited to small system sizes and simulation times. Less fundamental atomistic calculations use simpler parameterized functional expressions called force-fields to model atomic interactions. Atomistic simulations can describe systems and time-scales larger and longer than electronic-structure methods, but at the cost of chemical accuracy. In this thesis, both first-principles and phenomenological methods are addressed in the study of several encompassing problems dealing with charge transfer and orbital rehybridization. Firstly, a new charge-equilibration method is developed that improves upon existing models to allow next-generation force-fields to describe the electrostatics of changing chemical environments. Secondly, electronic structure calculations are used to investigate the doping dependent energy landscapes of several high

Dual fluorescence of excited state intra-molecular proton transfer of HBFO: mechanistic understanding, substituent and solvent effects.

Science.gov (United States)

Yang, Wenjing; Chen, Xuebo

2014-03-07

A combined approach of the multiconfigurational perturbation theory with the Rice-Ramsperger-Kassel-Marcus methodology has been employed to calculate the minimum potential energy profiles and the rates of excited state intra-molecular proton transfer (ESIPT) for the WOLED material molecule of HBFO and its four meta- or para-substituted compounds in gas phase, acetonitrile and cyclohexane solvents. The kinetic control for these reactions is quantitatively determined and extensively studied on the basis of the accurate potential energy surfaces when the thermodynamic factor associated with the free energy change becomes negligible in the case of the existence of a significant barrier in the ESIPT process. These computational efforts contribute to a deep understanding of the ESIPT mechanism, dual emission characteristics, kinetic controlling factor, substituent and solvent effects for these material molecules. The white light emission is generated by the establishment of dynamic equilibrium between enol and keto forms in the charge transfer excited SCT((1)ππ*) state. The performance of white light emission is quantitatively demonstrated to be mainly sensitive to the molecular tailoring approach of the electronic properties of meta- or para- substituents by the modulation of the forward/backward ESIPT rate ratio. The quality of white light emission is slightly tunable through its surrounding solvent environment. These computational results will provide a useful strategy for the molecular design of OLED and WOLED materials.

Molecular excited states from the SCAN functional

Science.gov (United States)

Tozer, David J.; Peach, Michael J. G.

2018-06-01

The performance of the strongly constrained and appropriately normed (SCAN) meta-generalised gradient approximation exchange-correlation functional is investigated for the calculation of time-dependent density-functional theory molecular excitation energies of local, charge-transfer and Rydberg character, together with the excited ? potential energy curve in H2. The SCAN results frequently resemble those obtained using a global hybrid functional, with either a standard or increased fraction of exact orbital exchange. For local excitations, SCAN can exhibit significant triplet instability problems, resulting in imaginary triplet excitation energies for a number of cases. The Tamm-Dancoff approximation offers a simple approach to improve the situation, but the excitation energies are still significantly underestimated. Understanding the origin of these (near)-triplet instabilities may provide useful insight into future functional development.

Decision making based on optical excitation transfer via near-field interactions between quantum dots

International Nuclear Information System (INIS)

Naruse, Makoto; Nomura, Wataru; Ohtsu, Motoichi; Aono, Masashi; Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge; Kim, Song-Ju

2014-01-01

Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

Decision making based on optical excitation transfer via near-field interactions between quantum dots

Energy Technology Data Exchange (ETDEWEB)

Naruse, Makoto, E-mail: naruse@nict.go.jp [Photonic Network Research Institute, National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795 (Japan); Nomura, Wataru; Ohtsu, Motoichi [Department of Electrical Engineering and Information Systems, Graduate School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Aono, Masashi [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguru-ku, Tokyo 152-8550 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012 (Japan); Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge [Université Grenoble Alpes, Inst. NEEL, F-38000 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Kim, Song-Ju [WPI Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

2014-10-21

Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

Effects of acid concentration on intramolecular charge transfer ...

Indian Academy of Sciences (India)

rate. Time-dependent density functional theory calculations have been performed to understand the observed spectroscopic results. Keywords. Intramolecular charge transfer; absorption and fluorescence; time resolved fluorescence measurements; acid concentration dependence; time-dependent density functional theory.

Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Gross, Dieter Konrad Michael

2013-11-08

-quenching vanishes when this offset approaches 0.0 eV. The fact that PL-quenching and its correlation with the energetic offset was observed for both clustered and layered assembly provides a strong indirect indication of charge separation via electron transfer from CdTe to CdSe nanocrystals. The main result of this thesis is the direct proof of the charge separation on the type II interface of CdTe and CdSe nanocrystal layers. SPV-measurements as a direct measurement methode showed clearly the directionality of charge separation since the SPV measures the electric field of the separated charges. Electrons are collected on CdSe nanocrystal layers, holes on CdTe nanocrystal layers. A change in the order between CdSe and CdTe therefore leads to a change in the sign of the SPV-signal. Both SPVspectra and time-resolved SPV-measurements support this finding and showed that the charge selectivity of the CdTe-CdSe interface is unidirectional for the whole excitation spectrum and the entire investigated time range. This indicates that the directionality of the CdTe-CdSe interface is the only dominant charge separation mechanism that was observed. Hence, the type II alignment of the self-assembled nanocrystals used was clearly proven. Introducing an additional barrier between the nanocrystal layers doubled the barrier width so that the SPV-signal is quenched. This is consistent with tunneling transfer which is exponentially dependent on barrier width. Moreover, we learned that both absorption in CdTe and CdSe nanocrystals and the sample thickness contribute to the SPV-signal. Thus, we could observe electron diffusion in CdSe multilayers which was faster than the charge carrier diffusion dynamics in CdTe nanocrystal multilayers. Future research may address the combination of energy transfer dynamics with the charge separation processes presented in this thesis. On the one hand, this may provide a better understanding of their fundamental processes and differentiate between excitonic FRET and

Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

International Nuclear Information System (INIS)

Gross, Dieter Konrad Michael

2013-01-01

-quenching vanishes when this offset approaches 0.0 eV. The fact that PL-quenching and its correlation with the energetic offset was observed for both clustered and layered assembly provides a strong indirect indication of charge separation via electron transfer from CdTe to CdSe nanocrystals. The main result of this thesis is the direct proof of the charge separation on the type II interface of CdTe and CdSe nanocrystal layers. SPV-measurements as a direct measurement methode showed clearly the directionality of charge separation since the SPV measures the electric field of the separated charges. Electrons are collected on CdSe nanocrystal layers, holes on CdTe nanocrystal layers. A change in the order between CdSe and CdTe therefore leads to a change in the sign of the SPV-signal. Both SPVspectra and time-resolved SPV-measurements support this finding and showed that the charge selectivity of the CdTe-CdSe interface is unidirectional for the whole excitation spectrum and the entire investigated time range. This indicates that the directionality of the CdTe-CdSe interface is the only dominant charge separation mechanism that was observed. Hence, the type II alignment of the self-assembled nanocrystals used was clearly proven. Introducing an additional barrier between the nanocrystal layers doubled the barrier width so that the SPV-signal is quenched. This is consistent with tunneling transfer which is exponentially dependent on barrier width. Moreover, we learned that both absorption in CdTe and CdSe nanocrystals and the sample thickness contribute to the SPV-signal. Thus, we could observe electron diffusion in CdSe multilayers which was faster than the charge carrier diffusion dynamics in CdTe nanocrystal multilayers. Future research may address the combination of energy transfer dynamics with the charge separation processes presented in this thesis. On the one hand, this may provide a better understanding of their fundamental processes and differentiate between excitonic FRET and

Probes of the metal-to-ligand charge-transfer excited states in ruthenium-Am(m)ine-bipyridine complexes: the effects of NH/ND and CH/CD isotopic substitution on the 77 K luminescence.

Science.gov (United States)

Chen, Yuan-Jang; Xie, Puhui; Endicott, John F; Odongo, Onduru S

2006-06-29

The effects of ligand perdeuteration on the metal-to-ligand charge-transfer (MLCT) excited-state emission properties at 77 K are described for several [Ru(L)(4)bpy](2+) complexes in which the emission process is nominally [uIII,bpy-] --> [RuII,bpy]. The perdeuteration of the 2,2'-bipyridine (bpy) ligand is found to increase the zero-point energy differences between the ground states and MLCT excited states by amounts that vary from 0 +/- 10 to 70 +/- 10 cm(-1) depending on the ligands L. This indicates that there are some vibrational modes with smaller force constants in the excited states than in the ground states for most of these complexes. These blue shifts increase approximately as the energy difference between the excited and ground states decreases, but they are otherwise not strongly correlated with the number of bipyridine ligands in the complex. Careful comparisons of the [Ru(L)(4)(d(8)-bpy)](2+) and [Ru(L)(4)(h(8)-bpy](2+) emission spectra are used to resolve the very weak vibronic contributions of the C-H stretching modes as the composite contributions of the corresponding vibrational reorganizational energies. The largest of these, 25 +/- 10 cm(-1), is found for the complexes with L = py or bpy/2 and smaller when L = NH(3). Perdeuteration of the am(m)ine ligands (NH(3), en, or [14]aneN(4)) has no significant effect on the zero-point energy difference, and the contributions of the NH stretching vibrational modes to the emission band shape are too weak to resolve. Ligand perdeuteration does increase the excited-state lifetimes by a factor that is roughly proportional to the excited-state-ground-state energy difference, even though the CH and NH vibrational reorganizational energies are too small for nuclear tunneling involving these modes to dominate the relaxation process. It is proposed that metal-ligand skeletal vibrational modes and configurational mixing between metal-centered, bpy-ligand-centered, and MLCT excited states are important in

Transition from the radiationless resonant Raman scattering to the normal Auger decay in a charge transfer system

International Nuclear Information System (INIS)

Ohno, Masahide

2006-01-01

The transition from the radiationless resonant Raman scattering to the normal Auger decay in resonant Auger-electron spectroscopy (RAES) spectra of charge transfer (CT) systems is discussed by treating the relaxation and the core-hole decay of the excited core-hole state on the same footing by a many-body theory. When the resonantly excited electron remains at the excited atomic site during the core-hole decay, the RAES spectrum shows the characteristic feature of the resonant Auger-Raman effect, whereas when the excited electron has been transferred from the atomic site before the core-hole decays, the RAES spectrum shows the normal Auger decay. The present theory supports the interpretation of the variation with photon energy of the intensity ratio of the latter spectrum to the former one in the RAES spectrum by the Ar 2p → 4s resonance of Ar atoms adsorbed on Ru(0 0 1) surface reported by Keller et al. [C. Keller, M. Stichler, G. Comelli, F. Esch, S. Lizzit, D. Menzel, W. Wurth, Phys. Rev. B 57 (1998) 11951]. The transition from the radiationless resonant Raman scattering to the normal Auger decay in the RAES spectrum of CuO reported by Finazzi et al. [M. Finazzi, G. Ghiringhell, O. Tjernberg, Ph. Ohresser, N.B. Brookes, Phys. Rev. B 61 (2000) 4629] is discussed in terms of the relaxation of the resonantly excited core-hole state to the core-electron ionized main-line state by the hole-particle excitations. The merging of the resonant Raman-Auger-electron kinetic energy into the normal one about 2 eV above the absorption maximum in Cu 2 O reported by Finazzi et al. [M. Finazzi, G. Ghiringhell, O. Tjernberg, Ph. Ohresser, N.B. Brookes, Phys. Rev. B 61 (2000) 4629] is explained in terms of the change in the characteristics of the screening electron in the two-hole final state. The Ti L 23 -M 23 V RAES spectra of TiO 2 and TiO 2-x are also analyzed

Energy and charge transfer cascade in methylammonium lead bromide perovskite nanoparticle aggregates.

Science.gov (United States)

Bouduban, Marine E F; Burgos-Caminal, Andrés; Ossola, Rachele; Teuscher, Joël; Moser, Jacques-E

2017-06-01

Highly photoluminescent hybrid lead halide perovskite nanoparticles have recently attracted wide interest in the context of high-stake applications, such as light emitting diodes (LEDs), light emitting transistors and lasers. In addition, they constitute ideal model systems to explore energy and charge transport phenomena occurring at the boundaries of nanocrystalline grains forming thin films in high-efficiency perovskite solar cells (PSCs). Here we report a complete photophysical study of CH 3 NH 3 PbBr 3 perovskite nanoparticles suspended in chlorobenzene and highlight some important interaction properties. Colloidal suspensions under study were constituted of dispersed aggregates of quasi-2D platelets of a range of thicknesses, decorated with 3D-like spherical nanoparticles. These types of nanostructures possess different optical properties that afford a handle for probing them individually. The photophysics of the colloidal particles was studied by femtosecond pump-probe spectroscopy and time-correlated single-photon counting. We show here that a cascade of energy and exciton-mediated charge transfer occurs between nanostructures: upon photoexcitation, localized excitons within one nanostructure can either recombine on a ps timescale, yielding a short-lived emission, or form charge-transfer states (CTSs) across adjacent domains, resulting in longer-lived photoluminescence in the millisecond timescale. Furthermore, CTSs exhibit a clear signature in the form of a strong photoinduced electroabsorption evidenced in femtosecond transient absorption measurements. Charge transfer dynamics at the surface of the nanoparticles have been studied with various quenchers in solution. Efficient hole transfer to N , N , N ', N '-tetrakis(4-methoxyphenyl)benzidine (MeO-TPD) and 1,4-bis(diphenyl-amino)benzene (BDB) donors was attested by the quenching of the nanoparticles emission. The charge transfer rate was limited by the organic layer used to stabilize the nanoparticles

Direct excitation in heavy atom collisions: A propensity rule for charge cloud orientation

International Nuclear Information System (INIS)

Andersen, N.; Aarhus Univ.; Nielsen, S.E.; Royal Danish School of Pharmacy, Copenhagen)

1985-01-01

The Massey Criterion prescribes maximum electronic excitation of atoms in heavy particle collisions for collision velocities v where Δε a/ℎv ≅ π. Here Δε is the energy defect and a is the effective interaction length. Experiments with planar symmetry have revealed a preferred way of rotation of the excited charge cloud in this velocity region. We demonstrate by analysis of a simple, yet realistic model why excitation favors states with a specific orientation. A general propensity rule is derived and its validity evaluated for a specific case, the Na-He system. Implications for future experiments are pointed out. In particular, the propensity rule predicts very different collisions behaviors of oppositely oriented atoms, as prepared e.g. by circular polarized laser light. (orig.)

Coupled spin and charge collective excitations in a spin polarized electron gas

International Nuclear Information System (INIS)

Marinescu, D.C.; Quinn, J.J.; Yi, K.S.

1997-01-01

The charge and longitudinal spin responses induced in a spin polarized quantum well by a weak electromagnetic field are investigated within the framework of the linear response theory. The authors evaluate the excitation frequencies for the intra- and inter-subband transitions of the collective charge and longitudinal spin density oscillations including many-body corrections beyond the random phase approximation through the spin dependent local field factors, G σ ± (q,ω). An equation-of-motion method was used to obtain these corrections in the limit of long wavelengths, and the results are given in terms of the equilibrium pair correlation function. The finite degree of spin polarization is shown to introduce coupling between the charge and spin density modes, in contrast with the result for an unpolarized system

Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

DEFF Research Database (Denmark)

Zhang, Wenkai; Kjær, Kasper Skov; Alonso-Mori, Roberto

2017-01-01

iron complexes with four cyanide (CN-;) ligands and one 2,2′-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL...... state lifetime of iron based complexes due to spin crossover-the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand...

High-energy behavior of the charge-transfer cross section in the eikonal approximation

International Nuclear Information System (INIS)

Dewangan, D.P.

1982-01-01

In the now popular version of the eikonal theory of charge transfer, the eikonal wave function does not satisfy the proper boundary conditions and the charge-transfer amplitude is uncertain by an undefined phase factor. The inclusion of the internuclear potential in a consistent way, in the eikonal theory overcomes theses difficulties. However, it also changes the high-energy asymptotic form of proton-hydrogen charge-transfer cross section from sigma/sub eik/ approx.(23/48) sigma/sub BK/ by a small amount to sigma/sub G/approx.(20.109/48)sigma/sub BK/ where sigma/sub BK/ is the Brinkman-Kramers cross section

Charge changing and excitation cross sections for 1-25 KeV hydrogen ions and atoms incident on sodium

International Nuclear Information System (INIS)

Howald, A.M.

1983-01-01

Measurements of charge changing and excitation cross sections for 1-25 keV beams of hydrogen atoms and ions incident on a sodium vapor target are reported. The charge changing cross sections are for reactions in which the incident H ion or atom gains or loses an electron during a collision with a Na atoms to form a hydrogen ion or atom in a different charge state. The six cross sections measured are sigma/sub +0/ and sigma/sub +-/ for incident protons, sigma/sub -0/ and sigma/sub -+/ for incident H - ions, and sigma/sub g-/ and sigma/sub g+/ for incident H(1s) atoms. Measurements are also reported for the negative, neutral, and positve equilibrium fractions for H beams in thick Na targets. The excitation cross sections are for reactions in which the Na target atom is excited to the 3p level by a collision with a H atom or ion. The five cross sections measured are for incident H + , H 2 + , H 3 + , and H - ions, and for H(1s) atoms. These cross sections are measured using a new technique that compares them directly to the known cross section for excitation by electron impact

Charge Transfer and Support Effects in Heterogeneous Catalysis

Energy Technology Data Exchange (ETDEWEB)

Hervier, Antoine [Univ. of California, Berkeley, CA (United States)

2011-12-21

The kinetic, electronic and spectroscopic properties of two-dimensional oxide-supported catalysts were investigated in order to understand the role of charge transfer in catalysis. Pt/TiO₂ nanodiodes were fabricated and used as catalysts for hydrogen oxidation. During the reaction, the current through the diode, as well as its I-V curve, were monitored, while gas chromatography was used to measure the reaction rate. The current and the turnover rate were found to have the same temperature dependence, indicating that hydrogen oxidation leads to the non-adiabatic excitation of electrons in Pt. A fraction of these electrons have enough energy to ballistically transport through Pt and overcome the Schottky barrier at the interface with TiO₂. The yield for this phenomenon is on the order of 10^-4 electrons per product molecule formed, similar to what has been observed for CO oxidation and for the adsorption of many different molecules. The same Pt/TiO₂ system was used to compare currents in hydrogen oxidation and deuterium oxidation. The current through the diode under deuterium oxidation was found to be greater than under hydrogen oxidation by a factor of three. Weighted by the difference in turnover frequencies for the two isotopes, this would imply a chemicurrent yield 5 times greater for D₂ compared to H₂, contrary to what is expected given the higher mass of D₂. Reversible changes in the rectification factor of the diode are observed when switching between D₂ and H₂. These changes are a likely cause for the differences in current between the two isotopes. In the nanodiode experiments, surface chemistry leads to charge flow, suggesting the possibility of creating charge flow to tune surface chemistry. This was done first by exposing a Pt/Si diode to visible light while using it as a catalyst for H₂ oxidation. Absorption of the light in the Si, combined with

Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves

OpenAIRE

Hashimoto, Yusuke; Bossini, Davide; Johansen, Tom H.; Saitoh, Eiji; Kirilyuk, Andrei; Rasing, Theo

2017-01-01

Using spin-wave tomography (SWaT), we have investigated the excitation and the propagation dynamics of optically-excited magnetoelastic waves, i.e. hybridized modes of spin waves and elastic waves, in a garnet film. By using time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves through coherent-energy transfer between optically-excited pure-elastic waves and spin waves via magnetoelastic coupling. This process realizes frequency and wavenumber selective excitation of s...

Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

Science.gov (United States)

He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

2015-12-03

Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

Na(3p left-arrow 3s) excitation by impact of slow multiply charged ions

International Nuclear Information System (INIS)

Horvath, G.; Schweinzer, J.; Winter, H.; Aumayr, F.

1996-01-01

We present a systematic experimental and theoretical study of Na(3p left-arrow 3s) excitation by slow (v NaI with projectile ion charge state q is investigated. Due to the dominance of the competing electron capture channels at low collision energies E, the excitation cross sections deviate significantly from a commonly applied σ/q=f(E/q) cross-section scaling relation. copyright 1996 The American Physical Society

The character of resonant charge exchange involving highly excited atoms

International Nuclear Information System (INIS)

Kosarim, A. V.; Smirnov, B. M.; Capitelli, M.; Laricchiuta, A.

2012-01-01

We study the process of resonant charge exchange involving excited helium atoms with the principal quantum number n = 5 colliding with the helium ion in the ground state in the collision energy range from thermal up to 10 eV. This information may be important for the analysis of planet atmospheres containing helium, in particular, for Jupiter’s atmosphere, but our basic interest is the transition from the quantum to classical description of this process, where, due to large cross sections, evaluations of the cross sections are possible. For the chosen process, quantum theory allows determining the cross section as a result of a tunnel electron transition, while classical theory accounts for over-barrier electron transitions. The classical theory additionally requires effective transitions between states with close energies. The analysis of these transitions for helium with n = 5 shows that electron momenta and their projections are mixed for a part of the states, while for other states, the mixing is absent. A simple criterion to separate such states is given. In addition, the main contribution to the cross section of resonant charge exchange follows from tunnel electron transitions. As a result, the quantum theory is better for calculating the cross sections of resonant charge exchange than the classical one and also allows finding the partial cross sections of resonant charge exchange, while the classical approach gives the cross section of resonant charge exchange in a simple manner with the accuracy of 20%.

Photo-induced charge transfer at heterogeneous interfaces: Dye-sensitized tin disulfide, the theory and the experiment

International Nuclear Information System (INIS)

Lanzafame, J.M.

1993-01-01

The study of photo-induced charge transfer is an endeavor that spans the entire industrial period of man's history. Its great importance demands an ever greater understanding of its underlying principles. The work discussed here attempts to probe elementary aspects of the charge transfer process. Investigations into the theory of charge transfer reactions are made in an attempt to isolate the relevant parameters. An analytical discussion is made of a simple Golden Rule type rate equation to describe the transfer kinetics. Then a quantum simulation is carried out to follow the wavefunction propagation as a test of the applicability of the assumptions made in deriving the simpler rate equation. Investigation of charge transfer at surfaces is bet served by the application of ultrafast optical spectroscopies to probe carrier dynamics. A discussion of the properties of the short pulse laser systems employed is included along with a discussion of the different optical spectroscopies available. These tools are then brought to bear upon dye-sensitized SnS 2 , a model system for the study of charge injection processes. The unique properties of the semiconductor are discussed with respect to the charge transfer process. The unique properties of the semiconductor are discussed with respect to the charge transfer process. The optical experiments performed on the dye/SnS 2 systems elucidate the fundamental carrier dynamics and these dynamics are discussed within the theoretical framework to provide a complete picture of the charge transfer kinetics

Describing long-range charge-separation processes with subsystem density-functional theory

Energy Technology Data Exchange (ETDEWEB)

Solovyeva, Alisa; Neugebauer, Johannes, E-mail: j.neugebauer@uni-muenster.de [Theoretische Organische Chemie, Organisch-Chemisches Institut and Center for Multiscale Theory and Simulation, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster (Germany); Pavanello, Michele, E-mail: m.pavanello@rutgers.edu [Department of Chemistry, Rutgers University, 73 Warren St., Newark, New Jersey 07102 (United States)

2014-04-28

Long-range charge-transfer processes in extended systems are difficult to describe with quantum chemical methods. In particular, cost-effective (non-hybrid) approximations within time-dependent density functional theory (DFT) are not applicable unless special precautions are taken. Here, we show that the efficient subsystem DFT can be employed as a constrained DFT variant to describe the energetics of long-range charge-separation processes. A formal analysis of the energy components in subsystem DFT for such excitation energies is presented, which demonstrates that both the distance dependence and the long-range limit are correctly described. In addition, electronic couplings for these processes as needed for rate constants in Marcus theory can be obtained from this method. It is shown that the electronic structure of charge-separated states constructed by a positively charged subsystem interacting with a negatively charged one is difficult to converge — charge leaking from the negative subsystem to the positive one can occur. This problem is related to the delocalization error in DFT and can be overcome with asymptotically correct exchange–correlation (XC) potentials or XC potentials including a sufficiently large amount of exact exchange. We also outline an approximate way to obtain charge-transfer couplings between locally excited and charge-separated states.

Describing long-range charge-separation processes with subsystem density-functional theory

International Nuclear Information System (INIS)

Solovyeva, Alisa; Neugebauer, Johannes; Pavanello, Michele

2014-01-01

Long-range charge-transfer processes in extended systems are difficult to describe with quantum chemical methods. In particular, cost-effective (non-hybrid) approximations within time-dependent density functional theory (DFT) are not applicable unless special precautions are taken. Here, we show that the efficient subsystem DFT can be employed as a constrained DFT variant to describe the energetics of long-range charge-separation processes. A formal analysis of the energy components in subsystem DFT for such excitation energies is presented, which demonstrates that both the distance dependence and the long-range limit are correctly described. In addition, electronic couplings for these processes as needed for rate constants in Marcus theory can be obtained from this method. It is shown that the electronic structure of charge-separated states constructed by a positively charged subsystem interacting with a negatively charged one is difficult to converge — charge leaking from the negative subsystem to the positive one can occur. This problem is related to the delocalization error in DFT and can be overcome with asymptotically correct exchange–correlation (XC) potentials or XC potentials including a sufficiently large amount of exact exchange. We also outline an approximate way to obtain charge-transfer couplings between locally excited and charge-separated states

Nuclear-charge polarization at scission in fission from moderately excited light-actinide nuclei

International Nuclear Information System (INIS)

Nishinaka, Ichiro

2009-01-01

Fragment mass yields and the average neutron multiplicity in the proton-induced fission of 232 Th and 238 U were measured by a double time-of-flight method. The most probable charges of secondary fragments were evaluated from the fragment mass yields measured by the double time-of-flight method and the fractional cumulative and independent yields reported in literature. The nuclear-charge polarization of primary fragments at scission was obtained by correcting the most probable charge of secondary fragments for neutron evaporation. The results show that the nuclear-charge polarization at scission is associated with the liquid-drop properties of nuclei and the proton shell effect with Z = 50 of heavy fragments and that it is practically insensitive to mass and excitation energy of the fissioning nucleus in the region of light-actinide nuclei. (author)

Luminescence and optical spectroscopy of charge transfer processes in solid solutions NiCMg1−CO and NixZn1−xO

International Nuclear Information System (INIS)

Sokolov, V.I.; Pustovarov, V.A.; Churmanov, V.N.; Gruzdev, N.B.; Uimin, M.A.; Byzov, I.V.; Druzhinin, A.V.; Mironova-Ulmane, N.A.

2016-01-01

In this work photoluminescence spectra for Ni c Mg 1−c O and Ni x Zn 1−x O solid solutions with the rock-salt crystal structure were obtained under synchrotron radiation excitation. Periodical peaks in the photoluminescence excitation spectrum of Ni c Mg 1−c O (c=0.008) have been discovered for a wide-gap oxide doped with 3d impurities for the first time. They can be considered as LO phonon repetitions of the narrow zero phonon line resulted from the optical transitions into the p–d charge transfer exciton [d 9 h] state. A close coincidence in energy of different peculiarities in the optical absorption and photoluminescence excitation spectra for the Ni c Mg 1−c O and Ni x Zn 1−x O solid solutions is due to the practically equal interatomic distances Ni–O in the investigated materials. The bulk of new experimental results is the trustworthy evidence that only the p–d charge transfer transitions manifest themselves in the spectral region of 3.5–6.5 eV. - Highlights: • Emission of Ni c Mg 1−c O nanocystals excited by synchrotron radiation is obtained. • LO phonon repetitions have been observed in PLE spectra of Ni c Mg 1−c O firstly for wide gap oxide materials doped with 3d impurities. • The [d 9 h] acceptor exciton state in Ni c Mg 1−c O (c=0.008) are indirectly revealed. • The begin of PLE spectra of Ni x Zn 1−x O are not virtually shifted with a change of composition x. • The near energy coincidence of absorption peaks for nanocrystals NiO and single crystal Ni c Mg 1−c O (c=0.0006) manifests itself.

Super-iron Nanoparticles with Facile Cathodic Charge Transfer

Energy Technology Data Exchange (ETDEWEB)

M Farmand; D Jiang; B Wang; S Ghosh; D Ramaker; S Licht

2011-12-31

Super-irons contain the + 6 valence state of iron. One advantage of this is that it provides a multiple electron opportunity to store additional battery charge. A decrease of particle size from the micrometer to the nanometer domain provides a higher surface area to volume ratio, and opportunity to facilitate charge transfer, and improve the power, voltage and depth of discharge of cathodes made from such salts. However, super-iron salts are fragile, readily reduced to the ferric state, with both heat and contact with water, and little is known of the resultant passivating and non-passivating ferric oxide products. A pathway to decrease the super-iron particle size to the nano-domain is introduced, which overcomes this fragility, and retains the battery capacity advantage of their Fe(VI) valence state. Time and power controlled mechanosynthesis, through less aggressive, dry ball milling, leads to facile charge transfer of super-iron nanoparticles. Ex-situ X-ray Absorption Spectroscopy is used to explore the oxidation state and structure of these iron oxides during discharge and shows the significant change in stability of the ferrate structure to lower oxidation state when the particle size is in the nano-domain.

[Electron transfer, ionization and excitation in atomic collisions

International Nuclear Information System (INIS)

1991-01-01

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

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

KAUST Repository

Gruenewald, Marco

2015-02-11

We investigate the prototypical hybrid interface formed between PTCDA and conductive n-doped ZnO films by means of complementary optical and electronic spectroscopic techniques. We demonstrate that shallow donors in the vicinity of the ZnO surface cause an integer charge transfer to PTCDA, which is clearly restricted to the first monolayer. By means of DFT calculations, we show that the experimental signatures of the anionic PTCDA species can be understood in terms of strong hybridization with localized states (the shallow donors) in the substrate and charge back-donation, resulting in an effectively integer charge transfer across the interface. Charge transfer is thus not merely a question of locating the Fermi level above the PTCDA electron-transport level but requires rather an atomistic understanding of the interfacial interactions. The study reveals that defect sites and dopants can have a significant influence on the specifics of interfacial coupling and thus on carrier injection or extraction.

Robust singlet fission in pentacene thin films with tuned charge transfer interactions.

Science.gov (United States)

Broch, K; Dieterle, J; Branchi, F; Hestand, N J; Olivier, Y; Tamura, H; Cruz, C; Nichols, V M; Hinderhofer, A; Beljonne, D; Spano, F C; Cerullo, G; Bardeen, C J; Schreiber, F

2018-03-05

Singlet fission, the spin-allowed photophysical process converting an excited singlet state into two triplet states, has attracted significant attention for device applications. Research so far has focused mainly on the understanding of singlet fission in pure materials, yet blends offer the promise of a controlled tuning of intermolecular interactions, impacting singlet fission efficiencies. Here we report a study of singlet fission in mixtures of pentacene with weakly interacting spacer molecules. Comparison of experimentally determined stationary optical properties and theoretical calculations indicates a reduction of charge-transfer interactions between pentacene molecules with increasing spacer molecule fraction. Theory predicts that the reduced interactions slow down singlet fission in these blends, but surprisingly we find that singlet fission occurs on a timescale comparable to that in pure crystalline pentacene. We explain the observed robustness of singlet fission in such mixed films by a mechanism of exciton diffusion to hot spots with closer intermolecular spacings.

Encapsulation of 3-hydroxyflavone and fisetin in β-cyclodextrins: Excited state proton transfer fluorescence and molecular mechanics studies

Science.gov (United States)

Banerjee, Anwesha; Sengupta, Pradeep K.

2006-06-01

Excited-state intramolecular proton-transfer (ESIPT) and dual emission properties (emission profile, anisotropy and decay kinetics) of 3-hydroxyflavone (a synthetic, model flavonol) and fisetin (3,7,3',4'-OH-flavone, a therapeutically active plant flavonol) have been exploited to study their encapsulation in nano-cavities comprising of natural and chemically modified β-cyclodextrins. In the presence of β-CDs, both the flavonols show significantly enhanced relative yields (along with changes in other emission parameters) of the tautomer emission. In addition, for fisetin, large blue shifts are observed for the normal emission (which has significant charge transfer character). From these we infer that the flavonols are encaged in predominantly hydrophobic micro-environments, where external hydrogen bonding perturbations (interfering with the intrinsic ESIPT), and dipolar relaxation effects, are minimized. This is further explained from results of molecular mechanics calculations which indicate selectivity in orientation of the encapsulated flavonols. Moreover, chemical modification of the β-CDs is found to profoundly influence the binding affinities of the guest flavonols.

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

International Nuclear Information System (INIS)

Hagelstein, P L; Chaudhary, I U

2008-01-01

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

Correlated charge changing ion-atom collisions. Progress report, March 15, 1985-March 14, 1986

International Nuclear Information System (INIS)

Bernstein, E.M.; Tanis, J.A.

1986-04-01

X-ray emission associated with projectile charge-changing events in ion-atom collisions has been used to isolate and investigate excitation, ionization, and charge transfer, as well as combinations of these processes. New measurements were made of K-shell and L-shell resonant transfer and excitation (RTE) for 210 to 300 MeV 20 Ca/sup 10,11+/ + H 2 collisions and 230 to 610 MeV 41 Nb 31+ + H 2 collisions, respectively. Nonresonant transfer and excitation (NTE) was studied for 40 to 160 MeV S 13+ + Ne. Single-electron capture and loss measurements, requiring accel-decel techniques, were made for 2.5 to 200 MeV S 13+ on He. In the case of Ca/sup 16,17,18,19 + / + H 2 collisions the single capture cross cross sections exhibit a nonmonotonic energy dependence which we attribute to RTE. Double-electron capture in single collisions was investigated for S 13+ + He and Ne and Ar 15+ + Ne and the cross sections were found to be 10 to 100 times smaller than the single-capture cross sections. Measured two-electron loss cross sections for Ca/sup q + / ions incident on H 2 vary with charge state and depend strongly on whether L- or K-shell electrons are removed. Measurements of simultaneous projectile excitation and electron loss for several collision systems indicate that K-vacancy production occurs primarily through excitation rather than loss of the 1s electron. 13 refs

Charge transfer in gold--alkali-metal systems

International Nuclear Information System (INIS)

Watson, R.E.; Weinert, M.

1994-01-01

Based on conventional electronegativity arguments, gold--alkali-metal compounds are expected to be among the most ''ionic'' of metallic compounds. The concepts of ionicity and charge transfer are difficult to quantify. However, the changes in bonding in the 50/50 Au--alkali-metal systems between the elemental metals and the compounds are so severe that observations can readily be made concerning their character. The results, as obtained from self-consistent electronic-structure calculations, lead to the apparently odd observation that the electron density at the alkali-metal sites in the compound increases significantly and this involves high l componennts in the charge density. This increase, however, can be attributed to Au-like orbitals spatially overlapping the alkali-metal sites. In a chemical sense, it is reasonable to consider the alkali-metal transferring charge to these Au orbitals. While normally the difference in heats of formation between muffin-tin and full-potential calculations for transition-metal--transition-metal and transition-metal--main-group (e.g., Al) compounds having high site symmetry are small, for the gold--alkali-metal systems, the changes in bonding in the compounds cause differences of ∼0.5 eV/atom between the two classes of potential. Any serious estimate of the electronic structure in these systems must account for these aspherical bonding charges. The origin of the semiconducting behavior of the heavy-alkali-metal Au compounds is shown to arise from a combination of the Au-Au separations and the ionic character of the compounds; the light-alkali-metal Au compounds, with their smaller Au-Au separations, do not have a semiconducting gap. Core-level shifts and isomer shifts are also briefly discussed

Interfacial Charge Transfer States in Condensed Phase Systems

Science.gov (United States)

Vandewal, Koen

2016-05-01

Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

Optimization of charge transfer and transport processes at the CdSe quantum dots/TiO2 nanorod interface by TiO2 interlayer passivation

International Nuclear Information System (INIS)

Jaramillo-Quintero, O A; Rincon, M E; Triana, M A

2017-01-01

Surface trap states hinder charge transfer and transport properties in TiO 2 nanorods (NRs), limiting its application on optoelectronic devices. Here, we study the interfacial processes between rutile TiO 2 NR and CdSe quantum dots (QDs) using TiO 2 interlayer passivation treatments. Anatase or rutile TiO 2 thin layers were deposited on an NR surface by two wet-chemical deposition treatments. Reduced interfacial charge recombination between NRs and CdSe QDs was observed by electrochemical impedance spectroscopy with the introduction of TiO 2 thin film interlayers compared to bare TiO 2 NRs. These results can be ascribed to in-gap trap state passivation of the TiO 2 NR surface, which led to an increase in open circuit voltage. Moreover, the rutile thin layer was more efficient than anatase to promote a higher photo-excited electron transfer from CdSe QDs to TiO 2 NRs due to a large driving force for charge injection, as confirmed by surface photovoltage spectroscopy. (paper)

Charge transfer processes in collisions of H+ ions with H2, D2, CO, CO2 CH4, C2H2, C2H6 and C3H8 molecules below 10 keV

International Nuclear Information System (INIS)

Kusakabe, T.; Buenker, R.J.; Kimura, M.

2002-01-01

Charge transfer processes resulting from collisions of H + ions with H 2 , D 2 , CO, CO 2 CH 4 , C 2 H 2 , C 2 H 6 and C 3 H 8 molecules have been investigated in the energy range of 0.2 to 4.0 keV experimentally and theoretically. The initial growth rate method was employed in the experiment for studying the dynamics and cross sections. Theoretical analysis based on a molecular-orbital expansion method for H 2 , D 2 , CO, CH 4 and C 2 H 2 targets was also carried out. The present results for the H 2 , CO and CO 2 molecules by H + impact are found to be in excellent accord with most of previous measurements above 1 keV, but they show some differences below this energy where our result displays a stronger energy-dependence. For CH 4 , C 2 H 2 , C 2 H 6 and C 3 H 8 targets, both experimental and theoretical results indicate that if one assumes vibrationally excited molecular ions (CH 4 + , C 2 H 2 + , C 2 H 6 + and C 3 H 8 + ) formed in the exit channel, then charge transfer processes sometimes become more favorable since these vibrationally excited fragments meet an accidental resonant condition. This is a clear indication of the role of vibrational excited states for charge transfer, and is an important realization for general understanding. (author)

Charge transfer through DNA/DNA duplexes and DNA/RNA hybrids: complex theoretical and experimental studies.

Science.gov (United States)

Kratochvílová, Irena; Vala, Martin; Weiter, Martin; Špérová, Miroslava; Schneider, Bohdan; Páv, Ondřej; Šebera, Jakub; Rosenberg, Ivan; Sychrovský, Vladimír

2013-01-01

Oligonucleotides conduct electric charge via various mechanisms and their characterization and understanding is a very important and complicated task. In this work, experimental (temperature dependent steady state fluorescence spectroscopy, time-resolved fluorescence spectroscopy) and theoretical (Density Functional Theory) approaches were combined to study charge transfer processes in short DNA/DNA and RNA/DNA duplexes with virtually equivalent sequences. The experimental results were consistent with the theoretical model - the delocalized nature of HOMO orbitals and holes, base stacking, electronic coupling and conformational flexibility formed the conditions for more effective short distance charge transfer processes in RNA/DNA hybrids. RNA/DNA and DNA/DNA charge transfer properties were strongly connected with temperature affected structural changes of molecular systems - charge transfer could be used as a probe of even tiny changes of molecular structures and settings. © 2013. Published by Elsevier B.V. All rights reserved.

Comparison of modified driver circuit and capacitor-transfer circuit in longitudinally excited N2 laser.

Science.gov (United States)

Uno, Kazuyuki; Akitsu, Tetsuya; Nakamura, Kenshi; Jitsuno, Takahisa

2013-04-01

We developed a modified driver circuit composed of a capacitance and a spark gap, called a direct-drive circuit, for a longitudinally excited gas laser. The direct-drive circuit uses a large discharge impedance caused by a long discharge length of the longitudinal excitation scheme and eliminates the buffer capacitance used in the traditional capacitor-transfer circuit. We compared the direct-drive circuit and the capacitor-transfer circuit in a longitudinally excited N2 laser (wavelength: 337 nm). Producing high output energy with the capacitor-transfer circuit requires a large storage capacitance and a discharge tube with optimum dimensions (an inner diameter of 4 mm and a length of 10 cm in this work); in contrast, the direct-drive circuit requires a high breakdown voltage, achieved with a small storage capacitance and a large discharge tube. Additionally, for the same input energy of 792 mJ, the maximum output energy of the capacitor-transfer circuit was 174.2 μJ, and that of the direct-drive circuit was 344.7 μJ.

Electronic excited states and relaxation dynamics in polymer heterojunction systems

Science.gov (United States)

Ramon, John Glenn Santos

The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally

Electric field changes on Au nanoparticles on semiconductor supports--the molecular voltmeter and other methods to observe adsorbate-induced charge-transfer effects in Au/TiO2 nanocatalysts.

Science.gov (United States)

McEntee, Monica; Stevanovic, Ana; Tang, Wenjie; Neurock, Matthew; Yates, John T

2015-02-11

Infrared (IR) studies of Au/TiO2 catalyst particles indicate that charge transfer from van der Waals-bound donor or acceptor molecules on TiO2 to or from Au occurs via transport of charge carriers in the semiconductor TiO2 support. The ΔνCO on Au is shown to be proportional to the polarizability of the TiO2 support fully covered with donor or acceptor molecules, producing a proportional frequency shift in νCO. Charge transfer through TiO2 is associated with the population of electron trap sites in the bandgap of TiO2 and can be independently followed by changes in photoluminescence intensity and by shifts in the broad IR absorbance region for electron trap sites, which is also proportional to the polarizability of donors by IR excitation. Density functional theory calculations show that electron transfer from the donor molecules to TiO2 and to supported Au particles produces a negative charge on the Au, whereas the transfer from the Au particles to the TiO2 support into acceptor molecules results in a positive charge on the Au. These changes along with the magnitudes of the shifts are consistent with the Stark effect. A number of experiments show that the ∼3 nm Au particles act as "molecular voltmeters" in influencing ΔνCO. Insulator particles, such as SiO2, do not display electron-transfer effects to Au particles on their surface. These studies are preliminary to doping studies of semiconductor-oxide particles by metal ions which modify Lewis acid/base oxide properties and possibly strongly modify the electron-transfer and catalytic activity of supported metal catalyst particles.

Steric control of the donor/acceptor interface: Implications in organic photovoltaic charge generation

KAUST Repository

Holcombe, Thomas W.; Norton, Joseph E.; Rivnay, Jonathan; Woo, Claire; Goris, Ludwig J.; Piliego, Claudia; Griffini, Gianmarco; Sellinger, Alan; Bré das, Jean Luc; Salleo, Alberto; Frechet, Jean

2011-01-01

The performance of organic photovoltaic (OPV) devices is currently limited by modest short-circuit current densities. Approaches toward improving this output parameter may provide new avenues to advance OPV technologies and the basic science of charge transfer in organic semiconductors. This work highlights how steric control of the charge separation interface can be effectively tuned in OPV devices. By introducing an octylphenyl substituent onto the investigated polymer backbones, the thermally relaxed charge-transfer state, and potentially excited charge-transfer states, can be raised in energy. This decreases the barrier to charge separation and results in increased photocurrent generation. This finding is of particular significance for nonfullerene OPVs, which have many potential advantages such as tunable energy levels and spectral breadth, but are prone to poor exciton separation efficiencies. Computational, spectroscopic, and synthetic methods were combined to develop a structure-property relationship that correlates polymer substituents with charge-transfer state energies and, ultimately, device efficiencies. © 2011 American Chemical Society.

Steric control of the donor/acceptor interface: Implications in organic photovoltaic charge generation

KAUST Repository

Holcombe, Thomas W.

2011-08-10

The performance of organic photovoltaic (OPV) devices is currently limited by modest short-circuit current densities. Approaches toward improving this output parameter may provide new avenues to advance OPV technologies and the basic science of charge transfer in organic semiconductors. This work highlights how steric control of the charge separation interface can be effectively tuned in OPV devices. By introducing an octylphenyl substituent onto the investigated polymer backbones, the thermally relaxed charge-transfer state, and potentially excited charge-transfer states, can be raised in energy. This decreases the barrier to charge separation and results in increased photocurrent generation. This finding is of particular significance for nonfullerene OPVs, which have many potential advantages such as tunable energy levels and spectral breadth, but are prone to poor exciton separation efficiencies. Computational, spectroscopic, and synthetic methods were combined to develop a structure-property relationship that correlates polymer substituents with charge-transfer state energies and, ultimately, device efficiencies. © 2011 American Chemical Society.

Large-Scale Quantum Many-Body Perturbation on Spin and Charge Separation in the Excited States of the Synthesized Donor-Acceptor Hybrid PBI-Macrocycle Complex.

Science.gov (United States)

Ziaei, Vafa; Bredow, Thomas

2017-03-17

The reliable calculation of the excited states of charge-transfer (CT) compounds poses a major challenge to the ab initio community because the frequently employed method, time-dependent density functional theory (TD-DFT), massively relies on the underlying density functional, resulting in heavily Hartree-Fock (HF) exchange-dependent excited-state energies. By applying the highly sophisticated many-body perturbation approach, we address the encountered unreliabilities and inconsistencies of not optimally tuned (standard) TD-DFT regarding photo-excited CT phenomena, and present results concerning accurate vertical transition energies and the correct energetic ordering of the CT and the first visible singlet state of a recently synthesized thermodynamically stable large hybrid perylene bisimide-macrocycle complex. This is a large-scale application of the quantum many-body perturbation approach to a chemically relevant CT system, demonstrating the system-size independence of the quality of the many-body-based excitation energies. Furthermore, an optimal tuning of the ωB97X hybrid functional can well reproduce the many-body results, making TD-DFT a suitable choice but at the expense of introducing a range-separation parameter, which needs to be optimally tuned. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

CERN Document Server

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

2001-01-01

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

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

International Nuclear Information System (INIS)

Sell, J F; Gearba, M A; Patterson, B M; Byrne, D; Jemo, G; Meeter, R; Knize, R J; Lilly, T C

2012-01-01

Measurements of the mixing rates and cross sections for collisional excitation transfer between the 5P 1/2 and 5P 3/2 states of rubidium (Rb) in the presence of 4 He buffer gas are presented. Selected pulses from a high repetition rate, mode-locked femtosecond laser are used to excite either Rb state with the fluorescence due to collisional excitation transfer observed by time-correlated single-photon counting. The time dependence of this fluorescence is fitted to the solution of rate equations which include the mixing rate, atomic lifetimes and any quenching processes. The variation in the mixing rate over a large range of buffer gas densities allows the determination of both the binary collisional transfer cross section and a three-body collisional transfer rate. We do not observe any collisional quenching effects at 4 He pressures up to 6 atm and discuss in detail other systematic effects considered in the experiment. (paper)

Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot

Science.gov (United States)

Ware, M. E.; Stinaff, E. A.; Gammon, D.; Doty, M. F.; Bracker, A. S.; Gershoni, D.; Korenev, V. L.; Bădescu, Ş. C.; Lyanda-Geller, Y.; Reinecke, T. L.

2005-10-01

We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory.

Science.gov (United States)

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G

2011-08-28

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. © 2011 American Institute of Physics

Positronium Inhibition and Quenching by Organic Electron Acceptors and Charge Transfer Complexes

DEFF Research Database (Denmark)

Jansen, P.; Eldrup, Morten Mostgaard; Jensen, Bror Skytte

1975-01-01

Positron lifetime measurements were performed on a series of organic electron acceptors and charge-transfer complexes in solution. The acceptors cause both positronium (Ps) inhibition (with maybe one exception) and quenching, but when an acceptor takes part in a charge-transfer complex...... in terms of the spur reaction model of Ps formation. Correlation was also made to gas phase reaction between electron acceptors and free electron, as well as to pulse radiolysis data....

Barrier discharge. The transferred charge and ozone synthesis

International Nuclear Information System (INIS)

Gibalov, V.I.; Samoilovich, V.G.

1991-01-01

We have undertaken an experimental investigation of the influence of the conditions of barrier discharge implementation such as: the discharge gap value, the type of gas, and the polarity and dielectric permittivity of the dielectric electrode on the value of charge transferred in a micro-discharge. It is shown that the increase in the specific capacitance of the electrodes leads to proportional increase in the transferred charge value, reaching 100-200 nC in a discharge gap 1 mm, in air. In this case the amplitude and duration of a current pulse in the microdischarge reach, respectively, 10 to 15 A and 40 ns. It is also demonstrated that in air with increase in the discharge gap value one can observe a decrease in the efficiency of the ozone synthesis whereas in oxygen there exists a more complicated dependence: the maximum of efficiency is observed at a discharge gap value of 0.7 to 1.0 mm. (orig.)

Charge exchange processes of high energy heavy ions channeled in crystals

International Nuclear Information System (INIS)

Andriamonje, S.; Dural, J.; Toulemonde, M.; Groeneveld, K.O.; Maier, R.; Quere, Y.

1990-01-01

The interaction of moving ions with single crystals is very sensitive to the orientation of the incident beam with respect to the crystalline directions of the target. The experiments show that high energy heavy ion channeling deeply modifies the slowing down and charge exchange processes. In this review, we describe the opportunity offered by channeling conditions to study the charge exchange processes. Some aspects of the charge exchange processes with high energy channeled heavy ions are selected from the extensive literature published over the past few years on this subject. Special attention is given to the work performed at the GANIL facility on the study of Radiative Electron Capture (REG), Electron Impact Ionisation (EII), and convoy electron emission. Finally we emphasize the interest of studying resonant charge exchange processes such as Resonant Coherent Excitation (RCE), Resonant Transfer and Excitation (RTE) or Dielectronic Recombination (DR) and the recently proposed Nuclear Excitation by Electron Capture (NEEC)

Changes in wetting and contact charge transfer by femtosecond laser-ablation of polyimide

Energy Technology Data Exchange (ETDEWEB)

Guo, X.D., E-mail: xiaodong.guo@uib.no [Department of Physics and Technology, Allegaten 55, 5020 Bergen, University of Bergen (Norway); Dai, Y.; Gong, M. [Department of Physics, Shanghai 200444, Shanghai University (China); Qu, Y.G. [Center for Geobiology, Allegaten 41, 5020 Bergen, University of Bergen (Norway); Helseth, L.E. [Department of Physics and Technology, Allegaten 55, 5020 Bergen, University of Bergen (Norway)

2015-09-15

Highlights: • Laser ablation significantly reduced the triboelectric charging of polyimide films. • Hierarchical micro/nanostructures formed on the surface of the sample. • Structural anisotropy leads to spatially varying contact angles of water droplets. • Raman spectroscopy revealed a carbonization of the polyimide sample. • The corresponding loss of insulation may explain the reduction of charge transfer. - Abstract: In this study it is demonstrated that the triboelectric charging of polyimide thin films is significantly reduced by using a femtosecond laser to nanostructure its. It is found that the contact charge transfer between laser-ablated Kapton and aluminum is almost negligible, and even much lower than the significant current occurring when non-treated Kapton touches the metal. Scanning electron microscopy demonstrates that laser ablation produces a hierarchical micro and nanostructure, and it is found that the structural anisotropy leads to spatially varying contact angles of water droplets residing on the surface. Raman spectra suggest that the centers of the laser-ablated tracks are carbonized; therefore, the loss of insulation can be responsible for the reduction of charge transfer.

Evaluation of the Intramolecular Charge-Transfer Properties in Solvatochromic and Electrochromic Zinc Octa(carbazolyl)phthalocyanines.

Science.gov (United States)

Majeed, Shereen A; Ghazal, Basma; Nevonen, Dustin E; Goff, Philip C; Blank, David A; Nemykin, Victor N; Makhseed, Saad

2017-10-02

2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato zinc(II) (3) and 2,3,9,10,16,17,23·24-octakis-(3,6-di-tert-butyl-9H-carbazole) phthalocyaninato zinc(II) (4) complexes were prepared and characterized by NMR and UV-vis spectroscopies, magnetic circular dichroism (MCD), matrix-assisted laser desorption ionization mass spectrometry, and X-ray crystallography. UV-vis and MCD data are indicative of the interligand charge-transfer nature of the broad band observed in 450-500 nm range for 3 and 4. The redox properties of 3 and 4 were probed by electrochemical and spectro-electrochemical methods, which are suggestive of phthalocyanine-centered first oxidation and reduction processes. Photophysics of 3 and 4 were investigated by steady-state fluorescence and time-resolved transient absorption spectroscopy demonstrating the influence of the carbazole substituents on deactivation from the first excited state in 3 and 4. Protonation of the meso-nitrogen atoms in 3 results in much faster deactivation kinetics from the first excited state. Spectroscopic data were correlated with density functional theory (DFT) and time-dependent DFT calculations on 3 and 4.

Effect of collective response on electron capture and excitation in collisions of highly charged ions with fullerenes.

Science.gov (United States)

Kadhane, U; Misra, D; Singh, Y P; Tribedi, Lokesh C

2003-03-07

Projectile deexcitation Lyman x-ray emission following electron capture and K excitation has been studied in collisions of bare and Li-like sulphur ions (of energy 110 MeV) with fullerenes (C(60)/C(70)) and different gaseous targets. The intensity ratios of different Lyman x-ray lines in collisions with fullerenes are found to be substantially lower than those for the gas targets, both for capture and excitation. This has been explained in terms of a model based on "solidlike" effect, namely, wakefield induced stark mixing of the excited states populated via electron capture or K excitation: a collective phenomenon of plasmon excitation in the fullerenes under the influence of heavy, highly charged ions.

Dissociative electron attachment and charge transfer in condensed matter

International Nuclear Information System (INIS)

Bass, A.D.; Sanche, L.

2003-01-01

Experiments using energy-selected beams of electrons incident from vacuum upon thin vapour deposited solids show that, as in the gas-phase, scattering cross sections at low energies are dominated by the formation of temporary negative ions (or resonances) and that molecular damage may be effected via dissociative electron attachment (DEA). Recent results also show that charge transfer between anionic states of target molecules and their environment is often crucial in determining cross sections for electron driven processes. Here, we review recent work from our laboratory, in which charge transfer is observed. For rare gas solids, electron exchange between the electron-exciton complex and either a metal substrate or co-adsorbed molecule enhances the desorption of metastable atoms and/or molecular dissociation. We discuss how transient electron capture by surface electron states of a substrate and subsequent electron transfer to a molecular adsorbate enhances the effective cross sections for DEA. We also consider the case of DEA to CF 2 Cl 2 condensed on water and ammonia ices, where electron exchange between pre-solvated electron states of ice and transient molecular anions can also increase DEA cross sections. Electron transfer from molecular resonances into pre-solvated electron states of ice is also discussed

Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

KAUST Repository

Aly, Shawkat Mohammede

2015-02-12

The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

KAUST Repository

Aly, Shawkat Mohammede; Usman, Anwar; Alzayer, Maytham; Hamdi, Ghada A.; Alarousu, Erkki; Mohammed, Omar F.

2015-01-01

The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

Time-resolved stimulated emission depletion and energy transfer dynamics in two-photon excited EGFP

Science.gov (United States)

Masters, T. A.; Robinson, N. A.; Marsh, R. J.; Blacker, T. S.; Armoogum, D. A.; Larijani, B.; Bain, A. J.

2018-04-01

Time and polarization-resolved stimulated emission depletion (STED) measurements are used to investigate excited state evolution following the two-photon excitation of enhanced green fluorescent protein (EGFP). We employ a new approach for the accurate STED measurement of the hitherto unmeasured degree of hexadecapolar transition dipole moment alignment ⟨α40 ⟩ present at a given excitation-depletion (pump-dump) pulse separation. Time-resolved polarized fluorescence measurements as a function of pump-dump delay reveal the time evolution of ⟨α40 ⟩ to be considerably more rapid than predicted for isotropic rotational diffusion in EGFP. Additional depolarization by homo-Förster resonance energy transfer is investigated for both ⟨α20 ⟩ (quadrupolar) and ⟨α40 ⟩ transition dipole alignments. These results point to the utility of higher order dipole correlation measurements in the investigation of resonance energy transfer processes.

Neutron scattering investigation of magnetic excitations at high energy transfers

International Nuclear Information System (INIS)

Loong, C.K.

1984-01-01

With the advance of pulsed spallation neutron sources, neutron scattering investigation of elementary excitations in magnetic materials can now be extended to energies up to several hundreds of MeV. We have measured, using chopper spectrometers and time-of-flight techniques, the magnetic response functions of a series of d and f transition metals and compounds over a wide range of energy and momentum transfer. In PrO 2 , UO 2 , BaPrO 3 and CeB 6 we observed crystal-field transitions between the magnetic ground state and the excited levels in the energy range from 40 to 260 MeV. In materials exhibiting spin-fluctuation or mixed-valent character such as Ce 74 Th 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

Momentum Dependence of Charge Excitations in YBa2Cu3O7-δ and Nd2-xCexCuO4

Science.gov (United States)

Ishii, Kenji

2006-03-01

Resonant inelastic x-ray scattering (RIXS) studies at Cu K-edge on high-Tc superconducting cuprates, YBa2Cu3O7-δ and Nd2-xCexCuO4 are presented. The superconductivity occurs in the vicinity of the Mott insulating state and it is important to clarify the nature of the Mott gap and its doping dependence. Because RIXS has an advantage that we can measure charge excitation in a wide energy-momentum space, it gives a unique opportunity to study the electronic structure of materials. We apply this technique to high-Tc superconducting cuprates. In particular the electronic structure of strongly correlated metals is in the focus of our RIXS study. The experiments were performed at BL11XU of SPring-8, Japan, where a specially designed spectrometer for inelastic x-ray scattering is installed. In optimally doped YBa2Cu3O7-δ, anisotropic spectra are observed in the ab plane of a twin-free crystal. The Mott gap excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the chain direction, while the excitation from the CuO2 plane is broad at 1.5-4 eV and almost independent of momentum. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed features in the RIXS spectra when smaller values of the on-site Coulomb energy of the chain than that of the plane are assumed. This means that the charge transfer gap of the chain is smaller than that of the plane. On the other hand, both interband excitation across the Mott gap and intraband excitation in the upper Hubbard band are observed in the electron-doped Nd2-xCexCuO4. The intensity of the interband excitation is concentrated at ˜ 2 eV near the zone boundary while a dispersion relation with a momentum-dependent width emerges in the intraband excitation. The author would like to acknowledge to his collaborators, K. Tsutsui, Y. Endoh, T. Tohyama, K. Kuzushita, T. Inami, K. Ohwada, M. Hoesch, M. Tsubota, Y. Murakami, J. Mizuki, S. Maekawa, T

Solvent effects on the excited-state double proton transfer mechanism in the 7-azaindole dimer: a TDDFT study with the polarizable continuum model.

Science.gov (United States)

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

2017-08-30

Solvent effects on the excited-state double proton transfer (ESDPT) mechanism in the 7-azaindole (7AI) dimer were investigated using the time-dependent density functional theory (TDDFT) method. Excited-state potential energy profiles along the reaction paths in a locally excited (LE) state and a charge transfer (CT) state were calculated using the polarizable continuum model (PCM) to include the solvent effect. A series of non-polar and polar solvents with different dielectric constants were used to examine the polarity effect on the ESDPT mechanism. The present results suggest that in a non-polar solvent and a polar solvent with a small dielectric constant, ESDPT follows a concerted mechanism, similar to the case in the gas phase. In a polar solvent with a relatively large dielectric constant, however, ESDPT is likely to follow a stepwise mechanism via a stable zwitterionic intermediate in the LE state on the adiabatic potential energy surface, although inclusion of zero-point vibrational energy (ZPE) corrections again suggests the concerted mechanism. In the meantime, the stepwise reaction path involving the CT state with neutral intermediates is also examined, and is found to be less competitive than the concerted or stepwise path in the LE state in both non-polar and polar solvents. The present study provides a new insight into the experimental controversy of the ESDPT mechanism of the 7AI dimer in a solution.

Charge-Transfer Complexes Studied by Dynamic Force Spectroscopy

Directory of Open Access Journals (Sweden)

Jurriaan Huskens

2013-03-01

Full Text Available In this paper, the strength and kinetics of two charge-transfer complexes, naphthol-methylviologen and pyrene-methylviologen, are studied using dynamic force spectroscopy. The dissociation rates indicate an enhanced stability of the pyrene-methylviologen complex, which agrees with its higher thermodynamic stability compared to naphthol-methylviologen complex.

Nuclear isovector giant resonances excited by pion single charge exchange

International Nuclear Information System (INIS)

King, B.H.

1993-07-01

This thesis is an experimental study of isovector giant resonances in light nuclei excited by pion single charge exchange reactions. Giant dipole resonances in light nuclei are known to be highly structured. For the mass 9 and 13 giant dipole resonances, isospin considerations were found to be very important to understanding this structure. by comparing the excitation functions from cross section measurements of the (π + , π 0 ) and (π, π 0 ) inclusive reactions, the authors determined the dominant isospin structure of the analog IVGR's. The comparison was made after decomposing the cross section into resonant and non-resonant components. This decomposition is made in the framework of strong absorption and quasi-free scattering. Measurements in the region of the isovector giant dipole resonances (IVGDR) were made to cover the inclusive angular distributions out to the second minimum. Study of the giant resonance decay process provides further understanding of the resonances. This study was carried out by observing the (π + , π 0 p) coincident reactions involving the resonances of 9 B and 13 N excited from 9 Be and 13 C nuclei. These measurements determined the spectra of the decay protons. This method also permitted a decomposition of the giant resonances into their isospin components. The multipolarities of the resonances were revealed by the decay proton angular correlations which, for dipoles, are of the form 1 + A 2 P 2 (cos θ)

Energy and charge transfer in ionized argon coated water clusters

International Nuclear Information System (INIS)

Kočišek, J.; Lengyel, J.; Fárník, M.; Slavíček, P.

2013-01-01

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H 2 O) n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar + and water occurs above the threshold; at higher electron energies above ∼28 eV, an excitonic transfer process between Ar + * and water opens leading to new products Ar n H + and (H 2 O) n H + . On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H 2 O) n H 2 2+ and (H 2 O) n 2+ ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent

Symmetric resonance double charge transfer in Kr++ + Kr and Xe++ + Xe systems

International Nuclear Information System (INIS)

Okuno, K.; Koizumi, T.; Kaneko, Y.

1978-01-01

Cross sections of processes Kr ++ + Kr → Ke + Kr ++ and Xe ++ + Xe → Xe + Xe ++ were measured by the injected-ion-drift-tube technique from 0.04 to 20 eV. For both cases, the cross section below 1 eV coincides with the orbiting cross sections with a charge-transfer probability 1/2. Above 1 eV, the energy dependence of the cross sectcion is like that for single charge transfer. Mobilities of Kr ++ and Xe ++ in He are presented also

Search for Charged Excited Leptons in $e^+ e^-$ Collisions at $\\sqrt{s}$ = 183-209 GeV

CERN Document Server

Abbiendi, G.; Akesson, P.F.; Alexander, G.; Allison, John; Amaral, P.; Anagnostou, G.; Anderson, K.J.; Arcelli, S.; Asai, S.; Axen, D.; Azuelos, G.; Bailey, I.; Barberio, E.; Barlow, R.J.; Batley, R.J.; Bechtle, P.; Behnke, T.; Bell, Kenneth Watson; Bell, P.J.; Bella, G.; Bellerive, A.; Benelli, G.; Bethke, S.; Biebel, O.; Bloodworth, I.J.; Boeriu, O.; Bock, P.; Bonacorsi, D.; Boutemeur, M.; Braibant, S.; Brigliadori, L.; Brown, Robert M.; Buesser, K.; Burckhart, H.J.; Cammin, J.; Campana, S.; Carnegie, R.K.; Caron, B.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Cohen, I.; Csilling, A.; Cuffiani, M.; Dado, S.; Dallavalle, G.Marco; Dallison, S.; De Roeck, A.; De Wolf, E.A.; Desch, K.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Elfgren, E.; Etzion, E.; Fabbri, F.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Furtjes, A.; Gagnon, P.; Gary, John William; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Giunta, Marina; Goldberg, J.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hamann, M.; Hanson, G.G.; Harder, K.; Harel, A.; Harin-Dirac, M.; Hauschild, M.; Hauschildt, J.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herten, G.; Heuer, R.D.; Hill, J.C.; Hoffman, Kara Dion; Homer, R.J.; Horvath, D.; Howard, R.; Huntemeyer, P.; Igo-Kemenes, P.; Ishii, K.; Jeremie, H.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klein, K.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Kokott, T.P.; Komamiya, S.; Kormos, Laura L.; Kowalewski, Robert V.; Kramer, T.; Kress, T.; Krieger, P.; von Krogh, J.; Krop, D.; Kupper, M.; Kyberd, P.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Layter, J.G.; Leins, A.; Lellouch, D.; Letts, J.; Levinson, L.; Lillich, J.; Lloyd, S.L.; Loebinger, F.K.; Lu, J.; Ludwig, J.; Macpherson, A.; Mader, W.; Marcellini, S.; Marchant, T.E.; Martin, A.J.; Martin, J.P.; Masetti, G.; Mashimo, T.; Mattig, Peter; McDonald, W.J.; McKenna, J.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Mendez-Lorenzo, P.; Menges, W.; Merritt, F.S.; Mes, H.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Moed, S.; Mohr, W.; Mori, T.; Mutter, A.; Nagai, K.; Nakamura, I.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oh, A.; Okpara, A.; Oreglia, M.J.; Orito, S.; Pahl, C.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Polok, J.; Pooth, O.; Przybycien, M.; Quadt, A.; Rabbertz, K.; Rembser, C.; Renkel, P.; Rick, H.; Roney, J.M.; Rosati, S.; Rozen, Y.; Runge, K.; Rust, D.R.; Sachs, K.; Saeki, T.; Sahr, O.; Sarkisyan, E.K.G.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schieck, J.; Schoerner-Sadenius, Thomas; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.; Skuja, A.; Smith, A.M.; Sobie, R.; Soldner-Rembold, S.; Spagnolo, S.; Spano, F.; Stahl, A.; Stephens, K.; Strom, David M.; Strohmer, R.; Tarem, S.; Tasevsky, M.; Taylor, R.J.; Teuscher, R.; Thomson, M.A.; Torrence, E.; Toya, D.; Tran, P.; Trefzger, T.; Tricoli, A.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Vachon, B.; Vollmer, C.F.; Vannerem, P.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Waller, D.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wyatt, T.R.; Yamashita, S.; Zacek, V.; Zer-Zion, D.; Zivkovic, Lidija

2002-01-01

A search for charged excited leptons decaying into a lepton and photon has been performed using approximately 680 pb-1 of e+e- collision data collected by the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV. No evidence for their existence was found. Upper limits on the product of the cross-section and the branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

Study on photophysical properties of Eu(III) complexes with aromatic β-diketones – Role of charge transfer states in the energy migration

Energy Technology Data Exchange (ETDEWEB)

Räsänen, Markus, E-mail: mpvras@utu.fi [Department of Chemistry, University of Turku, FIN-20014 Turku (Finland); Takalo, Harri [DHR Finland Oy, Innotrac Diagnostics, Biolinja 12, FIN-20750 Turku (Finland); Rosenberg, Jaana; Mäkelä, Joonas [Department of Biochemistry and Food Chemistry, University of Turku, FIN-20014 Turku (Finland); Haapakka, Keijo; Kankare, Jouko [Department of Chemistry, University of Turku, FIN-20014 Turku (Finland)

2014-02-15

We synthesized a set of aromatic β-diketones and measured the photophysical properties of their europium(III) complexes. According to these photophysical properties, the europium complexes can be divided into two groups: the complexes with or without the freely rotating amino-group (FRAG). On the basis of the experimental results, it can be concluded that in the FRAG complexes, the ligand-centered excitation energy is most probably transferred from a ligand to a coordinated europium via the intraligand charge transfer (ILCT) state. The temperature dependency of the lifetimes of the emissive {sup 5}D{sub 0} state revealed that in the FRAG complexes, the energy of the emissive {sup 5}D{sub 0} state is back-transferred to the ligand-to-metal charge transfer (LMCT) state and in the non-FRAG complexes, to the triplet state of the ligand. The most efficient complex synthesized was the europium complex of carbazole derivative L{sup 6} with the quantum yield of 47% and molar absorption coefficient of 70,400 M{sup −1}cm{sup −1}. -- Highlights: • We synthesized a set of substituted aromatic β-diketones and their Eu(III) complexes. • We measured the photophysical properties of these Eu(III) complexes. • Carbazole derivative of β-diketone forms the brightest Eu(III) complex. • The Jablonski diagrams proposed for the luminescence of these complexes.

A two-dimensional position sensitive gas chamber with scanned charge transfer readout

Energy Technology Data Exchange (ETDEWEB)

Gomez, F. E-mail: faustgr@usc.es; Iglesias, A.; Lobato, R.; Mosquera, J.; Pardo, J.; Pena, J.; Pazos, A.; Pombar, M.; Rodriguez, A

2003-10-21

We have constructed and tested a two-dimensional position sensitive parallel-plate gas ionization chamber with scanned charge transfer readout. The scan readout method described here is based on the development of a new position-dependent charge transfer technique. It has been implemented by using gate strips perpendicularly oriented to the collector strips. This solution reduces considerably the number of electronic readout channels needed to cover large detector areas. The use of a 25 {mu}m thick kapton etched circuit allows high charge transfer efficiency with a low gating voltage, consequently needing a very simple commutating circuit. The present prototype covers 8x8 cm{sup 2} with a pixel size of 1.27x1.27 mm{sup 2}. Depending on the intended use and beam characteristics a smaller effective pixel is feasible and larger active areas are possible. This detector can be used for X-ray or other continuous beam intensity profile monitoring.

A two-dimensional position sensitive gas chamber with scanned charge transfer readout

International Nuclear Information System (INIS)

Gomez, F.; Iglesias, A.; Lobato, R.; Mosquera, J.; Pardo, J.; Pena, J.; Pazos, A.; Pombar, M.; Rodriguez, A.

2003-01-01

We have constructed and tested a two-dimensional position sensitive parallel-plate gas ionization chamber with scanned charge transfer readout. The scan readout method described here is based on the development of a new position-dependent charge transfer technique. It has been implemented by using gate strips perpendicularly oriented to the collector strips. This solution reduces considerably the number of electronic readout channels needed to cover large detector areas. The use of a 25 μm thick kapton etched circuit allows high charge transfer efficiency with a low gating voltage, consequently needing a very simple commutating circuit. The present prototype covers 8x8 cm 2 with a pixel size of 1.27x1.27 mm 2 . Depending on the intended use and beam characteristics a smaller effective pixel is feasible and larger active areas are possible. This detector can be used for X-ray or other continuous beam intensity profile monitoring

Charge transfer in pi-stacked systems including DNA

International Nuclear Information System (INIS)

Siebbeles, L.D.A.

2003-01-01

Charge migration in DNA is a subject of intense current study motivated by long-range detection of DNA damage and the potential application of DNA as a molecular wire in nanoscale electronic devices. A key structural element, which makes DNA a medium for long-range charge transfer, is the array of stacked base pairs in the interior of the double helix. The overlapping pi-orbitals of the nucleobases provide a pathway for motion of charge carriers generated on the stack. This 'pi-pathway' resembles the columnarly stacked macrocyclic cores in discotic materials such as triphenylenes. The structure of these pi-stacked systems is highly disordered with dynamic fluctuations occurring on picosecond to nanosecond time scales. Theoretical calculations, concerning the effects of structural disorder and nucleobase sequence in DNA, on the dynamics of charge carriers are presented. Electronic couplings and localization energies of charge carriers were calculated using density functional theory (DFT). Results for columnarly stacked triphenylenes and DNA nucleobases are compared. The results are used to provide insight into the factors that control the mobility of charge carriers. Further, experimental results on the site-selective oxidation of guanine nucleobases in DNA (hot spots for DNA damage) are analyzed on basis of the theoretical results

High-frequency conductivity of optically excited charge carriers in hydrogenated nanocrystalline silicon investigated by spectroscopic femtosecond pump–probe reflectivity measurements

Energy Technology Data Exchange (ETDEWEB)

He, Wei [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom); Yurkevich, Igor V. [Aston University, Nonlinearity and Complexity Research Group, Birmingham B4 7ET (United Kingdom); Zakar, Ammar [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom); Kaplan, Andrey, E-mail: a.kaplan.1@bham.ac.uk [University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT (United Kingdom)

2015-10-01

We report an investigation into the high-frequency conductivity of optically excited charge carriers far from equilibrium with the lattice. The investigated samples consist of hydrogenated nanocrystalline silicon films grown on a thin film of silicon oxide on top of a silicon substrate. For the investigation, we used an optical femtosecond pump–probe setup to measure the reflectance change of a probe beam. The pump beam ranged between 580 and 820 nm, whereas the probe wavelength spanned 770 to 810 nm. The pump fluence was fixed at 0.6 mJ/cm{sup 2}. We show that at a fixed delay time of 300 fs, the conductivity of the excited electron–hole plasma is described well by a classical conductivity model of a hot charge carrier gas found at Maxwell–Boltzmann distribution, while Fermi–Dirac statics is not suitable. This is corroborated by values retrieved from pump–probe reflectance measurements of the conductivity and its dependence on the excitation wavelength and carrier temperature. The conductivity decreases monotonically as a function of the excitation wavelength, as expected for a nondegenerate charge carrier gas. - Highlights: • We study high‐frequency conductivity of excited hydrogenated nanocrystalline silicon. • Reflectance change was measured as a function of pump and probe wavelength. • Maxwell–Boltzmann transport theory was used to retrieve the conductivity. • The conductivity decreases monotonically as a function of the pump wavelength.

Charge-resonance excitations in symmetric molecules - Comparison of linear response DFT with CC3 for the excited states of a model dimer

DEFF Research Database (Denmark)

Kuhlman, Thomas Scheby; Mikkelsen, Kurt V.; Møller, Klaus Braagaard

2009-01-01

to a reference CC3 calculation revealing a better description of the excited states by CAM-B3LYP than that of B3LYP. The Λ parameter introduced by Peach et al. [M.J.G. Peach, P. Benfield, T. Helgaker, D.J. Tozer, J. Chem. Phys. 128 (2008) 044118] does not always reveal the problematic charge-resonance states...

The influence of electric charge transferred during electro-mechanical reshaping on mechanical behavior of cartilage

Science.gov (United States)

Protsenko, Dimitry E.; Lim, Amanda; Wu, Edward C.; Manuel, Cyrus; Wong, Brian J. F.

2011-03-01

Electromechanical reshaping (EMR) of cartilage has been suggested as an alternative to the classical surgical techniques of modifying the shape of facial cartilages. The method is based on exposure of mechanically deformed cartilaginous tissue to a low level electric field. Electro-chemical reactions within the tissue lead to reduction of internal stress, and establishment of a new equilibrium shape. The same reactions offset the electric charge balance between collagen and proteoglycan matrix and interstitial fluid responsible for maintenance of cartilage mechanical properties. The objective of this study was to investigate correlation between the electric charge transferred during EMR and equilibrium elastic modulus. We used a finite element model based on the triphasic theory of cartilage mechanical properties to study how electric charges transferred in the electro-chemical reactions in cartilage can change its mechanical responses to step displacements in unconfined compression. The concentrations of the ions, the strain field and the fluid and ion velocities within the specimen subject to an applied mechanical deformation were estimated and apparent elastic modulus (the ratio of the equilibrium axial stress to the axial strain) was calculated as a function of transferred charge. The results from numerical calculations showed that the apparent elastic modulus decreases with increase in electric charge transfer. To compare numerical model with experimental observation we measured elastic modulus of cartilage as a function of electric charge transferred in electric circuit during EMR. Good correlation between experimental and theoretical data suggests that electric charge disbalance is responsible for alteration of cartilage mechanical properties.

Theoretical studies of charge transfer and proton transfer complex formation between 3,5-dinitrobenzic acid and 1,2-dimethylimidazole

Science.gov (United States)

Afroz, Ziya; Faizan, Mohd.; Alam, Mohammad Jane; Ahmad, Shabbir; Ahmad, Afaq

2018-05-01

Natural atomic charge analysis and molecular electrostatic potential (MEP) surface analysis of hydrogen bonded charge transfer (HBCT) and proton transfer (PT) complex of 3,5-dinitrobenzoic acid (DNBA) and 1,2-dimethylimidazole (DMI) have been investigated by theoretical modelling using widely employed DFT/B3LYP/6-311G(d,p) level of theory. Along with this analysis, Hirshfeld surface study of the intermolecular interactions and associated 2D finger plot for reported PT complex between DNBA and DMI have been explored.

Characterising excited states in and around the semi-magic nucleus $^{68}$ Ni using Coulomb excitation and one-neutron transfer

CERN Multimedia

It is proposed to investigate the structure of excited states in $^{68, 70}$Ni(Z =28, N=40, 42) via the measurement of electromagnetic matrix elements in a Coulomb excitation experiment in order to study the N = 40 harmonic-oscillator shell and the Z = 28 proton shell closures. The measured B(E2) values connecting low-lying 0$^{+}$ and 2$^{+}$ can be compared to shell-model predictions. It is also proposed to perform the one-neutron transfer reaction ${d}$($^{68}$Ni,$^{69}$Ni)${p}$, with the aim of populating excited states in $^{69}$Ni. Comparisons with the states populated in the recently performed ${d}$($^{66}$Ni,$^{67}$Ni)${p}$ reaction will be useful in determining the role of the neutron $d_{5/2}$ orbital in the semi-magic properties of $^{68}$Ni.

Plasmon assisted control of photo-induced excitation energy transfer in a molecular chain

Science.gov (United States)

Wang, Luxia; May, Volkhard

2017-08-01

The strong and ultrafast laser pulse excitation of a molecular chain in close vicinity to a spherical metal nano-particle (MNP) is studied theoretically. Due to local-field enhancement around the MNP, pronounced excited-state formation has to be expected for the part of the chain which is in proximity to the MNP. Here, the description of this phenomenon will be based on a uniform quantum theory of the MNP-molecule system. It accounts for local-field effects due to direct consideration of the strong excitation energy transfer coupling between the MNP and the various molecules. The molecule-MNP distances are chosen in such a way as to achieve a correct description of the MNP via dipole-plasmon excitations. Short plasmon life-times are incorporated in the framework of a density matrix approach. By extending earlier work the present description allows for multi-exciton formation and multiple dipole-plasmon excitation. The region of less intense and not-too-short optical excitation is identified as being best suited for excitation energy localization in the chain.

Charge transfer in gas electron multipliers

Energy Technology Data Exchange (ETDEWEB)

Ottnad, Jonathan; Ball, Markus; Ketzer, Bernhard; Ratza, Viktor; Razzaghi, Cina [HISKP, Bonn University, Nussallee 14-16, D-53115 Bonn (Germany)

2015-07-01

In order to efficiently employ a Time Projection Chamber (TPC) at interaction rates higher than ∝1 kHz, as foreseen e.g. in the ALICE experiment (CERN) and at CB-ELSA (Bonn), a continuous operation and readout mode is required. A necessary prerequisite is to minimize the space charge coming from the amplification system and to maintain an excellent spatial and energy resolution. Unfortunately these two goals can be in conflict to each other. Gas Electron Multipliers (GEM) are one candidate to fulfill these requirements. It is necessary to understand the processes within the amplification structure to find optimal operation conditions. To do so, we measure the charge transfer processes in and between GEM foils with different geometries and field configurations, and use an analytical model to describe the results. This model can then be used to predict and optimize the performance. The talk gives the present status of the measurements and describes the model.

Intramolecular, Exciplex-Mediated, Proton-Coupled, Charge-Transfer Processes in N,N-Dimethyl-3-(1-pyrenyl)propan-1-ammonium Cations: Influence of Anion, Solvent Polarity, and Temperature.

Science.gov (United States)

Safko, Trevor M; Faleiros, Marcelo M; Atvars, Teresa D Z; Weiss, Richard G

2016-06-16

An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation O) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pKa*) has been estimated to be ca. -3.4 in tetrahydrofuran. The ratios between the intensities of emission from the exciplex and the locally excited state (IEx/ILE) appear to be much more dependent on the nature of the anion than are the rates of exciplex formation and decay, although the excited state data do not provide a quantitative measure of the anion effect on the C-O equilibrium. The activation energies associated with exciplex formation in THF are calculated to be 0.08 to 0.15 eV lower than for the neutral amine, N,N-dimethyl-3-(1-pyrenyl)propan-1-amine. Decay of the exciplexes formed from the deprotonation of PyS is hypothesized to occur through charge-recombination processes. To our knowledge, this is the first example in which photoacidity and intramolecular exciplex formation (i.e., a PCCT reaction) are coupled.

The charge transfer characteristic of tetraphenylporphyrin iron chloride Langmuir–Blodgett films

International Nuclear Information System (INIS)

Du, Y.; Li, Z.H.; Qi, P.; Wang, F.; Liu, D.

2013-01-01

The charge transfer characteristic of tetraphenylporphyrin iron (III) chloride (FeP) Langmuir–Blodgett (LB) films on the surface of the ITO glass electrode was reported. When the cyclic voltammetry (CV) scanning was running, the charge transfer characteristic was controlled by the oxidation–reduction process of Fe(III)/Fe(II). The charge transfer characteristic was related to the following factors: the cross-sectional area, relative to the electrode, of FeP as the electron donor (or acceptor). The greater the cross-sectional area of the aggregation of FeP as the electron donor (or acceptor) was, the larger the number of the donated (or accepted) electrons was. The projected area of the cross-section on the ITO electrode. The greater the projected area was, the larger the number of the donated (or accepted) electrons was. The distance between the center of the electron donor (or acceptor) of FeP and the surface of ITO electrode. The smaller the distance was, the greater the rate of donating (or accepting) electrons was. The monolayer coverage, which formed because of the FeP lying on the ITO surface in the form of the monomer and aggregate, was more sensitive to detect oxygen

The form of electron-atom excitation amplitudes at high momentum transfers in the Faddeev-Watson approximation

International Nuclear Information System (INIS)

Catalan, G.; Roberts, M.J.

1979-01-01

A form of the off-shell Coulomb T matrix, which has a well defined on-shell limit, is used in the Faddeev-Watson multiple-scattering expansion for a direct three-body collision process. Using the excitation of atomic hydrogen by electron impact as an example, approximations to the second-order terms, which are valid for high momentum transfers of the incident electron, are derived. It is shown how the resulting asymptotic behaviour of the second-order Faddeev-Watson approximation is related to the high momentum transfer limit of the second Born approximation. The results are generalised to the excitation of more complex atoms. The asymptotic forms of the Faddeev-Watson and Born approximations are compared with other theories and with measurements of differential cross sections and angular correlation parameters for the excitation of H(2p) and He(2 1 P). The results indicate that the Faddeev-Watson approximation converges more rapidly at high momentum transfers than does the Born approximation. (author)

Photoinduced charge transfer within polyaniline-encapsulated quantum dots decorated on graphene.

Science.gov (United States)

Nguyen, Kim Truc; Li, Dehui; Borah, Parijat; Ma, Xing; Liu, Zhaona; Zhu, Liangliang; Grüner, George; Xiong, Qihua; Zhao, Yanli

2013-08-28

A new method to enhance the stability of quantum dots (QDs) in aqueous solution by encapsulating them with conducting polymer polyaniline was reported. The polyaniline-encapsulated QDs were then decorated onto graphene through π-π interactions between graphene and conjugated polymer shell of QDs, forming stable polyaniline/QD/graphene hybrid. A testing electronic device was fabricated using the hybrid in order to investigate the photoinduced charge transfer between graphene and encapsulated QDs within the hybrid. The charge transfer mechanism was explored through cyclic voltammetry and spectroscopic studies. The hybrid shows a clear response to the laser irradiation, presenting a great advantage for further applications in optoelectronic devices.

Cost-Effectiveness Comparison of Coupler Designs of Wireless Power Transfer for Electric Vehicle Dynamic Charging

Directory of Open Access Journals (Sweden)

Weitong Chen

2016-11-01

Full Text Available This paper presents a cost-effectiveness comparison of coupler designs for wireless power transfer (WPT, meant for electric vehicle (EV dynamic charging. The design comparison of three common types of couplers is first based on the raw material cost, output power, transfer efficiency, tolerance of horizontal offset, and flux density. Then, the optimal cost-effectiveness combination is selected for EV dynamic charging. The corresponding performances of the proposed charging system are compared and analyzed by both simulation and experimentation. The results verify the validity of the proposed dynamic charging system for EVs.

Plasma effect on tunnelling, charge transfer and transient quasimolecular states

International Nuclear Information System (INIS)

Fisher, D V

2003-01-01

The influence of a dense plasma environment on electron tunnelling between two ion potential wells in collectivized states and in charge-transfer collisions is studied. We show that the tunnelling probabilities in dilute plasma (in a close ion-ion collision) and in dense plasma differ strongly. The difference is due to the mixing between Stark components of donor-ion energy levels, caused by the field of spectator ions in a dense plasma. The mixing is determined by an angle α between the nearest-neighbour ion field and the total electric field acting on the donor ion. In close ion-ion binary collisions the mixing may be considered weak. However, for most plasma ions charge transfer, electron state collectivization and transient quasimolecule formation are strongly affected by the field of spectator ions. We derive approximate analytical expressions for the distribution function of α in an ideal plasma and perform molecular dynamics simulations to find the distribution function of α in both ideal and nonideal plasmas. Both α-dependent and average mixing coefficients are determined. We have found that the mixing is strong, even in ideal plasmas, and increases further with an increase in plasma nonideality. It is shown that there is no resonant charge transfer in dense plasmas. The applicability of a transient 'dicenter' quasimolecule model for dense plasmas is discussed

On the rate of triplet excitation transfer in the diffuse limit

International Nuclear Information System (INIS)

Davidovich, M.A.; Knox, R.S.

1979-11-01

The usefulness of spectral data in estimating intermolecular triplet excitation transfer rates in found to be rather limited and to depend explicitly on the mechaisms which allow the optical transitions. Necessary conditions for the validity of such use of spectra are given, and the otherwise required correction factors are discussed and estimated. (Author) [pt

The behavior of exciplex decay processes and interplay of radiationless transition and preliminary reorganization mechanisms of electron transfer in loose and tight pairs of reactants.

Science.gov (United States)

Kuzmin, Michael G; Soboleva, Irina V; Dolotova, Elena V

2007-01-18

Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

Bands dispersion and charge transfer in β-BeH2

Science.gov (United States)

Trivedi, D. K.; Galav, K. L.; Joshi, K. B.

2018-04-01

Predictive capabilities of ab-initio method are utilised to explore bands dispersion and charge transfer in β-BeH2. Investigations are carried out using the linear combination of atomic orbitals method at the level of density functional theory. The crystal structure and related parameters are settled by coupling total energy calculations with the Murnaghan equation of state. Electronic bands dispersion from PBE-GGA is reported. The PBE-GGA, and PBE0 hybrid functional, show that β-BeH2 is a direct gap semiconductor with 1.18 and 2.40 eV band gap. The band gap slowly decreases with pressure and beyond l00 GPa overlap of conduction and valence bands at the r point is observed. Charge transfer is studied by means of Mullikan population analysis.

Transfer of energy or charge between quasi-zero-dimensional nanostructures

Czech Academy of Sciences Publication Activity Database

Král, Karel; Menšík, Miroslav

2016-01-01

Roč. 45, č. 4 (2016), s. 243-255 ISSN 2332-4309 R&D Projects: GA ČR(CZ) GA14-05053S; GA MŠk(CZ) LD14011; GA MŠk LH12236 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : charge transfer * electron-phonon interaction * energy transfer * nanostructures * quantum dots Subject RIV: BM - Solid Matter Physics ; Magnetism; CD - Macromolecular Chemistry (UMCH-V) Impact factor: 0.171, year: 2016

Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope

International Nuclear Information System (INIS)

Wu, S. W.; Ho, W.

2010-01-01

The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photoexcited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron-transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by the polarization measurement. Spatial dependence of the electron-transfer rate exhibits atomic-scale variations. A two-pulse correlation experiment reveals the ultrafast dynamic nature of photoinduced charging process in the STM junction. Results from these experiments are important for understanding photoinduced interfacial charge transfer in many nanoscale inorganic-organic structures.

Modeling charge transfer at organic donor-acceptor semiconductor interfaces

NARCIS (Netherlands)

Cakir, Deniz; Bokdam, Menno; de Jong, Machiel Pieter; Fahlman, M.; Brocks, G.

2012-01-01

We develop an integer charge transfer model for the potential steps observed at interfaces between donor and acceptor molecular semiconductors. The potential step can be expressed as the difference between the Fermi energy pinning levels of electrons on the acceptor material and holes on the donor

Study of radiative leptonic events with hard photons and search for excited charged leptons at $\\sqrt{s}$ = 130-136 GeV

CERN Document Server

Abreu, P; Adye, T; Agasi, E; Aleksan, Roy; Alekseev, G D; Alemany, R; Allport, P P; Almehed, S; Amaldi, Ugo; Amato, S; Andreazza, A; Andrieux, M L; Antilogus, P; Apel, W D; Arnoud, Y; Åsman, B; Augustin, J E; Augustinus, A; Baillon, Paul; Bambade, P; Barão, F; Barate, R; Barbi, M S; Barbiellini, Guido; Bardin, Dimitri Yuri; Baroncelli, A; Bärring, O; Barrio, J A; Bartl, Walter; Bates, M J; Battaglia, Marco; Baubillier, M; Baudot, J; Becks, K H; Begalli, M; Beillière, P; Belokopytov, Yu A; Benvenuti, Alberto C; Berggren, M; Bertini, D; Bertrand, D; Bianchi, F; Bigi, M; Bilenky, S M; Billoir, P; Bloch, D; Blume, M; Bolognese, T; Bonesini, M; Bonivento, W; Booth, P S L; Bosio, C; Botner, O; Boudinov, E; Bouquet, B; Bourdarios, C; Bowcock, T J V; Bozzo, M; Branchini, P; Brand, K D; Brenke, T; Brenner, R A; Bricman, C; Brown, R C A; Brückman, P; Brunet, J M; Bugge, L; Buran, T; Burgsmüller, T; Buschmann, P; Buys, A; Cabrera, S; Caccia, M; Calvi, M; Camacho-Rozas, A J; Camporesi, T; Canale, V; Canepa, M; Cankocak, K; Cao, F; Carena, F; Carroll, L; Caso, Carlo; Castillo-Gimenez, M V; Cattai, A; Cavallo, F R; Chabaud, V; Charpentier, P; Chaussard, L; Chauveau, J; Checchia, P; Chelkov, G A; Chen, M; Chierici, R; Chliapnikov, P V; Chochula, P; Chorowicz, V; Cindro, V; Collins, P; Contreras, J L; Contri, R; Cortina, E; Cosme, G; Cossutti, F; Crawley, H B; Crennell, D J; Crosetti, G; Cuevas-Maestro, J; Czellar, S; Dahl-Jensen, Erik; Dahm, J; D'Almagne, B; Dam, M; Damgaard, G; Dauncey, P D; Davenport, Martyn; Da Silva, W; Defoix, C; Deghorain, A; Della Ricca, G; Delpierre, P A; Demaria, N; De Angelis, A; de Boer, Wim; De Brabandere, S; De Clercq, C; La Vaissière, C de; De Lotto, B; De Min, A; De Paula, L S; De Saint-Jean, C; Dijkstra, H; Di Ciaccio, Lucia; Djama, F; Dolbeau, J; Dönszelmann, M; Doroba, K; Dracos, M; Drees, J; Drees, K A; Dris, M; Durand, J D; Edsall, D M; Ehret, R; Eigen, G; Ekelöf, T J C; Ekspong, Gösta; Elsing, M; Engel, J P; Erzen, B; Espirito-Santo, M C; Falk, E; Fassouliotis, D; Feindt, Michael; Fenyuk, A; Ferrer, A; Fichet, S; Filippas-Tassos, A; Firestone, A; Fischer, P A; Föth, H; Fokitis, E; Fontanelli, F; Formenti, F; Franek, B J; Frenkiel, P; Fries, D E C; Frodesen, A G; Frühwirth, R; Fulda-Quenzer, F; Fuster, J A; Galloni, A; Gamba, D; Gandelman, M; García, C; García, J; Gaspar, C; Gasparini, U; Gavillet, P; Gazis, E N; Gelé, D; Gerber, J P; Gibbs, M; Gokieli, R; Golob, B; Gopal, Gian P; Gorn, L; Górski, M; Guz, Yu; Gracco, Valerio; Graziani, E; Grosdidier, G; Grzelak, K; Gumenyuk, S A; Gunnarsson, P; Günther, M; Guy, J; Hahn, F; Hahn, S; Hajduk, Z; Hallgren, A; Hamacher, K; Hao, W; Harris, F J; Hedberg, V; Henriques, R P; Hernández, J J; Herquet, P; Herr, H; Hessing, T L; Higón, E; Hilke, Hans Jürgen; Hill, T S; Holmgren, S O; Holt, P J; Holthuizen, D J; Hoorelbeke, S; Houlden, M A; Hrubec, Josef; Huet, K; Hultqvist, K; Jackson, J N; Jacobsson, R; Jalocha, P; Janik, R; Jarlskog, C; Jarlskog, G; Jarry, P; Jean-Marie, B; Johansson, E K; Jönsson, L B; Jönsson, P E; Joram, Christian; Juillot, P; Kaiser, M; Kapusta, F; Karafasoulis, K; Karlsson, M; Karvelas, E; Katsanevas, S; Katsoufis, E C; Keränen, R; Khokhlov, Yu A; Khomenko, B A; Khovanskii, N N; King, B J; Kjaer, N J; Klein, H; Klovning, A; Kluit, P M; Köne, B; Kokkinias, P; Koratzinos, M; Korcyl, K; Kostyukhin, V; Kourkoumelis, C; Kuznetsov, O; Kramer, P H; Krammer, Manfred; Kreuter, C; Kronkvist, I J; Krumshtein, Z; Krupinski, W; Kubinec, P; Kucewicz, W; Kurvinen, K L; Lacasta, C; Laktineh, I; Lamblot, S; Lamsa, J; Lanceri, L; Lane, D W; Langefeld, P; Lapin, V; Last, I; Laugier, J P; Lauhakangas, R; Ledroit, F; Lefébure, V; Legan, C K; Leitner, R; Lemoigne, Y; Lemonne, J; Lenzen, Georg; Lepeltier, V; Lesiak, T; Libby, J; Liko, D; Lindner, R; Lipniacka, A; Lippi, I; Lörstad, B; Loken, J G; López, J M; Loukas, D; Lutz, P; Lyons, L; MacNaughton, J N; Maehlum, G; Maio, A; Malychev, V; Mandl, F; Marco, J; Marco, R P; Maréchal, B; Margoni, M; Marin, J C; Mariotti, C; Markou, A; Maron, T; Martínez-Rivero, C; Martínez-Vidal, F; Martí i García, S; Matorras, F; Matteuzzi, C; Matthiae, Giorgio; Mazzucato, M; McCubbin, M L; McKay, R; McNulty, R; Medbo, J; Merk, M; Meroni, C; Meyer, S; Meyer, W T; Myagkov, A; Michelotto, M; Migliore, E; Mirabito, L; Mitaroff, Winfried A; Mjörnmark, U; Moa, T; Møller, R; Mönig, K; Monge, M R; Morettini, P; Müller, H; Mundim, L M; Murray, W J; Muryn, B; Myatt, Gerald; Naraghi, F; Navarria, Francesco Luigi; Navas, S; Nawrocki, K; Negri, P; Némécek, S; Neumann, W; Neumeister, N; Nicolaidou, R; Nielsen, B S; Nieuwenhuizen, M; Nikolaenko, V; Niss, P; Nomerotski, A; Normand, Ainsley; Novák, M; Oberschulte-Beckmann, W; Obraztsov, V F; Olshevskii, A G; Onofre, A; Orava, Risto; Österberg, K; Ouraou, A; Paganini, P; Paganoni, M; Pagès, P; Palka, H; Papadopoulou, T D; Papageorgiou, K; Pape, L; Parkes, C; Parodi, F; Passeri, A; Pegoraro, M; Peralta, L; Pernegger, H; Pernicka, Manfred; Perrotta, A; Petridou, C; Petrolini, A; Petrovykh, M; Phillips, H T; Piana, G; Pierre, F; Pimenta, M; Pindo, M; Plaszczynski, S; Podobrin, O; Pol, M E; Polok, G; Poropat, P; Pozdnyakov, V; Prest, M; Privitera, P; Pukhaeva, N; Pullia, Antonio; Radojicic, D; Ragazzi, S; Rahmani, H; Rames, J; Ratoff, P N; Read, A L; Reale, M; Rebecchi, P; Redaelli, N G; Regler, Meinhard; Reid, D; Renton, P B; Resvanis, L K; Richard, F; Richardson, J; Rídky, J; Rinaudo, G; Ripp, I; Romero, A; Roncagliolo, I; Ronchese, P; Roos, L; Rosenberg, E I; Rosso, E; Roudeau, Patrick; Rovelli, T; Rückstuhl, W; Ruhlmann-Kleider, V; Ruiz, A; Rybicki, K; Saarikko, H; Sacquin, Yu; Sadovskii, A; Sahr, O; Sajot, G; Salt, J; Sánchez, J; Sannino, M; Schimmelpfennig, M; Schneider, H; Schwickerath, U; Schyns, M A E; Sciolla, G; Scuri, F; Seager, P; Sedykh, Yu; Segar, A M; Seitz, A; Sekulin, R L; Serbelloni, L; Shellard, R C; Siccama, I; Siegrist, P; Simonetti, S; Simonetto, F; Sissakian, A N; Sitár, B; Skaali, T B; Smadja, G; Smirnov, N; Smirnova, O G; Smith, G R; Solokov, A; Sosnowski, R; Souza-Santos, D; Spiriti, E; Sponholz, P; Squarcia, S; Stanescu, C; Stapnes, Steinar; Stavitski, I; Stevenson, K; Stichelbaut, F; Stocchi, A; Strauss, J; Strub, R; Stugu, B; Szczekowski, M; Szeptycka, M; Tabarelli de Fatis, T; Tavernet, J P; Thomas, J; Tilquin, A; Timmermans, J; Tkatchev, L G; Todorov, T; Todorova, S; Toet, D Z; Tomaradze, A G; Tomé, B; Tonazzo, A; Tortora, L; Tranströmer, G; Treille, D; Trischuk, W; Tristram, G; Trombini, A; Troncon, C; Tsirou, A L; Turluer, M L; Tyapkin, I A; Tyndel, M; Tzamarias, S; Überschär, B; Ullaland, O; Uvarov, V; Valenti, G; Vallazza, E; Van der Velde, C; van Apeldoorn, G W; van Dam, P; Van Doninck, W K; Van Eldik, J; Vassilopoulos, N; Vegni, G; Ventura, L; Venus, W A; Verbeure, F; Verlato, M; Vertogradov, L S; Vilanova, D; Vincent, P; Vitale, L; Vlasov, E; Vodopyanov, A S; Vrba, V; Wahlen, H; Walck, C; Weierstall, M; Weilhammer, Peter; Weiser, C; Wetherell, Alan M; Wicke, D; Wickens, J H; Wielers, M; Wilkinson, G R; Williams, W S C; Winter, M; Witek, M; Woschnagg, K; Yip, K; Yushchenko, O P; Zach, F; Zaitsev, A; Zalewska-Bak, A; Zalewski, Piotr; Zavrtanik, D; Zevgolatakos, E; Zimin, N I; Zito, M; Zontar, D; Zucchelli, G C; Zumerle, G

1996-01-01

During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of $5.9$ pb$^{-1}$ at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events ($e, \\mu, \\tau$) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits $m_{e^*} > 62.5$ GeV/$c^2$, $m_{\\mu^*} > 62.6$ GeV/$c^2$ and $m_{\\tau^*} > 62.2$ GeV/$c^2$ at 95\\% confidence level were established. For single excited lepton production, upper limits on the ratio $\\lambda/m_{\\ell^*}$ of the coupling of the excited charged lepton to its mass were derived.

Investigation of collisional excitation-transfer processes in a plasma by laser perturbation method

International Nuclear Information System (INIS)

Sakurai, Takeki

1983-01-01

The theoretical background and the experimental method of the laser perturbation method applied to the study of collisional excitation transfer process in plasma are explained. The atomic density at some specified level can be evaluated theoretically. By using the theoretical results and the experimentally obtained data, the total attenuation probability, the collisional transfer probability and natural emission probability were estimated. For the experiments, continuous wave laser (cw) and pulse laser are employed. It is possible by using pulse dye laser to observe the attenuation curve directly, and to bring in resonance to any atomic spectra. At the beginning, the experimental studies were made on He-Ne discharge. The pulse dye laser has been used for the excitation of alkali atoms. The first application of pulse laser to the study of plasma physics was the study on He. The cross section of disalignment has also been studied by the laser perturbation. The alignment of atoms, step and cascade transfer, the confinement of radiation and optogalvanic effect are discussed in this paper. (Kato, T.)

Cross sections for energy transfer in collisions between two excited sodium atoms

International Nuclear Information System (INIS)

Huennekens, J.; Gallagher, A.

1983-01-01

We have measured cross sections, sigma/sub n/L, for the excitation transfer process Na(3P)+Na(3P)→Na(3S)+Na(nL), where nL is the 4D or 5S level. Our results are sigma/sub 4D/ = 23 A 2 +- 35% and sigma/sub 5S/ = 16 A 2 +- 35% at Tapprox.600 K. To obtain these cross sections we have used pulsed excitation and measured the intensities of 4D, 5S, and 3P fluorescence emissions, and the spatial distribution of excited atoms resulting from radiation diffusion, as well as the excited atom density as a function of time. Additionally, we have accounted for (time-dependent) radiation trapping of 3P and nL level radiation and for the resulting anisotropies of these fluorescence emissions. Comparisons of our results with theory have been made, and their relevance to other experiments is discussed

Full counting statistics of a charge pump in the Coulomb blockade regime

Science.gov (United States)

Andreev, A. V.; Mishchenko, E. G.

2001-12-01

We study full charge counting statistics (FCCS) of a charge pump based on a nearly open single electron transistor. The problem is mapped onto an exactly soluble problem of a nonequilibrium g=1/2 Luttinger liquid with an impurity. We obtain an analytic expression for the generating function of the transmitted charge for an arbitrary pumping strength. Although this model contains fractionally charged excitations only integer transmitted charges can be observed. In the weak pumping limit FCCS correspond to a Poissonian transmission of particles with charge e*=e/2 from which all events with odd numbers of transferred particles are excluded.

Vibration transfers to measure the performance of vibration isolated platforms on site using background noise excitation

NARCIS (Netherlands)

Segerink, Franciscus B.; Korterik, Jeroen P.; Offerhaus, Herman L.

2011-01-01

This article demonstrates a quick and easy way of quantifying the performance of a vibration-isolated platform. We measure the vibration transfer from floor to table using background noise excitation from the floor. As no excitation device is needed, our setup only requires two identical sensors (in

Radiative transport and collisional transfer of excitation energy in Cs vapors mixed with Ar or He

International Nuclear Information System (INIS)

Vadla, Cedomil; Horvatic, Vlasta; Niemax, Kay

2003-01-01

This paper is a review (with a few original additions) on the radiative transport and collisional transfer of energy in laser-excited cesium vapors in the presence of argon or helium. Narrow-band excitation of lines with Lorentz, Doppler and Voigt profiles is studied in order to calculate effective rates for pumping of spectral lines with profiles comprising inhomogeneous broadening components. The radiative transport of excitation energy is considered, and a new, simple and robust, but accurate theoretical method for quantitative treatment of radiation trapping in relatively optically thin media is presented. Furthermore, comprehensive lists of experimental values for the excitation energy transfer cross-sections related to thermal collisions in Cs-Ar and Cs-He mixtures are given. Within the collected cross-section data sets, specific regularities with respect to the energy defect, as well as the temperature, are discerned. A particular emphasis is put on the radiative and collisional processes important for the optimization of resonance-fluorescence imaging atomic filters based on Cs-noble gas systems

Efficient Predictions of Excited State for Nanomaterials Using Aces 3 and 4

Science.gov (United States)

2017-12-20

energetics of the various isomers of the materials, obtained from computed heats of reactions that provide the enthalpy and free energy for the species... modeling , excited states, optical properties, structure, stability, activation barriers first principle methods, parallel computing 16. SECURITY...6 Figure 7. Charge- transfer from ethylene to tetrafluro ethylene

Heat transfer from the evaporator outlet to the charge of thermostatic expansion valves

DEFF Research Database (Denmark)

Langmaack, Lasse Nicolai; Knudsen, Hans-Jørgen Høgaard

2006-01-01

outlet with a special mounting strap. The heat transfer is quite complex because it takes place both directly through the contact points between bulb and pipe and indirectly through the mounting strap The TXV has to react to temperature changes at the evaporator outlet. Therefore, the dynamic behavior...... of the valve (and thereby the whole refrigeration system) depends greatly on the heat transfer between the evaporator outlet tube and the charge in the bulb. In this paper a model for the overall heat transfer between the pipe and the charge is presented. Geometrical data and material properties have been kept...... been found to predict the time constant for the temperature development in the bulb within 1-10 %. Furthermore it has been found that app. 20% of the heat transfer takes place trough the mounting strap....

Evidence for charge transfer in Bi-based superconductors studied by positron annihilation

International Nuclear Information System (INIS)

Tang, Z.; Wang, S.J.; Gao, X.H.; Ce, G.C.; Zhao, Z.X.

1993-01-01

We have measured Doppler-broadening annihilation radiation (DBAR) spectra and positron lifetimes in normal and superconducting states for three kinds of Bi-based superconductors: Bi2212, Pb-doped Bi2223, Pb- and F-doped Bi2223. The difference spectra after deconvolution between two states show a sharpening effect with increasing temperature; the F-doped sample has the greatest amplitude in difference spectra but nearly the same positron lifetimes as the Pb-doped sample. The results are interpreted in terms of charge transfer between the Cu-O and Bi-O planes. The role of oxygen defects in charge transfer is discussed. (orig.)

Charge-exchange breakup of the deuteron with the production of two protons and spin structure of the amplitude of the nucleon charge transfer reaction

International Nuclear Information System (INIS)

Glagolev, V.V.; Lyuboshits, V.L.; Lyuboshits, V.V.; Piskunov, N.M.

1999-01-01

In the framework of the impulse approximation, the relation between the effective cross section of the charge-exchange breakup of a fast deuteron d + a → (pp) + b and the effective cross section of the charge transfer process n + a → p + b is discussed. In doing so, the effects of the proton identity (Fermi-statistics) and of the Coulomb and strong interactions of protons in the final state are taken into account. The distribution over relative momenta of the protons, produced in the charge-exchange process d + p → (pp) + n in the forward direction, is investigated. At the transfer momenta being close to zero the effective cross section of the charge-exchange breakup of a fast deuteron, colliding with the proton target, is determined only by the spin-flip part of the amplitude of the charge transfer reaction n + p → p + n at the zero angle. It is shown that the study of the process d + p → (pp) + n in a beam of the polarized (aligned) deuterons allows one, in principle, to separate two spin-dependent terms in the amplitude of the charge transfer reaction n + p → p + n, one of which does not conserve and the other one conserves the projection of the nucleon spin onto the direction of momentum at the transition of the neutron into the proton

Charge transfer in ionic systems

International Nuclear Information System (INIS)

Bacchus-Montabonel, M.C.; Tergiman, Y.S.; Vaeck, N.; Baloitcha, E.; Desouter-Lecomte, M.

2002-01-01

Charge transfer involving multiply charged ions in collision with atomic or molecular targets are determinant processes in controlled thermonuclear fusion research and astrophysical plasma. In such processes, an electron is generally captured in a excited state of the ion, followed by line emission. The observation of line intensities provides important information on the electron temperature, density and spacial distributions in the emitting region of the plasma. From a theoretical point of view, different approaches may be used with regard to the collisional energy range of the process. A semi-classical method is currently used at keV energies, but the description of very low-velocity processes requires a complete quantum mechanical treatment of the dynamics of both electrons and nuclei. The first approach extensively used is the resolution of the stationary close-coupling equations, but we have analyzed recently the efficiency of a time-dependent wave packet method which provides a clear and physical insight into the dynamics of the processes and may be particularly interesting for polyatomic systems since it allows the possibility of developing a fully quantal mechanical treatment for some degrees of freedom, the other ones being treated classically. The keV energy range treatment is presented on two examples pointing out the case of complex ion-atom collision systems, as well as the differences between ion-atom and ion-molecule mechanisms. In connection with translation energy spectroscopy experiments of McLaughlin et al in the 4-28 keV impact energy range, we present a complete ab-initio theoretical approach of the N 4+ (2s) 2 S + He system taking into account both single and double electron capture channels. This is an extremely complex collisional system which involves numerous channels with short range interactions and a very intricate interaction region may be observed for interatomic distances around R = 3.5 a.u.. In agreement with experimental data, the

Low-Energy Charge Transfer in Multiply-Charged Ion-Atom Collisions Studied with the Combined SCVB-MOCC Approach

OpenAIRE

Cooper, D. L.; Stancil, P. C.; Turner, A. R.; Wang, J. G.; Clarke, N. J.; Zygelman, B.

2002-01-01

A survey of theoretical studies of charge transfer involving collisions of multiply-charged ions with atomic neutrals (H and He) is presented. The calculations utilized the quantum-mechanical molecular-orbital close-coupling (MOCC) approach where the requisite potential curves and coupling matrix elements have been obtained with the spin-coupled valence bond (SCVB) method. Comparison is made among various collision partners, for equicharged systems, where it is illustrated that even for total...

Possible charge analogues of spin transfer torques in bulk superconductors

Science.gov (United States)

Garate, Ion

2014-03-01

Spin transfer torques (STT) occur when electric currents travel through inhomogeneously magnetized systems and are important for the motion of magnetic textures such as domain walls. Since superconductors are easy-plane ferromagnets in particle-hole (charge) space, it is natural to ask whether any charge duals of STT phenomena exist therein. We find that the superconducting analogue of the adiabatic STT vanishes in a bulk superconductor with a momentum-independent order parameter, while the superconducting counterpart of the nonadiabatic STT does not vanish. This nonvanishing superconducting torque is induced by heat (rather than charge) currents and acts on the charge (rather than spin) degree of freedom. It can become significant in the vicinity of the superconducting transition temperature, where it generates a net quasiparticle charge and alters the dispersion and linewidth of low-frequency collective modes. This work has been financially supported by Canada's NSERC.

Charge-transfer complexes and their role in exciplex emission and near-infrared photovoltaics.

Science.gov (United States)

Ng, Tsz-Wai; Lo, Ming-Fai; Fung, Man-Keung; Zhang, Wen-Jun; Lee, Chun-Sing

2014-08-20

Charge transfer and interactions at organic heterojunctions (OHJs) are known to have critical influences on various properties of organic electronic devices. In this Research News article, a short review is given from the electronic viewpoint on how the local molecular interactions and interfacial energetics at P/N OHJs contribute to the recombination/dissociation of electron-hole pairs. Very often, the P-type materials donate electrons to the N-type materials, giving rise to charge-transfer complexes (CTCs) with a P(δ+) -N(δ-) configuration. A recently observed opposite charge-transfer direction in OHJs is also discussed (i.e., N-type material donates electrons to P-type material to form P(δ-) -N(δ+) ). Recent studies on the electronic structures of CTC-forming material pairs are also summarized. The formation of P(δ-) -N(δ+) -type CTCs and their correlations with exciplex emission are examined. Furthermore, the potential applications of CTCs in NIR photovoltaic devices are reviewed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal spike analysis of highly charged ion tracks

International Nuclear Information System (INIS)

Karlušić, M.; Jakšić, M.

2012-01-01

The irradiation of material using swift heavy ion or highly charged ion causes excitation of the electron subsystem at nanometer scale along the ion trajectory. According to the thermal spike model, energy deposited into the electron subsystem leads to temperature increase due to electron–phonon coupling. If ion-induced excitation is sufficiently intensive, then melting of the material can occur, and permanent damage (i.e., ion track) can be formed upon rapid cooling. We present an extension of the analytical thermal spike model of Szenes for the analysis of surface ion track produced after the impact of highly charged ion. By applying the model to existing experimental data, more than 60% of the potential energy of the highly charged ion was shown to be retained in the material during the impact and transformed into the energy of the thermal spike. This value is much higher than 20–40% of the transferred energy into the thermal spike by swift heavy ion. Thresholds for formation of highly charged ion track in different materials show uniform behavior depending only on few material parameters.

Deflection effects and charge transfer in inner-shell vacancy production

International Nuclear Information System (INIS)

Swafford, G.L.

1978-01-01

A method used in the calculation of inner shell ionization in asymmetric ion-atom collisions is extended to include projectile deflection effects and charge transfer to the projectile. Work is done in an independent electron model (Hartree-Fock) for the target, and the interaction is treated with the projectile as a time-dependent perturbation of the system. It is shown tht the time-dependent problem can be solved for the projectile moving along the classical hyperbolic trajectory that results from the nuclear repulsion. The method is very efficient due to the utilization the target-centered expansion of the system wave function. This means that all the required matrix elements can be pretabulated and are then available for use at all impact parameters. The method is first applied to the impact-parameter dependence of K-shell ionization by protons incident upon copper in the energy range 0.5 to 2 MeV. Excellent agreement with the experiments of Andersen et al., is found at the lower energy. Less satisfactory agreement is obtained in the higher energy region. Next the projectile is considered to move in a straight line path with constant velocity, and extend the method to include charge transfer between the target inner shells and the K-shell of the projectile. A critical feature of the results is the recognition of the importance of target continuum states of energy approximately equal to the kinetic energy (in the target frame) of the electron on the projectile. An approach is developed to properly include such resonance states in our pseudostate calculation. Selected numerical results are presented to illustrate the method and to demonstrate the projectile energy and nuclear charge dependence of the charge transfer cross sections

Impact of nuclear lattice relaxation on the excitation energy transfer along a chain of pi-conjugated molecules

NARCIS (Netherlands)

Schmid, S.A.; Abbel, R.J.; Schenning, A.P.H.J.; Meijer, E.W.; Herz, L.M.

2010-01-01

We have investigated the extent to which delocalization of the ground-state and excited-state wave functions of a p-conjugated molecule affects the excitation energy transfer (EET) between such molecules. Using femtosecond photoluminescence spectroscopy, we experimentally monitored the EET along

A strong steric hindrance effect on ground state, excited state, and charge separated state properties of a CuI-diimine complex captured by X-ray transient absorption spectroscopy

DEFF Research Database (Denmark)

Huang, J.; Mara, M.W.; Stickrath, A.B.

2014-01-01

of phenanthroline. The structural dynamics of the photoinduced charge transfer process in the [CuI(dppS)2]+/TiO2 hybrid is also investigated, which suggests a more restricted environment for the complex upon binding to TiO2 NPs. Moreover, the Cu-N bond length of the oxidized state of [CuI(dppS)2]+ after electron...... dynamics and structures as well as those of the charge separated state resulting from the interfacial electron injection from the MLCT state to TiO2 nanoparticles (NPs). The OTA results show the absence of the sub-picosecond component previously assigned as the time constant for flattening, while the two...... injection to TiO2 NPs shortens by 0.05 Å compared to that in the ground state. The interpretation of these observed structural changes associated with excited and charge separated states will be discussed. These results not only set an example for applying XTA in capturing the intermediate structure...

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

KAUST Repository

Filatov, Mikhail A.; Karuthedath, Safakath; Polestshuk, Pavel M.; Savoie, Huguette; Flanagan, Keith J.; Sy, Cindy; Sitte, Elisabeth; Telitchko, Maxime; Laquai, Fré dé ric; Boyle, Ross W.; Senge, Mathias O.

2017-01-01

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

KAUST Repository

Filatov, Mikhail A.

2017-04-14

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Effect of Molecular Packing and Charge Delocalization on the Nonradiative Recombination of Charge-Transfer States in Organic Solar Cells

KAUST Repository

Chen, Xiankai

2016-09-05

In organic solar cells, a major source of energy loss is attributed to nonradiative recombination from the interfacial charge transfer states to the ground state. By taking pentacene–C60 complexes as model donor–acceptor systems, a comprehensive theoretical understanding of how molecular packing and charge delocalization impact these nonradiative recombination rates at donor–acceptor interfaces is provided.

Ultrafast dynamics of hydrophilic carbonyl carotenoids - Relation between structure and excited-state properties in polar solvents

Czech Academy of Sciences Publication Activity Database

Chábera, P.; Fuciman, M.; Naqvi, K.R.; Polívka, Tomáš

2010-01-01

Roč. 373, 1-2 (2010), s. 56-64 ISSN 0301-0104 Institutional research plan: CEZ:AV0Z50510513 Keywords : hydrophilic carotenoids * excited-state dynamics * charge-transfer state Subject RIV: BO - Biophysics Impact factor: 2.017, year: 2010

Excited-state intramolecular proton transfer and photoswitching in hydroxyphenyl-imidazopyridine derivatives: A theoretical study

Science.gov (United States)

Omidyan, Reza; Iravani, Maryam

2016-11-01

The MP2/CC2 and CASSCF theoretical approaches have been employed to determine the excited state proton transfer and photophysical nature of the four organic compounds, having the main frame of hydroxyphenyl-imidzaopyridine (HPIP). The nitrogen insertion effect, in addition to amine (-NH2) substitution has been investigated extensively by following the transition energies and deactivation pathways of resulted HPIP derivatives. It has been predicted that the excited state intramolecular proton transfer with or without small barrier is the most important feature of these compounds. Also, for all of the considered HPIP derivatives, a conical intersection (CI) between ground and the S1 excited state has been predicted. The strong non-adiabatic coupling in the CI (S1/S0), drives the system back to the ground state in which the proton may either return to the phenoxy unit and thus close the photocycle, or the system can continue the twisting motion that results in formation of a γ-photochromic species. This latter species can be responsible for photochromism of HPIP derivative systems.

Improving radiation hardness in space-based Charge-Coupled Devices through the narrowing of the charge transfer channel