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Sample records for excited state charge

  1. Charge-displacement analysis for excited states

    SciTech Connect

    Ronca, Enrico Tarantelli, Francesco; Pastore, Mariachiara Belpassi, Leonardo; De Angelis, Filippo; Angeli, Celestino; Cimiraglia, Renzo

    2014-02-07

    We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.

  2. Charge-displacement analysis for excited states

    NASA Astrophysics Data System (ADS)

    Ronca, Enrico; Pastore, Mariachiara; Belpassi, Leonardo; De Angelis, Filippo; Angeli, Celestino; Cimiraglia, Renzo; Tarantelli, Francesco

    2014-02-01

    We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.

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

    SciTech Connect

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

    2014-04-28

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

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

    PubMed

    Theophilou, Iris; Tassi, M; Thanos, S

    2014-04-28

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations. PMID:24784248

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

    NASA Astrophysics Data System (ADS)

    Bohr, Henrik G.; Malik, F. Bary

    2013-11-01

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

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

    SciTech Connect

    Tolstikhina, Inga Yu.; Kato, Daiji

    2010-09-15

    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.

  7. Observation of slow charge redistribution preceding excited-state proton transfer

    SciTech Connect

    Spry, D. B.; Fayer, M. D.

    2007-11-28

    The photoacid 8-hydroxy-N,N,N{sup '},N{sup '},N{sup '},N{sup '}-hexamethylpyrene-1,3,6-trisulfonamide (HPTA) and related compounds are used to investigate the steps involved in excited-state deprotonation in polar solvents using pump-probe spectroscopy and time correlated single photon counting fluorescence spectroscopy. The dynamics show a clear two-step process leading to excited-state proton transfer. The first step after electronic excitation is charge redistribution occurring on a tens of picoseconds time scale followed by proton transfer on a nanosecond time scale. The three states observed in the experiments (initial excited state, charge redistributed state, and proton transfer state) are recognized by distinct features in the time dependence of the pump-probe spectrum and fluorescence spectra. In the charge redistributed state, charge density has transferred from the hydroxyl oxygen to the pyrene ring, but the OH sigma bond is still intact. The experiments indicate that the charge redistribution step is controlled by a specific hydrogen bond donation from HPTA to the accepting base molecule. The second step is the full deprotonation of the photoacid. The full deprotonation is clearly marked by the growth of stimulated emission spectral band in the pump-probe spectrum that is identical to the fluorescence spectrum of the anion.

  8. Probing excited state charge transfer dynamics in a heteroleptic ruthenium complex.

    PubMed

    Ghosh, Rajib; Palit, Dipak K

    2014-01-01

    Dynamics of metal to ligand charge transfer in the excited states of ruthenium polypyridyl complexes, which have shown promise as materials for artificial solar energy harvesting, has been of immense interest recently. Mixed ligand complexes are especially important for broader absorption in the visible region. Dynamics of ultrafast vibrational energy relaxation and inter-ligand charge transfer processes in the excited states of a heteroleptic ruthenium complex, [Ru(bpy)2(pap)](ClO4)2 (where bpy is 2,2'-bipyridine and pap is 2-(phenylazo)pyridine) have been investigated using femtosecond to nanosecond time-resolved transient absorption spectroscopic techniques. A good agreement between the TA spectrum of the lowest excited (3)MLCT state of [Ru(bpy)2(pap)](ClO4)2 complex and the anion radical spectrum of the pap ligand, which has been generated using the pulse radiolysis technique, confirmed the charge localization at the pap ligand. While the lifetime of the inter-ligand charge transfer from the bpy to the pap ligand in the (3)MLCT state is about 2.5 ps, vibrational cooling of the pap-localized(3)MLCT state occurs over a much longer time scale with a lifetime of about 35 ps. Ultrafast charge localization dynamics observed here may have important consequences in artificial solar energy harvesting systems, which employ heteroleptic ruthenium complexes. PMID:24247908

  9. Charge state dynamics of the nitrogen vacancy center in diamond under 1064-nm laser excitation

    NASA Astrophysics Data System (ADS)

    Ji, Peng; Dutt, M. V. Gurudev

    2016-07-01

    The photophysics and charge state dynamics of the nitrogen vacancy (NV) center in diamond has been extensively investigated, but is still not fully understood. In contrast to previous work, we find that NV0 converts to NV- under excitation with low power near-infrared (1064-nm) light, resulting in increased photoluminescence from the NV- state. We used a combination of spectral and time-resolved photoluminescence experiments and rate-equation modeling to conclude that NV0 converts to NV- via absorption of 1064-nm photons from the valence band of diamond. We report fast quenching and recovery of the photoluminescence from both charge states of the NV center under low power 1064-nm laser excitation, which has not been previously observed. We also find, using optically detected magnetic resonance experiments, that the charge transfer process mediated by the 1064-nm laser is spin dependent.

  10. The excited spin-triplet state of a charged exciton in quantum dots.

    PubMed

    Molas, M R; Nicolet, A A L; Piętka, B; Babiński, A; Potemski, M

    2016-09-14

    We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T  =  4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes  +  electron excitonic complex. PMID:27391126

  11. The excited spin-triplet state of a charged exciton in quantum dots

    NASA Astrophysics Data System (ADS)

    Molas, M. R.; Nicolet, A. A. L.; Piętka, B.; Babiński, A.; Potemski, M.

    2016-09-01

    We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T  =  4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes  +  electron excitonic complex.

  12. Nature and location of excited charge-transfer states in the porphine-magnesium porphine dimer

    NASA Astrophysics Data System (ADS)

    Petke, J. D.; Maggiora, G. M.

    1983-05-01

    The ground and excited states of a cofacial porphine-magnesium porphine dimer with a ring separation of 5.35 Å are investigated by ab initio configuration interaction calculations, using a floating gaussian basis. A pair of charge-transfer states are found ≈23000 cm -1 above the ground state, but are lowered by ≈7400 cm -1 upon coordination of the Mg atom with chloride ion.

  13. Excited states and valley effects in a negatively charged impurity in a silicon FinFET.

    SciTech Connect

    Hollenberg, Lloyd; Klimeck, Gerhard; Carroll, Malcolm S.; Rahman, Rajib; Muller, Richard Partain; Rogge, Sven; Verduijn, Arjan; Lansbergen, Gabriel

    2010-07-01

    The observation and characterization of a single atom system in silicon is a significant landmark in half a century of device miniaturization, and presents an important new laboratory for fundamental quantum and atomic physics. We compare with multi-million atom tight binding (TB) calculations the measurements of the spectrum of a single two-electron (2e) atom system in silicon - a negatively charged (D-) gated Arsenic donor in a FinFET. The TB method captures accurate single electron eigenstates of the device taking into account device geometry, donor potentials, applied fields, interfaces, and the full host bandstructure. In a previous work, the depths and fields of As donors in six device samples were established through excited state spectroscopy of the D0 electron and comparison with TB calculations. Using self-consistent field (SCF) TB, we computed the charging energies of the D- electron for the same six device samples, and found good agreement with the measurements. Although a bulk donor has only a bound singlet ground state and a charging energy of about 40 meV, calculations show that a gated donor near an interface can have a reduced charging energy and bound excited states in the D- spectrum. Measurements indeed reveal reduced charging energies and bound 2e excited states, at least one of which is a triplet. The calculations also show the influence of the host valley physics in the two-electron spectrum of the donor.

  14. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    SciTech Connect

    Van Tassle, Aaron Justin

    2006-09-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  15. Is dipole moment a valid descriptor of excited state's charge-transfer character?

    PubMed

    Petelenz, Piotr; Pac, Barbara

    2013-11-20

    In the ongoing discussion on excited states of the pentacene crystal, dipole moment values have been recently invoked to gauge the CT admixture to excited states of Frenkel parentage in a model cluster. In the present paper, a simple dimer model is used to show that, in general, the dipole moment is not a valid measure of the CT contribution. This finding eliminates some apparent disagreement between the computational results published by different research groups. The implications of our results and other related aspects of cluster-type quantum chemistry calculations are discussed in the context of the standing literature dispute concerning the mechanism of singlet fission in the pentacene crystal, notably the role of charge transfer contributions vs the involvement of an excimer-like doubly excited intermediate (D state). PMID:24138489

  16. Charge state dynamics of the nitrogen vacancy center in diamond under near-infrared excitation

    NASA Astrophysics Data System (ADS)

    Ji, Peng; Dutt, M. V. Gurudev

    2016-05-01

    The negatively charged NV defect center (NV-) in diamond has become prominent for applications in quantum information, nanoscale magnetic and electric field sensing, and fluorescent biological markers. Switching between NV- and neutral charge states (NV0) have been extensively studied and modeled using exciting laser wavelengths that are shorter than the NV- zero-phonon line (ZPL), and typically result in decreased fluorescence from the NV- state. In this work, we report on the experimental observation that NV0 converts to NV- under excitation with near-infrared (1064 nm) light, resulting in increased fluorescence from the NV- state. We have observed this effect in both ensembles of NVs in bulk diamond, and in diamond nanocrystals, and find that it is robust both at room and low temperature. We carried out microwave and two-color excitation combined with spectral and time-resolved experimental studies. We used rate-equation modeling and find evidence for competition between one-photon and two-photon processes for hole and electron ionization. This finding may help elucidate the study of the NV energy level structure, and impact recently emerging research in single-shot measurement of the NV- spin state via spin-to-charge conversion.

  17. Excited-state charging energies in quantum dots investigated by terahertz photocurrent spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Shibata, K.; Nagai, N.; Ndebeka-Bandou, C.; Bastard, G.; Hirakawa, K.

    2016-06-01

    We have investigated the excited-state (ES) charging energies in quantum dots (QDs) by measuring a terahertz (THz)-induced photocurrent in a single-electron transistor (SET) geometry that contains a single InAs QD between metal nanogap electrodes. A photocurrent is produced in the QD SETs through THz intersublevel transitions and the subsequent resonant tunneling. We have found that the photocurrent exhibits stepwise change even within one Coulomb blockaded region as the electrochemical potential in the QD is swept by the gate voltage. From the threshold for the photocurrent generation, we have determined the charging energies for adding an electron in the photoexcited state in the QD. Furthermore, the charging energies for the ESs with different electron configurations are clearly resolved. The present THz photocurrent measurements are essentially dynamical experiments and allow us to analyze electronic properties in off-equilibrium states in the QD.

  18. Observation of excited state charge transfer with fs/ps-CARS

    SciTech Connect

    Blom, Alex Jason

    2009-01-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  19. Excited state and charge dynamics of hybrid organic/inorganic heterojunctions. I. Theory

    NASA Astrophysics Data System (ADS)

    Renshaw, C. Kyle; Forrest, Stephen R.

    2014-07-01

    The different cohesive forces that bond organic (i.e. excitonic) and inorganic semiconductors lead to widely disparate dielectric constants, charge mobilities, and other fundamental optoelectronic properties that make junctions between these materials interesting for numerous practical applications. Yet, there are no detailed theories addressing charge and energy transport across interfaces between these hybrid systems. Here, we develop a comprehensive physical model describing charge transport and photocurrent generation based on first-principles charge and excited state dynamics at the organic/inorganic heterojunction. We consider interfaces that are trap-free, as well as those with an exponential distribution of trap states. We find that the hybrid charge-transfer state resulting from photon absorption near the junction that subsequently migrates to the heterointerface is often unstable at room temperature, leading to its rapid dissociation into free charges that are collected at the device contacts. In the companion Paper II [A. Panda et al., Phys. Rev. B 90, 045303 (2014), 10.1103/PhysRevB.90.045303], we apply our theories to understanding the optical and electronic properties of archetype organic/inorganic heterojunction diodes. Our analysis provides insights for developing high performance optoelectronic devices whose properties are otherwise inaccessible to either conventional excitonic or inorganic semiconductor junctions.

  20. Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

    NASA Technical Reports Server (NTRS)

    Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

    2001-01-01

    The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

  1. Tracking the charge and spin dynamics of electronic excited states in inorganic complexes

    NASA Astrophysics Data System (ADS)

    Gaffney, Kelly

    2015-03-01

    Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications. These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes. Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2'-bipyridine)N]2 N - 4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations. Work supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

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

    PubMed

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

    2016-02-26

    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. PMID:26820442

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Radiative charge-transfer lifetime of the excited state of (NaCa){sup +}

    SciTech Connect

    Makarov, Oleg P.; Cote, R.; Michels, H.; Smith, W.W.

    2003-04-01

    New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom-ion trap under high-vacuum conditions. We study the collisional cooling of laser precooled Ca{sup +} ions by ultracold Na atoms. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A {sup 1}{sigma}{sup +} state of the (NaCa){sup +} molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using complete active space self-consistent field and Moeller-Plesset second-order perturbation theory with an extended Gaussian basis, 6-311+G (3df). The semiclassical charge-transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition, we also present elastic collision cross sections and the spin-exchange cross section. The rate coefficient for charge transfer was found to be 2.3x10{sup -16} cm{sup 3}/sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1x10{sup -8} cm{sup 3}/sec and 2.3x10{sup -9} cm{sup 3}/sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms is favorable with the respect to low loss of calcium ions due to the charge transfer.

  5. Generation of excited coherent states for a charged particle in a uniform magnetic field

    SciTech Connect

    Mojaveri, B.; Dehghani, A. E-mail: alireza.dehghani@gmail.com

    2015-04-15

    We introduce excited coherent states, |β,α;nгЂ‰≔a{sup †n}|β,αгЂ‰, where n is an integer and states |β,αгЂ‰ denote the coherent states of a charged particle in a uniform magnetic field. States |β,αгЂ‰ minimize the Schrödinger-Robertson uncertainty relation while having the nonclassical properties. It has been shown that the resolution of identity condition is realized with respect to an appropriate measure on the complex plane. Some of the nonclassical features such as sub-Poissonian statistics and quadrature squeezing of these states are investigated. Our results are compared with similar Agarwal’s type photon added coherent states (PACSs) and it is shown that, while photon-counting statistics of |β,α,nгЂ‰ are the same as PACSs, their squeezing properties are different. It is also shown that for large values of |β|, while they are squeezed, they minimize the uncertainty condition. Additionally, it has been demonstrated that by changing the magnitude of the external magnetic field, B{sub ext}, the squeezing effect is transferred from one component to another. Finally, a new scheme is proposed to generate states |β,α;nгЂ‰ in cavities. .

  6. Exploring excited states of Pt(II) diimine catecholates for photoinduced charge separation.

    PubMed

    Scattergood, Paul A; Jesus, Patricia; Adams, Harry; Delor, Milan; Sazanovich, Igor V; Burrows, Hugh D; Serpa, Carlos; Weinstein, Julia A

    2015-07-14

    The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(II) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(II) complex. Pt(II) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(II) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-di(t)Bu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)((t)Bu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02–0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COO(I)Pr)2bpy)(3,5-di-(t)Bu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  8. Magnetospectroscopy of excited states in charge-tunable GaAs/AlGaAs [111] quantum dots

    NASA Astrophysics Data System (ADS)

    Durnev, M. V.; Vidal, M.; Bouet, L.; Amand, T.; Glazov, M. M.; Ivchenko, E. L.; Zhou, P.; Wang, G.; Mano, T.; Ha, N.; Kuroda, T.; Marie, X.; Sakoda, K.; Urbaszek, B.

    2016-06-01

    We present a combined experimental and theoretical study of highly charged and excited electron-hole complexes in strain-free (111) GaAs/AlGaAs quantum dots grown by droplet epitaxy. We address the complexes with one of the charge carriers residing in the excited state, namely, the "hot" trions X-* and X+*, and the doubly negatively charged exciton X2 -. Our magnetophotoluminescence experiments performed on single quantum dots in the Faraday geometry uncover characteristic emission patterns for each excited electron-hole complex, which are very different from the photoluminescence spectra observed in (001)-grown quantum dots. We present a detailed theory of the fine structure and magnetophotoluminescence spectra of X-*,X+*, and X2 - complexes, governed by the interplay between the electron-hole Coulomb exchange interaction and the heavy-hole mixing, characteristic for these quantum dots with a trigonal symmetry. Comparison between experiment and theory allows for precise charge state identification, as well as extraction of electron-hole exchange interaction constants and g factors for the charge carriers occupying excited states.

  9. Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: Temperature dependence

    SciTech Connect

    Pradhan, Tuhin; Gazi, Harun Al Rasid; Biswas, Ranjit

    2009-08-07

    Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO{sub 4}) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-{Delta}G{sub r}) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO{sub 4} concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-{Delta}G{sub r}), the former in ethanol and ACN increases only linearly with the increase in driving force (-{Delta}G{sub r}). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.

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

    SciTech Connect

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

    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.

  11. A donor-acceptor triptycene-coumarin hybrid dye featuring a charge separated excited state and AIE properties.

    PubMed

    Qian, Rui; Tong, Hongjuan; Huang, Cui; Li, Junhao; Tang, Yun; Wang, Rui; Lou, Kaiyan; Wang, Wei

    2016-06-14

    A triptycene-coumarin hybrid dye DCT-1 with a 1,4-dimethoxybenzene group as the electron donor and a coumarin fluorophore as the acceptor on the separated fins of a triptycene was synthesized. DCT-1 features a charge separated excited state with emissions sensitive to solvent polarities. Moreover, DCT-1 also exhibits aggregation-induced emission properties in water with excellent photostability and pH-stability for potential cell imaging applications. PMID:27186970

  12. Excited state and charge dynamics of hybrid organic/inorganic heterojunctions. II. Experiment

    NASA Astrophysics Data System (ADS)

    Panda, Anurag; Renshaw, C. Kyle; Oskooi, Ardavan; Lee, Kyusang; Forrest, Stephen R.

    2014-07-01

    In our companion paper (Paper I) [C. K. Renshaw and S. R. Forrest, Phys. Rev. B 90, 045302 (2014), 10.1103/PhysRevB.90.045302], we developed a model for charge transport and photogeneration at hybrid organic/inorganic semiconductor heterojunctions (OI-HJs). Here we apply the model to two planar bilayer hybrid photovoltaic devices: the first using the wide-band gap n-TiO2 in combination with the hole transporting tetraphenyl-dibenzoperiflanthene (DBP), and the second based on the moderate-band gap n-InP and the hole transporting pentacene (PEN). We measure the external quantum efficiency (EQE) and current density vs voltage (J-V) characteristics of both devices as functions of temperature. The EQE spectra for both TiO2/DBP and InP/PEN provide convincing evidence that Frenkel states generated in the organic form hybrid charge transfer excitons (HCTEs) at the OI-HJ that are subsequently dissociated into free charges, and then collected at the opposing electrodes. The dissociation efficiency is found to be strongly influenced by the presence of surface states, particularly in the InP/PEN device. We further develop the J-V model from Paper I to include an analytical expression for space-charge effects in the organic at high currents. Model fits to the J-V data suggest that the temperature-dependent hole mobilities in both DBP and PEN result in increasing space-charge effects at low temperatures. Furthermore, we find that the J-V characteristics of the TiO2/DBP device both in the dark and under illumination are governed by interface recombination. In contrast, the dark current in the InP/PEN device is governed by injection over the OI-HJ barrier, whereas the photocurrent is dominated by interface recombination. This work elucidates the role of the HCTE state in photogeneration, and the applicability of our model to a range of important optoelectronic devices.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Excited state structural evolution during charge-transfer reactions in betaine-30.

    PubMed

    Ruchira Silva, W; Frontiera, Renee R

    2016-07-27

    Ultrafast photo-induced charge-transfer reactions are fundamental to a number of photovoltaic and photocatalytic devices, yet the multidimensional nature of the reaction coordinate makes these processes difficult to model theoretically. Here we use femtosecond stimulated Raman spectroscopy to probe experimentally the structural changes occurring following photoexcitation in betaine-30, a canonical intramolecular charge-transfer complex. We observe changes in vibrational mode frequencies and amplitudes on the femtosecond timescale, which for some modes results in frequency shifts of over 20 cm(-1) during the first 200 fs following photoexcitation. These rapid mode-specific frequency changes track the planarization of the molecule on the 400 ± 100 fs timescale. Oscillatory amplitude modulations of the observed high frequency Raman modes indicate coupling between specific high frequency and low frequency vibrational motions, which we quantify for 6 low frequency modes and 4 high frequency modes. Analysis of the mode-specific kinetics is suggestive of the existence of a newly discovered electronic state involved in a relaxation pathway, which may be a low-lying triplet state. These results directly track the multiple nuclear coordinates involved in betaine-30's reactive pathway, and should be of use in rationally designing molecular systems with rapid electron transfer processes. PMID:26725657

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

    SciTech Connect

    Bobkov, K K; Rybaltovsky, A A; Vel'miskin, V V; Likhachev, M E; Bubnov, M M; Dianov, E M; Umnikov, A A; Gur'yanov, A N; Vechkanov, N N; Shestakova, I A

    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)

  16. Density functional investigation of the electronic structure and charge transfer excited states of a multichromophoric antenna

    NASA Astrophysics Data System (ADS)

    Basurto, Luis; Zope, Rajendra R.; Baruah, Tunna

    2016-05-01

    We report an electronic structure study of a multichromophoric molecular complex containing two of each borondipyrromethane dye, Zn-tetraphenyl-porphyrin, bisphenyl anthracene and a fullerene. The snowflake shaped molecule behaves like an antenna capturing photon at different frequencies and transferring the photon energy to the porphyrin where electron transfer occurs from the porphyrin to the fullerene. The study is performed within density functional formalism using large polarized Guassian basis sets (12,478 basis functions in total). The energies of the HOMO and LUMO states in the complex, as adjudged by the ionization potential and the electron affinity values, show significant differences with respect to their values in participating subunits in isolation. These differences are also larger than the variations of the ionization potential and electron affinity values observed in non-bonded C60-ZnTPP complexes in co-facial arrangement or end-on orientations. An understanding of the origin of these differences is obtained by a systematic study of the effect of structural strain, the presence of ligands, the effect of orbital delocalization on the ionization energy and the electron affinity. Finally, a few lowest charge transfer energies involving electronic transitions from the porphyrin component to the fullerene subunit of the complex are predicted.

  17. Solvent sensitive intramolecular charge transfer dynamics in the excited states of 4-N,N-dimethylamino-4'-nitrobiphenyl.

    PubMed

    Ghosh, Rajib; Nandi, Amitabha; Palit, Dipak K

    2016-03-21

    Organic molecules substituted with the nitro group show efficient nonlinear optical (NLO) properties, which are a consequence of the strong intramolecular charge transfer (ICT) character of the molecules because of the strong electron withdrawing nature of the nitro group and rapid responsiveness because of highly movable π-electrons. Dynamics of the ICT process in the excited states of a push-pull biphenyl derivative, namely, 4-N,N-dimethylamino-4'-nitrobiphenyl (DNBP), an efficient NLO material, has been investigated using ultrafast transient absorption spectroscopy. The experimental results have been corroborated with DFT and TDDFT calculations. In solvents of large polarity, e.g. acetonitrile, the ultrafast ICT process of DNBP is associated with the barrierless twisting of the N,N-dimethylaniline (DMA) group with respect to the nitrobenzene moiety to populate the twisted ICT (or TICT) state, and the rate of this process is solely governed by the viscosity of the medium. In solvents of moderate polarity, e.g. ethyl acetate, the rate of the twisting process is significantly slowed down and the LE and TICT states remain in equilibrium because of a low energy barrier for interconversion between these two states. By further lowering the polarity of the solvent, e.g. in dioxane, the twisting process is completely retarded. In nonpolar solvents, e.g. cyclohexane, a reverse twisting motion towards the planar geometry (i.e. the PICT process) has been evident in the excited state dynamics. In this solvent, the S1 state undergoes an ultrafast intersystem crossing to the triplet state because of its close proximity with the T2 state. PMID:26907751

  18. Shell-model description of the charge form factor and the first excited state in /sup 4/He

    SciTech Connect

    Bevelacqua, J.J.

    1982-09-01

    A /sup 4/He shell-model formalism, including two- and three-body forces, is used to calculate ground and first excited state properties. Inclusion of the three-body force improves the calculated ground state rms radius, ground state form factor, and position of the /sup 4/He first excited state.

  19. Influence of variations in the chromophoric ligand on the properties of metal-to-ligand charge-transfer excited states

    SciTech Connect

    Johnson, S.R.; Westmoreland, T.D.; Caspar, J.V.; Barqawi, K.R.; Meyer, T.J.

    1988-09-07

    The effects of variations in the chromophoric ligand on the properties of the metal-to-ligand charge-transfer (MLCT) excited states in the series (Os(PP)/sub 3/)/sup 2+/, ((PP)/sub 2/Os(py)/sub 2/)/sup 2+/, and ((PP)/sub 2/Os(LL))/sup 2+/ (PP = 2,2'-bipyridine, 1,10-phenanthroline, or a substituted derivative; py = pyridine; LL = das, dppm, dppb, dppene) have been investigated. From a series of electrochemical and photophysical measurements it has been determined that (1) substituent variations in the chromophoric ligands have a relatively minor effect on the d/pi/(Os) levels as evidenced by variations in E/sub 1/2/ values for the ground-state Os(III/II) couples, (2) linear correlations exist between metal-to-ligand charge-transfer (MLCT) absorption or emission band energies and the difference in metal-based oxidation and ligand-based reduction potentials, E/sub 1/2/(Os/sup III/II/) - E/sub 1/2/(PP/sup 0//minus//), and (3) a linear relationship between 1n k/sub nr/ and the emission energy, E/sub em/, exists, consistent with the energy gap law. It appears that for nonradiative decay both the pattern of acceptor vibrations and the vibrationally induced electronic coupling term remain relatively constant as the chromophoric ligand is varied. 26 references, 4 figures, 2 tables.

  20. Intramolecular Charge-Transfer Excited-State Processes in 4-(N,N-Dimethylamino)benzonitrile: The Role of Twisting and the πσ* State

    PubMed Central

    2015-01-01

    The structural processes leading to dual fluorescence of 4-(dimethylamino)benzonitrile in the gas phase and in acetonitrile solvent were investigated using a combination of multireference configuration interaction (MRCI) and the second-order algebraic diagrammatic construction (ADC(2)) methods. Solvent effects were included on the basis of the conductor-like screening model. The MRCI method was used for computing the nonadiabatic interaction between the two lowest excited ππ* states (S2(La, CT) and S1(Lb, LE)) and the corresponding minimum on the crossing seam (MXS) whereas the ADC(2) calculations were dedicated to assessing the role of the πσ* state. The MXS structure was found to have a twisting angle of ∼50°. The branching space does not contain the twisting motion of the dimethylamino group and thus is not directly involved in the deactivation process from S2 to S1. Polar solvent effects are not found to have a significant influence on this situation. Applying Cs symmetry restrictions, the ADC(2) calculations show that CCN bending leads to a strong stabilization and to significant charge transfer (CT). Nevertheless, this structure is not a minimum but converts to the local excitation (LE) structure on releasing the symmetry constraint. These findings suggest that the main role in the dynamics is played by the nonadiabatic interaction of the LE and CT states and that the main source for the dual fluorescence is the twisted internal charge-transfer state in addition to the LE state. PMID:25989536

  1. Light-induced excited spin state trapping and charge transfer in trigonal bipyramidal cyanide-bridged complexes.

    PubMed

    Funck, Kristen E; Prosvirin, Andrey V; Mathonière, Corine; Clérac, Rodolphe; Dunbar, Kim R

    2011-04-01

    Three members of the family of trigonal bipyramidal (TBP) complexes of general formula [M(tmphen)(2)](3)[M'(CN)(6)](2) (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) or [M(3)M'(2)], which are known to exhibit thermally induced spin crossover and charge transfer, have been investigated for optical and photomagnetic properties. The light-induced excited spin-state trapping (LIESST) effect found in classical spin crossover compounds, such as [Fe(phen)(2)(NCS)(2)], was explored for the [Fe(3)Fe(2)] and [Fe(3)Co(2)] compounds. Similarly, inspired by the light-induced charge-transfer properties of K(0.2)Co(1.4)[Fe(CN)(6)]·6.9H(2)O and related Prussian blue materials, the possibility of photo-induced magnetic changes was investigated for the [Co(3)Fe(2)] TBP complex. Optical reflectivity and magnetic susceptibility measurements were used to evaluate the photoactivity of these compounds. A comparison of these data before and after light irradiation demonstrates that (i) the spin crossover of the Fe(II) centers in the [Fe(3)Fe(2)] and [Fe(3)Co(2)] analogues and the (ii) charge transfer events in the [Co(3)Fe(2)] complex occur with temperature and irradiation. In addition, photomagnetic behavior is exhibited by all three compounds. The photo-conversion efficiency has been estimated at 20% of photo-induced high spin Fe(II) centers in [Fe(3)Co(2)], 30% of paramagnetic Co(II)-Fe(III) pairs in [Co(3)Fe(2)], and less than 2% of photo-induced high spin Fe(II) centers in [Fe(3)Fe(2)]. PMID:21391549

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

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kazuhiro J.

    2012-07-01

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

  3. Prediction of Excited-State Energies and Singlet-Triplet Gaps of Charge-Transfer States Using a Restricted Open-Shell Kohn-Sham Approach.

    PubMed

    Hait, Diptarka; Zhu, Tianyu; McMahon, David P; Van Voorhis, Troy

    2016-07-12

    Organic molecules with charge-transfer (CT) excited states are widely used in industry and are especially attractive as candidates for fabrication of energy efficient OLEDs, as they can harvest energy from nonradiative triplets by means of thermally activated delayed fluorescence (TADF). It is therefore useful to have computational protocols for accurate estimation of their electronic spectra in order to screen candidate molecules for OLED applications. However, it is difficult to predict the photophysical properties of TADF molecules with LR-TDDFT, as semilocal LR-TDDFT is incapable of accurately modeling CT states. Herein, we study absorption energies, emission energies, zero-zero transition energies, and singlet-triplet gaps of TADF molecules using a restricted open-shell Kohn-Sham (ROKS) approach instead and discover that ROKS calculations with semilocal hybrid functionals are in good agreement with experiments-unlike TDDFT, which significantly underestimates energy gaps. We also propose a cheap computational protocol for studying excited states with large CT character that is found to give good agreement with experimental results without having to perform any excited-state geometry optimizations. PMID:27267803

  4. Modulating the generation of long-lived charge separated states exclusively from the triplet excited states in palladium porphyrin-fullerene conjugates

    NASA Astrophysics Data System (ADS)

    O. Obondi, Christopher; Lim, Gary N.; Churchill, Brittani; Poddutoori, Prashanth K.; van der Est, Art; D'Souza, Francis

    2016-04-01

    This study demonstrates molecular engineering of a series of donor-acceptor systems to allow control of the lifetime and initial spin multiplicity of the charge-separated state. By tuning the rate of intersystem crossing (ISC) and the donor-acceptor distance, electron transfer can be made to occur exclusively from the triplet excited state of the electron donor resulting in long-lived charge separation. To achieve this, three new palladium porphyrin-fullerene donor-acceptor systems were synthesized. The heavy Pd atom enhances the rate of ISC in the porphyrin and the rates of electron and energy transfer are modulated by varying the redox potential of the porphyrin and the porphyrin-fullerene distance. In the case of the meso-tris(tolyl)porphyrinato palladium(ii)-fulleropyrrolidine, the donor-acceptor distance is relatively long (13.1 Å) and the driving force for electron transfer is low. As a result, excitation of the porphyrin leads to rapid ISC followed by triplet-triplet energy transfer to fullerene. When the fullerene is bound directly to the porphyrin shortening the donor-acceptor distance to 2.6 Å electron transfer from the singlet excited palladium porphyrin leading to the generation of a short-lived charge separated state is the main process. Finally, when the palladium porphyrin is substituted with three electron rich triphenylamine entities, the lower oxidation potential of the porphyrin and appropriate donor-acceptor distance (~13 Å), lead to electron transfer exclusively from the triplet excited state of palladium porphyrin with high quantum yield. The results show that when electron transfer occurs from the triplet state, its increased lifetime allows the distance between the donor and acceptor to be increased which results in a longer lifetime for the charge separated state.This study demonstrates molecular engineering of a series of donor-acceptor systems to allow control of the lifetime and initial spin multiplicity of the charge-separated state

  5. Surfactant-enhanced singlet energy transfer from the charge-transfer excited state of tris(2,2-bipyridine) ruthenium(II)

    NASA Astrophysics Data System (ADS)

    Mandal, Krishnagopal; Demas, J. N.

    1981-12-01

    Very efficient (45-75%) sodium lauryl sulfate (NaLS) enhanced singlet enengy transfer has been demonstrated from the spin-orbit charge-transfer excited state of [Ru(bpy) 3] 2+ (bpy = 2,2'-bipyridine) to the xxx violet, oxazine 1, and rhodamine 101 at concentrations of 10 -5 M, Energy transfer occurs in xxx.

  6. TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4'-dimethylaminoflavonol in ethanol solvent.

    PubMed

    Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

    2015-02-25

    Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4'-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule. PMID:25282020

  7. Excited Charm States

    SciTech Connect

    Shukla, S.

    1994-12-31

    Characteristics of mass spectra and decays of orbitally excited charm mesons and baryons, expected on the basis of quark models and Heavy Quark Symmetry, are briefly described. The difficulties associated with measurements on these excited states are discussed. The accuracy and reliability of currently available experimental information is examined. The reasons, for the widely accepted spin-parity assignments to the observed excited mesons and baryons, are stated. Finally, the experimental data, with the accepted spin-parity assignments, is compared with expectations based on quark models and Heavy Quark Symmetry.

  8. Excitation-Photon-Energy Selectivity of Photoconversions in Halogen-Bridged Pd-Chain Compounds: Mott Insulator to Metal or Charge-Density-Wave State

    NASA Astrophysics Data System (ADS)

    Matsuzaki, H.; Iwata, M.; Miyamoto, T.; Terashige, T.; Iwano, K.; Takaishi, S.; Takamura, M.; Kumagai, S.; Yamashita, M.; Takahashi, R.; Wakabayashi, Y.; Okamoto, H.

    2014-08-01

    Ultrafast photoinduced transitions of a one-dimensional Mott insulator into two distinct electronic phases, metal and charge-density-wave (CDW) state, were achieved in a bromine-bridged Pd-chain compound [Pd(en)2Br](C5-Y)2H2O (en =ethylenediamine and C5-Y=dialkylsulfosuccinate), by selecting the photon energy of a femtosecond excitation pulse. For the resonant excitation of the Mott-gap transition, excitonic states are generated and converted to one-dimensional CDW domains. For the higher-energy excitation, free electron and hole carriers are produced, giving rise to a transition of the Mott insulator to a metal. Such selectivity in photoconversions by the choice of initial photoexcited states opens a new possibility for the developments of advanced optical switching and memory functions.

  9. Convoy electron emission following ionization of highly-charged ions excited by resonant coherent excitation

    NASA Astrophysics Data System (ADS)

    Suda, S.; Nakano, Y.; Metoki, K.; Shindo, T.; Ohtsuki, S.; Azuma, T.; Hatakeyama, A.; Komaki, K.; Nakai, Y.; Takada, E.; Murakami, T.

    2012-11-01

    Projectile ionization of highly-charged Ar and Fe ions in the excited states passing relativistically fast through a thin crystalline foil was experimentally studied. We selectively controlled the population of the excited states of the projectiles, and their alignment by choosing a specific m-state through three-dimensional resonant coherent excitation technique by periodical electric fields in a crystalline. We measured energy-differential spectra of electron emission released from projectiles at zero degree. Under the resonance condition, we found an evident enhancement of the convoy electron yield, which reflects the electron momentum distribution of the initial bound state of the excited ions.

  10. Collective charge excitations along cell membranes

    NASA Astrophysics Data System (ADS)

    Manousakis, E.

    2005-07-01

    A significant part of the thin layers of counter-ions adjacent to the exterior and interior surfaces of a cell membrane form quasi-two-dimensional (2D) layers of mobile charge. Collective charge density oscillations, known as plasmon modes, in these 2D charged systems of counter-ions are predicted in the present paper. This is based on a calculation of the self-consistent response of this system to a fast electric field fluctuation. The possibility that the membrane channels might be using these excitations to carry out fast communication is suggested and experiments are proposed to reveal the existence of such excitations.

  11. Are Very Small Emission Quantum Yields Characteristic of Pure Metal-to-Ligand Charge-Transfer Excited States of Ruthenium(II)-(Acceptor Ligand) Chromophores?

    PubMed

    Tsai, Chia Nung; Mazumder, Shivnath; Zhang, Xiu Zhu; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F

    2016-08-01

    Metal to ligand charge-transfer (MLCT) excited state emission quantum yields, ϕem, are reported in 77 K glasses for a series of pentaammine and tetraammine ruthenium(II) complexes with monodentate aromatic acceptor ligands (Ru-MDA) such as pyridine and pyrazine. These quantum yields are only about 0.2-1% of those found for their Ru-bpy (bpy = 2,2'-bipyridine) analogs in similar excited state energy ranges (hνem). The excited state energy dependencies of the emission intensity are characterized by mean radiative decay rate constants, kRAD, resolved from ϕem/τobs = kRAD (τobs = the observed emission decay lifetime; τobs(-1) = kRAD + kNRD; kNRD = nonradiative decay rate constant). Except for the Ru-pz chromophores in alcohol glasses, the values of kNRD for the Ru-MDA chromophores are slightly smaller, and their dependences on excited state energies are very similar to those of related Ru-bpy chromophores. In principle, one expects kRAD to be proportional to the product of (hνem)(3) and the square of the transition dipole moment (Me,g).(2) However, from experimental studies of Ru-bpy chromophores, an additional hνem dependence has been found that originates in an intensity stealing from a higher energy excited state with a much larger value of Me,g. This additional hνem dependence is not present in the kRAD energy dependence for Ru-MDA chromophores in the same energy regime. Intensity stealing in the phosphorescence of these complexes is necessary since the triplet-to-singlet transition is only allowed through spin-orbit coupling and since the density functional theory modeling implicates configurational mixing between states in the triplet spin manifold; this is treated by setting Me,g equal to the product of a mixing coefficient and the difference between the molecular dipole moments of the states involved, which implicates an experimental first order dependence of kRAD on hνem. The failure to observe intensity stealing for the Ru-MDA complexes suggests

  12. Quantitative studies of ground and excited state charge transfer complexes of fullerenes with N,N-dimethylaniline and N,N-diethylaniline

    SciTech Connect

    Sun, Y.P.; Bunker, C.E.; Ma, B. )

    1994-10-19

    A comprehensive spectroscopic study of ground state charge transfer complexes and exciplexes of C[sub 60] and C[sub 70] with N,N-diethylaniline (DEA) and N,N-dimethylaniline (DMA) is reported. The pure absorption spectra of ground state complexes and pure exciplex fluorescence spectra of C[sub 60]/C[sub 70]-DEA/DMA are determined by use of a chemometrics method principal component analysis - self modeling spectral resolution. The exciplex emissions are strongly solvent dependent. In room-temperature toluene, exciplex emissions are absent and the quenching of monomer fluorescence involves both dynamic and static processes. In room-temperature hexane, the quenching of monomer excited state is dominated by the formation of exciplexes. The observed dual fluorescence for C[sub 60]/C[sub 70]-DEA/DMA in hexane can be explained by a mechanism in which contributions from both prompt and delayed monomer emissions are considered. 36 refs., 12 figs.

  13. Systematic investigation of electron impact excitation-autoionization from the groud state of highly charged GaI-like ions through. Delta. N=1 transitions

    SciTech Connect

    Oreg, J.; Bar-Shalom, A. . Nuclear Research Center-Negev); Goldstein, W.H. ); Mandlebaum, P.; Mittnik, D.; Meroz, E.; Schwob, J.L.; Klapisch, M. . Racah Inst. of Physics)

    1991-01-11

    A systematic variation in the line intensity ratios of GaI-like and ZnI-like ions of rare earth elements has been recently observed in spectra emitted in a low density, high temperature tokamak plasma. This variation is shown to be correlated with the gradual opening of autoionizing channels through inner-shell excited configurations of the GaI-like charge-state. These channels enhance the indirect ionization rate of GaI-like ions through excitation-autoionization (EA), effecting the ionization balance and temperatures of greatest abundance. We present a systematic investigation of EA and direct impact ionization (DI) in the GaI-like isoelectronic sequence from Mo (Z = 42) to Dy (Z = 66). As Z decreases from Dy to Pr (Z = 59) the levels of the configuration 3d{sup 9}4p4f, which are excited from the ground state by strong dipole collisional transitions, gradually cross the first ionization limit of the ion and are responsible for this ionization enhancement. When Z decreases further an additional channel is opened through the configuration 3d{sup 9}4p4d. 9 refs., 3 figs., 1 tab.

  14. Complexation of Donor-Acceptor Substituted Aza-Crowns with Alkali and Alkaline Earth Metal Cations. Charge Transfer and Recoordination in Excited State.

    PubMed

    Volchkov, Valery V; Gostev, Fedor E; Shelaev, Ivan V; Nadtochenko, Viktor A; Dmitrieva, Svetlana N; Gromov, Sergey P; Alfimov, Mikhail V; Melnikov, Mikhail Ya

    2016-03-01

    Complexation between two aza-15-crown-5 ethers bearing electron donor and acceptor fragments and alkali and alkaline earth perchlorates has been studied using absorption, steady-state fluorescence and femtosecond transient absorption spectroscopy. The spectral-luminescent parameters, the stability and dissociation constants of the complexes were calculated. The intramolecular charge transfer reaction takes place both in the excited state of the crowns and their complexes 1:1; the latter is subjected to photorecoordination resulting in a weakening or a complete disruption of coordination bond between nitrogen atom and metal cation, disposed within a cavity of the crown. The compounds investigated can be viewed as novel optical molecular sensors for alkali and alkaline-earth metal cations. The photoejection of a metal cation into the bulk was not observed. PMID:26670689

  15. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited

    SciTech Connect

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.

  16. Ultrafast Measurement Confirms Charge Generation through Cold Charge Transfer States

    NASA Astrophysics Data System (ADS)

    Gautam, Bhoj; Younts, Robert; Yan, Liang; Danilov, Evgeny; Ade, Harald; You, Wei; Gundogdu, Kenan

    2015-03-01

    The role of excess energy in generation and extraction of charges through charge transfer (CT) states in polymer solar cells is a subject of debate. There are reports suggesting increase of charge generation yield with excess energy based on ultrafast experiments. On the other hand time delayed collection field measurements shows that excess photon energy has no effect in photovoltaic efficiency. Here we resolved this discrepancy by studying the dynamics of CT excitons and polarons in blends of medium gap copolymers. We found that low-lying charge transfer (CT) excitons can generate charges over a long time period (nanosecond) and contribute photocurrent on the bulk heterojunction devices. By performing resonant CT excitation as well as above gap excitation transient absorption measurements we investigated that the charges are generated more efficiently through low-lying CT states in efficient devices independent of excitation energy. This work is supported by Office of Naval Research Grant N000141310526 P00002.

  17. Time-dependent density functional theory (TDDFT) study of the excited charge-transfer state formation of a series of aromatic donor-acceptor systems.

    PubMed

    Jamorski Jödicke, Christine; Lüthi, Hans Peter

    2003-01-01

    Singlet excitation energy calculations for a series of acceptor para-substituted N,N-dimethyl-anilines that are dual (4-(N,N-dimethylamino)benzonitrile, 4DMAB-CN, 4-(N,N-dimethylamino)benzaldhyde, 4DMAB-CHO, 1-methyl-7-cyano-2,3,4,5-tetrahydro-1H-1-benzazepine, NMC7) and nondual (4-aminobenzonitrile, 4AB-CN, 3-(N,N-dimethylamino)benzonitrile, 3DMAB-CN, and 4-nitro(N,N-dimethyl) aniline, 4DMAB-NO(2)) fluorescent have been performed using time-dependent density functional theory (TDDFT). The B3LYP and MPW1PW91 functionals with a 6-311+G(2d,p) (Bg) basis set have been used to compute excitation energies. Ground-state geometries were optimized using density functional theory (DFT) with both B3LYP and MPW1PW91 functionals combined with a 6-31G(d) basis set. For most of the molecules presented in this study, potential energy surfaces have been computed according to the coordinates related to the three following mechanisms proposed in the literature: twisting, wagging, and planar intramolecular charge transfer (ICT). Comparison of the three models for the different molecules leads to the conclusion that only the twisting ICT model is able to explain the low frequency, strongly solvent-dependent energy band present in the fluorescence spectra. According to this model, the 4AB-CN molecule is calculated to be nondual fluorescent in agreement with the experimental spectra. The single band observed in the fluorescence spectra of TMAB-CN (4-(N,N-dimethylamino)-3,5-(dimethyl)benzonitrile) is due to a large stabilization of the charge-transfer excited state along the twisting coordinate. The nondual fluorescence of the 4DMAB-NO(2) molecule is explained by the same mechanism. In the case of 3DMAB-CN, the single observed emission, which is solvent-dependent, has been assigned to the lowest charge-transfer excited state. The dual fluorescence of 4DMAB-CN and 4DMAB-CHO is explained within the twisting ICT model by a double mechanism (already proposed by Serrano et al.: Serrano

  18. Collective charge excitation in low dimensional organic salts

    NASA Astrophysics Data System (ADS)

    Naka, Makoto; Ishihara, Sumio

    2013-03-01

    Electronic ferroelectricity is known as phenomena where electric polarization is attributed to the charge order without inversion symmetry. This is seen in some transition metal oxides, e.g. LuFe2O4, and charge transfer salts. Quasi 2-dimesional organic salt kappa-(ET)2Cu2(CN)3\\ is one of the electronic ferroelectricities. Two ET molecules construct a dimer and are arranged on a triangular lattice. Recently, it is reported that a dielectric anomaly is experimentally observed around 30K. An origin of this dielectric anomaly is thought to be an ?electronic? dipole generated by a localized hole in one side of the ET molecules in dimers. Motivated by the experimental results, we study charge dynamics in dimer-Mott insulating system with internal charge degree of freedom in a dimer. We adopt the three kinds of models, extended Hubbard model, V-t model and its effective pseudo-spin model. We analyze these models by utilizing the exact diagonalization method and spin wave approximation, and focus on the collective charge excitation. In the ground state, paraelectric dimer-Mott phase and ferroelectric charge ordered phase compete with each other. We find the low-energy intra-dimer charge excitations which show a strong light polarization dependence. The collective excitation mode which is observable by light being parallel to the electric polarization shows a softening and a remarkable frequency dispersion around the phase boundary. This collective charge excitation of the ?electronic? dipole explains the recently observed peak structure in optical conductivity for the THz region.

  19. Direct evidence of complete charge separation in the excited triplet state of 1,2-( N-arylaziridino)-[60] fullerenes by means of time-resolved electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Yamauchi, Seigo; Iwasaki, Yohei; Ohba, Yasunori; Awen, Bahlul Z. S.; Ouchi, Akihiko

    2005-08-01

    Some of 1,6-( N-substituted) aza-[60] fulleroids ( 1) and their corresponding photochemical reaction products, 1,2-( N-substituted) aziridino-[60] fullerenes ( 2) showed peculiar transient absorption peaks depending on the N-substituents. Although these bands are considered to concern with very slow photochemical rearrangements 1 → 2 in the excited triplet state, no definitive evidence has been obtained yet. We report on the character of the excited triplet states in these compounds by means of a time-resolved electron paramagnetic resonance technique. Definitive evidence on the involvement of intra-molecular charge transfer states is shown in this Letter.

  20. Intramolecular charge transfer with the planarized 4-cyanofluorazene and its flexible counterpart 4-cyano-N-phenylpyrrole. Picosecond fluorescence decays and femtosecond excited-state absorption.

    PubMed

    Druzhinin, Sergey I; Kovalenko, Sergey A; Senyushkina, Tamara A; Demeter, Attila; Machinek, Reinhard; Noltemeyer, Mathias; Zachariasse, Klaas A

    2008-09-11

    The fluorescence spectrum of the rigidified 4-cyanofluorazene (FPP4C) in n-hexane consists of a dual emission from a locally excited (LE) and an intramolecular charge-transfer (ICT) state, with an ICT/LE fluorescence quantum yield ratio of Phi'(ICT)/Phi(LE) = 3.3 at 25 degrees C. With the flexible 4-cyano- N-phenylpyrrole (PP4C) in n-hexane, such an ICT reaction also takes place, with Phi'(ICT)/Phi(LE) = 1.5, indicating that for this reaction, a perpendicular twist of the pyrrole and benzonitrile moieties is not required. The ICT emission band of FPP4C and PP4C in n-hexane has vibrational structure, but a structureless band is observed in all other solvents more polar than the alkanes. The enthalpy difference Delta H of the LE --> ICT reaction in n-hexane, -11 kJ/mol for FPP4C and -7 kJ/mol for PP4C, is determined by analyzing the temperature dependence of Phi'(ICT)/Phi(LE). Using these data, the energy E(FC,ICT) of the Franck-Condon ground state populated by the ICT emission is calculated, 41 (FPP4C) and 40 kJ/mol (PP4C). These large values for E(FC,ICT) lead to the conclusion that with FPP4C and PP4C, direct ICT excitation, bypassing LE, does not take place. FPP4C has an ICT dipole moment of 15 D, similar to that of PP4C (16 D). Picosecond fluorescence decays allow the determination of the ICT lifetime, from which the radiative rate constant k'(f)(ICT) is derived, with comparable values for FPP4C and PP4C. This shows that an argument for a twisted ICT state of PP4C cannot come from k'(f)(ICT). After correction for the solvent refractive index and the energy of the emission maximum nu(max)(ICT), it appears that k'(f)(ICT) is solvent-polarity-independent. Femtosecond transient absorption with FPP4C and PP4C in n-hexane reveals that the ICT state is already nearly fully present at 100 fs after excitation, in rapid equilibrium with LE. In MeCN, the ICT state of FPP4C and PP4C is likewise largely developed at this delay time, and the reaction is limited by dielectric

  1. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations

    SciTech Connect

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor–acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene–perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  2. Lattice, spin, and charge excitations in cuprates

    NASA Astrophysics Data System (ADS)

    Lee, Wei-Sheng

    2014-03-01

    Tracking doping evolution of elementary excitations is a crucial approach to understand the complex phenomena exhibited in cuprates. In the first part of my talk, I will discuss the role of the lattice in the quasi-one-dimensional edge-sharing cuprate Y2+xCa2-xCu5O10. Using O K-edge RIXS, we resolve site-dependent harmonic phonon excitations of a 70 meV mode. Coupled with theory, this provides a direct measurement of electron-lattice coupling strength. We show that such electron-lattice coupling causes doping-dependent distortions of the Cu-O-Cu bond angle, which sets the intra-chain spin exchange interactions. In the second part of my talk, I will discuss collective excitations in the electron-doped superconducting cuprate, Nd2-xCexCuO4 observed using Cu L-edge RIXS. Surprisingly, despite the fact that the spin stiffness is zero and the AFM correlations are short-ranged, magnetic excitations harden significantly across the AFM-HTSC phase boundary, in stark contrast with the hole-doped cuprates. Furthermore, we found an unexpected and highly dispersive mode emanating from the zone center in superconducting NCCO that is undetected in the hole-doped compounds. This may signal a quantum phase distinct from superconductivity. Thus, our results indicate an asymmetry of the collective excitations in electron- and hole-doped cuprates, providing a new perspective on the doping evolution of the cuprate ground state. This work is supported by DOE Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract DE-AC02-76SF00515.

  3. Charge-transfer excitations steer the Davydov splitting and mediate singlet exciton fission in pentacene.

    PubMed

    Beljonne, D; Yamagata, H; Brédas, J L; Spano, F C; Olivier, Y

    2013-05-31

    Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments. PMID:23767738

  4. Charge-Transfer Excitations Steer the Davydov Splitting and Mediate Singlet Exciton Fission in Pentacene

    NASA Astrophysics Data System (ADS)

    Beljonne, D.; Yamagata, H.; Brédas, J. L.; Spano, F. C.; Olivier, Y.

    2013-05-01

    Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments.

  5. Atomic-Orbital Close-Coupling Calculations Of Electron Capture From Hydrogen Atoms Into Highly Excited Rydberg States Of Multiply Charged Ions

    SciTech Connect

    Igenbergs, Katharina; Wallerberger, Markus; Aumayr, Friedrich

    2011-06-01

    Collisions of neutral hydrogen atoms with multiply charged ions have been studied in the past using the semi-classical atomic-orbital close-coupling method. We present total and state-resolved cross sections for charge exchange as well as ionization. The advent of supercomputers and parallel programming facilities now allow treatment of collision systems that have been out of reach before, because much larger basis sets involving high quantum numbers are now feasible.

  6. Electron impact collision strengths for excitation of highly charged ions

    SciTech Connect

    Sampson, D.H. . Dept. of Astronomy and Astrophysics)

    1990-08-20

    The principle task given us by the Lawrence Livermore National Laboratory (LLNL) to perform under Subcontract 6181405 was to develop a method and corresponding computer programs to make very rapid, yet accurate, fully relativistic and quasirelativistic calculations of cross sections or collision strengths for electron impact excitation of highly charged ions with any value for the nuclear charge number Z. Also while this major code development was being done we were asked to calculate cross sections of interest using our previous rapid, more approximate codes, which used hydrogenic basis functions and screening constants with both the electron-electron Coulomb interaction and relativistic interactions included by perturbation theory. We were also asked to determine the branching ratio for ionization to various final states in complex cases, where two or more states corresponding to the final configuration of the ion were possible.

  7. Excited states in DNA strands investigated by ultrafast laser spectroscopy.

    PubMed

    Chen, Jinquan; Zhang, Yuyuan; Kohler, Bern

    2015-01-01

    Ultrafast laser experiments on carefully selected DNA model compounds probe the effects of base stacking, base pairing, and structural disorder on excited electronic states formed by UV absorption in single and double DNA strands. Direct π-orbital overlap between two stacked bases in a dinucleotide or in a longer single strand creates new excited states that decay orders of magnitude more slowly than the generally subpicosecond excited states of monomeric bases. Half or more of all excited states in single strands decay in this manner. Ultrafast mid-IR transient absorption experiments reveal that the long-lived excited states in a number of model compounds are charge transfer states formed by interbase electron transfer, which subsequently decay by charge recombination. The lifetimes of the charge transfer states are surprisingly independent of how the stacked bases are oriented, but disruption of π-stacking, either by elevating temperature or by adding a denaturing co-solvent, completely eliminates this decay channel. Time-resolved emission measurements support the conclusion that these states are populated very rapidly from initial excitons. These experiments also reveal the existence of populations of emissive excited states that decay on the nanosecond time scale. The quantum yield of these states is very small for UVB/UVC excitation, but increases at UVA wavelengths. In double strands, hydrogen bonding between bases perturbs, but does not quench, the long-lived excited states. Kinetic isotope effects on the excited-state dynamics suggest that intrastrand electron transfer may couple to interstrand proton transfer. By revealing how structure and non-covalent interactions affect excited-state dynamics, on-going experimental and theoretical studies of excited states in DNA strands can advance understanding of fundamental photophysics in other nanoscale systems. PMID:25326834

  8. Charge-transfer correction for improved time-dependent local density approximation excited-state potential energy curves: Analysis within the two-level model with illustration for H2 and LiH

    NASA Astrophysics Data System (ADS)

    Casida, Mark E.; Gutierrez, Fabien; Guan, Jingang; Gadea, Florent-Xavier; Salahub, Dennis; Daudey, Jean-Pierre

    2000-11-01

    Time-dependent density-functional theory (TDDFT) is an increasingly popular approach for calculating molecular excitation energies. However, the TDDFT lowest triplet excitation energy, ωT, of a closed-shell molecule often falls rapidly to zero and then becomes imaginary at large internuclear distances. We show that this unphysical behavior occurs because ωT2 must become negative wherever symmetry breaking lowers the energy of the ground state solution below that of the symmetry unbroken solution. We use the fact that the ΔSCF method gives a qualitatively correct first triplet excited state to derive a "charge-transfer correction" (CTC) for the time-dependent local density approximation (TDLDA) within the two-level model and the Tamm-Dancoff approximation (TDA). Although this correction would not be needed for the exact exchange-correlation functional, it is evidently important for a correct description of molecular excited state potential energy surfaces in the TDLDA. As a byproduct of our analysis, we show why TDLDA and LDA ΔSCF excitation energies are often very similar near the equilibrium geometries. The reasoning given here is fairly general and it is expected that similar corrections will be needed in the case of generalized gradient approximations and hybrid functionals.

  9. Accelerating slow excited state proton transfer.

    PubMed

    Stewart, David J; Concepcion, Javier J; Brennaman, M Kyle; Binstead, Robert A; Meyer, Thomas J

    2013-01-15

    Visible light excitation of the ligand-bridged assembly [(bpy)(2)Ru(a)(II)(L)Ru(b)(II)(bpy)(OH(2))(4+)] (bpy is 2,2'-bipyridine; L is the bridging ligand, 4-phen-tpy) results in emission from the lowest energy, bridge-based metal-to-ligand charge transfer excited state (L(-•))Ru(b)(III)-OH(2) with an excited-state lifetime of 13 ± 1 ns. Near-diffusion-controlled quenching of the emission occurs with added HPO(4)(2-) and partial quenching by added acetate anion (OAc(-)) in buffered solutions with pH control. A Stern-Volmer analysis of quenching by OAc(-) gave a quenching rate constant of k(q) = 4.1 × 10(8) M(-1) • s(-1) and an estimated pK(a)* value of ~5 ± 1 for the [(bpy)(2)Ru(a)(II)(L(•-))Ru(b)(III)(bpy)(OH(2))(4+)]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)(2)Ru(a)(II)(L)Ru(b)(II)(bpy)(OH)(3+)] in a H(2)PO(4)(-)/HPO(4)(2-) buffer, back proton transfer occurs from H(2)PO(4)(-) to give [(bpy)(2)Ru(a)(II)(L)Ru(b)(bpy)(OH(2))(4+)] with k(PT,2) = 4.4 × 10(8) M(-1) • s(-1). From the intercept of a plot of k(obs) vs. [H(2)PO(4)(-)], k = 2.1 × 10(6) s(-1) for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pK(a) values intermediate between pK(a)(H(3)O(+)) = -1.74 and pK(a)(H(2)O) = 15.7. PMID:23277551

  10. Singlet-Triplet Splittings in the Luminescent Excited States of Colloidal Cu(+):CdSe, Cu(+):InP, and CuInS2 Nanocrystals: Charge-Transfer Configurations and Self-Trapped Excitons.

    PubMed

    Knowles, Kathryn E; Nelson, Heidi D; Kilburn, Troy B; Gamelin, Daniel R

    2015-10-14

    The electronic and magnetic properties of the luminescent excited states of colloidal Cu(+):CdSe, Cu(+):InP, and CuInS2 nanocrystals were investigated using variable-temperature photoluminescence (PL) and magnetic circularly polarized luminescence (MCPL) spectroscopies. The nanocrystal electronic structures were also investigated by absorption and magnetic circular dichroism (MCD) spectroscopies. By every spectroscopic measure, the luminescent excited states of all three materials are essentially indistinguishable. All three materials show very similar broad PL line widths and large Stokes shifts. All three materials also show similar temperature dependence of their PL lifetimes and MCPL polarization ratios. Analysis shows that this temperature dependence reflects Boltzmann population distributions between luminescent singlet and triplet excited states with average singlet-triplet splittings of ∼1 meV in each material. These similarities lead to the conclusion that the PL mechanism in CuInS2 NCs is fundamentally different from that of bulk CuInS2 and instead is the same as that in Cu(+)-doped NCs, which are known to luminesce via charge-transfer recombination of conduction-band electrons with copper-localized holes. The luminescence of CuInS2 nanocrystals is explained well by invoking exciton self-trapping, in which delocalized photogenerated holes contract in response to strong vibronic coupling at lattice copper sites to form a luminescent excited state that is essentially identical to that of the Cu(+)-doped semiconductor nanocrystals. PMID:26389577

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

    PubMed

    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

  12. Low-charge-state linac

    SciTech Connect

    Shepard, K.W.; Kim, J.W.

    1995-08-01

    A design is being developed for a low-charge-state linac suitable for injecting ATLAS with a low-charge-state, radioactive beam. Initial work indicates that the existing ATLAS interdigital superconducting accelerating structures, together with the superconducting quadrupole transverse focussing element discussed above, provides a basis for a high-performance low-charge-state linac. The initial 2 or 3 MV of such a linac could be based on a normally-conducting, low-frequency RFQ, possibly combined with 24-MHz superconducting interdigital structures. Beam dynamics studies of the whole low-charge-state post-accelerator section were carried out in early FY 1995.

  13. Theoretical studies of electronically excited states

    SciTech Connect

    Besley, Nicholas A.

    2014-10-06

    Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.

  14. Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

    PubMed Central

    Rettig, L.; Cortés, R.; Chu, J.-H.; Fisher, I. R.; Schmitt, F.; Moore, R. G.; Shen, Z.-X.; Kirchmann, P. S.; Wolf, M.; Bovensiepen, U.

    2016-01-01

    Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time- and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of the dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. Our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order. PMID:26804717

  15. Resource Paper: Molecular Excited State Relaxation Processes.

    ERIC Educational Resources Information Center

    Rhodes, William

    1979-01-01

    Develops the concept of oscillatory v dissipative limits as it applies to electronic excited state processes in molecular systems. Main emphasis is placed on the radiative and nonradiative dynamics of the excited state of a molecule prepared by interaction with light or some other excitation source. (BT)

  16. Charge relaxation and recombination in photo-excited Mott insulators

    NASA Astrophysics Data System (ADS)

    Prelovšek, P.; Lenarčič, Z.

    2016-04-01

    Recent femtosecond pump-probe experiments on Mott insulators reveal charge recombination, which is in picosecond range, i.e., much faster than in clean bandgap semiconductors although excitation gaps in Mott insulators are even larger. The charge response in photo-excited insulators can be generally divided in femtosecond transient relaxation of charge excitations, which are holons and doublons, and a second slower, but still very fast, holon-doublon (HD) recombination. We present a theory of the recombination rate of the excited HD pairs, based on the two-dimensional (2D) model relevant for cuprates, which shows that such fast processes can be explained even quantitatively with the multi-magnon emission. We show that the condition for the exponential decay as observed in the experiment is the existence of the exciton, i.e., the bound HD pair. Its recombination rate is exponentially dependent on the charge gap and on the magnon energy, while the ultrafast process can be traced back to strong charge-spin coupling. We comment also fast recombination times in the one-dimensional (1D) Mott insulators, as e.g., organic salts. The recombination rate in the latter cases can be explained with the stronger coupling with phonon excitations.

  17. Fractionally Charged Zero-Energy Single-Particle Excitations in a Driven Fermi Sea.

    PubMed

    Moskalets, Michael

    2016-07-22

    A voltage pulse of a Lorentzian shape carrying half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasiparticle with an effectively fractional charge e/2. A prominent feature of such an excitation is a narrow peak in the energy distribution function lying exactly at the Fermi energy μ. Another spectacular feature is that the distribution function has symmetric tails around μ, which results in a zero-energy excitation. This sounds improbable since at zero temperature all available states below μ are fully occupied. The resolution lies in the fact that such a voltage pulse also excites electron-hole pairs, which free some space below μ and thus allow a zero-energy quasiparticle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in an experiment. PMID:27494490

  18. Fractionally Charged Zero-Energy Single-Particle Excitations in a Driven Fermi Sea

    NASA Astrophysics Data System (ADS)

    Moskalets, Michael

    2016-07-01

    A voltage pulse of a Lorentzian shape carrying half of the flux quantum excites out of a zero-temperature Fermi sea an electron in a mixed state, which looks like a quasiparticle with an effectively fractional charge e /2 . A prominent feature of such an excitation is a narrow peak in the energy distribution function lying exactly at the Fermi energy μ . Another spectacular feature is that the distribution function has symmetric tails around μ , which results in a zero-energy excitation. This sounds improbable since at zero temperature all available states below μ are fully occupied. The resolution lies in the fact that such a voltage pulse also excites electron-hole pairs, which free some space below μ and thus allow a zero-energy quasiparticle to exist. I discuss also how to address separately electron-hole pairs and a fractionally charged zero-energy excitation in an experiment.

  19. Intramolecular charge transfer in aminobenzonitriles and tetrafluoro counterparts: fluorescence explained by competition between low-lying excited states and radiationless deactivation. Part I: A mechanistic overview of the parent system ABN.

    PubMed

    Segado, Mireia; Gómez, Isabel; Reguero, Mar

    2016-03-01

    Recent theoretical and experimental studies on the Intramolecular Charge Transfer (ICT) reaction of some members of the aminobezonitrile family (ABN) suggest the involvement of a (π-σ*) excited state (called ICT(CN) in this work) in the ICT process and the existence of a partially twisted ICT species that could be responsible for the anomalous fluorescence observed. These suggestions made us to revise our previous study on the photophysics of ABN and dimethyl-ABN (DMABN), based on the analysis of the potential energy surfaces of the low-lying excited states by means of ab initio calculations, using the CASSCF/CASPT2 protocol. We have first focused our attention to ABN. We have found that the (π-σ*) excited state can be in fact an intermediary state in the path to populate the ICT bright state, although its involvement in the process is not very probable. Our results suggest that the ICT most stable species is the twisted ICT(TICT) and that the partially twisted ICT minimum found in previous studies could be an artefact of the computational method. We have also found that radiationless deactivation is a competitive reaction that must be taken into account to explain the fluorescence patterns of these systems. To confirm our theories, we have also studied other systems with a similar architecture but with a very different luminescence behaviour: dimethyl-ABN, and the 2,3,4,5-tetrafluoro derivatives of ABN and DMABN (ABN-4F and DMABN-4F). The extension of the work and the different approaches in the study of the parent system and of the derivatives make the division of the work in two parts advisable. Part I collects the characterization of the minima and reaction paths connecting the critical points of the potential energy surfaces of the states involved in the ICT reaction of ABN. We have obtained, for the first time, the pathways of radiationless deactivation for this compound. We have also computed transition energies from the excited minima, to interpret the

  20. Using RIXS to Uncover Elementary Charge and Spin Excitations

    NASA Astrophysics Data System (ADS)

    Jia, Chunjing; Wohlfeld, Krzysztof; Wang, Yao; Moritz, Brian; Devereaux, Thomas P.

    2016-04-01

    Despite significant progress in resonant inelastic x-ray scattering (RIXS) experiments on cuprates at the Cu L -edge, a theoretical understanding of the cross section remains incomplete in terms of elementary excitations and the connection to both charge and spin structure factors. Here, we use state-of-the-art, unbiased numerical calculations to study the low-energy excitations probed by RIXS in the Hubbard model, relevant to the cuprates. The results highlight the importance of scattering geometry, in particular, both the incident and scattered x-ray photon polarization, and they demonstrate that on a qualitative level the RIXS spectral shape in the cross-polarized channel approximates that of the spin dynamical structure factor. However, in the parallel-polarized channel, the complexity of the RIXS process beyond a simple two-particle response complicates the analysis and demonstrates that approximations and expansions that attempt to relate RIXS to less complex correlation functions cannot reproduce the full diversity of RIXS spectral features.

  1. Ground state structures and excited state dynamics of pyrrole-water complexes: Ab initio excited state molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Kumar, Anupriya; Kołaski, Maciej; Kim, Kwang S.

    2008-01-01

    Structures of the ground state pyrrole-(H2O)n clusters are investigated using ab initio calculations. The charge-transfer driven femtosecond scale dynamics are studied with excited state ab initio molecular dynamics simulations employing the complete-active-space self-consistent-field method for pyrrole-(H2O)n clusters. Upon the excitation of these clusters, the charge density is located over the farthest water molecule which is repelled by the depleted π-electron cloud of pyrrole ring, resulting in a highly polarized complex. For pyrrole-(H2O), the charge transfer is maximized (up to 0.34a.u.) around ˜100fs and then oscillates. For pyrrole-(H2O)2, the initial charge transfer occurs through the space between the pyrrole and the π H-bonded water molecule and then the charge transfer takes place from this water molecule to the σ H-bonded water molecule. The total charge transfer from the pyrrole to the water molecules is maximized (up to 0.53a.u.) around ˜100fs.

  2. State-of-charge coulometer

    NASA Technical Reports Server (NTRS)

    Rowlette, J. J. (Inventor)

    1985-01-01

    A coulometer for accurately measuring the state-of-charge of an open-cell battery utilizing an aqueous electrolyte, includes a current meter for measuring the battery/discharge current and a flow meter for measuring the rate at which the battery produces gas during charge and discharge. Coupled to the flow meter is gas analyzer which measures the oxygen fraction of the battery gas. The outputs of the current meter, flow meter, and gas analyzer are coupled to a programmed microcomputer which includes a CPU and program and data memories. The microcomputer calculates that fraction of charge and discharge current consumed in the generation of gas so that the actual state-of-charge can be determined. The state-of-charge is then shown on a visual display.

  3. Battery-Charge-State Model

    NASA Technical Reports Server (NTRS)

    Vivian, H. C.

    1985-01-01

    Charge-state model for lead/acid batteries proposed as part of effort to make equivalent of fuel gage for battery-powered vehicles. Models based on equations that approximate observable characteristics of battery electrochemistry. Uses linear equations, easier to simulate on computer, and gives smooth transitions between charge, discharge, and recuperation.

  4. Multiscale excited state lifetimes of protonated dimethyl aminopyridines.

    PubMed

    Soorkia, Satchin; Broquier, Michel; Grégoire, Gilles

    2016-09-14

    The excited state dynamics of protonated ortho (2-) and para (4-) dimethyl aminopyridine molecules (DMAPH(+)) has been studied through pump-probe photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Multiscale temporal dynamics has been recorded over 9 orders of magnitude from subpicosecond to millisecond. The initially locally excited ππ* state rapidly decays within about 100 fs into a charge transfer state following 90° twist motion of the dimethyl amino group. While this twisted intramolecular charge transfer (TICT) state does not trigger any fragmentation, it selectively leads to specific two-color photofragments through absorption of the probe photon at 355 nm. Besides, the optically dark TICT state provides an efficient deactivation path with high intersystem probability to non-dissociative long-lived triplet states. Such a multiscale pump-probe photodissociation scheme paves the way to systematic studies of charge transfer reactions in the excited state of cold ionic systems stored in a cryogenic cooled ion trap and probed continuously up to the millisecond time scale. PMID:27524459

  5. Dynamics of nonlinear excitations of helically confined charges

    NASA Astrophysics Data System (ADS)

    Zampetaki, A. V.; Stockhofe, J.; Schmelcher, P.

    2015-10-01

    We explore the long-time dynamics of a system of identical charged particles trapped on a closed helix. This system has recently been found to exhibit an unconventional deformation of the linear spectrum when tuning the helix radius. Here we show that the same geometrical parameter can affect significantly also the dynamical behavior of an initially broad excitation for long times. In particular, for small values of the radius, the excitation disperses into the whole crystal whereas within a specific narrow regime of larger radii the excitation self-focuses, assuming finally a localized form. Beyond this regime, the excitation defocuses and the dispersion gradually increases again. We analyze this geometrically controlled nonlinear behavior using an effective discrete nonlinear Schrödinger model, which allows us among others to identify a number of breatherlike excitations.

  6. Tuning ground states and excitations in complex electronic materials

    SciTech Connect

    Bishop, A.R.

    1996-09-01

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

  7. Excited States of Non-Isolated Chromophores

    NASA Astrophysics Data System (ADS)

    Matsika, S.; Kozak, C.; Kistler, K.

    2009-06-01

    The photophysical and photochemical behavior of nucleobases is very important because of their biological role as the building blocks in DNA and RNA. Great progress has been made in understanding the excited-state properties of single bases. In order to understand the photophysical properties of nucleobases in complex environments we have investigated their excited states (a) in aqueous solutions and (b) as π-stacked dimers in DNA. The solvatochromic shifts of the excited states of pyrimidine nucleobases in aqueous solution have been investigated using a combined QM/MM procedure where the quantum mechanical solute is described using high level multireference configuration interaction methods while molecular dynamics simulations are used to obtain the structure of the solvent around the solute in an average way. The excited states of π-stacked nucleobases have also been investigated using various ab initio methods. The effect of the environment on the excited states and conical intersections is investigated.

  8. Electronic and Nuclear Factors in Charge and Excitation Transfer

    SciTech Connect

    Piotr Piotrowiak

    2004-09-28

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

  9. Localized excitations of charged dust grains in dusty plasma lattices

    SciTech Connect

    Kourakis, Ioannis; Shukla, Padma Kant; Basios, Vassileios

    2005-10-31

    The nonlinear aspects of charged dust grain motion in a one-dimensional dusty plasma (DP) monolayer are discussed. Both horizontal (longitudinal, acoustic mode) and vertical (transverse, optic mode) displacements are considered, and various types of localized excitations are reviewed, in a continuum approximation. Dust crystals are shown to support nonlinear kink-shaped supersonic longitudinal solitary excitations, as well as modulated envelope (either longitudinal or transverse) localized modes. The possibility for Discrete Breather (DB-) type excitations (Intrinsic Localized Modes, ILMs) to occur is investigated, from first principles. These highly localized excitations owe their existence to lattice discreteness, in combination with the interaction and/or substrate (sheath) potential nonlinearity. This possibility may open new directions in DP- related research. The relation to previous results on atomic chains as well as to experimental results on strongly-coupled dust layers in gas discharge plasmas is discussed.

  10. Excited State Properties of Hybrid Perovskites.

    PubMed

    Saba, Michele; Quochi, Francesco; Mura, Andrea; Bongiovanni, Giovanni

    2016-01-19

    Metal halide perovskites have come to the attention of the scientific community for the progress achieved in solar light conversion. Energy sustainability is one of the priorities of our society, and materials advancements resulting in low-cost but efficient solar cells and large-area lighting devices represent a major goal for applied research. From a basic point of view, perovskites are an exotic class of hybrid materials combining some merits of organic and inorganic semiconductors: large optical absorption, large mobilities, and tunable band gap together with the possibility to be processed in solution. When a novel class of promising semiconductors comes into the limelight, lively discussions ensue on the photophysics of band-edge excitations, because just the states close to the band edge are entailed in energy/charge transport and light emission. This was the case several decades ago for III-V semiconductors, it has been up to 10 years ago for organics, and it is currently the case for perovskites. Our aim in this Account is to rationalize the body of experimental evidence on perovskite photophysics in a coherent theoretical framework, borrowing from the knowledge acquired over the years in materials optoelectronics. A crucial question is whether photon absorption leads to a population of unbound, conductive free charges or instead excitons, neutral and insulating bound states created by Coulomb interaction just below the energy of the band gap. We first focus on the experimental estimates of the exciton binding energy (Eb): at room temperature, Eb is comparable to the thermal energy kBT in MAPbI3 and increases up to values 2-3kBT in wide band gap MAPbBr3 and MAPbCl3. Statistical considerations predict that these values, even though comparable to or larger than thermal energy, let free carriers prevail over bound excitons for all levels of excitation densities relevant for devices. The analysis of photophysics evidence confirms that all hybrid halide

  11. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    NASA Astrophysics Data System (ADS)

    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

  12. Quantum dynamics of charge state in silicon field evaporation

    NASA Astrophysics Data System (ADS)

    Silaeva, Elena P.; Uchida, Kazuki; Watanabe, Kazuyuki

    2016-08-01

    The charge state of an ion field-evaporating from a silicon-atom cluster is analyzed using time-dependent density functional theory coupled to molecular dynamics. The final charge state of the ion is shown to increase gradually with increasing external electrostatic field in agreement with the average charge state of silicon ions detected experimentally. When field evaporation is triggered by laser-induced electronic excitations the charge state also increases with increasing intensity of the laser pulse. At the evaporation threshold, the charge state of the evaporating ion does not depend on the electrostatic field due to the strong contribution of laser excitations to the ionization process both at low and high laser energies. A neutral silicon atom escaping the cluster due to its high initial kinetic energy is shown to be eventually ionized by external electrostatic field.

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

    NASA Astrophysics Data System (ADS)

    Eriksen, Janus J.; Sauer, Stephan P. A.; Mikkelsen, Kurt V.; Christiansen, Ove; Jensen, Hans Jørgen Aa.; Kongsted, Jacob

    2013-07-01

    We investigate the failure of time-dependent density functional theory (TDDFT) with the CAM-B3LYP exchange-correlation (xc) functional coupled to the polarisable embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge-transfer excitation in para-nitroaniline (pNA) in water by comparing with results obtained with the coupled cluster singles and doubles (CCSD) model also coupled to the polarisable embedding scheme (PE-CCSD). We determine the amount of charge separation in the ground and excited charge-transfer state with both methods by calculating the electric dipole moments in the gas phase and for 100 solvent configurations. We find that CAM-B3LYP overestimates the amount of charge separation inherent in the ground state and TDDFT/CAM-B3LYP drastically underestimates this amount in the excited charge-transfer state. As the errors in the solvatochromatic shift are found to be inverse proportional to the change in dipole moment upon excitation, we conclude that the flaws in the description of the solvatochromic shift of this excitation are related to TDDFT itself and how it responds to the solvent effects modelled by the PE scheme. We recommend therefore to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge-transfer excitations in molecular systems similar to pNA against higher level ab initio wave function methods, like, e.g. CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a measure for charge-transfer character, we furthermore confirm that the difference between excitation energies calculated with TDDFT and with the Tamm-Dancoff approximation (TDA) to TDDFT is indeed correlated with the charge-transfer character of a given electronic transition both in vacuo and in solution. This is supported by a corresponding correlation between the change in dipole moment and the size of the Λ index diagnostic for the investigated CT excitation.

  14. Excitation and ionization of highly charged ions by electron impact

    SciTech Connect

    Sampson, D.H.

    1989-11-15

    Two approaches for very rapid calculation of atomic data for high temperature plasma modeling have been developed. The first uses hydrogenic basis states and has been developed and applied in many papers discussed in previous progress reports. Hence, it is only briefly discussed here. The second is a very rapid, yet accurate, fully relativistic approach that has been developed over the past two or three years. It is described in more detail. Recently it has been applied to large scale production of atomic data. Specifically, it has been used to calculate relativistic distorted wave collision strengths and oscillator strengths for the following: all transitions from the ground level to the n=3 and 4 excited levels in the 71 Neon-like ions with nuclear charge number Z in the range 22 {le} Z {le} 92; all transitions among the 2s{sub {1/2}}, 2p{sub {1/2}} and 2p{sub 3/2} levels and from them to all nlj levels with n=3,4 and 5 in the 85 Li-like ions with 8 {le} Z {le} 92; all transitions among the 3s{sub {1/2}}, 3p{sub 3/2}, 3d{sub 3/2} and 3d{sub 5/2} levels and from them to all nlj levels with n=4 and 5 in the 71 Na-like ions with 22 {le} Z {le} 92; and all transitions among 4s{sub {1/2}}, 4p{sub {1/2}}, 4p{sub 3/2}, 4d{sub 3/2}, 4d{sub 5/2}, 4f{sub 5/2} and 4f{sub 7/2} levels and from them to all nlj levels with n=5 in the 33 Cu-like ions with 60 {le} Z {le} 92. Also the program has been extended to give cross-sections for excitation to specific magnetic sublevels of the target ion by an electron beam and very recently it has been extended to give relativistic distorted wave cross sections for ionization of highly charged ions by electron impact.

  15. New Insights in 4f(12)5d(1) Excited States of Tm(2+) through Excited State Excitation Spectroscopy.

    PubMed

    de Jong, Mathijs; Biner, Daniel; Krämer, Karl W; Barandiarán, Zoila; Seijo, Luis; Meijerink, Andries

    2016-07-21

    Optical excitation of ions or molecules typically leads to an expansion of the equilibrium bond lengths in the excited electronic state. However, for 4f(n-1)5d(1) excited states in lanthanide ions both expansion and contraction relative to the 4f(n) ground state have been reported, depending on the crystal field and nature of the 5d state. To probe the equilibrium distance offset between different 4f(n-1)5d(1) excited states, we report excited state excitation (ESE) spectra for Tm(2+) doped in CsCaBr3 and CsCaCl3 using two-color excited state excitation spectroscopy. The ESE spectra reveal sharp lines at low energies, confirming a similar distance offset for 4f(n-1)5d(t2g)(1) states. At higher energies, broader bands are observed, which indicate the presence of excited states with a different offset. On the basis of ab initio embedded-cluster calculations, the broad bands are assigned to two-photon d-d absorption from the excited state. In this work, we demonstrate that ESE is a powerful spectroscopic tool, giving access to information which cannot be obtained through regular one-photon spectroscopy. PMID:27347766

  16. Charmonium excited state spectrum in lattice QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2008-02-01

    Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.

  17. Coulombic Effects on Excited States in a Small Quantum Dot

    NASA Astrophysics Data System (ADS)

    Goldhaber-Gordon, David; Duncan, David; Westervelt, R. M.; Maranowski, K. M.; Gossard, A. C.

    2000-03-01

    The excitation spectrum of a quantum dot varies with the addition of electrons, as successive single-particle eigenstates become filled in the ground state and so cannot accomodate additional electrons. Previous experiments have observed that each spatial state becomes unavailable for transport of further electrons after only one electron has occupied it. We have investigated state occupancy in the excitation spectrum of a small (200 nm X 200 nm) quantum dot laterally defined by capacitively coupled gate electrodes in a GaAs/AlGaAs heterostructure. For our dots, quantized level spacing Δ E ≈ 300 μeV and charging energy Ec ≈ 2 meV. We have studied the evolution of features in the excitation spectrum with magnetic field and equilibrium occupancy and have identified the pattern of spins for the added electrons. These results test the applicability of the spin-degenerate constant interaction picture as well as its limitations.

  18. Excitation wavelength dependence of the charge separation pathways in tetraporphyrin-naphthalene diimide pentads.

    PubMed

    Villamaina, Diego; Kelson, Melissa M A; Bhosale, Sheshanath V; Vauthey, Eric

    2014-03-21

    The excited-state dynamics of two multichromophoric arrays composed of a naphthalene diimide centre and four zinc or free-base porphyrins substituted on the naphthalene core via aniline bridges has been investigated using a combination of stationary and ultrafast spectroscopy. These pentads act as efficient antennae as they absorb over the whole visible region, with a band around 700 nm, associated with a transition to the S1 state delocalised over the whole arrays, and bands at higher energy due to transitions centred on the porphyrins. In non-polar solvents, population of these porphyrin states is followed by sub-picosecond internal conversion to the S1 state. The existence of a charge-separated state located above the S1 state could enhance this process. The decay of the S1 state is dominated by non-radiative deactivation on the 100 ps timescale, most probably favoured by the small S1-S0 energy gap and the very high density of vibrational states of these very large chromophores. In polar solvents, the charge-separated state lies just below the S1 state. It can be populated within a few picoseconds by a thermally activated hole transfer from the S1 state as well as via sub-picosecond non-equilibrium electron transfer from vibrationally hot porphyrin excited states. Because of the small energy gap between the charge-separated state and the ground state, charge recombination is almost barrierless and occurs within a few picoseconds. Despite their very different driving forces, charge separation and recombination occur on similar timescales. This is explained by the electronic coupling that differs considerably for both processes. PMID:24487483

  19. Electronically excited states of PANH anions.

    PubMed

    Theis, Mallory L; Candian, Alessandra; Tielens, Alexander G G M; Lee, Timothy J; Fortenberry, Ryan C

    2015-06-14

    The singly deprotonated anion derivatives of nitrogenated polycyclic aromatic hydrocarbons (PANHs) are investigated for their electronically excited state properties. These include single deprotonation of the two unique arrangements of quinoline producing fourteen different isomers. This same procedure is also undertaken for single deprotonation of the three nitrogenation isomers of acridine and the three of pyrenidine. It is shown quantum chemically that the quinoline-class of PANH anion derivatives can only produce a candidate dipole-bound excited state each, a state defined as the interaction of an extra electron with the dipole moment of the corresponding neutral. However, the acridine- and pyrenidine-classes possess valence excited states as well as the possible dipole-bound excited states where the latter is only possible if the dipole moment is sufficiently large to retain the extra electron; the valence excitation is independent of the radical dipolar strength. As a result, the theoretical vertically computed electronic spectra of deprotonated PANH anion derivatives is fairly rich in the 1.5 eV to 2.5 eV range significantly opening the possibilities for these molecules to be applied to longer wavelength studies of visible and near-IR spectroscopy. Lastly, the study of these systems is also enhanced by the inclusion of informed orbital arrangements in a simply constructed basis set that is shown to be more complete and efficient than standard atom-centered functions. PMID:25975430

  20. High-charge-state ion sources

    SciTech Connect

    Clark, D.J.

    1983-06-01

    Sources of high charge state positive ions have uses in a variety of research fields. For heavy ion particle accelerators higher charge state particles give greater acceleration per gap and greater bending strength in a magnet. Thus higher energies can be obtained from circular accelerators of a given size, and linear accelerators can be designed with higher energy gain per length using higher charge state ions. In atomic physics the many atomic transitions in highly charged ions supplies a wealth of spectroscopy data. High charge state ion beams are also used for charge exchange and crossed beam experiments. High charge state ion sources are reviewed. (WHK)

  1. Persistent order due to transiently enhanced nesting in an electronically excited charge density wave

    DOE PAGESBeta

    Rettig, L.; Cortés, R.; Chu, J. -H.; Fisher, I. R.; Schmitt, F.; Moore, R. G.; Shen, Z. -X.; Kirchmann, P. S.; Wolf, M.; Bovensiepen, U.

    2016-01-25

    Non-equilibrium conditions may lead to novel properties of materials with broken symmetry ground states not accessible in equilibrium as vividly demonstrated by non-linearly driven mid-infrared active phonon excitation. Potential energy surfaces of electronically excited states also allow to direct nuclear motion, but relaxation of the excess energy typically excites fluctuations leading to a reduced or even vanishing order parameter as characterized by an electronic energy gap. Here, using femtosecond time-and angle-resolved photoemission spectroscopy, we demonstrate a tendency towards transient stabilization of a charge density wave after near-infrared excitation, counteracting the suppression of order in the non-equilibrium state. Analysis of themore » dynamic electronic structure reveals a remaining energy gap in a highly excited transient state. In conclusion, our observation can be explained by a competition between fluctuations in the electronically excited state, which tend to reduce order, and transiently enhanced Fermi surface nesting stabilizing the order.« less

  2. Electron excitation from ground state to first excited state: Bohmian mechanics method

    NASA Astrophysics Data System (ADS)

    Yang, Song; Shuang, Zhao; Fu-Ming, Guo; Yu-Jun, Yang; Su-Yu, Li

    2016-03-01

    The excitation process of electrons from the ground state to the first excited state via the resonant laser pulse is investigated by the Bohmian mechanics method. It is found that the Bohmian particles far away from the nucleus are easier to be excited and are excited firstly, while the Bohmian particles in the ground state is subject to a strong quantum force at a certain moment, being excited to the first excited state instantaneously. A detailed analysis for one of the trajectories is made, and finally we present the space and energy distribution of 2000 Bohmian particles at several typical instants and analyze their dynamical process at these moments. Project supported by the Doctoral Research Start-up Funding of Northeast Dianli University, China (Grant No. BSJXM-201332), the National Natural Science Foundation of China (Grant Nos. 11547114, 11534004, 11474129, 11274141, 11447192, and 11304116), and the Graduate Innovation Fund of Jilin University, China (Grant No. 2015091).

  3. Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure

    SciTech Connect

    Valone, S. M.; Pilania, G.; Liu, X. Y.; Allen, J. R.; Wu, T.-C.; Atlas, S. R.; Dunlap, D. H.

    2015-11-14

    Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) model uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transfer hopping integrals T and on-fragment parameters U{sup (FH)}. The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. We demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U{sup (FH)}, thus providing new insight into the nature of metal-insulator transitions. This result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.

  4. Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure

    NASA Astrophysics Data System (ADS)

    Valone, S. M.; Pilania, G.; Liu, X. Y.; Allen, J. R.; Wu, T.-C.; Atlas, S. R.; Dunlap, D. H.

    2015-11-01

    Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) model uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transfer hopping integrals T and on-fragment parameters U(FH). The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. We demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U(FH), thus providing new insight into the nature of metal-insulator transitions. This result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.

  5. Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods.

    PubMed

    Prlj, Antonio; Sandoval-Salinas, María Eugenia; Casanova, David; Jacquemin, Denis; Corminboeuf, Clémence

    2016-06-14

    The description of low-lying ππ* states of linear acenes by standard electronic structure methods is known to be challenging. Here, we broaden the framework of this problem by considering a set of fused heteroaromatic rings and demonstrate that standard electronic structure methods do not provide a balanced description of the two (typically) lowest singlet state (La and Lb) excitations. While the Lb state is highly sensitive to correlation effects, La suffers from the same drawbacks as charge transfer excitations. We show that the comparison between CIS/CIS(D) can serve as a diagnostic for detecting the two problematic excited states. Standard TD-DFT and even its spin-flip variant lead to inaccurate excitation energies and interstate gaps, with only a double hybrid functional performing somewhat better. The complication inherent to a balanced description of these states is so important that even CC2 and ADC(2) do not necessarily match the ADC(3) reference. PMID:27144975

  6. Electron impact excitation of highly charged sodium-like ions

    NASA Technical Reports Server (NTRS)

    Blaha, M.; Davis, J.

    1978-01-01

    Optical transition probabilities and electron collision strengths for Ca X, Fe XVI, Zn XX, Kr XXVI and Mo XXXII are calculated for transitions between n equal to 3 and n equal to 4 levels. The calculations neglect relativistic effects on the radial functions. A semi-empirical approach provides wave functions of the excited states; a distorted wave function without exchange is employed to obtain the excitation cross sections. The density dependence of the relative intensities of certain emission lines in the sodium isoelectronic sequence is also discussed.

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

    PubMed

    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. PMID:25731863

  8. Integrating proton coupled electron transfer (PCET) and excited states

    SciTech Connect

    Gagliardi, Christopher J.; Westlake, Brittany C.; Kent, Caleb A.; Paul, Jared J.; Papanikolas, John M.; Meyer, Thomas J.

    2010-11-01

    In many of the chemical steps in photosynthesis and artificial photosynthesis, proton coupled electron transfer (PCET) plays an essential role. An important issue is how excited state reactivity can be integrated with PCET to carry out solar fuel reactions such as water splitting into hydrogen and oxygen or water reduction of CO2 to methanol or hydrocarbons. The principles behind PCET and concerted electron–proton transfer (EPT) pathways are reasonably well understood. In Photosystem II antenna light absorption is followed by sensitization of chlorophyll P680 and electron transfer quenching to give P680+. The oxidized chlorophyll activates the oxygen evolving complex (OEC), a CaMn4 cluster, through an intervening tyrosine–histidine pair, YZ. EPT plays a major role in a series of four activation steps that ultimately result in loss of 4e-/4H+ from the OEC with oxygen evolution. The key elements in photosynthesis and artificial photosynthesis – light absorption, excited state energy and electron transfer, electron transfer activation of multiple-electron, multiple-proton catalysis – can also be assembled in dye sensitized photoelectrochemical synthesis cells (DS-PEC). In this approach, molecular or nanoscale assemblies are incorporated at separate electrodes for coupled, light driven oxidation and reduction. Separate excited state electron transfer followed by proton transfer can be combined in single semi-concerted steps (photo-EPT) by photolysis of organic charge transfer excited states with H-bonded bases or in metal-to-ligand charge transfer (MLCT) excited states in pre-associated assemblies with H-bonded electron transfer donors or acceptors. In these assemblies, photochemically induced electron and proton transfer occur in a single, semi-concerted event to give high-energy, redox active intermediates.

  9. Resonant plasmon-axion excitations induced by charge density wave order in a Weyl semimetal

    NASA Astrophysics Data System (ADS)

    Redell, Matthew D.; Mukherjee, Shantanu; Lee, Wei-Cheng

    2016-06-01

    We investigate the charge excitations of a Weyl semimetal in the axionic charge density wave (axionic CDW) state. While it has been shown that the topological response (anomalous Hall conductivity) is protected against the CDW state, we find that the long-wavelength plasmon excitation is radically influenced by the dynamics of the CDW order parameter. In the normal state, we show that an undamped collective mode should exist at q ⃗≈Q⃗CDW if there is an attractive interaction favoring the formation of the CDW state. The undamped nature of this collective mode is attributed to a gaplike feature in the particle-hole continuum at q ⃗≈Q⃗CDW due to the chirality of the Weyl nodes, which is not seen in other materials with CDW instability. In the CDW state, the long-wavelength plasmon excitations become more dispersive due to the additional interband scattering not allowed in the normal state. Moreover, because the translational symmetry is spontaneously broken, umklapp scattering, the process conserving the total momentum only up to n Q⃗CDW , with n an integer and Q⃗CDW the ordering wave vector, emerges in the CDW state. We find that the plasmon excitation couples to the phonon mode of the CDW order via the umklapp scattering, leading to two branches of resonant collective modes observable in the density-density correlation function at q ⃗≈0 and q ⃗≈Q⃗CDW . Based on our analysis, we propose that measuring these resonant plasmon-axion excitations around q ⃗≈0 and q ⃗≈Q⃗CDW by momentum-resolved electron energy loss spectroscopy could serve as a reliable way to detect the axionic CDW state in Weyl semimetals.

  10. Impact of ground- and excited-state aromaticity on cyclopentadiene and silole excitation energies and excited-state polarities.

    PubMed

    Jorner, Kjell; Emanuelsson, Rikard; Dahlstrand, Christian; Tong, Hui; Denisova, Aleksandra V; Ottosson, Henrik

    2014-07-21

    A new qualitative model for estimating the properties of substituted cyclopentadienes and siloles in their lowest ππ* excited states is introduced and confirmed through quantum chemical calculations, and then applied to explain earlier reported experimental excitation energies. According to our model, which is based on excited-state aromaticity and antiaromaticity, siloles and cyclopentadienes are cross-hyperconjugated "aromatic chameleons" that adapt their electronic structures to conform to the various aromaticity rules in different electronic states (Hückel's rule in the π(2) electronic ground state (S0) and Baird's rule in the lowest ππ* excited singlet and triplet states (S1 and T1)). By using pen-and-paper arguments, one can explain polarity changes upon excitation of substituted cyclopentadienes and siloles, and one can tune their lowest excitation energies by combined considerations of ground- and excited-state aromaticity/antiaromaticity effects. Finally, the "aromatic chameleon" model can be extended to other monocyclic compound classes of potential use in organic electronics, thereby providing a unified view of the S0, T1, and S1 states of a range of different cyclic cross-π-conjugated and cross-hyperconjugated compound classes. PMID:25043523

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

    SciTech Connect

    Baldacchini, Chiara; Bizzarri, Anna Rita; Cannistraro, Salvatore

    2014-03-03

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

  12. Excited states in the soliton bag model

    SciTech Connect

    Saly, R.; Sundaresan, M.K.

    1984-02-01

    Numerical analysis of the solutions of the soliton bag model of Friedberg and Lee is performed. The recent analysis of Goldflam and Wilets is extended to include even-parity as well as odd-parity radially excited states. It is shown that the existence of the solutions (especially the odd-parity ones) restrict severely the allowed range of parameters.

  13. Limits on charge nonconservation studied by nuclear excitation of sup 127 I

    SciTech Connect

    Ejiri, H.; Kawasaki, M.; Kinoshita, H.; Ohsumi, H.; Okada, K.; Sano, H. ); Takasugi, E. )

    1991-07-01

    Lower limits on the mean lives of the charge-nonconserving (CNC) processes, {sup 127}I+{ital e}{sub {ital K}}{r arrow}{sup 127}I{sup *}+{nu}, leading to the first (second) excited state of {sup 127}I, were obtained as {tau}{gt}0.58(0.56){times}10{sup 23} yr by searching for the {gamma} decay from the first (second) excited state of {sup 127}I. Upper limits on the ratios of the CNC strengths to the charge-conserving ones through the weak boson and photon mediating processes are obtained as {epsilon}{sub {ital W}}{sup 2}{lt}11{times}10{sup {minus}25} and {epsilon}{sub {gamma}}{sup 2}{lt}4.8{times}10{sup {minus}40}.

  14. Excited intruder states in {sup 32}Mg

    SciTech Connect

    Tripathi, Vandana; Tabor, S. L.; Bender, P.; Hoffman, C. R.; Lee, Sangjin; Pepper, K.; Perry, M.; Utsuno, Y.; Otsuka, T.; Mantica, P. F.; Pinter, J. S.; Stoker, J. B.; Cook, J. M.; Pereira, J.; Weisshaar, D.

    2008-03-15

    The low energy level structure of N=20 {sup 32}Mg obtained via {beta}-delayed {gamma} spectroscopy is reported. The level structure of {sup 32}Mg is found to be completely dominated by intruders. An inversion between the 1p-1h and 3p-3h states is observed for the negative parity states, similar to the 0p-0h and 2p-2h inversion for the positive parity states in these N{approx}20 nuclei. The intruder excited states, both positive and negative parity, are reasonably explained by Monte Carlo shell model calculations, which suggest a shrinking N=20 shell gap with decreasing Z.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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*, π-π*, 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.

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

    SciTech Connect

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

    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.

  17. On the Electronically Excited States of Uracil

    SciTech Connect

    Epifanovsky, Evgeny; Kowalski, Karol; Fan, Peng-Dong; Valiev, Marat; Matsika, Spiridoula; Krylov, Anna

    2008-10-09

    Vertical excitation energies in uracil in the gas phase and in water solution are investigated by the equation-of-motion coupled-cluster and multi-reference configuration interaction methods. Basis set effects are found to be important for converged results. The analysis of electronic wave functions reveals that the lowest singlet states are predominantly of a singly excited character and are therefore well described by single-reference equation-of-motion methods augmented by a perturbative triples correction to account for dynamical correlation. Our best estimates for the vertical excitation energies for the lowest singlet n and are 5.0±0.1 eV and 5.3±0.1 eV, respectively. The solvent effects for these states are estimated to be +0.5 eV and ±0.1 eV, respectively. We attribute the difference between the computed vertical excitations and the maximum of the experimental absorption to strong vibronic interaction between the lowest A00 and A0 states leading to intensity borrowing by the forbidden transition.

  18. STIRAP on helium: Excitation to Rydberg states

    NASA Astrophysics Data System (ADS)

    Yuan, Deqian

    Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S→33P→nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of ~ 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable ~790 nm IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S → 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections.

  19. Protein-induced excited-state dynamics of protochlorophyllide.

    PubMed

    Hanf, Robert; Fey, Sonja; Dietzek, Benjamin; Schmitt, Michael; Reinbothe, Christiane; Reinbothe, Steffen; Hermann, Gudrun; Popp, Jürgen

    2011-07-14

    The light-driven NADPH:protochlorophyllide oxidoreductase (POR) is a key enzyme of chlorophyll biosynthesis in angiosperms. POR's unique requirement for light to become catalytically active makes the enzyme an attractive model to study the dynamics of enzymatic reactions in real time. Here, we use picosecond time-resolved fluorescence and femtosecond pump-probe spectroscopy to examine the influence of the protein environment on the excited-state dynamics of the substrate, protochlorophyllide (PChlide), in the enzyme/substrate (PChlide/POR) and pseudoternary complex including the nucleotide cofactor NADP(+) (PChlide/NADP(+)/ POR). In comparison with the excited-state processes of unbound PChlide, the lifetime of the thermally equilibrated S(1) excited state is lengthened from 3.4 to 4.4 and 5.4 ns in the PChlide/POR and PChlide/NADP(+)/POR complex, whereas the nonradiative rates are decreased by ∼30 and 40%, respectively. This effect is most likely due to the reduced probability of nonradiative decay into the triplet excited state, thus keeping the risk of photosensitized side reactions in the enzyme low. Further, the initial reaction path involves the formation of an intramolecular charge-transfer state (S(ICT)) as an intermediate product. From a strong blue shift in the excited-state absorption, it is concluded that the S(ICT) state is stabilized by local interactions with specific protein sites in the catalytic pocket. The possible relevance of this result for the catalytic reaction in the enzyme POR is discussed. PMID:21678944

  20. Photoionization from excited states of helium

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The cross sections for photoionization from the 2 1S, 2 3S, 2 1P and 2 3P excited states of helium are calculated for photoelectron energies below the n = 2 threshold of He(+) using Hylleraas bound state wave functions and 1s-2s-2p close coupling final state wave functions. The resonant structures associated with the lowest-lying 1S, 1P, 3P, and 1D autoionizing states of helium are found to be characterized by large values of the line profile parameter q. The cross sections and the photoelectron angular distribution asymmetry parameters for the P-states are calculated for various polarization states of the target atom and the incident photon. Experiments which would lead to the separate determinations of the S- and D- wave partial photoionization cross sections are discussed.

  1. Precision Study of Excited State Effects in Nucleon Matrix Elements

    SciTech Connect

    Simon Dinter, Constantia Alexandrou, Martha Constantinou, Vincent Drach, Karl Jansen, Dru B. Renner

    2011-10-01

    We present a dedicated precision analysis of the influence of excited states on the calculation of several nucleon matrix elements. This calculation is performed at fixed values of the lattice spacing, volume and pion mass that are typical of contemporary lattice computations. We focus on the nucleon axial charge, g{sub A}, for which we use 7,500 measurements, and on the average momentum of the unpolarized isovector parton distribution, x{sub u-d}, for which we use 23,000 measurements. All computations are done employing N{sub f}=2+1+1 maximally-twisted-mass Wilson fermions and non-perturbatively calculated renormalization factors. We find that excited state effects are negligible for g{sub A} and lead to a O(10%) downward shift for x{sub u-d}.

  2. Intermediate Excited States in Rhodopsin Photochemistry

    NASA Astrophysics Data System (ADS)

    Rothberg, L. J.; Yan, M.; Jedju, T. M.; Callender, R. H.; Chao, H.; Alfano, R. R.

    1996-03-01

    Recent work by Wang et.al. footnote Q. Wang et.al., Science 266, 422 (1994) reports rapid coherent photoisomerization in rhodopsin. The bathorhodopsin photoproduct appears in 200 fs and exhibits torsional oscillations which remain synchronized with the initial photoexcitation. We report transient absorption experiments which suggest that the fraction of excited rhodopsin molecules which does not isomerize in this fashion (approximately 1/3) remains in an electronically excited state, probably the twisted state described by Birge and Hubbard,footnote R. R. Birge and L. M. Hubbard, J. Am. Chem. Soc. 102, 2195 (1980) for ~ 3 ps and then reforms rhodopsin. This picture explains the long bleaching recovery time for rhodopsin and the controversial spectral dynamics which are observed in the red.

  3. Minimal-excitation states for electron quantum optics using levitons

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  4. Embedding potentials for excited states of embedded species

    SciTech Connect

    Wesolowski, Tomasz A.

    2014-05-14

    Frozen-Density-Embedding Theory (FDET) is a formalism to obtain the upper bound of the ground-state energy of the total system and the corresponding embedded wavefunction by means of Euler-Lagrange equations [T. A. Wesolowski, Phys. Rev. A 77(1), 012504 (2008)]. FDET provides the expression for the embedding potential as a functional of the electron density of the embedded species, electron density of the environment, and the field generated by other charges in the environment. Under certain conditions, FDET leads to the exact ground-state energy and density of the whole system. Following Perdew-Levy theorem on stationary states of the ground-state energy functional, the other-than-ground-state stationary states of the FDET energy functional correspond to excited states. In the present work, we analyze such use of other-than-ground-state embedded wavefunctions obtained in practical calculations, i.e., when the FDET embedding potential is approximated. Three computational approaches based on FDET, that assure self-consistent excitation energy and embedded wavefunction dealing with the issue of orthogonality of embedded wavefunctions for different states in a different manner, are proposed and discussed.

  5. Controlling excited-state contamination in nucleon matrix elements

    NASA Astrophysics Data System (ADS)

    Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank; Nucleon Matrix Elements NME Collaboration

    2016-06-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2 +1 -flavor ensemble with lattices of size 323×64 generated using the rational hybrid Monte Carlo algorithm at a =0.081 fm and with Mπ=312 MeV . The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a 2-state fit to data at multiple values of the source-sink separation tsep. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of tsep needed to demonstrate convergence of the isovector charges of the nucleon to the tsep→∞ estimates is presented.

  6. Excited state baryon spectroscopy from lattice QCD

    SciTech Connect

    Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.

    2011-10-31

    Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting of levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.

  7. Excited state baryon spectroscopy from lattice QCD

    DOE PAGESBeta

    Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.

    2011-10-31

    Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting ofmore » levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.« less

  8. Charge state manipulation of qubits in diamond

    PubMed Central

    Grotz, Bernhard; Hauf, Moritz V.; Dankerl, Markus; Naydenov, Boris; Pezzagna, Sébastien; Meijer, Jan; Jelezko, Fedor; Wrachtrup, Jörg; Stutzmann, Martin; Reinhard, Friedemann; Garrido, Jose A.

    2012-01-01

    The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV− into the neutral state NV0 under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV0, and the population of an ensemble of centres can be shifted from NV0 to NV−. Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV+. PMID:22395620

  9. Radiative and Excited State Charmonium Physics

    SciTech Connect

    Jozef Dudek

    2007-07-30

    Renewed interest in the spectroscopy of charmonium has arisen from recent unexpected observations at $e^+e^-$ colliders. Here we report on a series of works from the previous two years examining the radiative physics of charmonium states as well as the mass spectrum of states of higher spin and internal excitation. Using new techniques applied to Domain-Wall and Clover quark actions on quenched isotropic and anisotropic lattices, radiative transitions and two-photon decays are considered for the first time. Comparisons are made with experimental results and with model approaches. Forthcoming application to the light-quark sector of relevance to experiments like Jefferson Lab's GlueX is discussed.

  10. Exploring Photoinduced Excited State Evolution in Heterobimetallic Ru(II)-Co(III) Complexes.

    PubMed

    Kuhar, Korina; Fredin, Lisa A; Persson, Petter

    2015-06-18

    Quantum chemical calculations provide detailed theoretical information concerning key aspects of photoinduced electron and excitation transfer processes in supramolecular donor-acceptor systems, which are particularly relevant to fundamental charge separation in emerging molecular approaches for solar energy conversion. Here we use density functional theory (DFT) calculations to explore the excited state landscape of heterobimetallic Ru-Co systems with varying degrees of interaction between the two metal centers, unbound, weakly bound, and tightly bound systems. The interplay between structural and electronic factors involved in various excited state relaxation processes is examined through full optimizations of multiple charge/spin states of each of the investigated systems. Low-energy relaxed heterobimetallic states of energy transfer and excitation transfer character are characterized in terms of energy, structure, and electronic properties. These findings support the notion of efficient photoinduced charge separation from a Ru(II)-Co(III) ground state, via initial optical excitation of the Ru-center, to low-energy Ru(III)-Co(II) states. The strongly coupled system has significant involvement of the conjugated bridge, qualitatively distinguishing it from the other two weakly coupled systems. Finally, by constructing potential energy surfaces for the three systems where all charge/spin state combinations are projected onto relevant reaction coordinates, excited state decay pathways are explored. PMID:25719556

  11. Nuclear Spin Orientation Dependence of Magnetoconductance: A New Method for Measuring the Spin of Charged Excitations in the QHE

    SciTech Connect

    Bowers, C.R.; Reno, J.L.; Simmons, J.A.; Vitkalov, S.A.

    1998-12-01

    A new method for measuring the spin of the electrically charged ground state excitations m the Q$j~j quantum Hall effect ia proposed and demonstmted for the tirst time in GaAs/AIGaAs nndtiquantum wells. The method is &sed on the nuclear spin orientation dependence of" the 2D dc conductivity y in the quantum Hall regime due to the nuclear hyperfine interaction. As a demonstration of this method the spin of the electrically charged excitations of the ground state is determined at filling factor v = 1.

  12. Back-action-induced excitation of electrons in a silicon quantum dot with a single-electron transistor charge sensor

    SciTech Connect

    Horibe, Kosuke; Oda, Shunri; Kodera, Tetsuo

    2015-02-02

    Back-action in the readout of quantum bits is an area that requires a great deal of attention in electron spin based-quantum bit architecture. We report here back-action measurements in a silicon device with quantum dots and a single-electron transistor (SET) charge sensor. We observe the back-action-induced excitation of electrons from the ground state to an excited state in a quantum dot. Our measurements and theoretical fitting to the data reveal conditions under which both suitable SET charge sensor sensitivity for qubit readout and low back-action-induced transition rates (less than 1 kHz) can be achieved.

  13. Resonant charge-exchange involving excited helium atoms and reactive transport of local thermodynamic equilibrium helium plasma

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    The cross sections for charge-exchange and charge-transfer processes are evaluated for collisions of helium ions with parent-atoms in ground and excited states, with the principal quantum number n = 1-5, in the collision energy range from thermal up to 10 eV. Corresponding diffusion-type collision integrals are derived, and the role of "abnormal" transport of electronically excited states on the reactive thermal conductivity of equilibrium helium plasma, at atmospheric pressure, estimated in the frame of a simplified approach.

  14. Excited State Effects in Nucleon Matrix Element Calculations

    SciTech Connect

    Constantia Alexandrou, Martha Constantinou, Simon Dinter, Vincent Drach, Karl Jansen, Theodoros Leontiou, Dru B Renner

    2011-12-01

    We perform a high-statistics precision calculation of nucleon matrix elements using an open sink method allowing us to explore a wide range of sink-source time separations. In this way the influence of excited states of nucleon matrix elements can be studied. As particular examples we present results for the nucleon axial charge g{sub A} and for the first moment of the isovector unpolarized parton distribution x{sub u-d}. In addition, we report on preliminary results using the generalized eigenvalue method for nucleon matrix elements. All calculations are performed using N{sub f} = 2+1+1 maximally twisted mass Wilson fermions.

  15. Ultrafast excited-state dynamics of isocytosine.

    PubMed

    Szabla, Rafał; Góra, Robert W; Šponer, Jiří

    2016-07-27

    The alternative nucleobase isocytosine has long been considered as a plausible component of hypothetical primordial informational polymers. To examine this hypothesis we investigated the excited-state dynamics of the two most abundant forms of isocytosine in the gas phase (keto and enol). Our surface-hopping nonadiabatic molecular dynamics simulations employing the algebraic diagrammatic construction to the second order [ADC(2)] method for the electronic structure calculations suggest that both tautomers undergo efficient radiationless deactivation to the electronic ground state with time constants which amount to τketo = 182 fs and τenol = 533 fs. The dominant photorelaxation pathways correspond to ring-puckering (ππ* surface) and C[double bond, length as m-dash]O stretching/N-H tilting (nπ* surface) for the enol and keto forms respectively. Based on these findings, we infer that isocytosine is a relatively photostable compound in the gas phase and in these terms resembles biologically relevant nucleobases. The estimated S1 [radiolysis arrow - arrow with voltage kink] T1 intersystem crossing rate constant of 8.02 × 10(10) s(-1) suggests that triplet states might also play an important role in the overall excited-state dynamics of the keto tautomer. The reliability of ADC(2)-based surface-hopping molecular dynamics simulations was tested against multireference quantum-chemical calculations and the potential limitations of the employed ADC(2) approach are briefly discussed. PMID:27346684

  16. Doping evolution of spin and charge excitations in the Hubbard model

    SciTech Connect

    Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; Johnston, S.; Moritz, B.; Scalettar, R. T.; Devereaux, T. P.

    2015-11-05

    We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achieved in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.

  17. Doping evolution of spin and charge excitations in the Hubbard model

    DOE PAGESBeta

    Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; Johnston, S.; Moritz, B.; Scalettar, R. T.; Devereaux, T. P.

    2015-11-05

    We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achievedmore » in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.« less

  18. Explicit calculation of the excited electronic states of the photosystem II reaction centre.

    PubMed

    Frankcombe, Terry J

    2015-02-01

    The excited states of sets of the cofactors found in the photosystem II reaction centre have been calculated directly as a multi-monomer supermolecule for the first time. Time-dependent density functional theory was used with the CAM-B3LYP functional. Multiple excited states for each cofactor were found at lower energies than the lowest energy state corresponding to charge transfer states (in which an electron is shifted from one cofactor to another). The electrostatic environment was found to have a dramatic impact on the excited state energies, with the effect of a surrounding dielectric medium being less significant. PMID:25523136

  19. Excited-State Properties of Molecular Solids from First Principles

    NASA Astrophysics Data System (ADS)

    Kronik, Leeor; Neaton, Jeffrey B.

    2016-05-01

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion.

  20. Excited-State Properties of Molecular Solids from First Principles.

    PubMed

    Kronik, Leeor; Neaton, Jeffrey B

    2016-05-27

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion. PMID:27090844

  1. Ultrafast excited-state dynamics of copper(I) complexes.

    PubMed

    Iwamura, Munetaka; Takeuchi, Satoshi; Tahara, Tahei

    2015-03-17

    Bis-diimine Cu(I) complexes exhibit strong absorption in the visible region owing to the metal-to-ligand charge transfer (MLCT) transitions, and the triplet MLCT ((3)MLCT) states have long lifetimes. Because these characteristics are highly suitable for photosensitizers and photocatalysts, bis-diimine Cu(I) complexes have been attracting much interest. An intriguing feature of the Cu(I) complexes is the photoinduced structural change called "flattening". Bis-diimine Cu(I) complexes usually have tetrahedron-like D2d structures in the ground (S0) state, in which two ligands are perpendicularly attached to the Cu(I) ion. With MLCT excitation, the central Cu(I) ion is formally oxidized to Cu(II), which induces the structural change to the "flattened" square-planar-like structure that is seen for usual Cu(II) complexes. In this Account, we review our recent studies on ultrafast excited-state dynamics of bis-diimine Cu(I) complexes carried out using femtosecond time-resolved optical spectroscopy. Focusing on three prototypical bis-diimine Cu(I) complexes that have 1,10-phenanthroline ligands with different substituents at the 2,9-positions, i.e., [Cu(phen)2](+) (phen = 1,10-phenanthroline), [Cu(dmphen)2](+) (dmphen = 2,9-dimethyl-1,10-phenanthroline), and [Cu(dpphen)2](+) (dpphen = 2,9-diphenyl-1,10-phenanthroline), we examined their excited-state dynamics by time-resolved emission and absorption spectroscopies with 200 fs time resolution, observed the excited-state coherent nuclear motion with 30 fs time resolution and performed complementary theoretical calculations. This combined approach vividly visualizes excited-state processes in the MLCT state of bis-diimine Cu(I) complexes. It was demonstrated that flattening distortion, internal conversion, and intersystem crossing occur on the femtosecond-early picosecond time scale, and their dynamics is clearly identified separately. The flattening distortion predominantly occurs in the S1 state on the subpicosecond time

  2. Three Long Lived Excited States of Tm^-

    NASA Astrophysics Data System (ADS)

    O'Malley, Steven M.; Beck, Donald R.

    2004-05-01

    Recent measurements(V. T. Davis and J. S. Thompson, Phys. Rev. A 65), 010501 (2001). have yielded 2 Tm^- states with lifetimes >50 μs [2] with estimated electron affinities of ˜1 eV. Theory does not support a 4f attachment to the ground state(D. Datta and D. R. Beck, Phys. Rev. A 47), 5198 (1993)., and at most only a weak (<100 meV) 6p attachment(J. A. Chevary and S. H. Vosko, J. Phys. B 27), 657 (1994).. Our more accurate calculations for 4f, 5d, and 6p attachment to the ground state find no evidence of any bound state associated with these attachments. We then turned to attachment to ``low lying'' Tm I excited states. Candidates must have lifetimes >50 μs, unusually long for simpler species except for He^-, Be^-, and Ba^- (T. Andersen et al., J. Phys. Chem. Ref. Data 28), 1511 (1999).. Using a relativistic configuration interaction in the continuum methodology (Z. Cai, D. R. Beck, and W. F. Perger, Phys. Rev. A 43), 4660 (1991)., we have found 3 states, 4f^125d6s^26p (J=8,9,10), with lifetimes of 10 μs, 5 ms, and 3 ms, respectively. These are bound to their natural thresholds by 254, 258, and 173 meV and may represent what is being observed [2].

  3. Dichotomous Role of Exciting the Donor or the Acceptor on Charge Generation in Organic Solar Cells.

    PubMed

    Hendriks, Koen H; Wijpkema, Alexandra S G; van Franeker, Jacobus J; Wienk, Martijn M; Janssen, René A J

    2016-08-10

    In organic solar cells, photoexcitation of the donor or acceptor phase can result in different efficiencies for charge generation. We investigate this difference for four different 2-pyridyl diketopyrrolopyrrole (DPP) polymer-fullerene solar cells. By comparing the external quantum efficiency spectra of the polymer solar cells fabricated with either [60]PCBM or [70]PCBM fullerene derivatives as acceptor, the efficiency of charge generation via donor excitation and acceptor excitation can both be quantified. Surprisingly, we find that to make charge transfer efficient, the offset in energy between the HOMO levels of donor and acceptor that govern charge transfer after excitation of the acceptor must be larger by ∼0.3 eV than the offset between the corresponding two LUMO levels when the donor is excited. As a consequence, the driving force required for efficient charge generation is significantly higher for excitation of the acceptor than for excitation of the donor. By comparing charge generation for a total of 16 different DPP polymers, we confirm that the minimal driving force, expressed as the photon energy loss, differs by about 0.3 eV for exciting the donor and exciting the acceptor. Marcus theory may explain the dichotomous role of exciting the donor or the acceptor on charge generation in these solar cells. PMID:27452683

  4. Theory of ultrafast heterogeneous electron transfer: Contributions of direct charge transfer excitations to the absorbance

    NASA Astrophysics Data System (ADS)

    Wang, Luxia; Willig, Frank; May, Volkhard

    2007-04-01

    Absorption spectra related to heterogeneous electron transfer are analyzed with the focus on direct charge transfer transition from the surface attached molecule into the semiconductor band states. The computations are based on a model of reduced dimensionality with a single intramolecular vibrational coordinate but a complete account for the continuum of conduction band states. The applicability of this model to perylene on TiO2 has been demonstrated in a series of earlier papers. Here, based on a time-dependent formulation, the absorbance is calculated with the inclusion of charge transfer excitations. A broad parameter set inspired by the perylene TiO2 systems is considered. In particular, the description generalizes the Fano effect to heterogeneous electron transfer reactions. Preliminary simulations of measured spectra are presented for perylene-catechol attached to TiO2.

  5. Structures and Binding Energies of the Naphthalene Dimer in Its Ground and Excited States.

    PubMed

    Dubinets, N O; Safonov, A A; Bagaturyants, A A

    2016-05-01

    Possible structures of the naphthalene dimer corresponding to local energy minima in the ground and excited (excimer) electronic states are comprehensively investigated using DFT-D and TDDFT-D methods with a special accent on the excimer structures. The corresponding binding and electronic transition energies are calculated, and the nature of the electronic states in different structures is analyzed. Several parallel (stacked) and T-shaped structures were found in both the ground and excited (excimer) states in a rather narrow energy range. The T-shaped structure with the lowest energy in the excited state exhibits a marked charge transfer from the upright molecule to the base one. PMID:27080987

  6. Endoergic and resonant charge transfer excitation in He-Cu discharge

    NASA Astrophysics Data System (ADS)

    Mezei, P.; Rózsa, K.; Jánossy, M.; Apai, P.

    1987-09-01

    The intensity of Cu-II lines with upper level energies near and above those of the He ion was measured as a function of He pressure in a Cu hollow cathode tube. In this tube at low pressures the negative glow could expand above the cathode. The maximum intensity of the Cu-II 493.1 nm line was found in the low voltage, high pressure hollow cathode discharge region in accordance with a resonant charge transfer excitation process. Enhancement of the intensity of the Cu-II 436.5 nm and 417.9 nm lines was observed in the cathode glow at low pressures. Excitation of these lines is attributed to endoergic charge transfer collisions between He ions accelerated by the 2 kV tube voltage and ground state Cu atoms. The cross-section for this reaction exciting the 436.5 nm line was estimated to be of the order of 10-17 cm2.

  7. Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations.

    PubMed

    List, Nanna Holmgaard; Zaleśny, Robert; Murugan, N Arul; Kongsted, Jacob; Bartkowiak, Wojciech; Ågren, Hans

    2015-09-01

    We establish the relationships between the metric of charge transfer excitation (Δr) for the bright ππ* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push-pull π-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), Δr is a measure for the average hole-electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push-pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through Δr; if β ∼ (Δr)(k), then roughly, δ(TPA) ∼ (Δr)(k+1). Second, a simple power relation between Δr and the molecular hyperpolarizabilities of push-pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull π-conjugated systems through the metric of charge transfer. PMID:26575913

  8. Nonequilibrium solvent effects in Born-Oppenheimer molecular dynamics for ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Bjorgaard, J. A.; Velizhanin, K. A.; Tretiak, S.

    2016-04-01

    The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited state molecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited state molecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission.

  9. Multidirectional Angular Electronic Flux during Adiabatic Attosecond Charge Migration in Excited Benzene.

    PubMed

    Hermann, Gunter; Liu, ChunMei; Manz, Jörn; Paulus, Beate; Pérez-Torres, Jhon Fredy; Pohl, Vincent; Tremblay, Jean Christophe

    2016-07-14

    Recently, adiabatic attosecond charge migration (AACM) has been monitored and simulated for the first time, with application to the oriented iodoacetylene cation where AACM starts from the initial superposition of the ground state (φ0) and an electronic excited state (φ1). Here, we develop the theory for electronic fluxes during AACM in ring-shaped molecules, with application to oriented benzene prepared in the superposition of the ground and first excited singlet states. The initial state and its time evolution are analogous to coherent tunneling where φ0 and φ1 have different meanings; however, they denote the wave functions of the lowest tunneling doublet. This analogy suggests to transfer the theory of electronic fluxes during coherent tunneling to AACM, with suitable modifications which account for (i) the different time scales and (ii) the different electronic states, and which make use of (iii) the preparation of the initial state for AACM by a linearly polarized laser pulse. Application to benzene yields the multidirectional angular electronic flux with a pincer-motion type pattern during AACM: this unequivocal result confirms a previous working hypothesis. Moreover, the theory of AACM allows quantification of the electronic flux; that is, the maximum number of electrons (out of 42) which flow concertedly during AACM in benzene is 6 × 0.08 = 0.48. PMID:27046151

  10. Electronic Ground and Excited State Spectral Diffusion of a Photocatalyst

    NASA Astrophysics Data System (ADS)

    Kiefer, Laura M.; King, John T.; Kubarych, Kevin J.

    2014-06-01

    Re(bpy)(CO)_3Cl is a well studied CO_2 reduction catalyst, known for its ability as both a photosensitizer and a catalyst with a high quantum yield and product selectivity. The catalysis reaction is initiated by a 400 nm excitation, followed by an intersystem crossing (ISC) and re-equilibration in the lowest triplet state. We utilize the quasi-equilibrium nature of this long-lived triplet metal-to-ligand charge-transfer (3MLCT) state to completely characterize the solvent dynamics using the technique of transient two-dimensional infrared (t-2DIR) spectroscopy to extract observables such as the frequency-frequency correlation function (FFCF), an equilibrium function. The electronic ground state solvent dynamics are characterized using equilibrium two-dimensional infrared spectroscopy (2D IR). Our technique allows us to independently observe the solvent dynamics of different electronic states and compare them. In this study, three carbonyl stretching modes were utilized to probe both the intramolecular and solvent environments in each electronic state. In the electronic ground state, the totally symmetric mode exhibits pure homogeneous broadening and a lack of spectral dynamics, while the two other modes have similar FFCF decay times of ˜ 1.5 ps. In the 3MLCT, however, all three modes experience similar spectral dynamics and have a FFCF decay time of ˜ 4.5 ps, three times slower than in the electronic ground state. Our technique allows us to directly observe the differences in spectral dynamics of the ground and excited electronic states and allows us to attribute the differences to specific origins such as solvent-solute coupling and molecular flexibility.

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

    PubMed

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

    2003-03-01

    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. PMID:12689221

  12. Low-charge-state RFQ injector

    SciTech Connect

    Shepard, K.W.; Kim, J.W.

    1995-08-01

    Preliminary design work was done for a short, normally-conducting RFQ entrance section for a low-charge-state linac. Early results indicate that a low- frequency (12 MHz) RFQ, operated on a high-voltage platform, and injected with a pre-bunched beam, can provide ATLAS quality beams of ions of charge-to-mass ratio less than 1/132.

  13. State of charge sensing means

    SciTech Connect

    Whitford, D.R.

    1980-05-13

    Electrolyte from a battery cell is circulated by pump, through a container which contains a hydrometer float, and back to the cell. The float has an opaque neck which interrupts light passing from a light source assembly to a light receiving assembly, and the receiving assembly controls slave means, which can be an illuminated sign, as for example a group of visible light emitting diodes, the number of which illuminated indicating the density of the electrolyte. The slave means can alternatively be a volt meter, or a battery charger, the rate of charge of which is controlled by a voltage signal.

  14. Computing electronic structures: A new multiconfiguration approach for excited states

    SciTech Connect

    Cances, Eric . E-mail: cances@cermics.enpc.fr; Galicher, Herve . E-mail: galicher@cermics.enpc.fr; Lewin, Mathieu . E-mail: lewin@cermic.enpc.fr

    2006-02-10

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

  15. Probing the Locality of Excited States with Linear Algebra.

    PubMed

    Etienne, Thibaud

    2015-04-14

    This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable. PMID:26574379

  16. Excited state dynamics and isomerization in ruthenium sulfoxide complexes.

    PubMed

    King, Albert W; Wang, Lei; Rack, Jeffrey J

    2015-04-21

    Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect

  17. Excited-State Effective Masses in Lattice QCD

    SciTech Connect

    George Fleming, Saul Cohen, Huey-Wen Lin

    2009-10-01

    We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.

  18. Characterization of weakly excited final states by shakedown spectroscopy of laser-excited potassium

    SciTech Connect

    Schulz, J.; Heinaesmaeki, S.; Aksela, S.; Aksela, H.; Sankari, R.; Rander, T.; Lindblad, A.; Bergersen, H.; Oehrwall, G.; Svensson, S.; Kukk, E.

    2006-07-15

    3p shakedown spectra of laser excited potassium atoms as well as direct 3p photoemission of ground state potassium have been studied. These two excitation schemes lead to the same final states and thereby provide a good basis for a detailed study of the 3p{sup 5}(4s3d){sup 1} configurations of singly ionized potassium and the photoemission processes leading to these configurations. The comparison of direct photoemission from the ground state and conjugate shakedown spectra from 4p{sub 1/2} laser excited potassium made it possible to experimentally determine the character of final states that are only weakly excited in the direct photoemission but have a much higher relative intensity in the shakedown spectrum. Based on considerations of angular momentum and parity conservation the excitation scheme of the final states can be understood.

  19. Electronically shielded solid state charged particle detector

    DOEpatents

    Balmer, D.K.; Haverty, T.W.; Nordin, C.W.; Tyree, W.H.

    1996-08-20

    An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite. 1 fig.

  20. Electronically shielded solid state charged particle detector

    SciTech Connect

    Balmer, D.K.; Haverty, T.W.; Nordin, C.W.; Tyree, W.H.

    1995-12-31

    An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite.

  1. Electronically shielded solid state charged particle detector

    DOEpatents

    Balmer, David K.; Haverty, Thomas W.; Nordin, Carl W.; Tyree, William H.

    1996-08-20

    An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite.

  2. Recent Excitation, Charge Exchange, and Lifetime Results in Highly Charged Ions Relevant to Stellar, Interstellar, Solar and Comet Phenomena

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Hossain, S.; Mawhorter, R. J.; Smith, S. J.

    2006-01-01

    Recent JPL absolute excitation and charge exchange cross sections, and measurements of lifetimes of metastable levels in highly-charged ions (HCIs) are reported. These data provide benchmark comparisons to results of theoretical calculations. Theoretical approaches can then be used to calculate the vast array of data which cannot be measured due to experimental constraints. Applications to the X-ray emission from comets are given.

  3. Initial state dependence of convoy electrons emitted from the excited ions by resonant coherent excitation

    NASA Astrophysics Data System (ADS)

    Azuma, T.; Nakano, Y.; Metoki, K.; Hatakeyama, A.; Nakai, Y.; Komaki, K.; Yamazaki, Y.; Takada, E.; Murakami, T.

    2009-11-01

    Convoy electrons emitted from 416 MeV/u heliumlike Ar16+ ions excited by three-dimensional resonant coherent excitation (3D-RCE) have been explored. The 1s electron in the ground state was excited to the 2p state by a periodic crystal field during the passage through a Si crystal and released into the continuum by collisions with target atoms to form a cusp-shaped peak in the energy distribution, referred to as convoy electron. Under the resonance condition, we found not only enhancement of the convoy electron yield but also significant narrowing in the energy distribution, reflecting the initial bound state momentum distribution of the excited ions. This suggests that RCE is well-suited to study fast ion collisions involving the specific excited state.

  4. Benzonitrile: Electron affinity, excited states, and anion solvation

    NASA Astrophysics Data System (ADS)

    Dixon, Andrew R.; Khuseynov, Dmitry; Sanov, Andrei

    2015-10-01

    We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X ˜ 1 A 1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, a ˜ 3 A 1 , is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet A ˜ 1 A 1 , is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.

  5. Gapped excitations of unconventional fractional quantum Hall effect states in the second Landau level

    NASA Astrophysics Data System (ADS)

    Wurstbauer, U.; Levy, A. L.; Pinczuk, A.; West, K. W.; Pfeiffer, L. N.; Manfra, M. J.; Gardner, G. C.; Watson, J. D.

    2015-12-01

    We report the observation of low-lying collective charge and spin excitations in the second Landau level at ν =2 +1 /3 and also for the very fragile states at ν =2 +2 /5 and 2 +3 /8 in inelastic light scattering experiments. These modes exhibit a clear dependence on filling factor and temperature substantiating the unique access to the characteristic neutral excitation spectra of the incompressible fractional quantum Hall effect (FQHE) states. A detailed mode analysis reveals low-energy modes at around 70 μ eV and a sharp mode slightly below the Zeeman energy interpreted as gap and spin-wave excitation, respectively. The lowest-energy collective charge excitation spectrum at ν =2 +1 /3 exhibits significant qualitative similarities with its cousin state in the lowest Landau level at ν =1 /3 suggesting similar magnetoroton minima in the neutral excitations. The mode energies differ by a scaling of 0.15 indicating different interaction physics in the N =0 and N =1 Landau levels. The striking polarization dependence in elastic and inelastic light scattering is discussed in the framework of anisotropic electron phases that allow for the stabilization of nematic FQHE states. The observed excitation spectra provide new insights by accessing quantum phases in the bulk of electron systems and facilitate comparison with different theoretical descriptions of those enigmatic FQHE states.

  6. Excitation and Charge Exchange Phenomena in Astronomical Objects: Measurement of Cross Sections and Lifetimes

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara; Smith, S.; Lozano, J.; Cadez, I.; Greewnood, J.; Mawhovter, R.; Williams, I.; Niimura, M.

    2003-01-01

    This document addresses extreme ultraviolet radiation and X-ray emissions from comets, planets and heliospheric gases focusing on the measurement of charge-exchange cross sections and radiative lifetimes. Highly-charged heavy ions present in the solar wind, and their abundance relative to the total oxygen-ion abundance are detailed. The plan for the Jet Propulsion Laboratory high-charge ion facility is outlined detailing its ability to measure absolute collisional excitation cross sections, absolute charge-exchange cross sections, lifetimes of metastable ion levels, and X-ray emission spectra following charge changes.

  7. Excited state dynamics in photosynthetic reaction center and light harvesting complex 1

    NASA Astrophysics Data System (ADS)

    Strümpfer, Johan; Schulten, Klaus

    2012-08-01

    Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion process in which electronic excitation establishes a trans-membrane charge gradient. This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of these pigments interact very strongly and are simultaneously influenced by the surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls influenced in their excited state dynamics by strong interaction between the pigments and by interaction with the protein environment. Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical methods, which account for both pigment-pigment interaction and pigment-environment interaction. In the present study we describe the excitation dynamics within a RC and excitation transfer between light harvesting complex 1 (LH1) and RC, employing the hierarchical equation of motion method. For this purpose a set of model parameters that reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC is suggested. We find that the environment has a significant effect on LH1-RC excitation transfer and that excitation transfers incoherently between LH1 and RC.

  8. Radiative recombination and excited-state photoionization of lithium

    SciTech Connect

    Lahiri, J. ); Manson, S.T. )

    1993-11-01

    The radiative-recombination rate coefficients for electrons impinging on Li[sup +], along with the associated excited-state photoionization cross sections for Li, are calculated in the low-energy region. In addition to the totals, the contribution of the recombination of individual excited states to the total is discussed.

  9. Excited state mass spectra of Λc+ baryon

    NASA Astrophysics Data System (ADS)

    Shah, Zalak; Thakkar, Kaushal; Rai, Ajay Kumar; Vinodkumar, P. C.

    2016-05-01

    The radial and orbital excited state masses of singly charmed Λc+ baryon is calculated using the Hypercentral Constituent Quark Model (hCQM). The first order correction is applied to the confinement coulomb plus power potential. The ground and excited state masses for JP=3/2+ are calculated. Our results are in good agreement with experimental and other theoretical predictions.

  10. Experimental Investigation of Excited-State Lifetimes in Atomic Ytterbium

    SciTech Connect

    Bowers, C.J.; Budker, D.; Commins, E.D.; DeMille, D.; Freedman, S.J.; Nguyen, A.-T.; Shang, S.-Q.; Zolotorev, M.; /SLAC

    2011-11-15

    Lifetimes of 21 excited states in atomic Yb were measured using time-resolved fluorescence detection following pulsed laser excitation. The lifetime of the 4f{sup 14}5d6s {sup 3}D{sub 1} state, which is of particular importance for a proposed study of parity nonconservation in atoms, was measured to be 380(30) ns.

  11. Emission of charged particles from excited compound nucleus

    SciTech Connect

    Kalandarov, Sh. A.; Adamian, G. G.; Antonenko, N. V.

    2010-11-24

    The formation and decay of excited compound nucleus are studied within the dinuclear system model[1]. The cross sections of complex fragment emission are calculated and compared with experimental data for the reactions {sup 3}He+{sup 108}Ag, {sup 78,82}Kr+{sup 12}C. Angular momentum dependence of cluster emission in {sup 78}Kr+{sup 12}C and {sup 40}Ca+{sup 78}Kr reactions is demonstrated.

  12. Excited State Isomerization of a Stilbene Analog: E / Z Phenylvinylacetylene

    NASA Astrophysics Data System (ADS)

    Newby, Josh J.; Müller, Christian W.; Liu, Ching-Ping; Lee, Hsiupu D.; Zwier, Timothy S.

    2009-06-01

    The excited state isomerization of the E and Z forms of phenylvinylacetylene (PVA, 1-phenyl-1-buten-3-yne) has been studied using ultraviolet population transfer spectroscopy (UVPT). UVPT is a pump-probe experiment, where single isomers are selectively excited and after a wait time, the induced change in population of reactant and product isomers is probed. In these experiments, after initial cooling, an isomer of PVA is selectively excited to vibrational levels in the S_{1} electronic state. If the energy supplied by the excitation is above the barrier to isomerization population can be transferred into a product well. Excited molecules are collisionally cooled via supersonic expansion and a new population distribution can be detected downstream via R2PI spectroscopy. From these experiments, product isomerization quantum yields have been determined for both E to Z and Z to E excited state pathways as a function of excess energy above the S_{1} origin.

  13. Ion charge state fluctuations in vacuum arcs

    SciTech Connect

    Anders, Andre; Fukuda, Kentaro; Yushkov, Georgy Yu

    2004-12-14

    Ion charge state distributions of cathodic vacuum arcs have been investigated using a modified time-of-flight method. Experiments have been done in double gate and burst gate mode, allowing us to study both systematic and stochastic changes of ion charge state distributions with a time resolution down to 100 ns. In the double gate method, two ion charge spectra are recorded with a well-defined time between measurements. The elements Mg, Bi, and Cu were selected for tests, representing metals of very different properties. For all elements it was found that large stochastic changes occur even at the limit of resolution. This is in agreement with fast changing arc properties observed elsewhere. Correlation of results for short times between measurements was found but it is argued that this is due to velocity mixing rather than due to cathode processes. The burst mode of time-of-flight measurements revealed the systematic time evolution of ion charge states within a single arc discharge, as opposed to previous measurements that relied on data averaged over many pulses. The technique shows the decay of the mean ion charge state as well as the level of material-dependent fluctuations.

  14. Charge-state dependence of kinetic electron emission induced by slow ions in metals

    SciTech Connect

    Juaristi, J.I.; Dubus, A.; Roesler, M.

    2003-07-01

    A calculation is performed in order to analyze the charge-state dependence of the kinetic electron emission induced by slow ions in metals. All stages of the emission process are included: the excitation of the electrons, the neutralization of the projectile during its passage through the solid, and the transport of the excited electrons from where they are created to the surface. It is shown that the number of excited electrons depends strongly on the ion charge state. Nevertheless, due to the fast neutralization of the ions within the escape depth of the excited electrons, no significant initial charge-state dependence is expected in the kinetic electron yield. This result is consistent with available experimental data.

  15. Nonequilibrium solvent effects in Born-Oppenheimer molecular dynamics for ground and excited electronic states.

    PubMed

    Bjorgaard, J A; Velizhanin, K A; Tretiak, S

    2016-04-21

    The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited statemolecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited statemolecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission. PMID:27389206

  16. A new record excited state (3)MLCT lifetime for metalorganic iron(ii) complexes.

    PubMed

    Liu, Li; Duchanois, Thibaut; Etienne, Thibaud; Monari, Antonio; Beley, Marc; Assfeld, Xavier; Haacke, Stefan; Gros, Philippe C

    2016-05-14

    Herein we report the synthesis and time-resolved spectroscopic characterization of a homoleptic Fe(ii) complex exhibiting a record (3)MLCT lifetime of 26 ps promoted by benzimidazolylidene-based ligands. Time dependent density functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest (3)MC state lies higher in energy than the lowest (3)MLCT one. This unprecedented energetic reversal in a series of iron complexes, with the stabilization of the charge-transfer state, opens up new perspectives towards iron-made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels. PMID:27086578

  17. Investigation on the charge transfer excitation spectrum for nano-sized Y2O3:Eu3+

    NASA Astrophysics Data System (ADS)

    Shang, Chunyu; Fan, Honggang; Bu, Shupo; Xia, Hongyang; Du, Yanqiu

    2013-07-01

    In the harmonic oscillator mode of an optical center in charge transfer (CT) excitation, the vibration frequency ω (in ground state) and ω‧ (in CT state) would be decreased in nano-sized Y2O3:Eu3+, leading to the shrinkage in energy span Espan of CT excitation spectrum. The decrease of ω‧ results in the decrease of vibration energy Evib of an optical center obtained in CT excitation. In addition, the zero-phonon CT energy Ezp is decreased with the decrease of phosphor size in nano-scale. Based on the changing magnitudes in Ezp and Evib, the change in CT energy ECT was obtained, which is basically consistent with that measured in the experiment.

  18. Minimization of first-turn losses by excited neutrals in charge-changing injection of accumulator rings

    SciTech Connect

    Jason, A.J.; Blind, B.; Channel, P.; Wang, Tai-Sen

    1994-07-01

    Substantial beam losses, due to production of excited neutrals by the foil stripper, have been observed to occur immediately after injection in accumulator rings that utilize charge-changing injection. A technique is proposed, based on experimental and theoretical results for excited-state production and stripping, that is potentially capable of reducing such losses by a factor greater than 10{sup 4}. In the technique, foil stripping occurs in a shaped magnetic field that resolves the excited atomic levels into immediately stripped states that are within ring acceptance and those that can be ejected from the ring. An added magnetic-mirror-field configuration is Proposed as an effective means of minimizing interactions between stripped electrons and the foil.

  19. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite.

    PubMed

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons. PMID:27439874

  20. Charge asymmetry in pure vibrational states of the HD molecule

    NASA Astrophysics Data System (ADS)

    Bubin, Sergiy; Leonarski, Filip; Stanke, Monika; Adamowicz, Ludwik

    2009-03-01

    Very accurate variational calculations of all rotationless states (also called pure vibrational states) of the HD molecule have been performed within the framework that does not assume the Born-Oppenheimer (BO) approximation. The non-BO wave functions of the states describing the internal motion of the proton, the deuteron, and the two electrons were expanded in terms of one-center explicitly correlated Gaussian functions multiplied by even powers of the internuclear distance. Up to 6000 functions were used for each state. Both linear and nonlinear parameters of the wave functions of all 18 states were optimized with a procedure that employs the analytical gradient of the energy with respect to the nonlinear parameters of the Gaussians. These wave functions were used to calculate expectation values of the interparticle distances and some other related quantities. The results allow elucidation of the charge asymmetry in HD as a function of the vibrational excitation.

  1. The effects of nanoparticles and organic additives with controlled dispersion on dielectric properties of polymers: Charge trapping and impact excitation

    NASA Astrophysics Data System (ADS)

    Huang, Yanhui; Wu, Ke; Bell, Michael; Oakes, Andrew; Ratcliff, Tyree; Lanzillo, Nicholas A.; Breneman, Curt; Benicewicz, Brian C.; Schadler, Linda S.

    2016-08-01

    This work presents a comprehensive investigation into the effects of nanoparticles and organic additives on the dielectric properties of insulating polymers using reinforced silicone rubber as a model system. TiO2 and ZrO2 nanoparticles (d = 5 nm) were well dispersed into the polymer via a bimodal surface modification approach. Organic molecules with the potential of voltage stabilization were further grafted to the nanoparticle to ensure their dispersion. These extrinsic species were found to provide deep traps for charge carriers and exhibited effective charge trapping properties at a rather small concentration (˜1017 cm-3). The charge trapping is found to have the most significant effect on breakdown strength when the electrical stressing time is long enough that most charges are trapped in the deep states. To establish a quantitative correlation between the trap depth and the molecular properties, the electron affinity and ionization energy of each species were calculated by an ab initio method and were compared with the experimentally measured values. The correlation however remains elusive and is possibly complicated by the field effect and the electronic interactions between different species that are not considered in this computation. At high field, a super-linear increase of current density was observed for TiO2 filled composites and is likely caused by impact excitation due to the low excitation energy of TiO2 compared to ZrO2. It is reasoned that the hot charge carriers with energies greater than the excitation energy of TiO2 may excite an electron-hole pair upon collision with the NP, which later will be dissociated and contribute to free charge carriers. This mechanism can enhance the energy dissipation and may account for the retarded electrical degradation and breakdown of TiO2 composites.

  2. Excited states of methylene from quantum Monte Carlo.

    PubMed

    Zimmerman, Paul M; Toulouse, Julien; Zhang, Zhiyong; Musgrave, Charles B; Umrigar, C J

    2009-09-28

    The ground and lowest three adiabatic excited states of methylene are computed using the variational Monte Carlo and diffusion Monte Carlo (DMC) methods using progressively larger Jastrow-Slater multideterminant complete active space (CAS) wave functions. The highest of these states has the same symmetry, (1)A(1), as the first excited state. The DMC excitation energies obtained using any of the CAS wave functions are in excellent agreement with experiment, but single-determinant wave functions do not yield accurate DMC energies of the states of (1)A(1) symmetry, indicating that it is important to include in the wave function Slater determinants that describe static (strong) correlation. Excitation energies obtained using recently proposed pseudopotentials [Burkatzki et al., J. Chem. Phys. 126, 234105 (2007)] differ from the all-electron excitation energies by at most 0.04 eV. PMID:19791848

  3. Exceptionally Long-Lived Charge Separated State in Zeolitic Imidazolate Framework: Implication for Photocatalytic Applications.

    PubMed

    Pattengale, Brian; Yang, Sizhuo; Ludwig, John; Huang, Zhuangqun; Zhang, Xiaoyi; Huang, Jier

    2016-07-01

    Zeolitic imidazolate frameworks (ZIFs) have emerged as a novel class of porous metal-organic frameworks (MOFs) for catalysis application because of their exceptional thermal and chemical stability. Inspired by the broad absorption of ZIF-67 in UV-vis-near IR region, we explored its excited state and charge separation dynamics, properties essential for photocatalytic applications, using optical (OTA) and X-ray transient absorption (XTA) spectroscopy. OTA results show that an exceptionally long-lived excited state is formed after photoexcitation. This long-lived excited state was confirmed to be the charge-separated (CS) state with ligand-to-metal charge-transfer character using XTA. The surprisingly long-lived CS state, together with its intrinsic hybrid nature, all point to its potential application in heterogeneous photocatalysis and energy conversion. PMID:27322216

  4. Highly charged ion induced nanostructures at surfaces by strong electronic excitations

    NASA Astrophysics Data System (ADS)

    Wilhelm, Richard A.; El-Said, Ayman S.; Krok, Franciszek; Heller, René; Gruber, Elisabeth; Aumayr, Friedrich; Facsko, Stefan

    2015-08-01

    Nanostructure formation by single slow highly charged ion impacts can be associated with high density of electronic excitations at the impact points of the ions. Experimental results show that depending on the target material these electronic excitations may lead to very large desorption yields in the order of a few 1000 atoms per ion or the formation of nanohillocks at the impact site. Even in ultra-thin insulating membranes the formation of nanometer sized pores is observed after ion impact. In this paper, we show recent results on nanostructure formation by highly charged ions and compare them to structures and defects observed after intense electron and light ion irradiation of ionic crystals and graphene. Additional data on energy loss, charge exchange and secondary electron emission of highly charged ions clearly show that the ion charge dominates the defect formation at the surface.

  5. Reducing Space Charge Effects in a Linear Ion Trap by Rhombic Ion Excitation and Ejection.

    PubMed

    Zhang, Xiaohua; Wang, Yuzhuo; Hu, Lili; Guo, Dan; Fang, Xiang; Zhou, Mingfei; Xu, Wei

    2016-07-01

    Space charge effects play important roles in ion trap operations, which typically limit the ion trapping capacity, dynamic range, mass accuracy, and resolving power of a quadrupole ion trap. In this study, a rhombic ion excitation and ejection method was proposed to minimize space charge effects in a linear ion trap. Instead of applying a single dipolar AC excitation signal, two dipolar AC excitation signals with the same frequency and amplitude but 90° phase difference were applied in the x- and y-directions of the linear ion trap, respectively. As a result, mass selective excited ions would circle around the ion cloud located at the center of the ion trap, rather than go through the ion cloud. In this work, excited ions were then axially ejected and detected, but this rhombic ion excitation method could also be applied to linear ion traps with ion radial ejection capabilities. Experiments show that space charge induced mass resolution degradation and mass shift could be alleviated with this method. For the experimental conditions in this work, space charge induced mass shift could be decreased by ~50%, and the mass resolving power could be improved by ~2 times at the same time. Graphical Abstract ᅟ. PMID:27080008

  6. Reducing Space Charge Effects in a Linear Ion Trap by Rhombic Ion Excitation and Ejection

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaohua; Wang, Yuzhuo; Hu, Lili; Guo, Dan; Fang, Xiang; Zhou, Mingfei; Xu, Wei

    2016-07-01

    Space charge effects play important roles in ion trap operations, which typically limit the ion trapping capacity, dynamic range, mass accuracy, and resolving power of a quadrupole ion trap. In this study, a rhombic ion excitation and ejection method was proposed to minimize space charge effects in a linear ion trap. Instead of applying a single dipolar AC excitation signal, two dipolar AC excitation signals with the same frequency and amplitude but 90° phase difference were applied in the x- and y-directions of the linear ion trap, respectively. As a result, mass selective excited ions would circle around the ion cloud located at the center of the ion trap, rather than go through the ion cloud. In this work, excited ions were then axially ejected and detected, but this rhombic ion excitation method could also be applied to linear ion traps with ion radial ejection capabilities. Experiments show that space charge induced mass resolution degradation and mass shift could be alleviated with this method. For the experimental conditions in this work, space charge induced mass shift could be decreased by ~50%, and the mass resolving power could be improved by ~2 times at the same time.

  7. Structural and excited-state properties of oligoacene crystals from first principles

    NASA Astrophysics Data System (ADS)

    Rangel, Tonatiuh; Berland, Kristian; Sharifzadeh, Sahar; Brown-Altvater, Florian; Lee, Kyuho; Hyldgaard, Per; Kronik, Leeor; Neaton, Jeffrey B.

    2016-03-01

    Molecular crystals are a prototypical class of van der Waals (vdW) bound organic materials with excited-state properties relevant for optoelectronics applications. Predicting the structure and excited-state properties of molecular crystals presents a challenge for electronic structure theory, as standard approximations to density functional theory (DFT) do not capture long-range vdW dispersion interactions and do not yield excited-state properties. In this work, we use a combination of DFT including vdW forces, using both nonlocal correlation functionals and pairwise correction methods, together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire series of oligoacene crystals, from benzene to hexacene. We find that vdW methods can predict lattice constants within 1% of the experimental measurements, on par with the previously reported accuracy of pairwise approximations for the same systems. We further find that excitation energies are sensitive to geometry, but if optimized geometries are used MBPT can yield excited-state properties within a few tenths of an eV from experiment. We elucidate trends in MBPT-computed charged and neutral excitation energies across the acene series and discuss the role of common approximations used in MBPT.

  8. A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems

    NASA Astrophysics Data System (ADS)

    Liu, Wenlan; Lunkenheimer, Bernd; Settels, Volker; Engels, Bernd; Fink, Reinhold F.; Köhn, Andreas

    2015-08-01

    We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.

  9. A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems

    SciTech Connect

    Liu, Wenlan; Köhn, Andreas; Lunkenheimer, Bernd; Settels, Volker; Engels, Bernd; Fink, Reinhold F.

    2015-08-28

    We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.

  10. 18Ne Excited States Two-Proton Decay

    NASA Astrophysics Data System (ADS)

    de Napoli, M.; Rapisarda, E.; Raciti, G.; Cardella, G.; Amorini, F.; Giacoppo, F.; Sfienti, C.

    2008-04-01

    Two-proton radioactivity studies have been performed on excited states of 18Ne produced by 20Ne fragmentation at the FRS of the Laboratori Nazionali del Sud and excited via Coulomb excitation on a 209Pb target. The 18Ne levels decay has been studied by complete kinematical reconstruction. In spite of the low statistic, the energy and angular correlations of the emitted proton pairs indicate the presence of 2He emission toghether with the democratic decay.

  11. Influence of collective effects on lifetimes of condensed excited states

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, Jonas Stasys

    1987-01-01

    The possibility that collective effects may dramatically influence autoionization-limited lifetimes of condensed excited states is investigated in the context of a two-band model of an insulator in a strong magnetic field. Two different mechanisms for suppressing autoionization are discussed which may prevent the potentially catastrophic destruction of the excited state. Under appropriate circumstances, the residual low-density Auger electrons may be confined in a superconducting state and paired by excitonic fluctuations in the conduction band.

  12. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy.

    PubMed

    Shelby, Megan L; Lestrange, Patrick J; Jackson, Nicholas E; Haldrup, Kristoffer; Mara, Michael W; Stickrath, Andrew B; Zhu, Diling; Lemke, Henrik T; Chollet, Matthieu; Hoffman, Brian M; Li, Xiaosong; Chen, Lin X

    2016-07-20

    Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the ∼100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance. PMID:27286410

  13. Internal Stark effect mediates intramolecular excited-state proton transfer in 3-hydroxyflavone derivatives

    NASA Astrophysics Data System (ADS)

    Klymchenko, Andriy S.; Demchenko, Alexander P.

    2002-12-01

    Internal Stark effect in electronic spectra is the effect that is observed when the electronic bands shift udner the influence of promixal charges. In order to study the possible involvement of this effect in modulating the intramolecular proton transfer reactions in the excited state, we designed and studied several derivatives of 3-hydroxyflavone. They include the species containing neutral and positively charged substituents in 6 position of chromone ring. These compounds were studied in solvents of different polarities. In these experiments the shifts of both normal and tautomer flurosence bands are clearly observed in a manner predicted by Stark effect theory. In addition, a dramatic effect of suppression by introduced charge of intramolecular excited-state proton transfer was observed.

  14. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid.

    PubMed

    Rury, Aaron S; Sorenson, Shayne; Dawlaty, Jahan M

    2016-03-14

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm(-1) oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology. PMID:26979698

  15. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid

    NASA Astrophysics Data System (ADS)

    Rury, Aaron S.; Sorenson, Shayne; Dawlaty, Jahan M.

    2016-03-01

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm-1 oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.

  16. Study of excited nucleon states at EBAC: status and plans

    SciTech Connect

    Hiroyuki Kamano

    2009-12-01

    We present an overview of a research program for the excited nucleon states in Excited Baryon Analysis Center (EBAC) at Jefferson Lab. Current status of our analysis of the meson production reactions based on the unitary dynamical coupled-channels model is summarized, and the N* pole positions extracted from the constructed scattering amplitudes are presented. Our plans for future developments are also discussed.

  17. Superposition of Fragment Excitations for Excited States of Large Clusters with Application to Helium Clusters.

    PubMed

    Closser, Kristina D; Ge, Qinghui; Mao, Yuezhi; Shao, Yihan; Head-Gordon, Martin

    2015-12-01

    We develop a local excited-state method, based on the configuration interaction singles (CIS) wave function, for large atomic and molecular clusters. This method exploits the properties of absolutely localized molecular orbitals (ALMOs), which strictly limits the total number of excitations, and results in formal scaling with the third power of the system size for computing the full spectrum of ALMO-CIS excited states. The derivation of the equations and design of the algorithm are discussed in detail, with particular emphasis on the computational scaling. Clusters containing ∼500 atoms were used in evaluating the scaling, which agrees with the theoretical predictions, and the accuracy of the method is evaluated with respect to standard CIS. A pioneering application to the size dependence of the helium cluster spectrum is also presented for clusters of 25-231 atoms, the largest of which results in the computation of 2310 excited states per sampled cluster geometry. PMID:26609558

  18. Femtosecond insights into direct electron injection in dye anchored ZnO QDs following charge transfer excitation.

    PubMed

    Kumar, Pushpendra; Kumar, Sunil; Ghosh, Subrata; Pal, Suman Kalyan

    2016-07-27

    The role of the charge transfer (CT) state in interfacial electron transfer in dye-sensitized semiconductor nanocrystals is still poorly understood. To address this problem, femtosecond transient absorption (TA) spectroscopy is used as a probe to investigate the electron injection across a newly synthesized coumarin dye (8-hydroxy-2-oxo-4-phenyl-2 benzo[h]chromene-3-carbonitrile, coded BC5) and ZnO quantum dots (QDs). Steady state and time-resolved spectroscopic measurements reveal that BC5 dye interacts strongly with ZnO QDs in the ground state forming a CT complex. The BC5-ZnO QD complex absorbs more towards red compared to only the dye and QDs, and emits fluorescence due to radiative recombination of photogenerated charges. The formation of charges following the excitation of the CT complex has been demonstrated by observing the signature of dye radical cations and electrons in the conduction band (CB) of the QDs in the TA spectra. The TA signals of these charges grow sharply as a result of ultrafast direct electron injection into the QD. We have monitored the complete dynamics of photogenerated charges by measuring the TA signals of the charges up to a couple of nanoseconds. The injected electrons that are free or shallowly trapped recombine with a time constant of 625 fs, whereas deeply trapped electrons disappear slowly (526 ps) via radiative recombination. Furthermore, theoretical studies based on ab initio calculations have been carried out to complement the experimental findings. PMID:27412034

  19. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    NASA Astrophysics Data System (ADS)

    Winnerl, Andrea; Pereira, Rui N.; Stutzmann, Martin

    2015-10-01

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  20. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    SciTech Connect

    Winnerl, Andrea Pereira, Rui N.; Stutzmann, Martin

    2015-10-21

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  1. Rigid medium effects on photophysical properties of MLCT excited states of polypyridyl Os(II) complexes in polymerized poly(ethylene glycol)dimethacrylate monoliths.

    PubMed

    Ito, Akitaka; Knight, Troy E; Stewart, David J; Brennaman, M Kyle; Meyer, Thomas J

    2014-11-13

    Higher-energy emissions from the metal-to-ligand charge-transfer (MLCT) excited states of a series of polypyridyl Os(II) complexes were observed at the fluid-to-film transition in PEG-DMA550. The higher-energy excited states, caused by a "rigid medium effect" in the film, led to enhanced emission quantum yields and longer excited-state lifetimes. Detailed analyses of spectra and excited-state dynamics by Franck-Condon emission spectral analysis and application of the energy gap law for nonradiative excited-state decay reveal that the rigid medium effect arises from the inability of part of the local medium dielectric environment to respond to the change in charge distribution in the excited state during its lifetime. Enhanced excited-state lifetimes are consistent with qualitative and quantitative predictions of the energy gap law. PMID:24720473

  2. Excited State Processes in Transition Metal Complexes, Redox Splitting in Soluble Polymers

    SciTech Connect

    Meyer, T.J.; Papanikolas, J.M.

    2002-08-08

    The photochemical and photophysical properties of polypyridyl complexes of Ru, Os, and Re have been investigated by transient absorption, emission, resonance raman and infrared spectroscopies. The latter technique has been especially useful in defining the acceptor ligand in metal-to-ligand charge transfer (MLCT) excited states and probing the details of excited state electronic and molecular structure. Derivatives of these complexes have been attached to soluble polystyrene polymers. In the resulting metal complex polymer composites it has been possible to demonstrate long range energy transfer and the existence of an antenna effect and create a mimic for the active site in the photosynthetic membrane.

  3. Measurement of light charged particles in the decay channels of medium-mass excited compound nuclei

    NASA Astrophysics Data System (ADS)

    Valdré, S.; Barlini, S.; Casini, G.; Pasquali, G.; Piantelli, S.; Carboni, S.; Cinausero, M.; Gramegna, F.; Marchi, T.; Baiocco, G.; Bardelli, L.; Benzoni, G.; Bini, M.; Blasi, N.; Bracco, A.; Brambilla, S.; Bruno, M.; Camera, F.; Corsi, A.; Crespi, F.; D'Agostino, M.; Degerlier, M.; Kravchuk, V. L.; Leoni, S.; Million, B.; Montanari, D.; Morelli, L.; Nannini, A.; Nicolini, R.; Poggi, G.; Vannini, G.; Wieland, O.; Bednarczyk, P.; Ciemała, M.; Dudek, J.; Fornal, B.; Kmiecik, M.; Maj, A.; Matejska-Minda, M.; Mazurek, K.; Męczyński, W. M.; Myalski, S.; Styczeń, J.; Ziębliński, M.

    2014-03-01

    The 48Ti on 40Ca reactions have been studied at 300 and 600 MeV focusing on the fusion-evaporation (FE) and fusion-fission (FF) exit channels. Energy spectra and multiplicities of the emitted light charged particles have been compared to Monte Carlo simulations based on the statistical model. Indeed, in this mass region (A ~ 100) models predict that shape transitions can occur at high spin values and relatively scarce data exist in the literature about coincidence measurements between evaporation residues and light charged particles. Signals of shape transitions can be found in the variations of the lineshape of high energy gamma rays emitted from the de-excitation of GDR states gated on different region of angular momenta. For this purpose it is important to keep under control the FE and FF processes, to regulate the statistical model parameters and to control the onset of possible pre-equilibrium emissions from 300 to 600 MeV bombarding energy.

  4. Polarization dependence of charge-transfer excitations in La2CuO4

    NASA Astrophysics Data System (ADS)

    Lu, Li; Chabot-Couture, Guillaume; Hancock, Jason; Vajk, Owen; Yu, Guichuan; Ishii, Kenji; Mizuki, Jun'ichiro; Casa, Diego; Gog, Thomas; Greven, Martin

    2006-03-01

    We have carried out an extensive resonant inelastic x-ray scattering (RIXS) study of La2CuO4 at the Cu K-edge. Multiple charge-transfer excitations have been identified using the incident photon energy dependence of the cross section and studied carefully with polarizations E//c and E //ab. An analysis of the incident photon energy dependence, the polarization dependence, as well as the K-edge absorption spectra, indicates that the RIXS spectra reveal rich physics about the K-edge absorption process and momentum-dependent charge-transfer excitations in cuprates.

  5. Detailed theoretical investigation of excited-state intramolecular proton transfer mechanism of a new chromophore II

    NASA Astrophysics Data System (ADS)

    Cui, Yanling; Li, Yafei; Dai, Yumei; Verpoort, Francis; Song, Peng; Xia, Lixin

    2016-02-01

    In the present work, TDDFT has been used to investigate the excited state intramolecular proton transfer (ESIPT) mechanism of a new chromophore II [Sensors and Actuators B: Chemical. 202 (2014) 1190]. The calculated absorption and fluorescence spectra agree well with experimental results. In addition, two types of II configurations are found in the first excited state (S1), which can be ascribed to the ESIPT reaction. Based on analysis of the calculated infrared (IR) spectra of O-H stretching vibration as well as the hydrogen bonding energies, the strengthening of the hydrogen bond in the S1 state has been confirmed. The frontier molecular orbitals (MOs), Hirshfeld charge distribution and the Natural bond orbital (NBO) have also been analyzed, which displays the tendency of the ESIPT process. Finally, potential energy curves of the S0 and S1 states were constructed, demonstrating that the ESIPT reaction can be facilitated based on the photo-excitation.

  6. Excited-state transient of vanadyl uroporphyrin I detected by resonance Raman spectroscopy

    SciTech Connect

    Alden, R.G.; Sparks, L.D.; Ondrias, M.R. ); Crawford, B.A.; Shelnutt, J.A. )

    1990-02-22

    Transient Raman spectroscopy has been used to investigate excited states of vanadyl uroporphyrin I (VOUroP) in both monomeric and dimeric forms. Uroporphyrins are water-soluble porphyrins with propionic and acetic acid groups substituted at the {beta}-pyrrole carbon positions. Monomeric VOUroP in aqueous solution is known to be six-coordinate with a ligand trans to the oxo ligand. Upon dimerization, the sixth ligand site is inaccessible, and a five-coordinate species is observed. At high laser fluence, an excited-state transient is formed in the monomeric species. Raman spectra of this species are most consistent with an {sup 2}A{sub 1u} (a{sub 1u}({pi}) {yields} d{sub xy}) charge-transfer state. In contrast, dimeric VOUroP shows little evidence of an excited state in the transient Raman spectra during a 10-ns laser pulse.

  7. Vibronic coupling in the excited-states of carotenoids.

    PubMed

    Miki, Takeshi; Buckup, Tiago; Krause, Marie S; Southall, June; Cogdell, Richard J; Motzkus, Marcus

    2016-04-28

    The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S2 to the optically dark state S1. Extending this picture, some additional dark states (3A(g)(-) and 1B(u)(-)) and their interaction with the S2 state have also been suggested to play a major role in the ultrafast deactivation of carotenoids and their properties. Here, we investigate the interaction between such dark and bright electronic excited states of open chain carotenoids, particularly its dependence on the number of conjugated double bonds (N). We focus on the ultrafast wave packet motion on the excited potential surface, which is modified by the interaction between bright and dark electronic states. Such a coupling between electronic states leads to a shift of the vibrational frequency during the excited-state evolution. In this regard, pump-degenerate four-wave mixing (pump-DFWM) is applied to a series of carotenoids with different numbers of conjugated double bonds N = 9, 10, 11 and 13 (neurosporene, spheroidene, lycopene and spirilloxanthin, respectively). Moreover, we demonstrate in a closed-chain carotenoid (lutein) that the coupling strength and therefore the vibrational shift can be tailored by changing the energy degeneracy between the 1B(u)(+) and 1B(u)(-) states via solvent interaction. PMID:27055720

  8. Quantification of Entanglement Entropies for Doubly Excited States in Helium

    NASA Astrophysics Data System (ADS)

    Lin, Chien-Hao; Ho, Yew Kam

    2015-05-01

    In this work, we study the quantum entanglement for doubly excited resonance states in helium by using highly correlated Hylleraas type functions to represent such states of the two-electron system. The doubly-excited resonance states are determined by calculation of density of resonance states under the framework of the stabilization method. The spatial (electron-electron orbital) entanglement measures for the low-lying doubly excited 2 s 2, 2 s3 s, and 2 p 2 1 S e states are carried out. Once a resonance state wave function is obtained, the linear entropy and von Neumann entropy for such a state are quantified using the Schmidt-Slater decomposition method. To check the consistence, linear entropy is also determined by solving analytically the needed four-electron (12-dimensional) integrals.

  9. The examination of berberine excited state by laser flash photolysis

    NASA Astrophysics Data System (ADS)

    Cheng, Lingli; Wang, Mei; Zhao, Ping; Zhu, Hui; Zhu, Rongrong; Sun, Xiaoyu; Yao, Side; Wang, Shilong

    2009-07-01

    The property of the excited triplet state of berberine (BBR) was investigated by using time-resolved laser flash photolysis of 355 nm in acetonitrile. The transient absorption spectra of the excited triplet BBR were obtained in acetonitrile, which have an absorption maximum at 420 nm. And the ratio of excitation to ionization of BBR in acetonitrile solvent was calculated. The self-decay and self-quenching rate constants, and the absorption coefficient of 3BBR* were investigated and the excited state quantum yield was determined. Furthermore utilizing the benzophenone (BEN) as a triplet sensitizer, and the β-carotene (Car) as an excited energy transfer acceptor, the assignment of 3BBR* was further confirmed and the related energy transfer rate constants were also determined.

  10. Apparatus for measuring electron-impact excitation cross sections using fast metastable atoms produced via charge exchange

    SciTech Connect

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

    1996-08-01

    An apparatus for measuring absolute cross sections due to electron-impact excitation out of the metastable levels of rare-gas atoms via the optical method is described with the focus specifically on excitation out of the 2{sup 3}{ital S} metastable helium level. The metastable helium target (He{asterisk}) is prepared by charge exchange between 1.6 keV He{sup +} ions and cesium vapor. An electron beam crosses the fast metastable beam target at a right angle and the fluorescence is collected at right angles to both beams. The charge transfer reaction produces He atoms mainly in the {ital n}=2 He levels. Because the target contains a negligible ground state He fraction, we can measure excitation cross sections from excitation threshold up to an arbitrarily high energy (keV regime) which represents a major improvement over previous metastable excitation cross sections measurements. The He{asterisk} target density is extremely small ({approximately}10{sup 6} atoms/cm{sup 3}) yielding minuscule signal rates. We describe steps taken to maximize the signal-to-noise ratio. We discuss the implications of using a fast beam target including both the finite flight time of the excited atoms across the light gathering region and the reduction of the cascade contributions to the apparent cross sections. A discussion of the identification and elimination of various systematic effects is also given. To measure absolute cross sections, we explicitly determine the spatial distributions of both the electron and metastable beams, as well as the spatially dependent response of the fluorescence gathering region. We determine the absolute flux of fast metastable atoms using a thermal detector calibrated with a He{sup +} ion beam. As examples, we present absolute cross sections for excitation out of the 2{sup 3}{ital S} metastable level into the 3{sup 3}{ital D} and 4{sup 3}{ital D} levels. {copyright} {ital 1996 American Institute of Physics.}

  11. Quantum criticality and fractional charge excitations in itinerant ice-rule systems

    NASA Astrophysics Data System (ADS)

    Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi

    2013-03-01

    ``Ice rule'' is a configurational constraint on Ising-type variables defined on tetrahedron-based lattices, such as a pyrochlore lattice, so that two out of the four sites on a tetrahedron are in the opposite state to the other two. This concept plays an important role in many systems, such as water ice Ih, magnetite Fe3O4, and spin ice materials Ho(Dy)2Ti2O7. Under the ice-rule constraint, the ground state is disordered and retains macroscopic degeneracy. Nevertheless, the ice-rule configuration is not completely random but has a peculiar spatial structure with quasi-long-range correlation. It is interesting to ask how itinerant electrons change their properties by coupling to this anomalous spatial structure. To answer this problem, we adopt an extended Falicov-Kimball model as a minimal model, in which itinerant electrons interact with localized charge degrees of freedom under the ice rule. We exactly solve this model on a loop-less variant of the tetrahedron-based lattices, a tetrahedron Husimi cactus and clarify the ground-state phase diagram. The exact solution reveals a quantum critical point separating two insulating phases, where a novel non-Fermi-liquid behavior emerges. We also discuss the nature of fractional excitations breaking the ice-rule manifold.

  12. Low-lying electronic excited states of pentacene oligomers: a comparative electronic structure study in the context of singlet fission.

    PubMed

    Coto, Pedro B; Sharifzadeh, Sahar; Neaton, Jeffrey B; Thoss, Michael

    2015-01-13

    The lowest-lying electronic excited states of pentacene and its oligomers are investigated using accurate multireference wave function methods (CASPT2/CASSCF) and the many-body Greens's function approach (GW/BSE). The results obtained for dimers and trimers of different geometry reveal a complex electronic structure, which includes locally excited, charge transfer, and multiexciton states. For singlets of single-excitation character, both approaches yield excitation energies that are in good overall quantitative agreement. While the multiexciton states are located relatively high in energy in all systems investigated, charge transfer states exist in close proximity to the lowest-lying absorbing states. The implications of the results for the mechanisms of singlet fission in pentacene are discussed. PMID:26574213

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

    SciTech Connect

    Pavanello, Michele; Van Voorhis, Troy; Visscher, Lucas; Neugebauer, Johannes

    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.

  14. Peroxyacetyl radical: Electronic excitation energies, fundamental vibrational frequencies, and symmetry breaking in the first excited state

    SciTech Connect

    Copan, Andreas V.; Wiens, Avery E.; Nowara, Ewa M.; Schaefer, Henry F.; Agarwal, Jay

    2015-02-07

    Peroxyacetyl radical [CH{sub 3}C(O)O{sub 2}] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X{sup ~}) and first (A{sup ~}) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals.

  15. Investigation into chromophore excited-state coupling in allophycocyanin

    NASA Astrophysics Data System (ADS)

    Zheng, Xiguang; Zhao, Fuli; Wang, He Z.; Gao, Zhaolan; Yu, Zhenxin; Zhu, Jinchang; Xia, Andong; Jiang, Lijin

    1994-08-01

    Both theoretical and experimental studies are presented on chromophore excited-state coupling in linker-free allophycocyanin (APC), one of the antenna phycobiliproteins in algal photosynthesis. A three-site-coupling model has been introduced to describe the exciton interaction mechanism amoung the excited (beta) chromophore in APC, and the exciton energy splitting is estimated. Picosecond polarized fluorescence experiments both on monomeric and trimeric APC isolated from alga Spirulina platensis have been performed. The experimental results show that APC monomer and trimer exhibit remarkedly different spectropic characteristics, and satisfy the suggestion of strong excited- state coupling among chromophores in APC.

  16. Photoacoustic imaging of the excited state lifetime of fluorophores

    NASA Astrophysics Data System (ADS)

    Märk, Julia; Schmitt, Franz-Josef; Laufer, Jan

    2016-05-01

    Photoacoustic (PA) imaging using pump-probe excitation has been shown to allow the detection and visualization of fluorescent contrast agents. The technique relies upon inducing stimulated emission using pump and probe pulses at excitation wavelengths that correspond to the absorption and fluorescence spectra. By changing the time delay between the pulses, the excited state lifetime of the fluorophore is modulated to vary the amount of thermalized energy, and hence PA signal amplitude, to provide fluorophore-specific PA contrast. In this study, this approach was extended to the detection of differences in the excited state lifetime of fluorophores. PA waveforms were measured in solutions of a near-infrared fluorophore using simultaneous and time-delayed pump-probe excitation. The lifetime of the fluorophore solutions was varied by using different solvents and quencher concentrations. By calculating difference signals and by plotting their amplitude as a function of pump-probe time delay, a correlation with the excited state lifetime of the fluorophore was observed. The results agreed with the output of a forward model of the PA signal generation in fluorophores. The application of this method to tomographic PA imaging of differences in the excited state lifetime was demonstrated in tissue phantom experiments.

  17. Alpha-cluster excited states in 32S

    NASA Astrophysics Data System (ADS)

    Yoshida, Yuta; Y. Kanada-En'yo Collaboration; F. Kobayashi Collaboration

    2014-09-01

    Excited states having core +alpha cluster structure called the alpha-cluster excited state are known to exist in such nuclei as 16O and 20Ne. Meanwhile, the existence of alpha-cluster excited states in the middle of sd-shell nuclei is an open problem. Recently, the alpha-cluster excited state in 32S is suggested by experiments. In order to understand the dynamics of the core-alpha relative motion, we focus on the structure change of the core nuclei and the breaking of the alpha-cluster. In the present work, we construct 28Si +alpha model which has the structure change of the 28Si core and the alpha-cluster breaking. Using the present model, we calculate the energy expectation value of 28Si +alpha system. We found that the structure change of the core nuclei is energetically rather important while the alpha-cluster breaking is not significant when the alpha-cluster exists at the surface of the 28Si core. We calculate the ground and excited states with the generator coordinate method. As a result, we suggest the existence of alpha-cluster excited states in 32S.

  18. Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

    SciTech Connect

    Ralchenko, Yu. Janev, R.K.; Kato, T.; Fursa, D.V.; Bray, I.; Heer, F.J. de

    2008-07-15

    Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n{<=}4 are treated individually, while the states with n{>=}5 are considered degenerate. For the processes involving transitions to and from n{>=}5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.

  19. Metastable states of highly excited heavy ions

    NASA Technical Reports Server (NTRS)

    Pegg, D. J.; Griffin, P. M.; Sellin, I. A.; Smith, W. W.; Donnally, B.

    1973-01-01

    Description of the method used and results obtained in an experimental study of the metastable states of highly stripped heavy ions, aimed at determining the lifetimes of such states by the rates of autoionization and radiation. The significance and limitations of the results presented are discussed.

  20. State of charge indicators for a battery

    DOEpatents

    Rouhani, S. Zia

    1999-01-01

    The present invention relates to state of charge indicators for a battery. One aspect of the present invention utilizes expansion and contraction displacements of an electrode plate of a battery to gauge the state of charge in the battery. One embodiment of a battery of the present invention includes an anodic plate; a cathodic plate; an electrolyte in contact with the anodic and cathodic plates; plural terminals individually coupled with one of the anodic and cathodic plates; a separator intermediate the anodic and cathodic plates; an indicator configured to indicate an energy level of the battery responsive to movement of the separator; and a casing configured to house the anodic and cathodic plates, electrolyte, and separator.

  1. Isomeric States and Collective Excitations of Heaviest Nuclei

    NASA Astrophysics Data System (ADS)

    Adamian, G. G.; Antonenko, N. V.; Jolos, R. V.; Kuzmina, A. N.; Malov, L. A.; Shirikova, N. Yu.; Sushkov, A. V.

    2013-03-01

    The isotopic dependence of two-quasiparticle isomeric states in Fm and No is treated. An α-decay chain through the isomeric states of super-heavy nuclei is demonstrated. The excitation energies and the structure of the low lying states with Kπ = 0‒ 1‒ 2‒ are calculated with the quasiparticle phonon model.

  2. Microwave spectroscopy of furfural in vibrationally excited states

    NASA Astrophysics Data System (ADS)

    Motiyenko, R. A.; Alekseev, E. A.; Dyubko, S. F.

    2007-07-01

    The results of microwave spectrum investigation of the excited vibrational states of furfural in the frequency range between 49 and 149 GHz are reported. In total 15 excited vibrational states (9 for trans-furfural and 6 for cis-furfural) were assigned and analyzed. Six of the 15 investigated states were assigned for the first time. Accurate values of rigid rotor and quartic centrifugal distortion constants of asymmetric top Hamiltonian have been determined for 13 excited states. Also for some states several sextic and octic level constants were needed in order to fit the data within experimental accuracy. The vt = 3 and vs = 1, va = 1 states of trans-furfural were found to be strongly perturbed and only rotational transitions with low Ka values can be reliably identified in this study.

  3. Characterizing RNA Excited States using NMR Relaxation Dispersion

    PubMed Central

    Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M.

    2016-01-01

    Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of non-coding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as “excited states”. Compared to larger-scale changes in RNA secondary structure, transitions towards excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around non-canonical motifs. Here we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25–3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data is then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited state. Application is illustrated with a focus on the transactivation response element (TAR) from the human immune deficiency virus type 1 (HIV-1), which exists in dynamic equilibrium with at least two distinct excited states. PMID:26068737

  4. Solar wind ion composition and charge states

    SciTech Connect

    Vonsteiger, R.

    1995-06-01

    The solar wind, a highly tenuous plasma streaming from the Sun into interplanetary space at supersonic speed, is roughly composed of 95% hydrogen and 5% helium by number. All other, heavy elements contribute less than 0.1% by number and thus are truly test particles Nevertheless, these particles provide valuable information not present in the main components. The authors first discuss the importance of the heavy ions as tracers for processes in the solar atmosphere. Specifically, their relative abundances are found to be different in the solar wind as compared to the photosphere. This fractionation, which is best organized as a function of the first ionization time (FIT) of the elements under solar surface conditions, provides information on the structure of the chromosphere, where it is imparted on the partially ionized material by an atom-ion separation mechanism. Moreover, the charge states of the heavy ions can be used to infer the coronal temperature, since they are frozen-in near the altitude where the expansion time scale overcomes the ionization/recombination time scales. Next, the authors review the published values of ion abundances in the solar wind, concentrating on the recent results of the SWICS instrument on Ulysses. About 8 elements and more than 20 charge states can be routinely analyzed by this sensor. There is clear evidence that both the composition and the charge state distribution is significantly different in the fast solar wind from the south polar coronal hole, traversed by Ulysses in 1993/94, as compared to the solar wind normally encountered near the ecliptic plane. The fractionation between low- and high-FIT elements is reduced, and the charge states indicate a lower, more uniform coronal temperature in the hole. Finally, the authors discuss these results in the framework of existing theoretical models of the chromosphere and corona, attempting to identify differences between the low- and high-latitude regions of the solar atmosphere.

  5. Neutral Excitations in the Gaffnian state

    NASA Astrophysics Data System (ADS)

    Kang, Byungmin; Moore, Joel E.

    The Fractional Quantum Hall Effect (FQHE) is one of the most well-studied systems having topological order. Starting with the pioneering work by Laughlin, the model wave function approach has been shown to provide essential information for understanding topological order in gapped incompressible states. We study a model wave function called the Gaffnian state which is believed to represent a gapless, strongly correlated state that is very different from conventional metals. To understand this exotic gapless state better, we provide a representation in which the pairing structure of the Gaffnian state becomes more explicit. We employ the single-mode approximation of the Girvin-MacDonald-Platzman (GMP) mode, which is a neutral collective exitation mode, in order to have a physical picture of the gaplessness of the Gaffnian state. In particular, we discuss how to extract systematically the relevant physics in the long-distance, large electron number limit of the FQH states using a numerical calculation with relatively few electrons.

  6. Nitrogen molecule activation by excited states of copper

    SciTech Connect

    Sanchez-Zamora, M.; Novaro, O.; Ruiz, M.E. )

    1990-04-05

    Ab initio molecular orbital studies that include variational (with a multiconfiguration reference state of 200 states) and perturbational (including over 3 million configurations) configuration interaction calculations were addressed to the interaction of nitrogen molecules with copper. The Cu ground state {sup 2}S and first two excited states {sup 2}P and {sup 2}D were studied as they interact in different geometrical approaches (including side-on and end-on geometries) with ground-state N{sub 2} molecules.

  7. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    PubMed

    Papadakis, Raffaello; Ottosson, Henrik

    2015-09-21

    The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas. PMID:25960203

  8. Direct observation of photoinduced bent nitrosyl excited-state complexes

    SciTech Connect

    Sawyer, Karma R.; Steele, Ryan P.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Head-Gordon, Martin; Harris, Charles B.

    2008-06-28

    Ground state structures with side-on nitrosyl ({eta}{sup 2}-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited state structures with bent-NO ligands have been proposed for years but never directly observed. Here we use picosecond time-resolved infrared spectroscopy and density functional theory (DFT) modeling to study the photochemistry of Co(CO){sub 3}(NO), a model transition-metal-NO compound. Surprisingly, we have observed no evidence for ON and {eta}{sup 2}-NO structural isomers, but have observed two bent-NO complexes. DFT modeling of the ground and excited state potentials indicates that the bent-NO complexes correspond to triplet excited states. Photolysis of Co(CO){sub 3}(NO) with a 400-nm pump pulse leads to population of a manifold of excited states which decay to form an excited state triplet bent-NO complex within 1 ps. This structure relaxes to the ground triplet state in ca. 350 ps to form a second bent-NO structure.

  9. Photocyclization Reactions of Diarylethenes via the Excited Triplet State.

    PubMed

    Murata, Ryutaro; Yago, Tomoaki; Wakasa, Masanobu

    2015-11-12

    Cyclization reactions of three diarylethene derivatives, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), 1,2-bis(2-hexyl-3-benzothienyl)perfluorocyclopentene (BTHex), and 1,2-bis(2-isopropyl-3-benzothienyl)perfluorocyclopentene (BTiPr), via their excited triplet states were studied by means of steady-state and nanosecond transient absorption spectroscopy. The excited triplet states of BT, BTHex, and BTiPr were generated by energy transfer from the photoexcited triplet states of sensitizers such as xanthone, phenanthrene, and pyrene. The single-step quantum yields of the cyclization reactions from the excited triplet states of BT, BTHex, and BTiPr were determined to be 0.34, 0.53, and 0.65, respectively. The triplet energies of these three BTs were estimated to be 190-200 kJ mol(-1). PMID:26490486

  10. Controlling chimera states: The influence of excitable units

    NASA Astrophysics Data System (ADS)

    Isele, Thomas; Hizanidis, Johanne; Provata, Astero; Hövel, Philipp

    2016-02-01

    We explore the influence of a block of excitable units on the existence and behavior of chimera states in a nonlocally coupled ring-network of FitzHugh-Nagumo elements. The FitzHugh-Nagumo system, a paradigmatic model in many fields from neuroscience to chemical pattern formation and nonlinear electronics, exhibits oscillatory or excitable behavior depending on the values of its parameters. Until now, chimera states have been studied in networks of coupled oscillatory FitzHugh-Nagumo elements. In the present work, we find that introducing a block of excitable units into the network may lead to several interesting effects. It allows for controlling the position of a chimera state as well as for generating a chimera state directly from the synchronous state.

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

    NASA Astrophysics Data System (ADS)

    Guevara, Z. E.; Torres, D. A.

    2016-07-01

    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 106Cd to study excited states of 110Sn and the beam nuclei itself will be presented.

  12. State approaches to the system benefits charge

    SciTech Connect

    Fang, J M

    1997-07-01

    This report documents the consideration and implementation of a non-bypassable system benefits charge (SBC) in six states through mid-May 1997. The SBC is being established to sustain important public-policy programs during the electric industry restructuring process. The states covered include Arizona, California, Massachusetts, New York, Rhode Island, and Wisconsin. This report was prepared for the Office of Energy and Resource Planning, Utah Department of Natural Resources, under the National Renewable Energy Laboratory`s Sustainable Technology Energy Partnerships Initiative, Second Round (STEP-2). The purpose of the report is to provide decision makers in Utah, including the Utah Public Service Commission and the state legislature, with relevant information on the SBC for use in their deliberation on the matter. The issues faced by the six states are the SBC in general; surcharge rate or funding levels; administrative structure and procedures; and actions, guidelines, and principles by program area.

  13. Shape vibration and quasiparticle excitations in the lowest 0+ excited state in erbium isotopes

    NASA Astrophysics Data System (ADS)

    Chen, Fang-Qi; Egido, J. Luis

    2016-06-01

    The ground and first excited 0+ states of the -172Er156 isotopes are analyzed in the framework of the generator coordinate method. The shape parameter β is used to generate wave functions with different deformations which together with the two-quasiparticle states built on them provide a set of states. An angular momentum and particle number projection of the latter spawn the basis states of the generator coordinate method. With this ansatz and using the separable pairing plus quadrupole interaction we obtain a good agreement with the experimental spectra and E 2 transition rates up to moderate spin values. The structure of the wave functions suggests that the first excited 0+ states in the soft Er isotopes are dominated by shape fluctuations, while in the well deformed Er isotopes the two-quasiparticle states are more relevant. In between, both degrees of freedom are necessary.

  14. Nature of ground and electronic excited states of higher acenes.

    PubMed

    Yang, Yang; Davidson, Ernest R; Yang, Weitao

    2016-08-30

    Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle-particle random-phase approximation calculation. The (1)Ag ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state (3)B2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state (1)B2u is a zwitterionic state to the short axis. The excited (1)Ag state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the (1)B2u and excited (1)Ag states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved. PMID:27528690

  15. Two-photon transitions to excited states in atomic hydrogen

    SciTech Connect

    Quattropani, A.; Bassani, F.; Carillo, S.

    1982-06-01

    Resonant two-photon transition rates from the ground state of atomic hydrogen to ns excited states have been computed as a function of photon frequencies in the length and velocity gauges in order to test the accuracy of the calculation and to discuss the rate of convergence over the intermediate states. The dramatic structure of the transition rates produced by intermediate-state resonances is exhibited. A two-photon transparency is found in correspondence to each resonance.

  16. Excitation of Δ and N* resonances in isobaric charge-exchange reactions of heavy nuclei

    NASA Astrophysics Data System (ADS)

    Vidaña, I.; Benlliure, J.; Geissel, H.; Lenske, H.; Scheidenberger, C.; Vargas, J.

    2016-01-01

    We present a model for the study of the excitation of Δ(1232) and N*(1440) resonances in isobaric charge-exchange (AZ, A(Z ± 1)) reactions of heavy nuclei. Quasi-elastic and inelastic elementary processes contributing to the double differential cross sections of the reactions are described in terms of the exchange of virtual pions. The inelastic channel includes processes where the resonances are excited both in the target and in the projectile nucleus. We present results for reactions of 112Sn and 124Sn on different targets. Our results confirm that the position of the Δ peak is insensitive to targets with mass number A ≥ 12, and show that the origin of the Δ peak shift towards low excitation energies, with respect to its position in reactions with a proton target, can be easily explained in terms of the superposition of the different excitation mechanisms contributing to the reaction.

  17. Dynamics and spectroscopy of CH₂OO excited electronic states.

    PubMed

    Kalinowski, Jaroslaw; Foreman, Elizabeth S; Kapnas, Kara M; Murray, Craig; Räsänen, Markku; Gerber, R Benny

    2016-04-28

    The excited states of the Criegee intermediate CH2OO are studied in molecular dynamics simulations using directly potentials from multi-reference perturbation theory (MR-PT2). The photoexcitation of the species is simulated, and trajectories are propagated in time on the excited state. Some of the photoexcitation events lead to direct fragmentation of the molecule, but other trajectories describe at least several vibrations in the excited state, that may terminate by relaxation to the ground electronic state. Limits on the role of non-adiabatic contributions to the process are estimated by two different simulations, one that forces surface-hopping at potential crossings, and another that ignores surface hopping altogether. The effect of non-adiabatic transitions is found to be small. Spectroscopic implications and consequences for the interpretation of experimental results are discussed. PMID:27040614

  18. Characterization of adsorption and electronic excited states of quercetin on titanium dioxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Zdyb, Agata; Krawczyk, Stanisław

    2016-03-01

    Adsorption of quercetin on colloidal titanium dioxide nanoparticles in ethanol and its excited-state electronic structure were investigated by means of electronic and vibrational spectroscopies. The changes in electronic charge redistribution as reflected by the dipole moment difference, ∆μ, between the ground and excited electronic states were measured with electroabsorption spectroscopy and analyzed using results of TD DFT computations. Adsorption of quercetin causes a red shift of its absorption spectrum. Raman spectra of quercetin analyzed with reference to analogous data for morin indicate binding of quercetin through the hydroxy groups of the catechol moiety. The difference dipole moment, which is 5.5 D in free quercetin, increases to 11.8 D in opposite direction in adsorbed quercetin, and is associated with charge-transfer to the Ti atom. The computed transition energy, intensity, vector Δμ and molecular orbitals involved in the electronic transition at different molecular configurations indicate a bidentate chelating mode of binding of quercetin.

  19. Electronically Excited States of Anisotropically Extended Singly-Deprotonated PAH Anions.

    PubMed

    Theis, Mallory L; Candian, Alessandra; Tielens, Alexander G G M; Lee, Timothy J; Fortenberry, Ryan C

    2015-12-31

    Polycyclic aromatic hydrocarbons (PAHs) play a significant role in the chemistry of the interstellar medium (ISM) as well as in hydrocarbon combustion. These molecules can have high levels of diversity with the inclusion of heteroatoms and the addition or removal of hydrogens to form charged or radical species. There is an abundance of data on the cationic forms of these molecules, but there have been many fewer studies on the anionic species. The present study focuses on the anionic forms of deprotonated PAHs. It has been shown in previous work that PAHs containing nitrogen heteroatoms (PANHs) have the ability to form valence excited states giving anions electronic absorption features. This work analyzes how the isoelectronic pure PAHs behave under similar structural constructions. Singly deprotonated forms of benzene, naphthalene, anthracene, and tetracene classes are examined. None of the neutral-radicals possess dipole moments large enough to support dipole-bound excited states in their corresponding closed-shell anions. Even though the PANH anion derivatives support valence excited states for three-ringed structures, it is not until four-ringed structures of the pure PAH anion derivatives that valence excited states are exhibited. However, anisotropically extended PAHs larger than tetracene will likely exhibit valence excited states. The relative energies for the anion isomers are very small for all of the systems in this study. PMID:26645382

  20. The electronic excited states of a model organic endoperoxide: A comparison of TD-DFT and ab initio methods

    NASA Astrophysics Data System (ADS)

    Corral, Inés; González, Leticia

    2007-10-01

    The vertical excited spectrum of a model endoperoxide (cyclohexadieneendoperoxide) has been calculated using time dependent density functional theory (TD-DFT), resolution of the identity second order approximate coupled-cluster theory (RI-CC2), multiconfigurational complete active space self consistent field (CASSCF) and second order multi-state perturbation theory (MS-CASPT2). All theoretical methods predict the charge transfer πOO∗→πCC∗, and the πOO∗→σOO∗ excitation to be the lowest absorbing excited states. CASSCF optimized geometries for these states provide some hints about the photodissociation mechanisms as well as the emission spectrum of the molecule.

  1. Lifetime of the Excited State In Vivo

    PubMed Central

    Mar, T.; Govindjee; Singhal, G. S.; Merkelo, H.

    1972-01-01

    Using a mode-locked laser (λ, 632.8 nm), fluorescence decay of chlorophyll (Chl) a in the green alga Chlorella pyrenoidosa, the red alga Porphyridium cruentum, and the blue-green alga Anacystis nidulans was measured by the phase-shift method under conditions when photosynthesis was not operative (3-(3,4-dichlorophenyl)-1,1-dimethylurea [DCMU] poisoning, or cooling to 77°K). In the presence of 10-5 M DCMU, the lifetime of Chl a fluorescence (τ) at room temperature is about 1.7 nsec in Chlorella, 1.0 nsec in Porphyridium, and 0.7 nsec in Anacystis. At 77°K, τ is 1.4 nsec (for fluorescence at about 685 nm, F-685) and 2.3 nsec (for F-730) in Chlorella, 0.9 nsec (F-685) and 1.2 nsec (F-730) in Porphyridium, and 0.8 nsec (F-685 and F-730) in Anacystis. From the above measurement, and the assumption that τ0 (the intrinsic fluorescence lifetime) for Chl a in all three algae is 15.2 nsec, we have calculated the rate constants of radiationless transition (that includes energy transfer to weakly fluorescent system I) processes competing with fluorescence at room temperature to be about 5 × 108 sec-1 in Chlorella, 9 × 108 sec-1 in Porphyridium, and 13 × 108 sec-1 in Anacystis. At 77°K, this rate constant for Chl a that fluoresces at 685 nm remains, in the first approximation, the same as at room temperature. From the τ data, the rate constant for the trapping of excitation energy is calculated to be about 1.2 × 109 sec-1 for Chlorella, 2 × 109 sec-1 for Porphyridium, and 2 × 109 sec-1 for Anacystis. The efficiency of trapping is calculated to be about 66% (Chlorella), 68% (Porphyridium), and 60% (Anacystis). (It is recognized that variations in the above values are to be expected if algae grown under different conditions are used for experimentation.) The maximum quantum yield of Chl a fluorescence for system II (λ, 632.8 nm), calculated from τ measurements, is about 10% in Chlorella, 6-7% in Porhyridium, and 5% in Anacystis under conditions when photosynthesis

  2. Excitation energy transfer and charge separation in photosystem II membranes revisited.

    PubMed

    Broess, Koen; Trinkunas, Gediminas; van der Weij-de Wit, Chantal D; Dekker, Jan P; van Hoek, Arie; van Amerongen, Herbert

    2006-11-15

    We have performed time-resolved fluorescence measurements on photosystem II (PSII) containing membranes (BBY particles) from spinach with open reaction centers. The decay kinetics can be fitted with two main decay components with an average decay time of 150 ps. Comparison with recent kinetic exciton annihilation data on the major light-harvesting complex of PSII (LHCII) suggests that excitation diffusion within the antenna contributes significantly to the overall charge separation time in PSII, which disagrees with previously proposed trap-limited models. To establish to which extent excitation diffusion contributes to the overall charge separation time, we propose a simple coarse-grained method, based on the supramolecular organization of PSII and LHCII in grana membranes, to model the energy migration and charge separation processes in PSII simultaneously in a transparent way. All simulations have in common that the charge separation is fast and nearly irreversible, corresponding to a significant drop in free energy upon primary charge separation, and that in PSII membranes energy migration imposes a larger kinetic barrier for the overall process than primary charge separation. PMID:16861268

  3. Evaluating the GW Approximation with CCSD(T) for Charged Excitations Across the Oligoacenes.

    PubMed

    Rangel, Tonatiuh; Hamed, Samia M; Bruneval, Fabien; Neaton, Jeffrey B

    2016-06-14

    Charged excitations of the oligoacene family of molecules, relevant for astrophysics and technological applications, are widely studied and therefore provide an excellent system for benchmarking theoretical methods. In this work, we evaluate the performance of many-body perturbation theory within the GW approximation relative to new high-quality CCSD(T) reference data for charged excitations of the acenes. We compare GW calculations with a number of hybrid density functional theory starting points and with eigenvalue self-consistency. Special focus is given to elucidating the trend of GW-predicted excitations with molecule length increasing from benzene to hexacene. We find that GW calculations with starting points based on an optimally tuned range-separated hybrid (OTRSH) density functional and eigenvalue self-consistency can yield quantitative ionization potentials for the acenes. However, for larger acenes, the predicted electron affinities can deviate considerably from reference values. Our work paves the way for predictive and cost-effective GW calculations of charged excitations of molecules and identifies certain limitations of current GW methods used in practice for larger molecules. PMID:27123935

  4. Excited-state dynamics of astaxanthin aggregates

    NASA Astrophysics Data System (ADS)

    Fuciman, Marcel; Durchan, Milan; Šlouf, Václav; Keşan, Gürkan; Polívka, Tomáš

    2013-05-01

    Astaxanthin forms three types of aggregates in hydrated dimethyl sulfoxide (DMSO). In DMSO/water ratio of 1:1, a red-shifted J-aggregate with maximum at 570 nm is generated, while a ratio of 1:9 produces blue-shifted H-aggregates with peaks at 386 nm (H1) and 460 nm (H2). Monomeric astaxanthin in DMSO has an S1 lifetime of 5.3 ps, but a long-lived (33 ps) S∗ signal was also identified. Aggregation changes the S1 lifetimes to 17 ps (H1), 30 ps (H2), and 14 ps (J). Triplet state of astaxanthin, most likely generated via singlet homofission, was observed in H1 and H2 aggregates.

  5. Dynamics of ground and excited state vibrational relaxation and energy transfer in transition metal carbonyls.

    PubMed

    Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Spall, Steven J; Keane, Theo; Blake, Alexander J; Wilson, Claire; Meijer, Anthony J H M; Weinstein, Julia A

    2014-10-01

    Nonlinear vibrational spectroscopy provides insights into the dynamics of vibrational energy transfer in and between molecules, a crucial phenomenon in condensed phase physics, chemistry, and biology. Here we use frequency-domain 2-dimensional infrared (2DIR) spectroscopy to investigate the vibrational relaxation (VR) and vibrational energy transfer (VET) rates in different solvents in both the electronic ground and excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine), a prototypical transition metal carbonyl complex. The strong C≡O and ester C═O stretch infrared reporters, located on opposite sides of the molecule, were monitored in the 1600-2100 cm(-1) spectral region. VR in the lowest charge transfer triplet excited state ((3)CT) is found to be up to eight times faster than in the ground state. In the ground state, intramolecular anharmonic coupling may be solvent-assisted through solvent-induced frequency and charge fluctuations, and as such VR rates are solvent-dependent. In contrast, VR rates in the solvated (3)CT state are surprisingly solvent-insensitive, which suggests that predominantly intramolecular effects are responsible for the rapid vibrational deactivation. The increased VR rates in the excited state are discussed in terms of intramolecular electrostatic interactions helping overcome structural and thermodynamic barriers for this process in the vicinity of the central heavy atom, a feature which may be of significance to nonequilibrium photoinduced processes observed in transition metal complexes in general. PMID:25198700

  6. Importance of considering helium excited states in He+ scattering by an aluminum surface

    NASA Astrophysics Data System (ADS)

    Iglesias-García, A.; García, Evelina A.; Goldberg, E. C.

    2014-11-01

    The He+/Al system is a very interesting projectile-surface combination which was thought initially as an example of a pure Auger neutralization mechanism. Then, because of the measured reionization explained by the antibonding interaction of the projectile state with the core target states, the resonant charge exchange with the band states was considered as another important contribution to the neutralization. Nevertheless, by only considering the neutralization to the ground state of helium, the measured ion survival probability is still overestimated. On the other hand, measurements of electron emission from an Al surface bombarded by He positive ions suggested the possibility of occupied excited states of helium due to the ion-surface collision. In this work, we also include the excited states of He within the time-dependent scattering process in which both neutralization mechanisms, resonant and Auger, are simultaneously contemplated. Our starting point is a multiorbital Anderson Hamiltonian projected over the selected space of ground and excited atomic configurations. An extra term related to the Auger mechanism is added to this Hamiltonian. A difference with previous works is that this approach includes the electron spin and, therefore, the spin fluctuation statistics in the charge-exchange process is correctly taken into account. We find a notable improvement in the agreement with the experiments and also that the interference between both mechanisms is not dramatic.

  7. Quenching of excited triplet states by dissolved natural organic matter.

    PubMed

    Wenk, Jannis; Eustis, Soren N; McNeill, Kristopher; Canonica, Silvio

    2013-11-19

    Excited triplet states of aromatic ketones and quinones are used as proxies to assess the reactivity of excited triplet states of the dissolved organic matter ((3)DOM*) in natural waters. (3)DOM* are crucial transients in environmental photochemistry responsible for contaminant transformation, production of reactive oxygen species, and potentially photobleaching of DOM. In recent photochemical studies aimed at clarifying the role of DOM as an inhibitor of triplet-induced oxidations of organic contaminants, aromatic ketones have been used in the presence of DOM, and the question of a possible interaction between their excited triplet states and DOM has emerged. To clarify this issue, time-resolved laser spectroscopy was applied to measure the excited triplet state quenching of four different model triplet photosensitizers induced by a suite of DOM from various aquatic and terrestrial sources. While no quenching for the anionic triplet sensitizers 4-carboxybenzophenone (CBBP) and 9,10-anthraquinone-2,6-disulfonic acid (2,6-AQDS) was detected, second-order quenching rate constants with DOM for the triplets of 2-acetonaphthone (2AN) and 3-methoxyacetophenone (3MAP) in the range of 1.30-3.85 × 10(7) L mol(C)(-1) s(-1) were determined. On the basis of the average molecular weight of DOM molecules, the quenching for these uncharged excited triplet molecules is nearly diffusion-controlled, but significant quenching (>10%) in aerated water is not expected to occur below DOM concentrations of 22-72 mg(C) L(-1). PMID:24083647

  8. Quantum entanglement of localized excited states at finite temperature

    NASA Astrophysics Data System (ADS)

    Caputa, Pawel; Simón, Joan; Štikonas, Andrius; Takayanagi, Tadashi

    2015-01-01

    In this work we study the time evolutions of (Renyi) entanglement entropy of locally excited states in two dimensional conformal field theories (CFTs) at finite temperature. We consider excited states created by acting with local operators on thermal states and give both field theoretic and holographic calculations. In free field CFTs, we find that the growth of Renyi entanglement entropy at finite temperature is reduced compared to the zero temperature result by a small quantity proportional to the width of the localized excitations. On the other hand, in finite temperature CFTs with classical gravity duals, we find that the entanglement entropy approaches a characteristic value at late time. This behaviour does not occur at zero temperature. We also study the mutual information between the two CFTs in the thermofield double (TFD) formulation and give physical interpretations of our results.

  9. α-cluster excited states in 32S

    NASA Astrophysics Data System (ADS)

    Yoshida, Yuta; Kanada-En'yo, Yoshiko; Kobayashi, Fumiharu

    2016-04-01

    α -cluster excited states in ^{32}S are investigated with an extended ^{28}Si+α cluster model, in which the ^{28}Si core deformation and rotation and the α -cluster breaking are incorporated. In the generator coordinate method calculation with the extended ^{28}Si+α cluster model, the α -cluster excited states are obtained near the ^{28}Si+α threshold energy. The ^{28}Si core deformation and rotation effects, and also the α -clusters breaking in the ^{28}Si+α system, are discussed. It is found that the rotation of the oblately deformed ^{28}Si core has a significant effect on the α -cluster excited states whereas the α -cluster breaking has only a minor effect.

  10. Multi-pathway excited state relaxation of adenine oligomers in aqueous solution: a joint theoretical and experimental study.

    PubMed

    Banyasz, Akos; Gustavsson, Thomas; Onidas, Delphine; Changenet-Barret, Pascale; Markovitsi, Dimitra; Improta, Roberto

    2013-03-11

    The singlet excited states of adenine oligomers, model systems widely used for the understanding of the interaction of ultraviolet radiation with DNA, are investigated by fluorescence spectroscopy and time-dependent (TD) DFT calculations. Fluorescence decays, fluorescence anisotropy decays, and time-resolved fluorescence spectra are recorded from the femtosecond to the nanosecond timescales for single strand (dA)20 in aqueous solution. These experimental observations and, in particular, the comparison of the fluorescence behavior upon UVC and UVA excitation allow the identification of various types of electronic transitions with different energy and polarization. Calculations performed for up to five stacked 9-methyladenines, taking into account the solvent, show that different excited states are responsible for the absorption in the UVC and UVA spectral domains. Independently of the number of bases, bright excitons may evolve toward two types of excited dimers having π-π* or charge-transfer character, each one distinguished by its own geometry and spectroscopic signature. According to the picture arising from the joint experimental and theoretical investigation, UVC-induced fluorescence contains contribution from 1) exciton states with a different degree of localization, decaying within a few ps, 2) "neutral" excited dimers decaying on the sub-nanosecond timescale, being the dominant species, and 3) charge-transfer states decaying on the nanosecond timescale. The majority of the photons emitted upon UVA excitation are related to charge-transfer states. PMID:23335234

  11. State-Selective Excitation of Quantum Systems via Geometrical Optimization.

    PubMed

    Chang, Bo Y; Shin, Seokmin; Sola, Ignacio R

    2015-09-01

    We lay out the foundations of a general method of quantum control via geometrical optimization. We apply the method to state-selective population transfer using ultrashort transform-limited pulses between manifolds of levels that may represent, e.g., state-selective transitions in molecules. Assuming that certain states can be prepared, we develop three implementations: (i) preoptimization, which implies engineering the initial state within the ground manifold or electronic state before the pulse is applied; (ii) postoptimization, which implies engineering the final state within the excited manifold or target electronic state, after the pulse; and (iii) double-time optimization, which uses both types of time-ordered manipulations. We apply the schemes to two important dynamical problems: To prepare arbitrary vibrational superposition states on the target electronic state and to select weakly coupled vibrational states. Whereas full population inversion between the electronic states only requires control at initial time in all of the ground vibrational levels, only very specific superposition states can be prepared with high fidelity by either pre- or postoptimization mechanisms. Full state-selective population inversion requires manipulating the vibrational coherences in the ground electronic state before the optical pulse is applied and in the excited electronic state afterward, but not during all times. PMID:26575896

  12. Photoionization of furan from the ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došlić, Nada; Decleva, Piero

    2016-02-01

    Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy.

  13. Calculating helium atomic excited states in coordinate space

    NASA Astrophysics Data System (ADS)

    Hall, Shane; Siegel, P. B.

    2015-12-01

    Two coupled Schrödinger equations are used to calculate excited states of atomic helium. Using product state functions for the two-electron state, the shooting method is used to numerically determine the energies of the allowed singlet and triplet levels. The calculations agree well with the data, and the coordinate-space basis yields Schrödinger equations for helium that are familiar to students who have used similar methods for the hydrogen atom.

  14. Coherent excitation of a single atom to a Rydberg state

    SciTech Connect

    Miroshnychenko, Y.; Gaeetan, A.; Evellin, C.; Grangier, P.; Wilk, T.; Browaeys, A.; Comparat, D.; Pillet, P.

    2010-07-15

    We present the coherent excitation of a single Rubidium atom to the Rydberg state 58d{sub 3/2} using a two-photon transition. The experimental setup is described in detail, as are experimental techniques and procedures. The coherence of the excitation is revealed by observing Rabi oscillations between ground and Rydberg states of the atom. We analyze the observed oscillations in detail and compare them to numerical simulations which include imperfections of our experimental system. Strategies for future improvements on the coherent manipulation of a single atom in our settings are given.

  15. 2{sup +} excitation of the {sup 12}C Hoyle state

    SciTech Connect

    Freer, M.; Fujita, H.; Carter, J.; Usman, I.; Buthelezi, Z.; Foertsch, S. V.; Neveling, R.; Perez, S. M.; Smit, F. D.; Fearick, R. W.; Papka, P.; Swartz, J. A.

    2009-10-15

    A high-energy-resolution magnetic spectrometer has been used to measure the {sup 12}C excitation energy spectrum to search for the 2{sup +} excitation of the 7.65 MeV, 0{sup +} Hoyle state. By measuring in the diffractive minimum of the angular distribution for the broad 0{sup +} background, evidence is found for a possible 2{sup +} state at 9.6(1) MeV with a width of 600(100) keV. The implications for the {sup 8}Be+{sup 4}He reaction rate in stellar environments are discussed.

  16. First-principles Calculation of Excited State Spectra in QCD

    SciTech Connect

    Jozef Dudek,Robert Edwards,Michael Peardon,David Richards,Christopher Thomas

    2011-05-01

    Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I=2 pion-pion energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

  17. First-principles Calculation of Excited State Spectra in QCD

    SciTech Connect

    Dudek, Jozef J.; Edwards, Robert G.; Richards, David G.; Thomas, Christopher E.; Peardon, Michael J.

    2011-05-24

    Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I = 2{pi}{pi} energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

  18. Accurate Excited State Geometries within Reduced Subspace TDDFT/TDA.

    PubMed

    Robinson, David

    2014-12-01

    A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn-Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation. PMID:26583218

  19. Low-lying excited states in armchair polyacene within Pariser-Parr-Pople model: a density matrix renormalization group study.

    PubMed

    Das, Mousumi

    2014-03-28

    We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties. PMID:24697451

  20. Low-lying excited states in armchair polyacene within Pariser-Parr-Pople model: A density matrix renormalization group study

    SciTech Connect

    Das, Mousumi

    2014-03-28

    We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties.

  1. Characterizing the Locality of Diabatic States for Electronic Excitation Transfer by Decomposing the Diabatic Coupling

    SciTech Connect

    Vura-Weis, Josh; Newton, M. D.; Wasielewski, Michael R; Subotnik, J.E.

    2010-12-09

    A common strategy to calculate electronic coupling matrix elements for charge or energy transfer is to take the adiabatic states generated by electronic structure computations and rotate them to form localized diabatic states. In this paper, we show that, for intermolecular transfer of singlet electronic excitation, usually we cannot fully localize the electronic excitations in this way. Instead, we calculate putative initial and final states with small excitation tails caused by weak interactions with high energy excited states in the electronic manifold. These tails do not lead to substantial changes in the total diabatic coupling between states, but they do lead to a different partitioning of the total coupling between Coulomb (Förster), exchange (Dexter), and one-electron components. The tails may be reduced by using a multistate diabatic model or eliminated entirely by truncation (denoted as “chopping”). Without more information, we are unable to conclude with certainty whether the observed diabatic tails are a physical reality or a computational artifact. This research suggests that decomposition of the diabatic coupling between chromophores into Coulomb, exchange, and one-electron components may depend strongly on the number of states considered, and such results should be treated with caution.

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

    PubMed Central

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

    2008-01-01

    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. PMID:18647840

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

    PubMed

    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. PMID:18647840

  4. Ablation of GaAs by Intense, Ultrafast Electronic Excitation from Highly Charged Ions

    SciTech Connect

    Schenkel, T.; Hamza, A.V.; Barnes, A.V.; Schneider, D.H.; Banks, J.C.; Doyle, B.L.

    1998-09-01

    We have measured total ablation rates and secondary ion yields from undoped GaAs(100) interacting with slow (v=6.6{times}10{sup 5} m /s) , very highly charged ions. Ablation rates increase strongly as a function of projectile charge. Some 1400thinspthinsptarget atoms are removed when a single Th{sup 70+} ion deposits a potential energy of 152.6thinspthinspkeV within a few femtoseconds into a nanometer-sized target volume. We discuss models for ablation of semiconductors by intense, ultrafast electronic excitation. {copyright} {ital 1998} {ital The American Physical Society}

  5. Formation of metastable excited states during sputtering of transition metals

    SciTech Connect

    Wucher, A.; Sroubek, Z.

    1997-01-01

    We propose a simple model which treats the formation of metastable excited neutral atoms during sputtering of a transition metal as a two step process. First, the energy deposited into the electronic system of the solid by electronic energy losses of all moving particles in the collision cascade is considered to lead to a locally altered equilibrium electronic state of the solid. It is found that this step is dominated by collective interaction with the conduction band electrons rather than by electron promotion in binary atom-atom collisions. Second, sputtered excited atoms are assumed to be formed by resonant neutralization of excited ions (reflecting the altered equilibrium state) while crossing the surface. It is shown that this model explains the total as well as the velocity dependent excitation probability observed in recent experiments on sputtered neutral silver atoms, which cannot be understood in terms of existing theories describing the formation of excited states in sputtering. {copyright} {ital 1996} {ital The American Physical Society}

  6. Electronic structure and charge transfer excitation energies of three endohedral fullerene- ZnTPP/ZnPc dyads

    NASA Astrophysics Data System (ADS)

    Amerikheirabadi, Fatemeh; Basurto, Luis; Zope, Rajendra; Baruah, Tunna

    2015-03-01

    Organic donor-acceptor (D-A) moieties make up the main component of organic photovoltaics (OPVs). It has been proved that the open circuit voltage of these devices which is a parameter in efficiency determination, is directly related to the charge transfer excited states of the D-A pairs. Fullerenes having lots of interesting acceptor properties and porphyrins as well as phthalocyanines possessing intriguing donor characteristics, are shown to be promising nominees. In this work, we computationally analyze three donor-acceptor dyads of Zn-tetraphenyl porphyrin and Zn-phthalocyanine with novel endohedral fullerenes: Sc3N@C80_ZnTPP, Y3N@C80_ZnTPPandSc3N@C80_ZnPc.TheSc3N@C80_and Y3N@C80 belong to a particular class of fullerenes called trimetallic nitride endohedral fullerenes where the trimellatic nitrides form the endohedral units. Density functional theory, as implemented in NRLMOL code, is used to study the electronic structure and the related properties of these D-A complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group. We find that the CT excitation energies are larger for endohedral fullerene based dyads compared to similar C60 based dyads.

  7. Influence of a polarizable surrounding on the electronically excited states of aggregated perylene materials.

    PubMed

    Bellinger, Daniel; Settels, Volker; Liu, Wenlan; Fink, Reinhold F; Engels, Bernd

    2016-06-30

    To tune the efficiency of organic semiconductor devices it is important to understand limiting factors as trapping mechanisms for excitons or charges. An understanding of such mechanisms deserves an accurate description of the involved electronical states in the given environment. In this study, we investigate how a polarizable surrounding influences the relative positions of electronically excited states of dimers of different perylene dyes. Polarization effects are particularly interesting for these systems, because gas phase computations predict that the CT states lie slightly above the corresponding Frenkel states. A polarizable environment may change this energy order because CT states are thought to be more sensitive to a polarizable surrounding than Frenkel states. A first insight we got via a TD-HF approach in combination with a polarizable continuum model (PCM). These give limited insights because TD-HF overestimates excitation energies of CT states. However, SCS-CC2 approaches, which are sufficiently accurate, cannot easily be used in combination with continuum solvent models. Hence, we developed two approaches to combine gas phase SCS-CC2 results with solvent effects based on TD-HF computations. Their accuracies were finally checked via ADC(2)//COSMO computations. The results show that for perylene dyes a polarizable surrounding alone does not influence the energetic ordering of CT and Frenkel states. Variations in the energy order of the states only result from nuclear relaxation effects after the excitation process. © 2016 Wiley Periodicals, Inc. PMID:27030658

  8. Migration of excited charge carriers in arrays of phosphorus-doped silicon nanocrystals

    SciTech Connect

    Belyakov, V. A. Konakov, A. A.; Burdov, V. A.

    2010-11-15

    The rate of tunnel migration of excited charge carriers (electrons and holes) in the array of silicon nanocrystals doped with phosphorus is calculated. It is shown that, starting from certain phosphorus concentrations dependent on the relation between the dimensions of the emitting and accepting nanocrystals, the rate of tunneling of electrons sharply decreases (by several orders of magnitude) and becomes lower than the rate of interband radiative recombination

  9. Self-modulated dynamics of a relativistic charged particle beam in plasma wake field excitation

    NASA Astrophysics Data System (ADS)

    Akhter, T.; Fedele, R.; Nicola, S. De; Tanjia, F.; Jovanović, D.; Mannan, A.

    2016-09-01

    The self-modulated dynamics of a relativistic charged particle beam is provided within the context of the theory of plasma wake field excitation. The self-consistent description of the beam dynamics is provided by coupling the Vlasov equation with a Poisson-type equation relating the plasma wake potential to the beam density. An analysis of the beam envelope self-modulation is then carried out and the criteria for the occurrence of the instability are discussed thereby.

  10. Role of metastable charge states in a quantum-dot spin-qubit readout

    NASA Astrophysics Data System (ADS)

    Mason, J. D.; Studenikin, S. A.; Kam, A.; Wasilewski, Z. R.; Sachrajda, A. S.; Kycia, J. B.

    2015-09-01

    Readout of a spin qubit in a lateral gate-defined quantum-dot device typically involves a charge detector and a spin-to-charge conversion technique employing spin blockade. We investigate alternative mechanisms for spin-to-charge conversion involving metastable excited charge states made possible by an asymmetry in the tunneling rates to the leads. This technique is used to observe Landau-Zener-Stückelberg oscillations of the S -T+ qubit within the (1,0) ground state region of the charge stability diagram. The oscillations are π phase shifted relative to those detected using the standard technique and display a nonsinusoidal waveform due to the increased relaxation time from the metastable state.

  11. A semiempirical study for the ground and excited states of free-base and zinc porphyrin-fullerene dyads

    NASA Technical Reports Server (NTRS)

    Parusel, A. B.

    2000-01-01

    The ground and excited states of a covalently linked porphyrin-fullerene dyad in both its free-base and zinc forms (D. Kuciauskas et al., J. Phys. Chem. 100 (1996) 15926) have been investigated by semiempirical methods. The excited-state properties are discussed by investigation of the character of the molecular orbitals. All frontier MOs are mainly localized on either the donor or the acceptor subunit. Thus, the absorption spectra of both systems are best described as the sum of the spectra of the single components. The experimentally observed spectra are well reproduced by the theoretical computations. Both molecules undergo efficient electron transfer in polar but not in apolar solvents. This experimental finding is explained theoretically by explicitly considering solvent effects. The tenth excited state in the gas phase is of charge-separated character where an electron is transferred from the porphyrin donor to the fullerene acceptor subunit. This state is stabilized in energy in polar solvents due to its large formal dipole moment. The stabilization energy for an apolar environment such as benzene is not sufficient to lower this state to become the first excited singlet state. Thus, no electron transfer is observed, in agreement with experiment. In a polar environment such as acetonitrile, the charge-separated state becomes the S, state and electron transfer takes place, as observed experimentally. The flexible single bond connecting both the donor and acceptor subunits allows free rotation by ca. +/- 30 degrees about the optimized ground-state conformation. For the charge-separated state this optimized geometry has a maximum dipole moment. The geometry of the charge-separated state thus does not change relatively to the ground-state conformation. The electron-donating properties of porphyrin are enhanced in the zinc derivative due to a reduced porphyrin HOMO-LUMO energy gap. This yields a lower energy for the charge-separated state compared to the free

  12. Excited-State Electronic Structure in Polypyridyl Complexes Containing Unsymmetrical Ligands.

    PubMed

    Omberg, Kristin M.; Smith, Gregory D.; Kavaliunas, Darius A.; Chen, Pingyun; Treadway, Joseph A.; Schoonover, Jon R.; Palmer, Richard A.; Meyer, Thomas J.

    1999-03-01

    Step-scan Fourier transform infrared absorption difference time-resolved (S(2)FTIR DeltaA TRS) and time-resolved resonance Raman (TR(3)) spectroscopies have been applied to a series of questions related to excited-state structure in the metal-to-ligand charge transfer (MLCT) excited states of [Ru(bpy)(2)(4,4'-(CO(2)Et)(2)bpy)](2+), [Ru(bpy)(2)(4-CO(2)Et-4'-CH(3)bpy)](2+), [Ru(bpy)(4,4'-(CO(2)Et)(2)bpy)(2)](2+), [Ru(4,4'-(CO(2)Et)(2)bpy)(3)](2+), [Ru(bpy)(2)(4,4'-(CONEt(2))(2)bpy)](2+), [Ru(bpy)(2)(4-CONEt(2)-4'-CH(3)bpy)](2+), and [Ru(4-CONEt(2)-4'-CH(3)bpy)(3)](2+) (bpy is 2,2'-bipyridine). These complexes contain bpy ligands which are either symmetrically or unsymmetrically derivatized with electron-withdrawing ester or amide substituents. Analysis of the vibrational data, largely based on the magnitudes of the nu(CO) shifts of the amide and ester substituents (Deltanu(CO)), reveals that the ester- or amide-derivatized ligands are the ultimate acceptors and that the excited electron is localized on one acceptor ligand on the nanosecond time scale. In the unsymmetrically substituted acceptor ligands, the excited electron is largely polarized toward the ester- or amide-derivatized pyridine rings. In the MLCT excited states of [Ru(bpy)(2)(4,4'-(CO(2)Et)(2)bpy)](2+) and [Ru(bpy)(2)(4,4'-(CONEt(2))(2)bpy)](2+), Deltanu(CO) is only 60-70% of that observed upon complete ligand reduction due to a strong polarization interaction in the excited state between the dpi(5) Ru(III) core and the excited electron. PMID:11670867

  13. Excited states in the proton-unbound nuclide 158Ta

    NASA Astrophysics Data System (ADS)

    Carroll, R. J.; Page, R. D.; Joss, D. T.; O'Donnell, D.; Uusitalo, J.; Darby, I. G.; Andgren, K.; Auranen, K.; Bönig, S.; Cederwall, B.; Doncel, M.; Drummond, M. C.; Eeckhaudt, S.; Grahn, T.; Gray-Jones, C.; Greenlees, P. T.; Hadinia, B.; HerzáÅ, A.; Jakobsson, U.; Jones, P. M.; Julin, R.; Juutinen, S.; Konki, J.; Kröll, T.; Leino, M.; Leppänen, A.-P.; McPeake, C.; Nyman, M.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Revill, J.; Ruotsalainen, P.; Sandzelius, M.; Sarén, J.; Sayǧi, B.; Scholey, C.; Seweryniak, D.; Simpson, J.; Sorri, J.; Stolze, S.; Taylor, M. J.; Thornthwaite, A.

    2016-03-01

    Excited states in the neutron-deficient odd-odd proton-unbound nuclide 158Ta have been investigated in two separate experiments. In the first experiment, 166Ir nuclei were produced in the reactions of 380 MeV 78Kr ions with an isotopically enriched 92Mo target. The α -decay chain of the 9+ state in 166Ir was analyzed. Fine structure in the α decay of the 9+ state in 162Re established a 66 keV difference in excitation energy between the lowest-lying 9+ and 10+ states in 158Ta. Higher-lying states in 158Ta were populated in the reactions of 255 MeV 58Ni ions with an isotopically enriched 102Pd target. Gamma-ray decay paths that populate, depopulate, and bypass a 19- isomeric state have been identified. The general features of the deduced level scheme are discussed and the prospects for observing proton emission branches from excited states are considered.

  14. Direct Lifetime Measurements of the Excited States in (72)Ni.

    PubMed

    Kolos, K; Miller, D; Grzywacz, R; Iwasaki, H; Al-Shudifat, M; Bazin, D; Bingham, C R; Braunroth, T; Cerizza, G; Gade, A; Lemasson, A; Liddick, S N; Madurga, M; Morse, C; Portillo, M; Rajabali, M M; Recchia, F; Riedinger, L L; Voss, P; Walters, W B; Weisshaar, D; Whitmore, K; Wimmer, K; Tostevin, J A

    2016-03-25

    The lifetimes of the first excited 2^{+} and 4^{+} states in ^{72}Ni were measured at the National Superconducting Cyclotron Laboratory with the recoil-distance Doppler-shift method, a model-independent probe to obtain the reduced transition probability. Excited states in ^{72}Ni were populated by the one-proton knockout reaction of an intermediate energy ^{73}Cu beam. γ-ray-recoil coincidences were detected with the γ-ray tracking array GRETINA and the S800 spectrograph. Our results provide evidence of enhanced transition probability B(E2;2^{+}→0^{+}) as compared to ^{68}Ni, but do not confirm the trend of large B(E2) values reported in the neighboring isotope ^{70}Ni obtained from Coulomb excitation measurement. The results are compared to shell model calculations. The lifetime obtained for the excited 4_{1}^{+} state is consistent with models showing decay of a seniority ν=4, 4^{+} state, which is consistent with the disappearance of the 8^{+} isomer in ^{72}Ni. PMID:27058074

  15. Thermally induced excited-state coherent raman spectra of solids

    NASA Astrophysics Data System (ADS)

    Andrews, J. R.; Hochstrasser, R. M.

    1981-09-01

    A difference frequency resonance has been observed for the 747 cm -1 vibration in the first excited singlet state of pentacene in benzoic acid. The resonance is absent at low temperature (4.5 K) and its appearance is exponentially activated with an activation energy of 13.8 cm -1. These observations are compared to theoretical expectations.

  16. Detection of excited-state electron bubbles in superfluid helium.

    PubMed

    Konstantinov, Denis; Maris, Humphrey J

    2003-01-17

    We report on experiments in which the pressure oscillation associated with a sound wave is used to explode electron bubbles in liquid helium. Using this technique, we are able to detect the presence of electron bubbles in excited states. PMID:12570553

  17. Direct Lifetime Measurements of the Excited States in 72Ni

    NASA Astrophysics Data System (ADS)

    Kolos, K.; Miller, D.; Grzywacz, R.; Iwasaki, H.; Al-Shudifat, M.; Bazin, D.; Bingham, C. R.; Braunroth, T.; Cerizza, G.; Gade, A.; Lemasson, A.; Liddick, S. N.; Madurga, M.; Morse, C.; Portillo, M.; Rajabali, M. M.; Recchia, F.; Riedinger, L. L.; Voss, P.; Walters, W. B.; Weisshaar, D.; Whitmore, K.; Wimmer, K.; Tostevin, J. A.

    2016-03-01

    The lifetimes of the first excited 2+ and 4+ states in 72>Ni were measured at the National Superconducting Cyclotron Laboratory with the recoil-distance Doppler-shift method, a model-independent probe to obtain the reduced transition probability. Excited states in 72Ni were populated by the one-proton knockout reaction of an intermediate energy 73Cu beam. γ -ray-recoil coincidences were detected with the γ -ray tracking array GRETINA and the S800 spectrograph. Our results provide evidence of enhanced transition probability B (E 2 ;2+→0+) as compared to 68Ni, but do not confirm the trend of large B (E 2 ) values reported in the neighboring isotope 70Ni obtained from Coulomb excitation measurement. The results are compared to shell model calculations. The lifetime obtained for the excited 41+ state is consistent with models showing decay of a seniority ν =4 , 4+ state, which is consistent with the disappearance of the 8+ isomer in 72Ni.

  18. Describing excited state relaxation and localization in TiO2 nanoparticles using TD-DFT

    DOE PAGESBeta

    Berardo, Enrico; Hu, Han -Shi; van Dam, Hubertus J. J.; Shevlin, Stephen A.; Woodley, Scott M.; Kowalski, Karol; Zwijnenburg, Martijn A.

    2014-02-26

    We have investigated the description of excited state relaxation in naked and hydrated TiO2 nanoparticles using Time-Dependent Density Functional Theory (TD-DFT) with three common hybrid exchange-correlation (XC) potentials; B3LYP, CAM-B3LYP and BHLYP. Use of TD-CAM-B3LYP and TD-BHLYP yields qualitatively similar results for all structures, which are also consistent with predictions of coupled cluster theory for small particles. TD-B3LYP, in contrast, is found to make rather different predictions; including apparent conical intersections for certain particles that are not observed with TD-CAM-B3LYP nor with TD-BHLYP. In line with our previous observations for vertical excitations, the issue with TD-B3LYP appears to be themore » inherent tendency of TD-B3LYP, and other XC potentials with no or a low percentage of Hartree-Fock Like Exchange, to spuriously stabilize the energy of charge-transfer (CT) states. Even in the case of hydrated particles, for which vertical excitations are generally well described with all XC potentials, the use of TD-B3LYP appears to result in CT-problems for certain particles. We hypothesize that the spurious stabilization of CT-states by TD-B3LYP even may drive the excited state optimizations to different excited state geometries than those obtained using TD-CAM-B3LYP or TD-BHLYP. In conclusion, focusing on the TD-CAM-B3LYP and TD-BHLYP results, excited state relaxation in naked and hydrated TiO2 nanoparticles is predicted to be associated with a large Stokes’ shift.« less

  19. Excited-state evolution probed by convoy-electron emission in relativistic heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Takabayashi, Y.; Ito, T.; Azuma, T.; Komaki, K.; Yamazaki, Y.; Tawara, H.; Takada, E.; Murakami, T.; Seliger, M.; Tökési, K.; O. Reinhold, C.; Burgdörfer, J.

    2003-10-01

    We present a joint experimental and theoretical study of convoy-electron emission resulting from highly-charged-ion transport through carbon foils at moderately relativistic speeds. Energy spectra of electrons ejected at 0° have been measured for 390 MeV/u hydrogen-like Ar17+ ions and 460 MeV/u (β=v/c=0.74,γ=1.49) Fe25+ (1s), Fe24+ (1s2), and Fe23+ (1s22s) incident on carbon foils with thicknesses from 25 to 8700 μg/cm2. Due to this unprecedented wide range of thicknesses, the sequential excitation and ionization of initially deeply bound electrons to highly excited states and continuum states can be followed in considerable detail. The analysis of the spectra is aided by simulations based on the classical transport theory which has been extended to relativistic energies and to multielectron projectiles. The motion of the projectile electron inside the solid target is calculated taking into account the Coulomb potential of the projectile ion and the multiple stochastic collisions with target cores and target electrons. Different phases of the convoy-electron emissions can be disentangled: direct ejection to the continuum, the transient buildup of an excited-state wave packet followed by ionization, and postionization modification of the continuum spectrum. We find good agreement between experiment and simulation for the evolution of charge states and the emission spectrum.

  20. Excited-State Dipole and Quadrupole Moments: TD-DFT versus CC2.

    PubMed

    Jacquemin, Denis

    2016-08-01

    The accuracies of the excited-state dipole and quadrupole moments obtained by TD-DFT are assessed by considering 16 different exchange-correlation functionals and more than 30 medium and large molecules. Except for excited-state presenting a significant charge-transfer character, a relatively limited dependency on the nature of the functional is found. It also turns out that while DFT ground-state dipole moments tend to be too large, the reverse trend is obtained for their excited-state counterparts, at least when hybrid functionals are used. Consequently, the TD-DFT excess dipole moments are often too small, an error that can be fortuitously corrected for charge-transfer transition by selecting a pure or a hybrid functional containing a small share of exact exchange. This error-cancelation phenomena explains the contradictory conclusions obtained in previous investigations. Overall, the largest correlation between CC2 and TD-DFT excess dipoles is obtained with M06-2X, but at the price of a nearly systematic underestimation of this property by ca. 1 D. For the excess quadrupole moments, the average errors are of the order of 0.2-0.6 D·Å for the set of small aromatic systems treated. PMID:27385324

  1. Excited-State Dipole and Quadrupole Moments: TD-DFT versus CC2

    PubMed Central

    2016-01-01

    The accuracies of the excited-state dipole and quadrupole moments obtained by TD-DFT are assessed by considering 16 different exchange-correlation functionals and more than 30 medium and large molecules. Except for excited-state presenting a significant charge-transfer character, a relatively limited dependency on the nature of the functional is found. It also turns out that while DFT ground-state dipole moments tend to be too large, the reverse trend is obtained for their excited-state counterparts, at least when hybrid functionals are used. Consequently, the TD-DFT excess dipole moments are often too small, an error that can be fortuitously corrected for charge-transfer transition by selecting a pure or a hybrid functional containing a small share of exact exchange. This error-cancelation phenomena explains the contradictory conclusions obtained in previous investigations. Overall, the largest correlation between CC2 and TD-DFT excess dipoles is obtained with M06-2X, but at the price of a nearly systematic underestimation of this property by ca. 1 D. For the excess quadrupole moments, the average errors are of the order of 0.2–0.6 D·Å for the set of small aromatic systems treated. PMID:27385324

  2. First observation of excited states in {sup 12}Li

    SciTech Connect

    Hall, C. C.; Lunderberg, E. M.; DeYoung, P. A.; Denby, D. H.; Baumann, T.; Bazin, D.; Blanchon, G.; Bonaccorso, A.; Brown, B. A.; Christian, G.; Frank, N.; Gade, A.; Mosby, S.; Peters, W. A.; Spyrou, A.; Thoennessen, M.; Brown, J.; Finck, J.; Hinnefeld, J.; Hoffman, C. R.

    2010-02-15

    The neutron-unbound ground state and two excited states of {sup 12}Li were formed by the two-proton removal reaction from a 53.4-MeV/u {sup 14}B beam. The decay energy spectrum of {sup 12}Li was measured with the Modular Neutron Array (MoNA) and the Sweeper dipole superconducting magnet at the National Superconducting Cyclotron Laboratory. Two excited states at resonance energies of 250 +- 20 keV and 555 +- 20 keV were observed for the first time and the data are consistent with the previously reported s-wave ground state with a scattering length of a{sub s}=-13.7 fm.

  3. Calculation of neutral beam deposition accounting for excited states

    SciTech Connect

    Gianakon, T.A.

    1992-09-01

    Large-scale neutral-beam auxillary heating of plasmas has led to new plasma operational regimes which are often dominated by fast ions injected via the absorption of an energetic beam of hydrogen neutrals. An accurate simulation of the slowing down and transport of these fast ions requires an intimate knowledge of the hydrogenic neutral deposition on each flux surface of the plasma. As a refinement to the present generation of transport codes, which base their beam deposition on ground-state reaction rates, a new set of routines, based on the excited states of hydrogen, is presented as mechanism for computing the attenuation and deposition of a beam of energetic neutrals. Additionally, the numerical formulations for the underlying atomic physics for hydrogen impacting on the constiuent plasma species is developed and compiled as a numerical database. Sample results based on this excited state model are compared with the ground-state model for simple plasma configurations.

  4. Lattice QCD determination of patterns of excited baryon states

    SciTech Connect

    Subhasish Basak; Robert Edwards; George Fleming; Keisuke Juge; Adam Lichtl; Colin Morningstar; David Richards; Ikuro Sato; Stephen Wallace

    2007-10-01

    Energies for excited isospin I = 1/2 and I = 3/2 states that include the nucleon and Delta families of baryons are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G2 irreducible representations of the octahedral group. The decomposition of spin 5/2 or higher spin states is realized for the first time in a lattice QCD calculation. We observe patterns of degenerate energies in the irreducible representations of the octahedral group that correspond to the subduction of the continuum spin 5/2 or higher. The overall pattern of low-lying excited states corresponds well to the pattern of physical states subduced to the irreducible representations of the octahedral group.

  5. Direct excitation of butterfly states in Rydberg molecules

    NASA Astrophysics Data System (ADS)

    Lippe, Carsten; Niederpruem, Thomas; Thomas, Oliver; Eichert, Tanita; Ott, Herwig

    2016-05-01

    Since their first theoretical prediction Rydberg molecules have become an increasing field of research. These exotic states originate from the binding of a ground state atom in the electronic wave function of a highly-excited Rydberg atom mediated by a Fermi contact type interaction. A special class of long-range molecular states, the butterfly states, were first proposed by Greene et al.. These states arise from a shape resonance in the p-wave scattering channel of a ground state atom and a Rydberg electron and are characterized by an electron wavefunction whose density distribution resembles the shape of a butterfly. We report on the direct observation of deeply bound butterfly states of Rydberg molecules of 87 Rb. The butterfly states are studied by high resolution spectroscopy of UV-excited Rydberg molecules. We find states bound up to - 50 GHz from the 25 P1/2 , F = 1 state, corresponding to binding lengths of 50a0 to 500a0 and with permanent electric dipole moments of up to 500 Debye. This distinguishes the observed butterfly states from the previously observed long range Rydberg molecules in rubidium.

  6. Excited States of the Diatomic Molecule CrHe

    NASA Astrophysics Data System (ADS)

    Pototschnig, Johann V.; Ratschek, Martin; Hauser, Andreas W.; Ernst, Wolfgang E.

    2013-06-01

    Chromium (Cr) atoms embedded in superfluid helium nanodroplets (He_N) have been investigated by laser induced fluorescence, beam depletion and resonant two-photon ionization spectroscopy in current experiments at our institute. Cr is found to reside inside the He_N in the a^7S ground state. Two electronically excited states, z^7P and y^7P, are involved in a photoinduced ejection process which allowed us to study Fano resonances in the photoionisation spectra The need for a better understanding of the experimental observations triggered a theoretical approach towards the computation of electronically excited states via high-level methods of computational chemistry. Two well-established, wave function-based methods, CASSCF and MRCI, are combined to calculate the potential energy curves for the three states involved. The character of the two excited states z^7P and y^7P turns out to be significantly different. Theory predicts the ejection of the Cr atom in the case of an y^7P excitation as was observed experimentally. The quasi-inert helium environment is expected to weaken spin selection rules, allowing a coupling between different spin states especially during the ejection process. We therefore extend our theoretical analysis to the lowest state in the triplet- and quintet- manifold. Most of these alternative states show very weak bonding of only a few wn. A. Kautsch, M. Hasewend, M. Koch and W. E. Ernst, Phys. Rev. A 86, 033428 (2012). A. Kautsch, M. Koch and W. E. Ernst, J. Phys. Chem. A, accepted, doi:10.1021/jp312336m}.

  7. Ground and Excited State Spectra of a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Stewart, D. R.; Sprinzak, D.; Patel, S. R.; Marcus, C. M.; Duruoz, C. I.; Harris, J. S.

    1998-03-01

    We present linear and nonlinear magnetoconductance measurements of the ground and excited state spectra for successive electron occupancy in a gate defined lateral quantum dot. Previous measurementsfootnote D.R. Stewart, D. Sprinzak, C.M. Marcus, C.I. Duruoz and J.S. Harris Jr., Science 278, (1997). showed a direct correlation between the mth excited state of the N-electron system and the ground state of the (N+m)-electron system for m up to 4, consistent to a large degree with a single-particle picture. Here we report quantitative deviations of the excited state spectra from the spectrum of ground state magnetoconductances, attributed to many-body interactions in the finite system of N ~200 electrons. We also describe the behaviour of anticrossings in the ground state magnetoconductances. We acknowledge the support of JSEP (DAAH04-94-G-0058), ARO (DAAH04-95-1-0331), ONR-YIP (N00014-94-1-0622) and the NSF-PECASE program. D.S. acknowledges the support of MINERVA grant.

  8. Photodissociation of N2O: excitation of 1A" states.

    PubMed

    Schinke, Reinhard; Schmidt, Johan A

    2012-11-26

    We investigate the contributions of the lowest two (1)A" states in the UV photodissociation of N(2)O employing three-dimensional potential energy surfaces and transition dipole moment functions. Because the transition dipole moments are much smaller than for the 2 (1)A' state, we conclude that excitation of the (1)A" states has a marginal effect. The dense vibrational spectrum of the quasi-bound 2(1)A" state possibly explains some of the tiny, noise-like structures of the measured absorption spectrum. PMID:22536943

  9. Excited S-symmetry states of positronic lithium and beryllium

    NASA Astrophysics Data System (ADS)

    Strasburger, Krzysztof

    2016-04-01

    The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection.

  10. Excited S-symmetry states of positronic lithium and beryllium.

    PubMed

    Strasburger, Krzysztof

    2016-04-14

    The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection. PMID:27083730

  11. Description of electronic excited states using electron correlation operator.

    PubMed

    Nichols, Bryan; Rassolov, Vitaly A

    2013-09-14

    The electron correlation energy in a chemical system is defined as a difference between the energy of an exact energy for a given Hamiltonian, and a mean-field, or single determinant, approximation to it. A promising way to model electron correlation is through the expectation value of a linear two-electron operator for the Kohn-Sham single determinant wavefunction. For practical reasons, it is desirable for such an operator to be universal, i.e., independent of the positions and types of nuclei in a molecule. The correlation operator models the effect of electron correlation on the interaction energy in a electron pair. We choose an operator expanded in a small number of Gaussians as a model for electron correlation, and test it by computing atomic and molecular adiabatic excited states. The computations are performed within the Δ Self-Consistent Field (ΔSCF) formalism, and are compared to the time-dependent density functional theory model with popular density functionals. The simplest form of the correlation operator contains only one parameter derived from the helium atom ground state correlation energy. The correlation operator approach significantly outperforms other methods in computation of atomic excitation energies. The accuracy of molecular excitation energies computed with the correlation operator is limited by the shortcomings of the ΔSCF methodology in describing excited states. PMID:24050332

  12. 77 FR 60005 - Schedule of Charges Outside the United States

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-01

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF TRANSPORTATION Federal Aviation Administration Schedule of Charges Outside the United States AGENCY: Federal Aviation... of charges for services of FAA Flight Standards Aviation Safety Inspectors outside the United...

  13. Sub-50 fs excited state dynamics of 6-chloroguanine upon deep ultraviolet excitation.

    PubMed

    Mondal, Sayan; Puranik, Mrinalini

    2016-05-18

    The photophysical properties of natural nucleobases and their respective nucleotides are ascribed to the sub-picosecond lifetime of their first singlet states in the UV-B region (260-350 nm). Electronic transitions of the ππ* type, which are stronger than those in the UV-B region, lie at the red edge of the UV-C range (100-260 nm) in all isolated nucleobases. The lowest energetic excited states in the UV-B region of nucleobases have been investigated using a plethora of experimental and theoretical methods in gas and solution phases. The sub-picosecond lifetime of these molecules is not a general attribute of all nucleobases but specific to the five primary nucleobases and a few xanthine and methylated derivatives. To determine the overall UV photostability, we aim to understand the effect of more energetic photons lying in the UV-C region on nucleobases. To determine the UV-C initiated photophysics of a nucleobase system, we chose a halogen substituted purine, 6-chloroguanine (6-ClG), that we had investigated previously using resonance Raman spectroscopy. We have performed quantitative measurements of the resonance Raman cross-section across the Bb absorption band (210-230 nm) and constructed the Raman excitation profiles. We modeled the excitation profiles using Lee and Heller's time-dependent theory of resonance Raman intensities to extract the initial excited state dynamics of 6-ClG within 30-50 fs after photoexcitation. We found that imidazole and pyrimidine rings of 6-ClG undergo expansion and contraction, respectively, following photoexcitation to the Bb state. The amount of distortions of the excited state structure from that of the ground state structure is reflected by the total internal reorganization energy that is determined at 112 cm(-1). The contribution of the inertial component of the solvent response towards the total reorganization energy was obtained at 1220 cm(-1). In addition, our simulation also yields an instantaneous response of the first

  14. Excited state absorption in chromium doped Li2B4O7 glass

    NASA Astrophysics Data System (ADS)

    Koepke, Cz; Wisniewski, K.; Grinberg, M.; Majchrowski, A.; Han, T. P. J.

    2001-03-01

    Excited state absorption (ESA) measurements of the Cr:Li2B4O7 glass (Cr:LBO-glass) along with preliminary interpretation are presented. The presence of chromium in its tri- (d3) and hexa- (d0) valence states is observed. Both Cr3+ and Cr6+ ions appear to contribute in the de-excitation processes and can be attributed in the ESA spectra under excitation wavelengths at 308 nm, 488 nm, 515 nm and 610 nm. The ESA spectra detected with UV excitation have been interpreted in terms of transitions in the framework of the Cr5+O- centre, which forms after charge-transfer-type absorption in the [CrO4]2- group. Assumption of the double-electron state of the 3d22p4 electronic configuration together with crystal-field-split states of the 3d12p5 configuration allowed us to reproduce the obtained ESA spectra. The ESA spectra of the Cr3+ ions have different characteristics and are related to transitions to the conduction band.

  15. Metastable states of plasma particles close to a charged surface

    SciTech Connect

    Shavlov, A. V.; Dzhumandzhi, V. A.

    2015-09-15

    The free energy of the plasma particles and the charged surface that form an electroneutral system is calculated on the basis of the Poisson-Boltzmann equation. It is shown that, owing to correlation of light plasma particles near the charged surface and close to heavy particles of high charge, there can be metastable states in plasma. The corresponding phase charts of metastable states of the separate components of plasma, and plasma as a whole, are constructed. These charts depend on temperature, the charge magnitude, the size of the particles, and the share of the charge of the light carriers out of the total charge of the plasma particles.

  16. Twisting in the excited state of an N-methylpyridinium fluorescent dye modulated by nano-heterogeneous micellar systems.

    PubMed

    Cesaretti, A; Carlotti, B; Gentili, P L; Germani, R; Spalletti, A; Elisei, F

    2016-04-13

    A push-pull N-methylpyridinium fluorescent dye with a pyrenyl group as the electron-donor portion was investigated within the nano-heterogeneous media provided by some micellar systems. The molecule was studied by stationary and time-resolved spectroscopic techniques in spherical micellar solutions and viscoelastic hydrogels, in order to throw light on the role played by twisting in its excited state deactivation. As proven by femtosecond fluorescence up-conversion and transient absorption experiments, the excited state dynamics of the molecule is ruled by charge transfer and twisting processes, which, from the locally excited (LE) state initially populated upon excitation, progressively lead to twisted (TICT) and planar (PICT) intramolecular charge transfer states. The inclusion within micellar aggregates was found to slow down and/or limit the rotation of the molecule with respect to what had previously been observed in water, while its confinement within the hydrophobic domains of the gel matrixes prevents any molecular torsion. The increasing viscosity of the medium, when passing from water to micellar systems, implies that the detected steady-state fluorescence comes from an excited state which is not fully relaxed, as is the case with the TICT state in micelles or the LE state in hydrogels, where the detected emission changes its usual orange colour to yellow. PMID:26982966

  17. Super-atom molecular orbital excited states of fullerenes.

    PubMed

    Johansson, J Olof; Bohl, Elvira; Campbell, Eleanor E B

    2016-09-13

    Super-atom molecular orbitals are orbitals that form diffuse hydrogenic excited electronic states of fullerenes with their electron density centred at the centre of the hollow carbon cage and a significant electron density inside the cage. This is a consequence of the high symmetry and hollow structure of the molecules and distinguishes them from typical low-lying molecular Rydberg states. This review summarizes the current experimental and theoretical studies related to these exotic excited electronic states with emphasis on femtosecond photoelectron spectroscopy experiments on gas-phase fullerenes.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501970

  18. Excited states of the odd-odd nucleus 230Pa

    NASA Astrophysics Data System (ADS)

    Kotthaus, T.; Reiter, P.; Hess, H.; Kalkühler, M.; Wendt, A.; Wiens, A.; Hertenberger, R.; Morgan, T.; Thirolf, P. G.; Wirth, H.-F.; Faestermann, T.

    2013-04-01

    The completely unknown spectrum of excited states of the odd-odd nucleus 230Pa was studied employing the one-neutron transfer reaction 231Pa(d,t)230Pa at a beam energy of 22 MeV. The excitation energy and the cross section were measured for, in total, 81 states below 1.4 MeV. Level assignments of these states are based on a semiempirical model and comparison with theoretical predictions, based on distorted-wave Born approximation (DWBA) calculations for the cross sections. For 12 rotational bands the band-head energy and the rotational parameter are determined. The K quantum numbers and the Nilsson configurations are established. Empirical values for the Gallagher-Moszkowski splittings and for Newby shifts are obtained.

  19. Subpicosecond Excited State Lifetimes in DNA Polymers Require Unstacked Bases

    NASA Astrophysics Data System (ADS)

    de La Harpe, Kimberly; Su, Charlene; Kohler, Bern

    2009-06-01

    The femtosecond lifetimes of excited states of monomeric DNA bases are the result of nuclear motions that lead to one or more conical intersections (CIs). Surprisingly, femtosecond pump-probe experiments reveal that excitations in DNA base polymers, including ones with genomic or 'natural' sequences of the four bases, decay at least an order of magnitude more slowly. Although the reasons for this dramatic change in photophysics are unclear, evidence strongly suggests that the long-lived states are exciplexes formed when an electron is partially transferred from one base to its π-stacked neighbor. Experiments also show that monomer-like subpicosecond decay to the ground state is frequently observed in many DNA oligomers and polymers in addition to exciplex formation. We will present results from high-temperature and other experiments suggesting that monomer-like, CI-mediated dynamics are only possible when unstacked bases are present.

  20. Valence and excited states of LiH-

    NASA Astrophysics Data System (ADS)

    Gutsev, Gennady L.; Nooijen, Marcel; Bartlett, Rodney J.

    1998-03-01

    Valence and excited dipole-bound states of the LiH- anion are calculated with the recently developed electron-attachment equation-of-motion coupled-cluster technique. It is found that the first dipole-bound state of LiH- corresponds to the second dissociation channel LiH--->Li-(1S)+H(2S). The second (excited) dipole-bound state of LiH- is below the neutral ground-state potential energy curve only for some range of the Li-H internuclear distance. This state appears at bond lengths larger than ~2.0 Å and decays at Li-H distances longer than ~4.2 Å, where the dipole moment of LiH becomes smaller than the critical value of 2.5 D. The adiabatic electron affinity of LiH calculated at the coupled-cluster level with the iterative inclusion of all single, double, and triple excitations and a large atomic natural orbital basis set is 0.327 eV, almost matching the recently obtained experimental value of 0.342+/-0.012 eV.

  1. Excited state dynamics of the astaxanthin radical cation

    NASA Astrophysics Data System (ADS)

    Amarie, Sergiu; Förster, Ute; Gildenhoff, Nina; Dreuw, Andreas; Wachtveitl, Josef

    2010-07-01

    Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130 fs (decay of the S 2 excited state) and 5.2 ps (nonradiative decay of the S 1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880 nm (D 0 → D 3 transition), showing a weak additional band at 1320 nm (D 0 → D 1 transition). We found, that D 3 decays to the lower-lying D 2 within 100 fs, followed by a decay to D 1 with a time constant of 0.9 ps. The D 1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9 ps, while a small population decays on a longer timescale of 40 ps. Both transitions from D 1 were found to be fluorescent.

  2. A model for charge transfer in ultracold Rydberg ground-state atomic collisions

    NASA Astrophysics Data System (ADS)

    Markson, Samuel; Sadeghpour, H. R.

    2016-06-01

    In excited molecules, the interaction between the covalent Rydberg and ion-pair channels forms a unique class of excited states, in which the infinite manifold of vibrational levels are the equivalent of atomic Rydberg states with a heavy electron mass. Production of the ion-pair states usually requires excitation through one or several interacting Rydberg states; these interacting channels lead to loss of flux, diminishing the rate of ion-pair production. Here, we develop an analytical, asymptotic charge-transfer model for the interaction between ultracold Rydberg molecular states, and employ this method to demonstrate the utility of off-resonant field control over the ion-pair formation, with near unity efficiency.

  3. Reexamination of the excited states of {sup 12}C

    SciTech Connect

    Freer, M.; Munoz-Britton, T.; Nicoli, M. P.; Singer, S. M.; Sparks, N.; Boztosun, I.; Bremner, C. A.; Chappell, S. P. G.; Rae, W. D. M.; Cowin, R. L.; Dillon, G. K.; Fulton, B. R.; Greenhalgh, B. J.; Watson, D. L.; Weisser, D. C.

    2007-09-15

    An analysis of the {sup 12}C({sup 12}C,3{alpha}){sup 12}C reaction was made at beam energies between 82 and 106 MeV. Decays to both the ground state and the excited states of {sup 8}Be were isolated, allowing states of different characters to be identified. In particular, evidence was found for a previously observed state at 11.16 MeV. An analysis of the angular distributions of the unnatural parity states at 11.83 and 13.35 MeV, previously assigned J{sup {pi}}=2{sup -}, calls into question the validity of these assignments, suggesting that at least one of the states may correspond to J{sup {pi}}=4{sup -}. Evidence is also found for 1{sup -} and 3{sup -} strengths associated with broad states between 11 and 14 MeV.

  4. High-sensitivity single NV magnetometry by spin-to-charge state mapping

    NASA Astrophysics Data System (ADS)

    Jaskula, Jean-Christophe; Shields, Brendan; Bauch, Erik; Lukin, Mikhail; Walsworth, Ronald; Trifonov, Alexei

    2015-05-01

    Nitrogen-Vacancy (NV) centers in diamond are atom-like quantum system in a solid state matrix whom its structure allows optical readout of the electronic spin. However, the optimal duration of optical readout is limited by a singlet state lifetime making single shot spin readout out of reach. On the other side, the NV center charge state readout can be extremely efficient (up to 99% fidelity) by using excitation at 594 nm. We will present a new method of spin readout utilizing a spin-depending photoionization process to map the electronic spin state of the NV onto the its charge state. Moreover, pre-selection on the charged state allows to minimize data acquisition time. This scheme improves single NV AC magnetometry by a factor of 5 and will benefit other single NV center experiments as well.

  5. Excitation on the Coherent States of Pseudoharmonic Oscillator

    SciTech Connect

    Popov, Dusan; Pop, Nicolina; Sajfert, Vjekoslav

    2009-05-22

    In the last decades, much attention has been paid to the excitation on coherent states, especially for coherent states of the harmonic oscillator ([1] and references therein). But an interesting anharmonic oscillator with many potential applications is also the pseudoharmonic oscillator (PHO). So, in the present paper we have defined the excitation on the Klauder-Perelomov coherent states (E-KP-CSs) for the PHO. These states are obtained by repeatedly operating the raising operator K{sub +} on a usual Klauder-Perelomov coherent state (KP-CS) of the PHO [2]. We have verified that really, the E-KP-CSs fulfill all the properties of the coherent states, as stated by Klauder [3]. We have examined the nonclassical properties of the E-KP-CSs, by using the density matrix formalism and examining the dependence of the Mandel parameter Q{sub z,k;m}(|z|{sup 2}) on the |z|{sup 2} and on the m. It seems that these states can be used in optical communication field and in the physics of quantum information, as signal beams, due to the fact that in these fields the nonclassicality plays an important role.

  6. Hermite polynomial excited squeezed vacuum as quantum optical vortex states

    NASA Astrophysics Data System (ADS)

    Li, Ya-Zhou; Jia, Fang; Zhang, Hao-Liang; Huang, Jie-Hui; Hu, Li-Yun

    2015-11-01

    We introduce theoretically a kind of Hermite polynomial excited squeezed vacuum by extending the wave-packet states with a vortex structure to a general case. Its normalised factor is found to be the Legendre polynomial and the condition converting the general case to a special one is achieved. Then we consider its statistical properties according to the photon number distribution and the Wigner function. As an application, we investigate the performance of the teleportation of the coherent state. It is shown that these parameters in the generalised state can modulate all the above properties including the vortex structure.

  7. Strong-Field Photoionization as Excited-State Tunneling.

    PubMed

    Serebryannikov, E E; Zheltikov, A M

    2016-03-25

    We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling. PMID:27058079

  8. Strong-Field Photoionization as Excited-State Tunneling

    NASA Astrophysics Data System (ADS)

    Serebryannikov, E. E.; Zheltikov, A. M.

    2016-03-01

    We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling.

  9. Controlling autoionization in strontium two-electron-excited states

    NASA Astrophysics Data System (ADS)

    Fields, Robert; Zhang, Xinyue; Dunning, F. Barry; Yoshida, Shuhei; Burgdörfer, Joachim

    2016-05-01

    One challenge in engineering long-lived two-electron-excited states, i.e., so-called planetary atoms, is autoionization. Autoionization, however, can be suppressed if the outermost electron is placed in a high- n, n ~ 300 - 600 , high- L state because such states have only a very small overlap with the inner electron, even when this is also excited to a state of relatively high n and hence of relatively long lifetime. Here the L-dependence of the autoionization rate for high- n strontium Rydberg atoms is examined during excitation of the core ion 5 s 2S1 / 2 - 5 p 2P3 / 2 transition. Measurements in which the angular momentum of the Rydberg electron is controlled using a pulsed electric field show that the autoionization rate decreases rapidly with increasing L and becomes very small for values larger than ~ 20 . The data are analyzed with the aid of calculations undertaken using complex scaling. Research supported by the NSF and Robert A. Welch Foundation.

  10. Evidence for strong mixing between the LC and MLCT excited states in Bis(2-phenylpyridinato-C[sup 2], N')(2, 2'-bipyridine)iridium(III)

    SciTech Connect

    Colombo, M.G.; Hauser, A.; Guedel, H.U. )

    1993-07-07

    The well-resolved absorption, excitation, and luminescence spectra of [Ir(ppy)[sub 2]bpy][sup +] (ppyH = 2-phenylpyridine, bpy = 2, 2'-bipyridine) in different media at cryogenic temperatures are presented. In solutions and glasses at ambient temperature the lowest energy excited state corresponds to an Ir [yields] bpy charge-transfer excitation whereas in the crystalline host lattice [Rh(ppy)[sub 2]bpy]PF[sub 6] the lowest excited state at 21,450 cm[sup [minus]1] is assigned to a [sup 3][pi]-[pi]* excitation localized on the cyclometalating ppy[minus] ligands. The next higher excited Ir [yields] bpy charge-transfer state has shifted to 21,820 cm[sup [minus]1], only 300 cm[sup [minus]1] above the [sup 3]LC excited state. The close proximity of the [sup 3]LC and [sup 3]MLCT excited states and the large spin-orbit coupling constant of Ir[sup 3+] induce a strong mixing of charge-transfer character into the [sup 3]LC lowest excited states, resulting in increased oscillator strengths, reduced lifetimes, short axis polarized transitions, and a large zero-field splitting of 10-15 cm[sup [minus]1].

  11. The role of charge-transfer states in energy transfer and dissipation within natural and artificial bacteriochlorophyll-proteins

    PubMed Central

    Wahadoszamen, Md.; Margalit, Iris; Ara, Anjue Mane; van Grondelle, Rienk; Noy, Dror

    2014-01-01

    Understanding how specific protein environments affect the mechanisms of non-radiative energy dissipation within densely assembled chlorophylls in photosynthetic protein complexes is of great interest to the construction of bioinspired solar energy conversion devices. Mixing of charge-transfer and excitonic states in excitonically interacting chlorophylls was implicated in shortening excited states lifetimes but its relevance to active control of energy dissipation in natural systems is under considerable debate. Here we show that the degree of fluorescence quenching in two similar pairs of excitonically interacting bacteriochlorophyll derivatives is directly associated with increasing charge transfer character in the excited state, and that the protein environment may control non-radiative dissipation by affecting the mixing of charge transfer and excitonic states. The capability of local protein environments to determine the fate of excited states, and thereby to confer different functionalities to excitonically coupled dimers substantiates the dimer as the basic functional element of photosynthetic enzymes. PMID:25342121

  12. Physical Properties, Exciton Analysis, and Visualization of Core-Excited States: An Intermediate State Representation Approach.

    PubMed

    Wenzel, Jan; Dreuw, Andreas

    2016-03-01

    The theoretical simulation of X-ray absorption spectra is in general a challenging task. However, for small and medium-sized organic molecules, the algebraic diagrammatic construction scheme (ADC) for the polarization operator in combination with the core-valence separation approximation (CVS) has proven to yield core-excitation energies and transition moments with almost quantitative accuracy allowing for reliable construction of X-ray absorption spectra. Still, to understand core-excitation processes in detail, it is not sufficient to only compute energies, but also properties like static dipole moments and state densities are important as they provide deeper insight into the nature of core-excited states. Here, we present for the first time an implementation of the intermediate state representation (ISR) approach in combination with the CVS approximation (CVS-ISR), which gives, in combination with the CVS-ADC method, direct access to core-excited state properties. The performance of the CVS-ADC/CVS-ISR approach is demonstrated by means of small- and medium-sized organic molecules. Besides the calculation of core-excited state dipole moments, advanced analyses of core-excited state densities are performed using descriptors like exciton sizes and distances. Plotting electron and hole densities helps to determine the character of the state, and in particular, the investigation of detachment/attachment densities provides information about orbital relaxation effects that are crucial for understanding core excitations. PMID:26845396

  13. Excited states in large molecular systems through polarizable embedding.

    PubMed

    List, Nanna Holmgaard; Olsen, Jógvan Magnus Haugaard; Kongsted, Jacob

    2016-07-27

    In this perspective, we provide an overview of recent work within the polarizable embedding scheme to describe properties of molecules in realistic environments of increasing complexity. After an outline of the theoretical basis for the polarizable embedding model, we discuss the importance of using an accurate embedding potential, and how this may be used to significantly reduce the size of the part of the system treated using quantum mechanics without compromising the accuracy of the final results. Furthermore, we discuss the calculation of local electronic excited states based on response theory. We finally discuss aspects related to two recent extensions of the model (i) effective external field and (ii) polarizable density embedding emphasizing their importance for efficient yet accurate description of excited-state properties in complex environments. PMID:27416749

  14. Photoionization of potassium atoms from the ground and excited states

    SciTech Connect

    Zatsarinny, O.; Tayal, S. S.

    2010-04-15

    The Dirac-based B-spline R-matrix method is used to investigate the photoionization of atomic potassium from the 4s ground and 4p, 5s-7s, 3d-5d excited states. The effect of the core polarization by the outer electron is included through the polarized pseudostates. Besides the dipole core polarization, we also found a noticeable influence of the quadrupole core polarization. We obtained excellent agreement with experiment for cross sections of the 4s photoionization, including accurate description of the near-threshold Cooper-Seaton minimum. We also obtained close agreement with experiment for the 4p photoionization, but there are unexpectedly large discrepancies with available experimental data for photoionization of the 5d and 7s excited states.

  15. Tunable rubidium excited state Voigt atomic optical filter.

    PubMed

    Yin, Longfei; Luo, Bin; Xiong, Junyu; Guo, Hong

    2016-03-21

    A tunable rubidium excited state Voigt atomic optical filter working at optical communication wavelength (1.5 μm) is realized. The filter achieves a peak transmittance of 57.6% with a double-peak structure, in which each one has a bandwidth of 600 MHz. Benefiting from the Voigt type structure, the magnetic field of the filter can be tuned from 0 to 1600 gauss, and a peak transmittance tunability of 1.6 GHz can thus be realized. Different from the excited state Faraday type filter, the pump efficiency in the Voigt filter is affected a lot by the pump polarization. Measured absorption results of the pump laser and transmittances of the signal laser both prove that the vertical linear polarization pumping is the most efficient in the Voigt filter. PMID:27136803

  16. Temperature dependence of the excited state absorption of alexandrite

    SciTech Connect

    Shand, M.L.; Jenssen, H.P.

    1983-03-01

    The temperature dependence from 28 to 290/sup 0/C of the excited-state absorption cross section sigma /SUB 2a/ (E) in the gain wavelength region of alexandrite has been determined from the temperature dependence of the single pass gain (SPG) and of the fluorescence. sigma /SUB 2a/ (E) and the emission cross section increase with temperature at approximately the same rate.

  17. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    NASA Astrophysics Data System (ADS)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  18. Communication: Exciton analysis in time-dependent density functional theory: How functionals shape excited-state characters

    NASA Astrophysics Data System (ADS)

    Mewes, Stefanie A.; Plasser, Felix; Dreuw, Andreas

    2015-11-01

    Excited-state descriptors based on the one-particle transition density matrix referring to the exciton picture have been implemented for time-dependent density functional theory. State characters such as local, extended ππ∗, Rydberg, or charge transfer can be intuitively classified by simple comparison of these descriptors. Strong effects of the choice of the exchange-correlation kernel on the physical nature of excited states can be found and decomposed in detail leading to a new perspective on functional performance and the design of new functionals.

  19. Spin radical enhanced magnetocapacitance effect in intermolecular excited states.

    PubMed

    Zang, Huidong; Wang, Jianguo; Li, Mingxing; He, Lei; Liu, Zitong; Zhang, Deqing; Hu, Bin

    2013-11-14

    This article reports the magnetocapacitance effect (MFC) based on both pristine polymer MEH-PPV and its composite system doped with spin radicals (6R-BDTSCSB). We observed that a photoexcitation leads to a significant positive MFC in the pristine MEH-PPV. Moreover, we found that a low doping of spin radicals in polymer MEH-PPV causes a significant change on the MFC signal: an amplitude increase and a line-shape narrowing under light illumination at room temperature. However, no MFC signal was observed under dark conditions in either the pristine MEH-PPV or the radical-doped MEH-PPV. Furthermore, the magnitude increase and line-shape narrowing caused by the doped spin radicals are very similar to the phenomena induced by increasing the photoexcitation intensity. Our studies suggest that the MFC is essentially originated from the intermolecular excited states, namely, intermolecular electron-hole pairs, generated by a photoexcitation in the MEH-PPV. More importantly, by comparing the effects of spin radicals and electrically polar molecules on the MFC magnitude and line shape, we concluded that the doped spin radicals can have the spin interaction with intermolecular excited states and consequently affect the internal spin-exchange interaction within intermolecular excited states in the development of MFC. Clearly, our experimental results indicate that dispersing spin radicals forms a convenient method to enhance the magnetocapacitance effect in organic semiconducting materials. PMID:24144347

  20. Imaging Excited State Dynamics with 2d Electronic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Engel, Gregory S.

    2012-06-01

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

  1. Note: Excited State Studies of Ozone using State-Specific Multireference Coupled Cluster Methods

    SciTech Connect

    Bhaskaran-Nair, Kiran; Kowalski, Karol

    2012-12-07

    Vertical excitation energies obtained with state-specific multi-reference coupled cluster (MRCC) methods are reported for the ozone molecule. Using state-specific MRCC non-iterative methods with singles, doubles, and non-iterative triples (MRCCSD(T)) we obtain 4.40 eV for the challenging doubly excited 21A1 state when using a reliable model space. This estimate is in good agreement with experiment (4.5 eV). We also compare our MRCC results with the excitation energies obtained with high-order equation-of-motion coupled cluster methods

  2. Parametric excitation of electro-mechanical vibrations of carbon nano tube with distributed surface charge

    NASA Astrophysics Data System (ADS)

    Vijay, A.; Tripathi, V. K.

    2013-11-01

    Electromechanical vibrations of carbon nano tube (CNT), mounted on a metallic base and subjected to a sum of static and radio frequency (RF) electric fields parallel to its length, are investigated. The induced surface charge on the CNT is taken suitably distributed, following Landau and Lifshitz, so that the curved surface remains an equi-potential surface. The natural frequency of transverse vibrations of CNT, ωN depends on the dc electric field, besides the mechanical properties. When the RF frequency ω0 is close to 2ωN, the RF excites the vibrations as three mode parametric instability that saturates via nonlinearity in the restoration force.

  3. Quenching rate constants of excited halogen atoms in quartet states

    NASA Astrophysics Data System (ADS)

    Mizuta, K.; Kuramasu, T.; Ishikawa, Y.; Arai, S.

    1994-04-01

    Excited halogen atoms in quartet spin states F*(2p43s, 4P5/2), Cl*(3p44s, 4P5/2), and Br*(4p45s, 4P5/2) were produced from helium sensitized radiation chemical decomposition of SF6, CF3Cl, CF3Br, and CF2Br2. Quenching rate constants of these excited halogen atoms by simple gas molecules such as O2, N2, H2, CO, CO2, NO, NO2, N2O, CH4, C2H6, and Xe including parent molecules were determined from absorption decay curves at 685.8 nm for F*, 837.5 nm for Cl*, and 827.4 nm for Br*. The optical densities were assumed to be proportional to (number of excited atoms per one cubic centimeter)0.9. The quenching rate constants obtained here were compared to those reported of metastable rare-gas atoms and an excited oxygen atom O*(2p33s, 5S2), and further discussed in terms of several theoretical kinetic models.

  4. An incompressible state of a photo-excited electron gas

    PubMed Central

    Chepelianskii, Alexei D.; Watanabe, Masamitsu; Nasyedkin, Kostyantyn; Kono, Kimitoshi; Konstantinov, Denis

    2015-01-01

    Two-dimensional electrons in a magnetic field can form new states of matter characterized by topological properties and strong electronic correlations as displayed in the integer and fractional quantum Hall states. In these states, the electron liquid displays several spectacular characteristics, which manifest themselves in transport experiments with the quantization of the Hall resistance and a vanishing longitudinal conductivity or in thermodynamic equilibrium when the electron fluid becomes incompressible. Several experiments have reported that dissipationless transport can be achieved even at weak, non-quantizing magnetic fields when the electrons absorb photons at specific energies related to their cyclotron frequency. Here we perform compressibility measurements on electrons on liquid helium demonstrating the formation of an incompressible electronic state under these resonant excitation conditions. This new state provides a striking example of irradiation-induced self-organization in a quantum system. PMID:26007282

  5. Modular Hamiltonian for Excited States in Conformal Field Theory.

    PubMed

    Lashkari, Nima

    2016-07-22

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Z_{n} replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories. PMID:27494465

  6. Modular Hamiltonian for Excited States in Conformal Field Theory

    NASA Astrophysics Data System (ADS)

    Lashkari, Nima

    2016-07-01

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Zn replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.

  7. Solid state cloaking for electrical charge carrier mobility control

    DOEpatents

    Zebarjadi, Mona; Liao, Bolin; Esfarjani, Keivan; Chen, Gang

    2015-07-07

    An electrical mobility-controlled material includes a solid state host material having a controllable Fermi energy level and electrical charge carriers with a charge carrier mobility. At least one Fermi level energy at which a peak in charge carrier mobility is to occur is prespecified for the host material. A plurality of particles are distributed in the host material, with at least one particle disposed with an effective mass and a radius that minimize scattering of the electrical charge carriers for the at least one prespecified Fermi level energy of peak charge carrier mobility. The minimized scattering of electrical charge carriers produces the peak charge carrier mobility only at the at least one prespecified Fermi level energy, set by the particle effective mass and radius, the charge carrier mobility being less than the peak charge carrier mobility at Fermi level energies other than the at least one prespecified Fermi level energy.

  8. Ultrafast twisting dynamics of thioflavin-T: spectroscopy of the twisted intramolecular charge-transfer state.

    PubMed

    Ghosh, Rajib; Palit, Dipak K

    2014-12-15

    Understanding the excited-state properties of thioflavin-T (ThT) has been of immense importance, because of its efficient amyloid-sensing ability related to neurodegenerative disorders. The excited-state dynamics of ThT is studied by using sub-pico- and nanosecond time-resolved transient absorption techniques as well as density functional theory (DFT)/time-dependent DFT calculations. Barrierless twisting around the central C-C bond between two aromatic moieties is the dominant process that contributes to the ultrafast dynamics of the S1 state. The spectroscopic properties of the intramolecular charge-transfer state are characterized for the first time. The energetics of the S0 and S1 states has also been correlated with the experimentally observed spectroscopic parameters and structural dynamics. A longer-lived transient state populated with a very low yield has been characterized as the triplet state. PMID:25251013

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

    SciTech Connect

    Ye, ChuanXiang; Zhao, Yi E-mail: liangwz@xmu.edu.cn; Liang, WanZhen E-mail: liangwz@xmu.edu.cn

    2015-10-21

    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.

  10. Multiphoton resonance in a three-level system with nearly degenerate excited states

    SciTech Connect

    Berent, M.; Parzynski, R.

    2010-08-15

    An analytic study is presented of the efficient multiphoton excitation and strong harmonic generation in three-level systems specified by a pair of nearly degenerate, strongly dipole-coupled excited states. Such systems are physically formed by the three lowest states in, e.g., the hydrogen atom or evenly charged homonuclear diatomic molecular ions under reasonably chosen laser intensities. As a detailed analytic result, we found that the laser pulse of photon energy 2.05eV, duration 0.23ps, and intensity 5x10{sup 13}(W/cm{sup 2}) is able to produce complete inversion of the initial population in the hydrogen atom through the five-photon excitation. At the same photon energy, the pulse of duration 0.41ps and intensity 3.44x10{sup 14}(W/cm{sup 2}) was found to produce the same effect in the molecular ion but through the nine-photon excitation. We show that the accompanying scattering of light has very rich spectrum differing substantially from that of the two-level system.

  11. Observation of interference effects via four-photon excitation of highly excited Rydberg states in thermal cesium vapor

    NASA Astrophysics Data System (ADS)

    Kondo, Jorge M.; Šibalić, Nikola; Guttridge, Alexander; Wade, Christopher G.; De Melo, Natalia R.; Adams, Charles S.; Weatherill, Kevin J.

    2015-12-01

    We report on the observation of electromagnetically induced transparency (EIT) and absorption (EIA) of highly excited Rydberg states in thermal Cs vapor using a four-step excitation scheme. The advantage of this four-step scheme is that the final transition to the Rydberg state has a large dipole moment and one can achieve similar Rabi frequencies to two- or three-step excitation schemes using two orders of magnitude less laser power. This scheme enables new applications such as dephasing free Rydberg excitation. The observed lineshapes are in good agreement with simulations based on multilevel optical Bloch equations.

  12. Enhanced non-Gaussianity from excited initial states

    SciTech Connect

    Holman, R; Tolley, Andrew J E-mail: atolley@perimeterinstitute.ca

    2008-05-15

    We use the techniques of effective field theory in an expanding universe to examine the effect of choosing an excited inflationary initial state built over the Bunch-Davies state on the CMB bi-spectrum. We find that, even for Hadamard states, there are unexpected enhancements in the bi-spectrum for certain configurations in momentum space due to interactions of modes in the early stages of inflation. These enhancements can be parametrically larger than the standard ones and are potentially observable in future data. These initial state effects have a characteristic signature in l-space which distinguishes them from the usual contributions, with the enhancement being most pronounced for configurations corresponding to flattened triangles for which two momenta are collinear.

  13. The mechanism of excited state proton dissociation in microhydrated hydroxylamine clusters.

    PubMed

    Thisuwan, Jittima; Suwannakham, Parichart; Lao-ngam, Charoensak; Sagarik, Kritsana

    2016-02-21

    The dynamics and mechanism of excited-state proton dissociation and transfer in microhydrated hydroxylamine clusters are studied using NH2OH(H2O)n (n = 1-4) as model systems and the DFT/B3LYP/aug-cc-pVDZ and TD-DFT/B3LYP/aug-cc-pVDZ methods as model calculations. This investigation is based on the Förster acidity scheme and emphasizes the photoacid dissociation in the ground (S0) and lowest singlet-excited states (S1) and the interplay between the photo and thermal excitations. The quantum chemical results suggest that the intermediate complexes are formed only in the S1 state in a low local-dielectric environment (e.g., ε = 1) and that upon the S0→ S1 transition, the photon energy excites mostly NH2OH, which leads to a homolytic cleavage of the O-H bond and to dynamically stable charge-separated Rydberg-like H-bond complexes (e.g., NH2O˙-H3O(+)˙). The potential energy surfaces for proton displacement in the smallest Rydberg-like H-bond complex support the intersection of the S0 and S1 states in low local-dielectric environments, whereas in a high local-dielectric environment (e.g., ε = 78), these two states are completely separated. Based on the static results, a photoacid-dissociation mechanism that involves Rydberg-like H-bond complex formation, an H-bond chain extension and fluctuations in the local-dielectric environment is proposed. NVT-BOMD simulations confirm the static results and show that the dynamic behavior of the dissociating proton in the S1 state is not different from that of the protonated H-bond systems in the ground state, which consists of the oscillatory shuttling and structural diffusion motions. These findings allow our theoretical methods, which have been used successfully in protonated H-bond systems in the ground state, to be applied in the study of the photoacid-dissociation processes. The current theoretical study suggests effective steps as well as guidelines for the investigation of the dynamics of the photoacid-dissociation and

  14. Double, Rydberg and Charge Transfer Excitations from Pairing Matrix Fluctuation and Particle-Particle Random Phase Approximation

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    SciTech Connect

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

    2013-12-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  17. Calculations of heavy ion charge state distributions for nonequilibrium conditions

    NASA Technical Reports Server (NTRS)

    Luhn, A.; Hovestadt, D.

    1985-01-01

    Numerical calculations of the charge state distributions of test ions in a hot plasma under nonequilibrium conditions are presented. The mean ionic charges of heavy ions for finite residence times in an instantaneously heated plasma and for a non-Maxwellian electron distribution function are derived. The results are compared with measurements of the charge states of solar energetic particles, and it is found that neither of the two simple cases considered can explain the observations.

  18. Self-scattering for Dark Matter with an excited state

    SciTech Connect

    Schutz, Katelin; Slatyer, Tracy R. E-mail: tslatyer@mit.edu

    2015-01-01

    Self-interacting dark matter scenarios have recently attracted much attention, as a possible means to alleviate the tension between N-body simulations and observations of the dark matter distribution on galactic and sub-galactic scales. The presence of internal structure for the dark matter—for example, a nearly-degenerate state in the spectrum that could decay, or be collisionally excited or de-excited—has also been proposed as a possible means to address these discrepancies. Such internal structure can be a source of interesting signatures in direct and indirect dark matter searches, for example providing a novel explanation for the 3.5 keV line recently observed in galaxies and galaxy clusters. We analyze a simple model of dark matter self-scattering including a nearly-degenerate excited state, and develop an accurate analytic approximation for the elastic and inelastic s-wave cross sections, which is valid outside the perturbative regime provided the particle velocity is sufficiently low (this condition is also required for the s-wave to dominate over higher partial waves). We anticipate our results will be useful in incorporating inelastic self-scattering into N-body simulations, in order to study the quantitative impact of nearly-degenerate states in the dark matter spectrum on galactic structure and dynamics, and in computing the indirect signatures of multi-state dark matter.

  19. 78 FR 61446 - Schedule of Charges Outside the United States

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-03

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF TRANSPORTATION Federal Aviation Administration Schedule of Charges Outside the United States AGENCY: Federal Aviation... for services of FAA Flight Standards Aviation Safety Inspectors outside the United States....

  20. Transient absorption dynamics of sterically congested Cu(I) MLCT excited states.

    PubMed

    Garakyaraghi, Sofia; Danilov, Evgeny O; McCusker, Catherine E; Castellano, Felix N

    2015-04-01

    Subpicosecond through supra-nanosecond transient absorption dynamics of the homoleptic Cu(I) metal-to-ligand charge transfer (MLCT) photosensitizers including the benchmark [Cu(dmp)2](+) (dmp =2,9-dimethyl-1,10-phenanthroline) chromophore, as well as [Cu(dsbp)2](+) (dsbp =2,9-di(sec-butyl)-1,10-phenanthroline and [Cu(dsbtmp)2](+) (dsbtmp =2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline) were investigated in dichloromethane and tetrahydrofuran solutions. Visible and near-IR spectroelectrochemical measurements of the singly reduced [Cu(dsbp)2](+) and [Cu(dsbtmp)2](+) species were determined in tetrahydrofuran, allowing for the identification of redox-specific phenanthroline-based radical anion spectroscopic signatures prevalent in the respective transient absorption experiments. This study utilized four different excitation wavelengths (418, 470, 500, and 530 nm) to elucidate dynamics on ultrafast times scales spanning probe wavelengths ranging from the UV to the near-IR (350 to 1450 nm). With the current time resolution of ∼150 fs, initial excited state decay in all three compounds was found to be independent of excitation wavelength. Not surprisingly, there was little to no observed influence of solvent in the initial stages of excited state decay in any of these molecules including [Cu(dmp)2](+), consistent with results from previous investigators. The combined experimental data revealed two ranges of time constants observed on short time scales in all three MLCT chromophores and both components lengthen as a function of structure in the following manner: [Cu(dsbtmp)2](+) < [Cu(dsbp)2](+) < [Cu(dmp)2](+). The molecule with the most inhibited potential for distortion, [Cu(dsbtmp)2](+), possessed the fastest ultrafast dynamics as well as the longest excited state lifetimes in both solvents. These results are consistent with a small degree of excited state distortion, rapid intersystem crossing, and weak vibronic coupling to the ground state. The

  1. Scaling of collision strengths for highly-excited states of ions of the H- and He-like sequences

    NASA Astrophysics Data System (ADS)

    Fernández-Menchero, L.; Del Zanna, G.; Badnell, N. R.

    2016-08-01

    Emission lines from highly-excited states (n ≥ 5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n ≥ 6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, for example. We investigate the dependence on the relevant parameters: the principal quantum number n or the nuclear charge Z. We also estimate the importance of coupling to highly-excited states and the continuum by comparing the results of different sized calculations. We provide analytic formulae to calculate the electron-impact excitation collision strengths and effective collision strengths to highly-excited states (n ≥ 8) of H- and He-like ions. These extrapolated effective collision strengths can be used to interpret astrophysical and fusion plasma via collisional-radiative modelling. Tables of atomic data for Si xiii and S xv are only 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/viz-bin/qcat?J/A+A/592/A135

  2. Output power of a quantum dot laser: Effects of excited states

    SciTech Connect

    Wu, Yuchang; Jiang, Li Asryan, Levon V.

    2015-11-14

    A theory of operating characteristics of quantum dot (QD) lasers is discussed in the presence of excited states in QDs. We consider three possible situations for lasing: (i) ground-state lasing only; (ii) ground-state lasing at first and then the onset of also excited-state lasing with increasing injection current; (iii) excited-state lasing only. The following characteristics are studied: occupancies of the ground-state and excited-state in QDs, free carrier density in the optical confinement layer, threshold currents for ground- and excited-state lasing, densities of photons emitted via ground- and excited-state stimulated transitions, output power, internal and external differential quantum efficiencies. Under the conditions of ground-state lasing only, the output power saturates with injection current. Under the conditions of both ground- and excited-state lasing, the output power of ground-state lasing remains pinned above the excited-state lasing threshold while the power of excited-state lasing increases. There is a kink in the light-current curve at the excited-state lasing threshold. The case of excited-state lasing only is qualitatively similar to that for single-state QDs—the role of ground-state transitions is simply reduced to increasing the threshold current.

  3. Analytic energy gradient of excited electronic state within TDDFT/MMpol framework: Benchmark tests and parallel implementation

    SciTech Connect

    Zeng, Qiao; Liang, WanZhen

    2015-10-07

    The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well.

  4. Analytic energy gradient of excited electronic state within TDDFT/MMpol framework: Benchmark tests and parallel implementation.

    PubMed

    Zeng, Qiao; Liang, WanZhen

    2015-10-01

    The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well. PMID:26450289

  5. Excited States and Absorption Spectra of UF6: A RASPT2 Theoretical Study with Spin-Orbit Coupling.

    PubMed

    Wei, Fan; Wu, Guo-Shi; Schwarz, W H Eugen; Li, Jun

    2011-10-11

    Uranium hexafluoride (UF6) is an important compound in nuclear chemistry. The theoretical investigation of its excited states is difficult due to the large number of uranium valence orbitals and ligand lone pairs. We report here a detailed relativistic quantum chemical investigation of its excited states up to about 10 eV using restricted active space second-order perturbation theory (RASPT2). Scalar and spin-orbit (SO) relativistic effects are treated by a relativistic small-core pseudopotential. The RASPT2/SO results remain moderately accurate when the electrons in the active space are restricted to single and double excitations. All eight major spectral peaks corresponding to ligand-to-metal charge transfer have been reproduced within an accuracy of about 0.2 eV and are tentatively assigned. We find that BLYP-based hybrid density functional with 35% Hartree-Fock exchange well reproduce the excitation energies of UF6. PMID:26598158

  6. Photoexcited breathers in conjugated polyenes: An excited-state molecular dynamics study

    PubMed Central

    Tretiak, S.; Saxena, A.; Martin, R. L.; Bishop, A. R.

    2003-01-01

    π-conjugated polymers have become an important class of materials for electronic devices. Design of these devices requires understanding such processes as photochemical reactions, spatial dynamics of photoexcitations, and energy and charge transport, which in turn involve complex coupled electron-vibrational dynamics. Here we study nonlinear photoexcitation dynamics in the polyene oligomers by using a quantum-chemical method suitable for the simulation of excited-state molecular dynamics in extended molecular systems with sizes up to hundreds of atoms. The method is based on the adiabatic propagation of the ground-state and transition single-electron density matrices along the trajectory. The simulations reveal formation of a self-localized vibronic excitation (“breather” or multiquanta bound state) with a typical period of 34 fs and allows us to identify specific slow and fast nuclear motions strongly coupled to the electronic degrees of freedom. The effect of chain imperfections and chemical defects on the dynamics is also investigated. A complementary two-dimensional analysis of corresponding transition density matrices provides an efficient way to monitor time-dependent real-space localization of the photoexcitation by identifying the underlying changes in charge densities and bond orders. Possible correlated electronic and vibrational spectroscopic signatures of photoexcited breathers are predicted, and generalizations to energy localization in complex macromolecules are discussed. PMID:12594339

  7. Ultrafast excited-state excitation dynamics in a quasi-two-dimensional light-harvesting antenna based on ruthenium(II) and palladium(II) chromophores.

    PubMed

    Dietzek, Benjamin; Kiefer, Wolfgang; Blumhoff, Jörg; Böttcher, Lars; Rau, Sven; Walther, Dirk; Uhlemann, Ute; Schmitt, Michael; Popp, Jürgen

    2006-06-23

    A detailed study on the excited-state-excitation migration taking place within the tetranuclear complex [{(tbbpy)(2)Ru(tmbi)}(2){Pd(allyl)}(2)](PF(6))(2) (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine and tmbi = 5,6,5',6'-tetramethyl-2,2'-bibenzimidazolate) is presented. The charge transfer is initiated by the photoexcitation into the lowest metal-to-ligand charge-transfer (MLCT) band of one of the peripheral ruthenium(II) chromophores and terminates on the central structurally complex Pd(2) (II)(allyl)(2) subunit. Thus, the system under investigation can be thought of as a functional model for the photosynthesis reaction center in plants. The kinetic steps involved in the overall process are inferred from femtosecond time-resolved transient-grating kinetics recorded at spectral positions within the regions of ground-state bleach and transient absorption. The kinetics features a complex non-exponential time behavior and can be fitted to a bi-exponential rise (tau(1)> or =200 fs, tau(2) approximately 1.5 ps) and a mono- or bi-exponential decay, depending on the experimental situation. The data leads to the formulation of a model for the intramolecular excitation-hopping ascribing intersystem crossing and subsequent cooling as the two fastest observed processes. Following these initial steps, charge transfer from the ruthenium to the central complex Pd(2)(allyl)(2) moiety is observed with a characteristic time constant of 50 ps. A 220-ps component that is observed in the ground-state recovery only is attributed to excitation equilibration between the two identical Pd(allyl) chromophores. PMID:16628758

  8. Excited state dynamics of brightly fluorescent second generation epicocconone analogues.

    PubMed

    Chatterjee, Soumit; Karuso, Peter; Boulangé, Agathe; Franck, Xavier; Datta, Anindya

    2015-05-21

    The natural product epicocconone, owing to its unique fluorescence properties, has been developed into a range of products used in biotechnology, especially proteomics. However, its weak green fluorescence in its native state, while advantageous for proteomics applications, is a disadvantage in other applications that require two-color readouts. Here we report the photophysical characterization of two brightly fluorescent analogues of epicocconone. These analogues, with naphthyl or pyridyl groups replacing the heptatriene chain, resulted in bright fluorescence in both the native state and the long Stokes shifted enamine. Time-resolved fluorescence studies and DFT calculations were carried out to understand the excited state processes involved in fluorescence. Results showed the p-chloro group on the pyridyl is responsible for the high fluorescence of the native fluorophore. The application of one of these compounds for staining electrophoresis gels is exemplified. PMID:25902354

  9. Experimental and theoretical determination of cross sections and rate constants for charge transfer population of some excited Ag+, I+, and Cu+ levels

    NASA Astrophysics Data System (ADS)

    Temelkov, K. A.; Vuchkov, N. K.; Sabotinov, N. V.

    2007-04-01

    Cross-sections and rate constants for thermal energy charge transfer into some Ag+, I+, and Cu+ excited states are theoretically and experimentally obtained for a gas discharge in the He-CuBr, Ne-CuBr, He-AgI, and Ne-AgI mixtures. Besides the pumping process the formation of the inversion population is determined by the radiative transitions, which populate or depopulate the upper and lower laser levels.

  10. Ultrafast excited-state deactivation of flavins bound to dodecin.

    PubMed

    Staudt, Heike; Oesterhelt, Dieter; Grininger, Martin; Wachtveitl, Josef

    2012-05-18

    Dodecins, a group of flavin-binding proteins with a dodecameric quaternary structure, are able to incorporate two flavins within each of their six identical binding pockets building an aromatic tetrade with two tryptophan residues. Dodecin from the archaeal Halobacterium salinarum is a riboflavin storage device. We demonstrate that unwanted side reactions induced by reactive riboflavin species and degradation of riboflavin are avoided by ultrafast depopulation of the reactive excited state of riboflavin. Intriguingly, in this process, the staggered riboflavin dimers do not interact in ground and photoexcited states. Rather, within the tetrade assembly, each riboflavin is kept under the control of the respective adjacent tryptophan, which suggests that the stacked arrangement is a matter of optimizing the flavin load. We further identify an electron transfer in combination with a proton transfer as a central element of the effective excited state depopulation mechanism. Structural and functional comparisons of the archaeal dodecin with bacterial homologs reveal diverging evolution. Bacterial dodecins bind the flavin FMN instead of riboflavin and exhibit a clearly different binding pocket design with inverse incorporations of flavin dimers. The different adoption of flavin changes photochemical properties, making bacterial dodecin a comparably less efficient quencher of flavins. This supports a functional role different for bacterial and archaeal dodecins. PMID:22451648

  11. Radiative Decays of Low-Lying Excited-State Hyperons

    SciTech Connect

    Simon Taylor

    2000-05-01

    The quark wave-functions of the lower-lying excited-state hyperons Lambda(1405), Sigma(1385), and Lambda(1520) are not well understood. For example, the Lambda(1405) may not be a regular three-quark state but a {bar K}N molecule. Several competing models have been proposed, but none have been convincingly eliminated. Measuring radiative decays provides a means of discriminating between the models. The radiative branching of ratios are predicted to be small ({approx}1%), but the radiative widths vary by factors of 2-10 from model to model. The existing experimental data is sparse and inconsistent; moreover, the radiative decay of the Sigma(1385) has never been observed before (except for one event). These lower-lying excited state hypersons were produced in a tagged photon-beam experiment in the CLAS detector at TJNAF in the reaction gamma p {yields} K{sup +} Y* for photon energies from threshold to 2.4 GeV. The radiative branching ration for the Sigma{sup 0}(1385) relative to the Sigma{sup 0}(1385) {yields} Lambda pi{sup 0} channel was measured to be 0.021 {+-} 0.008{sub -0.007}{sup +0.004}, corresponding to a partial width of 640 {+-} 270{sub -220}{sup +130} keV.

  12. Decay width measurements of excited states in 14C

    NASA Astrophysics Data System (ADS)

    Haigh, P.; Ashwood, N.; Bloxham, T.; Curtis, N.; Freer, M.; Price, D.; Ziman, V.; Bohlen, H.; Kokalova, T.; Schulz, C.; von Oertzen, W.; Weldon, C.; Catford, W.; Harlin, C.

    2008-05-01

    Various excited states in 14C, above the α-decay threshold, are believed to possess a geometric arrangement of three α-particles covalently bound by the two delocalised valence neutrons. The 12C(16O, 14O)14C* reaction was studied at a beam energy of 234 MeV, at the ISL facility at the Hahn-Meitner-Institut (HMI), Berlin. The 14O ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the excited 14C recoil break-up fragments were measured in coincidence using a double sided silicon strip detector array comprised of four detectors at backwards angles. A complete kinematic reconstruction of the reaction was performed to reconstruct the 14C* → 10Be + α and 14C* → 13C + n decay channels and the branching ratios of these decays were calculated. Neutron emission was found to be favoured for the 12.96, 14.87, 16.72 and 18.6 MeV states. Evidence for α-decay was found for the 14.87, 18.6 and 21.4 MeV states; which are candidates for the three bodied molecular cluster structure of 14C.

  13. Role of carotenoid excited states and radicals in antioxidant activities

    NASA Astrophysics Data System (ADS)

    Lambert, Chris R.

    1995-05-01

    Carotenoids are linear polyenes that occur in nature and are known to have powerful antioxidant properties. They react efficiently with the excited states of many organic molecules. In the photosynthetic apparatus of plants they quench reactive excited states that may be formed and release the energy as heat. In photodynamic therapy they may be used to ameliorate the associated skin photosensitivity that is a consequence of many photosensitizers. This protection may be either through reaction with the sensitizer triplet state or through quenching of singlet oxygen. Carotenoids also form relatively stable radical species and react efficiently with the hydroxyl radical, superoxide and the solvated electron. In cells they are associated with the lipid core of the cell membrane and are effective against lipid peroxidation. The importance of the thermodynamic properties of these compounds and their organization within biological systems is pivotal to understanding carotenoid antioxidant activity. The present paper reviews some recent work on the energy level of (beta) -carotene, electron transfer involving the one electron reduced species and the resonance Raman spectra of some carotenoids in micellar solution.

  14. Lifetimes of electronic excitations in unoccupied surface states and the image potential states on Pd(110)

    SciTech Connect

    Tsirkin, S. S. Eremeev, S. V.; Chulkov, E. V.

    2012-10-15

    The contribution of inelastic electron-electron scattering to the decay rate of excitations in the surface states and first two image potential states at the Y-bar point on the surface is calculated in the GW approximation, and the quasi-momentum dependence of the corresponding contribution for the surface states is analyzed. The mechanisms of electron scattering in these states are studied, and the temperature dependence of the excitation lifetime is analyzed with allowance for the contribution of the electron-phonon interaction calculated earlier.

  15. Relativistic calculations of excitation and ionization of highly charged ions by electron impact. Final technical report

    SciTech Connect

    Sampson, D.H.

    1992-04-15

    Our rapid relativistic atomic structure program and relativistic distorted-wave programs for excitation and ionization of highly charged ions were further improved. The generalized Briet interaction and other QED corrections were added to the atomic structure program, and the speed of the distorted-wave excitation program was increased by over an order of magnitude over what it was when our initial large-scale relativistic calculations of excitation of Ne-like ions were made. The improved programs were then used to calculate collision strengths for 330 transitions in F-like ions with 22 {le} Z {le} 92 and 248 transitions in Ni-like ions with 60 {le} Z {le} 92. We expanded the relativistic collision program to include an option to use atomic structure data by the well-known multi-configuration Dirac-Fock (MCDF) program of Grant and A coworkers. This was used in calculating collision strengths for the 45 {Delta}n = 0 transitions with n=2 in Be-like ions with 8 {le} Z {le} 92. This relativistic collision strength program was also extended to include an option to include the generalized Breis interaction in the scattering matrix elements and the importance of this for He-like, He-like and Li-like ions with Z = 26, 54 and 92 was studied. The factorization method was applied to ionization. Regardless of the complexity of the ion the ionization cross sections could be written as a sum of the products of a readily calculated coefficient that depends only on ion properties and a hydrogen-like cross section. Work was also done on excitation and ionization by directive and, in some cases spin-polarized electrons, which is of interest for some EBIT experiments and the study of solar flares. We also used our extensive collision strength results to test the

  16. Relativistic calculations of excitation and ionization of highly charged ions by electron impact

    SciTech Connect

    Sampson, D.H.

    1992-04-15

    Our rapid relativistic atomic structure program and relativistic distorted-wave programs for excitation and ionization of highly charged ions were further improved. The generalized Briet interaction and other QED corrections were added to the atomic structure program, and the speed of the distorted-wave excitation program was increased by over an order of magnitude over what it was when our initial large-scale relativistic calculations of excitation of Ne-like ions were made. The improved programs were then used to calculate collision strengths for 330 transitions in F-like ions with 22 [le] Z [le] 92 and 248 transitions in Ni-like ions with 60 [le] Z [le] 92. We expanded the relativistic collision program to include an option to use atomic structure data by the well-known multi-configuration Dirac-Fock (MCDF) program of Grant and A coworkers. This was used in calculating collision strengths for the 45 [Delta]n = 0 transitions with n=2 in Be-like ions with 8 [le] Z [le] 92. This relativistic collision strength program was also extended to include an option to include the generalized Breis interaction in the scattering matrix elements and the importance of this for He-like, He-like and Li-like ions with Z = 26, 54 and 92 was studied. The factorization method was applied to ionization. Regardless of the complexity of the ion the ionization cross sections could be written as a sum of the products of a readily calculated coefficient that depends only on ion properties and a hydrogen-like cross section. Work was also done on excitation and ionization by directive and, in some cases spin-polarized electrons, which is of interest for some EBIT experiments and the study of solar flares. We also used our extensive collision strength results to test the

  17. Evidence and implications of direct charge excitation as the dominant mechanism in plasmon-mediated photocatalysis

    DOE PAGESBeta

    Boerigter, Calvin; Campana, Robert; Morabito, Matthew; Linic, Suljo

    2016-01-28

    Plasmonic metal nanoparticles enhance chemical reactions on their surface when illuminated with light of particular frequencies. It has been shown that these processes are driven by excitation of localized surface plasmon resonance (LSPR). The interaction of LSPR with adsorbate orbitals can lead to the injection of energized charge carriers into the adsorbate, which can result in chemical transformations. The mechanism of the charge injection process (and role of LSPR) is not well understood. Here we shed light on the specifics of this mechanism by coupling optical characterization methods, mainly wavelength-dependent Stokes and anti-Stokes SERS, with kinetic analysis of photocatalytic reactionsmore » in an Ag nanocube–methylene blue plasmonic system. We propose that localized LSPR-induced electric fields result in a direct charge transfer within the molecule–adsorbate system. Lastly, these observations provide a foundation for the development of plasmonic catalysts that can selectively activate targeted chemical bonds, since the mechanism allows for tuning plasmonic nanomaterials in such a way that illumination can selectively enhance desired chemical pathways.« less

  18. Evidence and implications of direct charge excitation as the dominant mechanism in plasmon-mediated photocatalysis

    PubMed Central

    Boerigter, Calvin; Campana, Robert; Morabito, Matthew; Linic, Suljo

    2016-01-01

    Plasmonic metal nanoparticles enhance chemical reactions on their surface when illuminated with light of particular frequencies. It has been shown that these processes are driven by excitation of localized surface plasmon resonance (LSPR). The interaction of LSPR with adsorbate orbitals can lead to the injection of energized charge carriers into the adsorbate, which can result in chemical transformations. The mechanism of the charge injection process (and role of LSPR) is not well understood. Here we shed light on the specifics of this mechanism by coupling optical characterization methods, mainly wavelength-dependent Stokes and anti-Stokes SERS, with kinetic analysis of photocatalytic reactions in an Ag nanocube–methylene blue plasmonic system. We propose that localized LSPR-induced electric fields result in a direct charge transfer within the molecule–adsorbate system. These observations provide a foundation for the development of plasmonic catalysts that can selectively activate targeted chemical bonds, since the mechanism allows for tuning plasmonic nanomaterials in such a way that illumination can selectively enhance desired chemical pathways. PMID:26817619

  19. Excited states of M(II,d sup 6 )-4 prime -Phenylterpyridine complexes: Electron localization

    SciTech Connect

    Amouyal, E.; Mouallem-Bahout, M. ); Calzaferri, G. )

    1991-10-03

    The authors spectroscopic and photophysical data of para-substituted phenylterpyridine (ptpy) Ru(II) complexes and molecular orbital studies of the Fe(II), Ru(II), and Os(II) compounds (M(R-ptpy){sub 2}){sup 2+}, R=H, CH{sub 3}, OH, OCH{sub 3}, and Cl. The visible charge-transfer absorption of the (Ru(R-ptpy){sub 2}){sup 2+} is almost twice as intense as observed for the corresponding 2,2{prime}-bipyridine (bpy) complex (Ru(bpy){sub 3}){sup 2+}, and it is red shifted by about 50 nm. The luminescence in solution and in membranes (Nafion, cellophane) is very weak at room temperature, and the luminescence decay time is on the order of a few nanoseconds. In a glass at 77K, however, the luminescence quantum yield is 0.4 and the decay time 13 {mu}s. Excited-state absorption spectra measured at room temperature by laser flash spectroscopy support the interpretation that the first excited state is of the MLCT type. The similarity of the excited-state absorptions to those of the ligand radical anions strengthens the idea that the excited electron is localized on a single ligand. The low luminescence quantum yield at room temperature is though to be due to low-energy intramolecular vibrations of the nonrigid complex and not to the coupling with d states. Lowering the temperature results in freezing these intramolecular movements and hence in significantly increasing the luminescence quantum yield. The molecular orbital studies indicate that it is reasonable to describe the MLCT state as ((L)Ru{sup III}(L{sm bullet}{sup {minus}})){sup 2+} because the perpendicular conformation of the two ligands causes all {pi} orbitals to be accidentally 2-fold degenerate and therefore a small asymmetric distortion is sufficient to favor the localized situation.

  20. Excited-state dynamics in rigid media: evidence for long-range energy transfer.

    PubMed

    Ito, Akitaka; Stewart, David J; Knight, Troy E; Fang, Zhen; Brennaman, M Kyle; Meyer, Thomas J

    2013-03-28

    In semirigid PEG-DMA550 films with the added anthracene derivatives PEG-An and Acr-An, energy transfer quenching of the metal-to-ligand charge transfer excited state Ru(bpy)3(2+)* to give -(3)An occurs by both rapid, static, and slow, diffusional quenching processes. The appearance of -(3)An was verified by transient absorption measurements. The kinetics of the two quenching processes have been analyzed by a Stern-Volmer kinetic analysis. The data for static quenching are consistent with energy transfer quenching with a distance dependence consistent with Dexter (exchange) energy transfer. On the basis of this analysis Bohr radii were found to be 26 and 11 Å for PEG-An and Acr-An, respectively. Evidence for triplet-triplet annihilation between triplet anthracene excited states in the films was obtained from the concentration dependences of excited-state decay. These results provide evidence for long-range energy migration between derivatized anthracenes in rigid, cross-linked PEG-DMA550 films. PMID:23458318

  1. Charge state hysteresis in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Yang, C. H.; Rossi, A.; Lai, N. S.; Leon, R.; Lim, W. H.; Dzurak, A. S.

    2014-11-01

    Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which accounts for the observed hysteretic behaviour by extending the established description for transport in double dots coupled to two reservoirs. We demonstrate that this type of device operates like a single-electron memory latch.

  2. Charge state hysteresis in semiconductor quantum dots

    SciTech Connect

    Yang, C. H.; Rossi, A. Lai, N. S.; Leon, R.; Lim, W. H.; Dzurak, A. S.

    2014-11-03

    Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which accounts for the observed hysteretic behaviour by extending the established description for transport in double dots coupled to two reservoirs. We demonstrate that this type of device operates like a single-electron memory latch.

  3. L X-ray emission from fast highly charged Cu ions in collisions with gaseous targets: Saturation effect in excitation and transfer

    NASA Astrophysics Data System (ADS)

    Kumar, Ajay; Misra, D.; Kadhane, U.; Kelkar, A. H.; Dhal, B. B.; Tribedi, L. C.

    2006-11-01

    We have measured L X-ray production cross sections for highly charged 156 MeV Be-like Cu ions in collisions with gaseous targets of H 2, Ne, Ar, Kr and Xe. In the present collision systems, measured projectile L X-ray intensity is contributed by the excitation as well as electron transfer processes. The projectile L X-ray production cross sections are found to increase initially and then saturate with increasing target atomic number. The charge state dependence of projectile L X-ray production cross sections have been measured with Kr target.

  4. The charge excitation in the Raman process as correlated from a classical theory for Raman optical activity: the case study of (+)-(R)-methyloxirane.

    PubMed

    Fang, Yan; Wu, Guozhen; Wang, Peijie

    2012-03-01

    We developed a classical algorithm to calculate the spectral signs in the Raman optical activity (ROA) spectrum. In this algorithm, the charge re-distributions among the bonds, which are associated to the bond polarizabilities, are included. For (+)-(R)-methyloxirane, we found that if these bond polarizabilities are attributed to the atoms and are properly scaled in order to be combined with the Mulliken charges on the atoms in the ground state, then the experimental ROA spectral signs can be well reproduced. Furthermore, in this process, we are able to determine that around 20% of the electrons in the molecule are excited in the Raman process. PMID:22226895

  5. Ground State and Excited State H-Atom Temperatures in a Microwave Plasma Diamond Deposition Reactor

    NASA Astrophysics Data System (ADS)

    Gicquel, A.; Chenevier, M.; Breton, Y.; Petiau, M.; Booth, J. P.; Hassouni, K.

    1996-09-01

    Ground electronic state and excited state H-atom temperatures are measured in a microwave plasma diamond deposition reactor as a function of a low percentage of methane introduced in the feed gas and the averaged input microwave power density. Ground state H-atom temperatures (T_H) and temperature of the H-atom in the n=3 excited state (T_{Hα}) are obtained from the measurements respectively of the excitation profile by Two-photon Allowed transition Laser Induced Fluorescence (TALIF) and the Hα line broadening by Optical Emission Spectroscopy (OES). They are compared to gas temperatures calculated with a 1D diffusive non equilibrium H{2} plasma flow model and to ground electronic state rotational temperatures of molecular hydrogen measured previously by Coherent Anti-Stokes Raman Spectroscopy.

  6. Charge transfer excitations in water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C60

    NASA Astrophysics Data System (ADS)

    Zope, Rajendra; Basurto, Luis; Olguin, Marco; Baruah, Tunna

    2013-03-01

    We present a study of charge transfer (CT) excited states for a recently synthesized group of water-soluble sulfonated zinc-phthalocyanine (ZnPcS) donor molecules coupled to C60. The ZnPcS donors (ZnPcS2, ZnPcS3, and ZnPcS4) are promising materials for achieving solar cell device production with the photoactive area prepared from aqueous solution. Experimentally, decreasing the number of sulfonate substituent groups for ZnPc increased the photocurrent and lowered the open circuit voltage VOC. Measurements show that the VOC is largest for ZnPc-S4/C60 and lowest for ZnPc-S3/C60. The degree of sulfonation and the measured device VOC does not result in the expected pattern of values based on donor-acceptor HOMO/LUMO energy differences. Variations in film morphology may account for the unexpected pattern of VOC values. Our charge transfer excited state calculations show that the lowest CT excitation energy among the group of ZnPcS/C60 donor-acceptor pairs corresponds to the disulfonated ZnPc/C60 system. The largest CT excited state energies belong to the tetrasulfonated ZnPc/C60 complex. We also examine the effect of geometrical orientation on the CT energies for the ZnPcS donor-acceptor pairs.

  7. Resonant Auger spectroscopy study of charge transfer phenomena in N 1s core-excited acetonitrile adsorbates on Si(0 0 1)-2 × 1

    NASA Astrophysics Data System (ADS)

    Gallet, J.-J.; Bournel, F.; Carniato, S.; Dufour, G.; Rochet, F.; Rangan, S.; Sirotti, F.

    2007-01-01

    Acetonitrile (CH 3CN) adsorbs on Si(0 0 1)-2 × 1 at room temperature under two forms, a cycloaddition-like adduct (Si-C dbnd N-Si) and a pendent cyano (Si-CH 2-C tbnd N) resulting from the decomposition of the molecule. Resonant Auger spectroscopy has been used to study the excited-state-dependent electron transfer from the N 1s core-excited molecular adsorbate to the silicon substrate, using the core-hole lifetime (˜6 fs) as an internal clock. It is shown that the π C dbnd N ∗ NEXAFS state lies within the silicon bandgap because of a core-excitonic effect. Therefore no charge transfer of the excited electron to the substrate is observed. On the other hand the π C tbnd N ∗ NEXAFS state is placed within the silicon conduction band. Excitation to this orbital leads to valence/Auger spectra in which both resonant and normal Auger contributions are observed. Therefore there is evidence for a charge transfer from the pendent C tbnd N to the silicon surface, on a timescale estimated to tens of femtoseconds.

  8. Coulometer battery state-of-charge indicator

    NASA Technical Reports Server (NTRS)

    Birchenough, A. G.; Secunde, R.

    1970-01-01

    Mercury-column electrochemical coulometer is a linear ampere-hour integrating device consisting of a sealed glass tube containing two columns of mercury separated by a gap containing an electrolyte. The drive circuit uses operational amplifier techniques to match nonlinear charge-discharge characteristics of an alkaline battery.

  9. Electronic excited states of guanine-cytosine hairpins and duplexes studied by fluorescence spectroscopy.

    PubMed

    Brazard, Johanna; Thazhathveetil, Arun K; Vayá, Ignacio; Lewis, Frederick D; Gustavsson, Thomas; Markovitsi, Dimitra

    2013-08-01

    Guanine-cytosine hairpins, containing a hexaethylene glycol bridge, are studied by steady-state fluorescence spectroscopy and time-correlated single photon counting; their properties are compared to those of duplexes with the same sequence. It is shown that, both in hairpins and in duplexes, base pairing induces quenching of the ππ* fluorescence, the quantum yield decreasing by at least two orders of magnitude. When the size of the systems increases from two to ten base pairs, a fluorescent component decaying on the nanosecond time-scale appears at energy higher than that stemming from the bright states of non-interacting mono-nucleotides (ca. 330 nm). For ten base pairs, this new fluorescence forms a well-defined band peaking at 305 nm. Its intensity is about 20% higher for the hairpin compared to the duplex. Its position (red-shifted by 1600 cm(-1)) and width (broader by 1800 cm(-1) FWHM) differ from those observed for large duplexes containing 1000 base pairs, suggesting the involvement of electronic coupling. Fluorescence anisotropy reveals that the excited states responsible for high energy emission are not populated directly upon photon absorption but are reached during a relaxation process. They are assigned to charge transfer states. According to the emerging picture, the amplitude of conformational motions determines whether instantaneous deactivation to the ground state or emission from charge transfer states will take place, while ππ* fluorescence is associated to imperfect base-pairing. PMID:23736116

  10. Spin Charge Separation in the Quantum Spin Hall State

    SciTech Connect

    Qi, Xiao-Liang; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    The quantum spin Hall state is a topologically non-trivial insulator state protected by the time reversal symmetry. We show that such a state always leads to spin-charge separation in the presence of a {pi} flux. Our result is generally valid for any interacting system. We present a proposal to experimentally observe the phenomenon of spin-charge separation in the recently discovered quantum spin Hall system.

  11. Surface hopping investigation of benzophenone excited state dynamics.

    PubMed

    Favero, Lucilla; Granucci, Giovanni; Persico, Maurizio

    2016-04-21

    We present a simulation of the photodynamics of benzophenone for the first 20 ps after n →π* excitation, performed by trajectory surface hopping calculations with on-the-fly semiempirical determination of potential energy surfaces and electronic wavefunctions. Both the dynamic and spin-orbit couplings are taken into account, and time-resolved fluorescence emission is also simulated. The computed decay time of the S1 state is in agreement with experimental observations. The direct S1→ T1 intersystem crossing (ISC) accounts for about 2/3 of the S1 decay rate. The remaining 1/3 goes through T2 or higher triplets. The nonadiabatic transitions within the triplet manifold are much faster than ISC and keep the population of T1 at about 3/4 of the total triplet population, and that of the other states (mainly T2) at 1/4. Two internal coordinates are vibrationally active immediately after n →π* excitation: one is the C[double bond, length as m-dash]O stretching and the other one is a combination of the conrotatory torsion of phenyl rings and of bending involving the carbonyl C atom. The period of the torsion-bending mode coincides with oscillations in the time-resolved photoelectron spectra of Spighi et al. and substantially confirms their assignment. PMID:27031566

  12. Excited state dynamics of thulium ions in yttrium aluminum garnets

    NASA Technical Reports Server (NTRS)

    Armagan, G.; Buoncristiani, A. M.; Dibartolo, B.

    1991-01-01

    The processes that take place in the excited states of a trivalent Thulium (Tm) ion in an Yttrium Aluminum Garnet (YAG) crystal, being relevant to the use of this system for laser applications, have been the object of several studies. We have reexamined this system focusing our attention on the dynamics of Tm following its excitation in the H-3(sub 4) level. Under these conditions the system relaxes through a cross-relaxation process. H-3(sub 4) yields F-3(sub 4), H-3(sub 6) yields F-3(sub 4), whose rate depends upon both the concentration of the Tm ion and the temperature of the crystal. The excitation spectrum obtained by monitoring the 1.8 micron emission of Tm (due to the F-3(sub 4) yields H-3(sub 6) transition) indicates an increase in the contribution to this emission from the H-3(sub 4) level relative to the H-3(sub 5) level as the Tm concentration increases; this shows the increased role played by the H-3(sub 4) level in pumping the infrared emission. Correspondingly, the duration of the luminescence originating in the H-3(sub 4) level is shortened as the concentration of Tm increases. The concentration quenching of this lifetime can be fit to a model which assumes that the cross-relaxation is due to a dipole-dipole interaction; from this fit, the intrinsic Tm lifetime in the absence of cross relaxation can be derived. We have used this lifetime to calculate the rate of the cross-relaxation process. We have evaluated this rate as a function of the temperature and found it to be fastest at 77 K. We have also calculated the microscopic interaction parameters for the cross-relaxation process by using two independent experimental features: (1) the time evolution of the emission from the H-3(sub 4) level; and (2) the spectral overlap between the H-3(sub 4) yields F-3(sub 4) emission and the H-3(sub 6) yields F-3(sub 4) absorption. We have also considered the migration of excitation among the Tm ions in the F-3(sub 4) level and calculated the relevant

  13. Approximating ground and excited state energies on a quantum computer

    NASA Astrophysics Data System (ADS)

    Hadfield, Stuart; Papageorgiou, Anargyros

    2015-04-01

    Approximating ground and a fixed number of excited state energies, or equivalently low-order Hamiltonian eigenvalues, is an important but computationally hard problem. Typically, the cost of classical deterministic algorithms grows exponentially with the number of degrees of freedom. Under general conditions, and using a perturbation approach, we provide a quantum algorithm that produces estimates of a constant number of different low-order eigenvalues. The algorithm relies on a set of trial eigenvectors, whose construction depends on the particular Hamiltonian properties. We illustrate our results by considering a special case of the time-independent Schrödinger equation with degrees of freedom. Our algorithm computes estimates of a constant number of different low-order eigenvalues with error and success probability at least , with cost polynomial in and . This extends our earlier results on algorithms for estimating the ground state energy. The technique we present is sufficiently general to apply to problems beyond the application studied in this paper.

  14. Excitation gap of fractal quantum hall states in graphene.

    PubMed

    Luo, Wenchen; Chakraborty, Tapash

    2016-01-13

    In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter's butterfly. In this work, we develop a Hartree-Fock theory to deal with the electron-electron interaction in the Hofstadter's butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation. PMID:26657089

  15. Excitation gap of fractal quantum hall states in graphene

    NASA Astrophysics Data System (ADS)

    Luo, Wenchen; Chakraborty, Tapash

    2016-01-01

    In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter’s butterfly. In this work, we develop a Hartree-Fock theory to deal with the electron-electron interaction in the Hofstadter’s butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation.

  16. Introducing QMC/MMpol: Quantum Monte Carlo in Polarizable Force Fields for Excited States.

    PubMed

    Guareschi, Riccardo; Zulfikri, Habiburrahman; Daday, Csaba; Floris, Franca Maria; Amovilli, Claudio; Mennucci, Benedetta; Filippi, Claudia

    2016-04-12

    We present for the first time a quantum mechanics/molecular mechanics scheme which combines quantum Monte Carlo with the reaction field of classical polarizable dipoles (QMC/MMpol). In our approach, the optimal dipoles are self-consistently generated at the variational Monte Carlo level and then used to include environmental effects in diffusion Monte Carlo. We investigate the performance of this hybrid model in describing the vertical excitation energies of prototypical small molecules solvated in water, namely, methylenecyclopropene and s-trans acrolein. Two polarization regimes are explored where either the dipoles are optimized with respect to the ground-state solute density (polGS) or different sets of dipoles are separately brought to equilibrium with the states involved in the electronic transition (polSS). By comparing with reference supermolecular calculations where both solute and solvent are treated quantum mechanically, we find that the inclusion of the response of the environment to the excitation of the solute leads to superior results than the use of a frozen environment (point charges or polGS), in particular, when the solute-solvent coupling is dominated by electrostatic effects which are well recovered in the polSS condition. QMC/MMpol represents therefore a robust scheme to treat important environmental effects beyond static point charges, combining the accuracy of QMC with the simplicity of a classical approach. PMID:26959751

  17. Electron-impact excitation of neon: a pseudo-state convergence study

    NASA Astrophysics Data System (ADS)

    Ballance, C. P.; Griffin, D. C.

    2004-07-01

    A number of convergent close-coupling and R-matrix with pseudo-state (RMPS) calculations for H-like, He-like, Li-like and Be-like ions have demonstrated that coupling to the target continuum can have large effects on the electron-impact excitation cross sections of neutral and low-charge species. However, no one has yet attempted such advanced calculations on a system as complex as neutral neon. We report on a series of RMPS calculations of electron-impact excitation of Ne using recently developed parallel Breit-Pauli R-matrix programs. Our largest calculation included 235 spectroscopic and pseudo-state levels in the close-coupling expansion of the target. Although the results clearly reveal the importance of coupling to the target continuum in this atom, the pseudo-state expansion is not yet sufficiently complete to provide reliable cross sections for energies above the ionization limit. However, this is the largest intermediate-coupling calculation that can be performed with present computer resources. Thus, we have also carried out a series of RMPS calculations in LS coupling with different pseudo-state expansions. Comparisons of these results have allowed us to determine the approximate size of the pseudo-state expansion required to achieve convergence in future intermediate-coupling calculations for neon.

  18. Polarization spectroscopy of x-ray transitions from beam-excited highly charged ions

    SciTech Connect

    Beiersdorfer, P.; Lopez-Urrutia, J.C.; Decaux, V.; Widmann, K.; Neill, P.

    1997-01-01

    Polarization spectroscopy of x-ray lines represents a diagnostic tool to ascertain the presence of electron beams in high-temperature plasmas. Making use of the Livermore electron beam ion trap, which optimizes the linear x-ray line polarization by exciting highly charged ions with a monoenergetic electron beam, we have begun to develop polarization diagnostics and test theoretical models. Our measurement relies on the sensitivity of crystal spectrometers to the linear polarization of x-ray lines which depends on the value of the Bragg angle. We employed two spectrometers with differing analyzing crystals and simultaneously recorded the K-shell emission from heliumlike Fe{sup 24+} and lithiumlike Fe{sup 23+} ions at two different Bragg angles. A clear difference in the relative intensities of the dominant transitions is observed, which is attributed to the amount of linear polarization of the individual lines. {copyright} {ital 1997 American Institute of Physics.}

  19. Production of vibrationally excited H(2)O from charge exchange of H(3)O(+) with cesium.

    PubMed

    Mann, Jennifer E; Xie, Zhen; Savee, John D; Bowman, Joel M; Continetti, Robert E

    2009-01-28

    The center-of-mass kinetic energy release for the dissociation of H(3)O following charge exchange of H(3)O(+) with cesium has been studied experimentally and modeled using quasiclassical trajectory calculations based on an ab initio potential energy surface for H(3)O(+) and "direct dynamics" for H(3)O. Branching fractions for the H(2)O+H and OH+H(2) dissociation channels have been measured and compared to the calculations. The dominant channel is found to be H(2)O+H and the experimental kinetic energy release spectrum reveals that H(2)O is formed with a vibrational inversion in stretching vibrations, coupled with low bending and rotational excitation. PMID:19191369

  20. Mixed Exciton–Charge-Transfer States in Photosystem II: Stark Spectroscopy on Site-Directed Mutants

    PubMed Central

    Romero, Elisabet; Diner, Bruce A.; Nixon, Peter J.; Coleman, Wiliam J.; Dekker, Jan P.; van Grondelle, Rienk

    2012-01-01

    We investigated the electronic structure of the photosystem II reaction center (PSII RC) in relation to the light-induced charge separation process using Stark spectroscopy on a series of site-directed PSII RC mutants from the cyanobacterium Synechocystis sp. PCC 6803. The site-directed mutations modify the protein environment of the cofactors involved in charge separation (PD1, PD2, ChlD1, and PheD1). The results demonstrate that at least two different exciton states are mixed with charge-transfer (CT) states, yielding exciton states with CT character: (PD2δ+PD1δ−ChlD1)∗673nm and (ChlD1δ+PheD1δ−)∗681nm (where the subscript indicates the wavelength of the electronic transition). Moreover, the CT state PD2+PD1− acquires excited-state character due to its mixing with an exciton state, producing (PD2+PD1−)δ∗684nm. We conclude that the states that initiate charge separation are mixed exciton-CT states, and that the degree of mixing between exciton and CT states determines the efficiency of charge separation. In addition, the results reveal that the pigment-protein interactions fine-tune the energy of the exciton and CT states, and hence the mixing between these states. This mixing ultimately controls the selection and efficiency of a specific charge separation pathway, and highlights the capacity of the protein environment to control the functionality of the PSII RC complex. PMID:22853895

  1. Neutron decay widths of excited states of {sup 11}Be

    SciTech Connect

    Haigh, P. J.; Freer, M.; Ashwood, N. I.; Bloxham, T.; Curtis, N.; McEwan, P.; Bohlen, H. G.; Dorsch, T.; Kokalova, Tz.; Schulz, Ch.; Wheldon, C.

    2009-01-15

    The two-neutron transfer reaction {sup 9}Be({sup 16}O, {sup 14}O){sup 11}Be[{sup 10}Be +n] has been used to measure the branching ratios for the neutron decay of excited states of {sup 11}Be. The {sup 14}O ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the {sup 10}Be fragments of the decaying {sup 11}Be* recoil were measured in coincidence with the {sup 14}O ejectile using a double-sided silicon strip detector array at backward angles. This enabled a kinematic reconstruction of the reaction to be performed. Theoretical decay branch ratios were calculated using barrier penetrability factors and were compared to the measured ratios to provide information on the relative reduced widths of the states. The decay widths have been used to link states in {sup 11}Be with a common structure and structurally to states in the daughter nucleus {sup 10}Be. The 3/2{sup -} 8.82-MeV state was identified as a candidate for a molecular band head.

  2. Molecular dynamics of excited state intramolecular proton transfer: 3-hydroxyflavone in solution

    SciTech Connect

    Bellucci, Michael A.; Coker, David F.

    2012-05-21

    The ultrafast enol-keto photoisomerization in the lowest singlet excited state of 3-hydroxyflavone is investigated using classical molecular dynamics in conjunction with empirical valence bond (EVB) potentials for the description of intramolecular interactions, and a molecular mechanics and variable partial charge model, dependent on transferring proton position, for the description of solute-solvent interactions. A parallel multi-level genetic program was used to accurately fit the EVB potential energy surfaces to high level ab initio data. We have studied the excited state intramolecular proton transfer (ESIPT) reaction in three different solvent environments: methylcyclohexane, acetonitrile, and methanol. The effects of the environment on the proton transfer time and the underlying mechanisms responsible for the varied time scales of the ESIPT reaction rates are analyzed. We find that simulations with our EVB potential energy surfaces accurately reproduce experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all three solvents. Furthermore, we find that the ultrafast ESIPT process results from a combination of ballistic transfer, and intramolecular vibrational redistribution, which leads to the excitation of a set of low frequency promoting vibrational modes. From this set of promoting modes, we find that an O-O in plane bend and a C-H out of plane bend are present in all three solvents, indicating that they are fundamental to the ultrafast proton transfer. Analysis of the slow proton transfer trajectories reveals a solvent mediated proton transfer mechanism, which is diffusion limited.

  3. Excited state properties of the astaxanthin radical cation: A quantum chemical study

    NASA Astrophysics Data System (ADS)

    Dreuw, Andreas; Starcke, Jan Hendrik; Wachtveitl, Josef

    2010-07-01

    Using time-dependent density functional theory, the excited electronic states of the astaxanthin radical cation (AXT rad + ) are investigated. While the optically allowed excited D 1 and D 3 states are typical ππ∗ excited states, the D 2 and D 4 states are nπ∗ states. Special emphasis is put onto the influence of the carbonyl groups onto the excited states. For this objective, the excited states of four hypothetical carotenoids and zeaxanthin have been computed. Addition of a carbonyl group to a conjugated carbon double bond system does essentially not change the vertical excitation energies of the optically allowed ππ∗ states due to two counter-acting effects: the excitation energy should increase due to the -M-effect of the carbonyl group and at the same time decrease owing to the elongation of the conjugated double bond system by the carbonyl group itself.

  4. Investigating the role of vibrational excitation in simulating charged-particle tracks in liquid pyrimidine

    NASA Astrophysics Data System (ADS)

    Brunger, Michael J.; Ratnavelu, Kuru; Buckman, Stephen J.; Jones, Darryl B.; Muñoz, Antonio; Blanco, Francisco; García, Gustavo

    2016-03-01

    We report on our results of a study into the sensitivity of charged-particle (electron) track simulations in liquid pyrimidine, to the vibrational cross sections and vibrational energy loss distribution function employed in those simulations. We achieve this by repeating the earlier investigation of Fuss et al. [J. Appl. Phys. 117, 214701 (2015)], but now incorporating more accurate data for the vibrational integral cross sections and the energy loss distribution function that have recently become available. We find that while changes in absorbed dose or particle range are quite minor, due to the energy transferred via vibrational excitations being low in comparison to that for other processes such as ionisation, at the very end of the tracks, where non-ionizing interactions dominate, the significantly large numbers of vibrational excitation processes increases the electrons' ability to induce other effects (e.g. sample heating, bond breaking and radical formation) that might cause damage. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.

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

    NASA Astrophysics Data System (ADS)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoıˆt

    2008-06-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  6. Periodic ground state for the charged massive Schwinger model

    SciTech Connect

    Nagy, S.; Sailer, K.; Polonyi, J.

    2004-11-15

    It is shown that the charged massive Schwinger model supports a periodic vacuum structure for arbitrary charge density, similar to the common crystalline layout known in solid state physics. The dynamical origin of the inhomogeneity is identified in the framework of the bosonized model and in terms of the original fermionic variables.

  7. Charging state of atmospheric nanoparticles during the nucleation burst events

    NASA Astrophysics Data System (ADS)

    Vana, M.; Tamm, E.; Hõrrak, U.; Mirme, A.; Tammet, H.; Laakso, L.; Aalto, P. P.; Kulmala, M.

    2006-12-01

    In this work, the charging state of atmospheric nanoparticles was estimated through simultaneous measurements of aerosol size distribution and air ions mobility distribution with the aim to elucidate the formation mechanisms of atmospheric aerosols. The measurements were performed as a part of the QUEST 2 campaign at a boreal forest station in Finland. The overlapping part of the measurement ranges of the particle size spectrometers and air ion mobility spectrometers in the mass diameter interval of 2.6-40 nm was used to assess the percentage of charged particles (charging probability). This parameter was obtained as the slope of the linear regression line on the scatterplot of the measured concentrations of total (neutral + charged) and charged particles for the same diameter interval. Charging probabilities as a function of particle diameter were calculated for different days and were compared with the steady state charging probabilities of the particles in the bipolar ion atmosphere. For the smallest particles detectable by the particle size spectrometers (2.6-5 nm), the high percentages of negatively charged particles were found during the nanometer particle concentration bursts. These values considerably exceeded the values for the steady charging state and it was concluded that negative cluster ions preferably act as condensation nuclei. This effect was found to be the highest in the case of comparatively weak nucleation bursts of nanoparticles, when the rate of the homogeneous nucleation and the concentration of freshly nucleated particles were low. The nucleation burst days were classified according to the concentration of the generated smallest detectable new particles (weak and strong bursts). Approximately the same classification was obtained based on the charge asymmetry on particles with respect to the charge sign (polarity). The probabilities of negative and positive charge on the particles with the diameter of 5-20 nm were found to be nearly equal

  8. Energy cascades, excited state dynamics, and photochemistry in cob(III)alamins and ferric porphyrins.

    PubMed

    Rury, Aaron S; Wiley, Theodore E; Sension, Roseanne J

    2015-03-17

    Porphyrins and the related chlorins and corrins contain a cyclic tetrapyrrole with the ability to coordinate an active metal center and to perform a variety of functions exploiting the oxidation state, reactivity, and axial ligation of the metal center. These compounds are used in optically activated applications ranging from light harvesting and energy conversion to medical therapeutics and photodynamic therapy to molecular electronics, spintronics, optoelectronic thin films, and optomagnetics. Cobalt containing corrin rings extend the range of applications through photolytic cleavage of a unique axial carbon-cobalt bond, permitting spatiotemporal control of drug delivery. The photochemistry and photophysics of cyclic tetrapyrroles are controlled by electronic relaxation dynamics including internal conversion and intersystem crossing. Typically the electronic excitation cascades through ring centered ππ* states, ligand to metal charge transfer (LMCT) states, metal to ligand charge transfer (MLCT) states, and metal centered states. Ultrafast transient absorption spectroscopy provides a powerful tool for the investigation of the electronic state dynamics in metal containing tetrapyrroles. The UV-visible spectrum is sensitive to the oxidation state, electronic configuration, spin state, and axial ligation of the central metal atom. Ultrashort broadband white light probes spanning the range from 270 to 800 nm, combined with tunable excitation pulses, permit the detailed unravelling of the time scales involved in the electronic energy cascade. State-of-the-art theoretical calculations provide additional insight required for precise assignment of the states. In this Account, we focus on recent ultrafast transient absorption studies of ferric porphyrins and corrin containing cob(III)alamins elucidating the electronic states responsible for ultrafast energy cascades, excited state dynamics, and the resulting photoreactivity or photostability of these compounds. Iron

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

    PubMed Central

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

    2015-01-01

    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. PMID:26508587

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

    PubMed

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

    2015-01-01

    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. PMID:26508587

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

    SciTech Connect

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

    2015-10-28

    In this study, 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.

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

    DOE PAGESBeta

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

    2015-10-28

    In this study, 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 recoverymore » 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.« less

  13. Electronic structure and excited state dynamics in optically excited PTCDA films investigated with two-photon photoemission.

    PubMed

    Marks, M; Sachs, S; Schwalb, C H; Schöll, A; Höfer, U

    2013-09-28

    We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate. PMID:24089789

  14. Electronic structure and excited state dynamics in optically excited PTCDA films investigated with two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Marks, M.; Sachs, S.; Schwalb, C. H.; Schöll, A.; Höfer, U.

    2013-09-01

    We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate.

  15. Beam charge and current neutralization of high-charge-state heavy ions

    SciTech Connect

    Logan, B.G.; Callahan, D.A.

    1997-10-29

    High-charge-state heavy-ions may reduce the accelerator voltage and cost of heavy-ion inertial fusion drivers, if ways can be found to neutralize the space charge of the highly charged beam ions as they are focused to a target in a fusion chamber. Using 2-D Particle-In- Cell simulations, we have evaluated the effectiveness of two different methods of beam neutralization: (1) by redistribution of beam charge in a larger diameter, preformed plasma in the chamber, and (2), by introducing a cold-electron-emitting source within the beam channel at the beam entrance into the chamber. We find the latter method to be much more effective for high-charge-state ions.

  16. High-resolution electronic spectroscopy of the doorway states to intramolecular charge transfer.

    PubMed

    Fleisher, Adam J; Bird, Ryan G; Zaleski, Daniel P; Pate, Brooks H; Pratt, David W

    2013-04-25

    Reported here are several of the ground, first, and second excited state structures and dipole moments of three benchmark intramolecular charge transfer (ICT) systems; 4-(1H-pyrrol-1-yl)benzonitrile (PBN), 4,4'-dimethylaminobenzonitrile (DMABN), and 4-(1-pyrrolidinyl)benzonitrile (PYRBN), isolated in the gas phase and probed by rotationally resolved spectroscopy in a molecular beam. The related molecules 1-phenylpyrrole (PP) and 4-aminobenzonitrile (ABN) also are discussed. We find that the S1 electronic state is of B symmetry in all five molecules. In PBN, a second excited state (S2) of A symmetry is found only ~400 cm(-1) above the presumed origin of the S1 state. The change in dipole moment upon excitation to the A state is measured to be Δμ ≈ 3.0 D, significantly smaller than the value predicted by theory and also smaller than that observed for the "anomalous" ICT band of PBN in solution. The B state dipole moments of DMABN and PYRBN are large, ~10.6 D, slightly larger than those attributed to "normal" LE fluorescence in solution. In addition, we find the unsaturated donor molecules (PP, PBN) to be twisted in their ground states and to become more planar upon excitation, even in the A state, whereas the saturated donor molecules (ABN, DMABN, PYRBN), initially planar, either remain planar or become more twisted in their excited states. It thus appears that the model that is appropriate for describing ICT in these systems depends on the geometry of the ground state. PMID:22913563

  17. Resonant coherent excitation of hydrogen-like ions planar channeled in a crystal; Transition into the first excited state

    NASA Astrophysics Data System (ADS)

    Babaev, A.; Pivovarov, Yu. L.

    2012-03-01

    observed in the outgoing beam behind the crystal. To get the probabilities for the ion to be in the ground state or in the first excited state, or to be ionized, the Schrödinger equation is solved for the electron of ion. The numerical solving of the Schrödinger equation is carried out taking into account the fine structure of electronic energy levels, the Stark effect due to the influence of the crystal electric field on electronic energy levels and the ionization of ion due to the collisions with crystal electrons. Solution method: The wave function of the electron of ion is the superposition of the wave functions of stationary states with time-dependent coefficients. These stationary wave functions and corresponding energies are defined from the stationary Schrödinger equation. The equation is reduced to the problem of the eigen values and vectors of Hermitian matrix. The corresponding matrix equation is considered as the linear equation system. Then the time-dependent coefficients of the electron wave function are defined from the Schrödinger equation, with a time-periodic crystal field. The time-periodic field is responsible for the transitions between the stationary states. The final time-dependent Schrödinger equation represents the matrix equation which has been solved by means of the QR-algorithm. Restrictions: As expected the program gives the correct results for relativistic hydrogen-like ions with the kinetic energies up to 1 GeV/u and at the crystal thicknesses of 1-100 μm. The restrictions are: first, the program might give inadequate results, when the ion kinetic energy is too large (>10 GeV/u); second, the unaccounted physical factors may be significant at specific conditions. For example, the spontaneous emission by exited highly charged ions, as well as both energy and angular spread of the incident beam, could lead to additional broadening of the resonance. The medium polarization by the electric field of ion can influence the electronic energy

  18. Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

    NASA Astrophysics Data System (ADS)

    Latha, V.; Balakrishnan, C.; Neelakantan, M. A.

    2015-07-01

    A fluorescent probe 2Z,2‧Z-3,3‧-(4,4‧-methylenebis(4,1-phenylene) bis(azanediyl))bis (1,3-diphenylprop-2-en-1-one) (L) was synthesized and characterized by IR, 1H NMR, ESI-mass, UV-visible and fluorescence spectral techniques. The single crystal analysis illustrates the existence of L in ketamine form. The crystal structure is stabilized by intramolecular and intermolecular hydrogen bonding. The thermal stability of L was studied by TG analysis. The fluorescence spectrum of L shows dual emission, and is due to excited state intramolecular proton transfer (ESIPT) process. This is supported by the high Stokes shift value. Electronic structure calculations of L in the ground and excited state have been carried out using DFT and TD-DFT at B3LYP/6-31G (d,p) level, respectively. The vibrational spectrum was computed at this level and compared with experimental values. Major orbital contributions for the electronic transitions were assigned with the help of TD-DFT. The changes in the Mulliken charge, bond lengths and bond angles between the ground and excited states of the tautomers demonstrate that twisted intramolecular charge transfer (TICT) process occurs along with ESIPT in the excited state.

  19. Excited-state dynamics of pentacene derivatives with stable radical substituents.

    PubMed

    Ito, Akitaka; Shimizu, Akihiro; Kishida, Noriaki; Kawanaka, Yusuke; Kosumi, Daisuke; Hashimoto, Hideki; Teki, Yoshio

    2014-06-23

    The excited-state dynamics of pentacene derivatives with stable radical substituents were evaluated in detail through transient absorption measurements. The derivatives showed ultrafast formation of triplet excited state(s) in the pentacene moiety from a photoexcited singlet state through the contributions of enhanced intersystem crossing and singlet fission. Detailed kinetic analyses for the transient absorption data were conducted to quantify the excited-state characteristics of the derivatives. PMID:24788384

  20. Resonant inelastic x-ray scattering study of charge excitations in superconducting and nonsuperconducting PrFeAsO₁₋y

    DOE PAGESBeta

    Jarrige, I.; Nomura, T.; Ishii, K.; Gretarsson, H.; Kim, Y.-J.; Kim, J.; Upton, M.; Casa, D.; Gog, T.; Ishikado, M.; et al

    2012-09-05

    We report the first observation by momentum-resolved resonant inelastic x-ray scattering of charge excitations in an iron-based superconductor and its parent compound, PrFeAsO₀.₇ and PrFeAsO, respectively, with two main results. First, using calculations based on a 16-band dp model, we show that the energy of the lowest-lying excitations, identified as dd interband transitions of dominant xz,yz orbital character, exhibits a dramatic dependence on electron correlation. This enables us to estimate the Coulomb repulsion U and Hund's coupling J, and to highlight the role played by J in these peculiar orbital-dependent electron correlation effects. Second, we show that short-range antiferromagnetic correlations,more » which are a prerequisite to the occurrence of these excitations at the Γ point, are still present in the superconducting state.« less

  1. Resonant inelastic x-ray scattering study of charge excitations in superconducting and nonsuperconducting PrFeAsO₁₋y

    SciTech Connect

    Jarrige, I.; Nomura, T.; Ishii, K.; Gretarsson, H.; Kim, Y.-J.; Kim, J.; Upton, M.; Casa, D.; Gog, T.; Ishikado, M.; Fukuda, T.; Yoshida, M.; Hill, J. P.; Liu, X.; Hiraoka, N.; Tsuei, K. D.; Shamoto, S.

    2012-09-05

    We report the first observation by momentum-resolved resonant inelastic x-ray scattering of charge excitations in an iron-based superconductor and its parent compound, PrFeAsO₀.₇ and PrFeAsO, respectively, with two main results. First, using calculations based on a 16-band dp model, we show that the energy of the lowest-lying excitations, identified as dd interband transitions of dominant xz,yz orbital character, exhibits a dramatic dependence on electron correlation. This enables us to estimate the Coulomb repulsion U and Hund's coupling J, and to highlight the role played by J in these peculiar orbital-dependent electron correlation effects. Second, we show that short-range antiferromagnetic correlations, which are a prerequisite to the occurrence of these excitations at the Γ point, are still present in the superconducting state.

  2. Quantum fluctuations of mesoscopic damped double resonance RLC circuit with mutual capacitance inductance coupling in thermal excitation state

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Lei; Li, Hong-Qi; Wang, Ji-Suo

    2007-08-01

    Based on the scheme of damped harmonic oscillator quantization and thermo-field dynamics (TFD), the quantization of mesoscopic damped double resonance RLC circuit with mutual capacitance-inductance coupling is proposed. The quantum fluctuations of charge and current of each loop in a squeezed vacuum state are studied in the thermal excitation case. It is shown that the fluctuations not only depend on circuit inherent parameters, but also rely on excitation quantum number and squeezing parameter. Moreover, due to the finite environmental temperature and damped resistance, the fluctuations increase with the temperature rising, and decay with time.

  3. Charge Transfer and Triplet States in High Efficiency OPV Materials and Devices

    NASA Astrophysics Data System (ADS)

    Dyakonov, Vladimir

    2013-03-01

    The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understanding of the processes involving the charge transfer and triplet states and their relation to nanoscale morphology and/or energetics of blends is essential for the

  4. Unraveling the nature of charge excitations in La2CuO4 with momentum-resolved Cu K-edge resonant inelastic X-ray scattering

    SciTech Connect

    Chen, Cheng-Chien

    2011-03-01

    Results of model calculations using exact diagonalization reveal the orbital character of states associated with different Raman loss peaks in Cu K-edge resonant inelastic X-ray scattering (RIXS) from La{sub 2}CuO{sub 4}. The model includes electronic orbitals necessary to highlight non-local Zhang-Rice singlet, charge transfer and d-d excitations, as well as states with apical oxygen 2p{sub z} character. The dispersion of these excitations is discussed with prospects for resonant final state wave-function mapping. A good agreement with experiments emphasizes the substantial multi-orbital character of RIXS profiles in the energy transfer range 1-6 eV.

  5. Theoretical description of excited state dynamics in nanostructures

    NASA Astrophysics Data System (ADS)

    Rubio, Angel

    2009-03-01

    There has been much progress in the synthesis and characterization of nanostructures however, there remain immense challenges in understanding their properties and interactions with external probes in order to realize their tremendous potential for applications (molecular electronics, nanoscale opto-electronic devices, light harvesting and emitting nanostructures). We will review the recent implementations of TDDFT to study the optical absorption of biological chromophores, one-dimensional polymers and layered materials. In particular we will show the effect of electron-hole attraction in those systems. Applications to the optical properties of solvated nanostructures as well as excited state dynamics in some organic molecules will be used as text cases to illustrate the performance of the approach. Work done in collaboration with A. Castro, M. Marques, X. Andrade, J.L Alonso, Pablo Echenique, L. Wirtz, A. Marini, M. Gruning, C. Rozzi, D. Varsano and E.K.U. Gross.

  6. Chimera states and excitation waves in networks with complex topologies

    NASA Astrophysics Data System (ADS)

    Schöll, Eckehard

    2016-06-01

    Chimera patterns, which consist of coexisting spatial domains of coherent (synchronized) and incoherent (desyn- chronized) dynamics are studied in networks of FitzHugh-Nagumo systems with complex topologies. To test the robustness of chimera patterns with respect to changes in the structure of the network, we study the following network topologies: Regular ring topology with R nearest neigbors coupled to each side, small-world topology with additional long-range random links, and a hierarchical geometry in the connectivity matrix. We find that chimera states are generally robust with respect to these perturbations, but qualitative changes of the chimera patterns in form of nested coherent and incoherent regions can be induced by a hierarchical topology. The suppression of propagating excitation waves by a small-world topology is also reviewed.

  7. Measurement of Atomic Oscillator Strength Distribution from the Excited States

    SciTech Connect

    Hussain, Shahid; Saleem, M.; Baig, M. A.

    2008-10-22

    Saturation technique has been employed to measure the oscillator strength distribution in spectra of helium lithium using an electrical discharge cell a thermionic diode ion detector respectively. The photoabsorption cross sections in the discrete or bound region (commonly known as f-values) have been determined form the Rydberg series accessed from a particular excited state calibrating it with the absolute value of the photoionization cross section measured at the ionization threshold. The extracted discrete f-values merge into the oscillator strength densities, estimated from the measured photoionization cross sections at different photon energies above the first ionization threshold. The experimental data on helium and lithium show continuity between the discrete and the continuous oscillator strengths across the ionization threshold.

  8. UV excited-state photoresponse of biochromophore negative ions.

    PubMed

    Bochenkova, Anastasia V; Klærke, Benedikte; Rahbek, Dennis B; Rajput, Jyoti; Toker, Yoni; Andersen, Lars H

    2014-09-01

    Members of the green fluorescent protein (GFP) family may undergo irreversible phototransformation upon irradiation with UV light. This provides clear evidence for the importance of the higher-energy photophysics of the chromophore, which remains essentially unexplored. By using time-resolved action and photoelectron spectroscopy together with high-level electronic structure theory, we directly probe and identify higher electronically excited singlet states of the isolated para- and meta-chromophore anions of GFP. These molecular resonances are found to serve as a doorway for very efficient electron detachment in the gas phase. Inside the protein, this band is found to be resonant with the quasicontinuum of a solvated electron, thus enhancing electron transfer from the GFP to the solvent. This suggests a photophysical pathway for photoconversion of the protein, where GFP resonant photooxidation in solution triggers radical redox reactions inside these proteins. PMID:25044707

  9. Masses of Ground- and Excited-State Hadrons

    NASA Astrophysics Data System (ADS)

    Roberts, Hannes L. L.; Chang, Lei; Cloët, Ian C.; Roberts, Craig D.

    2011-07-01

    We present the first Dyson-Schwinger equation calculation of the light hadron spectrum that simultaneously correlates the masses of meson and baryon ground- and excited-states within a single framework. At the core of our analysis is a symmetry-preserving treatment of a vector-vector contact interaction. In comparison with relevant quantities the root-mean-square-relative-error/degree-of freedom is 13%. Notable amongst our results is agreement between the computed baryon masses and the bare masses employed in modern dynamical coupled-channels models of pion-nucleon reactions. Our analysis provides insight into numerous aspects of baryon structure; e.g., relationships between the nucleon and Δ masses and those of the dressed-quark and diquark correlations they contain.

  10. Theoretical study on the excited states of HCN

    SciTech Connect

    Nayak, Malaya K.; Chaudhuri, Rajat K.; Krishnamachari, S.N.L.G.

    2005-05-08

    In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 A. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 A corresponds to the transition 4 {sup 3}-A{sup '}<{sup -}1 {sup 3}-A{sup '} of HCN.

  11. Excitation of Helium to the n=2 States in Intermediate Energy H^- + He Collisions.

    NASA Astrophysics Data System (ADS)

    Kvale, T. J.; Lu, C. E.; Theodosiou, D. G.; Seely

    1996-05-01

    The first measurements and calculations of excitation of helium to the n=2 states by H^- impact are reported. The experimental method that was employed in these measurements was Ion Energy-Loss Spectroscopy which resulted in absolute cross section determinations. A H^- ion beam was accelerated into a gas target cell containing helium and the scattered H^- beam was magnetically separated from the other charge state components of the emerging projectile beam and directed into an energy analyzer in the decelerator terminal. The potential placed on the accelerator was varied to produce the energy-loss spectra. These spectra were analyzed in order to deduce the cross section values. Cross section predictions using the VPSA model, with explicit allowance for the internal structure of H^-, are also reported and will be compared to the experimentally determined cross sections.

  12. New formalism in evaluation of the ground and few excited states of Hubbard chain nanostructures

    NASA Astrophysics Data System (ADS)

    Faizabadi, E.; Soleimani, M.

    2008-03-01

    A new, simple and efficient method is presented for calculation of the ground and a few excited states of Hubbard chain nanostructures. By using this method, the photoemission spectral function for organic charge transfer salt TTF-TCNQ, is calculated. For a chain with maximum 70 sites the result is in good agreement with the previous works but there is a difference for further number of sites in the chain, which is discussed in the text with all the specifics. We also show that a source of errors in density matrix renormalization group method for a one dimensional chain is the deficiency of the matrix product scheme for generating the desired states of the linear chain.

  13. Foil dissociation of fast molecular ions into atomic excited states

    SciTech Connect

    Berry, H.G.; Gay, T.J.; Brooks, R.L.

    1980-01-01

    The intensity and polarizations of light emitted from atomic excited states of dissociated molecular ions were measured. The dissociations are induced when fast molecular ions (50 to 500 keV/amu) are transmitted through thin carbon foils. A calculation of multiple scattering and the Coulomb explosion gives the average internuclear separation of the projectile at the foil surface. Experimentally, the foil thickness is varied to give varying internuclear separations at the foil surface and observe the consequent variation in light yield and optical polarization. Using HeH/sup +/ projectiles, factors of 1 to 5 enhancements of the light yields from n = 3, /sup 1/ /sup 3/P,D states of He I and some He II and H I emissions were observed. The results can be explained in terms of molecular level crossings which provide mixings of the various final states during dissociation of the molecular ions at the exit surface. They suggest a short range surface interaction of the electron pick-up followed by a slow molecular dissociation. Alignment measurements confirm the essential features of the model. Observations of Lyman ..cap alpha.. emission after dissociation of H/sub 2//sup +/ amd H/sub 3//sup +/ show rapid variations in light yield for small internuclear separations at the foil surface.

  14. Suppression of excited-state contributions to stellar reaction rates

    NASA Astrophysics Data System (ADS)

    Rauscher, T.

    2013-09-01

    It has been shown in previous work [Kiss , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.191101 101, 191101 (2008); Rauscher , Phys. Rev. C10.1103/PhysRevC.80.035801 80, 035801 (2009)] that a suppression of the stellar enhancement factor (SEF) occurs in some endothermic reactions at and far from stability. This effect is re-evaluated using the ground-state contributions to the stellar reaction rates, which were shown to be better suited to judging the importance of excited-state contributions than the previously applied SEFs. An update of the tables shown in the latter work is given. The new evaluation finds 2350 cases (out of a full set of 57 513 reactions) for which the ground-state contribution is larger in the reaction direction with a negative reaction Q value than in the exothermic direction, thus providing exceptions to the commonly applied Q value rule. The results confirm the Coulomb suppression effect but lead to a larger number of exceptions than previously found. This is due to the fact that often a large variation in the g.s. contribution does not lead to a sizable change in the SEF. On the other hand, several previously identified cases do not appear anymore because it is found that their g.s. contribution is smaller than inferred from the SEF.

  15. Evidence for Cation-Controlled Excited-State Localization in a Ruthenium Polypyridyl Compound.

    PubMed

    Beauvilliers, Evan E; Meyer, Gerald J

    2016-08-01

    The visible absorption and photoluminescence (PL) properties of the four neutral ruthenium diimine compounds [Ru(bpy)2(dcb)] (B2B), [Ru(dtb)2(dcb)] (D2B), [Ru(bpy)2(dcbq)] (B2Q), and [Ru(dtb)2(dcbq)] (D2Q), where bpy is 2,2'-bipyridine, dcb is 4,4'-(CO2(-))2-bpy, dtb is 4,4'-(tert-butyl)2-bpy, and dcbq is 4,4'-(CO2(-))2-2,2'-biquinoline, are reported in the presence of Lewis acidic cations present in fluid solutions at room temperature. In methanol solutions, the measured spectra were insensitive to the presence of these cations, while in acetonitrile a significant red shift in the PL spectra (≤1400 cm(-1)) was observed consistent with stabilization of the metal-to-ligand charge transfer (MLCT) excited state through Lewis acid-base adduct formation. No significant spectral changes were observed in control experiments with the tetrabutylammonium cation. Titration data with Li(+), Na(+), Mg(2+), Ca(2+), Zn(2+), Al(3+), Y(3+), and La(3+) showed that the extent of stabilization saturated at high cation concentration with magnitudes that scaled roughly with the cation charge-to-size ratio. The visible absorption spectra of D2Q was particularly informative due to the presence of two well-resolved MLCT absorption bands: (1) Ru → bpy, λmax ≈ 450 nm; and (2) Ru → dcbq, λmax ≈ 540 nm. The higher-energy band blue-shifted and the lower-energy band red-shifted upon cation addition. The PL intensity and lifetime of the excited state of B2B first increased with cation addition without significant shifts in the measured spectra, behavior attributed to a cation-induced change in the localization of the emissive excited state from bpy to dcb. The importance of excited-state localization and stabilization for solar energy conversion is discussed. PMID:27391279

  16. DFT calculations of molecular excited states using an orbital-dependent nonadiabatic exchange kernel

    SciTech Connect

    Ipatov, A. N.

    2010-02-15

    A density functional method for computing molecular excitation spectra is presented that uses a frequency-dependent kernel and takes into account the nonlocality of exchange interaction. Owing to its high numerical stability and the use of a nonadiabatic (frequency-dependent) exchange kernel, the proposed approach provides a qualitatively correct description of the asymptotic behavior of charge-transfer excitation energies.

  17. Effect of substitution on the ultrafast deactivation of the excited state of benzo[b]thiophene-arylamines.

    PubMed

    Pina, J; Queiroz, M-J R P; Seixas de Melo, J

    2016-08-01

    A complete and systematic study of the spectroscopic and photophysical properties of five novel diarylamines in the benzo[b]thiophene series (oligoanilines) was performed in solution at room (293 K) and low (77 K) temperature. The title compounds resulting from the link between one aniline unit with a benzo[b]thiophene unit (with two different methyl and methoxy substitution) were characterized using steady-state absorption, fluorescence and phosphorescence spectroscopy, as well as femto- to nano-second time resolved spectroscopies. The study involved the determination of the absorption, emission and triplet-triplet absorption together with all relevant quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion and singlet oxygen yields), excited state lifetimes and the overall set of deactivation rate constants (kF, kIC and kISC). This study was further complemented with theoretical calculations, namely with the determination of the optimized ground-state molecular geometries for the diarylamines together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The DFT results were found to corroborate the observed charge-transfer character of the singlet excited state. The experimental results showed that the radiationless decay processes (internal conversion and intersystem-crossing) constitute the main excited state deactivation pathways and that substitution with methyl and methoxy groups induces significant changes in the spectroscopic and photophysical behaviour of these compounds. This was also corroborated by the femtosecond transient absorption study, where it was found that the ultrafast dynamics of the diarylamines was best described by a sequential model featuring fast solvent relaxation followed by conformational relaxation to a more planar excited state, from where singlet excited state deactivation occurs through internal conversion and

  18. Stability of quantum-dot excited-state laser emission under simultaneous ground-state perturbation

    SciTech Connect

    Kaptan, Y. Herzog, B.; Schöps, O.; Kolarczik, M.; Woggon, U.; Owschimikow, N.; Röhm, A.; Lingnau, B.; Lüdge, K.; Schmeckebier, H.; Arsenijević, D.; Bimberg, D.; Mikhelashvili, V.; Eisenstein, G.

    2014-11-10

    The impact of ground state amplification on the laser emission of In(Ga)As quantum dot excited state lasers is studied in time-resolved experiments. We find that a depopulation of the quantum dot ground state is followed by a drop in excited state lasing intensity. The magnitude of the drop is strongly dependent on the wavelength of the depletion pulse and the applied injection current. Numerical simulations based on laser rate equations reproduce the experimental results and explain the wavelength dependence by the different dynamics in lasing and non-lasing sub-ensembles within the inhomogeneously broadened quantum dots. At high injection levels, the observed response even upon perturbation of the lasing sub-ensemble is small and followed by a fast recovery, thus supporting the capacity of fast modulation in dual-state devices.

  19. Excited states of the 5-chlorophyll photosystem II reaction center

    SciTech Connect

    Jankowiak, R.; Raetsep, M.; Picorel, R.; Seibert, M.; Small, G.J.

    1999-11-04

    Results of 4.2 K hole burning, chemical reduction (sodium dithionite, in dark and with illumination), and oxidation (ferricyanide) experiments are reported for the isolated PS II reaction center containing five chlorophyll (Chl) molecules (RC-5). Q{sub y} states at 679.6 and 668.3 nm are identified as being highly localized on pheophytin a of the D{sub 1} branch (Pheo{sub 1}) and pheophytin a of the D{sub 2} branch (Pheo{sub 2}), respectively. The Pheo{sub 1}-Q{sub x} and Pheo{sub 2}-Q{sub x} transitions were found to lie on the low and high energy sides of the single Pheo-Q{sub x} absorption band, at 544.4 and 541.2 nm, respectively. The Q{sub y} band of the 684 nm absorbing Chl, which is more apparent in absorption in RC-5 than in RC-6 samples, is assigned to the peripheral Chl on the D{sub 1} side. The results are consistent with that peripheral Chl being Chl{sub z}. The results indicate that P680, the primary electron donor, is the main acceptor for energy transfer from the Pheo{sub 1}-Q{sub y} state and that excitation energy transfer from the Pheo{sub 1}-Q{sub y} state and P680* to the 684 nm Chl is inefficient. It is concluded that the procedure used to prepare RC-5 has only a small effect on the energies of the Q{sub y} states associated with the core cofactors of the 6-Chl RC as well as the 684 nm Chl. Implications of the results for the multimer model are considered. In that model the Q{sub y}-states of the core are significantly delocalized over several cofactors. The results presented provide no support for this model.

  20. Microwave Spectroscopy of the Excited Vibrational States of Methanol

    NASA Astrophysics Data System (ADS)

    Pearson, John; Daly, Adam M.; Bermúdez, Celina

    2015-06-01

    Methanol is the simplest molecule with a three-fold internal rotation and the observation of its νb{8} band served the primary catalyst for the development of internal rotation theory(a,b). The 75 subsequent years of investigation into the νb{8} band region have yielded a large number assignments, numerous high precision energy levels and a great deal of insight into the coupling of νb{t}=3 & 4 with νb{8}, νb{7}, νb{11} and other nearby states(c). In spite of this progress numerous assignment mysteries persist, the origin of almost half the far infrared laser lines remain unknown and all attempts to model the region quantum mechanically have had very limited success. The C3V internal rotation Hamiltonian has successfully modeled the νb{t}=0,1 & 2 states of methanol and other internal rotors(d). However, successful modeling of the coupling between torsional bath states and excited small amplitude motion remains problematic and coupling of multiple interacting excited small amplitude vibrations featuring large amplitude motions remains almost completely unexplored. Before such modeling can be attempted, identifying the remaining low lying levels of νb{7} and νb{11} is necessary. We present an investigation into the microwave spectrum of νb{7}, νb{8} and νb{11} along with the underlying torsional bath states in νb{t}=3 and νb{t}= 4. (a) A. Borden, E.F. Barker J. Chem. Phys., 6, 553 (1938). (b) J. S. Koehler and D. M. Dennison, Phys. Rev. 57, 1006 (1940). (c) R. M. Lees, Li-Hong Xu, J. W. C. Johns, B. P. Winnewisser, and M. Lock, J. Mol. Spectrosc. 243, 168 (2007). (d) L.-H. Xu, J. Fisher, R.M. Lees, H.Y. Shi, J.T. Hougen, J.C. Pearson, B.J. Drouin, G.A. Blake, R. Braakman J. Mol. Spectrosc., 251, 305 (2008).

  1. Watching ultrafast barrierless excited-state isomerization of pseudocyanine in real time.

    PubMed

    Dietzek, Benjamin; Yartsev, Arkady; Tarnovsky, Alexander N

    2007-05-01

    The photoinduced excited-state processes in 1,1'-diethyl-2,2'-cyanine iodine are investigated using femtosecond time-resolved pump-probe spectroscopy. Using a broad range of probe wavelengths, the relaxation of the initially prepared excited-state wavepacket can be followed down to the sink region. The data directly visualize the directed downhill motion along the torsional reaction coordinate and suggest a barrierless excited-state isomerization in the short chain cyanine dye. Additionally, ultrafast ground-state hole and excited-state hole replica broadening is observed. While the narrow excited-state wavepacket broadens during pump-probe overlap, the ground-state hole burning dynamics takes place on a significantly longer time-scale. The experiment reported can be considered as a direct monitoring of the shape and the position of the photoprepared wavepacket on the excited-state potential energy surface. PMID:17417893

  2. Increasing Protein Charge State When Using Laser Electrospray Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Karki, Santosh; Flanigan, Paul M.; Perez, Johnny J.; Archer, Jieutonne J.; Levis, Robert J.

    2015-05-01

    Femtosecond (fs) laser vaporization is used to transfer cytochrome c, myoglobin, lysozyme, and ubiquitin from the condensed phase into an electrospray (ES) plume consisting of a mixture of a supercharging reagent, m-nitrobenzyl alcohol ( m-NBA), and trifluoroacetic acid (TFA), acetic acid (AA), or formic acid (FA). Interaction of acid-sensitive proteins like cytochrome c and myoglobin with the highly charged ES droplets resulted in a shift to higher charge states in comparison with acid-stable proteins like lysozyme and ubiquitin. Laser electrospray mass spectrometry (LEMS) measurements showed an increase in both the average charge states (Zavg) and the charge state with maximum intensity (Zmode) for acid-sensitive proteins compared with conventional electrospray ionization mass spectrometry (ESI-MS) under equivalent solvent conditions. A marked increase in ion abundance of higher charge states was observed for LEMS in comparison with conventional electrospray for cytochrome c (ranging from 19+ to 21+ versus 13+ to 16+) and myoglobin (ranging from 19+ to 26+ versus 18+ to 21+) using an ES solution containing m-NBA and TFA. LEMS measurements as a function of electrospray flow rate yielded increasing charge states with decreasing flow rates for cytochrome c and myoglobin.

  3. Excited-state Raman spectroscopy with and without actinic excitation: S{sub 1} Raman spectra of trans-azobenzene

    SciTech Connect

    Dobryakov, A. L.; Quick, M.; Ioffe, I. N.; Granovsky, A. A.; Ernsting, N. P.; Kovalenko, S. A.

    2014-05-14

    We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S{sub 1} and S{sub 0} spectra of trans-azobenzene in n-hexane. The S{sub 1} spectra were also measured conventionally, upon nπ* (S{sub 0} → S{sub 1}) actinic excitation. The results are discussed and compared to earlier reports.

  4. Excited-state positronium formation in positron–hydrogen collisions under weakly coupled plasmas

    NASA Astrophysics Data System (ADS)

    Rej, Pramit; Ghoshal, Arijit

    2016-06-01

    The effect of screening of weakly coupled plasma on positronium (Ps) formation in excited states in the scattering of a positron from the ground state of a hydrogen atom has been investigated using a distorted wave theory which includes screened dipole polarization potential. The effect of external plasma has been incorporated by using the Debye–Hückel screening model of the interacting charge particles. Variationally determined simple hydrogenic wave functions have been used to obtain the distorted wave scattering amplitude in a closed form. Effects of plasma screening on the differential and total cross sections have been studied in detail in the energy range 20–300 eV of incident positron. For the free atomic case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for Ps formation in highly excited states in positron–hydrogen collisions under weakly coupled plasma is reported first time in the literature.

  5. Excitation energy dependence of excited states dynamics in all- trans-carotenes determined by femtosecond absorption and fluorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Kosumi, Daisuke; Yanagi, Kazuhiro; Nishio, Tomohiro; Hashimoto, Hideki; Yoshizawa, Masayuki

    2005-06-01

    Ultrafast relaxation kinetics in β-carotene and lycopene has been investigated by femtosecond absorption and fluorescence spectroscopies using tunable excitation pulses. The transient signals induced by the photoexcitation with larger excess energy have broader bands and longer lifetimes both in the 11Bu+and21Ag- excited states. The excess vibrational energy remains longer than several picoseconds and slows the relaxation kinetics in carotenoids.

  6. Excited State Dynamics of 7-AZAINDOLE Homodimer in Frozen Nitrogen Matrix

    NASA Astrophysics Data System (ADS)

    Mukherjee, Moitrayee; Bandyopadhyay, Biman; Karmakar, Shreetama; Chakraborty, Tapas

    2011-06-01

    In a fluid medium (liquid or gas), the doubly hydrogen bonded dimer of 7-azaindole (7AI) undergoes tautomerization via simultaneous exchange of two H-atoms/protons between the two moieties upon UV excitation to lowest excited singlet state. The excited dimer emits exclusively visible fluorescence from tautomeric configuration, and no UV fluorescence is detected from the locally excited state. We show here for the first time that this generic excited state dynamics of 7AI dimer is totally altered if the species is synthesized and confined in frozen nitrogen at 8 K. The dimer has been found to emit only from the locally excited state, and the photophysical channel leading to excited state tautomerization is completely blocked. The formation of the centrosymmetric dimer in nitrogen matrix is ensured by recording the FTIR spectrum of the dimer before initiating the photophysical measurements. The details of our findings and interpretation of the measured data will be presented in the talk.

  7. Excitation of the Δ(1232) isobar in deuteron charge exchange on hydrogen at 1.6, 1.8, and 2.3 GeV

    NASA Astrophysics Data System (ADS)

    Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Imambekov, O.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H. J.; Steffens, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Uzikov, Yu.; Valdau, Yu.; Wilkin, C.

    2013-10-01

    The charge-exchange break-up of polarised deuterons d→p→{pp}sn, where the final {pp}s diproton system has a very low excitation energy and hence is mainly in the S01 state, is a powerful tool to probe the spin-flip terms in the proton-neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Δ(1232) isobar in the d→p→{pp}sX reaction. Values of the differential cross section and two deuteron tensor analysing powers, Axx and Ayy, have been extracted as functions of the momentum transfer to the diproton or the invariant mass MX of the unobserved system X. The unpolarised cross section in the high MX region is well described in a model that includes only direct excitation of the Δ isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low MX, even when Δ excitation in the projectile deuteron is included in the calculation. Furthermore, direct Δ production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

  8. Excited-State Dynamics in Colloidal Semiconductor Nanocrystals.

    PubMed

    Rabouw, Freddy T; de Mello Donega, Celso

    2016-10-01

    Colloidal semiconductor nanocrystals have attracted continuous worldwide interest over the last three decades owing to their remarkable and unique size- and shape-, dependent properties. The colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to tailor their optoelectronic and physical-chemical properties, yielding materials that combine size-, shape-, and composition-dependent properties with easy surface manipulation and solution processing. These features have turned the study of colloidal semiconductor nanocrystals into a dynamic and multidisciplinary research field, with fascinating fundamental challenges and dazzling application prospects. This review focuses on the excited-state dynamics in these intriguing nanomaterials, covering a range of different relaxation mechanisms that span over 15 orders of magnitude, from a few femtoseconds to a few seconds after photoexcitation. In addition to reviewing the state of the art and highlighting the essential concepts in the field, we also discuss the relevance of the different relaxation processes to a number of potential applications, such as photovoltaics and LEDs. The fundamental physical and chemical principles needed to control and understand the properties of colloidal semiconductor nanocrystals are also addressed. PMID:27573500

  9. Excited states of ribosome translocation revealed through integrative molecular modeling

    PubMed Central

    Whitford, Paul C.; Ahmed, Aqeel; Yu, Yanan; Hennelly, Scott P.; Tama, Florence; Spahn, Christian M. T.; Onuchic, José N.; Sanbonmatsu, Karissa Y.

    2011-01-01

    The dynamic nature of biomolecules leads to significant challenges when characterizing the structural properties associated with function. While X-ray crystallography and imaging techniques (such as cryo-electron microscopy) can reveal the structural details of stable molecular complexes, strategies must be developed to characterize configurations that exhibit only marginal stability (such as intermediates) or configurations that do not correspond to minima on the energy landscape (such as transition-state ensembles). Here, we present a methodology (MDfit) that utilizes molecular dynamics simulations to generate configurations of excited states that are consistent with available biophysical and biochemical measurements. To demonstrate the approach, we present a sequence of configurations that are suggested to be associated with transfer RNA (tRNA) movement through the ribosome (translocation). The models were constructed by combining information from X-ray crystallography, cryo-electron microscopy, and biochemical data. These models provide a structural framework for translocation that may be further investigated experimentally and theoretically to determine the precise energetic character of each configuration and the transition dynamics between them. PMID:22080606

  10. Excited states of ribosome translocation revealed through integrative molecular modeling.

    PubMed

    Whitford, Paul C; Ahmed, Aqeel; Yu, Yanan; Hennelly, Scott P; Tama, Florence; Spahn, Christian M T; Onuchic, José N; Sanbonmatsu, Karissa Y

    2011-11-22

    The dynamic nature of biomolecules leads to significant challenges when characterizing the structural properties associated with function. While X-ray crystallography and imaging techniques (such as cryo-electron microscopy) can reveal the structural details of stable molecular complexes, strategies must be developed to characterize configurations that exhibit only marginal stability (such as intermediates) or configurations that do not correspond to minima on the energy landscape (such as transition-state ensembles). Here, we present a methodology (MDfit) that utilizes molecular dynamics simulations to generate configurations of excited states that are consistent with available biophysical and biochemical measurements. To demonstrate the approach, we present a sequence of configurations that are suggested to be associated with transfer RNA (tRNA) movement through the ribosome (translocation). The models were constructed by combining information from X-ray crystallography, cryo-electron microscopy, and biochemical data. These models provide a structural framework for translocation that may be further investigated experimentally and theoretically to determine the precise energetic character of each configuration and the transition dynamics between them. PMID:22080606

  11. Charge-transfer excitations in the model superconductor HgBa(2)CuO(4+delta).

    PubMed

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

    2005-11-18

    We report a Cu -edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa(2)CuO(4+delta) at optimal doping (T(c)=96.5 K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly dispersive (<0.5 eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a remnant charge-transfer gap deep in the superconducting phase. Quite generally, our results, which include additional data for the Mott insulator La(2)CuO(4), demonstrate the importance of exploring the incident photon-energy dependence of the RIXS cross section. PMID:16384172

  12. Charge-Transfer Excitations in the Model Superconductor HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

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

    2005-11-01

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

  13. Investigation of excited 0+ states populated in the 162 Er (p,t) reaction

    NASA Astrophysics Data System (ADS)

    Burbadge, C.; Bildstein, V.; Diaz Varela, A.; Dunlop, M.; Dunlop, R.; Garrett, P. E.; Jamieson, D. S.; Kisliuk, D.; Leach, K. G.; Loranger, J.; Maclean, A.; Radich, A.; Rand, E.; Svensson, C. E.; Ball, G. C.; Triambak, S.; Faestermann, T.; Hertenberger, R.; Wirth, H.-F.

    2015-10-01

    A continuing challenge in nuclear structure physics is the determination of the nature of low-lying excited 0+ states. Various approaches have been implemented to interpret the occurence of these states, such as vibrational excitations in β and γ phonons or pairing excitations. One of the difficulties, however, in resolving the nature of these states is that there is a paucity of data; even the first excited state, 02+,is not always known. Direct two-neutron transfer reactions are a useful tool for locating and investigating the nature of excited 0+ states in well-deformed nuclei. Using the Q3D spectrograph at the Maier-Leibnitz Laboratory, the N = 92 nucleus 160Er was studied via (p , t) reactions with a highly-enriched 162Er target. Strong population of the 02+state was observed with large cross sections greater than any other excited 0+ state. Preliminary results will be presented.

  14. Difluorodiazirine (CF2N2): A comparative quantum mechanical study of the first triplet and first singlet excited states

    NASA Astrophysics Data System (ADS)

    Terrabuio, Luiz Alberto; Haiduke, Roberto Luiz Andrade; Matta, Chérif F.

    2016-07-01

    3,3‧-Difluorodiazirine is a precursor of difluorocarbene radical (:CF2) which is used in organic synthesis and photo affinity labelling. This molecule possesses no dipole moment in the ground electronic state (S0) but has a significant dipole moment (of magnitude ~0.97 D) in both its first (triplet, T1) and second (singlet S1) excited states. These equal dipole moments are shown to originate from widely differing atomic polarization and inter-atomic charge transfer terms (defined by the Quantum Theory of Atoms in Molecules (QTAIM)). The calculated vertical/adiabatic excitation energies for the T1 and S1 states are 2.81/2.63 and 3.99/3.78 eV, respectively. Geometries, vibrational frequencies, atomic charges and spin populations, and the localization-delocalization matrices (LDMs) (Matta, J. Comput. Chem. 35 (2014) 1165) of the excited states are compared with those of the ground state. All calculations have been conducted at the (U)QCISD/aug-cc-pVTZ level of theory.

  15. Phase Fluctuations and the Absence of Topological Defects in Photo-excited Charge Ordered Nickelate

    SciTech Connect

    Lee, W.S.; Chuang, Y.D.; Moore, R.G.; Zhu, Y.; Patthey, L.; Trigo, M.; Lu, D.H.; Kirchmann, P.S.; Krupin, O.; Yi, M.; Langner, M.; Huse, N.; Robinson, J.S.; Chen, Y.; Zhou, S.Y.; Coslovich, G.; Huber, B.; Reis, D.A.; Kaindl, R.A.; Schoenlein, R.W.; Doering, D.

    2012-05-15

    The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La{sub 1.75}Sr{sub 0.25}NiO{sub 4} to reveal unforeseen photoinduced phase fluctuations of the charge order parameter. Such fluctuations preserve long-range order without creating topological defects, distinct from thermal phase fluctuations near the critical temperature in equilibrium. Importantly, relaxation of the phase fluctuations is found to be an order of magnitude slower than that of the order parameter's amplitude fluctuations, and thus limits charge order recovery. This new aspect of phase fluctuations provides a more holistic view of the phase's importance in ordering phenomena of quantum matter.

  16. Phase fluctuations and the absence of topological defects in photo-excited charge ordered nickelate

    SciTech Connect

    Lee, W.S.; Chuang, Y.D.; Moore, R.G.; Zhu, Y.; Patthey, L.; Trigo, M.; Lu, D.H.; Kirchmann, P.S.; Krupin, O.; Yi, M.; Langner, M.; Huse, N.; Robinson, J.S.; Chen, Y.; Zhou, S.Y.; Coslovich, G.; Huber, B.; Reis, D.A.; Kaindl, R.A.; Schoenlein, R.W.; Doering, D.; Denes, P.; Schlotter, W.F.; Turner, J.J.; Johnson, S.L.; Först, M.; Sasagawa, T.; Kung, Y.F.; Sorini, A.P.; Kemper, A.F.; Moritz, B.; Devereaux, T.P.; Lee, D.-H.; Shen, Z.X.; Hussain, Z.

    2012-01-01

    The dynamics of an order parameter's amplitude and phase determines the collective behaviour of novel states emerging in complex materials. Time- and momentum-resolved pump-probe spectroscopy, by virtue of measuring material properties at atomic and electronic time scales out of equilibrium, can decouple entangled degrees of freedom by visualizing their corresponding dynamics in the time domain. Here we combine time-resolved femotosecond optical and resonant X-ray diffraction measurements on charge ordered La1.75Sr0.25NiO4 to reveal unforeseen photoinduced phase fluctuations of the charge order parameter. Such fluctuations preserve long-range order without creating topological defects, distinct from thermal phase fluctuations near the critical temperature in equilibrium. Importantly, relaxation of the phase fluctuations is found to be an order of magnitude slower than that of the order parameter's amplitude fluctuations, and thus limits charge order recovery. This new aspect of phase fluctuations provides a more holistic view of the phase's importance in ordering phenomena of quantum matter.

  17. Characterizing the Locality of Diabatic States forElectronic Excitation Transfer By Decomposing theDiabatic Coupling

    SciTech Connect

    Newton, M.D.; Vura-Weis, J.; Wasielewski, M.R.; Subotnik, J.E.

    2010-10-19

    A common strategy to calculate electronic coupling matrix elements for charge or energy transfer is to take the adiabatic states generated by electronic structure computations and rotate them to form localized diabatic states. In this paper, we show that, for intermolecular transfer of singlet electronic excitation, usually we cannot fully localize the electronic excitations in this way. Instead, we calculate putative initial and final states with small excitation tails caused by weak interactions with high energy excited states in the electronic manifold. These tails do not lead to substantial changes in the total diabatic coupling between states, but they do lead to a different partitioning of the total coupling between Coulomb (Forster), exchange (Dexter), and one-electron components. The tails may be reduced by using a multistate diabatic model or eliminated entirely by truncation (denoted as 'chopping'). Without more information, we are unable to conclude with certainty whether the observed diabatic tails are a physical reality or a computational artifact. This research suggests that decomposition of the diabatic coupling between chromophores into Coulomb, exchange, and one-electron components may depend strongly on the number of states considered, and such results should be treated with caution.

  18. Interfacial Charge Transfer States in Condensed Phase Systems

    NASA Astrophysics Data System (ADS)

    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.

  19. Interfacial Charge Transfer States in Condensed Phase Systems.

    PubMed

    Vandewal, Koen

    2016-05-27

    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. PMID:26980308

  20. Charged anisotropic matter with linear or nonlinear equation of state

    SciTech Connect

    Varela, Victor; Rahaman, Farook; Ray, Saibal; Chakraborty, Koushik; Kalam, Mehedi

    2010-08-15

    Ivanov pointed out substantial analytical difficulties associated with self-gravitating, static, isotropic fluid spheres when pressure explicitly depends on matter density. Simplifications achieved with the introduction of electric charge were noticed as well. We deal with self-gravitating, charged, anisotropic fluids and get even more flexibility in solving the Einstein-Maxwell equations. In order to discuss analytical solutions we extend Krori and Barua's method to include pressure anisotropy and linear or nonlinear equations of state. The field equations are reduced to a system of three algebraic equations for the anisotropic pressures as well as matter and electrostatic energy densities. Attention is paid to compact sources characterized by positive matter density and positive radial pressure. Arising solutions satisfy the energy conditions of general relativity. Spheres with vanishing net charge contain fluid elements with unbounded proper charge density located at the fluid-vacuum interface. Notably the electric force acting on these fluid elements is finite, although the acting electric field is zero. Net charges can be huge (10{sup 19}C) and maximum electric field intensities are very large (10{sup 23}-10{sup 24} statvolt/cm) even in the case of zero net charge. Inward-directed fluid forces caused by pressure anisotropy may allow equilibrium configurations with larger net charges and electric field intensities than those found in studies of charged isotropic fluids. Links of these results with charged strange quark stars as well as models of dark matter including massive charged particles are highlighted. The van der Waals equation of state leading to matter densities constrained by cubic polynomial equations is briefly considered. The fundamental question of stability is left open.

  1. On the origin of ultrafast nonradiative transitions in nitro-polycyclic aromatic hydrocarbons: Excited-state dynamics in 1-nitronaphthalene

    SciTech Connect

    Reichardt, Christian; Vogt, R. Aaron; Crespo-Hernandez, Carlos E.

    2009-12-14

    The electronic energy relaxation of 1-nitronaphthalene was studied in nonpolar, aprotic, and protic solvents in the time window from femtoseconds to microseconds. Excitation at 340 or 360 nm populates the Franck-Condon S{sub 1}({pi}{pi}{sup *}) state, which is proposed to bifurcate into two essentially barrierless nonradiative decay channels with sub-200 fs lifetimes. The first main decay channel connects the S{sub 1} state with a receiver T{sub n} state that has considerable n{pi}{sup *} character. The receiver T{sub n} state undergoes internal conversion to populate the vibrationally excited T{sub 1}({pi}{pi}{sup *}) state in 2-4 ps. It is shown that vibrational cooling dynamics in the T{sub 1} state depends on the solvent used, with average lifetimes in the range from 6 to 12 ps. Furthermore, solvation dynamics competes effectively with vibrational cooling in the triplet manifold in primary alcohols. The relaxed T{sub 1} state undergoes intersystem crossing back to the ground state within a few microseconds in N{sub 2}-saturated solutions in all the solvents studied. The second minor channel involves conformational relaxation of the bright S{sub 1} state (primarily rotation of the NO{sub 2}-group) to populate a dissociative singlet state with significant charge-transfer character and negligible oscillator strength. This dissociative channel is proposed to be responsible for the observed photochemistry in 1-nitronaphthalene. Ground- and excited-state calculations at the density functional level of theory that include bulk and explicit solvent effects lend support to the proposed mechanism where the fluorescent S{sub 1} state decays rapidly and irreversibly to dark excited states. A four-state kinetic model is proposed that satisfactorily explains the origin of the nonradiative electronic relaxation pathways in 1-nitronaphthalene.

  2. 20 CFR 416.2161 - Charges to States.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... determinations is charged in the following manner: (1) If making Medicaid determinations and providing basic SSI... the SSI program. (2) The State must pay half our additional cost caused by providing any information... basic SSI application information causes us additional cost, the State must pay our full additional...

  3. Excited state dipole moments of chloroanilines and chlorophenols from solvatochromic shifts in electronic absorption spectra: Support for the concept of excited state group moments

    NASA Astrophysics Data System (ADS)

    Prabhumirashi, L. S.; Satpute, R. S.

    The dipole moments of isomeric o-, m- and p-chloroanilines and chlorophenols in electronically excited L a and L b states are estimated from solvent induced polarization shifts in electronic absorption spectra. It is observed that μ e( L a) > μ e( L b) > μ g, which is consistent with the general theory of polarization red shift. The μ es are found to be approximately co-linear with the corresponding μ gs. The concept of group moments is extended to aromatic molecules in excited states. This approach is found to be useful in understanding correlations among the excited states of mono- and disubstituted benzenes.

  4. Recent experiments on near-threshold electron-impact excitation of multiply charged ions

    SciTech Connect

    Bannister, M.E.; Djuric, N.; Woitke, O.; Dunn, G.H. |; Chung, Y.S.; Smith, A.C.H.; Wallbank, B.

    1998-04-01

    Some recent measurements of excitation of multiply charged ions by electrons studied in beam-beam experiments are highlighted. The emphasis is on absolute total cross sections measured with the merged electron-ion beams energy-loss (MEIBEL) technique, although some results obtained with the crossed-beams fluorescence method are also presented. The MEIBEL technique allows the investigation of optically-allowed and forbidden transitions with sufficient energy resolution, typically about 0.2 eV, to resolve resonance structures in the cross sections. Results from the JILA/ORNL MEIBEL experiment on dipole-allowed transitions in several ions demonstrate the success of various theoretical methods in predicting cross sections in the absence of resonances. Comparisons of R-matrix calculations and measured cross sections for spin-forbidden transitions in Mg-like Si{sup 2+} and Ar{sup 6+}, however, show that further refinements to the theory are needed in order to more accurately predict cross sections involving significant contributions from dielectric resonance`s and interactions between neighboring resonances.

  5. Femtosecond switching of magnetism via strongly correlated spin-charge quantum excitations.

    PubMed

    Li, Tianqi; Patz, Aaron; Mouchliadis, Leonidas; Yan, Jiaqiang; Lograsso, Thomas A; Perakis, Ilias E; Wang, Jigang

    2013-04-01

    The technological demand to push the gigahertz (10(9) hertz) switching speed limit of today's magnetic memory and logic devices into the terahertz (10(12) hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation. By analogy to femtosecond chemistry and photosynthetic dynamics--in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states--femtosecond-laser-excited coherence between electronic states can switch magnetic order by 'suddenly' breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications. Here we show femtosecond (10(-15) seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10(-12) seconds) lattice-heating regime characterized by phase separation without threshold behaviour. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders. PMID:23552945

  6. Critical Assessment of TD-DFT for Excited States of Open-Shell Systems: I. Doublet-Doublet Transitions.

    PubMed

    Li, Zhendong; Liu, Wenjian

    2016-01-12

    A benchmark set of 11 small radicals is set up to assess the performance of time-dependent density functional theory (TD-DFT) for the excited states of open-shell systems. Both the unrestricted (U-TD-DFT) and spin-adapted (X-TD-DFT) formulations of TD-DFT are considered. For comparison, the well-established EOM-CCSD (equation-of-motion coupled-cluster with singles and doubles) is also used. In total, 111 low-lying singly excited doublet states are accessed by all the three approaches. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as the benchmark, it is found that both U-TD-DFT and EOM-CCSD perform well for those states dominated by singlet-coupled single excitations (SCSE) from closed-shell to open-shell, open-shell to vacant-shell, or closed-shell to vacant-shell orbitals. However, for those states dominated by triplet-coupled single excitations (TCSE) from closed-shell to vacant-shell orbitals, both U-TD-DFT and EOM-CCSD fail miserably due to severe spin contaminations. In contrast, X-TD-DFT provides balanced descriptions of both SCSE and TCSE. As far as the functional dependence is concerned, it is found that, when the Hartree-Fock ground state does not suffer from the instability problem, both global hybrid (GH) and range-separated hybrid (RSH) functionals perform grossly better than pure density functionals, especially for Rydberg and charge-transfer excitations. However, if the Hartree-Fock ground state is instable or nearly instable, GH and RSH tend to underestimate severely the excitation energies. The SAOP (statistically averaging of model orbital potentials) performs more uniformly than any other density functionals, although it generally overestimates the excitation energies of valence excitations. Not surprisingly, both EOM-CCSD and adiabatic TD-DFT are incapable of describing excited states with substantial double excitation characters. PMID:26672389

  7. Microwave Emission from Hybridized States in a Semiconductor Charge Qubit

    NASA Astrophysics Data System (ADS)

    Stockklauser, A.; Maisi, V. F.; Basset, J.; Cujia, K.; Reichl, C.; Wegscheider, W.; Ihn, T.; Wallraff, A.; Ensslin, K.

    2015-07-01

    We explore the microwave radiation emitted from a biased double quantum dot due to the inelastic tunneling of single charges. Radiation is detected over a broad range of detuning configurations between the dot energy levels, with pronounced maxima occurring in resonance with a capacitively coupled transmission line resonator. The power emitted for forward and reverse resonant detuning is found to be in good agreement with a rate equation model, which considers the hybridization of the individual dot charge states.

  8. Microwave Emission from Hybridized States in a Semiconductor Charge Qubit.

    PubMed

    Stockklauser, A; Maisi, V F; Basset, J; Cujia, K; Reichl, C; Wegscheider, W; Ihn, T; Wallraff, A; Ensslin, K

    2015-07-24

    We explore the microwave radiation emitted from a biased double quantum dot due to the inelastic tunneling of single charges. Radiation is detected over a broad range of detuning configurations between the dot energy levels, with pronounced maxima occurring in resonance with a capacitively coupled transmission line resonator. The power emitted for forward and reverse resonant detuning is found to be in good agreement with a rate equation model, which considers the hybridization of the individual dot charge states. PMID:26252704

  9. Evaluation of several state-of-charge algorithms

    NASA Astrophysics Data System (ADS)

    Espinosa, J. M.; Martin, M. E.; Burke, A. F.

    1988-09-01

    One of the important needs in marketing an electric vehicle is a device which reliably indicates battery state-of-charge for all types of driving. The purpose of the state-of-charge indicator is analogous to a gas gauge in an internal combustion engine powered vehicle. Many different approaches have been tried to accurately predict battery state-of-charge. This report evaluates several of these approaches. Four different algorithms were implemented into software on an IBM PC and tested using a battery test database for ALCO 2200 lead-acid batteries generated at the INEL. The database was obtained under controlled conditions which compare with the battery response in real EV use. Each algorithm is described in detail as to theory and operational functionality. Also discussed is the hardware and data requirements particular to implementing the individual algorithms. The algorithms were evaluated for accuracy using constant power, stepped power, and simulated vehicle (SFUDS79) discharge profiles. Attempts were made to explain the cause of differences between the predicted and actual state-of-charge and to provide possible remedies to correct them. Recommendations for future work on battery state-of-charge indicators are presented that utilize the hardware and software now in place in the INEL Battery Laboratory.

  10. Iron charge states observed in the solar wind

    NASA Technical Reports Server (NTRS)

    Ipavich, F. M.; Galvin, A. B.; Gloeckler, G.; Hovestadt, D.; Klecker, B.; Scholer, M.

    1983-01-01

    Solar wind measurements from the ULECA sensor of the Max-Planck-Institut/University of Maryland experiment on ISEE-3 are reported. The low energy section of approx the ULECA sensor selects particles by their energy per charge (over the range 3.6 keV/Q to 30 keV/Q) and simultaneously measures their total energy with two low-noise solid state detectors. Solar wind Fe charge state measurements from three time periods of high speed solar wind occurring during a post-shock flow and a coronal hole-associated high speed stream are presented. Analysis of the post-shock flow solar wind indicates the charge state distributions for Fe were peaked at approx +16, indicative of an unusually high coronal temperature (3,000,000 K). In contrast, the Fe charge state distribution observed in a coronal hole-associated high speed stream peaks at approx -9, indicating a much lower coronal temperature (1,400,000 K). This constitutes the first reported measurements of iron charge states in a coronal hole-associated high speed stream.

  11. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: Key role of the excited-state hydrogen-bond strengthening

    NASA Astrophysics Data System (ADS)

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-01

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  12. Photoelectron Spectroscopy of Hexachloroplatinate-Nucleobase Complexes: Nucleobase Excited State Decay Observed via Delayed Electron Emission

    SciTech Connect

    Sen, Ananya; Matthews, Edward M.; Hou, Gao-Lei; Wang, Xue B.; Dessent, Caroline

    2015-11-14

    We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.26-2.36 eV. The magnitudes of the repulsive Coulomb barriers (RCBs) of the complexes are all ~1.7 eV, values that are lower than the RCB of the uncomplexed PtCl6 2- dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four clusters. The 266 nm spectra of the PtCl6 2-∙thymine and PtCl6 2-∙adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN)4 2-∙nucleobase complexes [Sen et al, J. Phys. Chem. B, 119, 11626, 2015]. The observation of delayed electron emission bands in the PtCl6 2-∙nucleobase spectra obtained in this work, as for the previously studied Pt(CN)4 2-∙nucleobase complexes, is attributed to onephoton excitation of nucleobase-centred excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment. Moreover, the selective, strong excitation of the delayed emission bands in the 266 nm spectra is linked to fundamental differences in the individual nucleobase photophysics at this excitation energy. This strongly supports our previous suggestion that the dianion within these clusters can be viewed as a “dynamic tag” which has the propensity to emit electrons when the attached nucleobase decays over a timescale long enough to allow autodetachment.

  13. Excited State Proton Transfer in the Red Fluorescent Protein mKeima

    PubMed Central

    Henderson, J. Nathan; Osborn, Maire F.; Koon, Nayden; Gepshtein, Rinat; Huppert, Dan; Remington, S. James

    2009-01-01

    mKeima is an unusual monomeric red fluorescent protein (λemmax ~620 nm) that is maximally excited in the blue (λexmax ~440 nm). The large Stokes shift suggests that the chromophore is normally protonated. A 1.63 Å resolution structure of mKeima reveals the chromophore to be imbedded in a novel hydrogen bond network, different than in GFP, which could support proton transfer from the chromophore hydroxyl, via Ser142, to Asp157. At low temperatures the emission contains a green component (λemmax ~535 nm), enhanced by deuterium substitution, presumably resulting from reduced proton transfer efficiency. Ultrafast pump/probe studies reveal a rising component in the 610 nm emission with lifetime ~4 ps, characterizing the rate of proton transfer. Mutation of Asp157 to neutral Asn changes the chromophore resting charge state to anionic (λexmax ~565 nm, λemmax ~620 nm). Thus, excited state proton transfer (ESPT) explains the large Stokes shift. This work unambiguously characterizes green emission from the protonated acylimine chromophore of red fluorescent proteins. PMID:19708654

  14. Liquid ground state, gap, and excited states of a strongly correlated spin chain.

    PubMed

    Lesanovsky, Igor

    2012-03-01

    We present an exact solution of an experimentally realizable and strongly interacting one-dimensional spin system which is a limiting case of a quantum Ising model with long range interaction in a transverse and longitudinal field. Pronounced quantum fluctuations lead to a strongly correlated liquid ground state. For open boundary conditions the ground state manifold consists of four degenerate sectors whose quantum numbers are determined by the orientation of the edge spins. Explicit expressions for the entanglement properties, the exact excitation gap, as well as the exact wave functions for a couple of excited states are analytically derived and discussed. We outline how this system can be experimentally realized in a lattice gas of Rydberg atoms. PMID:22463419

  15. Wave packet dynamics in doubly excited states of He

    NASA Astrophysics Data System (ADS)

    Feist, Johannes; Nagele, Stefan; Persson, Emil; Burgdörfer, Joachim; Schneider, Barry

    2007-06-01

    We have developed a method for the ab initio simulation of the interaction of ultrashort laser pulses with helium atoms. We expand the two-electron Schr"odinger equation in coupled spherical harmonics and perform direct time integration utilizing either the Arnoldi-Lanczos or the Leapfrog method. The spatial discretization is performed in an FEDVR basis [1]. This allows for a numerically accurate description while possessing desirable computational features, e.g. a block-diagonal form of the kinetic energy matrix. We will present results on electron-electron correlation and wave packet dynamics in He. By using a suitable combination of attosecond XUV/EUV pulses, we prepare a wave packet in the doubly excited states of helium. The motion of this wave packet can be observed by using a probe pulse to induce ionization. We aim for a detailed understanding of the process by a careful study of the ionized electrons, e.g. by investigating doubly differential momentum spectra. [enumi] *B. I. Schneider and L. A. Collins. J. Non-Cryst. Solids 351, 1551.

  16. Electronic Structure and Dynamics of Higher-Lying Excited States in Light Harvesting Complex 1 from Rhodobacter sphaeroides.

    PubMed

    Dahlberg, Peter D; Ting, Po-Chieh; Massey, Sara C; Martin, Elizabeth C; Hunter, C Neil; Engel, Gregory S

    2016-06-23

    Light harvesting in photosynthetic organisms involves efficient transfer of energy from peripheral antenna complexes to core antenna complexes, and ultimately to the reaction center where charge separation drives downstream photosynthetic processes. Antenna complexes contain many strongly coupled chromophores, which complicates analysis of their electronic structure. Two-dimensional electronic spectroscopy (2DES) provides information on energetic coupling and ultrafast energy transfer dynamics, making the technique well suited for the study of photosynthetic antennae. Here, we present 2DES results on excited state properties and dynamics of a core antenna complex, light harvesting complex 1 (LH1), embedded in the photosynthetic membrane of Rhodobacter sphaeroides. The experiment reveals weakly allowed higher-lying excited states in LH1 at 770 nm, which transfer energy to the strongly allowed states at 875 nm with a lifetime of 40 fs. The presence of higher-lying excited states is in agreement with effective Hamiltonians constructed using parameters from crystal structures and atomic force microscopy (AFM) studies. The energy transfer dynamics between the higher- and lower-lying excited states agree with Redfield theory calculations. PMID:27232937

  17. State-averaged Monte Carlo configuration interaction applied to electronically excited states

    NASA Astrophysics Data System (ADS)

    Coe, J. P.; Paterson, M. J.

    2013-10-01

    We introduce state-averaging into the method of Monte Carlo configuration interaction (SA-MCCI) to allow the stable and efficient calculation of excited states. We show that excited potential curves for H3, including a crossing with the ground state, can be accurately reproduced using a small fraction of the full configuration interaction (FCI) space. A recently introduced error measure for potential curves [J. P. Coe and M. J. Paterson, J. Chem. Phys. 137, 204108 (2012)] is also shown to be a fair approach when considering potential curves for multiple states. We demonstrate that potential curves for LiF using SA-MCCI agree well with the FCI results and the avoided crossing occurs correctly. The seam of conical intersections for CH2 found by Yarkony [J. Chem. Phys. 104, 2932 (1996)] is used as a test for SA-MCCI and we compare potential curves from SA-MCCI with FCI results for this system for the first three triplet states. We then demonstrate the improvement from using SA-MCCI on the dipole of the 2 1A1 state of carbon monoxide. We then look at vertical excitations for small organic molecules up to the size of butadiene where the SA-MCCI energies and oscillator strengths are compared with CASPT2 values [M. Schreiber, M. R. Silva-Junior, S. P. A. Sauer, and W. Thiel, J. Chem. Phys. 128, 134110 (2008)]. We finally see if the SA-MCCI results for these excitation energies can be improved by using MCCIPT2 with approximate natural orbitals when the PT2 space is not onerously large.

  18. Describing excited state relaxation and localization in TiO2 nanoparticles using TD-DFT

    SciTech Connect

    Berardo, Enrico; Hu, Han -Shi; van Dam, Hubertus J. J.; Shevlin, Stephen A.; Woodley, Scott M.; Kowalski, Karol; Zwijnenburg, Martijn A.

    2014-02-26

    We have investigated the description of excited state relaxation in naked and hydrated TiO2 nanoparticles using Time-Dependent Density Functional Theory (TD-DFT) with three common hybrid exchange-correlation (XC) potentials; B3LYP, CAM-B3LYP and BHLYP. Use of TD-CAM-B3LYP and TD-BHLYP yields qualitatively similar results for all structures, which are also consistent with predictions of coupled cluster theory for small particles. TD-B3LYP, in contrast, is found to make rather different predictions; including apparent conical intersections for certain particles that are not observed with TD-CAM-B3LYP nor with TD-BHLYP. In line with our previous observations for vertical excitations, the issue with TD-B3LYP appears to be the inherent tendency of TD-B3LYP, and other XC potentials with no or a low percentage of Hartree-Fock Like Exchange, to spuriously stabilize the energy of charge-transfer (CT) states. Even in the case of hydrated particles, for which vertical excitations are generally well described with all XC potentials, the use of TD-B3LYP appears to result in CT-problems for certain particles. We hypothesize that the spurious stabilization of CT-states by TD-B3LYP even may drive the excited state optimizations to different excited state geometries than those obtained using TD-CAM-B3LYP or TD-BHLYP. In conclusion, focusing on the TD-CAM-B3LYP and TD-BHLYP results, excited state relaxation in naked and hydrated TiO2 nanoparticles is predicted to be associated with a large Stokes’ shift.

  19. Cyclometalated gold(III) trioxadiborrin complexes: studies of the bonding and excited states.

    PubMed

    Ayoub, Nicholas A; Browne, Amberle R; Anderson, Bryce L; Gray, Thomas G

    2016-03-01

    Trioxadiborrins are chelating ligands that assemble in dehydration reactions of boronic acids. They are structurally related to β-diketonate ligands, but have a 2-charge. Little is known of the bonding properties of trioxadiborrin ligands. Presented here are density-functional theory (DFT) studies of cyclometalated gold(III) trioxadiborrins. Substituent effects are evaluated, and comparison is made to the cyclometalating 2-(4-tolyl)pyridine (tpy) ligand on gold. The tpy ligand binds more strongly than any trioxadiborrin ligand considered here, and the two ligands bind competitively to gold. The 1,3-diphenyl trioxadiborrin ligand of 1 has a larger absolute binding enthalpy to gold than its β-diketonate analogue. Conjugation between boron and aryl substituents delocalizes charge and attenuates the trioxadiborrin's binding capacity. Steric effects that disrupt conjugation between boron and aryl substituents cause the trioxadiborrin to chelate more tightly. Fragment bond orders are divided into in-plane and out-of-plane contributions for square planar 1. In-plane bonding accounts for 88% of bond order between (tpy)Au2+ and the trioxadiborrin ligand. Cyclometalated gold(III) trioxadiborrin complexes were previously shown to be phosphorescent. Spin-unrestricted triplet-state geometry optimizations find that the ten largest excited-state distortions all occur on the tpy ligand. A plot of spin density in triplet 1 shows spin to reside predominantly on tpy. The 77 K luminescence spectrum of 1 is reported here. Time-dependent DFT and configuration interaction singles calculations (corrected for doubles excitations) overestimate the emission energy by ∼ 0.12 eV. PMID:26821088

  20. Measurements of charge state breeding efficiency at BNL test EBIS

    SciTech Connect

    Kondrashev, S.; Alessi, J.; Beebe, E.N.; Dickerson, C.; Ostroumov, P.N.; Pikin, A.; Savard, G.

    2011-04-02

    Charge breeding of singly charged ions is required to efficiently accelerate rare isotope ion beams for nuclear and astrophysics experiments, and to enhance the accuracy of low-energy Penning trap-assisted spectroscopy. An efficient charge breeder for the Californium Rare Isotope Breeder Upgrade (CARIBU) to the ANL Tandem Linear Accelerator System (ATLAS) facility is being developed using the BNL Test Electron Beam Ion Source (Test EBIS) as a prototype. Parameters of the CARIBU EBIS charge breeder are similar to those of the BNL Test EBIS except the electron beam current will be adjustable in the range from 1 to 2 {angstrom}. The electron beam current density in the CARIBU EBIS trap will be significantly higher than in existing operational charge state breeders based on the EBIS concept. The charge state breeding efficiency is expected to be about 25% for the isotope ions extracted from the CARIBU. For the success of our EBIS project, it is essential to demonstrate high breeding efficiency at the BNL Test EBIS tuned to the regime close to the parameters of the CARIBU EBIS at ANL. The breeding efficiency optimization and measurements have been successfully carried out using a Cs{sup +} surface ionization ion source for externally pulsed injection into the BNL Test EBIS. A Cs{sup +} ion beam with a total number of ions of 5 x 10{sup 8} and optimized pulse length of 70 {mu}s has been injected into the Test EBIS and charge-bred for 5.3 ms for two different electron beam currents 1 and 1.5 {angstrom}. In these experiments we have achieved 70% injection/extraction efficiency and breeding efficiency into the most abundant charge state 17%.

  1. The Structure of the Nucleon and it's Excited States

    SciTech Connect

    1995-02-20

    The past year has been an exciting and productive one for particle physics research at Abilene Christian University. The thrust of our experimental investigations is the study of the nucleon and its excited states. Laboratories where these investigations are presently being conducted are the AGS at Brookhaven, Fermilab and LAMPF. Some analysis of the data for experiments at the Petersburg Nuclear Physics Institute (Gatchina, Russia) is still in progress. Scheduling of activities at different laboratories inevitably leads to occasional conflicts. This likelihood is increased by the present budget uncertainties at the laboratories that make long-term scheduling difficult. For the most part, the investigators have been able to avoid such conflicts. Only one experiment received beam time in 1994 (E890 at the AGS). The situation for 1995-1996 also appears manageable at this point. E890 and another AGS experiment (E909) will run through May, 1995. El 178 at LAMPF is presently scheduled for August/September 1995. E866 at Fermilab is scheduled to start in Spring/Summer 1996. Undergraduate student involvement has been a key element in this research contract since its inception. Summer students participated at all of the above laboratories in 1994 and the same is planned in 1995. A transition to greater involvement by graduate students will provide cohesiveness to ACU involvement at a given laboratory and full-time on-site involvement in the longer running experiments at FNAL and BNL. Funds to support a full-time graduate student are requested this year. Finally, collaboration by Russian, Croatian and Bosnian scientists has proven to be mutually beneficial to these experimental programs and to the overall programs at the institutions involved. Past support has been augmented by other grants from government agencies and from the Research Council at Abilene Christian University. Additional funds are requested in this renewal to enable more programmatic support for these

  2. Ultrafast electron transfer reactions initiated by excited CT states of push pull perylenes

    NASA Astrophysics Data System (ADS)

    Miller, Scott E.; Zhao, Yongyu; Schaller, Richard; Mulloni, Viviana; Just, Eric M.; Johnson, Robert C.; Wasielewski, Michael R.

    2002-01-01

    Two new chromophores that absorb in the visible spectrum, the 9-( N-pyrrolidinyl)- and 9-( N-piperidinyl)perylene-3,4-dicarboximides, 5PMI and 6PMI, respectively, were synthesized and shown to possess lowest excited singlet states with about 70% charge transfer (CT) character. Changing the ring size of the cyclic amine from 5 to 6 significantly changes the energies of the CT states, as well as the redox potentials of the chromophores. These chromophores were linked to pyromellitimide (PI) and 1,8:4,5-naphthalenediimide (NI) electron acceptors using a single N-N bond between their respective imides to yield the corresponding donor-acceptor dyads 5PMI-PI, 5PMI-NI, 6PMI-PI, and 6PMI-NI. The donors and acceptors in these molecules are positioned relative to one another in a rod-like arrangement at fixed distances and restricted orientations. The rates of charge separation and recombination were measured using transient absorption spectroscopy. These chromophores were also used to prepare rigid donor-acceptor triads 5PMI-PI-NI and 6PMI-PI-NI, which display one- or two-step electron transfer mechanisms that depend on solvent polarity. These compounds exhibit a broad range of structure and media driven changes in electron transfer mechanism.

  3. Excited states properties of organic molecules: from density functional theory to the GW and Bethe-Salpeter Green's function formalisms.

    PubMed

    Faber, C; Boulanger, P; Attaccalite, C; Duchemin, I; Blase, X

    2014-03-13

    Many-body Green's function perturbation theories, such as the GW and Bethe-Salpeter formalisms, are starting to be routinely applied to study charged and neutral electronic excitations in molecular organic systems relevant to applications in photovoltaics, photochemistry or biology. In parallel, density functional theory and its time-dependent extensions significantly progressed along the line of range-separated hybrid functionals within the generalized Kohn-Sham formalism designed to provide correct excitation energies. We give an overview and compare these approaches with examples drawn from the study of gas phase organic systems such as fullerenes, porphyrins, bacteriochlorophylls or nucleobases molecules. The perspectives and challenges that many-body perturbation theory is facing, such as the role of self-consistency, the calculation of forces and potential energy surfaces in the excited states, or the development of embedding techniques specific to the GW and Bethe-Salpeter equation formalisms, are outlined. PMID:24516185

  4. Excited-state quantum phase transitions in the interacting boson model: Spectral characteristics of 0+ states and effective order parameter

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Zuo, Yan; Pan, Feng; Draayer, J. P.

    2016-04-01

    The spectral characteristics of the Lπ=0+ excited states in the interacting boson model are systematically investigated. It is found that various types of excited-state quantum phase transitions may widely occur in the model as functions of the excitation energy, which indicates that the phase diagram of the interacting boson model can be dynamically extended along the direction of the excitation energy. It has also been justified that the d -boson occupation probability ρ (E ) is qualified to be taken as the effective order parameter to identify these excited-state quantum phase transitions. In addition, the underlying relation between the excite-state quantum phase transition and the chaotic dynamics is also stated.

  5. A QM/MM Approach Using the AMOEBA Polarizable Embedding: From Ground State Energies to Electronic Excitations.

    PubMed

    Loco, Daniele; Polack, Étienne; Caprasecca, Stefano; Lagardère, Louis; Lipparini, Filippo; Piquemal, Jean-Philip; Mennucci, Benedetta

    2016-08-01

    A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented. The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation. PMID:27340904

  6. Adiabatic ab initio study of the BaH(+) ion including high energy excited states.

    PubMed

    Mejrissi, Leila; Habli, Héla; Ghalla, Houcine; Oujia, Brahim; Gadéa, Florent Xavier

    2013-07-01

    An adiabatic study of 1-34 (1,3)Σ(+) electronic states of barium hydride ion (BaH(+)) is presented for all states dissociating below the ionic limit Ba(2+)H(-). The 1-20 (1,3)Π and 1-12 (1,3)Δ states have been also investigated. In our approach, the valence electrons of the Ba(2+) ion described by an effective core potential (ECP) and core polarization potential (CPP) with l-dependent cutoff functions have been used. The ionic molecule BaH(+) has been treated as a two-electron system, and the full valence configuration interaction (CI) is easily achieved. The spectroscopic constants Re, De, Te, ωe, ωexe, and Be are derived. In addition, vibrational level spacing and permanent and transition dipole moments are determined and analyzed. Unusual potential shapes are found and also accidental quasidegeneracy in the vibrational spacing progression for various excited states. The (1)Σ(+) states exhibit ionic charge transfer avoided crossings series which could lead to neutralization or even H(-) formation in collisions of H(+) with Ba. PMID:23701525

  7. An insight into non-emissive excited states in conjugated polymers.

    PubMed

    Hu, Zhongjian; Willard, Adam P; Ono, Robert J; Bielawski, Christopher W; Rossky, Peter J; Vanden Bout, David A

    2015-01-01

    Conjugated polymers in the solid state usually exhibit low fluorescence quantum yields, which limit their applications in many areas such as light-emitting diodes. Despite considerable research efforts, the underlying mechanism still remains controversial and elusive. Here, the nature and properties of excited states in the archetypal polythiophene are investigated via aggregates suspended in solvents with different dielectric constants (ɛ). In relatively polar solvents (ɛ>∼ 3), the aggregates exhibit a low fluorescence quantum yield (QY) of 2-5%, similar to bulk films, however, in relatively nonpolar solvents (ɛ<∼ 3) they demonstrate much higher fluorescence QY up to 20-30%. A series of mixed quantum-classical atomistic simulations illustrate that dielectric induced stabilization of nonradiative charge-transfer (CT) type states can lead to similar drastic reduction in fluorescence QY as seen experimentally. Fluorescence lifetime measurement reveals that the CT-type states exist as a competitive channel of the formation of emissive exciton-type states. PMID:26391514

  8. An insight into non-emissive excited states in conjugated polymers

    PubMed Central

    Hu, Zhongjian; Willard, Adam P.; Ono, Robert J.; Bielawski, Christopher W.; Rossky, Peter J.; Vanden Bout, David A.

    2015-01-01

    Conjugated polymers in the solid state usually exhibit low fluorescence quantum yields, which limit their applications in many areas such as light-emitting diodes. Despite considerable research efforts, the underlying mechanism still remains controversial and elusive. Here, the nature and properties of excited states in the archetypal polythiophene are investigated via aggregates suspended in solvents with different dielectric constants (ɛ). In relatively polar solvents (ɛ>∼ 3), the aggregates exhibit a low fluorescence quantum yield (QY) of 2–5%, similar to bulk films, however, in relatively nonpolar solvents (ɛ<∼ 3) they demonstrate much higher fluorescence QY up to 20–30%. A series of mixed quantum-classical atomistic simulations illustrate that dielectric induced stabilization of nonradiative charge-transfer (CT) type states can lead to similar drastic reduction in fluorescence QY as seen experimentally. Fluorescence lifetime measurement reveals that the CT-type states exist as a competitive channel of the formation of emissive exciton-type states. PMID:26391514

  9. Exciton Transfer and Emergent Excitonic States in Oppositely-Charged Conjugated Polyelectrolyte Complexes.

    PubMed

    Hollingsworth, William R; Segura, Carmen; Balderrama, Jonathan; Lopez, Nathaniel; Schleissner, Pamela; Ayzner, Alexander L

    2016-08-11

    Photosynthetic organisms have mastered the use of "soft" macromolecular assemblies for light absorption and concentration of electronic excitation energy. Nature's design centers on an optically inactive protein-based backbone that acts as a host matrix for an array of light-harvesting pigment molecules. The pigments are organized in space such that excited states can migrate between molecules, ultimately delivering the energy to the reaction center. Here we report our investigation of an artificial light-harvesting energy transfer antenna based on complexes of oppositely charged conjugated polyelectrolytes (CPEs). The conjugated backbone and the charged side chains of the CPE lead to an architecture that simultaneously functions as a structural scaffold and an electronic energy "highway". We find that the process of ionic complex formation leads to a remarkable change in the excitonic wavefunction of the energy acceptor, which manifests in a dramatic increase in the fluorescence quantum yield. We argue that the extended backbone of the donor CPE effectively templates a planarized acceptor polymer, leading to excited states that are highly delocalized along the polymer backbone. PMID:27428604

  10. Investigation of plasma excitation. volume i. electron impact studies of selected ground state and excited state rare gas atoms. Final report 7 Jun 77-20 Sep 80

    SciTech Connect

    Lake, M.L.

    1981-08-01

    Experiments were undertaken to determine electron impact cross sections of atoms in metastable states. One or two electron guns were used to first produce atoms in metastable states, then further excite these atoms to other levels. Limits on certain cross sections of helium atoms were obtained, but the detection limits of the apparatus prevented exhaustive study. Excitation functions and cross sections of xenon were obtained in the wavelength range from 3000 A to 9000 A.

  11. Photodissociation path in H2 + induced by nonuniform optical near fields: Two-step excitation via vibrationally excited states

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Maiku; Nobusada, Katsuyuki

    2016-02-01

    In this paper, effects of the spatial nonuniformity of an optical near field (ONF) on the molecular photodissociation process are presented. The dissociation dynamics of H2 + was theoretically investigated by solving a non-Born-Oppenheimer Schrödinger equation. It was found that in addition to two dissociation mechanisms, which are one-photon and three-photon processes induced by uniform laser light excitation, the nonuniform ONF opens another dissociation path: two-step excitation mediated by vibrationally excited states. The nonuniformity of the ONF causes a transition between vibrational states that is forbidden according to conventional selection rules, leading to the dissociation path. The dependences of photodissociation on the intensity and nonuniformity of the ONF were calculated and the results validated the two-step dissociation mechanism.

  12. Silicon radiation detectors with oxide charge state compensation

    NASA Technical Reports Server (NTRS)

    Walton, J. T.; Goulding, F. S.

    1987-01-01

    This paper discusses the use of boron implantation on high resistivity P type silicon before oxide growth to compensate for the presence of charge states in the oxide and oxide/silicon interface. The presence of these charge states on high resistivity P type silicon produces an inversion layer which causes high leakage currents on N(+)P junctions and high surface conductance. Compensating the surface region by boron implantation is shown to result in oxide passivated N(+)P junctions with very low leakage currents and with low surface conductance.

  13. Excitation of atoms and molecules in collisions with highly charged ions. [Cyclotron Inst. , Texas A M Univ. , College Station, Texas

    SciTech Connect

    Watson, R.L.

    1993-01-01

    A study of the double ionization of He by high-energy N[sup 7+] ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N[sub 2], O[sub 2], and CO molecular ions produced in collisions with 97-MeV Ar[sup 14+] ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO[sup 2+] and CO[sup 3+] from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO[sup 1+] and CO[sup 2+] molecular ions, and the branching ratios for the most prominent charge division channels of CO[sup 2+] through CO[sup 7+] were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

  14. Excitation of atoms and molecules in collisions with highly charged ions. Progress report, January 1, 1990--December 1, 1992

    SciTech Connect

    Watson, R.L.

    1993-01-01

    A study of the double ionization of He by high-energy N{sup 7+} ions was extended up in energy to 40 MeV/amu. Coincidence time-of-flight studies of multicharged N{sub 2}, O{sub 2}, and CO molecular ions produced in collisions with 97-MeV Ar{sup 14+} ions were completed. Analysis of the total kinetic energy distributions and comparison with the available data for CO{sup 2+} and CO{sup 3+} from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization. The dissociation fractions for CO{sup 1+} and CO{sup 2+} molecular ions, and the branching ratios for the most prominent charge division channels of CO{sup 2+} through CO{sup 7+} were determined from time-of-flight singles and coincidence data. An experiment designed to investigate the orientation dependence of dissociative multielectron ionization of molecules by heavy ion impact was completed. Measurements of the cross sections for K-shell ionization of intermediate-Z elements by 30-MeV/amu H, N, Ne, and Ar ions were completed. The cross sections were determined for solid targets of Z = 13, 22, 26, 29, 32, 40, 42, 46, and 50 by recording the spectra of K x rays with a Si(Li) spectrometer.

  15. Double-hybrid density functional theory for excited electronic states of molecules

    NASA Astrophysics Data System (ADS)

    Grimme, Stefan; Neese, Frank

    2007-10-01

    Double-hybrid density functionals are based on a mixing of standard generalized gradient approximations (GGAs) for exchange and correlation with Hartree-Fock (HF) exchange and a perturbative second-order correlation part (PT2) that is obtained from the Kohn-Sham (GGA) orbitals and eigenvalues. This virtual orbital-dependent functional (dubbed B2PLYP) contains only two empirical parameters that describe the mixture of HF and GGA exchange (ax) and of the PT2 and GGA correlation (ac), respectively. Extensive testing has recently demonstrated the outstanding accuracy of this approach for various ground state problems in general chemistry applications. The method is extended here without any further empirical adjustments to electronically excited states in the framework of time-dependent density functional theory (TD-DFT) or the closely related Tamm-Dancoff approximation (TDA-DFT). In complete analogy to the ground state treatment, a scaled second-order perturbation correction to configuration interaction with singles (CIS(D)) wave functions developed some years ago by Head-Gordon et al. [Chem. Phys. Lett. 219, 21 (1994)] is computed on the basis of density functional data and added to the TD(A)-DFT/GGA excitation energy. The method is implemented by applying the resolution of the identity approximation and the efficiency of the code is discussed. Extensive tests for a wide variety of molecules and excited states (of singlet, triplet, and doublet multiplicities) including electronic spectra are presented. In general, rather accurate excitation energies (deviations from reference data typically <0.2eV) are obtained that are mostly better than those from standard functionals. Still, systematic errors are obtained for Rydberg (too low on average by about 0.3eV) and charge-transfer transitions but due to the relatively large ax parameter (0.53), B2PLYP outperforms most other functionals in this respect. Compared to conventional HF-based CIS(D), the method is more robust in

  16. Ultrafast excited state deactivation of doped porous anodic alumina membranes

    NASA Astrophysics Data System (ADS)

    Makhal, Abhinandan; Sarkar, Soumik; Pal, Samir Kumar; Yan, Hongdan; Wulferding, Dirk; Cetin, Fatih; Lemmens, Peter

    2012-08-01

    Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Förster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor-acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics.

  17. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    NASA Astrophysics Data System (ADS)

    Esboui, Mounir

    2015-07-01

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH3)2 complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH3)2 cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″(1πσ∗) and A'(1nσ∗) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A'(1ππ∗) and A″(1nπ∗) potential energy surfaces. For the unconstrained complex, potential energy profiles show two 1ππ∗-1πσ∗ conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  18. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    SciTech Connect

    Esboui, Mounir

    2015-07-21

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH{sub 3}){sub 2} complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH{sub 3}){sub 2} cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″({sup 1}πσ{sup ∗}) and A′({sup 1}nσ{sup ∗}) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A′({sup 1}ππ{sup ∗}) and A″({sup 1}nπ{sup ∗}) potential energy surfaces. For the unconstrained complex, potential energy profiles show two {sup 1}ππ{sup ∗}-{sup 1}πσ{sup ∗} conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  19. Early events associated with the excited state proton transfer in 2-(2{sup '}-pyridyl)benzimidazole

    SciTech Connect

    Burai, Tarak Nath; Mukherjee, Tushar Kanti; Lahiri, Priyanka; Panda, Debashis; Datta, Anindya

    2009-07-21

    2-(2{sup '}-pyridyl)benzimidazole (2PBI) undergoes excited state proton transfer (ESPT) in acidic solutions, leading to a tautomer emission at 460 nm. This photoprocess has been studied using ultrafast fluorescence spectroscopic techniques in acidic neat aqueous solutions, in viscous mixtures of glycerol with water, as well as in sucrose solutions. The tautomer is found to be stabilized in the more viscous medium, leading to a greater relative quantum yield as well as lifetime. The long rise time in tautomer emission is not affected by viscosity though. Rather, it appears to have the same value as the long component of the decay of the cationic excited state (C*). In addition to the subnanosecond lifetime reported earlier, C* is found to exhibit a decay time of 2 ps. This is assigned to its protonation to form the nonfluorescent dication in its excited state (D*) considering the ground and excited state pK{sub a} values reported earlier. An additional rising component of 100 ps is observed in the region of C* emission. This is likely to arise from a structural change or charge redistribution in C* immediately after its creation and before the phototautomerization.

  20. Haloalkane- Aromatic Complexes in the Ground and Excited States. Molecular Orbital Calculation

    NASA Astrophysics Data System (ADS)

    Brinn, I. M.

    1980-04-01

    CNDO/2 calculations have been carried out on a series of haloalkane-aromatic 1: 1 complexes in the ground and first excited singlet states and one 2 : 1 complex in the ground state. Calculated stabilities agree very well with reported experimental results for the ground state. Our calculations indicate that the substituent effect on complex stability in excited states will be the opposite of that found for the ground state.

  1. Effects of charge inhomogeneities on elementary excitations in La2-xSrxCuO₄

    DOE PAGESBeta

    Park, S. R.; Hamann, A.; Pintschovius, L.; Lamago, D.; Khaliullin, G.; Fujita, M.; Yamada, K.; Gu, G. D.; Tranquada, J. M.; Reznik, D.

    2011-12-12

    Purely local experimental probes of many copper oxide superconductors show that their electronic states are inhomogeneous in real space. For example, scanning tunneling spectroscopic imaging shows strong variations in real space, and according to nuclear quadrupole resonance (NQR) studies, the charge distribution in the bulk varies on the nanoscale. However, the analysis of the experimental results utilizing spatially averaged probes often ignores this fact. We have performed a detailed investigation of the doping dependence of the energy and linewidth of the zone-boundary Cu-O bond-stretching vibration in La2-xSrxCuO₄ by inelastic neutron scattering. Both our results as well as previously reported angle-dependentmore » momentum widths of the electronic spectral function detected by angle-resolved photoemission can be reproduced by including the same distribution of local environments extracted from the NQR analysis.« less

  2. Non-Abelian states in Fractional Quantum Hall effect in charge carrier hole systems

    NASA Astrophysics Data System (ADS)

    Simion, George; Lyanda-Geller, Yuli

    Quasiparticle excitations obeying non-Abelian statistics represent the key element of topological quantum computing. Crossing of levels and strong coupling between angular momentum and orbital motion, described by Luttinger Hamiltonian, make properties of charge carrier holes different from those of electrons. Peculiarities of hole spectrum in magnetic field provide an opportunity for controlling Landau level mixing in charge carier hole systems. In order to describe Fractional Quantum Hall effect for holes, we propose a method to map hole spectrum and wavefunctions using a spherical shell. We investigate the experimentally observed ν = 1 / 2 state in spherical geometry. Haldane pseudopotentials are computed and the effect of Landau level mixing is evaluated. Exact diagonalization of Coulomb interaction in systems with eight to fourteen holes is performed. We determine that the ground state superposition with Abelian 331 state is very small and the overlap with Moore-Read state is significant. The quasihole and quasielectron excitations are discussed. Research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010544.

  3. Influence of ligand substitution on excited state structural dynamics in Cu(I) bis-phenanthroline complexes.

    SciTech Connect

    Lockard, J. V.; Kabehie, S.; Zink, J. I.; Smolentsev, G.; Soldatov, A.; Chen, L. X.

    2010-01-01

    This study explores the influences of steric hindrance and excited state solvent ligation on the excited state dynamics of Cu{sup I} diimine complexes. Ultrafast excited state dynamics of Cu(I)bis(3,8-di(ethynyltrityl)-1,10-phenanthroline) [Cu{sup I}(detp){sub 2}]{sup +} are measured using femtosecond transient absorption spectroscopy. The steady state electronic absorption spectra and measured lifetimes are compared to those of Cu(I)bis(1,10-phenanthroline), [Cu{sup I}(phen){sub 2}]{sup +}, and Cu(I)bis(2-9-dimethyl-1,10-phenanthroline), [Cu{sup I}(dmp){sub 2}]{sup +}, model complexes to determine the influence of different substitution patterns of the phenanthroline ligand on the structural dynamics associated with the metal to ligand charge transfer excited states. Similarities between the [Cu{sup I}(detp){sub 2}]{sup +} and [Cu{sup I}(phen){sub 2}]{sup +} excited state lifetimes were observed in both coordinating and noncoordinating solvents and attributed to the lack of steric hindrance from substitution at the 2- and 9-positions. The solution-phase X-ray absorption spectra of [Cu{sup I}(detp){sub 2}]{sup +}, [Cu{sup I}(phen){sub 2}]{sup +}, and [Cu{sup I}(dmp){sub 2}]{sup +} are reported along with finite difference method calculations that are used to determine the degree of ground state dihedral angle distortion in solution and to account for the pre-edge features observed in the XANES region.

  4. Ab Initio Calculations of Singlet and Triplet Excited States of Chlorine Nitrate and Nitric Acid

    NASA Technical Reports Server (NTRS)

    Grana, Ana M.; Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    Ab initio calculations of vertical excitations to singlet and triplet excited states of chlorine nitrate and nitric acid are reported. The nature of the electronic transitions are examined by decomposing the difference density into the sum of detachment and attachment densities. Counterparts for the three lowest singlet excited states of nitric acid survive relatively unperturbed in chlorine nitrate, while other low-lying singlet states of chlorine nitrate appear to be directly dissociative in the ClO chromophore. These results suggest an assignment of the two main peaks in the experimental chlorine nitrate absorption spectrum. In addition, triplet vertical excitations and the lowest optimized triplet geometries of both molecules are studied.

  5. Excited state lifetime during photostimulated desorption of no from a Pt surface

    NASA Astrophysics Data System (ADS)

    Magkoev, T. T.

    1998-07-01

    We analyze the rotational energy distribution N(J) for NO molecules desorbed from a Pt (111) surface, taking into account the valence electron excitations, using a simple impulse model. We find a linear dependence between ln N(J) and (Er)1/2, where Er is the rotational energy of the desorbed molecules. The excited state lifetime and the critical residence time in the excited state, evaluated from the given dependences, are close to each other, and in order of magnitude are 10-15 s. We also estimate the frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state.

  6. Dynamic battery cell model and state of charge estimation

    NASA Astrophysics Data System (ADS)

    Wijewardana, S.; Vepa, R.; Shaheed, M. H.

    2016-03-01

    Mathematical modelling and the dynamic simulation of battery storage systems can be challenging and demanding due to the nonlinear nature of the battery chemistry. This paper introduces a new dynamic battery model, with application to state of charge estimation, considering all possible aspects of environmental conditions and variables. The aim of this paper is to present a suitable convenient, generic dynamic representation of rechargeable battery dynamics that can be used to model any Lithium-ion rechargeable battery. The proposed representation is used to develop a dynamic model considering the thermal balance of heat generation mechanism of the battery cell and the ambient temperature effect including other variables such as storage effects, cyclic charging, battery internal resistance, state of charge etc. The results of the simulations have been used to study the characteristics of a Lithium-ion battery and the proposed battery model is shown to produce responses within 98% of known experimental measurements.

  7. The calculation of electron chemical potential and ion charge state and their influence on plasma conductivity in electrical explosion of metal wire

    SciTech Connect

    Shi, Zongqian; Wang, Kun; Li, Yao; Shi, Yuanjie; Wu, Jian; Jia, Shenli

    2014-03-15

    The electron chemical potential and ion charge state (average ion charge and ion distribution) are important parameters in calculating plasma conductivity in electrical explosion of metal wire. In this paper, the calculating method of electron chemical potential and ion charge state is discussed at first. For the calculation of electron chemical potential, the ideal free electron gas model and Thomas-Fermi model are compared and analyzed in terms of the coupling constant of plasma. The Thomas-Fermi ionization model, which is used to calculate ion charge state, is compared with the method based on Saha equation. Furthermore, the influence of electron degenerated energy levels and ion excited states in Saha equation on the ion charge state is also analyzed. Then the influence of different calculating methods of electron chemical potential and ion charge state on plasma conductivity is discussed by applying them in the Lee-More conductivity model.

  8. Variational polaron self-interaction-corrected total-energy functional for charge excitations in insulators

    NASA Astrophysics Data System (ADS)

    Sadigh, Babak; Erhart, Paul; Ã berg, Daniel

    2015-08-01

    We conduct a detailed investigation of the polaron self-interaction (pSI) error in standard approximations to the exchange-correlation (XC) functional within density-functional theory (DFT). The pSI leads to delocalization error in the polaron wave function and energy, as calculated from the Kohn-Sham (KS) potential in the native charge state of the polaron. This constitutes the origin of the systematic failure of DFT to describe the polaron formation in band insulators. It is shown that the delocalization error in these systems is, however, largely absent in the KS potential of the closed-shell neutral charge state. This leads to a modification of the DFT total-energy functional that corrects the pSI in the XC functional. The resulting pSIC-DFT method constitutes an accurate parameter-free ab initio methodology for calculating polaron properties in insulators at a computational cost that is orders of magnitude smaller than hybrid XC functionals. Unlike approaches that rely on parametrized localized potentials such as DFT+U , the pSIC-DFT method properly captures both site and bond-centered polaron configurations. This is demonstrated by studying formation and migration of self-trapped holes in alkali halides (bond-centered) as well as self-trapped electrons in an elpasolite compound (site-centered). The pSIC-DFT approach consistently reproduces the results obtained by hybrid XC functionals parametrized by DFT+G0W0 calculations. Finally, we generalize the pSIC approach to hybrid functionals, and show that in stark contrast to conventional hybrid calculations of polaron energies, the pSIC-hybrid method is insensitive to the parametrization of the hybrid XC functional. On this basis, we further rationalize the success of the pSIC-DFT approach.

  9. Conformation-Controlled Diplatinum(II)-Ferrocene Dyads to Achieve Long-Lived Charge-Separated States.

    PubMed

    Wang, Ge-Xia; Feng, Ke; Crossley, Maxwell J; Xing, Ling-Bao; Xiao, Hong-Yan; Li, Wen; Tung, Chen-Ho; Wu, Li-Zhu

    2016-08-16

    Square-planar polypyridyl platinum(II) complexes possess a rich range of structural and spectroscopic properties that are ideal for designing artificial photosynthetic centers. Taking advantage of the directionality in the charge-transfer excitation from the metal to the polypyridyl ligand, we describe here diplatinum(II)-ferrocene dyads, open-butterfly-like dyad 1 and closed-butterfly-like dyad 2, which were designed to understand the conformation and orientation effects to prolong the lifetime of charge-separated state. In contrast to the open-butterfly-like dyad 1, the closed-butterfly-like dyad 2 shows three-times long lifetime of charge separated state upon photoexcitation, demonstrating that the orientation in the rigid structure of dyad 2 is a very important issue to achieve long-lived charge separated state. PMID:27339465

  10. UV-Induced Charge Transfer States in DNA Promote Sequence Selective Self-Repair.

    PubMed

    Bucher, Dominik Benjamin; Kufner, Corinna Lucia; Schlueter, Alexander; Carell, Thomas; Zinth, Wolfgang

    2016-01-13

    Absorption of UV-radiation in nucleotides initiates a number of photophysical and photochemical processes, which may finally cause DNA damage. One major decay channel of photoexcited DNA leads to reactive charge transfer states. This study shows that these states trigger self-repair of DNA photolesions. The experiments were performed by UV spectroscopy and HPLC on different single and double stranded oligonucleotides containing a cyclobutane pyrimidine dimer (CPD) lesion. In a first experiment we show that photoexcitation of adenine adjacent to a CPD has no influence on this lesion. However, excitation of a guanine (G) adenine (A) sequence leads to reformation of the intact thymine (T) bases. The involvement of two bases for the repair points to a long-living charge transfer state between G and A to be responsible for the repair. The negatively charged A radical anion donates an electron to the CPD, inducing ring splitting and repair. In contrast, a TA sequence, having an inverted charge distribution (T radical anion, A radical cation), is not able to repair the CPD lesion. The investigations show that the presence of an adjacent radical ion is not sufficient for repair. More likely it is the driving power represented by the oxidation potential of the radical ion, which controls the repair. Thus, repair capacities are strongly sequence-dependent, creating DNA regions with different tendencies of self-repair. This self-healing activity represents the simplest sequence-dependent DNA repair system. PMID:26651219

  11. Comprehensive investigation of the excited-state dynamics of push-pull triphenylamine dyes as models for photonic applications.

    PubMed

    Ishow, Eléna; Clavier, Gilles; Miomandre, Fabien; Rebarz, Mateusz; Buntinx, Guy; Poizat, Olivier

    2013-09-01

    A series of emitting push-pull triarylamine derivatives, models of their widely used homologues in photonics and organic electronics, was investigated by steady-state and time-resolved spectroscopy. Their structural originality stems from the sole change of the electron-withdrawing substituent X (-H: 1, -CN: 2, -NO2: 3, -CHC(CN)2: 4), giving rise to efficient emission tuning from blue to red upon increasing the X electron-withdrawing character. All compounds are highly fluorescent in alkanes. The more polar compounds 2-4 undergo considerable Stokes shift and emission quenching in polar solvents. Femtosecond transient absorption data allowed us to identify the nature of the emissive state which varies as a function of the compound and surrounding polarity. A long-lived ππ* excited state with weak charge transfer character was found for 1. This excited state evolves into a long-lived ICT state with red-shifted emission for 2 in polar solvents. For 3 and 4, the ICT state is directly populated in all solvents. Long-lived and emissive in n-hexane, it relaxes in toluene to a new ICT' conformation with stronger charge transfer character and enhanced Stokes shift. In more polar THF, ethanol, and nitrile solvents, ICT relaxes to a dark excited state ICT'' with viscosity-dependent kinetics (<10 ps). The ICT'' state lifetime drops with increasing solvent polarity (150 ps for 3 in THF, 8.5 ps in butyronitrile, 1.9 ps in acetonitrile), denoting an efficient radiationless deactivation to the ground state (back charge transfer). This result reveals a very small S0-S1 energy gap at the relaxed ICT'' geometry, with a possible close-lying S0-S1 conical intersection, which suggests that the ICT → ICT'' process results from a structural change involving a large-amplitude molecular distortion. This fast structural change can account for the strong fluorescence quenching observed for 3 and 4 in polar solvents. Finally, the magnitude of intersystem crossing between the singlet and

  12. Experimental and Quantum-Chemical Study of Electronically Excited States of Protolytic Isovanillin Species

    NASA Astrophysics Data System (ADS)

    Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Yu.

    2014-05-01

    Methods of electronic spectroscopy and quantum chemistry are used to compare protolytic vanillin and isovanillin species. Three protolytic species: anion, cation, and neutral are distinguished in the ground state of the examined molecules. Vanillin and isovanillin in the ground state in water possess identical spectral characteristics: line positions and intensities in the absorption spectra coincide. Minima of the electrostatic potential demonstrate that the deepest isomer minimum is observed on the carbonyl oxygen atom. However, investigations of the fluorescence spectra show that the radiative properties of isomers differ. An analysis of results of quantum-chemical calculations demonstrate that the long-wavelength ππ* transition in the vanillin absorption spectra is formed due to electron charge transfer from the phenol part of the molecule to oxygen atoms of the methoxy and carbonyl groups, and in the isovanillin absorption spectra, it is formed only on the oxygen atom of the methoxy group. The presence of hydroxyl and carbonyl groups in the structure of the examined molecules leads to the fact that isovanillin in the ground S0 state, the same as vanillin, possesses acidic properties, whereas in the excited S1 state, they possess basic properties. A comparison of the рKа values of aqueous solutions demonstrates that vanillin possesses stronger acidic and basic properties in comparison with isovanillin.

  13. Instability of insulating states in optical lattices due to collective phonon excitations

    NASA Astrophysics Data System (ADS)

    Yukalov, V. I.; Ziegler, K.

    2015-02-01

    The effect of collective phonon excitations on the properties of cold atoms in optical lattices is investigated. These phonon excitations are collective excitations, whose appearance is caused by intersite atomic interactions correlating the atoms, and they do not arise without such interactions. These collective excitations should not be confused with lattice vibrations produced by an external force. No such force is assumed. But the considered phonons are purely self-organized collective excitations, characterizing atomic oscillations around lattice sites, due to intersite atomic interactions. It is shown that these excitations can essentially influence the possibility of atoms' being localized. The states that would be insulating in the absence of phonon excitations can become delocalized when these excitations are taken into account. This concerns long-range as well as local atomic interactions. To characterize the region of stability, the Lindemann criterion is used.

  14. Fluorescence sensing of anions based on inhibition of excited-state intramolecular proton transfer.

    PubMed

    Wu, Yunkou; Peng, Xiaojun; Fan, Jiangli; Gao, Shang; Tian, Maozhong; Zhao, Jianzhang; Sun, Shiguo

    2007-01-01

    Condensation of 2-(2'-aminophenyl)benzoxazole with p-toluenesulfonyl chloride and phenyl isocyanate yields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular proton transfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbed by basic anions such as F-, CH3COO-, and H2PO4- by deprotonating the sulfonamide unit, whereas in the case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH3COO--urea intermolecular hydrogen bond complex, and these two types of inhibition mechanisms consequently result in different ratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit the ESIPT. Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these three anionic substrates of similar basicity and surface charge density. PMID:17194082

  15. Excitation energies of double isobar-analog states in heavy nuclei

    SciTech Connect

    Poplavskii, I. V.

    1988-12-01

    Several new relationships are established for isomultiplets on the basis of a theory in which the Coulomb coupling constant (CCC) is allowed to be complex. In particular, the following rule is formulated: the energies for fission or decay of members of an isomultiplet into a charged cluster and members of the corresponding daughter isomultiplet are equidistant. This relationship is well satisfied for isomultiplets with /ital A/less than or equal to60. By extrapolating the rule for fission and decay energies to the region of heavy nuclei, the excitation energies /ital E//sub /ital x// of double isobar-analog states (DIASs) are found for the nuclei /sup 197,199/Hg, /sup 205/Pb, /sup 205 - -209/Po, /sup 209/At, and /sup 238/Pu. A comparison of the computed energies /ital E//sub /ital x// with the experimentally measured values for /sup 208/Po attest to the reliability and good accuracy of the method proposed here when used to determine the excitation energies of DIASs in heavy nuclei.

  16. Fast electronic resistance switching involving hidden charge density wave states

    PubMed Central

    Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.

    2016-01-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T–TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483

  17. Fast electronic resistance switching involving hidden charge density wave states

    NASA Astrophysics Data System (ADS)

    Vaskivskyi, I.; Mihailovic, I. A.; Brazovskii, S.; Gospodaric, J.; Mertelj, T.; Svetin, D.; Sutar, P.; Mihailovic, D.

    2016-05-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states.

  18. Fast electronic resistance switching involving hidden charge density wave states.

    PubMed

    Vaskivskyi, I; Mihailovic, I A; Brazovskii, S; Gospodaric, J; Mertelj, T; Svetin, D; Sutar, P; Mihailovic, D

    2016-01-01

    The functionality of computer memory elements is currently based on multi-stability, driven either by locally manipulating the density of electrons in transistors or by switching magnetic or ferroelectric order. Another possibility is switching between metallic and insulating phases by the motion of ions, but their speed is limited by slow nucleation and inhomogeneous percolative growth. Here we demonstrate fast resistance switching in a charge density wave system caused by pulsed current injection. As a charge pulse travels through the material, it converts a commensurately ordered polaronic Mott insulating state in 1T-TaS2 to a metastable electronic state with textured domain walls, accompanied with a conversion of polarons to band states, and concurrent rapid switching from an insulator to a metal. The large resistance change, high switching speed (30 ps) and ultralow energy per bit opens the way to new concepts in non-volatile memory devices manipulating all-electronic states. PMID:27181483

  19. Calculation of Ion Charge State Distributions After Inner-Shell Ionization in Xe Atom

    SciTech Connect

    Mohammedein, Adel M.; Ghoneim, Adel A.; Kandil, Kandil M.; Kadad, Ibrahim M.

    2010-01-05

    The vacancy cascades following initial inner-shell vacancies in single and multi-ionized atoms often lead to highly charged residual ions. The inner-shell vacancy produced by ionization processes may decay by either a radiative or non-radiative transition. In addition to the vacancy filling processes, there is an electron shake off process due to the change of core potential of the atom. In the calculation of vacancy cascades, the radiative (x-ray) and non-radiative (Auger and Coster-Kronig) branching ratios give valuable information on the de-excitation dynamics of an atom with inner-shell vacancy. The production of multi-charged ions yield by the Auger cascades following inner shell ionization of an atom has been studied both experimentally and theoretically. Multi-charged Xe ions following de-excitation of K-, L{sub 1}-, L{sub 2,3}-, M{sub 1}-, M{sub 2,3}- and M{sub 4,5} subshell vacancies are calculated using Monte-Carlo algorithm to simulate the vacancy cascade development. Fluorescence yield (radiative) and Auger, Coster- Kronig yield (non- radiative) are evaluated. The decay of K hole state through radiative transitions is found to be more probable than non-radiative transitions in the first step of de-excitation. On the other hand, the decay of L, M vacancies through non-radiative transitions are more probable. The K shell ionization in Xe atom mainly yields Xe{sup 7+}, Xe{sup 8+}, Xe{sup 9+} and Xe{sup 10+} ions, and the charged X{sup 8+} ions are the highest. The main product from the L{sub 1}- shell ionization is found to be Xe{sup 8+}, Xe{sup 9+} ions, while the charged Xe{sup 8+} ions predominate at L{sub 2,3} hole states. The charged Xe{sup 6+}, Xe{sup 7+} and Xe{sup 8+} ions mainly yield from 3s{sub 1/2} and 3p{sub 1/2,3/2} ionization, while Xe in 3d{sub 3/2,5/2} hole states mainly turns into Xe{sup 4+} and Xe{sup 5+} ions. The present results are found to agree well with the experimental data.

  20. Charge-state enhancement for radioactive beam post-acceleration

    SciTech Connect

    Nolen, J.A.; Dooling, J.

    1995-08-01

    A critical question for an ISOL-type radioactive-beam facility, such as that being discussed by the North American Isospin Laboratory Committee, is the efficiency and q/m of the ion source for the radioactive species. ISOLDE at CERN demonstrated that high efficiency is obtained for a wide variety of species in the 1{sup +} charge state. These ion sources also generally have excellent transverse emittances and low energy spreads. One possibility is to use this proven technology plus an ionizer stage to increase the output of such sources to 2, 3, or 4{sup +} with high efficiency. We are currently investigating technical options for such charge-state enhancement. There is a proposal by a Heidelberg/ISOLDE collaboration to build a {open_quotes}charge-state breeder{close_quotes} as part of an experiment called REX-ISOLDE. This concept would deliver batches of radioactive ions with low duty cycle, optimized for relatively low-intensity secondary beams, on the order of 10{sup 6}/sec. We are independently doing simulations of an alternative approach, called the Electron-Beam Charge-State Amplifier (EBQA), which would yield DC beams with improved transverse emittance and would not have the intensity limitation of the batch transfer process. The cost and efficiency of the EBQA will have to be compared with those of a normally-conducting CW RFQ followed by ion stripping, as alternatives for the first stage of a secondary ion accelerator.