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Sample records for electronic excited states

  1. 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.

  2. 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.

  3. 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.

  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. 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.

  6. 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.

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

    PubMed

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

    2016-02-28

    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. PMID:26931702

  8. 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

  9. 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.

  10. 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.

  11. 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.

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

    PubMed

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

    2013-10-31

    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

  13. 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

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

    NASA Astrophysics Data System (ADS)

    Ramon, John Glenn Santos

    , we examine the effect of the nanoscale interfacial morphology and solvation on the electronic excited states of TFB/F8BT. Here, we employ time-dependent density functional theory (TD-DFT) to investigate the relevant excited states of two stacking configurations. We show that the calculated states agree with the excited states responsible for the experimentally observed emission peaks and that these states are blue shifted relative to those of the isolated chain. Furthermore, slight lateral shifts in the stacking orientation not only shift the excited state energies; more importantly, they alter the nature of these states altogether. Lastly, we see that solvation greatly stabilizes the charge-transfer states.

  15. Electronic excited States of polynucleotides: a study by electroabsorption spectroscopy.

    PubMed

    Krawczyk, Stanislaw; Luchowski, Rafal

    2007-02-01

    Electroabsorption spectra were obtained for single-stranded polynucleotides poly(U), poly(C), poly(A), and poly(G) in glycerol/water glass at low temperature, and the differences in permanent dipole moment (Deltamu) and polarizability (Deltaalpha) were estimated for several spectral ranges covering the lowest energy absorption band around 260 nm. In each spectral range, the electrooptical parameters associated with apparent features in the absorption spectrum exhibit distinct values representing either a dominant single transition or the resultant value for a group of a relatively narrow cluster of overlapping transitions. The estimated spacing in energy between electronic origins of these transitions is larger than the electronic coupling within the Coulombic interaction model which is usually adopted in computational studies. The electroabsorption data allow us to distinguish a weak electronic transition associated with a wing in polynucleotide absorption spectra, at an energy below the electronic origin in absorption spectra of monomeric nucleobases. In poly(C) and poly(G), these low-energy transitions are related to increased values of Deltamu and Deltaalpha, possibly indicating a weak involvement of charge resonance in the respective excited states. A model capable of explaining the origin of low-energy excited states, based on the interaction of pipi* and npi* transitions in neighboring bases, is introduced and briefly discussed on the grounds of point dipole interaction. PMID:17266277

  16. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  18. 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.

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

    SciTech Connect

    Campbell, L.; Green, M. A.; Brunger, M. J.; Teubner, P. J. O.; Cartwright, D. C.

    2000-02-01

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

  20. 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.

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

    PubMed

    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. Excited State Electronic Properties of Sodium Iodide and Cesium Iodide

    SciTech Connect

    Campbell, Luke W.; Gao, Fei

    2013-05-01

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

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

    PubMed

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

    2015-06-11

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

  4. Integral cross sections for electron impact excitation of vibrational and electronic states in phenol.

    PubMed

    Neves, R F C; Jones, D B; Lopes, M C A; Blanco, F; García, G; Ratnavelu, K; Brunger, M J

    2015-05-21

    We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15-250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties.

  5. Two-Photon Excitation of trans-Stilbene: Spectroscopy and Dynamics of Electronically Excited States above S1.

    PubMed

    Houk, Amanda L; Zheldakov, Igor L; Tommey, Tyler A; Elles, Christopher G

    2015-07-23

    The photoisomerization dynamics of trans-stilbene have been well studied in the lowest excited state, but much less is known about the behavior following excitation to higher-lying electronically excited states. This contribution reports a combined study of the spectroscopy and dynamics of two-photon accessible states above S1. Two-photon absorption (2PA) measurements using a broadband pump-probe technique reveal distinct bands near 5.1 and 6.4 eV. The 2PA bands have absolute cross sections of 40 ± 16 and 270 ± 110 GM, respectively, and a pump-probe polarization dependence that suggests both of the transitions access Ag-symmetry excited states. Separate transient absorption measurements probe the excited-state dynamics following two-photon excitation into each of the bands using intense pulses of 475 and 380 nm light, respectively. The initially excited states rapidly relax via internal conversion, leading to the formation of an S1 excited-state absorption band that is centered near 585 nm and evolves on a time scale of 1-2 ps due to intramolecular vibrational relaxation. The subsequent evolution of the S1 excited-state absorption is identical to the behavior following direct one-photon excitation of the lowest excited state at 4.0 eV. The complementary spectroscopy and dynamics measurements provide new benchmarks for computational studies of the electronic structure and dynamics of this model system on excited states above S1. Probing the dynamics of molecules in their higher-lying excited states is an important frontier in chemical reaction dynamics.

  6. Total Electron Scattering and Electronic State Excitations Cross Sections for O_2, CO, and CH_4

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    Available electron collision cross section data concerning total and elastic scattering, vibrationalexcitation, and ionization for O_2, CO, and CH_4 have been critically reviewed, and a set of crosssections for modeling of planetary atmospheric behavior is recommended. Utilizing theserecommended cross sections, we derived total electronic state excitation cross sections and upperlimits for dissociation cross sections, which in the case of CH_4 should very closely equal the actualdissociation cross section.

  7. 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.

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

    PubMed

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

    2015-02-12

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

  9. 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.

  10. 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.

  11. Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

    NASA Technical Reports Server (NTRS)

    Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.

  12. 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.

  13. Electron impact excitation and assignment of the low-lying electronic states of CO2

    NASA Technical Reports Server (NTRS)

    Hall, R. I.; Trajmar, S.

    1973-01-01

    Electron scattering spectra of CO2 are reported in the 7 to 10 eV energy-loss range, at energies of 0.2, 0.35, 0.6, 0.7, and 7.0 eV above threshold, and at a scattering angle of 90 deg. Several new distinct overlapping continua with weak, diffuse bands superimposed are observed to lie in this energy-loss range. The experimental spectra are discussed in the light of recent ab initio configuration-interaction calculations of the vertical transition energies of CO2. The experimental spectra are shown to be consistent with the excitation states of CO2.

  14. Dissociative excitation of the N(+)(5S) state by electron impact on N2 - Excitation function and quenching

    NASA Technical Reports Server (NTRS)

    Erdman, P. W.; Zipf, E. C.

    1986-01-01

    Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.

  15. Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States.

    PubMed

    Tuna, Deniz; Lu, You; Koslowski, Axel; Thiel, Walter

    2016-09-13

    The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments. PMID:27380455

  16. Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States.

    PubMed

    Tuna, Deniz; Lu, You; Koslowski, Axel; Thiel, Walter

    2016-09-13

    The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments.

  17. Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

    NASA Astrophysics Data System (ADS)

    Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

    2016-10-01

    We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

  18. Two-electron excitation in slow ion-atom collisions: Excitation mechanisms and interferences among autoionizing states

    SciTech Connect

    Kimura, M. Rice Univ., Houston, TX . Dept. of Physics)

    1990-01-01

    The two-electron capture or excitation process resulting from collisions of H{sup +} and O{sup 6+} ions with He atoms in the energy range from 0.5 keV/amu to 5 keV/amu is studied within a molecular representation. The collision dynamics for formation of doubly excited O{sup 4+} ions and He** atoms and their (n{ell}, n{prime}{ell}{prime}) populations are analyzed in conjunction with electron correlations. Autoionizing states thus formed decay through the Auger process. An experimental study of an ejected electron energy spectrum shows ample structures in addition to two characteristic peaks that are identified by atomic and molecular autoionizations. These structures are attributable to various interferences among electronic states and trajectories. We examine the dominant sources of the interferences. 12 refs., 5 figs.

  19. Nature of Electronically Excited States of Organic Compounds and Processes of Nonradiative Conversion

    NASA Astrophysics Data System (ADS)

    Mayer, G. V.; Plotnikov, V. G.; Artyukhov, V. Ya.

    2016-08-01

    Models of quantum-chemical calculation of rate constants for internal processes and intersystem crossing in polyatomic molecules are considered. The influence of the nature of electronically excited states in organic compounds is investigated. It is shown that the explicit allowance for the nature of wave functions of electronic states for estimation of electronic matrix elements of nonadiabaticity operators and spin-orbit interaction allows photophysical processes in organic compounds to be considered in detail.

  20. Electron energy-loss spectroscopy of excited states of the pyridine molecules

    NASA Astrophysics Data System (ADS)

    Linert, Ireneusz; Zubek, Mariusz

    2016-04-01

    Electron energy-loss spectra of the pyridine, C5H5N, molecules in the gas phase have been measured to investigate electronic excitation in the energy range 3.5-10 eV. The applied wide range of residual electron energy and the scattering angle range from 10° to 180° enabled to differentiate between optically-allowed and -forbidden transitions. These measurements have allowed vertical excitation energies of the triplet excited states of pyridine to be determined and tentative assignments of these states to be proposed. Some of these states have not been identified in the previous works. 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.

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

    SciTech Connect

    Hoffman, M.Z.

    1992-07-31

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

  2. UV-induced DNA Damage: The Role of Electronic Excited States.

    PubMed

    Markovitsi, Dimitra

    2016-01-01

    The knowledge of the fundamental processes induced by the direct absorption of UV radiation by DNA allows extrapolating conclusions drawn from in vitro studies to the in-vivo DNA photoreactivity. In this respect, the characterization of the DNA electronic excited states plays a key role. For a long time, the mechanisms of DNA lesion formation were discussed in terms of generic "singlet" and "triplet" excited state reactivity. However, since the beginning of the 21(st) century, both experimental and theoretical studies revealed the existence of "collective" excited states, i.e. excited states delocalized over at least two bases. Two limiting cases are distinguished: Frenkel excitons (delocalized ππ* states) and charge-transfer states in which positive and negative charges are located on different bases. The importance of collective excited states in photon absorption (in particular in the UVA spectral domain), the redistribution of the excitation energy within DNA, and the formation of dimeric pyrimidine photoproducts is discussed. The dependence of the behavior of the collective excited states on conformational motions of the nucleic acids is highlighted.

  3. Electron impact excitation of autoionising states of krypton

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.; Trajmar, S.

    1978-01-01

    Energy-loss spectra of krypton in the region between 21 and 29 eV have been obtained at electron impact energies of 30, 60 and 100 eV. For each energy, the angular distribution of intensities has been measured at 5, 10 and 15 deg scattering angles. Assignments of spectral features found in this region are suggested and a comparison is made with previous measurements.

  4. Ultrafast excited state relaxation dynamics of electron deficient porphyrins: Conformational and electronic factors

    NASA Astrophysics Data System (ADS)

    Okhrimenko, Albert N.

    Metallo-tetrapyrroles (MTP) are highly stable macrocyclic pi-systems that display interesting properties that make them potential candidates for various applications. Among these applications are optoelectronics, magnetic materials, photoconductive materials, non-linear optical materials and photo tumor therapeutic drugs. These applications are generally related to their high stability and efficient light absorption ability in the visible and near-infrared region of the optical spectrum. Metallo porphyrins are well known and widely studied representatives of metallotetrapyrroles. Electron deficient substituents in the meso positions are well known to greatly influence the interaction between the metal d-orbitals and the nitrogen orbitals of the tetrapyrrole macrocycle. In this work, a series of electron deficient porphyrins has been studied to gain some knowledge about the change in the excited state dynamics with structural and electronic modifications. Among these porphyrins is nickel and iron modified species bearing perfluoro-, perprotio-, p-nitrophenyl- and perfluorophenyl-meso substituents. Ultrafast transient absorption spectrometry has been used as the main research instrument along with other spectroscopic and electrochemical methods. A new technique has been employed to study the photophysical properties of zinc (II) tetraphenylporphine cation radical. It employs a combination of controlled potential coulometry and femtosecond absorption spectrometry. The fast transient lifetime of 17 ps of the pi-cation species originates in very efficient mixing of the a2u HOMO cation orbital that places electronic density mainly on pyrrolic nitrogens and metal d-orbitals. That explains the lack of any emission of the cationic species. This non-radiative decay process might elucidate the processes taking place in photosynthetic systems when electron is removed from porphyrinic moiety and the hole is produced. In this work zinc(II) meso-tetraphenylporphine radial cation

  5. Reactions of ground-state and electronically excited sodium atoms with methyl bromide and molecular chlorine

    SciTech Connect

    Weiss, P.S.; Mestdagh, J.M.; Schmidt, H.; Covinsky, M.H.; Lee, Y.T. )

    1991-04-18

    The reactions of ground- and excited-state Na atoms with methyl bromide (CH{sub 3}Br) and chlorine (Cl{sub 2}) have been studied by using the crossed molecular beams method. For both reactions, the cross sections increase with increasing electronic energy. The product recoil energies change little with increasing Na electronic energy, implying that the product internal energies increase substantially. For Na + CH{sub 3}Br, the steric angle of acceptance opens with increasing electronic energy.

  6. Nonadiabatic excited-state molecular dynamics: treatment of electronic decoherence.

    PubMed

    Nelson, Tammie; Fernandez-Alberti, Sebastian; Roitberg, Adrian E; Tretiak, Sergei

    2013-06-14

    Within the fewest switches surface hopping (FSSH) formulation, a swarm of independent trajectories is propagated and the equations of motion for the quantum coefficients are evolved coherently along each independent nuclear trajectory. That is, the phase factors, or quantum amplitudes, are retained. At a region of strong coupling, a trajectory can branch into multiple wavepackets. Directly following a hop, the two wavepackets remain in a region of nonadiabatic coupling and continue exchanging population. After these wavepackets have sufficiently separated in phase space, they should begin to evolve independently from one another, the process known as decoherence. Decoherence is not accounted for in the standard surface hopping algorithm and leads to internal inconsistency. FSSH is designed to ensure that at any time, the fraction of classical trajectories evolving on each quantum state is equal to the average quantum probability for that state. However, in many systems this internal consistency requirement is violated. Treating decoherence is an inherent problem that can be addressed by implementing some form of decoherence correction to the standard FSSH algorithm. In this study, we have implemented two forms of the instantaneous decoherence procedure where coefficients are reinitialized following hops. We also test the energy-based decoherence correction (EDC) scheme proposed by Granucci et al. and a related version where the form of the decoherence time is taken from Truhlar's Coherent Switching with Decay of Mixing method. The sensitivity of the EDC results to changes in parameters is also evaluated. The application of these computationally inexpensive ad hoc methods is demonstrated in the simulation of nonradiative relaxation in two conjugated oligomer systems, specifically poly-phenylene vinylene and poly-phenylene ethynylene. We find that methods that have been used successfully for treating small systems do not necessarily translate to large polyatomic

  7. Nonadiabtic electron dynamics in densely quasidegenerate states in highly excited boron cluster.

    PubMed

    Yonehara, Takehiro; Takatsuka, Kazuo

    2016-04-28

    Following the previous study on nonadiabatic reaction dynamics including boron clusters [T. Yonehara and K. Takatsuka, J. Chem. Phys. 137, 22A520 (2012)], we explore deep into highly excited electronic states of the singlet boron cluster (B12) to find the characteristic features of the densely quasi-degenerate electronic state manifold, which undergo very frequent nonadiabatic transitions and thereby intensive electronic state mixing among very many of the relevant states. So much so, isolating the individual adiabatic states and tracking the expected potential energy surfaces both lose the physical sense. This domain of molecular situation is far beyond the realm of the Born-Oppenheimer approximation. To survey such a violent electronic state-mixing, we apply a method of nonadiabatic electron wavepacket dynamics, the semiclassical Ehrenfest method. We have tracked those electron wavepackets and found the electronic state mixing looks like an ultrafast diffusion in the Hilbert space, which results in huge fluctuation. Furthermore, due to such a violent mixing, the quantum phases associated with the electronic states are swiftly randomized, and consequently the coherence among the electronic states are lost quickly. Besides, these highly excited states are mostly of highly poly-radical nature, even in the spin singlet manifold and the number of radicals amounts up to 10 electrons in the sense of unpaired electrons. Thus the electronic states are summarized to be poly-radical and decoherent with huge fluctuation in shorter time scales of vibrational motions. The present numerical study sets a theoretical foundation for unknown molecular properties and chemical reactivity of such densely quasi-degenerate chemical species. PMID:27131547

  8. Nonadiabtic electron dynamics in densely quasidegenerate states in highly excited boron cluster

    NASA Astrophysics Data System (ADS)

    Yonehara, Takehiro; Takatsuka, Kazuo

    2016-04-01

    Following the previous study on nonadiabatic reaction dynamics including boron clusters [T. Yonehara and K. Takatsuka, J. Chem. Phys. 137, 22A520 (2012)], we explore deep into highly excited electronic states of the singlet boron cluster (B12) to find the characteristic features of the densely quasi-degenerate electronic state manifold, which undergo very frequent nonadiabatic transitions and thereby intensive electronic state mixing among very many of the relevant states. So much so, isolating the individual adiabatic states and tracking the expected potential energy surfaces both lose the physical sense. This domain of molecular situation is far beyond the realm of the Born-Oppenheimer approximation. To survey such a violent electronic state-mixing, we apply a method of nonadiabatic electron wavepacket dynamics, the semiclassical Ehrenfest method. We have tracked those electron wavepackets and found the electronic state mixing looks like an ultrafast diffusion in the Hilbert space, which results in huge fluctuation. Furthermore, due to such a violent mixing, the quantum phases associated with the electronic states are swiftly randomized, and consequently the coherence among the electronic states are lost quickly. Besides, these highly excited states are mostly of highly poly-radical nature, even in the spin singlet manifold and the number of radicals amounts up to 10 electrons in the sense of unpaired electrons. Thus the electronic states are summarized to be poly-radical and decoherent with huge fluctuation in shorter time scales of vibrational motions. The present numerical study sets a theoretical foundation for unknown molecular properties and chemical reactivity of such densely quasi-degenerate chemical species.

  9. 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.

  10. Excitation of the a {sup 3{Pi}} state of CO by electron impact

    SciTech Connect

    Ristic, M. M.; Poparic, G. B.; Belic, D. S.

    2011-04-15

    Electron impact excitation of the a {sup 3{Pi}} valence state of the carbon-monoxide molecule has been studied in the energy region from threshold to 10 eV. Excitation functions for spin forbidden transitions from the {nu}=0 level of the ground X {sup 1}{Sigma}{sup +} state of CO to the {nu}{sup '}=0, 1, 2, 3, 4, and 5 levels of the a {sup 3{Pi}} state are measured. A crossed beam double trochoidal electron spectrometer is used. Forward and backward scattered electrons from the {nu}{sup '}=0 excitation channel are separated by electron beam modulation and a time-of-flight detection technique. The present results are normalized to the ground state {sup 2{Pi}} resonance vibrational excitation cross sections and absolute values of the differential cross sections at the border angles of 0 deg. and 180 deg. are determined. In this way the differential cross section measurements are completed in the full angular range from 0 deg. to 180 deg. The present results are compared to the existing literature data.

  11. Quantum-chemical study of electronically excited states of protolytic forms of vanillic acid

    NASA Astrophysics Data System (ADS)

    Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Y.

    2015-12-01

    The paper describes an analysis of possible ways of deactivation of electronically excited states of 4-hydroxy- 3-methoxy-benzoic acid (vanillic acid) and its protolytic forms with the use of quantum-chemical methods INDO/S (intermediate neglect of differential overlap with a spectroscopic parameterization) and MEP (molecular electrostatic potential). The ratio of radiative and non-radiative deactivation channels of the electronic excitation energy is established. The rate constants of photophysical processes (internal and intercombination conversions) occurring after the absorption of light in these forms are evaluated.

  12. Electron-impact ionization of moderately charged atomic ions in excited states

    SciTech Connect

    Pindzola, M. S.; Ballance, C. P.; Loch, S. D.

    2011-06-15

    Nonperturbative R-matrix and perturbative distorted-wave methods are used to calculate electron-impact ionization cross sections for C{sup 3+} in excited states. Convergence studies for the cross sections of the 1s{sup 2}5s excited configuration reveal that both the R-matrix and distorted-wave methods need fairly high ejected electron angular momenta. Reasonable agreement is found between the converged R-matrix and distorted-wave cross sections. Thus, the use of the computationally less demanding distorted-wave method as a tool for the n scaling of excited-state ionization cross sections appears to be reasonable for atomic ions with charge q{>=}3.

  13. The electronic origin and vibrational levels of the first excited singlet state of isocyanic acid (HNCO)

    SciTech Connect

    Berghout, H. Laine; Crim, F. Fleming; Zyrianov, Mikhail; Reisler, Hanna

    2000-04-15

    The combination of vibrationally mediated photofragment yield spectroscopy, which excites molecules prepared in single vibrational states, and multiphoton fluorescence spectroscopy, which excites molecules cooled in a supersonic expansion, provides detailed information on the energetics and vibrational structure of the first excited singlet state (S{sub 1}) of isocyanic acid (HNCO). Dissociation of molecules prepared in individual vibrational states by stimulated Raman excitation probes vibrational levels near the origin of the electronically excited state. Detection of fluorescence from dissociation products formed by multiphoton excitation through S{sub 1} of molecules cooled in a supersonic expansion reveals the vibrational structure at higher energies. Both types of spectra show long, prominent progressions in the N-C-O bending vibration built on states with different amounts of N-C stretching excitation and H-N-C bending excitation. Analyzing the spectra locates the origin of the S{sub 1} state at 32 449{+-}20 cm{sup -1} and determines the harmonic vibrational frequencies of the N-C stretch ({omega}{sub 3}=1034{+-}20 cm{sup -1}), the H-N-C bend ({omega}{sub 4}=1192{+-}19 cm{sup -1}), and the N-C-O bend ({omega}{sub 5}=599{+-}7 cm{sup -1}), values that are consistent with several ab initio calculations. The assigned spectra strongly suggest that the N-C stretching vibration is a promoting mode for internal conversion from S{sub 1} to S{sub 0}. (c) 2000 American Institute of Physics.

  14. Infrared/ultraviolet quadruple resonance spectroscopy to investigate structures of electronically excited states

    SciTech Connect

    Weiler, M.; Bartl, K.; Gerhards, M.

    2012-03-21

    Molecular beam investigations in combination with IR/UV spectroscopy offer the possibility to obtain structural information on isolated molecules and clusters. One of the demanding tasks is the discrimination of different isomers, e.g., by the use of isomer specific UV excitations. If this discrimination fails due to overlaying UV spectra of different isomers, IR/IR methods offer another possibility. Here, we present a new IR/UV/IR/UV quadruple resonance technique to distinguish between different isomers especially in the electronically excited state. Due to the IR spectra, structural changes and photochemical pathways in excited states can be assigned and identified. The method is applied to the dihydrated cluster of 3-hydroxyflavone which has been investigated as photochemically relevant system and proton wire model in the S{sub 1} state. By applying the new IR/UV/IR/UV technique, we are able to show experimentally that both in the electronic ground (S{sub 0}) and the electronically excited state (S{sub 1}) two isomers have to be assigned.

  15. 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

  16. Electron-impact ionization cross sections out of the ground and excited states of cesium

    SciTech Connect

    Lukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-15

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the 'trap loss' technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs state between 7 eV and 400 eV. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11 eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  17. Computational simulation and interpretation of the low-lying excited electronic states and electronic spectrum of thioanisole.

    PubMed

    Li, Shaohong L; Xu, Xuefei; Truhlar, Donald G

    2015-08-21

    Three singlet states, namely a closed-shell ground state and two excited states with (1)ππ* and (1)nσ* character, have been suggested to be responsible for the radiationless decay or photochemical reaction of photoexcited thioanisole. The correct interpretation of the electronic spectrum is critical for understanding the character of these low-lying excited states, but the experimental spectrum is yet to be fully interpreted. In the work reported here, we investigated the nature of those three states and a fourth singlet state of thioanisole using electronic structure calculations by multireference perturbation theory, by completely-renormalized equation-of-motion coupled cluster theory with single and double excitations and noniterative inclusion of connected triples (CR-EOM-CCSD(T)), and by linear-response time-dependent density functional theory (TDDFT). We clarified the assignment of the electronic spectrum by simulating it using a normal-mode sampling approach combined with TDDFT in the Tamm-Dancoff approximation (TDA). The understanding of the electronic states and of the accuracy of the electronic structure methods lays the foundation of our future work of constructing potential energy surfaces. PMID:26088195

  18. 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.

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

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick

    1993-01-01

    Most of the important chemical reactions which occur in the very high temperature air produced around space vehicles as they enter the atmosphere were investigated both experimentally and theoretically, to some extent at least. One remaining reaction about which little is known, and which could be quite important at the extremely high temperatures that will be produced by the class of space vehicles now contemplated - such as the AOTV - is the excitation of bound electron states due to collisions between heavy gas particles. Rates of electronic excitation due to free electron collisions are known to be very rapid, but because these collisions quickly equilibrate the free and bound electron energy, the approach to full equilibrium with the heavy particle kinetic energy will depend primarily on the much slower process of bound electron excitation in heavy particle collisions and the subsequent rapid transfer to free electron energy. This may be the dominant mechanism leading to full equilibrium in the gas once the dissociation process has depleted the molecular states so the transfer between molecular vibrational energy and free electron energy is no longer available as a channel for equilibration of free electron and heavy particle kinetic energies. Two mechanisms seem probable in electronic excitation by heavy particle impact. One of these is the collision excitation and deexcitation of higher electronic states which are Rydberg like. A report, entitled 'Semi-Classical Theory of Electronic Excitation Rates', was submitted previously. This presented analytic expressions for the transition probabilities, assuming that the interaction potential is an exponential repulsion with a perturbation ripple due to the dipole-induced dipole effect in the case of neutral-neutral collisions, and to the ion-dipole interaction in the case of ion-neutral collisions. However the above may be, there is little doubt that excitation of ground state species by collision occurs at the

  20. The repopulation of electronic states upon vibrational excitation of niobium carbide clusters.

    PubMed

    Chernyy, V; Logemann, R; Bakker, J M; Kirilyuk, A

    2016-07-14

    We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful. However, the data can be fully modeled by vibrationally and rotationally broadened discrete electronic levels obtained from Density Functional Theory (DFT) calculations. The application of this method to spectra with different IR pulse energies not only yields information about the excited electronic states in the vicinity of the HOMO level, populated by manipulation of the vibrational coordinates of a cluster, but also can serve as an extra indicator for the cluster isomeric structure and corresponding DFT-calculated electronic levels.

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

    SciTech Connect

    Hoffman, M.Z.

    1991-12-31

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

  2. The repopulation of electronic states upon vibrational excitation of niobium carbide clusters.

    PubMed

    Chernyy, V; Logemann, R; Bakker, J M; Kirilyuk, A

    2016-07-14

    We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful. However, the data can be fully modeled by vibrationally and rotationally broadened discrete electronic levels obtained from Density Functional Theory (DFT) calculations. The application of this method to spectra with different IR pulse energies not only yields information about the excited electronic states in the vicinity of the HOMO level, populated by manipulation of the vibrational coordinates of a cluster, but also can serve as an extra indicator for the cluster isomeric structure and corresponding DFT-calculated electronic levels. PMID:27421411

  3. The repopulation of electronic states upon vibrational excitation of niobium carbide clusters

    NASA Astrophysics Data System (ADS)

    Chernyy, V.; Logemann, R.; Bakker, J. M.; Kirilyuk, A.

    2016-07-01

    We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful. However, the data can be fully modeled by vibrationally and rotationally broadened discrete electronic levels obtained from Density Functional Theory (DFT) calculations. The application of this method to spectra with different IR pulse energies not only yields information about the excited electronic states in the vicinity of the HOMO level, populated by manipulation of the vibrational coordinates of a cluster, but also can serve as an extra indicator for the cluster isomeric structure and corresponding DFT-calculated electronic levels.

  4. Doubly excited states of ammonia by scattered electron-ion coincidence measurements

    NASA Astrophysics Data System (ADS)

    Yamamoto, Karin; Sakai, Yasuhiro

    2012-03-01

    To obtain information on the optically forbidden doubly excited states of ammonia (NH3), we performed scattered electron-ion coincidence measurements. First, we observed scattered electrons using electron energy-loss spectroscopy and determined the generalized oscillator strength distribution (GOSD) under 200 eV incident electron energy at a scattering angle of 8°. Ionic GOSDs were also determined by combination with the coincidence signal, which was observed by the time-of-flight mass spectrometer at each energy-loss value, for each ion. The total and partial ionic GOSDs were compared with the experimental results of both photon and fast electron impact. Moreover, the neutral GOSD determined by subtracting the total ionic GOSD from the total was compared with previous results. In addition to the optically forbidden doubly excited states, which were identified by Kato et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 3541) and Ishikawa et al (2008 J. Phys. B: At. Mol. Opt. Phys. 41 195204), we found a new optically forbidden doubly excited state at around 35 eV.

  5. Determination and Comparison of Carbonyl Stretching Frequency of a Ketone in Its Ground State and the First Electronic Excited State

    ERIC Educational Resources Information Center

    Bandyopadhyay, Subhajit; Roy, Saswata

    2014-01-01

    This paper describes an inexpensive experiment to determine the carbonyl stretching frequency of an organic keto compound in its ground state and first electronic excited state. The experiment is simple to execute, clarifies some of the fundamental concepts of spectroscopy, and is appropriate for a basic spectroscopy laboratory course. The…

  6. 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.

  7. Vibronic structure and coupling of higher excited electronic states in carotenoids

    NASA Astrophysics Data System (ADS)

    Krawczyk, Stanisław; Luchowski, Rafał

    2013-03-01

    Absorption spectra of all-trans carotenoids (lycopene, violaxanthin, ζ-carotene) at low temperature exhibit peculiar features in the UV range. The transition to the 11Ag+ state ('cis-band') weakens on cooling, indicating that it is induced by thermal deformations of the conjugated chain. The higher energy band has unique vibrational structure indicating the vibronic coupling of nBu with another electronic state. The electroabsorption spectra point to the electric field-induced mixing of the nBu state with the vibrational continuum of a lower-lying excited state (Fano effect). These observations widen the basis for elucidation of the vibronic coupling effects in the lower excited states.

  8. Minimal-excitation states for electron quan-tum optics using levitons

    NASA Astrophysics Data System (ADS)

    Roulleau, Preden; Jullien, Thibaut; Dubois, Julie; Portier, Fabien; Roche, Patrice; Cavanna, Antonella; Jin, Yong; Wegscheider, Werner; Glattli, D. Christian

    2014-03-01

    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.

  9. Electron Impact Excitation of Xenon from the Ground State and the Metastable State to the 5p57p Levels

    NASA Astrophysics Data System (ADS)

    Chen, Zhan-Bin; Dong, Chen-Zhong; Xie, Lu-You; Jiang, Jun

    2014-03-01

    Electron impact excitation cross sections from the ground state and the lowest metastable state 5p56s J = 2 to the excited states of the 5p57p configuration of xenon are calculated systematically using the fully relativistic distorted wave method. Special attention is paid to the configuration interaction effects in the wave-function expansion of target states. The results are in good agreement with the recent experimental data by Jung et al. [Phys. Rev. A 80 (2009) 062708] over the measured energy range. These accurate theoretical results can be used in the modeling and diagnosis of plasmas containing xenon.

  10. Ab initio study on electronically excited states of lithium isocyanide, LiNC

    NASA Astrophysics Data System (ADS)

    Yasumatsu, Hisato; Jeung, Gwang-Hi

    2014-01-01

    The electronically excited states of the lithium isocyanide molecule, LiNC, were studied by means of ab initio calculations. The bonding nature of LiNC up to ˜10 eV is discussed on the basis of the potential energy surfaces according to the interaction between the ion-pair and covalent states. The ion-pair states are described by Coulomb attractive interaction in the long distance range, while the covalent ones are almost repulsive or bound with a very shallow potential dent. These two states interact each other to form adiabatic potential energy surfaces with non-monotonic change in the potential energy with the internuclear distance.

  11. The contribution of electronically excited states to the radiation chemistry of organic systems

    SciTech Connect

    Lipsky, S.

    1992-01-01

    At low concentrations ({le}10{sup {minus}3}M) of aromatic solutes in saturated. hydrocarbon solvents, very efficient transport of electronic energy from photo-excited solvent to aromatic is observed. Effects of temperature, dilution, and quenching additives are being studied. Two-photon pulsed laser excitation gives no evidence of long lived metastable states. The fluorescence quantum yields of saturated hydrocarbon liquids have been studied for excitation wavelengths from 200 to 120 nm. For many compounds, the quantum yields for fluorescence are observed to decline to a minimum value at, or near, previously reported ionization thresholds. At higher energies, the magnitude of the quantum yield for fluorescence begins to increase. Magnetic field effects on intensity of steady-state recombination fluorescence have been observed both for photo-generated and {Beta}{sup {minus}} generated, electron and positive ion geminate pairs in saturated hydrocarbon liquids. The comparison indicates an important contribution . to observed recombination fluorescence from multiple ion-pairs under radiation chemical conditions. For photo-excited aromatic solutes dissolved in saturated hydrocarbon liquids, no magnetic field effect could be observed until surprisingly large excess energies above the threshold for ionization were achieved. This suggests a much smaller average range for the thermalized electron than expected from photoconductivity.

  12. A theoretical forecast of the hydrogen bond changes in the electronic excited state for BN and its derivatives

    NASA Astrophysics Data System (ADS)

    Wang, Dandan; Hao, Ce; Wang, Se; Dong, Hong; Qiu, Jieshan

    2012-02-01

    The relationship between electronic spectral shifts and hydrogen-bonding dynamics in electronically excited states of the hydrogen-bonded complex is put forward. Hydrogen bond strengthening will induce a redshift of the corresponding electronic spectra, while hydrogen bond weakening will cause a blueshift. Time-dependent density function theory (TDDFT) was used to study the excitation energies in both singlet and triplet electronically excited states of Benzonitrile (BN), 4-aminobenzonitrile (ABN), and 4-dimethylaminobenzonitrile (DMABN) in methanol solvents. Only the intermolecular hydrogen bond C≡N...H-O was involved in our system. A fairly accurate forecast of the hydrogen bond changes in lowlying electronically excited states were presented in light of a very thorough consideration of their related electronic spectra. The deduction we used to depict the trend of the hydrogen bond changes in excited states could help others understand hydrogen-bonding dynamics more effectively.

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

    NASA Astrophysics Data System (ADS)

    Olsen, Thomas; Gavnholt, Jeppe; Schiøtz, Jakob

    2009-01-01

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

  14. Determination of state-to-state electron-impact rate coefficients between Ar excited states: a review of combined diagnostic experiments in afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe

    2016-08-01

    Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1-5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.

  15. Determination of state-to-state electron-impact rate coefficients between Ar excited states: a review of combined diagnostic experiments in afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe

    2016-08-01

    Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1–5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.

  16. Proton coupled electron transfer from the excited state of a ruthenium(II) pyridylimidazole complex.

    PubMed

    Pannwitz, Andrea; Wenger, Oliver S

    2016-04-28

    Proton coupled electron transfer (PCET) from the excited state of [Ru(bpy)2pyimH](2+) (bpy = 2,2'-bipyridine; pyimH = 2-(2'-pyridyl)imidazole) to N-methyl-4,4'-bipyridinium (monoquat, MQ(+)) was studied. While this complex has been investigated previously, our study is the first to show that the formal bond dissociation free energy (BDFE) of the imidazole-N-H bond decreases from (91 ± 1) kcal mol(-1) in the electronic ground state to (43 ± 5) kcal mol(-1) in the lowest-energetic (3)MLCT excited state. This makes the [Ru(bpy)2pyimH](2+) complex a very strong (formal) hydrogen atom donor even when compared to metal hydride complexes, and this is interesting for light-driven (formal) hydrogen atom transfer (HAT) reactions with a variety of different substrates. Mechanistically, formal HAT between (3)MLCT excited [Ru(bpy)2pyimH](2+) and monoquat in buffered 1 : 1 (v : v) CH3CN/H2O was found to occur via a sequence of reaction steps involving electron transfer from Ru(ii) to MQ(+) coupled to release of the N-H proton to buffer base, followed by protonation of reduced MQ(+) by buffer acid. Our study is relevant in the larger contexts of photoredox catalysis and light-to-chemical energy conversion. PMID:27094541

  17. Influence of the excited states on the electron-energy distribution function in low-pressure microwave argon plasmas

    SciTech Connect

    Yanguas-Gil, A.; Cotrino, J.; Gonzalez-Elipe, A.R.

    2005-07-01

    In this work the influence of the excited states on the electron-energy distribution function has been determined for an argon microwave discharge at low pressure. A collisional-radiative model of argon has been developed taking into account the most recent experimental and theoretical values of argon-electron-impact excitation cross sections. The model has been solved along with the electron Boltzmann equation in order to study the influence of the inelastic collisions from the argon excited states on the electron-energy distribution function. Results show that under certain conditions the excited states can play an important role in determining the shape of the distribution function and the mean kinetic energy of the electrons, deplecting the high-energy tail due to inelastic processes from the excited states, especially from the 4s excited configuration. It has been found that from the populations of the excited states an excitation temperature can be defined. This excitation temperature, which can be experimentally determined by optical emission spectroscopy, is lower than the electron kinetic temperature obtained from the electron-energy distribution function.

  18. Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission.

    PubMed

    Sen, Ananya; Matthews, Edward M; Hou, Gao-Lei; Wang, Xue-Bin; Dessent, Caroline E H

    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 [A. 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 one-photon 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 time scale long enough to allow autodetachment.

  19. 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.

  20. Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission.

    PubMed

    Sen, Ananya; Matthews, Edward M; Hou, Gao-Lei; Wang, Xue-Bin; Dessent, Caroline E H

    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 [A. 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 one-photon 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 time scale long enough to allow autodetachment. PMID:26567662

  1. Experimental and computational studies on the electronic excited states of nitrobenzene

    NASA Astrophysics Data System (ADS)

    Krishnakumar, Sunanda; Das, Asim Kumar; Singh, Param Jeet; Shastri, Aparna; Rajasekhar, B. N.

    2016-11-01

    The gas phase electronic absorption spectrum of nitrobenzene (C6H5NO2) in the 4.5-11.2 eV region is recorded using synchrotron radiation with a view to comprehend the nature of the excited states. Electronic excited states of nitrobenzene are mainly classified as local excitations within the benzene ring or nitro group and charge transfer excitations between the benzene and nitro group, with some transitions showing percentage from both. The nature of molecular orbitals, their orderings and energies are obtained from density functional theory calculations which help in assigning partially assigned/unassigned features in earlier photoelectron spectroscopy studies. Optimized geometry of ionic nitrobenzene predicts redistribution of charge density in the benzene ring rather than the nitro group resulting in stabilization of the benzene ring π orbitals in comparison to the neutral molecule. Time dependent density functional theory computations are found to describe the experimental spectra well with respect to energies, relative intensities and nature of the observed transitions in terms of valence, Rydberg or charge transfer type. New insights into the interpretation of 1B2u←1A1g and 1B1u←1A1g shifted benzene transitions in light of the present computational calculations are presented. The first few members of the ns, np and nd type Rydberg series in nitrobenzene, converging to the first six ionization potentials, identified in the spectra as weak but sharp peaks are reported for the first time. In general, transitions to the lowest three unoccupied molecular orbitals 4b1, 3a2 and 5b1 are valence or charge transfer in nature, while excitations to higher orbitals are predominantly Rydberg in nature. This work presents a consolidated experimental study and theoretical interpretation of the electronic absorption spectrum of nitrobenzene.

  2. Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S{sub 1}(π,π{sup *}) electronic state

    SciTech Connect

    Shin, Hee Won; Ocola, Esther J.; Laane, Jaan; Kim, Sunghwan

    2014-01-21

    The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(π,π{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(π,π{sup *}) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(π,π{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(π,π{sup *}) excited state.

  3. Electron-phonon interaction and excited states relaxation in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Perebeinos, Vasili

    2008-03-01

    We will discuss the role of electron-phonon interaction on excited states relaxation and phonon spectra in carbon nanotubes (CNTs). The electron-phonon interaction leads to the polaronic effects of the charge carriers, but it also renormalizes the energy and the lifetime of phonons. We present a theoretical model that predicts the changes induced in the phonon modes of CNTs as a function of the charge carrier doping, i.e. position of the Fermi level. In agreement with the predictions, our experiments show sharpening and blue shifts of the G-phonons of metallic CNTs, but only blue shifts for semiconducting CNTs, making the Raman scattering a useful probe of local doping of CNTs [1]. The non-equilibrium dynamics of charge carriers under external electric field is determined by the electron-phonon scattering. The hot carriers under unipolar transport conditions can be produced, leading to the strong impact excitation and light emission, which intensity is determined by electric field, phonon scattering, and impact excitation cross section [2, 3]. In the reverse process of photoconductivity, light is absorbed creating excited states. We will discuss electronic relaxation of high energy excited states leading to the free carriers, contributing to the photoconductivity, and phonon relaxation, leading to the bound excitons [4]. The later can contribute to the photocurrent only after ionization by the external field [5]. Finally, we will discuss the role of phonons in the long puzzling question regarding the nature of the dominant decay channel of the low energy excited states and the potential of optoelectronic applications of CNTs. [1] J.C. Tsang, M. Freitag, V. Perebeinos, J. Liu, and Ph. Avouris, Nature Nanotechnology 2, 725 (2007); [2] J. Chen, V. Perebeinos, M. Freitag, J. Tsang, Q. Fu, J. Liu, Ph. Avouris, Science 310, 1171 (2005); [3] V. Perebeinos and Ph. Avouris, Phys. Rev. B. 74, 121410(R), (2006); [4] T. Hertel, V. Perebeinos, J. Crochet, K. Arnold, M. Kappes

  4. Direct Electron Impact Excitation of Rydberg-Valence States of Molecular Nitrogen

    NASA Astrophysics Data System (ADS)

    Malone, C. P.; Johnson, P. V.; Liu, X.; Ajdari, B.; Muleady, S.; Kanik, I.; Khakoo, M. A.

    2012-12-01

    Collisions between electrons and neutral N2 molecules result in emissions that provide an important diagnostic probe for understanding the ionospheric energy balance and the effects of space weather in upper atmospheres. Also, transitions to singlet ungerade states cause N2 to be a strong absorber of solar radiation in the EUV spectral range where many ro-vibrational levels of these Rydberg-valence (RV) states are predissociative. Thus, their respective excitation and emission cross sections are important parameters for understanding the [N]/[N2] ratio in the thermosphere of nitrogen dominated atmospheres. The following work provides improved constraints on absolute and relative excitation cross sections of numerous RV states of N2, enabling more physically accurate atmospheric modeling. Here, we present recent integral cross sections (ICSs) for electron impact excitation of RV states of N2 [6], which were based on the differential cross sections (DCSs) derived from electron energy-loss (EEL) spectra of [5]. This work resulted in electronic excitation cross sections over the following measured vibrational levels: b 1Πu (v‧=0-14), c3 1Πu (v‧=0-3), o3 1Πu (v‧=0-3), b‧ 1Σu+ (v‧=0-10), c‧4 1Σu+ (v‧=0-3), G 3Πu (v‧=0-3), and F 3Πu (v‧=0-3). We further adjusted the cross sections of the RV states by extending the vibronic contributions to unmeasured v‧-levels via the relative excitation probabilities (REPs) as discussed in [6]. This resulted in REP-scaled ICSs over the following vibrational levels for the singlet ungerade states: b(0-19), c3(0-4), o3(0-4), b‧(0-16), and c‧4(0-8). Comparison of the ICSs of [6] with available EEL based measurements, theoretical calculations, and emission based work generally shows good agreement within error estimations, except with the recent reevaluation provided by [1]. Further, we have extended these results, using the recent EEL data of [3], to include the unfolding of better resolved features above ~13

  5. Ab Initio Investigations of the Excited Electronic States of CaOCa

    NASA Astrophysics Data System (ADS)

    Fawzy, Wafaa M.; Heaven, Michael

    2016-06-01

    Chemical bonding in alkaline earth hypermetalic oxides is of fundamental interest. Previous Ab initio studies of CaOCa predicted a centrosymmetric linear geometry for both the 1Σg^+ ground state and the low lying triplet 3Σu^+ state. However, there have been no reports concerning the higher energy singlet and triplet states. The present work is focused on characterization of the potential energy surface (PES) of the excited 1Σu^+ state (assuming a centrosymmetric linear geometry) and obtaining predictions for the 1Σu^+←1Σg^+ vibronic transitions. We employed the multireference configuration interaction (MRCISD) method with state-averaged, full-valence complete active space self-consistent field (SA-FV-CASSCF) wavefunctions. In these calculations, the active space consisted of ten valence electrons in twelve orbitals, where all the valence electrons were correlated. Contributions of higher excitation and relativistic effects were taken into account using the Davidson correction and the Douglas-Kroll (DK) Hamiltonian, respectively. The correlation-consistent polarized weighed core-valence quadruple zeta basis set (cc-pwCVQZ-DK) was used for all three atoms. The full level of theory is abbreviated as SA-FV-CASSCF (10,12)-MRCISD-Q/cc-pwCVQZ-DK. The calculations were carried out using the MOLPRO2012 suite of programs. For the centrosymmetric linear geometry in all states, initial investigations of one-dimensional radial cuts provided equilibrium bond distances of 2.034 {Å}, 2.034 {Å}, and 1.999 {Å} for the 1Σg^+ , 3Σu^+ , and 1Σu^+ states, respectively. The vertical excitation frequency of the 1Σu^+←1Σg^+ optical transition was calculated to occur at 14801 wn. These predictions were followed by spectroscopic searches by Heaven et al. Indeed, rotationally resolved vibronic progressions were recorded in the vicinity of the predicted electronic band origin. Calculation of the three-dimensional PES showed that the potential minimum in the 1Σu^+ corresponds

  6. Excited state electron transfer from aminopyrene to graphene: a combined experimental and theoretical study.

    PubMed

    Chakraborti, Himadri; Bramhaiah, Kommula; John, Neena Susan; Pal, Suman Kalyan

    2013-12-01

    The quenching of the fluorescence of 1-aminopyrene (1-Ap) by reduced graphene oxide (rGO) has been investigated using spectroscopic techniques. In spite of the upward curvature in the Stern-Volmer plot, the unchanged spectral signature of the absorption of 1-Ap in the presence of rGO and the decrease in fluorescence lifetime with increasing rGO concentration point toward the dynamic nature of the quenching. Detailed analysis of steady state and time-resolved spectroscopic data has shown that the quenching arises due to the photoinduced electron transfer from 1-Ap to rGO. This is again supported by estimating the Gibb's free energy change for the ground as well as excited state electron transfer. Ab initio calculations under the density functional theory (DFT) formalism reveal that the possibility of π-π stacking is very slim in the 1-Ap-rGO system and the electron density resides completely on 1-Ap in the highest occupied molecular orbital (HOMO) and on graphene in the lowest unoccupied molecular orbital (LUMO), supporting the experimental findings of the intermolecular electron transfer between 1-Ap and rGO in the excited state.

  7. Electron-excited molecule interactions

    SciTech Connect

    Christophorou, L.G. Tennessee Univ., Knoxville, TN . Dept. of Physics)

    1991-01-01

    In this paper the limited but significant knowledge to date on electron scattering from vibrationally/rotationally excited molecules and electron scattering from and electron impact ionization of electronically excited molecules is briefly summarized and discussed. The profound effects of the internal energy content of a molecule on its electron attachment properties are highlighted focusing in particular on electron attachment to vibrationally/rotationally and to electronically excited molecules. The limited knowledge to date on electron-excited molecule interactions clearly shows that the cross sections for certain electron-molecule collision processes can be very different from those involving ground state molecules. For example, optically enhanced electron attachment studies have shown that electron attachment to electronically excited molecules can occur with cross sections 10{sup 6} to 10{sup 7} times larger compared to ground state molecules. The study of electron-excited molecule interactions offers many experimental and theoretical challenges and opportunities and is both of fundamental and technological significance. 54 refs., 15 figs.

  8. Electronic State Interferences in Resonant X-Ray Emission after K-Shell Excitation in HCl

    SciTech Connect

    Kavcic, M.; Zitnik, M.; Bucar, K.; Mihelic, A.; Carniato, S.; Journel, L.; Guillemin, R.; Simon, M.

    2010-09-10

    We have measured a series of high-resolution x-ray spectra emitted upon resonant photoexcitation of HCl. The photon energy was tuned across the dissociative 1s{yields}6{sigma}* resonance and the Rydberg states converging to the Cl 1s{sup -1} threshold, and inelastic photon scattering was observed in the region of KL emission lines. Excellent agreement is found between fully ab initio calculated and measured spectra if interferences between different excitation-emission paths are taken into account. The effect of electronic state interferences is enhanced due to dynamical broadening of the 6{sigma}* resonance in HCl.

  9. Excited states in hydrocarbons

    SciTech Connect

    Lipsky, S.

    1987-01-01

    In this brief review we first summarize some pertinent features of the photophysical properties of excited states of hydrocarbons and the mechanisms by which they transfer energy to solutes and then review their yields and their behavior under fast-electron irradiation conditions. 33 refs.

  10. Multicentered valence electron effective potentials: a solution to the link atom problem for ground and excited electronic states.

    PubMed

    Slavícek, Petr; Martínez, Todd J

    2006-02-28

    We introduce a multicentered valence electron effective potential (MC-VEEP) description of functional groups which succeeds even in the context of excited electronic states. The MC-VEEP is formulated within the ansatz which is familiar for effective core potentials in quantum chemistry, and so can be easily incorporated in any quantum chemical calculation. By demanding that both occupied and virtual orbitals are described correctly on the MC-VEEP, we are able to ensure correct behavior even when the MC-VEEP borders an electronically excited region. However, the present formulation does require that the electrons represented by the MC-VEEP are primarily spectators and not directly participating in the electronic excitation. We point out the importance of separating the electrostatic and exchange-repulsion components of the MC-VEEP in order that interactions between the effective potential and other nuclei can be modeled correctly. We present a MC-VEEP for methyl radical with one active electron which is tested in several conjugated molecules. We discuss the use of the MC-VEEP as a solution to the "link atom" problem in hybrid quantum mechanical/molecular mechanical methods. We also discuss the limitations and further development of this approach.

  11. On the excited electronic state dissociation of nitramine energetic materials and model systems

    NASA Astrophysics Data System (ADS)

    Guo, Y. Q.; Greenfield, M.; Bhattacharya, A.; Bernstein, E. R.

    2007-10-01

    In order to elucidate the difference between nitramine energetic materials, such as RDX (1,3,5-trinitro-1,3,5-triazacyclohexane), HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), and their nonenergetic model systems, including 1,4-dinitropiperazine, nitropiperidine, nitropyrrolidine, and dimethylnitramine, both nanosecond mass resolved excitation spectroscopy and femtosecond pump-probe spectroscopy in the UV spectral region have been employed to investigate the mechanisms and dynamics of the excited electronic state photodissociation of these materials. The NO molecule is an initial decomposition product of all systems. The NO molecule from the decomposition of energetic materials displays cold rotational and hot vibrational spectral structures. Conversely, the NO molecule from the decomposition of model systems shows relatively hot rotational and cold vibrational spectra. In addition, the intensity of the NO ion signal from energetic materials is proportional to the number of nitramine functional groups in the molecule. Based upon experimental observations and theoretical calculations of the potential energy surface for these systems, we suggest that energetic materials dissociate from ground electronic states after internal conversion from their first excited states, and model systems dissociate from their first excited states. In both cases a nitro-nitrite isomerization is suggested to be part of the decomposition mechanism. Parent ions of dimethylnitramine and nitropyrrolidine are observed in femtosecond experiments. All the other molecules generate NO as a decomposition product even in the femtosecond time regime. The dynamics of the formation of the NO product is faster than 180fs, which is equivalent to the time duration of our laser pulse.

  12. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film.

    PubMed

    Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D

    2015-06-01

    Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S(λ1,T̃2,λ3)) along the population time (T̃2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S(λ1,ν̃2,λ3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ν̃2) in the rephasing beating map and at negative frequency (-ν̃2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

  13. Standoff Trace Chemical Sensing via Manipulation of Excited Electronic State Lifetimes

    SciTech Connect

    Rudakov, Fedor M

    2013-01-01

    We present a technique for standoff trace chemical sensing that is based on the dependence of excited electronic state lifetimes on the amount of internal vibrational energy. Time resolved photoionization measurements show that the lifetime of the S1 state in N,N-dimethylisopropylamine (DMIPA) decreases exponentially with the amount of energy deposited into vibrational degrees of freedom. This property is employed to acquire spectral signatures of the molecule. Two nanosecond laser pulses are used, one (266 nm) to ionize the molecule through the S1 state and another, with tunable wavelength, to alter the lifetime of the S1 state by depositing energy into vibrations. Reduction of the S1 state lifetime results in a dip in ionization efficiency that is observed by remotely probing the laser-induced plasma with microwave radiation.

  14. An experimental and theoretical investigation into the excited electronic states of phenol

    SciTech Connect

    Jones, D. B.; Chiari, L.; Silva, G. B. da; Neves, R. F. C.; Duque, H. V.; Oliveira, E. M. de; Lima, M. A. P.; Lopes, M. C. A.; Costa, R. F. da; Varella, M. T. do N.; Bettega, M. H. F.; and others

    2014-08-21

    We present experimental electron-energy loss spectra (EELS) that were measured at impact energies of 20 and 30 eV and at angles of 90° and 10°, respectively, with energy resolution ∼70 meV. EELS for 250 eV incident electron energy over a range of angles between 3° and 50° have also been measured at a moderate energy resolution (∼0.9 eV). The latter spectra were used to derive differential cross sections and generalised oscillator strengths (GOS) for the dipole-allowed electronic transitions, through normalization to data for elastic electron scattering from benzene. Theoretical calculations were performed using time-dependent density functional theory and single-excitation configuration interaction methods. These calculations were used to assign the experimentally measured spectra. Calculated optical oscillator strengths were also compared to those derived from the GOS data. This provides the first investigation of all singlet and triplet excited electronic states of phenol up to the first ionization potential.

  15. Total photoionization cross-sections of excited electronic states by the algebraic diagrammatic construction-Stieltjes-Lanczos method

    SciTech Connect

    Ruberti, M.; Yun, R.; Averbukh, V.; Gokhberg, K.; Kopelke, S.; Cederbaum, L. S.; Tarantelli, F.

    2014-05-14

    Here, we extend the L{sup 2} ab initio method for molecular photoionization cross-sections introduced in Gokhberg et al. [J. Chem. Phys. 130, 064104 (2009)] and benchmarked in Ruberti et al. [J. Chem. Phys. 139, 144107 (2013)] to the calculation of total photoionization cross-sections of molecules in electronically excited states. The method is based on the ab initio description of molecular electronic states within the many-electron Green's function approach, known as algebraic diagrammatic construction (ADC), and on the application of Stieltjes-Chebyshev moment theory to Lanczos pseudospectra of the ADC electronic Hamiltonian. The intermediate state representation of the dipole operator in the ADC basis is used to compute the transition moments between the excited states of the molecule. We compare the results obtained using different levels of the many-body theory, i.e., ADC(1), ADC(2), and ADC(2)x for the first two excited states of CO, N{sub 2}, and H{sub 2}O both at the ground state and the excited state equilibrium or saddle point geometries. We find that the single excitation ADC(1) method is not adequate even at the qualitative level and that the inclusion of double electronic excitations for description of excited state photoionization is essential. Moreover, we show that the use of the extended ADC(2)x method leads to a substantial systematic difference from the strictly second-order ADC(2). Our calculations demonstrate that a theoretical modelling of photoionization of excited states requires an intrinsically double excitation theory with respect to the ground state and cannot be achieved by the standard single excitation methods with the ground state as a reference.

  16. Excited state structural dynamics in higher lying electronic states: S2 state of malachite green

    NASA Astrophysics Data System (ADS)

    Laptenok, Sergey P.; Addison, Kiri; Heisler, Ismael A.; Meech, Stephen R.

    2014-06-01

    The S2 fluorescence of malachite green is measured with sub 100 fs time resolution. Ultrafast spectral dynamics in the S2 state preceding S2 decay are resolved. Measurements in different solvents show that these sub 100 fs dynamics are insensitive to medium polarity and viscosity. They are thus assigned to ultrafast structural evolution between the S2 Franck-Condon and equilibrium configurations.

  17. Electronically excited states and photochemical reaction mechanisms of β-glucose.

    PubMed

    Tuna, Deniz; Sobolewski, Andrzej L; Domcke, Wolfgang

    2014-01-01

    Carbohydrates are important molecular components of living matter. While spectroscopic and computational studies have been performed on carbohydrates in the electronic ground state, the lack of a chromophore complicates the elucidation of the excited-state properties and the photochemistry of this class of compounds. Herein, we report on the first computational investigation of the singlet photochemistry of β-glucose. It is shown that low-lying singlet excited states are of nσ* nature. Our computations of the singlet vertical excitation energies predict absorption from 6.0 eV onward. Owing to a dense manifold of weakly-absorbing states, a sizable and broad absorption in the ultraviolet-C range arises. We have explored two types of photochemical reaction mechanisms: hydrogen-detachment processes for each of the five O-H groups and a C-O ring-opening process. Both types of reactions are driven by repulsive nσ* states that are readily accessible from the Franck-Condon region and lead to conical intersections in a barrierless fashion. We have optimized the geometries of the conical intersections involved in these photochemical processes and found that these intersections are located around 5.0 eV for the O-H hydrogen-detachment reactions and around 4.0 eV for the C-O ring-opening reaction. The energies of all conical intersections are well below the computed absorption edge. The calculations were performed using linear-response methods for the computation of the vertical excitation energies and multiconfigurational methods for the optimization of conical intersections and the computation of energy profiles. PMID:23959595

  18. Highlighting short-lived excited electronic states with pump-degenerate-four-wave-mixing.

    PubMed

    Marek, Marie S; Buckup, Tiago; Southall, June; Cogdell, Richard J; Motzkus, Marcus

    2013-08-21

    Detection of short-lived transient species is a major challenge in femtosecond spectroscopy, especially when third-order techniques like transient absorption are used. Higher order methods employ additional interactions between light and matter to highlight such transient species. In this work we address numerically and experimentally the detection of ultrafast species with pump-Degenerate Four Wave Mixing (pump-DFWM). In this respect, conclusive identification of ultrafast species requires the proper determination of time-zero between all four laser pulses (pump pulse and the DFWM sequence). This is addressed here under the light of experimental parameters as well as molecular properties: The role of pulse durations, amount of pulse chirp as well as excited state life time is investigated by measuring a row of natural pigments differing mainly in the number of conjugated double bonds (N = 9 to 13). A comparison of the different signals reveals a strikingly unusual behavior of spheroidene (N = 10). Complete analysis of the pump-DFWM signal illustrates the power of the method and clearly assigns the uniqueness of spheroidene to a mixing of the initially excited state with a dark excited electronic state.

  19. Graphene as a quencher of electronic excited states of photochemical probes.

    PubMed

    de Miguel, Maykel; Alvaro, Mercedes; García, Hermenegildo

    2012-02-01

    Graphene sheets quench the singlet and triplet excited states of a series of six photochemical probes including pyrene, acridine orange, tris(2,2́-bipyridyl)ruthenium(II) dichloride, methylene blue, meso-tetrakis(phenylsulphonate)porphyrin, and 5,10,15,20-tetraphenyl-21H,28H-porphine zinc. It was found that Stern-Volmer fluorescence quenching can fit to one or two different quenching regimes depending on the probe. In addition, the quenching can be either static or dynamic depending on the fluorophore. The occurrence of several quenching regimes has been interpreted considering that quenching arises from the crowding of the fluorophore on both graphene faces, or site isolation on the graphene sheets. Laser flash photolysis has shown that the triplet lifetime of the probes generally decreases due to graphene quenching and that no new transients appear except in the case of methylene blue, where a new absorption spectrum characterized by a continuous absorption band is observed and attributed to graphene radical ion. This spectroscopic evidence suggests that the most general quenching mechanism is energy transfer from the singlet or triplet excited state of the dye to graphene. This raises the issue of determining the energy of the electronic excited states of graphene.

  20. Vibrationally resolved photoelectron spectroscopy of electronic excited states of DNA bases: application to the ã state of thymine cation.

    PubMed

    Hochlaf, Majdi; Pan, Yi; Lau, Kai-Chung; Majdi, Youssef; Poisson, Lionel; Garcia, Gustavo A; Nahon, Laurent; Al Mogren, Muneerah Mogren; Schwell, Martin

    2015-02-19

    For fully understanding the light-molecule interaction dynamics at short time scales, recent theoretical and experimental studies proved the importance of accurate characterizations not only of the ground (D0) but also of the electronic excited states (e.g., D1) of molecules. While ground state investigations are currently straightforward, those of electronic excited states are not. Here, we characterized the à electronic state of ionic thymine (T(+)) DNA base using explicitly correlated coupled cluster ab initio methods and state-of-the-art synchrotron-based electron/ion coincidence techniques. The experimental spectrum is composed of rich and long vibrational progressions corresponding to the population of the low frequency modes of T(+)(Ã). This work challenges previous numerous works carried out on DNA bases using common synchrotron and VUV-based photoelectron spectroscopies. We provide hence a powerful theoretical and experimental framework to study the electronic structure of ionized DNA bases that could be generalized to other medium-sized biologically relevant systems.

  1. Excited electronic state decomposition mechanisms and dynamics of nitramine energetic materials and model systems

    NASA Astrophysics Data System (ADS)

    Greenfield, Margo

    Energetic materials play an important role in aeronautics, the weapon industry, and the propellant industry due to their broad applications as explosives and fuels. RDX (1,3,5-trinitrohexahydro-s-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) are compounds which contain high energy density. Although RDX and HMX have been studied extensively over the past several decades a complete understanding of their decomposition mechanisms and dynamics is unknown. Time of flight mass spectroscopy (TOFMS) UV photodissociation (ns) experiments of gas phase RDX, HMX, and CL-20 generate the NO molecule as the initial decomposition product. Four different vibronic transitions of the initial decomposition product, the NO molecule, are observed: A2Sigma(upsilon'=0)←X 2pi(upsilon"=0,1,2,3). Simulations of the rovibronic intensities for the A←X transitions demonstrate that NO dissociated from RDX, HMX, and CL-20 is rotationally cold (˜20 K) and vibrationally hot (˜1800 K). Conversely, experiments on the five model systems (nitromethane, dimethylnitramine (DMNA), nitropyrrolidine, nitropiperidine and dinitropiperazine) produce rotationally hot and vibrationally cold spectra. Laser induced fluorescence (LIF) experiments are performed to rule out the possible decomposition product OH, generated along with NO, perhaps from the suggested HONO elimination mechanism. The OH radical is not observed in the fluorescence experiments, indicating the HONO decomposition intermediate is not an important pathway for the excited electronic state decomposition of cyclic nitramines. The NO molecule is also employed to measure the dynamics of the excited state decomposition. A 226 nm, 180 fs light pulse is utilized to photodissociate the gas phase systems. Stable ion states of DMNA and nitropyrrolidine are observed while the energetic materials and remaining model systems present the NO molecule as the only

  2. Decoherence dynamics of coherent electronic excited states in the photosynthetic purple bacterium Rhodobacter sphaeroides.

    PubMed

    Liang, Xian-Ting; Zhang, Wei-Min; Zhuo, Yi-Zhong

    2010-01-01

    In this paper, we present a theoretical description to the quantum coherence and decoherence phenomena of energy transfer in photosynthesis observed in a recent experiment [Science 316, 1462 (2007)]. As a successive two-color laser pulses with selected frequencies cast on a sample of the photosynthetic purple bacterium Rb. sphaeroides two resonant excitations of electrons in chromophores can be generated. However, this effective two-level subsystem will interact with its protein environment and decoherence is inevitable. We describe this subsystem coupled with its environment as a dynamical spin-boson model. The non-Markovian decoherence dynamics is described using a quasiadiabatic propagator path integral (QUAPI) approach. With the photon-induced effective time-dependent level splitting energy and level flip coupling coefficient between the two excited states and the environment-induced non-Markovian decoherence dynamics, our theoretical result is in good agreement with the experimental data.

  3. Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

    NASA Astrophysics Data System (ADS)

    Cao, Jun; Xie, Zhi-Zhong; Yu, Xiaodong

    2016-08-01

    In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the Osbnd C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2sbnd 5 bond formation. The azirine and bicyclic intermediates in the S0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T1 state have been proposed for these phototranspositions.

  4. A simple method to determine bond lengths and excited state surfaces from electronic-vibrational spectra

    NASA Astrophysics Data System (ADS)

    Lee, Soo-Y.; Lai, Choy-Heng

    1990-03-01

    A fast and efficient method using the spectral moments of an electronic—vibrational spectrum is described to determine the harmonic and Morse potential fits to the excited state potential in the Franck—Condon region. Some of the drawbacks of the Franck—Condon least-squares fitting procedure are overcome by the moment method. The method is applied to some diatomics of current interest, spanning a wide range of bond length change in the electronic transition. The accuracy of the results suggests that the spectral moment method can be a replacement for the traditional and still popular Franck—Condon analysis.

  5. a Study of Quasi-One Systems: Excitation of the Active Electron to its First Excited State

    NASA Astrophysics Data System (ADS)

    Redd, Emmett Richter

    Experimental angular differential cross sections (ADCS) of four Quasi-One-Electron (QOE) scattering systems (Li('+), Na('+) + H and Be('+), Mg('+) + He) are reported. These ADCS are determined for exciting the 'active' electron to its first excited state. The angular range of the ADCS is from 0 to (TURN)3 mrad(,lab) with an angular resolution of (TURN)120 (mu)rad(,lab). The energy range is from 19.4 to 150 keV with an energy-loss resolution of (TURN)1 eV. The ADCS are compared to the available theories. The agreement between experiment and theory ranges from very poor to fair. No experiments exist which allow direct comparison to the present results. Integration of the present ADCS gives results which are compared to the experimental and theoretical total He targets cross section results. The agreement changes from energy to energy. Theoretical total cross section results exist in the cases involving H targets and are in very poor to fair agreement with the present results. No experimental total cross sections exist in the H target case for comparison with the present results. The most striking feature occurs in the Na('+) + H ADCS. Here the value of the ADCS at zero angle changes by 2 1/2 orders of magnitude from (3.96 (+OR-) 2.00) x 10('-15) cm('2)/sr at 35.9 keV (v = 1/4 a.u.) to (1.03 (+OR-) 0.25) x 10('-12) cm('2)/sr at 143.8 keV (v = 1/2 a.u.). This steep rise in the ADCS at zero angle is interpreted as showing the onset of a direct excitation mechanism (mechanism ii in the QOE literature). Qualitative agreement between previous QOE results (at lower energy using He targets) and the present Na('+) + H results is shown. Massey parameter scaling is shown to supply relatively little information on the ADCS. Finally, the results are probed to show the similarities of the underlying scattering mechanisms. For systems with the same target, the ADCS show quantitatively comparable results implying considerable similarities. Although all the systems are shown to be

  6. Excited state intramolecular proton transfer in electron-rich and electron-poor derivatives of 10-hydroxybenzo[h]quinoline.

    PubMed

    Piechowska, Joanna; Huttunen, Kirsi; Wróbel, Zbigniew; Lemmetyinen, Helge; Tkachenko, Nikolai V; Gryko, Daniel T

    2012-10-01

    Eight previously inaccessible derivatives of 10-hydroxybenzo[h]quinoline were prepared via a straightforward strategy comprising formation of the benzo[h]quinoline skeleton followed by C-H acetoxylation at position 10. The occurrence of excited state intramolecular proton transfer (ESIPT) was detected in all cases since emission was observed only from the excited keto-tautomer. Studies on derivatives bearing both electron-donating and electron-withdrawing groups adjacent to the pyridine ring allowed us to identify some design patterns giving rise to NIR emission and large Stokes shifts. For a derivative of 10-hydroxybenzo[c]acridine, emission at 745 nm was observed, one of the lowest energy fluorescence ever reported for ESIPT system. On the basis of time-resolved measurements, proton transfer was found to be extremely fast with time constants in the range (0.08-0.45 ps). PMID:22946783

  7. New Theoretical Developments in Exploring Electronically Excited States: Including Localized Configuration Interaction Singles and Application to Large Helium Clusters

    NASA Astrophysics Data System (ADS)

    Closser, Kristina Danielle

    This thesis presents new developments in excited state electronic structure theory. Contrasted with the ground state, the electronically excited states of atoms and molecules often are unstable and have short lifetimes, exhibit a greater diversity of character and are generally less well understood. The very unusual excited states of helium clusters motivated much of this work. These clusters consist of large numbers of atoms (experimentally 103--109 atoms) and bands of nearly degenerate excited states. For an isolated atom the lowest energy excitation energies are from 1s → 2s and 1s → 2 p transitions, and in clusters describing the lowest energy band minimally requires four states per atom. In the ground state the clusters are weakly bound by van der Waals interactions, however in the excited state they can form well-defined covalent bonds. The computational cost of quantum chemical calculations rapidly becomes prohibitive as the size of the systems increase. Standard excited-state methods such as configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) can be used with ≈100 atoms, and are optimized to treat only a few states. Thus, one of our primary aims is to develop a method which can treat these large systems with large numbers of nearly degenerate excited states. Additionally, excited states are generally formed far from their equilibrium structures. Vertical excitations from the ground state induce dynamics in the excited states. Thus, another focus of this work is to explore the results of these forces and the fate of the excited states. Very little was known about helium cluster excited states when this work began, thus we first investigated the excitations in small helium clusters consisting of 7 or 25 atoms using CIS. The character of these excited states was determined using attachment/detachment density analysis and we found that in the n = 2 manifold the excitations could generally be interpreted as

  8. Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission

    SciTech Connect

    Sen, Ananya; Matthews, Edward M.; Dessent, Caroline E. H. E-mail: xuebin.wang@pnnl.gov; Hou, Gao-Lei; Wang, Xue-Bin E-mail: xuebin.wang@pnnl.gov

    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 PtCl{sub 6}{sup 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 PtCl{sub 6}{sup 2−} ⋅ thymine and PtCl{sub 6}{sup 2−} ⋅ adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN){sub 4}{sup 2−} ⋅ nucleobase complexes [A. Sen et al., J. Phys. Chem. B 119, 11626 (2015)]. The observation of delayed electron emission bands in the PtCl{sub 6}{sup 2−} ⋅ nucleobase spectra obtained in this work, as for the previously studied Pt(CN){sub 4}{sup 2−} ⋅ nucleobase complexes, is attributed to one-photon 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 time scale long enough to

  9. Simulations of the dissociation of small helium clusters with ab initio molecular dynamics in electronically excited states

    SciTech Connect

    Closser, Kristina D.; Head-Gordon, Martin; Gessner, Oliver

    2014-04-07

    The dynamics resulting from electronic excitations of helium clusters were explored using ab initio molecular dynamics. The simulations were performed with configuration interaction singles and adiabatic classical dynamics coupled to a state-following algorithm. 100 different configurations of He{sub 7} were excited into the 2s and 2p manifold for a total of 2800 trajectories. While the most common outcome (90%) was complete fragmentation to 6 ground state atoms and 1 excited state atom, 3% of trajectories yielded bound, He {sub 2}{sup *}, and <0.5% yielded an excited helium trimer. The nature of the dynamics, kinetic energy release, and connections to experiments are discussed.

  10. The contribution of electronically excited states to the radiation chemistry of organic systems

    SciTech Connect

    Lipsky, S.

    1990-01-01

    The absorption of 160 nm light by cyclohexane in mixtures of cyclohexane, benzene and tetraphenylmethylenediamine results in an emission spectrum consisting of the simultaneous fluorescence from all three components. A mechanism for the development of this spectrum and its dependence on benzene concentration is constructed and shown to be quantitatively consistent with the results of independent measurements on the separate components. In the absence of tetraphenylmethylenediamine, the quenching of cyclohexane fluorescence by benzene is found to be well represented by the standard diffusion model but with important contributions from transient'' terms. The fluorescence from both cyclohexane and benzene in their irradiated mixtures has been studied as a function of benzene concentration from {approx equal}0.005 M to 0.1 M. The quenching of the cyclohexane emission by benzene is found to be significantly greater than obtains under optical excitation conditions suggesting an important role for benzene as a scavenger of the geminate ion-pair precursor of the fluorescing state of cyclohexane. From diffusion models, a lower bound is established for the scavenging rate constant. Minima have been located in the excitation spectra of neat cyclohexane and 2,3-dimethylbutane at approximately the positions of their ionization potentials. The implications is that electron + positive ion neutralizations generate excited neutral states at energies lower than the ionization threshold. 17 refs.,

  11. Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

    NASA Astrophysics Data System (ADS)

    Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco; Sorella, Sandro; Casula, Michele

    2015-06-01

    We study the ionization energy, electron affinity, and the π → π∗ (1La) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the 1La excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral 1La excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.

  12. Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

    SciTech Connect

    Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco Casula, Michele; Sorella, Sandro

    2015-06-07

    We study the ionization energy, electron affinity, and the π → π{sup ∗} ({sup 1}L{sub a}) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the {sup 1}L{sub a} excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral {sup 1}L{sub a} excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.

  13. Development and Application of Single-Referenced Perturbation and Coupled-Cluster Theories for Excited Electronic States

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    Recent work on the development of single-reference perturbation theories for the study of excited electronic states will be discussed. The utility of these methods will be demonstrated by comparison to linear-response coupled-cluster excitation energies. Results for some halogen molecules of interest in stratospheric chemistry will be presented.

  14. Differential cross sections for intermediate-energy electron scattering from α-tetrahydrofurfuryl alcohol: Excitation of electronic-states

    SciTech Connect

    Chiari, L.; Jones, D. B.; Thorn, P. A.; Pettifer, Z.; Duque, H. V.; Silva, G. B. da; Limão-Vieira, P.; Duflot, D.; Hubin-Franskin, M.-J.; Delwiche, J.; Blanco, F.; García, G.; and others

    2014-07-14

    We report on measurements of differential cross sections (DCSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol (THFA). The energy range of these experiments was 20–50 eV, while the scattered electron was detected in the 10°–90° angular range. There are currently no other experimental data or theoretical computations against which we can directly compare the present measured results. Nonetheless, we are able to compare our THFA DCSs with earlier cross section measurements for Rydberg-state electronic excitation for tetrahydrofuran, a similar cyclic ether, from Do et al. [J. Chem. Phys. 134, 144302 (2011)]. In addition, “rotationally averaged” elastic DCSs, calculated using our independent atom model with screened additivity rule correction approach are also reported. Those latter results give integral cross sections consistent with the optical theorem, and supercede those from the only previous study of Milosavljević et al. [Eur. Phys. J. D 40, 107 (2006)].

  15. State-specific tunneling lifetimes from classical trajectories: H-atom dissociation in electronically excited pyrrole

    NASA Astrophysics Data System (ADS)

    Xie, Weiwei; Domcke, Wolfgang; Farantos, Stavros C.; Grebenshchikov, Sergy Yu.

    2016-03-01

    A trajectory method of calculating tunneling probabilities from phase integrals along straight line tunneling paths, originally suggested by Makri and Miller [J. Chem. Phys. 91, 4026 (1989)] and recently implemented by Truhlar and co-workers [Chem. Sci. 5, 2091 (2014)], is tested for one- and two-dimensional ab initio based potentials describing hydrogen dissociation in the 1B1 excited electronic state of pyrrole. The primary observables are the tunneling rates in a progression of bending vibrational states lying below the dissociation barrier and their isotope dependences. Several initial ensembles of classical trajectories have been considered, corresponding to the quasiclassical and the quantum mechanical samplings of the initial conditions. It is found that the sampling based on the fixed energy Wigner density gives the best agreement with the quantum mechanical dissociation rates.

  16. An experiment to measure electron impact excitation of ions that have metastable states

    NASA Astrophysics Data System (ADS)

    Janzen, Paul Henry

    The research presented in this thesis includes an absolute measurement of the cross section for electron impact excitation (EIE) of metastable Si 2+(3s3p 3 P°) to 3s3p 1P°; several refinements in the experimental techniques and analyses used for measurements of EIE by the photon detection method; and the design, construction, and testing of an original 5 GHz electron cyclotron resonance (ECR) ion source. The above work enables EIE measurements in a large body of multiply-charged ions observed in a broad range of astrophysical plasmas. The measurement of the cross section for electron impact excitation of Si2+ (3s3p 3P ° → 3s3p 1 P°) covers energies from below threshold to the turn-on of the 3s3p 3 P° → 3p2 3P transition. A beams modulation technique with inclined electron and ion beams was used. Radiation at 120.65 nm from the decay of the excited ions to the 3s2 1S ground state was detected using an absolutely calibrated optical system. The fractional population of metastable Si 2+(3s3p 3 P°) in the incident ion beam was determined to be 0.256 +/- 0.035(1.65sigma). The experimental energy spread ranged from 0.85 eV (FWHM) at the lowest energies to 0.56 eV at the highest. Resonance features consistent with 12-state close-coupling R-matrix calculations were seen. Following this measurement, an ECR ion source to be used for future studies of collisions between electrons and multiply charged ions was designed and built. The magnetic field in the ion source is generated by a permanent-magnet hexapole and two electromagnet coils, and forms a closed surface inside the plasma chamber at over twice the ECR frequency when operated at 5 GHz. The design applies the lessons learned from new high-frequency designs to the lower frequency of 5 GHz, makes maximum use of equipment already present in the laboratory, and was accomplished within a relatively small budget. The initial performance of the source is described.

  17. Two-photon excitation of low-lying electronic quadrupole states in atomic clusters

    SciTech Connect

    Nesterenko, V. O.; Reinhard, P.-G.; Halfmann, T.; Pavlov, L. I.

    2006-02-15

    A simple scheme of population and detection of low-lying electronic quadrupole modes in free small deformed metal clusters is proposed. The scheme is analyzed in terms of the time-dependent local density approximation calculations. As a test case, the deformed cluster Na{sub 11}{sup +} is considered. Long-living quadrupole oscillations are generated via resonant two-photon (two-dipole) excitation and then detected through the appearance of satellites in the photoelectron spectra generated by a probe pulse. Femtosecond pump and probe pulses with intensities I=2x10{sup 10}-2x10{sup 11} W/cm{sup 2} and pulse duration T=200-500 fs are found to be optimal. The modes of interest are dominated by a single electron-hole pair and so their energies, being combined with the photoelectron data for hole states, allow us to gather full mean-field spectra of valence electrons near the Fermi energy. Besides, the scheme allows us to estimate the lifetime of electron-hole pairs and hence the relaxation time of electronic energy into ionic heat.

  18. Electron-acceptor-dependent light absorption, excited-state relaxation, and charge generation in triphenylamine dye-sensitized solar cells.

    PubMed

    Li, Renzhi; Zhang, Min; Yan, Cancan; Yao, Zhaoyang; Zhang, Jing; Wang, Peng

    2015-01-01

    By choosing a simple triphenylamine electron donor, we herein compare the influence of electron acceptors benzothiadiazole benzoic acid (BTBA) and cyanoacrylic acid (CA), on energy levels, light absorption, and dynamics of excited-state evolution and electron injection. DFT and time-dependent DFT calculations disclosed remarkable intramolecular conformational changes for the excited states of these two donor-acceptor dyes. Photoinduced dihedral angle variation occurs to the triphenylamine unit in the CA dye and backbone planarization happens to conjugated aromatic blocks in the BTBA dye. Femtosecond spectroscopic measurements suggested the crucial role of having a long excited-state lifetime in maintaining a high electron-injection yield because a reduced driving force for a low energy-gap dye can result in slower electron-injection dynamics.

  19. A Doubles Correction to Electronic Excited States from Configuration Interaction in the Space of Single Substitutions

    NASA Technical Reports Server (NTRS)

    Head-Gordon, Martin; Rico, Rudolph J.; Lee, Timothy J.; Oumi, Manabu

    1994-01-01

    A perturbative correction to the method of configuration interaction with single substitutions (CIS) is presented. This CIS(D) correction approximately introduces the effect of double substitutions which are absent in CIS excited states. CIS(D) is a second-order perturbation expansion of the coupled-cluster excited state method, restricted to single and double substitutions, in a series in which CIS is zeroth order, and the first-order correction vanishes. CIS (D) excitation energies are size consistent and the calculational complexity scales with the fifth power of molecular size, akin to second-order Moller-Plesset theory for the ground state. Calculations on singlet excited states of ethylene, formaldehyde, acetaldehyde, butadiene and benzene show that CIS (D) is a uniform improvement over CIS. CIS(D) appears to be a promising method for examining excited states of large molecules, where more accurate methods are not feasible.

  20. Note: Observation of a new electronically excited state of cobalt monoxide

    NASA Astrophysics Data System (ADS)

    Zang, Jianzheng; Zhang, Qun; Qin, Chengbing; Gu, Zhong; Bai, Xilin; Chen, Yang

    2012-11-01

    The laser-induced fluorescence excitation spectra of jet-cooled CoO molecules have been recorded in the energy region of 21 800—25 000 cm-1. Apart from the seven vibronic bands assigned to the known G4Φ9/2(υ') - X4Δ7/2(υ″ = 0) progression [M. Barnes, D. J. Clouthier, P. G. Hajigeorgiou, G. Huang, C. T. Kingston, A. J. Merer, G. F. Metha, J. R. D. Peers, and S. J. Rixon, J. Mol. Spectrosc. 186, 374 (1997), 10.1006/jmsp.1997.7456], we observed a new band system assignable to the [22.95]4Δ7/2(υ' = 0 - 4) - X4Δ7/2(υ″ = 0) progression. Extensive perturbations among these vibronic bands have been revealed by means of reduced energy plots. The new electronically excitedstate has been determined to be most likely of an electronic configuration (2pπ)3(4sσ)2(3dδ)3(3dπ)3 based on the charge-transferred promotion model.

  1. 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.

  2. 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.

  3. General active space commutator-based coupled cluster theory of general excitation rank for electronically excited states: Implementation and application to ScH

    SciTech Connect

    Hubert, Mickaël; Loras, Jessica; Fleig, Timo; Olsen, Jeppe

    2013-11-21

    We present a new implementation of general excitation rank coupled cluster theory for electronically excited states based on the single-reference multi-reference formalism. The method may include active-space selected and/or general higher excitations by means of the general active space concept. It may employ molecular integrals over the four-component Lévy-Leblond Hamiltonian or the relativistic spin-orbit-free four-component Hamiltonian of Dyall. In an initial application to ground- and excited states of the scandium monohydride molecule we report spectroscopic constants using basis sets of up to quadruple-zeta quality and up to full iterative triple excitations in the cluster operators. Effects due to spin-orbit interaction are evaluated using two-component multi-reference configuration interaction for assessing the accuracy of the coupled cluster results.

  4. The electronic structure of VO in its ground and electronically excited states: A combined matrix isolation and quantum chemical (MRCI) study

    SciTech Connect

    Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg

    2015-07-14

    The electronic ground and excited states of the vanadium monoxide (VO) molecule were studied in detail. Electronic absorption spectra for the molecule isolated in Ne matrices complement the previous gas-phase spectra. A thorough quantum chemical (multi-reference configuration interaction) study essentially confirms the assignment and characterization of the electronic excitations observed for VO in the gas-phase and in Ne matrices and allows the clarification of open issues. It provides a complete overview over the electronically excited states up to about 3 eV of this archetypical compound.

  5. 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.

  6. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

    SciTech Connect

    Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D.

    2015-06-07

    Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S(λ{sub 1},T{sup ~}{sub 2},λ{sub 3})) along the population time (T{sup ~}{sub 2}) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S(λ{sub 1},ν{sup ~}{sub 2},λ{sub 3})). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ν{sup ~}{sub 2}) in the rephasing beating map and at negative frequency (−ν{sup ~}{sub 2}) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

  7. Configuration interaction study on the ground and excited electronic states of the SrH molecule

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoting; Liang, Guiying; Zhang, Xiaomei; Xu, Haifeng; Yan, Bing

    2016-02-01

    High-level ab initio calculations on the ground and the excited states of the SrH molecule have been carried out utilizing the multi-reference configuration interaction method plus Davidson correction (MRCI+Q) method, with small-core relativistic effective core potentials together with the corresponding correlation consistent polarized valence basis sets. The potential energy curves (PECs) of the 16 Λ-S states have been obtained with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound states were calculated, most of which have been reported for the first time, with those pertaining to the X2Σ+, A2П, B2Σ+, and A‧2Δ states being in line with the available experimental and theoretical values. The calculated spin-orbit matrix element indicates a strong interaction between the X2Σ+ and A2П states in the Franck-Condon region. The spin-orbit coupling (SOC) splits the lowest strongly bound X2Σ+, A2П, A‧2Δ, B2Σ+, and D2Σ+ states into 9 Ω states. For the D2Σ+ state, the SOC shifts the potential-well minimum to higher energy and shortens the bond length. The transition properties of the bound Λ-S states were predicated, including the transition dipole moments (TDMs), the Franck-Condon factors, and the radiative lifetimes. The lifetimes were calculated to be 34.2 ns (v‧=0) and 55.0 ns (v‧=0) for A2П and B2Σ+, in good agreement with the experimental results of 33.8±1.9 ns and 48.4±2.0 ns.

  8. Electronically Excited States in Poly(p-phenylenevinylene): Vertical Excitations and Torsional Potentials from High-Level Ab Initio Calculations

    PubMed Central

    2013-01-01

    Ab initio second-order algebraic diagrammatic construction (ADC(2)) calculations using the resolution of the identity (RI) method have been performed on poly-(p-phenylenevinylene) (PPV) oligomers with chain lengths up to eight phenyl rings. Vertical excitation energies for the four lowest π–π* excitations and geometry relaxation effects for the lowest excited state (S1) are reported. Extrapolation to infinite chain length shows good agreement with analogous data derived from experiment. Analysis of the bond length alternation (BLA) based on the optimized S1 geometry provides conclusive evidence for the localization of the defect in the center of the oligomer chain. Torsional potentials have been computed for the four excited states investigated and the transition densities divided into fragment contributions have been used to identify excitonic interactions. The present investigation provides benchmark results, which can be used (i) as reference for lower level methods and (ii) give the possibility to parametrize an effective Frenkel exciton Hamiltonian for quantum dynamical simulations of ultrafast exciton transfer dynamics in PPV type systems. PMID:23427902

  9. 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.

  10. Zeeman spectroscopy of NiH: Landé factors of three Ω = 3/2 excited electronic states

    NASA Astrophysics Data System (ADS)

    Harker, H.; Richard, C.; Tourasse, G.; Crozet, P.; Ross, A. J.

    2013-10-01

    We report molecular Landé factors for three Ω‧ = 3/2 vibronic levels of NiH: E[17.8], D[17.6], and I[17.2], lying 17 000-18 000 cm-1 above the ground electronic state. The molecular Landé factors of these three states exhibit unusual variations with J and with parity. Also, molecular Landé factors of the D[17.6] excited electronic state are unexpectedly sensitive to Ni isotope substitution at low J. These observations provide evidence for extensive mixing among electronic states, deviation from Hund's case (a) coupling, and the existence of a local perturbing state. We also report polarization-dependent discrepancies between experimental and theoretical spectral intensities [1] for transitions involving the I[17.2] excited electronic state.

  11. The 1-silaketenyl radical (HSiCO): Ground and first excited electronic states

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Yukio; Petraco, Nicholas D. K.; Brown, Shawn T.; Schaefer, Henry F.

    2000-02-01

    The two lowest-lying (X˜ 2A″ and à 2A') electronic states and lowest linear stationary point (1 2Π) of the 1-silaketenyl radical (HSiCO) have been investigated systematically using ab initio electronic structure theory. The lowest linear stationary point possesses two distinct imaginary vibrational frequencies along the HSiC bending coordinates, indicating a strong Renner-Teller interaction. The ground and first excited states of HSiCO are found to have trans-planar bent structures and they are more distorted from linearity but less polar than the corresponding states of HCCO. Specifically, the X˜ 2A″ structure features a small HSiC bond angle of 84°. With our most reliable method, cc-pVQZ CCSD(T), the classical X˜-à splitting has been predicted to be 35.7 kcal/mol (1.55 eV, 12 500 cm-1). The barriers to linearity were determined to be 53.5 kcal/mol (2.32 eV, 18 700 cm-1) for the X˜ 2A″ state and 17.8 kcal/mol (0.77 eV, 6240 cm-1) for the à 2A' state. The ground state of HSiCO was found to be relatively stable thermodynamically against the two dissociation reactions HSiCO(X˜ 2A″)→H(2S)+SiCO(X˜ 3Σ-) and HSiCO(X˜ 2A″)→SiH(X˜ 2Π)+CO(X˜ 1Σ+). Due to the large infrared (IR) intensities of some of the vibrational modes, IR spectroscopic investigation of the HSiCO radical may be feasible. HSiCO is the global minimum for these four atoms, lying energetically below SiCOH (38.5 kcal/mol), HCSiO (40.7 kcal/mol), and CSiOH (76.3 kcal/mol) at the TZ2P(f,d) configuration interaction with single and double excitations (CISD) level of theory.

  12. Beyond the molecular orbital conception of electronically excited states through the quantum theory of atoms in molecules.

    PubMed

    Ferro-Costas, David; Pendás, Angel Martín; González, Leticia; Mosquera, Ricardo A

    2014-05-28

    We show that the use of the quantum theory of atoms in molecules (QTAIM) in electronically excited states allows expanding the knowledge that the molecular orbital (MO) framework provides about electronic rearrangements. Despite that historical prejudice seemed to preclude the use of QTAIM beyond the electronic ground state, this paper evidences that QTAIM is versatile enough to deal with excited states. As an example, the paradigmatic n → π* electronic transition of formaldehyde is analyzed. Using QTAIM, an energy partition of excited state energies into atomic and diatomic energies is carried out for the first time. This partition shows that upon electronic excitation the atoms of the CO bond experience a stabilization in their net energies, accompanied by a destabilization in their interaction, a fact which is in accordance with the idea of populating an antibonding π* MO. The associated C-O bond elongation in the nπ* state does not involve a change in the π atomic populations - as one would expect from a π* orbital - but in the σ ones. Moreover, it is also found that the nπ* state is characterized by a weaker C-O interaction energy in comparison to that in the electronic ground state. In order to strengthen this interaction, the electron-electron repulsion between C and O is reduced via a symmetry-breaking of the electron density, causing the C pyramidalization. A topological analysis based on the Laplacian of the electron density and on the electron localization function (ELF) reveals that the n → π* transition can be visualized as a rotation of 90° of the oxygen lone pairs.

  13. 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.

  14. 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

  15. 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.

  16. 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.

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

    PubMed

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

    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.

  18. Magnetic field dependence of spin-forbidden electronic excitations reflects the Haldane or paramagnetic ground state

    NASA Astrophysics Data System (ADS)

    Long, V. C.; Montague, J. R.; Kozen, A. C.; Wei, X.; Landry, B. R.; Pearson, K. R.; Turnbull, M. M.; Landee, C. P.

    2007-03-01

    We compare the zero-field and magnetic field-dependent optical spectra of the Haldane chain compound NENB (Ni[en]2NO2BF4; en = C2N2H8) and the paramagnetic compound, Ni(en) 3(ClO4)2,H2O. Due to similar electronic coordination of Ni^2+, the two materials show similar zero-field d-d electronic transitions, including a spin-forbidden (SF) transition at 1.58 eV, overlapping a broad spin-allowed band at 1.45 eV. The relatively greater intensity of the SF band in the Haldane compound suggests activation by a spin exchange mechanism, whereas a spin-orbit coupling origin is likely in the paramagnet. A second narrower SF spin flip transition appears in NENB at 1.66 eV. In both compounds, the SF excitations are sensitive to applied field H. In NENB, the SF intensity is suppressed by H, consistent with behavior of spin exchange-activated bands. In Ni(en)3(ClO4)-2,H2O, the SF field sensitivity appears to combine an energy shift and intensity decrease. Details of the H dependence reflect the magnetic ground state of the material: the field sensitivity commences only above HC 10 T, in the Haldane compound, whereas the field-induced modifications begin immediately at H = 0 T in the paramagnet.

  19. 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

  20. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying πσ{sup ∗} states

    SciTech Connect

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas

    2015-05-14

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S{sub 1}←S{sub 0} absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S{sub 1} origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of πσ{sup ∗} character in the vicinity of the lowest valence ππ{sup ∗} state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ππ{sup ∗} and a nearby dissociative πσ{sup ∗} state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H{sub 2}O){sub n} clusters (n = 1-11), intensities of a number of πσ{sup ∗} states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the

  1. Solvent effects on excited-state electron-transfer rate of pyrene-labeled deoxyuridine: A theoretical study

    NASA Astrophysics Data System (ADS)

    Maekawa, Shintaro; Sato, Ryuma; Hirao, Kimihiko; Shigeta, Yasuteru

    2016-01-01

    Solvent effects on the quenching process from the first excited state of 5-(1-pyrenyl)-2‧-deoxyuridine (Py-dU) were theoretically examined. Our results suggest that the excited-state electron transfer occurs without the so-called proton-coupled electron transfer process, which supports experimental results. Although there are no remarkable differences observed in the structure and the corresponding S1 excitation energy between the solutions of MeOH and MeCN within a polarizable continuum model, we report here that hydrogen bonds between the explicit MeOH molecule with the dU moiety, whose structure was frequently found in molecular dynamics simulations, result in an enhancement of the electron-transfer rate constant.

  2. Energy Dispersive XAFS: Characterization of Electronically Excited States of Copper(I) Complexes

    PubMed Central

    2013-01-01

    Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)2]+ (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)2]+ (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of [Cu(dbp)2]+ (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn–Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu–N distance of 0.03 Å. PMID:23718738

  3. Calculation of vibrational and electronic excited state absorption spectra of arsenic-water complexes using density functional theory

    NASA Astrophysics Data System (ADS)

    Huang, L.; Lambrakos, S. G.; Shabaev, A.; Massa, L.

    2016-05-01

    Calculations are presented of vibrational and electronic excited-state absorption spectra for As-H2O complexes using density function theory (DFT) and time-dependent density functional theory (TD-DFT). DFT and TD-DFT can provide interpretation of absorption spectra with respect to molecular structure for excitation by electromagnetic waves at frequencies within the IR and UV-visible ranges. The absorption spectrum corresponding to excitation states of As-H2O complexes consisting of relatively small numbers of water molecules should be associated with response features that are intermediate between that of isolated molecules and that of a bulk system. DFT and TD-DFT calculated absorption spectra represent quantitative estimates that can be correlated with additional information obtained from laboratory measurements and other types of theory based calculations. The DFT software GAUSSIAN was used for the calculations of excitation states presented here.

  4. Surface-catalyzed recombination into excited electronic, vibrational, rotational, and kinetic energy states: A review

    NASA Technical Reports Server (NTRS)

    Kofsky, I. L.; Barrett, J. L.

    1985-01-01

    Laboratory experiments in which recombined CO, CO2, D2O, OH, N2, H2, and O2 molecules desorb from surfaces in excited internal and translational states are briefly reviewed. Unequilibrated distributions predominate from the principally catalytic metal substrates so far investigated. Mean kinetic energies have been observed up to approx. 3x, and in some cases less than, wall-thermal; the velocity distributions generally vary with emission angle, with non-Lambertian particle fluxes. The excitation state populations are found to depend on surface impurities, in an as yet unexplained way.

  5. Lifetimes of Vibro-Rotational Levels in Excited Electronic States of Diatomic Hydrogen Isotopologues

    SciTech Connect

    Astashkevich, S. A. Lavrov, B. P.

    2015-06-15

    The current situation in studies of lifetimes of excited rovibronic levels for the H{sub 2}, D{sub 2}, T{sub 2}, HD, HT, and DT molecules is analyzed. All measured lifetime values (792 entries for 618 different vibro-rotational levels of 33 electronic states) reported in 61 publications before April 2015 are compiled and listed in tabular format together with an annotated bibliography. Experimental data are only available for the H{sub 2}, HD, and D{sub 2} molecules. The data collected in the present work show fragmentariness of experimental data. For the vast majority of the levels, the lifetime values were reported in one paper only and up to now are without independent experimental verification. A complete bibliography of publications concerning semiempirical determination and nonempirical calculations of the lifetimes is presented. Numerical results obtained in the framework of these two approaches are listed only in cases when experimental data are available. For more than half of the levels, the differences between measured and calculated values are three times higher than experimental errors. These discrepancies show necessity of more precise experimental and nonempirical studies. For some 79 rovibronic levels, our analysis makes it possible to propose certain set of recommended lifetime values.

  6. Lifetimes of Vibro-Rotational Levels in Excited Electronic States of Diatomic Hydrogen Isotopologues

    NASA Astrophysics Data System (ADS)

    Astashkevich, S. A.; Lavrov, B. P.

    2015-06-01

    The current situation in studies of lifetimes of excited rovibronic levels for the H2, D2, T2, HD, HT, and DT molecules is analyzed. All measured lifetime values (792 entries for 618 different vibro-rotational levels of 33 electronic states) reported in 61 publications before April 2015 are compiled and listed in tabular format together with an annotated bibliography. Experimental data are only available for the H2, HD, and D2 molecules. The data collected in the present work show fragmentariness of experimental data. For the vast majority of the levels, the lifetime values were reported in one paper only and up to now are without independent experimental verification. A complete bibliography of publications concerning semiempirical determination and nonempirical calculations of the lifetimes is presented. Numerical results obtained in the framework of these two approaches are listed only in cases when experimental data are available. For more than half of the levels, the differences between measured and calculated values are three times higher than experimental errors. These discrepancies show necessity of more precise experimental and nonempirical studies. For some 79 rovibronic levels, our analysis makes it possible to propose certain set of recommended lifetime values.

  7. The role of the excited electronic states in the C{sup +}+H{sub 2}O reaction

    SciTech Connect

    Flores, Jesus R.; Gonzalez, Adan B.

    2008-04-14

    The electronic excited states of the [COH{sub 2}]{sup +} system have been studied in order to establish their role in the dynamics of the C{sup +}+H{sub 2}O{yields}[COH]{sup +}+H reaction, which is a prototypical ion-molecule reaction. The most relevant minima and saddle points of the lowest excited state have been determined and energy profiles for the lowest excited doublet and quartet electronic states have been computed along the fragmentation and isomerization coordinates. Also, nonadiabatic coupling strengths between the ground and the first excited state have been computed where they can be large. Our analysis suggests that the first excited state could play an important role in the generation of the formyl isomer, which has been detected in crossed beam experiments [D. M. Sonnenfroh et al., J. Chem. Phys. 83, 3985 (1985)], but could not be explained in quasiclassical trajectory computations [Y. Ishikawa et al., Chem. Phys. Lett. 370, 490 (2003); J. R. Flores, J. Chem. Phys. 125, 164309 (2006)].

  8. Electronic and Structural Elements That Regulate the Excited-State Dynamics in Purine Nucleobase Derivatives

    PubMed Central

    2015-01-01

    The excited-state dynamics of the purine free base and 9-methylpurine are investigated using experimental and theoretical methods. Femtosecond broadband transient absorption experiments reveal that excitation of these purine derivatives in aqueous solution at 266 nm results primarily in ultrafast conversion of the S2(ππ*) state to the vibrationally excited 1nπ* state. Following vibrational and conformational relaxation, the 1nπ* state acts as a doorway state in the efficient population of the triplet manifold with an intersystem crossing lifetime of hundreds of picoseconds. Experiments show an almost 2-fold increase in the intersystem crossing rate on going from polar aprotic to nonpolar solvents, suggesting that a solvent-dependent energy barrier must be surmounted to access the singlet-to-triplet crossing region. Ab initio static and surface-hopping dynamics simulations lend strong support to the proposed relaxation mechanism. Collectively, the experimental and computational results demonstrate that the accessibility of the nπ* states and the topology of the potential energy surfaces in the vicinity of conical intersections are key elements in controlling the excited-state dynamics of the purine derivatives. From a structural perspective, it is shown that the purine chromophore is not responsible for the ultrafast internal conversion in the adenine and guanine monomers. Instead, C6 functionalization plays an important role in regulating the rates of radiative and nonradiative relaxation. C6 functionalization inhibits access to the 1nπ* state while simultaneously facilitating access to the 1ππ*(La)/S0 conical intersection, such that population of the 1nπ* state cannot compete with the relaxation pathways to the ground state involving ring puckering at the C2 position. PMID:25763596

  9. Theoretical Studies of Possible Synthetic Routes for the High Energy Density Material Td N4: Excited Electronic States

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Dateo, Christopher E.

    2001-01-01

    Vertical electronic excitation energies for single states have been computed for the high energy density material (HEDM) Td N4 in order to assess possible synthetic routes that originate from excited electronic states of N2 molecules. Several ab initio theoretical approaches have been used, including complete active space self-consistent field (CASSCF), state averaged CASSCF (SA-CASSCF), singles configuration interaction (CIS), CIS with second-order and third-order correlation corrections [CIS(D)) and CIS(3)], and linear response singles and doubles coupled-cluster (LRCCSD), which is the highest level of theory employed. Standard double zeta polarized (DZP) and triple zeta double polarized (TZ2P) one-particle basis sets were used. The CASSCF calculations are found to overestimate the excitation energies, while the SA-CASSCF approach rectifies this error to some extent, but not completely. The accuracy of the CIS calculations varied depending on the particular state, while the CIS(D), CIS(3), and LRCCSD results are in generally good agreement. Based on the LRCCSD calculations, the lowest six excited singlet states are 9.35(l(sup)T1), 10.01(l(sup)T2), 10.04(1(sup)A2), 10.07(1(sup)E), 10.12(2(sup)T1), and 10.42(2(sup)T2) eV above the ground state, respectively. Comparison of these excited state energies with the energies of possible excited states of N2+N2 fragments, leads us to propose that the most likely synthetic route for Td N4 involving this mechanism arises from combination of two bound quintet states of N2.

  10. Excited electronic states of limonene: A circular dichroism and photoelectron spectroscopy study of d-limonene

    NASA Astrophysics Data System (ADS)

    Brint, P.; Meshulam, Edna; Gedanken, Aharon

    1984-08-01

    The excited states of limonene are discussed in the light of vacuum-UV absorption, VUVCD and photoelectron spectroscopy measurements. Only one π → π* transition arising from the double bond of the ring is observed. The CD sign of the π → π* transition does not obey the octant rule formulated for chiral olefins.

  11. 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.

  12. 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

  13. Excited states of the high-frequency vibrational modes and kinetics of ultrafast photoinduced electron transfer

    NASA Astrophysics Data System (ADS)

    Barykov, V. Yu.; Ivanov, A. I.

    2016-02-01

    The effect of the carrier frequency of the exciting laser pulse on the kinetics of intramolecular photoinduced charge transfer in the multi-channel stochastic model is studied. It is shown that the population of different states of high-frequency intramolecular modes upon varying the frequency of the excitation pulse can considerably alter the rate constant of ultrafast charge transfer. It is found that a negative vibrational spectral effect is expected in the vicinity of a barrier-free area (the rate constant of photoinduced charge transfer decreases along with the carrier frequency of the excitation pulse), while a positive effect is predicted in areas of high and low exergonicity (an inverse dependence). It is concluded that the value of the spectral effect falls along with the time of vibrational relaxation. For ultrafast photo-induced charge transfer, however, it remains considerable up to relaxation times of 100 fs.

  14. Approximating electronically excited states with equation-of-motion linear coupled-cluster theory

    SciTech Connect

    Byrd, Jason N. Rishi, Varun; Perera, Ajith; Bartlett, Rodney J.

    2015-10-28

    A new perturbative approach to canonical equation-of-motion coupled-cluster theory is presented using coupled-cluster perturbation theory. A second-order Møller-Plesset partitioning of the Hamiltonian is used to obtain the well known equation-of-motion many-body perturbation theory equations and two new equation-of-motion methods based on the linear coupled-cluster doubles and linear coupled-cluster singles and doubles wavefunctions. These new methods are benchmarked against very accurate theoretical and experimental spectra from 25 small organic molecules. It is found that the proposed methods have excellent agreement with canonical equation-of-motion coupled-cluster singles and doubles state for state orderings and relative excited state energies as well as acceptable quantitative agreement for absolute excitation energies compared with the best estimate theory and experimental spectra.

  15. Excited electronic state mixing in 7-azaindole. Quantitative measurements using the Stark effect.

    PubMed

    Young, Justin W; Pozun, Zachary D; Jordan, Kenneth D; Pratt, David W

    2013-12-12

    Stark effect measurements of the +280 cm(-1) vibronic band at ∼286 nm in the high resolution S1-S0 fluorescence excitation spectrum of 7-azaindole (7AI) in a molecular beam show that the permanent (electric) dipole moment (PDM) of the upper state vibrational level reached in this transition is 4.6 D, twice as large as the PDM of the zero-point level of the S1 state. This large difference is attributed to state mixing with a more polar state. EOM-CSSD calculations suggest that this more polar state is σπ* in nature and that it crosses the ππ* state in energy along the coordinate connecting the two potential energy minima. Such state mixing apparently provides more facile access to conical intersections with the ground state, and subsequent hydrogen atom detachment reactions, since independent studies by Sakota and Sekiya have shown that the N-H stretching frequency of 7AI is significantly reduced when it is excited to the +280 cm(-1) vibrational level of the S1 state.

  16. Electron-impact ionization cross sections out of the ground and 6P2 excited states of cesium

    NASA Astrophysics Data System (ADS)

    Łukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-01

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the “trap loss” technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs 6P3/22 state between 7eV and 400eV . CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  17. 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.

  18. Calculation of Ground State Rotational Populations for Kinetic Gas Homonuclear Diatomic Molecules including Electron-Impact Excitation and Wall Collisions

    SciTech Connect

    David R. Farley

    2010-08-19

    A model has been developed to calculate the ground-state rotational populations of homonuclear diatomic molecules in kinetic gases, including the effects of electron-impact excitation, wall collisions, and gas feed rate. The equations are exact within the accuracy of the cross sections used and of the assumed equilibrating effect of wall collisions. It is found that the inflow of feed gas and equilibrating wall collisions can significantly affect the rotational distribution in competition with non-equilibrating electron-impact effects. The resulting steady-state rotational distributions are generally Boltzmann for N≥3, with a rotational temperature between the wall and feed gas temperatures. The N=0,1,2 rotational level populations depend sensitively on the relative rates of electron-impact excitation versus wall collision and gas feed rates.

  19. Excited electronic states from a variational approach based on symmetry-projected Hartree–Fock configurations

    SciTech Connect

    Jiménez-Hoyos, Carlos A.; Rodríguez-Guzmán, R.; Scuseria, Gustavo E.

    2013-12-14

    Recent work from our research group has demonstrated that symmetry-projected Hartree–Fock (HF) methods provide a compact representation of molecular ground state wavefunctions based on a superposition of non-orthogonal Slater determinants. The symmetry-projected ansatz can account for static correlations in a computationally efficient way. Here we present a variational extension of this methodology applicable to excited states of the same symmetry as the ground state. Benchmark calculations on the C{sub 2} dimer with a modest basis set, which allows comparison with full configuration interaction results, indicate that this extension provides a high quality description of the low-lying spectrum for the entire dissociation profile. We apply the same methodology to obtain the full low-lying vertical excitation spectrum of formaldehyde, in good agreement with available theoretical and experimental data, as well as to a challenging model C{sub 2v} insertion pathway for BeH{sub 2}. The variational excited state methodology developed in this work has two remarkable traits: it is fully black-box and will be applicable to fairly large systems thanks to its mean-field computational cost.

  20. Entanglement entropy of electronic excitations.

    PubMed

    Plasser, Felix

    2016-05-21

    A new perspective into correlation effects in electronically excited states is provided through quantum information theory. The entanglement between the electron and hole quasiparticles is examined, and it is shown that the related entanglement entropy can be computed from the eigenvalue spectrum of the well-known natural transition orbital (NTO) decomposition. Non-vanishing entanglement is obtained whenever more than one NTO pair is involved, i.e., in the case of a multiconfigurational or collective excitation. An important implication is that in the case of entanglement it is not possible to gain a complete description of the state character from the orbitals alone, but more specific analysis methods are required to decode the mutual information between the electron and hole. Moreover, the newly introduced number of entangled states is an important property by itself giving information about excitonic structure. The utility of the formalism is illustrated in the cases of the excited states of two interacting ethylene molecules, the conjugated polymer para-phenylene vinylene, and the naphthalene molecule.

  1. Entanglement entropy of electronic excitations

    NASA Astrophysics Data System (ADS)

    Plasser, Felix

    2016-05-01

    A new perspective into correlation effects in electronically excited states is provided through quantum information theory. The entanglement between the electron and hole quasiparticles is examined, and it is shown that the related entanglement entropy can be computed from the eigenvalue spectrum of the well-known natural transition orbital (NTO) decomposition. Non-vanishing entanglement is obtained whenever more than one NTO pair is involved, i.e., in the case of a multiconfigurational or collective excitation. An important implication is that in the case of entanglement it is not possible to gain a complete description of the state character from the orbitals alone, but more specific analysis methods are required to decode the mutual information between the electron and hole. Moreover, the newly introduced number of entangled states is an important property by itself giving information about excitonic structure. The utility of the formalism is illustrated in the cases of the excited states of two interacting ethylene molecules, the conjugated polymer para-phenylene vinylene, and the naphthalene molecule.

  2. Quartic force fields for excited electronic states: rovibronic reference data for the 1 (2)A' and 1 (2)A″ states of the isoformyl radical, HOC.

    PubMed

    Morgan, W James; Fortenberry, Ryan C

    2015-01-25

    Quartic force fields (QFFs) have been shown to be an effective, accurate, and relatively compact means of computing rovibrational spectroscopic data for numerous molecules with numerous applications. However, excited states have been nearly excluded from the this approach since most accurate QFFs are based on the "gold standard" coupled cluster singles, doubles, and perturbative triples [CCSD(T)] method which is not readily extended to excited states. In this work, rovibronic spectroscopic data is provided for the isoformyl radical, a molecule of significance in combustion and astrochemistry, both through the traditional means of variational access to excited states with CCSD(T) and in the novel extension of QFFs routinely to treat electronically excited states through the standard coupled cluster excited state approach, equation of motion (EOM) CCSD. It is shown here that the new EOM-based QFF provides structural parameters and rotational constants that are quite close to those from a related CCSD(T)-based QFF for the 1 (2)A(″) excited state of HOC. The anharmonic vibrational frequency percent differences between the two QFFs are less than 0.4% for the O-H stretch, less than 1.9% for the C-O stretch, and around 3.0% for the bend. Even so, the pure excited state EOM-QFF anharmonic frequencies are still very good abinitio representations that may be applied to systems where electronically excited states are not variationally accessible. Additionally, rovibrational spectroscopic data is provided for the 1 (2)A(') ground state of HOC and for both the ground and excited state of DOC.

  3. Excited State Lifetime Measurements in Rare Earth Nuclei with Fast Electronics

    NASA Astrophysics Data System (ADS)

    Werner, V.; Cooper, N.; Bonett-Matiz, M.; Williams, E.; Régis, J.-M.; Rudigier, M.; Ahn, T.; Anagnostatou, V.; Berant, Z.; Bunce, M.; Elvers, M.; Heinz, A.; Ilie, G.; Jolie, J.; Radeck, D.; Savran, D.; Smith, M.

    2011-09-01

    We investigated the collectivity of the lowest excited 2+ states of even-even rare earth nuclei. The B(E2) excitation strengths of these nuclei should directly correlate to the size of the valence space, and maximize at mid-shell. The previously identified saturation of B(E2) strength in well-deformed rotors at mid-shell is put to a high precision test in this series of measurements. Lifetimes of the 2+1 states in 168Hf and 174W have been measured using the newly developed LaBr3 scintillation detectors. The excellent energy resolution in conjunction with superb time properties of the new material allows for reliable handling of background, which is a source of systematic error in such experiments. Preliminary lifetime values are obtained and discussed in the context of previous and ongoing work.

  4. Excitation of the 3p states in electron-sodium scattering at intermediate energies

    SciTech Connect

    Kamali, M. Z. M.; Wong, B. R.; Chin, J. H.; Ratnavelu, K.

    2014-03-05

    A coupled-channel-optical method (CCOM), to investigate the excitation of the 3p states for e{sup −}-Na scattering at intermediate energies, is reported. Nine atomic states( Na(3s), Na(3p), Na(4s), Na(3d), Na(4p), Na(5s), Na(4d), Na(5p), Na(5d) ) together with three optical potentials are used in this work. The inelastic differential cross sections (DCS) as well as the reduced Stokes parameters are compared with latest theoretical data and experimental measurements.

  5. Laser double-resonance studies of electronic spectroscopy and state-resolved collisional relaxation in highly vibrationally excited acetylene

    SciTech Connect

    Tobiason, J.D.

    1992-01-01

    Vibrational overtone excitation combined with laser-induced fluorescence detection of acetylene molecules permits rotation-selected spectroscopy of the ([tilde A][sup 1]A[sub u]) electronic state and direct, state-resolved measurements of collisional energy transfer in the highly vibrationally excited ground electronic state. The author assigns energies of 1,045 transitions to previously unobserved ungerade vibrational states 2800-4500 cm[sup [minus]1] above the [tilde A] state origin. An analysis yields frequencies of 2856.4 and 3894.3 cm[sup [minus]1] for [nu][sub v][prime] and [nu][sub 3][prime] + [nu][sub 5][prime]. The author performs the first normal coordinate analysis of [tilde A] state acetylene based only on directly observed fundamentals. The spectroscopy measurements enable double-resonance experiments on the collisional dynamics of highly vibrationally excited acetylene. The quenching rate for single rotational states is twice the Lennard-Jones gas kinetic rate and fairly independent of vibrational energy level. Collision-induced detection of vibrational overtone excitation under single collision conditions allows direct measurements of state-of-state rotational and vibrational energy transfer. A collision-induced spectrum obtained by this new technique immediately identifies transfer channels and the [Delta]J and [Delta]E dependence of the transfer rates. The author observes changes of [vert bar][Delta]J[vert bar] and [Delta]E [approx] 3kT in a single collision. Directly measured rates for one set of vibrational relaxation pathways account for [approximately]3% of the total relaxation rate. The author also observes other vibrational relaxation pathways. The available pathways suggest that vibrational relaxation accounts for the rest of the total relaxation. Changes of [vert bar]J[vert bar] = 18 and [vert bar][Delta]E[vert bar] [approximately] 500 cm[sup [minus]1] in a single collision are observed.

  6. The Ground and Two Lowest-lying Singlet Excited Electronic States of Copper Hydroxide (CuOH)

    SciTech Connect

    Wang, Suyun; Paul, Ankan; DeYonker, Nathan John; Yamaguchi, Yukio; Schaefer, Henry F

    2005-07-12

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Various ab initio methods, including self-consistent field (SCF), configuration interaction, coupled cluster (CC), and complete-active-space SCF (CASSCF), have been employed to study the electronic structure of copper hydroxide (CuOH). Geometries, total energies, dipole moments, harmonic vibrational frequencies, and zero-point vibrational energies are reported for the linear 1Σ+ and 1Π stationary points, and for the bent ground-state1A', and excited-states 2 1A" and 1 1A". Six different basis sets have been used in the study, Wachters/DZP being the smallest and QZVPP being the largest. The ground- and excited-state bending modes present imaginary frequencies for the linear stationary points, indicating that bent structures are more favorable. The effects of relativity for CuOH are important and have been considered using the Douglas–Kroll approach with cc-pVTZ/cc-pVTZ_DK and cc-pVQZ/cc-pVQZ_DK basis sets. The bent ground and two lowest-lying singlet excited states of the CuOH molecule are indeed energetically more stable than the corresponding linear structures. The optimized geometrical parameters for the X˜ 1A' and 1 1A" states agree fairly well with available experimental values. However, the 2 1A' structure and rotational constants are in poor agreement with experiment, and we suggest that the latter are in error. The predicted adiabatic excitation energies are also inconsistent with the experimental values of 45.5 kcal mol-1 for the 2 1A' state and 52.6 kcal mol-1 for the 1 1A" state. The theoretical CC and CASSCF methods show lower

  7. Configuration interaction singles natural orbitals: An orbital basis for an efficient and size intensive multireference description of electronic excited states

    SciTech Connect

    Shu, Yinan; Levine, Benjamin G.; Hohenstein, Edward G.

    2015-01-14

    Multireference quantum chemical methods, such as the complete active space self-consistent field (CASSCF) method, have long been the state of the art for computing regions of potential energy surfaces (PESs) where complex, multiconfigurational wavefunctions are required, such as near conical intersections. Herein, we present a computationally efficient alternative to the widely used CASSCF method based on a complete active space configuration interaction (CASCI) expansion built from the state-averaged natural orbitals of configuration interaction singles calculations (CISNOs). This CISNO-CASCI approach is shown to predict vertical excitation energies of molecules with closed-shell ground states similar to those predicted by state averaged (SA)-CASSCF in many cases and to provide an excellent reference for a perturbative treatment of dynamic electron correlation. Absolute energies computed at the CISNO-CASCI level are found to be variationally superior, on average, to other CASCI methods. Unlike SA-CASSCF, CISNO-CASCI provides vertical excitation energies which are both size intensive and size consistent, thus suggesting that CISNO-CASCI would be preferable to SA-CASSCF for the study of systems with multiple excitable centers. The fact that SA-CASSCF and some other CASCI methods do not provide a size intensive/consistent description of excited states is attributed to changes in the orbitals that occur upon introduction of non-interacting subsystems. Finally, CISNO-CASCI is found to provide a suitable description of the PES surrounding a biradicaloid conical intersection in ethylene.

  8. Conformational analysis of N-methylformamide in ground S0 and excited S1 and T1 electronic states

    NASA Astrophysics Data System (ADS)

    Tukachev, N. V.; Bataev, V. A.; Godunov, I. A.

    2016-07-01

    For conformers of the N-methylformamide (HCONHCH3) molecule, calculations of equilibrium geometry parameters, harmonic vibration frequencies, energy differences and potential barriers to conformational transitions were performed in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states. In the S0 state, the molecule exists in trans and cis stable conformations (having Cs symmetry). Our calculations show that the electronic excitations T1←S0 and S1←S0 cause changes in the structure of conformers: both HCON and HNCC fragments become pyramidal and rotate around the CN bond. As a result, in each excited electronic state under consideration, there are 12 minima forming six pairs of equivalent conformers separated by relatively small potential barriers. One- and two-dimensional potential energy surface sections corresponding to different intramolecular large-amplitude motions were calculated using the MP2/aug-cc-pVTZ (S0) and CASPT2/cc-pVTZ (S1 and T1) methods. Anharmonic vibrational problems for large-amplitude motions were solved, and the corresponding frequencies were estimated.

  9. Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited ( S 1) electronic state

    NASA Astrophysics Data System (ADS)

    Koroleva, L. A.; Tyulin, V. I.; Matveev, V. K.; Pentin, Yu. A.

    2012-04-01

    The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited ( S 1) electronic state. The ν00 trans = 25861 cm-1 values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state ( S 1) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v') transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν00 trans trans origin allowed the table to be extended to high quantum numbers v'. The torsional vibration frequencies up to v' = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited ( S 1) electronic state.

  10. Fluorescence excitation involving multiple electron transition states of N{sub 2} and CO{sub 2}

    SciTech Connect

    Wu, C.Y.R.; Chen, F.Z.; Hung, T.; Judge, D.L.

    1997-04-01

    The electronic states and electronic structures of N{sub 2} and CO{sub 2} in the 8-50 eV energy region have been studied extensively both experimentally and theoretically. In the energy region higher than 25 eV there exists many electronic states including multiple electron transition (MET) states which are responsible for producing most of the dissociative photoionization products. The electronic states at energies higher than 50 eV have been mainly determined by Auger spectroscopy, double charge transfer, photofragment spectroscopy and ion-ion coincidence spectroscopy. The absorption and ionization spectra of these molecules at energies higher than 50 eV mainly show a monotonic decrease in cross section values and exhibit structureless features. The decay channels of MET and Rydberg (or superexcited) states include autoionization, ionization, dissociative ionization, predissociation, and dissociation while those of single ion and multiple ion states may involve predissociation. and dissociation processes. The study of fluorescence specifically probes electronically excited species resulting from the above-mentioned decay channels and provides information for understanding the competition among these channels.

  11. Two-Photon Study on the Electronic Interactions between the First Excited Singlet States in Carotenoid-Tetrapyrrole Dyads

    SciTech Connect

    Liao, Pen-Nan; Pillai, Smitha; Gust, Devens; Moore, Thomas A.; Moore, Ana L.; Walla, Peter J.

    2011-03-22

    Electronic interactions between the first excited states (S1) of carotenoids (Car) of different conjugation lengths (8-11 double bonds) and phthalocyanines (Pc) in different Car-Pc dyad molecules were investigated by two-photon spectroscopy and compared with Car S1-chlorophyll (Chl) interactions in photosynthetic light harvesting complexes (LHCs). The observation of Chl/Pc fluorescence after selective two-photon excitation of the Car S1 state allowed sensitive monitoring of the flow of energy between Car S1 and Pc or Chl. It is found that two-photon excitation excites to about 80% to 100% exclusively the carotenoid state Car S1 and that only a small fraction of direct tetrapyrrole two-photon excitation occurs. Amide-linked Car-Pc dyads in tetrahydrofuran demonstrate a molecular gear shift mechanism in that effective Car S1 → Pc energy transfer is observed in a dyad with 9 double bonds in the carotenoid, whereas in similar dyads with 11 double bonds in the carotenoid, the Pc fluorescence is strongly quenched by Pc → Car S1 energy transfer. In phenylamino-linked Car-Pc dyads in toluene extremely large electronic interactions between the Car S1 state and Pc were observed, particularly in the case of a dyad in which the carotenoid contained 10 double bonds. This observation together with previous findings in the same system provides strong evidence for excitonic Car S1-Pc Qy interactions. Very similar results were observed with photosynthetic LHC II complexes in the past, supporting an important role of such interactions in photosynthetic down-regulation.

  12. Electronic Structure of the Ground and Excited States of the CuA Site by NMR Spectroscopy

    PubMed Central

    Abriata, Luciano A.; Ledesma, Gabriela N.; Pierattelli, Roberta; Vila, Alejandro J.

    2009-01-01

    The electronic properties of Thermus thermophilus CuA in the oxidized form were studied by 1H and 13C NMR spectroscopy. All the 1H and 13C resonances from cysteine and imidazole ligands were observed and assigned in a sequence-specific fashion. The detection of net electron spin density on a peptide moiety is attributed to the presence of a H-bond to a coordinating sulfur atom. This hydrogen-bond is conserved in all natural CuA variants, and is important to maintain the electronic structure of the metal site, rendering the two Cys ligands nonequivalent. The anomalous temperature dependence of the chemical shifts is explained by the presence of a low-lying excited state located about 600 cm-1 above the ground state. The room temperature shifts can be described as the thermal average of a σu* ground state and a πu excited state. These results provide a detailed description of the electronic structure of the CuA site at atomic resolution in solution at physiologically relevant temperature. PMID:19146411

  13. Dynamics of electronic excitations relaxation in hydrophilic colloidal CdS quantum dots in gelatin with involvement of localized states

    NASA Astrophysics Data System (ADS)

    Smirnov, M. S.; Buganov, O. V.; Shabunya-Klyachkovskaya, E. V.; Tikhomirov, S. A.; Ovchinnikov, O. V.; Vitukhnovsky, A. G.; Perepelitsa, A. S.; Matsukovich, A. S.; Katsaba, A. V.

    2016-10-01

    Dynamics of the 1Se-1S3/2 exciton in colloidal CdS quantum dots with diameter of 3.1 ÷ 4.5 nm in gelatin with involvement of localized states was studied by means of femtosecond photoinduced absorption spectroscopy (pump-probe), thermally stimulated luminescence (TSL) observed under permanently excited luminescence. It was found that the bleaching band occurs in the energy region of exciton ground state under excitation by femtosecond laser pulses. The complex dynamics of bleaching recovery is caused by the capture of electron on localized states, found using TSL. The stochastic model describing the dynamics of bleaching recovery is discussed. It is shown that the low efficiency of exciton luminescence is caused by the rapid capture of holes by luminescence centers.

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

    SciTech Connect

    Hoffman, M.Z.

    1997-12-31

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

  15. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    NASA Astrophysics Data System (ADS)

    Arulmozhiraja, Sundaram; Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-01

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning's cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n-π∗ state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π∗ and n-π∗ states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm-1 band in the S1←S0 transition when compared to that of the zero-point level of the S1 state. The present study, however, shows that all the four lowest lying excited states, 1Lb π-π∗, 1La π-π∗, n-π∗, and π-σ∗, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm-1 band in the S1←S0 transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S1 excited vibrational level. This multistate mixing, and especially the involvement of π-σ∗ state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  16. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    SciTech Connect

    Arulmozhiraja, Sundaram Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-28

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning’s cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n–π{sup ∗} state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π{sup ∗} and n-π{sup ∗} states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition when compared to that of the zero-point level of the S{sub 1} state. The present study, however, shows that all the four lowest lying excited states, {sup 1}L{sub b} π-π{sup ∗}, {sup 1}L{sub a} π-π{sup ∗}, n-π{sup ∗}, and π-σ{sup ∗}, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S{sub 1} excited vibrational level. This multistate mixing, and especially the involvement of π-σ{sup ∗} state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

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

    PubMed Central

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

    2012-01-01

    Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, to Acr-An triplet energy transfer occurs followed by long-range, Acr-3An—Acr-An → Acr-An—Acr-3An, energy migration. With methyl viologen dication (MV2+) added as a trap, Acr-3An + MV2+ → Acr-An+ + MV+ electron transfer results in sensitized electron transfer quenching over a distance of approximately 90 Å. PMID:22949698

  18. Analysis of strongly coupled electronic states in diatomic molecules: Low-lying excited states of RbCs

    SciTech Connect

    Bergeman, T.; Fellows, C.E.; Gutterres, R.F.; Amiot, C.

    2003-05-01

    Analysis and assignment of spectra involving the lowest excited states of the heavier alkali-metal atom dimers are complicated by the strong spin-orbit coupling elements. Here we report an analysis of the Fourier-transform spectroscopy data from laser-induced fluorescence of the coupled A {sup 1}{sigma}{sup +} and b {sup 3}{pi} states of RbCs, using the discrete variable representation. Fitted parameters are given and special effects due to strong coupling are discussed.

  19. 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)

  20. Excitations of {sup 1}P levels of zinc by electron impact on the ground state

    SciTech Connect

    Fursa, Dmitry V.; Bray, Igor; Panajotovic, R.; Sevic, D.; Pejcev, V.; Marinkovic, B.P.; Filipovic, D.M.

    2005-07-15

    We present results of a joint theoretical and experimental investigation of electron scattering from the 4s{sup 2} {sup 1}S ground state of zinc. The 4s4p {sup 1}P{sup o} and 4s5p {sup 1}P{sup o} differential cross sections were measured at scattering angles between 10 degree sign and 150 degree sign and electron-energies of 15, 20, 25, 40, and 60 eV. Corresponding convergent close-coupling calculations have been performed and are compared with experiment.

  1. 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.

  2. Collisional relaxation of apocarotenals: identifying the S* state with vibrationally excited molecules in the ground electronic state S(0)*.

    PubMed

    Ehlers, Florian; Scholz, Mirko; Schimpfhauser, Jens; Bienert, Jürgen; Oum, Kawon; Lenzer, Thomas

    2015-04-28

    In recent work, we demonstrated that the S* signal of β-carotene observed in transient pump-supercontinuum probe absorption experiments agrees well with the independently measured steady-state difference absorption spectrum of vibrationally hot ground state molecules S0* in solution, recorded at elevated temperatures (Oum et al., Phys. Chem. Chem. Phys., 2010, 12, 8832). Here, we extend our support for this "vibrationally hot ground state model" of S* by experiments for the three terminally aldehyde-substituted carotenes β-apo-12'-carotenal, β-apo-4'-carotenal and 3',4'-didehydro-β,ψ-caroten-16'-al ("torularhodinaldehyde") which were investigated by ultrafast pump-supercontinuum probe spectroscopy in the range 350-770 nm. The apocarotenals feature an increasing conjugation length, resulting in a systematically shorter S1 lifetime of 192, 4.9 and 1.2 ps, respectively, in the solvent n-hexane. Consequently, for torularhodinaldehyde a large population of highly vibrationally excited molecules in the ground electronic state is quickly generated by internal conversion (IC) from S1 already within the first picosecond of relaxation. As a result, a clear S* signal is visible which exhibits the same spectral characteristics as in the aforementioned study of β-carotene: a pronounced S0 → S2 red-edge absorption and a "finger-type" structure in the S0 → S2 bleach region. The cooling process is described in a simplified way by assuming an initially formed vibrationally very hot species S0** which subsequently decays with a time constant of 3.4 ps to form a still hot S0* species which relaxes with a time constant of 10.5 ps to form S0 molecules at 298 K. β-Apo-4'-carotenal behaves in a quite similar way. Here, a single vibrationally hot S0* species is sufficient in the kinetic modeling procedure. S0* relaxes with a time constant of 12.1 ps to form cold S0. Finally, no S0* features are visible for β-apo-12'-carotenal. In that case, the S1 → S0 IC process is expected

  3. Measuring electron-impact cross sections of water: elastic scattering and electronic excitation of the ã3B1 and Ã1B1 states

    NASA Astrophysics Data System (ADS)

    Matsui, Midori; Hoshino, Masamitsu; Kato, Hidetoshi; Ferreira da Silva, Fillipe; Limão-Vieira, Paulo; Tanaka, Hiroshi

    2016-04-01

    Here, we report elastic differential cross sections (DCSs) for electron scattering from water in the incident energy range of 2-100 eV. Furthermore, we present a complete study on the electronic excitation of the ã3B1 and Ã1B1 states at electron impact energies of 15, 20, and 30 eV and in the scattering angle range of 10° - 130°. Integral cross sections (ICSs) are determined from the DCSs. Measuring elastic DCSs in various experimental conditions confirmed the reproducibility of the data. The present results agree with the data previously obtained from a conventional collimating tube gas source. Ambiguities associated with the unfolding procedure of the electron energy loss (EEL) spectra for the electronic excitations have been reduced by comparison against the EEL spectrum at high electron impact energy and for small scattering angle. The reliability of the extracted DCSs is improved significantly for optically forbidden contributions from the overlap of the ã3B1 and Ã1B1 electronic states. The BEf-scaling model is also confirmed to produce the integral cross section for the optical allowed transition of the Ã1B1 state in the intermediate electron energy region above 15 eV.

  4. Electronically Excited States of Higher Acenes up to Nonacene: A Density Functional Theory/Multireference Configuration Interaction Study.

    PubMed

    Bettinger, Holger F; Tönshoff, Christina; Doerr, Markus; Sanchez-Garcia, Elsa

    2016-01-12

    While the optical spectra of the acene series up to pentacene provide textbook examples for the annulation principle, the spectra of the larger members are much less understood. The present work provides an investigation of the optically allowed excited states of the acene series from pentacene to nonacene, the largest acene observed experimentally, using the density functional based multireference configuration method (DFT/MRCI). For this purpose, the ten lowest energy states of the B2u and B3u irreducible representations were computed. In agreement with previous computational investigations, the electronic wave functions of the acenes acquire significant multireference character with increasing acene size. The HOMO → LUMO excitation is the major contributor to the (1)La state (p band, B2u) also for the larger acenes. The oscillator strength decreases with increasing length. The (1)Lb state (α band, B3u), so far difficult to assign for the larger acenes due to overlap with photoprecursor bands, becomes almost insensitive to acene length. The (1)Bb state (β band, B3u) also moves only moderately to lower energy with increasing acene size. Excited states of B3u symmetry that formally result from double excitations involving HOMO, HOMO-1, LUMO, and LUMO+1 decrease in energy much faster with system size. One of them (D1) has very small oscillator strength but becomes almost isoenergetic with the (1)La state for nonacene. The other (D2) also has low oscillator strength as long as it is higher in energy than (1)Bb. Once it is lower in energy than the (1)Bb state, both states interact strongly resulting in two states with large oscillator strengths. The emergence of two strongly absorbing states is in agreement with experimental observations. The DFT/MRCI computations reproduce experimental excitation energies very well for pentacene and hexacene (within 0.1 eV). For the larger acenes deviations are larger (up to 0.2 eV), but qualitative agreement is observed. PMID

  5. Theoretical treatment of excited electronic states of adsorbates on metals: Electron attachment to CO 2 adsorbed on K-modified Pt(1 1 1)

    NASA Astrophysics Data System (ADS)

    Sremaniak, Laura S.; Whitten, Jerry L.

    Theoretical studies of photoinduced processes involving electron attachment to CO 2 adsorbed on Pt(1 1 1) in the presence of a coadsorbed K atom are reported. First principles theoretical methods suitable for describing electronic states embedded in a near continuum of metal to metal excitations are described. Wave functions are constructed by ab initio configuration interaction methods which allow a rigorous resolution of states and differentiation between competing pathways of molecular desorption and dissociation. An embedding theory is used to achieve high accuracy in the adsorbate-surface region. Compared to CO 2 adsorbed on Pt(1 1 1), the K promoter lowers the work function of the system from 5.6 to 5.2 eV and decreases the energy required to form the electron attached excited electronic state from 6.8 to 5.6 eV. However, stabilization of CO 2 depends strongly on orientation and proximity to the K adatom. The most favorable pathway leading to dissociation requires that CO 2 be adsorbed at a site that does not share Pt atoms with the K adsorption site, i.e., at next-nearest neighbor sites. As was found for Pt(1 1 1) without a K adatom, the dissociation pathway involves bending of CO 2 in the excited state followed by possible dissociation on the excited state surface where the barrier height is reduced from its value of 1.0 eV on the Pt surface to 0.34 eV. As is the case for the unmodified surface, dissociation could also occur after return to the ground state potential energy surface via vibrational processes.

  6. Theoretical study of Raman chirped adiabatic passage by X-ray absorption spectroscopy: Highly excited electronic states and rotational effects

    SciTech Connect

    Engin, Selma; Sisourat, Nicolas Selles, Patricia; Taïeb, Richard; Carniato, Stéphane

    2014-06-21

    Raman Chirped Adiabatic Passage (RCAP) is an efficient method to climb the vibrational ladder of molecules. It was shown on the example of fixed-in-space HCl molecule that selective vibrational excitation can thus be achieved by RCAP and that population transfer can be followed by X-ray Photoelectron spectroscopy [S. Engin, N. Sisourat, P. Selles, R. Taïeb, and S. Carniato, Chem. Phys. Lett. 535, 192–195 (2012)]. Here, in a more detailed analysis of the process, we investigate the effects of highly excited electronic states and of molecular rotation on the efficiency of RCAP. Furthermore, we propose an alternative spectroscopic way to monitor the transfer by means of X-ray absorption spectra.

  7. Free electrons and ionic liquids: study of excited states by means of electron-energy loss spectroscopy and the density functional theory multireference configuration interaction method.

    PubMed

    Regeta, Khrystyna; Bannwarth, Christoph; Grimme, Stefan; Allan, Michael

    2015-06-28

    The technique of low energy (0-30 eV) electron impact spectroscopy, originally developed for gas phase molecules, is applied to room temperature ionic liquids (IL). Electron energy loss (EEL) spectra recorded near threshold, by collecting 0-2 eV electrons, are largely continuous, assigned to excitation of a quasi-continuum of high overtones and combination vibrations of low-frequency modes. EEL spectra recorded by collecting 10 eV electrons show predominantly discrete vibrational and electronic bands. The vibrational energy-loss spectra correspond well to IR spectra except for a broadening (∼0.04 eV) caused by the liquid surroundings, and enhanced overtone activity indicating a contribution from resonant excitation mechanism. The spectra of four representative ILs were recorded in the energy range of electronic excitations and compared to density functional theory multireference configuration interaction (DFT/MRCI) calculations, with good agreement. The spectra up to about 8 eV are dominated by π-π* transitions of the aromatic cations. The lowest bands were identified as triplet states. The spectral region 2-8 eV was empty in the case of a cation without π orbitals. The EEL spectrum of a saturated solution of methylene green in an IL band showed the methylene green EEL band at 2 eV, indicating that ILs may be used as a host to study nonvolatile compounds by this technique in the future.

  8. Excited state electron distribution and role of the terminal amine in acidic and basic tryptophan dipeptide fluorescence

    NASA Astrophysics Data System (ADS)

    Eisenberg, Azaria S.; Nathan, Moshe; Juszczak, Laura J.

    2016-08-01

    The results of quantum yield (QY) study of tryptophanyl glutamate (Trp-Glu), tryptophanyl lysine (Trp-Lys) and lysinyl tryptophan (Lys-Trp) dipeptides over the pH range, 1.5-13, show that the charge state of the N-terminal amine, and not the nominal molecular charge determines the QY. When the terminal amine is protonated, QY is low (10-2) for all three dipeptides. As the terminal amine cation is found proximal to the indole ring in Trp-Glu and Trp-Lys conformers but not in those for Lys-Trp, its effect may lie only in the partitioning of energy between nonradiative processes, not on QY reduction. QY is also low when both the N-terminal amine and indole amine are deprotonated. These two low QY states can be distinguished by fluorescence lifetime measurement. Molecular dynamics simulation shows that the Chi 1 conformers persist for tens of nanoseconds such that 100-101 ns lifetimes may be associated with individual Chi 1 conformers. The ground state electron density or isosurface of high QY (0.30) 3-methyindole has a uniform electron density over the indole ring as do the higher QY Trp dipeptide conformers. This validates the association of ground state isosurfaces with QY. Excited state orbitals from calculated high intensity, low energy absorption transitions are typically centered over the indole ring for higher QY dipeptide species and off the ring in lower QY species. Thus excited state orbitals substantiate the earlier finding that the ground state isosurface charge density pattern on the indole ring can be predictive of QY.

  9. Formation of excited states of N,N,N',N'-tetramethyl-p-phenylenediamine in irradiated nonpolar liquids. [Electron beams

    SciTech Connect

    Choi, H.T.; Tweeten, D.W.; Lipsky, S.

    1984-11-22

    The yield of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) excited states, G/sub s/, has been obtained in irradiated tetramethylsilane, isooctane, cyclopentane, n-hexane, and cyclohexane as a function of TMPD concentration, c, over the range c = 0.5 x 10/sup -3/-50 x 10/sup -3/ M. In tetramethylsilane and isooctane, G/sub s/ is found to be linear on c as would be expected on the basis of a nondiffusional transfer of the solvent ion positive charge to TMPD followed by recombination of TMPD/sup +/ with the geminate electron. In cyclopentane, n-hexane, and cyclohexane, G/sub s/ becomes increasingly concave downward in its depedence on c. This concavity is attributed to an increasing contribution to G/sub s/ from excited states of the solvent that nonradiatively transfer their energy to TMPD. Optical excitation of cyclohexane at 147 nm and measurement of the quenching of its fluorescence by TMPD confirm this view.

  10. GAS-PHASE ELECTRONIC SPECTRA OF POLYACETYLENE CATIONS: RELEVANCE OF HIGHER EXCITED STATES

    SciTech Connect

    Rice, C. A.; Rudnev, V.; Dietsche, R.; Maier, J. P.

    2010-07-15

    Transitions to higher electronic states of polyacetylene cations (HC{sub 2n}H{sup +}, n = 4, 5, 6) have been measured in the gas phase at {approx}20 K. The absorption spectra were obtained using a resonant two-color, two-photon fragmentation technique in an ion trap, allowing a direct comparison between laboratory and astrophysical data. The purpose was to investigate the relevance of such transitions to astronomical observations because the general expectation is that the bands could be too broad due to fast intramolecular processes. It is shown that the origin bands are still narrow enough (1-10 cm{sup -1}) to be considered, especially as the higher-lying transitions often possess large oscillator strengths.

  11. Rotationally Resolved Spectroscopy of the Electronically Excited C and D States of {XeKr} and {XeAr}

    NASA Astrophysics Data System (ADS)

    Piticco, Lorena; Schäfer, Martin; Merkt, Frédéric

    2009-06-01

    Informations on excited electronic states of the heteronuclear rare-gas dimers XeRg (Rg=Kr, Ar) available in the literature are limited to the vibrational structure of several band systems in the VUV range of the electromagnetic spectrum. Using a near-Fourier-transform-limited vacuum-ultraviolet laser system spectra of the C ← X and D ← X band systems of several isotopomers of XeKr and XeAr were recorded at high resolution in the wavenumber range from 77 000 cm^{-1} to 77 350 cm^{-1} by resonance-enhanced two-photon ionization spectroscopy. The rotational and vibrational structures of the C ← X and D ← X band systems could be fully resolved and assigned on the basis of isotopic shifts, combination differences and the ground state microwave spectra. The orbital hyperfine structure of the C1 state could be resolved for the ^{129}Xe^{40}Ar and ^{131}Xe^{40}Ar isotopomers. Potential energy functions and a full set of spectroscopic parameters were derived for the ground and excited states. D. M. Mao, X. K. Hu, S. S. Dimov, R. H. Lipson}, J. Phys. B 29, L89 (1996). O. Zehnder, F. Merkt, Mol. Phys. 106, 1215 (2008). KrXe+ O. Zehnder, F. Merkt, J. Chem. Phys. 128, 014306 (2008). ArXe+ U. Hollenstein, H. Palm and F. Merkt, Rev. Sci. Instr. 71, 4023 (2000). W. Jäger, Y. Xu, M. C. L. Gerry, J. Chem. Phys. 99, 919 (1993).

  12. Theoretical Study on Vibronic Interactions and Photophysics of Low-Lying Excited Electronic States of Polycyclic Aromatic Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Samala, Nagaprasad Reddy; Mahapatra, S.

    2014-06-01

    Polycyclic aromatic hydrocarbons (PAHs), in particular, their radical cation (PAH^+), have long been postulated to be the important molecular species in connection with the spectroscopic observations in the interstellar medium. Motivated by numerous important observations by stellar as well as laboratory spectroscopists, we undertook detailed quantum mechanical studies of the structure and dynamics of electronically excited PAH^+ in an attempt to establish possible synergism with the recorded data In this study, we focus on the quantum chemistry and dynamics of the doublet ground (X) and low-lying excited (A, B and C) electronic states of the radical cation of tetracene (Tn), pentacene (Pn), and hexacene (Hn) molecule. This study is aimed to unravel photostability, spectroscopy, and time-dependent dynamics of their excited electronic states. In order to proceed with the theoretical investigations, we construct suitable multistate and multimode Hamiltonian for these systems with the aid of extensive ab initio calculations of their electronic energy surfaces. The diabatic coupling surfaces are derived from the calculated adiabatic electronic energies. First principles nuclear dynamics calculations are then carried out employing the constructed Hamiltonians and with the aid of time-independent and time-dependent quantum mechanical methods. We compared our theoretical results with available photoelectron spectroscopy, zero kinetic energy photoelectron (ZEKE) spectroscopy and matrix isolation spectroscopy (MIS) results. A peak at 8650 Å in the B state spectrum of Tn^+ is in good agreement with the DIB at 8648 Å observed by Salama et al. Similarly in Pn^+, a peak at 8350 Å can be correlated to the DIB at 8321 Å observed by Salama et al. J. Zhang et al., J. Chem. Phys., 128,104301 (2008).; F. Salama, Origins of Life Evol. Biosphere, 28, 349 (1998).; F. Salama et al., Planet. Space Sci., 43, 1165 (1995).; F. Salama et al., Astrophys. J., 526, 265 (1999).; J

  13. The geometry of electronically-excited states: Vibronic intensity distributions and bond length changes

    NASA Astrophysics Data System (ADS)

    Wood, Dorothy Marie

    2001-12-01

    An exact power series expression has been obtained for the Franck-Condon integral (FCI) in the harmonic approximation. This expression is a function of a parameter Δ where Δ --> 0 as the frequencies of vibration in the two combining electronic states approach equality. These two characteristics, that of a power series in Δ and the fact that Δ --> 0 in certain situations, permit truncation of various functions involving FCI's. Such truncation was performed for the ratio S2v'0'' /S2(v'-1) 0'' , where the S2v'v'' are the FCI's, and the subscripts, in the usual notation, denote the vibrational quantum numbers in the two different electronic states. As a result, two approximations to the S2v'0'' /S2(v'-1) 0'' ratio were obtained: a linear approximation in Δ and a quadratic expression in Δ2. Maps of the Franck-Condon integrals, FCIM's, were found to be very useful. An FCIM is a plot of S2v'0'' (DRe) versus ΔRe for various values of the parameter v'. These FCIM's facilitated a test of the linear and quadratic approximations and led to a precise specification of the ranges of a within which they are valid. They resulted in the concept of a ``Franck-Condon window''. A Franck-Condon window (FCW) is that specific region of the FCIM (i.e., the range of ΔRe) in which the gross (i.e., non-numerical, vibronic intensity) pattern of some vibronic spectrum is represented. The vibrational intensity distributions in 60 different electronic transitions were subjected to Franck-Condon analysis using (i)the linear approximation, (ii)the quadratic approximation, (iii)the FCW approach, and (iv)the best fit to the FCIM. It was found that method (ii), (iii) & (iv) provided excellent agreement with experiment whereas method (i) produced mixed results. The analysis had some incidental benefits: it caused a reassignment of one vibronic spectrum and permitted a choice between two proposed alternative assignments for another vibronic spectrum.

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

    PubMed

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

    2014-05-01

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

  15. Doubly excited {sup 3}P{sup e} resonance states of two-electron positive ions in Debye plasmas

    SciTech Connect

    Hu, Xiao-Qing; Wang, Yang; Kar, Sabyasachi E-mail: karsabyasachi@yahoo.com; Jiang, Zishi; Jiang, Pinghui

    2015-11-15

    We investigate the doubly excited {sup 3}P{sup e} resonance states of two-electron positive ions Li{sup +}, Be{sup 2+}, B{sup 3+}, and C{sup 4+} by employing correlated exponential wave functions. In the framework of the stabilization method, we calculate two series (3pnp and 3dnd) of {sup 3}P{sup e} resonances below the N = 3 threshold. The {sup 3}P{sup e} resonance parameters (resonance energies and widths) are reported for the first time as a function of the screening parameter. For free-atomic cases, comparisons are made with the reported results and few resonance states are reported for the first time.

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

    PubMed

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

    2014-10-21

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

  17. Helium doubly excited states with zero angular momentum and electrons located on the same side of the nucleus

    SciTech Connect

    de Prunele, E. )

    1992-09-01

    A particular set of two-electron atomic resonances for the helium atom with zero total orbital angular momentum ({ital S} states) has been recently studied theoretically (K. Richter and D. Wintgen, J. Phys. B 24, L565 (1991)). These resonances essentially have both electrons on the same side of the nucleus and the outer electron frozen.'' The present work suggests that the energies of these resonances correspond, when the degree of excitation of both electrons increases, to the energies of resonances associated with the Hamiltonian {ital H}={ital p}{sup 2}/2+{ital p}{prime}{sup 2}/2{minus}{ital Z}/{ital r}{minus}{ital Z}/{ital r}{prime}+1/{vert bar}{vert bar}{ital r}{vert bar}{minus}{vert bar}{ital r}{prime}{vert bar}{vert bar} in a space where both particles have zero angular momentum ({ital scrl}={ital scrl}{prime}=0). Moreover, the energy of each of these resonances appears to be that of the lowest member of an almost unperturbed Rydberg series of resonances converging to a single ionization threshold of He. The analysis of the problem relies on the method of o(4,2) operator replacements generalized by the method of complex scaling.

  18. Rotational and vibrational dynamics in the excited electronic state of deprotonated and protonated fluorescein studied by time-resolved photofragmentation in an ion trap

    PubMed Central

    Imanbaew, Dimitri; Gelin, Maxim F.; Riehn, Christoph

    2016-01-01

    Excited state dynamics of deprotonated and protonated fluorescein were investigated by polarization dependent femtosecond time-resolved pump-probe photofragmentation in a 3D ion trap. Transients of deprotonated fluorescein exhibit vibrational wavepacket dynamics with weak polarization dependence. Transients of protonated fluorescein show only effects of molecular alignment and rotational dephasing. The time resolved rotational anisotropy of protonated fluorescein is simulated by the calculated orientational correlation function. The observed differences between deprotonated and protonated fluorescein are ascribed to their different higher lying electronically excited states and corresponding structures. This is partially supported by time-dependent density functional theory calculations of the excited state structures. PMID:27376104

  19. Rotational and vibrational dynamics in the excited electronic state of deprotonated and protonated fluorescein studied by time-resolved photofragmentation in an ion trap.

    PubMed

    Imanbaew, Dimitri; Gelin, Maxim F; Riehn, Christoph

    2016-07-01

    Excited state dynamics of deprotonated and protonated fluorescein were investigated by polarization dependent femtosecond time-resolved pump-probe photofragmentation in a 3D ion trap. Transients of deprotonated fluorescein exhibit vibrational wavepacket dynamics with weak polarization dependence. Transients of protonated fluorescein show only effects of molecular alignment and rotational dephasing. The time resolved rotational anisotropy of protonated fluorescein is simulated by the calculated orientational correlation function. The observed differences between deprotonated and protonated fluorescein are ascribed to their different higher lying electronically excited states and corresponding structures. This is partially supported by time-dependent density functional theory calculations of the excited state structures. PMID:27376104

  20. Recent searches for double-electron capture of nuclei to excited states

    NASA Astrophysics Data System (ADS)

    Povinec, P. P.; Frekers, D.; Šimkovic, F.

    2015-10-01

    Double electron capture has been of interest of many theoretical and experimental works as a possible extension of double beta-decay investigations. The neutrinoless double-electron capture, similarly as the neutrinoless double beta-decay may help to clarify if neutrinos are Majorana or Dirac particles. Results obtained in several double electron capture experiments are reviewed and new experiments to be carried out in deep underground laboratories using enriched sources and multidimensional HPGe-HPGe gamma-ray spectrometry with a few years of counting time are proposed, which should be able to improve half-lives limits by at least an order of magnitude.

  1. Recent searches for double-electron capture of nuclei to excited states

    SciTech Connect

    Povinec, P. P.; Frekers, D.; Šimkovic, F.

    2015-10-28

    Double electron capture has been of interest of many theoretical and experimental works as a possible extension of double beta-decay investigations. The neutrinoless double-electron capture, similarly as the neutrinoless double beta-decay may help to clarify if neutrinos are Majorana or Dirac particles. Results obtained in several double electron capture experiments are reviewed and new experiments to be carried out in deep underground laboratories using enriched sources and multidimensional HPGe-HPGe gamma-ray spectrometry with a few years of counting time are proposed, which should be able to improve half-lives limits by at least an order of magnitude.

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

    SciTech Connect

    Hoffman, M.Z.

    1992-07-31

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

  3. Time-dependent density functional theory study of cobalt corrinoids: Electronically excited states of coenzyme B12

    NASA Astrophysics Data System (ADS)

    Andruniów, Tadeusz; Jaworska, Maria; Lodowski, Piotr; Zgierski, Marek Z.; Dreos, Renata; Randaccio, Lucio; Kozlowski, Pawel M.

    2009-09-01

    The analysis of the electronic spectra of adenosylcobalamin (AdoCbl) and its derivative in which the trans axial base was replaced by a water molecule (AdoCbi-H2O) has been performed by means of time-dependent density functional theory (TDDFT). The latter corresponds to the situation encountered in strongly acidic conditions. The TDDFT electronic transitions and oscillator strengths were calculated at the optimized B3LYP and BP86 ground state equilibrium geometries. A comparison of the orbital energy diagrams obtained with the B3LYP and BP86 functionals reveals a different orbital order and composition of the highest occupied and lowest unoccupied molecular orbitals. In B3LYP the lowest-energy transitions are of π /d→π*, π /d→σ*, and π /d→d characters while in the case of BP86 they are mainly d /π→π* and d →π*. The long range charge transfer transitions involving excitations from adenine π orbitals to antibonding corrin π* orbital can be observed at low energies, especially in BP86 results. Calculated electronic excitations were used to simulate the absorption spectra for a direct comparison with the absorption spectra recorded for AdoCbl at different pH values. As previously found for methylcobalamin [see Andruniów et al., J. Chem. Phys. 129, 085101 (2008)] also for AdoCbl the two-parameter scaling technique is required to obtain a satisfactory agreement between theoretical and experimental spectra. Both functionals correctly predict the shifting of the lowest intense transition toward blue by approximately 13nm upon changing pH from 7 to 1.

  4. 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.

  5. The contribution of electronically excited states to the radiation chemistry of organic systems

    SciTech Connect

    Lipsky, S.

    1990-01-01

    The photocurrent from anthracene in 2,2,4-trimethylpentane, 2.2- dimethylbutane, cyclohexane, cyclopentane, and tetramethylsilane has been studied as a function of excitation energy from the ionization threshold to the onset of strong solvent absorption. The fluroescence from solutions of hexafluorobenzene in cyclopentane, 2,2,4-trimethylpentane, 2,2-dimethylbutane and tetramethylsilane irradiated with {beta}-particles has been studied as a function of the hexafluorobenzene concentration from c = 10{sup {minus}3}-10{sup {minus}1} M. The data are analyzed to permit extraction of the geminate ion-pair scavenging probability. The absorption of 160 nm light by cyclohexane in mixtures of cyclohexane, benzene and tetraphenylmethylenediamine results in an emission spectrum consisting of the simultaneous fluorescence from all three components. A mechanism for the development of this spectrum and its dependence on benzene concentration is constructed and shown to be quantitatively consistent with the results of independent measurements on the separate components. 55 refs.

  6. Many-electron aspects of molecular promotion in ion-atom collisions - Production of core-excited states of Li in Li/+/-He collisions

    NASA Technical Reports Server (NTRS)

    Elston, S. B.; Vane, C. R.; Schumann, S.

    1979-01-01

    Production of core-excited autoionizing states of neutral Li having configurations of the form 1snln(prime)l(prime) has been observed over the impact-energy range from 10-50 keV. Although the results for production of all such states is remarkably consistent with a quasi-molecular-excitation model proposed by Stolterfoht and Leithaeuser (1976), production of individual lines in the observed spectra exhibits collision-velocity dependencies indicative of considerably more complex processes, including processes which appear to be inherently two-electron in nature. Excitation functions are presented for (1s2s/2/)/2/S, 1s(2s2p/3/P)/2/P, 1s(2s2p/1/P)/2/P, and (1s2p/2/)/2/D core-excited state of Li and for total core excitation.

  7. Analytical second derivatives for excited electronic states using the single excitation configuration interaction method: theory and application to benzo[a]pyrene and chalcone

    NASA Astrophysics Data System (ADS)

    Maurice, David; Head-Gordon, Martin

    A compact formulation and a semi-direct implementation are described of analytical second derivatives of the single excitation configuration interaction (CIS) energy. CPU time, memory usage and disc storage all scale with the same power of system size as the ground state Hartree-Fock (HF) method, with a coefficient only 2 to 3 times larger. Thus usually analytical excited state CIS frequencies are feasible when HF frequencies are feasible. As a computational example, analytical CIS/3-21G frequencies for benzo[a]pyrene are calculated more efficiently than with finite differences. As a chemical application, analytical CIS/6-31G* frequencies are used to investigate non-planarity in the lowest π→π* excited state of trans chalcone.

  8. Laser-induced dissociation dynamics of triatomic molecule in electronic excited states: A full-dimensional quantum mechanics study.

    PubMed

    Sun, Zhaopeng; Yang, Chuanlu; Zheng, Yujun

    2015-12-14

    We present a detailed theoretical approach to investigate the laser-induced dissociation dynamics of a triatomic molecule on its electronic excited state in full dimensional case. In this method, the time evolution of the time-dependent system is propagated via combined the split operator method and the expansion of Chebyshev polynomials (or short-time Chebyshev propagation) and the system wave functions are expanded in terms of molecular rotational bases. As an example of the application of this formalism, the dissociation dynamics of H3(+)→H2(+)+H induced by ultrashort UV laser pulses are investigated on new Born-Oppenheimer potential energy surfaces. Our numerical results show that the signals of dissociation products will be easier to observe as the increasing of field strength. Driving by a 266 nm laser beam, the calculated central value of kinetic-energy-release is 2.04 eV which shows excellent agreement with the experimental estimation of 2.1 eV. When the H3(+) ion is rotationally excited, the spatial distribution of product fragments will become well converged.

  9. Laser-induced dissociation dynamics of triatomic molecule in electronic excited states: A full-dimensional quantum mechanics study.

    PubMed

    Sun, Zhaopeng; Yang, Chuanlu; Zheng, Yujun

    2015-12-14

    We present a detailed theoretical approach to investigate the laser-induced dissociation dynamics of a triatomic molecule on its electronic excited state in full dimensional case. In this method, the time evolution of the time-dependent system is propagated via combined the split operator method and the expansion of Chebyshev polynomials (or short-time Chebyshev propagation) and the system wave functions are expanded in terms of molecular rotational bases. As an example of the application of this formalism, the dissociation dynamics of H3(+)→H2(+)+H induced by ultrashort UV laser pulses are investigated on new Born-Oppenheimer potential energy surfaces. Our numerical results show that the signals of dissociation products will be easier to observe as the increasing of field strength. Driving by a 266 nm laser beam, the calculated central value of kinetic-energy-release is 2.04 eV which shows excellent agreement with the experimental estimation of 2.1 eV. When the H3(+) ion is rotationally excited, the spatial distribution of product fragments will become well converged. PMID:26671377

  10. Localization of electrons and excitations

    NASA Astrophysics Data System (ADS)

    Larsson, Sven

    2006-07-01

    Electrons, electron holes, or excitations in finite or infinite 'multimer systems' may be localized or delocalized. In the theory of Hush, localization depends on the ratio Δ/ λ ( Δ/2 = coupling; λ = reorganization energy). The latter theory has been extended to the infinite system [S. Larsson, A. Klimkāns, Mol. Cryst. Liq. Cryst. 355 (2000) 217]. The metal/insulator transition often takes place abruptly as a function of Δ/ λ. It is argued that localization in a system with un-filled bands cannot be determined on the basis of Mott-Hubbard U alone, but depends on the number of accessible valence states, reorganization energy λ and coupling Δ (=2t). In fact U = 0 does not necessarily imply delocalization. The analysis here shows that there are many different situations for an insulator to metal transition. Charge transfer in doped NiO is characterized by Ni 2+ - Ni 3+ exchange while charge transfer in pure NiO is characterized by a disproportionation 2Ni 2+ → Ni + + Ni 3+. In spite of the great differences between these two cases, U has been applied without discrimination to both. The relevant localization parameters appear to be Δ and λ in the first case, with only two oxidation states, and U, Δ and λ in the second case with three oxidation states. The analysis is extended to insulator-metal transitions, giant magnetic resistance (GMR) and high Tc superconductivity (SC). λ and Δ can be determined quite accurately in quantum mechanical calculations involving only one and two monomers, respectively.

  11. All-electron first principles calculations of the ground and some low-lying excited states of BaI.

    PubMed

    Miliordos, Evangelos; Papakondylis, Aristotle; Tsekouras, Athanasios A; Mavridis, Aristides

    2007-10-01

    The electronic structure of the heavy diatomic molecule BaI has been examined for the first time by ab initio multiconfigurational configuration interaction (MRCI) and coupled cluster (RCCSD(T)) methods. The effects of special relativity have been taken into account through the second-order Douglas-Kroll-Hess approximation. The construction of Omega(omega,omega) potential energy curves allows for the estimation of "experimental" dissociation energies (De) of the first few excited states by exploiting the accurately known De experimental value of the X2Sigma+ ground state. All states examined are of ionic character with a Mulliken charge transfer of 0.5 e- from Ba to I, and this is reflected to large dipole moments ranging from 6 to 11 D. Despite the inherent difficulties of a heavy system like BaI, our results are encouraging. With the exception of bond distances that on the average are calculated 0.05 A longer than the experimental ones, common spectroscopic parameters are in fair agreement with experiment, whereas De values are on the average 10 kcal/mol smaller. PMID:17850123

  12. Electronic excited states as a probe of surface adsorbate structure and dynamics in liquid xenon

    SciTech Connect

    Peterson, E.S.

    1992-08-01

    A combination of second harmonic generation (SHG) and a simple dipole-dipole interaction model is presented as a new technique for determining adsorbate geometries on surfaces. The polarization dependence of SHG is used to define possible geometries of the adsorbate about the surface normal. Absorption band shifts using geometry constraints imposed by SHG data are derived for a dimer constructed from two arbitrarily placed monomers on the surface using the dipole-dipole interaction potential. These formulae can be used to determine the orientation of the two monomers relative to each other. A simplified version of this formalism is used to interpret absorption band shifts for rhodamine B adsorbed on fused silica. A brief history of the exciton is given with particular detail to Xe. Data are presented for transient absorption at RT in liquid xenon on the picosecond time scale. These are observations of both tunneling through the barrier that separates the free and trapped exciton states and the subsequent trapping of the exciton. In high densities both of these processes are found to occur within 2 to 6 picoseconds in agreement with theories of Kmiecik and Schreiber and of Martin. A threshold density is observed that separates relaxation via single binary collisions and relaxation that proceeds via Martin`s resonant energy transfer hopping mechanism.

  13. Electronic excited states as a probe of surface adsorbate structure and dynamics in liquid xenon

    SciTech Connect

    Peterson, E.S.

    1992-08-01

    A combination of second harmonic generation (SHG) and a simple dipole-dipole interaction model is presented as a new technique for determining adsorbate geometries on surfaces. The polarization dependence of SHG is used to define possible geometries of the adsorbate about the surface normal. Absorption band shifts using geometry constraints imposed by SHG data are derived for a dimer constructed from two arbitrarily placed monomers on the surface using the dipole-dipole interaction potential. These formulae can be used to determine the orientation of the two monomers relative to each other. A simplified version of this formalism is used to interpret absorption band shifts for rhodamine B adsorbed on fused silica. A brief history of the exciton is given with particular detail to Xe. Data are presented for transient absorption at RT in liquid xenon on the picosecond time scale. These are observations of both tunneling through the barrier that separates the free and trapped exciton states and the subsequent trapping of the exciton. In high densities both of these processes are found to occur within 2 to 6 picoseconds in agreement with theories of Kmiecik and Schreiber and of Martin. A threshold density is observed that separates relaxation via single binary collisions and relaxation that proceeds via Martin's resonant energy transfer hopping mechanism.

  14. Hydride stretch infrared spectra in the excited electronic states of indole and its derivatives: Direct evidence for the 1πσ* state

    NASA Astrophysics Data System (ADS)

    Dian, Brian C.; Longarte, Asier; Zwier, Timothy S.

    2003-02-01

    The hydride stretch infrared spectra of indole, indole-H2O, 3-methyl indole, 3-methyl indole-H2O, the main conformer of tryptamine (TRA), two conformers of N-acetyl tryptophan amide (NATA), and three conformers of N-acetyl tryptophan methyl amide (NATMA), have been recorded in the electronically excited singlet states using excited-state fluorescence-dip infrared spectroscopy. NATA and NATMA are methyl-capped dipeptides of tryptophan that have conformational flexibility and exhibit sensitivity in their electronic spectra to the conformation of the dipeptide backbone. In the indole monomer, the indole NH stretch fundamental at the S1 origin is shifted from its ground-state value (3525 cm-1) to 3478 cm-1. The corresponding band in the indole-H2O complex appears at 3387 cm-1, shifted by a similar amount from its ground-state position (3436 cm-1). Higher vibronic levels within 1500 cm-1 of the S1 origin, which have been identified previously [B. J. Fender et al., Chem. Phys. Lett. 239, 31 (1995)] as being 1Lb or 1La in character, all show similar excited state indole NH stretch absorptions. The corresponding spectra in 3-methyl indole, 3-methyl indole-H2O, TRA, and in the C5 conformers of NATA and NATMA all are missing the indole NH stretch absorption. In its place, a broad background absorption appears, spread over the entire 2800-3800 cm-1 region. In these molecules, other CH stretch or amide NH stretch absorptions remain sharp, appearing in their expected frequency ranges. Finally, the C7 conformations of NATA and NATMA, which possess an intramolecular hydrogen bond in the dipeptide backbone, have all infrared transitions washed out, replaced by a stronger broad background absorption. The entire data set can be explained by the presence of an excited 1πσ* state which is dissociative along the indole NH stretch coordinate, as recently predicted by Sobolewski and Domcke [Chem. Phys. Lett. 315, 293 (1999)]. In the weak coupling case (indole, indole-H2O), the gap

  15. Ground and excited electronic state analysis of PrF²⁺ and PmF²⁺.

    PubMed

    Schoendorff, George; Chi, Benjamin; Ajieren, Hans; Wilson, Angela K

    2015-03-01

    The ground state and excited state manifolds are computed for PrF(2+) and PmF(2+) at the CASSCF (n,8) level of theory where the active space spans the Ln 4f orbitals as well as the F 2pz orbital. Dynamical correlation is included using second-order multireference quasidegenerate perturbation theory (MCQDPT2). The spin-orbit multiplets for each of the excited states are resolved, and spin-orbit coupling constants are computed using the Breit-Pauli spin-orbit operator. Equilibrium geometries for each of the ground and excited states are computed, and the nature of the Ln-F bond is examined. Potential energy curves for the lowest four triplet states and lowest two quintet states are computed for PrF(2+), which split into 14 levels upon application of the spin-orbit Hamiltonian. Likewise, the lowest six quintet states are computed for PmF(2+) as well as the lowest triplet state and the lowest two septet states. These nine states split into 43 terms upon application of the spin-orbit Hamiltonian.

  16. Electronic bands and excited states of III-V semiconductor polytypes with screened-exchange density functional calculations

    SciTech Connect

    Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori; Freeman, Arthur J.

    2014-03-31

    The electronic band structures and excited states of III-V semiconductors such as GaP, AlP, AlAs, and AlSb for various polytypes are determined employing the screened-exchange density functional calculations implemented in the full-potential linearized augmented plane-wave methods. We demonstrate that GaP and AlSb in the wurtzite (WZ) structure have direct gap while III-V semiconductors in the zinc blende, 4H, and 6H structures considered in this study exhibit an indirect gap. Furthermore, we find that inclusion of Al atoms less than 17% and 83% in the hexagonal Al{sub x}Ga{sub 1−x}P and Al{sub x}Ga{sub 1−x}As alloys, respectively, leads to a direct transition with a gap energy of ∼2.3 eV. The feasibility of III-V semiconductors with a direct gap in WZ structure offers a possible crystal structure engineering to tune the optical properties of semiconductor materials.

  17. Molecular Level Understanding of Interfaces and Excited State Electronic Structure in Organic Solar Cells Using Soft X-ray Techniques

    NASA Astrophysics Data System (ADS)

    Gliboff, Matthew

    between structure and performance in active layer polymers for organic electronics is not yet well understood. To gain insight into the effect of the excited state electronic structure on device performance, we examine two similar donor-acceptor polymers: PCPDTBT and PCDTBT, which produce devices with internal quantum efficiency (IQE) of 70% and 100% respectively. We use time-dependent density functional theory (TD-DFT) in combination with near edge x-ray absorption fine structure (NEXAFS) and resonant Auger spectroscopy to predict the electronic structure of the lowest unoccupied molecular orbital (LUMO). The resonant Auger results are found to be independent of film morphology and likely dominated by monomer structure. We show that the degree of LUMO localization onto the benzothiadiazole acceptor group in each polymer is similar, indicating that that the differences in IQE between these two polymers are driven by larger-scale morphology and not explained by the electronic structure of the excited state.

  18. Ultrafast relaxation of electronically-excited states of a styryl dye in the cavity of cucurbit[n]urils (n = 6, 7)

    NASA Astrophysics Data System (ADS)

    Petrov, N. Kh.; Ivanov, D. A.; Shandarov, Yu. A.; Kryukov, I. V.; Ivanov, A. A.; Alfimov, M. V.; Lobova, N. A.; Gromov, S. P.

    2016-03-01

    The ultrafast relaxation of an electronically-excited styryl dye and its complexes with cucurbit[n]urils was studied by the fluorescence up-conversion technique at various fluorescence wavelengths. The relaxation is faster at a blue side of the fluorescence band than at a red one where a fluorescence rise was observed. Addition of either cucurbiturils significantly increases the longest decay time from about 50 ps to that in the range of 100-200 ps. Such features are attributed to displacements of the electronically-excited styryl dye deep into the cavity, increasing the potential barrier between the intramolecular charge transfer state and the conical intersection region.

  19. Laser cooling via excitation of localized electrons

    NASA Astrophysics Data System (ADS)

    Emin, David

    2007-07-01

    Under appropriate conditions, absorption of light by a solid can initiate a process by which it is cooled. In particular, energy is extracted from a material when its absorption of a photon is followed by emission of a photon of higher energy. This up-conversion requires some of the solid’s electrons to garner energy from atomic vibrations. Here, two schemes for laser cooling via localized electronic states are addressed. The first scheme utilizes the ground state and an excited state of a localized center. In this two-level scheme, the cooling process is initiated with photon absorption in the extreme low-energy tail of a localized state’s vibrationally broadened absorption spectrum. The subsequent atomic relaxation transfers energy of especially large vibratory atomic strains into electrical energy that is then extracted via photon emission. The second scheme involves the ground state and two excited states of a localized center. Cooling is facilitated when (i) the photoexcitation of an electron from its ground state to the lower excited level is followed by (ii) electron-phonon-induced promotion to the uppermost level and the subsequent (iii) return of the electron to its ground state with emission of a photon of higher energy than that of the absorbed photon. However, competing relaxation processes contribute to heating. The net cooling power per unit volume is maximized for both schemes, thereby determining characteristics of localized electronic systems that foster optical cooling. The cooling power per unit volume is greatest at high temperatures and falls rapidly as the thermal energy is reduced below each system’s luminescence Stokes shift. Moreover, cooling via the three-level scheme is most effective when (i) the energy separation between excited states is smaller than the thermal energy and (ii) the degeneracy of the highest-lying excited state is much larger than that of the center’s middle level. These restrictive conditions appear to be

  20. 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

  1. 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.

  2. Separation of ionization and subsequent electronic excitation for formation of electronically excited ethanol cation in intense laser fields

    NASA Astrophysics Data System (ADS)

    Ikuta, T.; Hosaka, K.; Akagi, H.; Yokoyama, A.; Yamanouchi, K.; Kannari, F.; Itakura, R.

    2011-10-01

    Ionization and subsequent electronic excitation occurring within the same laser pulse (400 nm, 96 fs, 1.3 ~ 18 TW cm-2) are separately investigated by measuring in coincidence an electron and a product ion produced from C2H5OH. It is revealed that the nascent population in the electronically excited C2H5OH+ prepared by the ionization decreases as the laser intensity increases, while the subsequent electronic excitation is enhanced through the resonant electronic transitions. Ionization and electronic excitation mechanisms are described based on the electronic-state distributions of C2H5OH+.

  3. Solvent Effects on the Electronic Absorption and Fluorescence Spectra of HNP: Estimation of Ground and Excited State Dipole Moments.

    PubMed

    Desai, Vani R; Hunagund, Shirajahammad M; Basanagouda, Mahantesha; Kadadevarmath, Jagadish S; Sidarai, Ashok H

    2016-07-01

    We report the effect of solvents on absorption and fluorescence spectra of biologically active 3(2H)-pyridazinone namely 5-(2-hydroxy-naphthalen-1-yl)-2-phenyl-2H-pyridazin-3-one (HNP) in different solvents at room temperature. The ground and the excited state dipole moments of HNP molecule was estimated from Lippert's, Bakshiev's and Kawski-Chamma-Viallet's equations using the solvatochromic shift method. The ground state dipole moment (μ g ) was also estimated by Guggenheim and Higasi method using the dielectric constant and refractive index of solute at different concentrations, the μ g value obtained from these two methods are comparable to the μ g value obtained by the solvatochromic shift method. The excited state dipole moment (μ e ) is greater than the ground state dipole moment (μ g ), which indicates that the excited state is more polar than the ground state. Further, we have evaluated the change in dipole moment (Δμ) from the solvatochromic shift method and on the basis of molecular-microscopic solvent polarity parameter[Formula: see text], later on the values were compared. PMID:27220623

  4. Step-scan FTIR absorption difference time-resolved spectroscopy studies the excited state electronic structures and decay kinetics of d6 transition metal polypyridine complexes

    NASA Astrophysics Data System (ADS)

    Smith, G. D.; Paegel, B. M.; Palmer, R. A.; Chen, P.; Omberg, K. M.; Meyer, T. J.

    1998-06-01

    Step-scan FTIR absorption difference time-resolved spectroscopy (S2 FTIR ΔA TRS) has been used to study the photo-excited states of several low-spin d6 transition metal polypyridine complexes. Insight into the distribution of electron density in the excited states is obtained by comparing the ground and excited state vibrational frequencies of various bands sensitive to electronic structure. The multiplex, registration, and IR throughput advantages of this interferometric technique are significant in comparison with other methods currently used to probe photo-excited processes on the nanosecond time scale. The S2 FTIR ΔA TR spectra were obtained by use of a step-scan modified Bruker IFS 88 FTIR spectrometer equipped with an AC/DC-coupled photovoltaic Kolmar Technologies MCT detector with a 20 ns rise time and a 100/200 MHz PAD82a transient digitizer. The complexes were excited with frequency-tripled pulses from a Q-switched Quanta-Ray DCR1A Nd:YAG laser (355 nm, 10 ns, 10 Hz, 3 mJ/pulse). Data were collected with 10 ns time resolution.

  5. Electron excitations in solids and novel materials

    NASA Astrophysics Data System (ADS)

    Spataru, Catalin-Dan

    Several applications of the use of ab initio many-body methods in condensed matter theory are presented. In particular, these methods are used for the study of electronic excitations in various kinds of materials, ranging from bulk to low dimensional systems, and from metals to semiconductors. Two types of electron excitations are considered: quasiparticle excitations and electron-hole excitations. The work is organized in five chapters as follows: (1) The first chapter gives an introduction to the concept of quasiparticle and electron-hole excitations, as well as to the many-body framework underlying the theoretical formalism used in this work. (2) Chapter two presents the calculation of quasiparticle lifetimes in graphite. The inverse lifetime of low energy quasi-electrons shows significant deviations from the quadratic behavior naively expected from Fermi liquid theory. The deviations are explained in terms of the unique features of the band structure of this material. (3) In chapter three, the real and imaginary parts of the quasiparticle self-energy in jellium and crystalline Al are calculated at high electron temperatures. We find a decrease in the electron lifetime and an increase in the valence and conduction band widths as the temperature is increased. Calculation of the spectral function suggests that the quasiparticle concept may still be reasonable at high electron temperatures. (4) Chapter four presents calculations of the quasiparticle spectrum of highly irradiated crystalline GaAs. Our results indicate that the valence-conduction band gap is a sensitive function of the amount of electrons excited above the ground state. However, contrary to previous results, we find that it is not possible to induce a complete band gap closure by purely electronic means. (5) In chapter five we present calculations of the electron-hole interaction effects on the optical spectra of several single-walled carbon nanotubes. We show that the optical spectra of both

  6. Hydrogen bonding and reactivity of water to azines in their S1 (n,π*) electronic excited states in the gas phase and in solution.

    PubMed

    Reimers, Jeffrey R; Cai, Zheng-Li

    2012-07-01

    A unified picture is presented of water interacting with pyridine, pyridazine, pyrimidine, and pyrazine on the S(1) manifold in both gas-phase dimers and in aqueous solution. As (n,π*) excitation to the S(1) state removes electrons from the ground-state hydrogen bond, this analysis provides fundamental understanding of excited-state hydrogen bonding. Traditional interpretations view the excitation as simply breaking hydrogen bonds to form dissociated molecular products, but reactive processes such as photohydrolysis and excited-state proton coupled electron transfer (PCET) are also possible. Here we review studies performed using equations-of-motion coupled-cluster theory (EOM-CCSD), multireference perturbation theory (CASPT2), time-dependent density-functional theory (TD-DFT), and excited-state Monte Carlo liquid simulations, adding new results from symmetry-adapted-cluster configuration interaction (SAC-CI) and TD-DFT calculations. Invariably, gas-phase molecular dimers are identified as stable local minima on the S(1) surface with energies less than those for dissociated molecular products. Lower-energy biradical PCET minima are also identified that could lead to ground-state recombination and hence molecular dissociation, dissociation into radicals or ions, or hydration reactions leading to ring cleavage. For pyridine.water, the calculated barriers to PCET are low, suggesting that this mechanism is responsible for fluorescence quenching of pyridine.water at low energies rather than accepted higher-energy Dewar-benzene based "channel three" process. Owing to (n,π*) excitation localization, much higher reaction barriers are predicted for the diazines, facilitating fluorescence in aqueous solution and predicting that the as yet unobserved fluorescence from pyridazine.water and pyrimidine.water should be observable. Liquid simulations based on the assumption that the solvent equilibrates on the fluorescence timescale quantitatively reproduce the observed spectral

  7. 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.

  8. Electron impact excitation of the electronic states of N2. III - Transitions in the 12.5-14.2-eV energy-loss region at incident energies of 40 and 60 eV

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Trajmar, S.; Cartwright, D. C.

    1977-01-01

    Analysis of electron energy-loss data at incident electron energies of 40 and 60 eV has led to the determination of normalized absolute differential cross sections for electron-impact excitation of five optically-allowed singlet states, two known triplet states, and two unknown triplet-like states of N2, lying in the energy-loss range 12.5-14.2 eV. The range of scattering angles was 5 to 138 deg. The optically allowed transitions and the known triplet excitations are identified. Cross sections for excitation to two unidentified triplet-like states at 13.155 and 13.395 eV were also obtained. The relationship of the generalized oscillator strength for the dipole-allowed states obtained from the described data to known optical oscillator strengths is discussed.

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

    SciTech Connect

    Hoffman, M.Z.

    1991-12-31

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

  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. Theoretical study of H2/+/ spectroscopic properties. II, III. [2p and 3d excited electronic states

    NASA Technical Reports Server (NTRS)

    Beckel, C. L.; Shafi, M.; Peek, J. M.

    1973-01-01

    Description of the theoretical spectroscopic properties of the 2p pi/sub u/ and 3d sigma/sub g/ excited states of the H2/+/ hydrogen molecular ion. Numerical integration of the Schrodinger equation is used to determine vibration-rotation eigenvalues. Dunham power series expansions are used to determine the equilibrium separation, potential coefficients, and spectroscopic constants. The eigenvalues are used to determine delta-G, Bv, Dv, and Hv.

  12. Contribution of electronically excited states to the radiation chemistry of organic systems. Progress report, July 1, 1985-February 28, 1986

    SciTech Connect

    Lipsky, S.

    1986-01-01

    The attachment of thermal electrons by cyclic perfluorocarbons has been shown to enhance the photocurrent from TMPD in solvents in which the electron thermalization range is low. The effect has been studied with perfluorodecalin and perfluoromethylcyclohexane in n-pentane and n-hexane as a function of scavenger concentration, excitation energy and applied electric field strength. The mechanism of the effect suggests a technique for separating epithermal from thermal electron scavenging processes. Contact charge transfer absorption maxima have been located in six hydrocarbon-cyclic perfluorocarbon systems, and correlate well with the known gas-phase ionization potentials of the hydrocarbon. Concentration studies indicate one to one complexes when the hydrocarbon is dissolved in a perfluorocarbon solvent. Fluorescence quantum yields and fluorescence spectra have been obtained for cyclopentane, cycloheptane, cyclooctane, cyclodecane and a number of their alkyl derivatives.

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

    SciTech Connect

    Filatov, Michael

    2014-09-28

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

  14. High temperature electronic excitation and ionization rates in gases

    NASA Technical Reports Server (NTRS)

    Hansen, Frederick

    1991-01-01

    The relaxation times for electronic excitation due to electron bombardment of atoms was found to be quite short, so that electron kinetic temperature (T sub e) and the electron excitation temperature (T asterisk) should equilibrate quickly whenever electrons are present. However, once equilibrium has been achieved, further energy to the excited electronic states and to the kinetic energy of free electrons must be fed in by collisions with heavy particles that cause vibrational and electronic state transitions. The rate coefficients for excitation of electronic states produced by heavy particle collision have not been well known. However, a relatively simple semi-classical theory has been developed here which is analytic up to the final integration over a Boltzmann distribution of collision energies; this integral can then be evaluated numerically by quadrature. Once the rate coefficients have been determined, the relaxation of electronic excitation energy can be evaluated and compared with the relaxation rates of vibrational excitation. Then the relative importance of these two factors, electronic excitation and vibrational excitation by heavy particle collision, on the transfer of energy to free electron motion, can be assessed.

  15. Electron paramagnetic resonance of the excited triplet state of metal-free and metal-substituted cytochrome c.

    PubMed Central

    Angiolillo, P J; Vanderkooi, J M

    1995-01-01

    The photoactivated metastable triplate states of the porphyrin (free-base, i.e., metal-free) zinc and tin derivatives of horse cytochrome c were investigated using electron paramagnetic resonance. Zero-field splitting parameters, line shape, and Jahn-Teller distortion in the temperature range 3.8-150 K are discussed in terms of porphyrin-protein interactions. The zero-field splitting parameters D for the free-base, Zn and Sn derivatives are 465 x 10(-4), 342 x 10(-4) and 353 x 10(-4) cm-1, respectively, and are temperature invariant over the temperature ranges studied. AN E value at 4 K of 73 x 10(-4) cm-1 was obtained for Zn cytochrome c, larger than any previously found for Zn porphyrins derivatives of hemeproteins, showing that the heme site of cytochrome c imposes an asymmetric field. Though the E value for Zn cytochrome c is large, the geometry of the site appears quite constrained, as indicated by a spectral line shape showing a single species. Intersystem crossing occurred predominantly to the T2 > zero-field spin sublevel. EPR line shape changes with respect to temperature of Zn cyt c are interpreted in terms of vibronic coupling, and a maximum Jahn-Teller crystal-field splitting of approximately 180 cm-1 is obtained. Sn cytochrome c in comparison with the Zn protein exhibits a photoactivated triplet line shape that is less well resolved in the X-Y region. The magnitude of E value is approximately 60 x 10(-4) cm-1 at 4 K; its value rapidly tends toward zero with increasing temperature, from which a value for the Jahn-Teller crystal-field splitting of > or = 40 cm-1 is estimated. In contrast to those for the metal cytochromes, the magnitude of E value for the free-base derivative was essentially zero at all temperatures studied. This finding is discussed as a consequence of an excited-state tautomerization process that occurs even at 4 K. PMID:7647253

  16. Differential and integrated cross sections for excitation to the 3s, 3p, and 3d states of atomic hydrogen by electron impact below the n=4 threshold

    SciTech Connect

    Bartlett, Philip L.; Bray, Igor; Stelbovics, Andris T.; Williams, J. F.; Mikosza, A. G.

    2006-08-15

    Integrated cross sections for the electron-impact excitation of ground-state hydrogen to the 3s, 3p, and 3d final states have been calculated using propagating exterior complex scaling and convergent close-coupling methods at energies between the n=3 and 4 excitation thresholds. The calculations are in excellent agreement and demonstrate that exterior complex scaling methods can accurately reproduce the resonance structure and magnitude of the excitation cross sections below the ionization threshold. Measurements of the separate 3s, 3p, and 3d differential cross sections were made at 12.24 eV, and are consistent with both calculations within a total experimental uncertainty of about 35%.

  17. Measurement of the autoionization lifetime of the energetically lowest doubly excited Q_1\\,^1\\Sigma ^+_{u} state in H2 using electron ejection asymmetry

    NASA Astrophysics Data System (ADS)

    Fischer, Andreas; Sperl, Alexander; Cörlin, Philipp; Schönwald, Michael; Meuren, Sebastian; Ullrich, Joachim; Pfeifer, Thomas; Moshammer, Robert; Senftleben, Arne

    2014-01-01

    The autoionization lifetime of doubly excited H2 created by single photon absorption has been measured by means of a kinematically complete study. For dissociative ionization the experimentally observed asymmetry in the electron ejection direction with respect to the emitted proton is used to disentangle the two interfering pathways, direct ionization and autoionization. This allows us to determine the autoionization lifetime of the energetically lowest doubly excited Q_1\\,^1\\Sigma _{u}^+(1) state for a large range of internuclear distances, including the previously inaccessible small values. Excellent agreement with available ab initio calculations is obtained.

  18. Role of the electronic excited-state hydrogen bonding in the nitro-explosives detection by [Zn2(oba)2(bpy)

    NASA Astrophysics Data System (ADS)

    Wang, Peipei; Song, Xuedan; Zhao, Zhengyan; Liu, Lei; Mu, Wensheng; Hao, Ce

    2016-09-01

    This paper investigates the luminescent properties of luminescent metal-organic framework (LMOF) [Zn2(oba)2(bpy)], and its selectivity for the detection of nitro-explosives via fluorescence quenching, using the density functional and time-dependent density functional theories. The luminescent mechanism of the LMOF follows the electron transfer from ligand to ZnO quantum dot. The hydrogen bondings formed between LMOF and electron-withdrawing nitro-explosives as well as electron-donating aromatic compounds have different influences on the luminescent mechanism of the LMOF. The hydrogen bonding in the excited state was investigated to display the relationship between hydrogen bonding and fluorescence.

  19. Time-dependent density functional theory study on the electronic excited-state hydrogen bonding of the chromophore coumarin 153 in a room-temperature ionic liquid.

    PubMed

    Wang, Dandan; Hao, Ce; Wang, Se; Dong, Hong; Qiu, Jieshan

    2012-03-01

    In the present work, in order to investigate the electronic excited-state intermolecular hydrogen bonding between the chromophore coumarin 153 (C153) and the room-temperature ionic liquid N,N-dimethylethanolammonium formate (DAF), both the geometric structures and the infrared spectra of the hydrogen-bonded complex C153-DAF(+) in the excited state were studied by a time-dependent density functional theory (TDDFT) method. We theoretically demonstrated that the intermolecular hydrogen bond C(1) = O(1)···H(1)-O(3) in the hydrogen-bonded C153-DAF(+) complex is significantly strengthened in the S(1) state by monitoring the spectral shifts of the C=O group and O-H group involved in the hydrogen bond C(1) = O(1)···H(1)-O(3). Moreover, the length of the hydrogen bond C(1) = O(1)···H(1)-O(3) between the oxygen atom and hydrogen atom decreased from 1.693 Å to 1.633 Å upon photoexcitation. This was also confirmed by the increase in the hydrogen-bond binding energy from 69.92 kJ mol(-1) in the ground state to 90.17 kJ mol(-1) in the excited state. Thus, the excited-state hydrogen-bond strengthening of the coumarin chromophore in an ionic liquid has been demonstrated theoretically for the first time.

  20. Electronic excitations in fast ion-solid collisions

    SciTech Connect

    Burgdoerfer, J. . Dept. of Physics and Astronomy Oak Ridge National Lab., TN )

    1990-01-01

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

  1. Time-dependent close-coupling studies of the electron-impact ionization of excited-state helium

    SciTech Connect

    Colgan, J.; Pindzola, M. S.

    2002-12-01

    The time-dependent close-coupling theory is applied to the study of the electron-impact ionization of helium from the excited (1s2s) configuration. Calculations are made in an effort to resolve the discrepancy between theoretical calculations and existing experimental measurements for this cross section. We find good agreement with the existing convergent close-coupling calculations of Bray and Fursa [J. Phys. B 28, L197 (1995)], but are in substantial disagreement with the experimental measurements of this quantity by Dixon et al. [J. Phys. B 9, 2617 (1976)].

  2. The contribution of electronically excited states to the radiation chemistry of organic systems. Progress report, January 1, 1991--April 30, 1992

    SciTech Connect

    Lipsky, S.

    1992-09-01

    At low concentrations ({le}10{sup {minus}3}M) of aromatic solutes in saturated. hydrocarbon solvents, very efficient transport of electronic energy from photo-excited solvent to aromatic is observed. Effects of temperature, dilution, and quenching additives are being studied. Two-photon pulsed laser excitation gives no evidence of long lived metastable states. The fluorescence quantum yields of saturated hydrocarbon liquids have been studied for excitation wavelengths from 200 to 120 nm. For many compounds, the quantum yields for fluorescence are observed to decline to a minimum value at, or near, previously reported ionization thresholds. At higher energies, the magnitude of the quantum yield for fluorescence begins to increase. Magnetic field effects on intensity of steady-state recombination fluorescence have been observed both for photo-generated and {Beta}{sup {minus}} generated, electron and positive ion geminate pairs in saturated hydrocarbon liquids. The comparison indicates an important contribution . to observed recombination fluorescence from multiple ion-pairs under radiation chemical conditions. For photo-excited aromatic solutes dissolved in saturated hydrocarbon liquids, no magnetic field effect could be observed until surprisingly large excess energies above the threshold for ionization were achieved. This suggests a much smaller average range for the thermalized electron than expected from photoconductivity.

  3. Nuclear excitation by electronic transition of 235U

    DOE PAGES

    Chodash, P. A.; Norman, E. B.; Burke, J. T.; Casperson, R. J.; Fisher, S. E.; Holliday, K. S.; Jeffries, J. R.; Wakeling, M. A.; Wilks, S. C.

    2016-03-11

    Here, nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that can occur in isotopes containing a low-lying nuclear excited state. Over the past 40 yr, several experiments have attempted to measure NEET of 235U and those experiments have yielded conflicting results.

  4. Contribution of electronically excited states to the radiation chemistry of organic systems. Progress report, September 1, 1980-November 30, 1981

    SciTech Connect

    Lipsky, S.

    1981-01-01

    The effect of a perfluorocarbon to quench the photoionization current of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) in a non-polar liquid has been studied as a function of temperature, excitation energy and the nature and composition of the solution. A model is developed to explain the results on the basis of an interaction of the quencher with an epithermal electron. Contact charge-transfer bands involving saturated hydrocarbons and perfluorocycloalkanes have been discovered. Similar bands are not observed for hydrocarbon contact with perfluoro-n-alkanes. Also, perfluorocycloalkanes are found to have very strong quenching effect on saturated hydrocarbon fluorescence. Analysis of the quenching behavior indicates unusually large (approx. = 14 A) encounter radii for this quenching interaction. A long-range charge transfer appears to be implicated. The fluorescence quantum yield of liquid cyclohexane has been determined for excitation wavelengths from 165 nm to 178 nm. This data together with new measurements on the intensity of fluorescence of cyclohexane liquid excited by /sup 85/Kr beta particles confirms that G(S/sub 1/) = 1.45. The ratio of excimer to monomer fluorescence of dilute solutions of polystyrene in various solvents has been observed to increase with increasing polymer molecular weight and decreasing thermodynamic quality of the solvent. The effects are demonstrated to be not attributable to excimer formation via non-adjacent sites.

  5. Ab initio potential energy surfaces of HCS+: A study of the ground and the low-lying excited electronic states

    NASA Astrophysics Data System (ADS)

    Kaur, Rajwant; Dhilip Kumar, T. J.

    2016-11-01

    Three dimensional ab initio potential energy surfaces (PESs) have been computed for the ground state and low-lying excited states of HCS+ molecular ion using the internally contracted multi-reference (single and double) configuration interaction and augmented correlation consistent polarized valence quadruple zeta (aug-cc-pVQZ) basis sets. Ground state global PES is analyzed as dissociation of molecular ion into H + CS+. The ground state PES (H + CS+) has been fitted by the inverse power series expansion function. The anisotropy of the surface has been analyzed in terms of the multipolar expansion coefficients for the rigid-rotor surface. The surface will be useful for detailed understanding of collision dynamics in terms of ro-vibrational cross sections and rate coefficients.

  6. Optical and time-resolved electron paramagnetic resonance studies of the excited states of a UV-B absorber (4-methylbenzylidene)camphor.

    PubMed

    Kikuchi, Azusa; Shibata, Kenji; Kumasaka, Ryo; Yagi, Mikio

    2013-02-21

    The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T(1)) state of MBC were determined. The energy level of the T(1) state of MBC is much lower than that of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S(1)) molecules undergoes intersystem crossing to the T(1) state and the deactivation process from the T(1) state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the (3)ππ* character in the T(1) state. The zero-field splitting parameters in the T(1) state are D = 0.0901 cm(-1) and E = -0.0498 cm(-1). The sublevel preferentially populated by intersystem crossing is T(y) (y close to in-plane short axis and to the C═O direction). PMID:23320917

  7. Resonance Raman scattering of butadiene: Vibronic activity of a bu mode demonstrates the presence of a 1Ag symmetry excited electronic state at low energy

    NASA Astrophysics Data System (ADS)

    Chadwick, Richard R.; Zgierski, Marek Z.; Hudson, Bruce S.

    1991-11-01

    Resonance Raman spectra of buta-1,3-diene-d0 and buta-1,3-diene-1,1,4,4-d4 have been obtained with ultraviolet excitation from 239.5 to 199.9 nm. Activity of the first overtone of mode 24, the bu symmetry CCC chain deformation mode, is observed with excitation energy below the origin of the 1 1Bu state. This vibronic activity of a nontotally symmetric mode is shown to be evidence of resonance with the 2 1Ag state of butadiene. A quantitative analysis of the ratio of intensities of 2ν24 to ν9, the ag symmetry CCC chain deformation mode, demonstrates that enhancement of 2ν24 cannot be due to resonance with the 1 1Bu state. The resonance enhancement behavior of this overtone band also shows that it is of vibronic origin rather than Franck-Condon allowed. The intensity pattern seen for the modes of bu symmetry is fully consistent with the results of a quantitative calculation of vibronic activity for the eight bu symmetry modes. The 2 1Ag electronic state is estimated to be ca. 0.25 eV below the 1 1Bu electronic state. Overtones of out-of-plane C-H bending and CH2 twisting modes are seen with excitation radiation near the peak of the transition to the 2 1Ag state, indicating that the 2 1Ag state of butadiene has appreciably lower resistance to deformation along out-of-plane coordinates than does the ground electronic state. This is consistent with the expectations of semiempirical calculations.

  8. Solvation of electronically excited I2 -

    NASA Astrophysics Data System (ADS)

    Maslen, P. E.; Papanikolas, J. M.; Faeder, J.; Parson, R.; ONeil, S. V.

    1994-10-01

    The interaction potentials between the six lowest electronic states of I-2 and an arbitrary discrete charge distribution are calculated approximately using a one-electron model. The model potentials are much easier to calculate than ab initio potentials, with the cost of a single energy point scaling linearly with the number of solvent molecules, enabling relatively large systems to be studied. Application of the model to simulation of electronically excited I-2 in liquids and CO2 clusters is discussed. In a preliminary application, solvent effects are approximated by a uniform electric field. If electronically excited (2Πg,1/2) I-2 undergoes dissociation in the presence of a strong electric field, the negative charge localizes so as to minimize the total potential energy. However, in a weak field the negative charge localizes in the opposite direction, maximizing the potential energy. Based on a study of the field-dependent potential surfaces, a solvent-transfer mechanism is proposed for the electronic relaxation of 2Πg,1/2I-2, in contrast to the conventional view of relaxation via electron transfer.

  9. Atomic electron excitation probabilities during orbital electron capture by the nucleus

    NASA Technical Reports Server (NTRS)

    Crasemann, B.; Chen, M. H.; Briand, J. P.; Chevallier, P.; Chetioui, A.; Tavernier, M.

    1979-01-01

    Approximate probabilities of electron excitation (shakeup/shakeoff) from various atomic states during nuclear ns electron capture have been calculated in the sudden approximation, using Hartree-Fock wave functions. Total excitation probabilities are much lower than during inner-shell ionization by photons or electrons, and ns states are more likely to be excited than np states. This latter result is borne out by K-alpha X-ray satellite spectra.

  10. Contribution of electronically excited states to the radiation chemistry of organic systems. Progress report, December 1, 1981-November 30, 1984. [Tetramethyl-p-phenylenediamine

    SciTech Connect

    Lipsky, S.

    1984-01-01

    The fluorescence of saturated hydrocarbon liquids excited by /sup 85/Kr beta particles has been studied as a function of the concentration of electron scavenger. It has been possible to extract the probability, p/sup +/, that the scavengers attach a geminate electron. The effect of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) to scavenge geminate positive ions in irradiated hydrocarbon liquids has been studied via examination of the recombination fluorescence of TMPD/sup +/ + e/sup -/ as a function of TMPD concentration. The scavenging probability p/sup +/ is found to be simply proportional to c. An effect of electron scavengers to reduce the photocurrent from TMPD excited optically above its ionization threshold in nonpolar liquids has been observed and explained in terms of interaction of the scavenger with epithermal electrons. The field and temperature dependences of the photocurrent has been studied in the presence and absence of electron scavengers and the results support the epithermal model. The fractional reduction in TMPD fluorescence in liquid tetramethylsilane caused by imposition of an electric field has been studied as a function of excitation energy (above the photoionization threshold) and as a function of field strength. It has been possible to extract the photoionization quantum yield and the electron thermalization range from approx. = 5.5 eV to 7.5 eV. From an absolute measurement of the yield of excited solute states in irradiated benzene and comparison with optical measurements, it is concluded that the energy transfer efficiency is representable by a Stern-Volmer function that extrapolates to unity at infinite solute concentration. The excimer to monomer ratio in photoexcited polystyrene in solution is found not to depend on polystyrene concentration.

  11. Electronic excited state transport and trapping in disordered systems: Picosecond fluorescence mixing, transient grating, and probe pulse experiments

    SciTech Connect

    Miller, R.J.D.; Pierre, M.; Fayer, M.D.

    1983-04-15

    A detailed experimental examination of the dynamics of energy transport and trapping in two component systems, using rhodamine 6G (R6G) as the donor and malachite green (MG) as the trap in both glycerol and ethanol solvents, is presented. The experiments were performed using fluorescence mixing and ground state recovery techniques providing temporal resolution of approx.50 ps. Samples ranging from high trap-low donor concentrations (the Foerster limit) to the opposite regime of high donor and low trap concentrations, were studied. These results were compared with no adjustable parameters to the recent theoretical work of Loring, Andersen, and Fayer (LAF). The excellent agreement between theory and experiment over the entire donor-trap concentration range confirms the theoretical results of LAF and yields a comprehensive description of excited-state dynamics in solution. A variety of dynamic properties are calculated using the LAF theory and the measured parameters associated with R6G-MG system.

  12. Electronic Raman scattering with excitation between localized states observed in the zinc M{sub 2,3} soft x-ray spectra of ZnS

    SciTech Connect

    Zhou, L.; Callcott, T.A.; Jia, J.J.

    1997-04-01

    Zn M{sub 2,3} soft x-ray fluorescence (SXF) spectra of ZnS and ZnS{sub .5}Se{sub .5} excited near threshold show strong inelastic scattering effects that can be explained using a simple model and an inelastic scattering theory based on second order perturbation theory. This scattering is often called electronic resonance Raman scattering. Tulkki and Aberg have developed this theory in detail for atomic systems, but their treatment can be applied to solid systems by utilizing electronic states characteristic of solids rather than of atomic systems.

  13. Using a Spreadsheet to Solve the Schro¨dinger Equations for the Energies of the Ground Electronic State and the Two Lowest Excited States of H[subscript2

    ERIC Educational Resources Information Center

    Ge, Yingbin; Rittenhouse, Robert C.; Buchanan, Jacob C.; Livingston, Benjamin

    2014-01-01

    We have designed an exercise suitable for a lab or project in an undergraduate physical chemistry course that creates a Microsoft Excel spreadsheet to calculate the energy of the S[subscript 0] ground electronic state and the S[subscript 1] and T[subscript 1] excited states of H[subscript 2]. The spreadsheet calculations circumvent the…

  14. Molecular orbital imaging of the acetone S2 excited state using time-resolved (e, 2e) electron momentum spectroscopy.

    PubMed

    Yamazaki, Masakazu; Oishi, Keiya; Nakazawa, Hiroyuki; Zhu, Chaoyuan; Takahashi, Masahiko

    2015-03-13

    We report a time-resolved (e, 2e) experiment on the deuterated acetone molecule in the S2 Rydberg state with a lifetime of 13.5 ps. The acetone S2 state was prepared by a 195 nm pump laser and probed with electron momentum spectroscopy using a 1.2 keV incident electron beam of 1 ps temporal width. In spite of the low data statistics as well as of the limited time resolution (±35  ps) due to velocity mismatch, the experimental results clearly demonstrate that electron momentum spectroscopy measurements of short-lived transient species are feasible, opening the door to time-resolved orbital imaging in momentum space.

  15. S1←S0 vibronic spectra and structure of cyclopropanecarboxaldehyde molecule in the S1 lowest excited singlet electronic state

    NASA Astrophysics Data System (ADS)

    Godunov, I. A.; Yakovlev, N. N.; Terentiev, R. V.; Maslov, D. V.; Bataev, V. A.; Abramenkov, A. V.

    2016-11-01

    The S1←S0 vibronic spectra of gas-phase absorption at room temperature and fluorescence excitation of jet-cooled cyclopropanecarboxaldehyde (CPCA, c-C3H5CHO)were obtained and analyzed. In addition, the quantum chemical calculation (CASPT2/cc-pVTZ)was carried out for CPCA in the ground (S0) and lowest excited singlet (S1) electronic states. As a result, it was proved that the S1←S0 electronic excitation of the CPCA conformers (syn and anti) causes (after geometrical relaxation) significant structural changes, namely, the carbonyl fragments become non-planar and the cyclopropyl groups rotate around the central C-C bond. As a consequence, the potential energy surface of CPCA in the S1 state has six minima, 1ab, 2ab, and 3ab, corresponding to three pairs of mirror symmetry conformers: a and b. It was shown that vibronic bands of experimental spectra can be assigned to the 2(S1)←syn(S0) electronic transition with the origin at 30,481 cm-1. A number of fundamental vibrational frequencies for the 2 conformer of CPCA were assigned. In addition, several inversional energy levels for the 2 conformer were found and the 2a↔2b potential function of inversion was determined. The experimental barrier to inversion and the equilibrium angle between the CH bond and the CCO plane were calculated as 570 cm-1 and 28°, respectively.

  16. Tight-binding approximations to time-dependent density functional theory — A fast approach for the calculation of electronically excited states

    NASA Astrophysics Data System (ADS)

    Rüger, Robert; van Lenthe, Erik; Heine, Thomas; Visscher, Lucas

    2016-05-01

    We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.

  17. Electronically excited-state properties and predissociation mechanisms of phosphorus monofluoride: A theoretical study including spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Yu, Le; Bian, Wensheng

    2012-07-01

    The 51 Ω states generated from the 22 Λ - S states of phosphors monofluoride have been investigated using the valence internally contracted multireference configuration interaction method with the Davidson correction and the entirely uncontracted aug-cc-pV5Z basis set. The spin-orbit coupling is computed using the state interaction approach with the Breit-Pauli Hamiltonian. Based on the calculated potential energy curves, the spectroscopic constants of the bound and quasibound Λ - S and Ω states are obtained, and very good agreement with experiment is achieved. Several quasibound states caused by avoided crossings are found. Various curve crossings and avoided crossings are revealed, and with the help of our computed spin-orbit coupling matrix elements, the predissociation mechanisms of the a1Δ, b1Σ+, e3Π, g1Π, and (3)3Π states are analyzed. The intricate couplings among different electronic states are investigated. We propose that the avoided crossing between the A3Π0 + and b^1 {Σ }_{{0 + }}^{+ } states may be responsible for the fact that the A3Π ν' ⩾ 12 vibrational levels can not be observed in experiment. The transition properties of the A3Π - X3Σ- transition are studied, and our computed Franck-Condon factors and radiative lifetimes match the experimental results very well.

  18. Excited-State Electronic Structure with Configuration Interaction Singles and Tamm–Dancoff Time-Dependent Density Functional Theory on Graphical Processing Units

    PubMed Central

    2011-01-01

    Excited-state calculations are implemented in a development version of the GPU-based TeraChem software package using the configuration interaction singles (CIS) and adiabatic linear response Tamm–Dancoff time-dependent density functional theory (TDA-TDDFT) methods. The speedup of the CIS and TDDFT methods using GPU-based electron repulsion integrals and density functional quadrature integration allows full ab initio excited-state calculations on molecules of unprecedented size. CIS/6-31G and TD-BLYP/6-31G benchmark timings are presented for a range of systems, including four generations of oligothiophene dendrimers, photoactive yellow protein (PYP), and the PYP chromophore solvated with 900 quantum mechanical water molecules. The effects of double and single precision integration are discussed, and mixed precision GPU integration is shown to give extremely good numerical accuracy for both CIS and TDDFT excitation energies (excitation energies within 0.0005 eV of extended double precision CPU results). PMID:21687784

  19. Extensive theoretical study on electronically excited states of calcium monochloride: Molecular laser cooling and production of ultracold chlorine atoms.

    PubMed

    Fu, Mingkai; Ma, Haitao; Cao, Jianwei; Bian, Wensheng

    2016-05-14

    Nine doublet Λ-S states of calcium monochloride (CaCl) are calculated using the internally contracted multireference configuration interaction method with the Davidson correction. Both the core subvalence and spin-orbit coupling effects are taken into account. Laser cooling of CaCl and production of ultracold chlorine atoms are investigated and assessed. Our computed spectroscopic constants and radiative lifetimes match the available experimental data very well. The determined Franck-Condon factors and vibrational branching ratios of the A(2)Π1/2(ν('))←X(2)Σ1/2 (+)(ν) transition are highly diagonally distributed and the evaluated radiative lifetime for the A(2)Π1/2(ν' = 0) state is 28.2 ns, which is short enough for rapid laser cooling. Subsequently, detection of cold molecules via resonance enhanced multiphoton ionization to determine the final quantum state populations is discussed and the ionization energy calculated. A multi-pulse excitation scheme is proposed for producing ultracold chlorine atoms from zero-energy photodissociation of the cooled CaCl. Our results demonstrate the possibility of producing ultracold CaCl molecules and Cl atoms.

  20. Extensive theoretical study on electronically excited states of calcium monochloride: Molecular laser cooling and production of ultracold chlorine atoms

    NASA Astrophysics Data System (ADS)

    Fu, Mingkai; Ma, Haitao; Cao, Jianwei; Bian, Wensheng

    2016-05-01

    Nine doublet Λ-S states of calcium monochloride (CaCl) are calculated using the internally contracted multireference configuration interaction method with the Davidson correction. Both the core subvalence and spin-orbit coupling effects are taken into account. Laser cooling of CaCl and production of ultracold chlorine atoms are investigated and assessed. Our computed spectroscopic constants and radiative lifetimes match the available experimental data very well. The determined Franck-Condon factors and vibrational branching ratios of the A 2 Π 1 / 2 ( ν ' ) ← X 2 Σ1 / 2 + ( ν ) transition are highly diagonally distributed and the evaluated radiative lifetime for the A2Π1/2(ν' = 0) state is 28.2 ns, which is short enough for rapid laser cooling. Subsequently, detection of cold molecules via resonance enhanced multiphoton ionization to determine the final quantum state populations is discussed and the ionization energy calculated. A multi-pulse excitation scheme is proposed for producing ultracold chlorine atoms from zero-energy photodissociation of the cooled CaCl. Our results demonstrate the possibility of producing ultracold CaCl molecules and Cl atoms.

  1. Photoinduced intercomponent excited-state decays in a molecular dyad made of a dinuclear rhenium(I) chromophore and a fullerene electron acceptor unit.

    PubMed

    Nastasi, Francesco; Puntoriero, Fausto; Natali, Mirco; Mba, Miriam; Maggini, Michele; Mussini, Patrizia; Panigati, Monica; Campagna, Sebastiano

    2015-05-01

    A novel molecular dyad, 1, made of a dinuclear {[Re2(μ-X)2(CO)6(μ-pyridazine)]} component covalently-linked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties - including pump-probe transient absorption spectroscopy in the visible and near-infrared region - have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((3)MLLCT) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.

  2. Rotationally Resolved Spectroscopy of the Electronically Excited C and D States of {ArXe} and {KrXe}

    NASA Astrophysics Data System (ADS)

    Piticco, Lorena; Schäfer, Martin; Merkt, Frédéric

    2011-06-01

    Rotationally resolved (1+1') resonance-enhanced two-photon ionization spectra of the D and C ← X 0^+ band systems of several isotopomers of ArXe and KrXe were recorded using a narrow-bandwidth VUV laser system at a resolution of 0.01 Cm-1 in the wave number range from 77000 Cm-1 to 77400 Cm-1. The analysis of the rotational structures enabled the characterization of the dissociation of the Ω = 1 states of ArXe and KrXe. In the case of Rg129Xe and Rg131Xe (Rg=Ar, Kr), the hyperfine structure could also be resolved and provided new information on these states, and on the nature of the perturbations. Model potentials for the perturbing and perturbed excited states were constructed in an attempt to rationalize the spectroscopic data. The spectra of the C and D states of ArXe and KrXe reveal strong Perturbations(c-e), and are subject to slow predissociation. U. Hollenstein, H. Palm and F. Merkt, Rev. Sci. Instr. 71, 4023 (2000). L. Piticco, F. Merkt, A. A. Cholewinski, F. R. W. Mc Court and R. J. Le Roy, J. Mol. Spectrosc. 264, 83 (2010). S. Liu, A. Hishikawa and K. Yamanouchi, J. Chem. Phys. 108, 5330 (1998). A. P. Hickman, D. L. Huestis and R. P. Saxon, J. Chem. Phys. 96, 2099 (1992) D. M. Mao, X. K. Hu, S. S. Dimov and R. H. Lipson}, J. Phys. B 29, L89 (1996).

  3. Atomistic modeling of two-dimensional electronic spectra and excited-state dynamics for a Light Harvesting 2 complex.

    PubMed

    van der Vegte, C P; Prajapati, J D; Kleinekathöfer, U; Knoester, J; Jansen, T L C

    2015-01-29

    The Light Harvesting 2 (LH2) complex is a vital part of the photosystem of purple bacteria. It is responsible for the absorption of light and transport of the resulting excitations to the reaction center in a highly efficient manner. A general description of the chromophores and the interaction with their local environment is crucial to understand this highly efficient energy transport. Here we include this interaction in an atomistic way using mixed quantum-classical (molecular dynamics) simulations of spectra. In particular, we present the first atomistic simulation of nonlinear optical spectra for LH2 and use it to study the energy transport within the complex. We show that the frequency distributions of the pigments strongly depend on their positions with respect to the protein scaffold and dynamics of their local environment. Furthermore, we show that although the pigments are closely packed the transition frequencies of neighboring pigments are essentially uncorrelated. We present the simulated linear absorption spectra for the LH2 complex and provide a detailed explanation of the states responsible for the observed two-band structure. Finally, we discuss the energy transfer within the complex by analyzing population transfer calculations and 2D spectra for different waiting times. We conclude that the energy transfer from the B800 ring to the B850 ring is mediated by intermediate states that are delocalized over both rings, allowing for a stepwise downhill energy transport.

  4. The electronic structure and charge transfer excited states of the endohedral trimetallic nitride C80 (I(h)) fullerenes-Zn-tetraphenyl porphyrin dyads.

    PubMed

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

    2015-02-28

    Endohedral fullerenes offer the possibility of tuning their properties through a choice of the endohedral unit. The Sc3N@C80 fullerene is the most abundant fullerene after C60 and C70. Recently, Sc3N@C80 has been tested for light harvesting properties with encouraging results. In this work, we study the electronic structure of three endohedral fullerene-Zn tetraphenyl porphyrin complexes using density functional theory. The binding between the components in these complexes arises due to van der Waals interaction. A fragment orbital analysis is carried out to examine the interaction between the two components which shows that a small charge transfer occurs in the ground state from the ZnTPP to the fullerenes and that the orientation of the Sc3N plane affects the ground state charge transfer. The charge transfer excited state energies are calculated using our perturbative delta-SCF method. A comparison with earlier calculations shows that the charge transfer excitation energy increases as C60-ZnTPP < C70-ZnTPP < Sc3N@C80-ZnTPP < Y3N@C80-ZnTPP. The orientation of the endohedral unit does not influence the excitation energy in the donor-acceptor complexes.

  5. Contribution of electronically excited states to the radiation chemistry of organic systems. Informal technical progress report, December 1, 1981-January 31, 1983

    SciTech Connect

    Lipsky, S.

    1983-01-01

    Summaries are presented for the research projects in progress and for the following three completed projects: (1) comparision of the quenching of the fluorescence of saturated hydrocarbons excited below and above the ionization threshold; (2) dependence on scavenger concentration of the efficiency of quenching genunate-ion recombination fluorescence of saturated hydrocarbon liquids; (3) positive charge transfer from saturated non-polar liquids to N,N,N'-tetramethyl-p-phenylenediamine. In addition to these projects the following investigations have been completed and published during the past two years: effect of perfluorocarbons on ultraviolet absorption and fluorescence characteristics of some saturated hydrocarbon liquids; note on the G value for the production of the lowest excited singlet state of cyclohexane; effect of electron scavengers to reduce the ionization current of photoexcited N,N,N',N'-tetramethyl-p-phenylediamine in non-polar organic fluids; polystyren fluorescence-effects of molecular weight in various solvents.

  6. Geometries and electronic structures of the ground and low-lying excited states of FeCO: An ab initio study

    NASA Astrophysics Data System (ADS)

    Hirano, Tsuneo; Okuda, Rei; Nagashima, Umpei; Jensen, Per

    2012-12-01

    FeCO is a molecule of astrophysical interest. We report here theoretical calculations of its geometrical parameters, electronic structures, and molecular constants (such as dipole moment and spin-orbit coupling constant) in the electronic ground state tilde{X}3Σ - and the low-lying triplet and quintet excited states. The calculations were made at the MR-SDCI+Q_DK3/[5ZP ANO-RCC (Fe, C, O)] and MR-AQCC_DK3/[5ZP ANO-RCC (Fe, C, O)] levels of theory. A multi-reference calculation was required to describe correctly the wavefunctions of all states studied. For all triplet states, the σ-donation through the 10σ molecular orbital (MO) as well as the π-back-donation through the 4π MO are observed, and the dipole moment vector points from O toward Fe as expected. However, in the excited quintet states 5Π, 5Φ, and 5Δ, the almost negligible contribution of Fe 4s to the 10σ MO makes the dipole moment vector point from Fe toward O, i.e., in the same direction as in CO. In the tilde{X}3Σ - state, the electron provided by the σ-donation through the 10σ MO is shared between the Fe atom and the C end of the CO residue to form a coordinate-covalent Fe-C bond. In the tilde{a}5Σ - state (the high-spin counterpart of tilde{X}3Σ -), the σ-donation through the 10σ MO is not significant and so the Fe-C bond is rather ionic. The π-back-donation through the 4π MO is found to be of comparable importance in the two electronic states; it has a slightly larger magnitude in the tilde{X}3Σ - state. The difference in the molecular properties of the low-spin tilde{X}3Σ - and the high-spin tilde{a}5Σ - states can be understood in terms of the dynamical electron correlation effects.

  7. Application of the Schwinger multichannel formulation to electron-impact excitation of the B 1Sigma(+)u state of H2

    NASA Technical Reports Server (NTRS)

    Gibson, Thomas L.; Lima, Marco A. P.; Mckoy, Vincent; Huo, Winifred M.

    1987-01-01

    The paper reports cross sections for electron-impact excitation of the X 1Sigma(+)g - BISigma(+)u transition in H2 for collision energies of 15, 20, and 30 eV. For this dipole-allowed transition with its associated long-range potential, the contributions of the more strongly scattered low-angular-momentum partial waves to the cross section were obtained from a two-state Schwinger multichannel calculation, and a modified Born-closure scheme was used to include the contributions from the remaining weakly scattered partial waves. Agreement between the calculated differential cross sections and available experimental data is encouraging.

  8. The contribution of electronically excited states to the radiation chemistry of organic systems: Progress report, June 30, 1988--April 30, 1989

    SciTech Connect

    Lipsky, S.

    1989-01-01

    The photoionization current from anthracene in liquid hydrocarbons has been studied as a function of excitation energy. From the dependence of the photocurrent spectrum on the magnitude of an externally applied electric field, it is deduced that the appearance of a fine structure in these spectra is mainly attributable, not to variability in the electron yield probability as others have conjectured, but rather to an energy dependence of the electron's thermalization range parameter. Solvent effects on the diffuseness of this structure are also explainable on this basis. By monitoring the fluorescence from hexafluorobenzene dissolved in the non-fluorescent hydrocarbon solvents, 2,3,4-trimethylpentane, 2,2-dimethylbutane, cyclopentane and tetramethylsilane excited with ..beta../sup /minus// particles, it has been possible to extract the geminate ion-pair scavenging probability, p/sup /dagger//. This is found to have a dependence on hexafluorobenzene concentration, c, entirely similar to what has previously been reported for p/sup /dagger// extracted from quenching of solvent fluorescence by perfluorocarbon scavengers. Thus it is now demonstrated that two different fluorescent techniques provide an expression for p/sup /dagger// that is distinctly disparate from that initially introduced by Warman, Asmus and Schuler to explain their results on chemical scavengers. Origins for this difference are considered. Preliminary attempts to locate a triplet-state emission from saturated hydrocarbons excited biphotonically with 307 nm XeCl excimer laser light have thus far been unsuccessful. 15 refs.

  9. Theoretical Studies of Chemical Reactions following Electronic Excitation

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.

    2003-01-01

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

  10. The role of dissociation channels of excited electronic states in quantum optimal control of ozone isomerization: A three-state dynamical model

    NASA Astrophysics Data System (ADS)

    Kurosaki, Yuzuru; Ho, Tak-San; Rabitz, Herschel

    2016-05-01

    The prospect of performing the open → cyclic ozone isomerization has attracted much research attention. Here we explore this consideration theoretically by performing quantum optimal control calculations to demonstrate the important role that excited-state dissociation channels could play in the isomerization transformation. In the calculations we use a three-state, one-dimensional dynamical model constructed from the lowest five 1A‧ potential energy curves obtained with high-level ab initio calculations. Besides the laser field-dipole couplings between all three states, this model also includes the diabatic coupling between the two excited states at an avoided crossing leading to competing dissociation channels that can further hinder the isomerization process. The present three-state optimal control simulations examine two possible control pathways previously considered in a two-state model, and reveal that only one of the pathways is viable, achieving a robust ∼95% yield to the cyclic target in the three-state model. This work represents a step towards an ultimate model for the open → cyclic ozone transformation capable of giving adequate guidance about the necessary experimental control field resources as well as an estimate of the ro-vibronic spectral character of cyclic ozone as a basis for an appropriate probe of its formation.

  11. Electronic states of thiophene/phenylene co-oligomers: Extreme-ultra violet excited photoelectron spectroscopy observations and density functional theory calculations

    SciTech Connect

    Kawaguchi, Yoshizo; Sasaki, Fumio; Mochizuki, Hiroyuki; Ishitsuka, Tomoaki; Tomie, Toshihisa; Ootsuka, Teruhisa; Watanabe, Shuji; Shimoi, Yukihiro; Yamao, Takeshi; Hotta, Shu

    2013-02-28

    We have investigated electronic states in the valence electron bands for the thin films of three thiophene/phenylene co-oligomer (TPCO) compounds, 2,5-bis(4-biphenylyl)thiophene (BP1T), 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5), and 1,4-bis{l_brace}5-[4-(trifluoromethyl)phenyl]thiophen-2-yl{r_brace}benzene (AC5-CF{sub 3}), by using extreme-UV excited photoelectron spectroscopy (EUPS). By comparing both EUPS spectra and secondary electron spectra between AC5 and AC5-CF{sub 3}, we confirm that CF{sub 3} substitution to AC5 deepens valence states by 2 eV, and increases the ionization energy by 3 eV. From the cut-off positions of secondary electron spectra, the work functions of AC5, AC5-CF{sub 3}, and BP1T are evaluated to be 3.8 eV, 4.8 eV, and 4.0 eV, respectively. We calculate molecular orbital (MO) energy levels by the density functional theory and compare results of calculations with those of experiments. Densities of states obtained by broadening MO levels well explain the overall features of experimental EUPS spectra of three TPCOs.

  12. Experimental observations of nonlinearly enhanced 2omega-UH electromagnetic radiation excited by steady-state colliding electron beams

    NASA Technical Reports Server (NTRS)

    Intrator, T.; Hershkowitz, N.; Chan, C.

    1984-01-01

    Counterstreaming large-diameter electron beams in a steady-state laboratory experiment are observed to generate transverse radiation at twice the upper-hybrid frequency (2omega-UH) with a quadrupole radiation pattern. The electromagnetic wave power density is nonlinearly enhanced over the power density obtained from a single beam-plasma system. Electromagnetic power density scales exponentially with beam energy and increases with ion mass. Weak turbulence theory can predict similar (but weaker) beam energy scaling but not the high power density, or the predominance of the 2omega-UH radiation peak over the omega-UH peak. Significant noise near the upper-hybrid and ion plasma frequencies is also measured, with normalized electrostatic wave energy density W(ES)/n(e)T(e) approximately 0.01.

  13. Theory of nuclear excitation by electron capture for heavy ions

    SciTech Connect

    Palffy, Adriana; Scheid, Werner; Harman, Zoltan

    2006-01-15

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

  14. Cross sections for electron impact excitation of the b 3Sigma(+)u state of H2 - An application of the Schwinger multichannel variational method

    NASA Technical Reports Server (NTRS)

    Lima, M. A. P.; Gibson, T. L.; Mckoy, V.; Huo, W. M.

    1985-01-01

    In this and the two accompanying letters, the results of calculations of the cross sections for electron impact excitation of the b 3Sigma(+)u state of H2, for collision energies from near threshold to 30 eV, are presented. These results are obtained using a multichannel extension of the Schwinger variational principle at the two-state level. The quantitative agreement between the integral cross sections of these three studies is very good. Inclusion of correlation terms in the scattering wavefunctions, which relax the orthogonality between bound and continuum orbitals, is seen to affect the cross sections substantially. Although a comparison of these calculated cross sections with available experimental data is encouraging, some seious discrepancies exist.

  15. 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.

  16. Calculation of electronic coupling matrix elements for ground and excited state electron transfer reactions: Comparison of the generalized Mulliken-Hush and block diagonalization methods

    NASA Astrophysics Data System (ADS)

    Cave, Robert J.; Newton, Marshall D.

    1997-06-01

    Two independent methods are presented for the nonperturbative calculation of the electronic coupling matrix element (Hab) for electron transfer reactions using ab initio electronic structure theory. The first is based on the generalized Mulliken-Hush (GMH) model, a multistate generalization of the Mulliken Hush formalism for the electronic coupling. The second is based on the block diagonalization (BD) approach of Cederbaum, Domcke, and co-workers. Detailed quantitative comparisons of the two methods are carried out based on results for (a) several states of the system Zn2OH2+ and (b) the low-lying states of the benzene-Cl atom complex and its contact ion pair. Generally good agreement between the two methods is obtained over a range of geometries. Either method can be applied at an arbitrary nuclear geometry and, as a result, may be used to test the validity of the Condon approximation. Examples of nonmonotonic behavior of the electronic coupling as a function of nuclear coordinates are observed for Zn2OH2+. Both methods also yield a natural definition of the effective distance (rDA) between donor (D) and acceptor (A) sites, in contrast to earlier approaches which required independent estimates of rDA, generally based on molecular structure data.

  17. Electron-pair excitations and the molecular Coulomb continuum

    SciTech Connect

    Colgan, James

    2009-01-01

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

  18. Ultrafast electronic dynamics in laser-excited crystalline bismuth

    NASA Astrophysics Data System (ADS)

    Melnikov, Alexey A.; Misochko, Oleg V.; Chekalin, Sergey V.

    2013-07-01

    Femtosecond spectroscopy is applied to study transient electronic processes in bismuth. The components with relaxation times of 1 ps, 7 ps, and ˜1 ns are detected in the photoinduced reflectivity response of the crystal. To facilitate assignment of the observed relaxation to the decay of particular excited electronic states, we use pump pulses with central wavelengths ranging from 400 to 2300 nm. Additionally, we examine the variation of parameters of coherent A1g phonons upon the change of excitation and probing conditions. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along Γ-T direction of the Brillouin zone.

  19. Dissociative excitation of molecular hydrogen by electron impact.

    NASA Technical Reports Server (NTRS)

    Misakian, M.; Zorn, J. C.

    1972-01-01

    A pulsed electron beam was employed in the experiment to excite a diffuse gas of hydrogen molecules. The energy resolution of the electron gun permitted careful measurements of the thresholds for the production of slow and fast H(2s) atoms. The experiment was conducted in a vacuum system that facilitated a systematic study of the angular distribution of the fragments in the dissociative excitation process. The results permit the identification of the several excited states that are involved in the production of the H(2s) fragments.

  20. Symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster studies of electronically excited states of copper tetrachloride and copper tetrabromide dianions

    NASA Astrophysics Data System (ADS)

    Ehara, Masahiro; Piecuch, Piotr; Lutz, Jesse J.; Gour, Jeffrey R.

    2012-05-01

    The valence excitation spectra of the copper tetrachloride and copper tetrabromide open-shell dianions, CuCl42- and CuBr42-, respectively, are investigated by a variety of symmetry-adapted-cluster configuration-interaction (SAC-CI) and equation-of-motion coupled-cluster (EOMCC) methods. The valence excited states of the CuCl42- and CuBr42- species that correspond to transitions from doubly occupied molecular orbitals (MOs) to a singly occupied MO (SOMO), for which experimental spectra are available, are examined with the ionized (IP) variants of the SAC-CI and EOMCC methods. The higher-energy excited states of CuCl42- and CuBr42- that correspond to transitions from SOMO to unoccupied MOs, which have not been characterized experimentally, are determined using the electron-attached (EA) SAC-CI and EOMCC approaches. An emphasis is placed on the scalar relativistic SAC-CI and EOMCC calculations based on the spin-free part of the second-order Douglass-Kroll-Hess Hamiltonian (DKH2) and on a comparison of the results of the IP and EA SAC-CI and EOMCC calculations with up to 2-hole-1-particle (2h-1p) and 2-particle-1-hole (2p-1h) excitations, referred to as the IP-SAC-CI SD-R and IP-EOMCCSD(2h-1p) methods in the IP case and EA-SAC-CI SD-R and EA-EOMCCSD(2p-1h) approaches in the EA case, with those obtained with the higher-level IP-EOMCC and EA-EOMCC theories with up to 3-hole-2-particle (3h-2p) and 3-particle-2-hole (3p-2h) excitations treated via active orbitals, abbreviated as IP-EOMCCSD(3h-2p) and EA-EOMCCSD(3p-2h), respectively, as well as with the available experimental data. It is demonstrated that all of the employed DKH2-based IP-SAC-CI and IP-EOMCC methods offer a reliable description of the valence excited states of the CuCl42- and CuBr42- complexes that correspond to transitions from doubly occupied MOs to SOMO, accurately reproducing the observed UV-vis absorption spectra in both peak positions and intensities, which enables a rigorous assignment of the

  1. Theoretical description of electronically excited vinylidene up to 10 eV: first high level ab initio study of singlet valence and Rydberg states.

    PubMed

    Boyé-Péronne, Séverine; Gauyacq, Dolores; Liévin, Jacques

    2014-11-01

    The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0-10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores (2)A1 and (2)B1 results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Δl = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the (2)B1 cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the (2)A1 ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic characterization of vinylidene.

  2. Ab initio adiabatic and quasidiabatic potential energy surfaces of H+ + CO system: A study of the ground and the first three excited electronic states

    NASA Astrophysics Data System (ADS)

    Saheer, V. C.; Kumar, Sanjay

    2016-01-01

    The global ground and first three excited electronic state adiabatic as well as the corresponding quasidiabatic potential energy surfaces is reported as a function of nuclear geometries in the Jacobi coordinates ( R → , r → , γ ) using Dunning's cc-pVTZ basis set at the internally contracted multi-reference (single and double) configuration interaction level of accuracy. Nonadiabatic couplings, arising out of relative motion of proton and the vibrational motion of CO, are also reported in terms of coupling potentials. The quasidiabatic potential energy surfaces and the coupling potentials have been obtained using the ab initio procedure [Simah et al., J. Chem. Phys. 111, 4523 (1999)] for the purpose of dynamics studies.

  3. 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'.

  4. Collisional excitation of electron Landau levels in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Langer, S. H.

    1981-01-01

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

  5. Electron-configuration-reset time-differential recoil-in-vacuum technique for excited-state g-factor measurements on fast exotic beams

    SciTech Connect

    Stuchbery, Andrew E.; Mantica, Paul F.; Wilson, Anna N.

    2005-04-01

    A modified version of the time-differential recoil-in-vacuum (or plunger) technique is proposed as a method for measuring the g factors of excited states in rapidly moving exotic nuclei with Z < or approx. 20.

  6. Electron impact excitation cross sections in F-like selenium

    SciTech Connect

    Chen Guoxin |; Ong, P.P.

    1998-09-01

    Cross sections for excitation induced by electron collision between low-lying 1s{sup 2}2s{sup 2}2p{sup 5} and 1s{sup 2}2s2p{sup 6} states of f-like selenium and from these states to singly excited states with the excited electron occupying the M shell have been calculated by relativistic distorted-wave Born procedures. The GRASP{sup 2} code was used for the atomic structure calculations. The continuum orbitals for the construction of continuum states were computed in the distorted-wave approximation, in which the distorted-wave potential used was the spherically averaged potential of the nucleus plus the potential of the bound electrons of the bound state. The cross sections for excitations were computed first by a 233-level multiconfiguration Dirac-Fock (MCDF) configuration expansion and then by a 279-level MCDF configuration expansion. The latter procedure, which also took into account contributions from all the participating singly excited N-shell states, was found to be necessary for improved accuracy. The cross section data should be a useful reference in the development of x-ray lasers and other related fields involving highly stripped ions.

  7. Electronic excitation spectrum of ABC-stacked multilayer graphene

    NASA Astrophysics Data System (ADS)

    Henni, Y.; Nogajewski, K.; Ojeda Collado, H. P.; Usaj, G.; Balseiro, C. A.; Potemski, M.; Faugeras, C.

    The electronic properties of ABC graphene trilayers has attracted lot of attention recently due to their potential applications in engineering carbon-based devices with gate tunable electrical conductivity. Morever,ABC-stacked thin layers of graphite are predicted to host peculiar surface electronic states, with a flat dispersion over most of the Brillouin zone. The associated high density of states is likely to favour the emergence of exotic electronic phases, such as charge density waves or even superconductivity. We present a micro-magneto-Raman scattering study of a thin graphite flake produced by exfoliation of natural graphite, composed of ~15graphene layers, and including a large ABC-stacked domain. Exploring the low temperature Raman scattering spectrum of this domain up to B=29T,we identify inter Landau level electronic excitations within the surface flat bands,together with electronic excitations involving the gapped states in the bulk. This interband electronic excitation at B=0T can be observed,up to room temperature, directly in the Raman scattering spectrum as a broad(~ 180 cm-1) feature. Because the energy gap strongly depends on the number of layers,this electronic excitation can be used to identify and characterize ABC-stacked graphite thin layers.

  8. Electron-impact vibrational excitation of cyclopropane

    SciTech Connect

    Čurík, R. Čársky, P.; Allan, M.

    2015-04-14

    We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10{sup ∘} to 180{sup ∘} and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by solving the two-channel Lippmann-Schwinger equation in the momentum space, and the interaction between the scattered electron and the target molecule was described by exact static-exchange potential corrected by a density functional theory (DFT) correlation-polarization interaction that models target’s response to the field of incoming electron. The theory is found to quantitatively reproduce the measured spectra for all normal modes, even at the difficult conditions of extreme angles and at low energies, and thus provides full understanding of the excitation mechanism. It is shown that the overlap of individual vibrational bands caused by limited experimental resolution and rotational excitation must be properly taken into account for correct comparison of experiment and theory. By doing so, an apparent discrepancy between published experimental data could be reconciled. A substantial cross section is found for excitation of the non-symmetric HCH twisting mode ν{sub 4} of A{sub 1}{sup ″} symmetry by the 5.5 eV A{sub 2}{sup ′} resonance, surprisingly because the currently accepted selection rules predict this process to be forbidden. The DMR theory shows that the excitation is caused by an incoming electron in an f-wave of A{sub 2}{sup ′} symmetry which causes excitation of the non-symmetric HCH twisting mode ν{sub 4} of the A{sub 1}{sup ″} symmetry and departs in p- and f-waves of A{sub 2}{sup ″} symmetry.

  9. Electron-impact vibrational excitation of cyclopropane.

    PubMed

    Čurík, R; Čársky, P; Allan, M

    2015-04-14

    We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10° to 180° and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by solving the two-channel Lippmann-Schwinger equation in the momentum space, and the interaction between the scattered electron and the target molecule was described by exact static-exchange potential corrected by a density functional theory (DFT) correlation-polarization interaction that models target's response to the field of incoming electron. The theory is found to quantitatively reproduce the measured spectra for all normal modes, even at the difficult conditions of extreme angles and at low energies, and thus provides full understanding of the excitation mechanism. It is shown that the overlap of individual vibrational bands caused by limited experimental resolution and rotational excitation must be properly taken into account for correct comparison of experiment and theory. By doing so, an apparent discrepancy between published experimental data could be reconciled. A substantial cross section is found for excitation of the non-symmetric HCH twisting mode ν4 of A1 (″) symmetry by the 5.5 eV A2 (') resonance, surprisingly because the currently accepted selection rules predict this process to be forbidden. The DMR theory shows that the excitation is caused by an incoming electron in an f-wave of A2 (') symmetry which causes excitation of the non-symmetric HCH twisting mode ν4 of the A1 (″) symmetry and departs in p- and f-waves of A2 (″) symmetry. PMID:25877583

  10. Excited-state dynamics of 3-hydroxyflavone anion in alcohols.

    PubMed

    Dereka, Bogdan; Letrun, Romain; Svechkarev, Denis; Rosspeintner, Arnulf; Vauthey, Eric

    2015-02-12

    The electronic absorption spectrum of 3-hydroxyflavone (3HF) in various solvents exhibits a long-wavelength (LW) band, whose origin has been debated. The excited-state dynamics of neutral and basic solutions of 3HF in alcohols upon excitation in this LW band has been investigated using a combination of fluorescence up-conversion and transient electronic and vibrational absorption spectroscopies. The ensemble of results reveals that, in neutral solutions, LW excitation results in the population of two excited species with similar fluorescence spectra but very different lifetimes, namely 40-100 ps and 2-3 ns, depending on the solvent. In basic solutions, the relative concentrations of these species change considerably in favor of that with the short-lived excited state. On the basis of the spectroscopic data and quantum chemistry calculations, the short lifetime is attributed to the excited state of 3HF anion, whereas the long one is tentatively assigned to an excited hydrogen-bonded complex with the solvent. Excited-state intermolecular proton transfer from the solvent to the anion yielding the tautomeric form of 3HF is not operative, as the excited anion decays to the ground state via an efficient nonradiative transition.

  11. Ground and Excited-Electronic-State Dissociations of Hydrogen-Rich and Hydrogen-Deficient Tyrosine Peptide Cation Radicals

    NASA Astrophysics Data System (ADS)

    Viglino, Emilie; Lai, Cheuk Kuen; Mu, Xiaoyan; Chu, Ivan K.; Tureček, František

    2016-09-01

    We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H]+● and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS3 dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%-94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in CuII(2,2 ':6 ',2 ″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR]+● that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing Cα-radical positions in peptide cation radical intermediates.

  12. Ultrafast electronic processes in highly excited solids: subpicosecond optical studies

    NASA Astrophysics Data System (ADS)

    Petite, Guillaume

    1998-09-01

    Modern short pulse lasers are efficient tools for production of high levels of electronic excitation in solids under irradiation, a state which mimics that of the same materials after the passage of any particle which deposits its energy under the form of electronic excitation. Because they can also be used in a number of optical experiments of charge carriers and defect detection, they offer the unique opportunity of unraveling the ultrafast kinetic aspects of atomic processes induced by the electronic excitation, whose final state is the only aspect accessible in the case of other irradiations. After mentioning a few orders of magnitudes concerning the energy deposition, we will show some examples of recent experiments concerning the mechanisms of irradiation defect creation in insulators. The perspectives opened by recent developments of light sources in a wide range of wavelengths will be finally presented.

  13. 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.

  14. Radiative and non radiative decay of electronically excited HNF (DNF)

    SciTech Connect

    Chen, J.; Dagdigian, P.J.

    1993-12-31

    Laser experiments probing the dynamics of the decay of electronically excited HNF/DNF({tilde A}{sup 2}A`) will be reported. Measured decay lifetimes of individual (J`,K) excited levels revealed the onset of a rapid nonradiative decay process at a threshold energy of 23,800 {+-} 500 cm{sup {minus}1} above the HNF({tilde X}{sup 2}A``) zero-point level. The assignment of this threshold to the predissociation process, HNF/DNF{sup *} {yields} NH/ND(X{sup 3}{Sigma}{sup {minus}}) + F({sup 2}P), has been confirmed by direct observation of the NH/ND fragment. Photofragmentation excitation spectra, which exhibits strong mixing between the excited and ground electronic states, will be presented and discussed.

  15. The Excited State Spectrum of QCD

    SciTech Connect

    Robert Edwards

    2010-08-01

    The determination of the highly excited state spectrum of baryons within QCD is a major theoretical and experimental challenge. I will present recent results from lattice QCD that give some indications on the structure of these highly excited states, and outline on-going and future work needed for a full determination of the spectrum, including strong decays.

  16. Photoionization of ground and excited states of Ti I

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2015-07-01

    Detailed photoionization of ground and many excited states with autoionizing resonances of neutral Ti are presented. Ti I with 22 electrons forms a large number of bound states, the present work finds a total of 908 bound states with n ⩽ 10 and l ⩽ 8 . Photoionization cross sections (σPI) for all these bound states have been obtained. Calculations were carried out in the close-coupling R-matrix method using a wave function expansion that included 36 states of core ion Ti II. It is found that the resonances enhance the low energy region of photoionization of the ground and low lying excited states. The resonant features will increase the opacity, as expected of astrophysical observation, and hence play important role in determination of abundances in the elements in the astronomical objects. The excited states also show prominent structures of Seaton or photo-excitation-of-core resonances.

  17. Atomic resolution mapping of the excited-state electronic structure of Cu2O with time-resolved x-ray absorption spectroscopy

    SciTech Connect

    Hillyard, P. W.; Kuchibhatla, S. V. N. T.; Glover, T. E.; Hertlein, M. P.; Huse, Nils; Nachimuthu, P.; Saraf, L. V.; Thevuthasan, S.; Gaffney, K. J.

    2010-05-02

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that the conduction-band and valence-band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  18. Atomic Resolution Mapping of the Excited-State Electronic Structure of Cu2O with Time-Resolved X-Ray Absorption Spectroscopy

    SciTech Connect

    Hillyard, Patrick B.; Kuchibhatla, Satyanarayana V N T; Glover, T. E.; Hertlein, M. P.; Huse, N.; Nachimuthu, Ponnusamy; Saraf, Laxmikant V.; Thevuthasan, Suntharampillai; Gaffney, Kelly J.

    2009-09-29

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that that the conduction band and valence band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  19. 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

  20. Investigations of ultrafast dynamics in electronically excited alkylbenzenes

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Gerber, T.; Radi, P.; Sych, Y.; Maksyutenko, P.; Knopp, G.

    2013-03-01

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

  1. Doubly Excited States in Be III

    NASA Astrophysics Data System (ADS)

    Andersen, T.; Bentzen, S. M.; Poulsen, O.

    1980-01-01

    The triplet spectrum of doubly excited Be III has been studied in the wavelength region of 75-5000 Å in order to test the validity of the theoretical term values reported by Lipsky et al. The beam-foil excitation technique was applied to effectively populate the doubly excited states. The identified lower-lying, doubly excited states 2p2 3P, 2pnp 3P, or 3D, and 2pnd 3P, or 3D (n = 3, 4) show that the theoretical term values should be slightly modified.

  2. Excitation of weakly bound molecules to trilobitelike Rydberg states.

    PubMed

    Bellos, M A; Carollo, R; Banerjee, J; Eyler, E E; Gould, P L; Stwalley, W C

    2013-08-01

    We observe "trilobitelike" states of ultracold (85)Rb(2) molecules, in which a ground-state atom is bound by the electronic wave function of its Rydberg-atom partner. We populate these states through the ultraviolet excitation of weakly bound molecules, and access a regime of trilobitelike states at low principal quantum numbers and with vibrational turning points around 35 Bohr radii. This demonstrates that, unlike previous studies that used free-to-bound transitions, trilobitelike states can also be excited through bound-to-bound transitions. This approach provides high excitation probabilities without requiring high-density samples, and affords the ability to control the excitation radius by selection of the initial-state vibrational level.

  3. Excitations and benchmark ensemble density functional theory for two electrons

    SciTech Connect

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

    2014-05-14

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

  4. Slow excited state phototautomerization in 3-hydroxyisoquinoline.

    PubMed

    Joshi, Neeraj Kumar; Arora, Priyanka; Pant, Sanjay; Joshi, Hem Chandra

    2014-06-01

    In the present work we report the spectral and photophysical properties of 3-hydroxyisoquinoline in various protic/aprotic solvents. Our steady state and time resolved fluorescence data indicates that in the monomer form of 3HIQ phototautomerization can take place in the excited state through excited state intramolecular proton, while as per earlier suggestions phototautomerization in 3HIQ occurs in dimer or complex (in the presence of acetic acid) form. Moreover, we find rather slow tautomerization (occurring on the nanosecond scale). It is found that proton transfer occurs both in the ground as well as excited states and is controlled by the polarity of the solvent.

  5. 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

  6. Excited-State Deactivation of Branched Phthalocyanine Compounds.

    PubMed

    Zhu, Huaning; Li, Yang; Chen, Jun; Zhou, Meng; Niu, Yingli; Zhang, Xinxing; Guo, Qianjin; Wang, Shuangqing; Yang, Guoqiang; Xia, Andong

    2015-12-21

    The excited-state relaxation dynamics and chromophore interactions in two phthalocyanine compounds (bis- and trisphthalocyanines) are studied by using steady-state and femtosecond transient absorption spectral measurements, where the excited-state energy-transfer mechanism is explored. By exciting phthalocyanine compounds to their second electronically excited states and probing the subsequent relaxation dynamics, a multitude of deactivation pathways are identified. The transient absorption spectra show the relaxation pathway from the exciton state to excimer state and then back to the ground state in bisphthalocyanine (bis-Pc). In trisphthalocyanine (tris-Pc), the monomeric and dimeric subunits are excited and the excitation energy transfers from the monomeric vibrationally hot S1 state to the exciton state of a pre-associated dimer, with subsequent relaxation to the ground state through the excimer state. The theoretical calculations and steady-state spectra also show a face-to-face conformation in bis-Pc, whereas in tris-Pc, two of the three phthalocyanine branches form a pre-associated face-to-face dimeric conformation with the third one acting as a monomeric unit; this is consistent with the results of the transient absorption experiments from the perspective of molecular structure. The detailed structure-property relationships in phthalocyanine compounds is useful for exploring the function of molecular aggregates in energy migration of natural photosynthesis systems.

  7. Eucken correction in high-temperature gases with electronic excitation

    SciTech Connect

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

    2014-05-14

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

  8. Electron excitations in Na_xCoO_2(*)

    NASA Astrophysics Data System (ADS)

    Restrepo, O. D.; Eguiluz, A. G.

    2004-03-01

    We report a study of electron-hole excitations in Na_xCoO2 for x=1/3. Starting from the paramagnetic LDA ground state, we then discuss the impact of correlation on the nature of the ground state within the correlated band theory LDA+U method. The possible significance of the neglect of quantum fluctuations is oulined. The excitation spectrum is also calculated within mean field theory (the random phase approximation). Novel loss structure in the energy domain ˜ U10 to 3U is reported; the same corresponds to low-energy electron-hole excitations in the half-metal LSDA regime, to collective electronic modes present more generally. These excitations should be observed rather directly with available loss spectroscopies (electrons and x-rays), thus providing an additional set of constraints on the description of the correlated ground state. (*) Collaboration supported by the PCSCS network, within the DOE-CMSN. (1) Supported by NSF-DMR 0219332 (2) Managed by UT-Battelle for the U.S. DOE under contract DE-AC05-00OR22725. (3) DOE Grant DE-FG03-01ER45876

  9. 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.

  10. Searching for nuclear excitation by electronic transition in U-235

    NASA Astrophysics Data System (ADS)

    Chodash, P.; Norman, E. B.; Swanberg, E.; Burke, J. T.; Casperson, R. J.; Wilks, S.

    2012-10-01

    Nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that is predicted to occur in numerous isotopes, including U-235. NEET can occur when a nuclear transition closely matches the energy and multipolarity of an electronic transition. U-235 has a 1/2+ isomeric state that decays to the 7/2- ground state with a transition energy of 77 eV and a half life of 26 minutes. Theory predicts that electronic transitions exist within a partially ionized uranium plasma that would allow NEET to occur. The NEET process would excite U-235 into its isomeric state and then it will subsequently decay to the ground state via internal conversion. It is currently not known if this excitation occurs in U-235 and at what rate. In order to generate the uranium plasma with the correct conditions, a high power Q-switched Nd:YAG laser will irradiate a sample of highly enriched uranium. The resulting plasma will be collected on a catcher foil and counted using a microchannel plate detector. Current progress on the experiment will be presented.

  11. Hydrogen Bonds in Excited State Proton Transfer

    NASA Astrophysics Data System (ADS)

    Horke, D. A.; Watts, H. M.; Smith, A. D.; Jager, E.; Springate, E.; Alexander, O.; Cacho, C.; Chapman, R. T.; Minns, R. S.

    2016-10-01

    Hydrogen bonding interactions between biological chromophores and their surrounding protein and solvent environment significantly affect the photochemical pathways of the chromophore and its biological function. A common first step in the dynamics of these systems is excited state proton transfer between the noncovalently bound molecules, which stabilizes the system against dissociation and principally alters relaxation pathways. Despite such fundamental importance, studying excited state proton transfer across a hydrogen bond has proven difficult, leaving uncertainties about the mechanism. Through time-resolved photoelectron imaging measurements, we demonstrate how the addition of a single hydrogen bond and the opening of an excited state proton transfer channel dramatically changes the outcome of a photochemical reaction, from rapid dissociation in the isolated chromophore to efficient stabilization and ground state recovery in the hydrogen bonded case, and uncover the mechanism of excited state proton transfer at a hydrogen bond, which follows sequential hydrogen and charge transfer processes.

  12. Theoretical Studies on the Reaction Pathways of Electronically Excited Daaf

    NASA Astrophysics Data System (ADS)

    Quenneville, J.; Moore, D. S.

    2009-12-01

    The use of temporally and spectrally shaped ultrafast laser pulses to initiate, as well as detect, high explosives is being explored at Los Alamos. High level ab initio calculations, presented here, are employed to help guide and interpret the experiments. The ground and first excited electronic states of 3, 3'-diamino-4, 4'-azoxyfurazan (DAAF) are investigated using complete active space self-consistent field (CASSCF) and time-dependent density functional theory (TD-DFT). The geometrical and energetic character of the excited state minima, conical intersections and reaction pathways of DAAF are described. Two radiative and two non-radiative excited state population quenching mechanisms are outlined, and possible pathways for photochemical and spectroscopic control are discussed.

  13. Measurements of Excitation Functions and Line Polarizations for Electron Impact Excitation of the n = 2, 3 States of Atomic Hydrogen in the Energy Range 11 - 2000 eV

    NASA Technical Reports Server (NTRS)

    James, G. K.; Ajello, J. M.; Kanik, I.; Slevin, J.; Franklin, B.; Shemansky, D.

    1993-01-01

    The electron-atomic hydrogen scattering system is an important testing ground for theoretical models and has received a great deal of attention from experimentalists and theoreticians alike over the years. A complete description of the excitation process requires a knowledge of many different parameters, and experimental measurements of these parameters have been performed in various laboratories around the world. As far as total cross section data are concerned it has been noted that the discrepancy between the data of Long et al. and Williams for n = 2 excitations needs to be resolved in the interests of any further refinement of theory. We report new measurements of total cross sections and atomic line polarizations for both n=2 and n=3 excitations at energies from threshold to 2000 eV...

  14. Statistics of excitations in the electron glass model

    NASA Astrophysics Data System (ADS)

    Palassini, Matteo

    2011-03-01

    We study the statistics of elementary excitations in the classical electron glass model of localized electrons interacting via the unscreened Coulomb interaction in the presence of disorder. We reconsider the long-standing puzzle of the exponential suppression of the single-particle density of states near the Fermi level, by measuring accurately the density of states of charged and electron-hole pair excitations via finite temperature Monte Carlo simulation and zero-temperature relaxation. We also investigate the statistics of large charge rearrangements after a perturbation of the system, which may shed some light on the slow relaxation and glassy phenomena recently observed in a variety of Anderson insulators. In collaboration with Martin Goethe.

  15. Intense field electron excitation in transparent materials

    NASA Astrophysics Data System (ADS)

    Modoran, Georgia C.

    The propagation of an intense laser through transparent materials can only be understood by considering a wide range of nonlinear effects and their simultaneous interaction. Electron plasma formation plays a crucial role and is the focus of this work. The mechanisms of the nonlinear ionization are not well understood. There are two proposed interactions that contribute to electron plasma formation: photoionization and avalanche ionization, but the individual contribution of each of these ionization processes is controversial. Keldysh theory has been proposed as a description of photoionization. Two models for avalanche ionization are used in the literature, but with different intensity dependence. We address and resolve these issues. In this thesis we present a spectrally resolved pump-probe experiment that directly measures the nonlinear ionization rates and plasma evolution in solid state media. Both pump and probe are derived from an 800 nm, 120 fs laser. The maximum ionization rates were obtained in sapphire (˜1.9x10 18 fs-1 ·cm-3), while in water (˜7.2x1017 fs-1 ·cm -3), fused silica (˜8.6x1017 fs -1 ·cm-3) and methanol (˜6.6x10 17 fs-1 ·cm-3) the ionization rates were slightly different. Our measured ionization rates are consistently larger that the theoretical rate given by Keldysh theory, suggesting that this theory does not correctly describe the photoionization process. We also present measurements that separate the two excitation processes and identify the role played by each in the ionization of media. The idea underneath these experiments is a very simple one: since the two ionization processes have different intensity dependence, the absorption of light in the medium should differ similarly. Therefore it should be possible to distinguish the two mechanisms by looking at the energy dependence of the absorption. From our result we find that avalanche and multiphoton ionization have varying relative contributions, depending on the band gap. For

  16. 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}

  17. How Geometric Distortions Scatter Electronic Excitations in Conjugated Macromolecules.

    PubMed

    Shi, Tian; Li, Hao; Tretiak, Sergei; Chernyak, Vladimir Y

    2014-11-20

    Effects of disorder and exciton-phonon interactions are the major factors controlling photoinduced dynamics and energy-transfer processes in conjugated organic semiconductors, thus defining their electronic functionality. All-atom quantum-chemical simulations are potentially capable of describing such phenomena in complex "soft" organic structures, yet they are frequently computationally restrictive. Here we efficiently characterize how electronic excitations in branched conjugated molecules interact with molecular distortions using the exciton scattering (ES) approach as a fundamental principle combined with effective tight-binding models. Molecule geometry deformations are incorporated to the ES view of electronic excitations by identifying the dependence of the Frenkel-type exciton Hamiltonian parameters on the characteristic geometry parameters. We illustrate our methodology using two examples of intermolecular distortions, bond length alternation and single bond rotation, which constitute vibrational degrees of freedom strongly coupled to the electronic system in a variety of conjugated systems. The effect on excited-state electronic structures has been attributed to localized variation of exciton on-site energies and couplings. As a result, modifications of the entire electronic spectra due to geometric distortions can be efficiently and accurately accounted for with negligible numerical cost. The presented approach can be potentially extended to model electronic structures and photoinduced processes in bulk amorphous polymer materials. PMID:26276475

  18. How Geometric Distortions Scatter Electronic Excitations in Conjugated Macromolecules.

    PubMed

    Shi, Tian; Li, Hao; Tretiak, Sergei; Chernyak, Vladimir Y

    2014-11-20

    Effects of disorder and exciton-phonon interactions are the major factors controlling photoinduced dynamics and energy-transfer processes in conjugated organic semiconductors, thus defining their electronic functionality. All-atom quantum-chemical simulations are potentially capable of describing such phenomena in complex "soft" organic structures, yet they are frequently computationally restrictive. Here we efficiently characterize how electronic excitations in branched conjugated molecules interact with molecular distortions using the exciton scattering (ES) approach as a fundamental principle combined with effective tight-binding models. Molecule geometry deformations are incorporated to the ES view of electronic excitations by identifying the dependence of the Frenkel-type exciton Hamiltonian parameters on the characteristic geometry parameters. We illustrate our methodology using two examples of intermolecular distortions, bond length alternation and single bond rotation, which constitute vibrational degrees of freedom strongly coupled to the electronic system in a variety of conjugated systems. The effect on excited-state electronic structures has been attributed to localized variation of exciton on-site energies and couplings. As a result, modifications of the entire electronic spectra due to geometric distortions can be efficiently and accurately accounted for with negligible numerical cost. The presented approach can be potentially extended to model electronic structures and photoinduced processes in bulk amorphous polymer materials.

  19. An Absolute Measurement of Resonance-Resolved Electron Impact Excitation

    NASA Astrophysics Data System (ADS)

    Reisenfeld, Daniel Brett

    1998-11-01

    An experiment to measure electron-impact excitation (EIE) of multiply-charged ions is described. An absolute measurement has been carried out of the cross section for EIE of Si2+(3s2/ 1S/to3s3p/ 1P) from energies below threshold to 11 eV above. A beams modulation technique with inclined electron and ion beams was used. Radiation at 120.7 nm from the excited ions was detected using an absolutely calibrated optical system. The analysis of the experimental data requires a determination of the population fraction of the Si2+ (3s3p/ 3Po) metastable state in the incident ion beam, which was measured to be 0.210 ± 0.018. The data have been corrected for contributions to the signal from radiative decay following excitation from the metastable state to 3s3p1P and 3p2/ 3P, and excitation of the ground state to levels above 3s3p/ 1P. The experimental 0.56 ± 0.08 eV energy spread has allowed us to resolve complex resonance structure throughout the studied energy range. At the reported ±14% uncertainty level (90% confidence limit), the measured structure and absolute scale of the cross section are in good agreement with 12-state close-coupling R-matrix calculations.

  20. Total and state-to-state electron capture and excitation cross-sections for Li+, Be{}^{2+}, and {{\\rm{B}}}^{3+} colliding with {\\rm{H}}(1\\;s) at low-to-intermediate energies

    NASA Astrophysics Data System (ADS)

    Domínguez-Gutiérrez, F. J.; Cabrera-Trujillo, R.

    2016-01-01

    The electron capture process plays an important role as a diagnostic tool for measuring the temperature, plasma rotation, and impurity densities of plasma in tokamaks. In this work we report the electron capture and excitation cross-sections for Li+, Be{}2+, and {{{B}}}3+ colliding with atomic hydrogen in the collision energy range 0.25-25 keV/amu. For this, we solve numerically the time dependent Schrödinger equation by using a finite difference approach. We model the ion projectile interaction with the target using a pseudopotential obtained within a Hartree-Fock method. We use classical trajectories, obtained self-consistently, for the projectile at collision energies lower than 2 keV/amu and a straight line trajectory at high collision energies. We report new results for the total, n=2,3, and 4 state projectile electron capture cross-section, as well as the n = 2-state target excitation cross-section. We find a good agreement between our cross-section results when compared with available theoretical and experimental data found in the literature. Finally, we find that the electron capture probability, as a function of the impact parameter, shows Stückelberg oscillations at low collision energies for the n = 2 of Be+ and n = 3 of {{{B}}}2+, in the radial range (large impact parameters). Our results assess the validity of the adiabatic basis set at low collision energies and confirm the use of a finite difference method as an accurate approach to study a time-dependent process in charge exchange collisions. A discussion of our results is provided.

  1. 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

  2. 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.

  3. Collective Excitations in Electron-Hole Bilayers

    SciTech Connect

    Kalman, G. J.; Hartmann, P.; Donko, Z.; Golden, K. I.

    2007-06-08

    We report a combined analytic and molecular dynamics analysis of the collective mode spectrum of a bipolar (electron-hole) bilayer in the strong coupling classical limit. A robust, isotropic energy gap is identified in the out-of-phase spectra, generated by the combined effect of correlations and of the excitation of the bound dipoles. In the in-phase spectra we identify longitudinal and transverse acoustic modes wholly maintained by correlations. Strong nonlinear generation of higher harmonics of the fundamental dipole oscillation frequency and the transfer of harmonics between different modes is observed.

  4. 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.

  5. Excitation of CO2/+/ by electron impact on CO2

    NASA Technical Reports Server (NTRS)

    Mentall, J. E.; Coplan, M. A.; Kushlis, R. J.

    1973-01-01

    Consideration of a discrepancy concerning the correct value of the cross section for excitation of the CO2(+) B state by electron impact on CO2. It is suggested that the reason for the disparate results obtained by various authors for the B state can be traced to a calibration error due to scattered light. In particular, the tungsten filament lamps used in the experiments cited have very low intensity at wavelengths below 3000 A where the B state emissions occur, so that even a small amount of scattered light in the spectrometer will produce a large error in the measured cross section. In a remeasurement of the cross section for excitation of the B state at an energy of 150 eV it was found that at 2900 A the scattered light signal, if uncorrected for, would introduce an error of about 50%.

  6. Electron-impact excitation of the Rb 7 2S1/2, 8 2S1/2, 5 2D3/2, and 6 2D3/2 states

    NASA Astrophysics Data System (ADS)

    Wei, Zuyi; Flynn, Connor; Redd, Aaron; Stumpf, Bernhard

    1993-03-01

    Electron-impact cross sections for excitation of the 7 2S1/2, 8 2S1/2, 5 2D3/2, and 6 2D3/2 states of rubidium have been measured from threshold to 1000 eV. The optical-excitation-function method has been employed in a crossed atom- and electron-beam apparatus. Relative, total (cascade including) experimental cross sections are made absolute by comparison with the known total cross section of the Rb D1 line. Total excitation cross sections are compared with theoretical calculations employing first Born approximation and theoretical branching ratios. Born cross sections for the 7 2S1/2 and 8 2S1/2 states are obtained from the literature, while Born cross sections for the 5 2D3/2, 6 2D3/2, and all cascading states are calculated in this paper. At high energies, the measured total 2D3/2 state cross sections show 1/E behavior and converge to first Born theory; for E>100 eV, experiment and theory agree within 6.7% for 5 2D3/2 and within 3.7% for 6 2D3/2. The total cross sections for the 2S1/2 states do not converge to Born theory even at 1000 eV, and it is shown that this cannot be attributed to cascading. At low energies, 2S1/2 and 2D3/2 state total excitation cross sections have similar shapes with sharply peaked maxima at about 0.9 eV above threshold. After cascading is corrected using first Born theory, estimated experimental cross sections for direct excitation of higher fine-structure states of rubidium are given.

  7. Shape and core excited resonances in electron collisions with diazines.

    PubMed

    Mašín, Zdeněk; Gorfinkiel, Jimena D

    2012-11-28

    We present a comprehensive ab-initio study of electron collisions with pyrazine, pyrimidine, and pyridazine. The emphasis is placed on the identification and characterization of electron resonances in these systems. We use the R-matrix method and show that analysing the time-delay reveals resonances whose signature is not visible in the eigenphase sums. In addition to the well known π∗ resonances below 5 eV, we find three core-excited shape resonances in the energy range 5.5-8.5 eV and a few Feshbach resonances in the dipolar molecules. Additionally, 11 resonances with little effect on the elastic scattering from ground state diazines (but significant effect in elastic collisions with the molecules in an excited state) are found and characterized. We correlate these resonances across the three molecules and discuss their possible correspondence to resonances described in earlier studies on uracil.

  8. Controlling chimera states: The influence of excitable units.

    PubMed

    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.

  9. 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.

  10. 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.

  11. 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.

  12. Coherent excitation with short electron pulses

    NASA Astrophysics Data System (ADS)

    Guertler, Andreas; Robicheaux, Francis; Noordam, Bart

    2000-06-01

    [1pt] The probability for a transition within an atom to be driven by a collision with a long pulse of electrons is proportional to the electron flux with the proportionality factor being the cross section for this transition. Recently it was shown [1] that for electron pulses shorter than the orbit time of the electron in the atom, a contribution of coherent scattering plays a role, which is proportional to the differential cross section in forward direction and the square of the electron flux. To investigate this effect, we are developing a picosecond electron gun [2]. Collision experiments will be done with Rydberg states in lithium around n=40 with Kepler orbit times in the order of 10 ps. For picosecond electron pulses, a quadratic dependance of the transition probability on the electron flux is expected in contrast to the linear dependance expected for nanosecond electron pulses. [1pt] References [1pt] [1] F. Robicheaux and L. D. Noordam, submitted to Phys. Rev. Lett. [1pt] [2] F. Robicheaux, G. M. Lankhuijzen, and L. D. Noordam, JOSA B 15, 1 (1998)

  13. Dynamics of two-electron excitations in helium

    SciTech Connect

    Caldwell, C.D.; Menzel, A.; Frigo, S.P.

    1997-04-01

    Excitation of both electrons in helium offers a unique window for studying electron correlation at the most basic level in an atom in which these two electrons and the nucleus form a three-body system. The authors utilized the first light available at the U-8 undulator-SGM monochromator beamline to investigate the dynamic parameters, partial cross sections, differential cross sections, and photoelectron angular distribution parameters ({beta}), with a high resolving power for the photon beam and at the highly differential level afforded by the use of their electron spectrometer. In parallel, they carried out detailed calculations of the relevant properties by a theoretical approach that is based on the hyperspherical close-coupling method. Partial photoionization cross sections {sigma}{sub n}, and photoelectron angular distributions {beta}{sub n} were measured for all possible final ionic states He{sup +}(n) in the region of the double excitations N(K,T){sup A} up to the N=5 threshold. At a photon energy bandpass of 12 meV below the thresholds N=3, 4, and 5, this level of differentiation offers the most critical assessment of the dynamics of the two-electron excitations to date. The experimental data were seen to be very well described by the most advanced theoretical calculations.

  14. The DIET from semiconductor surfaces by excitation of valence electrons

    NASA Astrophysics Data System (ADS)

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

    1995-06-01

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

  15. Chemical excitation of electrons: A dark path to melanoma.

    PubMed

    Premi, Sanjay; Brash, Douglas E

    2016-08-01

    Sunlight's ultraviolet wavelengths induce cyclobutane pyrimidine dimers (CPDs), which then cause mutations that lead to melanoma or to cancers of skin keratinocytes. In pigmented melanocytes, we found that CPDs arise both instantaneously and for hours after UV exposure ends. Remarkably, the CPDs arising in the dark originate by a novel pathway that resembles bioluminescence but does not end in light: First, UV activates the enzymes nitric oxide synthase (NOS) and NADPH oxidase (NOX), which generate the radicals nitric oxide (NO) and superoxide (O2(-)); these combine to form the powerful oxidant peroxynitrite (ONOO(-)). A fragment of the skin pigment melanin is then oxidized, exciting an electron to an energy level so high that it is rarely seen in biology. This process of chemically exciting electrons, termed "chemiexcitation", is used by fireflies to generate light but it had never been seen in mammalian cells. In melanocytes, the energy transfers radiationlessly to DNA, inducing CPDs. Chemiexcitation is a new source of genome instability, and it calls attention to endogenous mechanisms of genome maintenance that prevent electronic excitation or dissipate the energy of excited states. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin. PMID:27262612

  16. A multiconfigurational time-dependent Hartree-Fock method for excited electronic states. II. Coulomb interaction effects in single conjugated polymer chains

    NASA Astrophysics Data System (ADS)

    Miranda, R. P.; Fisher, A. J.; Stella, L.; Horsfield, A. P.

    2011-06-01

    Conjugated polymers have attracted considerable attention in the last few decades due to their potential for optoelectronic applications. A key step that needs optimisation is charge carrier separation following photoexcitation. To understand better the dynamics of the exciton prior to charge separation, we have performed simulations of the formation and dynamics of localised excitations in single conjugated polymer strands. We use a nonadiabatic molecular dynamics method which allows for the coupled evolution of the nuclear degrees of freedom and of multiconfigurational electronic wavefunctions. We show the relaxation of electron-hole pairs to form excitons and oppositely charged polaron pairs and discuss the modifications to the relaxation process predicted by the inclusion of the Coulomb interaction between the carriers. The issue of charge photogeneration in conjugated polymers in dilute solution is also addressed.

  17. Application of DSMC Electronic Excitation Modeling to Radiation Calculation of Hypersonic Reentry Flows

    NASA Astrophysics Data System (ADS)

    Li, Zheng; Sohn, Ilyoup; Levin, Deborah A.; Modest, Michael F.

    2011-05-01

    The current work implemented excited levels of atomic N and corresponding electron impact excitation/de-excitation and ionization processes in DSMC. Results show that when excitation models are included, the Stardust 68.9 km re-entry flow has an observable change in the ion number densities and electron temperature. Adding in the excited levels of atoms improves the degree of ionization by providing additional intermediate steps to ionization. The extra ionization reactions consume the electron energy and reduce the electron temperature. The DSMC results of number densities of excited levels are lower than the prediction of quasi steady state calculation. Comparison of radiation calculations using electronic excited populations from DSMC and QSS indicates that, at the stagnation point, there is about 20% difference of the radiative heat flux between DSMC and QSS.

  18. Excitation of the lowest electronic transitions in ethanol by low-energy electrons

    NASA Astrophysics Data System (ADS)

    Hargreaves, L. R.; Khakoo, M. A.; Winstead, C.; McKoy, V.

    2016-09-01

    We report absolute differential and integral cross sections for electronic excitation of ethanol, by low-energy electron impact. Cross sections for low-lying excited states were measured at incident electron energies from 9 to 20 eV and at scattering angles from {5}\\circ through {130}\\circ . Our results include cross sections for excitation of the 1{}3A\\prime \\prime and 1{}1A\\prime \\prime states as well as for the 2{}3A\\prime \\prime + 1{}3A\\prime and 2{}1A\\prime \\prime + 2{}1A\\prime cross section sums. Corresponding calculations were also performed using the Schwinger multichannel method, within an 11-channel close-coupling scheme.

  19. 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

  20. Formation of ground and excited states of antihydrogen

    SciTech Connect

    Nahar, S.N.; Wadehra, J.M.

    1988-06-01

    Differential and integrated cross sections for the formation of antihydrogen by the impact of intermediate-energy (20--500 keV) antiprotons on positronium are calculated using the first Born approximation. The calculations are carried out for the formation of antihydrogen in ground and various excited electronic states (n = 1--3) when positronium, the target atom, is in the ground state, and for the formation of antihydrogen in the ground state when the positronium is in various excited electronic states (n = 1--2). The 1/n/sup 3/ behavior for the capture cross sections is used to calculate the total (that is, all states added together) integrated cross sections. The cross sections for the formation of antihydrogen presented here are obtained from those for the formation of positronium by the impact of positrons on hydrogen atoms by using charge invariance and the principle of detailed balance.

  1. Electronic excitations and correlation effects in metals

    SciTech Connect

    Eguiluz, A.G.; Schoene, W.D. |

    1997-07-01

    Theoretical descriptions of the spectrum of electronic excitations in real metals have not yet reached a fully predictive, first-principles stage. In this paper the authors begin by presenting brief highlights of recent progress made in the evaluation of dynamical electronic response in metals. A comparison between calculated and measured spectra--they use the loss spectra of Al and Cs as test cases--leads them to the conclusion that, even in weakly-correlated metals, correlation effects beyond mean-field theory play an important role. Furthermore, the effects of the underlying band structure turn out to be significant. Calculations which incorporate the effects of both dynamical correlations and band structure from first principles are not yet available. As a first step towards such goal, they outline a numerical algorithm for the self-consistent solution of the Dyson equation for the one-particle Green`s function. The self-energy is evaluated within the shielded-interaction approximation of Baym and Kadanoff. Their method, which is fully conserving, is a finite-temperature scheme which determines the Green`s function and the self-energy at the Matsubara frequencies on the imaginary axis. The analytical continuation to real frequencies is performed via Pade` approximant. They present results for the homogeneous electron gas which exemplify the importance of many-body self-consistency.

  2. 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

  3. 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.

  4. Indistinguishability in electron-impact excitation-ionization of helium

    SciTech Connect

    Harris, A. L.; Milum, B.; Madison, D. H.

    2011-11-15

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

  5. Excited state solvatochromic and prototropic behaviour of 4-aminodiphenylamine and 4,4'-diaminodiphenylamine—A comparative study by electronic spectra

    NASA Astrophysics Data System (ADS)

    Nayaki, S. Kothai; Swaminathan, M.

    2006-06-01

    Solvatochromic and prototropic behaviour of 4-aminodiphenylamine (4ADA) and 4,4'-diaminodiphenylamine (DADA) have been investigated in the solvents of different polarity and at various acid-base concentrations in the ground and excited states using absorption and fluorescence spectra. Solvatochromic shifts have been analysed and observed shifts are explained by the hydrogen bonding interactions. The prototropic study reveals that (i) absorption maximum of monocation of DADA is red shifted to its neutral form, and (ii) the fluorescence of 4ADA is red shifted on protonation. The abnormal fluorescence of 4ADA + is found to be due to large solvent relaxation in polar medium.

  6. Search for Nuclear Excitation by Electronic Transition in U-235

    NASA Astrophysics Data System (ADS)

    Chodash, P. A.; Norman, E. B.; Burke, J. T.; Wilks, S. C.; Casperson, R. J.; Swanberg, E. L.; Wakeling, M. A.; Cordeiro, T. J.

    2013-10-01

    Nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that is predicted to occur in numerous isotopes, including U-235. When a nuclear transition matches the energy and the multipolarity of an electronic transition, there is a possibility that NEET will occur. If NEET were to occur in U-235, the nucleus would be excited to its 1/2 + isomeric state that subsequently decays by internal conversion with a decay energy of 77 eV and a half-life of 26 minutes. Theory predicts that NEET can occur in partially ionized uranium plasma with a charge state of 23 +. A pulsed Nd:YAG laser operating at 1064 nm with a pulse energy of 780 mJ and a pulse width of 9 ns was used to generate the uranium plasma. The plasma was collected on a plate and the internal conversion electrons were focused onto a microchannel plate detector by a series of electrostatic lenses. Depleted uranium and highly enriched uranium samples were used for the experiment. Preliminary results will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. This work was further supported by the U.S. DHS, UC Berkeley, and the NNIS Fellowship.

  7. Photophysical properties of some methylindoles and studies on quenching reactions in their excited singlet and triplet states in presence of the electron acceptor 2-nitrofluorene at 296 K as well as at 77 K

    NASA Astrophysics Data System (ADS)

    Sinha, S.; De, R.; Ganguly, T.

    1998-01-01

    Electronic absorption, steady state and time resolved, in the domain of nanosecond order, luminescence techniques were employed to study the photophysical properties of some electron donors methylindoles, e.g. 1-methylindole (1MI), 2-methylindole (2MI), 3-methylindole (3MI) and 5-methylindole (5MI) in nonpolar and polar environments at 296 K and in ethanol (EtOH) rigid glassy matrix at 77 K in the presence of electron acceptor 2-nitrofluorene (2NF). It has been proposed that at room temperature and in polar acetonitrile (ACN) solvent, MI (1, 2 or 3) emission originates mainly from the closely lying lowest excited states S 1 ( 1L b), S 2 ( 1L a) and the charge transfer (CT) exciplex state which is formed due to solute-highly polar solvent ACN interaction. This CT state has its origin in 1L a. The room temperature fluorescence quenchings of the MI donors in presence of acceptor 2NF are found to be mainly due to photoinduced electron transfer (ET), excitational energy transfer and transient quenching processes. Out of the three processes Förster's long range energy transfer seems to be the most dominant one. At 77 K singlet-singlet and triplet-triplet energy transfer processes seem to be responsible for the observed quenching in fluorescence and phosphorescence spectra of the donor molecules in presence of the acceptor 2NF.

  8. Electron-impact excitation for F-like selenium

    SciTech Connect

    Guo-xin, C.; Yu-bo, Q.

    1997-11-01

    Electron-impact excitation cross sections from the low-lying 1s{sup 2}2s{sup 2}2p{sup 5} state of F-like selenium to singly excited states have been calculated. Our relativistic distorted-wave Born procedures have been used for the present calculations. Instead of atomic structure code GRASP, the latest version GRASP{sup 2} code is used as multiconfiguration Dirac-Fock atomic structure calculations. The present results have been comprehensively compared with earlier calculations. One of the motivations for the present work is that there are some discrepancies between our results and those of others. {copyright} {ital 1997} {ital The American Physical Society}

  9. Doubly Excited Resonance States of Helium Atom: Complex Entropies

    NASA Astrophysics Data System (ADS)

    Kuroś, Arkadiusz; Kościk, Przemysław; Saha, Jayanta K.

    2016-09-01

    We provide a diagonal form of a reduced density matrix of S-symmetry resonance states of two electron systems determined under the framework of the complex scaling method. We have employed the variational Hylleraas type wavefunction to estimate the complex entropies in doubly excited resonance states of helium atom. Our results are in good agreement with the corresponding ones determined under the framework of the stabilization method (Lin and Ho in Few-Body Syst 56:157, 2015).

  10. 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.

  11. 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.

  12. Paramagnetic excited vortex states in superconductors

    NASA Astrophysics Data System (ADS)

    Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.

    2016-06-01

    We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.

  13. Cumulant approach for electronic excitations in x-ray and electron spectra

    NASA Astrophysics Data System (ADS)

    Rehr, J. J.

    A quantitative treatment of electronic excitations and other many-body effects in x-ray and electron spectra has long been challenging. Physically, electronic correlations and atomic vibrations lead to inelastic losses and damping effects that are ignored in ground state methods or approximations such as TDDFT. Quasi-particle (QP) approaches such as the GW approximation yield significant improvements, as demonstrated in real-space Green's function and GW/Bethe-Salpeter equation calculations, but still ignore multi-electron excitations. Recently such excitations have been treated with considerable success using cumulant expansion techniques and the quasi-boson approximation. In this beyond QP approach, excitations such as plasmons and electron-hole excitations appear as satellites in the spectral function. The method naturally accounts for multiple-satellites and can be extended to include extrinsic losses and interference effects. Extensions for effects of vibrations and strong correlations including charge-transfer satellites may also be possible. These advances are illustrated with a number of applications. Supported by DOE Grant DE-FG02-97ER45623.

  14. 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.

  15. 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

  16. Accelerating slow excited state proton transfer

    PubMed Central

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

    2013-01-01

    Visible light excitation of the ligand-bridged assembly [(bpy)2RuaII(L)RubII(bpy)(OH2)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−•)RubIII-OH2 with an excited-state lifetime of 13 ± 1 ns. Near–diffusion-controlled quenching of the emission occurs with added HPO42− 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 kq = 4.1 × 108 M−1⋅s−1 and an estimated pKa* value of ∼5 ± 1 for the [(bpy)2RuaII(L•−)RubIII(bpy)(OH2)4+]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)2RuaII(L)RubII(bpy)(OH)3+] in a H2PO4−/HPO42− buffer, back proton transfer occurs from H2PO4− to give [(bpy)2RuaII(L)Rub(bpy)(OH2)4+] with kPT,2 = 4.4 × 108 M−1⋅s−1. From the intercept of a plot of kobs vs. [H2PO4−], k = 2.1 × 106 s−1 for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pKa values intermediate between pKa(H3O+) = −1.74 and pKa(H2O) = 15.7. PMID:23277551

  17. CHARMONIUM EXCITED STATES FROM LATTICE QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2007-11-20

    We apply the variational method with a large basis of interpolating operators to demonstrate the feasibility of extracting multiple excited states in charmonium from lattice QCD. The calculation is performed in the quenched approximation to QCD, using the clover fermion action on an anisotropic lattice. A crucial element of our approach is a knowledge of the continuum limit of the interpolating operators, providing important additional information on the spin assignment of the states, even at a single value of the lattice spacing. Though we find excited-state masses that are systematically high with respect to the quark potential model, and the experimental masses where known, we attribute this as most likely an artifact of the quenched approximation.

  18. Electronic excitation and isentropic coefficients of high temperature planetary atmosphere plasmas

    SciTech Connect

    Colonna, Gianpiero; Capitelli, Mario

    2012-07-15

    In this paper, we have discussed the effects of electronically excited states of atomic species in affecting the isentropic coefficients of plasmas, focusing on mixtures representing the atmospheres of Jupiter, Mars, and Earth. General behaviors have been rationalized on the basis of simplified approaches. The contribution of the electronically excited states has been evidenced by comparing results obtained considering only the ground state and those obtained using either Fermi or Griem cutoff criteria.

  19. Broadband visible light-harvesting naphthalenediimide (NDI) triad: study of the intra-/intermolecular energy/electron transfer and the triplet excited state.

    PubMed

    Wu, Shuang; Zhong, Fangfang; Zhao, Jianzhang; Guo, Song; Yang, Wenbo; Fyles, Tom

    2015-05-21

    A triad based on naphthalenediimides (NDI) was prepared to study the intersystem crossing (ISC), the fluorescence-resonance-energy-transfer (FRET), as well as the photoinduced electron transfer (PET) processes. In the triad, the 2-bromo-6-alkylaminoNDI moiety was used as singlet energy donor and the spin converter, whereas 2,6-dialkylaminoNDI was used as the singlet/triplet energy acceptor. This unique structural protocol and thus alignment of the energy levels ensures the competing ISC and FRET in the triad. The photophysical properties of the triad and the reference compounds were studied with steady-state UV-vis absorption spectra, fluorescence spectra, nanosecond transient absorption spectra, cyclic voltammetry, and DFT/TDDFT calculations. FRET was confirmed with steady-state UV-vis absorption and fluorescence spectroscopy. Intramolecular electron transfer was observed in polar solvents, demonstrated by the quenching of both the fluorescence and triplet state of the energy acceptor. Nanosecond transient absorption spectroscopy shows that the T1 state of the triad is exclusively localized on the 2,6-dialkylaminoNDI moiety in the triad upon selective photoexcitation into the energy donor, which indicates the intramolecular triplet state energy transfer. The intermolecular triplet state energy transfer between the two reference compounds was investigated with nanosecond transient absorption spectroscopy. The photophysical properties were rationalized by TDDFT calculations. PMID:25919420

  20. Link atom bond length effect in ONIOM excited state calculations.

    PubMed

    Caricato, Marco; Vreven, Thom; Trucks, Gary W; Frisch, Michael J

    2010-08-01

    We investigate how the choice of the link atom bond length affects an electronic transition energy calculation with the so-called our own N-layer integrated molecular orbital molecular mechanics (ONIOM) hybrid method. This follows our previous paper [M. Caricato et al., J. Chem. Phys. 131, 134105 (2009)], where we showed that ONIOM is able to accurately approximate electronic transition energies computed at a high level of theory such as the equation of motion coupled cluster singles and doubles (EOM-CCSD) method. In this study we show that the same guidelines used in ONIOM ground state calculations can also be followed in excited state calculations, and that the link atom bond length has little effect on the ONIOM energy when a sensible model system is chosen. We also suggest further guidelines for excited state calculations which can help in checking the effectiveness of the definition of the model system and controlling the noise in the calculation.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  2. 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.

  3. Inner-shell excitation of acetylene by electron impact

    SciTech Connect

    Michelin, S.E.; Pessoa, O.; Oliveira, H.L.; Veiteinheimer, E.; Santos, A.M.S.; Fujimoto, M.M.; Iga, I.; Lee, M.-T.

    2005-08-15

    The distorted-wave approximation (DWA) is applied to study K-shell excitation in C{sub 2}H{sub 2} by electron impact. More specifically, calculated differential and integral cross sections for the X {sup 1}{sigma}{sub g}{sup +}{yields}{sup 1,3}{pi}{sub g}(1s{sigma}{sub g}{yields}1p{pi}{sub g}) and X {sup 1}{sigma}{sub g}{sup +}{yields}{sup 1,3}{pi}{sub u}(1s{sigma}{sub u}{yields}1p{pi}{sub g}) transitions in this target in the 300-800 eV incident energy range are reported. The triplet-to-singlet ratios of respective integral cross sections, namely, RI(3:1), calculated by dividing the integral cross sections for transitions leading to the triplet core-excited states by those leading to the corresponding singlet states, are also reported as a function of incident energies. In general, our calculated sums of the generalized oscillator strength for transitions leading to the {sup 1}{pi}{sub g} and {sup 1}{pi}{sub u} excited states are in good agreement with the available experimental data. On the other hand, the present calculated integral cross sections and the corresponding data for its isoelectronic species CO are significantly different. Possible physical origins for this difference are discussed.

  4. 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.

  5. Dissociative electron attachment and vibrational excitation of the chlorine molecule

    NASA Astrophysics Data System (ADS)

    Kolorenč, Přemysl; Horáček, Jiří

    2006-12-01

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

  6. Electronically excited rubidium atom in a helium cluster or film

    NASA Astrophysics Data System (ADS)

    Leino, Markku; Viel, Alexandra; Zillich, Robert E.

    2008-11-01

    We present theoretical studies of helium droplets and films doped with one electronically excited rubidium atom Rb∗ (P2). Diffusion and path integral Monte Carlo approaches are used to investigate the energetics and the structure of clusters containing up to 14 helium atoms. The surface of large clusters is approximated by a helium film. The nonpair additive potential energy surface is modeled using a diatomic in molecule scheme. Calculations show that the stable structure of Rb∗Hen consists of a seven helium atom ring centered at the rubidium, surrounded by a tirelike second solvation shell. A very different structure is obtained when performing a "vertical Monte Carlo transition." In this approach, a path integral Monte Carlo equilibration starts from the stable configuration of a rubidium atom in the electronic ground state adsorbed to the helium surface after switching to the electronically excited surface. In this case, Rb∗Hen relaxes to a weakly bound metastable state in which Rb∗ sits in a shallow dimple. The interpretation of the results is consistent with the recent experimental observations [G. Auböck et al., Phys. Rev. Lett. 101, 035301 (2008)].

  7. Excited state baryon spectroscopy from lattice QCD

    DOE PAGES

    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. Excited state baryon spectroscopy from lattice QCD

    SciTech Connect

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

    2011-10-01

    We present a calculation of the Nucleon and Delta excited state spectra 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) x O(3) representations and a counting of levels that is consistent with the nonrelativistic 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.

  9. 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.

  10. Left-eigenstate completely renormalized equation-of-motion coupled-cluster methods: Review of key concepts, extension to excited states of open-shell systems, and comparison with electron-attached and ionized approaches

    NASA Astrophysics Data System (ADS)

    Piecuch, Piotr; Gour, Jeffrey R.; Włoch, Marta

    The recently proposed left-eigenstate completely renormalized (CR) coupled-cluster (CC) method with singles, doubles, and noniterative triples, termed CR-CC(2,3) Piecuch and Włoch, J Chem Phys, 2005, 123, 224105; Piecuch et al. Chem Phys Lett, 2006, 418, 467 and the companion CR-EOMCC(2,3) methodology, which has been previously applied to singlet excited states of closed-shell molecular systems Włoch et al. Mol Phys, 2006, 104, 2149 and in which relatively inexpensive noniterative corrections due to triple excitations derived from the biorthogonal method of moments of CC equations (MMCC) are added to the CC singles and doubles (CCSD) or equation-of-motion (EOM) CCSD energies, have been extended to excited states of open-shell species. The resulting highly efficient computer codes for the open-shell CR-EOMCC(2,3) approach exploiting the recursively generated intermediates and fast matrix multiplication routines have been developed and interfaced with the GAMESS package, enabling CR-EOMCC(2,3) calculations for singlet as well as nonsinglet ground and excited states of closed- and open-shell systems using the restricted Hartree-Fock or restricted open-shell Hartree-Fock references. A number of important mathematical and algorithmic details related to formal aspects and computer implementation of the CR-EOMCC(2,3) method have been discussed, in addition to overviewing the key concepts behind the CR-EOMCC(2,3) and biorthogonal MMCC methodologies for ground and excited states, and the numerical results involving low-lying states of the CH, CNC, C2N, N3, and NCO species, including states dominated by two-electron transitions, have been presented. The results of the CR-EOMCC(2,3) calculations have been compared with other CC/EOMCC approaches, including the EOMCCSD and EOMCC singles, doubles, and triples methods, and their full and active-space valence counterparts based on the electron-attached and ionized EOMCC methodologies, and the predecessor of CR-EOMCC(2,3) termed

  11. 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.

  12. 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}.

  13. 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.

  14. Solvent Effects on Electronic Excitations of an Organic Chromophore.

    PubMed

    Zuehlsdorff, T J; Haynes, P D; Hanke, F; Payne, M C; Hine, N D M

    2016-04-12

    In this work we study the solvatochromic shift of a selected low-energy excited state of alizarin in water by using a linear-scaling implementation of large-scale time-dependent density functional theory (TDDFT). While alizarin, a small organic dye, is chosen as a simple example of solute-solvent interactions, the findings presented here have wider ramifications for the realistic modeling of dyes, paints, and pigment-protein complexes. We find that about 380 molecules of explicit water need to be considered in order to yield an accurate representation of the solute-solvent interaction and a reliable solvatochromic shift. By using a novel method of constraining the TDDFT excitation vector, we confirm that the origin of the slow convergence of the solvatochromic shift with system size is due to two different effects. The first factor is a strong redshift of the excitation due to an explicit delocalization of a small fraction of the electron and the hole from the alizarin onto the water, which is mainly confined to within a distance of 7 Å from the alizarin molecule. The second factor can be identified as long-range electrostatic influences of water molecules beyond the 7 Å region on the ground-state properties of alizarin. We also show that these electrostatic influences are not well reproduced by a QM/MM model, suggesting that full QM studies of relatively large systems may be necessary in order to obtain reliable results. PMID:26967019

  15. Excited States of {sup 11}Be

    SciTech Connect

    Cappuzzello, F.; Cunsolo, A.; Fortier, S.; Foti, A.; Laurent, H.; Lenske, H.; Maison, J.M.; Melita, A.L.; Nociforo, C.; Rosier, L.; Stephan, C.; Tassan-Got, L.; Winfield, J.S.; Wolter, H.H.

    2000-12-31

    The {sup 11}B({sup 7}Li,{sup 7}Be){sup 11}Be reaction at 57 MeV incident energy was used to explore the {sup 11}Be excitation energy spectrum at forward angles. Angular distributions were extracted for the transitions to the ground and to the states of {sup 11}Be at excitation energies of E*=0.32, 1.78, 2.69, 3.41, 3.89, 3.96, 6.05 MeV combined with the ground and the first excited state of {sup 7}Be. Also the SDR [1][2] oscillation mode was observed at E*=9.5 MeV and FWHM{approx}9 MeV and a new peak at E*=6.05 MeV and FWHM{approx}0.3 MeV was observed. QRPA calculations in the G-matrix representation are in progress in order to describe the continuum structure of {sup 11}Be. DWBA calculations have been started to evaluate transferred angular momenta both in the one step and in the two steps dynamical framework.

  16. 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.

  17. Plasmoelectronics: coupling plasmonic excitation with electron flow.

    PubMed

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

    2012-06-19

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

  18. 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.

  19. Suppression of excited-state absorption in laser crystals

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Elena; Kolesov, Roman; Kocharovskaya, Olga

    2004-10-01

    Currently, a lot of experimental effort in solid-state optics is devoted to searching for laser materials suitable for tunable lasing, primarily in UV and VUV spectral regions. Researchers mainly focus on optical crystals doped with either transition metal or rare-earth ions. The latter ones doped into wide bandgap dielectric crystals have spectrally broad vibronic emission bands associated with 4fn-15d â" 4fn interconfigurational transitions, whose energies lie mostly in UV and VUV regions of the spectrum. The transitions are electric-dipole-allowed, therefore have large absorption and emission cross-sections, and are promising for efficient tunable laser action. However, in almost all promising crystals laser action in UV and VUV is hindered or completely prohibited due to excited-state absorption (ESA), i.e. absorption from metastable laser levels to higher-energy states, which occurs at emission or/and pump wavelengths. A method of suppression of losses due to excited-state absorption (ESA) in laser crystals is proposed, based on a well-known phenomenon of electromagnetically induced transparency (EIT). Absorption from a populated excited electronic state can be reduced under the action of an additional driving coherent field, resonantly coupling the terminal state of ESA to some intermediate discrete state.

  20. Modeling of electronic excitation and radiation in non-continuum hypersonic reentry flows

    NASA Astrophysics Data System (ADS)

    Li, Zheng; Ozawa, Takashi; Sohn, Ilyoup; Levin, Deborah A.

    2011-06-01

    The modeling of hypersonic radiation in non-equilibrium, non-continuum flows is considered in the framework of the direct simulation Monte Carlo (DSMC) approach. The study explores the influence of electronic states on the flow chemistry and degree of ionization as well as the assumption that the electronic states can be described by a steady state solution to a system of rate equations of excitation, de-excitation, and radiative transfer processes. The work implements selected excited levels of atomic nitrogen and oxygen and the corresponding electron impact excitation/de-excitation and ionization processes in DSMC. The simulations show that when excitation models are included, the degree of ionization in the Stardust transitional re-entry flow increases due to additional intermediate steps to ionization. The extra ionization reactions consume the electron energy to reduce the electron temperature. The DSMC predicted excited state level populations are lower than those predicted by a quasi steady state calculation, but the differences can be understood in terms of the flow distribution functions.

  1. Characterising a configuration interaction excited state using natural transition geminals

    NASA Astrophysics Data System (ADS)

    Coe, J. P.; Paterson, M. J.

    2014-03-01

    We introduce natural transition geminals as a means to qualitatively understand a transition where double excitations are important. The first two A1 singlet states of the CH cation are used as an initial example. We calculate these states with configuration interaction singles and state-averaged Monte Carlo configuration interaction (SA-MCCI). For each method, we compare the important natural transition geminals with the dominant natural transition orbitals. We then compare SA-MCCI and full configuration interaction with regards to the natural transition geminals using the beryllium atom. We compare using the natural transition geminals with analysing the important configurations in the CI expansion to give the dominant transition for the beryllium atom and the carbon dimer. Finally, we calculate the natural transition geminals for two electronic excitations of formamide.

  2. 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

  3. Doubly excited states in some light atoms

    SciTech Connect

    Berry, H.G.; Brooks, R.L.; Hardis, J.E.; Ray, W.J.

    1981-01-01

    We have identified a singlet transition in doubly excited helium: 2p/sup 2/ /sup 1/D - 2p3d /sup 1/D, at 3298 +- 2A with a full width of 54A or 0.061 +- 0.005 eV. This width is in good agreement with a previous measurement and theory for the width of the 2p/sup 2/ /sup 1/D/sub 2/ state. We have remeasured the decay rate of 1s/sup 2/2p/sup 2/P - 1s2p/sup 2/ /sup 2/P in Li I and find it is in good agreement with theory. Several transitions in doubly excited Li II have been identified in the 1000A region. No evidence was found for doubly excited quartet transitions in Li I in the vacuum ultraviolet. We present measurements of wavelengths and fine structure of the 1s2s2p/sup 2/ /sup 5/P - 1s2p/sup 3/ /sup 5/S transitions in C III, N IV and O V.

  4. Theoretical and experimental differential cross sections for electron impact excitation of the electronic bands of furfural

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; Neves, R. F. C.; Lopes, M. C. A.; da Costa, R. F.; do N. Varella, M. T.; Bettega, M. H. F.; Lima, M. A. P.; García, G.; Limão-Vieira, P.; Brunger, M. J.

    2016-03-01

    We report results from a joint experimental and theoretical investigation into electron scattering from the important industrial species furfural (C5H4O2). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C5H4O2. The measurements were carried out at energies in the range 20-40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ˜80 meV. Corresponding Schwinger multichannel method with pseudo-potential calculations, for energies between 6-50 eV and with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were undertaken at the static exchange plus polarisation-level using a minimum orbital basis for single configuration interaction (MOB-SCI) approach. Agreement between the measured and calculated DCSs was qualitatively quite good, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOB-SCI. The role of multichannel coupling on the computed electronic-state DCSs is also explored in some detail.

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

    NASA Technical Reports Server (NTRS)

    Vuskovic, L.; Trajmar, S.

    1982-01-01

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

  6. 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.

  7. 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

  8. 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.

  9. Nuclear Excitation by Electronic Transition - NEET

    SciTech Connect

    Becker, J.A.

    2002-06-10

    Experiments seeking to demonstrate nuclear excitation induced by synchrotron radiation have been enabled by the development of intense synchrotron radiation. The phenomena has been demonstrated in {sup 197}Au, while realistic upper limits for {sup 189}Os have been established. A new experiment in {sup 189}Os is described. The experimental claim of NEET in isomeric {sup 178}Hf is not credible.

  10. Superelastic electron scattering from laser-excited cesium atoms

    SciTech Connect

    Slaughter, D. S.; Karaganov, V.; Brunger, M. J.; Teubner, P. J. O.; Bray, I.; Bartschat, K.

    2007-06-15

    We present results from a joint experimental and theoretical investigation of superelastic electron scattering from laser-excited Cs atoms in the (6p){sup 2}P{sub 3/2} state. Comparison of the measured pseudo-Stokes parameters P{sub 1}, P{sub 2}, and P{sub 3} and the total degree of polarization P{sup +} for incident energies of 5.5 eV and 13.5 eV, respectively, with theoretical predictions based upon a nonrelativistic convergent close-coupling method and a 24-state semirelativistic Breit-Pauli R-matrix approach indicates that driving channel coupling to convergence for these observables is more important than accounting for relativistic effects.

  11. Enhanced computational efficiency in the direct determination of the two-electron reduced density matrix from the anti-Hermitian contracted Schrödinger equation with application to ground and excited states of conjugated π-systems.

    PubMed

    Sand, Andrew M; Mazziotti, David A

    2015-10-01

    Determination of the two-electron reduced density matrix (2-RDM) from the solution of the anti-Hermitian contracted Schrödinger equation (ACSE) yields accurate energies and properties for both ground and excited states. Here, we develop a more efficient method to solving the ACSE that uses second-order information to select a more optimal step towards the solution. Calculations on the ground and excited states of water, hydrogen fluoride, and conjugated π systems show that the improved ACSE algorithm is 10-20 times faster than the previous ACSE algorithm. The ACSE can treat both single- and multi-reference electron correlation with the initial 2-RDM from a complete-active-space self-consistent-field (CASSCF) calculation. Using the improved algorithm, we explore the relationship between truncation of the active space in the CASSCF calculation and the accuracy of the energy and 2-RDM from the ACSE calculation. The accuracy of the ACSE, we find, is less sensitive to the size of the active space than the accuracy of other wavefunction methods, which is useful when large active space calculations are computationally infeasible. PMID:26450295

  12. Enhanced computational efficiency in the direct determination of the two-electron reduced density matrix from the anti-Hermitian contracted Schrödinger equation with application to ground and excited states of conjugated π-systems

    SciTech Connect

    Sand, Andrew M.; Mazziotti, David A.

    2015-10-07

    Determination of the two-electron reduced density matrix (2-RDM) from the solution of the anti-Hermitian contracted Schrödinger equation (ACSE) yields accurate energies and properties for both ground and excited states. Here, we develop a more efficient method to solving the ACSE that uses second-order information to select a more optimal step towards the solution. Calculations on the ground and excited states of water, hydrogen fluoride, and conjugated π systems show that the improved ACSE algorithm is 10-20 times faster than the previous ACSE algorithm. The ACSE can treat both single- and multi-reference electron correlation with the initial 2-RDM from a complete-active-space self-consistent-field (CASSCF) calculation. Using the improved algorithm, we explore the relationship between truncation of the active space in the CASSCF calculation and the accuracy of the energy and 2-RDM from the ACSE calculation. The accuracy of the ACSE, we find, is less sensitive to the size of the active space than the accuracy of other wavefunction methods, which is useful when large active space calculations are computationally infeasible.

  13. Enhanced computational efficiency in the direct determination of the two-electron reduced density matrix from the anti-Hermitian contracted Schrödinger equation with application to ground and excited states of conjugated π-systems.

    PubMed

    Sand, Andrew M; Mazziotti, David A

    2015-10-01

    Determination of the two-electron reduced density matrix (2-RDM) from the solution of the anti-Hermitian contracted Schrödinger equation (ACSE) yields accurate energies and properties for both ground and excited states. Here, we develop a more efficient method to solving the ACSE that uses second-order information to select a more optimal step towards the solution. Calculations on the ground and excited states of water, hydrogen fluoride, and conjugated π systems show that the improved ACSE algorithm is 10-20 times faster than the previous ACSE algorithm. The ACSE can treat both single- and multi-reference electron correlation with the initial 2-RDM from a complete-active-space self-consistent-field (CASSCF) calculation. Using the improved algorithm, we explore the relationship between truncation of the active space in the CASSCF calculation and the accuracy of the energy and 2-RDM from the ACSE calculation. The accuracy of the ACSE, we find, is less sensitive to the size of the active space than the accuracy of other wavefunction methods, which is useful when large active space calculations are computationally infeasible.

  14. Ultrafast internal conversion in ethylene. I. The excited state lifetime

    NASA Astrophysics Data System (ADS)

    Tao, H.; Allison, T. K.; Wright, T. W.; Stooke, A. M.; Khurmi, C.; van Tilborg, J.; Liu, Y.; Falcone, R. W.; Belkacem, A.; Martinez, T. J.

    2011-06-01

    Using a combined theoretical and experimental approach, we investigate the non-adiabatic dynamics of the prototypical ethylene (C2H4) molecule upon π → π* excitation. In this first part of a two part series, we focus on the lifetime of the excited electronic state. The femtosecond time-resolved photoelectron spectrum (TRPES) of ethylene is simulated based on our recent molecular dynamics simulation using the ab initio multiple spawning method with multi-state second order perturbation theory [H. Tao, B. G. Levine, and T. J. Martinez, J. Phys. Chem. A 113, 13656 (2009)], 10.1021/jp9063565. We find excellent agreement between the TRPES calculation and the photoion signal observed in a pump-probe experiment using femtosecond vacuum ultraviolet (hν = 7.7 eV) pulses for both pump and probe. These results explain the apparent discrepancy over the excited state lifetime between theory and experiment that has existed for ten years, with experiments [e.g., P. Farmanara, V. Stert, and W. Radloff, Chem. Phys. Lett. 288, 518 (1998), 10.1016/S0009-2614(98)00312-1 and K. Kosma, S. A. Trushin, W. Fuss, and W. E. Schmid, J. Phys. Chem. A 112, 7514 (2008)], 10.1021/jp803548c reporting much shorter lifetimes than predicted by theory. Investigation of the TRPES indicates that the fast decay of the photoion yield originates from both energetic and electronic factors, with the energetic factor playing a larger role in shaping the signal.

  15. Excitation of positive ions by low-energy electrons - Relevance to the Io Torus

    NASA Astrophysics Data System (ADS)

    Smith, S. J.; Chutjian, A.; Mawhorter, R. J.; Williams, I. D.; Shemansky, D. E.

    1993-03-01

    The importance of measuring electron-ion excitation cross sections in singly and multiply charged positive ions is outlined, and recent results for Mg II and O II ions are given using the JPL's electron energy-loss merged-beams apparatus. Theoretical comparisons are given with two five-state close-coupling calculations. The energy variation of the collision strength is fitted with a semiempirical analytic function which includes approximations to polarization, resonance, and exchange contributions. In O II, first spectra anywhere of electron excitation of the optically allowed transitions are presented. In addition, excitations of two low lying, optically forbidden transitions are detected for the first time.

  16. Impact excitation of neon atoms by heated seed electrons in filamentary plasma gratings.

    PubMed

    Shi, Liping; Li, Wenxue; Zhou, Hui; Ding, Liang'en; Zeng, Heping

    2013-02-15

    We demonstrate impact ionization and dissociative recombination of neon (Ne) atoms by means of seeded-electron heating and subsequent electron-atom collisions in an ultraviolet plasma grating, allowing for a substantial fraction of the neutral Ne atomic population to reside in high-lying excited states. A buffer gas with relatively low ionization potential (nitrogen or argon) was used to provide high-density seed electrons. A three-step excitation model is verified by the fluorescence emission from the impact excitation of Ne atoms.

  17. The dynamics of highly excited electronic systems: Applications of the electron force field

    NASA Astrophysics Data System (ADS)

    Su, Julius T.; Goddard, William A.

    2009-12-01

    Highly excited heterogeneous complex materials are essential elements of important processes, ranging from inertial confinement fusion to semiconductor device fabrication. Understanding the dynamics of these systems has been challenging because of the difficulty in extracting mechanistic information from either experiment or theory. We describe here the electron force field (eFF) approximation to quantum mechanics which provides a practical approach to simulating the dynamics of such systems. eFF includes all the normal electrostatic interactions between electrons and nuclei and the normal quantum mechanical description of kinetic energy for the electrons, but contains two severe approximations: first, the individual electrons are represented as floating Gaussian wave packets whose position and size respond instantaneously to various forces during the dynamics; and second, these wave packets are combined into a many-body wave function as a Hartree product without explicit antisymmetrization. The Pauli principle is accounted for by adding an extra spin-dependent term to the Hamiltonian. These approximations are a logical extension of existing approaches to simulate the dynamics of fermions, which we review. In this paper, we discuss the details of the equations of motion and potentials that form eFF, and evaluate the ability of eFF to describe ground-state systems containing covalent, ionic, multicenter, and/or metallic bonds. We also summarize two eFF calculations previously reported on electronically excited systems: (1) the thermodynamics of hydrogen compressed up to ten times liquid density and heated up to 200 000 K; and (2) the dynamics of Auger fragmentation in a diamond nanoparticle, where hundreds of electron volts of excitation energy are dissipated over tens of femtoseconds. These cases represent the first steps toward using eFF to model highly excited electronic processes in complex materials.

  18. Excited states of the helium-antihydrogen system.

    PubMed

    Sharipov, Vasily; Labzowsky, Leonti N; Plunien, Günter

    2007-03-01

    Potential energy curves for excited leptonic states of the helium-antihydrogen system are calculated within the Ritz variational approach. An explicitly correlated ansatz for the leptonic wave function is employed describing accurately the motion of the leptons (two electrons and positron) in the field of the helium nucleus and of the antiproton with an arbitrary orbital angular momentum projection Lambda onto the internuclear axis. Results for Lambda=0, 1, and 30 are presented. For quasibound states with large values of Lambda and rotational quantum numbers J>Lambda no annihilation and rearrangement decay channels occur; i.e., they are metastable.

  19. Vertical and adiabatic electronic excitations in biphenylene: A theoretical study

    NASA Astrophysics Data System (ADS)

    Beck, M. E.; Rebentisch, R.; Hohlneicher, G.; Fülscher, M. P.; Serrano-Andrés, L.; Roos, B. O.

    1997-12-01

    The low-lying singlet states of biphenylene have been studied using ab initio methods. Vertical excitation energies were calculated by multiconfigurational perturbation theory (CASPT2), starting from a complete active space self-consistent field (CASSCF) reference. The geometries of the most important low-lying excited states were individually optimized at the CASSCF level to study the difference between vertical and adiabatic excitations. Extended atomic natural orbital (ANO)-type basis sets were used to calculate state energies. Geometry optimizations were done with smaller ANO-type basis sets. Excitations from the ground state to the 1 1B3g and 1 1B2u excited singlet states lead to pronounced geometry changes which alter the bond alternation pattern. The theoretical results provide a solid basis for the assignment and interpretation of experimental spectra.

  20. Excited-State Conformational/Electronic Responses of Saddle-Shaped N,N'-Disubstituted-Dihydrodibenzo[a,c]phenazines: Wide-Tuning Emission from Red to Deep Blue and White Light Combination.

    PubMed

    Zhang, Zhiyun; Wu, Yu-Sin; Tang, Kuo-Chun; Chen, Chi-Lin; Ho, Jr-Wei; Su, Jianhua; Tian, He; Chou, Pi-Tai

    2015-07-01

    A tailored strategy is utilized to modify 5,10-dimethylphenazine (DMP) to donor-acceptor type N,N'-disubstituted-dihydrodibenzo[a,c]phenazines. The representative compounds DMAC (N,N'-dimethyl), DPAC (N,N'-diphenyl), and FlPAC (N-phenyl-N'-fluorenyl) reveal significant nonplanar distortions (i.e., a saddle shape) and remarkably large Stokes-shifted emission independent of the solvent polarity. For DPAC and FlPAC with higher steric hindrance on the N,N'-substituents, normal Stokes-shifted emission also appears, for which the peak wavelength reveals solvent-polarity dependence. These unique photophysical behaviors are rationalized by electronic configuration coupled conformation changes en route to the geometry planarization in the excited state. This proposed mechanism is different from the symmetry rule imposed to explain the anomalously long-wavelength emission for DMP and is firmly supported by polarity-, viscosity-, and temperature-dependent steady-state and nanosecond time-resolved spectroscopy. Together with femtosecond early dynamics and computational simulation of the reaction energy surfaces, the results lead us to establish a sequential, three-step kinetics. Upon electronic excitation of N,N'-disubstituted-dihydrodibenzo[a,c]phenazines, intramolecular charge-transfer takes place, followed by the combination of polarization stabilization and skeletal motion toward the planarization, i.e., elongation of the π-delocalization over the benzo[a,c]phenazines moiety. Along the planarization, DPAC and FlPAC encounter steric hindrance raised by the N,N'-disubstitutes, resulting in a local minimum state, i.e., the intermediate. The combination of initial charge-transfer state, intermediate, and the final planarization state renders the full spectrum of interest and significance in their anomalous photophysics. Depending on rigidity, the N,N'-disubstituted-dihydrodibenzo[a,c]phenazines exhibit multiple emissions, which can be widely tuned from red to deep blue and

  1. 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.

  2. 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

  3. Reconstruction of an excited-state molecular wave packet with attosecond transient absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Chini, Michael; Wang, Xiaowei; González-Castrillo, Alberto; Palacios, Alicia; Argenti, Luca; Martín, Fernando; Chang, Zenghu

    2016-08-01

    Attosecond science promises to allow new forms of quantum control in which a broadband isolated attosecond pulse excites a molecular wave packet consisting of a coherent superposition of multiple excited electronic states. This electronic excitation triggers nuclear motion on the molecular manifold of potential energy surfaces and can result in permanent rearrangement of the constituent atoms. Here, we demonstrate attosecond transient absorption spectroscopy (ATAS) as a viable probe of the electronic and nuclear dynamics initiated in excited states of a neutral molecule by a broadband vacuum ultraviolet pulse. Owing to the high spectral and temporal resolution of ATAS, we are able to reconstruct the time evolution of a vibrational wave packet within the excited B'Σ1u+ electronic state of H2 via the laser-perturbed transient absorption spectrum.

  4. Electrostatic excitations in carbon nanotubes including many-electron effects

    NASA Astrophysics Data System (ADS)

    Khan, Shabbir A.; Ikram, Muhammad

    2016-08-01

    Electrostatic excitations in single-walled carbon nanotubes are investigated taking into account both the many-electron effects of exchange and correlations and the Fermi degeneracy pressure. Quantum hydrodynamics equations for electrons and ions are employed and solved by using the Fourier transformation technique to obtain the dispersion equation relevant to the cylindrical geometry of tubules. The result shows the existence of low-frequency quantum ion-acoustic excitations exhibiting dispersion due to electron quantum effects. The electron Fermi degeneracy in the range of quantum ion-acoustic excitations turns out to be more pronounced compared to electron exchange and correlation effects. The results are explained numerically for typical systems to reveal the role of quantum degeneracy, geometrical parameters and electron exchange and correlation effects in the wave dynamics.

  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. Lifetime of the Excited State In Vivo

    PubMed Central

    Govindjee; Hammond, J. H.; Merkelo, H.

    1972-01-01

    Lifetime of the excited state (τ) of bacteriochlorophyll (BChl) in photosynthetic bacteria, measured with a mode-locked argon laser (oscillating at 488 nm; mode locked at 56 MHz) as light source, ranged from 0.3 to 2.5 nsec. These τ values are reported with a precision of ±0.1 nsec. The value of τ at high exciting light intensity (I) was two to three times that at low intensity. For young cultures of green bacterium Chloropseudomonas ethylicum, τ ranged from 0.5 (low I) to 1.0 nsec (high I); for those of the purple bacterium Rhodospirillum rubrum, from 0.4 (low I) to 1.0 nsec (high I); and for those of the BChl b-containing Rhodopseudomonas viridis, from 1.0 (low I) to 2.5 nsec (high I). These data provide information regarding the efficiencies of the photochemical process in these bacteria. Quantum yield (ø) of BChl fluorescence, calculated from ø = τ/τ0 (where τ0 is the intrinsic lifetime of fluorescence), ranges from 2-6% at low intensities to 6-14% at high intensities. PMID:4624833

  7. Signature of nonadiabatic coupling in excited-state vibrational modes.

    PubMed

    Soler, Miguel A; Nelson, Tammie; Roitberg, Adrian E; Tretiak, Sergei; Fernandez-Alberti, Sebastian

    2014-11-13

    Using analytical excited-state gradients, vibrational normal modes have been calculated at the minimum of the electronic excited-state potential energy surfaces for a set of extended conjugated molecules with different coupling between them. Molecular model systems composed of units of polyphenylene ethynylene (PPE), polyphenylenevinylene (PPV), and naphthacene/pentacene (NP) have been considered. In all cases except the NP model, the influence of the nonadiabatic coupling on the excited-state equilibrium normal modes is revealed as a unique highest frequency adiabatic vibrational mode that overlaps with the coupling vector. This feature is removed by using a locally diabatic representation in which the effect of NA interaction is removed. Comparison of the original adiabatic modes with a set of vibrational modes computed in the locally diabatic representation demonstrates that the effect of nonadiabaticity is confined to only a few modes. This suggests that the nonadiabatic character of a molecular system may be detected spectroscopically by identifying these unique state-specific high frequency vibrational modes. PMID:24844735

  8. Delayed fluorescence during the deactivation of highly excited triplet states

    SciTech Connect

    Skvortsov, V.I.; Alfimov, M.V.

    1987-06-01

    It has been suggested that the T state may be not only an electron donor but an acceptor, i.e., it may give a charge transfer state in a photoreduction reaction: A(T) + M ..-->.. /sup 3/(A/sup .-/M/sup +./). In this connection, it may be assumed that the quenching may also be connected with the nonradiative deactivation of excitation energy in charge transfer states (A/sup .-/M/sup +./). Aromatic molecules are characterized by an extremely low quantum yield for intramolecular intersystem crossing. However, in charge-transfer states the efficiency of intersystem crossing may be enhanced. The authors have investigated the laws governing DF in conditions where the deactivation of T states occurs. The systems studied were frozen (77 K) solutions of the aromatic additives naphthalene, diphenyl, and chrysene in toluene, MCH, and ethanol.

  9. 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.

  10. Coherence Measurements for Excited to Excited State Transitions in Barium

    NASA Technical Reports Server (NTRS)

    Trajmar, S.; Kanik, I.; Karaganov, V.; Zetner, P. W.; Csanak, G.

    2000-01-01

    Experimental studies concerning elastic and inelastic electron scattering by coherently ensembles of Ba (...6s6p (sub 1)P(sub 1)) atoms with various degrees of alignment will be described. An in-plane, linearly-polarized laser beam was utilized to prepare these target ensembles and the electron scattering signal as a function of polarization angle was measured for several laser geometries at fixed impact energies and scattering angles. From these measurements, we derived cross sections and electron-impact coherence parameters associated with the electron scattering process which is time reverse of the actual experimentally studied process. This interpretation of the experiment is based on the theory of Macek and Herte. The experimental results were also interpreted in terms of cross sections and collision parameters associated with the actual experimental processes. Results obtained so far will be presented and plans for further studies will be discussed.

  11. Differential cross sections for electron impact excitation of the electronic bands of phenol

    SciTech Connect

    Neves, R. F. C.; Jones, D. B.; Lopes, M. C. A.; Nixon, K. L.; Silva, G. B. da; Duque, H. V.; Oliveira, E. M. de; Lima, M. A. P.; Costa, R. F. da; Varella, M. T. do N.; Bettega, M. H. F.; and others

    2015-03-14

    We report results from a joint theoretical and experimental investigation into electron scattering from the important organic species phenol (C{sub 6}H{sub 5}OH). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C{sub 6}H{sub 5}OH. The measurements were carried out at energies in the range 15–40 eV, and for scattered-electron angles between 10{sup ∘} and 90{sup ∘}. The energy resolution of those experiments was typically ∼80 meV. Corresponding Schwinger multichannel method with pseudo-potentials calculations, with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were conducted at the static exchange plus polarisation (SEP)-level using a minimum orbital basis for single configuration interaction (MOBSCI) approach. Agreement between the measured and calculated DCSs was typically fair, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOBSCI.

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

    DOE PAGES

    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

  13. 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.

  14. Dynamics Of Electronic Excitation Of Solids With Ultrashort Laser Pulse

    SciTech Connect

    Medvedev, Nikita; Rethfeld, Baerbel

    2010-10-08

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

  15. 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.

  16. 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.

  17. [Long-range electron transfer in globular proteins by polaron excitation].

    PubMed

    Lakhno, V L; Chuev, G N

    1997-01-01

    Considering polaron model, we have calculated an electron state localized in the protein heme. Using these calculations: the electron density and electron energy, we estimated the self-exchange rate constant for cyt c (horse heart), its reorganization energy, matrix element, and dependence of this rate on the distance between hemes. The results are compared with the experimental data and other theoretical estimations. We discuss the role of polaron excitations in the long-range electron transfer in globular proteins.

  18. 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.

  19. 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

  20. 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.

  1. Excitation of metastable argon and helium atoms by electron impact

    NASA Technical Reports Server (NTRS)

    Borst, W. L.

    1974-01-01

    Using a time-of-flight method, the excitation of argon and helium metastables by electron impact is investigated in the energy range from threshold to about 50 eV. The secondary-electron yields of the metastable detector used are reviewed in detail. The effect of metastable recoil is also discussed. Comparisons with data from other investigators are presented.

  2. "Delta Plots"--A New Way to Visualize Electronic Excitation.

    ERIC Educational Resources Information Center

    Morrison, Harry; And Others

    1985-01-01

    Presents procedures for obtaining and examples of delta plots (a way of illustrating electron density changes associated with electronic excitation). These plots are pedagogically useful for visualizing simple and complex transitions and provide a way of "seeing" the origin of highest occupied molecular orbital (HOMO)-dictated carbonyl…

  3. Electron excitation collision strengths for positive atomic ions: a collection of theoretical data

    SciTech Connect

    Merts, A.L.; Mann, J.B.; Robb, W.D.; Magee, N.H. Jr.

    1980-03-01

    This report contains data on theoretical and experimental cross sections for electron impact excitation of positive atomic ions. It is an updated and corrected version of a preliminary manuscript which was used during an Atomic Data Workshop on Electron Excitation of Ions held at Los Alamos in November 1978. The current status of quantitative knowledge of collisional excitation collision strengths is shown for highly stripped ions where configuration mixing, relativistic and resonance effects may be important. The results show a reasonably satisfactory state for first-row isoelectronic ions and indicate that a considerable amount of work remains to be done for second-row and heavier ions.

  4. Electron-driven excitations and dissociation of molecules

    SciTech Connect

    Miller, Greg; Orel, Ann E.

    2015-02-13

    This program studied how energy is interchanged in electron and photon collisions with molecules leading to ex-citation and dissociation. Modern ab initio techniques, both for the photoionization and electron scattering, and the subsequent nuclear dynamics studies, are used to accurately treat these problems. This work addresses vibrational ex-citation and dissociative attachment following electron impact, and the dynamics following inner shell photoionzation. These problems are ones for which a full multi-dimensional treatment of the nuclear dynamics is essential and where non-adiabatic effects are expected to be important.

  5. Excited state absorption spectrum of chlorophyll a obtained with white-light continuum.

    PubMed

    De Boni, L; Correa, D S; Pavinatto, F J; dos Santos, D S; Mendonça, C R

    2007-04-28

    The study of excited state properties of chlorophyll a is a subject of foremost interest, given that it plays important roles in biological process and has also been proposed for applications in photonics. This work reports on the excited state absorption spectrum of chlorophyll a solution from 460 to 700 nm, obtained through the white-light continuum Z-scan technique. Saturation of absorption was observed due to the ground state depletion, induced by the white-light continuum region that is resonant with the Q band of chlorophyll a. The authors also observed reverse saturation of absorption related to the excitation from the first excited state to a higher energy level for wavelengths below 640 nm. An energy-level diagram, based on the electronic states of chlorophyll a, was employed to interpret their results, revealing that more states than the ones related to the Q and B bands participate in the excited state absorption of this molecule.

  6. Standoff alpha radiation detection via excited state absorption of air

    SciTech Connect

    Yao, Jimmy; Yin, Stuart Shizhuo; Brenizer, Jack; Hui, Rongqing

    2013-06-24

    A standoff alpha radiation detection technique based on the physical mechanism of excited state absorption of air molecules was explored and is presented in this paper. Instead of directly detecting the radiation via measuring the intensity of radiation induced air fluorescence, the radiation is detected via the excited state absorption of alpha radiation excited/ionized air molecules. Both theoretical analyses and experimental verifications were conducted. The experimental results confirmed that the radiation could be detected via excited state absorption of radiation excited/ionized air molecules at a 10 m standoff distance, which was consistent with the theoretical analyses.

  7. Comparison of Electronically Excited Photodissociation between Nitramine Energetic Materials and Model Systems

    NASA Astrophysics Data System (ADS)

    Guo, Yuanqing; Greenfield, Margo; Bhattacharya, Atanu; Bernstein, Elliot

    2007-03-01

    Nitramine energetic materials (RDX, HMX and CL20) have broad applications as explosives and fuels. Model systems (1,4-dinitropiperazine, nitropiperidine, nitropyrrolidine and DMNA) have similar molecular structures, but they are unable to be used as fuels and explosives. To elucidate the difference between them, both nanosecond and femtosecond mass resolved excitation spectroscopy have been employed to investigate the mechanisms and dynamics of the electronically excited photodissociation of these materials. NO is a dominant dissociation product. Based upon the experimental observation and calculations of potential energy surfaces for these systems, we suggest that energetic materials dissociate from their ground electronic states after relaxing from the first excited states, and that the model systems dissociate from their excited state. In both cases a nitro-nitrite isomerization is part of the reaction mechanism. Parent ions of DMNA and nitropyrrolidine are observed in fs experiments. All the other molecules generate NO as a product even in fs time regime.

  8. Properties of chrysene in the higher triplet excited state

    NASA Astrophysics Data System (ADS)

    Cai, Xichen; Hara, Michihiro; Kawai, Kiyohiko; Tojo, Sachiko; Majima, Tetsuro

    2003-01-01

    Properties of chrysene in the higher triplet excited state were studied by the two-color two-laser flash photolysis method. Triplet energy transfers from chrysene in the higher triplet excited state to quenchers such as biphenyl and naphthalene, and from the quenchers in the triplet excited state back to chrysene in the ground state were observed to proceed at the diffusion-controlled rate. From dependence of the quenching efficiency on the quencher concentration, the lifetime of chrysene in the higher triplet excited state was estimated to be 60 ps with considering the time-dependent quenching.

  9. Excited state quantum phase transitions in many-body systems

    SciTech Connect

    Caprio, M.A. Cejnar, P.; Iachello, F.

    2008-05-15

    Phenomena analogous to ground state quantum phase transitions have recently been noted to occur among states throughout the excitation spectra of certain many-body models. These excited state phase transitions are manifested as simultaneous singularities in the eigenvalue spectrum (including the gap or level density), order parameters, and wave function properties. In this article, the characteristics of excited state quantum phase transitions are investigated. The finite-size scaling behavior is determined at the mean-field level. It is found that excited state quantum phase transitions are universal to two-level bosonic and fermionic models with pairing interactions.

  10. 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.

  11. Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.; Salter, Latasha M.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

  12. 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

  13. 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.

  14. Proton release from Stentor photoreceptors in the excited states.

    PubMed Central

    Song, P S; Walker, E B; Auerbach, R A; Robinson, G W

    1981-01-01

    Steady-state and picosecond pulse excitations of the photophobic-phototactic receptors isolated from Stentor coeruleus produced anionic species predominantly in the excited singlet state, although neutral photoreceptors in the ground state were exclusively excited. The same photoreceptor in vivo also emits fluorescence from the excited state of its anionic species, with an excitation spectrum identical to the absorption spectrum of the neutral species in the ground state. The excited state dissociation of protons from the photoreceptor chromophore (stentorin; hypericin covalently linked to protein) efficiently occurs in less than 10 ps. A possible role of the transient-proton release from the photoreceptor, in the signal transduction photoresponse of Stentor, is briefly discussed. PMID:6791722

  15. Excited Spectator Electron Effects on Spectral Line Shapes

    SciTech Connect

    Iglesias, C A

    2009-10-12

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

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

    SciTech Connect

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

    2011-05-24

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

  17. On the ultrashort lifetime of electronically excited thiophenol

    NASA Astrophysics Data System (ADS)

    Ovejas, Virginia; Fernández-Fernández, Marta; Montero, Raúl; Longarte, Asier

    2016-09-01

    The relaxation dynamics of thiophenol, excited from the onset of the S1 (11ππ∗) state absorption, to the more intense S3 (21ππ∗) state band (290-244 nm), has been studied by time resolved ion yield spectroscopy. Along the studied energy range, the reached excited states relax in less 100 fs. These results evidence that the photophysics is dominated by the non-adiabatic coupling between the initially excited S1 and S31ππ∗ states, and the dissociative character 1πσ∗ state. Contrarily to phenol, the 11ππ∗/1πσ∗ crossing is reached from the origin of the 11ππ∗ state absorption, through a nearly barrierless pathway.

  18. Quantum defects and specific-isotopic-shift measurements in ns and np highly excited states of lithium: Exchange effects between Rydberg and core electrons

    SciTech Connect

    Goy, P.; Liang, J.; Gross, M.; Haroche, S.

    1986-10-01

    By high-resolution double-resonance spectroscopy experiments in the millimeter-wavelength domain, we have determined precise values of the quantum defects in the s and p Rydberg levels of /sup 6/Li and /sup 7/Li (principal quantum number n ranging from 18 to 40). A detailed comparison of the /sup 6/Li and /sup 7/Li data has yielded the value of the specific isotopic shift in the np series, which is the first evidence to our knowledge of an exchange effect between a tightly bound core electron and a very weakly bound Rydberg electron in an alkali-metal atom.

  19. Excited metastables electronic spin states in spin crossover compounds studies by atom-phonon coupling model: Gradual and two-step transition cases

    NASA Astrophysics Data System (ADS)

    Gindulescu, A.; Rotaru, A.; Linares, J.; Dimian, M.; Nasser, J.

    2010-05-01

    This contribution reports the study of metastable spin states in spin-crossover materials in the framework of the atom-phonon coupling model. Using this model for a linear chain we show theoretically for the first time that, even if the cooperativity is not strong enough to obtain hysteresis at high temperatures, metastable states exist at low temperatures for a high spin (HS) fraction of nHS=1. This gradual thermal transition featuring metastable states at low temperature has been observed experimentally by [Létard et al., J. Phys.: Conf. Ser. 21, 23 (2005)]. Moreover, for compounds showing a two-step thermal transition, we show that metastable states, corresponding to a HS fraction nHS=0.5, are present. This metastable states appear up to 50 K, fact that was observed by [Moussa et al., Phys. Rev. Lett. 94, 107205 (2005)] and [Matsumoto et al., J. Phys.: Conf. Ser. 148, 012029 (2009)].

  20. The contribution of electronically excited states to the radiation chemistry of organic systems: Progress report, June 30, 1985-December 30, 1987

    SciTech Connect

    Lipsky, S.

    1987-01-01

    Research progress is reported on the following topics: effects of electron scavengers on the escape probabilities of geminate ion pairs, mechanism of liquid scintillation counter, photoionization of solutes in nonpolar liquids, kinetics of recombination of geminate ion pairs, and fluorescence of saturated hydrocarbons. (DLC)

  1. 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.

  2. Tuning of superfine electron-nuclear interaction in structure of the ground states and the characteristics of the full systems electronic excited states for formation of effective phothophysics and spectral-energy of properties in the series of multinuclear compounds

    NASA Astrophysics Data System (ADS)

    Obukhov, A. E.

    2012-06-01

    The help of the measurements (the methods are the NMR 1H and 13C, infrared (IR) and the UV-absorption, Raman scattering of light, the fluorescence and the phosphorescence, the pumping of the lasers and lamps, the low-temperature of the spectroscopy in the solutions (77 K) and the Jet-spectroscopy of vapor (2,6 K) and others) and the calculations with application of the developed new complex of the computer of the programs realizing of the quantum-chemical LCAO-MO SCF extended-CI INDO / S of methods are investigated of the photophysical properties of some news and also some known the organic compounds for variations of the electronic and the spatial structures in the series is the mono-, bi-, three, penta- and quincli-cyclic and the bi- and the bis- phenyl, furyl- and tienyl- oxazoles and - oxadiazoles have been studied of the spectroscopy properties in the wavelength range max λ max abs,osc = 208 ÷ 760 nm.

  3. Excited states in 146Sm and 147Sm

    NASA Astrophysics Data System (ADS)

    Kownacki, J.; Sujkowski, Z.; Hammarén, E.; Liukkonen, E.; Piiparinen, M.; Lindblad, Th.; Ryde, H.; Paar, V.

    1980-03-01

    The 144, 146Nd(α, χn) and 146,148Nd( 3He, χn) reactions with Eα = 20-43 MeV and E3He , = 19-27 MeV are used to investigate excited states in the isotopes 146Sm and 147Sm. The experiments involve measurements of singles γ-ray spectra and conversion electron spectra, γ-ray angular distributions and three-parameter ( Eγ- Eγ-time) coincidences. From these experiments information is obtained for states with spin up to I = 13 +and I = {27}/{2}-, respectively. These states are interpreted within the framework of the cluster-vibration model (CVM) as well as the shell model. In the latter approach, the energies of several well established states, in both isotopes, are calculated using empirical singleparticle energies, empirical two-particle interaction matrix elements and angular momentum algebra. The average deviation between the calculated and the experimental energies is less than 100 keV. The CVM calculations involve the coupling of a three-particle neutron cluster to the quadrupole vibration of the core. For 147Sm, these calculations reproduce the observed sequence of states based on the I π = {7}/{2}- ground state, as well as the sequence of states based on the I π = {13}/{2}+ excited state. The CVM calculations also reproduce the ground band in 146Sm, while for the negative parity states based on the cluster (f {7}/{2}i {13}/{2}) 3 --10 - an additional shift in energy is expected due to the mixing with octupole phonons.

  4. Systematics of α -decay transitions to excited states

    NASA Astrophysics Data System (ADS)

    Delion, D. S.; Dumitrescu, A.

    2015-08-01

    We systematize the available experimental material concerning α -decay transitions to low-lying excited states in even-even and odd-mass emitters. We generalize our previous theoretical prediction concerning the linear dependence between hindrance factors and the excitation energy for transitions in even-even α emitters. Thus, we show that α intensities for transitions to excited states depend linearly upon the excitation energy for all known even-even and odd-mass α emitters. It turns out that the well-known Viola-Seaborg law for α -decay transitions between ground states can be generalized for transitions to excited states. This rule can be used to predict any α -decay half-life to a low-lying excited state.

  5. 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

  6. Contribution of electronic excitation to the structural evolution of ultrafast laser-irradiated tungsten nanofilms

    NASA Astrophysics Data System (ADS)

    Murphy, Samuel T.; Giret, Yvelin; Daraszewicz, Szymon L.; Lim, Anthony C.; Shluger, Alexander L.; Tanimura, Katsumi; Duffy, Dorothy M.

    2016-03-01

    The redistribution of the electron density in a material during laser irradiation can have a significant impact on its structural dynamics. This electronic excitation can be incorporated into two temperature molecular dynamics (2T-MD) simulations through the use of electronic temperature dependent potentials. Here, we study the structural dynamics of laser irradiated tungsten nanofilms using 2T-MD simulations with an electronic temperature dependent potential and compare the results to equivalent simulations that employ a ground-state interatomic potential. Electronic excitation leads to an expansion of the crystal and a decrease in the melting point of tungsten. During laser irradiation these factors ensure that the threshold fluences to the different melting regimes are reduced. Furthermore, both heterogenous and homogeneous melting are predicted to occur more rapidly due to excitation and oscillations in the film thickness will be accentuated.

  7. Radiative lifetimes of the bound excited states of Pt-

    NASA Astrophysics Data System (ADS)

    Chartkunchand, K. C.; Kamińska, M.; Anderson, E. K.; Kristiansson, M. K.; Eklund, G.; Hole, O. M.; Nascimento, R. F.; Blom, M.; Björkhage, M.; Källberg, A.; Löfgren, P.; Reinhed, P.; Rosén, S.; Simonsson, A.; Thomas, R. D.; Mannervik, S.; Davis, V. T.; Neill, P. A.; Thompson, J. S.; Hanstorp, D.; Zettergren, H.; Cederquist, H.; Schmidt, H. T.

    2016-09-01

    The intrinsic radiative lifetimes of the 5 d106 s1/2 2S and 5 d96 s2 3/2 2D bound excited states in the platinum anion Pt-have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5 d106 s 1/2 2S state was measured to be 2.54 ±0.10 s , while only a lifetime in the range of 50-200 ms could be estimated for the 5 d96 s2 3/2 2D fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13 K . The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.

  8. Radiative lifetimes of the bound excited states of Pt-

    NASA Astrophysics Data System (ADS)

    Chartkunchand, K. C.; Kamińska, M.; Anderson, E. K.; Kristiansson, M. K.; Eklund, G.; Hole, O. M.; Nascimento, R. F.; Blom, M.; Björkhage, M.; Källberg, A.; Löfgren, P.; Reinhed, P.; Rosén, S.; Simonsson, A.; Thomas, R. D.; Mannervik, S.; Davis, V. T.; Neill, P. A.; Thompson, J. S.; Hanstorp, D.; Zettergren, H.; Cederquist, H.; Schmidt, H. T.

    2016-09-01

    The intrinsic radiative lifetimes of the 5 d106 s 1/2 2S and 5 d96 s2 3/2 2D bound excited states in the platinum anion Pt-have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5 d106 s 1/2 2S state was measured to be 2.54 ±0.10 s , while only a lifetime in the range of 50-200 ms could be estimated for the 5 d96 s2 3/2 2D fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13 K . The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.

  9. Core excitation effects on oscillator strengths for transitions in four electron atomic systems

    NASA Astrophysics Data System (ADS)

    Chang, T. N.; Luo, Yuxiang

    2007-06-01

    By including explicitly the electronic configurations with two and three simultaneously excited electronic orbital, we have extended the BSCI (B-spline based configuration interaction) method [1] to estimate directly the effect of inner shell core excitation to oscillator strengths for transitions in four-electron atomic systems. We will present explicitly the change in oscillator strengths due to core excitations, especially for transitions involving doubly excited states and those with very small oscillator strengths. The length and velocity results are typically in agreement better than 1% or less. [1] Tu-nan Chang, in Many-body Theory of Atomic Structure and Photoionization, edited by T. N. Chang (World Scientific, Singapore, 1993), p. 213-47; and T. N. Chang and T. K. Fang, Elsevier Radiation Physics and Chemistry 70, 173-190 (2004).

  10. Electron impact excitation of Kr XXVIII

    SciTech Connect

    Aggarwal, K.M.; Keenan, F.P.; Lawson, K.D.

    2011-05-15

    Collision strengths ({Omega}) are calculated for all 6328 transitions among the lowest 113 levels belonging to the 2s{sup 2}2p{sup 5},2s2p{sup 6},2s{sup 2}2p{sup 4}3l,2s2p{sup 5}3l, and 2p{sup 6}3l configurations of fluorine-like krypton, Kr XXVIII, using the Dirac Atomic R-matrix Code. All partial waves with angular momentum J{<=}40 are included, sufficient for the convergence of {Omega} for forbidden transitions. For allowed transitions a top-up is employed to obtain converged values of {Omega} up to an energy of 400 Ryd. Resonances in the thresholds region are resolved on a narrow energy mesh, and results for effective collision strengths (Y) are obtained after averaging the values of {Omega} over a Maxwellian distribution of electron velocities. Values of Y are reported over a wide temperature range below 10{sup 7.1}K, and the accuracy of the results is assessed. In addition, effective collision strengths are listed for the temperature range 7.0{<=}logT{sub e}(K){<=}9.0, obtained from non-resonant collision strengths generated with the FAC code.

  11. Electron impact excitation of Kr XXXII

    SciTech Connect

    Aggarwal, K.M. Keenan, F.P.; Lawson, K.D.

    2009-09-15

    Collision strengths ({omega}) have been calculated for all 7750 transitions among the lowest 125 levels belonging to the 2s{sup 2}2p,2s2p{sup 2},2p{sup 3},2s{sup 2}3l,2s2p3l, and 2p{sup 2}3l configurations of boron-like krypton, Kr XXXII, for which the Dirac Atomic R-matrix Code has been adopted. All partial waves with angular momentum J{<=}40 have been included, sufficient for the convergence of {omega} for forbidden transitions. For allowed transitions, a top-up has been included in order to obtain converged values of {omega} up to an energy of 500 Ryd. Resonances in the thresholds region have been resolved in a narrow energy mesh, and results for effective collision strengths (Y) have been obtained after averaging the values of {omega} over a Maxwellian distribution of electron velocities. Values of Y are reported over a wide temperature range below 10{sup 7.3}K, and the accuracy of the results is assessed. Values of Y are also listed in the temperature range 7.3{<=}logT{sub e}(K){<=}9.0, obtained from the nonresonant collision strengths from the Flexible Atomic Code.

  12. Direct Visualization of Excited-State Symmetry Breaking Using Ultrafast Time-Resolved Infrared Spectroscopy.

    PubMed

    Dereka, Bogdan; Rosspeintner, Arnulf; Li, Zhiquan; Liska, Robert; Vauthey, Eric

    2016-04-01

    Most symmetric quadrupolar molecules designed for two-photon absorption behave as dipolar molecules in the S1 electronic excited state. This is usually explained by a breakup of the symmetry in the excited state. However, the origin of this process and its dynamics are still not fully understood. Here, excited-state symmetry breaking in a quadrupolar molecule with a D-π-A-π-D motif, where D and A are electron donating and accepting units, is observed in real time using ultrafast transient infrared absorption spectroscopy. The nature of the relaxed S1 state was found to strongly depend on the solvent polarity: (1) in nonpolar solvents, it is symmetric and quadrupolar; (2) in weakly polar media, the quadrupolar state observed directly after excitation transforms to a symmetry broken S1 state with one arm bearing more excitation than the other; and (3) in highly polar solvents, the excited state evolves further to a purely dipolar S1 state with the excitation localized entirely on one arm. The time scales associated with the transitions between these states coincide with those of solvation dynamics, indicating that symmetry breaking is governed by solvent fluctuations.

  13. Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

    SciTech Connect

    Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen; De Meyer, Thierry; De Clerck, Karen

    2014-04-07

    A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.

  14. 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.

  15. Method and apparatus for secondary laser pumping by electron beam excitation

    DOEpatents

    George, E. Victor; Krupke, William F.; Murray, John R.; Powell, Howard T.; Swingle, James C.; Turner, Jr., Charles E.; Rhodes, Charles K.

    1978-01-01

    An electron beam of energy typically 100 keV excites a fluorescer gas which emits ultraviolet radiation. This radiation excites and drives an adjacent laser gas by optical pumping or photolytic dissociation to produce high efficiency pulses. The invention described herein was made in the course of, or under, United States Energy Research and Development Administration Contract No. W-7405-Eng-48 with the University of California.

  16. 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.

  17. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: key role of the excited-state hydrogen-bond strengthening.

    PubMed

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-15

    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.

  18. Mid-infrared ultrafast laser pulses induced third harmonic generation in nitrogen molecules on an excited state

    PubMed Central

    Xie, Hongqiang; Li, Guihua; Yao, Jinping; Chu, Wei; Li, Ziting; Zeng, Bin; Wang, Zhanshan; Cheng, Ya

    2015-01-01

    We report on generation of third harmonic from nitrogen molecules on the excited state with a weak driver laser pulse at a mid-infrared wavelength. The excited nitrogen molecules are generated using a circularly polarized intense femtosecond pulse which produces energetic electrons by photoionization to realize collisional excitation of nitrogen molecules. Furthermore, since the third harmonic is generated using a pump-probe scheme, it enables investigation of the excited-state dynamics of nitrogen molecules produced under different conditions. We also perform a comparative investigation in excited argon atoms, revealing different decay dynamics of the molecules and atoms from the excited states in femtosecond laser induced filaments. PMID:26522886

  19. Mid-infrared ultrafast laser pulses induced third harmonic generation in nitrogen molecules on an excited state.

    PubMed

    Xie, Hongqiang; Li, Guihua; Yao, Jinping; Chu, Wei; Li, Ziting; Zeng, Bin; Wang, Zhanshan; Cheng, Ya

    2015-11-02

    We report on generation of third harmonic from nitrogen molecules on the excited state with a weak driver laser pulse at a mid-infrared wavelength. The excited nitrogen molecules are generated using a circularly polarized intense femtosecond pulse which produces energetic electrons by photoionization to realize collisional excitation of nitrogen molecules. Furthermore, since the third harmonic is generated using a pump-probe scheme, it enables investigation of the excited-state dynamics of nitrogen molecules produced under different conditions. We also perform a comparative investigation in excited argon atoms, revealing different decay dynamics of the molecules and atoms from the excited states in femtosecond laser induced filaments.

  20. Ion mobility studies of electronically excited States of atomic transition metal cations: development of an ion mobility source for guided ion beam experiments.

    PubMed

    Iceman, Christopher; Rue, Chad; Moision, Robert M; Chatterjee, Barun K; Armentrout, P B

    2007-07-01

    The design of an ion mobility source developed to couple to a guided ion beam tandem mass spectrometer is presented. In these exploratory studies, metal ions are created continuously by electron ionization of the volatile hexacarbonyls of the three group 6 transition metals. These ions are focused into a linear hexapole ion trap, which collects the ions and then creates high intensity pulses of ions, avoiding excessive ion losses resulting from the low duty cycle of pulsed operation. The ion pulses are injected into a six-ring drift cell filled with helium where ions having different electronic configurations can separate because they have different ion mobilities. Such separation is observed for chromium ions and compares favorably with the pioneering work of Kemper and Bowers (J. Phys. Chem.1991, 95, 5134). The results are then extended to Mo(+) and W(+), which also show efficient configuration separation. The source conditions needed for high intensities and good configuration separation are discussed in detail and suggestions for further improvements are also provided.

  1. Rotational excitation of physisorbed molecules by resonant electron scattering

    NASA Astrophysics Data System (ADS)

    Teillet-Billy, D.; Gauyacq, J. P.

    2002-04-01

    The resonant rotational excitation of physisorbed H 2 molecules by low energy electron impact is studied using the rotational sudden approximation. The rotational excitation efficiency is analysed as a function of the constraint imposed on the molecular rotation by the adsorption. This allows the description of the variation of the energy loss spectrum corresponding to rovibrational excitation as a function of the constraint on molecular rotation. This model study is then used to discuss the recent results by Svensson et al. [Phys. Rev. Lett. 83 (1999) 124] on the rovibrational excitation of H 2 molecules adsorbed at steps on Cu(5 1 0), in terms of quasi-2D rotor and of constrained 3D rotors.

  2. Absolute cross sections for one electron capture into excited projectile states in collisions between He 2+ (15-150 keV) and Li atoms

    NASA Astrophysics Data System (ADS)

    Kadota, K.; Dijkkamp, D.; Van Der Woude, R.; Yan, Pan Guang; De Heer, F. J.

    1982-03-01

    We have studied the He 2+-Li collision system at laboratory energies between 15 and 150 keV using optical methods. From the measured emission cross sections we derive state-selective capture cross sections for n = 2,3,4 and n ⩾ 5 states of the He + ions. Our data are consistent with theoretical predictions of Bransden and Ermolaev. The total capture cross sections as evaluated from our emission cross section data, agree very well with the results of McCullough et al. obtained from projectile charge detection measurements. Near 15 keV our emission cross sections for 30.4 nm and 25.6 nm are much larger than those measured previously by Barrett and Leventhal at slightly lower energies.

  3. Discrimination of nuclear spin isomers exploiting the excited state dynamics of a quinodimethane derivative

    SciTech Connect

    Obaid, Rana; Kinzel, Daniel; Oppel, Markus González, Leticia

    2014-10-28

    Despite the concept of nuclear spin isomers (NSIs) exists since the early days of quantum mechanics, only few approaches have been suggested to separate different NSIs. Here, a method is proposed to discriminate different NSIs of a quinodimethane derivative using its electronic excited state dynamics. After electronic excitation by a laser field with femtosecond time duration, a difference in the behavior of several quantum mechanical operators can be observed. A pump-probe experimental approach for separating these different NSIs is then proposed.

  4. Role of Geometric Distortion and Polarization in Localizing Electronic Excitations in Conjugated Polymers.

    PubMed

    Nayyar, Iffat H; Batista, Enrique R; Tretiak, Sergei; Saxena, Avadh; Smith, Darryl L; Martin, Richard L

    2013-02-12

    Five different Density Functional Theory (DFT) models (ranging from pure GGA to long-range-corrected hybrid functionals) were used to study computationally the nature of the self-trapped electronic states in oligophenylene vinylenes. The electronic excitations in question include the lowest singlet (S1) and triplet (T1(†)) excitons (calculated using Time Dependent DFT (TD-DFT) method), positive (P(+)) and negative (P(-)) polarons, and the lowest triplet (T1) states (computed with the Self-Consistent Field (SCF) scheme). The polaron formation (spatial localization of excitations) is observed only with the use of range-corrected hybrid DFT models including long-range electronic exchange interactions. The extent of localization for all studied excitations is found to be invariant with respect to the size of the oligomer chain in their corresponding optimal geometries. We have analyzed the interdependence between the extent of the geometrical distortion and the localization of the orbital and spin density, and have observed that the localization of the P(+) and P(-) charged species is quite sensitive to solvent polarization effects and the character of the DFT functional used, rather than the structural deformations. In contrast, the localization of neutral states, S1 and T1(†), is found to follow the structural distortions. Notably, T1 excitation obtained with the mean field SCF approach is always strongly localized in range-corrected hybrid DFT models. The molecular orbital energetics of these excitations was further investigated to identify the relationship between state localization and the corresponding orbital structure. A characteristic stabilization (destabilization) of occupied (virtual) orbitals is observed in hybrid DFT models, compared to tight-binding model-like orbital filling in semilocal GGA functionals. The molecular and natural orbital representation allows visualization of the spatial extent of the underlying electronic states. In terms of

  5. Electron impact excitation of argon in the extreme vacuum ultraviolet

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

  6. Dissociative excitation and fragmentation of S8 by electron impact.

    PubMed

    Brotton, S J; McConkey, J W

    2011-05-28

    The vacuum-ultraviolet emission spectrum from 136 nm to 168 nm following the dissociative excitation of a predominantly S(8) target by electron impact at 100 eV incident energy was measured. The relative cross sections for the dominant multiplets at 138.9, 142.9, 147.9, and 166.7 nm are presented. Excitation functions are shown for electron-impact energies from below threshold to 360 eV for the two most prominent emissions at 142.5 nm and 147.4 nm. Five thresholds are clearly apparent in both excitation functions. For the four highest energy channels, the energy separation between the adjacent thresholds is approximately constant and the cross sections reduce regularly as the threshold energies increase. We suggest possible fragmentation pathways of the dissociating S(8) molecule that reproduce the energies of our observed thresholds.

  7. 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.

  8. Excitation of electron Langmuir frequency harmonics in the solar atmosphere

    SciTech Connect

    Fomichev, V. V.; Fainshtein, S. M.; Chernov, G. P.

    2013-05-15

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

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

    NASA Astrophysics Data System (ADS)

    Tseng, Huan-Wei

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

  10. Effects of Thermal Electronic Excitations on the Diffusion of Oxygen Adatoms on Graphene.

    PubMed

    Sun, Tao; Yao, Xinxin; Fabris, Stefano

    2016-05-01

    We conduct first-principles calculations to study oxygen diffusion on the graphene surface as a function of temperature up to 3000 K. The minimum energy migration path and the corresponding activation energy are determined by the nudged elastic band method with explicit inclusion of thermal electronic excitations. Below 1000 K the activation energy for epoxy oxygen to migrate remains close to its room temperature value (0.72 eV). Above 1000 K the activation energy decreases near linearly with temperature, from 0.70 eV at 1000 K to 0.47 eV at 3000 K. We show that this reduction originates from thermal electronic excitations. In particular, the effect is determined by the large contrasts in the electronic structures of the initial and transition states: the transition state exhibits much larger electronic density of states near the Fermi level and is more susceptible to thermal electronic excitations. The reduction in activation energy leads to appreciable enhancement in the diffusivity of oxygen adatoms. A moderate decrease in the vibrational prefactor, also caused by thermal electronic excitations, does not alter this trend. These findings may facilitate future works to accurately describe the dynamics of O adatoms on graphene at high T, which are critical for determining surface thermodynamic properties such as equilibrium coverage. PMID:27074529

  11. Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study

    DOE PAGES

    Xiao, Haiyan Y.; Weber, William J.; Zhang, Yanwen; Zu, X. T.; Li, Sean

    2015-02-09

    In this study, the response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser,more » electron and ion irradiations.« less

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

    SciTech Connect

    Li, Shaohong L.; Truhlar, Donald G.

    2014-09-14

    Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH{sub 3}-F{sub 2} and on the potential energy curves of NH{sub 3} near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.

  13. How Electronic Excitation Can be Used to Inhibit Some Mechanisms Associated to Substituent Effects.

    PubMed

    Ferro-Costas, David; Francisco, Evelio; Martín Pendás, Ángel; Mosquera, Ricardo A

    2016-09-01

    Despite the fact that transferability and chemistry go hand in hand, transferability studies in electronically excited states (EESs) are normally omitted, although these states are becoming extremely important in modern processes and applications. In this work, it is shown that this kind of studies can be used to understand how substituent effects can be modified in EESs. Thus, for example, the analysis of the carbonyl oxygen transferability in different HCO-R molecules allowed us to find that the nO→πCO* excitation can be used to break the π conjugation associated to the resonance substituent effect. Moreover, as a direct consequence, the oxygen transferability is enhanced in the first electronically excited state.

  14. Validation of local hybrid functionals for TDDFT calculations of electronic excitation energies

    NASA Astrophysics Data System (ADS)

    Maier, Toni M.; Bahmann, Hilke; Arbuznikov, Alexei V.; Kaupp, Martin

    2016-02-01

    The first systematic evaluation of local hybrid functionals for the calculation of electronic excitation energies within linear-response time-dependent density functional theory (TDDFT) is reported. Using our recent efficient semi-numerical TDDFT implementation [T. M. Maier et al., J. Chem. Theory Comput. 11, 4226 (2015)], four simple, thermochemically optimized one-parameter local hybrid functionals based on local spin-density exchange are evaluated against a database of singlet and triplet valence excitations of organic molecules, and against a mixed database including also Rydberg, intramolecular charge-transfer (CT) and core excitations. The four local hybrids exhibit comparable performance to standard global or range-separated hybrid functionals for common singlet valence excitations, but several local hybrids outperform all other functionals tested for the triplet excitations of the first test set, as well as for relative energies of excited states. Evaluation for the combined second test set shows that local hybrids can also provide excellent Rydberg and core excitations, in the latter case rivaling specialized functionals optimized specifically for such excitations. This good performance of local hybrids for different excitation types could be traced to relatively large exact-exchange (EXX) admixtures in a spatial region intermediate between valence and asymptotics, as well as close to the nucleus, and lower EXX admixtures in the valence region. In contrast, the tested local hybrids cannot compete with the best range-separated hybrids for intra- and intermolecular CT excitation energies. Possible directions for improvement in the latter category are discussed. As the used efficient TDDFT implementation requires essentially the same computational effort for global and local hybrids, applications of local hybrid functionals to excited-state problems appear promising in a wide range of fields. Influences of current-density dependence of local kinetic

  15. Counting the number of excited states in organic semiconductor systems using topology

    SciTech Connect

    Catanzaro, Michael J.; Shi, Tian; Tretiak, Sergei; Chernyak, Vladimir Y.

    2015-02-28

    Exciton scattering theory attributes excited electronic states to standing waves in quasi-one-dimensional molecular materials by assuming a quasi-particle picture of optical excitations. The quasi-particle properties at branching centers are described by the corresponding scattering matrices. Here, we identify the topological invariant of a scattering center, referred to as its winding number, and apply topological intersection theory to count the number of quantum states in a quasi-one-dimensional system.

  16. Counting the number of excited states in organic semiconductor systems using topology.

    PubMed

    Catanzaro, Michael J; Shi, Tian; Tretiak, Sergei; Chernyak, Vladimir Y

    2015-02-28

    Exciton scattering theory attributes excited electronic states to standing waves in quasi-one-dimensional molecular materials by assuming a quasi-particle picture of optical excitations. The quasi-particle properties at branching centers are described by the corresponding scattering matrices. Here, we identify the topological invariant of a scattering center, referred to as its winding number, and apply topological intersection theory to count the number of quantum states in a quasi-one-dimensional system. PMID:25725718

  17. Spodumene and garnet luminescence excited by subnanosecond electron beams

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

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

  18. Estimation of first excited singlet-state dipole moments of aminoanthraquinones by solvatochromic method.

    PubMed

    Siddlingeshwar, B; Hanagodimath, S M

    2009-04-01

    The ground state (micro(g)) and the excited state (micro(e)) dipole moments of three substituted anthraquinones, namely 1-aminoanthracene-9,10-dione (AAQ), 1-(methylamino)anthracence-9,10-dione (MAQ) and 1,5-diaminoanthracene-9,10-dione (DAQ) were estimated in various solvents. The dipole moments (micro(g) and micro(e)) were estimated from Lippert, Bakhshiev, Kawski-Chamma-Viallet, McRae and Suppan equations by using the variation of Stokes shift with the solvent dielectric constant and refractive index. The excited state dipole moments were also calculated by using the variation of Stokes shift with microscopic solvent polarity parameter (Epsilon(T)(N)). It was observed that dipole moment values of excited states (micro(e)) were higher than corresponding ground state values (micro(g)), indicating a substantial redistribution of the pi-electron densities in a more polar excited state for all the molecules investigated.

  19. 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

  20. Excitation of local magnetic moments by tunneling electrons

    NASA Astrophysics Data System (ADS)

    Gauyacq, Jean-Pierre; Lorente, Nicolás; Novaes, Frederico Dutilh

    2012-05-01

    The advent of milli-kelvin scanning tunneling microscopes (STM) with inbuilt magnetic fields has opened access to the study of magnetic phenomena with atomic resolution at surfaces. In the case of single atoms adsorbed on a surface, the existence of different magnetic energy levels localized on the adsorbate is due to the breaking of the rotational invariance of the adsorbate spin by the interaction with its environment, leading to energy terms in the meV range. These structures were revealed by STM experiments in IBM Almaden in the early 2000s for atomic adsorbates on CuN surfaces. The experiments consisted in the study of the changes in conductance caused by inelastic tunneling of electrons (IETS, inelastic electron tunneling spectroscopy). Manganese and Iron adatoms were shown to have different magnetic anisotropies induced by the substrate. More experiments by other groups followed up, showing that magnetic excitations could be detected in a variety of systems: e.g. complex organic molecules showed that their magnetic anisotropy was dependent on the molecular environment, piles of magnetic molecules showed that they interact via intermolecular exchange interaction, spin waves were excited on ferromagnetic surfaces and in Mn chains, and magnetic impurities have been analyzed on semiconductors. These experiments brought up some intriguing questions: the efficiency of magnetic excitations was very high, the excitations could or could not involve spin flip of the exciting electron and singular-like behavior was sometimes found at the excitation thresholds. These facts called for extended theoretical analysis; perturbation theories, sudden-approximation approaches and a strong coupling scheme successfully explained most of the magnetic inelastic processes. In addition, many-body approaches were also used to decipher the interplay between inelastic processes and the Kondo effect. Spin torque transfer has been shown to be effective in changing spin orientations of an

  1. Electron scattering by laser-excited barium atoms

    NASA Technical Reports Server (NTRS)

    Register, D. F.; Trajmar, S.; Jensen, S. W.; Poe, R. T.

    1978-01-01

    Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.

  2. Double excitations and state-to-state transition dipoles in π-π∗ excited singlet states of linear polyenes: Time-dependent density-functional theory versus multiconfigurational methods

    NASA Astrophysics Data System (ADS)

    Mikhailov, Ivan A.; Tafur, Sergio; Masunov, Artëm E.

    2008-01-01

    The effect of static and dynamic electron correlation on the nature of excited states and state-to-state transition dipole moments is studied with a multideterminant wave function approach on the example of all-trans linear polyenes ( C4H6 , C6H8 , and C8H10 ). Symmetry-forbidden singlet nAg states were found to separate into three groups: purely single, mostly single, and mostly double excitations. The excited-state absorption spectrum is dominated by two bright transitions: 1Bu-2Ag and 1Bu-mAg , where mAg is the state, corresponding to two-electron excitation from the highest occupied to lowest unoccupied molecular orbital. The richness of the excited-state absorption spectra and strong mixing of the doubly excited determinants into lower- nAg states, reported previously at the complete active space self-consistent field level of theory, were found to be an artifact of the smaller active space, limited to π orbitals. When dynamic σ-π correlation is taken into account, single- and double-excited states become relatively well separated at least at the equilibrium geometry of the ground state. This electronic structure is closely reproduced within time-dependent density-functional theory (TD DFT), where double excitations appear in a second-order coupled electronic oscillator formalism and do not mix with the single excitations obtained within the linear response. An extension of TD DFT is proposed, where the Tamm-Dancoff approximation (TDA) is invoked after the linear response equations are solved (a posteriori TDA). The numerical performance of this extension is validated against multideterminant-wave-function and quadratic-response TD DFT results. It is recommended for use with a sum-over-states approach to predict the nonlinear optical properties of conjugated molecules.

  3. Direct and secondary nuclear excitation with x-ray free-electron lasers

    SciTech Connect

    Gunst, Jonas; Wu, Yuanbin Kumar, Naveen; Keitel, Christoph H.; Pálffy, Adriana

    2015-11-15

    The direct and secondary nuclear excitation produced by an x-ray free electron laser when interacting with a solid-state nuclear target is investigated theoretically. When driven at the resonance energy, the x-ray free electron laser can produce direct photoexcitation. However, the dominant process in that interaction is the photoelectric effect producing a cold and very dense plasma in which also secondary processes such as nuclear excitation by electron capture may occur. We develop a realistic theoretical model to quantify the temporal dynamics of the plasma and the magnitude of the secondary excitation therein. Numerical results show that depending on the nuclear transition energy and the temperature and charge states reached in the plasma, secondary nuclear excitation by electron capture may dominate the direct photoexcitation by several orders of magnitude, as it is the case for the 4.8 keV transition from the isomeric state of {sup 93}Mo, or it can be negligible, as it is the case for the 14.4 keV Mössbauer transition in {sup 57}Fe. These findings are most relevant for future nuclear quantum optics experiments at x-ray free electron laser facilities.

  4. Direct and secondary nuclear excitation with x-ray free-electron lasers

    NASA Astrophysics Data System (ADS)

    Gunst, Jonas; Wu, Yuanbin; Kumar, Naveen; Keitel, Christoph H.; Pálffy, Adriana

    2015-11-01

    The direct and secondary nuclear excitation produced by an x-ray free electron laser when interacting with a solid-state nuclear target is investigated theoretically. When driven at the resonance energy, the x-ray free electron laser can produce direct photoexcitation. However, the dominant process in that interaction is the photoelectric effect producing a cold and very dense plasma in which also secondary processes such as nuclear excitation by electron capture may occur. We develop a realistic theoretical model to quantify the temporal dynamics of the plasma and the magnitude of the secondary excitation therein. Numerical results show that depending on the nuclear transition energy and the temperature and charge states reached in the plasma, secondary nuclear excitation by electron capture may dominate the direct photoexcitation by several orders of magnitude, as it is the case for the 4.8 keV transition from the isomeric state of 93Mo, or it can be negligible, as it is the case for the 14.4 keV Mössbauer transition in 57Fe. These findings are most relevant for future nuclear quantum optics experiments at x-ray free electron laser facilities.

  5. Pseudopotential Calculation of the Excited States of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Williamson, Andrew; Wang, Lin-Wang; Fu, Hiauxiang; Zunger, Alex

    1998-03-01

    We present the results of our pseudopotential calculations of up to 10 single-exciton states in free standing InP, InAs and CdSe quantum dots with diameters ranging from 10 to 50ÅIn the first step we solve for ≈20-40 single particle hole and electron states using a screened atomic pseudopotential Hamiltonian[1], solved within a plane wave basis using the Folded Spectrum Method[2]. In the second step, we calculate the electron-hole Coulomb energy[3] and the dipole transition probability for each of the ≈1000 possible single particle excitations. We present a comparison of the size scaling of the peaks in absorption and emission spectra obtained in our calculations with those from recent experiments and those of the effective mass based, k.p method. We also compare pseudopotential and k.p predictions of the character of the initial and final single particle states associated with each of these emission peaks. [1] J. Kim, A.J. Williamson, L.W. Wang, S.H-. Wei and A. Zunger, submitted to Phys. Rev. B [2] L. W. Wang and A. Zunger, J. Chem. Phys. 100, 2394 (1994). [3] A. Franceschetti and A. Zunger, Phys. Rev. Lett. 78, 915 (1997). *Supported under BES/OER/DMS contract No. DE---AC36---83CH10093

  6. Electronic Relaxation after Resonant Laser Excitation of Cr in Superfluid Helium Nanodroplets

    PubMed Central

    2013-01-01

    Chromium (Cr) atoms embedded into helium nanodroplets (HeN) are ejected from the droplets upon photoexcitation. During ejection they undergo electronic relaxation resulting in bare Cr atoms in various excited states. In a study of the relaxation process we present absorption spectra observed via laser induced fluorescence and beam depletion as well as dispersed fluorescence spectra and time-resolved fluorescence measurements. Broad and shifted absorption structures were found for the strong z7P° ← a7S3 and y7P° ← a7S3 excitations from the ground state. Emission lines are, in contrast, very narrow, which indicates that fluorescence is obtained from bare excited Cr atoms after ejection. Upon excitation into the y7P2,3,4° states we observed fluorescence from y7P2°, z5P1,2,3°, and z7P2,3,4°, indicating that these states are populated by electronic relaxation during the ejection processes. Relative population ratios are obtained from the intensities of individual spectral lines. Excitation into the z7P2,3,4° states resulted in fluorescence only from z7P2°. Estimates of the time duration of the ejection process are obtained from time-resolved measurements. PMID:23410146

  7. Slow Intramolecular Vibrational Relaxation Leads to Long-Lived Excited-State Wavepackets.

    PubMed

    Rafiq, Shahnawaz; Scholes, Gregory D

    2016-09-01

    Broadband optical pump and compressed white light continuum probe were used to measure the transient excited-state absorption, ground-state bleach, and stimulated emission signals of cresyl violet solution in methanol. Amplitude oscillations caused by wavepacket motion in the ground and excited electronic states were analyzed. It was found that vibrational coherences in the excited state persist for more than the experimental waiting time window of 6 ps, and the strongest mode had a dephasing time constant of 2.4 ps. We hypothesize the dephasing of the wavepacket in the excited state is predominantly caused by intramolecular vibrational relaxation (IVR). Slow IVR indicates weak mode-mode coupling and therefore weak anharmonicity of the potential of this vibration. Thus, the initially prepared vibrational wavepacket in the excited state is not significantly perturbed by nonadiabatic coupling to other electronic states, and hence the diabatic and adiabatic representations of the system are essentially identical within the Born-Oppenheimer approximation. The wavepacket therefore evolves with time in an almost harmonic potential, slowly dephased by IVR and the pure vibrational decoherence. The consistency in the position of node (phase change in the wavepacket) in the excited-state absorption and stimulated emission signals without undergoing any frequency shift until the wavepacket is completely dephased conforms to the absence of any reactive internal conversion. PMID:27510098

  8. Slow Intramolecular Vibrational Relaxation Leads to Long-Lived Excited-State Wavepackets.

    PubMed

    Rafiq, Shahnawaz; Scholes, Gregory D

    2016-09-01

    Broadband optical pump and compressed white light continuum probe were used to measure the transient excited-state absorption, ground-state bleach, and stimulated emission signals of cresyl violet solution in methanol. Amplitude oscillations caused by wavepacket motion in the ground and excited electronic states were analyzed. It was found that vibrational coherences in the excited state persist for more than the experimental waiting time window of 6 ps, and the strongest mode had a dephasing time constant of 2.4 ps. We hypothesize the dephasing of the wavepacket in the excited state is predominantly caused by intramolecular vibrational relaxation (IVR). Slow IVR indicates weak mode-mode coupling and therefore weak anharmonicity of the potential of this vibration. Thus, the initially prepared vibrational wavepacket in the excited state is not significantly perturbed by nonadiabatic coupling to other electronic states, and hence the diabatic and adiabatic representations of the system are essentially identical within the Born-Oppenheimer approximation. The wavepacket therefore evolves with time in an almost harmonic potential, slowly dephased by IVR and the pure vibrational decoherence. The consistency in the position of node (phase change in the wavepacket) in the excited-state absorption and stimulated emission signals without undergoing any frequency shift until the wavepacket is completely dephased conforms to the absence of any reactive internal conversion.

  9. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics.

    PubMed

    Franklin-Mergarejo, R; Alvarez, D Ondarse; Tretiak, S; Fernandez-Alberti, S

    2016-01-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications. PMID:27507429

  10. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics

    NASA Astrophysics Data System (ADS)

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-08-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications.

  11. Carbon nanorings with inserted acenes: Breaking symmetry in excited state dynamics

    DOE PAGES

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-08-10

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation tomore » the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Lastly, our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications.« less

  12. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics

    PubMed Central

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-01-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications. PMID:27507429

  13. Self-Consistent Optimization of Excited States within Density-Functional Tight-Binding.

    PubMed

    Kowalczyk, Tim; Le, Khoa; Irle, Stephan

    2016-01-12

    We present an implementation of energies and gradients for the ΔDFTB method, an analogue of Δ-self-consistent-field density functional theory (ΔSCF) within density-functional tight-binding, for the lowest singlet excited state of closed-shell molecules. Benchmarks of ΔDFTB excitation energies, optimized geometries, Stokes shifts, and vibrational frequencies reveal that ΔDFTB provides a qualitatively correct description of changes in molecular geometries and vibrational frequencies due to excited-state relaxation. The accuracy of ΔDFTB Stokes shifts is comparable to that of ΔSCF-DFT, and ΔDFTB performs similarly to ΔSCF with the PBE functional for vertical excitation energies of larger chromophores where the need for efficient excited-state methods is most urgent. We provide some justification for the use of an excited-state reference density in the DFTB expansion of the electronic energy and demonstrate that ΔDFTB preserves many of the properties of its parent ΔSCF approach. This implementation fills an important gap in the extended framework of DFTB, where access to excited states has been limited to the time-dependent linear-response approach, and affords access to rapid exploration of a valuable class of excited-state potential energy surfaces.

  14. Rate-coefficients and polarization results for the electron-impact excitation of Ar+ ion

    NASA Astrophysics Data System (ADS)

    Srivastava, Rajesh; Dipti, Dipti

    2016-05-01

    A fully relativistic distorted wave theory has been employed to study the electron impact excitation in Ar+ ion. Results have been obtained for the excitation cross-sections and rate-coefficients for the transitions from the ground state 3p5 (J = 3/2) to fine-structure levels of excited states 3p4 4 s, 3p4 4 p , 3p4 5 s, 3p4 5 p, 3p4 3 d and 3p4 4 d. Polarization of the radiation following the excitation has been calculated using the obtained magnetic sub-level cross-sections. Comparison of the present rate-coefficients is also done with the previously reported theoretical results for some unresolved fine structure transitions. Work is supported by DAE-BRNS Mumbai and CSIR, New Delhi.

  15. Electron-impact excitation rate-coefficients and polarization of subsequent emission for Ar+ ion

    NASA Astrophysics Data System (ADS)

    Dipti; Srivastava, Rajesh

    2016-06-01

    Electron impact excitation in Ar+ ions has been studied by using fully relativistic distorted wave theory. Calculations are performed to obtain the excitation cross-sections and rate-coefficients for the transitions from the ground state 3p5 (J=3/2) to fine-structure levels of excited states 3p44s, 3p44p, 3p45s, 3p45p, 3p43d and 3p44d. Polarization of the radiation following the excitation has been calculated using the obtained magnetic sub-level cross-sections. Comparison of the present rate-coefficients is also done with the previously reported theoretical results for some unresolved fine structure transitions.

  16. Protolytic dissociation of cyano derivatives of naphthol, biphenyl and phenol in the excited state: A review

    NASA Astrophysics Data System (ADS)

    Szczepanik, Beata

    2015-11-01

    The excited state proton transfer (ESPT) has been extensively studied for hydroxyarenes, phenols, naphthols, hydroxystilbenes, etc., which undergo large enhancement of acidity upon electronic excitation, thus classified as photoacids. The changes of acidic character in the excited state of cyano-substituted derivatives of phenol, hydroxybiphenyl and naphthol are reviewed in this paper. The acidity constants pKa in the ground state (S0), pKa∗ in the first singlet excited state (S1) and the change of the acidity constant in the excited state ΔpKa for the discussed compounds are summarized and compared. The results of the acidity studies show, that the "electro-withdrawing" CN group in the molecules of naphthol, hydroxybiphenyl and phenol causes dramatic increase of their acidity in the excited state in comparison to the ground state. This effect is greatest for the cyanonaphthols (the doubly substituted CN derivatives are almost as strong as a mineral acid in the excited state), comparable for cyanobiphenyls, and smaller for phenol derivatives. The increase of acidity enables proton transfer to various organic solvents, and the investigation of ESPT can be extended to a variety of solvents besides water. The results of theoretical investigations were also presented and used for understanding the protolytic equilibria of cyano derivatives of naphthol, hydroxybiphenyl and phenol.

  17. 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.

  18. Disentangling intrinsic ultrafast excited-state dynamics of cytosine tautomers.

    PubMed

    Ho, Jr-Wei; Yen, Hung-Chien; Chou, Wei-Kuang; Weng, Chih-Nan; Cheng, Li-Hao; Shi, Hui-Qi; Lai, Szu-Hsueh; Cheng, Po-Yuan

    2011-08-01

    Gas-phase ultrafast excited-state dynamics of cytosine, 1-methylcytosine, and 5-fluorocytosine were investigated in molecular beams using femtosecond pump-probe photoionization spectroscopy to identify the intrinsic dynamics of the major cytosine tautomers. The results indicate that, upon photoexcitation in the first absorption band, the cytosine enol tautomer exhibits a significantly longer excited-state lifetime than its keto and imino counterparts. The initially excited states of the cytosine keto and imino tautomers decay with sub-picosecond dynamics for excitation wavelengths shorter than 300 nm, whereas that of the cytosine enol tautomer decays with time constants ranging from 3 to 45 ps for excitation between 260 and 285 nm.

  19. One-electron and multi-electron transitions observed in the excitation function of the dissociative photoionization excitation of ?

    NASA Astrophysics Data System (ADS)

    Kitajima, Masashi; Ukai, Masatoshi; Machida, Shuntaro; Kameta, Kosei; Ehresmann, Arno; Kouchi, Noriyuki; Hatano, Yoshihiko; Hayaishi, Tatsuji; Shigemasa, Eiji; Ito, Kenji

    1996-05-01

    The excitation function of the dissociative photoionization excitation ( DIE) of 0953-4075/29/9/017/img14 has been measured with the detection technique of coincidence between photoion 0953-4075/29/9/017/img15 and a fluorescence photon emitted from an excited atom N* using extreme- UV synchrotron radiation ( SR) as an excitation source in the energy region of 35 - 65 eV. The axis of the detection system was set at two angles, parallel or perpendicular with respect to the major axis of the elliptically polarized SR, in the present measurement. The coincidence spectra obtained in this energy region show at least two qualitatively different structures originating from two different DIE processes. The major components of the DIE in the present energy region are ascribed to the dissociation of the 0953-4075/29/9/017/img16 state which is strongly coupled with correlation states in the 0953-4075/29/9/017/img17 symmetry. In addition, DIE from other precursor states in the 0953-4075/29/9/017/img18 symmetry or dissociative photo-double ionization excitation ( DDIE) was also observed.

  20. 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.