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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. Electronically excited states of PANH anions.

    PubMed

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

    2015-06-14

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

  3. On the Electronically Excited States of Uracil

    SciTech Connect

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

    2008-10-09

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

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

    PubMed

    Nichols, Bryan; Rassolov, Vitaly A

    2013-09-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  6. 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.

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

    PubMed

    Konstantinov, Denis; Maris, Humphrey J

    2003-01-17

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. Dynamics and spectroscopy of CH₂OO excited electronic states.

    PubMed

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

    2016-04-28

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

  15. 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.

  16. 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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  19. Electron-impact excitation of the low-lying electronic states of formaldehyde

    NASA Technical Reports Server (NTRS)

    Chutjian, A.

    1974-01-01

    Electron-impact excitation has been observed at incident electron energies of 10.1 and 20.1 eV to the first five excited electronic states of formaldehyde lying at and below the 1B2 state at 7.10 eV. These excitations include two new transitions in the energy-loss range 5.6-6.2 eV and 6.7-7.0 eV which have been detected for the first time, either through electron-impact excitation or photon absorption. The differential cross sections of these new excitations are given at scattering angles between 15 and 135 deg. These cross-section ratios peak at large scattering angles - a characteristic of triplet - singlet excitations. The design and performance of the electron-impact spectrometer used in the above observations is outlined and discussed.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  2. Electron delocalization and electron density of small polycyclic aromatic hydrocarbons in singlet excited states.

    PubMed

    Estévez-Fregoso, Mar; Hernández-Trujillo, Jesús

    2016-04-28

    The four lowest singlet electronic states of benzene, the acenes from naphthalene to pentacene, phenanthrene and pyrene were studied by means of theoretical methods. Their vertical excitation energies from the ground electronic states were computed at the CASPT2 approximation. As an attempt to explain the trends observed in the excitation energies, several descriptors based on the electron density were used and the similarity of these molecules with their ground state counterparts was analyzed. It was found that the changes of the topological properties at the C-C bond critical points do not explain the decreasing trends for the excitation energies with the increase of the number of rings, in part because the small changes that take place in the electron density occur above and below the molecular plane. A similarity index based on electron delocalization between quantum topological atoms was defined to compare a molecule in two different electronic states. It was found that, mainly for the acenes, this index goes in line with the excitation energies to the first excited state. Implications of the changes in electron delocalization on the aromatic character of these molecules are also discussed. In general, local aromaticity decreases upon excitation. PMID:26795361

  3. Lifetimes of electronic excitations in unoccupied surface states and the image potential states on Pd(110)

    SciTech Connect

    Tsirkin, S. S. Eremeev, S. V.; Chulkov, E. V.

    2012-10-15

    The contribution of inelastic electron-electron scattering to the decay rate of excitations in the surface states and first two image potential states at the Y-bar point on the surface is calculated in the GW approximation, and the quasi-momentum dependence of the corresponding contribution for the surface states is analyzed. The mechanisms of electron scattering in these states are studied, and the temperature dependence of the excitation lifetime is analyzed with allowance for the contribution of the electron-phonon interaction calculated earlier.

  4. 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.

  5. 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.

  6. 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.

  7. 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. PMID:26001459

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

    SciTech Connect

    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.

  9. Imaging Excited State Dynamics with 2d Electronic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Engel, Gregory S.

    2012-06-01

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

  10. Electronic structure and excited state dynamics in optically excited PTCDA films investigated with two-photon photoemission.

    PubMed

    Marks, M; Sachs, S; Schwalb, C H; Schöll, A; Höfer, U

    2013-09-28

    We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate. PMID:24089789

  11. Electronic structure and excited state dynamics in optically excited PTCDA films investigated with two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Marks, M.; Sachs, S.; Schwalb, C. H.; Schöll, A.; Höfer, U.

    2013-09-01

    We present an investigation of the electronic structure and excited state dynamics of optically excited 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) thin films adsorbed on Ag(111) using two-photon photoemission spectroscopy (2PPE). 2PPE allows us to study both occupied and unoccupied electronic states, and we are able to identify signals from the highest occupied and the two lowest unoccupied electronic states of the PTCDA thin film in the 2PPE spectra. The energies for occupied states are identical to values from ultraviolet photoelectron spectroscopy. Compared to results from inverse photoelectron spectroscopy (IPES), the 2PPE signals from the two lowest unoccupied electronic states, LUMO and LUMO+1, are found at 0.8 eV and 1.0 eV lower energies, respectively. We attribute this deviation to the different final states probed in 2PPE and IPES and the attractive interaction of the photoexcited electron and the remaining hole. Furthermore, we present a time-resolved investigation of the excited state dynamics of the PTCDA film in the femtosecond time regime. We observe a significantly shorter inelastic excited state lifetime compared to findings from time-resolved photoluminescence spectroscopy of PTCDA single crystals which could originate from excitation quenching by the metal substrate.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Carotenoid Excited State Kinetics in Bacterial RCs with the Primary Electron Donor Oxidized

    NASA Astrophysics Data System (ADS)

    Lin, Su; Katilius, Evaldas; Woodbury, Neal W.

    Carotenoid singlet excited state kinetics in wild type reaction centers from Rhodobacter sphaeroides was investigated using ultrafast laser spectroscopy under conditions where the primary electron donor is either neutral or oxidized.

  17. 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.

  18. Differential cross sections for electron-impact excitation of the electronic states of N sub 2

    SciTech Connect

    Brunger, M.J.; Teubner, P.J.O. )

    1990-02-01

    Differential cross sections for the electron-impact excitation of the first ten electronic states of N{sub 2} have been determined at five incident energies ranging from 15 to 50 eV. These differential cross sections were obtained for the scattering range 10{degree}--90{degree} by analyzing electron-energy-loss spectra in N{sub 2} at a number of fixed scattering angles within that range. The present study represents a comprehensive remeasurement of the earlier work of Cartwright and co-workers (Phys. Rev. A 16, 1013 (1977)) and was undertaken with a view to resolving certain anomalies which have been reported in the literature when the earlier cross-section set has been applied to model calculations of swarm parameters.

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

    PubMed

    Frankcombe, Terry J

    2015-02-01

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

  20. 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.

  1. 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.

  2. 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

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

    SciTech Connect

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

    2010-12-09

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

  4. Measurement of the lifetime of excited-state electron bubbles in superfluid helium

    SciTech Connect

    Ghosh, Ambarish; Maris, Humphrey J.

    2005-08-01

    We report on the measurement of the lifetime of bubbles in superfluid helium that contain an electron in the 1P state. The 1P bubbles are produced by laser excitation of ground-state bubbles, and are detected by ultrasonic cavitation. Our measurements show that the lifetime of these excited bubbles is much less than the calculated lifetime for radiative decay and, hence, is determined by a nonradiative mechanism.

  5. Investigation of plasma excitation. volume i. electron impact studies of selected ground state and excited state rare gas atoms. Final report 7 Jun 77-20 Sep 80

    SciTech Connect

    Lake, M.L.

    1981-08-01

    Experiments were undertaken to determine electron impact cross sections of atoms in metastable states. One or two electron guns were used to first produce atoms in metastable states, then further excite these atoms to other levels. Limits on certain cross sections of helium atoms were obtained, but the detection limits of the apparatus prevented exhaustive study. Excitation functions and cross sections of xenon were obtained in the wavelength range from 3000 A to 9000 A.

  6. 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)

  7. Excited state dipole moments of chloroanilines and chlorophenols from solvatochromic shifts in electronic absorption spectra: Support for the concept of excited state group moments

    NASA Astrophysics Data System (ADS)

    Prabhumirashi, L. S.; Satpute, R. S.

    The dipole moments of isomeric o-, m- and p-chloroanilines and chlorophenols in electronically excited L a and L b states are estimated from solvent induced polarization shifts in electronic absorption spectra. It is observed that μ e( L a) > μ e( L b) > μ g, which is consistent with the general theory of polarization red shift. The μ es are found to be approximately co-linear with the corresponding μ gs. The concept of group moments is extended to aromatic molecules in excited states. This approach is found to be useful in understanding correlations among the excited states of mono- and disubstituted benzenes.

  8. 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.

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

    PubMed

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

    2015-01-13

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

  10. Excited-State Energies and Electronic Couplings of DNA Base Dimers

    SciTech Connect

    Kozak, Christopher R.; Kistler, Kurt A.; Lu, Zhen; Matsika, Spiridoula

    2010-02-04

    The singlet excited electronic states of two π-stacked thymine molecules and their splittings due to electronic coupling have been investigated with a variety of computational methods. Focus has been given on the effect of intermolecular distance on these energies and couplings. Single-reference methods, CIS, CIS(2), EOMCCSD, TDDFT, and the multireference method CASSCF, have been used, and their performance has been compared. It is found that the excited-state energies are very sensitive to the applied method but the couplings are not as sensitive. Inclusion of diffuse functions in the basis set also affects the excitation energies significantly but not the couplings. TDDFT is inadequate in describing the states and their coupling, while CIS(2) gives results very similar to EOM-CCSD. Excited states of cytosine and adenine π-stacked dimers were also obtained and compared with those of thymine dimers to gain a more general picture of excited states in π-stacked DNA base dimers. The coupling is very sensitive to the relative position and orientation of the bases, indicating great variation in the degree of delocalization of the excited states between stacked bases in natural DNA as it fluctuates.

  11. 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

  12. 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.

  13. Nonadiabatic excited-state molecular dynamics: Treatment of electronic decoherence

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    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

  14. 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.

  15. 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

  16. 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.

  17. Ground- and excited-state electronic structure of an iron-containing molecular spin photoswitch

    NASA Astrophysics Data System (ADS)

    Rodriguez, Jorge H.

    2005-09-01

    The electronic structure of the cation of [Fe(ptz)6](BF4)2, a prototype of a class of complexes that display light-induced excited-state spin trapping (LIESST), has been investigated by time-independent and time-dependent density-functional theories. The density of states of the singlet ground state reveals that the highest occupied orbitals are metal centered and give rise to a low spin configuration Fe2+(3dxy↑↓3dxz↑↓3dyz↑↓) in agreement with experiment. Upon excitation with light in the 2.3-3.3eV range, metal-centered spin-allowed but parity-forbidden ligand field (LF) antibonding states are populated which, in conjunction with electron-phonon coupling, explain the experimental absorption intensities. The computed excitation energies are in excellent agreement with experiment. Contrary to simpler models we show that the LF absorption bands, which are important for LIESST, do not originate in transitions from the ground to a single excited state but from transitions to manifolds of nearly degenerate excited singlets. Consistent with crystallography, population of the LF states promotes a drastic dilation of the ligand cage surrounding the iron.

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

    PubMed

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

    1999-03-01

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

  19. 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.

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

    SciTech Connect

    Hoffman, M.Z.

    1993-03-31

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

  2. 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.

  3. Electron impact excitation of the 3s3p 1P1 state in magnesium

    NASA Astrophysics Data System (ADS)

    Predojević, Branko

    2006-12-01

    Differential cross sections (DCSs) for electron-impact excitation of the 3s3p 1P1 resonance state of magnesium have been measured at 10, 15, 20, 40, 60, 80 and 100 eV incident electron energies (Eo). Scattered-electron intensities were measured over wide range of scattering angles from 2° to 150°. The absolute DCS scale for the 1P1 state was determined through normalizations of its relative DCSs to optical oscillator strength using forward scattering function method, except at Eo ⩽ 15 eV where the excitation function of the 3s3p 1P1 state experimentally obtained by Leep and Gallagher (1976 Phys. Rev. A 13 148) was utilized for normalization. These absolute DCSs were extrapolated to 0° and 180° and numerically integrated to yield integral, momentum transfer and viscosity cross sections. Our results are compared with available experimental and theoretical data.

  4. 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.

  5. Electron-impact excitation of the low-lying electronic states of HCN

    NASA Technical Reports Server (NTRS)

    Chutjian, A.; Tanaka, H.; Srivastava, S. K.; Wicke, B. G.

    1977-01-01

    The first study of the low-energy electron-impact excitation of low-lying electronic transitions in the HCN molecule is reported. Measurements were made at incident electron energies of 11.6 and 21.6 eV in the energy-loss range of 3-10 eV, and at scattering angles of 20-130 deg. Inelastic scattering spectra were placed on the absolute cross-section scale by determining first the ratio of inelastic-to-elastic scattering cross sections, and then separately measuring the absolute elastic scattering cross section. Several new electronic transitions are observed which are intrinsically overlapped in the molecule itself. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-sections measurements, high-energy electron scattering spectra, optical absorption spectra, and ab initio molecular orbital calculations.

  6. Stretching of hydrogen-bonded OH in the lowest singlet excited electronic state of water dimer.

    PubMed

    Chipman, Daniel M

    2006-01-28

    The lowest singlet excited electronic state of water monomer in the gas phase is strictly dissociative along a OH stretch coordinate but changes its nature when the stretched OH moiety is hydrogen bonded to a neighboring water molecule. This work extends previous exploration of the water dimer excited singlet potential-energy surface, using computational methods that are reliable even at geometries well removed from the ground-state equilibrium. First, the hydrogen-bonded OH moiety is stretched far enough to establish the existence of a barrier that is sufficient to support a quasibound vibrational state of the OH oscillator near the Franck-Condon region. Second, the constraint of an icelike structure is relaxed, and it is found that a substantial fraction of liquidlike structures also supports a quasibound vibrational state. These potential-energy explorations on stretching of the hydrogen-bonded OH moiety in a water dimer are discussed as a model for understanding the initial dynamics upon excitation into the lowest excited singlet state of condensed water. The possibility is raised that the excited-state lifetime may be long enough to allow for exciton migration, which would provide a mechanism for energy transport in condensed water phases. PMID:16460160

  7. 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.

  8. 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

  9. 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.

  10. Excited electronic state calculations by the transcorrelated variational Monte Carlo method: application to a helium atom.

    PubMed

    Umezawa, Naoto; Tsuneyuki, Shinji

    2004-10-15

    We have implemented the excited electronic state calculations for a helium atom by the transcorrelated variational Monte Carlo (TC-VMC) method. In this method, Jastrow-Slater-type wave function is efficiently optimized not only for the Jastrow factor but also for the Slater determinant. Since the formalism for the TC-VMC method is based on the variance minimization, excited states as well as the ground state calculations are feasible. It is found that both the first and the second excitation energies given by TC-VMC are much closer to the experimental data than those given by the variational Monte Carlo method with using the Hartree-Fock orbitals. The successful results in the TC-VMC method are considered to be due to the nodal optimization of the wave functions. PMID:15473772

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

    PubMed

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

    2015-12-31

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

  12. 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…

  13. 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

  14. 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

  15. 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.

  16. 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

  17. 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.

  18. Excited electronic states of complex heteroatomic molecules in series and in different aggregation states of matter

    NASA Astrophysics Data System (ADS)

    Obukhov, Alexandr E.

    1995-01-01

    -cycles aromatic molecule. Photonation of the nitrogen atoms in the azocycles molecules changes the structure of the excited electronic singlet (Si*) and (Ti) triplet states and in the transitions SO yields Sn*, S1* yields S0, S1* yields Sn*, T1 yields Tn, T1 yields S0, which determine the spectroscopic and generation characteristics of the complex compounds. The calculated geometry vapor complex molecules and [(sigma) (pi) ]-anion and [(sigma) (pi) ]-kation radicals compound AM-1/CI and PPP/CI methods in the ground state in their chemosorbtion state of the surface.

  19. 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.

  20. 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.

  1. Stark effect of interfering electronic states: Localization of the nπ* excitations in toluquinone

    NASA Astrophysics Data System (ADS)

    Galaup, J. P.; Trommsdorff, H. P.

    1984-04-01

    High-precision Stark measurements on oriented single crystals of toluquinone at low temperatures have been performed and lead to an assessment of the electronic parenthood of the levels giving rise to the complex spectral region of interference between the two nearby nπ* excited states. The origin bands of the lowest excited singlet and triplet states are characterized by a measure of their factor-group splittings and an evaluation of the change in dipole moment and in polarizability upon excitation. The value of the change in dipole moment is shown to vary strongly between different vibrational levels of the lower state and an evaluation of the degree of localization of the electronic excitation on one CO group is made. The previous assignment of the second nπ* state is confirmed by the sign of the corresponding Stark shift. From measurements on crystals having been oriented in an electric field the absolute orientation of the polar crystal as well as the sign of the pyroelectric coefficient are proposed.

  2. 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.

  3. Does electron-transfer theory explain large rate differences in singlet and triplet excited state electron-transfer reactions?

    SciTech Connect

    Zusman, L.D.; Kurnikov, I.V.; Beratan, D.N.

    1995-12-31

    Gray and coworkers have shown that intramolecular electron-transfer rates from singlet and triplet excited states in iridium(spacer)pyridinium complexes can be vastly different (>5 orders of magnitude). We have analyzed the possible sources of these differences, including effects that may arise from reorganization energies, free energies, and tunneling matrix elements. When distance dependent reorganization energies and energy dependent tunneling matrix elements are included, a systematic framework emerges to describe these electron-transfer reactions.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. State-averaged Monte Carlo configuration interaction applied to electronically excited states

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    We introduce state-averaging into the method of Monte Carlo configuration interaction (SA-MCCI) to allow the stable and efficient calculation of excited states. We show that excited potential curves for H3, including a crossing with the ground state, can be accurately reproduced using a small fraction of the full configuration interaction (FCI) space. A recently introduced error measure for potential curves [J. P. Coe and M. J. Paterson, J. Chem. Phys. 137, 204108 (2012)] is also shown to be a fair approach when considering potential curves for multiple states. We demonstrate that potential curves for LiF using SA-MCCI agree well with the FCI results and the avoided crossing occurs correctly. The seam of conical intersections for CH2 found by Yarkony [J. Chem. Phys. 104, 2932 (1996)] is used as a test for SA-MCCI and we compare potential curves from SA-MCCI with FCI results for this system for the first three triplet states. We then demonstrate the improvement from using SA-MCCI on the dipole of the 2 1A1 state of carbon monoxide. We then look at vertical excitations for small organic molecules up to the size of butadiene where the SA-MCCI energies and oscillator strengths are compared with CASPT2 values [M. Schreiber, M. R. Silva-Junior, S. P. A. Sauer, and W. Thiel, J. Chem. Phys. 128, 134110 (2008)]. We finally see if the SA-MCCI results for these excitation energies can be improved by using MCCIPT2 with approximate natural orbitals when the PT2 space is not onerously large.

  9. Molecular electronic excitations calculated from a solid-state approach: Methodology and numerics

    NASA Astrophysics Data System (ADS)

    Hahn, P. H.; Schmidt, W. G.; Bechstedt, F.

    2005-12-01

    We investigate the applicability and accuracy of a solid-state approach, which was developed originally for the relatively homogeneous electron gas, to describe electronic single-particle and electron-hole pair excitations in molecules. Thereby we start from the determination of the molecular ground state within the local density functional theory using repeated supercells and pseudopotentials for the electron-ion interaction. The electronic spectra are obtained from the Green’s function formalism. The exchange-correlation self-energy Σ is linearly expanded in the screened Coulomb interaction, i.e., the GW approximation is used. Optical spectra are obtained from the Bethe-Salpeter equation for the irreducible polarization propagator. The numerical implementation and possible pitfalls of this methodology are discussed using silane, disilane, and water molecules as examples. In particular the influence of the dynamics of the screening, the supercell size, and the number of empty states are studied. The resulting single- and two-particle excitation energies are compared with experiment and previous theoretical work.

  10. 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.

  11. 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

  12. Doubly excited 3Pe resonance states of two-electron positive ions in Debye plasmas

    NASA Astrophysics Data System (ADS)

    Hu, Xiao-Qing; Wang, Yang; Jiang, Zishi; Jiang, Pinghui; Kar, Sabyasachi

    2015-11-01

    We investigate the doubly excited 3Pe resonance states of two-electron positive ions Li+, Be2+, B3+, and C4+ by employing correlated exponential wave functions. In the framework of the stabilization method, we calculate two series (3pnp and 3dnd) of 3Pe resonances below the N = 3 threshold. The 3Pe 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.

  13. Electronic structure and excited state dynamics in a dicyanovinyl-substituted oligothiophene on Au(111).

    PubMed

    Bogner, Lea; Yang, Zechao; Corso, Martina; Fitzner, Roland; Bäuerle, Peter; Franke, Katharina J; Pascual, José Ignacio; Tegeder, Petra

    2015-10-28

    Dicyanovinyl (DCV)-substituted oligothiophenes are promising donor materials in vacuum-processed small-molecule organic solar cells. Here, we studied the structural and the electronic properties of DCV-dimethyl-pentathiophene (DCV5T-Me2) adsorbed on Au(111) from submonolayer to multilayer coverages. Using a multi-technique experimental approach (low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), atomic force microscopy (AFM), and two-photon photoemission (2PPE) spectroscopy), we determined the energetic position of several affinity levels as well as ionization potentials originating from the lowest unoccupied molecular orbitals (LUMO) and the highest occupied molecular orbitals (HOMO), evidencing a transport gap of 1.4 eV. Proof of an excitonic state was found to be a spectroscopic feature located at 0.6 eV below the LUMO affinity level. With increasing coverage photoemission from excitonic states gains importance. We were able to track the dynamics of several electronically excited states of multilayers by means of femtosecond time-resolved 2PPE. We resolved an intriguing relaxation dynamics involving four processes, ranging from sub-picosecond (ps) to several hundred ps time spans. These show a tendency to increase with increasing coverage. The present study provides important parameters such as energetic positions of transport levels as well as lifetimes of electronically excited states, which are essential for designing organic-molecule-based optoelectronic devices. PMID:26414934

  14. Electron impact excitation and assignment of the low-lying electronic states of N2O

    NASA Technical Reports Server (NTRS)

    Hall, R. I.; Chutjian, A.; Trajmar, S.

    1973-01-01

    Electron scattering spectra of nitrous oxide are reported in the 5- to 10-eV energy-loss range at scattering angles of 20, 30, 90, and 130 deg at a residual energy of 7.0 eV; and at residual energies of 10.0, 2.0, 1.0, 0.6, and 0.2 eV at a scattering angle of 90 deg. Several new distinct and overlapping continua are observed to lie in this energy-loss range. The experimental spectra are discussed in the light of semiempirical INDO calculations of Chutjian and Segal (1972) of the vertical transition energies of N2O. An assignment of the symmetries of the observed excitations consistent with the experimental and theoretical data is suggested.

  15. Electron Elevator: Excitations across the Band Gap via a Dynamical Gap State.

    PubMed

    Lim, A; Foulkes, W M C; Horsfield, A P; Mason, D R; Schleife, A; Draeger, E W; Correa, A A

    2016-01-29

    We use time-dependent density functional theory to study self-irradiated Si. We calculate the electronic stopping power of Si in Si by evaluating the energy transferred to the electrons per unit path length by an ion of kinetic energy from 1 eV to 100 keV moving through the host. Electronic stopping is found to be significant below the threshold velocity normally identified with transitions across the band gap. A structured crossover at low velocity exists in place of a hard threshold. An analysis of the time dependence of the transition rates using coupled linear rate equations enables one of the excitation mechanisms to be clearly identified: a defect state induced in the gap by the moving ion acts like an elevator and carries electrons across the band gap. PMID:26871327

  16. Electron-impact excitation of neon: a pseudo-state convergence study

    NASA Astrophysics Data System (ADS)

    Ballance, C. P.; Griffin, D. C.

    2004-07-01

    A number of convergent close-coupling and R-matrix with pseudo-state (RMPS) calculations for H-like, He-like, Li-like and Be-like ions have demonstrated that coupling to the target continuum can have large effects on the electron-impact excitation cross sections of neutral and low-charge species. However, no one has yet attempted such advanced calculations on a system as complex as neutral neon. We report on a series of RMPS calculations of electron-impact excitation of Ne using recently developed parallel Breit-Pauli R-matrix programs. Our largest calculation included 235 spectroscopic and pseudo-state levels in the close-coupling expansion of the target. Although the results clearly reveal the importance of coupling to the target continuum in this atom, the pseudo-state expansion is not yet sufficiently complete to provide reliable cross sections for energies above the ionization limit. However, this is the largest intermediate-coupling calculation that can be performed with present computer resources. Thus, we have also carried out a series of RMPS calculations in LS coupling with different pseudo-state expansions. Comparisons of these results have allowed us to determine the approximate size of the pseudo-state expansion required to achieve convergence in future intermediate-coupling calculations for neon.

  17. 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.

  18. 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.

  19. 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.

  20. Vibrational spectroscopy of the electronically excited state. 4. Nanosecond and picosecond time-resolved resonance Raman spectroscopy of carotenoid excited states

    SciTech Connect

    Dallinger, R.F.; Farquharson, S.; Woodruff, W.H.; Rodgers, M.A.J.

    1981-12-16

    Resonance Raman and electronic absorption spectra are reported for the S/sub 0/ and T/sub 1/ states of the carotenoids ..beta..-carotene, zeaxanthin, echinenone, canthaxanthin, dihydroxylycopene, astaxanthin, decapreno(C/sub 50/)-..beta..-carotene, ..beta..-apo-8'-carotenal, and ethyl ..beta..-apo-8'-carotenoate. The results reveal qualitatively similar ground-state spectra and similar frequency shifts in all observed resonance Raman modes between S/sub 0/ and T/sub 1/, regardless of carotenoid structure. Examinations of the relationship of the putative C--C and C==C frequencies in S/sub 0/ and T/sub 1/ reveals anomalous shifts to lower frequency in the ''single-bond'' mode upon electronic excitation. These shifts may be due to molecular distortions in the excited state which force changes in molecular motions comprising the observed modes. However, another possibility requiring no distortion is that the interaction (off-diagonal) force constants connecting the C--C and C==C modes change sign upon electronic excitation. This latter phenomenon may provide a unitary explanation for the ''anomalous'' frequency shifts in the C--C and C==C modes, both in the T/sub 1/ states of carotenoids and in the S/sub 1/ states of simpler polyenes, without postulating large, unpredicted structural changes upon excitation or general errors in existing vibrational or theoretical analyses. Resonance Raman and absorbance studies with 35-ps time resolution suggest that S/sub 1/ lifetime (of the /sup 1/B/sub u/ and/or the /sup 1/A/sub g/* states) of ..beta..-carotene in benzene is less than 1 ps.

  1. Excited states of M(II,d sup 6 )-4 prime -Phenylterpyridine complexes: Electron localization

    SciTech Connect

    Amouyal, E.; Mouallem-Bahout, M. ); Calzaferri, G. )

    1991-10-03

    The authors spectroscopic and photophysical data of para-substituted phenylterpyridine (ptpy) Ru(II) complexes and molecular orbital studies of the Fe(II), Ru(II), and Os(II) compounds (M(R-ptpy){sub 2}){sup 2+}, R=H, CH{sub 3}, OH, OCH{sub 3}, and Cl. The visible charge-transfer absorption of the (Ru(R-ptpy){sub 2}){sup 2+} is almost twice as intense as observed for the corresponding 2,2{prime}-bipyridine (bpy) complex (Ru(bpy){sub 3}){sup 2+}, and it is red shifted by about 50 nm. The luminescence in solution and in membranes (Nafion, cellophane) is very weak at room temperature, and the luminescence decay time is on the order of a few nanoseconds. In a glass at 77K, however, the luminescence quantum yield is 0.4 and the decay time 13 {mu}s. Excited-state absorption spectra measured at room temperature by laser flash spectroscopy support the interpretation that the first excited state is of the MLCT type. The similarity of the excited-state absorptions to those of the ligand radical anions strengthens the idea that the excited electron is localized on a single ligand. The low luminescence quantum yield at room temperature is though to be due to low-energy intramolecular vibrations of the nonrigid complex and not to the coupling with d states. Lowering the temperature results in freezing these intramolecular movements and hence in significantly increasing the luminescence quantum yield. The molecular orbital studies indicate that it is reasonable to describe the MLCT state as ((L)Ru{sup III}(L{sm bullet}{sup {minus}})){sup 2+} because the perpendicular conformation of the two ligands causes all {pi} orbitals to be accidentally 2-fold degenerate and therefore a small asymmetric distortion is sufficient to favor the localized situation.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Emission of highly excited electronic states of potassium from cryptomelane nanorods.

    PubMed

    Stelmachowski, P; Legutko, P; Jakubek, T; Indyka, P; Sojka, Z; Holmlid, L; Kotarba, A

    2015-10-21

    Cryptomelane (KMn8O16) nanorods were synthesized, characterized (XRD, Raman spectroscopy, TEM/SAED) and investigated by species resolved thermal desorption of potassium from the material in the range of 20-620 °C. The desorbing fluxes of ions, atoms and highly excited electronic states (field ionizable Rydberg states) were measured using an ion collector, surface ionization and field ionization detectors, respectively, in a vacuum apparatus. The non-equilibrium emission of potassium Rydberg species (principal quantum number > 30) strongly depends on the surface positive voltage bias with a broad maximum at 1-8 V. The stimulation of Rydberg species emission is discussed in terms of spatial and energetic overlapping between the electron cloud above the cryptomelane surface and the desorbing potassium ion. PMID:26388253

  5. Excited electronic states of MnO4-: Challenges for wavefunction and density functional response theories

    NASA Astrophysics Data System (ADS)

    Almeida, Nuno M. S.; McKinlay, Russell G.; Paterson, Martin J.

    2015-01-01

    The lowest excited electronic states of the permanganate ion MnO4- are calculated using a hierarchy of coupled cluster response approaches, as well as time-dependent density functional theory. It is shown that while full linear response coupled cluster with singles and doubles (or higher) performs well, that permanganate represents a stern test for approximate coupled cluster response models, and that problems can be traced to very large orbital relaxation effects. TD-DFT is reasonably robust although errors around 0.6 eV are still observed. In order to further investigate the strong correlations prevalent in the electronic ground state large-scale RASSCF calculations were also performed. Again very large orbital relaxation in the correlated wavefunction is observed. Although the system can qualitatively be described by a single configuration, multi-reference diagnostic values show that care must be taken in this and similar metal complexes.

  6. Benchmarks of electronically excited states: Basis set effects on CASPT2 results

    NASA Astrophysics Data System (ADS)

    Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.; Thiel, Walter

    2010-11-01

    Vertical excitation energies and one-electron properties are computed for the valence excited states of 28 medium-sized organic benchmark molecules using multistate multiconfigurational second-order perturbation theory (MS-CASPT2) and the augmented correlation-consistent aug-cc-pVTZ basis set. They are compared with previously reported MS-CASPT2 results obtained with the smaller TZVP basis. The basis set extension from TZVP to aug-cc-pVTZ causes rather minor and systematic shifts in the vertical excitation energies that are normally slightly reduced (on average by 0.11 eV for the singlets and by 0.09 eV for the triplets), whereas the changes in the calculated oscillator strengths and dipole moments are somewhat more pronounced on a relative scale. These basis set effects at the MS-CASPT2 level are qualitatively and quantitatively similar to those found at the coupled cluster level for the same set of benchmark molecules. The previously proposed theoretical best estimates (TBE-1) for the vertical excitation energies for 104 singlet and 63 triplet excited states of the benchmark molecules are upgraded by replacing TZVP with aug-cc-pVTZ data that yields a new reference set (TBE-2). Statistical evaluations of the performance of density functional theory (DFT) and semiempirical methods lead to the same ranking and very similar quantitative results for TBE-1 and TBE-2, with slightly better performance measures with respect to TBE-2. DFT/MRCI is most accurate among the investigated DFT-based approaches, while the OMx methods with orthogonalization corrections perform best at the semiempirical level.

  7. Electronic state-lifetime interference in resonant Auger spectra: a tool to disentangle overlapping core-excited states.

    PubMed

    Goldsztejn, Gildas; Marchenko, Tatiana; Céolin, Denis; Journel, Loïc; Guillemin, Renaud; Rueff, Jean-Pascal; Kushawaha, Rajesh K; Püttner, Ralph; Piancastelli, Maria Novella; Simon, Marc

    2016-06-01

    We have measured resonant-Auger decay following Cl 1s(-1) excitations in HCl and CH3Cl molecules, and extracted the pseudo-cross sections of different Cl 2p(-2) final states. These cross sections show clear evidence of shake processes as well as contributions of electronic state-lifetime interference (ELI). To describe the spectra we developed a fit approach that takes into account ELI contributions and ultrafast nuclear dynamics in dissociative core-excited states. Using this approach we utilized the ELI contributions to obtain the intensity ratios of the overlapping states Cl 1s(-1)4pπ/1s(-1)4pσ in HCl and Cl 1s(-1)4pe/1s(-1)4pa1 in CH3Cl. The experimental value for HCl is compared with theoretical results showing satisfactory agreement. PMID:27199185

  8. Resonant coherent excitation of Mg sup 11+ : Electronic collisions of state specified short-lived excited states in a crystal channel

    SciTech Connect

    Datz, S.; Dittner, P.F.; Gomez del Campo, J.; Krause, H.F.; Rosseel, T.M.; Vane, C.R. ); Iwata, I.; Komaki, I.; Kimura, M.; Yamazaki, Y. ); Fujimoto, F.; Honda, F. )

    1990-01-01

    Hydrogenic ions passing through axial and planar channels can be excited from n = 1 to n = 2 when the frequency of perturbation by the atoms in the crystal spaced a distance d apart comes into resonance with the spacing between eigenstates i and j {Delta}E{sub ij} = hK(v{sub i}/d) where K is a harmonic 1,2,3{hor ellipsis} of the (v{sub i}/d) frequency. The degeneracy in the n = 2 levels is removed; first by the assymetry in the crystal field and second by Stark mixing of 2s with 2p{sub x} which is caused by the wake field. Thus, the resonant frequency, and hence velocity, for excitation to 2p{sub x,y} is different than that for 2p{sub x} and they can be excited selectively. In the present work we used Mg{sup 11+}, where the n = 2 ionization cross section is small enough to permit escape of some of the excited ions from the crystal without being ionized by subsequent collisions and with the subsequent emission of radiation. Since we can excite different orientations of the ion selectively by varying the velocity we can measure the separate ionization cross sections for these states by determining the yields of totally stripped ions compared to those which emit a Ly {alpha} x-ray. A comparison of the two channels shows that the probability of escape from the crystal without ionizations is greater for ions in the 2p{sub x} state than those in the 2p{sub x,y} state. These RCE data and are presented as proof of principal for experiments which measure electron bombardment ionization cross sections for short lived excited states with specific polarization.

  9. 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

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

    NASA Astrophysics Data System (ADS)

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

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

  11. Explicitly correlated equation-of-motion coupled-cluster methods for excited and electron-attached states.

    PubMed

    Bokhan, Denis; Ten-No, Seiichiro

    2010-11-28

    Based on the linearly approximated F12 coupled cluster singles and doubles [CCSD(F12)] model, equation-of-motion [EOM-CCSD(F12)] methods for electron affinities (EAs) and excitation energies (EEs) have been formulated and implemented. Extended electron-attachment and excitation operators are introduced for balanced descriptions of both neutral and electron-attached (or excited) states. In our implementation the cusp conditions are used for the definition of extended electron-attachment (excitation) operators. It is shown that EA-EOM-CCSD(F12) provides vertical electron affinities accurate to 0.1 eV compared to those in the complete basis set limit. Numerical tests conducted on a selection of small molecules have also shown notable improvement in Rydberg excitation energies compared to valence ones by the use of correlation factors. PMID:21133437

  12. Double-hybrid density functional theory for excited electronic states of molecules

    NASA Astrophysics Data System (ADS)

    Grimme, Stefan; Neese, Frank

    2007-10-01

    Double-hybrid density functionals are based on a mixing of standard generalized gradient approximations (GGAs) for exchange and correlation with Hartree-Fock (HF) exchange and a perturbative second-order correlation part (PT2) that is obtained from the Kohn-Sham (GGA) orbitals and eigenvalues. This virtual orbital-dependent functional (dubbed B2PLYP) contains only two empirical parameters that describe the mixture of HF and GGA exchange (ax) and of the PT2 and GGA correlation (ac), respectively. Extensive testing has recently demonstrated the outstanding accuracy of this approach for various ground state problems in general chemistry applications. The method is extended here without any further empirical adjustments to electronically excited states in the framework of time-dependent density functional theory (TD-DFT) or the closely related Tamm-Dancoff approximation (TDA-DFT). In complete analogy to the ground state treatment, a scaled second-order perturbation correction to configuration interaction with singles (CIS(D)) wave functions developed some years ago by Head-Gordon et al. [Chem. Phys. Lett. 219, 21 (1994)] is computed on the basis of density functional data and added to the TD(A)-DFT/GGA excitation energy. The method is implemented by applying the resolution of the identity approximation and the efficiency of the code is discussed. Extensive tests for a wide variety of molecules and excited states (of singlet, triplet, and doublet multiplicities) including electronic spectra are presented. In general, rather accurate excitation energies (deviations from reference data typically <0.2eV) are obtained that are mostly better than those from standard functionals. Still, systematic errors are obtained for Rydberg (too low on average by about 0.3eV) and charge-transfer transitions but due to the relatively large ax parameter (0.53), B2PLYP outperforms most other functionals in this respect. Compared to conventional HF-based CIS(D), the method is more robust in

  13. 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.

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

    PubMed

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

    2015-06-01

    We study the ionization energy, electron affinity, and the π → π(∗) ((1)La) 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 (1)La 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 (1)La 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. PMID:26049481

  15. 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.

  16. 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)].

  17. 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.

  18. Electron-Impact Excitation of the B ^1SIGMA^+, C^1SIGMA^+ and E^1PI States of

    NASA Technical Reports Server (NTRS)

    Kanik, I.; Ratliff, M.; Trajmar, S.

    1993-01-01

    Electron impact excitation of CO plays an important role in planetary atmospheres andinterstellar clouds. At the present time, serious discrepancies exist among excitation cross sectionsreported in the literature for this molecule. We measured electron impact excitation cross sections forB^1SIGMA^+right arrowX^1SIGMA^+, C^1SIGMA^+right arrowX^1SIGMA^+ and E^1PIrightarrowX^1SIGMA^+ states of CO at 100eV impact energy using electron energy-loss spectroscopy.

  19. 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.

  20. 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.

  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. Role of Coulomb repulsion in correlated-electron emission from a doubly excited state in nonsequential double ionization of molecules

    NASA Astrophysics Data System (ADS)

    Huang, Cheng; Guo, Wenliang; Zhou, Yueming; Wu, Zhengmao

    2016-01-01

    With the classical ensemble model, we investigate nonsequential double ionization of aligned molecules by few-cycle laser pulses at low intensity, where the two electrons finally are ionized through a transition doubly excited state induced by recollision. The correlated electron momentum distribution of parallel molecules exhibits the line-shaped structure parallel to the diagonal. Our analysis indicates that besides the ionization time difference of two electrons from the doubly excited state, the final-state e-e Coulomb repulsion plays a vital role in the formation of the line-shaped structural momentum distribution. For perpendicular molecules, due to the prominent near half-cycle ionization time difference between the two electrons from the doubly excited state, the momentum distribution shows clear anticorrelation behavior.

  3. Dynamics of electron injection from the excited state of anchored molecules into semiconductors

    NASA Astrophysics Data System (ADS)

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

    A complete picture of different interfacial electron transfer dynamics has been obtained from transient absorption and two-photon photoemission data when inserting different anchor/bridge groups between the excited organic donor and the electrode surface.

  4. 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.

  5. Electronic excited states of guanine-cytosine hairpins and duplexes studied by fluorescence spectroscopy.

    PubMed

    Brazard, Johanna; Thazhathveetil, Arun K; Vayá, Ignacio; Lewis, Frederick D; Gustavsson, Thomas; Markovitsi, Dimitra

    2013-08-01

    Guanine-cytosine hairpins, containing a hexaethylene glycol bridge, are studied by steady-state fluorescence spectroscopy and time-correlated single photon counting; their properties are compared to those of duplexes with the same sequence. It is shown that, both in hairpins and in duplexes, base pairing induces quenching of the ππ* fluorescence, the quantum yield decreasing by at least two orders of magnitude. When the size of the systems increases from two to ten base pairs, a fluorescent component decaying on the nanosecond time-scale appears at energy higher than that stemming from the bright states of non-interacting mono-nucleotides (ca. 330 nm). For ten base pairs, this new fluorescence forms a well-defined band peaking at 305 nm. Its intensity is about 20% higher for the hairpin compared to the duplex. Its position (red-shifted by 1600 cm(-1)) and width (broader by 1800 cm(-1) FWHM) differ from those observed for large duplexes containing 1000 base pairs, suggesting the involvement of electronic coupling. Fluorescence anisotropy reveals that the excited states responsible for high energy emission are not populated directly upon photon absorption but are reached during a relaxation process. They are assigned to charge transfer states. According to the emerging picture, the amplitude of conformational motions determines whether instantaneous deactivation to the ground state or emission from charge transfer states will take place, while ππ* fluorescence is associated to imperfect base-pairing. PMID:23736116

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. On the internal rotations in p-cresol in its ground and first electronically excited states

    NASA Astrophysics Data System (ADS)

    Hellweg, Arnim; Hättig, Christof

    2007-07-01

    The overall rotation and internal rotation of p-cresol (4-methyl-phenol) has been studied by comparison of the microwave spectrum with accurate ab initio calculations using the principal axis method in the electronic ground state. Both internal rotations, the torsions of the methyl and the hydroxyl groups relative to the aromatic ring, have been investigated. The internal rotation of the hydroxyl group can be approximately described as the motion of a symmetrical rotor on an asymmetric frame. For the methyl group it has been found that the potential barrier hindering its internal rotation is very small with the first two nonvanishing Fourier coefficients of the potential V3 and V6 in the same order of magnitude. Different splittings of b-type transitions for the A and E species of the methyl torsion indicate a top-top interaction between both internal rotors through the benzene ring. An effective coupling potential for the top-top interaction could be estimated. The hindering barriers of the hydroxyl and methyl rotation have been calculated using second-order Møller-Plesset perturbation theory and the approximate coupled-cluster singles-and-doubles model (CC2) in the ground state and using CC2 and the algebraic diagrammatic construction through second order in the first electronically excited state. The results are in excellent agreement with the experimental values.

  12. 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.

  13. Characterizing the Locality of Diabatic States forElectronic Excitation Transfer By Decomposing theDiabatic Coupling

    SciTech Connect

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

    2010-10-19

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

  14. Coherent oscillations in the PC577 cryptophyte antenna occur in the excited electronic state.

    PubMed

    McClure, Scott D; Turner, Daniel B; Arpin, Paul C; Mirkovic, Tihana; Scholes, Gregory D

    2014-02-01

    Transient absorption spectroscopy is a useful measurement for investigating ultrafast dynamics in molecules. We have developed a transient absorption spectrometer that utilizes balanced and fast detection methods to suppress noise and maintain high temporal and spectral resolution. We use the spectrometer to investigate the ultrafast dynamics in a photosynthetic pigment-protein complex, the phycobiliprotein PC577 isolated from the cryptophyte alga Hemiselmis pacifica CCMP706. We analyze coherent oscillations in the transient absorption data and attribute them to vibrational coherences. Analysis of the dynamic Stokes shift and motion of the wave packet on the potential-energy surface indicate that the coherences arise from vibrational wave packets in the excited electronic state of the protein. PMID:24428706

  15. 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.

  16. 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.

  17. Highly Oxidizing Excited States of One-Electron Oxidized Guanine in DNA: Wavelength and pH Dependence

    PubMed Central

    Khanduri, Deepti; Adhikary, Amitava; Sevilla, Michael D.

    2011-01-01

    Excited states of one-electron oxidized guanine in DNA are known to induce hole transfer to the sugar moiety and on deprotonation result in neutral sugar radicals that are precursors of DNA-strand breaks. This work carried out in homogeneous aqueous glass (7.5 M LiCl) at low temperatures (77 to 175 K) shows the extent of photoconversion of one-electron oxidized guanine and the associated yields of individual sugar radicals and are crucially controlled by photon energy, protonation state, and strandedness of the oligomer. In addition to forming sugar radicals, highly oxidizing excited states of one-electron oxidized guanine are produced with 405 nm light at pH 5 and below that are able to oxidize chloride ion in the surrounding solution to form Cl2•− via an excited state hole transfer process. Among the various DNA model systems studied in this work, the maximum amount of Cl2•− is produced with ds (double stranded) DNA where the one-electron oxidized guanine exists in its cation radical (G•+:C) form. Thus, via excited state hole transfer, the dsDNA is apparently able to protect itself from cation radical excited states by transfer of damage to the surrounding environment. PMID:21381665

  18. Temperature Dependence of Electron Drift Velocity and Electron Collision Cross Section Sets for Ground State and Vibrationally Excited State of the CO2 Molecule

    NASA Astrophysics Data System (ADS)

    Hayashi, M.; Nakamura, Y.

    1998-10-01

    The electron drift velocity in carbon dioxide was calculated at gas temperatures ranging from 193 to 573 K and at E/N values up to 100 Td, assuming that the gas was a mixture of ground state and vibrationally excited molecules and that the mix-ratio was determined by the gas temperature. The elastic momentum cross sections for the ground and the vibrationally excited molecules used in the present calculation were based on the compilation of Hayashi (1990) and recent experiments of Nakamura (1995) and Strakeljahn (1998). We also assumed that all other inelastic cross sections for the ground and the vibrationally excited molecules were the same (Schulz 1969, Srivastava 1983). The calculated electron drift velocity showed marked temperature dependence which agreed fairly well with the measurement of Elford (1980).

  19. 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.

  20. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Amerikheirabadi, Fatemeh

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

  4. 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

  5. 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

  6. 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

  7. The generation of stationary π-electron rotations in chiral aromatic ring molecules possessing non-degenerate excited states.

    PubMed

    Yamaki, Masahiro; Teranishi, Yoshiaki; Nakamura, Hiroki; Lin, Sheng Hsien; Fujimura, Yuichi

    2016-01-21

    The electron angular momentum is a fundamental quantity of high-symmetry aromatic ring molecules and finds many applications in chemistry such as molecular spectroscopy. The stationary angular momentum or unidirectional rotation of π electrons is generated by the excitation of a degenerated electronic excited state by a circularly-polarized photon. For low-symmetry aromatic ring molecules having non-degenerate states, such as chiral aromatic ring molecules, on the other hand, whether stationary angular momentum can be generated or not is uncertain and has not been clarified so far. We have found by both theoretical treatments and quantum optimal control (QOC) simulations that a stationary angular momentum can be generated even from a low-symmetry aromatic ring molecule. The generation mechanism can be explained in terms of the creation of a dressed-state, and the maximum angular momentum is generated by the dressed state with an equal contribution from the relevant two excited states in a simple three-electronic state model. The dressed state is formed by inducing selective nonresonant transitions between the ground and each excited state by two lasers with the same frequency but having different polarization directions. The selective excitation can be carried out by arranging each photon-polarization vector orthogonal to the electronic transition moment of the other transition. We have successfully analyzed the results of the QOC simulations of (P)-2,2'-biphenol of axial chirality in terms of the analytically determined optimal laser fields. The present findings may open up new types of chemical dynamics and spectroscopy by utilizing strong stationary ring currents and current-induced magnetic fields, which are created at a local site of large compounds such as biomolecules. PMID:26670839

  8. Femtosecond stimulated Raman spectroscopy as a tool to detect molecular vibrations in ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Gelin, Maxim F.; Domcke, Wolfgang; Rao, B. Jayachander

    2016-05-01

    We give a detailed theoretical analysis of the simplest variant of femtosecond stimulated Raman spectroscopy, where a picosecond Raman pump pulse and a femtosecond Raman probe pulse are applied resonantly to a chromophore in thermal equilibrium in the ground electronic state. We demonstrate that this technique is capable of the detection of dephasing-free Raman-like lines revealing vibrational modes not only in the electronic ground state but also in the excited electronic state of the chromophore. The analytical results obtained with simplifying assumptions for the shape of the laser pulses are substantiated by numerical simulations with realistic laser pulses, employing the equation-of-motion phase-matching approach.

  9. 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.

  10. 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.

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

    SciTech Connect

    Hoffman, M.Z.

    1993-03-31

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

  12. 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

  13. 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.

  14. Contribution of the First Electronically Excited State of Molecular Nitrogen to Thermospheric Nitric Oxide

    NASA Astrophysics Data System (ADS)

    Yonker, Justin D.

    The chemical reaction of the first excited electronic state of molecular nitrogen, N2(A3 S+u ) or N2(A), with ground state atomic oxygen, O(3 P), is an important contributor to thermospheric nitric oxide (NO). The importance is assessed by including this reaction in a one-dimensional photochemical model. The method is to scale the photoelectron impact ionization rate of N2 by a Gaussian centered near 100 km. Large uncertainties remain in the temperature dependence and branching ratios of many reactions important to NO production and loss. Similarly large uncertainties are present in the solar soft x-ray irradiance, known to be the fundamental driver of the low-latitude NO. To illustrate, it is shown that the equatorial, midday NO density measured by the Student Nitric Oxide Explorer (SNOE) satellite near the Solar Cycle 23 maximum can be recovered by the model to within the 20% measurement uncertainties using two rather different but equally reasonable chemical schemes, each with their own solar soft-xray irradiance parameterizations. Including the N2(A) changes the NO production rate by an average of 11%, but the NO density changes by a much larger 44%. This is explained by tracing the direct, indirect, and catalytic contributions of N2(A) to NO, finding them to contribute 40%, 33%, and 27 % respectively. The contribution of N2(A) relative to the total NO production and loss is assessed by tracing both back to their origins in the primary photoabsorption and photoelectron impact processes. The photoelectron impact ionization of N2 (PEI N2) is shown to be the main driver of the midday NO production while the photoelectron impact dissociation of N2 (PED N2) is the main NO destroyer. The net photoelectron impact excitation rate of N2 (PEE N2), which is responsible for the N2(A) production, is larger than either PEI N2 or PED N2 and thus potentially very important. Although the conservative assumptions regarding the level-specific NO yield from the N2(A)+O reaction

  15. 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.

  16. Electronically excited states of DNA oligonucleotides with disordered base sequences studied by fluorescence spectroscopy.

    PubMed

    Vayá, Ignacio; Brazard, Johanna; Gustavsson, Thomas; Markovitsi, Dimitra

    2012-11-01

    DNA double-stranded oligomers are studied by steady-state and time-resolved fluorescence spectroscopy from the femtosecond to the nanosecond time-scale, following excitation at 267 nm. It is shown that emission arises from three types of excited states. (i) Bright ππ* states emitting around 330 nm and decaying on the sub-picosecond time-scale with an average lifetime of ca. 0.4 ps and a quantum yield lower than 4 × 10(-6). (ii) Excimers/exciplexes emitting around 430 nm and decaying on the sub-nanosecond time-scale. (iii) Excited states emitting mainly at short wavelengths (λ < 330 nm) and decaying on the nanosecond time-scale, possibly correlated to GC pairs. The properties of the examined duplexes, exhibiting significant disorder with respect to the nearest neighbour base sequence, are radically different than those of the much longer and disordered calf thymus DNA. Such behaviour suggests that long range and/or sequence effects play a key role in the fate of excitation energy. PMID:23034563

  17. 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

  18. Reactive and internal contributions to the thermal conductivity of local thermodynamic equilibrium nitrogen plasma: The effect of electronically excited states

    NASA Astrophysics Data System (ADS)

    Bruno, D.; Colonna, G.; Laricchiuta, A.; Capitelli, M.

    2012-12-01

    Internal and reactive contributions to the thermal conductivity of a local thermodynamic equilibrium nitrogen plasma have been calculated using the Chapman-Enskog method. Low-lying (LL) electronically excited states (i.e., states with the same principal quantum number of the ground state) and high-lying (HL) ones (i.e., states with principal quantum number n > 2) have been considered. Several models have been developed, the most accurate being a model that treats the LL states as separate species while disregarding the presence of HL states, on account of their enormous transport cross sections.

  19. Reactive and internal contributions to the thermal conductivity of local thermodynamic equilibrium nitrogen plasma: The effect of electronically excited states

    SciTech Connect

    Bruno, D.; Colonna, G.; Laricchiuta, A.; Capitelli, M.

    2012-12-15

    Internal and reactive contributions to the thermal conductivity of a local thermodynamic equilibrium nitrogen plasma have been calculated using the Chapman-Enskog method. Low-lying (LL) electronically excited states (i.e., states with the same principal quantum number of the ground state) and high-lying (HL) ones (i.e., states with principal quantum number n> 2) have been considered. Several models have been developed, the most accurate being a model that treats the LL states as separate species while disregarding the presence of HL states, on account of their enormous transport cross sections.

  20. Electron propagator calculations on the ground and excited states of C60(-).

    PubMed

    Zakrzewski, V G; Dolgounitcheva, O; Ortiz, J V

    2014-09-01

    Electron propagator calculations in two approximations—the third-order algebraic, diagrammatic construction and the outer valence Green’s function (OVGF)—have been performed on the vertical electron affinities of C60 and the vertical electron detachment energies of several states of C60(–) with a variety of basis sets. These calculations predict bound (2)T1u and (2)T1g anions, but fail to produce (2)T2u or (2)Hg anionic states that are more stable than ground-state C60. The electron affinity for the (2)Ag state is close to zero, but no definitive result on its sign has been obtained. This state may be a resonance or marginally bound anion. The OVGF prediction for the vertical electron detachment energy of (2)T1u C60(–), 2.63 eV, is in excellent agreement with recent anion photoelectron spectra. PMID:24813804

  1. 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.

  2. Excited states of a hydrated electron and aqueous chloride by computer simulation

    NASA Astrophysics Data System (ADS)

    Borgis, Daniel; Staib, Arnulf

    1994-12-01

    Results of adiabatic molecular dynamics simulations for a hydrated electron and the aqueous chloride anion are reported. A novel technical feature is the efficient representation of solute electronic wavefunctions in terms of floating spherical Gaussian orbitals. The simulations account for the coupling of the excess electron to the solvent electronic polarization in an explicit and self-consistent fashion. The computed electronic ground state absorption spectrum for e(-)/H2O and the charge-transfer-to-solvent spectra for Cl(-)/H2O are analyzed. The energetic aspects of the models and the short time solute electronic dynamics are discussed.

  3. 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.

  4. Analytical Hessian of electronic excited states in time-dependent density functional theory with Tamm-Dancoff approximation.

    PubMed

    Liu, Jie; Liang, WanZhen

    2011-07-01

    We present the analytical expression and computer implementation for the second-order energy derivatives of the electronic excited state with respect to the nuclear coordinates in the time-dependent density functional theory (TDDFT) with Gaussian atomic orbital basis sets. Here, the Tamm-Dancoff approximation to the full TDDFT is adopted, and therefore the formulation process of TDDFT excited-state Hessian is similar to that of configuration interaction singles (CIS) Hessian. However, due to the replacement of the Hartree-Fock exchange integrals in CIS with the exchange-correlation kernels in TDDFT, many quantitative changes in the derived equations are arisen. The replacement also causes additional technical difficulties associated with the calculation of a large number of multiple-order functional derivatives with respect to the density variables and the nuclear coordinates. Numerical tests on a set of test molecules are performed. The simulated excited-state vibrational frequencies by the analytical Hessian approach are compared with those computed by CIS and the finite-difference method. It is found that the analytical Hessian method is superior to the finite-difference method in terms of the computational accuracy and efficiency. The numerical differentiation can be difficult due to root flipping for excited states that are close in energy. TDDFT yields more exact excited-state vibrational frequencies than CIS, which usually overestimates the values. PMID:21744894

  5. Electronic Structure and Dynamics of Higher-Lying Excited States in Light Harvesting Complex 1 from Rhodobacter sphaeroides.

    PubMed

    Dahlberg, Peter D; Ting, Po-Chieh; Massey, Sara C; Martin, Elizabeth C; Hunter, C Neil; Engel, Gregory S

    2016-06-23

    Light harvesting in photosynthetic organisms involves efficient transfer of energy from peripheral antenna complexes to core antenna complexes, and ultimately to the reaction center where charge separation drives downstream photosynthetic processes. Antenna complexes contain many strongly coupled chromophores, which complicates analysis of their electronic structure. Two-dimensional electronic spectroscopy (2DES) provides information on energetic coupling and ultrafast energy transfer dynamics, making the technique well suited for the study of photosynthetic antennae. Here, we present 2DES results on excited state properties and dynamics of a core antenna complex, light harvesting complex 1 (LH1), embedded in the photosynthetic membrane of Rhodobacter sphaeroides. The experiment reveals weakly allowed higher-lying excited states in LH1 at 770 nm, which transfer energy to the strongly allowed states at 875 nm with a lifetime of 40 fs. The presence of higher-lying excited states is in agreement with effective Hamiltonians constructed using parameters from crystal structures and atomic force microscopy (AFM) studies. The energy transfer dynamics between the higher- and lower-lying excited states agree with Redfield theory calculations. PMID:27232937

  6. 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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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 C2 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 C2v insertion pathway for BeH2. 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.

  9. Excited Charm States

    SciTech Connect

    Shukla, S.

    1994-12-31

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

  10. 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.

  11. 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. PMID:27208936

  12. Dynamics of electron injection from the excited state of anchored organic molecules into rutile (110)TiO II

    NASA Astrophysics Data System (ADS)

    Gundlach, Lars; Ernstorfer, Ralph; Willig, Frank

    2006-08-01

    Hot electron injection from the excited electronic singlet state of perylene chromophores into the (110) surface of rutile TiO II single crystals was measured with femtosecond two-photon photoemission (2PPE) for different anchor/bridge groups attached to the perylene chromophore. Femtosecond 2PPE probes the time and energy dependence of the population of firstly the excited state of the chromophore and secondly of the hot electrons injected into the surface layer of the semiconductor. Measuring both these contributions gives a complete picture of the ultrafast photo-induced injection process and bridges the gap to conventional measurements of the rise time of the corresponding photocurrent. Studying the system in ultra-high-vacuum (UHV) makes all the tools of surface science available. Impurities on the surface were studied with XPS, the alignment of the occupied and unoccupied electronic levels at the interface with UPS and with 2PPE, respectively. The orientation of the elongated chromophores with respect to the crystal surface was deduced from angle and polarization dependent 2PPE signals making use of the known orientation of the dipole moment for the optical transition, the energy distribution of the injected hot electrons was determined with 2PPE from the energy distribution of the photoemitted electrons, and finally the escape of the injected electrons from the surface to bulk states of the semiconductor was obtained from femtosecond 2PPE transients.

  13. 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.

  14. Time-resolved electron transfer from the excited singlet state of anchored perylene into Ag(1 1 0)

    NASA Astrophysics Data System (ADS)

    Gundlach, Lars; Willig, Frank

    2007-11-01

    Perylene chromophores were adsorbed on the Ag(1 1 0) surface via surface bond formation of the -CH 2-SH group that was covalently attached to the perylene moieties. The lowest excited singlet state of perylene was populated with a laser pulse of 440 nm wavelength. The decay of this donor state due to ultrafast electron transfer to the Ag electrode was probed with a second, delayed laser pulse centered at 280 nm that gave rise to a photoemission signal detected in ultra-high-vacuum by a spectrometer. The fit to the measured data revealed a time constant of 15 fs for the electron injection reaction.

  15. Infrared spectra and molecular structure of excited electronic metastable states of the nitroprusside anion, [Fe(CN) 5NO] 2-

    NASA Astrophysics Data System (ADS)

    Güida, J. A.; Aymonino, P. J.; Piro, O. E.; Castellano, E. E.

    1993-04-01

    Na 2[Fe(CN) 5NO].2H 2O (SNP) and Ba[Fe(CN) 5NO].3H 2O (BNP) irradiated at low temperature with light in the green—blue region exhibit two new sets of infrared (IR) bands. These can be assigned to two, long-lived, electronically excited metastable states of the [Fe(CN) 5NO] 2- (NP) ion. Upon heating, these states depopulate following decay processes with different onset temperatures. We considerably extend here previous polarized IR data on irradiated SNP (100) plates to include the other basal planes. All IR-active CN, NO and FeN stretching modes and FENO bending modes of NP in both metastable states exhibit frequency down shifts This points to a softening of the corresponding bonds upon excitation. Relative frequency shift values observed for modes associated with the FeNO group are about one order of magnitude larger than the corresponding values for CN stretching modes. This supports the conclusion that the metastable states are reached through an electronic transition involving mainly the metal( nd)-NO bonding. We employ dichroic measurements in SNP to estimate the orientation in the lattice of the transition dipole moment vector corresponding to the NO mode of NP in both metastable states. Results show that the FeNO group is not appreciably bent upon excitation of NP to either of these states.

  16. 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

  17. Electronic structure of fluorides: general trends for ground and excited state properties

    NASA Astrophysics Data System (ADS)

    Cadelano, E.; Cappellini, G.

    2011-05-01

    The electronic structure of fluorite crystals are studied by means of density functional theory within the local density approximation for the exchange correlation energy. The ground-state electronic properties, which have been calculated for the cubic structures CaF2, SrF2, BaF2, CdF2, HgF2, β-PbF2, using a plane waves expansion of the wave functions, show good comparison with existing experimental data and previous theoretical results. The electronic density of states at the gap region for all the compounds and their energy-band structure have been calculated and compared with the existing data in the literature. General trends for the ground-state parameters, the electronic energy-bands and transition energies for all the fluorides considered are given and discussed in details. Moreover, for the first time results for HgF2 have been presented.

  18. 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.

  19. Novel push-pull dendrons with high excited state dipole moments. Synthesis and theoretical analysis of unusual "branched electron distribution"

    NASA Astrophysics Data System (ADS)

    Guadarrama, Patricia; Terán, Gerardo; Ramos, Estrella; Gutiérrez, Jorge; Hernández, Madelyn

    2015-04-01

    The synthesis of novel highly delocalized push-pull dendrons is described. A modified protocol to conventional Csbnd C coupling reaction was used with moderate yields. The excited state dipole moments of synthesized dendrons were estimated by the solvatochromic model using the ETN polarity scale. In case of dendron of second generation with donor-acceptor groups, values around 23 D are obtained, denoting an efficient charge separation crucial in photovoltaic processes. From the theoretical analysis, there is a clear evidence of highly efficient electron delocalization in case of push-pull dendrons. The chosen theoretical model (M05-2X/cc-pVDZ) to describe the electronic behavior of the molecules under study was very precise in the estimation of dipole moments in excited state, with differences of 0.5-2.2 D, compared with the values obtained by the solvatochromic model.

  20. Electron impact excitation of 5p states of rubidium at 20 eV incident energy

    NASA Astrophysics Data System (ADS)

    Hou Chin, Jia; Ratnavelu, Kuru; Zhou, Yajun

    2014-06-01

    The coupled-channel optical method (CCOM) is implemented in this work to study the scattering of electron on rubidium atom at 20 eV. In order to provide a realistic calculation, the continuum effect of the scattering system is accounted by incorporate an ab initio optical potential into the CCOM calculation. The differential cross sections (DCS), as well as the reduced Stokes parameters of 5p excitation are reported and compared to the available experimental and theoretical data. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.

  1. 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.

  2. 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.

  3. 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.

  4. Femtosecond stimulated Raman spectroscopy as a tool to detect molecular vibrations in ground and excited electronic states.

    PubMed

    Gelin, Maxim F; Domcke, Wolfgang; Rao, B Jayachander

    2016-05-14

    We give a detailed theoretical analysis of the simplest variant of femtosecond stimulated Raman spectroscopy, where a picosecond Raman pump pulse and a femtosecond Raman probe pulse are applied resonantly to a chromophore in thermal equilibrium in the ground electronic state. We demonstrate that this technique is capable of the detection of dephasing-free Raman-like lines revealing vibrational modes not only in the electronic ground state but also in the excited electronic state of the chromophore. The analytical results obtained with simplifying assumptions for the shape of the laser pulses are substantiated by numerical simulations with realistic laser pulses, employing the equation-of-motion phase-matching approach. PMID:27179484

  5. 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.

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

    PubMed

    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(∗) 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, (1)Lb π-π(∗), (1)La 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. PMID:26627956

  7. 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.

  8. 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.

  9. 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.

  10. 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)

  11. 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.

  12. 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.

  13. Double-Beta Decay of 96Zr and Double-Electron Capture of 156Dy to Excited Final States

    NASA Astrophysics Data System (ADS)

    Finch, Sean W.

    Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the two-neutrino double-beta decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a by product of this experiment, the beta decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect gamma rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 10 20 yr were produced. Measurements of this decay are important to test neutrinoless double-beta decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the neutrinoless double-beta decay half-life. The second experiment is a search for the resonantly-enhanced neutrinoless double-electron capture decay of 156Dy to excited states in 156Gd. Double-electron capture is a possible experimental alternative to neutrinoless-double beta decay, which could distinguish the Dirac or Majorana nature of the neutrino. Two clover high-purity germanium detectors were used in coincidence to investigate the decay. A 213.5 mg enriched 156Dy sample was observed for 0.635 year, producing half-life limits of 10 17 yr. The limits produced by both of these experiments are currently the most stringent limits available for these decays.

  14. Numerology, hydrogenic levels, and the ordering of excited states in one-electron atoms

    NASA Astrophysics Data System (ADS)

    Armstrong, Lloyd, Jr.

    1982-03-01

    We show that the observed ordering of Rydberg states of one-electron atoms can be understood by assuming that these states are basically hydrogenic in nature. Much of the confusion concerning this point is shown to arise from the failure to differentiate between hydrogenic ordering as the nuclear charge approaches infinity, and hydrogenic ordering for an effective charge of one. The origin of κ ordering of Rydberg levels suggested by Sternheimer is considered within this picture, and the predictions of κ ordering are compared with those obtained by assuming hydrogenic ordering.

  15. 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

  16. The properties of LiH in its ground and first excited electronic state

    NASA Astrophysics Data System (ADS)

    Bishop, David M.; Cheung, Lap M.

    1983-09-01

    With the aid of recently produced potential curves for the X 1Σ+ and A 1Σ+ states of lithium hydride, the rovibronic energies of 7LiH have been calculated. From these energies the standard spectroscopic constants have been evaluated. The effect on these constants of inclusion of adiabatic corrections (for diagonal nuclear motion) in the potential curves is discussed. The expectation values of certain powers of the electronic coordinates are also tabulated.

  17. 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.

  18. Triplet excited electronic state switching induced by hydrogen bonding: A transient absorption spectroscopy and time-dependent DFT study.

    PubMed

    Ravi Kumar, Venkatraman; Ariese, Freek; Umapathy, Siva

    2016-03-21

    The solvent plays a decisive role in the photochemistry and photophysics of aromatic ketones. Xanthone (XT) is one such aromatic ketone and its triplet-triplet (T-T) absorption spectra show intriguing solvatochromic behavior. Also, the reactivity of XT towards H-atom abstraction shows an unprecedented decrease in protic solvents relative to aprotic solvents. Therefore, a comprehensive solvatochromic analysis of the triplet-triplet absorption spectra of XT was carried out in conjunction with time dependent density functional theory using the ad hoc explicit solvent model approach. A detailed solvatochromic analysis of the T-T absorption bands of XT suggests that the hydrogen bonding interactions are different in the corresponding triplet excited states. Furthermore, the contributions of non-specific and hydrogen bonding interactions towards differential solvation of the triplet states in protic solvents were found to be of equal magnitude. The frontier molecular orbital and electron density difference analysis of the T1 and T2 states of XT indicates that the charge redistribution in these states leads to intermolecular hydrogen bond strengthening and weakening, respectively, relative to the S0 state. This is further supported by the vertical excitation energy calculations of the XT-methanol supra-molecular complex. The intermolecular hydrogen bonding potential energy curves obtained for this complex in the S0, T1, and T2 states support the model. In summary, we propose that the different hydrogen bonding mechanisms exhibited by the two lowest triplet excited states of XT result in a decreasing role of the nπ(∗) triplet state, and are thus responsible for its reduced reactivity towards H-atom abstraction in protic solvents. PMID:27004870

  19. Triplet excited electronic state switching induced by hydrogen bonding: A transient absorption spectroscopy and time-dependent DFT study

    NASA Astrophysics Data System (ADS)

    Ravi Kumar, Venkatraman; Ariese, Freek; Umapathy, Siva

    2016-03-01

    The solvent plays a decisive role in the photochemistry and photophysics of aromatic ketones. Xanthone (XT) is one such aromatic ketone and its triplet-triplet (T-T) absorption spectra show intriguing solvatochromic behavior. Also, the reactivity of XT towards H-atom abstraction shows an unprecedented decrease in protic solvents relative to aprotic solvents. Therefore, a comprehensive solvatochromic analysis of the triplet-triplet absorption spectra of XT was carried out in conjunction with time dependent density functional theory using the ad hoc explicit solvent model approach. A detailed solvatochromic analysis of the T-T absorption bands of XT suggests that the hydrogen bonding interactions are different in the corresponding triplet excited states. Furthermore, the contributions of non-specific and hydrogen bonding interactions towards differential solvation of the triplet states in protic solvents were found to be of equal magnitude. The frontier molecular orbital and electron density difference analysis of the T1 and T2 states of XT indicates that the charge redistribution in these states leads to intermolecular hydrogen bond strengthening and weakening, respectively, relative to the S0 state. This is further supported by the vertical excitation energy calculations of the XT-methanol supra-molecular complex. The intermolecular hydrogen bonding potential energy curves obtained for this complex in the S0, T1, and T2 states support the model. In summary, we propose that the different hydrogen bonding mechanisms exhibited by the two lowest triplet excited states of XT result in a decreasing role of the nπ∗ triplet state, and are thus responsible for its reduced reactivity towards H-atom abstraction in protic solvents.

  20. 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.

  1. 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. PMID:26018044

  2. 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.

  3. 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.

  4. Electronic excited states responsible for dimer formation upon UV absorption directly by thymine strands: joint experimental and theoretical study.

    PubMed

    Banyasz, Akos; Douki, Thierry; Improta, Roberto; Gustavsson, Thomas; Onidas, Delphine; Vayá, Ignacio; Perron, Marion; Markovitsi, Dimitra

    2012-09-12

    The study addresses interconnected issues related to two major types of cycloadditions between adjacent thymines in DNA leading to cyclobutane dimers (T<>Ts) and (6-4) adducts. Experimental results are obtained for the single strand (dT)(20) by steady-state and time-resolved optical spectroscopy, as well as by HPLC coupled to mass spectrometry. Calculations are carried out for the dinucleoside monophosphate in water using the TD-M052X method and including the polarizable continuum model; the reliability of TD-M052X is checked against CASPT2 calculations regarding the behavior of two stacked thymines in the gas phase. It is shown that irradiation at the main absorption band leads to cyclobutane dimers (T<>Ts) and (6-4) adducts via different electronic excited states. T<>Ts are formed via (1)ππ* excitons; [2 + 2] dimerization proceeds along a barrierless path, in line with the constant quantum yield (0.05) with the irradiation wavelength, the contribution of the (3)ππ* state to this reaction being less than 10%. The formation of oxetane, the reaction intermediate leading to (6-4) adducts, occurs via charge transfer excited states involving two stacked thymines, whose fingerprint is detected in the fluorescence spectra; it involves an energy barrier explaining the important decrease in the quantum yield of (6-4) adducts with the irradiation wavelength. PMID:22894169

  5. 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

  6. 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

  7. Observation of temporary-negative-ion states in condensed methanol via vibrational excitation induced by slow electron scattering

    SciTech Connect

    Wen, A.T.; Michaud, M.; Sanche, L.

    1996-11-01

    We report the measurements of electron-impact vibrational excitation of amorphous methanol condensed on a polycrystalline Pt substrate over incident energies of 1{endash}20 eV at a large off-specular angle. The spectra obtained show that vibrations within solid methanol in its ground state are rather sensitive to the variation of impact energy and there is tangible evidence of the formation of at least three compound temporary-negative-ion (TNI) states. The low-energy feature lying between 3 and 6 eV is assigned tentatively to a {sup 2}{ital A}{prime} valence-shape resonance with a {sup 2}[{ital N},(8{ital a}{prime}{sigma}{asterisk}){sup 1}] configuration, whose parent state is the ground state {sup 1}{ital A}{prime} of the molecule. The origin of the second broad structure centered around 7.0 eV in the excitation functions may be threefold: a Feshbach-type resonance {sup 2}{ital A}{double_prime} of the electronic configuration {sup 2}[(2{ital a}{double_prime}){sup 1},(3{ital sa}{prime}){sup 2}] (about 7 eV); a nearby shape resonance {sup 2}{ital A}{prime} of {sup 2}[({ital N}),(9{ital a}{prime}{sigma}{asterisk}){sup 1}] (about 8 eV); and probably also a minor contribution from another {sup 2}[(7{ital a}{prime}){sup 1},(3{ital sa}{prime}){sup 2}] Feshbach resonance {sup 2}{ital A}{prime} (about 9 eV). The third broad bandlike resonant feature, extending from 11 up to 17 eV, may consist of overlapping TNI states, dominated by the {sup 2}[(6{ital a}{prime}){sup 1},(3{ital sa}{prime}){sup 2}] Feshbach resonance {sup 2}{ital A}{prime}. Plausible decay channels from their configurations are discussed. {copyright} {ital 1996 The American Physical Society.}

  8. 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.

  9. Quantum Chemical Benchmark Studies of the Electronic Properties of the Green Fluorescent Protein Chromophore. 1. Electronically Excited and Ionized States of the Anionic Chromophore in the Gas Phase.

    PubMed

    Epifanovsky, Evgeny; Polyakov, Igor; Grigorenko, Bella; Nemukhin, Alexander; Krylov, Anna I

    2009-07-14

    We present the results of quantum chemical calculations of the electronic properties of the anionic form of the green fluorescent protein chromophore in the gas phase. The vertical detachment energy of the chromophore is found to be 2.4-2.5 eV, which is below the strongly absorbing ππ* state at 2.6 eV. The vertical excitation of the lowest triplet state is around 1.9 eV, which is below the photodetachment continuum. Thus, the lowest bright singlet state is a resonance state embedded in the photodetachment continuum, whereas the lowest triplet state is a regular bound state. Based on our estimation of the vertical detachment energy, we attribute a minor feature in the action spectrum as due to the photodetachment transition. The benchmark results for the bright ππ* state demonstrated that the scaled opposite-spin method yields vertical excitation within 0.1 eV (20 nm) from the experimental maximum at 2.59 eV (479 nm). We also report estimations of the vertical excitation energy obtained with the equation-of-motion coupled cluster with the singles and doubles method, a multireference perturbation theory corrected approach MRMP2 as well as the time-dependent density functional theory with range-separated functionals. Expanding the basis set with diffuse functions lowers the ππ* vertical excitation energy by 0.1 eV at the same time revealing a continuum of "ionized" states, which embeds the bright ππ* transition. PMID:26610014

  10. 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. PMID:25200683

  11. Electronic excitation of CO by positron impact

    SciTech Connect

    Silva, Euclimar P. da; Varella, Marcio T. do N; Lima, Marco A. P.

    2005-12-15

    We report calculated cross sections for the electronic excitation of carbon monoxide by positron impact. The calculations were carried out with the Schwinger multichannel method and included six collision channels, namely the ground (X {sup 1}{sigma}{sup +}) and five electronically excited (A {sup 1}{pi}, I {sup 1}{sigma}{sup -} and D {sup 1}{delta}) states. Present calculated excitation cross sections to the A {sup 1}{pi} state did not present any resonant features, being in this sense consistent with previous calculations for the isoelectronic nitrogen molecule. The experimental a {sup 1}{pi}{sub g} excitation cross section of N{sub 2} presented a resonantlike structure which would also be expected in the A {sup 1}{pi} excitation of CO. We discuss possible reasons for the disagreement between experiment and theory.

  12. 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

  13. 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

  14. 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.

  15. 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)

  16. 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

  17. Ligand structure, conformational dynamics, and excited-state electron delocalization for control of photoinduced electron transfer rates in synthetic donor-bridge-acceptor systems.

    PubMed

    Meylemans, Heather A; Lei, Chi-Fong; Damrauer, Niels H

    2008-05-19

    Synthesis, ground-, and excited-state properties are reported for two new electron donor-bridge-acceptor (D-B-A) molecules and two new photophysical model complexes. The D-B-A molecules are [Ru(bpy)2(bpy-phi-MV)](PF6)4 (3) and [Ru(tmb)2(bpy-phi-MV)](PF6)4 (4), where bpy is 2,2'-bipyridine, tmb is 4,4',5,5'-tetramethyl-2,2'-bipyridine, MV is methyl viologen, and phi is a phenylene spacer. Their model complexes are [Ru(bpy)2(p-tol-bpy)](PF6)2 (1) and [Ru(tmb)2(p-tol-bpy)](PF6)2 (2), where p-tolyl-bpy is 4-(p-tolyl)-2,2'-bipyridine. Photophysical characterization of 1 and 2 indicates that 2.17 eV and 2.12 eV are stored in their respective (3)MLCT (metal-to-ligand charge transfer) excited state. These values along with electrochemical measurements show that photoinduced electron transfer (D*-B-A-->D (+)-B-A(-)) is favorable in 3 and 4 with DeltaG degrees(ET)=-0.52 eV and -0.62 eV, respectively. The driving force for the reverse process (D(+)-B-A(-) --> D-B-A) is also reported: DeltaG degrees(BET)=-1.7 eV for 3 and -1.5 eV for 4. Transient absorption (TA) spectra for 3 and 4 in 298 K acetonitrile provide evidence that reduced methyl viologen is observable at 50 ps following excitation. Detailed TA kinetics confirm this, and the data are fit to a model to determine both forward (k(ET)) and back (k(BET)) electron transfer rate constants: k(ET)=2.6 x 10(10) s(-1) for 3 and 2.8 x 10(10) s(-1) for 4; k(BET)=0.62 x 10(10) s(-1) for 3 and 1.37 x 10(10) s(-1) for 4. The similar rate constants k ET for 3 and 4 despite a 100 meV driving force (DeltaG degrees(ET)) increase suggests that forward electron transfer in these molecules in room temperature acetonitrile is nearly barrierless as predicted by the Marcus theory. The reduction in electron transfer reorganization energy necessary for this barrierless reactivity is attributed to excited-state electron delocalization in the (3)MLCT excited states of 3 and 4, an effect that is made possible by excited-state conformational

  18. Electron (positron) impact excitation (2p state) of lithium at intermediate energies

    NASA Astrophysics Data System (ADS)

    Kamali, M. Z. M.; Chin, J. H.; Ng, S. Y.; Ratnavelu, Kuru

    2014-03-01

    In this work, studies have been carried out to investigate theoretically the electron (positron)-impact-induced 2s → 2p lithium (Li) transition at 20 and 60 eV using the coupled-channel optical method (CCOM). The inelastic differential cross sections (DCS) together with the reduced Stokes parameters (bar{P1}, bar{P2}, bar{P3}) and other parameters such as the alignment (γ, bar{Pl}), orientation (L⊥) and coherence parameters (P+) are reported in the present calculations. Comparison is made with other available theoretical and experimental measurements. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.

  19. Effect of Size and Structure on the Ground-State and Excited-State Electronic Structure of TiO2 Nanoparticles.

    PubMed

    Cho, Daeheum; Ko, Kyoung Chul; Lamiel-García, Oriol; Bromley, Stefan T; Lee, Jin Yong; Illas, Francesc

    2016-08-01

    We investigated the influence of size and structure on the electronic structure of TiO2 nanoparticles 0.5-3.2 nm in diameter, in both vacuum and water, using density functional theory (DFT) calculations. Specifically, we tracked the optical and electronic energy gap of a set of (TiO2)n nanoparticles ranging from small non-bulklike clusters with n = 4, 8, and 16, to larger nanoparticles derived from the anatase bulk crystal with n = 35 and 84. As the difference between these two energy gaps (the exciton binding energy) becomes negligible in the bulk, this magnitude provides an indicator of the bulklike character of the electronic structure of the nanoparticles under study. Extrapolating our results to larger sizes, we obtain a rough estimate of the nanoparticle size at which the electronic structure will begin to be effectively bulklike. Our results generally confirmed that the electronic structure of the nanoparticle ground state and excited state has a more pronounced structure dependency than size dependency within a size range of 0.5-1.5 nm. We also showed that the thermodynamic preference for the photocatalytic species is the first S1 exciton. This S1 exciton is stable under vacuum but may evolve to free charge carriers upon structural relaxation in an aqueous environment for particles 0.5-1.5 nm in size studied in the present article. An analysis of ionization potentials and electron affinities, relative to the standard reduction potential for the water splitting half-reactions, revealed the importance of considering the structural relaxation in the excited states and the presence of water for assessing the thermodynamic conditions for photocatalytic water splitting. PMID:27379415

  20. 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

  1. Density functional theory calculations on rhodamine B and pinacyanol chloride. Optimized ground state, dipole moment, vertical ionization potential, adiabatic electron affinity and lowest excited triplet state.

    PubMed

    Delgado, Juan C; Selsby, Ronald G

    2013-01-01

    The ground state configuration of the gas phase cationic dyes pinacyanol chloride and rhodamine B are optimized with HF/6-311 + G(2d,2p) method and basis set. B3PW91/6-311 + G(2df,2p) functional and basis set is used to calculate the Mulliken atom charge distribution, total molecular energy, the dipole moment, the vertical ionization potential, the adiabatic electron affinity and the lowest excited triplet state, the last three as an energy difference between separately calculated open shell and ground states. The triplet and extra electron states are optimized to find the relaxation energy. In the ground state optimization of both dyes the chloride anion migrates to a position near the center of the chromophore. For rhodamine B the benzoidal group turns perpendicular to the chromophore plane. For both dyes, the LUMO is mostly of π character associated with the aromatic part of the molecule containing the chromophore. The highest occupied MOs consist of three almost degenerate eigenvectors involving the chloride anion coordinated with σ electrons in the molecular framework. The fourth highest MO is of π character. For both molecules in the gas phase ionization process the chloride anion loses the significant fraction of electric charge. In electron capture, the excess charge goes mainly on the dye cation. PMID:22891949

  2. Low-energy electron-impact excitation of the sup 3,1 A sub 2 ( n r arrow. pi. sup * ) states of formaldehyde

    SciTech Connect

    Sun, Q.; Winstead, C.; McKoy, V. ); Germano, J.S.E. ); Lima, M.A.P. )

    1992-09-01

    A three-state calculation of electron-impact excitation of formaldehyde to the {ital {tilde a}} {sup 3}{ital A}{sub 2} and {ital {tilde A}} {sup 1}{ital A}{sub 2} states is carried out using the Schwinger multichannel variational method. The integral and differential cross sections so obtained agree fairly well with theoretical results obtained using the complex Kohn method. Though agreement between the calculated integral cross section and the single available experimental measurement is qualitative, similar conclusions regarding the excitation mechanism are reached. A generalization of the selection rule for ({Sigma}{sup +}{leftrightarrow}{Sigma}{sup {minus}}) electron-impact excitation of diatomic molecules is used to explain the shape of the differential cross sections for the {ital {tilde a}} {sup 3}{ital A}{sub 2} and {ital {tilde A}} {sup 1}{ital A}{sub 2} excitations.

  3. 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.

  4. 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.

  5. Electron paramagnetic resonance determination of a low-lying excited state in Chromatium vinosum high-potential iron protein.

    PubMed Central

    Blum, H; Salerno, J C; Prince, R C; Leigh, J S; Ohnishi, T

    1977-01-01

    The temperature dependence of the EPR spectrum of oxidized high-potential iron protein from Chromatium vinosum has been studied. From line width and intensity measurements it is possible to determine the position of the first excited unoccupied state, 160 +/- 10 cm-1 above the ground state orbital. PMID:198036

  6. Hydrogen bonding and coordination bonding in the electronically excited states of Cu2(L)2 (L = 5-(4-pyridyl)tetrazole)MeOH: A TDDFT study

    NASA Astrophysics Data System (ADS)

    Meng, Yanfang; Zhang, Chunqing; Ji, Min; Hao, Ce; Qiu, Jieshan

    2013-05-01

    The luminescent metal organic framework (MOF), Cu2(L)2·MeOH (L = 5-(4-pyridyl)tetrazole), was studied using time-dependent density functional theory (TDDFT). A combination of frontier molecular orbitals and electronic configuration analysis revealed that the emission mechanism was a ligand to metal charge transition (LMCT) rather than a metal to ligand charge transfer (MLCT). Hydrogen bonding significantly changed the nature of the frontier orbital and the luminescence. Electronic transition energies predicted that the hydrogen bonding in excited state would become weaker with an electronic spectral blue-shift. The bond lengths, frequencies, and binding energies indicated weakening of the hydrogen bonding in the excited state, which can affect emissions in two ways, including: (i) a decrease in the electronic coupling between methanol and the motif and suppressing the occurrence of the photo-induced electron transfer (PET); and (ii) increasing the energy gap between S1 and S0, leading to radiative transition. Coordination bonding was also investigated in the excited state through bond lengths, frequencies, and bond orders. Coordination bonds were found to become stronger in the excited state leading to an enhancement of the luminescence.

  7. LETTER TO THE EDITOR: The validity of classical trajectory and perturbative quantal methods for electron-impact ionization from excited states in H-like ions

    NASA Astrophysics Data System (ADS)

    Griffin, D. C.; Ballance, C. P.; Pindzola, M. S.; Robicheaux, F.; Loch, S. D.; Ludlow, J. A.; Witthoeft, M. C.; Colgan, J.; Fontes, C. J.; Schultz, D. R.

    2005-06-01

    To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from excited states in H, Li2+ and B4+ using the R-matrix with pseudo states and the time-dependent close-coupling methods. Comparisons with our classical trajectory Monte Carlo (CTMC) and distorted-wave (DW) calculations show that the CTMC method is more accurate than the DW method for H, but does not improve with n and grows substantially worse with Z, while the DW method improves with Z and grows worse with n.

  8. Potential energy curves and dipole transition moments for excited electronic states of XeKr and ArNe

    NASA Astrophysics Data System (ADS)

    Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula; Liebermann, Heinz-Peter; Buenker, Robert J.

    2002-08-01

    Relativistic core-potential calculations have been carried out on Omega states resulting from the interaction of Xe* (5p56s, 3P, 1)P with ground-state Kr atoms as well as for the system Ar* (3p54s, 3P, 1)P with ground-state Ne, using different basis sets and configuration interaction procedures. The present calculations on ArNe, employing larger sets of Rydberg functions than those of the previous calculations, yield totally repulsive potentials for the excited states of ArNe. Similar calculations on XeKr obtain shallow minima (600-860 cm-1) in the potential energy curves of the excited states at large internuclear distances (6.9-7.8 bohr). Dipole transition moments have been calculated and strong radiative transitions are predicted from excited states to the ground state. The 1(I) state, correlating with the metastable 3P2 state of Xe is found to have a small but nonzero dipole transition moment at short and intermediate nuclear distances leading to a radiative lifetime for the v=0 level of this state of 21.0 mus.

  9. Femtosecond Timescale Evolution of Pyrrole Electronic Excitation

    NASA Astrophysics Data System (ADS)

    Montero, Raul; Conde, Alvaro Peralta; Ovejas, Virginia; Castano, Fernando; Longarte, Asier

    2012-06-01

    Pyrrole is a simple aromatic molecule with relevantchromophoric properties in biology. Although its apparent simplicity, it shows a complicated dynamics after excitation in the near part of the UV absorption spectrum, which results from the interplay between the bright ππ^* and the dark dissociative πσ^* electronic transitions. Herein, we present a time resolved study with ultrafast resolution on the relaxation dynamics of isolated pyrrole, after excitation in the 265-217 nm range. Two lifetimes of 19 and 15 fs, which are associated with the internal conversion from the bright 1B2 ππ^* state and the propagation of the wavepacket on the πσ^* state, respectively, are found in the studied energy interval. The work also explores the consequences of non resonant adiabatic excitation of the system when broadband femtosecond pulses are employed to prepare the molecule in the targeted electronic states, revealing the key implication of this type of coherent phenomena. The collected data reveal that the bright 1B2 ππ^* state is adiabatically populated at excitation wavelengths far away from resonance, providing an efficient way to reach the πσ^* state. The recorded transients are fit employing a coherent model that provides a comprehensive view of the dynamical processes pyrrole undergoes after excitation by ultrashort light pulses. M. N. R. Ashfold, B. Cronin, A. L. Devine, R. N. Dixon and M. G. D. Nix Science, 312, 1637-1640, 2006.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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 AlxGa1-xP and AlxGa1-xAs 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.

  12. Solving the electron and electron-nuclear Schrodinger equations for the excited states of helium atom with the free iterative-complement-interaction method.

    PubMed

    Nakashima, Hiroyuki; Hijikata, Yuh; Nakatsuji, Hiroshi

    2008-04-21

    Very accurate variational calculations with the free iterative-complement-interaction (ICI) method for solving the Schrodinger equation were performed for the 1sNs singlet and triplet excited states of helium atom up to N=24. This is the first extensive applications of the free ICI method to the calculations of excited states to very high levels. We performed the calculations with the fixed-nucleus Hamiltonian and moving-nucleus Hamiltonian. The latter case is the Schrodinger equation for the electron-nuclear Hamiltonian and includes the quantum effect of nuclear motion. This solution corresponds to the nonrelativistic limit and reproduced the experimental values up to five decimal figures. The small differences from the experimental values are not at all the theoretical errors but represent the physical effects that are not included in the present calculations, such as relativistic effect, quantum electrodynamic effect, and even the experimental errors. The present calculations constitute a small step toward the accurately predictive quantum chemistry. PMID:18433191

  13. 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.

  14. 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

  15. Measurement of the Total Cross Section for Excitation of the 2p State of Atomic Hydrogen by Electron Impact

    NASA Astrophysics Data System (ADS)

    James, Geoffrey

    1996-10-01

    The excitation function of prompt Lyman-α radiation, produced by electron impact excitation of atomic hydrogen in the energy range from threshold to 1.8keV, has been measured in a crossed-beam experiment footnote This work was performed in collaboration with J.A.Slevin, D.E.Shemansky, J.W.McConkey, D.Dziczek, I.Kanik and J.M.Ajello. Measurements were carried out using both magnetically confined and electrostatically focused electron beams in collision with atomic hydrogen produced by an intense discharge source. A vacuum ultraviolet monochromator was used to measure the emitted Lyman-α radiation. The absolute H (1s - 2p) cross section was obtained from the experimental excitation function by normalization to the known oscillator strength, with appropriate corrections for polarization and cascade. The present data are significantly different from earlier experimental results footnote R.L.Long, D.M.Cox and S.J.Smith, J.Res.Nat.Bur.Stand.Sect.A:Phys. Chem. 72A, 521 (1968) footnote J.F.Williams, J.Phys.B.:At.Mol.Opt.Phys. 14, 1197 (1981) and are in good agreement with recent theoretical convergent close coupling calculations footnote I.Bray, private communication (1996) over a two order of magnitude range in impact energy. Multistate coupling affecting the excitation function to 1keV is apparent in both the present experimental and recent theoretical results.

  16. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  18. 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+.

  19. Application of the Schwinger multichannel formulation to electron-impact excitation of the b 3Sigma(+) state of CO

    NASA Technical Reports Server (NTRS)

    Weatherford, Charles A.; Huo, Winifred M.

    1990-01-01

    The Chi 1Sigma - b 3Sigma(+) transition of CO is described using the Schwinger multichannel method in the two-state approximation, in an energy range from threshold to 20 eV. The resonance structure is analyzed by performing a partial-wave decomposition and the resonance positions are established based on the typical discontinuous behavior in the K-matrix elements as well as the pi radian change in the partial-wave eigenphases. The resonance behavior is related to the concept of core-excited resonances and the 'grandparent' model of resonances. The results are related to the formation of the negative ion by carrying out bound-state calculations on the (5 sigma)(3 s sigma)-squared core-excited Rydberg state of CO(-), and the position is found to agree well with the low-energy resonance positions.

  20. Theoretical study of the excited states of the photosynthetic reaction center in photosystem II: electronic structure, interactions, and their origin.

    PubMed

    Kitagawa, Yuya; Matsuda, Kenji; Hasegawa, Jun-ya

    2011-12-01

    The excited states of the chlorophyll 6-mer in the photosystem II (PSII) reaction center (RC) were investigated theoretically using ab initio quantum chemical calculations, and the results are compared with those of the bacterial reaction center (bRC). A significant difference in the peak at the lowest energy in the absorption spectra arises from the structural asymmetry of the special pair (SP). The origin can be traced back to the structural difference in the CD helix. The low-lying excited states are characterized as a linear combination of the excited states of the chlorophyll monomers, which verifies the applicability of exciton theory. Analysis of the molecular interactions clearly explains the cause of the constructive/destructive interferences in the state transition moment. The protein electrostatic potential (ESP) decreases the energy of the charge-transfer (Chl(D1)→Pheo(D1)) state. The ESP also localizes the HOMO distribution to the P(D1) moiety and increases the ionization potential. PMID:21816534

  1. 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

  2. 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.

  3. 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.

  4. Electronic and vibronic states of the acceptor-bound-exciton complex (A0,X) in CdS. II. Determination of the fine structure of the (A0,XB) electronic states by high-resolution excitation spectroscopy

    NASA Astrophysics Data System (ADS)

    Gutowski, J.

    1985-03-01

    In a previous paper [R. Baumert, I. Broser, J. Gutowski, and A. Hoffman, Phys. Rev. B 27, 6263 (1983)] it has been shown that high-density, high-resolution excitation spectroscopy gives new information on the electronic and vibronic excited states of the acceptor-bound-exciton complex (A0,XA) with two holes from the A valence band in CdS. We now report on corresponding results for the (A0,XB) configuration which includes one hole from the second B valence band. This complex is unstable for a very fast B-->A hole conversion, and therefore gives rise to a set of excitation resonances of the I1 luminescence arising from the (A0,XA) recombination. A detailed theoretical analysis of the energetic structure of the (A0,XB) complex including the dependence on the excitation intensity and on an applied magnetic field allows the correct assignment of the excitation resonances to the (A0,XB) fine-structure levels originating from the interparticle-exchange interactions. It is shown that the magnetic field is a suitable means of distinguishing the different (A0,XB) ground-state levels. The magnetic field also creates allowed transitions which are dipole forbidden in the zero-field case. A self-contained model of the (A0,XB) complex thus can be developed, including all symmetry states and yielding adequate values for the exchange energies within the complex.

  5. Heavy atom nitroxyl radicals. I: An ab initio study of the ground and lower electronic excited states of the H2As=O free radical

    NASA Astrophysics Data System (ADS)

    Tarroni, Riccardo; Clouthier, Dennis J.

    2009-09-01

    A series of ab initio calculations have been undertaken to predict the spectroscopic properties of the ground and first two excited states of the recently discovered arsenyl (H2AsO) free radical. This 13 valence electron species can be viewed as similar to the formaldehyde radical anion with a ground state electron configuration of ⋯(π)2(n)2(π∗)1. The arsenyl radical is nonplanar (pyramidal) in the ground state with a 59° out-of-plane angle and a 1.67 Å AsO bond length. It has a low-lying n-π ∗(Ã A2″) excited state (Te˜5000 cm-1) which has a much larger out-of-plane angle (86°) and longer AsO bond length (1.81 Å). The π-π ∗(B˜ A2') excited state at ˜20 500 cm-1 is less pyramidal (out-of-plane angle=70°) and has a somewhat shorter AsO bond (1.77 Å). Similar trends are found for the H2PO and H2NO free radicals, although the latter has a planar ground state, due to sp2 hybridization of the N atom, and a very long B˜ state AsO bond length. The geometric variations of the ground and excited states of the H2EO (E=N, P, As) radicals, as well as the ground states of the corresponding anions and cations, can be readily rationalized from the Walsh diagram of the anion. The variations in the E-O bond length are a result of changes in both the orbital occupancy and pyramidalization of the molecule. The results of the present work have been employed in the analysis of the B˜ A2'-X˜ A2' electronic band system of the H2AsO free radical as reported in the companion paper.

  6. Geometric and electronic structure of ground and excited states of group VA diatomics. A theoretical LCGTO-MP-LSD study

    NASA Astrophysics Data System (ADS)

    Toscano, M.; Russo, N.

    1992-12-01

    LCGTO-MP-LSD calculation was performed for the ground and several low-lying excited states of homo- (N2, P2, As2, and Sb2) and hetero-nuclear (PN, AsN, AsP, AsSb, SbN, and SbP) group VA diatomics. For all the systems the ground state is found to be1Σ+. For N2 and P2, the1Σ{/g +} ground state is followed by the3Σ{/u +},3Π g ,3Δ u ,1Π g , and1Δ u low-lying exited states while for As2 the order is found to be3Σ{/u +},3Δ u ,3Π g ,1Δ u ,1Π g . Finally for Sb2 the relative stability of excited states is3Σ{/u +},3Δ u ,1Δ u ,3Π g ,1Π g . For the hetero-nuclear diatomics the1Σ+ ground state is, in the case of PN, AsN, AsP, SbN, and SbP, followed by the3Σ+,3Δ,3Π,1Π and1Δ low-lying excited states while for the AsSb diatomic an inversion of stability of the two last singlets occurs. The calculated spectroscopic parameters ( Re, ω e, and De) are in good agreement with all the available experimental results while, the Te values are overestimated by about 0.5 eV. Mulliken population analysis shows that both homo- and hetero-nuclear group VA diatomics are essentially triple bonded systems.

  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. Two-temperature equation of state for aluminum and gold with electrons excited by an ultrashort laser pulse

    NASA Astrophysics Data System (ADS)

    Petrov, Yu. V.; Migdal, K. P.; Inogamov, N. A.; Zhakhovsky, V. V.

    2015-06-01

    A short laser pulse converts metal into a two-temperature state with the electron temperature higher than the ion temperature. To describe the electron contributions to the total internal energy and pressure arising as a result of electron heating, we develop the new analytic approximation formulae for two-temperature thermodynamics of metal. Those approximations are based on quantum calculations performed with density functional theory (DFT) packages. DFT calculations provide the internal energies and pressures for densities of the order of solid-state density and for electron temperatures up to 55 kK. The new analytic approximations give a better accuracy in hydrodynamic simulation of laser-matter interaction and should be used instead of the less accurate expressions based on the Fermi model of ideal electron gas, which is widely used for two-temperature states of metal.

  9. Excited electronic state decomposition of furazan based energetic materials: 3,3'-diamino-4,4'-azoxyfurazan and its model systems, diaminofurazan and furazan

    NASA Astrophysics Data System (ADS)

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

    2008-01-01

    We report the first experimental and theoretical study of gas phase excited electronic state decomposition of a furazan based, high nitrogen content energetic material, 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and its model systems, diaminofurazan (DAF) and furazan (C2H2N2O). DAAF has received major attention as an insensitive high energy explosive; however, the mechanism and dynamics of the decomposition of this material are not clear yet. In order to understand the initial decomposition mechanism of DAAF and those of its model systems, nanosecond energy resolved and femtosecond time resolved spectroscopies and complete active space self-consistent field (CASSCF) calculations have been employed to investigate the excited electronic state decomposition of these materials. The NO molecule is observed as an initial decomposition product from DAAF and its model systems at three UV excitation wavelengths (226, 236, and 248nm) with a pulse duration of 8ns. Energies of the three excitation wavelengths coincide with the (0-0), (0-1), and (0-2) vibronic bands of the NO A∑+2←X∏2 electronic transition, respectively. A unique excitation wavelength independent dissociation channel is observed for DAAF, which generates the NO product with a rotationally cold (20K ) and a vibrationally hot (1265K) distribution. On the contrary, excitation wavelength dependent dissociation channels are observed for the model systems, which generate the NO product with both rotationally cold and hot distributions depending on the excitation wavelengths. Potential energy surface calculations at the CASSCF level of theory illustrates that two conical intersections between the excited and ground electronic states are involved in two different excitation wavelength dependent dissociation channels for the model systems. Femtosecond pump-probe experiments at 226nm reveal that the NO molecule is still the main observed decomposition product from the materials of interest and that the formation

  10. Excited electronic state decomposition of furazan based energetic materials: 3,3'-diamino-4,4'-azoxyfurazan and its model systems, diaminofurazan and furazan.

    PubMed

    Guo, Y Q; Bhattacharya, A; Bernstein, E R

    2008-01-21

    We report the first experimental and theoretical study of gas phase excited electronic state decomposition of a furazan based, high nitrogen content energetic material, 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and its model systems, diaminofurazan (DAF) and furazan (C2H2N2O). DAAF has received major attention as an insensitive high energy explosive; however, the mechanism and dynamics of the decomposition of this material are not clear yet. In order to understand the initial decomposition mechanism of DAAF and those of its model systems, nanosecond energy resolved and femtosecond time resolved spectroscopies and complete active space self-consistent field (CASSCF) calculations have been employed to investigate the excited electronic state decomposition of these materials. The NO molecule is observed as an initial decomposition product from DAAF and its model systems at three UV excitation wavelengths (226, 236, and 248 nm) with a pulse duration of 8 ns. Energies of the three excitation wavelengths coincide with the (0-0), (0-1), and (0-2) vibronic bands of the NO A 2Sigma+<--X 2Pi electronic transition, respectively. A unique excitation wavelength independent dissociation channel is observed for DAAF, which generates the NO product with a rotationally cold (20 K) and a vibrationally hot (1265 K) distribution. On the contrary, excitation wavelength dependent dissociation channels are observed for the model systems, which generate the NO product with both rotationally cold and hot distributions depending on the excitation wavelengths. Potential energy surface calculations at the CASSCF level of theory illustrates that two conical intersections between the excited and ground electronic states are involved in two different excitation wavelength dependent dissociation channels for the model systems. Femtosecond pump-probe experiments at 226 nm reveal that the NO molecule is still the main observed decomposition product from the materials of interest and that the formation

  11. Stepwise Two-Photon-Induced Fast Photoswitching via Electron Transfer in Higher Excited States of Photochromic Imidazole Dimer.

    PubMed

    Kobayashi, Yoichi; Katayama, Tetsuro; Yamane, Takuya; Setoura, Kenji; Ito, Syoji; Miyasaka, Hiroshi; Abe, Jiro

    2016-05-11

    Stepwise two-photon excitations have been attracting much interest because of their much lower power thresholds compared with simultaneous two-photon processes and because some stepwise two-photon processes can be initiated by a weak incoherent excitation light source. Here we apply stepwise two-photon optical processes to the photochromic bridged imidazole dimer, whose solution instantly changes color upon UV irradiation and quickly reverts to the initial color thermally at room temperature. We synthesized a zinc tetraphenylporphyrin (ZnTPP)-substituted bridged imidazole dimer, and wide ranges of time-resolved spectroscopic studies revealed that a ZnTPP-linked bridged imidazole dimer shows efficient visible stepwise two-photon-induced photochromic reactions upon excitation at the porphyrin moiety. The fast photoswitching property combined with stepwise two-photon processes is important not only for the potential for novel photochromic materials that are sensitive to the incident light intensity but also for fundamental photochemistry using higher excited states. PMID:27088169

  12. 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.

  13. 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

  14. 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%.

  15. 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)].

  16. 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.

  17. Electron-impact excitation of the singlet states of N2. I - The Birge-Hopfield system /b 1 pi u - X 1 Sigma g +/. [in auroral zones

    NASA Technical Reports Server (NTRS)

    Zipf, E. C.; Gorman, M. R.

    1980-01-01

    Results of a study of the electron-impact excitation of the b 1 pi u state of N2, one of the singlet states thought to be excited by precipitating electrons in the auroral zones, and of its predissociation and radiative relaxation through the emission of the Birge-Hopfield band system (b 1 pi u - X 1 Sigma g +) are presented. A collimated electron beam was passed through N2 gas producing a variety of atomic states through dissociative excitation, and the radiation resulting from relaxation of these states was observed by VUV and visible-IR monochromators. Absolute emission cross sections for 11 Birge-Hopfield bands are obtained for energies from threshold to 500 eV, and used to calculate the absolute transition probabilities for BH(1, v-prime) bands and the variation of the electric dipole moment with internuclear distance. With the exception of the v-prime equals 1, 5 and 6 vibrational levels, all b 1 pi u levels are found to predissociate with a specific predissociation branching ratio greater than 0.99, representing a major source of nitrogen atoms.

  18. Nuclear excitation by electronic transition of 235U

    DOE PAGESBeta

    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.

  19. 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

  20. Undulations of the potential-energy curves for highly excited electronic states in diatomic molecules related to the atomic orbital undulations

    NASA Astrophysics Data System (ADS)

    Yiannopoulou, Alexandra; Jeung, Gwang-Hi; Park, Su Jin; Lee, Hyo Sug; Lee, Yoon Sup

    1999-02-01

    We present potential-energy curves for highly excited electronic states of diatomic molecules showing spectacular undulations including multiple barriers and wells. Those undulations unrelated to avoided crossings are closely correlated with the oscillations of atomic radial electron density in the Rydberg states. The LiHe, LiNe, and LiH cases are examined with an accurate quantum chemical calculation. For the Σ+ states originating from the ns, np, nd, or nf states of lithium atom, n-2 potential barriers and the same number of potential wells exist. The 4 1Σ+g(F) state of Li2 also shows the energy barrier of the same origin. This spectroscopic property is supposed to be more general in diatomic molecules and other small molecules.

  1. 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.

  2. 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…

  3. 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.

  4. One-electron oxidation of alcohols by the 1,3,5-trimethoxybenzene radical cation in the excited state during two-color two-laser flash photolysis.

    PubMed

    Cai, Xichen; Sakamoto, Masanori; Fujitsuka, Mamoru; Majima, Tetsuro

    2007-03-15

    One-electron oxidation of alcohols such as methanol, ethanol, and 2-propanol by 1,3,5-trimethoxybenzene radical cation (TMB*+) in the excited state (TMB*+*) was observed during the two-color two-laser flash photolysis. TMB*+ was formed by the photoinduced bimolecular electron-transfer reaction from TMB to 2,3,5,6-tetrachlorobenzoquinone (TCQ) in the triplet excited-state during the first 355-nm laser flash photolysis. Then, TMB*+* was generated from the selective excitation of TMB*+ during the second 532 nm laser flash photolysis. Hole transfer rate constants from TMB*+* to methanol, ethanol, and 2-propanol were calculated to be (5.2 +/- 0.5) x 10(10), (1.4 +/- 0.3) x 10(11), and (3.2 +/- 0.6) x 10(11) M-1 s-1, respectively. The order of the hole transfer rate constants is consistent with oxidation potentials of alcohol. Formation of TCQH radical (TCQH*) with a characteristic absorption peak at 435 nm was observed in the microsecond time scale, suggesting that deprotonation of the alcohol radical cation occurs after the hole transfer and that TCQ radical anion (TCQ*-), generated together with TMB*+ by the photoinduced electron-transfer reaction, reacts with H+ to give TCQH*. PMID:17295459

  5. 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.

  6. The electronic couplings in electron transfer and excitation energy transfer.

    PubMed

    Hsu, Chao-Ping

    2009-04-21

    The transport of charge via electrons and the transport of excitation energy via excitons are two processes of fundamental importance in diverse areas of research. Characterization of electron transfer (ET) and excitation energy transfer (EET) rates are essential for a full understanding of, for instance, biological systems (such as respiration and photosynthesis) and opto-electronic devices (which interconvert electric and light energy). In this Account, we examine one of the parameters, the electronic coupling factor, for which reliable values are critical in determining transfer rates. Although ET and EET are different processes, many strategies for calculating the couplings share common themes. We emphasize the similarities in basic assumptions between the computational methods for the ET and EET couplings, examine the differences, and summarize the properties, advantages, and limits of the different computational methods. The electronic coupling factor is an off-diagonal Hamiltonian matrix element between the initial and final diabatic states in the transport processes. ET coupling is essentially the interaction of the two molecular orbitals (MOs) where the electron occupancy is changed. Singlet excitation energy transfer (SEET), however, contains a Frster dipole-dipole coupling as its most important constituent. Triplet excitation energy transfer (TEET) involves an exchange of two electrons of different spin and energy; thus, it is like an overlap interaction of two pairs of MOs. Strategies for calculating ET and EET couplings can be classified as (1) energy-gap-based approaches, (2) direct calculation of the off-diagonal matrix elements, or (3) use of an additional operator to describe the extent of charge or excitation localization and to calculate the coupling value. Some of the difficulties in calculating the couplings were recently resolved. Methods were developed to remove the nondynamical correlation problem from the highly precise coupled cluster

  7. Nonradiative Decay Pathways of the First Excited Electronic States of 1:1 Hydrogen Bonded Complexes of 7-AZAINDOLE with Phenol and Formamide

    NASA Astrophysics Data System (ADS)

    Mukherjee, Moitrayee; Mukhopadhyay, Anamika; Chakraborty, Tapas

    2009-06-01

    On UV excitation, the monomer and doubly hydrogen-bonded homodimer of 7-azaindole decay via two radically different photophysical pathways. While the monomer emits intense UV fluorescence, the dimer undergoes ultrafast nonradiative relaxation to a tautomeric configuration and emits green fluorescence. The latter channel is also preferred by the complexes of 7-azaindole with aliphatic alcohols, and the propensity of the tautomerization process is determined by acidity of the alcohols. In contrast, we report here that in spite of being a stronger acid the aromatic alcohol phenol hinders the said tautomerization in a 1:1 complex environment, and the excitation energy is funnelled through a new nonradiative decay channel. We also have measured the medium effect on the process, and propose a mechanism for relaxation of the locally excited state in terms of electronic energy transfer coupled with proton transfer between the two dimer moieties. On the other hand, in case of 7-azaindole-formatide 1:1 complex, sharp bands in the gas phase fluorescence excitation spectrum are displayed only for excitations with about 200 cm^{-1} excess vibronic energy. The medium effect of the onset of the nonradiative decay process has been probed by performing the measurement in a cyclohexane solution at room temperature. The details of the finding will be presented in the talk.

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

    PubMed

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

    2016-05-14

    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. PMID:27179467

  9. 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.

  10. Electron-Phonon Coupling and CT-Character in the lowest Triplet Excited State of Anthracene EDA-Complex Crystals

    NASA Astrophysics Data System (ADS)

    Maier, S.; Port, H.

    1987-11-01

    Photoexcitation spectra of triplet (T1← S0) zero-phonon lines and phonon sidebands in different anthracene electron donor-acceptor (EDA) complex crystals (A-PMDA, A-TCNB, A-TCPA) have been analyzed between 1.3 K and 50 K at high spectral resolution. From the electron-phonon coupling strength at T = 0 K values of the charge-transfer (CT) character in the range between 6% and 10% are calculated. The differences in these values are found to be correlated with the energetic positions of the triplet state, which are explained within the framework of the Mulliken theory.

  11. Excited-state absorption and third-order optical nonlinearities in symmetric π-electron organic molecules

    NASA Astrophysics Data System (ADS)

    Williams, G. R. J.

    1996-07-01

    Excited-State Absorption (ESA), Two-Photon Absorption (TPA) and the third-order polarizability γ(ω;ω,ω, - ω) have been investigated for a model dichloride derivative of a symmetrically substituted benzylidene analine (SBAC), using a multielectron configuration-interaction procedure. The calculations indicate that SBAC exhibits ESA across the visible region of the spectrum, but that it is not as extensive as for molecules such as the phthalocyanines. The magnitude of the third-order polarizability is dominated by resonance enhancement from a very strong A g → B u one-photon absorption. The calculated off-resonance value for γ(ω;ω,ω, - ω) suggests that SBAC is a potential candidate for ultrafast switching applications.

  12. a. Structural Perturbations of the Electronic Excited States of Zinc Complexes. B. Construction of a Thermal Modulation Emission Apparatus.

    NASA Astrophysics Data System (ADS)

    Jordan, Kevin James

    Zinc(II) complexes containing both 2,9-dimethyl -1,10,-phenanthroline and substituted benzenethiol ligands were found to crystallize in different phases. Subtle changes in emission lifetimes and bandshapes recorded over periods of months from the same batch were manifestations of slow interphase conversions. Heating the crystals to near their melting points generated the unique high temperature phases. Two phases of the benzenethiol complex were characterized by x-ray crystallography. The 2500 cm^ {-1} energy difference between the peak of the 77 K emission from the ligand-ligand charge-transfer (LLCT) transition in the two phases was considered to arise from the sensitivities of the donor orbitals to rotation of the benzene rings about the sulfur-carbon bonds. The energy of the ^3pipi^ * emission from the nitrogen heterocycle was found to be insensitive both to complexation with Zn(II) and to the presence of the LLCT transitions. The intensity decrease of the ^3pipi^ * phosphorescence in alcoholic glasses with UV exposure was related to the generation of free radicals. Multiple LLCT lifetimes and emission bands with the longer-lived components at higher energies were found in the rigid glasses. LLCT emissions from an analogous dithiol complex revealed similar characteristics. Also the relative intensities of the LLCT components were independent of excitation wavelength. These results indicated that the multiple emissions were not attributable to multiple geometrical conformations. Thermally -modulated emission (TME) spectra were obtained from compounds dispersed in rigid glasses. For bis(cis-1,2-bis(diphenylphosphino)ethylene)Rh(I) perchlorate the maximum temperature excursion was 3.5 and 4.5 K for the resistive and infra-red absorption heating methods respectively. The TME spectrum of crystalline (Cr(urea)_6) Cl_3 .3H_2O demonstrated the technique's advantages for the vibronic analysis of emissions from near-degenerate excited states. The negative signal of the

  13. 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.

  14. 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. PMID:27179479

  15. 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.

  16. Electron-impact excitation of neon

    NASA Astrophysics Data System (ADS)

    Ballance, Connor; Griffin, Don

    2004-05-01

    A number of convergent close-coupling and R-matrix with pseudo-state (RMPS) calculations on H-like, He-like, Li-like, and Be-like ions have demonstrated that coupling to the target continuum can have large effects on the electron-impact excitation cross sections of neutral and low-charge species. However, no one has yet attempted such advanced calculations on a system as complex as neutral neon. We report on a series of RMPS calculations of electron-impact excitation of Ne using recently developed parallel Breit-Pauli (BP) R-matrix programs. Our largest calculation was a BP calculation with 235 spectroscopic and pseudo levels in the close-coupling expansion. Although the results of this calculation clearly reveal the importance of coupling to the target continuum in this atom, the pseudo-state expansion is not yet sufficiently complete to provide reliable cross sections for energies above the ionization limit. However, this is the largest BP calculation that can be performed with present computer resources. Thus, we have also carried out a series of RMPS calculations in LS coupling with different pseudo-state expansions. Comparisons of these results have allowed us to determine the approximate size of the pseudo-state expansion required to achieve convergence in future BP calculations for neon.

  17. State-selective vibrational excitation and dissociation of H2+ by strong infrared laser pulses: below-resonant versus resonant laser fields and electron-field following.

    PubMed

    Paramonov, Guennaddi K; Kühn, Oliver

    2012-11-26

    The quantum dynamics of vibrational excitation and dissociation of H(2)(+) by strong and temporally shaped infrared (IR) laser pulses has been studied on the femtosecond (fs) time scale by numerical solution of the time-dependent Schrödinger equation with explicit treatment of nuclear and electron motion beyond the Born-Oppenheimer approximation. Using sin(2)-shaped laser pulses of 120 fs duration with a peak intensity of I(0) > 10(14) W/cm(2), it has been found that below-resonant vibrational excitation with a laser carrier frequency of ω < ω(10)/2 (where ω(10) is the frequency of the |v = 0> → |v = 1> vibrational transition) is much more efficient than a quasi-resonant vibrational excitation at ω ≈ ω(10). In particular, at the below-resonant laser carrier frequency ω = 0.3641 × 10(-2) au (799.17 cm(-1)), dissociation probabilities of H(2)(+) (15.3% at the end of the 120 fs laser pulse and 21% at t = 240 fs) are more than 3 orders of magnitude higher than those obtained for the quasi-resonant laser frequency ω = 1.013 × 10(-2) au (2223.72 cm(-1)). Probabilities of state-selective population transfer to vibrational states |v = 1>, |v = 2>, and |v = 3> from the vibrational ground state |v = 0> of about 85% have been calculated in the optimal below-resonant cases. The underlying mechanism of the efficient below-resonant vibrational excitation is the electron-field following and simultaneous transfer of energy to the nuclear coordinate. PMID:22916791

  18. Excited S 1 state dipole moments of nitrobenzene and p-nitroaniline from thermochromic effect on electronic absorption spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2006-11-01

    The effect of temperature on the absorption spectra of nitrobenzene (NB) and p-nitroaniline (NA) in 1,2-dichloroethane was studied for temperature ranging from 295 K to 378 K and from 296 K to 408 K, respectively. With temperature increase the absorption bands of both compounds are blue shifted, which is caused by the decrease of permittivity ɛ and refractive index n. From the band shifts and by using the Bilot and Kawski theory [ L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621] the dipole moments in the excited singlet state μe = 6.59 D of NB and μe = 13.35 D of NA were determined. The influence of polarizability α, the Onsager cavity radius a and dipole moment in the ground state μg on the determined values of μe are discussed. A comparison of the obtained μe values with those of other authors is given. In the case of p-NA a strong intramolecular charge transfer (ICT) was confirmed.

  19. Electronic excitation in bulk and nanocrystalline alkali halides.

    PubMed

    Bichoutskaia, Elena; Pyper, Nicholas C

    2012-11-14

    The lowest energy excitations in bulk alkali halides are investigated by considering five different excited state descriptions. It is concluded that excitation transfers one outermost halide electron in the fully ionic ground state to the lowest energy vacant s orbital of one closest cation neighbour to produce the excited state termed dipolar. The excitation energies of seven salts were computed using shell model description of the lattice polarization produced by the effective dipole moment of the excited state neutral halogen-neutral metal pair. Ab initio uncorrelated short-range inter-ionic interactions computed from anion wavefunctions adapted to the in-crystal environment were augmented by short-range electron correlation contributions derived from uniform electron-gas density functional theory. Dispersive attractions including wavefunction overlap damping were introduced using reliable semi-empirical dispersion coefficients. The good agreement between the predicted excitation energies and experiment provides strong evidence that the excited state is dipolar. In alkali halide nanocrystals in which each ionic plane contains only four ions, the Madelung energies are significantly reduced compared with the bulk. This predicts that the corresponding intra-crystal excitation energies in the nanocrystals, where there are two excited states depending on whether the halide electron is transferred to a cation in the same or in the neighbouring plane, will be reduced by almost 2 eV. For such an encapsulated KI crystal, it has been shown that the greater polarization in the excited state of the bulk crystal causes these reductions to be lowered to a 1.1 eV-1.5 eV range for the case of charge transfer to a neighbouring plane. For intra-plane charge transfer the magnitude of the polarization energy is further reduced thus causing the excitation in these encapsulated materials to be only 0.2 eV less than in the bulk crystal. PMID:23163361

  20. 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.

  1. Excited-State Deactivation of Adenine by Electron-Driven Proton-Transfer Reactions in Adenine-Water Clusters: A Computational Study.

    PubMed

    Wu, Xiuxiu; Karsili, Tolga N V; Domcke, Wolfgang

    2016-05-01

    The reactivity of photoexcited 9H-adenine with hydrogen-bonded water molecules in the 9H-adenine-(H2 O)5 cluster is investigated by using ab initio electronic structure methods, focusing on the photoreactivity of the three basic sites of 9H-adenine. The energy profiles of excited-state reaction paths for electron/proton transfer from water to adenine are computed. For two of the three sites, a barrierless or nearly barrierless reaction path towards a low-lying S1 -S0 conical intersection is found. This reaction mechanism, which is specific for adenine in an aqueous environment, can explain the substantially shortened excited-state lifetime of 9H-adenine in water. Depending on the branching ratio of the nonadiabatic dynamics at the S1 -S0 conical intersection, the electron/proton transfer process can enhance the photostability of 9H-adenine in water or can lead to the generation of adenine-H(⋅) and OH(⋅) free radicals. Although the branching ratio is yet unknown, these findings indicate that adenine might have served as a catalyst for energy harvesting by water splitting in the early stages of the evolution of life. PMID:26833826

  2. Electron impact excitation of helium: A polarization correlation study of the 3(1)P state at 40 eV incident energy

    NASA Astrophysics Data System (ADS)

    Harris, Clifford Lee

    The present work reports the development and implementation of an electron scattering apparatus able to investigate a wide range of electron impact processes by coincidence methods. The electron gun is capable of producing a collimated electron beam of approximately 1 μ A throughout an energy range of 30eV to 200eV. A hemispherical electrostatic analyzer is used to collect scattered electrons. It was designed to allow constant energy resolution independent of the scattered energy. The gas target used was an effusive gas jet. The linear and circular polarization state of deexcitation photons emitted perpendicular to the scattering plane can be determined by a vertically mounted polarization analyzer. Polarization analysis of photons emitted in the scattering plane and perpendicular to the incident electron beam direction is also possible. In addition, detection of photons over a wide angular range in the scattering plane is possible. Two automated coincidence data accumulation systems were developed. One is based on a Nucleus PCA card, and the other on a Scientific Solution LabMaster DMA card. Basic modules were written to control Polaroid rotation, and to provide synchronization between data acquisition computers. Custom software packages were developed to provide Pulse-Height Analysis and Multi-Channel Scaling capabilities for the collection of coincidence and energy-loss spectra. The performance of the system has been tested and verified using the polarization correlation technique to study electron impact excitation of He (3 1P) from the ground state. Values of the relative Stokes parameters and the Electron Impact Coherence Parameters over a range of electron scattering angles from 45° to 120°, and at an energy of 40eV, are reported here for the first time. The data are in good agreement with recent predictions of a 111-state convergent close coupling calculation.

  3. 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.

  4. Observation of a new phosphorus-containing reactive intermediate: Electronic spectroscopy and excited-state dynamics of the HPBr free radical

    NASA Astrophysics Data System (ADS)

    Tackett, Brandon S.; Clouthier, Dennis J.

    2005-10-01

    The ÃA'2-X˜A″2 electronic spectra of jet-cooled HPBr and DPBr have been obtained for the first time using the pulsed electric discharge technique with a precursor mixture of PBr3 and H2/D2. Laser-induced fluorescence and single vibronic level emission spectra gave the bending and P-Br stretching frequencies in the ground and excited states of both isotopomers. Rotational analyses of the HPBr and DPBr 000 bands showed small spin splittings characteristic of a doublet-doublet transition of an asymmetric-top molecule. From the ground- and excited-state rotational constants, effective (r0) structures were derived with r″(PH)=1.4307(86)Å, r″(PBr)=2.2021(9)Å, and θ″=95.2(8)°, and r'(PH)=1.434(31)Å, r'(PBr)=2.1669(26)Å, and θ'=115.5(16)°. In a few favorable cases, further hyperfine splitting of the spin-rotation energy levels has been observed, due to the excited-state Fermi contact interaction of the unpaired electron with the spin magnetic moment of the P31 nucleus, with aF'=0.064(9)cm-1 for HPBr. Fluorescence depletion spectroscopy and lifetime measurements indicate that higher vibrational levels of the ÃA'2 state are predissociated by a X˜A″2 dissociative continuum. CCSD(T )/aug-cc-pVTZ calculations predict that the most likely dissociation process is HPBr (X˜A″2)→PH(Σ-3)+Br(Pu2).

  5. 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.

  6. Electronic coupling between photo-excited stacked bases in DNA and RNA strands with emphasis on the bright states initially populated.

    PubMed

    Nielsen, Lisbeth Munksgaard; Hoffmann, Søren Vrønning; Nielsen, Steen Brøndsted

    2013-08-01

    In biology the interplay between multiple light-absorbers gives rise to complex quantum effects such as superposition states that are of extreme importance for life, both for harvesting solar energy and likely protecting nucleic acids from radiation damage. Still the characteristics of these states and their quantum dynamics are a much debated issue. While the electronic properties of single bases are fairly well understood, the situation for strands is complicated by the fact that stacked bases electronically couple when photoexcited. These newly arising states are denoted as exciton states and are simply linear combinations of localised wavefunctions that involve N - 1 ground-state bases and one base in its excited state (cf. the Frenkel exciton model). There is disagreement over the number of bases, N, that coherently couple, i.e., the spatial extent of the exciton, and how electronic deexcitation back to the ground state occurs. The importance of dark charge-transfer states has been inferred both from time-resolved fluorescence and transient absorption experiments. These states were suggested to be responsible for long deexcitation times but it is unclear whether 'long' is tens of picoseconds or nanoseconds. In this review paper, we focus on the bright states initially populated and discuss their nature based on information obtained from systematic absorption and circular dichroism experiments on single strands of different lengths. Our results from the last five years are compared with those from other groups, and are discussed in the context of successive deexcitation schemes. Pieces to the puzzle have come from different experiments and theory but a complete description has yet to emerge. As such the story about DNA/RNA photophysical decay mechanisms resembles the tale about the blind men and the elephant where all see the beast in different, correct but incomplete ways. PMID:23545881

  7. Importance of polarization in quantum mechanics/molecular mechanics descriptions of electronic excited states: NaI(H2O)n photodissociation dynamics as a case study.

    PubMed

    Koch, Denise M; Peslherbe, Gilles H

    2008-01-17

    Sodium iodide has long been a paradigm for ionic and covalent curve crossing and ultrafast nonadiabatic dynamics, and our interest lies in the influence of solvation on this process. The NaI(H2O)n photodissociation dynamics are simulated with the molecular dynamics with quantum transitions method. A quantum mechanics/molecular mechanics (QM/MM) description is adopted for the NaI(H2O)n electronic states, in which a semiempirical valence bond approach is used to describe the NaI electronic structure, and a polarizable optimized potential for cluster simulations model is used to describe solute-solvent and solvent-solvent interactions. In contrast to previous work with a nonpolarizable MM model [Koch et al., J. Phys. Chem. A, 2006, 110, 1438], this approach predicts that the NaI ionic ground- to covalent first-excited-state Franck-Condon energy gaps reach a plateau by cluster size 16, in relatively good agreement with experiment and electronic structure calculations; this allows us to safely extend our previous simulations to larger cluster sizes, i.e., n > 4. The simulations suggest that the disappearance of the two-photon ionization probe signals observed in femtosecond pump-probe experiments of NaI(H2O)n, n >/= 4, is due to the shift of the NaI curve-crossing region toward larger NaI internuclear separations because of solvent stabilization of the NaI ionic state. Further, the latter causes the adiabatic ground and excited states to acquire pure ionic and covalent character, respectively, by cluster 8, resulting in NaI ionic ground-state recombination or dissociation. To make a connection with electron transfer in solution, free energy curves have been generated as a function of a solvent coordinate similar to that of solution theory. Inspection of the free energy curves together with the results of excited-state simulations reveal that the electron-transfer process in clusters is not governed by the collective motion of the solvent molecules, as in solution, but

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

    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{5-[4-(trifluoromethyl)phenyl]thiophen-2-yl}benzene (AC5-CF3), by using extreme-UV excited photoelectron spectroscopy (EUPS). By comparing both EUPS spectra and secondary electron spectra between AC5 and AC5-CF3, we confirm that CF3 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-CF3, 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.

  10. 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.

  11. Electron-impact excitation of holmium atoms

    SciTech Connect

    Smirnov, Yu M

    2000-06-30

    The electron-impact excitation of holmium atoms was studied by the method of extended crossing beams. The cross sections and the optical excitation functions were obtained for odd levels of Ho I, including the 22014 cm{sup -1} laser level. Over 99% of the atoms were shown to reside in the ground level prior to collisions with electrons. Also measured were the excitation cross sections for six even levels, which presumably participate in the formation of inversion population in a gas-discharge holmium vapour laser. (laser applications and other topics in quantum electronics)

  12. Electron impact excitation cross sections for carbon

    NASA Astrophysics Data System (ADS)

    Ganas, P. S.

    1981-04-01

    A realistic analytic atomic independent particle model is used to generate wave functions for the valence and excited states of carbon. Using these wave functions in conjunction with the Born approximation and the Russell-Saunders LS-coupling scheme, we calculate generalized oscillator strengths and integrated cross sections for various excitations from the 2p 2( 3P O) valence state.

  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. Radiative recombination and excited-state photoionization of lithium

    SciTech Connect

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

    1993-11-01

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

  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. PMID:25326834

  16. Intermediate Excited States in Rhodopsin Photochemistry

    NASA Astrophysics Data System (ADS)

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

    1996-03-01

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

  17. 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.

  18. Experimental apparatus for measurements of electron impact excitation

    NASA Technical Reports Server (NTRS)

    Lafyatis, G. P.; Kohl, J. L.; Gardner, L. D.

    1987-01-01

    An ion beam apparatus for the absolute measurement of collision cross sections in singly and multiply charged ions is described. An inclined electron and ion beams arrangement is used. Emitted photons from the decay of collision produced excited states are collected by a mirror and imaged onto a photomultiplier. Absolute measurements of the electron impact excitation of the 2s-2p transition in C(3+) were used to demonstrate the reliability of the apparatus.

  19. Electron impact vibrational excitation of methyl chloride

    NASA Astrophysics Data System (ADS)

    Sakaamini, Ahmad; Hargreaves, Leigh; Khakoo, Murtadha

    2016-05-01

    Low energy differential cross sections and excitation functions for vibrational excitation of CH3 Cl are presented for five vibrational features in the electron energy loss spectrum of this molecule. Electron energies range from 1 eV to 15 eV and scattering angles from 10o to 125o. Results will be compared to existing data for CH3 Cl in the literature. Funded by a NSF-AMOP-RUI Grant.

  20. Double-resonance spectroscopy of radicals: higher electronic excited states of 1- and 2-naphthylmethyl, 1-phenylpropargyl and 9-anthracenylmethyl

    NASA Astrophysics Data System (ADS)

    O'Connor, Gerard D.; Woodhouse, Gabrielle V. G.; Troy, Tyler P.; Schmidt, Timothy W.

    2015-08-01

    Multiple pulsed-laser frequencies are used to extract the excitation spectra of Dn ← D0 transitions (n > 1) of the 1- and 2-naphthylmethyl, 1-phenylpropargyl and 9-anthracenylmethyl radicals. Bands are, respectively, observed at 27993, 27478, 32437 and 25063 cm-1, with respective widths (at half maximum) of 292, 290, 149 and 326 cm-1. On the basis of comparison with ab initio vertical excitation energies, the transitions for 2-naphthylmethyl, 1-phenylpropargyl and 9-anthracenylmethyl radical are assigned as D3 ← D0. The observed transition of 1-naphthylmethyl is ambiguously either or both D3 ← D0 and D4 ← D0. From the wide Lorentzian profiles observed, lifetimes of a few tens of fs are inferred, the spectral widths precluding this class of molecule from being responsible for the long-unidentified diffuse interstellar bands.

  1. Electronic excited-state behavior of rhodamine 3B in AOT reverse micelles sensing contact ion pair to solvent separated ion pair interconversion.

    PubMed

    Ferreira, José A B; Costa, Sílvia M B

    2010-08-19

    The amphiphile Aerosol OT (1,4-bis(2-ethylhexyl)sodium sulfosuccinate, AOT) forms, in reverse micellar nanoaggregates of water, RM, in isooctane, ion pairs (IPs) with the cationic fluorescent probe dye, rhodamine 3B, (3,6-bis(ethylamino)-9-[2-(ethoxycarbonyl)phenyl]-9H-xanthen-9-ylium, R3B), as either contact ion pairs, CIPs, or solvent (water) separated ion pairs, SSIPs. The ground-state AOT R3B ion pairs' equilibria as well as the dynamics of R3B electronic excited states show the progressive hydration of AOT(-) R3B(+) toward solvent separated ion pairs, SSIPs as the characteristic reverse micelle parameter w(0) = [H(2)O]/[AOT] increases. The apparent limiting hydration constant of R3B ion pairs, K(hyd) = 2.8 +/- 0.2, corresponds to full hydration of AOT, consistent with 1-3 water molecules per AOT polar head. Transient relaxations at w(0) = 0.2, with a 375 +/- 15 ps decay at 550 nm decrease to 115 +/- 15 ps at w(0) = 7.2 turning into corresponding rises at 588 nm. At higher w(0), water induced dynamics becomes faster. The lifetime is longer in RM with smaller w(0), due to the presence of CIPs that inhibit intrinsic nonradiative decay processes, which in contrast shorten the decay times at higher w(0), due to the presence of SSIPs. The pairs' electronic excited-state properties are sensitive to viscosity and local polarity of the surrounding environment of the interfacial regions of AOT reverse micellar nanoaggregates. PMID:20666438

  2. Ultrafast excited-state dynamics of isocytosine.

    PubMed

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

    2016-07-27

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

  3. 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. PMID:25381524

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

    NASA Astrophysics Data System (ADS)

    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 2A1 and 2B1 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 2B1 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 2A1 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.

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

    SciTech Connect

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

    2014-11-07

    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 {sup 2}A{sub 1} and {sup 2}B{sub 1} 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 {sup 2}B{sub 1} 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 {sup 2}A{sub 1} 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

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

    NASA Astrophysics Data System (ADS)

    Lin, Chien-Hao; Ho, Yew Kam

    2015-05-01

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

  7. 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.

  8. 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.

  9. An exploration of electronic structure and nuclear dynamics in tropolone: II. The A~ 1B2 (π*π) excited state

    NASA Astrophysics Data System (ADS)

    Burns, Lori A.; Murdock, Daniel; Vaccaro, Patrick H.

    2009-04-01

    The first excited singlet state of tropolone (à B12) and the attendant π∗←π electronic transition have been examined computationally by applying several quantum chemical treatments built upon the aug-cc-pVDZ basis set, including time-dependent density functional theory (TDDFT/B3LYP), configuration interaction singles with perturbative corrections [CIS and CIS(D)], and equation-of-motion coupled-cluster schemes [EOM-CCSD and CR-EOMCCSD(T)]. As in the case of the X˜ A11 ground state [L. A. Burns, D. Murdock, and P. H. Vaccaro, J. Chem. Phys. 124, 204307 (2006)], geometry optimization procedures and harmonic force-field calculations predict the electronically excited potential surface to support a global minimum-energy configuration of rigorously planar (Cs) symmetry. Minimal Hartree-Fock (HF/CIS) and density-functional (DFT/TDDFT) approaches yield inconsistent results for the X˜ A11 and à B12 manifolds; however, coupled-cluster (CCSD/EOM-CCSD) methods give fully relaxed proton-transfer barrier heights of ΔEptX˜=3296.1 cm-1 and ΔEptÃ=1270.6 cm-1 that are in accordance with the experimentally observed increase in vibrationless tunneling splitting upon electronic excitation. Detailed analyses show that this reduction in ΔEpt stems from a variety of complementary factors, most notably an overall contraction of the proton-transfer reaction site (whereby the equilibrium O⋯O donor-acceptor distance decreases from 2.53 to 2.46 Å) and a concomitant shortening of the intramolecular hydrogen bond. Further refinement of à B12 energies through single-point perturbative triples corrections [CR-EOMCCSD(T)] leads to 1316.1 cm-1 as the best current estimate for ΔEptÃ. Direct comparison of the lowest-lying out-of-plane torsional mode [ν39(a2)] for X˜ A11 and à B12 tropolone reveals that its disparate nature (cf. ν39X˜=101.2 cm-1 and ν39Ã=42.0 cm-1) mediates vibrational-averaging effects which can account for inertial defects extracted by rotationally

  10. 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.

  11. Electronic structure, transport properties, and excited states in CoTiSb, CoZrSb, and CoHfSb half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Janotti, Anderson; Gui, Zhigang; Kawasaki, Jason; Palmstrom, Chris; Himmetoglu, Burak

    CoTiSb is a member of a large family of half-Heusler compounds with 18 valence electrons. CoTiSb is semiconductor material with a band gap a little over 1 eV, and it has been considered promising for thermoelectric applications. It can be grown on conventional III-V semiconductors, and could potentially be integrated in III-V devices. Here we present results of first-principles calculations of electronic structure, transport properties, and excited states in CoTiSb, as well as CoZrSb and CoHfSb. Electronic structures are studied using density functional theory within the local density approximation, hybrid functional and quasiparticle GW methods. Both room-temperature Seebeck coefficient and carrier mobility are calculated from first-principles. We also determine the band alignments to III-V semiconductors, and all the results are presented and discussed in the light of available experimental data. This work was supported by the DOE.

  12. 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.

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

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, Jonas Stasys

    1987-01-01

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

  14. 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.

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

    PubMed

    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-MS(3) 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 Cu(II)(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. Graphical Abstract ᅟ. PMID:27278824

  16. 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

    2016-06-01

    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.

  17. Relativistic and correlated all-electron calculations on the ground and excited states of AgH and AuH

    NASA Astrophysics Data System (ADS)

    Witek, Henryk A.; Nakijima, Takahito; Hirao, Kimihiko

    2000-11-01

    We report relativistic all-electron multireference based perturbation calculations on the low-lying excited states of gold and silver hydrides. For AuH, we consider all molecular states dissociating to the Au(2S)+H(2S) and Au(2D)+H(2S) atomic limits, and for AgH, the states corresponding to the Ag(2S)+H(2S), Ag(2P)+H(2S), and Ag(2D)+H(2S) dissociation channels. Spin-free relativistic effects and the correlation effects are treated on the same footing through the relativistic scheme of eliminating small components (RESC). Spin-orbit effects are included perturbatively. The calculated potential energy curves for AgH are the first reported in the literature. The computed spectroscopic properties agree well with experimental findings; however, the assignment of states does not correspond to our calculations. Therefore, we give a reinterpretation of the experimentally observed C 1Π, a 3Π, B 1Σ+, b(3Δ1)1, D 1Π, c13Π1, and c0(3Π0) states. A labeling suggested by us is a1, C0+, b0-, c2, B3Π0+, d3Π1, e1, f1 and g1, respectively. The spin-orbit states corresponding to Ag(2D)+H(2S) have not well defined the Λ and S quantum numbers, and therefore, they probably correspond to Hund's coupling case c. For AuH, we present a comparison of the calculated potential energy curves and spectroscopic parameters with the previous configuration interaction study and the experiment.

  18. 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.

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

    PubMed

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

    2016-04-28

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

  20. Raman scattering in high-{Tc} superconductors: Electronic excitations

    SciTech Connect

    Cardona, M.; Strohm, T.; Kircher, J.

    1996-12-31

    Since the discovery of the high {Tc} superconductors Raman scattering has proven to be an excellent technique to characterize them and to investigate basic physical properties relevant to the elusive mechanism responsible for their superconductivity. The authors discuss here several aspects of the technique as applied to superconductivity, including scattering by lattice vibrations, magnetic excitations, and electronic excitations, with particular emphasis on the latter, both in the normal and the superconducting state. 47 refs., 8 figs., 1 tab.

  1. Electronic excitation energy transfer between nucleobases of natural DNA.

    PubMed

    Vayá, Ignacio; Gustavsson, Thomas; Douki, Thierry; Berlin, Yuri; Markovitsi, Dimitra

    2012-07-18

    Transfer of the electronic excitation energy in calf thymus DNA is studied by time-resolved fluorescence spectroscopy. The fluorescence anisotropy, after an initial decay starting on the femtosecond time scale, dwindles down to ca. 0.1. The in-plane depolarized fluorescence decays are described by a stretched exponential law. Our observations are consistent with one-dimensional transfer mediated by charge-transfer excited states. PMID:22765050

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2000-03-01

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

  5. Three Long Lived Excited States of Tm^-

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

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

  6. 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

  7. Electron-impact excitation of nitric oxide.

    NASA Technical Reports Server (NTRS)

    Stone, E. J.; Zipf, E. C.

    1972-01-01

    The absolute cross sections for the excitation of the nitrosyl cation Baer-Miescher bands, two nitric oxide bands, and several atomic nitrogen multiplets in the vacuum UV by electron impact on NO have been measured over an energy range extending from threshold to 300 eV. The variation of the dipole transition moment for the nitrosyl cation band system was also determined.

  8. Excited States of Non-Isolated Chromophores

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

  9. Excited states of methylene from quantum Monte Carlo.

    PubMed

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

    2009-09-28

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

  10. Isomer Triggering via Nuclear Excitation by Electron Capture

    SciTech Connect

    Palffy, Adriana; Evers, Joerg; Keitel, Christoph H.

    2007-10-26

    Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient.

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

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

  14. Excitation of atomic nitrogen by electron impact.

    NASA Technical Reports Server (NTRS)

    Stone, E. J.; Zipf, E. C.

    1973-01-01

    Measurement of the absolute cross sections for the excitation of a number of N I multiplets by electron impact on atomic nitrogen. Two of these cross sections - 1134 and 1200 A - are found to be large, reaching 2.0 x 10 to the minus 16th and 2.5 x 10 to the minus 16th sq cm at their peaks, respectively. The presence of vibrationally excited molecular nitrogen in the discharged gas is confirmed, and its effect on the measurements is discussed. The ratio of the oscillator strengths of the 1200- and 1134-A resonance transitions is measured to be 2.6 plus or minus 0.3.

  15. 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

  16. Strong-Field Photoionization as Excited-State Tunneling

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  17. Electronic Alignment of HYDROGEN(2P) from Oriented Excited State Dihydrogen Cation Produced in 4.0 KEV Dihydrogen Cation Collisions with Helium

    NASA Astrophysics Data System (ADS)

    Calabrese, Dominic

    The electronic alignment of H(2p) from oriented (H{2}{+})^ {*} produced in 4.0 keV H {2}{+} collisions with helium is investigated for a variety of center-of-mass energies of the fragment particles. The experiment is performed by measuring the polarization of L_alpha in coincidence with the charged particle scattered at a specific laboratory scattering angle. The laboratory scattering angle and the laboratory energy of the charged particle not only specifies the instantaneous orientation of the parent molecule relative to the incident beam velocity, but also the center-of-mass energy of the fragment particles. Photon and proton detection systems were specially designed and implemented to increase data collection efficiency. This was important because of the time-consuming nature of the photon-particle coincidence method. In special cases, symmetry arguments for the collision system are employed in order to qualitatively assess and predict the characteristics of the nascent charge cloud. These arguments also help one to qualitatively predict the possible symmetries of the excited states of the parent molecule. The results are discussed in order to determine the efficacy of existing models for the (HeH_2) ^+ complex.

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

    PubMed

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

    2015-09-01

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

  19. 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.

  20. Ultrafast Structural Dynamics of Tertiary Amines upon Electronic Excitation

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  1. Concepts of Highly Excited Electronic Systems

    NASA Astrophysics Data System (ADS)

    Berakdar, Jamal

    2003-05-01

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

  2. Search for excited electrons at HERA

    NASA Astrophysics Data System (ADS)

    H1 Collaboration; Adloff, C.; Andreev, V.; Andrieu, B.; Anthonis, T.; Astvatsatourov, A.; Babaev, A.; Bähr, J.; Baranov, P.; Barrelet, E.; Bartel, W.; Baumgartner, S.; Becker, J.; Beckingham, M.; Beglarian, A.; Behnke, O.; Belousov, A.; Berger, Ch.; Berndt, T.; Bizot, J. C.; Böhme, J.; Boudry, V.; Braunschweig, W.; Brisson, V.; Bröker, H.-B.; Brown, D. P.; Bruncko, D.; Büsser, F. W.; Bunyatyan, A.; Burrage, A.; Buschhorn, G.; Bystritskaya, L.; Campbell, A. J.; Caron, S.; Cassol-Brunner, F.; Clarke, D.; Collard, C.; Contreras, J. G.; Coppens, Y. R.; Coughlan, J. A.; Cousinou, M.-C.; Cox, B. E.; Cozzika, G.; Cvach, J.; Dainton, J. B.; Dau, W. D.; Daum, K.; Davidsson, M.; Delcourt, B.; Delerue, N.; Demirchyan, R.; de Roeck, A.; de Wolf, E. A.; Diaconu, C.; Dingfelder, J.; Dixon, P.; Dodonov, V.; Dowell, J. D.; Droutskoi, A.; Dubak, A.; Duprel, C.; Eckerlin, G.; Eckstein, D.; Efremenko, V.; Egli, S.; Eichler, R.; Eisele, F.; Eisenhandler, E.; Ellerbrock, M.; Elsen, E.; Erdmann, M.; Erdmann, W.; Faulkner, P. J. W.; Favart, L.; Fedotov, A.; Felst, R.; Ferencei, J.; Ferron, S.; Fleischer, M.; Fleischmann, P.; Fleming, Y. H.; Flügge, G.; Fomenko, A.; Foresti, I.; Formánek, J.; Franke, G.; Frising, G.; Gabathuler, E.; Gabathuler, K.; Garvey, J.; Gassner, J.; Gayler, J.; Gerhards, R.; Gerlich, C.; Ghazaryan, S.; Goerlich, L.; Gogitidze, N.; Grab, C.; Grabski, V.; Grässler, H.; Greenshaw, T.; Grindhammer, G.; Hadig, T.; Haidt, D.; Hajduk, L.; Haller, J.; Heinemann, B.; Heinzelmann, G.; Henderson, R. C. W.; Hengstmann, S.; Henschel, H.; Heremans, R.; Herrera, G.; Herynek, I.; Hildebrandt, M.; Hilgers, M.; Hiller, K. H.; Hladký, J.; Höting, P.; Hoffmann, D.; Horisberger, R.; Hovhannisyan, A.; Hurling, S.; Ibbotson, M.; Işsever, Ç.; Jacquet, M.; Jaffre, M.; Janauschek, L.; Janssen, X.; Jemanov, V.; Jönsson, L.; Johnson, C.; Johnson, D. P.; Jones, M. A. S.; Jung, H.; Kant, D.; Kapichine, M.; Karlsson, M.; Karschnick, O.; Katzy, J.; Keil, F.; Keller, N.; Kennedy, J.; Kenyon, I. R.; Kiesling, C.; Kjellberg, P.; Klein, M.; Kleinwort, C.; Kluge, T.; Knies, G.; Koblitz, B.; Kolya, S. D.; Korbel, V.; Kostka, P.; Kotelnikov, S. K.; Koutouev, R.; Koutov, A.; Kroseberg, J.; Krüger, K.; Kuhr, T.; Lamb, D.; Landon, M. P. J.; Lange, W.; Laštovička, T.; Laycock, P.; Lebailly, E.; Lebedev, A.; Leißner, B.; Lemrani, R.; Lendermann, V.; Levonian, S.; List, B.; Lobodzinska, E.; Lobodzinski, B.; Loginov, A.; Loktionova, N.; Lubimov, V.; Lüders, S.; Lüke, D.; Lytkin, L.; Malden, N.; Malinovski, E.; Mangano, S.; Maraček, R.; Marage, P.; Marks, J.; Marshall, R.; Martyn, H.-U.; Martyniak, J.; Maxfield, S. J.; Meer, D.; Mehta, A.; Meier, K.; Meyer, A. B.; Meyer, H.; Meyer, J.; Michine, S.; Mikocki, S.; Milstead, D.; Mohrdieck, S.; Mondragon, M. N.; Moreau, F.; Morozov, A.; Morris, J. V.; Müller, K.; Murín, P.; Nagovizin, V.; Naroska, B.; Naumann, J.; Naumann, Th.; Newman, P. R.; Niebergall, F.; Niebuhr, C.; Nix, O.; Nowak, G.; Nozicka, M.; Olivier, B.; Olsson, J. E.; Ozerov, D.; Panassik, V.; Pascaud, C.; Patel, G. D.; Peez, M.; Perez, E.; Petrukhin, A.; Phillips, J. P.; Pitzl, D.; Pöschl, R.; Potachnikova, I.; Povh, B.; Rauschenberger, J.; Reimer, P.; Reisert, B.; Risler, C.; Rizvi, E.; Robmann, P.; Roosen, R.; Rostovtsev, A.; Rusakov, S.; Rybicki, K.; Sankey, D. P. C.; Schätzel, S.; Scheins, J.; Schilling, F.-P.; Schleper, P.; Schmidt, D.; Schmidt, D.; Schmidt, S.; Schmitt, S.; Schneider, M.; Schoeffel, L.; Schöning, A.; Schörner, T.; Schröder, V.; Schultz-Coulon, H.-C.; Schwanenberger, C.; Sedlák, K.; Sefkow, F.; Shekelyan, V.; Sheviakov, I.; Shtarkov, L. N.; Sirois, Y.; Sloan, T.; Smirnov, P.; Soloviev, Y.; South, D.; Spaskov, V.; Specka, A.; Spitzer, H.; Stamen, R.; Stella, B.; Stiewe, J.; Strauch, I.; Straumann, U.; Tchetchelnitski, S.; Thompson, G.; Thompson, P. D.; Tomasz, F.; Traynor, D.; Truöl, P.; Tsipolitis, G.; Tsurin, I.; Turnau, J.; Turney, J. E.; Tzamariudaki, E.; Uraev, A.; Urban, M.; Usik, A.; Valkár, S.; Valkárová, A.; Vallée, C.; van Mechelen, P.; Vargas Trevino, A.; Vassiliev, S.; Vazdik, Y.; Veelken, C.; Vest, A.; Vichnevski, A.; Wacker, K.; Wagner, J.; Wallny, R.; Waugh, B.; Weber, G.; Wegener, D.; Werner, C.; Werner, N.; Wessels, M.; White, G.; Wiesand, S.; Wilksen, T.; Winde, M.; Winter, G.-G.; Wissing, Ch.; Wobisch, M.; Woehrling, E.-E.; Wünsch, E.; Wyatt, A. C.; Žáček, J.; Zálešák, J.; Zhang, Z.; Zhokin, A.; Zomer, F.; Zur Nedden, M.

    2002-11-01

    A search for excited electron (e*) production is described in which the electroweak decays e*-->eγ, e*-->eZ and e*-->νW are considered. The data used correspond to an integrated luminosity of 120 pb-1 taken in e+/-p collisions from 1994 to 2000 with the H1 detector at HERA at centre-of-mass energies of 300 and 318 GeV. No evidence for a signal is found. Mass dependent exclusion limits are derived for the ratio of the couplings to the compositeness scale, /f/Λ. These limits extend the excluded region to higher masses than has been possible in previous direct searches for excited electrons.

  3. Search for excited electrons at HERA

    NASA Astrophysics Data System (ADS)

    Adloff, C.; Andreev, V.; Andrieu, B.; Anthonis, T.; Astvatsatourov, A.; Babaev, A.; Bähr, J.; Baranov, P.; Barrelet, E.; Bartel, W.; Baumgartner, S.; Becker, J.; Beckingham, M.; Beglarian, A.; Behnke, O.; Belousov, A.; Berger, Ch.; Berndt, T.; Bizot, J. C.; Böhme, J.; Boudry, V.; Braunschweig, W.; Brisson, V.; Bröker, H.-B.; Brown, D. P.; Bruncko, D.; Büsser, F. W.; Bunyatyan, A.; Burrage, A.; Buschhorn, G.; Bystritskaya, L.; Campbell, A. J.; Caron, S.; Cassol-Brunner, F.; Clarke, D.; Collard, C.; Contreras, J. G.; Coppens, Y. R.; Coughlan, J. A.; Cousinou, M.-C.; Cox, B. E.; Cozzika, G.; Cvach, J.; Dainton, J. B.; Dau, W. D.; Daum, K.; Davidsson, M.; Delcourt, B.; Delerue, N.; Demirchyan, R.; De Roeck, A.; De Wolf, E. A.; Diaconu, C.; Dingfelder, J.; Dixon, P.; Dodonov, V.; Dowell, J. D.; Droutskoi, A.; Dubak, A.; Duprel, C.; Eckerlin, G.; Eckstein, D.; Efremenko, V.; Egli, S.; Eichler, R.; Eisele, F.; Eisenhandler, E.; Ellerbrock, M.; Elsen, E.; Erdmann, M.; Erdmann, W.; Faulkner, P. J. W.; Favart, L.; Fedotov, A.; Felst, R.; Ferencei, J.; Ferron, S.; Fleischer, M.; Fleischmann, P.; Fleming, Y. H.; Flügge, G.; Fomenko, A.; Foresti, I.; Formánek, J.; Franke, G.; Frising, G.; Gabathuler, E.; Gabathuler, K.; Garvey, J.; Gassner, J.; Gayler, J.; Gerhards, R.; Gerlich, C.; Ghazaryan, S.; Goerlich, L.; Gogitidze, N.; Grab, C.; Grabski, V.; Grässler, H.; Greenshaw, T.; Grindhammer, G.; Hadig, T.; Haidt, D.; Hajduk, L.; Haller, J.; Heinemann, B.; Heinzelmann, G.; Henderson, R. C. W.; Hengstmann, S.; Henschel, H.; Heremans, R.; Herrera, G.; Herynek, I.; Hildebrandt, M.; Hilgers, M.; Hiller, K. H.; Hladký, J.; Höting, P.; Hoffmann, D.; Horisberger, R.; Hovhannisyan, A.; Hurling, S.; Ibbotson, M.; İşsever, Ç.; Jacquet, M.; Jaffre, M.; Janauschek, L.; Janssen, X.; Jemanov, V.; Jönsson, L.; Johnson, C.; Johnson, D. P.; Jones, M. A. S.; Jung, H.; Kant, D.; Kapichine, M.; Karlsson, M.; Karschnick, O.; Katzy, J.; Keil, F.; Keller, N.; Kennedy, J.; Kenyon, I. R.; Kiesling, C.; Kjellberg, P.; Klein, M.; Kleinwort, C.; Kluge, T.; Knies, G.; Koblitz, B.; Kolya, S. D.; Korbel, V.; Kostka, P.; Kotelnikov, S. K.; Koutouev, R.; Koutov, A.; Kroseberg, J.; Krüger, K.; Kuhr, T.; Lamb, D.; Landon, M. P. J.; Lange, W.; Laštovička, T.; Laycock, P.; Lebailly, E.; Lebedev, A.; Leißner, B.; Lemrani, R.; Lendermann, V.; Levonian, S.; List, B.; Lobodzinska, E.; Lobodzinski, B.; Loginov, A.; Loktionova, N.; Lubimov, V.; Lüders, S.; Lüke, D.; Lytkin, L.; Malden, N.; Malinovski, E.; Mangano, S.; Maraček, R.; Marage, P.; Marks, J.; Marshall, R.; Martyn, H.-U.; Martyniak, J.; Maxfield, S. J.; Meer, D.; Mehta, A.; Meier, K.; Meyer, A. B.; Meyer, H.; Meyer, J.; Michine, S.; Mikocki, S.; Milstead, D.; Mohrdieck, S.; Mondragon, M. N.; Moreau, F.; Morozov, A.; Morris, J. V.; Müller, K.; Murín, P.; Nagovizin, V.; Naroska, B.; Naumann, J.; Naumann, Th.; Newman, P. R.; Niebergall, F.; Niebuhr, C.; Nix, O.; Nowak, G.; Nozicka, M.; Olivier, B.; Olsson, J. E.; Ozerov, D.; Panassik, V.; Pascaud, C.; Patel, G. D.; Peez, M.; Perez, E.; Petrukhin, A.; Phillips, J. P.; Pitzl, D.; Pöschl, R.; Potachnikova, I.; Povh, B.; Rauschenberger, J.; Reimer, P.; Reisert, B.; Risler, C.; Rizvi, E.; Robmann, P.; Roosen, R.; Rostovtsev, A.; Rusakov, S.; Rybicki, K.; Sankey, D. P. C.; Schätzel, S.; Scheins, J.; Schilling, F.-P.; Schleper, P.; Schmidt, D.; Schmidt, D.; Schmidt, S.; Schmitt, S.; Schneider, M.; Schoeffel, L.; Schöning, A.; Schörner, T.; Schröder, V.; Schultz-Coulon, H.-C.; Schwanenberger, C.; Sedlák, K.; Sefkow, F.; Shekelyan, V.; Sheviakov, I.; Shtarkov, L. N.; Sirois, Y.; Sloan, T.; Smirnov, P.; Soloviev, Y.; South, D.; Spaskov, V.; Specka, A.; Spitzer, H.; Stamen, R.; Stella, B.; Stiewe, J.; Strauch, I.; Straumann, U.; Tchetchelnitski, S.; Thompson, G.; Thompson, P. D.; Tomasz, F.; Traynor, D.; Truöl, P.; Tsipolitis, G.; Tsurin, I.; Turnau, J.; Turney, J. E.; Tzamariudaki, E.; Uraev, A.; Urban, M.; Usik, A.; Valkár, S.; Valkárová, A.; Vallée, C.; Van Mechelen, P.; Vargas Trevino, A.; Vassiliev, S.; Vazdik, Y.; Veelken, C.; Vest, A.; Vichnevski, A.; Wacker, K.; Wagner, J.; Wallny, R.; Waugh, B.; Weber, G.; Wegener, D.; Werner, C.; Werner, N.; Wessels, M.; White, G.; Wiesand, S.; Wilksen, T.; Winde, M.; Winter, G.-G.; Wissing, Ch.; Wobisch, M.; Woehrling, E.-E.; Wünsch, E.; Wyatt, A. C.; Žáček, J.; Zálešák, J.; Zhang, Z.; Zhokin, A.; Zomer, F.; zur Nedden, M.; H1 Collaboration

    2002-11-01

    A search for excited electron (e∗) production is described in which the electroweak decays e∗→eγ, e∗→eZ and e∗→νW are considered. The data used correspond to an integrated luminosity of 120 pb-1 taken in e±p collisions from 1994 to 2000 with the H1 detector at HERA at centre-of-mass energies of 300 and 318 GeV. No evidence for a signal is found. Mass dependent exclusion limits are derived for the ratio of the couplings to the compositeness scale, f/Λ. These limits extend the excluded region to higher masses than has been possible in previous direct searches for excited electrons.

  4. Mechanisms for Ultrafast Nonradiative Relaxation in Electronically Excited Eumelanin Constituents

    PubMed Central

    Meng, Sheng; Kaxiras, Efthimios

    2008-01-01

    We investigate the relaxation dynamics of melanin model constituents including monomers, dimers, and tetramers, upon excitation, using state-of-the-art, time-dependent, density functional theory calculations. The results explain the ability of these molecules to transform photon energy into thermal energy in a remarkably short timescale of ∼100 fs. We find that after electronic excitation by light absorption, ultrafast energy conversion takes place through two novel mechanisms: proton transfer on a timescale of 110 fs and state mixing upon oligomerization on a timescale of <50 fs. These results are in good agreement with available experiments and help elucidate melanin's role in photoprotection against ultraviolet radiation. PMID:18676639

  5. 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.

  6. 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...

  7. Electron impact excitation of SF6

    NASA Technical Reports Server (NTRS)

    Trajmar, S.; Chutjian, A.

    1977-01-01

    A study of the electron impact energy-loss spectrum of SF6 under both optical (low scattering angle, high impact energy) and non-optical conditions (high scattering angle, low impact energy) has revealed a number of electronic excitation processes. With the help of theoretical calculations, several of these transitions have been assigned and approximate cross sections associated with four features have been determined. In addition, a strong resonance at 12 eV has been observed in both elastic and vibrationally inelastic (delta E = 0.092 eV) channels.

  8. Adiabatic quantum dynamics of CH(X2Π) + H(2S) reactions on the CH2(X̃3A″) surface and role of the excited electronic states.

    PubMed

    Gamallo, P; Defazio, P; Akpinar, S; Petrongolo, C

    2012-08-16

    We present the Born-Oppenheimer (BO) quantum mechanical (QM) dynamics of the CH decay (d) CH(X2Π) + H(2S) → C(3P) + H2(X1Σ(g)(+)) and of the H exchange reaction (e) CH(X2Π) + H′(2S) → CH′(X2Π) + H(2S) on the CH2 X̃3A″ adiabatic potential energy surface (PES) of Harding et al. (J. Phys. Chem. 1993, 97, 5472). A thorough analysis of the correlation diagram of the four lowest CH2 electronic states, as well as Renner-Teller and spin–orbit nonadiabatic test calculations on the X̃3A″, ã1A′, and b̃1A″ coupled PESs, validate the X̃3A″ BO results, confirming that these reactions occur essentially on the uncoupled X̃3A″ ground surface. We consider the CH molecule in the ground vibrational state and in the four lowest rotational states j0. Thus, we obtain initial-state resolved reaction probabilities, cross sections, and rate constants by propagating coupled-channel real wave packets and performing flux analyses. If J is the total angular momentum quantum number and K is its projection along the body-fixed z axis, CH + H gives essentially the C + H2 products via a barrierless K-inhibited insertion, CH2 resonances at low J, and large cross sections near the threshold. These cross sections decrease strongly with collision energy and depend slightly on j0. On the other hand, the small cross sections obtained for the (e) channel are nearly independent of energy. From initial-state resolved rate constants and Boltzmann populations at temperature T, we obtain QM thermal rate constants from 100 to 400 K: at 300 K, k(d) = (9.57 ± 0.96) × 10(-11) and k(e) = (1.41 ± 0.14) × 10(-11) cm(3) s(-1) for (d) and (e) reactions, respectively. The k(d) value is in good agreement with previous quasi-classical trajectory (QCT) results on the same PES, but it is larger than that observed at 297 K by a factor of 7. On the contrary, and in agreement with the small role of CH2 excited electronic states, X̃3A″ QCT and experimental rate constants agree at high

  9. 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}

  10. 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.

  11. Tracing molecular electronic excitation dynamics in real time and space.

    PubMed

    Dutoi, Anthony D; Cederbaum, Lorenz S; Wormit, Michael; Starcke, Jan Hendrik; Dreuw, Andreas

    2010-04-14

    We present a method for studying the movement of electrons and energy within and between electronically excited molecules. The dynamically changing state is a many-electron wavepacket, for which we numerically integrate the Schrodinger equation using the ADC(2) effective Hamiltonian for the particle-hole propagator. We develop the tools necessary for following the separate motions of the particles and holes. Total particle and hole densities can be used to give an overview of the dynamics, which can be atomically decomposed in a Mulliken fashion, or individual particle and hole states give a more detailed look at the structure of an excitation. We apply our model to a neon chain, as an illustrative example, projecting an excited eigenstate of an isolated atom onto the coupled system as the initial state. In addition to demonstrating our propagation and analysis machinery, the results show a dramatic difference in excitation-energy transfer rates as a consequence of initial polarization. Furthermore, already in a system with three constituents, an important aspect of multiple coupled systems appears, in that one absorbing system essentially shields another, changing the effective sitewise coupling parameters. PMID:20405991

  12. 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.

  13. Absolute cross sections for electronic excitation of pyrimidine by electron impact.

    PubMed

    Regeta, Khrystyna; Allan, Michael; Mašín, Zdeněk; Gorfinkiel, Jimena D

    2016-01-14

    We measured differential cross sections for electron-impact electronic excitation of pyrimidine, both as a function of electron energy up to 18 eV, and of scattering angle up to 180°. The emphasis of the present work is on recording detailed excitation functions revealing resonances in the excitation process. The differential cross sections were summed to obtain integral cross sections. These are compared to results of R-matrix calculations, which successfully reproduce both the magnitude of the cross section and the major resonant features. Comparison of the experiment to the calculated contributions of different symmetries to the integral cross section permitted assignment of several features to specific core-excited resonances. Comparison of the resonant structure of pyrimidine with that of benzene revealed pronounced similarities and thus a dominant role of π-π(∗) excited states and resonances. Electron energy loss spectra were measured as a preparation for the cross section measurements and vibrational structure was observed for some of the triplet states. A detailed analysis of the electronic excited states of pyrimidine is also presented. PMID:26772566

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

    PubMed Central

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

    2016-01-01

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

  15. 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.

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

    PubMed

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

    2016-09-13

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

  17. Photoreduction of indigo dyes by electron donors. One- and two-electron-transfer reactions as a consequence of excited-state quenching

    SciTech Connect

    Schanze, K.S.; Lee, L.Y.C.; Giannotti, C.; Whitten, D.G.

    1986-05-14

    The indigoid dyes, thioindigo (TI), N,N'-diacetylindigo, (NDI) and oxalylindigo (OI), all undergo reduction upon irradiation of the dyes in the presence of electron donors such as triethylamine (TEA) or N-benzyl-1,4-dihydronicotinamide (BNAH). Product analysis by NMR and high-resolution mass spectrometry has shown that the products for TI and NDI are the formal H/sub 2/ adducts TIH/sub 2/ and NDIH/sub 2/; the product for OI has been shown to be the semireduced radical OIH which is readily detected by its characteristic ESR spectrum. Mechanistic studies have been carried out for the visible-light-induced reduction of the three dyes.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. A technique for the measurement of electron attachment to short-lived excited species

    SciTech Connect

    Christophorou, L.G.; Pinnaduwage, L.A. ); Bitouni, A.P. . Dept. of Physics)

    1990-01-01

    A technique is described for the measurement of electron attachment to short-lived ({approx lt}10{sup {minus}9} s) excited species. Preliminary results are presented for photoenhanced electron attachment to short-lived electronically-excited states of triethylamine molecules produced by laser two-photon excitation. The attachment cross sections for these excited states are estimated to be >10{sup {minus}11} cm{sup 2} and are {approximately}10{sup 7} larger compared to those for the unexcited (ground-state) molecules. 8 refs., 4 figs.

  3. Theoretical studies on the reaction pathways of electronically excited DAAF

    SciTech Connect

    Quenneville, Jason M; Moore, David S

    2009-01-01

    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{prime}-diamino-4,4{prime}-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. The use of laser light to control chemical reactions has many applications. The initiation and the detection of explosives are two such applications currently under development at Los Alamos. Though inherently experimental, the project can be aided by theory through both prediction and interpretation. When the laser light is in the UV/visible region of the electromagnetic spectrum, the absorbing molecule is excited electronically and excitation decay may occur either radiatively (fluorescence or phosphorescence) or non-radiatively (through internal conversion). In many cases decay of the excitation occurs through a mixture of processes, and maximizing the desired result requires sophisticated laser pulses whose amplitude has been optimally modulated in time and/or frequency space. Control of cis-stilbene photochemistry was recently demonstrated in our group, and we aim to extend this work to high explosive compounds. Maximizing radiative decay leads to increased fluorescence quantum yields and enhances the possibility of spectral detection of the absorbing molecule. Maximizing non-radiative decay can lead to chemistry, heating of the sample and possibly detonation initiation in

  4. Model for the hyperfine structure of electronically excited KCs molecules

    NASA Astrophysics Data System (ADS)

    Orbán, A.; Vexiau, R.; Krieglsteiner, O.; Nägerl, H.-C.; Dulieu, O.; Crubellier, A.; Bouloufa-Maafa, N.

    2015-09-01

    A model for determining the hyperfine structure of the excited electronic states of diatomic bialkali heteronuclear molecules is formulated from the atomic hyperfine interactions and is applied to the case of bosonic 39KCs and fermionic 40KCs molecules. The hyperfine structure of the potential-energy curves of the states correlated to the K (4 s 2S1 /2) +Cs (6 p 2P1 /2 ,3 /2) dissociation limits is described in terms of different coupling schemes depending on the internuclear distance R . These results provide a step in the calculation of the hyperfine structure of rovibrational levels of these excited molecular states in the perspective of the identification of efficient paths for creating ultracold ground-state KCs molecules.

  5. Calculating helium atomic excited states in coordinate space

    NASA Astrophysics Data System (ADS)

    Hall, Shane; Siegel, P. B.

    2015-12-01

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

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

    SciTech Connect

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

    1991-01-11

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

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

    PubMed

    Papadakis, Raffaello; Ottosson, Henrik

    2015-09-21

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

  8. Quenching of the 1.0 and 2.3 µm excited electronic states of PuF6 at room temperature by selected rare gases and small polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Barefield, J. E., II; Rice, W. W.; Dye, B. A.

    1985-07-01

    The quenching rate constants kq for the following rare gases and small molecules (He, Ar, Xe, H2, D2, N2, O2, F2, Cl2, HF, CO, CO2, CH4, CHF3, CF4, NO2F, SOF4, SF6, and UF6) are reported in units of cm3 molecule-1 s-1 for both the 1.0 and 2.3 μm excited electronic states of PuF6 (see Table I). The self-quenching rate constants for PuF6 at room temperture are kq(1.0 μm) =1.12±0.01×10-12 and kq(2.3 μm)=5.01±0.11×10-15 cm3 molecule-1 s-1. The magnitude of the quenching rate constants for most all of the gases considered above suggest that the dominant process in the collisional deexcitation of excited state PuF*6 (1.0 or 2.3 μm) molecules at room temperature is physical quenching (i.e., E-T or electronic-to-translational collisional energy transfer). Our data also indicate that E-V (electronic-to-vibrational) energy transfer is responsible for the efficient quenching of electronically excited PuF6 by H2, HF, CH4, and CHF3. There is also evidence from our data that the efficient quenching of the excited states of PuF6 by ground state PuF6 molecules proceeds via resonant energy transfer.

  9. 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.

  10. 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

  11. Ground and Excited State Spectra of a Quantum Dot

    NASA Astrophysics Data System (ADS)

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

    1998-03-01

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

  12. 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.

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

    PubMed

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

    2016-06-14

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

  14. Excited states in the soliton bag model

    SciTech Connect

    Saly, R.; Sundaresan, M.K.

    1984-02-01

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

  15. 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.

  16. 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.

  17. 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.

  18. Cold chemistry with electronically excited Ca+ Coulomb crystals.

    PubMed

    Gingell, Alexander D; Bell, Martin T; Oldham, James M; Softley, Timothy P; Harvey, Jeremy N

    2010-11-21

    Rate constants for chemical reactions of laser-cooled Ca(+) ions and neutral polar molecules (CH(3)F, CH(2)F(2), or CH(3)Cl) have been measured at low collision energies (/k(B)=5-243 K). Low kinetic energy ensembles of (40)Ca(+) ions are prepared through Doppler laser cooling to form "Coulomb crystals" in which the ions form a latticelike arrangement in the trapping potential. The trapped ions react with translationally cold beams of polar molecules produced by a quadrupole guide velocity selector or with room-temperature gas admitted into the vacuum chamber. Imaging of the Ca(+) ion fluorescence allows the progress of the reaction to be monitored. Product ions are sympathetically cooled into the crystal structure and are unambiguously identified through resonance-excitation mass spectrometry using just two trapped ions. Variations of the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of (40)Ca(+) involved in the laser-cooling cycle, and these are modeled by solving the optical Bloch equations for the eight-level system. Systematic variation of the steady-state populations over a series of reaction experiments allows the extraction of bimolecular rate constants for reactions of the ground state ((2)S(1/2)) and the combined excited states ((2)D(3/2) and (2)P(1/2)) of (40)Ca(+). These results are analyzed in the context of capture theories and ab initio electronic structure calculations of the reaction profiles. In each case, suppression of the ground state rate constant is explained by the presence of a submerged or real barrier on the ground state potential surface. Rate constants for the excited states are generally found to be in line with capture theories. PMID:21090857

  19. Cold chemistry with electronically excited Ca+ Coulomb crystals

    NASA Astrophysics Data System (ADS)

    Gingell, Alexander D.; Bell, Martin T.; Oldham, James M.; Softley, Timothy P.; Harvey, Jeremy N.

    2010-11-01

    Rate constants for chemical reactions of laser-cooled Ca+ ions and neutral polar molecules (CH3F, CH2F2, or CH3Cl) have been measured at low collision energies (⟨Ecoll⟩/kB=5-243 K). Low kinetic energy ensembles of C40a+ ions are prepared through Doppler laser cooling to form "Coulomb crystals" in which the ions form a latticelike arrangement in the trapping potential. The trapped ions react with translationally cold beams of polar molecules produced by a quadrupole guide velocity selector or with room-temperature gas admitted into the vacuum chamber. Imaging of the Ca+ ion fluorescence allows the progress of the reaction to be monitored. Product ions are sympathetically cooled into the crystal structure and are unambiguously identified through resonance-excitation mass spectrometry using just two trapped ions. Variations of the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of C40a+ involved in the laser-cooling cycle, and these are modeled by solving the optical Bloch equations for the eight-level system. Systematic variation of the steady-state populations over a series of reaction experiments allows the extraction of bimolecular rate constants for reactions of the ground state (S21/2) and the combined excited states (D23/2 and P21/2) of C40a+. These results are analyzed in the context of capture theories and ab initio electronic structure calculations of the reaction profiles. In each case, suppression of the ground state rate constant is explained by the presence of a submerged or real barrier on the ground state potential surface. Rate constants for the excited states are generally found to be in line with capture theories.

  20. 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.

  1. 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

  2. Nuclear excitation by electronic transition of 235U

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Background: 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. Purpose: An experiment was performed to determine whether NEET of 235U occurs and to determine its excitation rate. Method: A pulsed Nd:YAG laser operating at 1064 nm with a pulse energy of 790 mJ and a pulse width of 9 ns was used to generate a uranium plasma. The plasma was collected on a catcher plate and electrons from the catcher plate were accelerated and focused onto a microchannel plate detector. An observation of a decay with a 26-min half-life would suggest the creation of Um235 and the possibility that NEET of 235U occurred. Results: A 26-min decay consistent with the decay of Um235 was not observed and there was no evidence that NEET occurred. An upper limit for the NEET rate of 235U was determined to be λNEET<1.8 ×10-4 s-1, with a confidence level of 68.3%. Conclusions: The upper limit determined from this experiment is consistent with most of the past measurements. Discrepancies between this experiment and past measurements can be explained by assuming that past experiments misinterpreted the data.

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

    SciTech Connect

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

    1990-08-20

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

  4. 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

  5. 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.

  6. 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.

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

    PubMed

    Theophilou, Iris; Tassi, M; Thanos, S

    2014-04-28

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

  8. 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.

  9. 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.

  10. Excited State Properties of Hybrid Perovskites.

    PubMed

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

    2016-01-19

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

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

    PubMed

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

    2015-04-15

    A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. PMID:25731863

  12. Electron emission from fast heavy ions associated with resonant coherent excitation

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    We observed convoy electrons emitted from 416 MeV/u He-like Ar16+ passing through a thin Si crystal under the condition of three-dimensional resonant coherent excitation (3D-RCE). The convoy electrons, which originate from electrons released from ions into the continuum by collisions with target atoms, emerged in the forward direction and formed a cusp-shaped peak in the energy distribution. We selectively controlled the population of the ground and excited states of ions traveling through the crystal by using 3D-RCE, where the 1s electron was excited to the 2p state by a periodic crystal field. Under the resonance condition, we found an enhancement of the convoy electrons with a narrowing in the energy distribution, which reflects the electron momentum distribution of the initial bound state of the excited ions.

  13. Excited state properties of the astaxanthin radical cation: A quantum chemical study

    NASA Astrophysics Data System (ADS)

    Dreuw, Andreas; Starcke, Jan Hendrik; Wachtveitl, Josef

    2010-07-01

    Using time-dependent density functional theory, the excited electronic states of the astaxanthin radical cation (AXT rad + ) are investigated. While the optically allowed excited D 1 and D 3 states are typical ππ∗ excited states, the D 2 and D 4 states are nπ∗ states. Special emphasis is put onto the influence of the carbonyl groups onto the excited states. For this objective, the excited states of four hypothetical carotenoids and zeaxanthin have been computed. Addition of a carbonyl group to a conjugated carbon double bond system does essentially not change the vertical excitation energies of the optically allowed ππ∗ states due to two counter-acting effects: the excitation energy should increase due to the -M-effect of the carbonyl group and at the same time decrease owing to the elongation of the conjugated double bond system by the carbonyl group itself.

  14. Electron Impact Excitation Of Ti XIX

    NASA Astrophysics Data System (ADS)

    Aggarwal, Kanti M.; Keenan, F. P.

    2012-05-01

    Emission lines of Ti XIX are important for the modeling and diagnostics of lasing, fusion and astrophysical plasmas, for which atomic data are required for a variety of parameters, such as energy levels, radiative rates (A- values), and excitation rates or equivalently the effective collision strengths (Υ), which are obtained from the electron impact collision strengths (Ω). Experimentally, energy levels are available for Ti XIX on the NIST website, but there is paucity for accurate collisional atomic data. Therefore, here we report a complete set of results (namely energy levels, radiative rates, and effective collision strengths) for all transitions among the lowest 98 levels of Ti XIX. These levels belong to the (1s2) 2s2, 2s2p, 2p2, 2s3l, 2p3l, 2s4l, and 2p4l configurations. Finally, we also report the A- values for four types of transitions, namely electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2), because these are also required for plasma modeling. For our calculations of wavefunctions, we have adopted the fully relativistic GRASP code, and for the calculations of Ω, the Dirac atomic R-matrix code (DARC) of PH Norrington and IP Grant. Additionally, parallel calculations have also been performed with the Flexible Atomic Code (FAC) of Gu, so that all atomic parameters can be rigorously assessed for accuracy.

  15. Electron impact excitation of helium atom

    NASA Astrophysics Data System (ADS)

    Han, Xiao-Ying; Zeng, De-Ling; Gao, Xiang; Li, Jia-Ming

    2015-08-01

    A method to deal with the electron impact excitation cross sections of an atom from low to high incident energies are presented. This method combines the partial wave method and the first Born approximation (FBA), i.e., replacing the several lowest partial wave cross sections of the total cross sections within FBA by the corresponding exact partial wave cross sections. A new set of codes are developed to calculate the FBA partial wave cross sections. Using this method, the convergent e-He collision cross sections of optical-forbidden and optical-allowed transitions at low to high incident energies are obtained. The calculation results demonstrate the validity and efficiency of the method. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921501 and 2013CB922200), the National Natural Science Foundation of China (Grant Nos. 11274035, 11275029, 11328401, 11371218, 11474031, 11474032, and 11474034), and the Foundation of Development of Science and Technology of Chinese Academy of Engineering Physics (Grant Nos. 2013A0102005 and 2014A0102005).

  16. 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.

  17. Excited state baryon spectroscopy from lattice QCD

    DOE PAGESBeta

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

    2011-10-31

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

  18. Radiative and Excited State Charmonium Physics

    SciTech Connect

    Jozef Dudek

    2007-07-30

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

  19. 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.

  20. 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.

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

    PubMed

    Wenzel, Jan; Dreuw, Andreas

    2016-03-01

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

  2. 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}.

  3. 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)].

  4. Embedding potentials for excited states of embedded species

    SciTech Connect

    Wesolowski, Tomasz A.

    2014-05-14

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

  5. Valence and excited states of LiH-

    NASA Astrophysics Data System (ADS)

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

    1998-03-01

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

  6. Molecular-state treatment of He sup + (2 p ) excitation through electron capture in He sup 2+ -H sub 2 collisions at low energies

    SciTech Connect

    Saha, B.C.; Lane, N.F. ); Kimura, M. Department of Physics, Rice University, Houston, Texas 77251 )

    1991-07-01

    We report the calculation of low-energy state-selective electron-capture cross sections in an {alpha}-particle collision with molecular hydrogen. The semiclassical molecular-orbital expansion method is used and electron translation effects are taken into account. The calculated He{sup +}(2{ital p}) formation cross sections are in good overall agreement with the recent measurements of Hoekstra {ital et} {ital al}. (J. Phys. B 22, L603 (1989)). However, the experimental cross sections show a pronounced plateau between {ital E}=0.7 and 2.0 keV/amu. In the same energy region the calculated results exhibit an oscillatory structure that arises from a combination of Landau-Zener and Rosen-Demkov oscillations.

  7. Ultraviolet Photodissociation Dynamics of the Allyl Radical via the B̃(2)A1(3s), C̃(2)B2(3py), and Ẽ(2)B1(3px) Electronic Excited States.

    PubMed

    Song, Yu; Lucas, Michael; Alcaraz, Maria; Zhang, Jingsong; Brazier, Christopher

    2015-12-17

    Ultraviolet (UV) photodissociation dynamics of jet-cooled allyl radical via the B̃(2)A1(3s), C̃(2)B2(3py), and Ẽ(2)B1(3px) electronically excited states are studied at the photolysis wavelengths from 249 to 216 nm using high-n Rydberg atom time-of-flight (HRTOF) and resonance-enhanced multiphoton ionization (REMPI) techniques. The photofragment yield (PFY) spectra of the H atom products are measured using both allyl chloride and 1,5-hexadiene as precursors of the allyl radical and show a broad peak centered near 228 nm, whereas the previous UV absorption spectra of the allyl radical peak around 222 nm. This difference suggests that, in addition to the H + C3H4 product channel, another dissociation channel (likely CH3 + C2H2) becomes significant with increasing excitation energy. The product translational energy release of the H + C3H4 products is modest, with the P(ET) distributions peaking near 8.5 kcal/mol and the fraction of the average translational energy in the total excess energy, ⟨fT⟩, in the range 0.22-0.18 from 249 to 216 nm. The P(ET)'s are consistent with production of H + allene and H + propyne, as suggested by previous experimental and theoretical studies. The angular distributions of the H atom products are isotropic, with the anisotropy parameter β ≈ 0. The H atom dissociation rate constant from the pump-probe study gives a lower limit of 1 × 10(8)/s. The dissociation mechanism is consistent with unimolecular decomposition of the hot allyl radical on the ground electronic state after internal conversion of the electronically excited state. PMID:26334360

  8. CW silver ion laser with electron beam excitation

    NASA Astrophysics Data System (ADS)

    Wernsman, B.; Prabhuram, T.; Lewis, K.; Gonzalez, F.; Villagran, M.

    1988-08-01

    A CW laser power of 140 mW was obtained in the 840.39-nm transition of Ag II by electron-beam excitation. The electron-beam excited metal-vapor ion laser is capable of operating using metals with high vaporization temperatures, and is of interest for generation of CW coherent radiation in the 220-260-nm spectral region.

  9. Addition by subtraction in coupled cluster theory. II. Equation-of-motion coupled cluster method for excited, ionized, and electron-attached states based on the nCC ground state wave function

    NASA Astrophysics Data System (ADS)

    Musiał, Monika; Bartlett, Rodney J.

    2007-07-01

    New iterative double and triple excitation corrections to the equation-of-motion coupled cluster (EOM-CC) based upon the recently developed nCC methods [Bartlett and Musiał, J. Chem. Phys. 125, 204105-1 (2006)] are applied to excitation energies (EEs), ionization potentials (IPs), and electron affinities (EAs). The methods have been tested by the evaluation of the vertical EEs, IPs, and EAs for Ne, BH, CH2, H2O, N2, C2, CH+, CO, and C2H4 compared to full configuration interaction, EOM-CCSD, EOM-CCSDT, and experimental data.

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

    PubMed

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

    2016-05-01

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

  11. Excitation gap of fractal quantum hall states in graphene.

    PubMed

    Luo, Wenchen; Chakraborty, Tapash

    2016-01-13

    In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter's butterfly. In this work, we develop a Hartree-Fock theory to deal with the electron-electron interaction in the Hofstadter's butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation. PMID:26657089

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

  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. 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

  16. 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

  17. Electronic energy states

    NASA Technical Reports Server (NTRS)

    1976-01-01

    One-electron wave functions are reviewed and approximate solutions of two-electron systems are given in terms of these one-electron functions. The symmetry effects associated with electron spin are reviewed and the effects of electron exchange on energy levels of the two-electron system are given. The coupling of electronic orbital and spin angular momentum is considered next and the Lande interval rule for Russell-Saunders or LS coupling is derived. The configurations possible for various multi-electron LS couplings are enumerated (examples from the first two rows of the periodic table are given), and the meaning of the spectroscopic nomenclature is discussed, particularly with respect to the degeneracies of the electron states involved. Next the nomenclature, symmetries, and degeneracies for electron states of diatomic molecules are discussed, and some examples for N2, O2, and NO are presented. The electronic partition functions and derivative thermodynamic properties are expressed in terms of these energies and degeneracies, and examples are given for some of the simple gas species encountered in the earth's atmosphere.

  18. 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.

  19. Electron impact excitation of resonance transitions in atomic potassium

    SciTech Connect

    Tayal, S.S.; Msezane, A.Z.

    1993-05-01

    Cross sections for electron impact excitation of the 4 s{sup 2}S - 4p {sup 2}P{sup o} and 4s {sup 2}S - 5p {sup 2}P{sup o} transitions in atomic potassium are calculated in the low-energy region from 1.5 to 30 eV using the R-matrix method. We included eight target states (4s {sup 2}S, 4p {sup 2}P{sup o}, 5s {sup 2}S, 3d {sup 2}D, 5p {sup 2}P{sup o}, 4d {sup 2}D, 6S {sup 2}S, and 4f {sup 2}F{sup o}) in the close-coupling expansion. These states are represented by extensive configuration- interaction wavefunctions constructed from the orthogonal one-electron orbitals: 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, and 6s. The calculated results are compared with the available experiments and other calculations. The present calculation shows a resonance structure in the cross section for the excitation of the resonance 4s {sup 2}S - 4p {sup 2}P{sup o} transition around 2.5 eV.

  20. VUV study of electron impact dissociative excitation of thymine

    NASA Astrophysics Data System (ADS)

    Tiessen, C. J.; Trocchi, J. A.; Hein, J. D.; Dech, J.; Kedzierski, W.; McConkey, J. W.

    2016-06-01

    Dissociative excitation of thymine following electron impact was studied in the energy range up to 430 eV. Emissions in the vacuum ultra-violet spectral region below 150 nm were studied and found to be dominated by the hydrogen Lyman series. Emission cross section data reveal that Lyman-α excitation displays a broad maximum at an electron impact energy of 160 eV. The probability of extracting other excited atoms from the parent molecule is found to be insignificant. Possible excitation and dissociation mechanisms in the parent molecule are discussed.

  1. 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.

  2. 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

  3. Electronic excitations in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Unger, P.; Fulde, P.

    1995-04-01

    We calculate the electronic single-particle spectrum of an electron-doped cuprate superconductor such as Nd2-xCexCuO4-y. The dynamics of holes in the Cu-O planes is described by the extended Hubbard or Emery model. We consider the system at half-filling (one hole per unit cell, nh=1) and in the case of electron doping where the ground state is paramagnetic. The projection technique of Mori and Zwanzig is applied to derive the equations of motion for the Green's functions of Cu and O holes. These equations are solved self-consistently as in a previous calculation, where we considered the case of hole doping. At half-filling the system exhibits a charge-transfer gap bounded by Zhang-Rice singlet states and the upper Hubbard band. Upon electron doping the upper Hubbard band crosses the Fermi level and the system becomes metallic. With increasing electron doping the singlet band loses intensity and finally vanishes for nh=0. The corresponding spectral weight is transferred to the upper Hubbard band, which becomes a usual tight-binding band for zero hole concentration. The shape of the flat band crossing the Fermi level fits well to angle-resolved photoemission spectra of Nd2-xCexCuO4-y for x=0.15 and 0.22. Furthermore, our findings are in excellent agreement with exact diagonalization studies of 2×2 CuO2 cluster with periodic boundary conditions.

  4. Avoiding entanglement loss when two-qubit quantum gates are controlled by electronic excitation

    NASA Astrophysics Data System (ADS)

    Rodriquez, R.; Fisher, A. J.; Greenland, P. T.; Stoneham, A. M.

    2004-04-01

    A solid-state two-qubit quantum gate was recently proposed that might be made in a silicon fabrication plant in the near future. In this class of device, entanglement between two quantum bits is controlled by a change from a largely unentangled ground electronic state to an excited state in which useful entanglement can be produced. Such gates have potential advantages, both because they exploit known solid-state behaviour and they separate the storage and manipulation of quantum information. It is important that the excitation step does not create decoherence. We analyse a type of gate proposed before, in which the excitation involves a control electron that interacts with the qubit spins in the excited state. The dynamics of an idealized (but fairly general) gate of this type show that it can be operated to produce a standard two-qubit entangling state.

  5. Doubly-excited {sup 1,3}D{sup e} resonance states of two-electron positive ions Li{sup +} and Be{sup 2+} in Debye plasmas

    SciTech Connect

    Kar, Sabyasachi; Wang, Yang; Jiang, Zishi; Li, Shuxia; Ratnavelu, K.

    2014-01-15

    We investigate the bound {sup 1,3}D states and the doubly-excited {sup 1,3}D{sup e} resonance states of two-electron positive ions Li{sup +} and Be{sup 2+} by employing correlated exponential wave functions. In the framework of the stabilization method, we are able to extract three series (2pnp, 2snd, 2pnf) of {sup 1}D{sup e} resonances and two series (2pnp, 2snd) of {sup 3}D{sup e} resonances below the N = 2 threshold. The {sup 1,3}D{sup e} resonance parameters (resonance energies and widths) for Li{sup +} and Be{sup 2+} along with the bound-excited 1s3d {sup 1,3}D state energies are reported for the first time as functions of the screening parameter. Accurate resonance energies and widths are also reported for Li{sup +} and Be{sup 2+} in vacuum. For free-atomic cases, comparisons are made with the reported results and few resonance states are reported for the first time.

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

    PubMed

    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

    2016-03-28

    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. PMID:27036450

  7. 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.

  8. 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

  9. 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.

  10. 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

    NASA Astrophysics Data System (ADS)

    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.

  11. Imaging Excited Orbitals of Quantum Dots: Experiment and Electronic Structure Theory.

    PubMed

    Nienhaus, Lea; Goings, Joshua J; Nguyen, Duc; Wieghold, Sarah; Lyding, Joseph W; Li, Xiaosong; Gruebele, Martin

    2015-11-25

    Electronically excited orbitals play a fundamental role in chemical reactivity and spectroscopy. In nanostructures, orbital shape is diagnostic of defects that control blinking, surface carrier dynamics, and other important optoelectronic properties. We capture nanometer resolution images of electronically excited PbS quantum dots (QDs) by single molecule absorption scanning tunneling microscopy (SMA-STM). Dots with a bandgap of ∼1 eV are deposited on a transparent gold surface and optically excited with red or green light to produce hot carriers. The STM tip-enhanced laser light produces a large excited-state population, and the Stark effect allows transitions to be tuned into resonance by changing the sample voltage. Scanning the QDs under laser excitation, we were able to image electronic excitation to different angular momentum states depending on sample bias. The shapes differ from idealized S- or P-like orbitals due to imperfections of the QDs. Excitation of adjacent QD pairs reveals orbital alignment, evidence for electronic coupling between dots. Electronic structure modeling of a small PbS QD, when scaled for size, reveals Stark tuning and variation in the transition moment of different parity states, supporting the simple one-electron experimental interpretation in the hot carrier limit. The calculations highlight the sensitivity of orbital density to applied field, laser wavelength, and structural fluctuations of the QD. PMID:26518039

  12. 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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-01-01

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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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. PMID:23455081

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

  1. Role of carotenoid excited states and radicals in antioxidant activities

    NASA Astrophysics Data System (ADS)

    Lambert, Chris R.

    1995-05-01

    Carotenoids are linear polyenes that occur in nature and are known to have powerful antioxidant properties. They react efficiently with the excited states of many organic molecules. In the photosynthetic apparatus of plants they quench reactive excited states that may be formed and release the energy as heat. In photodynamic therapy they may be used to ameliorate the associated skin photosensitivity that is a consequence of many photosensitizers. This protection may be either through reaction with the sensitizer triplet state or through quenching of singlet oxygen. Carotenoids also form relatively stable radical species and react efficiently with the hydroxyl radical, superoxide and the solvated electron. In cells they are associated with the lipid core of the cell membrane and are effective against lipid peroxidation. The importance of the thermodynamic properties of these compounds and their organization within biological systems is pivotal to understanding carotenoid antioxidant activity. The present paper reviews some recent work on the energy level of (beta) -carotene, electron transfer involving the one electron reduced species and the resonance Raman spectra of some carotenoids in micellar solution.

  2. 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.

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

    PubMed

    Mondal, Sayan; Puranik, Mrinalini

    2016-05-18

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

  4. 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.

  5. 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.

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

    PubMed

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

    2013-11-14

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

  7. 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.

  8. 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.

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

    NASA Technical Reports Server (NTRS)

    Lee, J.-H.

    1985-01-01

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

  10. 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.

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

    DOE PAGESBeta

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

    2016-01-25

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

  12. Excited state dynamics in pyrrole water clusters: First-principles simulation

    NASA Astrophysics Data System (ADS)

    Frank, Irmgard; Damianos, Konstantina

    2008-01-01

    The excited state dynamics in pyrrole-water clusters is investigated using restricted open-shell Kohn-Sham theory. While the isolated pyrrole molecule dissociates in the excited state, no dissociation is observed in the presence of water molecules. Instead an electron is transferred to water and moves as solvated electron between the water molecules. The results are compared to data obtained from other first-principles and ab initio calculations.

  13. 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.

  14. 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

  15. Electron-impact excitation of ions

    SciTech Connect

    Crandall, D.H.

    1981-01-01

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

  16. 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.

  17. Tryptamine in the gas phase. A high resolution laser study of the structural and dynamic properties of its ground and electronically excited states

    NASA Astrophysics Data System (ADS)

    Nguyen, T. V.; Korter, T. M.; Pratt, D. W.

    High resolution S1←S0 fluorescence excitation spectra of tryptamine have been observed in the collision-free environment of a supersonic molecular beam. Each origin band has been assigned to a unique conformer of the isolated molecule based on its observed rotational constants. For the first time, subbands have been detected in the rotationally resolved spectra of bands Cblue and D. A possible hindered motion is proposed to account for the appearance of these subbands. This motion connects the minima associated with the Antipy and Antiph conformers, and thus explores new regions of the energy landscape of this important biomolecule.

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

    PubMed

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

    2016-07-20

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

  19. 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.

  20. 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

  1. 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.

  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-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.

  4. Absolute cross sections for electronic excitations of cytosine by low energy electron impact

    PubMed Central

    Bazin, M.; Michaud, M.; Sanche, L.

    2013-01-01

    The absolute cross sections (CS) for electronic excitations of cytosine by electron impact between 5 and 18 eV were measured by electron-energy loss (EEL) spectroscopy of the molecule deposited at low coverage on an inert Ar substrate. The lowest EEL features found at 3.55 and 4.02 eV are ascribed to transitions from the ground state to the two lowest triplet 1 3A′(π→π*) and 2 3A′(π→π*) valence states of the molecule. Their energy dependent CS exhibit essentially a common maximum at about 6 eV with a value of 1.84 × 10−17 cm2 for the former and 4.94 × 10−17 cm2 for the latter. In contrast, the CS for the next EEL feature at 4.65 eV, which is ascribed to the optically allowed transition to the 2 1A′(π→π*) valence state, shows only a steep rise to about 1.04 × 10−16 cm2 followed by a monotonous decrease with the incident electron energy. The higher EEL features at 5.39, 6.18, 6.83, and 7.55 eV are assigned to the excitations of the 3 3, 1A′(π→π*), 4 1A′(π→π*), 5 1A′(π→π*), and 6 1A′(π→π*) valence states, respectively. The CS for the 3 3, 1A′ and 4 1A′ states exhibit a common enhancement at about 10 eV superimposed on a more or less a steep rise, reaching respectively a maximum of 1.27 and 1.79 × 10−16 cm2, followed by a monotonous decrease. This latter enhancement and the maximum seen at about 6 eV in the lowest triplet states correspond to the core-excited electron resonances that have been found by dissociative electron attachment experiments with cytosine in the gas phase. The weak EEL feature found at 5.01 eV with a maximum CS of 3.8 × 10−18 cm2 near its excitation threshold is attributed to transitions from the ground state to the 1 3, 1A″(n→π*) states. The monotonous rise of the EEL signal above 8 eV is attributed to the ionization of the molecule. It is partitioned into four excitation energy regions at about 8.55, 9.21, 9.83, and 11.53 eV, which correspond closely to the ionization energies of

  5. 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.

  6. Anharmonicity Effects in IR Spectra of [Re(X)(CO)3(α-diimine)] (α-diimine = 2,2'-bipyridine or pyridylimidazo[1,5-a]pyridine; X = Cl or NCS) Complexes in Ground and Excited Electronic States.

    PubMed

    Kvapilová, Hana; Vlček, Antonín; Barone, Vincenzo; Biczysko, Malgorzata; Záliš, Stanislav

    2015-10-01

    Infrared spectra of [Re(X)(CO)(3)(α-diimine)] (α-diimine = 2,2'-bipyridine, X = Cl, NCS, or pyridylimidazo[1,5-a]pyridine, X = Cl) in the ground and the lowest triplet electronic states were calculated by a global hybrid density functional going beyond the harmonic level by means of second-order vibrational perturbation theory (VPT2) and including bulk solvent effects by the polarizable continuum model (PCM). The full-dimensionality (FD) VPT2 is compared with the reduced-dimensionality (RD) model, where only selected vibrational modes are calculated anharmonically. The simulated difference IR spectra (excited state minus ground state) in the ν(CO) region closely match experimental time-resolved infrared (TRIR) spectra. Very good agreement was also obtained for ground-state spectra in the fingerprint region. In comparison with the harmonic simulated spectra, the calculated anharmonic frequencies are closer to experimental values and do not require scaling when the B3LYP functional is used. Several spectral features due to combination bands have been identified by VPT2 simulations in the ν(CO) spectral region, which are of importance for a correct interpretation of TRIR experiments. PMID:26367031

  7. 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.

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

    SciTech Connect

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

    2006-07-15

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

  9. 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

  10. 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.

  11. 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.

  12. Adsorbate-induced absorption redshift in an organic-inorganic cluster conjugate: Electronic effects of surfactants and organic adsorbates on the lowest excited states of a methanethiol-CdSe conjugate

    NASA Astrophysics Data System (ADS)

    Liu, Christopher; Chung, Sang-Yoon; Lee, Sungyul; Weiss, Shimon; Neuhauser, Daniel

    2009-11-01

    Bioconjugated CdSe quantum dots are promising reagents for bioimaging applications. Experimentally, the binding of a short peptide has been found to redshift the optical absorption of nanoclusters [J. Tsay et al., J. Phys. Chem. B 109, 1669 (2005)]. This study examines this issue by performing density functional theory (DFT) and time-dependent-DFT calculations to study the ground state and low-lying excited states of (CdSe)6[SCH3]-, a transition metal complex built by binding methanethiolate to a CdSe molecular cluster. Natural bond orbital results show that the redshift is caused by ligand-inorganic cluster orbital interaction. The highest occupied molecular orbital (HOMO) of (CdSe)6 is dominated by selenium 4p orbitals; in contrast, the HOMO of (CdSe)6[SCH3]- is dominated by sulfur 3p orbitals. This difference shows that [SCH3]- binding effectively introduces filled sulfur orbitals above the selenium 4p orbitals of (CdSe)6. The resulting smaller HOMO-LUMO gap of (CdSe)6[SCH3]- indeed leads to redshifts in its excitation energies compared to (CdSe)6. In contrast, binding of multiple NH3 destabilizes cadmium 5p orbitals, which contribute significantly to the lowest unoccupied molecular orbital (LUMO) of (CdSe)6, while leaving the selenium 4p orbitals near the HOMO relatively unaffected. This has the effect of widening the HOMO-LUMO gap of (CdSe)6ṡ6NH3 compared to (CdSe)6. As expected, the excitation energies of the passivated (CdSe)6ṡ6NH3 are also blueshifted compared to (CdSe)6. As far as NH3 is a faithful representation of a surfactant, the results clearly illustrate the differences between the electronic effects of an alkylthiolate versus those of surfactant molecules. Surface passivation of (CdSe)6[SCH3]- is then simulated by coating it with multiple NH3 molecules. The results suggest that the [SCH3]- adsorption induces a redshift in the excitation energies in a surfactant environment.

  13. S1 and S2 Excited States of Gas-Phase Schiff-Base Retinal Chromophores

    NASA Astrophysics Data System (ADS)

    Nielsen, I. B.; Lammich, L.; Andersen, L. H.

    2006-01-01

    Photoabsorption studies of 11-cis and all-trans Schiff-base retinal chromophore cations in the gas phase have been performed at the electrostatic ion storage ring in Aarhus. A broad absorption band due to the optically allowed excitation to the first electronically excited singlet state (S1) is observed at around 600 nm. A second “dark” excited state (S2) just below 400 nm is reported for the first time. It is located ˜1.2eV above S1 for both chromophores. The S2 state was not visible in a solution measurement where only one highly blueshifted absorption band corresponding to the first excited state was visible. Knowledge of the position of the excited states in retinal is essential for the understanding of the fast photoisomerization in, for example, visual pigments.

  14. 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.

  15. Resonant vibrational excitation of CO by low-energy electrons

    SciTech Connect

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

    2006-06-15

    Electron impact vibrational excitation of the CO molecule, via the {sup 2}{pi} resonance, in the 0-4 eV energy region has been investigated. The energy dependence of the resonant excitation of the first ten vibrational levels, v=1 to v=10, has been measured by use of a crossed-beams double trochoidal electron spectrometer. Obtained relative differential cross sections are normalized to the absolute values. Integral cross sections are determined by using our recent results on scattered electrons angular distributions, which demonstrate clear p-partial wave character of this resonance. Substructures appear in the {sup 2}{pi} resonant excitation of the CO molecule which have not been previously observed.

  16. 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

  17. 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.

  18. Ultrafast excited-state deactivation of flavins bound to dodecin.

    PubMed

    Staudt, Heike; Oesterhelt, Dieter; Grininger, Martin; Wachtveitl, Josef

    2012-05-18

    Dodecins, a group of flavin-binding proteins with a dodecameric quaternary structure, are able to incorporate two flavins within each of their six identical binding pockets building an aromatic tetrade with two tryptophan residues. Dodecin from the archaeal Halobacterium salinarum is a riboflavin storage device. We demonstrate that unwanted side reactions induced by reactive riboflavin species and degradation of riboflavin are avoided by ultrafast depopulation of the reactive excited state of riboflavin. Intriguingly, in this process, the staggered riboflavin dimers do not interact in ground and photoexcited states. Rather, within the tetrade assembly, each riboflavin is kept under the control of the respective adjacent tryptophan, which suggests that the stacked arrangement is a matter of optimizing the flavin load. We further identify an electron transfer in combination with a proton transfer as a central element of the effective excited state depopulation mechanism. Structural and functional comparisons of the archaeal dodecin with bacterial homologs reveal diverging evolution. Bacterial dodecins bind the flavin FMN instead of riboflavin and exhibit a clearly different binding pocket design with inverse incorporations of flavin dimers. The different adoption of flavin changes photochemical properties, making bacterial dodecin a comparably less efficient quencher of flavins. This supports a functional role different for bacterial and archaeal dodecins. PMID:22451648

  19. Excitation of symmetric surface wavesby electron tubular beams

    NASA Astrophysics Data System (ADS)

    Akimov, Yu A.; Olefir, V. P.; Azarenkov, N. A.

    2006-08-01

    The nonlinear theory of symmetric surface wave excitation by a low-density electron tubular beam in a cylindrical plasma-vacuum-metal waveguide is presented. A set of nonlinear equations is derived that describes the time evolution of the plasma-beam interaction. The influence of the beam and waveguide structure parameters on the saturation amplitude and excitation efficiency of the surface wave is investigated both numerically and analytically. Thermalization of the electron beam in the wave-fields is studied as well.

  20. 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.

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

    PubMed

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

    2015-06-18

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

  2. The 5p autoionization spectra of Ba atoms excited by electron impact: identification of lines

    NASA Astrophysics Data System (ADS)

    Hrytsko, V.; Kerevičius, G.; Kupliauskienė, A.; Borovik, A.

    2016-07-01

    The ejected-electron spectra corresponding to the radiationless decay of 5p5 {n}1{l}1{n}2{l}2{n}3{l}3 states in Ba atoms have been measured precisely for different incident electron energies ranging from the appearance of the first autoionizing line at 15.68 eV up to 140 eV. The spectra have been obtained at an observation angle of 54.7° and with incident-electron and ejected-electron energy resolutions of 0.2 eV and 0.07 eV, respectively. In total, 63 lines with excitation thresholds below 22 eV have been observed between 9.8 and 16.6 eV ejected-electron kinetic energy. Based on measured excitation energies, intensity behavior of lines, calculated excitation energies, cross sections and decay rates of states in 5p56s{}2{nl}, 5p55d{}2{nl} and 5p55d6snl configurations, assignments for all 63 lines are proposed. The excitation and decay processes for classified autoionizing states have been examined and compared with existing data. The excitation threshold of the 5{{{p}}}6 subshell has been established at 15.61 ± 0.05 eV.

  3. 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.

  4. 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.

  5. Excited state mass spectra of Λc+ baryon

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  6. 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.

  7. 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.

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

    SciTech Connect

    Igenbergs, Katharina; Wallerberger, Markus; Aumayr, Friedrich

    2011-06-01

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

  9. 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.

  10. 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.

  11. Inelastic X-ray Scattering Studies of Electronic Excitations

    NASA Astrophysics Data System (ADS)

    Ishii, Kenji; Tohyama, Takami; Mizuki, Jun'ichiro

    2013-02-01

    Inelastic x-ray scattering (IXS) has developed into one of the most powerful momentum-resolved spectroscopies. Especially in the last decade, it has achieved significant progress utilizing brilliant x-rays from third-generation synchrotron radiation facilities. Simultaneously, theoretical efforts have been made to predict or interpret the experimental spectra. One of the scientific fields studied intensively by IXS is strongly correlated electron systems, where the interplay of charge, spin, and orbital degrees of freedom determines their physical properties. IXS can provide a new insight into the electron dynamics of the systems through the observation of charge, spin, and orbital excitations. Focusing on the momentum-resolved electronic excitations in strongly correlated electron systems, we review IXS studies and the present capabilities of IXS for the study of the dynamics of materials. With nonresonant inelastic x-ray scattering (NIXS), one can directly obtain dynamical charge correlation and we discuss its complementary aspects with inelastic neutron scattering. NIXS also has a unique capability of measuring higher multipole transitions, which are usually forbidden in conventional optical absorption. Resonant inelastic x-ray scattering (RIXS) is now established as a valuable tool for measuring charge, spin, and orbital excitations in a momentum-resolved manner. We describe RIXS works on cuprates in detail and show what kind of electronic excitations have been observed. We also discuss RIXS studies on other transition-metal compounds. Finally, we conclude with an outlook on IXS using next-generation x-ray sources.

  12. Low energy electronic excitations and fano resonance in K doped C 60 from Raman scattering excited at 1.16 eV

    NASA Astrophysics Data System (ADS)

    Danieli, R.; Denisov, V. N.; Ruani, G.; Zamboni, R.; Taliani, C.; Zakhidov, A. A.; Ugawa, A.; Imaeda, K.; Yakushi, K.; Inokuchi, H.; Kikuchi, K.; Ikemoto, I.; Suzuki, S.; Achiba, Y.

    1992-01-01

    We present a Raman scattering study of pristine and K doped C 60 at various doping levels by exciting in the near-IR at 1.16 eV. The normal metallic state of K 3C 60 is characterized by a broad scattering background and by the resonance of low energy phonons in the range of 250-500 cm -1. We assign the broad background to an electronic Raman scattering due to low energy electronic excitations. This spectral feature is indicative of an anomalous normal state behaviour and is similar to the case of high temperature ceramic superconductors. In the overdoped K 6C 60 the squashing mode at 278 cm -1 shows a Fano resonance with the electronic scattering associated with localized electronic excitations which are characteristic of isolated regions of K 3C 60 into the matrix of K 6C 60 as a result of inhomogeneous doping. The Fano resonance indicates a specific electron-phonon coupling of this Jahn-Teller mode with low energy excitations and suggests that the symmetry of this electronic excitation is h g (i.e. the same of the coupled phonon mode). We discuss the nature of the anomalous electronic Raman scattering in terms of scattering from low energy excitations involving a low lying singlet band resulting from electron correlation and/or dynamical J-T distortion caused by the squashing mode.

  13. 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

  14. An amorphous phase formation at palladium / silicon oxide (Pd/SiOx) interface through electron irradiation - electronic excitation process

    NASA Astrophysics Data System (ADS)

    Nagase, Takeshi; Yamashita, Ryo; Yabuuchi, Atsushi; Lee, Jung-Goo

    2015-11-01

    A Pd-Si amorphous phase was formed at a palladium/silicon oxide (Pd/SiOx) interface at room temperature by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Solid-state amorphization was stimulated without the electron knock-on effects. The total dose required for the solid-state amorphization decreases with decreasing acceleration voltage. This is the first report on electron irradiation induced metallic amorphous formation caused by the electronic excitation at metal/silicon oxide interface.

  15. Studies of metastable neon atoms produced by electron-beam excitation

    SciTech Connect

    Schulman, M.B.

    1988-01-01

    In the optical method, electron-excitation cross sections of radiative atomic or molecular levels are measured by absolutely calibrating the optical radiation emitted when the excited species are produced by electron-beam excitation of a high-purity gas sample, However, this method is not applicable to metastable (nonradiating) excited levels. With a continuous-wave dye-laser beam intersecting the electron beam, the metastable species produced can be pumped to a higher, radiative level. The intensity of the resulting laser-induced fluorescence from the higher level can be measured to obtain the excitation cross section for production of the metastable level. The absolute number density of the metastable species can be determined by a similar method which uses a pulsed dye laser. This work describes the application of the pulsed-laser technique to the investigation of several aspects of electron-beam excitation of neon atoms in a static gas sample to the metastable 1s{sub 5} (2p{sup 5}3s{sup 3}P{sub 2}) level. In addition to spatially resolved number-density measurements, the temporal disappearance of the metastables from the collision region has been investigated. In the first 50 {mu}s after a fast cutoff of the electron beam, the decay curve of the metastable density is close to a single exponential form, with a time constant of 20 {mu}s. The magnitude of the laser-induced fluorescence per unit electron-beam current has been studied as a function of electron energy and ground-state neon density. Attempts to measure the cross section for exciting form the metastable levels to the higher excited 2p{sub 9} level (2p{sup 5}3p, J = 3) are also described.

  16. (e,2e) Reactions for He+ and Li2+ Ions from their Excited States. Scaling Law

    NASA Astrophysics Data System (ADS)

    Stia, C. R.; Fojón, O. A.; Rivarola, R. D.

    In this work, theoretical triply differential cross sections for ionization of several hydrogenic atoms from excited states by fast electron impact are computed'in the case of asymmetric coplanar geometry. The final wavefunction is chosen as an approximate solution to the three-body scattering problem with correct asymptotic conditions. The initial wavefunction also satisfies correct boundary conditions. Results for Li2+ ions in their 2s and 2p excited states are presented. In addition, it is shown that a simple scaling law for the triply differential cross sections obtained for ionization of hydrogenic targets from their ground state is also satisfied by excited hydrogenic targets.

  17. Investigation of the Electronic Excited States of Small Gold Clusters in Rare Gas Matrices: Spin-Orbit Time-Dependent Density Functional Theory Calculation.

    PubMed

    Jamshidi, Zahra; Kaveei, Elham; Mohammadpour, Mozhdeh

    2015-08-13

    The effects of the weak interactions of rare gas atoms on the UV-visible absorption spectra of gold dimer and tetramer clusters are investigated. The time-dependent density functional theory based on the two-component relativistic zeroth-order regular approximation that considered spin-orbit coupling is performed to estimate the absorption spectra of Au2,4-Rgn (Rg = Ne-Xe, and n = 1-6) complexes. Using spin-orbit, including the appropriate functional, shows a close correlation between experiment and our calculations. It is also demonstrated that the weak interactions between rare gas atoms and gold clusters affect the UV-vis spectra of Au2,4 clusters by shifting the electronic transition toward the blue. Moreover, we find that the order of change in peak position, Δν̃, is proportional to the strength of interactions: Δν̃Au2,4-Xe > Δν̃Au2,4-Kr > Δν̃Au2,4-Ar > Δν̃Au2,4-Ne. In addition, comparing the UV-visible spectra of Au2,4-Rgn complexes with those of isolated Au2 and Au4 clusters shows that for Au2,4-Rg2,4,6 complexes in which Rg atoms interacted symmetrically with gold clusters no additional peaks are observed compared to isolated clusters; however, for Au2,4-Rg1,3,5 complexes, extra peaks appear because of the decrease in symmetry. PMID:26186279

  18. 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.

  19. Electron impact elastic scattering and vibrational excitation of ethylene

    NASA Astrophysics Data System (ADS)

    Khakoo, Murtadha; Khakoo, Sabaha; Sakaamini, Ahmad; Hargreaves, Leigh; Winstead, Carl; McKoy, Vince

    2015-09-01

    Experimental and theoretical (Schwinger Multi-Channel model) differential scattering cross sections for low energy electron elastic scattering plus vibrational excitation (4 energy loss features) of ethylene are presented. The incident electron energy range is from 0.5eV to 100eV and scattering angles of 5 to 130 degrees. Comparisons with theory and past available measurements show good agreement in general. Funded by a National Science Foundation Collaborative Research Grant to CSUF and Caltech.

  20. 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