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Andreas Osterwalder - One of the best experts on this subject based on the ideXlab platform.

  • investigation of the low energy stereodynamics in the ne 3p2 n2 co reactions
    Journal of Chemical Physics, 2020
    Co-Authors: Junwen Zou, Andreas Osterwalder
    Abstract:

    We report on an experimental investigation of the low-energy stereodynamics of the energy transfer reactions Ne(3P2) + X, producing Ne(1S) + X+ and [Ne–X]+ (X = N2 or CO). Collision energies in the range 0.2 K–700 K are obtained by using the merged beam technique. Two kinds of product ions are generated by Penning and associative ionization, respectively. The intermediate product [Ne–X]+ in vibrationally Excited States can predissociate into bare ions (X+). The experimental ratio of the NeX+ and X+ product ion yields is similar for both molecules at high collision energies but diverge at collision energies below 100 K. This difference is explained by the first Excited Electronic State of the product ions, which is accessible in the case of CO but lies too high in energy in the case of N2.

Jennifer P. Ogilvie - One of the best experts on this subject based on the ideXlab platform.

  • strongly coupled bacteriochlorin dyad studied using phase modulated fluorescence detected two dimensional Electronic spectroscopy
    Optics Express, 2018
    Co-Authors: Vivek Tiwari, Christine Kirmaier, David F Bocian, Dewey Holten, Yassel Acosta Matutes, Marcin Ptaszek, Arkaprabha Konar, Jennifer P. Ogilvie
    Abstract:

    Fluorescence-detected two-dimensional Electronic spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an Excited Electronic State population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the Excited State Electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the Excited States of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using the phase-modulation approach to F-2DES.

  • strongly coupled bacteriochlorophyll dyad studied using two dimensional phase modulated fluorescence detected Electronic spectroscopy
    arXiv: Chemical Physics, 2018
    Co-Authors: Vivek Tiwari, Christine Kirmaier, David F Bocian, Dewey Holten, Yassel Acosta Matutes, Marcin Ptaszek, Arkaprabha Konar, Jennifer P. Ogilvie
    Abstract:

    Fluorescence-detected two-dimensional Electronic spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an Excited Electronic State population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. However, none have demonstrated analysis of kinetics and coherences routine in photon-echo 2DES. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the Excited State Electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the Excited States of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using any variant of F-2DES.

Christoph Riehn - One of the best experts on this subject based on the ideXlab platform.

  • rotational and vibrational dynamics in the Excited Electronic State of deprotonated and protonated fluorescein studied by time resolved photofragmentation in an ion trap
    Structural Dynamics, 2016
    Co-Authors: Dimitri Imanbaew, Maxim F Gelin, Christoph Riehn
    Abstract:

    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.

Junwen Zou - One of the best experts on this subject based on the ideXlab platform.

  • investigation of the low energy stereodynamics in the ne 3p2 n2 co reactions
    Journal of Chemical Physics, 2020
    Co-Authors: Junwen Zou, Andreas Osterwalder
    Abstract:

    We report on an experimental investigation of the low-energy stereodynamics of the energy transfer reactions Ne(3P2) + X, producing Ne(1S) + X+ and [Ne–X]+ (X = N2 or CO). Collision energies in the range 0.2 K–700 K are obtained by using the merged beam technique. Two kinds of product ions are generated by Penning and associative ionization, respectively. The intermediate product [Ne–X]+ in vibrationally Excited States can predissociate into bare ions (X+). The experimental ratio of the NeX+ and X+ product ion yields is similar for both molecules at high collision energies but diverge at collision energies below 100 K. This difference is explained by the first Excited Electronic State of the product ions, which is accessible in the case of CO but lies too high in energy in the case of N2.

Andrew M Moran - One of the best experts on this subject based on the ideXlab platform.

  • Solvent Effects on Ground and Excited Electronic State Structures of the Push-Pull Chromophore Julolidinyl-n-N,N′-diethylthiobarbituric Acid
    2020
    Co-Authors: Andrew M Moran, Claire Delbecque, Anne Myers Kelley
    Abstract:

    Resonance Raman spectra and cross sections of a "push-pull" chromophore containing a julolidine donor and a thiobarbituric acid acceptor have been measured in dilute solution in five solvents having a wide range of polarities (cyclohexane, 1,4-dioxane, dichloromethane, acetonitrile, and methanol) at excitation wavelengths spanning the strong visible charge-transfer absorption band. The absolute Raman excitation profiles and absorption spectra are simulated using time-dependent wave packet propagation techniques to determine the Excited-State geometry changes along the ∼30 Raman-active vibrations as well as the solvent reorganization energies. Several vibrational modes undergo significant (5-15 cm -1 ) frequency changes as the solvent is varied, signaling solvent polarity effects on the ground-State Electronic structure. The Excited-State geometry changes are solvent dependent for some vibrational modes but not for others. The total vibrational reorganization energy decreases, and the solvent reorganization energy increases with increasing solvent polarity in all solvents except the one protic solvent, methanol, which is anomalous in both respects. Tentative assignments are made for the ground-State vibrational modes by comparison of the Raman frequencies and infrared frequencies and intensities with those calculated using density functional theory, as well as by comparison with model compounds. The results are discussed within the context of the two-State valence-bond model for the Electronic properties of conjugated push-pull chromophores

  • optical coherence and theoretical study of the excitation dynamics of a highly symmetric cyclophane linked oligophenylenevinylene dimer
    Journal of Chemical Physics, 2006
    Co-Authors: Andrew M Moran, Shaul Mukamel, Jeremy B Maddox, Janice W Hong, Jeongho Kim, Rene A Nome, Guillermo C Bazan, Norbert F Scherer
    Abstract:

    OptoElectronic properties of a polyphenylenevinylene-based oligomer and its paracylophane-linked dimer are studied using a variety of experimental and theoretical techniques. Despite the symmetrical structure and redshifted absorption of the dimer versus the monomer, an exciton picture is not the most appropriate. Electronic structure calculations establish changes in charge density upon optical excitation and show localized excitations that cannot be accounted for by a simple Frenkel exciton model. Visible frequency pump-probe anisotropy measurements suggest that the dimer should be considered as a three-level system with a fast, ∼130fs, internal conversion from the higher to lower energy Excited Electronic State. Signatures of nuclear relaxation processes are compared for electric field-resolved transient grating and two-dimensional photon echo spectra. These measurements reveal that nuclear relaxation occurs on similar time scales for the monomer and dimer. The connection between the spectral phase of ...

  • solvent effects on ground and Excited Electronic State structures of p nitroaniline
    Journal of Chemical Physics, 2001
    Co-Authors: Andrew M Moran, Anne Myers Kelley
    Abstract:

    Resonance Raman intensities of p-nitroaniline, a prototypical “push–pull” chromophore with a large first hyperpolarizability (β), have been measured in dilute solution in five solvents having a wide range of polarities (cyclohexane, 1,4-dioxane, dichloromethane, acetonitrile, and methanol) at excitation wavelengths spanning the strong near-ultraviolet charge-transfer absorption band. The absolute Raman excitation profiles and absorption spectra are simulated using time-dependent wave packet propagation techniques to determine the Excited-State geometry changes along the five or six principal Raman-active vibrations as well as estimates of the solvent reorganization energies. The total vibrational reorganization energy decreases and the solvent reorganization energy increases with increasing solvent polarity in all solvents except methanol, where specific hydrogen-bonding interactions may be important. The dimensionless normal coordinate geometry changes obtained from the resonance Raman analysis are conve...