Efficient partitioning technique for computing the dynamics of intramolecular processes: Radiationless transitions in pyrazine

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Coherent control of bound state processes via the interfering overlapping resonance scenario [Christopher et al., J. Chem. Phys. 123, 064313 (2006)] is developed to control intramolecular vibrational redistribution (IVR). The approach is applied to the flow of population between bonds in a model of chaotic OCS vibrational dynamics, showing the ability to significantly alter the extent and rate of IVR by varying quantum interference contributions.

“…Larger systems can take advantage of the "QP algorithm". 5 The Feshbach partitioning technique is based on defining two projection operators…”

Section: B the Feshbach Partitioning Techniquementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Overlapping resonances in the control of intramolecular vibrational redistribution

Gerbasi

Sanz

Christopher

et al. 2007

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“…[4] In still stronger fields, electrons are removed and subsequent chemistry takes place on a cationic surface. [5] The pyrazine molecule has been used as a benchmark case for many theoretical control schemes [6][7][8][9][10][11][12][13][14][15][16][17] as well as for experimental time-resolved studies of internal conversion (IC). [19][20][21] Reasons for interest in this molecule are its simple heterocyclic structure (C 4 N 2 H 4 ), symmetry (D 2h ), and small number of valence electrons.…”

Section: Introductionmentioning

confidence: 99%

Coherent phase control of internal conversion in pyrazine

Seideman

Singha

et al. 2015

Shaped ultrafast laser pulses were used to study and control the ionization dynamics of electronically excited pyrazine in a pump and probe experiment. For pump pulses created without feedback from the product signal, the ion growth curve (the parent ion signal as a function of pump/probe delay) was described quantitatively by the classical rate equations for internal conversion of the S 2 and S 1 states. Very different, non-classical behavior was observed when a genetic algorithm (GA) was used to minimize the ion signal at some pre-determined target time, T. Two qualitatively different control mechanisms were identified for early (T< 1.5 ps) and late (T> 1.5 ps) target times. In the former case, the ion signal was largely suppressed for t < T , while for t T the ion signal produced by the GA-optimized pulse and a transform limited (TL) pulse coalesced. In contrast, for T > 1.5 ps the ion growth curve followed the classical rate equations for t < T , while for t T the quantum yield for the GA-optimized pulse was much smaller than for a TL pulse. We interpret the first type of behavior as an indication that the wave packet produced by the pump laser is localized in a region of the S 2 potential energy surface where the vertical ionization energy exceeds the probe photon energy, whereas the second type of behavior may be described by a reduced absorption cross section for S 0 → S 2 followed by incoherent decay of the excited molecules. * rjgordon@uic.edu 2

“…Semiclassical initial value calculations utilizing the mapping approach to describe the pyrazine system were reported by Thoss et al 21 Several approaches based on the propagation of sets of coherent states or Gaussian wavepackets were tested employing the pyrazine problem as a benchmark: the coupled coherent state or multi-configuration Ehrenfest approaches by Shalashilin,22,23 the MPSOFT approach by Chen and Bastita, 24 and the variation multi-configuration Gaussian approach by Burghard et al 25 Other studies investigated the accuracy of projection operator based system-bath decoupling schemes [26][27][28] and mixed quantum-classical approaches, 29 the efficiency of configuration selection schemes for MCTDH wavefunctions, 30 or the convergence behavior of multi-layer MCTDH representations. 31 The present work also investigates methodological developments employing the S 0 → S 2 excitation in pyrazine as a prototypical example of complex non-adiabatic quantum dynamics.…”

Section: Introductionmentioning

confidence: 99%

Decoherence induced by conical intersections: Complexity constrained quantum dynamics of photoexcited pyrazine

Westermann

Manthe

2012

Decoherence effects induced by conical intersecting potential energy surfaces are studied employing the correlation-based von Neumann (CvN) entropy which provides a measure of the complexity of the underlying wavefunction. As a prototypical example, the S(0) → S(2) excitation in pyrazine is investigated. The 24-dimensional wavepacket dynamics calculations presented utilize the multi-layer extension of the multi-configurational time-dependent Hartree (MCTDH) approach. An efficient numerical scheme is introduced which facilitates CvN entropy constrained wavepacket propagation within the multi-layer MCTDH approach. In unconstrained multi-layer MCTDH calculations, the CvN-entropy is found to provide a valuable analytical tool for studying the decoherence phenomena present. Investigating the CvN entropy after the S(0) → S(2) excitation as a function of time, a clear separation of time scales is obtained. It can be related to the different dynamical phenomena present: the initial transfer from the upper (S(2)) to the lower (S(1)) adiabatic electronic states rapidly generates vast amounts of CvN-entropy, while the subsequent motion on the anharmonic lower adiabatic potential energy surface only yields a slow increase of the CvN-entropy. Employing CvN-entropy constrained calculations, the sensitivity of the autocorrelation function, the absorption spectrum, and the diabatic electronic population dynamics to complexity constraints is analyzed in detail.