Hannover 2013 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 21: Femtosecond Spectroscopy V
MO 21.2: Vortrag
Donnerstag, 21. März 2013, 11:15–11:30, F 102
Molecular wave packets decelerated by solvent environment: The dynamic continuum ansatz — •Sebastian Thallmair1,2, Markus Kowalewski1, and Regina de Vivie-Riedle1 — 1Department Chemie, LMU München — 2LS für BioMolekulare Optik, LMU München
Most reactions in organic as well as biochemistry take place in solution. Electrostatic solvent effects are known to change the reactivity of the solute dramatically. The same holds for photochemical reactions where often dissociative processes are included. Here not only the electrostatic influence but also the dynamic impact of the solvent becomes important. For bulky leaving groups, like in phosphonium salts, the solvent cage substantially decelerates the photogenerated fragments depending on the viscosity of the solvent. Subsequent distance dependent processes like electron or energy transfer between the photofragments become feasible as the fragments are kept at a reasonable distance.
Also on the shorter time scale below 200 fs frictional deceleration is essential. The molecular system gets the chance to deposit energy into motions additional to the primary dissociation coordinate. Thereby regions decisive for the branching into competing product channels can be reached.
We present a new dynamic continuum ansatz to describe the frictional force exerted on moving wave packets in a solvent cage. The frictional deceleration is treated in the quantum mechanical formalism including the dynamic viscosity and Stokes' law. The solvent interferes on the fs time scale, but decides the reaction outcome.