Heidelberg 2015 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 22: Femtosecond Spectroscopy 3

MO 22.3: Vortrag

Freitag, 27. März 2015, 11:30–11:45, PH/HS1

Comparative quantum dynamical studies of two diphenylmethyl halide species in a quasi-diabatic picture states including three-state conical intersections — •Matthias K. Roos, Sebastian Thallmair, and Regina de Vivie-Riedle — Department Chemie, Ludwig-Maximilians-Universität München

Carbocations and -radicals are key intermediates of many reactions both in organic synthesis and biochemistry. Such reactive species can be generated by UV laser irradiation of diphenylmethyl halides. This so triggered sub-picosecond ultrafast dissociation occurs via a local π-π^* excitation and finally the carbon-halide σ-bond cleavage is either homolytic or heterolytic. The halide, i.e. chlorine or bromine, acts as leaving group. We use both quantum chemical and quantum dynamical methods to model the bond cleavage and evaluate the branching ratio between the two product pathways. Based on a reduced coordinate space that explicitly includes geometry relaxation for the carbon skeleton the kinetic Hamiltonian is expressed via the Wilson G-Matrix approach. Potential energy surfaces are calculated on the ONIOM(CASSCF(12,10)/B3LPYP) level of theory showing consecutive conical intersections near the Franck-Condon region. Especially three-state conical intersections play the key role for the product splitting. Using ab initio properties the adiabatic potentials are transformed to a quasi-diabatic picture, therefore the off-diagonal potential terms are accounting for the non-adiabatic behaviour. The dynamics for both leaving groups is discussed and compared with experimental results.