Hamburg 2009 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 9: Femtosekundenspektroskopie 3

MO 9.5: Vortrag

Dienstag, 3. März 2009, 17:30–17:45, VMP 6 HS-F

Dissociation and bond formation dynamics in the laser induced S_N1 reaction of diarylmethane derivates — •Benjamin Fingerhut and Regina de Vivie-Riedle — Department Chemie and Biochemie, Ludwig-Maximilians-Universität München, 81377 München, Germany

The primary processes in the formation of electrophilic precursor ions, key intermediates in organic synthesis, are studied on a microscopic scale by quantum chemical and quantum dynamical methods. We investigate ultrafast dissociation processes of diphenylmethyl chloride in gas phase. For the competing reaction channels of ion pair and radical pair formation, induced by a femtosecond laser pulse, the interaction of different electronic states leads to ultrafast bond cleavage.

Based on ab initio data we derived a system Hamiltonian which is suitable to describe the multidimensional dissociation process in a reduced reactive coordinate space [1]. Quantum dynamical calculations suggest that dissociation induced by a Fourier limited femtosecond laser pulse provides the ion pair as the main product in gas phase despite its higher potential energy.

Subsequent bimolecular recombination leading to bond formation, which constitutes the second part of the S_N1 reaction, is investigated by on-the fly molecular dynamics simulations. The direct reaction with solvent molecules restricts the lifetime of generated carbo cations to several picoseconds.

[1] B. Fingerhut, D. Geppert and R. de Vivie-Riedle, Chem. Phys. 343, 329 (2008).