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MO: Fachverband Molekülphysik
MO 9: Femtosecond Spectroscopy II
MO 9.6: Talk
Tuesday, March 15, 2011, 12:00–12:15, TOE 317
Non-statistical molecular dynamics: wavepacket bond cleavage — •Nils Krebs1, Christian F. Sailer1, Benjamin P. Fingerhut2, Regina de Vivie-Riedle2, and Eberhard Riedle1 — 1Lehrstuhl für BioMolekulare Optik, LMU München — 2Department Chemie, LMU München
After 270 nm excitation diphenylmethyl chloride (DPMC) dissociates into a benzhydryl cation and a chlorine anion (heterolysis) or into a radical pair (homolysis). DPMC and the products are spectrally well separated and therefore the dynamics can be recorded with 40 fs resolution in a two-color transient absorption measurement in a liquid jet. We find the appearance of the radical signal at 330 nm to be delayed by about 80 fs with respect to the optical excitation. Ab-initio calculations show that this non-rate behavior is due to wavepacket motion in the Franck-Condon region and its subsequent evolution along the dissociation coordinate through a conical intersection [1]. The transient signal then increases within 300 fs due to the planarization of the DPM radical, the quasi-exponential signal increase is not due to a statistical behavior of the dissoziation process. Measurements at 430 nm show that the cation appears with a delay of 125 fs. This means that the nascent radical and cation populations evolve from different conical intersections and follow differing bond cleavage pathways. The combination of the time resolved experiment and ab-initio dynamics render a first complete description of the bond cleavage on the atomistic level.
[1] B. P. Fingerhut, D. Geppert, and R. de Vivie-Riedle, Chem. Phys. 343, 329 (2008).