Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
MO: Fachverband Molekülphysik
MO 21: Photochemie 2
MO 21.1: Vortrag
Donnerstag, 5. März 2009, 14:00–14:15, VMP 6 HS-G
Ultrafast bimolecular reactions of benzhydryl cations in the ground state — •Christian Sailer1, Johannes Ammer2, Christoph Nolte2, Igor Pugliesi1, Herbert Mayr2, and Eberhard Riedle1 — 1Lehrstuhl für BioMolekulare Optik, LMU München — 2Department Chemie und Biochemie, LMU München
We investigate the ultrafast reactions of selected benzhydryl cations with different alcohols which are used as solvents. The benzhydryl cations are photogenerated in the electronic ground state from precursor molecules by fs-UV-excitation (270 nm) and sub-ps dissociation and are detected by their characteristic absorption band at about 450 nm. The subsequent reaction of the cation with the solvent to form an ether is observed by quenching of the cation absorption signal. We are able to show that the decay times vary systematically from 2.6 ps for the most reactive educts to several hundred picoseconds for the less reactive pairs. This behavior is in surprisingly good agreement with measurements on longer timescales up to minutes [1]. To the best of our knowledge these extremely short decay times are the fastest measured bimolecular reaction times in the electronic ground state. The ultrafast dynamics suggest that the alcohol molecules are not randomly distributed around the precursor, as the rotational relaxation of alcohols (several picoseconds) is slower than the fastest observed reaction times. It is therefore inferred that the reactants are already suitably aligned before the optical excitation.
[1] S. Minegishi, S. Kobayashi, and H. Mayr, J. Am. Chem. Soc. 126 (2004), 5174