München 2004 – wissenschaftliches Programm
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MO: Molekülphysik
MO 12: Poster I
MO 12.5: Poster
Dienstag, 23. März 2004, 14:00–16:00, Schellingstr. 3
Photoisomerization dynamics of azobenzene analyzed by time-resolved photoelectron spectroscopy — •Thomas Schultz1,2, Jason Quenneville3, Todd J. Martinez3, Susanne Ullrich1, Marek Zgierski1, and Albert Stolow1 — 1Steacie Institute for Molecular Sciences, National Research Council, Ottawa, Canada — 2Now at: Max-Born-Institut Berlin, Max-Born Str. 2a, 12489 Berlin — 3Department of Chemistry, University of Illinois, Urbana, USA
The excited state dynamics of trans-azobenzene were investigated by time-resolved photoelectron spectroscopy. Two excited ππ*-states with distinct dynamics were identified in the wavelength region 285-350 nm. Based on the experimental results and ab initio molecular-dynamics calculations, we present a new model to explain the photoisomerization mechanism of azobenzene: (1) Two excited electronic states S2 and S3 are near-degenerate. (2) Both, S2 and S3 absorb with similar absorption cross sections. (3) S2 undergoes direct and very efficient internal conversion to the ground state, violating Kasha’s rule, while S3 relaxes to the first excited state S1 and thus obeys Kasha’s rule. The presented results can resolve a long-standing dispute about the isomerization mechanism in azobenzene.