München 2004 – scientific programme
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MO: Molekülphysik
MO 12: Poster I
MO 12.15: Poster
Tuesday, March 23, 2004, 14:00–16:00, Schellingstr. 3
Ultrafast Infrared Spectroscopy on Ground State Dynamics during Photoisomerisations — •Florian Koller, Tobias Schrader, Wolfgang Schreier, Arne Sieg, Wolfgang Zinth, and Peter Gilch — Sektion Physik, Ludwig-Maximilians-Universität, Oettingenstr. 67, D-80538 München, Germany
Photoisomerisations are often accompanied by a rapid (100 fs – 1 ps) depletion of the excited state. These dynamics can be studied by femtosecond fluorescence and absorption spectroscopy. Little is known on the ensuing processes in the electronic ground state. Time resolved IR spectroscopy can open the route to a detailed understanding of the structural re-arrangements and the vibrational relaxation in the ground state. This is demonstrated by IR experiments (in the range of 1520 – 1050 cm−1 ) on the isomerisation of 4−nitro−4′(dimethylamino)−azobenzene (NA). The decay of the excited state was followed by the disappearance of an IR line at 1275 cm−1 reproducing the fluorescence decay time. At later stages, apart from cooling processes on the 5 ps time scale, surprisingly slow dynamics (up to 200 ps) due to structural re-arrangements are detected.