Hamburg 2009 – scientific programme

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MO: Fachverband Molekülphysik

MO 21: Photochemie 2

MO 21.2: Talk

Thursday, March 5, 2009, 14:15–14:30, VMP 6 HS-G

Biphasic kinetics in fast ground state chemistry due to vibrational excitation — •Thomas Schmierer, Wolfgang Schreier, and Peter Gilch — Ludwig-Maximilians-Universität München, Lehrstuhl für BioMolekulare Optik, 80538 München, Deutschland

Internal conversion processes and photo-chemical reactions often result in vibrationally highly excited intermediates. On time-scales which are short compared to vibrational relaxation this excitation can influence chemical kinetics in the electronic ground state.

The photo-chemistry of ortho-nitrobenzaldehyde (NBA) offers an example for such a kinetic. UV-excitation triggers a hydrogen transfer which results in a ketene intermediate within 400 fs [1]. In aprotic solvents, e.g. THF, nanosecond lifetimes for this ketene have been reported [2,3]. Femtosecond UV/Vis and IR experiments show that the decay in THF is biphasic with time-constants of 10 ps and some nanoseconds. The 10 ps constant matches the decay of the vibrational excitation and the rise of a secondary product.

[1] S. Laimgruber et al., Angew. Chem. Int. Ed.(2005) 44

[2] R. W. Yip et al., Res. Chem. Int., (1989) 11

[3] S. Laimgruber et al., Phys. Chem. Chem. Phys., (2008) 10