Frankfurt 2006 – scientific programme

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MO: Molekülphysik

MO 15: Molecular Clusters II

MO 15.4: Talk

Monday, March 13, 2006, 17:15–17:30, H10

Excited state hydrogen transfer in aminopyridine dimer: details of the reaction coordinate — •Thomas Schultz, Hans-Hermann Ritze, Elena Samoylova, Valoris Reid Smith, Ingolf Volker Hertel, and Wolfgang Radloff — Max Born Institut, Max Born Str. 2A, 12489 Berlin, Germany

The doubly hydrogen-bonded aminopyridine dimer (APd) resembles a Watson-Crick base pair and served as model system for a theoretically predicted hydrogen-transfer process in the excited state. We characterized this reaction experimentally by femtosecond pump-probe ionization spectroscopy. The reaction rate (1.2-1.8 $∖ast 10^{10}$ s$^{-1}$) varied non-monotonously with the excitation energy and showed a considerable H/D isotope effect. Based on our observations and ab initio calculations, we propose an excited state reaction pathway with a rate determining barrier for the H-transfer. The cluster structure appears to be a crucial factor determining the occurrence and rate of the H-transfer reaction. This may explain why the corresponding reaction was not observed for the adenine-thymine base pair, which adopts a non-Watson-Crick structure in the gas phase.