Frankfurt 2006 – scientific programme
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MO: Molekülphysik
MO 45: Biomolecules II
MO 45.8: Talk
Wednesday, March 15, 2006, 18:15–18:30, H10
Photoinduced processes in microhydrated adenine clusters — •Elena Samoylova, V. R. Smith, T. Schultz, H.-H. Ritze, W. Radloff, and I.V. Hertel — Max-Born-Institut Berlin, Max-Born Strasse 2a, 12489 Berlin, Germany
Photochemical reactions can be efficiently quenched by fast radiationless decay to the electronic ground state. We investigate such mechanisms in DNA, first, in isolated bases followed by bigger and microhydrated clusters using time-resolved ion and electron spectroscopy. For adenine-monomer the excited state dynamics could be characterized by an exponential decay containing two components with 100 fs and 1 ps life time. The 100 fs component is due to a very short living electronic state of π π ∗ character and the 1 ps component is due to an optically dark nπ ∗ state. In the microhydrated adenine we did not observed the 1 ps contribution. That indicated a different very fast relaxation pathway due to a π σ ∗ electronic state. In adenine-dimer we found a similar mechanism of excited state deactivation as for A(H2O), with a minor contribution of the nπ ∗ state. Very different behaviour was observed in adenine-dimer cluster with three or more water molecules when the cluster changed from a planar, H-bound to a π -stacked structure. With photoelectron-photoion coincidence spectroscopy an additional relaxation pathway with ns life time was identified which we assigned to the formation of an eximer state. Our observations in the gas phase reproduce similar experiments in water solution and are discussed in the context of high-level theoretical calculation.