Probing nucleobase photoprotection with soft x-rays
1 PULSE, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
2 Departments of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA
3 Physics Department, Western Michigan University, Kalamazoo, MI 49008, USA
4 LCLS, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
5 Department of Physics, Uppsala University, Uppsala, Sweden
6 Department of Chemistry, Stanford University, Stanford, CA 94305, USA
7 Max-Born-Institut, 12489 Berlin, Germany
8 Dipartimento di Chimica, Universita di Perugia, and ISTM-CNR, 06123 Perugia, Italy
Nucleobases absorb strongly in the ultraviolet region, leading to molecular excitation into reactive states. The molecules avoid the photoreactions by funnelling the electronic energy into less reactive states on an ultrafast timescale via non-Born-Oppenheimer dynamics. Current theory on the nucleobase thymine discusses two conflicting pathways for the photoprotective dynamics. We present our first results of our free electron laser based UV-pump soft x-ray-probe study of the photoprotection mechanism of thymine. We use the high spatial sensitivity of the Auger electrons emitted after the soft x-ray pulse induced core ionization. Our transient spetra show two timescales on the order of 200 fs and 5 ps, in agreement with previous (all UV) ultrafast experiments. The timescales appear at different Auger kinetic energies which will help us to decipher the molecular dynamics.
© Owned by the authors, published by EDP Sciences, 2013
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