Frankfurt 2006 – scientific programme
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MO: Molekülphysik
MO 12: Ultrafast Structural Changes
MO 12.3: Talk
Monday, March 13, 2006, 14:45–15:00, H12
Ultrafast X-ray diffraction study of the molecular crystal DIABN — •Clemens von Korff Schmising1, Mareike Kiel1, Matias Bargheer1, Michael Woerner1, Thomas Elsaesser1, Christopher Root2, Markus Braun2, and Wolfgang Zinth2 — 1Max-Born-Institut, Max-Born-Str. 2a, 12047 Berlin — 2Lehrstuhl für Biomolekulare Optik, Oettingenstrasse 67, Ludwig-Maximilians-Universität München, 80538 München
We present x-ray diffraction data taken on single crystals and powder samples of the molecular crystal diisopropylaminobenzonitrile (DIABN), recorded with a femtosecond x-ray plasma source providing a time-resolution of few 100 fs. DIABN represents a model system for photoinduced charge transfer, and the induced intra-molecular motion is subject of a long standing controversy. The molecules are excited with 400 nm pump pulses to the locally excited state (LE). We measure the intensity of several Bragg refections as a function of the time-delay between the pump pulse and the x-ray probe pulse. The diffraction transients are modulated on a 10 ps timescale with a surprisingly large amplitude of several percent, although the excitation density is only 10−4. This suggests an interpretation in terms of inter-molecular dynamics, which we attribute to solvation of the excited state dipole in the polar solvent of the crystal itself. On the basis of the experimental findings we discuss the perspectives for studying ultrafast molecular processes by femtosecond x-ray diffraction.