W0057

Photo-induced Transient Structural Changes in Organic Solids Probed by Time-resolved X-ray Diffraction. S. Techert, Max-Planck-Institute for Biophysical Chemistry, Dept. Spectroscopy and Photochemical Kinetics, 37070 Goettingen, Germany, stecher@gwdg.de.

In this contribution we report on the experimental characterization of the geometry of short-lived electronically excited states by time-resolved x-ray diffraction (nanosecond – picosecond time scale). Here, the structure factors of a system as a function of time are measured. Since this technique gives complete structural information, it is a very useful tool for learning more about atom motions on the excited-state energy surface — "beyond" the broad band typical of common UV/VIS spectroscopy. We will report about photo-induced disorder-order phenomena in organic solids and photo-induced solid-state reactions. Both common are dynamical pathways which are determined by the rigidity of the crystal lattice. Therefore the reactions will be discussed in the framework of the topochemical principle.