Dear colleagues,

this Wednesday we have a colloquium about

Ultrafast electronic and structural changes in liquids probed by Ultrafast X-ray Absorption Spectroscopy, 12. Mai 2004

Majed Chergui EPFL

"The first event of any light induced process is the rearrangement of charges, which in turn triggers structural changes in the system, be it a solid, a molecule or a protein. Ultrafast laser spectroscopy allows to follow in "real-time" the electronic and structural changes. However, in the latter case the information has to be indirectly extracted. Ideally, a tool is needed that delivers information about both the structural and electronic structure on the time scale over which they take place. We have recently developed a pump-probe scheme based on the use of femtosecond lasers coupled to ultrashort picosecond X-ray pulses from a synchrotron, and studied the photoinduced cycle of a coordination chemistry complex, Ruthenium-tris-bipyridine, in aqueous solutions. X-ray Near-edge spectroscopy (XANES) delivers a high degree of insight into the changes of the valence orbitals of the metal atom, while the Extended X-ray Absorption Fine Structure (EXAFS) delivers information about the structural changes. Our results will be presented and compared to simulations of the spectra. In addition, we also demonstrate an optical-X-ray cross-correlator with femtosecond resolution to be used with future sources."

See also http://www.physik.unizh.ch/teaching/kolloquium.html for details.