Düsseldorf 2007 – wissenschaftliches Programm

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SYSX: Symposium Soft X-ray induced ultafast processes on the atomic scale

SYSX 1: Soft X-ray induced ultrafast processes I

SYSX 1.2: Hauptvortrag

Donnerstag, 22. März 2007, 14:30–15:00, 6G

Ultrafast processes on the atomic scale studied with hard (and soft) x-radiation — •Christian Bressler — LSU-ISIC-BSP. EPFL. CH-1015 Lausanne, Switzerland

Electronic structure changes are at the origin of chemical reactivity, which drive the forming and breaking of bonds. Ultrafast x-ray absorption fine structure spectroscopy (XAFS) delivers both the electronic and geometric transient structure changes, when interfaced with a femtosecond laser in a pump-probe scheme. In addition, XAFS methods are element-selective and can be applied to disordered bulk systems, in particular liquids. On the femtosecond time scale one would obtain a rather complete picture via XAFS, since the propagation from a reaction center is limited to a few Angstroms on these time scales. We have recently recorded high-quality transient XAFS spectra at 3rd generation synchrotrons with currently < 100 ps temporal resolution, corresponding to the electron bunch width at the synchrotron. Examples of excited state structures of solvated coordination chemistry compounds and of short-lived atomic radicals in aqueous solution will be presented. Extending these studies into the femtosecond time domain is straightforward in concept, while pico- to nanosecond resolved studies still offer a high potential for research on short-lived reaction intermediates, whose structures can not be determined by other means. The continued efforts using pulsed x-rays on the femto- to nanosecond time scales will be closely linked to the developments of novel photon sources, including, e.g., femtosecond x-rays at SLS and BESSY, next to soft x-rays < 1 keV to become available at FLASH.