Abstract

Different x-ray spectroscopic tools allow monitoring quite complementary properties in chemical media. X-Ray absorption fine structure (XAFS) methods, such as XANES and EXAFS, reveal details about the local geometric and electronic structure in molecular systems, and x-ray emission spectroscopy (XES) has proven to be a spin-sensitive tool.

We have extended these mature tools into the time domain via the pump-probe scheme to permit recording dynamic processes involving changing nuclear, electronic and spin degrees of freedom. Dynamic oxidation state shifts and geometric structure changes are reliably captured with XAFS tools, while spin-changes can be extracted from time-resolved XES studies. An important goal aims to deliver a femtosecond motion picture of a photoexcited chemical species in real-time, which should permit us to understand the elementary steps involved in photochemical reactivity.

This talk will introduce these ultrafast structural tools, and present key examples for exploiting them on both the picosecond-nanosecond and femtosecond time scales. These include typical photochemical reactions, such as charge transfer and dynamic solvent response processes. Recent studies with femtosecond time resolution at the linac coherent light source (LCLS) reveal new details about the elementary process of spin-switching in transition metal compounds (Fig. 1), and our current understanding of the highly correlated dynamics will be given.