Seminars Archive

Towards time-resolved laser T-jump/X-ray absorption probe spectroscopy

Abstract
Understanding the mechanism of chemical and biochemical reactions in water is of primarily importance due to their importance in Nature. Photo-induced reactions have been widely studied using pump-probe techniques in the optical and X-rays domains with high time resolution, gaining precious insights. However, most of the processes in solution are non-light driven and require a different investigation scheme. The temperature jump (T-jump) represent an ideal tool to study thermally driven (bio)chemical reactions in water, as demonstrated by several optical studies. Its extension to the X-ray domain would add structural sensitivity and element selectivity, offering unprecedented details to the investigations. In our work we show the extreme sensitivity of the X-ray absorption spectroscopy (XAS) probe to investigate a thermally activated multistep substitution reaction on a Cobalt center. An IR laser pulse was used to photo-excite the vibrational degrees of freedom of the solvent, which relaxes within 2-5 ps and locally increases the bulk solution, triggering the chemical reaction. The structural information provided by the XAS at the Cobalt K-edge allowed us to study the effect of the pump, which led to the conversion of the reagent into intermediate species, without a sensitive formation of products. The present study represents a first step to the extension of a pure T-jump scheme with hard X-ray spectroscopic probe for the investigation of thermally-driven processes, broadening the opportunities for pump-probe applications at synchrotrons and free-electron lasers, not only with XAS probe but also X-ray emission and photoemission on liquids.