Nearly all of the chemical processes involved in energy conversion or in chemical industry utilize catalytic chemical transformations at interfaces between solids and liquids or gases. While most of our existing understanding is based on a static view of reactions at interfaces, the development of x-ray lasers opens up the dynamic regime where studies of the reaction mechanism to observe transformations on timescales down to femtoseconds becomes possible. I will here present how we can study chemical reactions on surfaces using X-ray free-electron lasers from recent work at the Linac Coherent Light Source, or LCLS, at SLAC National Accelerator Laboratory. We induced the hot electron and phonon mediated excitation of adsorbates on Ru(0001) with synchronized excitation by a femtosecond optical laser pulse. We have followed the ultrafast evolution of the bond distortions, weakening and breaking, using x-ray absorption spectroscopy (XAS) and x ray emission spectroscopy (XES) resonantly tuned to the oxygen core level with ultrashort x-ray pulses delivered from LCLS. Thereby directly follow the time evolution of the molecular orbitals in an atom-specific way on a subpicosecond timescale. Four examples will be shown CO desorption, Oxygen activation, CO oxidation and CO hydrogenation on Ru(0001). I will demonstrate that both transient intermediates and the transition state regions can be detected in surface chemical reactions.

http://yoshinobu.issp.u-tokyo.ac.jp/Nilsson_Ultrafast_2015v3.pdf