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Femtosecond x-ray laser pulses are used to probe the CO oxidation reaction on Ru initiated by an optical laser pulse. On a timescale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and O on the surface allowing the reactants to collide and, with a transient close to a picosecond (ps), new electronic states appear in the O K-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond-formation between CO and O with a distribution of OC—O bond lengths close to the transition state (TS). After 1 ps 10 % of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.


This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Science, volume 347, in 2015 following peer review. The definitive publisher-authenticated version is available online at DOI: 10.1126/science.1261747


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