Reaction pathways in surface femtochemistry: routes to desorption and reaction in CO/O2/Pt(111)

We present new data that address the chemical pathway to desorption of O2 and formation of CO2 in CO/O2/Pt(111) induced by subpicosecond laser pulses. The data show conclusively that the O2 desorbs molecularly. We also find that if the CO oxidizes by an atomic pathway then the capture of oxygen atoms by the CO is highly efficient; if the CO oxidizes by a molecular pathway then the oxygen atoms in the CO3∗ transition state are inequivalent.