Phonon- versus electron-mediated desorption and oxidation of CO on Ru(0001)

Heating of a ruthenium surface on which carbon monoxide and atomic oxygen a re coadsorbed leads exclusively to desorption of carbon monoxide. In contra st, excitation with femtosecond infrared laser pulses enables also the form ation of carbon dioxide. The desorption is caused by coupling of the adsorb ate to the phonon bath of the ruthenium substrate, whereas the oxidation re action is initiated by hot substrate electrons, as evidenced by the observe d subpicosecond reaction dynamics and density functional calculations. The presence of this laser-induced reaction pathway allows elucidation of the m icroscopic mechanism and the dynamics of the carbon monoxide oxidation reac tion.