Photoinduced CO Desorption Dominates over Oxidation on Different O + CO Covered Ru(0001) Surfaces

High Resolution Image Download MS PowerPoint Slide The photoinduced desorption and oxidation of CO on Ru(0001) is simulated using ab initio molecular dynamics with electronic friction that accounts for the nonequilibrated excited electrons and phonons. Different (O,CO) coverages are considered, the experimental room temperature coverage consisting in 0.5 ML-O + 0.25 ML-CO (low coverage), the saturation coverage achieved experimentally at low temperatures (0.5 ML-O + 0.375 ML-CO, intermediate coverage), and the equally mixed monolayer that is stable according to our calculations but not experimentally observed yet (0.5 ML-O + 0.5 ML-CO, high coverage). The results of our simulations for the three coverages are consistent with femtosecond laser experiments showing that the CO photodesorption largely dominates over CO photo-oxidation. These results cannot be explained in terms of the distinct activation energies calculated for the relaxed surfaces. Different (dynamical) factors such as the coupling to the laser-excited electrons and, more importantly, the interadsorbate energy exchange and the strong surface distortions induced in the more crowded surfaces are fundamental to understand the competition between these two processes under the extremely nonequilibrated conditions created by the laser.