Electronic processes producing O+ ion photodesorption from oxygen adsorbed on Si(1 1 1)7 × 7

The resonant core photon excitation of adsorbates on surfaces is expected to produce well-controlled electronic processes leading to selective photodesorbed products. Here, we have investigated O+ ion photodesorption from oxygen adsorbed on Si(1 1 1)7 × 7 induced by synchrotron radiation excitation at the Si 2p threshold. We have measured the isotope effects on the ion yield and the kinetic energy distribution of photodesorbed O+ ions (18O+ versus 16O+). We have compared these experimental isotope effects with calculated results from analytical models. From this comparison, it has been found that the desorption mechanism involves a cascade of very short electronic relaxations (of the order of a fs) from at least two different repulsive electronic states.