Direct access to subsurface sites in gas-surface O2/Ag210 interactions using supersonic molecular beams

We show with supersonic molecular beams and surface vibrational spectroscopy that, contrary to the case of Ag(100) and Ag(110), O2 undergoes total dissociation on Ag(210) at 105 K. Moreover, metastable subsurface sites can be accessed either directly or indirectly. For the direct channel, the final configuration of the oxygen atoms depends on the angle and the energy with which the gas-phase molecules collide with the surface, being largest for normal incidence on the (100) nanofacets. Access into the subsurface site is enabled only in the presence of preadsorbed oxygen adatoms.