Basic studies of the oxygen surface chemistry of silver: Chemisorbed atomic and molecular species on pure Ag(111)

The interaction of oxygen with Ag(111) has been studied over the pressure range 10^?2?1.0 Torr. Thermal desorption measurements using isotopically labelled molecules unambiguously establish the presence of a stable chemisorbed dioxygen species which co-exists with adsorbed atomic oxygen. Dissolved oxygen undergoes exchange with the latter species but not with the former. The maximum dioxygen population is found to be markedly sensitive to gas dosing pressure; a model is proposed which accounts for these observations and for related observations on alkali-doped Ag. XP and UP spectral features can be correlated with the two types of oxygen species; angle-resolved XP and Auger spectra indicate that O₂ (a) resides on the metal surface whereas O(a) is located within the surface. The XP spectra also suggest that in the case of O₂(a) the molecular axis may lie perpendicular to the surface.