Photoemission study of oxygen adsorbed on coldly deposited silver films

UPS spectra of coldly deposited silver films differ from those of films deposited at room temperature by electronic states localized at surface defects with an energy about 4.2 eV below E_F. Changes after exposure at 140 K to oxygen only occur in the presence of these defects, demonstrating that oxygen is only adsorbed at defects. Raman vibrational spectroscopy shows that oxygen is adsorbed nominally as O₂^? and O₂^2?. Possible assignments of the oxygen related UPS structures are discussed.