A combined EELS-XPS study of molecularly chemisorbed oxygen on silver surfaces: Evidence for superoxo and peroxo species

Both superoxo and peroxo species are formed when oxygen is adsorbed on a polycrystalline Ag surface as evidenced by the characteristic OO stretching frequencies in the EEL spectra. Based on temperature-variation studies of the vibration bands in the EELS and of the O(1s) core level peaks in the XPS, characteristic O(1s) binding energies are assigned to the two molecular species; the superoxo species is associated with a significantly higher binding energy as expected. The superoxo species appears to be relatively less thermally stable than the peroxo species, being associated with a ∼ 1300 cm−1 stretching vibration, the highest OO stretching frequency observed so far due to a chemisorbed species.