A REFLECTION ABSORPTION INFRARED-SPECTROSCOPY STUDY OF THE ADSORPTION OF ATOMIC OXYGEN ON SILVER

The adsorption of oxygen has been studied on a polycrystalline silver surface using reflection-absorption infrared spectroscopy (RAIRS). Three distinct species are found following the adsorption of oxygen which are identified using thermal desorption spectroscopy and RAIRS using isotopically labelled compounds. Two of these are dioxygen and the third is dissociatively adsorbed atomic oxygen. Atomic oxygen is shown to adsorb onto the silver surface via Langmuir kinetics, and the heat of adsorption obtained by measuring the atomic oxygen coverage in the presence of an external oxygen pressure is 25 +/- 3 kcal/mol. The desorption activation energy, measured by analyzing the leading-edge region of the thermal desorption spectrum, is 37 +/- 1 kcal/mol. The difference between these two values is ascribed to the presence of an activation barrier to dissociative adsorption of 12 +/- 4 kcal/mol.