ISOTOPIC STUDIES OF THE REACTION OF NO ON SILVER SURFACES

The isotopomers (NO)-N-14-O-16 and (NO)-N-15-O-18 were used to obtain information on the mechanisms of NO reaction on silver layers on Ru(001), by observation of the isotopic distributions of the products. NO adsorption on Ag in the 75-100 K range produces adsorbed N2O and oxygen atoms. Very different isotopic distributions of product N2O are observed, depending on whether the NO isotopomers are dosed simultaneously or sequentially. The observed N2O distributions favor a non-dissociative reaction pathway with a NO dimer as the reaction intermediate. The isotopic distribution of a high temperature NO desorption state can be explained by dissociation of a NO2 surface species that is formed at a low temperature. The N2O which is produced by reaction of NO on the surface is found to have a higher desorption temperature than N2O adsorbed on either the clean Ag surface or on an oxygenated Ag surface. This is attributed to a strong binding interaction with surface NO2.