Effects of Coadsorbed Oxygen on the Infrared Driven Decomposition of N₂O on isolated Rh₅⁺ Clusters

The thermally induced decomposition of nitrous oxide on isolated Rh5+ and Rh5O+ clusters has been investigated using mid-infrared multiple photon dissociation spectroscopy. The presence of a single co-adsorbed oxygen atom is observed to have a profound effect on the cluster surface processes which ensue following infrared heating of the cluster. Exciting the infrared active N2O bending transition in Rh5N2O+ results predominantly (≥ 85%) in molecular desorption of the N2O moiety whilst the same excitation in Rh5ON2O+ leads instead to N2O dissociation on the cluster surface producing Rh5O2+ (≥ 85%). Calculations of the reaction pathway using density functional theory indicate that the change in branching ratio arises from a 0.4 eV greater binding energy of N2O to Rh5O+ compared with Rh5+ taking the desorption threshold above the reaction barrier for the surface reaction channel whose energy is unchanged