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

The thermally induced decomposition of nitrous oxide on isolated Rh-5(+) and Rh5O+ clusters has been investigated using mid-infrared multiple photon dissociation spectroscopy. The presence of a single coadsorbed oxygen atom is observed to have a profound effect on the cluster surface processes that 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, while 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 Rh-5(+), taking the desorption threshold above the reaction barrier for the surface reaction channel whose energy is unchanged.