Kinetics and dynamics of the initial adsorption of nitric oxide on Ir(111)

The interaction of nitric oxide (NO) with an Ir(111) surface has been studied with supersonic molecular beam techniques and electron energy loss spectroscopy. Initial adsorption probability S0, measurements as a function of incident kinetic energy Ei, surface temperature Ts, and angle of incidence θi reveal that separate mechanisms govern adsorption at low and high kinetic energy. This distinction is reflected in measurements of the initial molecular adsorption probability where a decrease in the value of S0 with increasing Ts (between 77 and 300 K) is observed at low kinetic energy (Ei<0.45 eV), but no surface temperature dependence is detected at high kinetic energy in this temperature range. We present a model describing both the molecular and dissociative chemisorption of NO on Ir(111). At low kinetic energy, NO adsorbs initially as a physically adsorbed species. From this state, desorption to the gas phase or conversion to a molecularly chemisorbed state on the surface are competing processes which d...