INTERMEDIATE STATES IN THE ADSORPTION OF NO ON IR(111) : SUBSTRATE TEMPERATURE EFFECTS

Measurements of the initial adsorption probability, S0, of nitric oxide (NO) on Ir(111) as a function of incident kinetic energy, Ei, and surface temperature, Ts, are presented. We observe a decrease in S0 with increasing kinetic energy, Ei, from 0.052 to 1.3 eV. At low kinetic energies, the initial molecular adsorption probability decreases with increasing surface temperature (ranging between 77 and 300 K in this study), while at high kinetic energies, this quantity is independent of surface temperature. We propose a trapping‐mediated mechanism for adsorption at low kinetic energies. In this low energy regime, the surface temperature dependence reflects a kinetic competition between desorption from a physically adsorbed state and conversion to a more strongly bound, molecularly chemisorbed state. At high kinetic energies, we propose that adsorption initially occurs directly into the molecular chemisorption well. Indeed, electron energy loss spectroscopy measurements show no evidence for direct dissociati...