The interaction of CO and Ar molecular beams with Ir(110)

Abstract

Supersonic molecular beam techniques were used to study the scattering of CO and Ar from clean and CO-covered Ir(110) surfaces over a wide range of kinetic energies of the incident species. The initial sticking coefficient, S0, for CO on a clean Ir(110) surface decreases from 0.80 at 2 kcal/mol beam energy to 0.35 at 34 kcal/mol. At each beam enery S0 is independent of surface temperature in the interval 200≤Ts≤500 K. Scattering of CO from a CO-saturated surface shows a transition from mainly trapping/desorption scattering at low beam energy to direct inelastic scattering at high beam energy. The trapping probability for CO on the covered surface decreases with beam energy. Ar and CO scattering from the covered surface are very similar. The dependence of the trapping probability on beam energy for CO and Ar is identical within the margin of error of the experiment. Comparison of the Ar scattering from the CO-covered surface with that from the clean surface reveals much smaller trapping probabilities for Ar on the clean surface. This indicates that the adsorbed CO layer increases the efficiency of the energy transfer from the gas to the surface.