Abstract: Chemisorption of carbon monoxide on the (110) surface of iridium

The chemisorption of carbon monoxide on well-characterized and oxidized [1] Ir(110) surfaces has been well studied in an ultrahigh vacuum environment. On both surfaces, adsorption occurs via a mobile precursor state. At surface temperatures of 90 and 300 K, the adsorption kinetics are independent of whether the surface is clean or oxidized. LEED and thermal desorption data indicate that saturation coverage is approximately 10^15 molecules/cm^2 or one monolayer under all conditions. No evidence for physical adsorption of CO exists, even at 90 K. The sticking probability at that temperature is nearly unity until saturation coverage is reached. At 300 K, the sticking probability is unity at low coverages but decreases drastically at 0.8 of saturation coverage. This decrease is attributed to intermolecular repulsions. A kinetic model suggests a repulsive interaction of 2 kcal/mol exists between CO molecules at that coverage [1]. This result is in good agreement with the repulsion expected from a two-dimensional Lenard-Jones model for CO.