Surface diffusion of carbon monoxide on Ru(001) studied using laser-induced thermal desorption

Abstract

Abstract The surface diffusion of CO on Ru(001) was measured using laser-induced thermal desorption techniques. The surface diffusion coefficients displayed a strong dependence on the CO coverage. For CO coverages below θ = 0.33 ML, the surface diffusion coefficient at 290 K was approximately constant at D 1× 10−8 p cm 2 s . As the CO coverage increased from θ = 0.33 to θ = 0.58 ML, the surface diffusion coefficient at 290 K increased dramatically from 1 × 10t8 to 1 × 10 t 6 cm 2 s . The surface diffusion coefficients at 250 K also exhibited a similar increase versus CO coverage. At various temperatures and CO coverages, the surface diffusion coefficients displayed Arrhenius behavior. For θ = 0.27 ML, the Arrhenius parameters were E dif = 11 kcal mol and D 0 = 0.38 p cm 2 s in the temperature range between 300 and 370 K. For θ 0.45 ML, Edif and D0 both decreased as a function of increasing CO coverage at temperatures between 210 and 290 K. At θ = 0.45 ML, the Arrhenius parameters were E dif = 8.0 kcal mol and D 0 = 0.28 cm 2 s . At θ = 0.58 ML, the Arrhenius parameters were E dif = 6.2 kcal mol and D 0 = 0.06 cm 2 s . The coverage dependence of CO surface diffusion on Ru(001) was consistent with strong repulsive nearest-neighbor CO interactions. A repulsive CO-CO pairwise interaction energy of Ω = −1.4 kcal mol was obtained using a model for D(θ) derived from the quasichemical approximation.