Interaction of Coadsorbed CO and Deuterium on a Bimetallic, Pt Monolayer Island Modified Ru(0001) Surface

We have investigated the coadsorption of CO and deuterium on structurally well-defined bimetallic, Pt monolayer island modified Ru(0001) surfaces, focusing on the interactions between the coadsorbed species and their impact on the adsorption and desorption characteristics. Temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS) measurements after adsorption at 90 K reveal considerable differences between adlayers formed by preadsorption of deuterium and subsequent saturation by CO or in the reverse way. We demonstrate that these differences are caused by the limited mobility of adsorbed CO at low temperatures and spillover of COad from Pt monolayer areas to Ru(0001) areas upon heating, e.g., during a TPD measurement. The interplay between energetics, including the presence of weakly adsorbing Pt monolayer sites and strongly adsorbing Ru(0001) sites as well as interactions between coadsorbed species, and the onset of COad spillover on the adsorption and desorption behavior of deuterium, which results in complex deuterium desorption spectra, are illustrated and discussed.