Phase diagram and adsorption-desorption kinetics of CO on Ru(0001) from first principles.

A kinetic lattice gas model is used to study the equilibrium properties and the desorption kinetics of CO on Ru(0001). The authors compute all relevant on-site binding and interaction energies of CO molecules within density functional theory and import them in two different models. The first model allows the CO molecules to adsorb upright on top and hollow sites. The authors calculate the phase diagram, coverage isobars, and temperature programed desorption spectra. Up to a coverage of 1/3 ML, very good agreement is obtained between theory and experiment when considering top sites only. For coverages beyond 1/3 ML, hollow sites are included and disagreement between theory and experiment occurs. The second model allows adsorption on top sites only but allows them to tilt and shift from their upright positions. The authors show that this model resolves many of the deficiencies of their first one. Furthermore, the authors demonstrate that this model is more consistent with experiment since it is the only model that is able to explain the results from IR-spectroscopy experiments.