Coverage-dependent desorption measurements for CO/Ag(011)

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Abstract
We report time‐resolved electron energy loss spectroscopy results for the thermal desorption of CO physisorbed onto Ag(011). The measurements were performed isothermally and effectively at constant coverage. We observe that the logarithm of the measured pseudo‐first‐order desorption rate constant increases approximately linearly with coverage over the temperature and coverage ranges accessible to our measurements. The results are analyzed in terms of a quasiequilibrium model in which the desorption rate constant is expressed analytically as a virial expansion. Using this analysis, we determine that at low coverage the molecules adsorb with their axes parallel to the surface plane and are oriented with respect to the crystalline axes. We find that long‐range interactions extending out to 7–8 neighbor shells must be included to fit our results. The magnitude of these long‐range interactions is reasonably well described by the gas phase intermolecular potential if screening by substrate image charges is included.