Abstract
Infrared spectroscopy has been used to study the physical adsorption of CO onto a Rh/Al/sub 2/O/sub 3/ surface. In addition to absorption bands related to monolayer and multilayer physisorbed CO species, an interaction between the physisorbed species and chemisorbed CO has been observed causing a decrease of the chemisorbed CO wavenumber. Similar effects between physisorbed Xe and chemisorbed N/sub 2/ on Rh surfaces have also been observed, suggesting that the effect is a general one. Correlation of these measurements with measurements of CO trapped in CO matrices suggests that inductive and dispersive effects are the main factors responsible for the negative shift in chemisorbed species wavenumber. It has been found that physisorbed CO preferentially adsorbs in the vicinity of ionic sites, and that the change in entropy of adsorption is approximately equal to 5.6 +/- 2 kcal mol/sup -1/ for CO physisorption near Rh/sup I/(CO)/sub 2/ species.
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