An infrared study of the adsorption of CO on a stepped platinum surface

Abstract

The adsorption of CO at 85 K on the Pt-s[4(111)×(100)] surface has been investigated using infrared reflection-absorption spectroscopy (IRAS). TPD and LEED. Both IRAS and TPD measurements indicate that adsorption of CO takes place initially in a linearly bound configuration at sites associated with the steps (ν(CO) = 2065–2078 cm −1). Subsequently CO adsorbs with a reduced sticking coefficient on the (111) terraces, giving rise to a second band in the linear region (ν(CO) = 2086–2097 cm −1). The observed vibrational coupling is indicative of one-dimensional domains of step CO at low coverage and of two-dimensional domains, containing both step and terrace CO, at high coverages. The frequency of the step CO singleton is surprisingly close to that of the (hypothetical) terrace CO singleton. The IR extinction coefficient for CO adsorbed at the step site is a factor 2.7 greater than for CO in the two-dimensional domains at high coverage. Unlike Pt(111), adsorption on the stepped surface does not give rise to a bridging species.