Energetics and kinetics of step-terrace adsorbate distribution: C2H2 on Pt{211}

The availability of simultaneous measurements as a detailed function of surface coverage of both the sticking probability and the differential heat for adsorption on a stepped surface provides a means of analyzing the coverage-dependent adsorbate distribution on a stepped surface. For C2H2 on Pt{211}, the initial heat of adsorption is measured as 270 +/- 10 kJ mol(-1) and the initial sticking probability is 0.84. On the basis of previously measured Pt-C bond strengths for adsorbates and steric considerations, it is concluded that at all coverages vinylidene is formed on the surface at 300 K. At low coverages step sites are preferred, where the adsorption heat is 280 kJ mol(-1), with a Pt-C bond energy of 255 kJ mol(-l). The terrace sites are occupied at higher coverages with an estimated adsorption heat of similar to 210 kT mol(-1) and Pt-C bond energy of similar to 220 W mol(-1). Sticking probabilities on step and terrace sites are estimated as 1 and 0.78, respectively, at low coverage.