The molecular adsorption of ethane on sulfur- and ethylidyne-covered surfaces of Pt(111)

Initial adsorption probabilities, alpha(0), were determined for ethane incident on sulfur- and ethylidyne-covered surfaces of Pt(111) at 95 K for incident translational energies from 10 to 44 kJ mol(-1) and incident angles from 0 to 60 degrees. At normal incidence and for all translational energies studied, alpha(0) on these surfaces was found to be enhanced relative to clean Pt(111). The initial adsorption probabilities on both adsorbate-covered surfaces were found to be independent of the angle of incidence, suggesting a highly corrugated static gas-surface potential. The interconversion of normal and parallel momenta due to this corrugation appears to be the mechanism which best explains these results. The notion of increased energy transfer from a match in mass of the collision partners (ethane/sulfur) is clearly not consistent with the data, since the adsorption probability of ethane on the sulfur-covered surface at glancing incidence (60 degrees) is less than that on the clean surface at this same angle. Ethylidyne was found to increase alpha(0) more than sulfur for all incident conditions, apparently due to energy transfer to the internal degrees of freedom of ethylidyne, a mechanism which is not available to the sulfur adsorbate.