Two-dimensional phase transition in xenon submonolayer films adsorbed on (0001) graphite

Ultra high vacuum molecular beam techniques coupled with LEED and Auger electron spectroscopy are particularly well suited to the study of surface chemical reactions because of the ability to assess the effect of the surface conditions on the reaction probability. Investigation of the hydrogen-deuterium exchange reaction on a series of low and high Miller index platinum single crystals has indicated that the steps present on the high index surfaces are necessary for the dissociation and subsequent recombination of hydrogen. We have undertaken a systematic study of a series of small molecule reactions on these stepped surfaces to determine the reaction probability on stepped platinum surfaces. Reactions involving dissociation of Ha₂, D₂, O₂, OH, NH, and CH bonds proceed on the stepped surfaces with much higher reaction probabilities than reactions requiring dissociation of N₂, or CO bonds. All of the reactions studied resulted in cosine product angular distributions except for the formation of CO₂, which exhibited a distribution more peaked at the normal to the surface.