HE-DIFFRACTION STUDIES OF HYDROGEN CHEMISORPTION ON RHODIUM(311)

The (311) surfaces of fee materials are of special interest as they of fer, due to the existence of (111) and (100) microfacets, a large vari ety of differently coordinated adsorption sites. He atom beam diffract ion experiments were performed on Rh(311) in order to investigate the formation of ordered chemisorption structures of hydrogen. The observa tion of c(1 x 3), p(1 x 1) and p(1 x 1)(REC) phases is in agreement wi th previous LEED studies. However, before the formation of the c(1 x 3 ), ac(1 x 1) phase was identified with He diffraction, which requires a coverage of 1 ML. Therefore, the initial sticking coefficient of hyd rogen is practically unity and the saturation H-coverage reached in th e p(1 x 1)(REC) phase is 2-3 ML, much larger than anticipated.