Helium scattering from (1×1) H–Pt(111)

Abstract

Lee et al. have recently reported measurements of helium diffraction data for a (1×1) chemisorbed layer of hydrogen on Pt(111) and obtained the corrugation parameters of a hard wall model fit to the data. We have calculated the corrugation parameters using a first principles approach for determining the helium-surface interaction potential. We have performed calculations of helium interaction potential for H in a (1×1) overlayer for fcc and hcp threefold sites and for on top sites at various distances above the Pt(111) surface. By comparing our results with the experimentally determined corrugation we conclude (in agreement with Lee et al.) that H chemisorbs in a threefold site. Furthermore we establish that the vertical height of the H above the top plane of Pt atoms is about 1.0 Å. This corresponds to Pt–H bond length of about 1.9 Å, a value somewhat larger than the Pt–H diatomic bond length of 1.6 Å. Our results compare favorably with the conclusion drawn from vibrational spectroscopy. Our calculated potential is soft with the softness parameter of about 2.6 Å−1. We are unable to distinguish between the fcc and hcp threefold sites on the basis of the corrugation alone, but in combination with the experimental helium diffraction and x-ray data of Lee et al., we confirm their tentative suggestion that the H adsorbs in hcp sites.