A LEED crystallographic analysis for the [formula omitted] surface structure

Abstract

An intensity analysis with low-energy electron diffraction is reported for the ( 3 × 3 )30° surface structure obtained by the adsorption and presumed dissociation of H 2S on the (111) surface of rhodium. Intensity-versus-energy curves were measured with a video LEED analyser for nine diffracted beams at normal incidence, and comparisons made with the renormalised forward scattering method for four different types of structural models in which the metal atoms remain in their regular bulk positions. The best correspondence between the experimental and calculated intensities occurs with sulphur atoms adsorbed in the “expected” 3-coordinate adsorption sites. The reliability index proposed by Pendry is minimised with S atoms 1.53 Å above the topmost metal layer; this corresponds to nearest-neighbour RhS bond distances equal to 2.18 Å. Comparisons are made with structural data available for related systems, and with the predictions of a model analysis of surface bond lengths given recently by one of the authors.