Bond length inequalities and relaxations at the Rh(110)-c(2 × 2)-S surface structure studied by LEED crystallography

Abstract

A tensor LEED analysis has been made for the Rh(110)-c(2 × 2)-S surface structure using intensity-versus-energy curves measured for twelve independent beams at normal incidence. Each S atom chemisorbs on a centre site of the Rh(110) surface. It bonds to the second layer Rh atom directly below, with a bond distance equal to about 2.27 Å, and to four neighbouring first layer Rh atoms at close to 2.47 Å. A significant feature of this structure is that the second metal layer is buckled; those Rh atoms directly below the S atoms relax down by about 0.11 Å compared with the other second layer Rh atoms. This buckling is apparently driven by the need to reduce the difference that would otherwise occur between these two types of S-Rh bond lengths. A component in the observed difference between the S-Rh distances appears to be dependent on the metallic coordination number for the Rh atoms; in this regard, a comparison is made with the structural details for O chemisorbed on reconstructed Ni(110).