THE RH(110)-P2MG(2X1)-2O SURFACE-STRUCTURE DETERMINED BY AUTOMATED TENSOR LEED - STRUCTURE CHANGES WITH OXYGEN COVERAGE

Oxygen is dissociatively chemisorbed on Rh(110) and forms an ordered ( 2 X 1) surface structure at one monolayer coverage. The automated tens er LEED approach has been applied to the determination of atomic posit ions in the Rh(110)-p2mg(2 X 1)-20 structure. The oxygen atoms are con firmed to be in a zig-zag fashion in the (110) troughs to produce the glide plane symmetry observed in the LEED pattern. The clean surface i nterlayer relaxations are reduced and the oxygen atoms are bound asymm etrically in the three-fold fee hollow-sites to the (111) facets of th e steps. Two Rh-O bonds are formed to Rh atoms in the top metal layer with bond lengths of 1.86 +/- 0.11 Angstrom and a third Rh-O bond of 2 .07 +/- 0.16 Angstrom is formed to a Rh atom in the second metal layer . A novel finding is that the second metal layer Rh atoms are shifted towards the oxygen positions, introducing a zig-zag lateral displaceme nt of the atoms in the row by 0.10 +/- 0.07 Angstrom.