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 tenser LEED approach has been applied to the determination of atomic positions in the Rh(110)-p2mg(2 X 1)-20 structure. The oxygen atoms are confirmed 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 interlayer relaxations are reduced and the oxygen atoms are bound asymmetrically in the three-fold fee hollow-sites to the (111) facets of the 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 displacement of the atoms in the row by 0.10 +/- 0.07 Angstrom.