STRUCTURE OF RH(110)(1X2) AND RH(110) (2X2)P2MG-O SURFACES

The structure of the oxygen-induced Rh{110}(2x2)p2mg-O phase has been determined using low-energy electron diffraction intensity-voltage (LEED I-V) analysis, and consists of a missing row reconstructed substrate with oxygen atoms in a zigzag arrangement. The oxygen atoms occupy the upper threefold sites on the {111} microfacets, and the nearest-neighbour bonding geometry is the same as for the (2 x 1) oxygen-induced low-temperature phase. In spite of the similar geometries, the reactivities of these structures for CO oxidation are very different. When the oxygen is removed from the (2 x 2)p2mg surface at low temperature, the substrate retains the (1 x 2) missing row reconstruction. LEED analysis of the (1 x 2) surface indicates that the first interlayer contraction is 11%, which is lower than the value determined previously by He scattering.