On the basis of a low energy electron diffraction I-V structural investigation, the surface geometry of the Rh(100)+(2 x 2)-2O phase was determined. The oxygen was found to adsorb in an unusual threefold site of the rhombi created by the reconstruction of the first rhodium layer, producing a pg symmetry, in agreement with theoretical predictions but at variance with previous experimental conclusions. The results indicated that there was a strong tendency of oxygen to adsorb in threefold sites on all Rh surfaces.

Oxygen Induced Reconstruction of the Rh(100) Surface - General Tendency Towards Threefold Oxygen Adsorption Site on Rh Surfaces. A.Baraldi, J.Cerdá, J.A.Martín-Gago, G.Comelli, S.Lizzit, G.Paolucci, R.Rosei: Physical Review Letters, 1999, 82, 4874-7