Surface extended x-ray-absorption fine-structure measurements have been made for the structure of two weakly ordered phases of chlorine adsorbed on Ag(111) at coverages of one-third and two-thirds of a monolayer. The Cl atoms are found to occupy threefold hollows on the silver surface, at a Cl-Ag distance of 2.70±0.01 Å, independent of coverage. A full multishell fit, including neighbor shells as far as about 5.2 Å, allows a complete structural determination: At frac23; monolayers the Cl forms a vacancy honeycomb structure, while at the lower coverage Cl-Cl nearest-neighbor sites are avoided.

• Received 8 May 1986

DOI:https://doi.org/10.1103/PhysRevB.34.2975