Leed structural studies of benzene monolayers on Rh(111) with and without CO coadsorption

Benzene, molecularly adsorbed on the Rh(111) single crystal surface, presents several periodically ordered arrangements, as a function of the relative amount of coadsorbed CO. The following Low Energy Electron Diffraction (LEED) patterns are observed: (2 √ 3 x 3) rect in the absence of CO, c(2 √ 3 x 4) rect for a 1:1 ratio of CO to benzene, and (3 x 3) for a 2:1 ratio. The CO to benzene ratios were obtained by High Resolution Electron Energy Loss Spectroscopy and Thermal Desorption Spectroscopy. The c(2 √ 3 x 4) rect structure has been solved in detail by a LEED intensity analysis: it consists of a strongly distorted benzene and an elongated CO in a three fold hollow site. The two other ordered structures are at present the subject of LEED intensity analyses