A DIFFUSE LEED STUDY OF THE ADSORPTION STRUCTURE OF DISORDERED BENZENE ON PT(111)

Previous LEED structural studies of benzene chemisorption on transition metal surfaces have relied on the presence of coadsorbed carbon monoxide to induce ordering in the overlayer. To investigate the effect of CO on the benzene structure, the disordered pure benzene layer chemisorbed on Pt(111) is studied by diffuse LEED intensity analysis. The diffuse LEED intensity has been measured using a digital LEED apparatus and analysed using an extension of the beam set neglect method. The benzene is found to chemisorb in a two-fold bridge site rotated by 30-degrees with respect to the site found for the ordered phase formed in the presence of coadsorbed CO. In addition, the benzene ring is found to be distorted. Parallel distortions are subject to large error bars, but perpendicular spacings have been more accurately determined. These include a buckling distortion not previously seen for benzene chemisorption on transition metal surfaces.