SELECTED MOLECULAR-SURFACE STRUCTURES DETERMINED BY MODERN LOW-ENERGY-ELECTRON DIFFRACTION

This article surveys a series of structural results obtained for the a dsorption of small molecules (from CO to benzene) on the closest-packe d metal surfaces by low-energy electron diffraction (LEED). Most of th ese results were obtained by detailed fitting of many structural param eters, primarily with automated tensor LEED. We discuss mainly qualita tive aspects: adsorption sites, adsorbate orientation, molecular disto rtions and adsorbate-induced relaxations. Cases of special interest in clude: CO and NO monolayers adsorbed on metal surfaces, which require a revision of adsorption site assignments based on vibrational frequen cies; various coadsorption structures exhibiting site changes due to t he electron donor vs, acceptor character of the coadsorbates; intact d i-sigma ethylene adsorbed in a disordered and asymmetrical manner on P t(111); intact acetylene on MgO(100), the first molecular and also fir st physisorbed adsorption structure determined in detail on an oxide s urface; and the surface of an ultra-thin ice film, exhibiting unusuall y large vibration amplitudes of the outermost molecules. (C) 1998 Else vier Science B.V.