Molecular structure of hydrocarbon monolayers on metal surfaces

Recent studies of the molecular structure and chemical bonding of organic monolayers on metal surfaces are reviewed. Most of the research is concentrated on alkenes and alkynes adsorbed on Pt and Rh. The applications of low-energy electron diffraction, high-resolution electron energy loss spectroscopy and thermal desorption spectroscopy provided most of the structural and bonding information in studies that utilized single-crystal metal surfaces. Hydrocarbon monolayers exhibit a rich and diverse structural chemistry that may be correlated to analogous organometallic clusters. Alkylidyne ( equivalent to C(CH sub 2 ) sub n CH sub 3 ) bonding predominates near 300K on Pt and Rh although a variety of different molecular conformations is found. Perhaps the most pronounced characteristic of the organic monolayers is the temp.-dependent variation of their structure and bonding. The bonding also varies markedly across the periodic table; much stronger for the early transition metals (W,Fe) and much weaker on Ag and Cu than on Pt and Rh. These temp.- and metal-dependent trends are altered to some extent when considering different crystallographic planes for the metal surface. The possible directions that this field of research may take are discussed. 51 ref.--AA