An X-ray absorption study of saturated hydrocarbons physisorbed on metal surfaces

Monolayers of linear and cyclic saturated hydrocarbons (n-hexane, cyclohexa ne, n-octane, n-hexatriacontane) physisorbed on several metal surfaces (Cu( 111), Au(111), Ru(0001) and Pt(111)) have been investigated by K-edge X-ray absorption spectroscopy (XAS). Whereas the corresponding multilayer data q ualitatively resembles the core excitation spectrum observed for the free m olecules, a strong quenching of the Rydberg R-resonance at 287.7 eV is obse rved for molecules in direct contact with the metal surfaces. In addition, the broad feature observed in the saturated hydrocarbon monolayer XAS-spect ra at 285.1 eV is identified as a transition into metal-molecule hybrid orb itals. (C) 1999 Elsevier Science B.V. All rights reserved.