UPS OF THIOLS AND DISULFIDES ADSORBED ON CU(410) - CH3SH, C2H5SH, C3H7SH, (CH3S)2, (C2H5S)2, (C3H7S)2

The Hel spectra of the thiols (RSH) and the disulfides (RSSR) adsorbed on copper at room temperature are, in all cases, substantially different to those in the gas-phase, but are the same for the thiols as for the corresponding disulfides. This identifies the adsorbed species as the mercaptide (RS). Fractional-difference spectra allow the structure within the d-band region to be resolved into a number of components. Common to all adsorbates is the predominant attenuation of the Cu 3dxz,yz band, which is responsible for the minimum in the difference spectra. This implies that, of the various d-orbitals, it is this component which is principally involved in the adsorbate bonding. Also common is the identification of two bands on the Fermi level side of the dxz,yz minimum, and three on the high binding energy side. In both cases there are contributions from both nonbonding substrate d-components and from adsorbate-induced bands (antibonding above the d-band, and bonding below). Using molecular-orbital calculations for various RS-H and RS-SR geometries provides a model for the RS-[M] preadsorbed species. The interaction between its energy levels and those of the substrate yields a set of adsorbate-substrate bands, which lead to a detailed assignment of the d-band region of the spectrum. The calculations allow an assignment also of the higher-binding-energy molecular-like bands. © 1990.