Adsorption of Thiolates to Singly Coordinated Sites on Au(111) Evidenced by Photoelectron Diffraction

The adsorption structure of methylthiolate (${\mathrm{C}\mathrm{H}}_3\mathrm{S}$) adsorbed on Au(111), a long-standing controversial issue, has been unambiguously determined by scanned-energy and scanned-angle S $2p$ photoelectron diffraction. The methylthiolate molecules are found to occupy atop sites with a S-Au distance of $2.42\pm 0.03\AA$. The angular distribution of the S $2p$ photoelectrons due to forward scattering reveals that the S-C bond is inclined by approximately 50° from the surface normal towards both the $[\overline{2}11]$ and $[\overline{1}2\overline{1}]$ (nearest-neighbor thiolate) directions.