The surface chemistry of dimethyl disulfide (DMDS) is studied on a Cu(111) single crystal and a polished copper foil in ultrahigh vacuum as a basis for understanding its tribological chemistry using a combination of temperature-programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (X PS). Low-energy electron diffraction reveals that the polished foil becomes ordered on heating in vacuo and displays identical surface chemistry to that found on the Cu(1 11) surface. Dimethyl disulfide reacts with the copper surface at 80 K to form thiolate species. Heating the surface to similar to 230 K causes a small portion of the thiolate species to decompose to form methyl groups adsorbed on the surface. Further heating results in methane and C-2 hydrocarbon desorption at similar to 426 K, due to a reaction of adsorbed methyl species, to completely remove carbon from the surface and to deposit atomic sulfur.