XP spectra of a Cu(110) surface exposed to methyl mercaptan at 290 K show the presence of an adsorbate assigned to mercaptide, CH 3 S(a). Scanning tunneling microscopic (STM) images show that the formation of the adsorbed mercaptide (CH 3 S(a)) is accompanied by a restructuring of the surface. The reconstructed surface is characterized by very narrow terraces (typically 10-15 Å wide) oriented mainly in the <110> direction with a `zig-zag' structure. Higher resolution images of the terraces reveal an atomic scale structure with a c(2x2) unit cell, each cell containing two bright features. The combination of STM and X-ray photoelectron spectroscopy (XPS) shows that the c(2x2) structure is complete at a surface concentration of ~5x10 1 4 cm - 2 , consistent with the c(2x2) unit cell containing two equivalent mercaptide species. On heating to 450 K the mercaptide dissociates to give chemisorbed sulfur adatoms and the desorption of all of the surface carbon. The STM images show that following the decomposition of the mercaptide adlayer the copper surface regains its original structure of broad terraces (typically 100-200 Å wide), though an adlayer of chemisorbed sulfur atoms is now present.