ADSORPTION AND REACTIONS OF BENZENETHIOL ON THE NI(111) SURFACE

The adsorption and reactions of benzenethiol have been analyzed on the Ni(111) surface using TPD, XPS, LEED and HREELS. At 110 K, benzenethi ol adsorbs on the surface through the sulfur atom. The vibrational dat a indicate that the S-H bond in benzenethiol breaks upon adsorption at 110 K for all exposures. The primary surface intermediate observed fo r high coverages of benzenethiol at 190 K is phenyl thiolate. HREELS r esults indicate that the aromatic ring in phenyl thiolate is neither p arallel nor perpendicular to the surface, but tilted. For low coverage s of benzenethiol, decomposition of the molecule to gaseous hydrogen, atomic sulfur, and carbon is the favored reaction pathway, while benze ne formation is the dominant reaction for higher coverages. Two pathwa ys are observed for the desorption of the benzene product. At intermed iate coverages a desorption-limited process occurs near 400 K, while a t high coverages benzene desorption is limited by hydrogenolysis of ph enyl thiolate at 263 K. Above 300 K, a stable aromatic hydrocarbon int ermediate, most Likely a phenyl fragment, is observed on the sulfur-co vered Ni(111) surface. This intermediate stays almost parallel to the surface at 450 K. Annealing benzenethiol overlayers on the Ni(111) sur face to 800 K results in a complex (root 39 x root 39)-S LEED pattern possibly as the result of the reconstruction of the top Ni layer over a broad coverage range.