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Published online by Cambridge University Press: 26 February 2011
We have studied a novel surface reaction in which acetylene (C2H2) cyclizes with sulfur atoms on the Pd(111) surface to form thiophene (C4H4 S). The reaction occurs at defects in the (√7 ×√7)R19° sulfur overlayer that is formed on this surface. The surfaces were prepared by decomposing H2S on the clean Pd(111) surface and annealing to temperatures in the range 600K to 1100K to produce defects i the sulfur overlayer. The reaction occurs to greatest extent on surfaces annealed to high temperatures and only on surfaces with coverages approaching saturation. The defects have been characterized by adsorption of CO using both vibrational spectroscopyand measurementsof desorption kinetics. On the sulfided surface CO is bound in a linear configuration to a single Pd atom. At defects in the sulfur overlayer CO is bound in a bridging site between two atoms, as on the clean surface.