THE DECOMPOSITION OF H2S ON NI(110)

Adsorbed H2S decomposes on Ni(110) to form primarily surface S and H for coverages of less than 0.5 ML. The hydrogen evolves in two separate TPD peaks, characteristic of hydrogen recombination and desorption from the clean surface and from regions perturbed by chemisorbed sulfur. XPS and HREELS indicate the presence of SH and possibly H2S groups on the surface at 110 K. The XPS data indicates that for coverages less than about 0.5 ML, the concentration of molecular H2S is small, but it is difficult to asess the coverage of SH groups. However, all of the molecular species decompose prior to hydrogen desorption (for high coverage, 180 K). Physisorbed H2S is observed on the surface for coverages greater than about 0.5 ML. The sulfur Auger lineshape was observed to be a function of both coverage and temperature. The changes in the lineshape were attributed tp perturbations in local bonding interactions between the S and Ni surface, perhaps involving some change in either bonding sites or distances but not involving SH bond scission. The decomposition reaction was modeled using a bond order conservation method which successfully reproduced the experimental results.