AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM7
Chemistry of SO@sub 2@ on Ru(001): Formation of SO@sub 3@ and SO@sub 4@

Monday, November 2, 1998, 10:20 am, Room 309

Session: Molecular Adsorbates on Metals
Presenter: T. Jirsak, Brookhaven National Laboratory
Authors: T. Jirsak, Brookhaven National Laboratory
J.A. Rodriguez, Brookhaven National Laboratory
S. Chaturvedi, Brookhaven National Laboratory
J. Hrbek, Brookhaven National Laboratory
Correspondent: Click to Email
The interaction of SO@sub 2@ with Ru(001) at 300 and 100 K was studied using synchrotron-based high-resolution photoemission, INDO/S MO calculations, and a thermochemical analysis based on the bond-order conservation Morse-potential (BOC-MP) formalism. At 300 K and small exposures of SO@sub 2@, sulfur dioxide completely decomposes (SO@sub 2@ -> S@sub a@ + 2O@sub a@). Several coordination modes for adsorbed SO@sub 2@ were examined using INDO/S and the BOC-MP formalism. It was found that adsorption geometries in which the molecule is di-coordinated via O,O or S,O are the most probable precursors for dissociation. For large exposures of SO@sub 2@ at 300 K, SO@sub 3@ and SO@sub 4@ species appear on the Ru(001) surface confirming thus the theoretical predictions derived from the BOC-MP method which indicate that formation of SO@sub 3@ and SO@sub 4@ can take place only when the number of empty adsorption sites is limited. This prediction was also proved during the adsorption of SO@sub 2@ on a O/Ru(001) surface with @theta@@sub O@ = 0.25 ML, producing similar types of species as at saturation of SO@sub 2@ on Ru (S@sub n@+O, SO@sub 4@ and S). When a Ru surface partially covered by sulfur (@theta@@sub S@ = 0.2 ML) was exposed to molecular oxygen at 300 K, formation of SO@sub 3@ and SO@sub 4@ species was not observed. Experiments performed at a surface temperature of 100 K showed a very rich surface chemistry. Five different surface species were observed after SO@sub 2@ dosing: atomic S, S@sub n@+O, SO@sub 2@, SO@sub 3@ and SO@sub 4@. The S 2p spectrum of a Ru(001)surface saturated at 100 K is dominated by a very intensive peak of a multilayer of SO@sub 2@, which entirely disappeared upon annealing to 160 K. Further annealing to 260 K leaves mainly atomic S and SO@sub 4@ on the surface and the latter is completely decomposed by 350 K.