AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM8
Direct Evidence of Surface Intermediates from the Reactions of C@sub 3@ Hydrocarbons on Cu(100)

Monday, October 25, 1999, 10:40 am, Room 607

Session: Catalysis on Metals
Presenter: H. Celio, University of Texas, Austin
Authors: H. Celio, University of Texas, Austin
K.C. Smith, University of Texas, Austin
J.M. White, University of Texas, Austin
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Using reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD), we have characterized important intermediates of the thermal and electron-induced surface chemistry of C3 hydrocarbons on Cu(100). The molecules that have been studied include allyl bromide, allyl chloride, propene, and cyclopropane. We find that the allyl halides dissociate to form pi-bonded allyl groups and halogen atomns at a wide temperature range (110-350 K). Furthermore, we observed an exceptionally facile carbon-carbon coupling between allyl bromide and pi-bonded allyl groups that lead to the formation of 1,5-hexadiene at 110 K. Conversely, allyl chloride principally forms pi-bonded allyl groups, which remained inert in the presence of allyl chloride molecules on the second layer. The implications of the dissimilar surface reactions of these allyl halides are discussed in terms of an Eley-Rideal rather than a diffusion-limited reaction. Electron irradiation (<50 eV) of weakly adsorbed cyclopropane lead to the formation of metallacyclobutane and cyclopropyl groups at 100 K. The thermal chemistry of the latter products yield propene but not pi-bonded allyl groups. The results of the allyl halides and cyclopropane are also compared and discussed for Ag(111).