THE CHEMISTRY OF METHYL AND ETHYL RADICALS ON PT(111) FROM THE DECOMPOSITION OF TRI-ALKYL BISMUTH COMPOUNDS

The chemistry of trimethyl and triethyl bismuth compounds adsorbed on Pt(111) have been studied using thermal desorption spectroscopy, Auger electron spectroscopy, and high resolution electron energy loss spect roscopy. The tri-alkyl bismuth compounds adsorb molecularly on Pt(111) at 110 K. Upon heating, the R3Bi compound decomposes and alkyl radica ls are introduced to the surface. Alkyl radicals and bismuth atoms are delivered to the Pt(111) surface in a 3:1 (alkyl : bismuth) ratio. In the presence of Bi, it is expected that the alkyl radical chemistry i s not perturbed substantially. Below multilayer coverage, the methyl a nd ethyl radicals, delivered to the surface by thermal decomposition o f the parent, show similar trends in their chemistry. There is some fr action of parent (BiR3) desorption at approximately 190 K. The remaini ng methyl or ethyl radicals follow two reaction pathways. The first re action channel is dehydrogenation of the methyl or ethyl radical leadi ng to CH or ethylidyne species, respectively, remaining on the surface . The second channel is hydrogenation involving surface hydrogen produ ced by the dehydrogenation channel which leads to CH4 or CH3CH3 format ion, respectively. This pathway leads to reaction rate limited desorpt ion of CH4 with a peak temperature at 280 K and CH3CH3 with a peak tem perature at 295 K.