The chemistry of methyl and ethyl radicals on Pt(111) from the decomposition of tri-alkyl bismuth compounds

Abstract

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 spectroscopy. The tri-alkyl bismuth compounds adsorb molecularly on Pt(111) at 110 K. Upon heating, the R 3Bi compound decomposes and alkyl radicals 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 is not perturbed substantially. Below multilayer coverage, the methyl and ethyl radicals, delivered to the surface by thermal decomposition of the parent, show similar trends in their chemistry. There is some fraction of parent (BiR 3) desorption at ~ 190 K The remaining methyl or ethyl radicals follow two reaction pathways. The first reaction channel is dehydrogenation of the methyl or ethyl radical leading to CH or ethylidyne species, respectively, remaining on the surface. The second channel is hydrogenation involving surface hydrogen produced by the dehydrogenation channel which leads to CH 4 or CH 3CH 3 formation, respectively. This pathway leads to reaction rate limited desorption of CH 4 with a peak temperature at 280 K and CH 3CH 3 with a peak temperature at 295 K.