EVIDENCE FOR A SURFACE-BOUND FREE-RADICAL MECHANISM DURING THE DECOMPOSITION OF (I)PR2TE IN THE PRESENCE OR ABSENCE OF MERCURY AND OR ME2CD UNDER MOVPE CONDITIONS OBTAINED FROM DEUTERIUM-LABELED PRECURSORS

The presence of the cross-over products, d1- and d7-propane, along with d0- and d8-propane, d0- and d6-propene, d0-, d7- and d14-2,3-dimethylbutane (DMB) and small amounts of d7-iPr2Te from the co-decomposition of d0- and d14-iPr2Te in helium is interpreted in terms of homolytic fission of the Te-C bond to form (i)Pr. and (i)PrTe.. The small amount of DMB, as well as its labelling pattern, indicate that the main fate of the (i)Pr. formed is to abstract H. from intact iPr2Te to give propane, 2 x propene, Te and H.. A kinetic isotope effect (k(H)/k(D) approximately 2) is observed for this abstraction reaction. The relative ratios of propene: propane: DMB and the labelling pattern for DMB suggest that the latter arises from coupling reactions of surface bound (i)Pr.. (i)PrTe. probably releases more (i)Pr.. In the presence of Me2Cd, Me. releases more (i)Pr. and MeTe(i)Pr from iPr2Te via MeiPr2Te.. The larger amounts of free radicals in this system mean that combination reactions of surface bound radicals dominate over abstraction of H. from iPr2Te. Reactions carried out in hydrogen show that many of the free radicals react with H-2 at rates comparable with the other available pathways. Finally, decomposition of (Me2CD)2Te in helium provides unequivocal evidence that all hydrogen abstraction reactions occur from the methyl groups rather than from the secondary carbon atom, since d1-propene and d1-propane are the only observable products.