Theoretical Study of the Reaction Mechanism for the Interaction of Si sub + with Methylsilane.

The chemical reactions of small silicon cluster ions with many different reagent molecules in the gas phase have been studied recently by several groups. Most of these experiments have been performed under carefully controlled conditions in the ion trap of a Fourier transform mass spectrometer and have yielded detailed information about the reaction rates and product distributions in such ion-molecule reactions. However, theoretical understanding of the underlying reaction mechanisms is lacking in most cases. In this paper, the reaction for the interaction of Si sup + with H sub 3 C-SiH sub 3 has been studied by means of ab initio quantum chemical techniques using polarized basis sets and including the effects of electron correlation and zero-point corrections. The mechanism involves the initial insertion of Si sup + into the Si-H bond of methylsilane followed by 1,2-H migration as well as H sub 2 elimination reactions. Two different exthermic reaction channels have been found which do not have any overall activation barriers. One involves the elimination of H sub 2 to yield the isomer H sub 3 C-SiH- Si sup + and the other involves Si-Si bond cleavage after H migration to yield Si-CH sup + sub 3 and SiH sub 3. The results are consistent with the experimental observations of Mandich, Reents and Bondybey. The implications of our mechanism for isotopic labelling experiments are outlined and are in agreement with recent observations.