Formation of C6HnSi+ (n=5-8) from phenylsilane:: an experimental and theoretical study

The metastable ion decomposition (MID) spectra of C6HnSi+ (n=6-8) generated by electron ionization of phenylsilane were obtained using mass-analyzed ion kinetic energy spectrometry (MIKES). H and H-2 losses were the main channels in the MID of C6H8Si.+ (1). The dominant product ion in the MIDS of C6H7Si+ (2) and C6H6Si.+ (3) was C6H5Si+ (4) formed by H-2 and H losses, respectively. Density functional theory calculations were performed to investigate isomerizations and dissociations of 1-3 at the B3LYP/6-311++G(d,p) level. RRKM model calculations were performed to understand their dissociation kinetics. These theoretical results predict that the consecutive dissociation 1 --> 3 (+ H-2) --> 4 + H-. dominates at low energies, while 1 --> 2 (+ H-.) --> 4 + H-2 at high energies. It has been found that several isomers of 1-3 including ion-molecule complexes, (C6H6SiHx+)-Si-. (x = 0-2), play important roles in the dissociation of 1. Reaction mechanisms are proposed for the formation of several isomers of 1-4 from the phenylsilane molecular ion. (C) 2004 Elsevier B.V. All rights reserved.