EXPERIMENTAL AND THEORETICAL CHARACTERIZATION OF ISOMERIC ADDUCT IONS OF SI-BULLET+ AND BENZENE AND THEIR NEUTRAL COUNTERPARTS

Results of gas-phase experiments and theoretical investigations are reported which provide evidence for the stability of the pi-complex Si.+-C6H6 and the C-H insertion complex C6H5SiH.+. Theory also predicts the stability of the ring-insertion complex for which the experiments could not provide unambiguous experimental evidence. The pi-complex and C-H insertion complex are distinguished with neutralization-reionization (NR) mass spectrometry experiments at 8 keV which also provide evidence for the stability of the corresponding neutral molecules. The [C6,H6,Si].+ cations were generated either by electron-impact ionization of phenylsilane or a mixture of benzene and Si(CH3)4 at 70 eV, or by charge reversal of an anion produced from a mixture of phenylsilane and N2O. At the MP2/6-31G**//UHF/3-21G* level, ab initio MO calculations predict the stability order for the cations as pi-complex > C-H insertion complex > ring-insertion complex and the order for the corresponding neutral species as C6H5SiH > ring-insertion complex > pi-Si-C6H6.