Mechanisms and kinetics of the thermal decompositions of trichlorosilane, dichlorosilane, and monochlorosilane

Abstract

Decomposition studies of trichlorosilane, dichlorosilane, and monochlorosilane at 921 K, 872 K, and 806 K, respectively, are reported. The studies were made at fixed reactant pressures over a range of total pressures in a wall conditioned, quartz reactor connected to a quadrupole mass-spectrometer. Products were monitored sequentially and continuously in time. The dichlorosilane decomposition was also studied by the comparative-rate single-pulse shock-tube method at temperatures around 1250 K. Two mechanisms of decomposition are considered: a silylene based mechanism initiated by molecular elimination reactions (Scheme I), and a free radical based mechanism initiated by bond fission reactions (Scheme V). Modeling tests of these mechanisms show that only the former is consistent with the experimental data. The decompositions are shown to be essentially nonchain processes initiated by the following pressure dependent reactions: HSiCl3(SINGLEBOND)4→ SiCl2+HCl, H2SiCl2(SINGLEBOND)1→ SiCl2+H2 and H3SiCl(SINGLEBOND)5→ HSiCl+H2. High pressure Arrhenius parameters recommended for these reactions are A4,∞=A1,∞=A5,∞=1014.5±0.5 s−1, E4,∞=71.9±2.1 kcal/mol, E1,∞=69.2±2.0 kcal/mol, and E5,∞=60.6±1.8 kcal/mol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 69–88, 1998.