Computational modeling of the SiH3+O2 reaction and silane combustion

Recent theoretical and experimental studies have provided improved estimates of thermochemical and chemical kinetic data for the silicon-hydrogen-oxygen system. In particular, the SiH3 + O-2 reaction has been the subject of considerable interest. Estimates of rate coefficients for specific SiH3 + O-2 channels as a function of temperature and of pressure and branching fraction assignments are made in the current work using Quantum Rice-Ramsperger-Kassel (QRRK) analyses for k(E) and Master Equation (ME) analyses for fall-off. The QRRK/ME analyses were based on potential energy Surface data provided by previous ab initio studies. The overall rate coefficient for SiH3 + O-2 --> products shows a slight negative temperature dependence, which agrees with previous experimental Studies. The results indicate significant pressure and temperature dependence for the product branching fractions and are in good agreement with experimental measurements of the SiH3 + O-2 product channels. In particular, the channel producing H atoms (SiH3 + O-2 --> cyclic-OSiH2O + H) is dominant at high temperatures and/or low pressures. and the O-atom channel (SiH3 + O-2 --> H3SiO + O) is not significant (>5% branching fraction) below 1000 K at any pressure examined in the QRRK study (P = 0.001-10 atm). A detailed chemical mechanism for silane combustion is presented based on the QRRK estimates and other evaluated rate coefficient and thermochemical parameters. The mechanism is validated at high temperatures by comparison of calculated ignition delay times with shock-tube data and by comparison of calculated OH radical profiles with atmospheric pressure burner data. The mechanism is validated at low temperatures by comparison of ignition times with constant volume explosion data. (C) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.