An ab initio Rice-Ramsperger-Kassel-Marcus/master equation investigation of SiH(4) decomposition kinetics using a kinetic Monte Carlo approach.

The unimolecular reaction of decomposition of SiH(4) to SiH(2) and H(2) and the bimolecular reaction between SiH(3) and H were investigated by solving the master equation using a stochastic kinetic Monte Carlo (KMC) approach. Rice-Ramsperger-Kassel-Marcus (RRKM) microcanonical kinetic constants were determined using classic transition state theory for the reaction of decomposition to SiH(2) and H(2) and microcanonical J-resolved variational transition state theory for decomposition to SiH(3) and H. Structures of reactants and transition states were determined at the B3LYP/aug-cc-pVTZ level, while energies were calculated at the CCSD(T) level and extended to the complete basis set limit. Unimolecular kinetic constants were directly computed from the results of KMC simulations using a new algorithm while bimolecular rate constants were calculated from stochastic reaction probabilities. The simulation results are in good agreement with experimental data for the unimolecular decomposition of SiH(4), which is in the falloff regime in the temperature (1100-1700 K) and pressure (10(-3)-10(1) bar) range investigated. The calculated high and low pressure limit kinetic constants for SiH(4) decomposition to SiH(2) and H(2) are k(infinity)=1.2x10(13)T(0.477) exp(-28 988/T) and k(0)=1.4x10(42)T(-7.245) exp(-33 153/T). The calculated Troe falloff parameter is F(cent)=0.979 exp(-T/1427)+0.021 exp(T/1489). The rate of the bimolecular reaction between SiH(3) and H to give SiH(2) and H(2) is pressure independent between 10(-3) and 100 bar and slightly temperature dependent between 300 and 2000 K. The kinetic constant interpolated in this temperature and pressure range is 6.9x10(11)T(0.736) exp(134.8/T(K)) cm(3) mol(-1) s(-1), which is among the highest values proposed in the literature for this process.