An ab initio Rice-Ramsperger-Kassel-Marcus/master equation investigation of SiH4 decomposition kinetics using a kinetic Monte Carlo approach

The unimolecular reaction of decomposition of SiH4 to SiH2 and H-2 and the bimolecular reaction between SiH3 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 SiH2 and H-2 and microcanonical J-resolved variational transition state theory for decomposition to SiH3 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 SiH4, 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 SiH4 decomposition to SiH2 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 SiH3 and H to give SiH2 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.