An ab initio Rice-Ramsperger-Kassel-Marcus/master equation investigationof SiH_4decomposition kinetics using a kinetic Monte Carlo approach

摘要

The unimolecular reaction of decomposition of SiH4 to SiH2 and H2 and the bimolecular reactionbetween SiH3 and H were investigated by solving the master equation using a stochastic kineticMonte Carlo (KMC) approach. Rice-Ramsperger-Kassel-Marcus (RRKM) microcanonical kineticconstants were determined using classic transition state theory for the reaction of decomposition to SiH2 and H2 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 thecomplete basis set limit. Unimolecular kinetic constants were directly computed from the results ofKMC simulations using a new algorithm while bimolecular rate constants were calculated fromstochastic reaction probabilities. The simulation results are in good agreement with experimentaldata for the unimolecular decomposition of SiH4, which is in the falloff regime in the temperature(1100-1700 K) and pressure (10-3-101 bar) range investigated. The calculated high and lowpressure limit kinetic constants for SiH4 decomposition to SiH2 and H2 are k∞=1.2 ×10~(13)T(0.477)exp(-28 988/ T) and k_0=1.4 ×10~(42)T~(-7.245)exp(-33 153/ T). The calculated Troe falloff parameter is F_(cent)=0.979 exp(–T/ 1427) + 0.021 exp(1489). The rate of the bimolecular reactionbetween SiH3 and H to give SiH2 and H2 is pressure independent between 10-3 and 100 bar andslightly temperature dependent between 300 and 2000 K. The kinetic constant interpolated in thistemperature and pressure range is 6.9 × 10~(11)T~(0.736)exp(134.8/ T(K)) cm~3mol~(-1)s~(-1),which is amongthe highest values proposed in the literature for this process.