Pressure Dependence of Rate Coefficients of Unimolecular and Chemical Activation Reactions Connected to the Potential Energy Wells of Si₂H₂Cl₄, Si₂Cl₆, and Si₂Cl₄via Rice-Ramsperger-Kassel-Marcus Calculations

Rate coefficients for elementary reactions connected to the potential energy wells of Si₂H₂Cl₄, Si₂Cl₆, and Si₂Cl₄, which are important Si₂species in chemical vapor deposition (CVD) processes that use chlorosilanes as silicon source gases, were determined through the Rice-Ramsperger-Kassel-Marcus theory under various conditions of temperature and pressure. The optimized structures and vibrational frequencies of the reactants, products, and transition state were obtained using (U)B3LYP/6-31+G(d,p), and the single-point energies of the optimized structures were recalculated using the coupled cluster method with single and double excitations plus triple perturbation (U)CCSD(T) with complete basis set extrapolation. Many of the unimolecular decomposition channels and chemical activation reactions investigated in this work were found to be in the fall-off regime under subatmospheric to moderately high-pressure conditions so that it is expected that accurate modeling of the gas phase in the chlorosilane CVD reactor requires careful determination of the rate coefficients as functions of temperature and pressure for the conditions of interest, instead of using high-pressure limit rate coefficients. The rate coefficients determined here were expressed through Chebyshev coefficients and also modified Arrhenius parameters to be used in simulations of systems under a wide range of temperature and pressure conditions.