Theoretical Reassessment and Model Validation of Some Kinetic Parameters Relevant to Si/Cl/H Systems

The increasing demand for silicon-based materials requires the optimization of silicon deposit manufacturing processes and therefore a better understanding of the gas-phase reactivity of silicon precursors such as silicon tetrachloride (SiCl₄). In the present work, hydrogen atom resonance absorption spectroscopy (H-ARAS) has been used to investigate the high-temperature reactivity of SiCl₄ behind reflected shock waves at ∼1.5 atm in the presence of either ethyl iodide or molecular hydrogen, used as H atom precursors. Several key reactions of SiCl₄ and its main gas-phase decomposition products (SiCl₃, Cl, SiHCl₃, SiHCl₂) have been determined theoretically. The structures and vibrational frequencies of reactants, products, and tight transition states were determined at the B2PLYP-D3/aug-cc-pVTZ level and final single-point energies refined from extrapolated RCCSD(T)/aug-cc-pVnZ (n = D, T, and Q) calculations. The minimum-energy paths of barrierless reactions were calculated at the NEVPT2 level. Final rate constants were then derived from the transition-state theory (TST) and the variational TST/master equation analysis within the rigid rotor harmonic oscillation framework. A kinetic mechanism was assembled, based on the present ab initio calculations, to successfully model and interpret the experimental absorption profiles. Sensitivity analysis unambiguously highlighted the need to account for pressure dependence in the SiCl₄ decomposition (SiCl₄ ⇄ SiCl₃ + Cl) while discarding previous theoretical and experimental determinations of this rate constant.