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.