Thermal decomposition pathways and rates for silane, chlorosilane, dichlorosilane, and trichlorosilane

Calculations have been carried out for the thermal decomposition of silane, chlorosilane; dichlorosilane, and trichlorosilane. In each case, the stationary point geometries and harmonic frequencies were characterizing using CASSCF/derivative methods and the cc-pVDZ basis set. Accurate energetics were obtained by combining the CCSD(T) results using the a-cc-pVTZ basis set with an extrapolation to the basis set limit using the a-cc-pVDZ, a-cc-pVTZ, and a-cc-pVQZ basis sets at the MP2 level. The geometries, energetics, and harmonic frequencies were used to obtain rate constants using conventional transition state theory. The barrier heights obtained in the present work (kcal/mol) are the following: SiH4 --> SiH2 + H-2 (61.9); SiClH3 --> SiClH + H-2 (66.7); SiClH3 --> SiH2 + HCl (76.9); SiCl2H2 --> SiCl2 + H-2 (77.2); SiCl2H2 --> SiClH + HCl (74.8); SiCl3H --> SiCl2 + HCl (72.7). The computed barrier heights are believed to be accurate to within 1 kcal/mol. The rate coefficients obtained in the present work are in fair accord with most of the experimental results.