Theoretical kinetic and thermodynamic study on the disilene-silylsilylene isomerization

Abstract

The titled isomerization has been studied at the HF/3–21G level. The changes in thermodynamic functions, equilibrium constant K(T), conversion efficiency C(T), and the rate constant k(T) for the isomerization have been calculated using our energies of the reactant (R), transition state (TS), and product (P), their harmonic vibrational frequencies, and the classical and corrected barrier (by vibrational zero-point energies). In the range of temperature, 300–1200K, ΔH < 0, ΔS > 0 and ΔG < 0; i.e., it is exothermic, increasing in the entropy, and spontaneous reaction. ΔS≠ < 0, log A is about 12.0 ±0.15 (s−1), but the k(T) is from 2.627 × 10(−33) to 6.933 × 10(8) (5−1); i.e., it passes through a tight TS, the A factor changes little, but the rate constant varies rapidly with the temperature. These results agree with the fact that the isomerization occurs readily at high temperature. Furthermore, Newman's mechanism, 2SiH2 → (H2SiSiH2)* → (HSiSiH3)* → Si2H2 + H2, is supported. Similarly, the isomerization, HDSiSiH2 → HSiSiDH2, is also studied.