A study of the (CH3)4Si + H ⇌ H2+(CH3)3SiCH2 system

Abstract

The reaction system H +(CH₃)₄Si ⇌ H₂+(CH₃)₃SiCH₂(1, –1) has been studied in pulsed photolysis experiments in the temperature range 425–570 K. H atoms were generated by Hg-sensitized photolysis of H₂, and were monitored by Lyman-α absorption. The rate constant for the forward reaction, measured at an H₂ pressure of 133 Pa, is given by the expression k(1)/cm³ s^–1=(7.5 ± 4.0)× 10^–11 exp[(–3990 ± 300)/T].

The rate constant of the reverse reaction, determined by computer simulation from the results of experiments with H₂ pressures up to 7 × 10⁴ Pa, is given by k(–1)/cm³ s^–1= 3 × 10^–12 exp(–6000/T).

Stationary photolyses assisted in establishing the mechanism of the system. Combination of the Arrhenius parameters of the forward and reverse reactions yields the bond-dissociation energy and entropy values D[(CH₃)₃SiCH₂–H]= 420 ± 8 kJ mol^–1 and S[(CH₃)₃SiCH₂]= 364 J K^–1 mol^–1.