Theoretical study of the thermochemistry and kinetics of the addition of silyl radical to ethylene

The thermochemistry and kinetics of the H3Si + C2H4 → H3Si-CH2CH2 reaction were studied using UQCISD(T)/aug-cc-pVTZ//UQCISD/aug-cc-pVDZ. Our results show that the Arrhenius activation energy, Ea, for the reaction is 3.3 kcal/mol, substantially lower than the 6 kcal/mol value determined experimentally by Loh et al. [S.K. Loh, D.B. Beach, J.M. Jasinski, Chem. Phys. Lett. 169 (1990) 55]. Loh et al.’s high Ea was the result of an estimate of the experimental A-factor that was two orders of magnitude too high. Our calculated rate constant of 1.41 × 106 M−1 s−1 is in very good agreement with the upper bound of 1.81 × 106 M−1 s−1 determined by Loh et al. A study of the thermochemistry and kinetics of the addition reaction using 15 density functional theory methods with 6-31G(d) basis sets indicates that BHandHLYP predicts results in best agreement with high-level theory.