Mechanism and Interpolated Variational Transition State Rate Constant for the Reaction of Atomic H with Monoethylsilane

Abstract

The reaction of atomic H and EtSiH3 (CH3CH2SiH3) has been studied theoretically by ab initio direct dynamics methods for the first time. This reaction involves three channels: H abstraction from the silicyl group (SiH3), H abstraction from the methylene group (CH2), and H abstraction from the methyl group (CH3). At the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(2d,p) level, H abstraction from the silicyl group has the smallest potential barrier (4.58 kcal/mol). The potential barriers of H abstraction from the methylene and methyl groups are higher by 4−6 kcal/mol than that of H abstraction from the silicyl group. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction paths for all the channels are discussed and compared. On the basis of the ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory (CVT) with a small-curvature tunneling (SCT) correction method over a wide temperatures range of 200−3000 K. The theoretical result has been compared with available experimental data. The kinetics calculations show that the variational effect is small, and in the low-temperature range (200−500 K), the small curvature tunneling effect is important for all the channels. The detailed branching ratios have been discussed.

Modeling the Kinetics of Bimolecular Reactions

“…Direct dynamics with VTST/MT has now become a widely used method for calculating rate constants of bimolecular reactions in the gas phase without dimensionality reduction. Although the present review is mainly concerned with methodology, and not with complete lists of applications, Table provides some prototype examples ,,,,,,,,,− of applications of VTST/MT to reactions with rate-limiting potential energy barriers.…”

Direct dynamics study on hydrogen abstraction reaction of CF3CHOHCF3 with OH radical

“…This is an unusual case of dynamics calculation in which quantum effects preclude particles (supermolecules) to pass over the classical barrier. There are many reactions showing this phenomenon [29][30][31][32][33]. As we know that the semiclassical transmission probability accounts for both nonclassical reflection at energies above the quasiclassical threshold and also nonclassical transmission, i.e., tunneling, at energies below that threshold.…”