Kinetic and mechanistic studies on the abstraction reactions of atomic O (3P) with (CH3)2SiH2 and (CH3)3SiH

Abstract

A theoretical investigation on the mechanism and kinetics for the reaction of atomic O ( 3 P) with CH 3 CHCl 2Theoretical studies on the variational transitional state theory rate constants for the hydrogen abstraction reaction of O ( 3 P) with CH 3 Cl and CH 2 Cl 2 Potential energy surface for the CH 3 + HBr → CH 4 + Br hydrogen abstraction reaction: Thermal and stateselected rate constants, and kinetic isotope effectsThe reactions of atomic O ( 3 P) with (CH 3 ) 2 SiH 2 and (CH 3 ) 3 SiH have been studied theoretically using ab initio molecular orbital theory for the first time. Geometries have been optimized at the MP2 level with the 6-311G(d,p) and 6-311G(2d,2 p) basis sets. The single-point energy calculations have been carried at the QCISD(T)/6-311ϩG(3d f ,2p) level. Theoretical analysis provides conclusive evidence that the main process occurring in each reaction is the hydrogen abstraction from the Si-H bonds leading to the formation of the H 2 and silyl radical; the hydrogen abstraction from the C-H bonds has higher barrier and is difficult to react. Two nearly degenerate transition states of 3 AЉ and 3 AЈ symmetries have been located for each hydrogen abstraction reaction from the Si-H bonds. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction paths are discussed and compared. The rate constants have been deduced over a wide temperature range of 200-3000 K using canonical variational transition-state theory ͑CVT͒ with small curvature tunneling effect ͑SCT͒. The calculated CVT/SCT rate constants exhibit typical non-Arrhenius behavior, three-parameter rate-temperature formulas are fitted as follows ͑in units of cm 3 molecule Ϫ1 s Ϫ1 ): k 1 (T)ϭ(3.41ϫ10 Ϫ16 )T 1.65 ϫexp(Ϫ411.72/T) and k 2 (T)ϭ(1.85ϫ10 Ϫ15 )T 1.42 exp(Ϫ372.57/T) for the reactions of O ( 3 P) with (CH 3 ) 2 SiH 2 and (CH 3 ) 3 SiH, respectively. The calculated rate constants are compared with the available experimental values.

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

“…Rate Constant. The canonical variational transition state theory (CVT) with a small curvature tunneling correction (SCT), which has been successfully performed for several analogous reactions, − is an effective method to calculate the rate constant. In this paper, we used this method to calculate the rate constants for all the channels involved in the reaction of atomic H with EtSiH 3 over a wide temperature range from 200 to 3000 K. The calculated CVT/SCT rate constants are shown in Figure .…”