Qingzhu Zhang

Direct ab initio and kinetic calculation for the abstraction reaction of atomic O (3P) with CH3Br

Abstract The hydrogen abstraction reaction of O ( 3 P ) with CH 3 Br has been studied theoretically for the first time. Two nearly degenerate transition states of 3 A ″ and 3 A ′ symmetries have been located for this abstraction reaction. Geometries have been optimized at the UMP2 level with the 6-311G(2d, p) basis set. The G2MP2 method has been used for the final single-point energy calculation. On the basis of the ab initio data, the rate constants have been deduced over a wide temperature range 200–3000 K using canonical variational transition-state theory (CVT) with a small curvature tunneling effect (SCT). The calculated CVT/SCT rate constants exhibit typical non-Arrhenius behavior, a three-parameter rate-temperature formula is fitted in units of cm 3 molecule −1 s −1 as follows: k ( T )=(2.83×10 −19 ) T 2.33 exp(−2115.97/ T ).

Ab initio mechanism and thermal rate constants for the reaction of atomic H with Ge2H6

The reaction of digermane Ge2H6 with atomic H has been studied theoretically. The detailed mechanism has been revealed for the first time. This reaction involves not only abstraction but also substitution. The calculation shows that there are two transition states for the substitution reaction: (1) frontside attack of the Ge–Ge bond by the hydrogen atom and (2) backside attack of the GeH3 group by the hydrogen atom along the Ge–Ge axis, forming a transition state structure with C3v symmetry. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction path for each channel 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 the small-curvature tunneling (SCT) correction method over the temperature range of 200–3000 K. The theoretical results have been compared with available experimental data. The kinetics calculations show that the variational effect is small for all the channels and in the lower temperature range, the small-curvature tunneling effect is important for the abstraction channel and the substitution channel with backside attack. At lower temperatures, the major product channel is direct hydrogen abstraction leading to Ge2H5 and H2, whereas the substitution reaction with frontside attack becomes the dominant channel at higher temperatures. The substitution reaction with backside attack is a minor channel over the whole studied temperature range.

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

The reactions of atomic Ou2009(3P) with (CH3)2SiH2 and (CH3)3SiH 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,2p) basis sets. The single-point energy calculations have been carried at the QCISD(T)/6-311+G(3df,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 H2 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 3A″ and 3A′ 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 can...

Ab initio and kinetic calculation for the abstraction reaction of atomic O (3P) with Si2H6

Abstract The hydrogen abstraction reaction of O ( 3 P ) with Si2H6 has been studied theoretically for the first time. Two transition states of 3 A ″ and 3 A ′ symmetries have been located for this abstraction reaction. Geometries have been optimized at the MP2 level with 6-311G+(d) basis set. A modified G3MP2 method has been used for the final single-point energy calculation. Based on the ab initio data, the rate constants have been calculated over a wide temperature range of 200–3000 K using canonical variational transition state theory (CVT) with small curvature tunneling effect (SCT). The calculated CVT/SCT rate constants match well with the experimental value.

A theoretical investigation on the mechanism and kinetics for the reaction of atomic O(3P) with CH3CHCl2

The reaction of atomic O(3P) with CH3CHCl2 has been studied theoretically using ab initio direct dynamics methods for the first time. This reaction involves two channels: H abstraction from the methyl group (CH3), and H abstraction from the methyne group (CH). Two nearly degenerate saddle points of 3A″ and 3A′ symmetries have been located for each hydrogen abstraction channel. At the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) level, the potential barrier of H abstraction from the CH3 group is higher about 6 kcal/mol than that of H abstraction from the CH 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 with small-curvature tunneling correction method over a wide temperatures range of 200–3000 K. The theoretical results have been compared with ava...

Theoretical studies on the variational transitional state theory rate constants for the hydrogen abstraction reaction of O (3P) with CH3Cl and CH2Cl2

The hydrogen abstraction reactions of atomic Ou200a(3P) with CH3Cl and CH2Cl2 have been studied theoretically using ab initio molecular orbital theory for the first time. In the Cs symmetry, both reactions proceed over two potential-energy surfaces, 3A″ and 3A′ generated by the pseudo-Jahn–Teller effect. Two nearly degenerate transition states of 3A″ and 3A′ symmetries have been located for each hydrogen abstraction reaction from the C–H bonds. Geometries of the reactants, transition states, and products have been optimized at the second-order Moller–Plesset (MP2) level with the 6-311G(2d,p) basis set. The single-point energy calculations have been carried at the [QCISD(T)]/6-311+G(3df,2p) level. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction paths are discussed and compared. The total thermal rate constants were obtained from the sum of the calculated rate constants for the two surfaces using canonical variational transition-state theory (CVT...

A theoretical investigation on the mechanism and kinetics for the reaction of SiH2Cl2 with atomic O (3P)

Abstract The hydrogen abstraction reaction of SiH2Cl2 with O ( 3 P ) has been studied theoretically for the first time. Two transition states of 3 A ′′ and 3 A ′ symmetries have been located for this abstraction reaction. Geometries have been optimized at the MP2 level with the 6-311G(2d,p) basis set. A modified G3MP2 method has been used for the final single-point energy calculation. On the Basis of the ab initio data, the rate constants have been deduced over a wide temperature range of 200–3000 K using canonical variational transition-state theory (CVT) with small curvature tunneling effect (SCT). The calculated rate constants have been compared with the experimental values.

Ab initio and kinetic calculations for the reactions of H with SiH(4−n)Fn (n= 1–3)

The reactions of H with SiH3F, SiH2F2 and SiHF3 have been studied systematically using the direct dynamics method for the first time. A direct hydrogen abstraction mechanism has been revealed. The geometries of reactants, products and transition states have been optimized at the UMP2 level. Single-point calculations have been carried out at the G2MP2 level of theory. Based on the ab initio data, the rate constants have been calculated using the canonical variational transition state theory with the small-curvature tunneling correction method (CVT/SCT) over a wide temperature range of 200–3000 K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior. Three-parameter rate–temperature formulas are fitted as follows: k1(T) = (1.81 × 10−19)T2.85 exp(−694.74/T) for nthe reaction of H with SiH3F, k2(T) = (1.43 × 10−20)T3.19 exp(−1102.60/T) for the reaction of H with SiH2F2, k3(T) = (2.34 × 10−20)T2.87 exp(−2002.20/T) for the reaction of H with SiHF3, in units of cm3 molecule−1 s−1. The theoretical results are in good agreement with the available experimental data. The fluorine substitution decreases the reactivity of the Si–H bond.

Theoretical study on the abstract reaction of O(3P) with CHFCl2

Abstract The reaction of O( 3 P ) with CHFCl 2 has been studied using ab initio molecular orbital theory. Two nearly degenerate transition states of 3 A ″ and 3 A ′ symmetries were located for this reaction. The kinetic nature is obtained using canonical variational transition state theory with small-curvature tunneling correction method. The calculated rate constants exhibit typical non-Arrhenius behavior, a three-parameter rate-temperature formula is fitted as follows: k(T)=2.627×10 −22 T 3.55 exp (−2525.56/T) cm 3 molecule −1 s −1 over a wide temperature range of 200–3000 K. The calculated results match well with the experimental values.