The direct hydrogen abstraction reactions of H atoms with SiH3Cl, SiH2Cl2, and SiHCl3 have been studied systematically using ab initio molecular orbital theory. Geometries have been optimized at the UMP2 level with the 6-311G(2d, p) basis set. The G3MP2 theory has been used for the final single-point energy calculation. Theoretical analysis provides conclusive evidence that the main process occurring in each case is the hydrogen abstraction from the Si-H bond; the chlorine abstraction from the Si-Cl bond has a higher barrier and is difficult to react. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction path of the reactions are discussed and compared. The kinetic calculations of the title reactions have been deduced using canonical variational transition state theory (CVT) with the smallcurvature tunneling (SCT) correction method over a wide temperature range of 200-3000K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior. Three-parameter rate-temperature formulas have been fitted as follows: k1=1.54

The reactions of atomic O (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)/6-3111G(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 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 canonical variational transition-state theory (CVT) with small curvature tunneling effect (SCT). The calculated CVT/SCT rate constants exhibit typical non-Arrhenius behavior, three-parameter rate-temperature formulas are fitted as follows (in units of cm3 molecule21 s21): k1(T)=(3.41×10216)T1.65 3exp(2411.72/T) and k2(T)＝(1.85×10215)T1.42 exp(2372.57/T) for the reactions of O (3P) with (CH3)2SiH2 and (CH3)3SiH, respectively. The calculated rate constants are compared with the available experimental values.

The hydrogen abstraction reactions of atomic O (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 M

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)/6-3111G(3d f, 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 200-3000K. The theoretical results have been compared with available experimental data. The kinetics calculations show that the variational effect is small and in the low temperature range (200-800K), the small curvature tunneling contribution is important for all the channels. The detailed branching ratios have been discussed.

The direct hydrogen abstraction reactions of H atom with GeH4, CH3GeH3, (CH3)2GeH2, and (CH3)3GeH have been studied systematically using ab initio molecular orbital theory. Geometries have been optimized at the UMP2 level with 6-31G (d) and 6-311G (2df,p) basis sets. G2MP2 theory has been used in the final singlepoint energy calculation. Theoretical analysis provided conclusive evidence that the main process occurring in each case is the hydrogen abstraction from the Ge-H bond leading to the formation of the H2 and germyl radicals; the hydrogen abstraction from the C-H bond has higher barriers and is difficult to react. The kinetic calculations of the title reactions have been deduced using the canonical variational transition-state theory (CVT) with the small-curvature tunneling correction method (SCT) over the temperature range of 200-3000K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior. Three-parameter rate-temperature formulas have been fitted as follows: k1＝(2.17×10-17)T2.16 exp(-294.2/T), k2＝(2.21×10-17)T2.22 exp(-161.6/T), k3＝(1.96×10-17)T2.18 exp(-108.0/T), and k4＝(6.66×10-18)T2.33 exp(-60.3/T) for the reactions of H with GeH4, CH3GeH3, (CH3)2GeH2, and (CH3)3GeH, respectively (in units of cm3 molecule-1 s-1). Studies show that the methyl substitution has an effect on the strength and reactivity of the Ge-H bond in (CH3) (4-n)GeHn (n) 1-3). The calculated CVT/SCT rate constants are in excellent agreement with the available experimental values.