The gas phase reaction of oxo-species CrO2+ ((2)A(1)/(4)A") with CH4 was selected as a system of C-H bond activation by MO2+. The reaction mechanism has been investigated with density functional theory at the B3LYP/6-311 + + G** level. Four reaction path channels have been studied on both the doublet and quartet potential energy surfaces. The geometries for reactants, the transition states and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. The potential energy curve-crossing dramatically affecting reaction mechanism and reaction rate has been discussed detailedly. The Hammond postulate and the IRC analyses used by Yoshizawa et al. have been used to locate and character a series of crossing points involving the structures and energy values. In addition, the orbital analysis of C-H bond activation has been carried out by fragment molecular orbital.

The mechanisms for the abstraction reactions of alkylidenecarbenes and its substituted species with oxirane have been characterized in detail by density functional theory. All the stationary points were determined at the B3LYP/6-311G(d,p) level of the theory. The transition states both to the reactant and the product directions in the reaction paths were examined by using the intrinsic reaction coordinate. A configuration mixing model based on the work of Pross and Shaik was used to rationalize the computational results. The results show that the electro negativity of the substituents played an important role to predict its activity for the abstraction reactions. The major conclusion was that the stronger the a-donation or the more electronegative the substituents, the smaller the Delta E-ST Of XYC = C: and the lower the activation energy for the abstraction reactions. In other words, it is the electronic factors, rather than the steric ones, that play a decisive role in the chemistry of the alkylidenecarbene species.

The mechanisms of the abstraction reactions of alkylidenecarbenes have been characterized in detail using density functional theory. All the stationary points were determined at the B3LYP/6-311G(d, p) level of the theory. The transition states both to the reactants and the product direction in the reaction paths were examined by using the intrinsic reaction coordinate. A configuration mixing model based on the work of Pross and Shaik was used to rationalize the computational results. The results show that the electro negativity of the substituents played an important role in predicting its activity for the abstraction reactions. The major conclusion was that the stronger the pi-donation or the more electro negativity the substituents, the smaller the Delta E-ST of XYC = C and the lower the activation energy for the abstraction reactions. In other words, it is the electronic factors, rather than the steric factors, that play a decisive role in the chemistry of the alkylidenecarbene species. Furthermore, a comparison with oxirane also led to the same result.

The reaction between silyl radicals and nitric oxide was studied by using the B3LYP/6-311G** and the high-level electron-correlation CCSD (T) /6-311G** methods. The geometries for reactants, the transition states and the products were completely optimized. All the transition states are verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. The results show that the reaction is via multi-channel and multistep. Five products may be formed via the complex reaction channels, i.e. association, H-shift and dissociation.

The reactivity of X(3P) (X=Ge, Sn, Pb) with N2O(X1Σ) on both singlet and triplet potential energy surfaces have been investigated at the B3LYP level of theory. To accurately evaluate the activation barrier and reaction energy, the coupled cluster single point calculations using the B3LYP structures is performed. The calculated results are in good agreement with experimental observations. The X(P3)+N2O(X1Σ)→XO(X1Σ)+N2(X1Σg+) (X=Ge, Sn, and Pb) reactions that Arthur Fontijn has been observed are spin-forbidden for formation of ground state products in the experiments. The present paper is discussed with the aid of the direct abstraction (DA) mechanism (also called the surface crossing model), a correlation argument based on separated fragments X+O+N2 can explain the inefficiency of the X(P3)+N2O(X1Σ)→XO(X1Σ)+N2(X1Σg+) (X=Ge, Sn, and Pb) reactions at 298K by the need to switch electron configurations along low-energy adiabatic paths from ground-state reactants to energetically accessible XO(X1Σ)+N2(X1Σg+) product states.

The reaction of Sc+ or Ti+ with CS2, which was selected as a representative system of reactions of first early transition-metal ions with CS2. The reaction mechanism of Sc+ or Ti+ in ground state and excitated state with CS2 has been studied using the density functional theory (DFT) at B3LYP/6-311+G* level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. A potential energies curve-crossing diagram was investigated for state correlation between early intermediate IMI and reactants in the reaction of Sc+, Ti+ with CS, The result showed that the reaction mechanism between first early transition-metal ions and CS2 was an insertion-elimination mechanism. The main reaction path channel was detected in the reaction of Sc' or Ti+ in ground state and excitated state with CS2.

The potential energy surfaces for the abstraction reaction of germylene with thiirane have been characterized in detail using density functional theory (DFT). All the stationary points were determined at the B3LYP/6-311++G (d, p) level of the theory. The transition states both to the reactants and the product direction in the reaction paths were examined by using the intrinsic reaction coordinate (IRC). The major conclusion is as follows: the reaction is in two steps, (1)germylenes and thiirane form an intermediate complex through an exothermal reaction without any barrier; (2) the intermediate complexes isomerize to give the products. Furthermore, the stronger the pi-donation is or the more electronegative the substituents are the bigger the Delta E-ST of X2Ge, the higher the activation energy for the abstraction reactions will be. In other words, it is the electronic factors, rather than the steric factors, that play a decisive role in the chemistry of the germylene species. A configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results.

Five optimized geometries of F-.(H2O), (n = 1, 2) were obtained with ab initio calculation at the B3LYP/6-311++G** level. The accurate intermonomer interaction energy was calculated using the MP2 electron correlation correction as well as the basis set superposition error correction by the Boys-Bemardi "counterpoise" protocol. Natural bond orbital (NBO) theory was applied to quantify the relative strength of these interactions and account for their effects on the stability, structural and vibrational parameters of F-(H2O), (n = 1, 2). It is shown that the charge transferring from the lone pair of F-1 to the sigma*(OH(...F)) antibonding orbital is important. The results indicate the occupancy of sigma*(OH(...F)) is increased (denoted Delta sigma*(OH(...F))) and the sigma(OH(...F)) bond is lengthened (denoted Delta R-OH(...F)), leading to the red-shift and the red-shift values have linear correlation with both Delta sigma*(OH(...F)) and Delta R-OH(...F).

The multi-bond dissociation dynamics of oxalyl bromide ((BrCO)(2)) has been investigated by DFT and CIS calculations. Upon the results, conclusion could be drawn that dissociation of C-Br bond of oxalyl bromide at the ground state (S-0) is of barrierless. After the absorption of a photon, (BrCO)2 is excited to the first excited state and one of its C-Br bonds is broken to yield Br (.) *and BrCOCO (.) *free radicals. In addition, BrCOCO (.)* with high energy is apt to release energy, and ultimately, turns into BrCOCO (.) of the ground state. The energy is adequate for BrCOCO (.) to break down into Br (.) and 2CO; at the same time the C-C and C-Br bonds of BrCOCO (.) free radicals dissociate.

The reaction mechanism between ozone and ethylene radical (C2H3) has been studied using the density functional theory (DFT) at B3LYP/6-311G* * level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states are verified by the vibrational analysis and the intrisic reaction coordinate (IRC) calculations. The results show that the ethylene radical (C2H3) trends intensively to react with the ozone.