The gas phase reaction of oxo-species CrO₂⁺ (²A₁/⁴A") with CH₄ was selected as a system of C—H bond activation by CrO₂⁺. 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.

Key words: activation of C—H bond of methane, two-state reactivity, potential energy surfaces crossing point (CP), fragment molecular orbital