气相中CrO2+和H2反应的理论研究

用密度泛函UB3LYP/6-311++G(3df, 3pdpd)//6-311G(2dd, p)方法计算研究了在二重态和四重态两个势能面上的气相反应：CrO₂⁺ + H₂→CrO⁺+ H₂O. 对影响反应机理和反应速率的势能面交叉进行了讨论, 并运用Hammond 假设和Yoshizawa 等的内禀反应坐标(IRC)单点垂直激发计算的方法找出了势能面交叉点(crossing point (CP)). 运用碎片分子轨道(fragment molecular orbital(FMO))理论, 对初始复合物2IM1和4IM1的轨道相关进行了分析, 解释了CrO₂⁺活化H—H σ键及H₂迁移的机理.

Theoretical Study of Gas-phase Reaction of CrO2+ with H2

The gas-phase reaction of CrO₂⁺(²A₁/⁴A″) with H₂ to yield CrO+(²Σ_g/⁵Σ_g) and H₂O is selected as a representative system of activation of H—H σ bond by MO₂⁺. The reaction mechanism has been investigated with density functional theory (DFT) at the UB3LYP/6-311++G(3df, 3pd)//6-311G(2d, p) 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 calculations. The H—H bond has been activated by CrO₂⁺(²A₁) on the doublet PES(potential energy surface) while dihydrogen transfer from Cr to O (in longer Cr—O) on the quartet PES. The involving potential energy curve-crossing, with dramatically affecs reaction mechanism and reaction rate, has been discussed in detail. The crossing points (CPs) are localized by means of the Hammond postulate and the intrinsic reaction coordinate (IRC) approach. The formation of the transition metal dihydrogen complex (H₂)CrO₂⁺(²IM1 and ⁴IM1) involves donation of the H₂ σ bonding orbital to the metal and the back-donation by the metal electron to the H₂ σ* antibonding orbital, as illustrated by the fragment molecular orbital(FMO). In addition, the orbital analysis on the activation of the H—H bond and dihydrogen transfer has been carried out by FMO.