气相中Ir^＋与CH4分子自旋禁阻反应中C—H键活化机理的理论研究

采用密度泛函理论和高级电子相关耦合簇方法,在CCSD（T）/6-311＋＋G（3df,3pd）//B3LYP/6-311＋G（d,p）的理论水平下,研究了3个自旋态势能面上自旋禁阻反应Ir^＋（^5F）＋CH4（^1A1）→IrCH2^＋（3A″）＋H2（1Σg^＋）的微观机理,通过自旋-轨道耦合的计算,讨论了势能面交叉和可能的自旋翻转过程.结果表明,Ir^＋与CH4的反应中不同势能面之间的“系间窜越”（ISC）将会发生,分子体系通过3次自旋翻转沿着热力学最有利的反应路径进行,最优的反应路径总放热量为44.64 kJ/mol.运用Harvey等的方法优化出最低能量交叉点（MECP）,并计算了MECP处相应的自旋-轨道耦合常数（SOC）,分别为346.95,2 545.62,2 990.98 cm^-1,较大的SOC值说明了自旋翻转是有效的.

Theoretical Study of the Mechanism for C-H Bond Activation in Spin-forbidden Reaction between Ir+ and CH4

The mechanism of the spin-forbidden reaction Ir^＋（^5F）＋CH4（^1A1）→IrCH2^＋（3A″）＋H2（1Σ^＋g） on quintet,triplet and singlet potential energy surfaces（PESs） has been investigated at the CCSD（T）/6-311＋＋G（3df,3pd）//B3LYP/6-311＋G（d,p）levels.Crossing points between the different potential energy surfaces and the possible spin inversion process are discussed by spin-orbit coupling（SOC） calculations.The calculated results indicate that the intersystem crossing（ISC） between different potential energy surfaces will occur,the molecular system may change its spin mulitiplicity three times in this reaction,and preferentially move on the minimum-energy pathways.The overall exothermicity is 44.64 kJ/mol.The minimum energy crossing points（MECPs） that obtained by the mathematical algorithm proposed by Harvey et al.has been also employed.The values of the SOC constants at MECP1,MECP2 and MECP3 are 346.95 cm^-1,2 545.62 cm^-1 and 2 990.98 cm^-1,respectively,which indicates that the spin crossing process in this reaction can occur efficiently due to the large SOC involved.