两态反应Ni_2^+与c-C_6H_(12)的机理及自旋-轨道耦合研究

Mechanism and Spin-orbit Coupling Study for Two State Reaction Ni_2^+ with Cyclohexane

在密度泛函理论的B3LYP方法下,对两态反应2Ni+与环己烷体系进行了较为系统的研究.结果表明,反应分别在第一个氢迁移(4IM1→4TS1/2),第三个氢迁移(4TS15/16→4IM15)以及2Ni+翻转过程(4IM5→4TS5/6,2TS11/12→2IM12)发生了二、四重态势能面的交叉,本文运用内禀反应坐标单点垂直激发计算的方法得到势能面大致的交叉点(CP),进一步利用Crossing2004程序获得精确的最低能量交叉点(MECP).对MECP附近的自旋轨道耦合(SOC)常数进行了计算.MECP1~MECP4处的SOC值分别为318.01,396.89,268.74和306.67 cm-1.较大的SOC值说明不同势能面间发生了有效地跃迁并使反应沿着最低反应通道进行.对反应通道的研究发现,反应中同面脱氢是主要反应通道.异面脱氢由于翻转过程中决速步骤势垒为33 kcal/mol(吸热3 kcal/mol),只生成少量的异面脱氢产物.计算结果解释了实验现象.

Two-state reaction mechanism of2Ni?with c-C6H12 on the quartet and doublet potential energy surfaces has been investigated at the B3 LYP level. As a result, the ground state for reactants is doublet state, for products is quartet state. A further study on different potential energy surfaces indicates that the title reaction contains four potential energy surfaces crossing in doublet and quartet state, which occurs during the first hydrogen migration step(4IM1 → 4TS1/2), the third hydrogen migration step(4TS15/16→4IM15) and2Ni?flip step(4IM5→4TS5/6, 2TS11/12→2IM12), respectively. The first,second and third potential energy surfaces crossing are the transitions of quartet to doublet state, and the last one is doublet to quartet state. Using single-point energy calculations based on IRC of the different states to locate the approximate structure of crossing points(CPs) between potential energy surfaces, and more accurate structure of CPs, minimal energy crossing points(MECPs), have been obtained by the Crossing 2004 procedure. The spin-orbit coupling(SOC) constant was calculated to discuss the possible spin inversion processes. The values of SOC constants near the MECP1~MECP4 were calculated to be318.01, 396.89, 268.74 and 306.67 cm-1, respectively, the large values of SOC constants indicate the transition from one potential energy surface to another proceeding smoothly and reducing the barrier of reaction in large extent. Based on the result of our calculation, the reaction contains two different channels, one face dehydrogenation and different face dehydrogenation, the first one is confirmed as the dominant channel due to the large exothermicity. Flip process, the critical factor leading to the different face dehydrogenation, has a large barrier of 33 kcal/mol in rate limiting step(2IM9→2TS9/10→2IM10) leading to a few different face dehydrogenation products. Our calculation can well explain the experiment observation.