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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Gas-Phase Ni~+(~2D_(5/2))+ n-C_4H_(10) Reaction Dynamics in Real Time: Experiment and Statistical Modeling Based on Density Functional Theory
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Gas-Phase Ni~+(~2D_(5/2))+ n-C_4H_(10) Reaction Dynamics in Real Time: Experiment and Statistical Modeling Based on Density Functional Theory

机译：气相Ni〜+（〜2D_（5/2））+ n-C_4H_（10）实时反应动力学：基于密度泛函理论的实验和统计建模

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摘要

A beam of Ni~+(~2D_(5/2)) is formed at a sharp zero of time by resonant two-photon ionization with a nanosecond dye laser pulse and crossed with a beam of n-butane-h_(10) or n-butane-d_(10) gas. The ion-molecule reaction occurs under single-collision conditions in field-free space in the extraction region of a time-of-flight mass spectrometer. After a variable time delay t_(ext) = 0.5 - 8 #mu#s, a fast high-voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. Analysis of the metastable decay of NiC_4H_(10)~+ complexes from tailing of fragment ion peaks and from retarding field separation reveals detailed information about the formation of elimination products (primarily ethane and H_2) and the decay back to Ni~+ reactants in different time windows from 0.2 to 25 #mu#s after initiation of the collision. To understand the data, we have used density functional theory in its B3LYP variant to locate and characterize the geometries, potential energies, and vibrational frequencies of some 25 stationary points on the ground-state doublet potential energy surface for Ni~+ + n-C_4H_(10). As in earlier work on Ni~+ + C_3H_8, we find that the highest potential energy points along pathways leading to H_2, CH_4, and C_2H_6 elimination are multi-center transition states (MCTSs) involving simultaneous motion of many atoms about the Ni~+ center. The extensive body of information from the electronic structure calculations provides realistic input to a statistical (RRKM) rate model of the reaction. Many details of the time evolution of long-lived complexes for both NiC_4H_(10)~+ and NiC_4D_(10)~+ can be understood semiquantitatively when conservation of angular momentum is accounted for in approximate fashion. In our best model, the energetics of the MCTSs leading to C_2H_6 and H_2 elimination must be adjusted downward by 2-3 and 7 kcal/mol, respectively, from the calculated barrier heights. According to this model, essentially all of the C_2H_6 and H_2 products come from initial insertion of Ni~+ into the central CC bond, the weakest bond in the alkane. The lowest energy path to H_2 elimination is novel, involving initial insertion into the central CC bond followed by simultaneous migration of two #beta#-hydrogens toward each other while being stabilized by the metal cation center. Insertion into a terminal CC bond or into either type of CH bond leads to substantially higher energy MCTSs that are likely unimportant a low collision energy.
机译：通过以纳秒级染料激光脉冲共振双光子电离并与正丁烷-h_（10）光束交叉，在一个零的时间形成Ni〜+（〜2D_（5/2））光束。正丁烷（10）气体。离子分子反应在飞行时间质谱仪提取区域的无场空间中的单碰撞条件下发生。在可变的延迟时间t_（ext）= 0.5-8＃mu＃s之后，一个快速的高压脉冲将产物离子和残留的反应物离子提取到无场飞行管中进行质量分析。 NiC_4H_（10）〜+配合物从碎片离子峰的拖尾和延迟场分离的亚稳态衰变的分析揭示了有关消除产物（主要是乙烷和H_2）的形成以及在不同情况下回到Ni〜+反应物的衰变的详细信息碰撞开始后的时间窗从0.2到25＃mu＃s。为了理解数据，我们在其B3LYP变体中使用了密度泛函理论来定位和表征Ni〜+ n-C_4H_的基态双态势能面上约25个固定点的几何形状，势能和振动频率（10）。正如在早期关于Ni〜+ C_3H_8的工作中一样，我们发现导致H_2，CH_4和C_2H_6消除的路径上的最高势能点是多中心过渡态（MCTS），涉及许多原子同时围绕Ni〜+运动。中央。来自电子结构计算的大量信息为反应的统计（RRKM）速率模型提供了现实的输入。当以近似方式考虑角动量守恒时，可以半定量地理解NiC_4H_（10）〜+和NiC_4D_（10）〜+的长寿命复合物的时间演化的许多细节。在我们的最佳模型中，导致C_2H_6和H_2消除的MCTS的能量必须从计算出的势垒高度分别向下调整2-3和7 kcal / mol。根据该模型，基本上所有的C_2H_6和H_2产物都来自Ni〜+初始插入到中心CC键（烷烃中最弱的键）上。消除H_2的最低能量途径是新颖的，涉及最初插入中心CC键，然后同时使两个＃beta＃-氢彼此相对迁移，同时被金属阳离子中心稳定。插入末端CC键或插入任一类型的CH键会导致实质上更高的能量MCTS，这可能与低碰撞能量无关紧要。

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