Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, P.O. Box 23-166, Taipei, 10617, Taiwan.
Chem Soc Rev. 2017 Dec 11;46(24):7517-7547. doi: 10.1039/c7cs00601b.
Over the past ten years or so, great advances in our understanding of the dynamics of elementary (bimolecular) polyatomic reactions in the gas-phase have occurred. This has been made possible by critical improvements (a) in crossed molecular beam (CMB) instruments with rotating mass spectrometric detection and time-of-flight analysis, especially following the implementation of soft ionization (by tunable low energy electrons or vacuum-ultraviolet synchrotron radiation) for product detection with increased sensitivity and universal detection power, and (b) in REMPI-slice velocity map ion imaging (VMI) detection techniques in pulsed CMB experiments for obtaining product pair-correlated information through high-resolution measurements directly in the center of mass system. The improved universal CMB method is permitting us to identify all primary reaction products, characterize their formation dynamics, and determine the branching ratios (BRs) for multichannel non-adiabatic reactions, such as those of ground state oxygen atoms, O(P), with unsaturated hydrocarbons (alkynes, alkenes, dienes). The improved slice VMI CMB technique is permitting us to explore at an unprecedented level of detail, through pair-correlated measurements, the reaction dynamics of a prototype polyatomic molecule such as CH (and isotopologues) in its ground state with a variety of important X radicals such as F, Cl, O, and OH. In this review, we highlight this recent progress in the field of CMB reaction dynamics, with an emphasis on the experimental side, but with the related theoretical work, at the level of state-of-the-art calculations of both the underlying potential energy surfaces and the reaction dynamics, noted throughout. In particular, the focus is (a) on the effect of molecular complexity and structure on product distributions, branching ratios and role of intersystem crossing for the multichannel, addition-elimination reactions of unsaturated hydrocarbons with O atoms, and (b) on the very detailed dynamics of the abstraction reactions of ground-state methane (and isotopologues) with atoms (F, Cl, O) and diatoms (OH), with inclusion of also rotational mode specificity in the vibrationally excited methane reactions.
在过去的十年左右，我们对气相中基本（双分子）多原子反应动力学的理解取得了重大进展。这是通过以下关键改进实现的：(a) 带有旋转质谱检测和飞行时间分析的交叉分子束 (CMB) 仪器的改进，特别是在采用软电离（可调谐低能电子或真空紫外同步辐射）进行产物检测后，灵敏度和通用检测能力得到提高；(b) 在脉冲 CMB 实验中采用 REMPI 切片速度映射离子成像 (VMI) 检测技术，通过在质心系统中直接进行高分辨率测量，获得产物对相关信息。改进后的通用 CMB 方法使我们能够识别所有主要的反应产物，描述它们的形成动力学，并确定多通道非绝热反应（如基态氧原子 O(P) 与不饱和烃（炔烃、烯烃、二烯烃）的分支比 (BR)。改进后的切片 VMI CMB 技术使我们能够通过对相关测量，以前所未有的详细程度探索原型多原子分子（如 CH（及其同位素））在基态与各种重要 X 自由基（如 F、Cl、O 和 OH）的反应动力学。在这篇综述中，我们强调了 CMB 反应动力学领域的这一最新进展，重点是实验方面，但相关的理论工作也得到了关注，包括基础势能面和反应动力学的最新计算水平。特别是，重点是(a) 分子复杂性和结构对产物分布、分支比和不饱和烃与 O 原子的多通道加成消除反应中系间窜跃的影响，以及(b) 基态甲烷（及其同位素）与原子（F、Cl、O）和双原子（OH）的抽提反应的非常详细的动力学，包括振动激发甲烷反应中的旋转模式特异性。
