Li Hongwei, Suits Arthur G
Department of Chemistry, University of Missouri, Columbia, MO 65211, USA.
Phys Chem Chem Phys. 2020 May 28;22(20):11126-11138. doi: 10.1039/d0cp00522c. Epub 2020 Mar 30.
The marriage between high level quantum calculations and experimental advances in laser technology, quantum state control, and detection techniques have opened the door to the study of molecular collision dynamics at a new level of detail. However, one current challenge lies in adapting these powerful strategies to address questions beyond the scope of the small ground state systems that have largely been the focus of reaction dynamics investigations to-date. For molecules with intermediate or large size (more than 6 atoms), lack of spectroscopic information and spectral congestion limit quantum state preparation, control and detection for experiment, and the large number of degrees of freedom of the system makes accurate quantum dynamics calculations prohibitively expensive. Nevertheless, studies of the chemical dynamics of such systems can reveal novel aspects of reactivity not anticipated based upon the behavior of smaller model systems. This Perspective will highlight applications of soft vacuum ultraviolet photoionization at 157 nm as a universal probe in combination with crossed beams and DC slice velocity map ion imaging to study bimolecular reaction dynamics of molecules of intermediate or large size, illuminated with support of high-level ab initio calculations. Here, we report on the chemical dynamics of atomic oxygen or chlorine reactions with organic compounds: propanol isomers, alkylamines (N(CH) and NH(CH)), and isobutene ((CH)CCH) studied using this approach. The polyatomic radical products from the hydrogen abstraction process have been detected by 157 nm photoionization and their slice ion images embody translational energy and angular information that directly reflect the underlying collision dynamics. Various reaction mechanisms (such as direct abstraction and addition-elimination) along with the involvement of roaming dynamics and novel intersystem crossing pathways are presented. These demonstrate the power of this technique to reveal fundamentally new aspects of reaction dynamics that arise in larger reaction systems.
高水平量子计算与激光技术、量子态控制及检测技术方面的实验进展相结合，开启了在新的精细程度上研究分子碰撞动力学的大门。然而，当前的一个挑战在于如何调整这些强大的策略，以解决超出小基态系统范围的问题，而小基态系统在很大程度上一直是迄今为止反应动力学研究的重点。对于中等或较大尺寸（超过6个原子）的分子，缺乏光谱信息和光谱拥堵限制了实验中的量子态制备、控制和检测，并且系统的大量自由度使得精确的量子动力学计算成本高得令人望而却步。尽管如此，对这类系统化学动力学的研究可以揭示基于较小模型系统行为无法预期的反应性新方面。本展望将重点介绍157 nm软真空紫外光电离作为通用探针，结合交叉束和直流切片速度成像离子成像技术，在高水平从头计算的支持下，研究中等或较大尺寸分子的双分子反应动力学的应用。在此，我们报告了使用这种方法研究的原子氧或氯与有机化合物（丙醇异构体、烷基胺（N(CH)和NH(CH)）以及异丁烯（(CH)CCH））的化学动力学。通过157 nm光电离检测到了氢提取过程产生的多原子自由基产物，其切片离子图像体现了直接反映潜在碰撞动力学的平动能和角信息。文中介绍了各种反应机制（如直接提取和加成-消除）以及漫游动力学和新型系间窜越途径的参与情况。这些展示了该技术揭示较大反应系统中出现的反应动力学全新基本方面的能力。
