Chemical bonding via anion photoelectron imaging spectroscopy

在这个由化学系化学结构、动力学和机理(CSDM-A)计划资助的项目中，亚利桑那大学的安德烈·萨诺夫教授正在使用尖端的激光技术和一种称为光电子成像的技术来研究化学键。这项研究的目标是孤立的分子，以及发生化学变化或与邻近物种相互作用的分子。其广泛的目标是揭示所有化学物质在逐渐变大的系统中结合在一起的原理和机制：从原子到分子，从分子到分子簇和大分子，从单体到聚合物，甚至更远。化学键的性质由电子定义，正是它们的行为控制着化学反应的结果。萨诺夫教授和他的研究小组通过捕捉分子阴离子(具有额外电子的分子)发射的电子与激光相互作用的图像，确定了化学键的形成和解离所涉及的基本相互作用。这项研究定义了一个向学生介绍量子概念的教学框架。该计划为本科生和研究生提供继续培训，为他们在学术界、政府实验室和行业的高级职业生涯做好准备。量子概念与计算、传感和网络安全领域的职业相关。萨诺夫教授正在继续开发光电子成像(他也将其称为“量子摄影”)作为量子概念的教学工具。该项目主要关注瞬变物种，如自由基和双自由基反应中间体，以及涉及几个电子态和/或自旋禁忌跃迁的复杂反应路径。所研究的特定体系的例子包括瞬时双自由基和在大气化学和燃烧过程中具有重要作用的有机杂环的自由基物种。在实验中，自由基和双自由基物种是通过从相应的分子阴离子中光分离电子来获得的。释放的电子携带有关阴离子的初始状态和生成的中性分子的最终状态的信息。通过成像质量选择的目标阴离子与可见光或紫外光激光脉冲相互作用产生的光分离电子分布，以光谱方式记录这一信息。从光解反应和阴离子与溶剂分子相互作用中观察到的新生产物的量子态分布，获得了更多的结构和动力学方面的见解。在电子结构计算的帮助下，结果被解释，使得观察到的量子态与理论模型相比较。这项工作的更广泛的影响包括增加对活性中间体的结构和热化学的知识以及更好地了解化学键和反应的一般机制所产生的潜在的社会效益。该项目为培训学生设计、建造和操作先进仪器和复杂的理论分析提供了机会。

In this project funded by the Chemical Structure, Dynamics and Mechanisms -A(CSDM-A) program of the Chemistry Division, Professor Andrei Sanov at the University of Arizona is using sophisticated laser techniques combined with a technique called photoelectron imaging to study chemical bond­ing. This research targets isolated molecules, as well as molecules undergoing chemical change or interacting with neighboring species. The broad objective is to uncover the prin­ci­ples and mechanisms by which all chemical matter binds together in progressively larger systems: from atoms to mol­e­cu­les, from molecules to molecular clusters and macromolecules, from mono­mers to poly­mers, and beyond. The nature of chemical bonding is defined by electrons and it is their behavior that controls the outcomes of chemical reactions. By capturing images of electrons ejected from molecular anions (molecules with an extra electron) interacting with laser light, Professor Sanov and his research group identify the funda­mental interactions involved in the formation and dissociation of chemical bonds. This research defines a pedagogical framework for introducing students to quantum concepts. The program provides continuing training for undergraduate and graduate students, preparing them for advanced careers in academia, government labs, and industry. Quantum concepts have relevance to careers in computing, sensing, and cybersecurity. Prof. Sanov is continuing to develop photoelectron imaging (which he also refers to as "quantum photography") as a teaching tool for quantum concepts.The project focuses primarily on transient species, such as radical and diradical reactive intermediates, as well as complex reactive pathways involv­ing seve­ral electronic states and/or spin-forbidden transitions. Examples of the specific systems studied include transient diradicals and the radical species of organic heterocyclics with important roles in atmospheric chemistry and combustion processes. In the experiments, the radical and diradical species are accessed by photodetaching electrons from the corresponding molecular anions. The freed electrons carry information about both the initial state of the anion and the final state of the resultant neutral molecule. This information is recorded spectroscopically, by imaging the photodetached electron distributions, generated in interactions of the mass-selected target anions with visible or ultraviolet laser pulses. Additional structural and dynamical insights are obtained from the quantum-state distribu­tions of the nascent products observed in photodissociation reactions and in interactions of anions with solvent molecules. The results are interpreted with the help of electronic-structure calculations, enabling a comparison of observed quantum states with theoretical models. The broader impacts of this work include potential societal benefits resulting from increased knowledge of the structures and thermochemistry of reactive intermediates and an improved understanding of the general mechanisms of chemical bonding and reactivity. The project provides opportunities for the training of students in the design, construction, and operation of advanced instrumentation and complex theoretical analyses.