A look at atmospheric chemistry through the back door: PEI spectroscopy of anionic precursors to transient species

大气化学的许多主要驱动力是被称为“自由基”的短寿命活性小分子，其表征具有挑战性，因为很难在实验室中制备足够数量的它们来研究它们。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，Caroline Chick Jarrold教授使用了一种独特的方法来制备自由基，方法是(1)用负电荷稳定它们，然后(2)通过使用激光选择性地分离电子来收集关于中性自由基的详细信息，以使电子的能量准确地反映自由基的性质。感兴趣的特定分子参与了部分大气中臭氧的产生，对人类健康产生了负面影响。该项目将自由基物种及其阴离子前体的低温制备与阴离子光电子成像(PEI)光谱相结合。这种工具组合被应用于异戊二烯加成物，以及异戊二烯臭氧分解形成的物种，其中可能包括Criegee中间体(据信在臭氧分解过程中形成的羰基氧化物)，以及与H2O和O2形成的非共价复合体。异戊二烯(2-甲基-1，3-丁二烯)被羟基和臭氧氧化生成一系列活性开壳分子，其动力学一直是一个非常活跃的研究领域。拟议研究的光谱数据补充了动力学研究，提供了更详细的电子和分子结构信息。此外，影响异构化和反应势垒高度的水和可以光敏并与瞬变反应的O2的影响正在被探索中。光谱分析得到量子波包从头算分子动力学研究的共同支持。该项目的更广泛影响包括增进目前对复杂、相互关联的大气过程网络的了解，以及在一个具有全球重要性的领域对博士后研究助理、研究生和本科生进行高技术培训。

Many of the principal drivers of atmospheric chemistry are short-lived reactive small molecules known as "radicals," the characterization of which is challenging because it is difficult to prepare them in a laboratory in sufficient quantities to study them. In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Caroline Chick Jarrold uses a unique approach to preparing radicals by (1) stabilizing them with a negative charge, then (2) gleaning detailed information about the neutral radicals by using lasers to selectively detach the electrons in a way that the energy of the electrons precisely reflects the properties of the radicals. The specific molecules of interest are involved in production of ozone in the part of the atmosphere with negative impact on human health. Outreach is being done, in part, through her institution's STEM Summer Scholars Institute.This project combines low-temperature preparation of radical species and their anionic precursors with anion photoelectron imaging (PEI) spectroscopy. This combination of tools is being applied to OH-isoprene adducts, and species formed by ozonolysis of isoprene, which may include Criegee intermediates (carbonyl oxides believed to be formed during ozonolysis), along with non-covalent complexes the intermediates form with H2O and O2. The oxidation of isoprene (2-methyl-1,3-butadiene) by OH and O3 leads to the formation of a wide range of reactive open-shell molecules, the kinetics of which has been a very active area of research. The spectroscopic data from the proposed studies complements kinetics studies with more detailed electronic and molecular structural information. Additionally, the effects of water, which influences isomerization and reaction barrier heights, and O2, which can both photosensitize and react with the transients, are being probed. Spectroscopic analysis is supported collaboratively by quantum wavepacket ab initio molecular dynamics studies. The broader impacts of this project include an increase in current understanding of the complex, interconnected web of atmospheric processes, in addition to highly technical training for a postdoctoral research associate, graduate students, and undergraduates in the context of an area of global importance.