RUI: The Tropospheric Oxidation of Biogenic Hydrocarbons: Probing Temperature Dependence and Autoxidation

通过这一奖项，化学系的环境化学科学项目和大气和地球空间科学系的大气化学项目共同资助麦卡莱斯特学院的Keith T.Kuwata教授和威斯康星大学河瀑布分校的Stacey A.Stoffregen副教授和他们的本科生研究异戊二烯的化学反应，异戊二烯是大气中含量最丰富的不饱和有机化合物。异戊二烯是不饱和的，这一事实使其容易被氧的活性形式氧化，如羟基自由基(OH)和臭氧。库瓦塔和斯托夫勒根实验室使用计算方法来预测异戊二烯被OH和臭氧氧化的所有途径。项目的最终目标是预测(1)异戊二烯+羟基和异戊二烯+臭氧反应的产物，(2)这些反应中关键步骤的速率，以及(3)这些速率如何随温度变化。这些预测将指导合作者在实验中研究相同的反应，并有可能提高大气化学模型的准确性和精确度。参与该项目的本科生接受各种方法的研究培训，通常在全国科学会议和中西部计算化学本科生协会一年两次的会议上展示结果。正在考虑的化学反应构成了重大的理论挑战，活性中间体通常被化学激活，并具有具有显著水平的动态和静态电子关联的电子结构。预测化学活化物种的命运需要主方程模拟，微正则速率常数要么由莱斯-拉姆斯佩格-卡塞尔-马库斯理论确定，要么由变分过渡态理论确定。使用复合电子结构方法，如Weizmann-1 Brueckner偶理论，提供了对动态关联的精确处理，而运动方程自旋翻转耦合团簇理论提供了对静态关联的合理估计。库瓦塔和斯托夫勒根实验室将应用这些方法来研究在OH引发的异戊二烯氧化过程中自氧化和自由基终止过程之间的竞争，以及研究异戊二烯臭氧化中迄今未测量到的羟基羰基的生成。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With this award, the Environmental Chemical Sciences Program in the Division of Chemistry and the Atmospheric Chemistry Program in the Division of Atmospheric and Geospace Sciences are jointly funding Professor Keith T. Kuwata of Macalester College and Associate Professor Stacey A. Stoffregen of the University of Wisconsin-River Falls and their undergraduate research students to study chemical reactions of isoprene, the most abundant unsaturated organic compound in the atmosphere. The fact that isoprene is unsaturated makes it prone to oxidation by reactive forms of oxygen such as hydroxyl radical (OH) and ozone. The Kuwata and Stoffregen laboratories use computational methods to predict all pathways by which isoprene is oxidized by OH and ozone. The ultimate project goals are to predict (1) the products of the isoprene + OH and isoprene + ozone reactions, (2) the rates of key steps in these reactions, and (3) how these rates vary with temperature. These predictions will guide collaborators studying the same reactions experimentally and have the potential to improve the accuracy and precision of atmospheric chemistry models. The undergraduates working on the project receive research training in a variety of methods and typically present results at national scientific meetings and at twice-yearly meetings of the Midwest Undergraduate Computational Chemistry Consortium.The chemical reactions under consideration pose significant theoretical challenges, with reactive intermediates often being chemically activated and possessing electronic structures with significant levels of both dynamic and static electron correlation. Predicting the fates of chemically activated species requires master equation simulations, with microcanonical rate constants being determined either by Rice-Ramsperger-Kassel-Marcus theory or variational transition state theory. Use of a composite electronic structure method such as Weizmann-1 Brueckner Doubles theory provides an accurate treatment of dynamic correlation, while equation-of-motion spin-flip coupled-cluster theory provides a reasonable estimate of static correlation. The Kuwata and Stoffregen laboratories will apply these methods to study the competition between autoxidation and radical-terminating processes in the OH-initiated oxidation of isoprene, as well as study the generation of heretofore unmeasured hydroxycarbonyls in isoprene ozonolysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.