Spectroscopy and Dynamics of Reaction Intermediates in Atmospheric Chemistry

在这项由化学系化学结构动力学和机制A和B计划(CSDM-A和CSDM-B)资助的项目中，宾夕法尼亚大学的MarashI.Lester教授和她的学生正在使用先进的激光技术来研究臭氧(O3)与挥发性有机分子，特别是植物排放的烯烃(一类含有碳-碳双键的分子)在大气中反应形成的中间产物。臭氧与烯烃的反应可以产生一类非常活跃的分子，称为Criegee中间体。众所周知，Criegee中间体会分解并释放羟基(OH)分子，这种分子通常被称为大气的洗涤剂，因为它们可以反应(并使)空气中其他潜在的有害污染物失效。莱斯特教授和她的学生在实验室中产生这些中间体，然后使用红外激光脉冲激发Criegee分子，使其解体。另一种被称为激光诱导荧光(LIF)的技术被用来检测随着时间的推移OH自由基的产生。从事这项研究的学生在现代激光技术和分析方法方面获得了宝贵的经验，以确定产生不同产品的识别反应路径。学生们还利用理论模型和计算工具来帮助解释实验数据。这个项目侧重于在大气中产生羟基自由基的活性中间体。这些中间体来自臭氧与含有碳-碳双键的挥发性有机化合物的反应，例如植物大量排放的异戊二烯。当这些活性中间体在大气中形成时，它们有足够的内能自发地分解成有机碎片和羟基自由基，这一过程称为单分子衰变，或者与其他分子反应。Lester教授和她的团队在实验室中生成了这些具有不同取代基和构象的活性中间体，并使用红外作用光谱、激光诱导荧光和理论模拟(RRKM理论和隧道效应)研究了它们到羟基自由基的单分子衰变过程。与莱斯特教授合作的学生获得了探索化学反应中活性中间体物理性质的复杂实验和理论方法，因此该项目的一个重要的更广泛的影响是它对未来科学家的培训。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。

In this project funded by the Chemical Structure Dynamics and Mechanisms A and B Programs (CSDM-A and CSDM-B) of the Chemistry Division, Professor Marsha I. Lester and her students at the University of Pennsylvania is using sophisticated laser techniques to study intermediates formed in the atmospheric reactions of ozone (O3) with volatile organic molecules, especially alkenes (a class of molecules containing carbon-carbon double bonds) emitted by plants. The reactions of O3 with alkenes can produce a very reactive class of molecules called Criegee intermediates. Criegee intermediates are known to decay and release hydroxyl radical (OH) molecules, which are often called the atmosphere’s detergent because they can react (and deactivate) other potentially harmful pollutants in the air. Prof. Lester and her students generate these intermediates in the laboratory and then use an infrared laser pulse to excite the Criegee molecule and cause it to fall apart. Another technique called laser-induced fluorescence (LIF) is used to detect the production of OH radicals over time. The students engaged in this research are gaining valuable experience in modern laser technology, and analysis approaches for determining the identifying reaction pathways that create different products. The students are also utilizing theoretical models and computational tools to aid in the interpretation of the experimental data.This project focuses on reactive intermediates that give rise to hydroxyl radicals in the atmosphere. These intermediates originate from reaction of ozone with volatile organic compounds containing carbon-carbon double bonds, such as isoprene that is emitted in large quantities by plants. When formed in the atmosphere, these reactive intermediates have enough internal energy to spontaneously fall apart into an organic fragment and hydroxyl radical, in a process known as unimolecular decay, or react with other molecules. Professor Lester and her group generate these reactive intermediates with various substituents and conformations in the laboratory, and study their unimolecular decay processes to hydroxyl radicals using infrared action spectroscopy, LIF and theoretical modeling (Rice–Ramsperger–Kassel–Marcus (RRKM) theory with tunneling). The students working with Professor Lester gain experience is sophisticated experimental and theoretical methods that probe the physical properties of reactive intermediates in chemical reactions, and thus a significant broader impact of the project is its training of future scientists.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.