CAS: Spectroscopy and Unimolecular Dynamics of Reaction Intermediates in Atmospheric Chemistry

在化学系化学结构，动力学和机制A（CSDM-A）计划的支持下，宾夕法尼亚大学的Marsha Lester教授和她的团队正在使用分子光谱和理论方法研究通过烯烃臭氧分解产生的羰基氧化中间体的单分子衰变动力学。这些反应中间体是导致大多数挥发性有机化合物氧化的羟基自由基的重要来源，并且是大气中新颗粒形成的前体。莱斯特教授和她的学生将研究导致不同产物的羰基氧化物中间体的新重排机制。这些研究可以更好地了解大气中羟基自由基的产生以及可能影响新颗粒形成的其他产品。 这些研究将为培养和发展从事物理化学和大气科学之间接口工作的下一代科学家提供一个激励环境。Lester教授和她的学生将把联合收割机红外激光激活羰基氧化物中间体与利用激光时间分辨检测羟基自由基产物相结合。诱导荧光来测量单分子衰变速率，并提供对导致产物的过渡态势垒的直接洞察。计划中的实验研究和理论建模将通过1，3环闭合机制研究氧化羰中间体的单分子衰变过程。将探索具有更大碳链长度和/或杂原子取代的羰基氧化物的延伸，这可能导致新的低能量途径，具有闭环和次级臭氧化物形成的潜力。其他研究将实施各种激光光谱技术，以确定和表征羰基氧中间体单分子衰变中碎片内漫游反应产生的替代产品。 在这种情况下，分离的羟基自由基可以重新定向并在长距离范围内漫游，可能通过加成和/或提取反应产生各种各样的产物，这可能会影响羟基自由基的产量。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Marsha Lester of the University of Pennsylvania and her team are using molecular spectroscopic and theoretical methods to study the unimolecular decay dynamics of carbonyl oxide intermediates generated through ozonolysis of alkenes. These reaction intermediates are an important source of hydroxyl radicals, which result in the oxidation of most volatile organic compounds, and are precursors to new particle formation in the atmosphere. Professor Lester and her students will investigate novel rearrangement mechanisms of the carbonyl oxide intermediates that lead to different products. These studies could lead to a better understanding of the generation of hydroxyl radicals in the atmosphere and other products that may impact on new particle formation. These studies will provide a stimulating environment for training and development of next generation scientists working at the interface between physical chemistry and atmospheric science.Professor Lester and her students will combine infrared laser activation of carbonyl oxide intermediates with time-resolved detection of hydroxyl radical products utilizing laser-induced fluorescence to measure unimolecular decay rates and provide direct insight on transition state barriers leading to products. The planned experimental studies and theoretical modeling will examine unimolecular decay processes of carbonyl oxide intermediates via 1,3 ring closure mechanisms. Extension to carbonyl oxides with greater carbon chain length and/or heteroatom substitution will be explored, which may lead to new low energy pathways with the potential for ring closure and secondary ozonide formation. Additional studies will implement various laser spectroscopic techniques to identify and characterize alternative products resulting from intra-fragment roaming reactions in the unimolecular decay of carbonyl oxide intermediates. In this case, the separating hydroxyl radical can reorient and roam at long-range, potentially leading to a wide range of products via addition and/or abstraction reactions, which may impact the yield of hydroxyl radicals.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.