Heterogeneous Organic Oxidation Reactions of Atmospheric Importance Studied by Broadband Vibrational Sum Frequency and Second Harmonic Generation

西北大学的Franz盖革教授得到了大气科学系大气化学项目和化学系分析与表面化学项目的支持，研究大气气溶胶表面有机化合物的化学性质及其化学反应。对流层气相中存在的部分氧化的有机物质可以通过其极性末端结合到气溶胶表面，其剩余的双键暴露于气相中与大气氧化剂反应。在本实验室研究中，将在与大气相关的条件下研究环状和非环状表面结合烯烃的非均相碳-碳双键氧化反应，特别是在ppb水平的臭氧存在下和1 atm的总压力下。定制的环状和非环状有机化合物将通过有机硅烷化学被束缚到固体基质上，然后暴露于臭氧。将确定臭氧吸收率。仅对界面敏感的非线性光学光谱方法，特别是二次谐波产生（SHG）和振动和频产生（VSFG），将用于探测臭氧与表面活性有机化合物的相互作用。这将允许识别表面结合的反应物和反应中间体和产物。此外，亦会利用化学电离质谱仪研究反应产物，为研究固体/空气界面的多相有机氧化反应机制提供新的见解，并提供有关有机化合物及臭氧在大气中的化学归宿的详细分子资料。该项目将支持一名研究生，并将与主要研究员针对K-12学生和公众的外联活动联系起来。

Professor Franz Geiger of Northwestern University is supported by the Atmospheric Chemistry program in the Division of Atmospheric Sciences and the Analytical and Surface Chemistry program in the Division of Chemistry to investigate the chemistry of organic compounds at the surface of atmospheric aerosols and their chemical reactions. Partially oxidized organic species present in the tropospheric gas phase can bind to aerosol surfaces through their polar ends, with their remaining double bonds exposed to the gas phase for reaction with atmospheric oxidants. In this laboratory study, heterogeneous carbon-carbon double bond oxidation reactions of cyclic and acyclic surface-bound olefins will be studied under conditions relevant to the atmosphere, specifically in the presence of ppb-levels of ozone and at a total pressure of 1 atm. Tailored cyclic and acyclic organic compounds will be tethered to solid substrates through organosilane chemistry, and then exposed to ozone. The rate of ozone uptake will be determined. Nonlinear optical spectroscopy methods that are sensitive to interfaces only, specifically second harmonic generation (SHG) and vibrational sum frequency generation (VSFG), will be used to probe the interaction of ozone with the surface-active organic compounds. This will allow identification of the surface-bound reactants and the reaction intermediates and products. Reaction products will also be studied using a chemical ionization-mass spectrometer (CIMS).This study will provide new insights into the mechanisms of heterogeneous organic oxidation reactions at solid/air interfaces and detailed, molecular-level information on chemical fate of organic compounds and ozone in the atmosphere. This project will support one graduate student and will be linked to outreach activities by the principal investigator aimed at K-12 students and the public.