Kinetics and Thermochemistry Studies of Carboxylic and Other Acids Using Negative Ion Proton Transfer Mass Spectrometry (NI-PTMS)

该项目主要围绕1)开发用于检测大气中羧酸的负离子质子转移质谱法（NI-PTRMS）和2)提高对该方法所依赖的气相离子化学的理解。NI-PTRMS涉及通过质子转移到醋酸离子的酸性物质选择性电离。由于醋酸是普通羧酸中最弱的，所以醋酸离子能与所有气相羧酸反应，也能与强无机酸反应。将探讨几种方案，例如选定起始材料（例如乙酸酯或酸酐）的高压放射性电离，并评估其产生所需离子的强烈、无簇源的潜力。测定简单羧酸（丙酸、丁酸等）和一些醋酸同位素体的相对气相酸度。测定醋酸离子与羧酸的第一次水合反应的热化学性质和反应速率。更广泛的科学影响包括空气质量和气候变化方面的应用，因为羧酸是对流层臭氧和气溶胶形成的关键中间体。教育计划包括让来自在大气科学领域代表性不足的社区的本科生和研究生参与。

This project is centered around 1) the development of Negative Ion Proton Transfer Mass Spectrometry (NI-PTRMS) for the detection of carboxylic acids in the atmosphere and 2) an improved understanding of the gas phase ion chemistry on which the method relies. NI-PTRMS involves selective ionization of acidic species via transfer of a proton to an acetate ion. Since acetic acid is the weakest of the common carboxylic acids, acetate ions will react with all gas-phase carboxylic acids, and with strong inorganic acids as well. Several schemes, such as the high-pressure radioactive ionization of selected starting materials (acetic esters or anhydrides, for example) will be explored and evaluated for their potential to produce an intense, cluster-free source of the desired ion. The relative gas-phase acidities of simple carboxylic acids (propionic, butyric, and others) and some isotopomers of acetate will be measured. Thermochemistry and reaction rates of the first hydrate of acetate ion with carboxylic acids will also be determined.Broader scientific impacts include applications to air quality and climate change because carboxylic acids are key intermediates in the formation of both tropospheric ozone and aerosols. Education plans include participation by both undergraduate and graduate students from communities that are underrepresented in the atmospheric sciences.