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

该项目围绕1）负离子质子转移质谱（NI-PTRMS）的开发，用于检测大气中的羧酸和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乙酸根离子来选择性电离酸性物质。 由于乙酸是常见羧酸中最弱的，乙酸根离子将与所有气相羧酸反应，并且也与强无机酸反应。 几个方案，如高压放射性电离选定的起始材料（乙酸酯或酸酐，例如）将被探索和评估其潜力，以产生一个强烈的，无团簇源所需的离子。 将测量简单羧酸（丙酸、丁酸等）和乙酸盐的某些同位素异构体的相对气相酸度。 还将确定醋酸根离子与羧酸的第一水合物的热化学和反应速率。更广泛的科学影响包括对空气质量和气候变化的应用，因为羧酸是对流层臭氧和气溶胶形成的关键中间体。 教育计划包括来自大气科学代表性不足的社区的本科生和研究生的参与。

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.