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

North Carolina Agricultural & Technical State University, Greensboro NC

Investigators

Abstract

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.