A selected ion flow tube study of the ion molecule association reactions of protonated (MH+), nitrosonated (MNO+) and dehydroxidated (M−OH)+ carboxylic acids (M) with H2O

Abstract

A selected ion flow tube, SIFT, study has been carried out of the reactions of H3O+, NO+ and O2+ with four carboxylic acids: formic acid, acetic acid, propionic acid and butyric acid. Ethanol was also included in order to provide data that could facilitate SIFT-MS analyses of formic acid in its presence. The product ion branching ratios of the primary reactions were obtained and compared with the already known values, thus improving the certainty of kinetic data for quantification of these compounds. The primary products of the H3O+ reactions, the protonated molecules MH+, and the primary products of the NO+ reactions, nitrosonated (MNO+) and dehydroxidated (M−OH)+ molecules, are observed to react with the molecules of water by three body association. Original data were obtained for the kinetics of these cluster-forming reactions. The three body rate constant for the associations of MH+ with H2O in He have been determined in the units of 10−27cm3s−1 for formic, acetic, propionic and butyric acids as 1.4, 2.4, 3.8 and 4.9, respectively. The three body rate constant for the associations of MNO+ with H2O in He were obtained in the same units as 2.1, 1.1, 0.15 and 0.7. Results will improve the certainty of identification and accuracy of quantification of vapors of carboxylic acids by SIFT-MS in medical and food science research.