SIFT studies of the reactions of H3O+, NO+ and O+2 with a series of volatile carboxylic acids and esters

We report the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+ and O-2(+) with some nine carboxylic acids and eight esters. We assume that all the exothermic proton transfer reactions of H3O+ with all the acid and esters molecules occur at the collisional rate, i.e. the rate coefficients, k, are equal to k(c); then it is seen that k values for most of the NO+ and O-2(+) reactions also are equal to or close to k(c). The major ionic products of the H3O+ reactions with both the acids and esters are the protonated parent molecules, MH+, but minor channels are also evident, these being the result of H2O elimination from the excited (MH+)* in some of the acid reactions and an alcohol molecule elimination (CH3OH or C2H5OH) in some of the ester reactions. The NO+ reactions with the acids and esters result in both ion-molecule association producing NO+.M in parallel with hydroxide ion (OH-) transfer with some of the acids, and parallel methoxide ion (CH3O-) and ethoxide ion (C2H5O-) transfer as appropriate with some of the esters. The O-2(+) reactions proceed by dissociative charge transfer with the production of two or more ionic fragments of the parent molecules, the different isomeric forms of both the acid and the ester molecules resulting in different product ions. (C) 1998 Elsevier Science B.V.