SIFT STUDIES OF THE REACTIONS OF H3O-2(+) WITH A SERIES OF VOLATILE CARBOXYLIC-ACIDS AND ESTERS(, NO+ AND O)

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 reacti ons of H3O+ with all the acid and esters molecules occur at the collis ional 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 ar e equal to or close to k(c). The major ionic products of the H3O+ reac tions with both the acids and esters are the protonated parent molecul es, MH+, but minor channels are also evident, these being the result o f H2O elimination from the excited (MH+) in some of the acid reaction s and an alcohol molecule elimination (CH3OH or C2H5OH) in some of the ester reactions. The NO+ reactions with the acids and esters result i n both ion-molecule association producing NO+.M in parallel with hydro xide ion (OH-) transfer with some of the acids, and parallel methoxide ion (CH3O-) and ethoxide ion (C2H5O-) transfer as appropriate with so me of the esters. The O-2(+) reactions proceed by dissociative charge transfer with the production of two or more ionic fragments of the par ent molecules, the different isomeric forms of both the acid and the e ster molecules resulting in different product ions. (C) 1998 Elsevier Science B.V.