REACTIONS OF H3O+ AND OH- IONS WITH SOME ORGANIC-MOLECULES - APPLICATIONS TO TRACE GAS-ANALYSIS IN AIR

The reactions of H3O+ and OH- ions with several hydrocarbons and several oxygen-bearing organic molecules, MH, have been studied using a selected-ion flow tube (SIFT) and a flowing afterglow (FA) apparatus at 300 K. Most of the reactions are fast, proceeding via proton transfer producing a single product, viz. MH(2)(+) for the H3O+ reactions and M(-) or the OH- reactions, but in seven of the twenty-eight reactions two products are observed. In the reaction of H3O+ with trans-2-hexenal only one product is observed whereas in its reaction with the cis-3-hexenal isomer two products are observed. The significance of these observations and the value of the data obtained in this study to trace gas analysis in atmospheric air and on human breath using H3O+ and OH- as chemical ionisation agents is discussed. A by-product of these studies is an estimation of the proton affinity of methylcyclohexane.