SIFT studies of the reactions of H 3O +, NO + and O 2+ with a series of alcohols

Abstract

We report the results of a selected ion flow tube (SIFT) study of the reactions of H 3O +, NO + and O 2 + with some 17 alcohols ranging in complexity from methanol to octanol and menthol, and including some structural isomers. This study was carried out in order to extend the database (i.e. rate coefficients and product ions of appropriate ion/molecule reactions) required for the SIFT method of trace gas analysis which utilises the aforementioned ions for chemical ionisation. The H 3O + reactions proceed via exothermic proton transfer, which we assume to proceed at the collisional rate. Thus all of the 51 reactions (except two) occur at or close to the collisional rate. Only in a minority of these proton transfer reactions is the protonated parent molecule the single ion product; rather it is seen that the protonation of most of these alcohols by H 3O + is followed by the ejection of an H 2O molecule from the excited product ion thus leaving the appropriate hydrocarbon ion. The NO + reactions proceed largely via the processes of hydride ion transfer producing the appropriate carboxy ion (and HNO), and hydroxide ion transfer producing the appropriate hydrocarbon ion (and HNO 2). The O 2 + reactions proceed via charge transfer, the large majority of the reactions resulting in more than one product ion, which are mostly hydrocarbon fragment ions but in a few cases carboxy ions are formed. The product ions for the reactions of the various structural isomers are sometimes different, and this offers a way of distinguishing between the isomeric forms of some alcohols.