In previous investigations8–11 it was shown that this is not always true and a series of gas-phase ion-molecule reactions, as well as isomerization processes, can take place in the atmospheric pressure regime. In particular it was shown that the benzene molecular ion easily reacts with molecular oxygen, giving rise to the production in high yield of the phenol molecular ion11 (with a [Mþ. phenol]/[Mþ. benzene] ratio of the order of 30), through the mechanism reported in Scheme 1. This reaction is to some extent reminiscent of the reactivity observed in some gas-phase reactions of alkyl radicals. It has been reported that, under tropospheric conditions, alkyl radicals R