A state-selected study of

An experimental method is presented which combines state selection of reactant ions by threshold photoelectron-photoion coincidence following VUV photoionization with radiofrequency octopole ion guides. Absolute cross sections were measured for the charge transfer between state-selected Ar+(2Pj) ions and molecular oxygen as a function of collision energy in the 0.4–4 eV (CM) range. A critical analysis of the absolute values of both this study and studies reported in the literature is given, in which possible artifacts are identified mainly from coincidence time-of-flight spectra of O2+ product ions. Charge transfer mechanisms are discussed as a function of collision energy and fine structure state of Ar+ reactant ions.