A state-selected study of Ar+(P-2(3/2,1/2))+O-2 charge transfer at collision energies below 4 eV using synchrotron radiation and guided beam techniques

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+(P-2(J)) 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 O-2(+) product ions, Charge transfer mechanisms are discussed as a function of collision energy and fine structure state of Ar+ reactant ions.