State-selected ion-molecule reactions: N2+(X, v″), N2+(A, v′) + Ar → N2 + Ar+

Abstract

Abstract The total, absolute cross sections for charge transfer between N2+(X, A, v) and Ar have been measured at 8, 14 and 20 eV center of mass translational energy. The internal energy of the N2+ ions was selected by threshold photoelectron-photoion coincidence using pulsed synchrotron radiation from the ACO storage ring. The vibrational levels investigated were v″ = 0−4 for the X state, and v′ = 0−6 for the A state. The data for the A state were corrected for the fraction of ions which fluoresced to the X state prior to reaction with Ar. The N2+(X, v″ = 0) state was found to be much less reactive (by a factor ≥ 10) than the other X-state levels, at all three translational energies. The levels N2+(A, v′ ⩾ 3) were found to react with cross-sections which depend strongly on the relative translational energy. The data are interpreted in terms of the interaction between vibronic curves as discussed by Bauer, Fisher and Gilmore. This model accounts well for the low reactivity of the N2+(X, 0) level. It is proposed that the variation in the cross section of the N2+(A, v′ ⩾ 3) + Ar reactions is a result of competition with a radiationless transition which converts N2+(A, v′) ions into N2+(X, v″) ions.