Observation of fine-structure transitions in argon charge transfer at low energies using a crossed-beam technique

Abstract

The crossed-beam method was used to investigate the charge–transfer reaction of Ar+(2P3/2) with Ar(1S0) as a function of collision energy over the range of 2–100 eV (center of mass). Both the exactly resonant channel and the endoergic fine-structure transition with ΔJ=1 were detected and the cross section ratio σ3/2→1/2/(σ3/2→1/2+σ3/2→3/2) was found first to increase with increasing collision energy to a maximum value of about 0.5 at 30 eV and then decrease at higher energy. The relative abundance of the fine-structure transition channel at low energy is much higher than that predicted by the accepted general theory for these processes. It is suggested that a curve-crossing mechanism not previously considered and the perturbation of trajectories at low energies resulting from the strongly bound Ar+2 intermediate may be responsible for the unexpected observations.