Imaging state-to-state reactive scattering in the Ar⁺ + H₂ charge transfer reaction

The charge transfer reaction of Ar⁺ with H₂ and D₂ has been investigated in an experiment combining crossed beams with three-dimensional velocity map imaging. Angle-differential cross sections for two collision energies have been obtained for both neutral species. We find that the product ions are highly internally excited. In the reaction with H₂, the spin-orbit excited Ar⁺ state's coupling to the "resonant" vibrationally excited product H₂⁺ (υ = 2) dominates for both investigated energies, in line with previous investigations. The observed angular distributions, however, show significantly less back-scattering than was found previously. Furthermore, we discovered that the product ions are highly rotationally excited. In the case of Ar⁺ reacting with D₂, the energetically closest lying vibrational levels are not strictly preferred and higher-lying vibrational levels are also populated. For both species, the backward-scattered products show higher internal excitation.