The mutual neutralisation of O+ with O− has been studied in a double ion-beam storage ring with combined merged-beams, imaging and timing techniques. Branching ratios were measured at the collision energies of 55, 75 and 170 (± 15) meV, and found to be in good agreement with previous single-pass merged-beams experimental results at 7 meV collision energy. Several previously unidentified spectral features were found to correspond to mutual neutralisation channels of the first metastable state of the cation (O+(2Do), τ ≈ 3.6 hours), while no contributions from the second metastable state (O+(2Po), τ ≈ 5 seconds) were observed. Theoretical calculations were performed using the multi-channel Landau–Zener model combined with the anion centered asymptotic method, and gave good agreement with several experimentally observed channels, but could not describe well observed contributions from the O+(2Do) metastable state as well as channels involving the O(3s 5So) state.

The double ion storage ring DESIREE has been used in combination with position- and time-sensitive detectors to study the mutual neutralization of N⁺ with O⁻ at 40 meV collision energy. Several previously unassigned spectral features observed in a recent single-pass merged-beams experiment at 7 meV collision energy [Phys. Rev. Lett. 121, 083401 (2018)], were also observed in the present experiment. It was found that neutralization channels of the first metastable state of the cation [N⁺(¹D),τ≈256s] could explain the majority of these features, while the second metastable state [N⁺(¹S),τ≈0.9s] was not found to contribute significantly. The branching ratios into the different electronically excited states of N were determined and found to be in good agreement between the two experiments. Theoretical calculations using the multichannel Landau-Zener model were found to yield good results for a number of channels, but could not describe some observed contributions, possibly due to the presence of other processes not accounted for in the model.

We have studied the mutual neutralization reaction of atomic iodine ions (i.e., I⁺+I⁻→I+I) in a cryogenic double electrostatic ion-beam storage-ring apparatus. Our results show that the reaction forms iodine atoms either in the ground-state configuration (I(5p⁵²P∘), ∼40%) or with one atom in an electronically excited state (I(6s²[2]), ∼60%), with no significant variation over the branching ratios in the studied collision-energy range (0.1–0.8 eV). We estimate the total charge-transfer cross section to be of the order of 10⁻¹³cm² at 0.1 eV collision energy. Ab initio relativistic electronic structure calculations of the potential-energy curves of I₂ suggest that the reaction takes place at short internuclear distances. The results are discussed in view of their importance for applications in electric thrusters.