Mutual neutralisation of O with O: investigation of the role of metastable ions in a combined experimental and theoretical study.

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(D), ≈ 3.6 hours), while no contributions from the second metastable state (O(P), ≈ 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(D) metastable state as well as channels involving the O(3s S) state.