Vibrationally-dependent molecular dynamics in mutual neutralisation reactions of molecular oxygen ions
- Mathias Poline
- Arnaud Dochain
- Stefan Rosén
- MingChao Ji
- Henrik Cederquist
- Henning Zettergren
- Henning T. Schmidt
- Mats Larsson
- Shaun G. Ard
- Nicholas S. Shuman
- Albert A. Viggiano
- Richard D. Thomas
2025-09-26
Product distributions and dynamics of low-collision-energy mutual neutralisation reactions involving even simple molecular ions are largely unknown. Reactions which involve oxygen ions, e.g., $${{{\rm{O}}}}_{2}^{+}$$ O 2 + with O − , are expected to be important in atmospheric phenomena such as sprites and in high-pressure air or oxygen discharges. Here we show, by combining cryogenically stored-and-merged ion beams with coincident product-imaging techniques, that the $${{{\rm{O}}}}_{2}^{+}$$ O 2 + with O − mutual neutralisation reaction results predominantly in dissociation of the $${{{\rm{O}}}}_{2}^{+}$$ O 2 + molecule. Three competing reaction pathways yields both O( 3 P) (84%) and O( 1 D) (16%) products, but no O( 1 S) products. Analysis of the momentum-correlated dynamics of the reaction reveals the dominance of two-step mechanisms involving the 3p λ u and 3s σ g Rydberg states of O 2 . Furthermore, use of the 16,18 $${{{\rm{O}}}}_{2}^{+}$$ O 2 + isotopologue shows that the reaction products strongly depend on the vibrational levels of the $${{{\rm{O}}}}_{2}^{+}$$ O 2 + ion for the channel leading to two O( 1 D) products.