Elucidating the role of a molecular anion in mutual neutralisation reactions

We have studied the MN of NO ⁺ with NO ₂ ^- under single-collision conditions at a collision energy of ≈0.1 eV. Combining cryogenically stored-and-merged ion beams with coincident-product imaging, we determine that the reaction predominantly produces ground-state NO and electronically excited NO ₂ , a fraction of which rapidly dissociates to ground-state NO + O. As a consequence, prior studies, based on fluorescence detection, missed more than 97% of the reaction products. New high-level calculations reveal a complex charge-transfer interaction, in which both Renner--Teller and Jahn--Teller couplings in the neutralised anion play key roles. These aspects illustrate that charge-transfer reactions involving polyatomic anions may be extremely sensitive to the neutralised anion's electronic structure and geometry