Probing molecular mutual neutralization reactions of atmospheric importance using the ion storage facility DESIREE

The cryogenic Double ElectroStatic Ion Ring ExpEriment (DESIREE) facility at Stockholm University, Sweden, uniquely allows for studies of mutual neutralization (MN) between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to ~20 K and ~50 meV, respectively [1-7]. We aim for a better understanding of how molecules are formed and processed in, e.g., atmospheric plasmas, where we combine novel experimental methods to build a fundamental picture of the transfer of charge-, energy- and mass in collisional reactions.

Historically, it was only possible to study the overall reactivity of MN reactions, mostly in flow tubes, though some beams experiments are reported. Only with the advent of new techniques, i.e., combining merged ion beams with coincident product imaging, as at DESIREE [1-7], can detailed product information and dynamics be derived, i.e., only in early 2024 was the first final-state distributions and reaction dynamics of MN reactions involving molecular ions reported [6,7].

I focus on MN relevant to atmospheric plasmas and phenomenon such as Sprites, looking at reactions involving atomic and molecular oxygen and nitrogen ions. Starting with O- + NO+ [6], to O- + O2+ & O- + N2+, to demonstrate the power of these techniques to elucidate fractionation into two- and three-body product channels and unravel effects of rovibrational energy on the reaction.

[1] R. D. Thomas et al., Rev. Sci. Instrum. 82, 065112 (2011)

[2] H. T. Schmidt et al., Rev. Sci. Instrum. 84, 055115 (2013)

[3] H. T. Schmidt et al., Phys. Rev. Lett. 119, 073001 (2017)

[4] M. Poline et al., Phys. Chem. Chem. Phys. 23, 24607 (2021)

[5] M. Poline et al., Phys. Rev. A, 105, 062825 (2022)

[6] M. Poline et al., Phys. Rev. Lett. 132, 023001 (2024)

[7] A. Bogot et al., Science 383, 285 (2024)