How oxygen molecules neutralize each other – and why their vibrations matter

When positively and negatively charged oxygen molecules meet, they usually neutralize and fall apart into separate atoms. Using ultra-cold ion beams and advanced imaging, researchers have shown that most of these reactions produce oxygen atoms in their normal state, while a smaller fraction end up excited. The study reveals that tiny molecular vibrations can change how the reaction unfolds — a key insight for understanding processes in phenomena like lightning sprites and electrical discharges in air. The editors at Nature Communications have put together an Editors’ Highlights webpage of recent research called “Inorganic and physical chemistry” and are pleased to inform that the editor chose to feature your article, entitled “Vibrationally-dependent molecular dynamics in mutual neutralisation reactions of molecular oxygen ions”.

a Dalitz representation analysis showing (i) the relation between Dalitz coordinates η₁, η₂ and break-up geometries, with the red dotted lines indicating the energy axis of each atomic product; (ii), (iii), and (iv): Experimental Dalitz plots for the

E_{K_{f}}

in the following reaction channels: (2) O(³P)+O(³P)+O(³P); (3) O(¹D)+O(³P)+O(³P); and (4) O(¹D)+O(¹D)+O(³P), respectively. The white arrows denote the energy axis of each oxygen atom, and the white dashed lines are shown to highlight the observed structures.

In this study, we used extremely cold and precisely controlled beams of oxygen ions, allowing them to meet under near-perfect conditions. Using advanced imaging techniques, we could see what happened to the reaction products in real time. We found that when oxygen ions neutralize each other, the resulting oxygen molecule usually breaks apart. Most of the atoms produced end up in their normal energetic state, but about 16% are created in an excited form — and none in the highest-energy state.

By analyzing how the atoms moved after the reaction, we discovered that the process mostly follows a two-step mechanism involving specific excited “Rydberg” states of the oxygen molecule. We also showed that which products are formed depends strongly on how much the molecule was vibrating before the reaction — revealing how even tiny motions within a molecule can shape the outcome of a fundamental chemical process.

Vibrationally-dependent molecular dynamics in mutual neutralisation reactions of molecular oxygen ions

Swedish National Infrastructure, DESIREE

Research at the Department of Physics, Stockholm University

This work was performed at the Swedish National Infrastructure, DESIREE at the Department of Physics at Stockholm University. The views expressed are those of the authors and do not reflect the official guidance or position of the Department of the Air Force, the Department of Defence (DoD), or the U.S. government.

The authors and affiliations of the article are:

Department of Physics, Stockholm University, Stockholm: Mathias Poline, Arnaud Dochain, Stefan Rosén, MingChao Ji, Henrik Cederquist, Henning Zettergren, Henning T. Schmidt, Mats Larsson & Richard D. Thomas
Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Louvain-la-Neuve, Belgium: Arnaud Dochain
Space Vehicles Directorate, Air Force Research Laboratory, Kirtland AFB, Albuquerque, 87117, New Mexico, USA: Shaun G. Ard, Nicholas S. Shuman & Albert A. Viggiano

Theme

Physics

Research subject

Atomic Physics

Research group

DESIREE

The Atomic Physics division is pursuing experimental research in atomic collision physics dealing with interactions of positively and negatively charged atomic ions, molecular ions such as fullerenes, polycyclic aromatic hydrocarbons (PAHs), biomolecules, and clusters.

Last updated: October 21, 2025

Source: Gunilla Häggström, Communications Officer, Fysikum