Direct three-body atom recombination: Halogen atoms

The recombination of halogen atoms has been a research topic in chemical physics for over a century. All theoretical descriptions of atom recombination depend on a two-step assumption, where two colliding atoms first form an unstable complex before a third colliding body either relaxes or reacts with it to yield a diatomic molecule. These mechanisms have served well in describing some of the dynamics of atom recombination but have not yet provided a full theoretical understanding. In this work, we consider the role of the direct three-body recombination mechanism in halogen recombination reactions X + X + M → X₂ + M, where X is a halogen atom and M is a rare gas atom. Our results agree well with experimental bromide and iodine recombination measurements, demonstrating that direct three-body recombination is essential in halogen recombination reactions.