Langevin Dynamics Modeling of Gas-Phase Ion Recombination with Dilute Ion Concentration

Ion recombination in the gas phase plays an important role in the stability of plasmas and their chemistry that is closely related to various applications in combustion and materials processing. Due to the lack of robust theoretical models of three body ion recombination, we present a Langevin dynamics-based ion recombination rate constant model that is applicable for a broad pressure and temperature range combination considering the effect of ionic structure of polyatomic ions. Ion recombination is modeled within the framework of classical physics and thus does not explicitly model the quantum nature of electron transfer kinetics. We hypothesized that electron transfer takes place with near certainty when two atoms that are part of the recombining ions have a nuclear separation less than or equal to σ - distance σ between two atoms at which the potential energy (due to van der Waals or polarization interaction) between the ions is zero. The comparison with experimental data for several ion pairs reveals an agreement of ±50% for most of the tested ion pairs at high pressure. At low pressure, good agreement is observed as well between polyatomic ion pairs.