The importance of three-body processes to reaction kinetics at atmospheric pressures. III. Reactions of He2+ with selected atomic and molecular reactants

For pt.II see ibid., vol.22, p.47-50 (1986). Results are presented from studies of the reactions He₂⁺ with five species displaying a wide variation of molecular structures and polarizabilities: Ar, Xe, Ne, O₂, and CO₂. Measurements were made in the afterglows of preionized discharges into the reactant gas mixtures diluted in 1-6-atm pressures of helium. Effective rates of reaction were obtained that could be separated into contributions from bimolecular and termolecular channels. The latter generally dominated, showing no evidence of saturation up to 6 atm pressure of diluent. These results continue to confirm earlier reports that the initial capture step in the reaction is not limited by the Langevin rate as usually applied. Such super-Langevin rates appear to be a general phenomenon at high pressures, at least for the reactions of He ₂⁺. In the most extreme case examined, He₂ ⁺+CO₂, the effective rate of reaction contributed by all channels was found to exceed Langevin by a factor of five at 6-atm pressure of diluent