The importance of three-body processes to reaction kinetics at atmospheric pressures--I: Archetype reactions of He species with N2

This paper concerns a reexamination of the significance of three-body effects that enhance the reaction rates for energy transfer and for ion-molecule reactions that occur in atmospheric pressures of inert gas diluent, even in the absence of any formation of product clusters. The archetype case of the reactions of the energy-storing species of helium with molecular nitrogen has been studied in two different preionized discharge systems capable of operation to 6 atm pressure. Earlier results suggesting the critical importance to kinetic modeling of three-body channels were confirmed in this work. The termolecular rate coefficient for the particular reaction He+2+ N2+ He was concluded to be cm⁶/s with no evidence of saturation up to pressures of 6.0 atm. Effective rates of reaction were observed to be increased by this channel to a value three times in excess of the Langevin rate that has been traditionally considered to be an upper limit on the overall rate of reaction. The close conformity to the older -beam results in this test case implies that the general conclusion of those studies must be seriously considered. In 95 percent of the cases of the reactions of inert gas ions with other species diluted in inert gases at atmospheric pressures it must be expected that rates can greatly exceed the traditional bimolecular values and can even exceed the Langevin rates by substantial amounts.