Measurement of the rate coefficients for the bimolecular and termolecular charge transfer reactions of He2+ with Ne, Ar, N2, CO, CO2, and CH4

Abstract

This work reports the measurement of termolecular charge transfer reactions of He₂⁺ into nonassociative product channels. In this study ion destruction frequencies have been experimentally determined from the selectively excited fluorescence of N₂⁺ in high pressure afterglows of mixed gases excited by an intense electron beam discharge. Data have been obtained as functions of helium pressure over the range from 300 to 1500 torr and as functions of the partial pressure of reactant from 25 to 400 μ Hg. From these data, pressure‐dependent rate coefficients have been extracted and subsequently resolved into contributions from bimolecular and termolecular components for reactions of He₂⁺ with Ne, Ar, N₂, CO, CO₂, and CH₄. The bimolecular components have been found to agree with the ESSA flowing afterglow results to within experimental error, and in some cases the values reported here represent an improvement in precision. The sensitivity of the method has been sufficient to detect termolecular components as small as 2×10⁻³⁰ cm⁶/sec and values were found to range widely from 2×10⁻³⁰ for Ne to 67×10⁻³⁰ cm⁶/sec for CO₂. The size of these termolecular rates suggests the general importance of three‐body ion–molecule reactions in higher pressure plasmas such as those found in e‐beam lasers.