Measurement of the rate coefficients for the bimolecular and termolecular ion–molecule reactions of Ne2+ with selected atomic and molecular species

Abstract

This work reports the measurement of second and third order ion–molecule reactions of diatomic neon ions with eight reactants selected because of their widely varying values of polarizability and dipole moment. In this study Ne₂⁺ destruction frequencies have been experimentally determined from measurements of the selectively excited fluorescence of N₂⁺ in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of neon pressure over the range from 500 to 1500 Torr and as functions of the partial pressure of reactant from 100 to 900 mTorr. From this data pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from second order, bimolecular, and third order, termolecular, components. The bimolecular components have been found to agree with tabulated values appearing in the literature. The sensitivity of the method has been sufficient to detect termolecular components as small as 2×10⁻³⁰ cm⁶ sec⁻¹ and values were found to range from 3.5×10⁻³⁰ cm⁶ sec⁻¹ for Ar to 10⁻²⁸ cm⁶ sec⁻¹ for HBr. A classical approximation to the three‐body capture rate has been evaluated which explains these values in terms of the rates at which third body encounters change glancing collisions into inwardly spiraling orbits. The data reported here are in agreement with this model and indicate that the reaction probabilities in this channel are generally high. The sizes of these termolecular rates suggest their general importance in charge transfer reactions in plasmas at atmospheric pressures.