Formation and destruction of molecular ions in a Townsend discharge in neon

Production of molecular ions by termolecular association and by associative ionization as well as the destruction of these ions by collisional dissociation has been investigated experimentally in a low-current-density discharge in neon. Space-charge effects and all cumulative processes can be neglected so that a simple model of the discharge can be used. Measurements have been carried out by mass discriminated ion sampling through the cathode. The results show values of the product kr τ of the associative ionization rate and the unproductive lifetime ranging from (0.6 up to 1.9)×10−23 m3 at values of the reduced electric field strength E/N from 45 up to 245 Townsend. In the same range of E/N, values for the termolecular association rate kc appear to be in good agreement with previous studies and show a T−.05 temperature dependence. Finally in the same E/N range dissociation rates kd of Ne2+ ions increase from 3×10−19 to 3.5×10−17 m3s−1. These values are in excellent agreement with values calculated with a detailed balance argument from values for the termolecular association rate.