Reactions of singly and doubly charged argon ions with N2 and O2 in a steady state hollow cathode discharge

Abstract

Ion–molecule reactions between the ions Ar⁺, Ar⁺⁺, and N₂ molecules are studied in the negative glow region of a cylindrical steady‐state hollow cathode discharge at pressures between 0.25 and 0.5 torr and at [N₂]/[Ar] density ratios of 0.001, 0.002, 0.005, and 0.01. The following rate constants are obtained: for Ar⁺⁺+N₂→N₂⁺+Ar⁺, k=2×10⁻¹⁰ cm³ s⁻¹; Ar⁺⁺+N₂→N⁺+N+Ar, k =1×10⁻¹⁰ cm³ s⁻¹; Ar⁺+N₂→N₂⁺+Ar, k =0.2–1.5×10⁻¹¹ cm³ s⁻¹. A value of k=4×10⁻¹³ cm³ s⁻¹ for the partial charge exchange Ar⁺⁺+Ar→2 Ar⁺ is consistent with the measurements. For comparison the rates of Ar⁺⁺+O₂ (k=1.7×10⁻⁹ cm³ s⁻¹) and of Ar⁺+O₂ (k=5.8×10⁻¹¹ cm³ s⁻¹) are determined. The error limits of the k values are ±45%. Dissociative volume recombination of Ar₂⁺ with slow plasma electrons (α=3.1±1.1×10⁻⁷ cm³ s⁻¹ at an electron temperature of 1200 K) is the dominant loss process for these ions. Wherever possible, the results are compared with previous ones.