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

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.