Positive ion ratio measurements in Ar, Kr, and Xe glow discharges

Results are presented of an experimental study of the relative concentration of ions in the positive column of small-diameter noble-gas discharges. The ratio of the molecular ion concentration to the atomic ion concentration has been measured as a function of discharge pressure and current for dc discharges in argon, krypton, and xenon. Discharge pressures and currents were varied from 0.1 to 10 Torr and 15 to 40 mA. A simple theoretical model of the positive column was developed and the pressure dependence of the ion concentration ratio was calculated. By parametrically fitting the predicted ion ratio equation to the experimental data, estimates of several reaction rate coefficients could be derived. Where possible, the ion ratio data and the derived rate coefficients have been compared to previously published data.