Kinetic-energy distributions of positive and negative ions in Townsend discharges in oxygen

Translational flux-energy distributions of positive and negative ions have been measured at high electric field-to-gas density ratios (E/N) up to 40 x 10(-18) V m(2) (40 kTd) in diffuse, parallel-plate Townsend discharges in oxygen using an ion energy analyzer-mass spectrometer. The O-2(+) ion is th e most abundant ion detected in the discharge, and exhibits Maxwellian ener gy distributions for E/N<20 x 10(18) V m(2), which is consistent with predi ctions based upon the assumption that resonant symmetric charge exchange is the dominant ion-molecule collision process. The less abundant ions O+, O- 2(-), and O- exhibit non-Mawellian ion kinetic-energy distributions at near ly all E/N, indicative of multiple ion-molecule reactions affecting the ion transport. Mean energies are obtained for each ion as a function of E/N fr om an analysis of the energy distributions, and symmetric charge-exchange c ross sections are calculated:from the data where appropriate.