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 m2 (40 kTd) in diffuse, parallel-plate Townsend discharges in oxygen using an ion energy analyzer-mass spectrometer. The O2+ ion is the most abundant ion detected in the discharge, and exhibits Maxwellian energy distributions for E/N < 20 x 10 -18 V m2, which is consistent with predictions based upon the assumption that resonant symmetric charge exchange is the dominant ion-molecule collision process. The less abundant ions, O+, O2-, and O-, exhibit non-Mawellian ion kinetic energy distributions at nearly 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 from analysis of the energy distributions, and symmetric charge-exchange cross sections are calculated from the data where appropriate.
Citation: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)
Pub Type: Journals
cross-sections, ion-molecule reactions, kinetic-energy distributions, O2, oxygen, Townsend discharge