Mass Spectrometry of Ions in Glow Discharges. I. Apparatus and Its Application to the Positive Column in Rare Gases

Abstract

An apparatus is described which samples and analyzes ions from a glow discharge. Results are given for the positive column of discharges in argon, krypton, and mixtures of the two, at pressures between 0.4 and 1.0 mm and current densities in the range 0.035 to 0.105 ma/cm2. In general, the results are in reasonable agreement with those of other workers, but some differences are noted. The results appear to favor the formation of A2+ by the reaction Ar*+Ar→A2++e, but it is not possible to rule out conclusively the three-body process Ar++2Ar→Ar2++Ar. Traces of hydrogenous impurities (especially water) appear to interfere with molecule ion formation. The formation of ArH+ from impurities is also studied and the results suggest that it may be formed from any or all of Ar+, Ar2+ or Ar*. Experiments in which 1.25% hydrogen is added to the argon suggest that ArH+ is not formed mainly by the reaction of Ar+ with H2 but that the reaction of metastable argon atoms with hydrogen atoms should be seriously considered. The visible structure of a striated positive column is found to be reflected in the ion concentrations which vary differently for different ions. The effect seems to be related to fluctuations in the potential gradient which may be enhanced by the formation of negative ions.