Energy Dependence for Single and Double Ionization by Electron Impact Between 250 and 2200 eV

Abstract

We have completed a preceding work by studying Rb, Zn, Mg, NH3, NO, N2, CO, COS, CS2, and H2S. All the results prove that the direct double-ionization cross section (simultaneous ejection of two electrons) can be written as σ ∝ E−1, where E is the energy of incident ions. When doubly charged ions are formed, not by direct ionization, but by the Auger effect, we observed departure from an E−1 dependence. Experiment shows that molecular ions COS++, CS2++, H2S++, and NH3++ can be formed by the Auger effect. Discussion suggests that some of these ions are stable only in excited states. Furthermore, our experiments show that for all studied species, excepting magnesium, the single-ionization cross section satisfies the usual dependence σ ∝ E−1log B E, where B has a reasonable value. The magnesium cross section decreases anomalously rapidly and we were unable to find a satisfactory interpretation of this phenomena.