State-selective study of Ar2+, Ar3+ and N22+ formation by electron impact ionization near threshold

The threshold behaviour of electron impact ionization of argon atoms and nitrogen molecules is investigated state selectively using the translational energy spectrometry (TES) method. A power law of the form sigma (Eel) varies as (Eel-Ethr)kappa can be fitted to the measured ionization functions. For double ionization of Ar and N2 the authors found good agreement with the theoretical predictions based on the Wannier theory for the electron triple escape process. Coefficients for the triple ionization of Ar are closer to those predicted by a statistical model.