Dynamics of the double-ionization process from (e, 3e) experiments: II. Fivefold differential cross sections for neon

Using a new multi-parameter multi-coincidence spectrometer, we have measured relative, coplanar (e, 3e) angular distributions for the double ionization of neon at ∼ 5.5 keV impact energy, under a small scattering angle, 0.45 deg., and equal energy sharing among the two 'ejected' electrons, Eb = Ec = 10 eV. The general features of the distributions are outlined and compared with similar measurements on argon (El Marji et al 1997 J. Phys. B: At. Mol. Opt. Phys. 30 3677). It is found that the distributions are dominated by the simultaneous backward emission of both ejected electrons. On the basis of qualitative arguments, this may be attributed, as in argon, to a double-hit process (a so-called 'two step 2' mechanism). However, additional structures are found for neon, which are not present for argon, namely a forward emission of both ejected electrons. Though their origin could not be explained in terms of intuitive double-ionization mechanisms, they clearly indicate that the recoil ion actively participates during the collision. (author)