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 me asured relative, coplanar (e, 3e) angular distributions for the double ionization of neon at similar to 5.5 keV impact energy, under a small scattering angle, 0.45 degrees, and equal energy sharing among the tw o 'ejected' electrons, E-b = E-c = 10 eV. The general features of the distributions are outlined and compared with similar measurements on a rgon (El Marji et al 1997 J. Phys. B: At. Mel. Opt. Phys. 30 3677). It is found that the distributions are dominated by the simultaneous bac kward emission of both ejected electrons. On the basis of qualitative arguments, this may be attributed, as in argon, to a double-hit proces s (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 cle arly indicate that the recoil ion actively participates during the col lision.