Dynamics of the double ionization process from experiments: I. Absolute cross sections for argon

Abstract

Using a new multiparameter multicoincidence spectrometer, we measure coplanar angular distributions from the double ionization of argon at impact energy, under a small scattering angle, , and equal energy sharing among the two `ejected' electrons, . The absolute scale for the cross sections is determined within a factor of 2. General features and possible trends of the distributions are outlined. The data are discussed in terms of double ionization mechanisms and it is proposed here, using qualitative arguments, that the angular distributions are dominated by a double hit process (the so-called `two-step 2' mechanism). Such predominance is shown to be due to the chosen kinematical conditions, characterized by both an energy selectivity (equal ejected electrons energies) and a spatial selectivity (ejected electrons observed in opposite half-planes).