Angular variation of the partial doubly differential cross sections for multiple ionization of argon atoms by electron impact

Partial doubly differential cross sections d²{{{σ}}}⁽ⁿ⁾$/dEd{Ω} for the production by electron impact of argon ions having charge states from n=1 to n=4 have been measured as a function of the angle of ejection {θ} in the range 40^∘{}113^∘{}, with the energies of the incident and ejected electrons being 1.0 keV and 200 eV, respectively. A comparison has been made with similar data from the literature and explanations have been offered for the behavior of the measured angular variations.