Figure 6: Presently calculated total ionization cross sections (in the units of ) for electron impact ionization of (designated by solid line) in comparison with the various experimental data sets designated by —Perrin et al. , —Chatham et al. , —Krishnakumar and Srivastava , and —Basner et al.  and theoretical data sets designated by BEB calculations [13, 28] and —Joshipura et al. [16, 17].