Origin of dips and peaks in the absolute fully resolved cross sections for the electron-impact double ionization of He

Using a multiparameter multicoincidence spectrometer, we have measured the coplanar (e,3e) angular distributions following the double ionization of helium at an incident energy of approximate to 5.6 keV and under a small projectile's scattering angle of 0.45 degrees. The two ejected electrons have been detected with equal energies E-b = E-e= 10 eV. The absolute value of the cross section is determined with an accuracy of 25%. The origin of dips and peaks in the spectra is exposed by analyzing the corresponding theoretical calculations. These calculations have been done using a four-body final-state wave function for the three electrons moving in the field of He2+ . The dipolar limit is investigated and the manifestation of the deviation from this limit are pointed out. General features and possible trends for other targets are proposed. [S1050-2947(99)02805-X].