(e, 2e) Reaction as a Probe for Details of the Helium Wave Function

The differential-cross-section ratios have been measured for excitation of the $n=2\mathrm{}$ and $n=1\mathrm{}$ ${\mathrm{He}}^{+}$ states in the electron-impact ionization of helium using the coplanar symmetric geometry. This reaction is a crucial test of the reaction model and of the helium wave function. The experiment is sensitive enough to rule out the Hartree-Fock function. Excellent agreement is obtained by using a configuration-interaction wave function.