TDCS FOR THE ELECTRON-IMPACT IONIZATION APPROACHING THE DIPOLAR LIMIT

The parametrization of the multidifferential cross sections recently p roposed by Klar and Fehr is specialized to the case of the triple diff erential cross section for asymmetric (e, 2e) reactions. By comparison with experimental data at 8 keV incident energy it is shown that the first-order interaction models could properly account for the experime nt provided the expansion of the exponential operator does not stop at the dipolar term. This is found to be true no matter how small the mo mentum transfer is.