A STUDY OF AUTOIONIZATION PHENOMENA IN HELIUM USING (E, 2E) SPECTROSCOPY

Results are presented for the triple differential (e, 2e) cross sectio ns in the region encompassing the helium n = 2 autoionization resonanc es at the respective incident energies 94.6, 96.6 and 99.6 eV. The sca ttered-electron angle in each case is 20 degrees and the range of ejec ted-electron angles are between -30 degrees and -135 degrees. The meas ured coincidence ejected-electron spectra are analysed in terms of the Shore-Balashov parametrization to obtain the direct (e, 2e) cross sec tion f(r) and the resonance parameters a(r) and b(r) for the (2s(2))S- 1, (2p(2))D-1 and (2s2p)P-1 resonances as a function of ejected-electr on momentum. These derived parameters are compared against the results of a calculation where configuration-interaction expansions for the r esonances and helium ground state, which employed hydrogenic and multi configuration Hartree-Fock orbitals, respectively. were used. Here the distorted-wave Born approximation was employed for the (e, 2e) cross section calculation. The calculated parameters agree quite well with t he experimental results indicating that the theoretical description of the reaction mechanism is physically realistic. Further, both experim ent and theory show strong correlations between the resonance amplitud es and the direct ionization amplitudes. Finally, we report and discus s our results of an experimental investigation into the post-collision interaction effects for the present kinematical conditions.