AN (E, 2E) STUDY OF HELIUM AUTOIONIZATION EXPERIMENT AND THEORY

Results are presented for the triple differential (e, 2e) cross sectio ns in helium in the region encompassing the (2s(2))S-1, (2s2p)P-3, (2p (2))D-1 and (2s2p)P-1 resonances at an incident energy of 94.6 eV for a scattered electron angle of 30 degrees and for ejected-electron scat tering angles in the range -25 to -135 degrees. The measured coinciden ce ejected-electron spectra are compared against those calculated in a n equivalent local form of the distorted-wave impulse approximation wi th the resonant scattering amplitudes being evaluated by a six-state m omentum-space coupled-channels method. In each case the calculation is folded with the experimental energy resolution. The data are analysed in terms of the Shore-Balashov parametrization to obtain the direct ( e, 2e) cross section f(r) and the resonance parameters a, and b, for t he (2s(2))S-1, (2p(2))D-1 and (2s2p)P-1 resonances as a function of ej ected-electron momentum. These derived parameters are compared against the results of a calculation where configuration interaction expansio ns for the resonances and helium ground state, which employed hydrogen ic and multiconfiguration Hartree-Fock orbitals, respectively, were us ed. Here the distorted-wave Born approximation was employed for the (e , 2e) cross section calculation. The calculated parameters agree quite well with the experimental results with both indicating strong correl ations between the resonance amplitudes and the direct ionization ampl itudes. Finally we report and discuss our results of an experimental i nvestigation into post-collision interaction effects for the present k inematical conditions.