High resolution study of the autoionizing states of He in their exchange interference energy region

The electron impact excitation (and their decay into the same final ionic state) of the autoionizing states of helium (2s2(S1), 2s2p(P3), 2p2(D1) and 2s2p(P1)) have been studied. The interference of these states can occur when the energies of the autoionizing electrons match that of the scattered electrons. The observation of this exchange interference is disturbed by the Fano interference, which occurs at all primary energies. We intend to study it separately in the neighborhood of the critical energy, and then to estimate its measure for the critical energy. The present measurements were made at 88 eV and 97 eV primary energies (where the groups of the ejected and the scattered electron peaks are well separated), at 130°, 90° and 50° scattering angles. The measured spectra were evaluated by a computer code, using the Shore parametrization. We give the obtained peak parameter values in tabulated form. We found an anomaly of the fitted values of Lorentz width of 2s2(S1) peak.