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

Highlights: • We studied the autoionized states of He induced by electron impact. • The experimental spectra were measured at the neighborhood of critical primary energy. • We determined the parameters of the autoionized peaks using the Shore parametrization. • We found an anomaly of the fitted values of Lorentz width of $2s^2\left({}_{1}S\right)$ peak. - Abstract: The electron impact excitation (and their decay into the same final ionic state) of the autoionizing states of helium ($2s^2\left({}_{1}S\right)$, $2s2p\left({}_{3}P\right)$, $2p^2\left({}_{1}D\right)$ and $2s2p\left({}_{1}P\right)$) 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 $2s^2\left({}_{1}S\right)$ peak.