Electron Impact Excitation-Autoionisation of the (2s2)1S, (2p2)1D and (2s2p)1P Autoionising States of Helium

Abstract

The electron impact excitation of the (2s2)1S, (2p2)1D and (2s2p)1p autoionising states of helium and their subsequent radiationless decay was studied by observation of the ejected electrons. The present work was carried out at an incident energy of 94·6 e V and for ejected electron scattering angles in the range 25-135°? This study was conducted simultaneously with an (e, 2e) investigation into these same autoionising states with the results of this latter work being discussed elsewhere. The lineshapes observed in the present ejected electron spectra are analysed using the Shore-Balashov parametrisation. As part of the analysis procedure we determine numerically rigorous confidence limits for the derived parameters. We believe this is the first time that such error limits are presented in the literature for the derived parameters. No previous experimental or theoretical work has been undertaken at the incident energy of the present investigation but, where possible, the resulting parameters are qualitatively compared against the 80 eV results of other experiments and theory.