Emission-line profiles of helium autoionization states after excitation by fast Li and He ions.

Abstract

We report the angle-dependent electron emission from the (2${s}^{2}$${)\mathrm{}}^{1}$S, (2s2p${)\mathrm{}}^{1}$P, and (2${p}^{2}$${)\mathrm{}}^{1}$D autoionizing states of helium, after excitation by 100-keV/amu ${\mathrm{Li}}^{+}$, ${\mathrm{Li}}^{2+}$, and 500-keV/amu ${\mathrm{He}}^{+}$, ${\mathrm{He}}^{2+}$, ${\mathrm{Li}}^{+}$, ${\mathrm{Li}}^{2+}$, and ${\mathrm{Li}}^{3+}$ ions. All of the peak profiles are strongly affected by the electron-ion interaction that occurs after ionization. A method that accounts for this post-collision interaction, and allows comparison with theoretical calculations, is presented, and some previously unexplained discrepancies between theoretical and experimental line profiles are resolved. The differently charged ions cause systematic changes in the observed line profiles. We report some projectile-charge-dependent emission intensities for the different peaks. Accurate energy differences between the excited states are reported.