Electron spectroscopy of doubly excited states in He produced by slow collisions of He2+ ions with Ba atoms - art. no. 062709

We measured ejected electron spectra caused by autoionization of doubly exc ited states in He atoms; the excited He was made by double electron capture of low-energy He2+ ions colliding with Ba atoms. Measurements were perform ed by means of zero degree electron spectroscopy at projectile energies fro m 40 to 20 keV. Electron spectra due to autoionization from the states He(2 lnl') to He+(1s) for n greater than or equal to2, and those from He(3lnl') to He+ (2s or 2p) for n greater than or equal to3, were observed. Line peak s in the spectra were identified by comparing observed electron spectra wit h those of several theoretical calculations. It was found that doubly excit ed states of relatively high angular momenta such as the D and F terms were conspicuously created in a quite different manner from the cases of the pr oduction of doubly excited states by the use of photon, electron, or ion im pacts on neutral He atoms. Rydberg states with large n values were observed with high population in both the He(2lnl') and He(3lnl') series. Other rem arkable features in the electron spectra are described and the mechanisms f or the production of these electron spectra are discussed qualitatively.