Electron capture into excited states by helium ions incident on helium

Abstract

A study has been made of capture of an electron into an excited state by helium ions incident on helium gas with impact energies between 5 and 100 keV. Absolute cross sections have been determined for capture into singlet and triplet He I levels with principal quantum numbers n varying between 3 and 6. For a few of the corresponding spectral lines and a smaller energy interval the degree of polarization was measured. We compare the capture cross sections with the excitation cross sections, which have been obtained also for He + on He in former experiments. Then it is mostremarkable, that the capture and excitation cross sections are almost equal at lower impact energies for equivalent levels. This suggests the existence of intermediate molecular states in these collision processes. Similarity has also been found in the polarization of radiation from the mentioned capture and excitation processes. Maxima in the capture cross sections are found for D and P levels. The maxima of the D levels are reached at the lowest energies, those of the S levels will appear at the largest energies.