Simultaneous ionization and excitation of helium to the 4S,P,D,F states of He+ by electron impact

The simultaneous ionization and excitation process of helium by electron impact has been studied by observing the fine structure of the He II 4686 A radiation (4S,4P,4D,4F → 3S,3P,3D) at electron energies of 80 to 300 eV. A dual etalon 150 mm aperture, high-resolution scanning Fabry--Perot interference spectrometer was used to resolve the thirteen fine structure components. The ionization-excitation cross sections of the 4S states are in reasonable agreement with theoretical values. Over the energy range of 4P cross sections are about three times larger than the 4S and 4D cross sections, which are of comparable magnitude, and much larger than the 4F cross sections. The pressure dependence of the apparent excitation cross sections was measured at an electron energy of 200 eV over the region 2 to 140 milli-torr at 850K and 18 to 140 milli-torr at 3000K