Die differentiellen Anregungsfunktionen dern+2-Zustände von Helium

Energy and angular dependences for the electron impact excitation of the Helium 2³ S, 2¹ S, 2³ P, and 2¹ P states have been measured using monochromatic (0.05 eV) electrons in the energy range from 19 to 23 eV and for scattering angles ranging from 0 to 110°. The structures near the 2³ S-threshold have been analyzed in terms of resonant and non resonant i.e. direct scattering phase shifts. The first peak in this excitation function at 19.95 eV is mostly due to the rapid change with collision energy of the directs-wave phase of the inelastic scattering, which in turn is a consequence of the existence of the 2² S-resonance at 19.3 eV. The energy position and behaviour with collision energy of the first peak at 20.7 eV in the 2¹ S-channel is in agreement with the predictions for the existence of a virtual resonance state ofBurke et al. A term sceme of the He^? resonances with assignments of configurations is presented.