Observation of doubly excited states in the N+ 2 2?-1 u partial ionization cross section measured by (e, 2e) experiments

The partial ionization cross section of the N+2 2?-1 u state has been measured in an asymmetric (e, 2e) experiment at about 1000 eV incident energy. The measured partial ionization cross section is characterized by features that we have assigned to the autoionization of N2 neutral doubly excited states to the 2?-1 u continuum by a comparison with previous photoexcitation experiments and theory. In the experimental conditions of our measurements, up to 50% of the partial ionization cross section of theN+ 2 2?- 1 u state is due to the autoionization of the doubly excited states. The comparison with previous photoexcitation experiments and theory also shows the full richness of the electron-impact spectrum with the contribution of optically forbidden transitions.