Structure near autoionizing energies in the excitation of bound states of helium, neon and argon by electron impact

Cross sections for the excitation of bound states of atoms by electron impact have been found to contain structures at incident energies near to the energies of short-lived autoionizing states of the target atoms. These structures look superficially like resonances, but in fact they seem to be caused by a post-collision interaction between inelastically scattered and ejected electrons. Examples are given of these structures in He, Ne and Ar. A quantum-mechanical model, which is termed 'shake-down', is advanced to explain these structures and comparison is made with the experimental data.