Parameterised close-coupling calculations on the electron impact excitation of helium in the autoionisation region

The He - resonances lying near the thresholds of the doubly excited states of helium have been studied. In particular the effect of these resonances on the excitation of doubly excited states has been investigated. This was done using a close-coupling model in which a free parameter was introduced. The approach is discussed and results are presented which may explain the magnitude of 'post-collision-interaction' structures in the excitation of singly excited states.