Post-collision interactions in excitation of autoionising states of krypton and xenon by electron impact within 100 meV of threshold

The PCI energy shifts observed in previous threshold electron spectra and high-n excitation functions of atomic krypton and xenon are analysed. Classical and quantum mechanical treatments are developed for the energy shifts that occur very close to threshold and are found to give almost identical results. The approximately constant difference between the energy shifts in the threshold spectra and the high-n excitation functions is explained. The widths of the autoionising states are deduced.