Sub-shell excitations of rare gas atoms by electron impact

The sub-shell excitations of rare gas atoms have been investigated by electron energy-loss spectroscopy at various impact energies. In energy-loss spectra, we have observed several structures involving ones by the optically forbidden transitions, which are embedded in a continuum. Besides, we have found new states formed by two-electron excitations. In this region, above the first ionization limit the rare gas atoms can be ionized either directly or via the other excited states like inner-shell excited states or doubly excited states, which are coupled to the ionization continuum. These resonance line profiles have been theoretically studied by Fano. We have found that the line profile depend on the incident electron energy and scattering angle. In particular, the line profile parameters q for each state of spectra of argon have been determined. Besides, for 3s → 4p excitation it has been found that the q parameters which are described as a function of momentum transfer has fallen on the straight line. (author)