Low energy (e,2e) ionization of Argon in the equal energy sharing   geometry
  Quantum Defect theory is a well established theoretical concept in modern spectroscopy. We show that this approach is useful in electron impact ionization problems where state of the art theoretical methods are presently restricted mostly to simple atomic targets. For the well documented Argon ionization case in equal energy sharing geometry the approach suggested leads to significant improvements compared to previous calculations. 
S. Mazevet, G. Nguyen Vien, J. Langlois, R. J. Tweed, O. Robaux, C.   Tannous and K. Fakhreddine