Absolute cross section measurements for electron impact ionization of Ar7+

The first absolute cross section measurements for single and double electron impact ionization of sodium-like Ar 7+ are reported. The animated crossed beams method has been employed in the energy range from threshold to 3000 eV. The measured cross sections for single ionization are higher than the theoretical and semi-empirical predictions by about 20-50%. This discrepancy has been associated with the contribution of the indirect ionization processes. The double ionization cross section is only 1% of the single one.