Absolute electron impact ionization cross-sections have been measured for the neon-like Ar 8+ in the energy range from below the threshold for the metastable state to 2500 eV. No contribution of metastable states is observed. The results are well reproduced by the distorted wave Born approximation.
Defrance, P., Rachafi, S., Jureta, J., Meyer, F., & Chantrenne, S. (1987). Electron impact ionization of Ar 8+. Conference on the Physics of Multiply Charged Ions, Groningen, Netherlands. https://doi.org/10.1016/0168-583X(87)90458-7