title: DISTORTED WAVE CALCULATIONS FOR ELECTRON IMPACT IONIZATION OF Si$^{4+}$ AND Si$^{5+}$ author: Huaguo Teng affiliation: Institut f\"ur Kernphysik, Justus-Liebig-Universit\"at Giessen, D-35392 Giessen, Germany summary: Cross sections for electron-impact ionization of Si$^{4+}$ and Si$^{5+}$ ions have been calculated in the distorted wave approximation. In the present calculations both direct ionization and excitation-autoionization processes are included. The present results are in resonable agreement with the experimental measurements of Thompson and Gregory (Phys. Rev. A{\bf 50}, 1377(1994)). Remaining discrepancies between the experiment and theory are discussed.