Electron-impact ionization of Si6+ and Si7+ ions

Crossed beams of electrons and ions have been used to measure absolute cross sections for single ionization of Si6+ and Si7+ ions from below threshold to 1400 eV. The measurements for Si6+ and Si7+ agree with distorted-wave calculations for direct ionization within 20% and 5%, respectively, suggesting that this mechanism is the dominant contribution to the cross section. The bulk of the measurements were performed with the more abundant Si28 isotope; however, due to beam impurities, measurements with Si29 were used to correct the Si28 data.