Electron capture and target ionization in collisions of bare projectile ions incident on helium.

Abstract

Absolute cross sections for the processes of single capture, transfer ionization, and single and double ionization were measured for ${\mathrm{C}}^{6+}$, ${\mathrm{N}}^{7+}$, ${\mathrm{O}}^{8+}$, and ${\mathrm{F}}^{9+}$ projectiles incident on a helium target in the projectile velocity range of 0.25--2.0 MeV/amu. The cross sections were determined by measuring projectile-ion final charge states in coincidence with target recoil-ion final charge states. The single-capture and transfer-ionization cross sections were corrected for ionization from impurity charge states in the beam and for double-collision processes in the target gas cell. These corrections, which are necessary for the relative as well as the absolute cross sections, were found to be as large as 50% of the cross section. The measured cross sections are compared to the multistate, coupled-channel calculations of Shingal and Lin using an independent-electron model.