Electron-capture and impact-ionization cross sections for multiply charged ions colliding with helium

The classical-trajectory Monte Carlo method has been used to calculate the single-electron capture and impact-ionization cross sections for collisions between fully stripped ions (H⁺ to O⁺⁸) and He at energies of 100-500 keV/amu. Except for the H⁺ and He⁺⁺ systems, electron capture dominates over impact ionization at the lower energies, whereas at higher energies impact ionization is the dominant mechanism for electron loss from He. The sum of the calculated electron-capture and impact-ionization cross sections is well represented by the expression σ_ec+ion=3.1×10^-16q{(52q/E)[1-exp(-E/52q)]} cm², where q is the charge state of the incident ion and E is expressed in units of keV/amu. The calculated cross sections are in reasonable agreement with available experimental values.