Calculation of charge-changing cross sections in collisions of ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{2+}$, and ${\mathrm{Li}}^{3+}$ with He atoms

Cross sections for single and double ionization ${\sigma }^{i1}$ and ${\sigma }^{i2}$, the single and double electron capture to the ground state ${\sigma }^{c1}$ and ${\sigma }^{c2}$, and the ionization with electron capture to the ground state ${\sigma }^{\mathrm{ic}}$ in collisions of ${\mathrm{H}}^{+}$, ${\mathrm{He}}^{2+}$, and ${\mathrm{Li}}^{3+}$ nuclei with He atoms at nuclei energies from 0.025 to 4 MeV/amu are calculated. The independent-electron approximation is used with probabilities that are unitarized at the lower energies. Two kinds of calculations are performed: (i) The cross sections for all charge-changing processes are calculated including both the ionization and capture channels; (ii) the ionization cross sections ${\sigma }^{i1}$ and ${\sigma }^{i2}$ are calculated with neglect of the capture channel, the capture cross sections ${\sigma }^{c1}$ and ${\sigma }^{c2}$ are calculated with neglect of the ionization channel, and the cross sections ${\sigma }^{\mathrm{ic}}$ for ionization with capture are calculated with the single-electron transition probabilities obtained separately for ionization and capture. The direct-ionization calculations are based on the semiclassical Coulomb approximation, and electron capture is calculated with use of the approximation of Bassel and Gerjuoy [Phys. Rev. 113, 749 (1960)]. The calculation results show that in single and double ionization the capture to the ground state strongly affects the value of ${\sigma }^{i1}$ and ${\sigma }^{i2}$ only in collisions of He atoms with the ${\mathrm{He}}^{2+}$ nuclei whereas the ionization channel leads to a marked decrease of the cross sections ${\sigma }^{c1}$ and ${\sigma }^{c2}$ in collisions with the ${\mathrm{He}}^{2+}$ and ${\mathrm{Li}}^{3+}$ nuclei.