Electron-loss and excitation cross sections for aHe+ion colliding with various atoms

A unitarized impact-parameter method is applied to calculate the electron-loss and excitation cross sections for ${\mathrm{He}}^{+}$ ions colliding with atoms. The projectile ionization and excitation are dominantly caused by the average potential field of the target atom (atomic number $Z_2$). The inelastic process of exciting the target atom contributes negligibly except for light target elements. We adopt the Molière potential to describe this average potential field. The energy dependences of the electron-loss cross sections in He, ${\mathrm{N}}_2$, and Ar targets are in good agreement with the reported data. In the case of the Kr target, the present theory yields larger cross sections than the data, especially below 1 MeV impact energy of a ${\mathrm{He}}^{+}$ projectile. The calculated loss cross sections at impact velocity ranging from 2$v_0$ to 6$v_0$ ($v_0$=2.18×${10}^8$ cm/s) show a weaker $Z_2$ dependence in the large $Z_2$ region than that given by the Bohr formula. As for the cross section for exciting the ground state of a projectile to the first excited state, a similar weak $Z_2$ dependence can be found. The recent experimental results using 40-MeV ${\mathrm{F}}^{8+}$ ions colliding with He, Ne, Ar, and Kr targets have supported this tendency.