Electron-loss and excitation cross sections for a He+ ion colliding with various atoms.

Abstract

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 Moli\`ere 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\ifmmode\times\else\texttimes\fi{}${10}^{8}$ 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.