Calculations of two-electron transition cross sections between fully stripped ions and helium atoms

Abstract

One- and two-electron collision processes between fully stripped ions (Z=2-9) and helium atoms have been investigated in the intermediate energy range within the independent electron approximation. The transition probabilities for single excitation, single ionization and electron capture for an effective one-electron helium atom colliding with bare ions calculated in the coupled channel semiclassical impact parameter model employing a travelling atomic orbital expansion were combined to obtain cross sections for two-electron processes, such as transfer ionization, double capture and double ionization. It is found that all one-electron processes are well described by an independent electron approximation where the effective potential of the target atom gives the correct single ionization energy, while accurate cross sections for all two-electron transitions can be obtained only if one adopts a different effective potential where the single ionization energy of each electron is half the double ionization energy of helium.