Excitation of autoionization resonances in collisions of helium atoms with fast ions

A theoretical model of collisions between fast ions and atoms is proposed which describes the effect of projectiles on the excitation of autoionization resonances. The model takes into account the change in the binding energy of electrons in a target atom induced by the field of a projectile, the effect of the field of the atom on the kinematics of the ion scattering, as well as the effect of the intermediate (1snl)¹ L states on the two-electron excitation mechanism. The charge dependence of the excitation cross section of the (2s ²)¹ S and (2s2p)¹ P resonances is found to be weaker than in the first order of the perturbation theory and is in qualitative agreement with experimental data. The reasons for the emergence of such a charge dependence are analyzed.