On the effect of distortion of the initial state of an atom by the field of a multiply charged ion on doubly-differential ionization cross-sections

A theoretical description is suggested for the ionization of an atom by multiply charged ions, in which, along with the interaction in the terminal state for $Z_1/V_i <1$ (where $Z_1$ is the charge of the incident particle and $V_i$ is the velocity of the colliding particles), allowance is correctly made for the distortion of the initial state of the target atom produced by the incident ion field. It is shown that the effect of the distortion of the initial state on the angular and energy distributions of electrons increases with increasing charge and decreasing ion velocity. The calculation results for collisions of the ions with helium atoms are compared with experimental data.