Excitation of autoionization resonances in collisions of helium atoms withfast ions

A theoretical model of collisions between fast ions and atoms is proposed w hich describes the effect of projectiles on the excitation of autoionizatio n 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 ef fect of the field of the atom on the kinematics of the ion scattering, as w ell as the effect of the intermediate (1snl )L-1 states on the two-electron excitation mechanism. The charge dependence of the excitation cross sectio n of the (2s(2))S-1 and (2s2p)P-1 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 depe ndence are analyzed. (C) 2001 MAIK "Nauka/Interperiodica".