Stabilization of autoionizing states during ion-atom collisions

Electron capture by slow multiply charged ions colliding on rare-gas targets is known to populate highly excited states of the projectile with very large cross sections. For double electron capture, (n,n') series with n∼n' are, in general, preferentially populated. Though these states are almost completely autoionizing, important radiative decay following double capture has been reported. Recently the fluorescence from n<<n' Rydberg states has been observed. These findings are important since they strongly modify the charge and radiation balance of the multiple charge exchange reactions. We propose here a mechanism based on post-collisional effects which feeds Rydberg states from the quasi-symmetrical doubly excited states initially populated. A simple quantitative estimate of this effect is proposed on the basis of the well known 'Barker and Berry' formula. (author)