Auto transfer to Rydberg states and indirect stabilization following double capture

Abstract

Two-electron capture by slow multiply charged ions colliding on rare-gas targets at keV energies populates doubly excited states of the projectile with large cross sections. Though these states are dominantly autoionizing, important radiative decay following double capture have been reported, among which the direct observation of the fluorescence from Rydberg states. These findings are important since they modify the charge and radiation balance of the multiple charge exchange reactions. A mechanism based on post-collisional effects was proposed, in which Rydberg states are fed from the quasi-symmetrical doubly excited states initially populated. A quantitative analysis of this effect is developed leading to a simple model which is applied to N7+ on He and Ar collisions. The evolution of the competition between autoionization and fluorescence yields of the Rydberg states with the internuclear distance is emphasized.