Investigation by high resolution electron spectroscopy of the helium-like 3lnl' Rydberg series in double capture processes at low collision velocity: auto transfer to Rydberg states and electron stabilization

Abstract

A high resolution electron spectrometry of the (3lnl') Rydberg series populated in N7++He and Ne10++He collisions at 10 q keV, 10 degrees allows us to observe, for the first time by this method, two post-collisional effects. First, it is found with nitrogen ions that, when n increases from n=4 to 9, the L-distribution peaks more and more on the high angular momentum states. This is qualitatively understood as a Stark deformation of the Rydberg orbit by the Coulomb field of the receding ion. Also, in the n range where the double capture process populates symmetrical 4l4l' states (n>9), an enhancement of the intensities of the 3lnl' Rydberg lines is observed for both collisional systems. This is thought to be a signature of the so-called auto transfer to Rydberg states effect. The transfer of population from the 4l4l' to the 3lnl' states is found to be favoured against a direct autoionization of these 4l4l' states into the n=2 continuum. These experimental findings together with preliminary spectroscopic calculations concerning the configuration interaction of the Ne8+(4l4l') states with the Ne8+(3lnl') Rydberg series are also discussed within the context of the electron stabilization which follows a double capture.