Double Rydberg states in stabilized triple capture in bare ions (Z=6-10) on rare gas target collisions

We report converging evidence from two different coincidence experiments of the formation of triply excited states C3+(2, n, n') and Ne7+(3, n, n') with two n, n' (n and n' much greater than 3) Rydberg electrons. They are formed by triple electron capture in collision of C6+ and Ne10+ bare ions with Ar at few keV. This detailed study was triggered by measurements of surprisingly large cross sections of stabilized triple electron capture (STC) for which a full radiative decay leaves the three electrons bound to the projectile. Both the energy gains and the visible photon spectra support the interpretation in term of a large population of triply excited double Rydberg states among which some states decay without autoionization. For both systems, possible population mechanisms are discussed in term of purely atomic mechanisms occurring in the post collisional evolution of the quasi symmetrical triply excited states initially populated by the collision.