Electrons emitted from high Rydberg states formed by penetration of 2.0 MeV/u Ar6, 13, 14, 15+ ions through C-foil targets of various thicknesses (4.0 - 20 µg/cm²) have been measured with high resolution utilizing zero-degree electron spectroscopy. Intense series of Coster-Kronig peaks due to Ar14+ 1s²2p(²P3/2,1/2)nl - 1s²2s(²S1/2)epsilonl' and Ar13+ 1s²2s2p(³P2,1,0)nl - 1s²2s² (¹S0)epsilonl' transitions, in which the principal quantum number, n, starts at 10 and increases with increasing peak energy, have been observed for every combination of initial charge state and foil thickness, and quite a few number of other peaks remain unassigned in the electron energy region investigated. Intensities of each series of Coster-Kronig electron peaks follow the n-3 law. The mean charge states after the foil penetration have been found to be the same within 10% uncertainty and the total intensity of the Coster-Kronig transitions including Ar15+ 1s²2p(²P) and Ar14+ 1s²2s2p(³P) cores have also been found to remain constant for all the collision systems investigated. The total Ar15+ 1s²2p(²P) population derived from n = 10 transition peaks is found to be almost the same as those of Ar14+ 1s²2s2p(³P), which is in contrast to the ratio of Ar15+ to Ar14+ fractions measured downstream the foil.
Rydberg state; Coster-Kronig transition; Charge state; Density effect
