High resolution zero degree electron spectroscopy of argon ions through carbon foil

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)el' and Ar13+ 1s22s2p(3P2,1,0)nl - 1s22s2 (1S0)el' 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.