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

Abstract

Electrons emitted from high Rydberg states formed by penetration of 2.0 MeV/u Ar 6,13,14,15+ ions through C-foil targets of various thicknesses (4.0 -20 µg/cm 2 ) have been measured with high resolution utilizing zero-degree electron spectroscopy. Intense series of Coster-Kronig peaks due to Ar 14+ 1s 2 2p( 2 P 3/2,1/2 )nl1s 2 2s( 2 S 1/2 )εl and Ar 13+ 1s 2 2s2p( 3 P 2,1,0 )nl -1s 2 2s 2 ( 1 S 0 )εl 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 Ar 15+ 1s 2 2p( 2 P) and Ar 14+ 1s 2 2s2p( 3 P) cores have also been found to remain constant for all the collision systems investigated. The total Ar 15+ 1s 2 2p( 2 P) population derived from n = 10 transition peaks is found to be almost the same as those of Ar 14+ 1s 2 2s2p( 3 P), which is in contrast to the ratio of Ar 15+ to Ar 14+ fractions measured downstream the foil.