The role of multiple ionization and subshell coupling effects inL-shell ionization of Au by oxygen ions

Abstract

The ionization of L-subshell electrons in gold by the impact of0.4-2.2 MeV amu-1 O ions was studied by observing excitedLγ(L-N, O) x-rays. We demonstrate that both the multipleionization in outer M- and N-shells as well as the couplingeffects in the L-shell play an important role in understandingthe measured L-subshell ionization cross sections. The multipleionization was found to be important in two aspects: first, theanalysis of x-ray energy shifts and line broadening was crucialfor proper interpretation of measured x-ray spectra; second,the additional vacancies in the M- and N-shells substantially influenced the L1-subshell fluorescence and Coster-Kronig (CK)yields, mainly by closing strong L1-L3M4,5 CKtransitions. The data are compared with the simplifiedcoupled-channels calculations using the `coupled-subshell model'(CSM) based on the semiclassical approximation (SCA), whichdescribes both direct Coulomb ionization as well as theL-subshell couplings within the same theoretical approach. Agood agreement of the present data with the theoreticalpredictions based on the discussed SCA-CSM approach is observed.Present findings partly explain the long-standing problem ofinadequate theoretical description of L-shell ionization byheavy ion impact.