Dielectronic recombination ofPb79+via high angular momenta

Abstract

We have used the AUTOSTRUCTURE code to carry out semirelativistic calculations for the dielectronic recombination of Pb 79+ via the 2s 1/2 −2p 1/2 core excitation. We obtain excellent agreement between these semirelativistic results and measurements made at Gesellschaft für Schwerionenforschung, in particular, for the high angular momentum peak of the 2p 1/2 20l j resonances. The factor of 3 underestimate in the result for this peak that was originally obtained by Mitnik et al., which has led some to conclude that only a fully relativistic approach can describe dielectronic recombination via high angular momenta in very heavy highly charged ions, are found to be in error. DOI: 10.1103/PhysRevA.70.054701 PACS number(s): 34.80.KwDielectronic recombination (DR) of very heavy highly charged Li-like ions has been a testbed for experimental and theoretical studies of relativistic effects in DR [1][2][3][4][5]. The heavy-ion Experimental Storage Ring (ESR) at Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, has been used to test quantum electrodynamics (QED) in strong fields by measuring the series of DR resonances occurring via a 2s 1/2 −2p 1/2 core excitation so as to determine the coreenergy splitting to high precision [2,3]. The DR resonances themselves are particularly interesting because the relatively small 2s 1/2 −2p 1/2 energy splitting means that DR via high angular momentum states (to l ϳ 20) makes a significant contribution to the n-resolved total.Prior to measurements at GSI, Mitnik et al.[4] carried out calculations for the DR of Pb 79+ over 0 -300 eV. This covered all DR resonances that arise via the 2s 1/2 −2p 1/2 core excitation and the first ͑n =6͒ resonances associated with the 2s 1/2 −2p 3/2 core excitation. Multiconfiguration Dirac-Fock (MCDF) calculations were carried out for the 2p 3/2 6l resonances, and for l =0-5 of the 2p 1/2 nl resonances (for n ജ 20). The contribution from higher l for the 2p 1/2 nl resonances was determined using the multiconfiguration BreitPauli (MCBP) semirelativistic approach incorporated within the AUTOSTRUCTURE code [6], which includes the massvelocity and Darwin terms within the solution of the radial equations. Subsequently, measurements were made at GSI [2] for DR via the 2p 1/2 20l resonances and these were found to be in good agreement with MCDF calculations [2], which were made for all l. Good agreement was found also with the MCDF results of Mitnik et al. [4], but the semirelativistic results reported by them were found to be a factor of 3 smaller than the measurements and MCDF results of Brandau et al. [2]. This led [2] to conclude that "Contributions from very high angular momenta must be included and considered in a fully relativistic framework in order to understand the dynamics involved in the DR process."While the semirelativistic approach of AUTOSTRUCTURE cannot hope to give energy splittings to high precision in such highly relativistic systems (and so makes use of the best available N-electron energies instead [6]), its description of r...