Abstract
SynopsisIn order to resolve major discrepancies between a number of previous calculations for electron impact excitation of Mg4+, we carried out extensive B-Spline R-matrix calculations for this problem. In particular, we investigate the effect of the target structure description and the number of states included in the close-coupling expansion on the final results. Finally, we provide an uncertainty estimate the current predictions.
Highlights
Accurate and reliable electron-impact excitation rates and transition probabilities are required for the modeling and spectroscopic diagnostics of various nonequilibrium astrophysical and laboratory plasmas
As seen from the table, the multiconfiguration Hartree-Fock (MCHF) and B-spline R-matrix (BSR)-86 (TS) calculations show the best agreement with the NIST-recommended data, whereas the Dirac Atomic R-matrix Code (DARC)-86 energies lack considerably in accuracy due to the limited configuration interaction (CI) expansions used in the target wavefunctions
In response to recent criticism of the BSR method, and in order to resolve the reasons for the large discrepancies between existing datasets, we have presented new extensive calculations of the oscillator strengths and effective collision strengths for the Mg4+ ion
Summary
Accurate and reliable electron-impact excitation rates and transition probabilities are required for the modeling and spectroscopic diagnostics of various nonequilibrium astrophysical and laboratory plasmas. Many references and examples are given in the recent publications by Hudson and co-workers [1], Tayal and Sossah [2], and Aggarwal and Keenan [3] All these works employed the advanced R-matrix (close-coupling) method for the collision process, but different computer codes and different representations of the target structure. Both the atomic structure (GRASP) and scattering (DARC) codes are available at the website http://www.apap-network.org/ codes.html They adopted fully relativistic codes for their calculations of both the ionic structure and the collision parameters, Aggarwal and Keenan [3] stressed the well-known fact that relativistic effects are not expected to be very important in the predicted collisions rates for such a comparatively light ion as Mg4+.
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