Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5493475 | Atomic Data and Nuclear Data Tables | 2017 | 105 Pages |
Abstract
Energy levels and radiative rates (A-values) for four types of transitions (E1, E2, M1, and M2) are reported for an astrophysically important Mg-like ion Si III, whose emission lines have been observed in a variety of plasmas. For the calculations, well-known and widely-used grasp code has been adopted, and results are listed for transitions among the 141 levels of the 3â3ââ² and 3â4â configurations. Experimental energies are available for only the lowest 58 levels but there is no major discrepancy with theoretical results. Similarly, the A-values and lifetimes show a satisfactory agreement with other available results, particularly for strong E1 transitions. Collision strengths are also calculated, with the darc code, and listed for resonance transitions over a wide energy range, up to 30 Ryd. No similar results are available in the literature for comparisons. However, comparisons are made with the more important parameter, effective collision strength (Î¥), for which recent R-matrix results are available for a wide range of transitions, and over a large range of temperatures. To determine Î¥, resonances have been resolved in a narrow energy mesh, although these are not observed to be as important as for other ions. Unfortunately, large discrepancies in Î¥ values are noted for about half the transitions. The differences increase with increasing temperature and worsen as the upper level J increases. In most cases the earlier results are overestimated, by up to (almost) two orders of magnitude, and this conclusion is consistent with the one observed earlier for Be-like ions.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Nuclear and High Energy Physics
Authors
Kanti M. Aggarwal,