Opened 4 weeks ago

#402 new enhancement

Si III atomic data

Reported by: Gary J. Ferland Owned by: nobody
Priority: good to do Milestone:
Component: atomic/molecular data base Version:
Keywords: Cc:

Description

Energy levels, radiative rates and electron impact excitation rates for transitions in Si III 
Aggarwal, K. M.
2017, Atomic Data and Nuclear Data Tables, 117, 320-424

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 3 l 3l' and 3 l 4 l 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 (Upsilon), for which recent R-matrix results are available for a wide range of transitions, 
and over a large range of temperatures. To determine Upsilon, 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 Upsilon 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.

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