9 The sulphur isoelectronic sequence

9.1 FeXI

 Previously, only the strongest transitions into and out of the metastables had been fitted for this ion from Bhatia & Doscheck (1996). The remaining transitions have now been added. This was found to change the level populations for some of the metastables and, in the worst case ([3s 2][3p 3][3d ] [5 D 4]), the population was lowered by 20%. However, this has a negligible effect on the Fe XI allowed transitions.

9.2 NiXIII

The adopted atomic model for Ni XIII includes 4 different configurations ([3s 2][3p 4], [3s3p 5], [3s 2][3p 3][3d ] and [3p 6]) corresponding to 48 fine-structure energy levels. Experimental energy levels are taken from the NIST database, although for the majority of the [3s 2][3p 3][3d ] energy levels no value is available.

Theoretical energy levels, radiative transition probabilities and collision strengths are taken from Bhatia & Doscheck (1998a). The authors provide Distorted Wave collision strengths for all possible transitions between the included levels; these are calculated for five values of the incident electron energy between 10 and 50 Ry. To our knowledge this is the first complete calculation for Ni XIII collision strengths.

Radiative transition probabilities have been compared with previous calculations (Fawcett 1986b; Saloman & Kim 1989), and good agreement has been found.