10 The chlorine isoelectronic sequence

10.1 FeX

As with Fe XI (see Sect. 9.1), only the strongest transitions into and out of the metastables had been fitted for Paper I. The remaining transitions have now been added. In addition, due to large discrepancies found for the allowed [3s 2][3p 5] - [3s 2][3p 4][3d ] transitions when comparing the Bhatia & Doschek (1995) model and the more detailed SSTRUCT model (described in Sect. 4.18 of Paper I), it was decided to scale the collision strengths for these transitions via the method of Flower & Nussbaumer (1974).

These changes serve to lower the theoretical emissivities of the allowed transitions, while also the populations of the metastables are altered by up to 30%.

10.2 NiXII

The adopted atomic model for Ni XII includes three configurations ([3s 2][3p 5], [3s3p 6] and [3s 2][3p 4][3d ]) corresponding to 31 fine-structure energy levels. Experimental energy levels are taken from the NIST database (Martin et al. 1995).

Theoretical energy levels and radiative transition probabilities have been calculated using SSTRUCT. The following cofigurations were included: [3s 2][3p 5], [3s3p 6], [3s 2][3p 4][3d ], [3s3p 5][3d ], [3p 6][3d ], [3s 2][3p 3][3d 2], [3s3p 4][3d 2], [3p 5][3d 2], [3s 2][3p 2][3d 3], [3s3p 3][3d 3], [3p 4][3d 3], [3s 2][3p 4][4s ], [3s 2][3p 4][4d ], [3s 2][3p 4][4f ]. The resulting A values and oscillator strengths have been compared with the calculations by Fawcett (1987), showing reasonable agreement.

Ni XII thermally-averaged collision strengths have been calculated by Matthews et al. (1998) in the temperature range 10^3.2-10^6.6 K. The authors used the R-Matrix method. To our knowledge, these are the only large-scale electron-ion collision calculations performed in the literature.

For the same reasons as described in Sect. 2.1, thermally-averaged collision strengths for temperatures lower than 10^4.7 K have been omitted from the database.