Paper XI

The $P^{o}_{1/2}$ - $P^{o}_{3/2}$ fine-structure lines of Ar-VI, K-VII and Ca-VIII

Saraph.HE, Storey.PJ

Astronomy & Astrophysics Supplement Series, 1996, Vol.115, No.1, pp.151-159

We give collision strengths and collision rates for electron excitation of the $P^{o}_{1/2}$ - $P^{o}_{3/2}$ fine-structure transitions in the aluminium-like ions Ar VI, K VII and Ca VIII, a; 4.53, 3.19 and 2.32 mu respectively. The ground configuration of ions in the aluminium sequence has three electrons in the M-shell. Electron correlation effects are very strong in these ions because the subshells are energetically very close. They manifest themselves in large resonance structures that dominate the collision strengths. The accuracy of calculated collision rates depends critically on the accuracy with which the positions and shapes of these resonances are determined. This paper is a first attempt to provide collision rates for aluminium sequence ions that have been calculated taking full account of these electron correlation effects.