Atomic data from the IRON Project. IX. Electron excitation of the ^2^P^0^_3/2_-^2^P^0^_1/2_ fine-structure transition in chlorine-like ions, from AR II to NI XII.

Calculated effective collision strengths for the ground term fine-structure transitions of 11 chlorine-like ions (17 electrons) from Ar II to Ni XII are presented. There is currently very little published data for this sequence and so there is a strong motivation to satisfy the need for this information and to improve upon the accuracy of previous work where it does exist. The data are calculated using R-matrix techniques and are provided over a temperature range from 10^3^K up to 10^7^K over which the target models should be valid. Accuracy for the effective collision strengths is in the region of 10%. An independent calculation on Fex recently published by Mohan et al. (ApJ 434, 389) is shown to be wrong for this transition because of their omission of important low-energy contributions.