Comparison of collision strengths Ω from the present ICFT R-matrix calculation in with those of Goett & Sampson (1983). a) O⁵⁺: 1s²2s   ²S_1/2  →  1s2s2p   ⁴P_3/2 excitation (u line in Table 3); b) Ar¹⁵⁺: 1s²2s   ²S_1/2  →  1s2p^2   2P_1/2 excitation (1-37, ID is as list in Table 2); c) Fe²³⁺: 1s²2s   ²S_1/2  →  1s2s2p   ²P_1/2 excitation (r line in Table 3). AS-DW corresponds to the present Breit-Pauli distorted-wave calculation using autostructure; d) Kr³³⁺: 1s²2p   ²P_1/2  →  1s2p^2   2D_3/2 excitation (k line in Table 3). [Colour online]