(Effective) collision strengths for Kr²¹⁺. Left: present collision strengths for 2s²2p   ²P_1/2–2s2p^2   4P_3/2 (1–4), 2s²2p   ²P_1/2–2s2p^2   2P_3/2 (1–10), and 2s²2p   ²P_1/2–2p^3   2P_3/2 (1–15) transitions along with the distorted-wave calculation by Zhang & Sampson (1994a, ZS94). Right: ratio of effective collision strength between the present ICFT R-matrix calculation and DW results available from the Open-ADAS database⁷ at a temperature of 1.0 × 10⁸ K. Double-horizontal lines correspond to agreement within 20%.