Collision strength 1–9 and 1–10: solid black curve – our DARC results, solid blue circle – DW calculation of Zhang & Sampson (1992), open red circle – DW calculation of Landi & Bhatia (2008). The insets in the graphs compare the corresponding effective collision strength (Υ) as a function of the electron temperature: open black circle – our DARC results, open star – R-matrix interpolated work of Keenan (1988), open upward triangle – DW calculations from Landi & Bhatia (2008).