Partial energy level (or Grotrian) diagram for the relevant lower terms of the three lowest configurations of Fe iii: 3d⁶, 3d⁵4s and 3d⁵4p (indicated at the top). The horizontal solid lines depict the energy levels, labelled with the term and J-value. Selected transitions are shown with dotted lines between levels. For each transition, we list the logarithm of the transition probability (or Einstein A-coefficient, in (s^-1)) of the strongest transition between the terms, adopting the Raassen & Uylings values (see Sect. 3.1).