Energy level diagrams for the Fe ii multiplets, UV1 (a), UV2 (b), and UV3 (c), where the ground and the excited states have multiple levels due to fine-structure splitting. Resonant transitions are shown in blue, and non-resonant transitions are shown in red. Whether non-resonant emission is likely to occur depends on the de-excitation rates and on the number (0, 1, or 2) of potential re-emission channels (Tang et al. 2014; Zhu et al. 2015). For example, the Fe ii λ2382 transition from the UV2 multiplet has no associated Fe ii* emission lines and thus behaves like a purely resonant transition (e.g., Lyα or Mg ii).