English: The Tanabe–Sugano diagram for a d5 transition metal ion. The energies are calculated using a Racah C = 4.5 B, and only selected states are depicted. The multiplicity of the ground state switches from a sextet to a doublet at the vertical line. Quartet states have dotted lines and transitions to these are spin forbidden no matter the crystal field strength. Thick solid lines show states sharing a multiplicity with the ground state. Thin solid lines show states with a multiplicity differing from the ground state. Therefore, only transitions between thick solid lines are spin-allowed.