Tanabe-Sugano Diagram
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A diagram which plots the (normalized) energy difference of an electronic transition (in units of E/B) on the vertical axis and the (normalized) crystal field splitting energy (in units of Δ/B, where Δ is the ligand field splitting energy and B is the Racah interelectronic repulsion parameter) on the horizontal axis for each possible electronic state of the system. The lowest energy state is usually placed along the x-axis, and all other states plotted relative to it. The number of curves intersected by a vertical line for a given Δ/B gives the number of possible transitions and therefore the number of expected spectroscopic absorption features. For more than 1 and less than 9 d electrons, there are more than 2 ways of arranging electrons in orbitals leading to different configurations, called Russell-Saunders (or spectroscopic) states.
