What does a curved line in a Tanabe Sugano diagram signify?

In a Tanabe-Sugano diagram, a curved line indicates the mixing of orbitals due to symmetry. This occurs in coordination complexes where d-orbitals are influenced by the ligand field strength and symmetry of the surrounding ligands. The curvature in the diagram reflects the interaction between different electronic states, specifically how differing orbital symmetries lead to mixing when the environment created by ligands affects the energies of these orbitals. Understanding this concept is crucial for predicting electronic transitions and the spectral properties of transition metal complexes, as it highlights how electron configurations evolve under varying ligand field strengths.