Which spectrum is represented by a Tanabe-Sugano graph?

A Tanabe-Sugano graph is specifically designed to illustrate the relationship between the energy levels of d-electrons in transition metal complexes and the absorption of light. These graphs depict how different electronic transitions occur between various d-orbitals when a complex is subjected to light, particularly in the visible region.

The vertical axis of a Tanabe-Sugano diagram represents the energy levels of the electronic states, while the horizontal axis often reflects the ligand field strength or ratio of crystal field splitting energy to the pairing energy. The ordinate showcases transitions that result in electronic absorbance, which is critically important for understanding how transition metal complexes interact with light—a key feature in coordination chemistry and spectroscopy.

In contrast, the emission spectrum, the electromagnetic spectrum, and the infrared spectrum do not specifically relate to the d-electron transitions described in a Tanabe-Sugano diagram. Emission spectra involve light emitted as electrons return to lower energy states, while the electromagnetic spectrum encompasses a wide range of wavelengths of electromagnetic radiation beyond just the absorption-related transitions of d-electrons. Infrared spectroscopy primarily focuses on vibrational transitions rather than electronic transitions involved in d-orbitals. Thus, the choice of electronic absorbance spectrum accurately represents the concept captured by a Tanabe-Sugano