Intensities in Octahedral Complexes of 4d and 5d Transition-Metal Ions

The theory of the intensity of vibronically allowed electric dipole transitions for octahedral complexes is investigated. The calculation is carried out within the confines of ligand field theory and full account is taken of spin–orbit coupling. Of particular interest are those transitions which take place with a considerable change of internuclear configuration and which may be characterized as mainly involving a $t_{\text{2g}}^n{\mathrm{\hspace{0.17em}\to \hspace{0.17em}t}}_{\text{2g}}^{\text{n−1}}{e}_g$ transition. Certain selection rules are determined and an approximate two‐parameter form is found for the intensity of the allowed transitions. This calculation is particularly useful as an aid in assigning transitions in regions where there are many possible states. Application is made to the low‐temperature optical spectra of Os⁴⁺ and of Re⁴⁺ in single crystals of Cs₂ZrCl₆. The spectra of OsF₆ are also discussed. Some predictions are made about the low‐temperature optical spectra of W⁴⁺, Ir⁴⁺, and Pt⁴⁺ in single crystals of Cs₂ZrCl₆.