Vibronic Contributions to Ligand-Induced Pseudo-Quadrupole Absorption of Rare-Earth Ions

The intensities of certain lines in the absorption spectra of rare-earth or actinide ions are very sensitive to the neighboring ligands. The contributions to these intensities coming from vibronic transitions (combined electronic and vibrational transitions) are calculated by tensorial techniques with particular reference to octahedral complexes. The expansions that are used possess leading terms that indicate that the strongest vibronic lines should be associated with electronic transitions that satisfy the selection rules on J (the total angular momentum) that are identical to those for quadrupole radiation. General agreement is obtained with the recent work of Faulkner and Richardson on the transition 7 F 0 → 5 D 2 of Eu 3+ , though some of the approximations and assumptions, as well as much of the mathematics, are different.