Parameterization of electric-dipole intensities in the vibronic spectra of rare-earth complexes

Abstract

A parameterization scheme for the electric dipole intensities of one-phonon vibronic (f-f) transitions in rare-earth (lanthanide and actinide) complexes is proposed. This parameterization is perfectly general within the one-electron, one-phonon, one-photon approximation for ion-ligand-radiation field interactions, and it is directly related to a general intensity parameterization scheme proposed previously for purely electronic (zero-phonon) f-f transitions. The parameters in this scheme can provide a basis for characterizing one-phonon vibronic line intensities in f-f optical spectra without recourse to specific model (or mechanism)-dependent considera tions. Applications of this parameterization to the vibronic spectra of octahedral (O _h) REL₆ systems are discussed, and it is shown how the intensity parameters for these systems may be expressed in terms of a set of ‘intrinsic’ intensity parameters (in the superposition approximation for RE-L interactions). Finally, the parameterization scheme is applied to the v ₃(t ₁ u) vibronic line intensities reported in the literature for the UCl₆ ^2- complex.