Optically Active Vibrations of Cesium Actinide(V) Hexafluorides (CsUF 6,CsNpF 6,and CsPuF 6 )

Abstract

Normal coordinate analysis of the optically active vibrations of CsUF₆ has been made, with the assumption of an idealized structural model. On the basis of the results of this treatment, all of the observed bands so far reported have been successfully assigned to the intramolecular vibrations (UF₆⁻) as well as the optically active lattice vibrations (the motions of Cs⁺ against UF₆⁻ octahedra, abbreviated to Cs⁺—UF₆⁻). The force constants concerning U-F and Cs-F bonds have been obtained within the framework of the modified valence force field. These force constants have been transferred to predict fundamental vibrational frequencies of CsNpF₆ and CsPuF₆. It has been found that the present analysis based on a whole crystal is powerful not only for assigning the optically active lattice vibrations but also for elucidating the vibronic structures of the electronic absorption spectra obtained at low-temperature measurements.