Optically Active Vibrations of Lithium and α-Sodium Uranium Hexafluorides (LiUF 6 and α-NaUF 6 )

Abstract

Normal coordinate analyses of the optically active vibrations of LiUF₆ and α-NaUF₆ have 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 [M⁺(Li, Na) … UF₆⁻]. The force constants concerning U-F and M-F bonds have been obtained within the framework of the modified valence force field. 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 structure of the electronic absorption spectra obtained at low-temperature measurements.