Isotropic and anisotropic Raman scattering from molten alkali-metal fluorides

Isotropic and anisotropic Raman scattering spectra of molten LiF, KF, and C sF and of molten mixtures KF-LiF and CsF-LiF have been measured at temperat ures up to 900 degrees C. For the single component molten salts the reduced representations of the spectra show one anisotropic and two isotropic band s. The data are discussed and interpreted in terms of interaction induced p olarisability fluctuations. The dipole-induced-dipole interactions predomin ate the CsF anisotropic spectra while polarisability fluctuation due to ani on-cation overlap interactions give rise to the strong isotropic scattering in LiF. The anisotropic Raman scattering intensity from the binary mixture s appears to be a superposition of the corresponding intensities of the com ponent salts, while the isotropic spectra are characterised by a new band a t similar to 325 cm(-1) which is common for both the KF-LiF and the CsF-LiF binaries. The origin of this band is attributed to the formation of long l ived associated configurations of the type (LiFx)A, (A=K, Cs) in the melt m ixtures.