The observation of longitudinal optic vibrational modes in molten rubidium chloride

The authors have measured the inelastic scattering spectra of two samples of molten RbCl with different isotopic chlorine compositions using the IN6 time-of-flight spectrometer at the Institut Laue-Langevin in Grenoble. By a first-order subtraction they have substantially separated the contributions from the longitudinal mass-mass (acoustic-type mode) and charge-charge (optic-type mode) current-current correlation functions. Over the accessible Q range these have the form of single broad peaks, with the mass peaks being approximately twice as wide and half as high as the charge peaks. A quasidispersion curve has been derived from the peak positions and comparisons have been made with the low-temperature crystalline state.