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.