Evidences for optic modes in molten NaI

About 30 years ago molecular dynamics simulations showed propagating charge fluctuations in a molten salt similar to solid state optic phonons. We have investigated molten sodium iodide by inelastic X-ray scattering at the synchrotron SPring-8, Japan. Additionally to acoustic-like excitations, inelastic intensity was found in the spectra at positions which coincide with predictions from MD-simulations for optic modes.