Detection of collective optic excitations in molten NaI

Abstract

High-resolution inelastic x-ray scattering measurements were carried out on molten NaI near the melting point at 680°C at SPring-8. Small and damped indications of longitudinal optic excitation modes were observed on the tails of the longitudinal acoustic modes at small momentum transfers, Q∼5 nm^{-1}. The measured spectra are in good agreement, in both frequency and linewidth, with ab initio molecular dynamics (MD) simulations but not classical MD simulations. The observation of these modes at small Q and a good agreement with the simulation permits clear identification of these as collective optic modes with well defined phasing between different ionic motions.

Keywords

• inelastic x-ray scattering
• molten salt
• optic excitations
• ab initio simulations