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 {\it 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.
@article{arxiv.1801.04196,
title = {Detection of collective optic excitations in molten NaI},
author = {S. Hosokawa and M. Inui and T. Bryk and I. Mryglod and W. -C. Pilgrim and Y. Kajihara and K. Matsuda and Y. Ohmasa and S. Tsutsui},
journal= {arXiv preprint arXiv:1801.04196},
year = {2019}
}