Raman scattering in hcp rare gas solids under pressure

Abstract

We present Raman measurements of hcp rare gas solids (RGSs) at megabar pressures together with lattice dynamics calculations. The ${E}_{2g}$ phonon was measured in Xe up to metallization near 135 GPa and in Ar up to 58 GPa. A comparative analysis of first-principles and semiempirical calculations shows that three-body forces contribute to the energetics at low pressures and that at volume compressions greater than $\ensuremath{\sim}2.6$ higher-order many-body forces become important. The distinct behavior of He under pressure relative to that of the rest of the RGS family is discussed.