Intermolecular coupling and fluxional behavior of hydrogen in phase IV

TL;DR

This study investigates hydrogen's phase IV using Raman and IR spectroscopy at high pressures, revealing that intermolecular coupling varies significantly between layers and increases with pressure, highlighting hydrogen's fluxional behavior.

Contribution

It provides new insights into the layer-dependent intermolecular coupling and fluxional dynamics of hydrogen in phase IV under high pressure.

Findings

Stronger intermolecular coupling in graphene-like layers compared to Br2-like layers.

Intermolecular coupling increases faster with pressure in G layers.

Hydrogen phase IV exhibits unique fluxional lattice dynamics.

Abstract

We performed Raman and infrared (IR) spectroscopy measurements of hydrogen at 295 K up to 280 GPa at an IR synchrotron facility of SSRF. To reach the highest pressure, hydrogen was loaded into toroidal diamond anvils with 40 micrometers central culet. The intermolecular coupling has been determined by concomitant measurements of the IR and Raman vibron modes. In phase IV, we find that the intermolecular coupling is much stronger in the graphene (G) like layer of elongated molecules compared to the Br2 like layer of shortened molecules and it increases with pressure much faster in the G layer compared to the Br2 layer. These heterogeneous lattice dynamical properties are unique features of highly fluxional hydrogen phase IV.