Quantum and Classical Orientational Ordering in Solid Hydrogen

TL;DR

This paper provides a unified theoretical framework for understanding orientational ordering in different phases of solid hydrogen, explaining spectroscopic observations and the nature of molecular and angular momentum ordering.

Contribution

It introduces a unified view of orientational ordering in solid hydrogen phases, linking molecular and angular momentum orderings to spectroscopic phenomena.

Findings

Quantitative explanation of vibron softening.

Correlation between effective charge and vibrational frequency shifts.

Linear relationship between order parameter and spectroscopic quantities.

Abstract

We present a unified view of orientational ordering in phases I, II, and III of solid hydrogen. Phases II and III are orientationally ordered, while the ordering objects in phase II are angular momenta of rotating molecules, and in phase III the molecules themselves. This concept provides quantitative explanation of the vibron softening, libron and roton spectra, and increase of the IR vibron oscillator strength in phase III. The temperature dependence of the effective charge parallels the frequency shifts of the IR and Raman vibrons. All three quantities are linear in the order parameter.