Quantum Reorientational Excitations in the Raman Spectrum of Hydrogen
Abstract
Low-frequency Raman peaks, below 250 cm-1, are observed in hydrogen between 2-174 GPa and 13-300 K. The origin of these features is attributed to reorientational transitions (DeltaJ = 0; Q0-branch), which shift from the Rayleigh line as anisotropic intermolecular interactions lift the mJ degeneracy. This family of excitations closely follows the behavior of the S0-branches, sharing their dependence on pressure, temperature, and ortho-H2 concentration. Above 65 K, spectra corrected by the Bose-Einstein population factor reveal a broad continuum arising from populated higher J-states and increased ortho-para disorder. Upon entering phase III, where molecular rotation is inhibited, this continuum is quenched, giving way to well-established optical phonons. Below 25 K, equilibrated samples demonstrate a fine structure from isolated and pair excitations from impurity ortho-H2 molecules in a parahydrogen lattice, the latter a sensitive probe to anisotropic intermolecular interactions relevant to the quantum modeling of solid H2.
Keywords
Cite
@article{arxiv.2511.16010,
title = {Quantum Reorientational Excitations in the Raman Spectrum of Hydrogen},
author = {Philip Dalladay-Simpson and Eric Edmund and Huixin Hu and Mario Santoro and Federico Aiace Gorelli},
journal= {arXiv preprint arXiv:2511.16010},
year = {2025}
}
Comments
8 pages, 6 figures