Observation of {\Delta}J=0 Rotational Excitation in Dense Hydrogens

TL;DR

This study reports the observation of a unique {}J=0 rotational excitation in dense hydrogen isotopes, which remains isotope-independent and exhibits complex behavior across different phases and pressures.

Contribution

It is the first to identify and characterize the }J=0 rotational excitation in dense hydrogen, revealing its independence from isotope mass and complex phase-dependent behavior.

Findings

{}J=0 mode appears in dense H2 and D2 with phase-dependent shifts.

The excitation frequency is isotope-independent, unlike typical rotational modes.

Splitting of the mode in phase II indicates complex molecular environments.

Abstract

Raman measurements performed on dense H2, D2 and H2+D2 in a wide pressure-temperature range reveal the presence of the {\Delta}J=0 rotational excitation. In the gas/fluid state this excitation has zero Raman shift, but in the solid, the crystal field drive s it away from the zero value e.g. 75 cm-1 at around 50 GPa and 10 K for both isotopes and their mixture. In the case of deuterium, the {\Delta}J=0 mode splits upon entering phase II suggesting a very complex molecular environment of the broken symmetry phase (BSP). In the fluid state and phases I and II the frequencies (energies) of the {\Delta}J=0 transition for H2 and D2 do not scale either as rotational (by factor of 2) nor vibrational (by square 2) modes and appear to be completely isotope independent. This independence on mass marks this transition as unique and a fundamentally different type of excitation from the commonly considered harmonic oscillator and quantum rotor.