Vibrational Raman spectra of hydrogen and deuterium mixtures at high pressures

Room-temperature mixtures of hydrogen and deuterium in the fluid and solid states have been studied to 60.5 GPa (605 kbar). Raman-scattering measurements performed on these mixtures showed substantial deviations in the pressure dependence of the vibrational stretching frequencies of the molecules as compared with spectra from monomolecular hydrogenic samples. Most notably, the maximum in the vibron-frequency shift occurs at higher pressures. These observations are explained in terms of the coupling interaction between identical molecules, the same interaction that governs the ${\mathit{Q}}_1$(0) and ${\mathit{Q}}_1$(1) frequency shifts in ortho-para hydrogen mixtures.