Raman measurements of the vibrational properties ofH2as a guest molecule in dense helium, neon, argon, and deuterium systems up to 40 GPa

The vibron peak of the ${\mathrm{H}}_2$ molecule diluted in helium, neon, argon, and deuterium host systems have been measured up to 40 GPa by Raman scattering. A blue shift of the vibron frequency is observed in all these systems. The line shape of the vibron peak is seen to be essentially due to inhomogeneous broadening. The experimental data allow a quantitative analysis of the various contributions to the vibron frequency shift: static shift, dynamical shift, and vibrational coupling. The strong differences between the vibron frequency shift of the ${\mathrm{H}}_2$ molecule embedded in solid ${\mathrm{D}}_2$ and in solid ${\mathrm{H}}_2$ are seen to result essentially from the vibrational coupling contribution. The large negative vibrational constant associated with it could be an indication of the presence of the charge-transfer interaction, already important in this density range.