Brillouin Measurements of Solid $n$-${\mathrm{H}}_2$ and $n$-${\mathrm{D}}_2$ to 200 kbar at Room Temperature

Using a five-pass interferometric Brillouin spectrometer, we have measured the pressure dependence of longitudinal- and transverse-acoustic velocities and refractive index of solid $n$-${\mathrm{H}}_2$ and $n$-${\mathrm{D}}_2$ at room temperature in a diamond-anvil cell up to 200 kbar. The equations of state have been determined ($55<~P<~200$ kbar: $\rho =0.0734\mathrm{}{P}^{0.334}-0.0214\mathrm{}$ for solid $n$-${\mathrm{H}}_2$, and $\rho =0.148\mathrm{}{P}^{0.334}-0.0627\mathrm{}$ for solid $n$-${\mathrm{D}}_2$, with $P$ in kbar and $\rho$ in g/${\mathrm{cm}}^3$.