Figure 1: (Inset) The face-centered-cubic (fcc) based structure of the newly discovered compound ${\text{SiH}}_4({\text{H}}_2{)}_2$, in which 8 out of 9 atoms are hydrogen. The blue spheres indicate ${\text{SiH}}_4$ units (which may not have definite orientations) and the red spheres represent ${\text{H}}_2$ pairs (with also as yet unknown orientational physics). (Raman spectrum, right) ${\text{SiH}}_4({\text{H}}_2{)}_2$ at $8\text{GPa}$ and an average electron density $50\%$ greater than that of silane shows excitations characteristic of molecular hydrogen (${\text{H}}_2$) and plausibly connected with the placement of the ${\text{H}}_2$ pairs. (Spectrum, left) The deuterated system ${\text{SiH}}_4({\text{D}}_2{)}_2$ again shows excitations characteristic of the ${\text{D}}_2$ molecule. (Spectrum, middle) The presence of the mixed isotope pair $\text{HD}$ means that there is time dependent migration of $\text{H}$ from the blue regions into the red regions (and $\text{D}$ can be migrated into the blue regions).