  Through a series of Raman spectroscopy studies, we investigate the behaviour
of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across wide
ranging concentrations. We find that there is no evidence of chemical
association, miscibility, nor any demixing of hydrogen and helium in the solid
state up to pressures of 250 GPa at 300 K. In contrast, we observe the
formation of concentration-dependent N$_2$-H$_2$ van der Waals solids, which
react to form N-H bonded compounds above 50 GPa. Through this combined study,
we can demonstrate that the recently claimed chemical association of H$_2$-He
can be attributed to significant N$_2$ contamination and subsequent formation
of N$_2$-H$_2$ compounds.
