Reactivity of Hydrogen-Helium and Hydrogen-Nitrogen Mixtures at High Pressures

Through a series of Raman spectroscopy studies, we investigate the behavior of hydrogen-helium and hydrogen-nitrogen mixtures at high pressure across a wide range of concentrations. We find that there is no evidence of chemical association or increased miscibility 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 reported chemical association of H_{2}-He can be attributed to significant N_{2} contamination and subsequent formation of N_{2}-H_{2} compounds.