High pressure study of sodium trihydride.

The reactivity between NaH and H has been investigated through a series of high-temperature experiments up to pressures of 78 GPa in diamond anvil cells combined with calculations. Powder X-ray diffraction measurements show that heating NaH in an excess of H to temperatures around 2000 K above 27 GPa yields sodium trihydride (NaH), which adopts an orthorhombic structure (space group ). Raman spectroscopy measurements indicate that NaH hosts quasi-molecular hydrogen () within a NaH lattice, with the stretching mode downshifted compared to pure H (Δ ∼-120 cm at 50 GPa).