A Fresh Look at a Well-Known Solid: Structure, Vibrational Spectra, and Formation Energy of NaNH2

Sodium amide (NaNH2) in its alpha form isa commoncompound that has recently seen renewed interest, mainly for its potentialuse as a solid-state hydrogen storage material. In this work, we presenta synergic theoretical and experimental characterization of the compound,including novel measured and simulated vibrational spectra (IR andRaman) and X-ray diffraction patterns. We put forward the hypothesisof a low-temperature symmetry breaking of the structure to space group C2/c, while space group Fddd is commonly reported in the literature and experimentally founddown to 80 K. Additionally, we report a theoretical estimate of theheat of formation of sodium amide from ammonia to be equal to -12.2kcal/mol at ambient conditions.