Vibrational property study of SrGa₂H₂ and BaGa ₂H₂ by inelastic neutron scattering and first principles calculations

Vibrational properties of the gallium hydrides SrGa₂H ₂ and BaGa₂H₂ have been investigated by means of inelastic neutron scattering (INS) and first-principles calculations. The compounds contain Ga-H units being part of a two-dimensional polyanionic layer, [(GaH)(GaH)]^2-. The INS spectra are composed of dispersed internal Ga-H bending and stretching modes at frequencies above 600 cm^-1 and external lattice modes at frequencies below 220 cm^-1. Frequencies of the internal modes are not susceptible to the metal countercation, indicating a strong integrity of the polyanionic layer as a building unit in the structures of SrGa₂H₂ and BaGa₂H₂. The Ga-H stretching modes have frequencies between 1200 and 1400 cm^-1, which is very low compared to molecular gallium hydrides. The weak Ga-H bond in SrGa₂H₂ and BaGa₂H₂ is balanced by Sr(Ba)-H interactions.