Vibration Spectra of the Orthorhombic Alkaline-Earth Hydrides by the Inelastic Scattering of Cold Neutrons and by Infrared Transmission Measurements

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Abstract
The vibration spectra of the orthorhombic alkaline-earth hydrides have been investigated by measuring the energy distribution of cold neutrons which have been scattered inelastically from polycrystalline samples. In each case the measured spectrum consists of a band or bands primarily due to the metal atom vibrations (below ∼300 cm−1) and two broad optical hydrogen vibration bands (above ∼300 cm−1) presumably caused by hydrogen occupying two different sites in the metal lattice. An approximate frequency distribution has been derived for each hydride sample. The optical bands are peaked at 1050 and 720 cm−1 for YbH2, at 1010 and 690 cm−1 for CaH2, at 940 and 600 cm−1 for SrH2, and at 810 and 560 cm−1 for BaH2. Splitting and fine structure of the optical peaks have been observed and have been attributed to the asymmetry of the hydrogen sites in the metal lattice. Infrared transmission measurements on the same compounds are in good agreement with the neutron results. Additional splitting of the optical peaks have been observed in the infrared.