Vibration Spectra of Yttrium and Uranium Hydrides by the Inelastic Scattering of Cold Neutrons

Abstract

The vibration spectra of the hydrides and deuterides of yttrium and uranium have been investigated by the energy-gain scattering of cold neutrons. The measured spectra are all split into two bands, one at higher energies, due to the optical hydrogen vibrations, and another at lower energies due to metal—atom vibrations. Values have been obtained for the peaks and widths of the single optical hydrogen bands in YH2, YD2, UH3, and UD3 by the calculation of approximate frequency distributions from the observed neutron time-of-flight spectra. The derived peak frequencies in cm−1 are: YH2, 1025±60; YD2, 725±40; UH3, 970±60; UD3, 710±40. The relative width at half-maximum for the hydrogen band in UH3 is about double that for YH2. The distribution of hydrogen vibrations in hexagonal YH3 and YD3 is considerably broader, and exhibits several maxima, due to hydrogens at different sites in the lattice. The hydrogen modes in all the compounds can be correlated reasonably well with the known crystal structures. The results are in satisfactory agreement with hydrogen frequencies calculated previously from heat-capacity data.