Low Temperature Infrared and Raman Spectra of Lithium Borohydride

Abstract

The infrared spectra of polycrystalline LiBH4 and LiBD4 have been recorded in the region 4000–50 cm−1 at 80 °K. Raman spectra of polycrystalline samples were also recorded at this temperature. The spectra of the [Formula: see text]and [Formula: see text]lattice vibrations are consistent with symmetrically equivalent borohydride ions which lie on either general positions, two-fold axes or mirror-planes. Six lattice vibrations of translatory origin appear in the infrared spectrum of LiBH4 and a mode of libratory origin is inferred from an absorption tentatively assigned as a second overtone of a librational mode. Similar spectral results are obtained for LiBD4. The inferred librational frequencies are 418 cm–1 for the [Formula: see text] ions and 319 cm–1 for the [Formula: see text] ions.