The infrared spectra of polycrystalline LiBH, and LiBD, have been recorded in the region 4000-50 cm-' at 80 OK. Raman spectra of polycrystalline samples were also recorded at this temperature. The spectra of the BH4-and BD,-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 LiBH, and a mode of libratory origin is inferred from an absorption tentatively assigned as a second overtone of a librational mode.

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Using both infrared and laser Raman techniques the low temperature vibrational spectra of KBH,, KBD,, NaBH,, and NaBD, have been recorded. The spectra of the external lattice vibrations are consistent with the following borohydride ion site symmetries: Td for potassium borohydride and D,, for sodium borohydride. Translational frequencies are assigned and librational frequencies are inferred from absorptions tentatively assigned as second overtones. Comparison of the low and high temperature vibrational spectra suggests the following disorder-order phase changes: Oh5 + TdZ for potassium borohydride and Oh5 3 DZd9 for sodium borohydride.En utilisant les techniques de I'infrarouge et du laser Raman, les spectres de vibration a basse temperature de KBH,, KBD,, NaBH, et NaBD, ont ete enregistres. Les spectres de vibration du reseau externe sont consistants avec les sites de symetrie suivants pour les ions borohydrures: Td pour le borohydrure de potassium et D2, pour le borohydrure de sodium. Les frequences de translation sont assignees et les frequences de vibration deduites a partir des absorptions qu'il est possible d'assigner aux deuxiemes harmoniques. La colllparaison des spectres de vibration a basse et haute temperature suggere les changements de phase desordre-ordre suivants: Oh5 + TdZ pour le borohydrure de potassium et Oh5 + D2,' pour le borohydrure de sodium.

The infrared absorp~ion of formaldehyde in both the polycrystalline and the 111onomeric form has been measured a t 4' I<. In the latter case the molec~~les were suspended in an inert matrix of Ar or Nz. The fine structure of the matrix spectra is discussed from the point of view of rotation of the monomers but this interpretation is ruled out in favor of one based on multiple trapping sites in the matrix.

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