The specific heats of7LiH and7LiD at low temperatures

Measurements of the specific heats of 7 LiH and 7 LiD between approximately 5 and 320 K are reported. These results are believed to be accurate within 2% down to 50 K, falling to approximately 10% at the lowest temperatures. It is suggested that peaks in the otherwise smooth variations of specific heat with temperature, which occur at 11.1+or-0.2 K in the case of 7 LiH and 12.8+or-0.2K in the case of 7 LiD, may be associated with transformations to the caesium chloride structure. Using the present data in association with the limited ancillary data available from other sources, it is concluded that the Gruneisen parameters probably rise with falling temperature. Moments of the frequency distributions of the compounds have been calculated with the aid of the quasiharmonic approximation, some of which have been used to deduce properties of the vibrational frequency spectra which are consistent with infrared absorption and transmission characteristics.