The vibration spectrum of lithium fluoride and the evaluation of its specific heat

Summary

The records of the transmission percentages of infra-red radiation by thin plates of lithium fluoride enable the frequency of the vibration of the lithium and fluorine nuclei against each other in opposite phases to be precisely determined. The frequencies of the four inactive modes can be computed therefrom. Four other modes are active as overtones and their frequencies can be directly determined from the records. A theoretical computation of the specific heat of lithium fluoride on the basis of the spectroscopic data alone thus becomes possible. A very satisfactory agreement emerges between the theoretically computed and experimentally determined values of the atomic heats of the crystal over the entire range of temperatures from absolute zero to 500° K.