Modified Scattering by Crystalline HCl and HBr

The values of the modified frequencies of radiation scattered by crystalline HCl and HBr at temperatures just below their freezing points are found to be 2784 cm-1 and 2480 cm-1, respectively, for the long wave edge. As with gases and liquids, the intensities of scattering are in the reverse order of intensities of absorption and the difference in the Raman shifts with change of state is too great to be attributed to Lorentz-Lorenz forces alone. The Raman band of crystalline HCl corresponds to the high frequency branch of two absorption bands found by Hettner, not to the center of the bands; on the possibility that, because of this correspondence, this branch is a Q-branch, the temperature variations of the absorption bands and the heat capacity at low temperatures can be accounted for. The non-existence of a third branch, for the R, is noted.