The Raman spectrum of an oriented single crystal of CaSO4∙2H2O has been recorded from 20 to 3600 cm−1 at 300 °K and 77 °K using polarized laser excitation. The symmetries of the observed Raman lines have been determined and the spectrum has been analyzed in terms of external lattice vibrations, internal vibrations of the SO4 and H2O groups, hydrogen bond vibrations, and combinations of these vibrations. The translatory and rotatory lattice modes of the H2O molecules have been identified and the latter have been correlated with the principal moments of inertia of the water molecule. The hydrogen bond vibration was observed at 210 cm−1 at 300 °K and 217 cm−1 at 77 °K. The assignments of the internal modes were found to be consistent with the results of previous workers. Several overtone and combination frequencies were observed, especially in the region of the ν1 and ν3 vibrations of H2O.

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The infrared and Raman spectra of polycrystalline samples of Be1 3 , BBr 3 , and BI3 at 80 and 18 K have been recorded. In the intramolecular region, isotopic and crystalline field splittings are observed in substantial agreement with earlier work. In the lattice region, no far-infrared absorption has been found, in accordance with predictions from a group theoretical analysis based on the known structures of these isomorphous crystals. The three observed Raman lattice modes are assigned according to these procedures, and their frequencies are compared with those derived from calculations of the lattice statics and dynamics of these crystals. It is found that a four-parameter model using the rigid molecule approximation and simple pairwise interaction potentials between X-X and B-X atoms is capable of giving acceptable values of the zone center frequencies while simultaneously satisfying the static equilibrium conditions for these crystals.

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