Single-crystal Raman spectra at 77 K in the 80-3500 cm−1 range are reported for CaCl2·6H2O(D2O) and SrCl2·6H2O(D2O). Excellent fits to the experimental spectra were obtained with the use of a thirteen-parameter force field based on the rigid-on model supplemented with stretching and bending force constants for the water molecules and selected short-range force constants in the Bravais cell. The libration frequencies of both the bridging (four-coordinate) and the terminal (three-coordinate) water molecules were found to depend almost exclusively on their partial charges.
W. Kevin Winnett and Charles P. Nash, "Rigid-Ion-Model Treatment of the Vibrational Spectra of Calcium and Strontium Chloride Hexahydrate Crystals," Appl. Spectrosc. 42, 60-64 (1988)