LATTICE VIBRATION-SPECTRA .22. INFRARED AND RAMAN-SPECTRA OF STRONTIUM CHLORIDE DIHYDRATE, SRCL2.2H2O AND SRCL2.2(H,D)2O

The infrared absorption and Raman spectra of SrCl2·2H2O powder as well as SrCl2·2D2O, and partially deuterated and isotopically dilute samples, have been recorded in the range from 30 to 4000 cm−1 at 95 and 295 K and analysed with regard to the strongly asymmetric force field in the H2O molecules. This is shown by an unusually large splitting of the OH and OD stretching fundamentals of the HDO molecules: 3426 and 3243 cm−1 and 2534 and 2408 cm−1 respectively at 95 K. Uncoupled OD stretching frequencies of SrCl2·6H2O and SrCl2·H2O are also presented. In SrCl2·2H2O both a relatively strong and a weak hydrogen bond to chloride ions are present; these are essentially straight. The spectra of SrCl2·2H2O exhibit the following characteristics: (1) no intramolecular coupling of the OH stretching vibrations; (2) very large Fermi resonance of νOH and 2δ H 2O; (3) the same high intensity of H2O twisting librations in the infrared spectra as for wagging and rocking modes; (4) splitting of the librational fundamentals of the HDO molecules, as large as 100 cm−1, caused by different structural arrangements of the H and D atoms in the asymmetric H2O molecules; and (5) strong intermolecular coupling of bending and librational fundamentals, which results in correlation splittings up to 75 cm−1. Possibilities of assigning the librational modes of H2O molecules which are in an asymmetric force field are discussed. Copyright © 1979 Heyden & Son Ltd.