Lattice vibration spectra. XXII —infrared and Raman spectra of strontium chloride dihydrate, SrCl 2 ·2H 2 O and SrCl 2 ·2(H, D) 2 O

The infrared absorption and Raman spectra of SrCl 2 ·2H 2 O powder as well as SrCl 2 ·2D 2 O, 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 H 2 O 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 SrCl 2 ·6H 2 O and SrCl 2 ·H 2 O are also presented. In SrCl 2 ·2H 2 O both a relatively strong and a weak hydrogen bond to chloride ions are present; these are essentially straight. The spectra of SrCl 2 ·2H 2 O exhibit the following characteristics: (1) no intramolecular coupling of the OH stretching vibrations; (2) very large Fermi resonance of ν OH and 2δ   H   2 O ; (3) the same high intensity of H 2 O 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 H 2 O 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 H 2 O molecules which are in an asymmetric force field are discussed.