Gitterschwingungsspektren. XIX—infrarot‐ und Ramanspektren von BaBr₂·2H₂O und BaBr₂·2D₂O

Abstract

Abstract Low temperature infrared and Raman spectra of polycrystalline BaBr 2 ·2H 2 O at different degrees of deuteration are studied in the frequency range from 4000 to 30 cm −1 . The single peaks observed for the bending fundamentals of isotopically dilute H 2 O and D 2 O show that the molecules of the water of crystallization are equivalent, as required by Bang's structure determination. The singlets observed for the three fundamentals of isotopically dilute HDO show that there is a symmetric force field in the water molecules which is not predicted from the structure determination. In BaBr 2 ·2H 2 O weak hydrogen bonds to the bromine ions are present which are largely bent. From the shift of the stretching modes relative to the frequencies of free water the hydrogen bond enthalpy was found to be 20 kJ. The temperature shifts of all the stretching modes are positive, which is not in agreement with Falk's results on bent hydrogen bridges. The internal modes and the twisting libration of the water molecules show an unusual large correlation splitting due to intermolecular coupling of the vibrations of the two water molecules in the 2Br − ·2H 2 O structure unit.