Raman spectrum of HDO in rare earth perchlorate solutions

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Abstract
Raman data were obtained of the OD stretching vibrations of HDO at 23.0±0.5°C in nine or 10 concentrations of aqueous La(ClO4)3, Gd(ClO4)3, and Lu(ClO4)3 solutions in which the total water content was about 5 mole% D2O. The rare earth salt concentration was varied from approximately 0.25 to 4.0 or 4.5m. A differential analysis technique, previously reported, was used to identify and to correlate changes in the frequency distribution of the OD band with water molecules that are being diversely affected by the rare earth salt ions. At least four general types of water molecules are discernible in solution at various salt concentrations. In dilute solutions, cation‐affected, anion‐affected, and unaffected free water molecules are clearly distinguished, whereas at high perchlorate salt concentrations water molecules associated with ion pairs are also identified. In addition, results are presented to indicate that the La3+ cation affects water somewhat differently than do either the Gd3+ or Lu3+ cations, and this is interpreted as reflecting a difference in the hydration number between these RE3+ cations.