The D/H fractionation factor between crystal water in copper chloride dihydrate and water vapor was calculated from Raman spectral data for single crystals of CuCl 2 2H 2 O and CuCl 2 2D 2 O based on statistical mechanics. Single crystals of CuCl 2 2H 2 O and CuCl 2 2D 2 O were synthesized from supersaturated solutions of pure H 2 O and 99.75% D 2 O at 25°C. The calculations were made for 25°C using the reduced partition function ratio (RPFR) for gaseous equilibrium, which was assumed to be valid for crystal water-water vapor system in equilibrium. Published H 2 O and D 2 O spectroscopic data were used to calculate the RPFR for water vapor molecules.The D/H fractionation factor calculated using the 22 observed vibrational frequencies was 0.936, which is less than the experimental value of 0.999 ± 0.002 by about 6%. Including estimations of the two unobserved librational frequency ratios, the calculated value became 1.014, which is closer to the experimental value, indicating that contribution of librations is not negligible, though smaller than that of the stretching and bending vibrations.

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