D/H fractionation factor between water vapor and crystal water of copper chloride dihydrate: Statistical mechanical approach based on Raman spectra

Abstract

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 CuCl22H2O and CuCl22D2O based on statistical mechanics. Single crystals of CuCl22H2O and CuCl22D2O were synthesized from supersaturated solutions of pure H2O and 99.75% D2O 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 H2O and D2O 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.