Vapor Pressures of Tritium Oxide and Deuterium Oxide. Interpretation of the Isotope Effects

Jones, Wesley M.

doi:10.1063/1.1667903

Measurements are reported on the difference in vapor pressures of H₂O and T₂O ( − 9°‐114°C) and of H₂O and D₂O (4°‐114°C). The relative vapor pressures of the pure liquids are represented by $\ln (p H_{2} O / p T_{2} O {) = ( − 103.87 ± 0.57) / T + (46 480 ± 210) / T}^{2}$ and $\ln (p H_{2} O / p D_{2} O {) = ( − 70.87 ± 0.43) / T + (33 630 ± 160) / T}^{2}$ ⁠. The normal boiling points of T₂O and D₂O are 101.51° and 101.42°C. Isotopic differences in heats of vaporization are given from 10° to 110°C. Triple‐point temperatures and pressures are summarized. Vapor‐pressure crossover temperatures are: D₂O–T₂O, 116.2° ± 0.5°C; H₂O–T₂O, 190 ± 10°C (estimated); H₂O–D₂O, 220.7° ± 0.1°C (literature).

The data were also fitted to extensions of the above equations which included correction terms based on Bigeleisen's formulation of the vapor‐pressure isotope effect and a uniformist harmonic‐oscillator model of water. Estimates of the coefficients of $1 / T$ and ${1 / T}^{2}$ for H₂O–D₂O from Raman spectra are in reasonable agreement with coefficients from this data fit. Ratios of corresponding coefficients for H₂O–D₂O and H₂O–T₂O agree with theory.

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