Diffusivity fractionations of H216O/H217O and H216O/H218O in air and their implications for isotope hydrology

We have determined the isotope effects of O-17 and O-18 substitution of O-16 in H2O on molecular diffusivities of water vapor in air by the use of evaporation experiments. The derived diffusion fractionation coefficients (17)alpha(diff) and (18)alpha(diff) are 1.0146 +/- 0.0002 and 1.0283 +/- 0.0003, respectively. We also determined, for the first time, the ratio In((17)alpha(diff))/In((18)alpha(diff)) as 0.5185 +/- 0.0002. This ratio, which is in excellent agreement with the theoretical value of 0.5184, is significantly smaller than the ratio in vapor-liquid equilibrium (0.529). We show how this new experimental information gives rise to O-17 excess in meteoric water, and how it can be applied in isotope hydrology. Copyright (c) 2007 John Wiley & Sons, Ltd.