Title: First-Principles Diffusivity Ratios for Kinetic Isotope Fractionation of Water in Air
Authors: Hellmann, Robert 
Harvey, Allan H.
Language: eng
Keywords: Diffusion;First-principles calculations;Isotope fractionation;Kinetic theory;Water
Issue Date: 28-Sep-2020
Document Type: Article
Journal / Series / Working Paper (HSU): Geophysical Research Letters
Volume: 47
Issue: 18
Abstract: 
Kinetic isotope fractionation between water vapor and liquid water or ice depends on the ratio of the diffusivities of the isotopic species in air, but there is disagreement as to the values of these ratios and limited information about their temperature dependence. We use state-of-the-art intermolecular potential-energy surfaces for the water-nitrogen and water-oxygen pairs, along with the kinetic theory of molecular gases, to calculate from first principles the diffusivities of water isotopologues in air. The method has sufficient precision to produce accurate diffusivity ratios. For the HDO/H2O ratio, we find that the often used hard-sphere kinetic theory is significantly in error and confirm the 1978 experimental result of Merlivat. For the ratios involving 17O and 18O, the simple kinetic theory is relatively close to our more rigorous results. We provide diffusivity ratios from 190 K to 500 K, greatly expanding the range of temperatures for which these ratios are available.
Organization Units (connected with the publication): Thermodynamik 
ISSN: 00948276
Publisher DOI: 10.1029/2020GL089999
Appears in Collections:Publications of the HSU Researchers

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