Communications: The fractional Stokes-Einstein equation: application to water.
Previously [K. R. Harris, J. Chem. Phys. 131, 054503 (2009)] it was shown that both real and model liquids fit the fractional form of the Stokes-Einstein relation [fractional Stokes-Einstein (FSE)] over extended ranges of temperature and density. For example, the self-diffusion coefficient and viscosity of the Lennard-Jones fluid fit the relation (D/T) = (1/eta)(t) with t = (0.921+/-0.003) and a range of molecular and ionic liquids for which high pressure data are available behave similarly, with t values between 0.79 and 1. At atmospheric pressure, normal and heavy water were also found to fit FSE from 238 to 363 K and from 242 to 328 K, respectively, but with distinct transitions in the supercooled region at about 258 and 265 K, respectively, from t = 0.94 (high temperature) to 0.67 (low temperature). Here the recent self-diffusion data of Yoshida et al. [J. Chem. Phys. 129, 214501 (2008)] for the saturation line are used to extend the high temperature fit to FSE to 623 K for both isotopomers. The FSE transition temperature in bulk water can be contrasted with much lower values reported in the literature for confined water.
Harris
Kenneth R
KR
School of Physical, Environmental and Mathematical Sciences, University College, University of New South Wales, Australian Defence Force Academy, Canberra, ACT 2600, Australia. k.harris@adfa.edu.au