The self-diffusion of aquated metal cations has been shown via experiments and molecular dynamics (MD) simulations to be a viable mechanism for fractionating isotopes of Li+ and K+. Isotopic self-diffusivities follow an inverse power-law dependence on isotopic mass: lighter isotopes diffuse faster than heavier isotopes of the same species1,2. In order to better elucidate the role of the solvent in this process, we performed a series of MD simulations of Li+ and K+ in pure D2O and pure methanol at 25�C. Simulation results indicate that, as expected, cations diffuse more slowly in D2O than in pure H2O; however, the mass dependence describing fractionation for a given cation in D2O is within error of that determined for the same cation in pure H2O. Simulation results for K+ self-diffusion in methanol at 25�C indicate that heavier isotopes of K+ diffuse faster than light isotopes; results for Li+self-diffusion suggest a more complicated mass dependence. We are currently pursuing experimental verification of our simulation results.1) Richter FM, et al. (2006) Geochim. Cosmochim. Acta 70: 277�289.2) Bourg IC et al. (2010) Geochim. Cosmochim. Acta 74: 2249�2256.

Diffusion-driven isotopic fractionation of ionic species in D<sub>2</sub>O and methanol

245th National Meeting (2013)

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Diffusion-driven isotopic fractionation of ionic species in D2O and methanol

Diffusion-driven isotopic fractionation of ionic species in D₂O and methanol