Key words: Fractionation of hydrogen isotopes, Aqueous lithium chloride solution. Hydrophobic platinum catalyst, Dependence of D/H fractionation on molality, Comparison of hydrogen and oxygen isotope effects. Introduction

The D/H ratio of hydrogen gas in equilibrium with water vapor over aqueous lithium chloride solutions was measured at 25 °C, using a hydrophobic platinum catalyst. Experimental details are described. The hydrogen isotope effect between the solution and pure water depends linearly on the LiCl concentration up to ca. 12 m, and at higher concentrations a marked deviation from linearity takes place, as was also observed for the oxygen isotope effect measured by Bopp et al. On the basis of these hydrogen and oxygen isotope effects it is concluded that H2lsO is enriched in the water molecules coordinated to Li+ ions and HDieO is enriched in the free water molecules of the solution. The observed deviation from linearity for concentrations higher than ca. 12m is interpreted in terms of structural changes in the hydration sphere of the Li+ ions.