Isotopic fractionation processes will be studied theoretically for a number of geochemically important elements, including Boron (B), Oxygen (O), Sulfur (S), Copper (Cu), Molybdenum (Mo). These studies will employ state-of-the-art quantum chemical methods and will carefully assess the agreement of calculation and experiment, focusing both upon the ratios of vibrational frequencies for different isotopomers and the available experimental data on isotopic fractionation equilibria. We will employ supermolecule or nanocluster models for aqueous species and test for convergence in both accuracy of the quantum chemical method and size of the cluster. The energies of chemical reactions involving these species will also be calculated, since chemical equilibria must be considered along with isotopic equilibria to determine the extent of isotopic fractionation. Our recent successes in calculating and interpreting B and Mo isotopic fractionations (Liu and Tossell, 2005; Tossell, 2005c) will be used as foundations for the proposed work. We will also extend our studies both to other elements (O, S and Cu) and to conditions of high T and P, in the supercritical regime, just as we have recently done for the oligomerization reactions of silicic acid (Tossell, 2005a). We will also study isotopic fractionation in heterogeneous processes involving adsorption of borate species onto carbonate mineral surfaces and the interaction of borosilicate minerals with B-containing glasses or melts. For each element considered we will try to semiquantitatively interpret the isotopic fractionation equilibria using bond strength arguments or by correlation with other calculated properties, such as NMR shifts. Intellectual merit: More accurate isotopic fractionation equilibrium constants and reaction equilibrium constants will be calculated and the identity of the chemical species involved in the fractionation processes will be clarified. Information on such processes will also be extended to new geochemical regimes of T and P and to heterogeneous systems. Finally, relationships between isotopic fractionation and mineral structural and spectroscopic properties will be established. Broader impacts: Computational science will be extended into new areas of geosciences. The need for combined experimental and theoretical studies in geosciences will again be demonstrated and the explanatory power of stable isotope geochemistry increased. Graduate students and postdocs will be trained in both geochemistry and computational chemistry. Standard procedures for calculating isotopic fractionation constants, supported by readily available software, will be disseminated to all researchers in the field.
