HYDROXIDE ION IN LIQUID WATER - STRUCTURE, ENERGETICS, AND PROTON-TRANSFER USING A MIXED DISCRETE-CONTINUUM AB-INITIO MODEL

The hydroxide solvation process is studied by means of discrete-continuum and discrete models. The structure and energetics are analyzed. Calculations have been carried out at the HF/6-31+G* and MP2/6-31+G*//HF/6-31+G'' levels. In agreement with experimental studies, the first solvation shell is shown to be composed of three water molecules in a branched structure. Both discrete and discrete-continuum models predict similar geometric changes in the first shell upon solvation. Discrepancies in these changes between both models are related to the noninclusion of charge transfer beyond the cavity. In spite of some deficiencies, the discrete-continuum model is shown to be good enough to predict solvation free energies of charged species in agreement with experimental values. Finally, a possible mechanism for hydroxide migration in liquid water is discussed. It implies proton transfer from a water molecule of the first solvation shell to the hydroxide anion. Second solvation shell water molecules play an important role in this process.