MONTE-CARLO SIMULATIONS OF M(+)CL(-)(H2O)(N) (M=LI NA) CLUSTERS AND THE DISSOLVING MECHANISM OF ION-PAIRS IN WATER

The dissolving mechanism of ion pairs in water was analyzed by means of radial distribution functions and the pair energies obtained from Monte Carlo simulations for M(+)Cl(-)(H2O)(n)(M=Li, Na) (n=1-8) at room temperature. The minimum-energy geometries of these clusters for n greater than or equal to 3 are water-shared ion pairs. Although the interionic distances for Na+Cl-(H2O)(n) clusters are about 0.2 Angstrom longer than those for Li+Cl-(H2O)(n) for n=1-2, this reversed at n=4. This trend originates because the water-shared structure for the Li+Cl-(H2O)(n) clusters suddenly becomes dominant at n=4, whereas for the Na+Cl-(H2O)(n) clusters, the change is more gradual.