Large ionic clusters in concentrated aqueous NaCl solution

The stability of the local structure of aqueous 1.0 M NaCl solution at 293 K was investigated by molecular dynamics simulations. The mean and maximum life-times of the ion pairs were determined to be 0.13, 0.14 and 0.27 ps fo r negatively charged, neutral and positively charged ions pairs, respective ly. The stability of non-neutral ion pairs was studied from the structure o f the anion-cation radial distribution function and other structural functi ons. We found that non-neutral ions pairs are stabilized by at least one co unter-ion forming in this way large ionic clusters that include the hydrati on molecules. About 25% of the ions are included in neutral clusters formed by a minimum of four ions. The existence of these large clusters obfuscate s the commonly accepted chemical reaction scheme for the interconvention of ion pairs in aqueous solutions. (C) 1999 American Institute of Physics. [S 0021-9606(99)50134-7].