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 for negatively charged, neutral and positively charged ions pairs, respectively. The stability of non-neutral ion pairs was studied from the structure of the anion-cation radial distribution function and other structural functions. We found that non-neutral ions pairs are stabilized by at least one counter-ion forming in this way large ionic clusters that include the hydration molecules. About 25% of the ions are included in neutral clusters formed by a minimum of four ions. The existence of these large clusters obfuscates the commonly accepted chemical reaction scheme for the interconvention of ion pairs in aqueous solutions. (C) 1999 American Institute of Physics. [S0021-9606(99)50134-7].