The quest for ion pairing in supercritical aqueous electrolytes

We have investigated the local structure around the bromine ion in three different alkali-brominated electrolytes in both ambient and supercritical conditions by means of the Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and Molecular Dynamics (MD) simulations. Some defects of the ion-ion contributions obtained in the simulations were observed, although further measurements would be necessary to correct the potential parameters. The phase contrast method presented in this paper, based on a substitution of the ion which acts as an X-ray scatterer in the ion absorber environment, offers new opportunities for the exploration of ion-pairing in other systems or thermodynamic conditions. (C) 2002 Elsevier Science B.V. All fights reserved.