Hydration of the bromine ion in a supercritical 1 : 1 aqueous electrolyte - art. no. 134202

Extended x-ray absorption fine structure (EXAFS) measurements have been car ried out on 0.2 molal RbBr aqueous solutions at the Br-K edge from ambient to supercritical (SC) conditions, i.e., from density rho = 1.02 to rho = 0. 42 g cm(-3) and temperatures from 35 to 450 degreesC. Molecular dynamics (M D) simulations have been used to calculate EXAFS (MDXAS) spectra in ambient and SC conditions. The model used leads to an excellent agreement of the E XAFS spectra computed from the generated configurations with the experiment al ones. Both show, in particular, a strong persistence of the Br- ion firs t shell coordination at supercritical conditions. This result is in clear c ontrast with results found in the literature. The disagreement is interpret ed as a consequence of a fundamental limitation of the use of the classic E XAFS perturbative techniques on such severely disordered fluids characteriz ed by weak interatomic interactions and large local density concentration f luctuations.