Hydration of the bromine ion in a supercritical 1:1 aqueous electrolyte

Extended x-ray absorption fine structure (EXAFS) measurements have been carried out on 0. 2 molal RbBr aqueous solutions at the Br-K edge from ambient to supercritical (SC) conditions, i. e. , from density =1. 02 to =0. 42gcm^-3 and temperatures from 35 to 450^. Molecular dynamics (MD) simulations have been used to calculate EXAFS (MDXAS) spectra in ambient and SC conditions. The model used leads to an excellent agreement of the EXAFS spectra computed from the generated configurations with the experimental ones. Both show, in particular, a strong persistence of the Br^-ion first shell coordination at supercritical conditions. This result is in clear contrast with results found in the literature. The disagreement is interpreted as a consequence of a fundamental limitation of the use of the classic EXAFS perturbative techniques on such severely disordered fluids characterized by weak interatomic interactions and large local density concentration fluctuations.