Hydrogen bond breaking in aqueous solutions near the critical point

The nature of water-anion bonding is examined using X-ray absorption fine s tructure spectroscopy on a Im ZnBr2/6m NaBr aqueous solution, to near criti cal conditions. Analyses show that upon heating the solution from 25 degree sC to 500 degreesC, a 63% reduction of waters occurs in the solvation shell of ZnBr42-, which is the predominant complex at all pressure-temperature c onditions investigated. A similar reduction in the hydration shell of water s in the Br- aqua ion was found. Our results indicate that the water-anion and water-water bond breaking mechanisms occurring at high temperatures are essentially the same. This is consistent with the hydration waters being w eakly hydrogen bonded to halide anions in electrolyte solutions. (C) 2001 E lsevier Science B.V. All rights reserved.