An EXAFS study of solvation and ion pairing in aqueous strontium solutionsto 300 degrees C

X-ray absorption fine structure (EXAFS) measurements on 0.10-m strontium-co ntaining solutions from 25 to 300 degrees C at saturated Vapour pressure in dicate that the first shell Sr2+-oxygen (water) bond length decreases from 2.57 to 2.52 (+/-0.01) Angstrom. Over the same temperature range, the numbe r of coordinated first shell water molecules decreases from 8 to 6. Simulat ions of a 1.35-m SrCl2 using both rigid (SPC) and flexible (BJH) water mode ls over the range from 25 to 330 degrees C also show a decrease in the Sr2-oxygen distance of 0.03 Angstrom, which is independent of density. EXAFS m easurements and molecular dynamics simulations of concentrated SrCl2, solut ions up to 270 degrees C and 300 degrees C, respectively, show the presence of polynuclear cluster molecules, further underlining the importance of su ch species in defining the solute chemistry of hydrothermal solutions in th e earth's crust. These data represent the first direct spectroscopic confir mation of solute clustering in high temperature aqueous solutions of alkali metal or alkali earth metal salts. Copyright (C) 1999 Elsevier Science Ltd .