AN X-RAY-ABSORPTION (EXAFS) SPECTROSCOPIC STUDY OF AQUATED AG-DEGREES-C( IN HYDROTHERMAL SOLUTIONS TO 350)

The first direct measurements over a range of temperatures from 25-350 degrees C are reported for cation-oxygen (water) distances in aqueous solutions at equilibrium saturated vapour pressures. The silver-oxyge n (first shell water) bond lengths in AgNO3 and AgClO4 solutions were obtained using extended X-ray absorption fine structure (EXAFS) measur ements on the silver K-edge. At 25 degrees C and 1 bar, the Ag+ ion is coordinated by four inner sphere water ligands with an average silver -oxygen distance of 2.32 (+/-0.01) Angstrom. With increasing temperatu re to 350 degrees C, the silver-oxygen (H2O) bond length decreases by about 0.10 (+/-0.01) Angstrom and the coordination number decreases fr om 4 to similar to 3. The Debye-Waller factors remain approximately co nstant with increasing temperature. Silver-nitrate ion pairing (as AgN O30) was observed only at 200 and 300 degrees C in an 0.10 AgNO3/3.00 m HNO3 solution for which the silver-nitrogen (nitrate) distances of 3 .24 and 3.27 Angstrom, respectively, were obtained.