XAFS measurements of Rb-O bonds in ambient and supercritical water

M. Newville, J. L. Fulton, D. M. Pfund, S. L. Wallen, E. A. Stern, Y. Ma

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Abstract

XAFS measurements and analyses of Rb+ ions in 0.5 molal RbBr at ambient and several supercritical (P > Pc = 220 bar, T > Tc = 374°C) conditions are presented. The first coordination shell of Rb+ ion is seen to be dominated by oxygen from nearby water molecules. Upon going from ambient to supercritical conditions, the Rb-O coordination number decreases significantly, and the Rb-O distance decreases by ∼ 0.10 Å relative to the ambient Rb-O distance (∼ 2.93 Å). Although ion pairing has been predicted for supercritical conditions (due in part to a substantial decrease of the dielectric constant at the critical point), and has been observed with XAFS in other aqueous solutions, we see no direct evidence of pairing of Br- with Rb+ in our measurements.

Original languageEnglish
Pages (from-to)C2-1007-C2-1008
JournalJournal De Physique. IV : JP
Volume7
Issue number2 Part 2
DOIs
StatePublished - 1997
Externally publishedYes

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