The ion pairing and hydration structure of Ni{sup 2+} in supercritical water at 425{degree}C determined by x-ray absorption fine structure and molecular dynamics studies

Journal Article · Sun Mar 01 04:00:00 EST 1998 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.475838· OSTI ID:580018

Wallen, S L; Palmer, B J; Fulton, J L ^[1]

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1. Environmental and Health Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

The ion pairing structure of Ni(Br){sub 2} solutions (0.2 and 0.4 molal) under supercritical conditions was determined using x-ray absorption fine structure (XAFS) spectroscopy. These first measurements of the average bulk structure show that approximately one Br{sup {minus}} counterion is associated with each Ni{sup 2+}. The Ni{sup 2+}-to-Br{sup {minus}} distance of 2.40 {Angstrom} is very accurately determined and the strength of this interaction, as indicated by the Debye{endash}Waller factor ({sigma}{sup 2}=0.009{Angstrom}{sup 2}), shows that the bromine anion is very tightly bound to the nickel cation under these supercritical conditions. In addition to the onset of ion pairing interactions, there is also a dramatic transition in the hydration structure. Results show a loss of about 50{percent} of the waters in the first shell upon going from ambient to a hydrothermal condition of 425{degree}C and 690 bar. Finally, we use molecular dynamics simulations with refined intermolecular potentials to directly calculate XAFS spectra that are shown to quantitatively reproduce the experimental results for the ion pair and hydration structure. {copyright} {ital 1998 American Institute of Physics.}

• OSTI ID: 580018
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 10 Vol. 108; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
DEBYE-WALLER FACTOR
HYDRATION
ION PAIRS
MOLECULAR DYNAMICS METHOD
NICKEL IONS
SOLVATION
SUPERCRITICAL STATE
TEMPERATURE RANGE 0400-1000 K
WATER
X-RAY SPECTROSCOPY