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Title: Nature of the Aqueous Hydroxide Ion Probed by X-ray AbsorptionSpectroscopy

Abstract

X-ray absorption spectra of aqueous 4 and 6 M potassium hydroxide solutions have been measured near the oxygen K edge. Upon addition of KOH to water, a new spectral feature (532.5 eV) emerges at energies well below the liquid water pre-edge feature (535 eV) and is attributed to OH{sup -} ions. In addition to spectral changes explicitly due to absorption by solvated OH- ions, calculated XA spectra indicate that first-solvation-shell water molecules exhibit an absorption spectrum that is unique from that of bulk liquid water. It is suggested that this spectral change results primarily from direct electronic perturbation of the unoccupied molecular orbitals of first-shell water molecules and only secondarily from geometric distortion of the local hydrogen bond network within the first hydration shell. Both the experimental and the calculated XA spectra indicate that the nature of the interaction between the OH{sup -} ion and the solvating water molecules is fundamentally different than the corresponding interactions of aqueous halide anions with respect to this direct orbital distortion. Analysis of the Mulliken charge populations suggests that the origin of this difference is a disparity in the charge asymmetry between the hydrogen atoms of the solvating water molecules. The charge asymmetry ismore » induced both by electric field effects due to the presence of the anion and by charge transfer from the respective ions. The computational results also indicate that the OH{sup -} ion exists with a predominately 'hyper-coordinated' solvation shell and that the OH{sup -} ion does not readily donate hydrogen bonds to the surrounding water molecules.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Director. Office of Science. Basic EnergySciences
OSTI Identifier:
917054
Report Number(s):
LBNL-62752; #341
Journal ID: ISSN 1089-5639; JPCAFH; R&D Project: 403501; BnR: KC0301020; TRN: US0804419
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A; Journal Volume: 111; Related Information: Journal Publication Date: 2007
Country of Publication:
United States
Language:
English
Subject:
75; ABSORPTION; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; ELECTRIC FIELDS; HYDROGEN; HYDROXIDES; POTASSIUM HYDROXIDES; SPECTRA; WATER

Citation Formats

Cappa, Christopher D., Smith, Jared D., Messer, Benjamin M., Cohen, Ronald C., and Saykally, Richard J. Nature of the Aqueous Hydroxide Ion Probed by X-ray AbsorptionSpectroscopy. United States: N. p., 2007. Web. doi:10.1021/jp070551c.
Cappa, Christopher D., Smith, Jared D., Messer, Benjamin M., Cohen, Ronald C., & Saykally, Richard J. Nature of the Aqueous Hydroxide Ion Probed by X-ray AbsorptionSpectroscopy. United States. doi:10.1021/jp070551c.
Cappa, Christopher D., Smith, Jared D., Messer, Benjamin M., Cohen, Ronald C., and Saykally, Richard J. Sun . "Nature of the Aqueous Hydroxide Ion Probed by X-ray AbsorptionSpectroscopy". United States. doi:10.1021/jp070551c.
@article{osti_917054,
title = {Nature of the Aqueous Hydroxide Ion Probed by X-ray AbsorptionSpectroscopy},
author = {Cappa, Christopher D. and Smith, Jared D. and Messer, Benjamin M. and Cohen, Ronald C. and Saykally, Richard J.},
abstractNote = {X-ray absorption spectra of aqueous 4 and 6 M potassium hydroxide solutions have been measured near the oxygen K edge. Upon addition of KOH to water, a new spectral feature (532.5 eV) emerges at energies well below the liquid water pre-edge feature (535 eV) and is attributed to OH{sup -} ions. In addition to spectral changes explicitly due to absorption by solvated OH- ions, calculated XA spectra indicate that first-solvation-shell water molecules exhibit an absorption spectrum that is unique from that of bulk liquid water. It is suggested that this spectral change results primarily from direct electronic perturbation of the unoccupied molecular orbitals of first-shell water molecules and only secondarily from geometric distortion of the local hydrogen bond network within the first hydration shell. Both the experimental and the calculated XA spectra indicate that the nature of the interaction between the OH{sup -} ion and the solvating water molecules is fundamentally different than the corresponding interactions of aqueous halide anions with respect to this direct orbital distortion. Analysis of the Mulliken charge populations suggests that the origin of this difference is a disparity in the charge asymmetry between the hydrogen atoms of the solvating water molecules. The charge asymmetry is induced both by electric field effects due to the presence of the anion and by charge transfer from the respective ions. The computational results also indicate that the OH{sup -} ion exists with a predominately 'hyper-coordinated' solvation shell and that the OH{sup -} ion does not readily donate hydrogen bonds to the surrounding water molecules.},
doi = {10.1021/jp070551c},
journal = {Journal of Physical Chemistry A},
number = ,
volume = 111,
place = {United States},
year = {Sun Mar 04 00:00:00 EST 2007},
month = {Sun Mar 04 00:00:00 EST 2007}
}