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Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
1991 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 95, no 5, 3578-3588 p.Article in journal (Refereed) Published
Abstract [en]

In contrast to the OH stretching frequencies of bound H2O molecules, which are always found at lower wave numbers compared to the free molecule, the experimentally determined frequency of the OH- ion can be either lower or higher than the free-ion value. Optimized geometries and fundamental stretching frequency of OH- have been calculated here by ab initio methods at the Hartree-Fock and second-order Moller-Plesset levels for a number of cation-OH-, HOH...OH-, cation-OH-.q-, and cation-OH-.OH2 complexes for Li+, Mg2+, and Al3+. The importance of electrostatic effects on the OH- frequency has been assessed by comparison with calculations of different point-charge and homogenous-field OH- systems. As long as the interaction is not dominated by electronic overlap, the frequency shift is found to be largely determined by electrostatic forces: with increasing field strength the OH- frequency rises to a maximum and then decreases. The OH- dipole moment and Mulliken charges vary monotonically with the field strength, whereas the equilibrium OH distance goes through a minimum and the bond electron density through a maximum. In strongly polarizing fields, such as in the optimized Al3+.OH- and Mg2+.OH-...OH2 systems, the OH- frequency falls below the free-ion value. Ar experimentally observed frequency downshift for an OH- ion in the condensed phase cannot be used as a criterion for the existence of H bonding. The OH- ion acts as an H-bond donor only when strongly polarized by a neighbor on its oxygen side.

Place, publisher, year, edition, pages
1991. Vol. 95, no 5, 3578-3588 p.
National Category
Chemical Sciences
URN: urn:nbn:se:uu:diva-228774DOI: 10.1063/1.460808ISI: A1991GD05500058OAI: oai:DiVA.org:uu-228774DiVA: diva2:734861
Available from: 2014-07-21 Created: 2014-07-21 Last updated: 2014-07-21

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