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Reinterpretation of the Spectra of Hydrated Co++: An ab initio Study



H S. Gilson, Morris Krauss


The absorption spectrum of aqueous Co++ is reinterpreted in light of ab initio calculations. MCSCF and MR-MP calculations yield the spectral states and their oscillator strengths, as well as the spin-orbit coupling between the quartet and doublet states of four-,five- and six-coordinate C-++-water complexes. Spectral states and oscillator strengths are also computed for these complexes with one water replaced by a hydroxide ion. The results of the calculations are compared with measured spectra obtained from room temperature and high temperature Co++ solutions. We find that the six-coordinate species has zero oscillator strength because of its octahedral symmetry. The calculated oscillator strength remains very small even when the symmetry of this species is allowed to relax. Therefore, the six-coordinate species can contribute little to the observed spectrum, even though experimental data suggest that it is the dominant form of Co++ in solution. On the other hand, the computed spectra of other aqueous coordination states of Co++ do show features of the observed spectra. We propose that the observed absorption spectra result from a mixture of thermodynamically disfavored but optically active species, with the largest contribution coming from the five-coordinate Co++-water complex.
Journal of Physical Chemistry A
No. 32


ad initio, colbalt dication, electronic spectra, solution


Gilson, H. and Krauss, M. (1998), Reinterpretation of the Spectra of Hydrated Co++: An ab initio Study, Journal of Physical Chemistry A (Accessed May 24, 2024)


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Created July 1, 1998, Updated February 17, 2017