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Water Exchange Mechanism in the First Excited State of Hydrated Uranyl(VI)
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
2009 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, no 23, 11310-11313 p.Article in journal (Refereed) Published
Abstract [en]

The water exchange mechanism of the uranyl(VI) aquo ion in the luminescent state, 3Δg in the spin-orbit free nomenclature, has been investigated using quantum chemical methods and compared to the corresponding reaction in the electronic ground state. The reaction mechanism was studied by calculation of the enthalpy of reaction of the A- and D- intermediates relative to the reactant, using a penta-aquo ion model with one additional water molecule in the second hydration sphere. The reaction barriers around the intermediates are low, and they are therefore a good approximation for the activation enthalpy. The energy of the D-intermediate is significantly larger than that of the A-intermediate both in the luminescent and in the ground states, suggesting that the water exchange is the same in both states. This suggestion is supported by the experimental rate constants for luminescence decay and water exchange in the electronic ground state that are 0.5 x 106 s-1 and 1.3 x 106 s-1, respectively.

Place, publisher, year, edition, pages
2009. Vol. 48, no 23, 11310-11313 p.
National Category
Physical Sciences
URN: urn:nbn:se:su:diva-54865DOI: 10.1021/ic9017689ISI: 000272037500062OAI: diva2:398733
Available from: 2011-02-18 Created: 2011-02-18 Last updated: 2015-07-29Bibliographically approved
In thesis
1. Theoretical Actinide Chemistry – Methods and Models
Open this publication in new window or tab >>Theoretical Actinide Chemistry – Methods and Models
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The chemistry of actinides in aqueous solution is important, and it is essential to build adequate conceptual models and develop methods applicable for actinide systems. The complex electronic structure makes benchmarking necessary. In the thesis a prototype reaction of the water exchange reaction for uranyl(VI), for both ground and luminescent states, described with a six-water model, was used to study the applicability of density functional methods on actinides and different solvation models. An excellent agreement between the wave function methods CCSD(T) and MP2 was obtained in the ground state, implying that near-minimal CASPT2 can be used with confidence for the reaction in the luminescent state of uranyl(VI), while density functionals are not suited to describe energetics for this type of reaction. There was an ambiguity concerning the position of the waters in the second hydration sphere. This issue was resolved by investigating a larger model, and prop- erly used the six-water model was found to adequately describe the water exchange reaction. The effect of solvation was investigated by comparing the results from conductor-like polarizable continuum models using two cavity models. Scattered numbers made it difficult to determine which solvation model to use. The final conclusion was that the water exchange reaction in the luminescent state of uranyl(VI) should be addressed with near-minimal CASPT2 and a solvation model without explicit cavities for hydrogens. Finally it was shown that no new chemistry appears in the luminescent state for this reaction. The thesis includes a methodological investigation of a multi-reference density functional method based on a range separation of the two-electron interaction. The method depends on a universal parameter, which has been determined for lighter elements. It is shown here that the same parameter could be used for actinides, a prerequisite for further development of the method. The results are in that sense promising.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 89 p.
Actinide, Quantum chemistry, Wave function, Density functional theory, Solvent models, Water exchange, Molecular configurations, Multi-reference density functional method
Research subject
Theoretical Physics
urn:nbn:se:su:diva-54848 (URN)978-91-7447-232-5 (ISBN)
Public defence
2011-03-28, FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Available from: 2011-03-06 Created: 2011-02-18 Last updated: 2011-03-16Bibliographically approved

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Wåhlin, PernillaWahlgren, Ulf
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Department of PhysicsNordic Institute for Theoretical Physics (Nordita)
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