The Water Exchange Mechanism in the First Excited State of Hydrated Uranyl(VI)

Pernilla Wåhlin (1) , Valérie Vallet (2) , Ulf Wahlgren (1, 3) , Ingmar Grenthe (4)

1 Institute of Physics
2 PhLAM - Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523
3 NORDITA - Nordic Institute for Theoretical Physics
4 School of Chemical Sciences and Engineering, Department of Chemistry, Inorganic Chemistry

The water exchange mechanism of the uranyl(VI) aquo ion in the luminescent state, ³Δ_g 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 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 0.5x10⁶ s^-1 and 1.3x10⁶ s^-1, respectively.

Mots clés: actinide; ab initio; uranyl; water exchange

Domaines: Chimie-Physique [physics.chem-ph]

Pernilla Wåhlin, Valérie Vallet, Ulf Wahlgren, Ingmar Grenthe. The Water Exchange Mechanism in the First Excited State of Hydrated Uranyl(VI). Inorganic Chemistry, 2009, 48, pp.11310. ⟨10.1021/ic9017689⟩. ⟨hal-00424940⟩