The AtO+ cation is one of the happy few astatine chemical species that can predominate in aqueous solution. Although its ground spin-orbit-free state in the gas phase is a spin-triplet state, this species can readily react with closed-shell reagents in aqueous solution. In this talk, we will first identify a new chemical species that must be introduced in the astatine Pourbaix (E−pH) diagram. A speciation change starting from AtO(OH), the first hydrolysis product of AtO+, as evidenced from experiments, suggests that this speciation change involves one proton and leads to the formation of an anionic species. Quantum mechanical calculations are used to check the two hypotheses that may arise from this information, the computed reaction constants being compared to the experimental one. In the second part of the presentation, we will revisit the hydration-induced ground-state change of AtO+ by means of relativistic and multiconfigurational wave function approaches for which the spin-orbit coupling is introduced a posteriori. By tracking the nature of the electronic states as a function of the geometry and the hydration spheres, we will further justify that such ground-state-change actually occurs and reveal for the first time the nature of the involved many-electron states.
Université Paul Sabatier - Bat. 3R1b4 - 118 route de Narbonne 31062 Toulouse Cedex 09, France