Dimers in photochemistry and chemistry of f elements

The neptunium, plutonium, cerium, and europium ions in acid solutions and a mericium and cerium ions in deaerated carbonate solutions are oxidized or r educed with water under UV irradiation. The mechanisms of these processes w ere proposed. They include the following stages. Actinide or lanthanide ion takes up light quantum and switches over to the excited state. The excited ion forms a dimer (so-called excimer) with the unexcited metal ion. Decomp osition of an excimer is accompanied by liberation of an H-2 molecule and f ormation off-element ions in a higher oxidation state, or by formation of H 2O2 and f-element ions in a lower oxidation state. The chemical reduction o f Np(VII), Am(VI), and Ce(IV) with water molecules in acid solution, Pu(VII ) in alkaline medium, and oxidation of U(III) and Eu(II) with water in acid solutions also proceed via formation of dimers, which decompose with forma tion of H2O2 (reduction) or H-2 (oxidation).