Photochemical electron transfer from cerous ions to the lowest excited state of uranyl ions in aqueous media, studied by laser photolysis

A high-intensity beam of a Nd laser at 353.3 nm was used to produce the first excited state of the uranyl ion. Cerous ions, in acidic aqueous solutions, were found to react with it. The products of this reaction are ceric ions and uranium(V) ions. The absorption of the Ce(IV) ions was followed and the yields and decay kinetics of the ions were studied. The quantum yield of Ce(IV) formation is 0.85 ± 0.15, 1.00 ± 0.2, and 0.95 ± 0.25 in 0.1-0.5 M H₂SO₄, 0.57-2 M HNO₃, and 2 M HClO₄, respectively. The photochemical electron transfer is followed by a reaction of the products to produce the ground states of the initial reactants by a second-order reaction. The rate constant of this reaction is 5 × 10⁶ M^-1 s^-1 in 0.1-0.5 M H₂SO₄, ∼2 × 10⁷ M^-1 s^-1 in 2 M HNO₃, and ∼3 × 10⁷ M^-1 s^-1 in 2 M HClO₄. The interpretation of the photochemical results is supported by pulse radiolysis experiments.