Pulse Radiolysis Studies in Lanthanide Aqueous Solutions. II. Formation, Spectrum, and Some Chemical Properties of Praseodymium(IV) in Aqueous Solution

Pulse radiolysis of Pr(III) gives a transient absorption spectrum with a maximum at 290. This is due to the formation of Pr(IV) through the reaction of OH radicals and Pr(III). The rate of the reaction has been determined by four different methods and the rate constant was found to be ${\text{1–4 × 10}}^6{M}^{\text{−1}}\hspace{0.17em}{\sec }^{\text{−1}}$ . The variation of the optical density of Pr(IV) ions with pH lead to the conclusion that the form of Pr(IV) is Pr(OH)³⁺ and Pr⁴⁺ in neutral and acid solutions, respectively. The equilibrium constant of hydrolysis, ${\mathrm{Pr}}^{\text{4+}}+{\mathrm{H}}_2\mathrm{O}\rightleftarrows \mathrm{Pr}({\mathrm{OH)}}^{\text{3+}}+{\mathrm{H}}^{+}$ , was found to be ${\text{7 × 10}}^{\text{−4}}$ . The spectrum obtained is assigned to the Laporte‐allowed transition between 4f and 5d. The specific reaction rate constants of Pr(IV) with water, ${\mathrm{HSO}}_4^{-}\mathrm{,\hspace{0.17em}}{\mathrm{NO}}_2^{-}$ , H₂O₂, and Br⁻ have been determined, as well as those of Pr(III) with $e_{\mathrm{aq}}^{-}$ and H atoms.