Formation of Excited Uranyl Ion in Oxidation of U(IV) with Xenon Trioxide in Aqueous Solutions of H_(2)SO_(4) and HClO_(4): II. Influence of H_(2)O_(2) on the Reaction Kinetics

摘要

The kinetics and mechanism of chemiluminescent oxidation of U(IV) with xenon trioxide [mono-exponential decay of chemiluminescence (CL)] dramatically changes in the presence of H_(2)O_(2). First the CL intensity slightly decreases (induction period), then increases by a factor of several units (autocatalytic oxidation), and finally sharply decreases by several orders of magnitude after reaching a maximum. Radical chain mechanism of the reaction was proposed. The elementary step of formation of CL emitter, electronically excited (UO_(2)~(2+))~(*), is electron transfer from the uranyl(V) ion (UO_(2)~(+)) to the oxidizing agent (OH radical). In the presence of H_(2)O_(2) in the solution, OH radicals are formed non only by reaction of U(IV) with XeO_(3) but also by reaction of H_(2)O_(2) with XeO_(3), which complicates the CL kinetics.