Confirmation of hydrated electrons formation during the moving single-bubble sonolysis: Activation of Tb3+ ion sonoluminescence by [formula omitted] acceptors in an aqueous solution

Abstract

The acoustically excited (26 kHz, acoustic pressure of 1.34 bar) luminescence of Tb3+ ions in aqueous solutions of TbCl3 is activated by selective acceptors of hydrated electron (eaq-), namely H+, and Cd2+ ions and other, during the moving single-bubble sonolysis. Sonoluminescence of Tb3+ is quenched when solvated electrons are present. The Tb3+ ions penetrate into the bubble across the liquid-gas interface, which is deformed during the bubble movement with the formation of microjets and nanodroplet injection. Then these ions are transferred to the electronically excited state upon inelastic collisions with particles having excess kinetic energy. The excited ions (*Tb3+, lifetime more than 400 μs) partly emit photons in the bubble and partly migrate to the solution, together with other sonolysis products as a result of their ejection from a bubble into a liquid. In the solution, the *Tb3+ ions react with the radical products of H2O sonolysis. The detected activation of the Tb3+ sonoluminescence is similar to the known activation of Tb3+ radioluminescence by eaq- acceptors (radiolysis generates eaq- together with *Tb3+). However, such activation is absent in the case of multibubble sonolysis, for which *Tb3+ generation was established previously, but no eaq- was formed among the primary products of H2O sonolysis (H and OH•). These facts indicate that acceptors suppress the reaction in which eaq- eliminates the excited state of the terbium ion *Tb3+ + eaq- → Tb2+. It is obvious considering the known redox potentials of the reactants. Consequently, hydrated electrons are generated in the moving single-bubble sonolysis of water.