Isotope effect in the formation of hydrogen peroxide by the sonolysis of light and heavy water

The kinetics of the formation of hydrogen peroxide by the sonolysis of light and heavy water in argon and oxygen atmospheres was investigated. The sonochemical reaction has a zero order with respect to hydrogen peroxide (H2O2, D2O2 or DHO2). The measurement of the kinetic isotope effect (alpha), defined as the ratio of the reaction rates in H2O and D2O. carried out under argon gave a value of 2.2 +/- 0.3. The observed isotope effect decreases with an increase in the concentration of light water in H2O-D2O mixtures. No isotope effect is displayed in the oxygen atmosphere (alpha = 1.05 +/- 0.10). The isotope effect is determined presumably by the mechanism of sonochemical decomposition of water molecules, which includes the H2O-Ar* and D2O-Ar* energy exchange (where Ar* are argon atoms in the P-3(2.0) excited state) in the nonequilibrium plasma generated by a shock wave, arising upon a cavitation collapse.