Isotope effect in hydrogen peroxide formation during H2O and D2O sonication

The kinetics of hydrogen peroxide formation have been studied during H2O and D2O sonication in the presence of argon and oxygen (f=22 kHz, I=3.0 W cm−2, Pac=0.52 W ml−1, V=20 ml, T=20°C). It was found that the sonochemical reaction rate W has a zero order with respect to hydrogen peroxide (H2O, D2O or DHO2) concentration. In argon atmosphere the kinetic isotope effect was found to be equal to α=WH2O/WD2O=2.2±0.3. The α value decreases in H2O–D2O mixtures with increasing H2O concentration. In oxygen atmosphere the isotope effect is not observed (α=1.05±0.10). It is assumed that the revealed isotope effect is related to the mechanism of water sonolysis including the H2O–Ar∗ and D2O–Ar∗ energy transition, where Ar∗ is an argon atom in an excited state, in nonequilibrium plasma generated by the shock-wave.