Isotope effect in hydrogen peroxide formation during H2O and D2O sonication

The kinetics of hydrogen peroxide formation have been studied during H2O an d D2O sonication in the presence of argon and oxygen (f=22 kHz, 1=3.0 W cm( -2), P-ac=0.52 W ml(-1), V=20 ml, T=20 degrees C). It was found that the so nochemical reaction rate W has a zero order with respect to hydrogen peroxi de (H2O, D2O or DHO2)concentration. In argon atmosphere the kinetic isotope effect was found to be equal to alpha = W-H2O/W-D2O = 2.2+/-0.3. The or va lue decreases in H2O-D2O mixtures with increasing H2O concentration. In oxy gen atmosphere the isotope effect is not observed (alpha=1.05+/-0.10). It i s assumed that the revealed isotope effect is related to the mechanism of w ater sonolysis including the H2O-Ar* and D2O-Ar* energy transition, where A r* is an argon atom in an excited state, in nonequilibrium plasma generated by the shock-wave. (C) 2000 Elsevier Science B.V. All rights reserved.