Sonochemistry in light of third reactivity paradigm

Abstract

Large number of chemical reactions can be described rigorously using classical thermodynamics and classical kinetics. However, there are an increasing number of examples of chemical reactions that deviate from “classical” behavior. Describing them requires considering quantum effects. The purpose of this review is to emphasize the importance of such “non-classical” reactions in sonochemistry. Quantum effects in sonochemistry are a direct consequence of the formation of nonequilibrium plasma inside collapsing bubbles. Spectroscopic studies of multibubble sonoluminescence revealed that intrabubble processes cannot be described by a single gas temperature. Rather, vibrational excitation and ionization must also be considered. Most clearly, quantum effects in sonochemistry, like those in “classical” chemistry, appeared for kinetic isotope effects, KIE. The anomalous H/D KIE during water sonolysis in the presence of noble gases can be understood in terms of electron quantum tunneling during the heterolytic splitting of a water molecule. In addition, the inverse ¹³C/¹²C KIE observed during water sonolysis in the presence of CO indicated a similarity with a non-equilibrium plasma generated by CO excitation in a gas phase. This KIE originated from the quantum vibration–vibration pumping mechanism. In the concluding part of the review, some perspective research directions are discussed.