Simultaneous H/D and ¹³C/¹²C Anomalous Kinetic Isotope Effects during the Sonolysis of Water in the Presence of Carbon Monoxide

Splitting of water molecules driven by ultrasound plays a central role in sonochemistry. While studies of sonoluminescence revealed the formation of a plasma inside the cavitation bubble, much less is known about the contribution of plasma chemical processes to the sonochemical mechanisms. Herein, we report for the first time sonochemical processes in water saturated with pure CO. The presence of CO causes a large increase in the H/D kinetic isotope effect (KIE) to α_H = 14.6 ± 1.8 in a 10% H₂O/D₂O mixture under 20 kHz ultrasound. The anomalous H/D KIE is attributed to electron quantum tunneling in the plasma produced by cavitation. In addition, CO₂ formed simultaneously with hydrogen during the sonochemical process is enriched with the ¹³C isotope, which indicates a V–V pumping mechanism typical for non-equilibrium plasma. Both observed KIEs unambiguously point to the contribution of quantum effects in sonochemical mechanisms.