Quantum-Driven Anomalous Isotopic Effect at the Liquid Water-Oxide Interface

The intricate nature of water has long been a subject of scientific curiosity. In recent decades, nuclear quantum effects (NQEs) have entered the mainstream and greatly advanced our fundamental understanding of water. These effects, including quantum tunneling, quantum fluctuations, and zero-point energy, result in isotope substitution behaviors that deviate from the limit when nuclei are treated as classical particles. While NQEs in bulk water have been extensively studied, their specific roles at water interfaces — where most energy- and mass-exchange processes occur — remained largely unexplored, particularly under ambient conditions. Here, using in situ nonlinear optical vibrational spectroscopy, we uncover a giant anomalous isotopic effect on reactions at the liquid water and silicon oxide interface, showcasing a cooperative nature of interfacial protonic sites beyond classical kinetic effects at ambient temperature. With ab initio path integral molecular dynamics simulations, a quantum proton-sharing behavior is revealed for aqueous oxide surface sites, accompanied by a dynamic, Grotthuss-like proton transport network across the interface. The results shed light on the indispensable role played by NQEs that shapes water interfaces in the natural ambient environment.