Evolution of High-Temperature Oxygen Clusters and Radical Release: A Molecular Dynamics Study in Pure Oxygen and...

Despite decades of research into high-temperature oxidation kinetics, the atomic-scale origin of oxygen radical formation-a critical driver of the synthesis of functional oxide materials, oxidation corrosion of alloys, and combustion of fuels-remains elusive. Here, we unveil a previously unrecognized "oxygen clustering-radical release" pathway at the molecular level, wherein transient van der Waals aggregates of oxygen molecules, rather than isolated O₂, serve as the primary radical source. Through an integrated computational strategy combining first-principles calculations and deep neural network potential function molecular dynamics, we demonstrate that oxygen clusters exhibit a pronounced odd-even oscillation in stability: even-numbered clusters (especially O₆/O₈ subunits) are chemically inert, whereas odd-numbered clusters (dominated by O₃) possess high reactivity. Kinetically, clusters evolve via reversible aggregation-dissociation, and upon reaching a critical size, undergo structural collapse accompanied by radical release-a process initiated predominantly by large odd-numbered clusters. This mechanism persists in both pure O₂ and TiCl₄-containing environments, with TiCl₄ modulating only the aggregation kinetics, not the fundamental pathway. Our work establishes oxygen clustering as a universal, spontaneous source of radicals in high-temperature oxidation, providing a new molecular-level mechanistic framework for understanding and controlling radical-driven processes in materials synthesis, corrosion and combustion.