Roaming dynamics in highly excited-state unimolecular and complex bimolecular reactions

Roaming has been established as an unconventional reaction pathway that produces unexpected molecular products by circumventing the minimum-energy path associated with traditional transition states. Since its initial identification in 2004, this mechanism has attracted significant attention and has been reported not only in numerous unimolecular dissociation processes but also in some bimolecular reactions. In recent years, our group has made substantial advances in elucidating roaming dynamics in highly excited unimolecular systems as well as in complex bimolecular reactions. Several of these roaming mechanisms have been corroborated by high-resolution experimental measurements, providing compelling explanations for puzzling experimental observations. Here, we review these advances and show that dynamical simulations based on accurate full-dimensional potential energy surfaces offer robust evidence for roaming and enable detailed characterization of its distinctive dynamical features, energy redistribution pathways, product branching ratios and reaction rates. These studies significantly deepen our understanding of nontraditional reaction mechanisms and extend the scope of chemical dynamics and kinetics beyond the conventional minimum-energy-path framework, offering new insights into the prediction and interpretation of complex chemical reactivity.