Roaming

In this review the roaming pathway in chemical reaction dynamics is described and illustrated. After a brief review and illustration of this pathway, an update on the chemical reactions where this pathway has been reported is given. Then the focus is on two recent systems where new aspects of roaming have been reported, namely roaming-isomerisation in CH3NO2 unimolecular dissociation and multi-electronic-state roaming in NO3 photodissociation. Full-dimensional potentials for these systems have been developed and used in quasiclassical trajectory calculations. Selected results from these studies are reviewed. So-called roaming saddle points and associated intrinsic reaction coordinate paths have been determined for these systems. These will be reviewed and investigated by making relevant comparisons with quasiclassical trajectories. Manifestations of roaming in quantum scattering and resonance calculations of the MgH + H → Mg + H2 reaction are reviewed. That is followed by a review of several statistical theories of roaming. The review concludes with some ‘editorial’ comments about the challenges that roaming presents to approximate theories and comments about possible future research directions.