Roaming

Abstract

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.

Keywords:

• roaming
• methylnitrate dissociation
• NO₃ dissociation
• reaction dynamics

Acknowledgements

I thank my many collaborators in roaming and especially Bina Fu (Dalian Institute of Chemical Physics) and Zahra Homayoon for investigating the behaviour of classical trajectories initiated from roaming saddle points in NO₃ and CH₃NO₂, respectively. I thank Hua Guo for preparing Figure 9 of this paper and Keiji Morokuma for sending the IRC data for NO₃. I thank Bill Stwalley for comments about roaming and cold molecule collision.

Additional information

Funding

Financial support, past and present, from the Department of Energy [grant number DE-FG02-97ER14782] and Army Research Office [grant number W911NF-11-1-0477] is gratefully acknowledged.