Roaming radicals.

Roaming is a recently verified unusual pathway to molecular products from unimolecular dissociation of an energized molecule. Here we present the evidence for this pathway for H(2)CO and CH(3)CHO. Theoretical analysis shows that this path visits the plateau region of the potential energy surface near dissociation to radical products. It is not clear whether roaming is a distinct isolated pathway, in addition to the conventional one via the well-known molecular saddle-point transition state. Evidence is presented to suggest that the two pathways may originate from a single, but highly complicated, dividing surface. Other examples of unusual reaction dynamics are also reviewed.