  We examine the phase space structures that govern reaction dynamics in the
absence of critical points on the potential energy surface. We show that in the
vicinity of hyperbolic invariant tori it is possible to define phase space
dividing surfaces that are analogous to the dividing surfaces governing
transition from reactants to products near a critical point of the potential
energy surface. We investigate the problem of capture of an atom by a diatomic
molecule and show that a normally hyperbolic invariant manifold exists at large
atom-diatom distances, away from any critical points on the potential. This
normally hyperbolic invariant manifold is the anchor for the construction of a
dividing surface in phase space, which defines the outer or loose transition
state governing capture dynamics. We present an algorithm for sampling an
approximate capture dividing surface, and apply our methods to the
recombination of the ozone molecule. We treat both 2 and 3 degree of freedom
models with zero total angular momentum. We have located the normally
hyperbolic invariant manifold from which the orbiting (outer) transition state
is constructed. This forms the basis for our analysis of trajectories for ozone
in general, but with particular emphasis on the roaming trajectories.
