  In this paper, we explore the phase space structures characterising transport
for a double-well van der Waals potential. Trajectories are classified as
inter-well, intra-well, and escaping-from-a-well to define different dynamical
fates. In particular, roaming trajectories which are a new paradigm in chemical
reaction dynamics are observed. We apply the method of Lagrangian descriptors
to uncover the boundaries between the fates. And we find that the boundaries
between different fates are the stable and unstable manifolds of the hyperbolic
periodic orbits, which bifurcate with increasing energy of the system. The
methodology presented here is applicable to other open systems with a double
well potential.
