  This paper explores the phase space structures characterising transport for a
double-well van der Waals potential surface. 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. We find that the
boundaries between different fates are the stable and unstable manifolds of the
hyperbolic periodic orbits, which bifurcate when the energy increases. The
methodology presented here applies to other open systems with a double-well
potential.
