Transport and roaming on the double van der Waals potential energy surface

•Phase space analysis of transport for a double-well van der Waals potential.•Roaming trajectories associated with chemical reaction dynamics are observed.•Different fates defined by the invariant manifolds of the hyperbolic periodic orbits.•Main hyperbolic periodic orbits bifurcate when energy is increased. 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.