Heavy Rydberg system

A heavy Rydberg system consists of a weakly bound positive and negative ion orbiting their common centre of mass. Such systems share many properties with the conventional Rydberg atom and consequently are sometimes referred to as heavy Rydberg atoms. While such a system is a type of ionically bound molecule, it should not be confused with a molecular Rydberg state, which is simply a molecule with one or more highly excited electrons.The most commonly studied system to date is the H + / H − {displaystyle H^{+}/H^{-}}   system, consisting of a proton bound with a H − {displaystyle H^{-}}   ion. The H + / H − {displaystyle H^{+}/H^{-}}   system was first observed in 2000 by a group at the University of Waterloo in Canada.The difficulty in the production of heavy Rydberg systems arises in finding an energetic pathway by which a molecule can be excited with just the right energy to form an ion pair, without sufficient internal energy to cause autodissociation (a process analogous to autoionization in atoms) or rapid dissociation due to collisions or local fields.The bond length in a heavy Rydberg system is 10,000 times larger than in a typical diatomic molecule. As well as producing the characteristic hydrogen-like behaviour, this also makes them extremely sensitive to perturbation by external electric and magnetic fields.