Heavy Rydberg states

Abstract

This paper discusses the nature of heavy Rydberg states, i.e. quantum states in molecular systems that are bound by the almost pure Coulomb potential between pairs of ions. A theoretical framework is developed in terms of mass–scaling laws for heavy Rydberg systems of certain reduced mass, so that the physics of electronic Rydberg states can be straightforwardly applied to heavier ion–pair systems, or any other system bound by a 1/r potential. The general description of such quantum systems is supported by an experimental investigation of the energy region near the H+H− ion–pair dissociation limit, using a 1 XUV + 1 UV laser excitation scheme. Such a scheme allows for preparation of a single intermediate rovibrational quantum state, from which the ion–pair threshold region can be explored with a narrowband Fourier–transform limited laser. Field–induced lowering of the H+H− dissociation limit was observed in the presence of an electric field. Using a combination of DC and pulsed electric fields two–photon induced threshold ion–pair production spectroscopy (TIPPS) was performed for a variety of field strengths. Below the field–dissociation limit coherent wave packets of bound heavy Rydberg states are excited in an electric field. The coherent evolution of the Stark states, giving rise to oscillations in angular momentum space, can be quantitatively understood in terms of the linear Stark effect in the hydrogen atom, where the light electron is replaced by the heavier H− particle. The dynamics of wave packets of heavy Rydberg states is slower than in ordinary electronic Rydberg states, according to their larger mass. For a wide variety of binding energy and external electric field, the observed oscillation frequencies of the Stark wave packets match this model. An important parameter describing the specific properties of the H+H− Rydberg states is the scaled lifetime, which may be considered as a material constant, and it is determined atτ= (5.8±2.0)×10−21 s n 4.