Heavy Rydberg and ion-pair states: chemistry, spectroscopy and theory

Recent advances in our knowledge of heavy Rydberg and ion-pair states are critically reviewed, with emphasis placed on the close kinship between the two. Heavy Rydberg states are long-range vibrational states, reaching far beyond  Å for higher levels. Enhanced chemical reactivity and efficient energy transfer are frequently encountered. Unusual physical properties result from the large dipole moments, including laser-induced reactions and amplified spontaneous emission, and are discussed in the context of the underlying electronic structure. Heavy Rydberg states have a rich spectroscopy which is amenable to quantum defect analysis, as illustrated for a wide range of UV and VUV spectra previously analyzed in terms of Dunham coefficients. The lifetimes of heavy Rydberg states can be long, enabling them to be isolated in cryogenic matrices or as high angular momentum states in the gas phase. Heavy Rydberg and electronic Rydberg states often occupy the same energy region and this, together with the high density of heavy Rydberg vibrational levels, leads to vibronic mixing and numerous perturbations that are a fertile field for analysis by multichannel quantum defect theory and reactive scattering calculations.