Spectroscopy of the Hydrogen Molecular Ion at its Dissociation Limit

Previous theoretical and experimental work on the ion H₂⁺ and its deuterium isotopes HD⁺ and D₂⁺ is briefly reviewed. Spectroscopic studies of the vibration--rotation levels are discussed, and recent work on the infrared photodissociation of the high-lying vibrational levels is described. Earlier work that made use of ion-beam techniques to study the vibration--rotation levels of HD⁺ is reviewed, and compared with the most recent theoretical predictions. The nuclear-hyperfine and spin--rotation structure of HD⁺ is described, and recent observations of the vibration--rotation satellite lines that will yield absolute values of the deuterium hyperfine constants are presented. We conclude by describing our attempts to observe radiofrequency--infrared double-resonance spectra.