Vibration-rotation spectroscopy of the HD+ ion

A new method of detecting vibration-rotation transitions in HD⁺ is described. The ion-beam laser-resonance method employs Doppler tuning and relies upon the detection of infrared photodissociation of levels close to the dissociation limit of HD⁺. Measurements of nine rotational components of the v = 18 ? 16 band are described. A review of the theoretical methods for the calculation of energy levels in HD⁺ is given, followed by a comparison of the experimental results with the best available theoretical values. The resolution of structure arising from proton hyperfine interaction is also described.