Vibration-rotation spectroscopy of the HD+ion near the dissociation limit

Vibration-rotation transitions between levels of the HD+ ion near the dissociation limit are detected by a sequential two-photon photodissociation method. Using a CO infrared laser we have measured seven rotational components of the v = 17-14 band. The results, which are accurate to ± 0·001 cm-1, show significant discrepancies from the best available theoretical predictions. The high resolution of ion-laser beam spectroscopy has allowed the observation of structure arising from the proton hyperfine interaction.