Microwave spectra of the HD+ and D2 + ions at their dissociation limits

Abstract

We have observed microwave transitions in the HD⁺ and D₂ ⁺ ions involving energy levels very close to their dissociation limits. In HD⁺ the spectrum detected arises from a rotational transition between the two highest bound vibration-rotation levels in the 1sσ ground state, whilst in D₂ ⁺ we have detected electronic transitions between high-lying vibration-rotation levels of the ground 1sσ_g electronic state and the 2pσ_u long-range van der Waals state.