Radiofrequency/infrared double resonance spectroscopy of the HD⁺ ion

Abstract

We describe a double resonance technique for obtaining radiofrequency spectra of the HD⁺ ion in vibration-rotation levels close to the dissociation limit. Infrared transitions are driven by Doppler tuning an HD⁺ ion beam into resonance with a carbon dioxide infrared laser, and are detected by measuring H⁺ fragment ions produced by electric field dissociation of the upper vibration-rotation level. Radiofrequency transitions between nuclear hyperfine components of the lower vibration-rotation level are then detected through resonant increases in the H⁺ fragment ion current. The high spectroscopic resolution obtained, and the ability to measure magnetic dipole hyperfine transitions, will enable the hyperfine constants to be determined accurately.