Vacuum Ultraviolet Spectroscopy of H- in a Heavy Ion Storage Ring: The Region near the H(n=2) Threshold

The negative hydrogen ion has been investigated by a new spectroscopic approach in the region near the n=2 threshold of the neutral hydrogen atom. The technique is based on Doppler-tuned spectroscopy using an H- beam stored in a heavy ion storage ring collinearly overlapped with a fixed-frequency narrow-bandwidth vacuum ultraviolet laser beam (118 nm). The position of the Feshbach resonance is determined as 10.9243(3) eV which is in good agreement with recent theoretical calculations but deviates significantly from the previously reported experimental result.