Autoionizing Rydberg States in Triplet Molecular Hydrogen

We report the first observation of the autoinizing triplet nd series of H₂ covering the region from $n=10$ to the series limit. The autoionizing states are produced by excitation of H₂ c³Πᵤ^- molecules in a fast (1 keV) beam with a frequency-doubled pulsed dye laser, and the resulting H₂⁺ ions are detected. We have also resolved members of the high-lying nd series ($25<n<35$) converging to the lowest vibrational state of the H₂⁺ ion by field ionization. A qualitative interpretation of the spectra in terms of a noninteracting single-channel Rydberg electron model is given.