Absolute cross sections for dissociative recombination of ${\mathrm{HD}}^{+}$: Comparison of experiment and theory

Absolute cross sections for dissociative recombination of ${\mathrm{HD}}^{+}$ were measured in the ion storage CRYRING for incident electron energies in the range 0.01–20 eV. The ions were stored for about 25 s before data taking, which is several orders of magnitude longer than their vibrational lifetimes towards spontaneous emission of infrared radiation. A broad resonance in the cross section at 5–12 eV is due to recombination into a manifold of doubly excited states. Multichannel quantum-defect theory was used to calculate the absolute cross section of this resonance. The calculations required inclusion of different mechanisms, such as dissociative autoionization, and many molecular states in order to reproduce the resonance region. Very good agreement of experiment and theory is found, and the results strongly reinforce that vibrationally cold ions were used in the experiment.