Dissociative Recombination ofHD+with an Ultracold Electron Beam in a Cooler Ring

Dissociative recombination of ${\mathrm{HD}}^{+}$ was studied with an adiabatically expanded low-temperature electron beam in a cooler ring TARN II. Measurements were performed over a wide energy range from 0 to 40 eV in the center of mass system. The spectrum at low electron energies less than 1 eV clearly shows structures even in the energy region of the order of 1 meV. The results agree well with the theoretical calculations based on a multichannel quantum defect theory including rotational motions and off-the-energy-shell effects.