Dissociative recombination of molecular ions in a cooler ring

The dissociative recombination of HD+ was studied with an adiabatically expanded low‐temperature electron beam in the 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 of less than 1 eV shows structures even in the energy region less than 10 meV. The experimental results agree well with theoretical calculations based on a multichannel quantum‐defect theory including rotational motions. The dissociative recombination of 4HeH+ with the expanded electron beam is also described.