DISSOCIATIVE RECOMBINATION OF HEH-COLD ELECTRON-BEAM FROM A SUPERCONDUCTING ELECTRON COOLER IN A STORAGE-RING( ISOTOPES WITH AN ULTRA)

The dissociative recombinations of (HeH+)-He-3, (HeH+)-He-4, (HeD+)-He -3 and (HeD+)-He-4 were studied with an extremely low-temperature elec tron beam of the order of 1 meV produced by a superconducting electron cooler at the storage ring TARN II. The dissociative recombination sp ectra show a fine new structure and a clear isotope dependence in the low-energy region. Those features are well reproduced by the theoretic al calculations based on a multichannel quantum-defect theory includin g rotational motion and discretized dissociative states. According to the theory, the newly observed structure is evidence for a new indirec t mechanism where the intermediate states are not vibrationally excite d Rydberg states but virtual dissociative states.