Theoretical study of the dissociative recombination of HeH⁺

The dissociative recombination (DR) of HeH⁺ is studied using the multichannel quantum defect theory (MQDT) of molecules. The MQDT is extended to include the dissociative Rydberg states. The idea of a “closed dissociative channel” is introduced for a precise description. The calculated DR cross section sensitively depends upon rotational motion, which enhances the DR at a collision energy lower than 0.2  eV . Calculations in the present study reproduced the DR rate coefficient measured by two facilities of storage rings (CRYRING and TARN II). A great change of the adiabatic quantum defect with internuclear distance induced a large DR cross section in the noncrossing system. This mechanism is an alternative to the electronic resonance of the crossing existing system.