We review recent advances in the study of the dissociative recombination of molecular ions with electrons with a primary emphasis on experimental studies. In particular, we focus on previous experimental measurements of recombination rates for N2+, O2+, and NO+ ions. In the context of this review, we present temperature dependent rate coefficients from recent merged beam studies of the dissociative recombination of N2+, O2+, and NO+ ions with electrons. Identifying underlying physical differences between the various experimental techniques enables a discussion of the effects of vibrational excitation on the dissociative recombination of these major ionospheric species of ions. For T < 1200 K, we conclude that the recombination rates for N2+, O2+, and NO+ ions in the ground electronic and vibrational states respectively are 2.2 × 10−7 (Te/300)−0.39 cm3 s−1, 1.95 × 10−7(Te/300)−0.70 cm3 s−1, and (3.5 ± 0.5) × 10−7(Te/300)−0.69 cm3 s−1. Vibrational excitation is shown to play a significant role in laboratory measurements of these recombination rates. For each of these species, vibrationally excited ions yielded a lower recombination rate than the ground state. We also discuss the recombination of these species of ions for T > 1200 K.

Cross sections for the dissociative recombination of HCO + ions have been measured in the energy range from 0.01-1.0 eV. The large values measured for low-energy electrons are supported by an earlier extensive quantum mechanical study by Talbi and co-workers which is reviewed. A broad maximum has been found in the region from 0.3-0.8 eV and this is attributed to the opening up of a second product channel leading to CH + O.

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Cross sections for the dissociative recombination of isomeric HCN+/HNC+ ions with electrons were measured using the single-pass merged beam experiment located at the University of Western Ontario in Canada. The source conditions were varied so that an HCN+/HNC+ mixture was first studied. The HNC+ ion was then isolated via the fast ion-molecule reaction HCN++CO2HNC++CO2. The two sets of measurements, which both refer to vibrationally (and electronically) excited states of HCN+ and HNC+, exhibit differences in the magnitudes of the cross sections. Thermal rate coefficients have been calculated for both species. An attempt has been made to identify the valence states involved in the dissociation to the CN+H channel for HCN+ recombination.