Analytic three-channel model for resonance-averaged direct and indirect dissociative recombination processes of molecular ions

An analytic three-channel model is developed for the description of simultaneous direct and indirect dissociative recombination (DR) cross sections of molecular ions with electrons. The model is formulated in terms of three parameters describing the interactions between the electron-ion entrance channel e, the dissociation channel d, and an ``active'' quasibound molecular Rydberg channel a and yields resonance-averaged cross sections for low incident electron energies. The relative magnitudes of the parameters determine (i) the height of the downward steps at the ion vibrational thresholds and (ii) the relative contributions of the direct and indirect processes. The model is intended to serve for the empirical analysis of observed DR cross sections, and in particular it allows the assessment of the extent to which reionization of the capture complex competes with dissociation. The model is applied to the DR of H₃{}⁺$ and HCO${}⁺$.