Dissociative recombination of CH$_2$NH$_2^+$ and NH$_2$CH$_2$O$^+$ ions

Cross sections for dissociation recombination (DR) and vibrational excitation of the CH$_2$NH$_2^+$ and NH$_2$CH$_2$O$^+$ ions in collisions with electrons are determined theoretically using an approach that combines the normal modes approximation for the vibrational states of the target ion with use of the UK R-matrix code to evaluate electron–ion scattering matrices. The corresponding thermally averaged rate coefficients are computed and fitted to analytical formulas. The obtained DR rate value for CH$_2$NH$_2^+$ is significantly smaller than the values recently employed in the photochemical models of the upper atmosphere of Titan, which has an important impact on the models that aim to reproduce the Titan ammonia abundance. On the other hand, the present results support the astrophysical models reproducing the abundance of the methanimine (CH$_2$NH) detected in massive star formation regions. In these models, the CH$_2$NH$_2^+$ DR is a major route of formation of this molecule with a high prebiotic potential. CH$_2$NH$_2^+$ and NH$_2$CH$_2$O$^+$ are the largest molecular ions for which the DR process was studied theoretically.