The reactivity of the molecular anion cacdfe9bee59c2222753764" title="Click to view the MathML source">C₃N⁻,${\mathrm{C}}_3{\mathrm{N}}^{-},$ proposed to be abundant in Titan’s ionosphere, is explored.

The kinetics and branching ratios of the ${\mathrm{C}}_3^{15}{\mathrm{N}}^{-}+{\mathrm{HC}}_3^{14}\mathrm{N}$ and ${\mathrm{C}}_3^{14}{\mathrm{N}}^{-}+{\mathrm{HC}}_3^{14}\mathrm{N}$ reactions are investigated in the laboratory down to 50 K with the CRESU method.

Proton transfer is the main exit channel which is indistinguishable with non-isotopically labeled reactants.

A minor exit channel, reactive detachment, has been uncovered, although the nature of the neutral products has not been identified.

It is concluded that the C₃N⁻+HC₃N${\mathrm{C}}_3{\mathrm{N}}^{-}+{\mathrm{HC}}_3\mathrm{N}$ reaction cannot contribute to the growth of anions in the upper atmosphere of Titan.