Calculated abundances of NCCNH⁺ and NCCN as a function of time using the UMIST RATE12 chemical network (solid lines) and after removing the reactions of destruction of NCCN with C and N atoms (dashed lines), in both cases adopting ζ = 1.3 × 10^-17 s^-1. The range of abundances of NCCNH⁺ observed in TMC-1 and L483 is also indicated. The calculated abundance ratio [NCCNH⁺]/[NCCN] is shown in the upper panel as a function of time.