Abundances of C₃, C₃H⁺, H₂CCC, and H₂CCCH⁺ as a function of time predicted by our model (continuous lines). The horizontal colored areas represent the observations in TMC-1 assuming an uncertainty of 3 on the measurements (Cernicharo et al. 2022 for C₃H⁺ and this work for H₂CCCH⁺). Dashed lines: Same, but with a threefold decrease in the H₂ + C₃H⁺ and a fivefold increase in the H₂CCCH⁺ + e⁻ rate coefficients. The vertical gray area represents the values given by the most probable chemical age for TMC-1, due to the better agreement between calculations and observations for 67 key species.