Physical structures and the evolution of HCNH⁺ abundances in C-type shocks, calculated from the UCLCHEM models (Holdship et al. 2017). Top: C-shock physical structures of our models for the three different shock velocities. The black and orange lines represent the density and temperature profiles of shock models. Bottom: HCNH⁺ abundances as a function of time for C-type shocks. The preshock gas density is fixed to 10³ cm⁻³ in the models. Different lines correspond to different cosmic ray ionization rates and shock velocities which are shown in the legend. The cyan-shaded region indicates the observed HCNH⁺ abundances in this study. GIF animations of the shock models at a given ζ = 10³ζ₀ and ζ = 10⁵ζ₀ are available via link1 and link2, respectively.