Environmental influence on HCNH⁺ abundances relative to H₂ as a function of time, calculated from the static models of Chempl (Du 2021). (a) Modeling results for different gas temperatures with $n_{{\text{H}}_2}={10}^3{\text{cm}}^{-3}$, A_v =10, G₀=1, and ζ = ζ₀. (b) Modeling results for different H₂ number densities with T_K = 300 K, A_v =10, G₀ =1, and ζ = ζ₀. (c) Modeling results for different visual extinctions with T_K = 300 K, $n_{{\text{H}}_2}={10}^3{\text{cm}}^{-3}$, G₀=1, and ζ = ζ₀. (d) Modeling results for different interstellar radiation fields with T_K = 300 K, $n_{{\text{H}}_2}={10}^3{\text{cm}}^{-3}$ , A_v =20, and ζ = ζ₀. (e) Modeling results for different cosmic ray ionization rates with T_K = 300 K, $n_{{\text{H}}_2}={10}^3{\text{cm}}^{-3}$, A_v =20, and G₀ = 10⁵. In all panels, the cyan-shaded regions indicate the observed HCNH⁺ abundances derived from our non-LTE analysis (see Table 2).