Comparison between the semi-analytical chemical model employed in this study and a chemical reaction network, for the fiducial model described in Sect. 5. The panels show various species abundances as a function of height, z, at r =5 au and r = 100 au (upper and lower rows, respectively). Left panels: Free electron abundance from the chemical reaction network (solid green lines) and the semi-analytical model (dotted black lines). Central panels: Total ion abundance from the chemical reaction network (solid green lines) and the semi-analytical model (dotted black lines). Right panels: Abundances of individual ion species from the chemical reaction network. The solid black line corresponds to HCO⁺, the solid blue line to H, the solid red line to C⁺, the solid green line to He⁺, and the solidpurple line to H⁺.