Evolution of the average fractional ortho- and para-NH₃ abundances according to different varieties of our chemistry model: “const CD” means chemical desorption (CD) with a constant (1%) efficiency, “dyn CD” means changing efficiency of CD depending on the composition of the grain surface, “FS” means full scrambling of protons in proton donation and hydrogen abstraction reactions, and “PH” means proton hop in these reactions (see text). The averages are column density ratios N(mol)/N(H₂) taken through the density maximum of the core model used in chemical simulations. The shaded area in the lower panel shows the range of similarly taken average of the fractional pNH₃ abundance through the three-dimensional model of H-MM1 based on the results of Pineda et al. (2022).