Evolution of the fractional abundances of oNH₂D, pNH₂D, oNHD₂, and pNHD₂ in the core model. The abundances correspond to the column density ratios N(mol)/N(H₂) towards the centre of the core, smoothed to the resolution of the ${18}_{\cdot }^{\mathrm{\prime }\mathrm{\prime }}7$ APEX beam at 333 GHz. Predictions from the PH scenario in the chemical network (a) and the FS scenario (b). In this simulation, a = 0.2 μm and ζ_H2 = 2.6 × 10⁻¹⁷ s⁻¹. The horizontal dashed lines and thick semi-transparent lines represent the fractional abundances and their formal 1σ errors derived towards (0,0) in Sect. 3. These abundances are listed in Table 3.