Pseudo-1D model profiles of the core. Upper box: n(H₂) Plummer-like profile in black. In red, temperature profile treated separately for the east (left) and the west (right) parts of the core, with three different minimum temperatures (10 K in plain line, 8 and 12 K in dashed lines). Middle box: ortho-H₂D⁺ (black) and para-D₂H⁺ (red) abundance profiles relative to H₂ and computed separately for each side for the 10 K model, error bars are 1σ deviation from best model. Arrows mark upper limits. In particular, for ortho-H₂D⁺ in the centre of the core, the dotted line represents the abundance to stay just below 1σ difference with the observations, and the upper error bar represents a difference of 2σ with the observations. Lower box: para-D₂H⁺/ortho-H₂D⁺ ratio for the 10 K model. Error bars are computed by taking the opposite error bars of both species when available, otherwise lower or upper limits are indicated by arrows. The long dashed and dash-dotted lines mark a ratio of 1 and 2, respectively, 2 being the upper limit of the models of Bovino et al. (2021) at 10 K.