Observed intensities along the horizontal cut (solid lines with error bars, corresponding to the spectra from Fig. 3) and corresponding model intensities (dashed lines). For ortho-H₂D⁺ we present an additional model (orange dashed line) for which the abundance is kept constant across the core. Para-D₂H⁺ observations and model (in red) have their own intensity axis (also in red) on the right side of the plot.