Abundance profiles of N₂H⁺, N₂D⁺, HCO⁺, and DCO⁺ (from top-left to bottom-right panel) in the model , using the original kinetic temperature profile from Keto et al. (2015) (in black), and increasing or decreasing the temperature by 1 K (red and blue curves respectively). With respect to all other figures in this work, here we use the linear scale, since in the logarithmic scale the small variations would not be visible. The x-axis is limited to the central 0.2 pc.