N(o-H₂D⁺)/N(p-D₂H⁺) ratio for different T_ex assumptions. We report the following three main cases: our reference case T_ex = T_dust and two additional cases where we assumed lower temperatures, T_ex = 10 K and T_ex = 0.7 × T_dust. The values in the coloured boxes mark the lower limits we calculated for the cases where para-D₂H⁺ was not detected. The green shaded area represents the range of values obtained from our simulations.