Comparison of the N[o-H₂D⁺]/N[p-D₂H⁺] ratio between observations and simulations. The different curves in the left panel refer to the time evolution of the cores identified within the simulations with a different set of physical and chemical conditions (see Tables 3 and 4 for details). We note that some cores are the result of merging and dissolving processes, which produce the visible oscillations in the curves. The stars represent t_age, i.e. the time at which the minimum o-H₂D⁺/p-D₂H⁺ ratio is reached for each core and the point where we performed the calculations of the properties reported in Table 4 and the comparison with the observed cores. The right panel shows the observed values: the ones labelled 1–6 represent our APEX data, 16293E (blue circle) refers to previous observations of the two studied isotopologues (Vastel et al. 2004), and HMM1-10K and HMM1-13K (green squares) are taken from observations in the L1688 cloud(Parise et al. 2011). The grey shaded area represents the range of observed values with secure detection, considering their uncertainties.