Column density per km s^-1 of HF, H₂O⁺, ArH⁺, and H, in descending order of f(H₂) traced by the species. The color coding of the frequencies is explained in Table 1. The error estimate for ArH⁺ was done using the MAGIX Interval Nested Sampling algorithm (Möller et al. 2013), which implements a Markov chain Monte Carlo (MCMC) method to calculate the Bayesian evidence and Bayesian confidence interval. Hi column density errors were calculated by propagating uncertainties from the input emission and absorption spectra using a Monte-Carlo sampling technique. For the other species, a ±20% error of the column densities was assumed. The uncertainty is marked by the blue shading around the curves.