Comparison between the observed abundance of H₂S in Barnard 1b (black dots) and the chemical models. In the left panel of the top row, the observed abundances are compared to models with different initial sulfur abundances and the binding energies of Model 1 from Table 8. The sets of models that best fit the observations are shown with solid lines. The top right panel shows the same comparison, but with the binding energies of Model 16 from Table 8, evidencing the low impact of lower binding energies in the predicted gas-phase abundances of H₂S. The dependence between the sulfur abundance and the extinction is shown in the bottom left panel. The filled area S_H2S represents the appropriate ranges of sulfur abundances that models with other sets of binding energies,apart from Model 1 (Table 8), require.