Distribution of key species abundances in the base model: CO, CO#, CO₂, CO₂#, HCO⁺, OH, H₂O#, CN, HCN, HCN#, NH₃, NH₃#. For CO, the black contour shows the PDR parameter log χ/ ⟨ n_H ⟩ = −3.5 and the blue contour T_dust = 20 K where CO starts to freeze out on dust grains. For CO#, the white dashed contours show dust temperatures of 15, 20 and 25 K and the blue dashed line shows the CO ice line estimate from rate equilibrium (Antonellini 2016). For water ice, two approximations of the snow line are indicated: (1) estimate based on the local density, dust temperature and radiation field (Min et al. 2016a, yellow dashed) and (2) estimate from rate equilibrium (Antonellini 2016, blue dashed).