Dust mass opacity spectra for a standard gas-to-dust mass ratio of 100. The dashed lines show the results of Ossenkopf & Henning (1994)’s simulations after 10⁵ yr of dust coagulation with gas densities of 10⁶ cm⁻³ and 10⁸ cm⁻³ and for dust grains without ice mantle and with thin ice mantle. The blue solid line shows the κ_ν (of gas) usedto compute H₂ column densities in Bonfand et al. (2017). The black solid line shows the κ_ν (of gas)used in this paper, computed with Eq. (4), and based on Ossenkopf & Henning (1994)’s model for grains without ice mantle and for gas densities of 10⁶ cm⁻³ (magenta dashed line).