Left panel: H₂ volume density profile (n) in thephysical model of L1544. Central panel: column density profile. Right panel: ζ₂ profiles for the (dashed bluecurve), (solid red), and (dashed-dotted green) models. The profiles for the models and PI18 have been derived integrating the volume density profile of the core model to obtain the column density profile, and then using the relation between ζ₂ and N.