Integrated cooling rates (in erg cm^-2 s^-1) as a function of A_V for the various cooling mechanisms included in the PDR code. The curves for the total cooling (blue with crosses) and the FS cooling curve overlap. The remaining solid curves (MS for meta-stable line cooling, RV for ro-vibrational cooling of H₂, and LyA for the Lyman-alpha cooling) are shown for completeness. The dotted curves (with filled circles) are the first rotational transitions for the molecular species computed using LVG models.