Top: gas density distribution on the left and strength of the UV radiation field log   (χ), on the right. Contour lines showing A_{v,rad = 1.0} (white) and min(A_v,ver, A_v,rad) = 1.0 (black) are overplotted on both. Middle: gas temperature on the left and CO abundance on the right. Contour lines showing the gas temperatures of 200 K, 800 K, and 2k = 2000 K (the temperatures in the gap should reflect those in a very low density ISM medium) are overplotted on both. Lower left: the ro-vibrational bands of the CO molecule. Lower right: the modelled SED with observational data overplotted as blue dots.