Modelled 69 μm feature shape (solid lines) compare to the PACS observations (grey error bars) for models R20 with a 0.1 μm shift towards longer wavelengths (left) and model RW30 with a 0.05 μm shift (right). Overplotted are the optically thin fit from Sturm et al. (2010) (grey solid line), and contributions from the individual temperature components. The bottom panels show the difference between the PACS observations and the modelled spectra.