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Published online by Cambridge University Press: 23 September 2016
We discuss the fraction of the infrared cirrus emission radiated out of thermal equilibrium using the IRAS data. Recent spectrophotometric data (Giard et al., 1988a, 1988b) are presented which confirm that aromatic infrared bands account for at least a fraction of their near and mid-infrared cirrus emission as was suspected from indirect arguments. Large variations of the energy distribution among the IRAS bands are shown to be present in molecular clouds. Abundances of polycyclic aromatic hydrocarbons (PAH's) required to account for the emission are discussed.