The profiles of the aromatic infrared bands explained with molecular carriers

Using a compilation of the photophysical properties of molecules such as coronene, C24H12, we have constructed a numerical model to calculate the IR emission spectrum of a population of polycyclic aromatic hydrocarbon (PAH) species subjected to UV photons. The model enables us to calculate not only the energy emitted in the IR bands but also the detailed band profiles. The calculated spectrum for a PAH size distribution following N-C(-3.5) with N-Cmin = 30 was found to provide a good match to the Aromatic Infrared Bands (AIBs) observed in the planetary nebula IRAS 21282+5050. The match is especially good for the intensities and for the profiles of the 6.2 and 11.3 mum bands. This work provides a coherent picture of the AIB problem supporting the PAH molecular hypothesis. It further underlines the poor spectral diversity contained in the AIB spectrum putting new constraints on the nature of the emitting population.