Photodestruction of PAHs in the interstellar medium --- I. Photodissociation rates for the loss of an acetylenic group

T. Allain, S. Leach, and E. Sedlmayr

Astronomy & Astrophysics, Vol. 305, 602-615 (1996)

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Abstract:

We have developed a model for interstellar polycyclic aromatic hydrocarbons (PAHs) in order to estimate their rate of photodissociation in the interstellar medium. These photoreactions include the loss of atomic and molecular hydrogen and the loss of the acetylene molecule. We have studied the stability of PAHs in the regions of high UV radiation where the infrared emission bands attributed to PAHs are observed (reflection nebulae, planetary nebulae, active galactic nuclei, HII regions...) by comparing the rate of acetylene loss to the rate of accretion of carbon to PAHs. This comparison shows that only PAHs with more than 50 carbon atoms may survive the UV radiation field of these regions, whereas smaller PAHs such as coronene or ovalene are destroyed within a few years.

Keywords:

ISM:molecules - molecular processes - ultraviolet:ISM