PAH molecules and carbon dust in interstellar clouds

An analysis of possible chemical reactions between PAH molecules and atoms and ions in the interstellar gas shows that a variety of destruction channels exist for these molecules. PAH molecules will have lifetimes of |$\tilde {\lt} 10^5$| yr under diffuse cloud conditions, and therefore are unlikely to be a ubiquitous component of interstellar dust clouds. The destruction of PAH molecules is enhanced by temperature fluctuations, although PAH molecules may be observable as transient species in shocked regions. The relationship between PAH and carbon dust (HAC) is also discussed.