5 Photon-stimulated processes in model interstellar ices

Introduction Balancing the universal carbon budget remains one of the outstanding problems in astrochemistry. The extra stability conferred to carbocycles by aromatisation suggests that polycyclic aromatic hydrocarbons (PAHs) and their heteroatomic analogues (HPAHs) may represent a significant sink for carbon in the interstellar medium (ISM). While there are no definitive identifications of (H)PAHs from observations of the ISM, there is increasing evidence, from studies of infrared absorption and emission in the 2.8 to 3.7 μm region that such species are likely to exist in high abundances .