2017ApJ...848..112D

This work presents the photochemistry of ultraviolet (UV) irradiated coronene in water ices at 15 K studied using mid-infrared Fourier transform (FTIR) spectroscopy for C₂₄H₁₂:H₂O at concentrations of (1:50), (1:150), (1:200), (1:300), and (1:400). Previous UV irradiation studies of anthracene:H₂O, pyrene:H₂O, and benzo[ghi]perylene:H₂O ices at 15 K have shown that aromatic alcohols and ketones, as well as CO₂ and H₂CO, are formed at very low temperatures. Likewise, here, in addition to the coronene cation, hydroxy-, keto-, and protonated coronene (coronene H⁺) are formed. The rate constants for the decay of neutral coronene and for the formation of photoproducts have been derived. It is shown that Polycyclic Aromatic Hydrocarbons (PAHs) and their UV induced PAH:H₂O photoproducts have mid-infrared spectroscopic signatures in the 5-8 µm region that can contribute to the interstellar ice components described by Boogert et al. as C1-C5. Our results suggest that oxygenated and hydrogenated PAHs could be in UV-irradiated regions of the interstellar medium where water-rich ices are important.