  The photochemistry of ices with polycyclic aromatic hydrocarbons (PAHs) has
been extensively studied, but to date no investigation has been made of PAHs in
interaction with low numbers (n < 4) of molecules of water. We performed
photochemical matrix isolation studies of coronene:water complexes, probing the
argon matrix with FTIR spectroscopy. We find that coronene readily reacts with
water upon irradiation with a mercury vapour lamp to produce oxygenated PAH
photoproducts, and we postulate a reaction mechanism via a charge transfer
Rydberg state. This result suggests that oxygenated PAHs should be widely
observed in regions of the ISM with sufficiently high water abundances, for
example near the edges of molecular clouds where water molecules begin to form,
but before icy layers are observed, that is at AV <3. In order to explain the
low derived observational abundances of oxygenated PAHs, additional destruction
routes must be invoked.
