Spectroscopy and chemistry of interstellar ice analogues

Mid-infrared (mid-IR) astronomical observations show that molecules freeze out on interstellar grains to form interstellar ices. These ices play an important role in the chemical evolution of molecules in space. Understanding the physical interactions and chemical reactions that take place in these ices gives us important clues to how the ices are formed and which role they play in the formation of complex molecules. The physical interactions in H2O:CO binary ices and in CH3OH and NH3 containing ices are studied both in the laboratory and in space by means of mid-IR spectroscopy, resulting in the unambiguous detection of NH3 in a low-mass protostar. Additionally, mid-IR and near-UV/VIS spectroscopic measurements on the ultraviolet induced photochemistry of large molecules, Polycyclic Aromatic Hydrocarbons (PAHs), trapped in ices are described. These molecules are known to be abundantly present in space, but their influence on the chemical evolution of interstellar ices has never been studied in detail. The experiments indicate that the processes are important in the formation of complex and charged molecules and that new astrochemical models should take the role of PAHs in ice into account.