INFRARED STUDY OF UV/EUV IRRADIATION OF NAPHTHALENE IN <roman>H</roman>2<roman>O</roman>+<roman>NH</roman>3 ICE

We have carried out photon irradiation study of naphthalene (C₁₀H₈), the smallest polycyclic aromatic hydrocarbon (PAH) in water and ammonia ice mixtures. Photons provided by a synchrotron radiation light source in two broad-band energy ranges in the ultraviolet/near extreme ultraviolet (4-20 eV) and the extreme ultraviolet (13-45 eV) ranges were used for the irradiation of H₂O+NH₃+C₁₀H₈ = 1:1:1 ice mixtures at 15K. We could identify several photo-products, namely CH₄, C₂H₆, C₃H₈, CO, CO₂, HNCO, OCN^-, and probably quinoline (C₉H₇N) and phenanthridine (C₁₃H₉N). We found that the light hydrocarbons are preferably produced for the ice mixture subjected to 4-20 eV photons. However, the production yields of CO, CO₂, and OCN^- species seem to be higher for the mixture subjected to EUV photons (13-45 eV). Therefore, naphthalene and its photo-products appear to be more efficiently destroyed when high energy photons (E > 20 eV) are used. This has important consequences on the photochemical evolution of PAHs in astrophysical environments.