FORMATION OF N 3 , CH 3 , HCN, AND HNC FROM THE FAR-UV PHOTOLYSIS OF CH 4 IN NITROGEN ICE

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The irradiation of pure solid N2 at 3 K with far-ultraviolet light from a synchrotron produced infrared absorption lines at 1657.7, 1655.6, and 1652.4 cm−1 and an ultraviolet absorption line at 272.0 nm, which are characteristic of the product N3. The threshold wavelength at which N3 was generated was 145.6 ± 2.9 nm, corresponding to an energy of 8.52 ± 0.17 eV. The photolysis of isotopically labeled 15N2 at 3 K consistently led to the formation of 15N3 with the same threshold wavelength of 145.6 ± 2.9 nm for its formation. The photolysis of CH4 in nitrogen ice in low concentrations also led to the formation of N3, together with CH3, HCN, and HNC, with the same threshold wavelength of 145.6 ± 2.9 nm. These results indicate that N3 radicals may play an important role in the photochemistry of nitrogen ices in astronomical environments.