SIMBAD references

In dense clouds of the interstellar medium, dust grains are covered by ice mantles, dominated by H₂O. CO and CO₂ are common ice components observed in infrared spectra, while infrared inactive N₂ is expected to be present in the ice. Molecules in the ice can be dissociated, react, or desorb by exposure to secondary ultraviolet photons. Thus, different physical scenarios lead to different ice mantle compositions. This work aims to understand the behaviour of ¹³CO : N₂ and ¹³CO₂ : N₂ ice mixtures submitted to ultraviolet radiation in the laboratory. Photochemical processes and photodesorption were studied for various ratios of the ice components. Experiments were carried out under ultrahigh vacuum conditions at 12 K. Ices were irradiated with a continuous emission ultraviolet lamp simulating the secondary ultraviolet in dense interstellar clouds. During the irradiation periods, fourier-transform infrared spectroscopy was used for monitoring changes in the ice, and quadrupole mass spectrometry for gas phase molecules. In irradiated ¹³CO₂ : N₂ ice mixtures, ¹³CO, ¹³CO₂, ¹³CO₃, O₂, and O₃ photoproducts were detected in the infrared spectra. N₂ molecules also take part in the photochemistry, and N-bearing molecules were also detected: NO, NO₂, N₂O, and N₂O₄. Photodesorption rates and their dependence on the presence of N₂ were also studied. As it was previously reported, ¹³CO and ¹³CO₂ molecules can transfer photon energy to N₂ molecules. As a result, ¹³CO and ¹³CO₂ photodesorption rates decrease as the fraction of N₂ increases, while N₂ photodesorption is enhanced with respect to the low UV-absorbing pure N₂ ice.