2018A&A...620A..46M

Aims. In this paper we investigate the detectability of the molecular oxygen in icy dust grain mantles towards astronomical objects.
Methods. We present a systematic set of experiments with O₂-H₂O ice mixtures designed to disentangle how the molecular ratio affects the O₂ signature in the mid- and near-infrared spectral regions. All the experiments were conducted in a closed-cycle helium cryostat coupled to a Fourier transform infrared spectrometer. The ice mixtures comprise varying thicknesses from 8 x 10^–3 to 3µm. The absorption spectra of the O₂-H₂O mixtures are also compared to the one of pure water. In addition, the possibility to detect the O₂ in icy bodies and in the interstellar medium is discussed.
Results. We are able to see the O₂ feature at 1551 cm^–1 even for the most diluted mixture of H₂O:O₂=9:1, comparable to a ratio of O₂/H₂O=10% which has already been detected in situ in the coma of the comet 67P/Churyumov-Gerasimenko. We provide an estimate for the detection of O₂ with the future mission of the James Webb Space Telescope (JWST).