O2 signature in thin and thick O2-H2O ices

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 × 10-3 to 3 μm. 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). © ESO 2018.Acknowledgements. The authors thank the anonymous referee, who greatly helped us to enhance the clarity of the paper. We thank Christian Deysenroth for the very valuable contribution in the designing and mechanical work of the experimental setup. We are also grateful to Miwa Goto, Wing-Fai Thi, and Seyit Hocuk for fruitful discussion. The work of Birgitta Müller was supported by the IMPRS on Astrophysics at the Ludwig-Maximilians University, as well as by the funding the IMPRS receives from the Max-Planck Society. The work of Anton Vasyunin is supported by the Russian Science Foundation via the Project No. 18-12-00351