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H2O and CO molecules are the main constituents of the interstellar dust grain ice mantles. Infrared spectra of the ices in line of sights of young stellar objects and background stars have shown that the CO stretching vibration band can be decomposed into three main components: 2143, 2139 and 2136 cm−1, assigned to CO in different environment sites. The relative strengths between the components have been associated to an evolutionary track of the interstellar molecular clouds. H2O:CO (3:2) and (10:1) ices samples were irradiated by 0.79 MeV/u 58Ni13 + ions to simulate the effects produced by heavy ion cosmic rays in typical interstellar ices mixtures. The CO stretching vibration band is decomposed into six Gaussians functions (2150, 2144, 2141, 2138, 2136 and 2133 cm−1) and their integrated absorbances were measured as a function of fluence. The results have shown that, at the final fluence, the component 2138 cm−1 is the main component of the CO stretching vibration band. The component 2150 cm−1 disappears at the beginning of irradiation. Based on the present and previous results, a time scale for the components in the interstellar ices is proposed. For H2O:CO ice in the ISM it is predicted that, after 1 Myrs, the main components of the CO stretching vibration band are the 2138 cm−1 and 2141 cm−1, due to the CO monomers and dimers, respectively.

Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object (YSO) that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This process, known as X-ray photodesorption, needs to be quantified for methanol-containing ices. We aim at experimentally measuring X-ray photodesorption yields of methanol and its photo-products from binary mixed ices: $^{13}$CO:CH$_3$OH ice and H$_2$O:CH$_3$OH ice. We irradiated these ices at 15 K with X-rays in the 525 - 570 eV range. The release of species in the gas phase was monitored by quadrupole mass spectrometry, and photodesorption yields were derived. For $^{13}$CO:CH$_3$OH ice, CH$_3$OH X-ray photodesorption yield is estimated to be 10$^{-2}$ molecule/photon at 564 eV. X-ray photodesorption of larger COMs, which can be attributed to either ethanol, dimethyl ether, and/or formic acid, is detected with a yield of 10$^{-3}$ molecule/photon. When methanol is mixed with water, X-ray photodesorption of methanol and of the previous COMs is not detected. X-ray induced chemistry, dominated by low-energy secondary electrons, is found to be the main mechanism that explains these results. We also provide desorption yields that are applicable to protoplanetary disk environments for astrochemical models. The X-ray emission from YSOs should participate in the enrichment of the protoplanetary disk gas phase with COMs such as methanol in the cold and X-ray dominated regions because of X-ray photodesorption from methanol-containing ices., Comment: arXiv admin note: text overlap with arXiv:2101.06179