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The presence of methanol among the common ice components in interstellar clouds and protostellar envelopes has been confirmed by the James Webb Space Telescope (McClure et al. 2023). Methanol is often detected in the gas phase towards lines of sight shielded from UV radiation. We measured the volumetric density of methanol ice grown under simulated interstellar conditions and the infrared spectroscopy at different deposition temperatures and during the warm-up. The IR band strengths are provided, and the experimental spectra are compared to those computed with a model. The transition from amorphous to crystalline methanol ice was also explored. Finally, we propose new observations of methanol ice at high resolution to probe the methanol ice structure. [ABSTRACT FROM AUTHOR]

The motivation to study experimentally CO ice under mimicked interstellar conditions is supported by the large CO gas abundances and ubiquitous presence of CO in icy grain mantles. Upon irradiation in its pure ice form, this highly stable species presents a limited ion and photon-induced chemistry, and an efficient non-thermal desorption. Using infrared spectroscopy, single laser interference, and quadrupole mass spectrometry during CO ice deposition, the CO ice density was estimated as a function of deposition temperature. Only minor variations in the density were found. The proposed methodology can be used to obtain the density of other ice components at various deposition temperatures provided that this value of the density is known for one of these temperatures, which is typically the temperature corresponding to the crystalline form. The apparent tendency of the CO ice density to decrease at deposition temperatures below 14 K is in line with recently published colorimetric measurements. This work allowed us to revisit the value of the infrared band strength needed for calculation of the CO ice column density in infrared observations, 8.7 × 10−18 cm molecule−1 at 20 K deposition temperature. [ABSTRACT FROM AUTHOR]