Optical Characterization of Interstellar Ice Analogues

Since its first identification, water ice has been observed in the insterstellar medium (ISM) along several lines of sight and in different sources, mainly in dense molecular clouds. Water is the most abundant component of ice observed in space. However, other molecular species have been identified as minor ice components by their spectroscopic features in the infrared (IR) region. There are still many open questions about the role of the ice mantles in phenomena, such as low-temperature dust coagulation, or non-thermal desorption mechanisms. To tackle such questions, it is important to identify the physical state and molecular composition of ices, and this relies on preliminary laboratory characterization.

An experiment has been developed with the goal in mind to characterize the optical properties of astrophysically-relevant solids (ice mixtures, silicates, and carbonaceous materials). For this experiment, we use a cryostat coupled to both a Fourier Transform Infrared (FTIR) spectrometer and a Terahertz Time-Domain Spectrometer (TDS), to characterize samples in two different spectral regions. This combination of spectral studies provides information regarding their chemical, physical, and optical properties. When analyzed together with astronomical observations and theoretical models, we will better understand the roles of solid materials for several different environments.

Spectra of all H2O−O2 composition ratios mixtures investigated, magnified around the O2 feature (marked by the vertical red dashed line). The spectra for the different compositions are shifted in the absorbance scale for helping their visualization.
Derivation of the optical properties of CO ice. (a) Real part of the refractive index, (b) amplitude absorption coefficient.
Derivation of the optical properties of CO ice. (c) real and (d) imaginary parts of the dielectric permittivity.
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