Infrared Spectroscopy and Programmed Thermal Desorption of Ice Mixtures
In the coldest regions of the interstellar medium, ice mantles are accreted on the surface of dust grains. These ice mantles are detected by infrared telescopes, revealing their composition, structure, etc. This wouldn’t be possible without a proper characterization of ice analogs in laboratories under astrophysically relevant conditions. In this Chapter, we highlight the differences in the infrared features of the different components that are usually detected in interstellar ice mantles that arise when the spectrum of a pure ice is compared with the spectrum of an ice mixture. These differences are due to molecular interactions, and give us information on both the composition and the structure of the ice mantle. In addition, thermal processing of the ice mantles may induce structural changes that are also studied here. In space, thermal processing of the ice mantles during a star formation event ultimately leads to the sequential sublimation or desorption of the different ice components, leading to the formation of a chemically-rich hot core around the forming protostar. In the laboratory, this process can be also simulated, as it is explained by the end of the Chapter.