Photodesorption of Water Ice from Dust Grains and Thermal Desorption of Cometary Ices Studied by the INSIDE Experiment

A new experimental setup, INterStellar Ice-Dust Experiment (INSIDE), was designed for studying cosmic grain analogs represented by ice-coated carbon- and silicate-based dust grains. With the new instrument, we can simulate the physical and chemical conditions prevailing in interstellar and circumstellar environments. The setup combines ultrahigh vacuum and low-temperature conditions with infrared spectroscopy and mass spectrometry. Using INSIDE, we plan to investigate physical and chemical processes, such as adsorption, desorption, molecule formation, on the surface of dust/ice samples. First experiments on the photodesorption of water ice molecules from the surface of silicate and carbon grains by UV photons revealed a strong influence of the surface properties on the desorption yield, in particular in the monolayer regime. In the second experiment, the thermal desorption of cometary ice analogs composed of six molecular components was studied for the first time. Codesorption of CO₂ and CH₃OH with O₂ indicates that at high O₂ concentrations in cometary or interstellar ices, “heavy” ice molecules can be partly trapped in O₂ and enter the gas phase much earlier than expected. This effect could explain astronomical detections of complex organic molecules in cold dense interstellar clouds.