Photodesorption of water ice from dust grains and thermal desorption of cometary ices studied by the INSIDE experiment

Abstract

A new experimental set-up INterStellar Ice-Dust Experiment (INSIDE), was designed for studying cosmic grain analogues represented by ice-coated carbon- and silicate-based dust grains. In the new instrument, we can simulate physical and chemical conditions prevailing in interstellar and circumstellar environments. The set-up 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, and formation of molecules, 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 analogues composed of six molecular components was studied for the first time. Co-desorption 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 release to the gas phase much earlier than expected. This effect could explain astronomical detections of complex organic molecules in cold dense interstellar clouds.