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17–28 mai 2021
Fuseau horaire Europe/Paris

Session

Thermal and photon-induced desorption dependence on ice mantle composition and physical properties

27 mai 2021, 14:00

Description

Energetic photons and ions impinging on dust grains can lead to desorption of ice molecules, and could therefore account for the observed gas phase abundances toward very cold regions. Several studies reproduced CO ice irradiation with UV in the laboratory because this molecule is not directly dissociated at photon energies below 11 eV, which leads to an efficient photodesorption that can be measured by the decrease of its infrared absorption band. The linear decrease of the CO photodesorption yield as a function of ice deposition temperature is intriguing and cannot be explained by variations in the ice amorphicity or density, since these physical properties only change during the onset of crystallization above 20 K. We will provide an alternative explanation for this behavior of the photodesorption. Other molecular ice components are, either efficiently photodissociated, or not active in the infrared: CH3OH, CO2, O2, CH4, NH3, etc. Their photon-induced desorption is two or more orders of magnitude lower than that of CO. Interestingly, some of the photoproducts in these experiments are found to desorb during irradiation. The desorption of photoproducts follows two different patterns: a) an increasing desorption up to a maximum as the concentration of the product grows in the ice bulk, and b) a constant desorption that results from photochemical processes on the ice surface that we refer to as ¨photochemidesorption¨, which leads to the desorption of fragments or molecules due to their excess energy of formation. In our presentation we will discuss the intriguing CO photodesorption dependence on the physical ice properties, and the different desorption mechanisms of large photoproducts like C2H6 and C3H8, which may open a route toward the desorption of other COMs in cold regions

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