UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption

Abstract : Carbon monoxide is after H 2 the most abundant molecule identified in the interstellar medium (ISM), and is used as a major tracer for the gas phase physical conditions. Accreted at the surface of water-rich icy grains, CO is considered as the starting point of a complex organic – presumably prebiotic – chemistry. Non-thermal desorption processes, and especially photodesorption by UV photons, are seen as the main cause that drives the gas-to-ice CO balance in the colder parts of the ISM. The process is known to be efficient and 10 wavelength-dependent, but, the underlying mechanism and the physical-chemical parameters governing the photodesorption are still largely unknown. Using monochromatized photons from a synchrotron beamline, we reveal that the molecular mechanism responsible for CO photoejection is an indirect, (sub)surface-located process. The local environment of the molecules plays a key role in the photodesorption efficiency, and is quenched by at least an order of magnitude for CO interacting with a water ice surface.
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Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2012, 14 (28), pp.9929-9935 〈10.1039/C2CP41177F〉
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Mathieu Bertin, Edith C. Fayolle, Claire Romanzin, Karin I. Öberg, Xavier Michaut, et al.. UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption. Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2012, 14 (28), pp.9929-9935 〈10.1039/C2CP41177F〉. 〈hal-01620008〉

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