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

• DOI: 10.1039/c2cp41177f
• Publication Date: 2012-05-14T15:03:27Z
• Authors: Mathieu Bertin; Edith C. Fayolle; Claire Romanzin; Karin I. Öberg; Xavier Michaut; Audrey Moudens; Laurent Philippe; Pascal Jeseck; Harold Linnartz; Jean-Hugues Fillion
• Keywords: [PHYS.ASTR.GA]Physics [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA]; 13. Climate action; [PHYS.ASTR.GA] Physics [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA]; 0103 physical sciences; 500; [PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph]; 540; 01 natural sciences; [PHYS.PHYS.PHYS-SPACE-PH] Physics [physics]/Physics [physics]/Space Physics [physics.space-ph]; [PHYS.PHYS.PHYS-SPACE-PH]Physics [physics]/Physics [physics]/Space Physics [physics.space-ph]; [PHYS.PHYS.PHYS-CHEM-PH] Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph]

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 to be 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 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.