Photon-Stimulated Desorption from Cold Molecular Films with Synchrotron Radiation
(Université Pierre et Marie Curie, Paris (France))
Aula Bruno Touschek (LNF INFN)
Aula Bruno Touschek
In cold regions of the Interstellar Medium (ISM), like star-forming regions or protoplanetary disks, molecules form or accrete on the surface of micron-sized dust particles. The resulting icy mantles represent the main reservoir of molecular material (beside H2). In these regions, thermal desorption can be neglected, but energetic processes, for instance induced by cosmic rays or photon impact on the ices, can promote their desorption into gas phase. Providing experimental constraints on these processes is important for astrophysical modelling and for explaining the presence of organic compounds in UV-X irradiated regions. Desorption of neutral particles and ions is also crucial for the vacuum performance of cryogenic parts present in accelerators, such as the superconducting magnets of the Large Hadron Collider (LHC) at CERN or in use at synchrotron radiation facilities, which depends critically on the photodesorption of molecular gases by synchrotron emission originating from the relativistic particles.
We have developed an experimental approach for the study of the photodesorption from thin molecular films at low temperatures (10-15 K), using the brilliance and the tunability of synchrotron radiation at the SOLEIL facility in order to get absolute desorption yields in the UV energy range (DESIRS beamline) and more recently in the soft X-ray energy range (SEXTANTS beamline). The main results obtained from the irradiation of pure and mixed-ices of weakly bound species will be reviewed. Emphasis will be put an efficient desorption induced by the electronic relaxation of the first electronic excited state of CO in the 8-10 eV range and on indirect desorption effects involving co-adsorbates. Recent experimental studies of UV-X photon-stimulated desorption from Amorphous Solid Water will be also presented.