Computer Science – Performance
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.398m&link_type=abstract
The Molecular Universe, Proceedings of the 280th Symposium of the International Astronomical Union held in Toledo, Spain, May 30
Computer Science
Performance
Scientific paper
ISAC is an ultra-high-vacuum (UHV) setup, with a base pressure down to P = 2.5 √ó 10-11 mbar, dedicated to the study of ice processes. The UHV conditions of ISAC allow experiments under extremely clean conditions. Transmittance FTIR spectroscopy coupled to QMS proved to be ideal for in situ monitoring of ice processes that include radiation and thermal annealing. The optimal performance of ISAC becomes evident after an analysis of the results. As an example, thermal desorption of CO starting at 15 K, induced by the release of H2 from the CO ice, was observed. We measured the photodesorption yield of CO ice per incident photon at 7, 8, and 15 K, respectively yielding 6.4 ± 0.5 10-2} 5.4± 0.5 10-2, and 3.5± 0.5 10-2 CO molecules photon (7.3-10.5 eV)-1. Our value of the photodesorption yield of CO ice at 15 K is about one order of magnitude higher than the previous estimate. We confirmed that the photodesorption yield is constant during irradiation and independent of the ice thickness. Only below ˜ 5 monolayers ice thickness the photodesorption rate decreases, which suggests that only the UV photons absorbed in the top 5 monolayers led to photodesorption. The measured CO photodesorption quantum yield at 7 K per absorbed photon in the top 5 monolayers is 3.4 molecules photon-1. We also studied the UV-photochemistry of H2S ice, leading to the formation of more refractory products such as H2S2, S2, and S8. X-ray irradiation experiments of ice were also performed with ISAC. These experiments are challenging because the flux of current X-ray sources emitting in the 0.1-1 keV range is very low, and therefore the product abundances are at the trace level. In our experiments, the typical irradiation dose was of 10-5 - 10-6 photons molecule-1. Despite that, we were able to detect for the first time X-ray irradiation products of several ices of astrophysical interest.
Cecchi-Pestellini Cesare
Ciaravella Angela
Cruz Diaz G. A.
Jimenez Escobar A.
Muñoz Caro Guillermo Manuel
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