X-Ray Photo-desorption of H2O:CO:NH3 Circumstellar Ice Analogs: Gas-phase Enrichment

We study the photo-desorption occurring in H2O:CO:NH3 ice mixtures irradiated with monochromatic (550 and 900 eV) and broadband (250-1250 eV) soft X-rays generated at the National Synchrotron Radiation Research Center (Hsinchu, Taiwan). We detect many masses photo-desorbing, from atomic hydrogen (m/...

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Bibliographic Details
Published in:The Astrophysical journal 2018-11, Vol.868 (1)
Main Authors: Jiménez-Escobar, A., Ciaravella, A., Cecchi-Pestellini, C., Huang, C.-H., Sie, N.-E., Chen, Y.-J., Muñoz Caro, G. M.
Format: Article
Language:English
Subjects:
Ammonia
Analogs
astrochemistry
Astrophysics
Broadband
Desorption
Enrichment
Excitons
Hydrogen
ISM: molecules
Photons
Porosity
Protoplanetary disks
Radiation
Radiation research
Research facilities
Soft x rays
Substrates
Synchrotron radiation
T Tauri stars
Vapor phases
X-rays: ISM
Yield
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Summary:We study the photo-desorption occurring in H2O:CO:NH3 ice mixtures irradiated with monochromatic (550 and 900 eV) and broadband (250-1250 eV) soft X-rays generated at the National Synchrotron Radiation Research Center (Hsinchu, Taiwan). We detect many masses photo-desorbing, from atomic hydrogen (m/z = 1) to complex species with m/z = 69 (e.g., C3H3NO, C4H5O, C4H7N), supporting the enrichment of the gas phase. At low numbers of absorbed photons, substrate-mediated, exciton-promoted desorption dominates the photo-desorption yield, inducing the release of weakly bound (to the surface of the ice) species; as the number of weakly bound species declines, the photo-desorption yield decreases about one order of magnitude, until porosity effects, reducing the surface/volume ratio, produce a further drop of the yield. We derive an upper limit to the CO photo-desorption yield, which in our experiments varies from 1.4 to 0.007 molecules photon−1 in the range ∼1015-1020 absorbed photons cm−2. We apply these findings to a protoplanetary disk model irradiated by a central T Tauri star.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aae711