X-Ray Photo-desorption of H2O:CO:NH3Circumstellar Ice Analogs: Gas-phase Enrichment

Journal
Date Issued
2018
Author(s)
•
•
•
Huang, C.-H.
•
Sie, N.-E.
•
Chen, Y.-J.
•
Muñoz Caro, G. M.
DOI
Abstract
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 10^15-10^20 absorbed photons cm-2. We apply these findings to a protoplanetary disk model irradiated by a central T Tauri star.
Volume
868
Issue
1
Start page
73
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2018ApJ...868...73J
Rights
open.access
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