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

A. Jiménez-Escobar, A. Ciaravella, C. Cecchi-Pestellini, C. H. Huang, N. E. Sie, Y. J. Chen, G. M. Munoz Caro

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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 ∼1015-1020 absorbed photons cm-2. We apply these findings to a protoplanetary disk model irradiated by a central T Tauri star.

Original languageEnglish
Article number73
JournalAstrophysical Journal
Volume868
Issue number1
DOIs
StatePublished - 20 Nov 2018

Keywords

  • astrochemistry
  • ISM: molecules
  • X-rays: ISM

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