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Title: FORMATION OF S-BEARING SPECIES BY VUV/EUV IRRADIATION OF H{sub 2}S-CONTAINING ICE MIXTURES: PHOTON ENERGY AND CARBON SOURCE EFFECTS

Carbonyl sulfide (OCS) is a key molecule in astrobiology that acts as a catalyst in peptide synthesis by coupling amino acids. Experimental studies suggest that hydrogen sulfide (H{sub 2}S), a precursor of OCS, could be present in astrophysical environments. In the present study, we used a microwave-discharge hydrogen-flow lamp, simulating the interstellar UV field, and a monochromatic synchrotron light beam to irradiate CO:H{sub 2}S and CO{sub 2}:H{sub 2}S ice mixtures at 14 K with vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) photons in order to study the effect of the photon energy and carbon source on the formation mechanisms and production yields of S-containing products (CS{sub 2}, OCS, SO{sub 2}, etc.). Results show that (1) the photo-induced OCS production efficiency in CO:H{sub 2}S ice mixtures is higher than that of CO{sub 2}:H{sub 2}S ice mixtures; (2) a lower concentration of H{sub 2}S enhances the production efficiency of OCS in both ice mixtures; and (3) the formation pathways of CS{sub 2} differ significantly upon VUV and EUV irradiations. Furthermore, CS{sub 2} was produced only after VUV photoprocessing of CO:H{sub 2}S ices, while the VUV-induced production of SO{sub 2} occurred only in CO{sub 2}:H{sub 2}S ice mixtures. More generally, the production yieldsmore » of OCS, H{sub 2}S{sub 2}, and CS{sub 2} were studied as a function of the irradiation photon energy. Heavy S-bearing compounds were also observed using mass spectrometry during the warm-up of VUV/EUV-irradiated CO:H{sub 2}S ice mixtures. The presence of S-polymers in dust grains may account for the missing sulfur in dense clouds and circumstellar environments.« less
Authors:
; ; ; ;  [1] ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6]
  1. Department of Physics, National Central University, Jhongli City, Taoyuan County 32054, Taiwan (China)
  2. NASA Ames Research Center, Moffett Field, CA 94035 (United States)
  3. Centro de Astrobiología, INTA-CSIC, Torrejón de Ardoz, E-28850 Madrid (Spain)
  4. Space Sciences Center and Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089-1341 (United States)
  5. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China)
  6. Graduate Institute of Astronomy, National Central University, Jhongli City, Taoyuan County 32049, Taiwan (China)
Publication Date:
OSTI Identifier:
22364676
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 798; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; CARBON DIOXIDE; CARBON MONOXIDE; CARBON OXYSULFIDE; CARBON SULFIDES; COSMIC DUST; EXTREME ULTRAVIOLET RADIATION; FAR ULTRAVIOLET RADIATION; HYDROGEN SULFIDES; MASS SPECTROSCOPY; MONOCHROMATIC RADIATION; PHOTONS; SULFUR DIOXIDE; VISIBLE RADIATION