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Author Gavilan, Lisseth ♦ Carrasco, Nathalie ♦ Remusat, Laurent ♦ Roskosz, Mathieu ♦ Popescu, Horia ♦ Jaouen, Nicolas ♦ Sandt, Christophe ♦ Jäger, Cornelia ♦ Henning, Thomas ♦ Simionovici, Alexandre ♦ Lemaire, Jean Louis ♦ Mangin, Denis
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ ABSORPTION SPECTROSCOPY ♦ ASTROPHYSICS ♦ DEUTERIUM ♦ ENRICHMENT ♦ INFRARED SPECTRA ♦ IRRADIATION ♦ KEV RANGE ♦ MASS ♦ MASS SPECTROSCOPY ♦ METEORITES ♦ NITROGEN ♦ ORGANIC MATTER ♦ PENETRATION DEPTH ♦ PLASMA ♦ PROTOPLANETS ♦ SOFT X RADIATION ♦ STARS ♦ STELLAR RADIATION ♦ SYNCHROTRON RADIATION ♦ THERMAL DEGRADATION
Abstract The deuterium enrichment of organics in the interstellar medium, protoplanetary disks, and meteorites has been proposed to be the result of ionizing radiation. The goal of this study is to simulate and quantify the effects of soft X-rays (0.1–2 keV), an important component of stellar radiation fields illuminating protoplanetary disks, on the refractory organics present in the disks. We prepared tholins, nitrogen-rich organic analogs to solids found in several astrophysical environments, e.g., Titan’s atmosphere, cometary surfaces, and protoplanetary disks, via plasma deposition. Controlled irradiation experiments with soft X-rays at 0.5 and 1.3 keV were performed at the SEXTANTS beamline of the SOLEIL synchrotron, and were immediately followed by ex-situ infrared, Raman, and isotopic diagnostics. Infrared spectroscopy revealed the preferential loss of singly bonded groups (N–H, C–H, and R–N≡C) and the formation of sp{sup 3} carbon defects with signatures at ∼1250–1300 cm{sup −1}. Raman analysis revealed that, while the length of polyaromatic units is only slightly modified, the introduction of defects leads to structural amorphization. Finally, tholins were measured via secondary ion mass spectrometry to quantify the D, H, and C elemental abundances in the irradiated versus non-irradiated areas. Isotopic analysis revealed that significant D-enrichment is induced by X-ray irradiation. Our results are compared to previous experimental studies involving the thermal degradation and electron irradiation of organics. The penetration depth of soft X-rays in μ m-sized tholins leads to volume rather than surface modifications: lower-energy X-rays (0.5 keV) induce a larger D-enrichment than 1.3 keV X-rays, reaching a plateau for doses larger than 5 × 10{sup 27} eV cm{sup −3}. Synchrotron fluences fall within the expected soft X-ray fluences in protoplanetary disks, and thus provide evidence of a new non-thermal pathway to deuterium fractionation of organic matter.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-05-01
Publisher Place United States
Journal Astrophysical Journal
Volume Number 840
Issue Number 1


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