Publication
Reference
Gavilan Lisseth, Remusat Laurent, Roskosz Mathieu, Popescu Horia, Jaouen Nicolas, Sandt Christophe, Jäger Cornelia, Henning Thomas, Simionovici Alexandre, Lemaire Jean Louis, Mangin Denis, Carrasco Nathalie (2017). X-Ray-induced Deuterium Enrichment of N-rich Organics in Protoplanetary Disks: An Experimental Investigation Using Synchrotron Light. Astrophys. J., 840, 35.
Names
  • Lisseth Gavilan
  • Laurent Remusat
  • Mathieu Roskosz
  • Horia Popescu
  • Nicolas Jaouen
  • Christophe Sandt
  • Cornelia Jäger
  • Thomas Henning
  • Alexandre Simionovici
  • Jean Louis Lemaire
  • Denis Mangin
  • Nathalie Carrasco
Article and keywords
Title
X-Ray-induced Deuterium Enrichment of N-rich Organics in Protoplanetary Disks: An Experimental Investigation Using Synchrotron Light
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 3 carbon defects with signatures at ∼1250–1300 cm −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 27 eV cm −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.
Keywords
spectroscopy, ellipsometry, transmission, Raman microscopy, XAS - X-Ray Absorption Spectroscopy, optical constants spectra, absorbance spectra, soft X-rays, visible, mid-IR, data analysis, band position, band width, band intensity, molecular bond, irradiation process - X-rays, tholins, X-Ray stars, protoplanetary disk, ISM - Interstellar medium
Content
sample, spectral data, astrophysics, planetary sciences
Year
2017
Journal
The Astrophysical Journal
Volume
840
Number
1
Pages
35
Document type
article
Publication state
published
Comments
None
Doi
10.3847/1538-4357/aa6bfc
Identifiers
Publications