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Title: EVIDENCE FOR DCO{sup +} AS A PROBE OF IONIZATION IN THE WARM DISK SURFACE

In this Letter, we model the chemistry of DCO{sup +} in protoplanetary disks. We find that the overall distribution of the DCO{sup +} abundance is qualitatively similar to that of CO but is dominated by a thin layer located at the inner disk surface. To understand its distribution, we investigate the different key gas-phase deuteration pathways that can lead to the formation of DCO{sup +}. Our analysis shows that the recent update in the exothermicity of the reaction involving CH{sub 2}D{sup +} as a parent molecule of DCO{sup +} favors deuterium fractionation in warmer conditions. As a result, the formation of DCO{sup +} is enhanced in the inner warm surface layers of the disk where X-ray ionization occurs. Our analysis points out that DCO{sup +} is not a reliable tracer of the CO snow line as previously suggested. We thus predict that DCO{sup +} is a tracer of active deuterium and, in particular, X-ray ionization of the inner disk.
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
  2. Univ. Bordeaux, LAB, UMR 5804, F-33270 Floirac (France)
  3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  4. Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan)
Publication Date:
OSTI Identifier:
22518832
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 802; 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; CARBON MONOXIDE; DEUTERATION; DEUTERIUM; DEUTERIUM COMPOUNDS; FRACTIONATION; IONIZATION; LAYERS; MOLECULAR IONS; MOLECULES; PROBES; PROTOPLANETS; SNOW; STARS; SURFACES; THIN FILMS; X RADIATION