2015A&A...584A..98F


C.D.S. - SIMBAD4 rel 1.7 - 2021.04.13CEST00:26:39

2015A&A...584A..98F - Astronomy and Astrophysics, volume 584A, 98-98 (2015/12-1)

Hydrogen isotope exchanges between water and methanol in interstellar ices.

FAURE A., FAURE M., THEULE P., QUIRICO E. and SCHMITT B.

Abstract (from CDS):

The deuterium fractionation of gas-phase molecules in hot cores is believed to reflect the composition of interstellar ices. The deuteration of methanol is a major puzzle, however, because the isotopologue ratio [CH2DOH]/[CH3OD], which is predicted to be equal to 3 by standard grain chemistry models, is much larger (∼20) in low-mass hot corinos and significantly lower (∼1) in high-mass hot cores. This dichotomy in methanol deuteration between low-mass and massive protostars is currently not understood. In this study, we report a simplified rate equation model of the deuterium chemistry occurring in the icy mantles of interstellar grains. We apply this model to the chemistry of hot corinos and hot cores, with IRAS 16293-2422 and the Orion KL Compact Ridge as prototypes, respectively. The chemistry is based on a statistical initial deuteration at low temperature followed by a warm-up phase during which thermal hydrogen/deuterium (H/D) exchanges occur between water and methanol. The exchange kinetics is incorporated using laboratory data. The [CH2DOH]/[CH3OD] ratio is found to scale inversely with the D/H ratio of water, owing to the H/D exchange equilibrium between the hydroxyl (-OH) functional groups of methanol and water. Our model is able to reproduce the observed [CH2DOH]/[CH3OD] ratios provided that the primitive fractionation of water ice [HDO]/[H2O] is ∼2% in IRAS 16293-2422 and ∼0.6% in Orion KL. We conclude that the molecular D/H ratios measured in hot cores may not be representative of the original mantles because molecules with exchangeable deuterium atoms can equilibrate with water ice during the warm-up phase.

Abstract Copyright:

Journal keyword(s): astrochemistry - molecular processes - solid state: volatile - ISM: molecules

Simbad objects: 8

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Number of rows : 8

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 W 3(H2O) Mas 02 27 04.6 +61 52 25           ~ 125 0
2 IRAS 03258+3104 Y*O 03 28 55.30 +31 14 27.8           ~ 160 1
3 [JCC87] IRAS 2A Y*O 03 28 55.55 +31 14 36.7           ~ 408 3
4 [JCC87] IRAS 4B Y*O 03 29 12.058 +31 13 02.05           ~ 568 0
5 NAME OMC1 Ridge reg 05 35 13.4 -05 23 07           ~ 124 0
6 NAME Orion-KL SFR 05 35 14.16 -05 22 21.5           ~ 2062 1
7 IRAS 16293-2422 cor 16 32 22.56 -24 28 31.8           ~ 1086 1
8 GAL 024.78+00.08 HII 18 36.2 -07 13           ~ 75 0

    Equat.    Gal    SGal    Ecl

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2021.04.13-00:26:39

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