Deuterium Fractionation upon the Formation of Hexamethylenetetramines through Photochemical Reactions of Interstellar Ice Analogs Containing Deuterated Methanol Isotopologues

Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Akira Kouchi, Naoki Watanabe

Research output: Contribution to journalArticle

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Abstract

Hexamethylenetetramine (HMT) is a representative product after the photolysis of interstellar ice analogs containing methanol followed by warming-up to room temperature. Since interstellar methanol is often significantly enriched in deuterium (D), the HMT photoproduct is expected to inherit D atoms from deuterated methanol. However, D fractionation upon the formation of HMT is not well understood, especially when it is produced from partly deuterated methanol isotopologues such as CH 2 DOH and CH 3 OD. Here, we experimentally studied the composition of deuterated HMT (d n -HMT, where n is the number of D atoms) at the isotopologue level formed by the photolysis of ice mixtures containing deuterated methanol, CH 2 DOH or CH 3 OD, at 10 or 77 K. The analyses were performed using a state-of-the-art high-resolution mass spectrometer coupled with a compound-specific separation technique. The formation of d n -HMT (n = 0-8) was confirmed under all experimental conditions. In addition, methyl- and hydroxyl-substituted HMT and their deuterated isotopologues were also obtained in the products. The deuterium enrichment was outstanding when CH 2 DOH was used rather than CH 3 OD, and when photolysis was performed at 77 K rather than 10 K. We found that the deuteration level of the formed HMT far exceeded that of the reactants under the present experimental conditions. These results obtained during stable isotope probing of deuterium strongly suggest that HMT can play a role as an organic pool of interstellar D atoms. These may be distributed into other chemical species through molecular evolution in space.

Original languageEnglish
Article number122
JournalAstrophysical Journal
Volume849
Issue number2
DOIs
Publication statusPublished - Nov 10 2017

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hexamethylenetetramine
deuterium
fractionation
photochemical reactions
methanol
ice
methyl alcohol
analogs
photolysis
methylidyne
stable isotope
spectrometer
warming
atoms
photochemical reaction
products
mass spectrometers
isotopes
temperature

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Deuterium Fractionation upon the Formation of Hexamethylenetetramines through Photochemical Reactions of Interstellar Ice Analogs Containing Deuterated Methanol Isotopologues. / Oba, Yasuhiro; Takano, Yoshinori; Naraoka, Hiroshi; Kouchi, Akira; Watanabe, Naoki.

In: Astrophysical Journal, Vol. 849, No. 2, 122, 10.11.2017.

Research output: Contribution to journalArticle

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