Confirmation of interstellar HOC+: Reevaluating the [HCO+]/[HOC+] abundance ratio

L. M. Ziurys, A. J. Apponi

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66 Scopus citations


The identification of interstellar HOC+ has been confirmed through new observations of this species at 3, 2, and 1.2 mm using the NRAO 12 m telescope. Toward Sgr B2 (OH), the J = 2 → 1 and J = 3 → 2 lines of this ion at 179 and 268 GHz were detected for the first time. In addition, the J = 1 → 0 line of HOC+ at 89 GHz was observed toward several new sources, including Orion-KL. In conjunction with past observations of the J = 1 → 0 transition toward Sgr B2 (OH), these data clearly establish the presence of this species in the interstellar medium. The column density toward Sgr B2 (OH) is estimated to be Ntot ~ 3 X 1012 cm-2, which corresponds to a fractional abundance relative to H2 of f ~ 10-12. Measurements of HCO+ were also carried out toward Sgr B2 (OH), resulting in an abundance ratio of [HCO+]/[HOC+] ~ 140-360 at gas densities of m(H2) > 105 cm-3. This ratio contradicts past predictions of ion-molecule models by several orders of magnitude and suggests that the reaction HOC+ + H2 → HCO+ + H2 is not as fast as previously thought.

Original languageEnglish (US)
Pages (from-to)L73-L76
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 1995


  • Galaxy: Center
  • ISM: Abundances
  • ISM: Molecules
  • Line: Identification

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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