Detection of the quadrupole hyperfine structure in HCNH

L. M. Ziurys, A. J. Apponi, J. T. Yoder

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31 Scopus citations


We report the first measurement of the electric quadrupole hyperfine structure of HCNH+ . The J = 1 → 0 transition of this interstellar molecular ion was observed toward the cold, dark cloud TMC-1, using the NRAO 12m telescope at 74 GHz. The three hyperfine components of this transition were clearly detected and resolved, enabling the first experimental determination of the quadrupole coupling constant eqQ of HCNH+. The value of this constant is calculated to be eqQ = -0.49 ± 0.07 MHz. The column density of HCNH+ toward TMC-1 was found to be Ntot, ∼ 2.8 × 1013 cm-2, corresponding to a fractional abundance relative to H2 of f ∼ 3 × 10-9. This abundance is at least one order of magnitude higher than the predictions of ionmolecule chemistry. Detection of the hyperfine structure clearly establishes the presence of HCNH+ in interstellar space.

Original languageEnglish (US)
Pages (from-to)L123-L126
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - Oct 1 1992


  • ISM: abundances
  • ISM: molecules
  • Line: identification
  • Radio lines: molecular: interstellar

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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