New detections of interstellar HNO at 2 and 1.2 millimeters: More N-O bonds

L. M. Ziurys, J. M. Hollis, L. E. Snyder

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20 Scopus citations


The 202-101 and 303-202 transitions of HNO at 163 and 244 GHz have been detected toward several molecular clouds. In conjunction with previous measurements of the 101-000 line at 81 GHz, these observations secure the identification of interstellar HNO. The 202-101 transition of this species has been detected toward NGC 2024, Sgr B2 (NW), W51M, and DR 21 (OH), while the 303-202 line at 1.2 mm was observed only in NGC 2024. Typical column densities of HNO observed toward these sources are Ntot ∼ 1012-1014 cm-2, corresponding to fractional abundances of fHNO ∼ 10-11 to 10-10. These values imply NO/HNO ratios of ∼ 100-800. Both the HNO fractional abundances and NO/HNO ratios are in reasonable agreement with predictions of ion-molecule-type models of interstellar chemistry, provided early-time calculations are used. Such behavior contrasts with that of other nitrogen compounds, whose observed abundances are best duplicated by steady-state calculations. The chemistries of HNO and NO are thus likely to be related. These observations also suggest that interstellar N-O bonds may be more common than previously thought.

Original languageEnglish (US)
Pages (from-to)706-712
Number of pages7
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 1 1994


  • ISM: molecules
  • Line: identification
  • Radio lines: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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