New Detections of Interstellar HNO at 2 and 1.2 Millimeters: More N-O Bonds
Abstract
The 202 to 101 and 303 to 202 transitions of HNO at 163 and 244 GHz have been detected toward several molecular clouds. In conjunction with previous measurements of the 101 to 000 line at 81 GHz, these observations secure the identification of interstellar HNO. The 202 to 101 transition of this species has been detected toward NGC 2024, Sgr B2 (NW), W51M, and Dr 21 (OH), while the 303 to 202 line at 1.2 mm was observed only in NGC 2024. Typical column densities of HNO observed toward these sources are Ntot approximately 1012 to 1014/sq cm, corresponding to fractional abundances of fHNO approximately 10-11 to 10-10. These values imply NO/HNO ratios of approximately 100 to 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1994
- DOI:
- 10.1086/174442
- Bibcode:
- 1994ApJ...430..706Z
- Keywords:
-
- Abundance;
- Interstellar Matter;
- Line Spectra;
- Molecular Clouds;
- Nitrogen Oxides;
- Radio Emission;
- Cosmology;
- Interstellar Chemistry;
- Spectrum Analysis;
- Astrophysics;
- ISM: MOLECULES;
- LINE: IDENTIFICATION;
- RADIO LINES: ISM