Detection of H2 18O and an abundance estimate for interstellar water.
Abstract
Detection is reported of the 3(13) - 2(20) (203.4075 GHz) transition of interstellar H2(O-18) in the molecular clouds of Orion and DR 21 (OH). An excitation calculation shows that far-infrared radiation from dust provides the primary mechanism for populating the 3(12) state, although collisions with the H2 gas are also of importance in the case of H2(O-16). The density of para-H2(O-18) in the Orion cloud is estimated as 0.004 per cu cm and that of water (ortho- and para-) as 8 per cu cm. The estimated H2O/H2 abundance ratio is about 1:100,000, implying that water is second only to CO in abundance among the trace molecules observed in molecular clouds.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1978
- DOI:
- 10.1086/182692
- Bibcode:
- 1978ApJ...222L..59P
- Keywords:
-
- Abundance;
- Interstellar Matter;
- Molecular Excitation;
- Water;
- Clouds;
- Far Infrared Radiation;
- Gas Density;
- Gas Temperature;
- Molecular Spectra;
- Astrophysics;
- Interstellar Matter:Water;
- Molecular Clouds:Orion Nebula