A Survey of N 2H + in Dense Clouds: Implications for Interstellar Nitrogen and Ion-Molecule Chemistry
Abstract
Attention is given to spectra of the N2(H(+) J = 1 - 0, J = 3 - 2 and (N-15)NH(+) and N(N-15)H(+) J = 1 - 0 rotational transitions obtained toward a sample of star-forming and cold dark clouds in the Galaxy. Toward the star-forming regions, line profiles are relatively narrow (typically 1-5 km/s) and show no evidence of line wings, in contrast to the spectra of HCO(+). It is inferred from the apparent absence of N2H(+) in hot, shocked gas that this ion may be a selective tracer of extended, quiescent material. Column densities of N2H(+) were found to be about 5 x 10 exp 12/sq cm toward cold clouds and about 10 exp 14/sq cm toward warm clouds. These values correspond to fractional abundances, relative to H2, of about 4 x 10 exp -10 toward both the warm and cold clouds. It is concluded that the abundance and distribution of N2H(+) is well explained by the ion-molecule chemistry, provided it has reached the steady state, as is found for interstellar NH3. The N2H(+) results are advanced as further evidence that interstellar nitrogen chemistry is anomalous.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1992
- DOI:
- 10.1086/171094
- Bibcode:
- 1992ApJ...387..417W
- Keywords:
-
- Azo Compounds;
- Interstellar Chemistry;
- Interstellar Matter;
- Molecular Clouds;
- Dark Matter;
- Electron Transitions;
- Emission Spectra;
- Formyl Ions;
- Molecular Rotation;
- Spectral Line Width;
- Astrophysics;
- ISM: ABUNDANCES;
- ISM: MOLECULES;
- MOLECULAR PROCESSES