Estimates of N2 abundances in dense molecular clouds

M. Womack, L. M. Ziurys, S. Wyckoff

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46 Scopus citations


Interstellar N2 abundances toward 13 dark clouds and warm star-forming regions are derived from column densities measured for N2H+. The N2H+ abundances were determined from a millimeter-wavelength study of the molecule's J = 1 → 0 and J = 3 → 2 rotational transitions, as well as from observations of the 2NNH+ and N15NH+ isotopic spectra. Abundances of N2 were estimated from N2H+ assuming the chemistry had achieved steady state. Fractional abundances of N2 with respect to H2 are typically f ∼ 3 × 10-6 for eight warm clouds and f ∼ 6 × 10-6 for four cold clouds, with an average value of f ∼ 4 × 10-6 These abundances are in good agreement with predictions of ion-molecule models of interstellar chemistry in quiescent clouds which have reached steady state. The relatively high N2 concentrations suggest that the most of the nitrogen in dense clouds is in the form of molecular nitrogen. Given that the N2 abundances are comparable in both warm and cold clouds, condensation onto grains may not play a large role in the nitrogen chemistry of dense gas.

Original languageEnglish (US)
Pages (from-to)188-192
Number of pages5
JournalAstrophysical Journal
Issue number1
StatePublished - 1992


  • ISM: abundances
  • ISM: clouds
  • ISM: molecules
  • Molecular processes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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