Discovery of interstellar NH

David M. Meyer*, Katherine C. Roth

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

138 Scopus citations


We report the discovery of interstellar NH in the diffuse clouds toward ζ Per and HD 27778 from highresolution, high signal-to-noise spectra of the NH A 3Π-X3Σ (0, 0) absorption band near 3358 Å. These observations represent the first detection of this molecule anywhere in the interstellar medium. Our measured equivalent widths of 0.37 ± 0.08 and 1.1 ± 0.3 mÅ for the NH R1(0) lines toward ζ Per and HD 27778 correspond to respective NH column densities of 9.0 × 1011 and 2.7 × 1012 cm-2. Our value for N(NH) in the ζ Per cloud is close to previous upper limits and much greater than that predicted by current models of the gas-phase nitrogen chemistry. The incorporation of a more rapid rate for the reaction N+ + H2 → NH+ + H in these models may provide an effective gas-phase route to explain the NH abundance. A contribution involving the direct or indirect production of NH from grain surface reactions is also possible. In any case, our NH measurements have additional implications for a better understanding of the observed CN abundances in diffuse interstellar clouds.

Original languageEnglish (US)
Pages (from-to)L49-L52
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - Aug 1 1991


  • Interstellar
  • Molecules

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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