This diatomic radical, containing nitrogen and hydrogen, has been detected in both the diffuse interstellar medium, where it is seen in absorption against the light of background stars, and in denser gas toward the center of our Milky Way galaxy. In the latter case the relative abundances of NH3, NH2, and NH have been interpreted in terms of low-velocity shock activity (Goicoechea et al. 2004).
NH was first detected at near ultraviolet wavelengths in 1991 by D. M. Meyer and K. C. Roth. The subsequent observations of the Galactic center were made with the Infrared Space Observatory (ISO). It has been recently observed using the Herschel satellite towards other molecular clouds (Persson et al. 2010, 2012).