The Schuster band, which can be excited by electrical discharges or electron impact in ammonia, is a broad diffuse emission band with maxima at 5672 and 5639 Å. The corresponding band in ND3 has resolved rotational line structure, which is shown here to be consistent with assignment to the 211 vibrational band of the C ̃′ 1A′1- A ̃1A″2 electronic transition of ND3. The corresponding 0-0 vibrational band also appears to be present, although much weaker. The wavelength of the diffuse NH3 band agrees with this assignment. The previous identification by Herzberg of this band as a transition of the ammonium radical (NH4) was based on the number of intermediate bands for mixtures of NH3 and ND3, but this evidence is not unambiguous and can be interpreted consistently with the present assignment. © 1986.