High-resolution NO (X2&Pgr;, Δv = 1) emission data, obtained in an aurora between 100 and 125 km by the rocket-borne HIRIS cryogenic interferometer spectrometer, have been analyzed by a spectral simulation/least squares technique. The vibrational state population distribution determined by this method exhibit significant population of up to six vibrational states of NO and a multimodal behavior with vibrational quantum number that is not predicted by present models. This result is interpreted in terms of direct auroral formation of NO(v) by the chemiluminescent reaction of N(2D) with O2, coupled with excitation of NO(v = 1) by collisions between thermal atomic oxygen and aurorally enhanced NO(v = 0). The distribution shapes and their apparent invariance between 100 and 125 km suggest that collisional relaxation of NO(v), probably by atomic oxygen, prevails over radiative cascade at these altitudes; this result is not in keeping with the present understanding of the kinetics and component densities in this region. The apparant auroral photoefficiency for NO(Δv = 1) radiation deduced from these measurements is 1.1¿0.4% over the range 100--125 km, with a calibration uncertainty of a factor of 2.5; approximately 70-90% of the observed radiation is directly excited via the N(2D) precursor.