Nitric oxide excited under auroral conditions: Excited state densities andband emissions

Electron impact excitation of vibrational levels in the ground electronic s tate and nine excited electronic states in NO has been simulated for an IBC II aurora (i.e., similar to 10 kR in 3914 Angstrom radiation) in ol der to predict NO excited state number densities and band emission intensities. N ew integral electron impact excitation cross sections for NO were combined with a measured IBC II auroral secondary electron distribution, and the vib rational populations of 10 NO electronic states were determined under condi tions of statistical equilibrium. This model predicts an extended vibration al distribution in the NO ground electronic state produced by radiative cas cade from the seven higher-lying doublet excited electronic states populate d by electron impact. In addition to significant energy storage in vibratio nal excitation of the ground electronic state, both the a (4)Pi L(2)Phi exc ited electronic states are predicted to have relatively high number densiti es because they are only weakly connected to lower electronic stales by rad iative decay. Fundamental mode radiative transitions involving the lowest n ine excited vibrational levels in the ground electronic state are predicted to produce infrared (IR) radiation from 5.33 to 6.05 mu m with greater int ensity than any single NO electronic emission band. Fundamental mode radiat ive transitions within the a (4)Pi, electronic state, in the 10.08-11.37 mu m region, are predicted to have IR intensities comparable to individual el ectronic emission bands in the Heath and epsilon band systems. Results from this model quantitatively predict the vibrational quantum number dependenc e of the NO IR measurements of Espy et al. [1988].