Excitation of Nitrogen by Protons of a Few kev Energy

To aid in interpreting auroral spectra, we have investigated the excitation of nitrogen by protons of a few kev energy. The dependence of the intensity of the various spectral features on the proton current and gas pressure gives evidence about the excitation mechanisms. The conclusions are that the first negative and Meinel systems of N₂⁺ are excited through charge exchange, that the first positive system of N₂ is excited, not by proton impact, but by the impact of fast neutral atoms, that allowed N i lines are excited by a single process involving dissociation and excitation, and that the Balmer lines result from charge capture directly into an excited state. As compared with excitation by electron impact, vibration is enhanced in the upper level of the first positive system, but rotational temperatures derived from the first negative system of N₂ agree with the gas temperature.