Translational spectroscopy of metastable fragments produced by dissociative excitation of atmospheric gases by electron impact. I. Nitrogen

Kinetic-energy spectra of long-lived high-Rydberg nitrogen atoms produced by electron impact dissociative excitation were measured using a time-of-flight apparatus. Four principal features were found in the fragment kinetic-energy spectra with peaks at 0.6, 2.4, 3.4, and 6.7 eV. The excitation function exhibited a sharp resonance-like behavior near a threshold of 24.1 eV, corresponding to fragment production of $\mathrm{N}\left({}_{}{}^4{}_{}{}^{}S\right)+{\mathrm{N}}^{**}$, where N** is a high-Rydberg atom with an energy near the ionization limit of N(14.54 eV). The observed features are discussed in terms of the core-ion model of high-Rydberg dissociation. The data are compared with other dissociative excitation and dissociative ionization work. The maximum differentil cross section for the production of energetic long-lived high-Rydberg N atoms was found to be $\frac{d\sigma }{d\Omega }\simeq 9\times {10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{sr}}^{-1\mathrm{}}$ within a factor of 2 at an electron energy of 180 eV and at an angle of 90° with respect to the electron beam. Geophysical implications of these measurements concerning heating of the atmosphere, radiative transfer of resonance radiation, and chemical reactions are mentioned briefly.