An experimental survey of the low energy electron scattering spectrum of nitrogen

Abstract

The electron energy loss spectrum of nitrogen has been studied at incident energies from 9 to 50 eV with an electron spectrometer. Scattering angles from 4° to 30° were used. Energy resolution varied from 35 to 100 meV (FWHM). The spectra show that at incident energies less than 20 eV, which are of greatest relevance to atmospheric processes, the energy loss spectrum is dominated by the electric quadrupole transition X 1 σ g +→ a 1 Π g and the spin-forbidden singlet-triplet transitions X 1 Σ g +→ A 3 σ u , X 1 Σ g +→ B 3 Π g , and X 1 Σ g +→ C 3 Π u . These electron excitations are responsible for the first and second positive groups and Lyman-Birge-Hopfield bands which are the most prominent of the atmospheric N 2 emissions. The electric dipole transition X 1 Π g +→ b 1 Π u which is one of the strongest features of the 50 eV electron energy loss spectrum is shown to be extremely weak at an incident energy of 15 eV. The results suggest that the observed intensities of atmospheric N 2 emissions in the aurora are entirely compatible with low energy electron impact excitation mechanisms.