Electron impact excitation of the electronic states ofN2. I. Differential cross sections at incident energies from 10 to 50 eV

Abstract

Normalized differential cross sections (DCS's) for the electron impact excitation of the lowest three singlet ($a^{\prime }, a, \omega$), and lowest five triplet ($A, B, W, {\mathrm{B}}^{\prime }, C$) valence electronic states of ${\mathrm{N}}_2$, and of the two ($3s{\sigma }_g$) Rydberg states ($E, a^{\prime \prime }$) have been determined at seven incident electron energies ranging from 10 to 50 eV. These DCS's were obtained for the scattering-angle range 5° to 138° by analyzing electron energy-loss spectra in ${\mathrm{N}}_2$ at a number of fixed scattering angles within that range. These data, which are the first that cover such a large incident energy and scattering-angle range for such a wide variety of final target states, show that each of the DCS's for the ten final target states falls into one of four classes. Since the initial molecular target state is a singlet, and none of the final states studied here is dipole allowed, these four classes are determined according to whether the final target state is triplet, singlet, parity-unfavored, or Rydberg in character. The DCS's for all the final target states change rapidly in shape as the incident electron energy is varied. Theoretical DCS's obtained from first-order perturbation models (Born-Ochkur and Ochkur-Rudge) agree poorly with the measured DCS's.