Low-Energy Electron-Impact Study of the 12–14-eV Transitions in Nitrogen

A high‐resolution low‐energy electron spectrometer has been constructed and used to study the nitrogen energy‐loss spectrum in the 12–14‐eV region. The relative intensities of the $\text{υ′\hspace{0.17em}=\hspace{0.17em}2}$ , 3, and 4 bands of the $b^1{\Pi }_u{\mathrm{\leftarrow X}}^1{\Sigma }_g^{+}$ transition between 12.65–12.84 eV and the intense 12.92‐eV composite transition have been studied in detail at primary energies from 15–50 eV and scattering angles of 1°–40°. The relative intensities of the bands of $b^1{\Pi }_u{\mathrm{\leftarrow X}}^1{\Sigma }_g^{+}$ up to $\text{υ′\hspace{0.17em}=\hspace{0.17em}4}$ were found to remain invariant with respect to changes in primary energy and scattering angle. However, the ratio of the 12.93‐eV peak to the $\text{12.84‐}\mathrm{eV}{b}^1{\Pi }_u{\mathrm{\leftarrow X}}^1{\Sigma }_g^{+}\text{(4\hspace{0.17em}−\hspace{0.17em}0)}$ transition decreased by a factor of 3, with increasing scattering angle from 1° to 40°, independent of primary energy. The strong angular dependence of the relative intensities for these transitions suggests that the differential‐scattering cross section for the ${\mathrm{p\prime }}^1{\Sigma }_u^{+}$ Rydberg state at 12.93 eV is much more strongly peaked in the forward direction than that for the $b^1{\Pi }_u$ state. The effect of multiple scattering on these transitions was investigated. At low energies, the intensity of a peak at 13.2 eV increased relative to the $b^1{\Pi }_u$ bands with increasing scattering angle. There may be a singlet–triplet transition at this energy.