LOW-ENERGY ELECTRON-IMPACT STUDY OF 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 v′-2, 3, and 4 bands of the b 1IIu←X1∑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 b1H u←X1∑g+ up to v′=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 12.84-eV b 1∏u←X 1∑g+ (4-0) 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 p′ 1∑ u+ Rydberg state at 12.93 eV is much more strongly peaked in the forward direction than that for the b1∏ 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∏u bands with increasing scattering angle. There may be a singlet-triplet transition at this energy.