Intensity Perturbations Due to Configuration Interaction Observed in the Electron Energy-Loss Spectrum of N2

The electron energy-loss spectrum of 25-keV electrons in molecular nitrogen has been re-investigated in the 12.5–14.9 eV energy-loss range with improved energy resolution of 10 meV. The band intensities of the b and b′ progressions, which consist of the bands j, b, m, p, q, and b′, g, f, r, s, t as recently turned out, exhibit strong perturbations due to configuration interaction with the c and c′ state, respectively. The disturbed intensity in the progressions is quite analogous to the one in the two-electron excitation region of helium. Intensity perturbations in the o series, if any, should be very weak.