Quadrupole-Allowed Transitions in the Electron-Impact Spectrum of N2

The forbidden transitions observed in the nitrogen spectrum below 12.5 V have been studied by electron-impact methods. Since the theory indicates that electric quadrupole transitions are preferred to singlet—triplet in electron-impact spectra at intermediate energies, the observed transitions are probably electric quadrupole allowed. This has been demonstrated for the 12.25-V transition by studying its relative intensity as a function of the scattering angle. The data on the 11.86-V transition are also compatible with an electric quadrupole transition. In addition, new data on the Lyman—Birge—Hopfield bands in the 60–400-V energy range indicate that the intensity distribution among vibrational levels is independent of energy.