Forbidden Vibrational Transitions in the Electron-Impact Spectra of Molecular Oxygen and Nitrogen

The excitation of forbidden vibrational transitions by electron impact has been studied at 45-eV electron kinetic energy. The relative intensities of these transitions in N2 and O2 referred to the elastic peak, are independent of the scattering angle between 3° and 14°. For comparison we have also included data on vibrational transitions in CO and NO at one angle (4°). These are allowed by electric-dipole selection rules. In molecular oxygen we have also observed the forbidden electronic transitions a 1Δg ← X 3Σg− and b 1Σg+ ← X 3Σg− although the latter can be barely detected above background.