Quantum mechanical and crossed beam study of vibrational excitation of N₂ by electron impact at 30-75 eV

The ratios of differential cross sections for excitation of the first excited vibrational state and for elastic scattering for electron impact on N₂ have been measured at scattering angles ranging from 20° to 135° at 30, 35, 40, 45, and 75 eV impact energies and from 25° to 90° scattering angle at 20 eV impact energy. The results at 20 eV are in good agreement with two previous sets of measurements. Using previously measured and normalized elastic differential cross sections for N₂, the ratios have been converted to inelastic cross sections. Calculations using a four-state vibrational-rotational basis set and an effective interaction potential developed previously are reported at the five energies in the 30-75 eV region. It is shown that the potential scattering model can account for the magnitude and the qualitative behavior of the cross sections at 35-75 eV but there are some significant quantitative differences between theory and experiment. The most striking of these is the way the theoretical model overestimates the scattering at scattering angles less than about 50°. Core-excited resonances apparently make an appreciable contribution to the vibrationally inelastic scattering at 30 eV.