Low-energy electron impact excitation of the nitrogen molecule: Optically forbidden transitions

Ab initio calculations are performed on the e^--N₂ scattering system, at low impact energies, using the R-matrix technique. The X 1Σ⁺_g ground state and the lowest seven valence excited states, A ³Σ⁺_u, B ³Π_g, W ³Δ_u, B′ ³Σ^-_u, a′ ¹Σ^-_u, a ¹Π_g and w ¹Δ_u, of N₂ are included in the close coupling expansion with each state being represented by a configuration interaction wavefunction in a hybrid orbital set. Various approximations for the representation of the correlation between the target and the incident electron are investigated. Integrated and differential scattering cross sections are presented, and compared to experiment, for excitation from the ground level to optically forbidden levels. The results compare favourably with recent experiments in this energy region and remove a number of problems with our previous work.