High energy-resolution studies of electron impact optical excitation functions. II. The first positive system of N2

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Abstract
The relative emission cross sections for the (4,1), (4,2), and (5,2) bands of the N2 first positive system were measured in the threshold region using a high energy‐resolution electron spectrometer coupled to an optical detection system. The maxima in the relative emission cross section for the (4,1) and (4,2) bands occurred at 10.68±0.08 eV and the maximum for the (5,2) band occurred at 11.00±0.08 eV. Structure was observed in the excitation functions which arose from the presence of channels for the population of the N2 B 3Πg state other than direct excitation by electron impact at certain energies. The contribution from C 3Πu→B 3Πg cascade is the major source of additional B 3Πg state population. The contribution from this process reaches a maximum at an incident electron energy near 14 eV. The E 3Σ+g state is observed to contribute slightly to the B state population near 12 eV through cascade and/or collisional deactivation. A third secondary feature is observed in the optical excitation functions close to threshold. Measurement of direct electron excitation functions for the v=4 and v=5 vibrational levels of the B 3Πg state by electron scattering techniques as well as delayed coincidence optical experiments on the first positive (4,1) band emission confirm the presence of a secondary process in this region. Radiative cascade from the N2 A 3Σ+u and/or W 3Δu states is the most reasonable explanation of this effect.