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

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.