Excitation of N₂(B³Pig) in the nitrogen short-lived afterglow

The excitation of the N 2 (B 3 g ) state in microwave discharges ignited in flowing nitrogen and in their short-lived afterglow is investigated. Simultaneous measurements in the post-discharge on this species and the N 2 + (B 2 u + ) ion through emissions, and also on the electronic ground state of N 2 by spontaneous Raman scattering, provide information of their vibrational distribution function. A spatial study has been carried out, showing a quite slow evolution of the vibrational populations along the short-lived afterglow, and in particular the first proof of a steady vibrational distribution of N 2 (X 1 g + ) from the beginning to the bulk of this ionized region. The N 2 (B 3 g vibrational distribution is analysed by a steady-state kinetic model taking into account all the B state excitation processes, i.e. electron collisions and reactions between molecular excited states, and quenching. The reaction between the vibrationally excited N 2 (X 1 g + ) and N 2 (A 3 u + ) is shown to be the pre-eminent excitation mechanism in the short-lived afterglow.