Excitation of N₂(B ³_g) in the nitrogen short-lived afterglow

The excitation of the N₂(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 N₂⁺(B ²_u⁺) ion through emissions, and also on the electronic ground state of N₂ 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 N₂(X ¹_g⁺) from the beginning to the bulk of this ionized region. The N₂(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 N₂(X ¹_g⁺) and N₂(A³_u⁺) is shown to be the pre-eminent excitation mechanism in the short-lived afterglow.