Time-resolved CO₂, CO, and N₂ Vibrational Populations in In Ns Pulse Discharge Plasmas

Time-resolved CO₂, CO, and N₂ vibrational populations and translational-rotational temperature are measured in a ns pulse burst discharge plasma. The discharge is sustained in a CO₂-N₂ mixture slowly flowing through a rectangular cross section quartz channel, with two parallel plate electrodes external to the channel. CO₂ and CO vibrational populations are measured by mid-IR, tunable Quantum Cascade Laser (QCL) Absorption Spectroscopy, and N₂ vibrational populations are measured by the ns broadband, collinear CARS. The results indicate that a ns pulse discharge operated at a high pulse repetition rate, 100 kHz, results in a modest vibrational excitation of N₂ and CO₂. The number density of CO, a major product of CO₂ dissociation, is also inferred from the QCL measurements. The present diagnostics allow in situ monitoring of the time-resolved, state-specific CO₂ vibrational excitation and relaxation during the discharge and in the afterglow, along with the time-resolved CO vibrational populations. This makes possible isolating and quantifying two major mechanisms of CO₂ dissociation, (i) decay via excited electronic states populated by electron impact, and (ii) stepwise anharmonic vibration-vibration (V-V) pumping of the asymmetric stretch vibrational mode.