Kinetics of metastable N <sub>2</sub> (A <sup>3</sup> Σ <sub>u</sub> <sup> <b>+</b> </sup> , v) molecules in high-pressure nonequilibrium plasmas
Elijah Jans, Sai Raskar, Xin Yang, Igor Adamovich
Abstract
Abstract Absolute, time-resolved populations of N 2 (A 3 Σ u + , v = 0–5) vibrational levels in high-pressure ns pulse discharge plasmas are measured by Tunable Diode Laser Absorption Spectroscopy (TDLAS). The diffuse plasma is generated by a repetitively pulsed, double dielectric barrier, ns discharge across a 10 mm gap in a plane-to-plane geometry, at pressures of up to 400 Torr. The results of TDLAS measurements in nitrogen and in H 2 –N 2 , O 2 –N 2 , and NO–N 2 plasmas are compared with kinetic modeling predictions, identifying the mechanisms of N 2 (A 3 Σ u + ) generation and decay during the discharge pulses and in the afterglow. Comparison with the modeling predictions indicates that electron impact dissociation of N 2 from the ground electronic state significantly underpredicts the yield of N atoms. The present data suggest that N 2 dissociation in the plasma also occurs during the energy pooling process in collisions of two N 2 (A 3 Σ u + ) molecules. The results also show that high-pressure, high repetition rate, volume-scalable ns pulse discharges can be used for efficient generation of atomic species for plasma chemical and plasma catalysis syntheses. In an NO–N 2 mixture, it is shown that the N 2 (A 3 Σ u + ) decay is controlled by the rapid energy transfer to NO, resulting in its electronic excitation and UV emission (NO γ bands). The diagnostics used in the present work can be used for the accurate characterization of both high-pressure, low-temperature gas discharge plasmas and high-temperature nonequilibrium flows generated in pulsed facilities such as shock tubes and expansion tunnels.