Vibrational excitation of N2 in the spark-and-glow phases of a long-pulse air discharge at atmospheric pressure

The influence of N2 molecule vibrational excitation on plasma chemical synthesis, particularly nitrogen fixation and ammonia formation, is investigated in this study. Despite its pivotal role in lowering the energy barrier of chemical reactions, there exists a scarcity of experimental data regarding its energy efficiency. Employing the coherent anti-Stokes Raman scattering (CARS), the energy efficiency of N2 vibrational excitation under different discharge conditions was investigated. The impact of pulse width, discharge current, and discharge modes were studied. The CARS results reveal that under the short spark discharge mode, strong vibrational-rotational non-equilibrium existed and the vibrational temperature was as high as 5500 K. However, under the steady state glow discharge mode, the fast vibrational-rotational energy exchange by N2(v)-O reaction significantly heats the background gas and the rotational temperature was as high as 3500 K. Additionally, the research reveals that as the discharge current of glow discharge decreases, both rotational and vibrational temperatures of nitrogen molecules decrease. However, reducing the pulse width of the glow discharge does not result in significant changes in the discharge process. To determine the energy efficiency of N2 vibrational excitation, a 0D simulation was conducted with ZDPlaskin. Discharge power and reaction rates for electron collision excitation of N2 vibrational states were used to calculate the energy efficiency of N2 vibrational excitation. The result shows that the spark is more efficient.