N₂(A³Σ_u⁺,v) Energy Transfer Kinetics in Reacting N₂-CO₂-CH₄ Plasmas

Energy transfer from metastable N₂(A³Σ_u⁺,v=0,1) molecules in plasmas sustained in mixtures of nitrogen with CO₂, CH₄, and H₂ is studied using Tunable Diode Laser Absorption Spectroscopy. The plasma is generated at 150 Torr using a repetitive ns pulse discharge sustained between two parallel copper electrodes external to a quartz cell. The pulse repetition rate is up to 100 kHz, with up to 50 pulses produced during each discharge burst, and the burst repetition rate of 20-40 Hz. The plasma remains diffuse and is confined between the electrodes, such that the absorption path is well defined. During the experiment, time-resolved, absolute populations of N₂(A³Σ_u⁺) are measured. The experimental data are compared with kinetic modeling to identify the dominant N₂(A³Σ_u⁺) generation and decay processes. Adding CO₂, CH₄, or H₂ to the mixture does not affect the N₂(A³Σ_u⁺) quenching in the beginning of the burst due to their slow quenching rates. However, dissociation of the added gases into H and O atoms results in a faster N₂(A³Σ_u⁺) quenching. Therefore, the increase of the N₂(A³Σ_u⁺) quenching rate can be used to indirectly indicate the enhanced reactivity of the mixture. The experimental results also show that methane results in a rapid vibrational relaxation of N₂(A³Σ_u⁺) molecules.