Time evolution of NO X ²Π (ground), A ²Σ⁺ state and O ³P atomic ground state density in downstream of a nitrogen-oxygen pulsed microwave surfaguide discharge

Nitric oxide is the dominant product in low pressure N₂-O₂ (1:1) microwave plasma used for oxidative nitrogen fixation [1].This study was focued to understand the formation of Nitric oxide in a pulsed (500 Hz 50-50 duty cycle) 2.45 GHz surfaguide microwave discharge. Laser Induced Fluorescence(LIF) of NO was used to determine the absolute X ²Π NO ground state density over the duration of the pulse(on and off time) in the downstream. The NO X molecules were excited to A(0,0) state using a 10 Hz tuneable pulsed dye laser at 226.23 nm(frequency doubled from 452.46 nm). The fluorescence at 247 nm of A→X (0,2) was recorded using an ICCD camera with a 248/10 nm filter and a lens. The 247 nm A→X(0,2) emission [1] naturally occurring from the electronic excitation in the plasma showed reverse trend of time evolution than the X state density. O atom plays vital role in both formation and annihilation of NO in the plasma [2]*. To correlate O atomic density evolution in an identical plasma condition(2,5 Torr total pressure; 0.7 kW power) we used Two photon Absorption LIF(TALIF,excitation wavelength: 225.6 nm 2p ³P → 3p ³P ). The 844 nm fluorescence was recored with the ICCD camera with a lens and 840/10 nm bandpass filter.