Spectroscopic Examination of Vibrational and Rotational Properties of NO A2Σ+ Metastable State from NO γ-Band Spectra in N2-O2 Mixture Microwave Discharge
The spectra are observed in our microwave discharge plasma experiments. N2-O2 mixture plasma is generated by using a rectangular waveguide. We measured the spectra at 0, 60, 100 and 140 mm with the discharge pressure several Torrs. From these results, we can find that both NO and N2 molecules experience a cooling down process both on vibrational and rotational temperatures as the plasma flows to the downstream direction. And NO molecule has always a higher rotational temperature than N2. Meanwhile, we can see that in this nonequilibrium plasma, both NO and N2 molecules tend to get higher energy for vibrational motion than for rotational motion. We also change the gas partial pressure rate, when O2 molar ratio of the mixture increases, the NO experiences an increasing vibrational temperature. This is because that the NO A2Σ+ metastable state is excited from two main paths: N2(A 3Σ+u)+NO(X 2Π)→N2(X 1Σ+g)+NO(A 2Σ+), (1) NO(X 2Π)+e−→NO(A 2Σ+)+e− (2) When O2 or N2 is the majority of the discharge species, reaction (2) or (1) dominates the excitation process of NO A2Σ+, respectively. Therefore, under our plasma conditions, vibration-vibration energy transition of the reaction (1) results in a strong vibrational relaxation of NO A2Σ+ state molecules when N2 is the majority in the discharge gas. In conclusion, the admixture of N2 gas can lead to the reduction of average vibrational temperature significantly.
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