Fig. 6: Plasma nonequilibrium and chemical activity.

a The distributions of the rotational temperature (T_rot) and vibrational temperature (\(T_{{\mathrm{vib}}}\)) along the plasma jet (z-axis). The red solid square shows the case of rotational temperature, while the blue solid inverted triangle indicates the case of vibrational temperature. The plots show an average of five experimental measurements, and the measurement uncertainty (one standard deviation) is indicated by the error bars and is estimated to be 5–9% for the rotational temperature and 2–4% for the vibrational temperature. b The distributions of the OES of active species along the plasma jet (or z-axis). The black solid square shows the case of excited hydroxyl radical (OH), the red solid circle indicates the case of excited nitrogen molecule (N₂), and the blue solid triangle represents the case of excited argon atom (Ar). The plots show an average of five experimental measurements and the measurement uncertainty (one standard deviation) is estimated to be 7–9%. Since the error bars are too small to be shown distinctly, especially in the range of larger plasma jet length, they are not displayed. The shaded region is introduced in order to focus the attention on the plasma jet area at the gas flowrate of 2.2 l min⁻¹.