Gas temperature determination of non-thermal atmospheric plasmas from the collisional broadening of argon atomic emission lines

- A new method to measure the gas temperature in non-thermal plasmas from the collisional broadening of some Ar I lines is presented.
- These lines correspond to transitions into both resonance levels s2 and s4 of the 3p54s configuration of the Ar I system.
- For these lines, the van der Waals contribution should not be ever discarded in gas temperature determination.
- Analytic expressions allowing straightforward determination of the gas temperature from the collisional broadening are given.
- No assumptions on the degree of equilibrium existing in the plasma are needed.

In this work we propose a new method allowing gas temperature determination in argon non-thermal plasma jets, based on the measurement of the collisional broadening of different argon atomic lines corresponding to transitions into both resonance levels s2 and s4 of the 3p54s configuration. The method was developed for fourteen lines: Ar I 978.45, 935.42, 922.45, 852.14, 840.82, 826.45, 750.39 (corresponding to transitions falling to level s2) and 965.77, 842.46, 810.37, 800.62, 751.46, 738.40, 727.29 nm (corresponding to transitions falling to level s4). A carefully study of the relative importance of all broadening mechanisms to the whole profile for these lines, under a broad range of experimental conditions, revealed that for electron densities and gas temperature lower than 1015 cm−3 and 2000 K, the Stark and Doppler broadenings can be neglected in the method, but the van der Waals contribution should not be ever discarded for gas temperature determination. The gas temperature of a microwave non-thermal plasma jet was determined using nine of these lines. Results were consistent with each other, and with those obtained from the rotational temperature derived from OH ro-vibrational band. Also, the influence of the air entrance on the collisional broadening of the lines has been studied and the way the method should be modified to include this effect is indicated.

151