Gas temperature determination in microwave discharges at atmospheric pressure by using different Optical Emission Spectroscopy techniques

• We measured the gas temperatures of different 2.45 GHz plasmas.
• We obtained the gas temperature from N2 and OH molecular spectra.
• We compared with an alternative method using 588.99 and 589.59 nm Na I lines.
• A very good agreement between the values of Tgas obtained was found.
• Τhe alternative method could be very helpful in plasmas containing nitrogen.

Non-thermal plasmas sustained at atmospheric pressure are considered as a very promising technology for different purposes, in which the knowledge of the gas temperature is an important issue. In this paper, the gas temperatures of different argon microwave (2.45 GHz) plasma torches were determined by using different Optical Emission Spectroscopy techniques. Thus, they were estimated through the analysis of N2+(B-X) and OH(A-X) molecular spectra. On the other hand, a method based on the measurement of the van der Waals broadening of 588.99 nm Na I line was employed, and the temperatures obtained from it were compared to the rotational temperatures derived from N2+(B-X) and OH(A-X) rotational bands. A reasonable good agreement was found between the values of temperatures obtained by using the 588.99 nm Na I line and those obtained from N2+ rotational band.