Spectroscopic method for the determination of the electron temperature in quasi-thermal air discharges. Application to an inductively coupled air plasma at atmospheric pressure

Abstract

A method for the approximation of the electron temperature, θ_e, in quasi-thermal air discharges, based on measurements of the relative emissivities of the weakly resolved OH and NO vibrational bands in the 210–320 nm spectral range, is described. The method is very sensitive and particularly suitable between 2000 and 6000 K, where intensities emitted by atomic lines cannot be easily distinguished from the molecular vibrational bands. It is shown that departures from thermodynamic equilibrium induced by radiative losses or by a difference between the electron temperature, θ_e, and the heavy particle temperature, θ_g, cannot lead to large systematic errors as long as the ratio X=θ_e:θ_g stays below 1.2. The uncertainty of the temperature determination is discussed together with an application to an inductively coupled air plasma at atmospheric pressure.