Spatially resolved temperature measurements in an atmospheric plasma torch using the<i>A</i>² Σ⁺,<i>v</i>′ = 0 →<i>X</i>² Π,<i>v</i>″ = 0 OH band

Abstract

Molecular emission spectra of the OH rotational bands were measured to determine a two dimensional temperature profile of a microwave heated air plasma torch. The method is based on the simulation of rotational line intensities and the comparison with experimental results. A very high accuracy in simulation was obtained by the implementation of the Λ-doubling. The torch itself can be divided into a small (few millimetres in diameter) plasma and a flame which can reach up to 30 mm in diameter and 250 mm in height. While the plasma centre emits a variety of spectral lines, the whole flame is only accessible with the A2 Σ+, v' = 0 → X2 Π, v'' = 0 transition in the free radical OH at 306.36 nm.