Validation of gas temperature measurements by OES in an atmospheric air glow discharge with water electrode using Rayleigh scattering

Rayleigh scattering is used to determine the gas temperature of an atmospheric pressure dc excited glow discharge in air with a water electrode. The obtained temperatures are compared with calculated rotational temperatures measured by optical emission spectroscopy of OH(A-X) and N₂(C-B). At a current of 15 mA a deviation is found between T_rot(OH) and the gas temperature obtained from Rayleigh scattering of about 1000 K. The gas temperatures obtained from Rayleigh scattering, N₂(C) and OH(A) in the positive column are, respectively, 2600 ± 100 K, 2700 ± 150 K and 3600 ± 200 K. It is shown that the rotational temperature of N ₂(C) is a reliable measurement of the gas temperature while this is not the case for OH(A). The results are explained in the context of quenching processes of the excited states. Spatially resolved gas temperatures in both longitudinal and radial directions are presented. The observed strong temperature gradients near the electrodes are checked to be consistent with the power dissipation and the heat transfer in the discharge. The effect of the polarity of the water electrode and filamentation on the measured temperatures is discussed.