TEMPERATURE-MEASUREMENTS BASED ON THE 1ST NEGATIVE SPECTRUM OF NITROGEN

Noisy, non-resolved emission spectra of the (0,0) 391.4 nm N2+ molecular band are employed for the rotational (and in some case vibrational) temperature evaluation in different sources in the range of 320-7900 K when the apparatus function of the recording system is unknown. The following sources are examined: an ovoid-shaped transferred arc at atmospheric pressure, a low-pressure transferred arc, a high-voltage high-pressure electric discharge, a low-pressure radio-frequency discharge, and an atmospheric pressure laminar plasma jet. The described method is based on a normalization of the experimental spectrum with respect to the (0,0) band-head amplitude followed by a point-to-point comparison of the real spectrum with respect to a computer simulated spectrum using the best-square fit criterion. This criterion is found as the good one: the relative error on temperature evaluation had the same order of magnitude as the noise-to-signal ratio, even if the last one was relatively high. It was also found that the rotational and vibrational temperatures in the radio-frequency discharge are very different, which indicates an out of thermodynamic equilibrium characteristic of such a discharge. The proposed method of temperature evaluation is shown as quite precise and simple to use for even the non-spectroscopists.