Evaluation of Plasma Temperature from the OH Violet Molecular Emission System

The violet OH system (A$^{2}\Sigma^{+}$ - X$^{2}\Pi_{\mathrm{i}})$ molecular emission spectrum is frequently observed in plasma sources containing water it is a good tool for diagnosing plasmas containing this molecule. We have simulated the spectrum of (0,0) band of this system from 3064 {\AA} for different rotational temperature. The method proposed permit to evaluate, by comparing point to point a real spectrum with the simulated one, temperature and apparatus function, approximated by the gauss function (the half-width at 1/e height). Moreover, it is shown, by noised spectra simulation, the influence of noise to signal ratio at the calculated temperature values. If the noise to signal ratio is about 10{\%} we found an error of 6{\%} at temperature 3000K and 10{\%} at 6000K. This method has been used to determine the combustion temperature from a real spectrum recording in Polymethyl methacrylate rocket plume taken 0 mm from the nozzle of fuel grain. The rotational temperature of about 3000 $\pm$ 350 K, has been found and noise to signal ratio is about 20{\%}.