UV OH spectrum used as a molecular pyrometer

For the UV OH band at 306.357 nm (transition A2, ν = 0 → X2, ν ′ = 0) that is frequently observed in hot gases containing oxygen and hydrogen (flames, arc plasmas), a very sensitive variation of two groups of unresolved rotational lines as a function of the temperature has been found. Using a numerical simulation, this variation has been calibrated as a function of the temperature and of the optical apparatus function. This calibration allows us to easily determine the rotational temperature without computing any line intensity. 1.