Determination of Gas Temperatures at 295–1273 K Using CO Vibrational-Rotational Absorption Spectra Recorded with an FT-IR Spectrometer

Fourier transform infrared absorption spectroscopy has been used to determine the rotational temperatures of high-temperature (≤1273 K) CO/N₂ gas samples. To achieve this objective, a special gas cell was constructed which permitted the acquisition of absorption spectra of samples containing CO at concentrations of 1–10% by volume in N₂ and at temperatures between 295 and 1273 K. The absorption spectra were recorded with the use of a moderate-resolution (0.25 cm⁻¹) FT-IR spectrometer. The rotational temperatures were calculated from the spectra after rigorous correction for photometric errors. Temperatures calculated from the P branch of CO spectra had accuracies of 3.2% or better. In all cases, the calculated temperatures were lower than temperatures recorded with a thermocouple, which had an accuracy of ±0.75%. An important factor in the success of these determinations was the adoption of measures to prevent the modulated spectral emission of the hot gases from reaching the detector.