Experimental Determination of Line Strengths for Selected Carbon Monoxide and Carbon Dioxide Absorption Lines at Temperatures between 295 and 1250 K

Abstract

Fourier transform infrared absorption spectroscopy has been used for the determination of the line strengths of 41 CO and CO₂ absorption lines at temperatures between 295 and 1250 K. The CO vibrational-rotational lines were from the P branch of the fundamental absorption band (2150–1950 cm⁻¹) while the CO₂ vibrational-rotational lines were from the far wing of the R branch of the v₃ fundamental band (2395–2380 cm⁻¹). The intensities of the lines were measured from absorption spectra recorded in a high-temperature gas cell containing known concentrations of CO/CO₂/N₂ gas mixtures at atmospheric pressure. Absorption spectra were recorded through the cell with the use of a moderate-resolution Fourier transform infrared spectrometer. The absorption spectra were mathematically corrected for distortions resulting from the finite resolution of the spectrometer and for peak overlap. Line strength measurements were made from the corrected peaks by using the Bouguer-Lambert law and assuming a Lorenztian line profile. The experimentally obtained line strengths were evaluated (1) by statistical calculations, (2) by consideration of the validity of the Bouguer-Lambert assumption for these data, (3) by comparison with existing room-temperature and high-temperature data, and (4) by comparison with theoretical calculations. For CO, the statistical analysis suggests that the reported values have an uncertainty of ±10–12%, which is similar to the observed discrepancies with other reported values at room temperature. At high temperatures, the difference between these data and previously reported data and theoretical predictions is less than 10%. For CO₂, the statistical uncertainty associated with the line strength calculations is less than 5%, which is also the approximate level of agreement with existing room-temperature data. For lines with m indicies of 65–89, at high temperatures, the values reported in this work agree within 5 to 10% of theoretical calculations.