High-temperature absorption line shape parameters for CO2 in the 6800-7000 cm-1 region from dual frequency comb measurements up to 1000 K

We present the first systematic study of self-broadened CO2 line shape parameters in the 00031←00001 and 01131←01101 bands at high temperature. We report temperature-dependent broadening coefficients and pressure shifts for more than 40 transitions in the 00031←00001 band, and 70 transitions in the 01131←01101 hot band. The majority of these parameters have never been measured at high temperature. The new parameters are determined from spectra measured with a broadband, high resolution dual frequency comb absorption spectrometer in a high-temperature gas cell up to 981 K. We fit the measured spectra using a multispectrum fitting approach to derive line shape parameters with both a Voigt and speed-dependent Voigt profile. We compare the measured parameters to calculated line shape parameters, including those used in the HITRAN2020 database. For the bands included in this study, these comparisons identify several deviations between the measured and calculated line shape parameters that ultimately limit the accuracy of absorption models when using the calculated parameters. Additionally, we fit the measured line shape parameters using empirical expressions for the broadening coefficient and pressure shift, which we validate for high-temperature transitions up to |m|≈90. We use these models to construct a set of database files that can be used to supplement the HITRAN database for self-broadened CO2 in the 6800 – 7000 cm-1 region. These new parameters significantly improve the accuracy of absorption models for high-temperature CO2 in this frequency range, and also provide useful data to test and improve methods used to calculate CO2 line shape parameters.