Updating the carbon dioxide line list in HITEMP

An updated carbon dioxide line list for the HITEMP spectroscopic database is presented. This line list covers the 0–17 697 cm −1 ( > 565 nm) spectral range and is built upon the AI-3000K semi-empirical line list for 12 C 16 O 2 , 13 C 16 O 2 , 16 O 12 C 18 O, and 16 O 12 C 17 O (Huang et al., 2023), combined with HITRAN2020 data, additional isotopologues, and further improvements described in this work. In order to make the line list practical for applications, over 36 billion individual transitions of the original AI-3000K line list have been separated into “strong” and “weak”. “Strong” transitions were adapted directly, while the weak transitions were then combined into so-called “effective” lines. The latter can accurately account for the intensity contribution of underlying weak AI-3000K transitions while reducing the database by over two orders of magnitude (to ∼ 326 million). In addition, pressure broadening parameters have been revised for this work to improve applicability at high temperatures. The line list has been added to HITEMP and is suitable for modeling the spectrum of carbon dioxide at temperatures up to 3000 K. Multiple validations have been carried out against terrestrial CO 2 retrievals, as well as high-resolution experimental measurements of CO 2 at different temperatures (up to 2000 K). The updated HITEMP line list includes 12 isotopologues of CO 2 and is provided in the standard HITRAN/HITEMP format, which is accepted by many community tools. It is demonstrated to be practical, accurate, and sufficiently complete for high-temperature environments. This work will be suitable for various high-temperature spectroscopic applications including exoplanet retrievals and remote sensing of combustion environments. • The updated CO 2 line list for HITEMP spans the 0–17 697 cm −1 ( > 565 nm) range. • The AI-3000K line list is used as a base for the new list, with multiple modifications. • Implements a novel approach for “effective” lines to combine intensities of weakest transitions • Significantly fewer lines than AI-3000K line list and accurately reproduce absorption at different temperatures. • Validated against experimental measurements and demonstrates a marked improvement over HITEMP2010.