Updating the carbon dioxide line list in HITEMP

Abstract

An updated carbon dioxide line list for the HITEMP spectroscopic database is presented. This line list covers the 0–17697 cm−1 (>565 nm) spectral range and is built upon the AI-3000K semi-empirical line list for 12C16O2, 13C16O2, 16O12C18O, and 16O12C17O (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.