Also available through HITRANonline are a selection of supplemental data and tools that can be accessed below.
A line-mixing package for CO2 is provided as part of HITRAN2020 [1, 2]. Further details and an explanation of usage is available via the following link. Please not that the line-mixing package previously available for HITRAN2016  is not recommended for use with the HITRAN2020 data:
HITRANonline provides access to the Total Internal Partition Sums (TIPS) from Ref.  for all molecules (and their isotopologues) contained in the line-by-line section for HITRAN2020; accessed via the isotopologue metadata page. The following link contains further details and software for calculating the TIPS for each molecule:
The link below provides access to supplemental absorption cross sections described in Ref. , as well as those from previous HITRAN editions:
Line lists for three radioactive isotopologues of CO have been provided in Ref. . Users should be aware that the line intensities have not been scaled by isotopic abundances. We therefore advise users to refer to the manuscript and corresponding readme before using the data. The radioactive isotopologue data for CO (and readme) are available by clicking the following link:
 I. E. Gordon, L. S. Rothman, R. J. Hargreaves, R. Hashemi, E. V. Karlovets, F. M. Skinner, et al., "The HITRAN2020 molecular spectroscopic database", J. Quant. Spectrosc. Radiat. Transfer 277, 107949 (2022).
 J. Lamouroux, L. Régalia, X. Thomas, J. Vander Auwera, R. R. Gamache, J.-M. Hartmann, "CO2 line-mixing database and software update and its tests in the 2.1 μm and 4.3 μm regions ", J. Quant. Spectrosc. Radiat. Transfer 151, 88-96 (2015).
 I. E. Gordon, L. S. Rothman, C. Hill, R. V. Kochanov, Y. Tan, P. F. Bernath, et al., "The HITRAN2016 molecular spectroscopic database", J. Quant. Spectrosc. Radiat. Transfer 203, 3-69 (2017).
 R. R. Gamache, B. Vispoel, M. Rey, A. Nikitin, V. Tyuterev, O. Egorov, et al., "Total internal partition sums for the HITRAN2020 database", J. Quant. Spectrosc. Radiat. Transfer 271, 107713 (2021).
 R. V. Kochanov, I. E. Gordon, L.S. Rothman, K.P. Shine, S.W. Sharpe, T. J. Johnson, et al., "Infrared absorption cross-sections in HITRAN2016 and beyond: Expansion for climate, environment, and atmospheric applications", J. Quant. Spectrosc. Radiat. Transfer, 230, 172-221 (2019).
 G. Li, I. E. Gordon, L. S. Rothman, Y. Tan, S.-M. Hu, S. Kassi, et al., "Rovibrational line lists for nine isotopologues of the CO molecule in the X1Σ+ ground electronic state", Astrophys. J. Supp. Ser. 216, 15 (2015).