Also available through HITRANonline are a selection of supplemental data and tools that can be accessed below.
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; 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, 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).
 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).
 R. R. Gamache, C. Roller, E. Lopes, I. E. Gordon, L. S. Rothman, O. L. Polyansky, et al., "Total internal partition sums for 166 isotopologues of 51 molecules important in planetary atmospheres: Application to HITRAN2016 and beyond", J. Quant. Spectrosc. Radiat. Transfer 203, 70-87 (2017).
 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).