The HITRAN2020 molecular spectroscopic database

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables, including partition sums, that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the interveningyears).All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition ranges from updating a few lines of specic molecules to complete replacements of the lists and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increasedsubstantially, often featuring sub-percent uncertainties. Broadening parameters associated with the water vapor's ambient pressure were introduced to HITRAN for the first time and are available now for several molecules. The HITRAN2020 edition will continue taking advantage of the relational structure and thecient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition.