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Using HITRAN to Model Opacities for Planetary Atmospheres: Test case of Microwave Spectra of NH$_3$, SO$_2$ and PH$_3$

The latest version of the HITRAN molecular spectroscopic database, HITRAN2020, has recently been released featuring many updates, including line-by-line broadening parameters (and their temperature dependence) appropriate for the dominant constituents of planetary atmospheres. In this work, line shape codes suitable for calculating microwave spectra have been implemented within the HITRAN Application Programming Interface (HAPI). These new additions allow for spectroscopic calculations of microwave absorbing species pertinent to current and future studies of the atmospheres of Jupiter and Venus, and more generally for the atmospheres of gas giants and rocky planets. The inversion spectrum of the NH$_3$ molecule broadened by H$_2$, He and H$_2$O dominates the microwave region of Jupiter. Whereas for Venus, accurate spectroscopic data of SO$_2$ broadened by CO$_2$ is necessary in order to determine its significance, if any, on the reported detection of PH$_3$ in the Venusian upper cloud deck. Comparisons have been made to available microwave laboratory opacities and the following results illustrate that HITRAN data can be used in conjunction with HAPI to reproduce the existing experimental measurements and provide reliable calculation of planetary opacities. Users should be mindful regarding selection of appropriate parameters in HITRAN and selecting suitable line shape functions in HAPI, depending on the spectral region, target molecular species, as well as ambient chemical and thermodynamic conditions.