The HITRAN2020 database will be publicly released this year. It is a coordinated effort of experimentalists, theoreticians, atmospheric and planetary scientists who measure, calculate and validate the HITRAN data. The lists for most of the HITRAN molecules in the line-by-line section were updated in comparison with the previous compilation HITRAN2016Gordon et al., (2017). JQSRT. 203, 3–69. The extent of the updates ranges from updating a few lines of certain molecules to complete replacements of the lists and introducing additional isotopologues. Six new molecules (SO, CH₃F, GeH₄, CS₂, CH₃I, and NF₃) were also added to HITRAN. In addition, the accuracy of the parameters for major atmospheric absorbers has been increased, often featuring sub-percent uncertainties. The number of parameters was also increased significantly, now incorporating, for instance, non-Voigt line profiles for many gases; broadening by water vaporTan et al., (2019) J. Geophys. Res. Atmos. 2019JD030929. update of collision-induced absorption setsKarman et al., (2019) Icarus 328, 160–175. The new edition will continue taking advantage of the modern structure and interface available at www.hitran.org and the HITRAN Application Programming InterfaceKochanov et al., ( 2016) JQSRT. 177, 15–30. Their functionality has been extended for the new edition. This talk will provide a brief overview of HITRAN2020This work is supported by NASA.nd its main improvements with respect to the previous edition.

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Gordon et al., (2017). JQSRT. 203, 3–69.. Tan et al., (2019) J. Geophys. Res. Atmos. 2019JD030929.; Karman et al., (2019) Icarus 328, 160–175.. Kochanov et al., ( 2016) JQSRT. 177, 15–30.. This work is supported by NASA.a

This work was motivated by difficulties encountered while trying to calibrate laser excitation spectra, taken in short (1 cm⁻¹) scans around 438 nm, by matching optogalvanic transitions from a Uranium-Argon hollow cathode lamp to peaks listed in a widely-circulated `informal report' on the Uranium spectrum (11000 -25900 cm⁻¹) from Los AlamosAn atlas of uranium emission intensities in a hollow cathode discharge; Palmer, Keller & Engleman, Los Alamos report LA 8251-MS, (1980) Short pieces of excitation spectra often fell between secure calibration lines, because many of the weaker features had been excluded from the printed linelist. To remedy this, we have re-recorded emission from a commercial Uranium hollow-cathode lamp 19800 - 27400 cm⁻¹ on a Fourier transform spectrometer, at an instrumental resolution of at 0.04 cm⁻¹. The wavenumber scale was fine-tuned to match earlier reference data^aComparing the emission spectra of U and Th hollow cathode lamps, and a new U line list; Sarmiento et  al., A & A, 618, A118, (2018)Uranium and iodine standards measured by means of Fourier-transform spectroscopy; Gerstenkorn, et  al., A & A, 58, 255-66, (1977) to within 0.003 cm⁻¹. This spectrum (together with its peak list) is proposed in ascii formatA uranium atlas, from 365 to 505 nm; Ross et  al. J Mol Spectrosc , 369, 111270, (2020)s a possible aid to calibration of laser excitation spectra in the blue, violet and near UV. It extends the spectrum reported by Sarmiento and co-workers^b that focused on calibration of astronomical spectrographs in the near IR and visible. An atlas of uranium emission intensities in a hollow cathode discharge; Palmer, Keller & Engleman, Los Alamos report LA 8251-MS, (1980). Comparing the emission spectra of U and Th hollow cathode lamps, and a new U line list; Sarmiento et  al., A & A, 618, A118, (2018)

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A uranium atlas, from 365 to 505 nm; Ross et  al. J Mol Spectrosc , 369, 111270, (2020)a

Owing to their molecular symmetry, many transitions of homonuclear diatomic molecules are forbidden in the electric dipole approximation. Instead their spectra are dominated by higher order transition moments, including the magnetic dipole moment and electric quadrupole moment. r0pt Figure Here we present a new implementation of electric quadrupole transition moments in DUOS. N. Yurchenko, L. Lodi, J. Tennyson, A. V. Stolyarov, Comput. Phys. Commun., 2016, 202, 262 - 275; publicly available at https://github.com/Trovemaster/Duo. The implementation is validated against the highly accurate linelist of Roueff et al. The full infrared spectrum of molecular hydrogen, Astron. Astrophys, 630 (2019)or rovibrational transitions of the hydrogen molecule. We also perform ab initio calculations for potential energy curves (PECs), electric quadrupole moment curves (EQCs), and spin-orbit coupling curves (SOCs) and demonstrate rovibronic linestrength calculations for the three lowest lying states (X³Σ_g⁻, a¹∆_g and b²Σ_g⁺) of molecular oxygen. Further demonstrations are provided for various other molecules of interest, including CO and HF as part of the ExoMol project J. Tennyson et al. J. Quant. Spectrosc. Radiat. Transf., 2020, 255, 107228; www.exomol.com. Absorption cross-sections are calculated using the EXOCROSS programS. N. Yurchenko, A. F. Al-Refaie, J. Tennyson, Astron. Astrophys;, 2018, 614, A131; publicly available at https://github.com/Trovemaster/ExoCross.

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S. N. Yurchenko, L. Lodi, J. Tennyson, A. V. Stolyarov, Comput. Phys. Commun., 2016, 202, 262 - 275; publicly available at https://github.com/Trovemaster/Duo.. The full infrared spectrum of molecular hydrogen, Astron. Astrophys, 630 (2019)f J. Tennyson et al. J. Quant. Spectrosc. Radiat. Transf., 2020, 255, 107228; www.exomol.com.. S. N. Yurchenko, A. F. Al-Refaie, J. Tennyson, Astron. Astrophys;, 2018, 614, A131; publicly available at https://github.com/Trovemaster/ExoCross..

Sodium oxide (NaO) is observed in airglows in the Earth's atmosphere and likely has astronomical importance. This study concerns the transitions with X ²Π and and to the very low-lying (T₀ < 2000 cm⁻¹) A ²Σ⁺ state. A line list consisting of energy levels, allowed transitions, Einstein coefficients, and a partition function are produced based on variational solution of the coupled rovibronic Schrödinger equations using program DuoS. Yurchenko, L. Lodi, J. Tennyson, A.V. Stolyarov, Comput. Phys. Comm., 2016, 202, 262-275 Ab initio calculations which characterized the potential energy, spin-orbit, Λ-doubling and (transition) dipole moment curves were used as starting points to form the final model. Ab initio PECs were parameterized using Morse potentials and improved by least-squares fitting to experimental data on the rotational spectrum by Yamada et al C. Yamada, M. Fujitake, E. Hirota, J. Chem. Phys, 1989, 90, 3033nd the electronic spectrum by Joo et al S. Joo, D.R. Worsnop, C.E. Kolb, S.K. Kim, D.R. Herschbach, J. Phys. Chem., 1999, 103, 3193-3199 A lack of data detailing the dissociation energies and vibrational structure of the X and A states prompts a request for further experimental study into the species which would allow further improvement of the model.

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S. Yurchenko, L. Lodi, J. Tennyson, A.V. Stolyarov, Comput. Phys. Comm., 2016, 202, 262-275. C. Yamada, M. Fujitake, E. Hirota, J. Chem. Phys, 1989, 90, 3033a S. Joo, D.R. Worsnop, C.E. Kolb, S.K. Kim, D.R. Herschbach, J. Phys. Chem., 1999, 103, 3193-3199.

CASSCF + MRCI calculations for the diatomic molecules, SiN and SO, have been performed using the C_2v point group symmetry. For SiN, five lowest bound electronic have been were considered, X ²Σ⁺, A ²Π, B ²Σ⁺, a ⁴Π, b ⁴Σ⁺, while for SO, 9 electronic states were selected, X ³Σ⁻, A ³Π, A′ ³∆, A" ³Σ⁺, B ³Σ⁻, C ³Π, a ¹∆, b ¹Σ⁺ and c ¹Σ⁻, due to their importance for the spectroscopic applications in the IR, Visible and UV regions. For all the excited states potential energy, electronic angular momenta, spin orbit and (transition) dipole moment curves were generated. We use these ab initio curves to predict rovibronic spectra of SO and SiN as well as their lifetimes. We aim to construct accurate molecular line lists for these molecules, which will require an empirical refinement of the ab initio curves in order to improve the quality of the predictions of experimental spectra.

We report an ab initio study on the rovibronic spectroscopy of the open-shell diatomic molecule phosphorous mononitride, PN. The study considers nine lowest electronic states, X¹Σ⁺, A¹Π, C¹Σ⁻, D¹∆, E¹Σ⁻, a³Σ⁺, b³Π, d³∆ and e³Σ⁻, using high level electronic structure theory and accurate nuclear motion calculations. Using the ab initio data for bond lengths ranging from 1 to 3.16Å, we compute 9 potential energy, 9 spin-orbit coupling, 7 electronic angular momentum coupling, 9 electric dipole moments, and 9 transition dipole moment curves. The Duo nuclear motion program S. N. Yurchenko, L. Lodi, J. Tennyson, A. V. Stolyarov, Comput. Phys. Commun., 2016, 202, 262 - 275; see https://github.com/exomol.s used to solve the coupled nuclear motion Schrödinger equations for these nine electronic states. The spectra of ³¹P¹⁴N simulated for different temperatures are compared with several available high-resolution experimental studies. Lifetimes are calculated for all states and reported here with comparison to previous results in the literature. We then produce a separate line list for the X¹Σ⁺, A¹Π, E1Σ⁻ states, with the potential energy functions and some couplings being fitted the experimental energy values inverted using the MARVEL procedure.

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S. N. Yurchenko, L. Lodi, J. Tennyson, A. V. Stolyarov, Comput. Phys. Commun., 2016, 202, 262 - 275; see https://github.com/exomol.i

We present broadband dual frequency comb laser measurements of pure and air-broadened H₂O absorption from 6656 to 7540 cm⁻¹ (1326-1502 nm) with a spectral point spacing of 0.0068 cm⁻¹. Sample pressure and temperature were carefully controlled for each of the 56 datasets collected, with measured temperatures between 300 and 1100 K and pressures ranging from 0.5 to 16 Torr and 20 to 600 Torr for the pure H₂O and 2% H₂O in air, respectively. We employ a multispectrum fitting routine based on the quadratic speed-dependent Voigt profile to extract self- and air-broadening and shift parameters, along with corresponding power-law temperature dependence exponents for the thousands of visible absorption features. These results are then compared against existing high temperature H₂O linelists.

A procedure to generate the exact kinetic energy operator in valence coordinates, based on Sørensen's method for constructing non-rigid Hamiltonians, is presented. This method is currently being applied to the thioformaldehyde (H₂CS) molecule, where the TROVE program is used to compute ro-vibrational energy levels and transition intensities. Moreover, the ab initio PES is refined with the MARVEL approach. The exact kinetic energy operator itself is produced using the symbolic computation program Mathematica and acts as TROVE input.

Observation of HONO concentration change in the atmosphere can improve our understanding of atmospheric chemistry details and their effects on the regional air quality and global climate [1]. However, highly desired spectral line parameters of the most intense bands of HONO in the mid-IR for optical sensing are not available in the common databases like the HITRAN or the GEISA. We report on recent investigation of about 60 new line positions and their effective line strengths of cis-HONO of the ν₂ band in the range of 1660.0-1662.2 cm⁻¹using direct quantum cascade laser absorption spectroscopy coupled to a multi-pass cell (L_eff =100 m). The HONO absorption frequencies were absolutely determined using a λ-meter with an accuracy of  0.002 cm⁻¹. The effective line intensities were determined by scaling the measured HONO absorption intensities to the line strengths of two previously reported HONO lines located in the same spectral region near 1659.85 cm⁻¹[2]. The experimental details and the preliminary results will be presented and discussed. Acknowledgments. The authors thank the financial supports from the regional CPER CLIMIBIO program, the national ANR projects of Labex CaPPA (ANR-10-LABX005) and MULTIPAS-2 (ANR-16-CE04-0012). References [1] B.J. Finlayson-Pitts, and J.N. Pitts, Jr., Chemistry of the Upper and Lower Atmosphere, Academic Press, New York, 273–276 (2000). [2] B.H. Lee, E.C. Wood, J. Wormhoudt, J.H. Shorter, S.C. Herndon, M.S. Zahniser, and J.W. Munger, Effective line strengths of trans-nitrous acid near 1275 cm⁻¹and cis-nitrous acid at 1660 cm⁻¹, J. Quant. Spectrosc. Radiat. Transfer 113 (2012) 1905-1912.

l0pt Figure An infrared absorption cross-section database for gas-phase molecules at high-temperatures and high-pressures is under construction to address a growing cross-disciplinary need for experimental data at these conditions. Recently developed broad-scan, rapid-tuning external-cavity quantum cascade lasers (QCL) have enabled the application of shock tube facilities, commonly used to study high-temperature chemical kinetics, to the efficient acquisition of absorption spectra under short-duration shock-heated test gas conditions. Available shock tube facilities can produce temperatures from 500 to 10,000 K and pressures from 0.1 to 1000 atm with test time durations ranging from 500 μs to 50 ms. Uncertainties in the known thermodynamic conditions as low as ±1% can be achieved. Presently available laser systems enable the rapid acquisition ( < 10 ms) of approximately 300 cm⁻¹ wide spectral regions at any location within the QCL-accessible wavelength region of 3.6 -11.7 μm (850 - 2800 cm⁻¹). The resulting spectra are composed of discrete data points at a spectral interval ranging from 0.3 - 0.6 cm⁻¹ and an instrument broadening function defined by the laser linewidth ( ≤ 0.0033 cm⁻¹). Present efforts are focused on studying large polyatomic molecules (4+ atoms) dilute in a bath gas of argon under conditions for which dissociation is negligible and test time durations are favorable (T < 1600K and P < 5atm). The database currently includes ethylene, methanol, and ethanol with over a dozen more species measured and being prepared for inclusion soon. Database permanent URL: https://purl.stanford.edu/cy149sv5686

r0pt Figure To address the notable lack of knowledge on high-temperature absorption cross sections of important molecular species in combustion and exoplanets, a new strategy is proposed and deployed to collect broad-band absorption spectra in shock-heated gases. The methodology utilizes a broad-scan, rapid-tuning external-cavity quantum cascade laser in conjunction with a shock tube and is capable of providing quantitative spectroscopic information across full vibrational bands spanning over 200 cm⁻¹within 6 ms ( > 30,000 cm⁻¹/s), with a spectral resolution between 0.3 – 0.6 cm⁻¹. This experimental approach is demonstrated with absorption spectra measurements on the ν₇ vibrational band of ethylene (C₂H₄) from 8.4 μm to 11.7 μm at temperature/pressure conditions between 800 – 1600 K, 1 – 5 atm. The measured spectra are compared against spectral simulations using existing spectroscopic databases, showing better agreement with the line list of Rey et al.M. Rey, T. Delahaye, A. V. Nikitin, and V. G. Tyuterev, “First theoretical global line lists of ethylene (¹²C₂H₄) spectra for the temperature range 50-700 K in the far-infrared for quantification of absorption and emission in planetary atmospheres,” Astron. Astrophys., vol. 594, pp. 1–16, 2016.han of HITRAN 2016I. E. Gordon et al., “The HITRAN2016 molecular spectroscopic database,” J. Quant. Spectrosc. Radiat. Transf., vol. 203, pp. 3–69, 2017. With the current set of instruments available, this methodology could be applied to numerous gas-phase molecules that have attractive absorption features in the spectral range of 3.6 – 11.7 μm and opens an efficient pathway towards improving knowledge on radiation absorption in the mid-infrared at high temperatures.

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M. Rey, T. Delahaye, A. V. Nikitin, and V. G. Tyuterev, “First theoretical global line lists of ethylene (¹²C₂H₄) spectra for the temperature range 50-700 K in the far-infrared for quantification of absorption and emission in planetary atmospheres,” Astron. Astrophys., vol. 594, pp. 1–16, 2016.t I. E. Gordon et al., “The HITRAN2016 molecular spectroscopic database,” J. Quant. Spectrosc. Radiat. Transf., vol. 203, pp. 3–69, 2017..