Many small molecules have strong vibrational bands between 1000 to 1500 cm⁻¹. This spectral range overlaps with the atmospheric water window and lies within the sensitivity range of space observatories such as the James Webb Space Telescope. Therefore, it is well suited for detecting such molecules in the Earth's atmosphere or on celestial bodies. However, the current line lists in this range are still largely based on conventional FTIR measurements. Optical frequency comb spectroscopy offers superior frequency accuracy and precision but was hindered by the lack of comb sources in that spectral range. We recently developed a Fourier-transform spectrometer A. Hjältén, M. Germann, K. Krzempek et al., J. Quant. Spectrosc. Radiat. Transfer 271, 107734 (2021).ased on an 8-μm difference-frequency-generation comb sourceK. Krzempek, D. Tomaszewska, A. Gluszek et al., Opt. Express 27, 37435 (2019). Here, we present low-pressure spectra of methane (CH₄), a potent greenhouse gas and constituent of (exo-) planetary atmospheres, and formaldehyde (H₂CO), an atmospheric pollutant and constituent of the interstellar medium, measured with this spectrometer using the sub-nominal resolution sampling-interleaving methodL. Rutkowski, P. Maslowski, A. C. Johansson et al., J. Quant. Spectrosc. Radiat. Transfer 204, 63 (2018). From these spectra, we retrieved line positions and intensities of several hundred rovibrational transitions of the ¹²CH₄ and ¹³CH₄ ν₄ fundamental bands and two ¹²CH₄ hot bands, as well as of the H₂CO ν₄ and ν₆ bands, achieving uncertainties of line positions and line intensities of a few hundred kilohertz and a few percent, respectively. The line positions and intensities of ¹²CH₄ were used to improve the global fit of the effective Hamiltonian and dipole-operator parameters, leading to a reduction of the line-position fit residuals by over one order of magnitude relative to the previously used dataB. Amyay, A. Gardez, R. Georges et al., J. Chem. Phys. 148, 134306 (2018).

---

Footnotes:

A. Hjältén, M. Germann, K. Krzempek et al., J. Quant. Spectrosc. Radiat. Transfer 271, 107734 (2021).b K. Krzempek, D. Tomaszewska, A. Gluszek et al., Opt. Express 27, 37435 (2019).. L. Rutkowski, P. Maslowski, A. C. Johansson et al., J. Quant. Spectrosc. Radiat. Transfer 204, 63 (2018).. B. Amyay, A. Gardez, R. Georges et al., J. Chem. Phys. 148, 134306 (2018)..

Previously published high temperature CO₂ IR line lists either do not cover the region > 10,000 cm⁻¹, or lack convergence due to cutoffs, or have noticeable noises. We report a new CO₂ IR line list improved for applications in the range from 1500K to 3000K, denoted Ames-3000K.Funded by NASA Grants 18-APRA18_0013 and NASA/SETI Co-op Agreements 80NSSC20K1358 & 80NSSC19K1036.ith at least 7 billion lines of CO₂ 626, 636, 628 and 627, it covers the whole range from 0 to 20,000 cm⁻¹. We estimate it is converged up to 20,000 cm⁻¹at 1000K, up to 10,000-15,000 cm⁻¹at 2000K, or up to 5000-8000 cm⁻¹at 3000K, but needs further PES and DMS improvements for 4000K and above. Compared to our earlier CO₂ line list work, e.g., Ames-296K/1000K and Ames-4000K, the Ames-3000K combines the advantages of two sets of IR line lists. The 1^st set focuses on the low energy region, with intensity computed using the best available Ames-2 PES, and the best available ab initio DMS, Ames-2021. The Ames-2021 DMS based IR intensity represents a major improvement for theoretical CO₂ intensity calculations. Our predictions for the CO₂ 2001x and 3001x bands matched high accurate experiments to -0.1±0.1% (NIST) or 0.2±0.4% (DLR). But the Ames-2021 DMS was fit only up to 30,000 cm⁻¹. The 2^nd set of line lists provides reliable prediction for IR transitions with E′ up to 36,000 cm⁻¹. Related calculations were run on a different PES, X01d. To enhance the success rate of Ames vs. CDSD matches in the range of 15,000 - 22,000 cm⁻¹, the X01d PES was refined specifically using selected CDSD Effective Hamiltonian model levels up to 24,000 cm⁻¹, but at a price of the accuracy reduced for lower energy levels and transitions. The ab initio dipole dataset of Ames-2021 DMS was refitted with 40,000 cm⁻¹cutoff to generate an DMS suitable for the intensity calculation at higher energy, denoted Ames-2021-40K. The two sets of line lists are then combined and updated using the CDSD energy levels to get accurate line positions for E′ < 15,000 cm⁻¹and J < 150 transitions. The accuracy, consistency, and issues of the Ames-3000K IR line list will be evaluated by comparing with high temperature experiments and databases.

---

Footnotes:

Funded by NASA Grants 18-APRA18_0013 and NASA/SETI Co-op Agreements 80NSSC20K1358 & 80NSSC19K1036.W

l0pt Figure To fill in the CS₂ data gaps in IR databases, Ames-1 296K IR Line lists are reported in the range of 0 - 10,000 cm⁻¹, with line intensity cut off at 1E-30 cm/molecule.Funded by NASA Grant 18-XRP18_2-0029 and through NASA/SETI Co-operative Agreement 80NSSC19M0121.ive most abundant isotopologues (222, 224, 223, 232, and 424) are included in a "natural" CS₂ combo list with their terrestrial abundances. The Ames-1 potential energy surface (PES) for CS₂ was refined using experimental levels compiled in Karlovets et al [JQSRT 258:1, 2021], with fitting σ_rms=0.02 cm⁻¹. The Ames-1 dipole moment surface (DMS) was fit from extrapolated CCSD(T)/aug-cc-pV(T,Q,5+d)Z dipoles, with fitting σ_rms = 5.2E-6 a.u. for 2416 points in 0 - 25,000 cm⁻¹. The Ämes-1 PES + Ames-1 DMS" intensity should be consistently reliable with better than 95% accuracy, but needs more experiment evaluation beyond a few strong peaks below 5000 cm⁻¹. Differences between Ames and HITRAN model extrapolations increase to 0.2-0.7 cm⁻¹at J=150. We plan to update the 222 line list with Tashkun's EH model levels [JQSRT 279:108072, 2022]. Future work may focus on states > 10,000 cm⁻¹, the accuracy for J > 100, and high density of states for high temperature line lists. See http://huang.seti.org for latest update.

---

Footnotes:

Funded by NASA Grant 18-XRP18_2-0029 and through NASA/SETI Co-operative Agreement 80NSSC19M0121.F

l0pt Figure To fill in the OCS data gaps in IR databases, Ames-1 296K IR line lists are reported for OCS isotopologues in the range of 0 - 16,000 cm⁻¹, with line intensity cut off at 1E-30 cm/molecule.Funded by NASA Grant 18-XRP18_2-0029 and through NASA/SETI Co-operative Agreement 80NSSC19M0121.even isotopologues (622,624,632,623,822,634,and 722) are included in a "natural" OCS line list with their terrestrial abundances. The Ames-1 potential energy surface (PES) for OCS was refined using selected HITRAN data and band origins up to 13,952 cm⁻¹(with reduced weight). It can reproduce most HITRAN levels with σ_rms < 0.01 cm⁻¹, except a few bands of the main isotopologue: 5002, 4112 and 9110. The Ames-1 dipole moment surface (DMS) was fit from extrapolated CCSD(T)/aug-cc-pV(T,Q,5+d)Z dipoles, with fitting σ_rms = 5.8E-7 a.u. for 1862 points in 0 - 20,000 cm⁻¹. In general, the Ames-1 296K intensity finds good agreement with experiment and HITRAN. Agreements for bands > 10,000 cm⁻¹are also reasonable. In future, we need to identify the source of discrepancies observed in the Ames-1 vs Expt/HITRAN comparisons, and focus on higher energy and higher temperature line lists. See http://huang.seti.org for latest update.

---

Footnotes:

Funded by NASA Grant 18-XRP18_2-0029 and through NASA/SETI Co-operative Agreement 80NSSC19M0121.S

l0pt Figure Ames-1 296K IR Line lists are reported for N₂O in the range of 0 - 15,000 cm⁻¹, with line intensity cut off at 1E-30 cm/molecule.Funded by NASA Grant 18-APRA18-0013 and through NASA/SETI Co-operative Agreement 80NSSC20K1358.ix isotopologues (446,456,546,448,447 and 556) are included in a "natural" N₂O combo list with their terrestrial abundances. The Ames-1 potential energy surface (PES) for N₂O was refined using selected HITRAN data (J < 80) up to 8000 cm⁻¹and additional levels (J=0-1) up to 15,000 cm⁻¹with reduced weights. For 6908 J=0-98 levels of ¹⁴N₂¹⁶O in HITRAN2020, the Ames-1 based levels agree with σ_rms=0.021 cm⁻¹. The Ames-1 dipole moment surface (DMS) was fit from extrapolated CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles, with fitting σ_rms = 2.7E-5 a.u. for 5184 points in 0 - 20,000 cm⁻¹. In general, the Ämes-1 PES + Ames-1 DMS" intensity finds good agreement with HITRAN, and a few bands > 10,000 cm⁻¹. Isotopologue line lists are compared to published Effective Hamiltonian models for potential combination of reliable intensities and accurate line positions. Future improvements are planned for PES, DMS and line lists. See http://huang.seti.org for latest update. Funded by NASA Grant 18-APRA18-0013 and through NASA/SETI Co-operative Agreement 80NSSC20K1358.S

The increasingly frequent observations of hot, rocky, Earth-like exoplanets make the production of hot high-resolution line lists for geo-chemically relevant species all the more important. Furthermore, molecular oxygen (O₂) is a critical biosignature molecule in atmospheric exoplanet retrievals and plays an important role in many chemical processes. Ab initio spectroscopy of the O₂ molecule is uniquely challenging due to the fact that dipole transitions are forbidden within the three lowest lying electronic levels of, and thus transitions in infrared and visible regions are due solely to higher order electric quadrupole and magnetic dipole moments. Nonetheless, accurate line lists for these spectral regions are vital for astronomical applications. We present results of MRCI calculations on the the X³Σ⁻_g, a¹∆_g, b¹Σ⁺_g and d¹Π_g states, and related spin-orbit, and electric quadrupole couplings. Using the Duo program we then obtain a variational solution to the rovibronic Schrödinger equation, and perform empirical refinement of the energy levels by fitting a Morse/Long-range potential energy curve, along with spin-orbit and spin-spin coupling functions. We also discuss ongoing and future work for the magnetic dipole moment transitions.

OH spectroscopy has been heavily studied due to its importance in combustion, atmospheric and interstellar chemistry, and as a key constituent of the Earth's atmosphere. Recently, OH has been detected in the atmosphere of the Ulta-Hot Jupiter WASP-76b and has also been found in the stellar spectra of M-dwarfsR. Landman, A. Sánchez-López, P. Mollière, A. Y. Kesseli, A. J. Louca, I. A. G. Snellen, A&A, 2021, 656, A119 Novel MolPro electronic structure calculations for ground and excited electronic state PECs will be presented along with associated coupling curves and (transition) dipole moments. These ab initio calculations are used to produce a ExoMol rovibronic linelist using the programs Duo and ExoCross. Photodissociation is a primary destructor of OH in diffuse interstellar clouds, particularly the direct X ²Π→ 1²Σ⁻ photodissociation. A ²Σ⁺ predissociation is also studied. Temperature-dependent photodissociation cross sections using the method established by Pezzella et al.M. Pezzella, J. Tennyson, S. N. Yurchenko, Phys. Chem. Chem. Phys., 2021, 23, 16390re calculated and presented. Gaussian line profile optimization of photodissociation cross sections has been automated and applied to the cases of direct photodissociation for OH, HCl, and HCN.

---

Footnotes:

R. Landman, A. Sánchez-López, P. Mollière, A. Y. Kesseli, A. J. Louca, I. A. G. Snellen, A&A, 2021, 656, A119. M. Pezzella, J. Tennyson, S. N. Yurchenko, Phys. Chem. Chem. Phys., 2021, 23, 16390a

We present a high level ab initio study of the rovibronic spectra of Sulfur Monoxide (SO) using internally contracted multireference configuration interaction (IC-MRCI) method using aug-cc-pv5z basis sets and a fully diabatised model for the molecule. The diabatic model covers the lowest 13 singlet and triplet electronic states of SO X³Σ⁻, a¹∆, b¹Σ⁺, c¹Σ⁻, A^3′∆, A^3′′Σ⁺, A³Π, B³Σ⁻, C³Π, C^3′Π, d¹Π, e¹Π, and (3)¹Π ranging up to 66,800 cm⁻¹. The ab initio spectroscopic model includes potential energy curves, dipole and transition dipole moment curves, spin-orbit curves and electronic angular momentum curves. A diabatic representation is built by removing avoiding crossings between the C³Π-C^3′Π and e¹Π-(3)¹Π states through a unitary transformation who's rotation angle is determined on the fly by enforcing smoothness properties of the diabatic potential energy curves. A rovibronic line list of SO is computed covering the wavelength range up to 167 nm.

The TiO B³Π- X³∆ electronic transition (γ^′ system) is an important opacity source in the atmospheres of M dwarfs and hot Jupiter exoplanets. The 0–0, 1–0, and 2–1 bands of the B³Π- X³∆ band system have been analyzed using a TiO emission spectrum recorded at the McMath-Pierce Solar Telescope, operated by the National Solar Observatory at Kitt Peak, Arizona. Improved spectroscopic and equilibrium constants were determined. Line strengths were calculated from an ab initio transition dipole moment function scaled using an experimental lifetime. A new line list for v^′ = 0-2 and v^′′= 0-4 of the B³Π- X³∆ band system is provided.

The HITEMP database [1] provides line-by-line spectroscopic parameters for use at high temperatures. HITEMP line lists are used for numerous applications that include spectral modeling of exoplanets, brown dwarfs, and stellar atmospheres, as well as the high-resolution remote sensing of combustion environments. It is therefore necessary that these spectroscopic line lists are sufficiently complete in order to reproduce high-temperature spectra, but it is also essential that the line positions, intensities, and broadening parameters are accurate for high-resolution studies. Over recent years, HITEMP has been undergoing a significant upgrade that has improved the quality and extent of the available spectroscopic data and the number of line lists available: H₂O, CO₂, N₂O, CO, CH₄, NO, NO₂, OH [1-4]. HITEMP line lists are typically built upon a state-of-the-art ab initio (or semi-empirical) line list that is cross-evaluated against other works. The line list is then combined with HITRAN (when possible), and broadening parameters are applied for each line. The resultant line list is validated against available high-resolution experimental studies at elevated temperatures, and improvements are incorporated where necessary. This methodology will be presented for the recent additions to HITEMP [3,4], along with an "effective line" technique that was used for CH₄ [4]. The presentation will also discuss the forthcoming planned updates for the H₂O and CO₂ line lists. [1] Rothman, et al. (2010), JQSRT 111, 2139 [2] Li, et al. (2015), ApJS 216, 15 [3] Hargreaves, et al. (2019), JQSRT 232, 35 [4] Hargreaves, et al. (2020), ApJS 247, 55

We propose a digital record of the absorption spectrum of ¹³⁰Te₂ vapour as an aid to calibration of laboratory spectra currently referenced to the paper atlas of Cariou and LucAtlas du spectre d'absorption de la molécule de téllure, Luc & Cariou, Laboratoire Aimé Cotton, CNRS publications, (1980) The strong and crowded A0_u⁺ -X0_g⁺ bands of Te₂ have long provided useful benchmarks for calibration beyond 20000 cm⁻¹, where room-temperature B -X I₂ absorption cuts off. Molecular tellurium offers more lines per wavenumber than atomic uranium, whose atlas is also useful in this region.A uranium atlas, from 365 to 505 nm; Ross et  al. J Mol Spectrosc 369 111270 (2020) Absorption spectra were recorded through the emission port of a Fourier transform spectrometer, using an external sample and light source. The sample was a sealed, evacuated 10-cm cell containing a small quantity of ¹³⁰Te₂. The cell was heated to temperatures between 600 and 640 ^°C, generating tellurium vapour pressures 8-11 Torr, to produce strong absorption without saturation. Optical filters were used to select 2000 cm⁻¹ spectral sections; interferograms were taken at nominal apodized resolution of 0.02 to 0.033 cm⁻¹. The pieces were spliced together to cover the range 19000 - 24000 cm⁻¹. The wavenumber scale was fine-tuned to match earlier (and sometimes absolute) reference data^aAbsolute wavelength determinations in molecular tellurium: new reference lines for precision laser spectroscopy, Gillaspy and Sansonetti, J. Opt. Soc. Am. B 8, 2414 (1991)Absolute wavenumber measurements in ¹³⁰Te₂: reference lines in the 420.9 to 464.6-nm region, Scholl et al J. Opt. Soc. Am. B 22(5), 1128 (2005)Cavity dispersion tuning spectroscopy of tellurium near 444.4 nm, Coker et al J. Opt. Soc. Am. B 28 (12), 2934 (2011) Measured linewidths of isolated peaks vary from 0.04 to 0.09 cm⁻¹, i.e. broader than expected from Doppler broadening and instrumental resolution considerations, but we believe the wavenumber scale to be good to ± 0.005 cm⁻¹ . Ascii data files with Te₂ transmittance and absorbance data are freely available for download from J. Mol. Spectrosc.,Te₂ absorption spectrum from 19000 to 24000 cm⁻¹, Ross and Cardon, J. Mol. Spectrosc. 384 (2022) 111589nd from the Mendeley database, at https://data.mendeley.com/datasets/kmkbwtjhd3/1.

---

Footnotes:

Atlas du spectre d'absorption de la molécule de téllure, Luc & Cariou, Laboratoire Aimé Cotton, CNRS publications, (1980). A uranium atlas, from 365 to 505 nm; Ross et  al. J Mol Spectrosc 369 111270 (2020). Absolute wavelength determinations in molecular tellurium: new reference lines for precision laser spectroscopy, Gillaspy and Sansonetti, J. Opt. Soc. Am. B 8, 2414 (1991)\end Absolute wavenumber measurements in ^130Te_2: reference lines in the 420.9 to 464.6−nm region, Scholl et al J. Opt. Soc. Am. B 22(5), 1128 (2005) Cavity dispersion tuning spectroscopy of tellurium near 444.4 nm, Coker et al J. Opt. Soc. Am. B 28 (12), 2934 (2011). Te₂ absorption spectrum from 19000 to 24000 cm⁻¹, Ross and Cardon, J. Mol. Spectrosc. 384 (2022) 111589a

Sulfur monoxide (SO) is found in several astronomical sources including the atmospheres of Io and Venus. Continuing our previous workP.F. Bernath, R.M. Johnson, J. Liévin. Line Lists for the b¹Σ⁺−X³Σ⁻ and a¹∆−X³Σ⁻ Transitions of SO. JQSRT 272,107772(2021)o make a more complete line list for SO, we used our previous fits of rotational constants for v=0-6 for the X³Σ⁻ state and v=0-5 for the a¹∆ state along with high-level ab initio calculations to produce line strengths and positions for the all of the vibration-rotation transitions. All possible vibrational bands were calculated and line strengths included the Herman-Wallis effect caused by vibration-rotation interaction. P.F. Bernath, R.M. Johnson, J. Liévin. Line Lists for the b¹Σ⁺−X³Σ⁻ and a¹∆−X³Σ⁻ Transitions of SO. JQSRT 272,107772(2021)t