The ExoMol project (www.exomol.com) provides comprehensive line lists for the study of exoplanets and other hot bodies. As part of the ERC-funded ExoMolHD project these line lists are being refactored to facilitate their use in characterization of exoplanets using high resolution Doppler shift spectroscopy. This technique is based the use of MARVEL (measured active rotation vibration energy level) to obtain empirical energy levels and illustrated by a recent study on formaldhyde (H₂CO).A. R. Al-Derzi, S. N. Yurchenko, J. Tennyson, M. Melosso, Ningjing Jiang, C. Puzzarini, L. Dore, T. Furtenbacher, R. Tobias and A G. Császár, 2021, J. Quant. Spectrosc. Radiat. Transf., doi = 10.1016/j.jqsrt.2021.107563or formaldehyde we analysed of 16 596 non-redundant transitions from 43 experimental sources and resulted in the determination of 5029 empirical energy levels. As part of this work new measurements were performed in Bologna yielding high-accuracy rotational transitions within the ground, ν₃, ν₄ and ν₆ vibrational states, significantly improving the overall accuracy of the network. Eleven artificial transitions determined from effective Hamiltonian fits were added to the network to both fix the gap between ortho and para levels, and to join free-standing networks of transitions to the main network. r0pt Figure The empirical energies were used to update the AYTY ExoMol line list for formaldehyde. This yielded 367 779 transition frequencies determined using the empirical energy levels of which 183 673 lie above the dynamic HITRAN intensity cutoff, see the example in the figure. The generation of line lists which combine empirically-determined transition wavenumbers with ab initio transition dipoles is suitable for high resolution studies of both the Earth's and exoplanetary atmospheres. High resoltion line lists for other molecules starting with AlO, VO and the isotopologues of H₃⁺ are currently being prepared. A. R. Al-Derzi, S. N. Yurchenko, J. Tennyson, M. Melosso, Ningjing Jiang, C. Puzzarini, L. Dore, T. Furtenbacher, R. Tobias and A G. Császár, 2021, J. Quant. Spectrosc. Radiat. Transf., doi = 10.1016/j.jqsrt.2021.107563F

The high-temperature molecular spectroscopic database, HITEMP [1], aims to provide line lists for use in the modeling of high-temperature environments. Usage can range from the sensing of specific transitions in combustion processes to simulating the broadband opacities of exoplanet atmospheres. One challenge has been to balance the substantial quantity of transitions necessary for high-temperature applications, while remaining practical for use in line-by-line radiative transfer calculations. For methane [2], a method was devised to compress the very weak intensities of the underlying ab initio transitions into "effective" lines, which can be used in regular radiative transfer calculations. The HITEMP database currently constitutes line lists for eight molecules (H₂O, CO₂, N₂O, CO, CH₄, NO, NO₂, OH) and this talk will summarize the recent updates and additions to the HITEMP2010 data [2,3,4], including the new line list for water vapor [5]. A brief discussion of the remaining updates and proposed additions will also be included. [1] L.S. Rothman, et al. (2010), JQSRT 111, 2139-2150 [2] R.J. Hargreaves, et al. (2020), ApJS 247, A55 [3] R.J. Hargreaves, et al. (2019), JQSRT 232, 35-53 [4] G. Li, et al. (2015), ApJS 216, A15 [5] E.K. Conway, et al. (2021), JQSRT, in prep

This talk describes our recent development of two robust methods for calculating non-local thermal equilibrium (non-LTE) spectra of polyatomic molecules. Specifically, we look at molecules produced in reactive or dissociative environments, with vibrational populations outside local thermal equilibrium (LTE). The methodology is based on ExoMol's accurate and extensive ro-vibrational line lists containing transitions with high vibrational excitations and relies on the detailed ro-vibrational assignments. Two approaches for non-LTE vibrational populations of the product are introduced: a simplistic 1D approach based on the Harmonic approximation, and full 3D model incorporating accurate vibrational wavefunctions computed variationally with the TROVE (Theoretical ROVibrational Energy) program. The developed methodology is applied to two molecules, silylene (SiH₂) produced in a decomposition of disilane (Si₂H₆), and carbon monoxide (CO) produced by formamide (CH₃NO) glow discharge. We show how the two approaches compare well to each other and to experimentally obtained spectra, and how their non-LTE spectral signatures can be used to trace different reaction channels of molecular dissociations.

Stellar, substellar, and planetary atmosphere models are all highly sensitive to the input absorption cross-sections and subject to errors arising from incomplete line lists and the lack of appropriate pressure-broadening parameters. Generational differences between various state-of-the-art stellar and planetary models are primarily because of incomplete and outdated atomic and molecular line lists. Addressing this, here we present a database of pre-computed molecular absorption cross-sections for all isotopologues of key atmospheric absorbers relevant to late-type stellar, brown dwarf, and planetary atmospheres: MgH, AlH, CaH, TiH, CrH, FeH, SiO, TiO, VO, and H₂O. The pressure and temperature ranges of the computed data are between 10⁻⁶-3000 bar and 75-4000 K, and their spectral ranges are 0.25-330 cm⁻¹for many cases where possible. Some details on absorption cross-sections such as wing cut-off and pressure broadening have been either ignored or forgotten even though they have an instrumental impact on radiative transfer atmospheric modelings. Furthermore, for most molecules such as TiO, VO, and H₂O, multiple sets of cross-section data exist which lead to extensive biases and inaccuracies on the interpretation of observational data including uncertainty in the C/O ratio, thermal structure, and composition of exoplanetary atmospheres. In sum, we present (1) a database of pre-computed molecular absorption cross-sections to mitigate shortcomings for pre-existing incomplete line lists, and (2) quantify biases that arise when characterizing substellar/exoplanet atmospheres due to line list differences. Lastly, our team’s endeavors at NASA Ames research center to leverage these disagreements and concerns on cross-section data and the lack of sufficient pre-computed and evaluated dataset will be addressed. Our comprehensive database platform, MAESTRO, will be introduced.

The HITRAN (high-resolution transmission molecular spectroscopic database) is an international standard for reference molecular spectroscopy, particularly in simulating planetary and terrestrial atmospheric spectra [1]. HITRAN recently added new broadening parameters that are relevant to planetary atmospheres for many chemical species in the database. For NH₃, new broadening parameters include H₂, He, CO₂ [2] and H₂O [3]. These additional broadening parameters for NH₃ allowed for validations of HITRAN data with the HITRAN Application Programming Interface (HAPI) [4] against the NH₃ opacity models and laboratory data utilized by the Juno Mission. The Juno spacecraft carries with it a microwave radiometer which probes the atmospheric composition of Jupiter in the microwave range (0.02-0.73 cm⁻¹) [5,6]. At these frequencies, Jupiter’s atmospheric spectra is dominated by the inversion of NH₃ and is broadened by H₂, He, and H₂O. This work required three new line shapes to be incorporated into HAPI in order to accurately compare to available laboratory data and standard NH₃ opacity models (the Ben-Reuven [7], Gross [8] and Van Vleck and Weisskopf [9] line shapes). The results of this work demonstrate that HAPI can be used with HITRAN data, to model NH₃ opacities under Jovian conditions in the microwave region. It also shows great promise to produce opacities for other species of interest to the planetary community.

The atmospheres of hot rocky super-Earths will have very different spectroscopic signatures compared to gas giants or cooler objects. Many of these exoplanets possess short orbital periods, hence hot atmospheres, and will have a lot in common with early Earth; the massive amounts of water and elevated temperatures are expected to turn the atmospheres into a (high pressure) steam bath containing the remains of melted rock.
We will present recent progress on the production of molecular line lists for hot rocky super-Earths. A number of molecules containing silicon, alkali and alkaline earth metals are to be included in the ExoMol database. For the temperature and wavelength ranges considered, line lists will have to come from rigorous, first-principles calculations. However, these species pose new challenges and there is a pressing need for laboratory observations to improve the accuracy of our spectroscopic models.

Indications of aluminium monoxide (AlO) in the atmospheres of exoplanets are being reported and it is predicted to be an important source of opacity in hot Jupiters. Studies using high resolution spectroscopy should allow for a strong detection but require high accuracy reference data observed in a laboratory setting. A MARVEL (measured active rotational-vibrational energy levels) analysis is performed on the available, measured spectroscopic data for ²⁷Al¹⁶O: 22 679 validated transitions are used to determine 6 512 distinct energy levels. These empirical energy levels are used to provide an improved, spectroscopically accurate version of the ExoMol ATP line list for ²⁷Al¹⁶O; at the same time the accuracy of the line lists for the isotopically-substituted species ²⁶Al¹⁶O, ²⁷Al¹⁷O and ²⁷Al¹⁸O are improved by correcting levels in line with the corrections used for ²⁷Al¹⁶O. The four, newly updated line lists include full uncertainties and are made available via www.exomol.com as part of the ExoMol project.

We computed an accurate line list, called XABC, for nitric oxide (NO) which covers its pure rotational, vibrational and rovibronic spectra belonging to the lowest four electronic states of NO, i.e. X ²Π, A ²Σ⁺, B ²Π and C ²Π. XABC is a major extension and update of the ExoMol NOname line list which was calculated within the X ²Π state of NO. As first step we built a spectroscopic model which represents the rovibronic structure of A ²Σ⁺, B ²Π, C ²Π states of NO. Empirical energy levels for the three electronic states are determined using the a combination of the MARVEL procedure and ab initio calculations, and the available experimental data are critically evaluated. Ab inito methods which deal simultaneously with the Rydberg-like A ²Σ⁺ and C ²Π, and the valence B ²Π state are tested. Methods of modeling the sharp avoided crossing between the B ²Π and C ²Πstates are tested. A rovibronic Hamiltonian matrix is constructed using variational nuclear motion program DUO whose eigenvalues are fitted to the MARVEL energy levels. The matrix also includes coupling terms obtained from the refinement of the ab initio potential energy and spin-orbit coupling curves. Calculated and observed energy levels agree well with each other, validating the applicability of our method and providing a useful model for this open shell system. This part has been published in J. Chem. Phys. https://doi.org/10.1063/5.0038527. A mixture of empirical and theoretical electronic transition dipole moments are used for the final calculation of NO rovibronic transitions belong to the A ²Σ⁺ - X ²Π, B ²Π - X ²Π and C ²Π - X ²Π which correspond to the γ, β and δ band systems, respectively, as well as minor improvements to transitions within the X ²Π ground state. Our model generates a high-accuracy NO ultraviolet line list covering the complicated regions where the B ²Π -C ²Π states interact. Technical details of this part are given in the XABC line list paper submitted to Mon. Not. Roy. Astron. Soc.. XABC provides comprehensive data for λ > 160 nm (&̃#957; < 63000 cm⁻¹) for the analysis of atmospheric NO on Earth, Venus or Mars, other astronomical observations and applications. It is available via www.exomol.com.

Accurate high-temperature methane spectroscopic models are needed to support the discovery and evaluation of methane in hot exoplanet atmospheres. We present data taken with dual frequency comb absorption spectroscopy with a 0.0067 cm⁻¹ frequency point spacing of the methane icosad (6770-7630 cm⁻¹) of five temperatures up to 1000 K and three pressures up to 300 torr. A comparison of this data to HITRAN2016, HITEMP2020, and ExoMol reveals a best match with HITRAN2016 at room temperatures. However, there are significant mismatches with all three databases at elevated temperatures. Via a multispectrum fitting routine, we demonstrate that significant improvements can be made between HITRAN2016 high-temperature models and our data by updating several spectroscopic parameters. In particular, we update 4381 lower state energies, add 293 new hot absorption features, and apply band-wide changes to line-positions, self-widths, and temperature-dependence exponents for self-widths and self-shifts. r0pt Figure

The ro-vibrational spectrum of HC₃N has been recently the object of a comprehensive studyL. Bizzocchi, F. Tamassia, et al., Astoph. J. Supp. Ser. 233:11, 2017hich put together new high-resolution mid-infrared measurements and all existing rotational data for the vibrationally excited states located below  ∼  1000 cm⁻¹. The resulting global analysis yielded accurate and physically sound spectroscopic parameters for 12 states, thanks to the careful treatment of the l-type resonance effects in bending states and the consideration of various anharmonic resonances, in particular those connecting the polyad of states v₄ = 1, v₆ = 2, v₅ = v₇ = 1, and v₇ = 4. Here, the extension of the study to the second polyad of interacting states is presented, they are: v₄ = v₇ = 1, (v₆ = 2, v₇ = 1), (v₅ = 1, v₇ = 2), and v₇ = 5, and are located in the energy interval 1100-1300 cm⁻¹. New far- and mid-infrared spectra have been recorded at SOLEIL, with a resolution of 0.001 cm⁻¹, and further measurements of the millimeter and sub-millimeter spectra of the four interacting states have been performed at Garching and Bologna. The results of a new global analysis including all the states below  ∼  1300 cm⁻¹are presented and discussed.

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Footnotes:

L. Bizzocchi, F. Tamassia, et al., Astoph. J. Supp. Ser. 233:11, 2017w

Recently published workDM Hewett, PF Bernath, BE Billinghurst. 2019 “Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases.” Journal of Quantitative Spectroscopy and Radiative Transfer 227:226–229.as called into question the absolute infrared absorption cross-section values for isobutane presented in the Northwest Infrared (NWIR) database. As a result, we have remeasured these cross-sections. In all, four data sets were acquired, analyzed and compared to the original NWIR database with excellent agreement. All new data sets were measured with a nominal pathlength of 20 cm and sample temperature of 25.0 ^°C. Three data sets were acquired using a Bruker IFS 125HR spectrometer equipped with a HgCdTe detector. Spectra were first recorded between 600 and 5000 cm⁻¹at 0.112 cm⁻¹instrument resolution using thirteen burdens of isobutane (0.3 to 22 Torr), each pressure-broadened to one atmosphere using N₂ gas. The second and third data sets were recorded using thirteen burdens of isobutane (0.1 to 23 Torr), at an instrument resolution of 0.01 cm⁻¹. A spectrum of each sample was recorded neat and then recorded pressure-broadened to one atmosphere using N₂ gas, producing two data sets. A fourth data set, using eleven burdens of neat isobutane (0.5 to 23 Torr) was recorded using a Bruker IFS 66v/S with a DTGS detector. Spectra were recorded between 400 and 6500 cm⁻¹at 2 cm⁻¹instrument resolution. Each of the four data sets was fitted using a weighted linear least squares algorithm and resulted in a “composite” log₁₀ absorbance spectrum of isobutane with concentration-pathlength units of ppm⁻¹ m⁻¹. The wavenumber axis is in units of cm⁻¹. For the 125HR data sets, the integrated band strengths for both the C-H stretch and CH₂ bend regions are within 2% of the original NWIR integrated band strengths, and the 66v/S integrated band strengths for both spectral regions are within 5% of the NWIR data. The agreement between the original and new cross-section data is close to the original experimental error, 3%, reported for the NWIR database.

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Footnotes:

DM Hewett, PF Bernath, BE Billinghurst. 2019 “Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases.” Journal of Quantitative Spectroscopy and Radiative Transfer 227:226–229.h

Hydrocarbons are of considerable importance in studies of planetary atmospheres such as Titan and Giant Planets. In Titan, ethane (C₂H₆) is the second most abundant hydrocarbon and is also widespread in Giant Planets. Neopentane (C(CH₃)₄) may be detected in these planetary atmospheres. This talk will present the absorption cross sections of ethane and neopentane. Infrared absorption spectra of ethane and neopentane were recorded in the 2600-3300 cm⁻¹ region by high resolution Fourier transform spectroscopy at the Canadian Light Source. Absorption cross sections for neopentane were obtained for pure samples and samples broadened by nitrogen. The data were taken at temperatures of 203 K, 232 K, 266 K and 293 K with broadening gas pressures of 10 Torr, 30 Torr and 100 Torr. Cross sections for ethane were obtained for pure samples and samples broadened by hydrogen and helium at the same temperatures and pressures. Calibration of cross sections for ethane was carried out using data from the Pacific Northwest National Laboratory (PNNL).

In search of elusive species that might be captured in the Cassini/CIRS and the JWST/MIRI spectral observations, high-precision laboratory spectroscopy constitutes a critical input to Titan atmospheric modeling emission features. For this, we have conducted a series of laboratory studies on hydrocarbons that are likely to be present in the Titan atmosphere (Sung et al. 2020, 2018, 2016, 2013). In this work, we report the measurements of temperature-dependent cross-sections of toluene in the mid-infrared (7-15 μ m) region. For this, we obtained 23 pure and N₂-mixture spectra at 240–298 K using a high-resolution Fourier transform spectrometer (Bruker IFS 125 HR) at the Jet Propulsion Laboratory. Moreover, we have generated empirical spectroscopic pseudoline parameters by fitting all the 23 laboratory spectra together. We observed that the pseudoline parameters (which consist of line position, intensities, and effective lower state energies) could reproduce most of the observed features within 3 % through line-by-line radiative transfer calculations, showing the pseudoline parameters are an excellent practical alternative until the line-by-line spectroscopic line parameters become available. We will present the results and comparisons to existing lower resolution spectra from the PNNL (Sharpe et al.2004).Government support acknowledged.html:<hr /><h3>Footnotes: Government support acknowledged.