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ExoMolHR is an empirical, high-resolution molecular spectrum calculator for the high-temperature molecular line lists available from the ExoMol molecular database. Uncertainties, where available, in recommended ExoMol data sets are used to select highly accurate spectral lines. These lines largely rely on empirical energy levels generated through the MARVEL procedure, which is being systematically used to improve the energy and transition data provided by the ExoMol database. The freely accessible ExoMolHR database provides line positions with calculated intensities for a user-specified wavenumber/wavelength range and temperature. Spectra can be plotted on the ExoMolHR website https://www.exomol.com/exomolhr/ or downloaded as a .csv file. Cross sections can be calculated using the Python program PyExoCross. The ExoMolHR database currently provides 24,307,135 spectral lines for 33 molecules and 58 isotopologues; these numbers will increase as the ExoMol database is updated.

The ExoMol project is dedicated to providing molecular line lists for exoplanet and other hot atmospheres. The ExoMol procedure uses a mixture of ab initio calculations and available laboratory data. The actual line lists are generated using variational nuclear motion calculations. These line lists form the input for opacity models for cool stars and brown dwarfs as well as for radiative transport models involving exoplanets. This paper is a collection of molecular opacities for 52 molecules (130 isotopologues) at two reference temperatures, 300 K and 2000 K, using line lists from the ExoMol database. So far, ExoMol line lists have been generated for about 30 key molecular species. Other line lists are taken from external sources or from our work predating the ExoMol project. An overview of the line lists generated by ExoMol thus far is presented and used to evaluate further molecular data needs. Other line lists are also considered. The requirement for completeness within a line list is emphasized and needs for further line lists discussed.

Because of elevated temperatures and high fluxes of stellar radiation irreproducible in laboratory conditions, molecules and molecular ions found or expected in exoplanetary atmospheres are generally poorly characterized from the viewpoint of their spectroscopic line-shape parameters; in many cases, there are no data at all. Advanced theoretical approaches (classical, semiclassical, and quantum mechanical), without mentioning their high computational cost, are also impracticable due to the lack of potential energy surfaces. To fill this gap of crucially missing line-broadening parameters, we provide estimated values issued from a simple rotationally independent semiclassical expression. Only the index related to the leading long-range interaction term, molecular masses and kinetic diameters, as well as temperature are used as input parameters. A wide range of absorbers and perturbation by He, Ar, H2, N2, O2, CO, NO, CO2, H2O, CH4, and NH3 as well as self-perturbation are considered. The explicit temperature dependence T−0.5 allows calculations to be limited to the single reference temperature of 296 K; for other temperatures a simple scaling can be used. The full set of line-broadening coefficients obtained with various possible values of kinetic diameters is provided by the new Collisional Line-broadening Parameters database, which is specifically designed for this purpose. “Midvalue” (or more recent) kinetic diameters are retained to create one-value line-broadening data required to populate the ExoMol database. A way to generate rotationally dependent line widths is proposed.

Being one of the first exoplanets observed by the James Webb Space Telescope, WASP-39 b has become an iconic target, and many transit spectra recorded with different instruments (NIRISS, NIRCAM, NIRSpec G395H, NIRSpec PRISM, and MIRI) are currently available, allowing in-depth studies of its atmosphere. We present here a novel approach to interpret WASP-39 b’s transit spectroscopic data, consisting of a multistep process where ab initio equilibrium chemistry models and blind retrievals are used iteratively to find physically robust, optimal solutions. Following this approach, we have identified a new scenario to explain WASP-39 b’s atmospheric composition, in which silicon-based chemistry plays a major role. In this scenario, SiO may explain the spectral absorption at 4.1 μm, currently interpreted as being due to SO2. SiO and the other gas species identified by the retrieval models, i.e., H2O, CO2, Na, and K, are consistent with an atmosphere in chemical equilibrium with a temperature–pressure profile constrained by H2O and CO2 absorption bands. In addition, silicate clouds and hazes can produce the spectral features observed by MIRI in the spectral window 5–12 μm. While we advocate the need for more data, possibly at higher spectral resolution, to confirm our results for WASP-39 b’s atmospheric composition, we highlight a refined atmospheric retrieval strategy with preselection and post-reconstruction to guide the next generation of transit spectroscopy.

The TIRAMISU code, a new program for computing on-the-fly non-LTE molecular spectra and opacities for solving self-consistent radiative transfer problems in exoplanet atmospheres, is presented. The ultra-hot Jupiter KELT-20 b is used as a case study to identify the wavelength regions at which non-LTE effects may be detectable. It is shown that upper atmospheric OH in vibrational non-LTE should be observable primarily via hot bands in the mid-infrared and enhanced photodissociation in the visible. Varying the abundance of OH in non-LTE demonstrates a nonlinear relationship between the abundance and the strength of non-LTE effects. Using recent calculations of the photodissociation probabilities of OH, it is shown that non-LTE effects can increase the total photodissociation rate by 2 orders of magnitude in the upper atmosphere, which is likely to have a significant impact on atmospheric and chemical modelling. Increases and reductions in the molecular opacities under non-LTE conditions may lead to the mischaracterization of molecular abundances in retrievals that only consider opacities computed under LTE. Collisional data requirements to support future non-LTE modeling for a variety of exoplanet atmospheres and across a wide range of wavelengths are discussed.

Individual vibrational band spectroscopy presents an opportunity to examine exoplanet atmospheres in detail, by distinguishing where the vibrational state populations of molecules differ from the current assumption of a Boltzmann distribution. Here, retrieving vibrational bands of OH in exoplanet atmospheres is explored using the hot Jupiter WASP-33b as an example. We simulate low-resolution spectroscopic data for observations with the JWST's NIRSpec instrument and use high-resolution observational data obtained from the Subaru InfraRed Doppler instrument (IRD). Vibrational band–specific OH cross-section sets are constructed and used in retrievals on the (simulated) low- and (real) high-resolution data. Low-resolution observations are simulated for two WASP-33b emission scenarios: under the assumption of local thermal equilibrium (LTE) and with a toy non-LTE model for vibrational excitation of selected bands. We show that mixing ratios for individual bands can be retrieved with sufficient precision to allow the vibrational population distributions of the forward models to be reconstructed. A fit for the Boltzmann distribution in the LTE case shows that the vibrational temperature is recoverable in this manner. For high-resolution, cross-correlation applications, we apply the individual vibrational band analysis to an IRD spectrum of WASP-33b, applying an “unpeeling” technique. Individual detection significances for the two strongest bands are shown to be in line with Boltzmann-distributed vibrational state populations, consistent with the effective temperature of the WASP-33b atmosphere reported previously. We show the viability of this approach for analyzing the individual vibrational state populations behind observed and simulated spectra, including reconstructing state population distributions.

Hot methane spectra are important in environments ranging from flames to the atmospheres of cool stars and exoplanets. A new spectroscopic line list, 10to10, for ¹²CH ₄ containing almost 10 billion transitions is presented. This comprehensive line list covers a broad spectroscopic range and is applicable for temperatures up to 1,500 K. Previous methane data are incomplete, leading to underestimated opacities at short wavelengths and elevated temperatures. Use of 10to10 in models of the bright T4.5 brown dwarf 2MASS 0559-14 leads to significantly better agreement with observations and in studies of the hot Jupiter exoplanet HD 189733b leads to up to a 20-fold increase in methane abundance. It is demonstrated that proper inclusion of the huge increase in hot transitions which are important at elevated temperatures is crucial for accurate characterizations of atmospheres of brown dwarfs and exoplanets, especially when observed in the near-infrared.

In this study, we present a current state-of-the-art review of middle-to-near IR emission spectra of four simple astrophysically relevant molecular radicals—OH, NH, CN and CH. The spectra of these radicals were measured by means of time-resolved Fourier transform infrared spectroscopy in the 700–7500 cm−1 spectral range and with 0.07–0.02 cm−1 spectral resolution. The radicals were generated in a glow discharge of gaseous mixtures in a specially designed discharge cell. The spectra of short-lived radicals published here are of great importance, especially for the detailed knowledge and study of the composition of exoplanetary atmospheres in selected new planets. Today, with the help of the James Webb telescope and upcoming studies with the help of Plato and Ariel satellites, when the investigated spectral area is extended into the infrared spectral range, it means that detailed knowledge of the infrared spectra of not only stable molecules but also the spectra of short-lived radicals or ions, is indispensable. This paper follows a simple structure. Each radical is described in a separate chapter, starting with historical and actual theoretical background, continued by our experimental results and concluded by spectral line lists with assigned notation.

Many methods have been proposed for efficient storage of molecular hydrogen for fuel cell applications. However, despite intense research efforts, the twin U.S. Department of Energy goals of 6.5% mass ratio and 62 kg/ m3volume density has not been achieved either experimentally or via theoretical simulations on reversible model systems. Carbon-based materials, such as carbon nanotubes, have always been regarded as the most attractive physisorption substrates for the storage of hydrogen. Theoretical studies on various model graphitic systems, however, failed to reach the elusive goal. Here, we show that insufficiently accurate carbon- H2interaction potentials, together with the neglect and incomplete treatment of the quantum effects in previous theoretical investigations, led to misleading conclusions for the absorption capacity. A proper account of the contribution of quantum effects to the free energy and the equilibrium constant for hydrogen adsorption suggest that the U.S. Department of Energy specification can be approached in a graphite-based physisorption system. The theoretical prediction can be realized by optimizing the structures of nano-graphite platelets (graphene), which are light-weight, cheap, chemically inert, and environmentally benign.

High-level ab initio quantum chemical (QC) molecular potential energy surfaces (PESs) are crucial for accurately simulating molecular rotation-vibration spectra. Machine learning (ML) can help alleviate the cost of constructing such PESs, but requires access to the original ab initio PES data, namely potential energies computed on high-density grids of nuclear geometries. In this work, we present a new structured PES database called VIB5, which contains high-quality ab initio data on 5 small polyatomic molecules of astrophysical significance (CH 3 Cl, CH 4 , SiH 4 , CH 3 F, and NaOH). The VIB5 database is based on previously used PESs, which, however, are either publicly unavailable or lacking key information to make them suitable for ML applications. The VIB5 database provides tens of thousands of grid points for each molecule with theoretical best estimates of potential energies along with their constituent energy correction terms and a data-extraction script. In addition, new complementary QC calculations of energies and energy gradients have been performed to provide a consistent database, which, e.g., can be used for gradient-based ML methods. Measurement(s) potential energy surfaces Technology Type(s) quantum chemistry computational methods