Groupe de Spectrométrie Moléculaire et Atmosphérique

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition.

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition.

Abstract The report of an IUPAC Task Group, formed in 2011 on “Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory” (Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules is presented. The well-documented inadequacies of the Voigt profile (VP), used almost universally by databases and radiative-transfer codes, to represent pressure effects and Doppler broadening in isolated vibrational-rotational and pure rotational transitions of the water molecule have resulted in the development of a variety of alternative line-profile models. These models capture more of the physics of the influence of pressure on line shapes but, in general, at the price of greater complexity. The Task Group recommends that the partially Correlated quadratic-Speed-Dependent Hard-Collision profile (pCqSD-HCP) should be adopted as the appropriate model for high-resolution spectroscopy. For simplicity this should be called the Hartmann–Tran profile (HTP). The HTP is sophisticated enough to capture the various collisional contributions to the isolated line shape, can be computed in a straightforward and rapid manner, and reduces to simpler profiles, including the Voigt profile, under certain simplifying assumptions.

The detections of atomic hydrogen, heavy atoms and ions surrounding the extrasolar giant planet (EGP) HD209458b constrain the composition, temperature and density profiles in its upper atmosphere. Thus the observations provide guidance for models that have so far predicted a range of possible conditions. We present the first hydrodynamic escape model for the upper atmosphere that includes all of the detected species in order to explain their presence at high altitudes, and to further constrain the temperature and velocity profiles. This model calculates the stellar heating rates based on recent estimates of photoelectron heating efficiencies, and includes the photochemistry of heavy atoms and ions in addition to hydrogen and helium. The composition at the lower boundary of the escape model is constrained by a full photochemical model of the lower atmosphere. We confirm that molecules dissociate near the 1 μbar level, and find that complex molecular chemistry does not need to be included above this level. We also confirm that diffusive separation of the detected species does not occur because the heavy atoms and ions collide frequently with the rapidly escaping H and H+. This means that the abundance of the heavy atoms and ions in the thermosphere simply depends on the elemental abundances and ionization rates. We show that, as expected, H and O remain mostly neutral up to at least 3Rp, whereas both C and Si are mostly ionized at significantly lower altitudes. We also explore the temperature and velocity profiles, and find that the outflow speed and the temperature gradients depend strongly on the assumed heating efficiencies. Our models predict an upper limit of 8000 K for the mean (pressure averaged) temperature below 3Rp, with a typical value of 7000 K based on the average solar XUV flux at 0.047 AU. We use these temperature limits and the observations to evaluate the role of stellar energy in heating the upper atmosphere.

Abstract A methane line list for the HITEMP spectroscopic database, covering 0–13,400 cm −1 (>746 nm), is presented. To create this compilation, ab initio line lists of 12 CH 4 from Rey et al. ApJ, 847, 105 (provided at separate temperatures in the TheoReTS information system), are now combined with HITRAN2016 methane data to produce a single line list suitable for high-temperature line-by-line calculations up to 2000 K. An effective-temperature interpolation model was created in order to represent continuum-like features over the temperature range of study. This model is advantageous to previously used approaches that employ so-called “super-lines,” which are suitable only at a given temperature and require separate line lists for different temperatures. The resultant HITEMP line list contains ∼32 million lines and is significantly more flexible than alternative line lists of methane, while accuracy required for astrophysical or combustion applications is retained. Comparisons against experimental observations of methane absorption at high temperatures have been used to demonstrate the accuracy of the new work. The line list includes both strong lines and quasi-continuum features and is provided in the common user-friendly HITRAN/HITEMP format, making it the most practical methane line list for radiative-transfer modeling at high-temperature conditions.

High‐resolution NO 2 absorption cross sections have been obtained in the near‐IR (NIR) and visible regions using a Fourier transform spectrometer coupled to a multiple reflection cell. Spectra were recorded at 0.05 cm −1 in the NIR region (10,800–15,100 cm −1 ) and at 0.1 cm −1 in the visible region (13,800–26,000 cm −1 ), under various pressure conditions (pure NO 2 and NO 2 /air mixtures) and at three temperatures (220, 240, and 294 K). The effects of the temperature and the pressure on the NO 2 cross sections have been investigated. As expected, an increase of temperature results in a decrease of the absorption at the maxima of the absorption bands and an increase at the minima. From the measurements performed with pure NO 2 at different temperatures a linear regression of the cross section with temperature has been carried out. This enabled the cross sections to be reproduced within 2% at room temperature and 7% at the lower temperatures. The variation of the cross sections with the total pressure of NO 2 /air mixtures has also been investigated at high resolution.

Abstract We present Hubble Space Telescope ( HST ) near-ultraviolet (NUV) transits of the hot Jupiter WASP-121b, acquired as part of the PanCET program. Time-series spectra during two transit events were used to measure the transmission spectra between 2280 and 3070 Å at a resolution of 30,000. Using HST data from 61 Space Telescope Imaging Spectrograph visits, we show that data from HST ’s Pointing Control System can be used to decorrelate the instrument systematic errors (jitter decorrelation), which we used to fit the WASP-121b light curves. The NUV spectra show very strong absorption features, with the NUV white light curve found to be larger than the average optical and near-infrared value at 6 σ confidence. We identify and spectrally resolve absorption from the Mg ii doublet in the planetary exosphere at a 5.9 σ confidence level. The Mg ii doublet is observed to reach altitudes of R pl / R star = 0.284 ± 0.037 for the 2796 Å line and 0.242 ± 0.0431 for the 2804 Å line, which exceeds the Roche lobe size as viewed in transit geometry ( R eqRL / R star = 0.158). We also detect and resolve strong features of the Fe ii UV1 and UV2 multiplets, and observe the lines reaching altitudes of R pl / R star ≈ 0.3. At these high altitudes, the atmospheric Mg ii and Fe ii gas is not gravitationally bound to the planet, and these ionized species may be hydrodynamically escaping or could be magnetically confined. Refractory Mg and Fe atoms at high altitudes also indicate that these species are not trapped into condensate clouds at depth, which places constraints on the deep interior temperature.

Abstract The Integrated Carbon Observation System Research Infrastructure aims to provide long-term, continuous observations of sources and sinks of greenhouse gases such as carbon dioxide, methane, nitrous oxide, and water vapour. At ICOS ecosystem stations, the principal technique for measurements of ecosystem-atmosphere exchange of GHGs is the eddy-covariance technique. The establishment and setup of an eddy-covariance tower have to be carefully reasoned to ensure high quality flux measurements being representative of the investigated ecosystem and comparable to measurements at other stations. To fulfill the requirements needed for flux determination with the eddy-covariance technique, variations in GHG concentrations have to be measured at high frequency, simultaneously with the wind velocity, in order to fully capture turbulent fluctuations. This requires the use of high-frequency gas analysers and ultrasonic anemometers. In addition, to analyse flux data with respect to environmental conditions but also to enable corrections in the post-processing procedures, it is necessary to measure additional abiotic variables in close vicinity to the flux measurements. Here we describe the standards the ICOS ecosystem station network has adopted for GHG flux measurements with respect to the setup of instrumentation on towers to maximize measurement precision and accuracy while allowing for flexibility in order to observe specific ecosystem features.

Bubble bursting is a ubiquitous phenomenon, impacting the climate by producing sea spray aerosols above the ocean, while also controlling the fineness of the effervescence of sparkling wine. Numerical and laboratory experiments are used to rationalize the velocity of jets formed by bubble bursting.

Abstract. Atmospheric aerosols impose direct and indirect effects on the climate system, for example, by absorption of radiation in relation to cloud droplets size, on chemical and organic composition and cloud dynamics. The first step in the formation of Organic primary aerosols, i.e. the transfer of dissolved organic matter from the marine surface into the atmosphere, was studied. We present a molecular level description of this phenomenon using the high resolution analytical tools of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and nuclear magnetic resonance spectroscopy (NMR). Our experiments confirm the chemoselective transfer of natural organic molecules, especially of aliphatic compounds from the surface water into the atmosphere via bubble bursting processes. Transfer from marine surface water to the atmosphere involves a chemical gradient governed by the physicochemical properties of the involved molecules when comparing elemental compositions and differentiating CHO, CHNO, CHOS and CHNOS bearing compounds. Typical chemical fingerprints of compounds enriched in the aerosol phase were CHO and CHOS molecular series, smaller molecules of higher aliphaticity and lower oxygen content, and typical surfactants. A non-targeted metabolomics analysis demonstrated that many of these molecules corresponded to homologous series of oxo-, hydroxy-, methoxy-, branched fatty acids and mono-, di- and tricarboxylic acids as well as monoterpenes and sugars. These surface active biomolecules were preferentially transferred from surface water into the atmosphere via bubble bursting processes to form a significant fraction of primary organic aerosols. This way of sea spray production leaves a selective biological signature of the surface water in the corresponding aerosol that may be transported into higher altitudes up to the lower atmosphere, thus contributing to the formation of secondary organic aerosol on a global scale or transported laterally with possible deposition in the context of global biogeocycling.

Abstract We present an atmospheric transmission spectrum for the ultra-hot Jupiter WASP-121b, measured using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope . Across the 0.47–1 wavelength range, the data imply an atmospheric opacity comparable to—and in some spectroscopic channels exceeding—that previously measured at near-infrared wavelengths (1.15–1.65 ). Wavelength-dependent variations in the opacity rule out a gray cloud deck at a confidence level of 3.7 σ and may instead be explained by VO spectral bands. We find a cloud-free model assuming chemical equilibrium for a temperature of 1500 K and a metal enrichment of 10–30× solar matches these data well. Using a free-chemistry retrieval analysis, we estimate a VO abundance of dex. We find no evidence for TiO and place a 3 σ upper limit of −7.9 dex on its abundance, suggesting TiO may have condensed from the gas phase at the day–night limb. The opacity rises steeply at the shortest wavelengths, increasing by approximately five pressure scale heights from 0.47 to 0.3 in wavelength. If this feature is caused by Rayleigh scattering due to uniformly distributed aerosols, it would imply an unphysically high temperature of 6810 ± 1530 K. One alternative explanation for the short-wavelength rise is absorption due to SH (mercapto radical), which has been predicted as an important product of non-equilibrium chemistry in hot Jupiter atmospheres. Irrespective of the identity of the NUV absorber, it likely captures a significant amount of incident stellar radiation at low pressures, thus playing a significant role in the overall energy budget, thermal structure, and circulation of the atmosphere.

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This paper is a detailed critical review of the production processes and reactions of N, N+, N+2 , N++, and N++2 of relevance to Titan’s atmosphere. The review includes neutral, ion–molecule, and recombination reactions. The review covers all possible active nitrogen species under Titan’s atmospheric conditions, specifically N2 (A 3Σ+u), N (4S), N (2D), N (2P), N+2 , N+ (3P), N+ (1D), N++2 , and N++ species, and includes a critical survey of the reactions of N, N+, N+2 , N++, and N++2 with N2, H2, D2, CH4, C2H2, C2H4, C2H6, C3H8 and the deuterated hydrocarbon analogs, as well as the recombination reactions of N+2 , N+, N++2, and N++. Production processes, lifetimes, and quenching by collisions with N2 of all reactant species are reviewed. The N (4S) state is reactive with radicals and its reactions with CH2, CH3, C2H3, and C2H5 are reviewed. Metastable states N2 (A 3Σ+u), N (2D), and N (2P) are either reactive or quenched by collisions with the target molecules reviewed. The reactions of N+ (1D) have similar rate constants as N+ (3P), but the product branching ratios differ significantly. Temperature effects and the role of the kinetic energy content of reactants are investigated. In all cases, experimental uncertainties of laboratory data are reported or estimated. Recommended values with uncertainties, or estimated values when no data are available, are given for rate constants and product branching ratios at 300 K and at the atmospheric temperature range of Titan (150–200 K for neutral reactions and 150 K for ion reactions)

Photochemically produced aerosols are common among the atmospheres of our solar system and beyond. Observations and models have shown that photochemical aerosols have direct consequences on atmospheric properties as well as important astrobiological ramifications, but the mechanisms involved in their formation remain unclear. Here we show that the formation of aerosols in Titan's upper atmosphere is directly related to ion processes, and we provide a complete interpretation of observed mass spectra by the Cassini instruments from small to large masses. Because all planetary atmospheres possess ionospheres, we anticipate that the mechanisms identified here will be efficient in other environments as well, modulated by the chemical complexity of each atmosphere.

New long path length, high resolution, Fourier transform spectrometer measurements for water are presented. These spectra cover the near infrared, visible, and near ultraviolet regions and contain water transitions belonging to all polyads from 3ν to 8ν. Transitions in the range 13 100–21 400 cm−1 are analyzed using line lists computed using variational first-principles calculations. 2286 new transitions are assigned to H216O. These result in the observation of transitions in 15 new overtone and combination bands of water. Energy levels for these and other newly observed levels are presented. It is suggested that local mode rather than normal mode vibrational assignments are more appropriate for the vibrational states of water in polyads 4ν and above.

An accurate description of the complicated shape of the potential energy surface (PES) and that of the highly excited vibration states is of crucial importance for various unsolved issues in the spectroscopy and dynamics of ozone and remains a challenge for the theory. In this work a new analytical representation is proposed for the PES of the ground electronic state of the ozone molecule in the range covering the main potential well and the transition state towards the dissociation. This model accounts for particular features specific to the ozone PES for large variations of nuclear displacements along the minimum energy path. The impact of the shape of the PES near the transition state (existence of the "reef structure") on vibration energy levels was studied for the first time. The major purpose of this work was to provide accurate theoretical predictions for ozone vibrational band centres at the energy range near the dissociation threshold, which would be helpful for understanding the very complicated high-resolution spectra and its analyses currently in progress. Extended ab initio electronic structure calculations were carried out enabling the determination of the parameters of a minimum energy path PES model resulting in a new set of theoretical vibrational levels of ozone. A comparison with recent high-resolution spectroscopic data on the vibrational levels gives the root-mean-square deviations below 1 cm(-1) for ozone band centres up to 90% of the dissociation energy. New ab initio vibrational predictions represent a significant improvement with respect to all previously available calculations.

Transits in the H I 1216 Å (Lyman α), O I 1334 Å, C II 1335 Å, and Si III 1206.5 Å lines constrain the properties of the upper atmosphere of HD209458b. In addition to probing the temperature and density profiles in the thermosphere, they have implications for the properties of the lower atmosphere. Fits to the observations with a simple empirical model and a direct comparison with a more complex hydrodynamic model constrain the mean temperature and ionization state of the atmosphere, and imply that the optical depth of the extended thermosphere of the planet in the atomic resonance lines is significant. In particular, it is sufficient to explain the observed transit depths in the H I 1216 Å line. The detection of O at high altitudes implies that the minimum mass loss rate from the planet is approximately 6 × 106 kg s−1. The mass loss rate based on our hydrodynamic model is higher than this and implies that diffusive separation is prevented for neutral species with a mass lower than about 130 amu by the escape of H. Heavy ions are transported to the upper atmosphere by Coulomb collisions with H+ and their presence does not provide as strong constraints on the mass loss rate as the detection of heavy neutral atoms. Models of the upper atmosphere with solar composition and heating based on the average solar X-ray and EUV flux agree broadly with the observations but tend to underestimate the transit depths in the O I, C II, and Si III lines. This suggests that the temperature and/or elemental abundances in the thermosphere may be higher than expected from such models. Observations of the escaping atmosphere can potentially be used to constrain the strength of the planetary magnetic field. We find that a magnetic moment of m ≲ 0.04mJ, where mJ is the jovian magnetic moment, allows the ions to escape globally rather than only along open field lines. The detection of Si2+ in the thermosphere indicates that clouds of forsterite and enstatite do not form in the lower atmosphere. This has implications for the temperature and dynamics of the atmosphere that also affect the interpretation of transit and secondary eclipse observations in the visible and infrared wavelengths.

First-principles computations and experimental measurements of transition energies are carried out for vibrational overtone lines of the triatomic hydrogen ion ${\mathrm{H}}_{3}^{+}$ corresponding to floppy vibrations high above the barrier to linearity. Action spectroscopy is improved to detect extremely weak visible-light spectral lines on cold trapped ${\mathrm{H}}_{3}^{+}$ ions. A highly accurate potential surface is obtained from variational calculations using explicitly correlated Gaussian wave function expansions. After nonadiabatic corrections, the floppy ${\mathrm{H}}_{3}^{+}$ vibrational spectrum is reproduced at the $0.1\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ level up to $16\text{ }600\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$.

We report global calculations of rovibrational spectra and dipole transition intensities of methane using our recent ab initio dipole moment and potential surfaces [Nikitin et al., Chem. Phys. Lett., 2011, 501, 179; 2013, 565, 5]. For the full symmetry account, a recently published variational tensor formalism in normal modes [Rey et al., J. Chem. Phys., 2012, 136, 244106] is applied, the convergence of high-J calculations being improved by the use of vibrational eigenfunctions to make a compressed basis set for solving the rovibrational problem. Comparisons of theoretical predictions up to J = 25 for various complex polyads of methane involving strongly coupled vibration-rotation bands support the validity of this new approach. For the first time, positions and line intensities at 80 K and 296 K are shown to be in excellent agreement with raw experimental data, even for high energy ranges. The theoretical predictions also correctly describe the isotopic effects in line positions and intensities due to the CH4 → CD4 substitution which is considered as the test for the method. This work is a first step toward the theoretical interpretation of numerous methane bands which remain still unassigned and detailed line-by-line absorption/emission spectra analyses for atmospheric and planetological applications.

A rovibrational model based on the normal-mode complete nuclear Hamiltonian is applied to methane using our recent potential energy surface [A. V. Nikitin, M. Rey, and Vl. G. Tyuterev, Chem. Phys. Lett. 501, 179 (2011)]. The kinetic energy operator and the potential energy function are expanded in power series to which a new truncation-reduction technique is applied. The vibration-rotation Hamiltonian is transformed systematically to a full symmetrized form using irreducible tensor operators. Each term of the Hamiltonian expansion can be thus cast in the tensor form whatever the order of the development. This allows to take full advantage of the symmetry properties for doubly and triply degenerate vibrations and vibration-rotation states. We apply this model to variational computations of energy levels for (12)CH(4), (13)CH(4), and (12)CD(4).