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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 com- pilation 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 particu- lar, 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 replace- ments of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH 3 F, GeH 4 , CS 2 , CH 3 I and NF 3 . Many new vibrational bands were added, extending the spectral cov- erage 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 param- eters 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.

International audience; We investigate collisional line-shape effects that are present in highly accurate experimental spectra of the 3-0 S(1) and 2-0 Q(1) molecular hydrogen absorption lines perturbed by helium. We clearly distin-guish the influence of six different collisional effects (i.e.: collisional broadening and shift, their speed dependencies and the complex Dicke effect) on the shapes of H-2 lines. We demonstrate that only a very specific combination of these six contributions, determined from our ab initio calculations, gives unprece-dentedly good agreement with experimental spectra. If any of the six contributions is neglected, then the experiment-theory comparison deteriorates at least several times. We also analyze the influence of the centrifugal distortion on our ab initio calculations and we demonstrate that the inclusion of this effect slightly improves the agreement with the experimental spectra. (C) 2021 The Author(s). Published by Elsevier Ltd.

This paper describes the updates of the line positions and intensities for the carbon dioxide transitions in the 2020 edition of the HITRAN spectroscopic database. The new line list for all 12 naturally abundant isotopologues of carbon dioxide replaces the previous one from the HITRAN2016 edition. This update is primarily motivated by several issues related to deficient HITRAN2016 line positions and intensities that have been identified from laboratory and atmospheric spectra. Critical validation tests for the spectroscopic data were carried out to find problems caused by inaccuracies in CO2 line parameters. New sources of data were selected for the bands that were deemed problematic in the HITRAN2016 edition. Extra care was taken to retain the consistency in the data sources within the bands. The comparisons with the existing theoretical and semi-empirical databases (including ExoMol, NASA Ames, and CDSD-296) and with available experimental works were carried out. The HITRAN2020 database has been extended by including additional CO2 bands above 8000 cm−1, and magnetic dipole lines of CO2 were introduced in HITRAN for the first time by including the ν2+ν3 band in the 3.3-µm region. Although the main topic of this article is line positions and intensities, for consistency a recent algorithm for the line-shape parameters proposed in Hashemi et al. JQSRT (2020) was reapplied (after minor revisions) to the line list.

Room temperature absorption spectra of ammonia have been recorded by high-resolution Fourier transform spectroscopy in the range 3900-4700 cm−1 at four pressures (13, 46, 140, and 304 Pa). The investigated spectral region overlaps the important 2.3 µm atmospheric transparency window. 8419 absorption lines were retrieved from the recorded spectra. Line intensities range between 1 × 10−25 and 1.6 × 10−20 cm/molecule. The rovibrational assignments, relying on the position and intensity agreement with the C2018 theoretical line list (Coles et al. 2018), were validated by the systematic use of Lower State Combination Difference (LSCD) relations. 6052 transitions were assigned to 51 vibrational bands of the main isotopologue, 14NH3, and 625 transitions of the 15NH3 minor isotopologue were identified. Overall, the assigned transitions represent over 99.8% of the integrated absorption at room temperature in the region. The upper state empirical energy of a total of 2287 rovibrational levels of 14NH3 were derived. Among them, 1870 are newly reported. The achieved quality of the LSCD relations indicates that the accuracy of the derived energy levels is better than 0.001 cm−1. Comparison with the HITRAN2020 list shows that the present results will be valuable in improving the ammonia spectroscopic databases in the region, both in terms of completeness and accuracy of the line positions and line intensities. A recommended line list for ammonia in natural isotopic abundance is provided for the studied region.

The weak low frequency tail of the ozone Wulf band is newly studied by high sensitivity cavity ring down spectroscopy (CRDS) in the 7920–8700 cm−1 range. Although strongly obscured by impurity lines, the ozone absorption signature shows up in the recorded spectra as two mostly unresolved absorption bands. These two bands with maximum near 8154 and 8450 cm−1 are hot bands from the (020) and (100) ground state vibrational levels reaching the same predissociated 3A2(000) upper state of 16O3. The observed bands include a mostly structureless continuum and lines exhibiting a clear broadening due to the predissociation of the 3A2(000) upper state. On the basis of assignments of the rotational structure available in the literature for the 3A2(000)-X1A1(000) cold band centered near 9553 cm−1, seventy-four relatively narrow lines could be rotationally assigned to the 3A2(000)-X1A1(020) and 3A2(000)-X1A1(100) hot bands. A line shape analysis, performed using a Voigt profile, provided the width of the Lorentzian component. Additional recordings performed at various pressures for 18 lines allowed to disentangle the pressure and predissociation contributions to the fitted Lorentzian widths. As a result, the newly derived pressure broadening coefficients of the considered rovibronic transitions are found to be similar to those of the rovibrational infrared bands. All the lines studied are affected by significant predissociation due the spin-orbit coupling between the 3A2(000) level and high lying dissociative vibrational levels of the X1A1 electronic ground state. The resulting set of predissociation widths for sixty lines ranges between 9 × 10−3 and 0.2 cm−1 corresponding to upper state lifetime of 560 and 25 ps, respectively. The reported results are discussed in relation with previous experimental and theoretical studies.

The weak high-resolution absorption spectrum of natural acetylene has been recorded by high sensitivity cavity ring down spectroscopy (CRDS) near 1.2 µm. The frequency scale of the spectra was obtained by coupling the CRDS spectrometer to a self-referenced frequency comb. The room temperature recordings, performed at a pressure of 10.0 Torr, cover the 8210–8670 cm−1 spectral interval. A list of more than 11,000 lines was constructed in the region. The smallest intensity values are on the order of 10−29 cm/molecule which is more than two orders of magnitude smaller than previous measurements by Fourier transform spectroscopy (FTS). More than 2600 lines were rovibrationally assigned using previous observations and predictions based on the effective operator approach. They include 2270, 338 and 28 absorption lines of 12C2H2, 12C13CH2 and 12C2HD, respectively, belonging to a total of 52 vibrational bands, thirty-six of them being newly reported. For comparison, the HITRAN2016 database provides line parameters of only two 12C2H2 bands, in the same region. Spectroscopic parameters of the upper vibrational levels were derived from standard band-by-band fits of the line positions (typical rms values of the (obs.-calc.) deviations are better than 0.002 cm–1). The vibrational transition dipole moment squared and Herman-Wallis coefficients of 39 bands were derived from a fit of the intensity values measured in this work and combined with previous FTS data for the strongest bands. A recommended list is constructed in the region using calculated line parameters for the unperturbed bands and experimental positions and intensities for the others. The recommended list including a total of 3139 transitions will help to complete acetylene spectroscopic databases in the near-infrared.

International audience; We review progress, since publication of the book "Collisional effects on molecular spectra Laboratory experiments and models, consequences for applications" (Elsevier, Amsterdam, 2008), on measuring, modeling and predicting the influence of pressure (ie of intermolecular collisions) on the spectra of gas molecules. We first introduce recently developed experimental techniques of high accuracy and sensitivity. We then complement the aforementioned book by presenting the theoretical approaches, results and data proposed (mostly) in the last decade on the topics of isolated line shapes, line-broadening and-shifting, line-mixing, the far wings and associated continua, and collision-induced absorption. Examples of recently demonstrated consequences of the progress in the description of spectral shapes for some practical applications (metrology, probing of gas media, climate predictions) are then given. Remaining issues and directions for future research are finally discussed.

International audience; The 1.27 μm O2 band is increasingly called upon for air-mass determination from ground-based and space-borne atmospheric spectra because of its spectral proximity to CO2, and CH4 bands at 1.6 μm, in contrast to the more distant A-band at 0.76 μm. For this purpose, it is important to well characterize not only the narrow absorption lines but also the strong underlying broad collision-induced absorption (CIA) structure and its temperature dependence. Spectra of pure O2, and of O2 in N2, were recorded by cavity ring down spectroscopy (CRDS) at 271 K and 332 K, with the help of a newly developed temperature regulated cell. The quality of the spectra allowed determining the small variations (at the few percent level) of the urn:x-wiley:2169897X:media:jgrd57131:jgrd57131-math-0001, urn:x-wiley:2169897X:media:jgrd57131:jgrd57131-math-0002, and urn:x-wiley:2169897X:media:jgrd57131:jgrd57131-math-0003 binary coefficients with temperature. Together with the binary coefficients at 297 K reported previously, they allow characterizing the temperature dependence of the O2 CIA at 1.27 µm in atmospheric conditions. The obtained results are compared with previous measurements by Fourier transform spectroscopy (FTS) and recent theoretical calculations. In the wings of the O2-O2 CIA, an increase with temperature is observed in agreement with calculations but contrary to these calculations, a decrease is observed near the maximum of the CIA band. The temperature dependence is found in good agreement with the theoretical urn:x-wiley:2169897X:media:jgrd57131:jgrd57131-math-0004values and the experimental urn:x-wiley:2169897X:media:jgrd57131:jgrd57131-math-0005 values derived from the FTS measurements. Binary coefficients integrated over the entire band show almost no variation with temperature for O2-N2 and a small increase for pure O2, in agreement with the theoretical predictions.

This paper describes the 2020 release of the GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), developed and maintained at LMD since 1974. GEISA is the reference database for several current or planned Thermal and Short-Wave InfraRed (TIR and SWIR) space missions IASI (Infrared Atmospheric Sounding Interferometer), IASI-NG (IASI New Generation), MicroCarb (Carbon Dioxide Monitoring Mission), Merlin (MEthane Remote sensing LIdar missioN). It is actually a compilation of three databases: the “line parameters database”, the “cross-section sub-database” and the “microphysical and optical properties of atmospheric aerosols sub-database”. The new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data. The GEISA-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10−6 to 35877 cm−1. In this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (HONO, COFCl, CH3F, CH3I, RuO4, H2C3H2 (isomer of C3H4)) corresponding to 15 isotopic species. The compilation can be accessed through the AERIS data and services center for the atmosphere website (https://geisa.aeris-data.fr/), with the development of a powerful graphical tool and convenient searching, filtering, and plotting of data using modern technologies (PostgreSQL database, REST API, VueJS, Plotly). Based on four examples (H2O, O3, O2 and SF6), this paper also shows how the LMD in house validation algorithm SPARTE (Spectroscopic Parameters And Radiative Transfer Evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into GEISA and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer).

The recent detections of electric-quadrupole (E2) transitions in water vapor and magnetic-dipole (M1) transitions in carbon dioxide have opened a new field in molecular spectroscopy. While in their present status, the spectroscopic databases provide only electric-dipole (E1) transitions for polyatomic molecules (H$_2$O, CO$_2$, N$_2$O, CH$_4$, O$_3$…), the possible impact of weak E2 and M1 bands to the modeling of the Earth and planetary atmospheres has to be addressed. This is especially important in the case of carbon dioxide for which E2 and M1 bands may be located in spectral windows of weak E1 absorption. In the present work, a high sensitivity absorption spectrum of CO$_2$ is recorded by Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OFCEAS) in the 3.3 µm transparency window of carbon dioxide. The studied spectral interval corresponds to the region where M1 transitions of the $ν_{2}+ν_{3}$band of carbon dioxide were recently identified in the spectrum of the Martian atmosphere. Here, both M1 and E2 transitions of the $ν_{2}+ν_{3}$ band are detected by OFCEAS. Using recent ab initio calculations of the E2 spectrum of $^{12}$C$^{16}$O$_2$, intensity measurements of five M1 lines and three E2 lines allow us to disentangle the M1 and E2 contributions. Indeed, E2 intensity values (on the order of a few 10$^{–29}$ cm/molecule) are found in reasonable agreement with ab initio calculations while the intensity of the M1 lines (including an E2 contribution) agree very well with recent very long path measurements by Fourier Transform spectroscopy. We thus conclude that both E2 and M1 transitions should be systematically incorporated in the CO$_2$ line list provided by spectroscopic databases.

The MERLIN mission (MEthane Remote LIdar missioN) is a space mission dedicated to the methane atmospheric retrieval based on absorption LIDAR measurements at nadir. The methane columns will be obtained by difference between the LIDAR signal at the on-line wavelength corresponding to the R(6) manifold of the 2ν3 band of methane at 6077 cm−1 and the off-line signal at a wavenumber about 1 cm−1 below. As atmospheric water vapor lines may affect the methane retrievals, the present study is dedicated to a detailed laboratory characterization of the interfering water vapor absorption in the targeted region. To this aim, high sensitivity absorption spectra of pure water vapor and water vapor in air are recorded at room temperature using a cavity ring down spectrometer (CRDS) combined with a self-referenced frequency comb. The CRDS recordings cover the 6071.4–6080.0 cm−1 interval with a noise equivalent absorption, αmin, on the order of 5 × 10−11 cm−1 for a 10−3 cm−1 sampling of the spectra. The measured pure and air-broadened spectra are analyzed using the Nelkin-Ghatak (NG) or the speed-dependent Nelkin-Ghatak (sdNG) profile. A multi-spectrum fitting procedure in which series of spectra recorded at different pressures (between 0.7 and 12 Torr for pure water vapor and between 100 and 700 Torr for H2O in air) are simultaneously adjusted, is used to retrieve the spectroscopic parameters. Accurate line parameters including self- and air-pressure shifts, self- and air-broadenings, Dicke narrowing and the speed-dependent coefficients are determined for most of the lines with intensity larger than 10−28 cm/molecule at 296 K. The list is complemented with literature data (in particular from the HITRAN database) to be complete down to a 10−29 cm/molecule intensity cut-off. The obtained spectroscopic results are discussed in comparison with literature data.

The high resolution absorption spectrum of the NO2 molecule is recorded between 5855 and 6006 cm−1 by high sensitivity cavity ring down spectroscopy (CRDS). Positions and intensities in the 5 × 10−27 − 4 × 10−23 cm/molecule range are derived from the profile fitting of more than 6900 lines. The absorption is dominated by the transitions of the (103)–(000) vibrational band centered at 5984.704 cm−1. The spectrum is assigned and modeled using an effective Hamiltonian (EH) which explicitly takes into account a spin–rotational interaction and interaction of the (103) bright state with three “dark” states: (122), (080) and (410). The ν1 + 3ν3 band was already analyzed by Fourier transform spectroscopy (FTS) in Miljanic S., Perrin A., Orphal J., Fellows C.E., Chelin, J. Mol. Spectrosc. 2008, V. 251, P. 9–15, where resonance interactions between the (103) state and the (122) and (080) “dark” states were taken into account. More than 3000 lines are presently assigned with rotational quantum numbers N and Ka up to 59 and 13, respectively, while 1147 transitions with maximum N and Ka values of 47 and 8, respectively, were previously identified by FTS. The measured line positions are reproduced with an (obs.-calc.) rms of 0.0023 cm−1 by variation of 41 EH parameters. About 80 transitions reaching the (080) highly excited bending upper state and borrowing their intensity from the resonance coupling with the (103)–(000) band were assigned for the first time. The main parameter in the transition moment series of the ν1 + 3ν3 band is determined from the fitting of the measured intensities.

This work presents the characterisation and comparison of daytime and nighttime mountain breezes observed at three sites through the analysis of tower data. The sites are located: (i) in the foothills of the Guadarrama Mountains in Spain, (ii) on a plateau adjacent to the Pyrenees in France, and (iii) in the Salt Lake Valley (SLV) in the southwest of the United States. The thermally-driven winds are detected through a systematic algorithm which considers both synoptic and local meteorological conditions. The characteristics of the mountain breezes depend on the scale of the breeze at each site. Nighttime events are associated with stronger wind speeds at the two sites located farther away from the mountains due to larger-scale phenomena (valley winds and mountain-plain winds). The arrival of both nighttime and daytime flows to the sites are observed approximately when the buoyancy heat flux changes sign, being a few hours delayed at the sites farther from the mountains. In addition, the impacts of these breezes on CO2 mixing ratios are analysed. The characteristic increase of CO2 mixing ratio observed during the evening transition takes place approximately when the nocturnal breeze arrives at the site. Nonetheless, both processes are not always simultaneous, indicating that CO2 advection is not the main mechanism controlling the drastic CO2 increase. An analogous result is obtained for the CO2 decrease at the morning transition. However, we have found that the CO2 mixing ratio is sensitive to wind direction (horizontal advection) in highly heterogeneous areas like the SLV, where CO2 emissions from the nearby city centre play an important role. Finally, a clear relationship is found between the CO2 mixing ratio and near-surface turbulence at night. Maximum CO2 mixing ratios are found for specific turbulence thresholds, which depend on the height of the CO2 sensor. Conditions associated with both stronger and weaker turbulence levels lead to reduced CO2 mixing ratios at the local measurement height due to excessive and ineffective mixing, respectively.

The water vapor continuum absorption is studied in a spectral range covering most of the pure rotational spectrum of water molecule up to 500 cm−1. The continuum absorption was derived from the broadband water vapor spectra recorded by Fourier transform spectrometer equipped with the 151-m multipass gas cell at the AILES beam line of the SOLEIL synchrotron. The coherent (10–35 cm−1) and standard (40–500 cm−1) radiation modes of the synchrotron were used. In order to refine the magnitude and clarify the physical origin of the continuum, spectra of the two major water isotopologues, H216O and H218O, were considered. Recordings at several water vapor pressures were used to check the expected quadratic pressure dependence of the continuum. The new data extend and supplement previous measurements filling, in particular, the gap between 200 and 350 cm−1, which was never studied before. The H216O and H218O absorption continua in the range of 50–650 cm−1 show similar frequency dependence and magnitude. In particular, both continua exhibit a clear water dimer spectral signature near 15 cm−1, in good agreement with previous ab initio calculations. The present data confirm that the MT-CKD empirical continuum model widely used in atmospheric applications, overestimates importantly the continuum magnitude in the whole range of the rotational band. The observed irregular frequency dependence of the retrieved self-continuum cross-section values is tentatively interpreted as due to uncertainties on the resonance lines of the water monomer spectrum which is subtracted from the recorded spectra. On the basis of spectra simulations, the inadequate description of the line shapes in the range of the intermediate wings (detuning of 5–10 cm−1 from line center) and the uncertainties on the self-broadening coefficients of water monomer lines are identified as possible mechanisms responsible of the observed irregular fluctuations.

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The weak high-resolution absorption spectrum of natural nitrous oxide has been recorded by high sensitivity cavity ring down spectroscopy (CRDS) near 1.18 µm. The frequency scale of the spectra was obtained by coupling the CRDS spectrometer to a self-referenced frequency comb. The room temperature recordings, performed with a pressure of 1 Torr, cover the 8325-8622 cm−1 spectral interval where previous observations were very scarce. More than 3300 lines belonging to four N2O isotopologues (14N216O, 14N15N16O, 15N14N16O, and 14N218O) are measured with a position accuracy better than 1 × 10−3 cm−1 for most of the lines. Line intensities at room temperature range between 1.2 × 10−25 and 3.8 × 10−30 cm/molecule. The rovibrational assignments were obtained by comparison with predictions based on the global modeling of the line positions and intensities performed within the framework of the method of effective operators. The band-by-band analysis led to the determination of the rovibrational parameters of a total of 47 bands. All identified bands belong to the ΔP= 14-16 series of transitions, where P=2V1+V2+4V3 is the polyad number (Vi= 1-3 are the vibrational quantum numbers). Among these bands, only five were previously observed and bands of the ΔP= 15 series are reported for the first time. Local resonance perturbations affecting two bands are identified and analyzed. The position and intensity comparisons to the HITRAN2016 and HITEMP2019 spectroscopic databases are discussed. The HITRAN line list is limited to only four (calculated) bands of the 14N218O isotopologue in the studied region while ΔP= 15 bands are missing in the HITEMP list. The present work will help to improve future versions of the spectroscopic databases of nitrous oxide, a strong greenhouse gas. © 2021 Elsevier Ltd This work is jointly supported by CNRS (France) in the frame of the International Research Project “ SAMIA ” with IAO-Tomsk.

We investigated the continuum absorption of water vapour diluted in nitrogen, oxygen and air in the range of the pure rotational band of the water molecule (50-500 cm−1). Spectra recordings were performed at room temperature with a Fourier transform spectrometer associated to a 151-m multipass gas cell located at the AILES beamline of SOLEIL synchrotron facility. The study includes the first laboratory measurements in the wide 90-330 cm−1 interval. Tests of the baseline stability, crucial for the continuum determination, are reported together with the expected pressure dependences of the continuum absorption, measured over different pressure ramps. Retrieved foreign-continuum cross-sections are found in good agreement with literature values available in the lower and upper parts of the studied frequency range. The reported results validate the MT_CKD foreign-continuum empirical model, widely used in atmospheric applications, even if some overestimation of the MT_CKD values is noted in the centre of the band where experimental data were absent.

International audience; The room temperature spectrum of the very weak third overtone band of carbon monoxide in natural isotopic abundance is recorded by cavity ring down spectroscopy (CRDS) referenced to a frequency comb, between 8206 and 8465 cm-1. The sensitivity of the recordings (noise equivalent absorption on the order of min~ 5×10-12 cm-1) allowed for measuring lines with intensity as weak as 1×10-30 cm/molecule at a recording pressure limited to 10.0 Torr. The use of low pressure values (1.0 and 10.0 Torr) helped to minimize the impact of profile effects on the derived line positions and line intensities. The line profile analysis was performed using the speed dependent Nelkin-Ghatak model for the 10 Torr recordings while the Voigt profile was found sufficient to account for the line shapes recorded at 1.0 Torr. Overall, line parameters of 227 transitions are derived. The observed transitions belong to the 4-0 band of the 12C16O, 13C16O, 12C18O and 12C17O isotopologues present in natural abundance in the sample and to the 5-1 hot band of 12C16O. For a large part of the observations, line positions are reported with accuracy as good as 4×10-6 cm-1 (~120 kHz). The selfinduced line shift of the 4-0 band is reported for the first time from the position values at 1 and 10 Torr. Using literature values of the 1-0, 2-0 and 3-0 bands, the vibrational dependence of the self-induced pressure shift in CO is discussed. The experimental values of the 12C16O v= 4 energy levels J < 26 are reproduced with a standard deviation of 2.5×10-6 cm-1 (75 kHz). The intensities of the 12C16O lines reported with an accuracy better than 1% show an overall good agreement with literature values in particular with those included in the HITRAN database.

The oxygen A-band near 760 nm is used to determine the air-mass along the line of sight from ground or space borne atmospheric spectra. This band is located in a spectral region of very weak absorption of water vapor. The increased requirements on the determination of the air columns make suitable to accurately characterize water absorption spectrum in the region. In the present work, we use a cavity ring down spectrometer newly developed in Tomsk, to measure with unprecedented sensitivity and accuracy the water spectrum in the 12969 - 13172 cm−1 region. While about fifty transitions were previously detected in the region, a total of about 580 water lines are measured by CRDS and rovibrationally assigned, leading to the determination of 103 new levels and correction of 134 levels of H216O. Spectroscopic line lists available in the region (HITRAN, W2020 and theoretical line lists) show some important deviations compared to observations. In particular, line intensities are poorly predicted by available ab initio calculations for transitions involving a highly bending excitation. © 2021 Elsevier Ltd. The support of the CNRS (France) in the frame of International Research Project SAMIA is acknowledged. CRDS measurements and spectrum analysis were performed at IAO-Tomsk and funded by RFBR project 20-32-70054.

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International audience; Recent advances in high sensitivity spectroscopy have made it possible, in combination with accurate theoretical predictions, to observe, for the first time, very weak electric quadrupole transitions in a polar polyatomic molecule of water. Here, we present accurate theoretical predictions of the complete quadrupole rovibrational spectrum of a non-polar molecule CO2, important in atmospheric and astrophysical applications. Our predictions are validated by recent cavity enhanced absorption spectroscopy measurements and are used to assign few weak features in the recent ExoMars Atmospheric Chemistry Suite mid-infrared spectroscopic observations of the Martian atmosphere. Predicted quadrupole transitions appear in some of the mid-infrared CO2 and water vapor transparency regions, making them important for detection and characterization of the minor absorbers in water- and CO2-rich environments, such as those present in the atmospheres of Earth, Venus, and Mars.

Ozone formation and depletion play a key role in various physical and chemical atmospheric processes which remain to be understood in more detail. The modeling of such phenomena based on ozone dynamics calculations requires a detailed knowledge of quantum states, transition probabilities, and ozone potential energy surface (PES) near the dissociation threshold ${D}_{0}$. Knowledge of highly excited rovibrational states with energies approaching ${D}_{0}$ is necessary for a reliable interpretation of satellite measurements of the ozone absorption or emission in the upper atmosphere in nonlocal thermodynamic equilibrium conditions. In addition, these states provide an ideal probe of PESs computed by ab initio methods but their detection by absorption spectroscopy is particularly challenging due to the sharp decrease of the intensity with the energy of the corresponding vibrational combination and overtone bands. In this work, two very high-energy vibrational bands are detected by high sensitivity cavity ring-down spectroscopy providing a noise equivalent absorption ${\ensuremath{\alpha}}_{\mathrm{min}}$ on the order of a few ${10}^{\ensuremath{-}11}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. The corresponding cold bands, assigned as ${\ensuremath{\nu}}_{1}+6{\ensuremath{\nu}}_{2}+3{\ensuremath{\nu}}_{3}$ and $6{\ensuremath{\nu}}_{1}+{\ensuremath{\nu}}_{2}+{\ensuremath{\nu}}_{3}$ centered at 7969 and $7993\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$, respectively, are about nine orders of magnitude less intense than the well-known ${\ensuremath{\nu}}_{3}$ fundamental band near 10 \textmu{}m. The spectrum analysis allowed for the experimental determination of 240 rovibrational energy levels of the upper vibrational states. The corresponding rotational patterns, located between 93.1% and 96.7% of the dissociation threshold, are the most excited ones measured so far by absorption spectroscopy. The values of the band centers and rotational constants derived from the spectrum analysis provide further confirmation of the absence of an activation barrier on the minimum-energy path towards the dissociation threshold [Tyuterev et al., Phys. Rev. Lett. 113, 143002 (2014)]. The vibrational dynamics is discussed in the context of the radiative transition probabilities and related Einstein coefficients for the observed bands. Another important question in the context of the nuclear dynamics concerns the interaction among the three identical potential wells of the ozone molecule in the ground electronic state, which appears to be due to the Jahn-Teller effect. Recent theoretical results accounting for the three potential wells in a full symmetry approach predicted that vibration states should exhibit deviations from the conventional one-potential-well ab initio calculations, near the dissociation threshold. In the present work, we observe a better agreement of the experimentally determined energy value with the three-wells prediction for the (1,6,3) vibrational state involving a large simultaneous excitation of both bending (${\ensuremath{\upsilon}}_{2}=6$) and asymmetric stretch (${\ensuremath{\upsilon}}_{3}=3$) vibrations pointing towards a nearby well. This could be tentatively interpreted as a manifestation of the three-wells effect.

The rotational spectrum of water vapour highly enriched in 18O has been studied by high resolution (≈ 0.001 cm−1) Fourier transform spectroscopy at the AILES beam line of the SOLEIL synchrotron. The room temperature absorption spectrum has been recorded between 40 and 700 cm−1. The 18O enrichment of the sample was about 97% while the gas pressure and the absorption pathlength were set to 0.97 mbar and 151.75 m, respectively. The spectrum contains more than 4800 rotational transitions from seven water isotopologues (H218O, H216O, H217O, HD18O, HD16O, HD17O, D218O). The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Schwenke and Partridge. The amount and accuracy of the reported line positions represent an important extension compared to previous works. Overall, lines of about 2570 transitions are observed for the first time and 35, 41, 50, and 16 new energy levels are determined for H218O, H217O, HD18O, and HD17O, respectively. The set of derived energy levels shows a number of important differences from those recommended by an IUPAC-task group. Compared to the HITRAN2016 database, numerous deviations of line positions (up to 0.15 cm−1) are found for the H217O, H218O, HD17O, and HD18O species. Incomplete and wrong HITRAN's assignments of more than 90 transitions for H218O, H217O and HD18O are identified. Overall, the measured line positions will allow to significantly refine and complete the sets of empirical energy levels of H218O, H217O, HD18O and HD17O in the ground vibrational state.

A room temperature Fourier Transform absorption spectrum of ammonia measured in 1991 and available from the Kitt Peak data center is analyzed in the 5650 - 6350 cm−1 region. This spectral interval is part of the important 1.6 µm atmospheric transparency window where ammonia could be detected as trace species. The centers and intensities of 2779 ammonia lines were retrieved using a multiline fitting procedure. The spectrum was assigned by the joint use of a recent variational line list and of lower state combination difference relations. Overall, 1762 lines were assigned to 29 bands providing 914 new experimental energies. The obtained assignments and upper state experimental energies are the first for ammonia in the studied region. The comparison of our line list to the variational line list, to the HITRAN2016 list and to a very recent experimental line list is presented and discussed.

Series of spectra of the S(0) and Q(1)-Q(4) transitions of the (2-0) band of D2 near 5860 cm−1 are recorded by comb-referenced cavity ring down spectroscopy, at four pressures up to 200 Torr. After averaging, high resolution (30 MHz step) and low noise (noise equivalent absorption, αmin≈ 1.5 × 10−11 cm−1) spectra are obtained for each pressure value. This leads to signal to noise ratios of several hundred for the considered very weak electric quadrupole transitions with intensities ranging between 4 × 10−29 and 4 × 10−28 cm/molecule. The Q(3) and Q(4) transitions are newly detected. A multi-spectrum treatment of the D2 line profiles at different pressures performed using a quadratic speed-dependent Nelkin-Ghatak profile leads to residuals close to the noise level. Considering statistical fit errors and possible biases, total uncertainties on the frequencies extrapolated at zero pressure are estimated to be between 0.30 MHz and 1.83 MHz. The derived experimental frequencies and intensities of (2-0) transitions are gathered with literature values and compared to ab initio values reported in J. Komasa, M. Puchalski, P. Czachorowski, G. Łach, K. Pachucki, Phys. Rev. A 100, 032519 (2019). An agreement within the combined uncertainties is achieved for the S(0), Q(1), Q(2) and Q(3) transitions. Line intensities are also discussed in relation with literature values.

Nowadays, the spectroscopic databases used for the modeling of Earth and planetary atmospheres provide only electric-dipole transitions for polyatomic molecules (H2O, CO2, N2O, CH4, O3…). Very recently, electric-quadrupole transitions have been detected in the high sensitivity cavity ring down spectrum (CRDS) of water vapour near 1.3 μm [A. Campargue et al., Phys. Rev. Res., 2020, 2, 023091, DOI: 10.1103/PhysRevResearch.2.023091]. This discovery paved the way to systematic searches of quadrupole transitions in water vapor and other polyatomic molecules. In the present work, on the basis of high accuracy ab initio predictions, H216O quadrupole lines are detected for the first time in the 5.4 μm and 2.5 μm regions where they are predicted to have their largest intensities (up to 10-26 cm per molecule). A total of twelve quadrupole lines are identified in two high sensitivity Fourier transform spectra recorded with a 1064 m path length. Ten lines in the 4030-4150 cm-1 region are assigned to the ν3 band while the lines near 1820 and 1926 cm-1 belong to the ν2 band. The derived line intensities which are largely above the dipole intensity cut-off of the standard spectroscopic databases, agree nicely with the theoretical predictions. We thus conclude that the calculated line list of quadrupole transitions, validated by the present measurements, should be incorporated in the spectroscopic databases.

We present new measurements and analysis of the water absorption spectra in the region of the rotational band, between 70 and 700 cm−1. The higher pressures of the recordings (up to 16 mbar) as compared to our previous measurements allowed us to extend the retrieval of the water vapor self-continuum absorption from 500 to 700 cm−1 and to test our earlier results up to 500 cm−1. As a result, the continuum amplitude at high wavenumbers, determined with smaller uncertainty, shows an improved agreement with literature experimental data. The measurements were performed at two temperatures (296 and 326 K) using two radiation sources of significantly different power ranges: SOLEIL synchrotron and globar. The quadratic pressure dependence of the self-continuum absorption was verified leading to consistent values of cross-sections derived at various experimental conditions. In addition, we obtained the first data concerning the water vapor self-continuum temperature dependence in the 84-365 cm−1 spectral range for which we present the preliminary analysis considering the available measurements and theoretical data.

The very weak absorption spectrum of natural CO2 is studied at high sensitivity near 1.18 µm. The investigated region corresponds to a transparency window of particular interest for Venus. Low pressure (10 Torr) spectra are recorded with unprecedented sensitivity in the 8311–8679 cm−1 interval. A noise equivalent absorption, αmin, on the order of 5 × 10−12 cm−1 is achieved using a cavity ring down spectrometer (CRDS) coupled with a self-referenced frequency comb. 669 lines are accurately measured and rovibrationnally assigned to 15 bands of the three first carbon dioxide isotopologues, 12C16O2, 13C16O2 and 16O12C18O. For all but one band, line intensities are smaller than 10−28 cm/molecule at 296 K and the weakest lines have intensity as low as 5 × 10−31 cm/molecule. In the large 8310–8645 cm−1 interval where no CO2 absorption lines were previously detected, about 500 lines are measured. In spite of the weakness of the considered transitions, line centers could be accurately determined and spectroscopic parameters are determined from standard band-by-band fit of the line positions (typical rms deviations are 5 × 10−4 cm−1). These newly observed bands provide critical validation tests for the most recent spectroscopic databases of carbon dioxide. The comparison to the recent updated version of the Carbon Dioxide Spectroscopic Databank (CDSD2019), to the current HITRAN2016 database and ab initio line lists is presented. The CDSD and HITRAN positions deviate from the measurements by less than 0.01 cm−1. Measured line intensities show an overall good agreement in particular with ab initio values but reveal that a few bands have inaccurate intensities in HITRAN2016 and CDSD2019. Three very weak bands are missing in CDSD2019. The reported experimental information will help to improve the quality of the CO2 spectroscopic databases in the region.

Molecular absorption of infrared radiation is generally due to rovibrational electric-dipole transitions. Electric-quadrupole transitions may still occur, but they are typically a million times weaker than electric-dipoletransitions, rendering their observation extremely challenging. In polyatomic or polar diatomic molecules,rovibrational quadrupole transitions have never been observed. Here, we report the direct detection of quadrupoletransitions in water vapor. The detected quadrupole lines have intensity largely above the standard dipoleintensity cutoff of spectroscopic databases and thus are important for accurate atmospheric and astronomicalremote sensing.

The oxygen absorption spectrum in the 50–170 cm-1 spectral range is studied at the AILES beam line of the SOLEIL synchrotron with a Fourier transform spectrometer equipped with a 151-m multipass gas cell. The spectrum recorded at room temperature (23.15 °C) with a pressure of 19.76 Torr is formed by weak pure rotational magnetic dipole transitions. Line parameters of 26 lines are derived and compared to literature values. In particular, measured line intensities confirm the 45 years-old previous values reported by Boreiko et al. (J. Quant. Spectrosc. Radiat. Transfer 32 (1984)109–117). The agreement with HITRAN intensities (within 1% level for the strongest lines) indicates that the 20% HITRAN error estimate was overly cautious: we show that the error is more likely within 2%.

The room temperature absorption spectrum of 13CH4 is recorded by high sensitivity cavity ring down spectroscopy (CRDS) near 1.58 µm. The investigated region (6147–6653 cm−1) corresponds to a spectral region of weak absorption located between the strong bands of the tetradecad and icosad. The sensitivity of the recordings allowed for the measurement of more than 13000 lines for which line centers and line intensities are derived using a multiline fitting program. The obtained list is the first extensive list of 13C enriched methane in the region. It is believed to include a significant number of lines of 13CH3D. In addition, 185 lines were measured at 80 K by direct absorption spectroscopy (DAS) near 6600 cm−1. The line intensity detectivity threshold is on the order of a few 10−29 cm/molecule for the CRDS recordings at 296 K and 10−26 cm/molecule for the DAS recordings at 80 K. From the intensity ratio of the lines in common in the 296 K and 80 K empirical line lists near 6600 cm−1, 438 empirical values of the lower state energy level (Eemp) were derived. An additional set of 200 Eemp values were obtained by combining the present CRDS line intensities to DAS literature data near 6150 cm−1. The comparison to the TheoReTS ab initio line list shows an overall very good agreement for the line intensities. Significant deviations on the order of 0.1 cm−1 are noted for line positions. The obtained experimental data will be valuable to tune ab initio line positions to empirical values in future versions of the theoretical line lists. Finally, a first set of 900 lines belonging to the 5ν4 and ν2 + 4ν4 bands of the icosad are rovibrationally assigned on the basis of an effective Hamiltonian model. The energy values of the involved vibrational sublevels are reported.

While chemotherapy is one of the most used treatments in oncology, the systemic administration of chemotherapeutics generally results in undesired damages to healthy tissues and cells, side effects such as severe nausea and leukopenia, and reduced efficacy due to multidrug resistance and poor target accessibility. The limitations of conventional chemotherapy formulation have prompted the development of alternative nanomaterials‐based strategies to achieve targeted and stimuli sensitive payload delivery to reach optimal local drug concentration at tumor sites. In this study, the anticancer drug chlorambucil (Clb) was conjugated to the surface of silica coated lithium niobate (LNO) harmonic nanoparticles (HNPs) using a photocaging tether based on coumarin‐4‐yl methyl derivative. Upon laser pulsed femtosecond irradiation at 790 nm, the second harmonic emission from the metal oxide core induced the efficient release of Clb, with concomitant contribution from the nonlinear absorption of the coumarin (CM)‐based moiety.

International audience; Fully quantum ab initio calculations of the collision-induced shapes of two rovibrational H-2 lines perturbed by He provide an unprecedented subpercent agreement with ultra-accurate cavity-enhanced measurements. This level of consistency between theory and experiment hinges on a highly accurate potential energy surface and a realistic treatment of the velocity changing and dephasing collisions. In addition to the fundamental importance, these results show that ab initio calculations can provide reference data for spectroscopic studies of planet atmospheres at the required accuracy level and can be used to populate spectroscopic line-by-line databases.

We introduce a nonlinear all-optical theranostics protocol based on the excitation wavelength decoupling between imaging and photoinduced damage of human cancer cells labeled by bismuth ferrite (BFO) harmonic nanoparticles (HNPs). To characterize the damage process, we rely on a scheme for in situ temperature monitoring based on upconversion nanoparticles: by spectrally resolving the emission of silica coated NaGdF4:Yb3+/Er3+ nanoparticles in close vicinity of a BFO HNP, we show that the photointeraction upon NIR-I excitation at high irradiance is associated with a temperature increase >100 °C. The observed laser–cell interaction implies a permanent change of the BFO nonlinear optical properties, which can be used as a proxy to read out the outcome of a theranostics procedure combining imaging at 980 nm and selective cell damage at 830 nm. The approach has potential applications to monitor and treat lesions within NIR light penetration depth in tissues.

Water vapour foreign-continuum absorption cross-sections, CF, are measured for the first time at room temperature in the 1.6 µm transparency window, of importance for atmospheric applications. The measurements are performed by cavity ring down spectroscopy (CRDS) at 15 selected spectral data points. These data, covering the 5700–6640 cm−1 spectral range, are derived from the variation of the absorption signal during pressure ramps of humidified air up to 1 atm with a typical 1% water vapour relative concentration. The foreign-continuum absorption was obtained as the excess of the measured loss rate compared to the sum of the loss rate measured with dry air, the local water monomer contribution and the self-continuum absorption. CF values were derived from the linear dependence of the foreign-continuum absorption with the product of the partial pressures of water vapour and air. The semi-empirical MT_CKD CF values are found significantly underestimated in the centre of the window.

The very weak absorption spectrum of natural CO2 near 1.74 µm (5702–5879 cm−1) is studied at high sensitivity. The investigated region corresponds to a transparency window of very weak opacity which is of particular interest for Venus. Very weak lines with intensity value as low as 10−30 cm/molecule at 296 K are detected by Cavity Ring Down Spectroscopy. On the basis of the predictions of effective Hamiltonian models, 1135 lines of six carbon dioxide isotopologues - 12C16O2, 13C16O2, 16O12C18O, 16O12C17O, 16O13C18O and 16O13C17O - were rovibrationnally assigned to 26 bands. The accurate spectroscopic parameters of 16 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are 8 × 10−4 cm−1). These newly observed bands include perturbed bands, weak hot bands and bands of minor isotopologues (in particular 16O12C18O in natural abundance) and provide critical validation tests for the most recent spectroscopic databases. The comparison to the Carbon Dioxide Spectroscopic Databank (CDSD), HITRAN2016 database and recent ab initio line lists is presented. Deficiencies are evidenced for some weak perpendicular bands of the HITRAN2016 list and identified as due to inaccurate CDSD intensities which were preferred to ab initio intensities. While Ames and UCL ab initio intensities are believed to be accurate within a few % for the strong unperturbed bands, the reported measurements allow testing important (>50%) differences between ab initio values of some weak perturbed bands.

International audience

The atmospheric band of O2 near 1.27 µm plays an important role in determining the sounded air-mass from ground or space borne atmospheric spectra. This band consists of narrow absorption lines of the a 1 Δ g − X 3 Σ g − ( 0 − 0 ) transitions superimposed to a much broader collision-induced absorption structure. The present contribution is part of a long standing project aiming to improve different aspects of the spectroscopy of this band by highly sensitive cavity ring down spectroscopy (CRDS). In the present contribution, low pressure (5 and 10 Torr) spectra of pure O2 were recorded with unprecedented sensitivity in the 7920–8085 cm−1 interval (noise equivalent absorption, αmin, on the order of 10−12 cm−1) using an external cavity diode laser. About 170 lines including electric quadrupole transitions were accurately measured. The weakest lines have intensity on the order of 10−30 cm/molecule. The coupling of the CRDS spectrometer with a self-referenced frequency comb allows for an important gain on the accuracy of the line center determination. Detailed line profile analysis using the quadratic speed-dependent Nelkin-Ghatak profile was performed for a series of twelve lines recorded for pressures up to 150 Torr. In particular, the very weak self-pressure shifts (on the order of 10−3 cm−1/atm) could be determined for the first time. Line intensities with uncertainty of 1% are reported for lines with intensity larger than 10−28 cm/molecule. Accurate spectroscopic parameters of the a1Δg(v = 0) upper level were fitted to the zero-pressure line centers. An rms value of 108 kHz (3.6 × 10−6 cm−1) is achieved for the (meas.-calc.) differences of the 16O2 a1Δg(v = 0) upper level (Jmax= 37). Significant deviations compared to the HITRAN database are discussed.

The high-resolution absorption spectrum of acetylene has been recorded at room temperature by high sensitivity cavity ring down spectroscopy (CRDS) in the 5693–5882 cm–1 region. The noise level of the recordings corresponds to a typical minimum detectable absorption, αmin, below 10-10 cm−1. The positions and intensities of about 4000 lines were determined and analyzed together with about 3900 lines left unassigned in a previous CRDS study in the 5850–6340 cm−1 region. In total, about 2620 12C2H2 and 250 12C13CH2 absorption lines are assigned in the present work, most of them being newly reported. The 12C2H2 lines belong to 53 bands and include 24 bands newly identified or improved in the region of the previous study. Altogether, 107 bands in the entire 5693–6340 cm−1 while the HITRAN database provides line parameters of only nine 12C2H2 bands in the same region. The lines of 12C13CH2 in normal abundance (2.2%) belong to eight bands whose intensities are reported for the first time. Spectroscopic parameters of the upper vibrational levels were derived from standard band-by-band fits of the line positions (typical rms values of the (obs.-calc.) deviations are better than 0.002 cm–1). The vibrational transition dipole moment squared and Herman–Wallis coefficients of each band were derived from a fit of the measured intensity values. A recommended line list is provided for the bands newly assigned with positions calculated using empirical spectroscopic parameters of the lower and upper energy vibrational levels and intensities computed using the derived Herman–Wallis coefficients. As a result, the constructed line list includes a total of 4471 transitions belonging to 53 bands of 12C2H2 and 8 bands of 12C13CH2. This list of acetylene transitions above 5693 cm−1 extends to lower energy and completes our empirical spectroscopic database for acetylene in the 5850–9415 cm−1 range.

The design of stimuli-responsive nanocarriers has raised much attention to achieve higher local concentration of therapeutics and mitigate the appearance of drug resistance. The combination of imaging properties and controlled photorelease of active molecules within the same nanoconjugate has a great potential for theranostic applications. In this study, a system for NIR light-triggered release of molecular cargos induced by the second harmonic emission from bismuth ferrite harmonic nanoparticles (BFO HNPs) is presented. Silica-coated BFO HNPs were covalently conjugated to a photocaging tether based on coumarin (CM) and l-tryptophan (Trp) as a model molecular cargo. Upon femtosecond pulsed irradiation at 790 nm, Trp was efficiently released from the NP surface in response to the harmonic emission of the nanomaterial at 395 nm. The emitted signal induced the photocleavage of the CM-Trp carbamate linkage resulting in the release of Trp, which was monitored and quantified by ultrahigh performance liquid chromatography-mass spectrometry (UHPLC-MS). While a small fraction of the uncaging process could be attributed to the nonlinear absorption of CM derivatives, the main trigger responsible for Trp release was established as the second harmonic signal from BFO HNPs. This strategy may provide a new way for the application of functionalized HNPs in dual imaging delivery theranostic protocols.

In spite of being a greenhouse gas with a large global warming potential, the absorption spectrum of nitrous oxide in the near infrared is insufficiently characterized. In the present work, the spectral region near 1.74 µm (5696–5910 cm−1) is investigated by high sensitivity cavity ring down spectroscopy (CRDS). The noise level of the CRDS spectra corresponds to a typical minimum detectable absorption, αmin, below 10-10 cm−1. 3326 transitions are measured and rovibrationally assigned to 50 bands of five nitrous oxide isotopologues (14N216O, 14N15N16O, 15N14N16O, 14N218O and 14N217O) in natural isotopic abundance. The assigned weakest lines have an intensity below 10−28 cm/molecule. For comparison, only three 14N216O bands are included in the HITRAN database in the region, with a 2 × 10−25 cm/molecule intensity cut off. The rovibrational assignments were performed by comparison with predictions performed for each isotopologue in the frame of the effective operator approach. The overall quality of the predictions is satisfactory for line positions. Deviations larger than 0.1 cm−1 are nevertheless noted for 14N216O and 14N218O. The spectroscopic parameters of the upper level of the observed bands were derived from the standard band-by-band fit of the measured line positions. A significant number of bands were found to be perturbed by local rovibrational perturbations and in some cases, extra lines due to an intensity transfer could be assigned. The interaction mechanisms and the perturbers were univocally identified on the basis of the effective Hamiltonian model. In particular, interpolyad couplings were evidenced indicating that the polyad version of the effective Hamiltonian has to be extended to include Coriolis and interpolyad anharmonic interactions. No satisfactory modeling of the N2O line intensities is yet available in the region. The CRDS intensity values derived in this work provide a solid set of measurements for future semi-empirical intensity modeling in the region.

New measurements of the water vapour continuum in the 1.6 µm and 2.3 µm windows are obtained at room temperature using highly stable and sensitive cavity ring down (CRD) spectrometers. In the 1.6 µm window, self-continuum cross-sections, CS, are derived for 30 selected spectral points between 5700 and 6850 cm−1 using pressure ramps of pure water vapour (up to 15 Torr). Purely quadratic pressure dependence is obtained for each measurement point. Compared to our previous dataset (Mondelain et al., 2014), the retrieved Cs values are more accurate and show a general agreement. The spectral coverage is extended both on the high and low frequency edges of the 1.6 µm window. In addition, new CS values are derived in the 5120–5137 cm−1 interval extending to higher energy the coverage of the 2.3 µm window. The measurements near 5700 cm−1 and 5130 cm−1 are found lower than the MT_CKD_3.2 values by a factor of about 2 and 1.5, respectively. Foreign-continuum cross-sections, CF, are newly obtained in the 2.3 µm window from CRDS spectra of moist air in flow regime. Spectra were recorded for different water vapour partial pressures while maintaining the total pressure constant in the high finesse CRDS cavity. After subtraction of the monomer and self-continuum contributions, CF values were derived from the linear variation of the foreign-continuum absorption with the water vapour partial pressure. CF values determined at four spectral points between 4430 and 5000 cm−1 are larger by up a factor of five than the corresponding MT_CKD values. Considering these CRDS data at room temperature and literature values at 400 K the temperature dependence of the foreign-continuum is confirmed to be weak.

Highly sensitive cavity enhanced laser techniques are used for accurate measurements of the absorption of dinitrogen (N2) at two spectral points of the fundamental and first overtone bands. Spectra of pure N2 and of a N2/O2 mixture were recorded near 2491 and 4720 cm−1 by Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) and Cavity Ring Down Spectroscopy (CRDS), respectively. The noise level of the OF-CEAS and CRDS spectra corresponds to a minimum detectable absorption, αmin, of about 10-9 and 10-11 cm−1, respectively. Measurements involve both the N2 collision-induced absorption (CIA) bands and the very weak 2–0 S(10) and S(11) electric quadrupolar transitions. Accurate CIA binary coefficients, B N 2 − N 2 and B N 2 − O 2 , are derived from the pressure-squared dependence of the baseline level of the spectra recorded at pressures below 1 atm. These CIA values are compared to previous determinations from high pressure spectra (up to 90 atm) and to recent classical molecular dynamics simulations (CMDS). An overall good agreement is obtained although a significant deviation is observed for the first overtone CIA near 4720 cm−1. The line position and intensity (on the order of a few 10−30 cm/molecule) of the 2–0 S(10) and S(11) electric quadrupolar transitions are determined experimentally for the first time and compared to theoretical values provided in the HITRAN2016 database.

The room temperature absorption spectrum of 17O enriched carbon dioxide is investigated by high sensitivity cavity ring down spectroscopy (CRDS) between 5695 and 5850 cm−1. About 1100 lines are measured and assigned to 26 bands of the six 17O containing carbon dioxide isotopologues: 16O12C17O, 16O13C17O, 17O12C18O, 17O13C18O, 12C17O2 and 13C17O2. The set of observed lines are rovibrationnally assigned on the basis of the predictions of the effective Hamiltonian (EH) model. The observed bands belong to the ΔP = 8 and 9 series of transitions where P = 2 V1 + V2 + 3 V3 is the polyad number (Vi being the vibrational quantum numbers). They consist in 12 previously unobserved bands and 14 already-known bands, for which additional high J lines are assigned. Bands of the 12C17O2 and 13C17O2 isotopologues (two for each) are observed for the first time in this spectral interval. The spectroscopic parameters of the upper vibrational levels are determined from a band-by-band fit of the line positions (typical rms deviations are less than 0.001 cm−1). The comparison to the most recent carbon dioxide spectroscopic databases is presented. The reported data will be used to improve the modeling of the line positions of 17O containing carbon dioxide isotopologues.

The 1.74 µm spectral region corresponds to a very weak absorption interval of carbon dioxide (or “transparency window”) of particular importance to sound the deep atmosphere and the surface of Venus. In the present work, we extend the characterization of this spectral interval by the study of the 13CO2 isotopologues by high sensitivity cavity ring down spectroscopy (CRDS) with a highly enriched 13C sample. Indeed, in spite of their low natural abundances, the 13C minor isotopologues (in particular 16O13C18O with natural abundance less than 4.5 × 10−5) contribute importantly to the small residual opacity. In the studied 5694–5851 cm−1 spectral interval about 980 lines with intensity values as low as a few 10−30 cm/molecule at 296 K were detected. On the basis of the predictions of effective Hamiltonian models, the measured CO2 transitions were assigned to six isotopologues: 12C16O2, 13C16O2, 16O12C18O, 16O13C18O, 16O13C17O and 13C18O2. A total of 20 bands were assigned to the 13C isotopologues. Six of them are newly reported while the set of observed rotational transitions is enlarged for the others. The spectroscopic parameters of nineteen 13CO2 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are 8 × 10−4 cm−1). The new data show an overall good agreement with the Carbon Dioxide Spectroscopic Databank (CDSD-296), HITRAN2016 database and ab initio CO2 line lists. The previously identified issue related to the mixing of line intensities with CDSD or ab initio origins in the HITRAN database is illustrated by the 41104-00001 band of 13C16O2. A general discussion of the bands affected by this issue in the HITRAN2016 list is included.

The weak 2ν1 + 3ν2 + ν3 absorption band of the nitrogen dioxide main isotopologue (14N16O2) is investigated near 6350 cm−1. The absorption spectrum was recorded by high sensitivity Cavity Ring Down Spectroscopy with a noise equivalent absorption of αmin ≈ 1 × 10−10 cm−1. In total, 1069 lines of the 2ν1 + 3ν2 + ν3 band were assigned with rotational quantum numbers N and Ka up to 48 and 8, respectively, that corresponds to 1276 vibration-rotation transitions. The derived set of line positions is reproduced with an effective Hamiltonian with an rms of 2.35 × 10−3 cm−1 for the (obs.-calc.) deviations. The effective Hamiltonian takes explicitly into account the Coriolis interactions between the spin rotational levels of the (2,3,1) upper vibrational state and those of two nearby dark states - (2,5,0) and (2,1,2) - together with the electron spin-rotation interactions. Using the corresponding eigenfunctions the principal effective dipole moment parameter responsible for the line intensities of the 2ν1 + 3ν2 + ν3 band is fitted to selected measured line intensities which are reproduced with an rms deviation of 6.2%.

Various spectroscopic data for absorption lines due to the magnetic dipole transitions of the a 1 Δ g − X 3 Σ g − ( 0 − 0 ) band of O2 centered at 1.27 µm are tested by comparison with high-resolution ground-based atmospheric measurements recorded by Fourier Transform Spectrometers at Park Falls and Caltech (USA). This band is of importance for atmospheric remote sensing since it will be used (together with the O2 A-band near 760 nm) by the passive short wave infrared spectrometer onboard the MicroCarb satellite mission (i.e. this band includes the B4 band of MicroCarb, from about 7800 cm−1 to 7912 cm−1) for the determination of surface pressure and atmospheric aerosols. Spectroscopic data of the HITRAN2016 and GEISA2015 databases as well as those from recent laboratory studies are here used in a radiative transfer code to simulate atmospheric transmissions under the conditions of the measurements. Comparisons are made for different solar zenith angles and for the whole B4 spectral range considered by MicroCarb. Spectroscopic data of water vapor are also tested by considering both relatively dry and humid atmospheric conditions. Averaging the “calculated-observed” residuals over numerous recordings made for close values of the solar zenith angle and humidity enables reduction of the uncertainties due to the radiometric noise of the instrument and to the imperfect description of the atmospheric state. This enables the detection of systematic differences in the spectral residuals caused by small changes in spectroscopic data. The results show that the spectroscopic parameters in the HITRAN2016 and GEISA2015 databases lead to large residuals while data of two recent laboratory studies, obtained from spectra measured with the cavity ring-down spectroscopy technique using the speed-dependent Nelkin-Ghatak profile lead to much better agreement with atmospheric measurements. Significant residuals are noted for water vapor absorption lines simulated using parameters provided by both the HITRAN and GEISA databases.

We demonstrate a new method for populating line-by-line spectroscopic databases with beyond-Voigt line-shape parameters, which is based on ab initio quantum scattering calculations. We report a comprehensive dataset for the benchmark system of He-perturbed H2 (we cover all the rovibrational bands that are present in the HITRAN spectroscopic database). We generate the entire dataset of the line-shape parameters (broadening and shift, their speed dependence, and the complex Dicke parameter) from fully ab initio quantum-scattering calculations. We extend the previous calculations by taking into account the centrifugal distortion for all the bands and by including the hot bands. The results are projected on a simple structure of the quadratic speed-dependent hard-collision profile. We report a simple and compact formula that allows the speed-dependence parameters to be calculated directly from the generalized spectroscopic cross sections. For each line and each line-shape parameter, we provide a full temperature dependence within the double-power-law (DPL) representation, which makes the dataset compatible with the HITRAN database. The temperature dependences cover the range from 20 to 1000 K, which includes the low temperatures relevant for the studies of the atmospheres of giant planets. The final outcome from our dataset is validated on highly accurate experimental spectra collected with cavity ring-down spectrometers. The methodology can be applied to many other molecular species important for atmospheric and planetary studies.

Spectroscopic catalogues, such as GEISA and HITRAN, do not yet include information on the water vapour continuum that pervades visible, infrared and microwave spectral regions. This is partly because, in some spectral regions, there are rather few laboratory measurements in conditions close to those in the Earth’s atmosphere; hence understanding of the characteristics of the continuum absorption is still emerging. This is particularly so in the near-infrared and visible, where there has been renewed interest and activity in recent years. In this paper we present a critical review focusing on recent laboratory measurements in two near-infrared window regions (centred on 4700 and 6300cm−1) and include reference to the window centred on 2600cm−1 where more measurements have been reported. The rather few available measurements, have used Fourier transform spectroscopy (FTS), cavity ring down spectroscopy, optical-feedback – cavity enhanced laser spectroscopy and, in very narrow regions, calorimetric interferometry. These systems have different advantages and disadvantages. Fourier Transform Spectroscopy can measure the continuum across both these and neighbouring windows; by contrast, the cavity laser techniques are limited to fewer wavenumbers, but have a much higher inherent sensitivity. The available results present a diverse view of the characteristics of continuum absorption, with differences in continuum strength exceeding a factor of 10 in the cores of these windows. In individual windows, the temperature dependence of the water vapour self-continuum differs significantly in the few sets of measurements that allow an analysis. The available data also indicate that the temperature dependence differs significantly between different near-infrared windows. These pioneering measurements provide an impetus for further measurements. Improvements and/or extensions in existing techniques would aid progress to a full characterisation of the continuum – as an example, we report pilot measurements of the water vapour self-continuum using a supercontinuum laser source coupled to an FTS. Such improvements, as well as additional measurements and analyses in other laboratories, would enable the inclusion of the water vapour continuum in future spectroscopic databases, and therefore allow for a more reliable forward modelling of the radiative properties of the atmosphere. It would also allow a more confident assessment of different theoretical descriptions of the underlying cause or causes of continuum absorption.