Search

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.

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 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.

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.

We revisit the room temperature absorption spectrum of natural nitrous oxide recorded by high sensitivity cavity ring down spectroscopy between 7647 and 7918 cm(-1) (1.31-1.26 mu m) reported by Liu et al. (doi: 10.1016/j.jms.2011.03.025). In this previous analysis, 2272 transitions could be assigned in the region and no intensity information was provided. In the present work, on the basis of improved predictions of the effective operator models, the assignments could be extended to more than 3200 transitions and, more importantly, line intensities are provided for all the transitions. The assigned transitions belong to 49 bands of the (N2O)-N-14-O-16, (NNO)-N-14-N-15-O-16, (NNO)-N-15-N-14-O-16, (N2O)-N-14-O-18, and (N2O)-N-14-O-17 isotopologues, 16 being newly assigned. All the identified bands correspond to the ?P= 14 series of transitions, except for four ?P= 12 and two ?P= 13 bands of the (N2O)-N-14-O-16 isotopologue (P= 2V(1)+V-2+4V(3) is the polyad number where V-i= 1-3 are the vibrational quantum numbers). For comparison, the HITRAN2020 database includes only the nu(1)+3 nu(3) band of the main isotopologue and a number of calculated line parameters for the fourth minor isotopologue, (N2O)-N-14-O-18. The band-by-band analysis provides accurate spectroscopic parameters of 46 bands from a fit of the measured line positions. Nine resonance perturbations were identified including a few extra lines for two (N2O)-N-14-O-16 bands. The interaction mechanisms and the perturbers were assigned on the basis of the effective Hamiltonian models. The comparison with current spectroscopic databases (HITRAN, HITEMP, NOSD) is discussed. All show significant deviations compared to our observations (e.g. for ?P= 13 band intensities). The reported results will be thus valuable to more accurately account for the absorption of nitrous oxide in the region. (C) 2022 Elsevier Ltd. All rights reserved.

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.

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.

International audience; 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.

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.

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.

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.

International audience; The high-resolution absorption spectrum of acetylene has been recorded at room temperature by high sensitivity cavity ring down spectroscopy (CRDS) in the 6627-7065 cm-1 region. The studied spectral range corresponds to a spectral interval of very weak absorption (an acetylene transparency window). The positions and intensities of more than 7000 lines are determined in the considered interval where previous intensity information was mostly missing. On the basis of previous studies and on effective Hamiltonian predictions, 3062 12C2H2, 462 12C13CH2 and 104 12C2HD absorption lines belonging to a total of 123 vibrational bands are assigned. For comparison, the HITRAN2016 database provides line parameters of only ten 12C2H2 bands in the same region. Spectroscopic parameters of 113 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 0.003 cm-1). Many bands are found to be affected by perturbations. The vibrational transition dipole moment squared and Herman-Wallis coefficients of 47 bands were derived from a fit of the measured intensity values. In order to generate a recommended line list in the region, the derived spectroscopic parameters and Herman-Wallis coefficients were used to compute the line parameters for these 47 bands while experimental position and intensity values were kept for the other bands. Overall, the obtained recommended list including a total of 5260 transitions will help to fill a spectral gap around 1.47 µm where very scarce spectroscopic information is provided in the current spectroscopic databases. When compared to the HITRAN list in the region, some important deviations concerning both line positions and line intensities are evidenced as a result of inaccurate high J extrapolations.

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.

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.

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.

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.

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.

The absorption spectrum of acetylene has been recorded at room temperature (296 K) using high sensitivity Cavity Ring Down Spectroscopy in the 7914 and 8252 cm−1 interval. The noise equivalent absorption of the spectra is αmin ∼ 5×10−11 cm−1. A list of about 5600 absorption features was constructed. The smallest intensities are on the order of 10−29 cm/molecule. A total of 1325 rovibrational lines of 12C2H2 were assigned by comparison with accurate predictions provided by a global effective operator model. In addition, 132 rovibrational lines of 12C13CH2 present in natural isotopic abundance were assigned on the basis of their published positions. The assigned 12C2H2 lines belong to 12 new and 6 already known bands, for which additional J-lines were assigned. The line intensities of the three cold bands of 12C13CH2 are reported for the first time. The new data will be valuable to refine the parameters of the global effective Hamiltonian and dipole moments of 12C2H2 in the region. Spectroscopic parameters of the 12C2H2 and 12C13CH2 upper vibrational levels were derived from a band-by-band fit of the line positions (typical rms values are on the order of 0.001 cm−1). A few of the analyzed bands were found to be affected by rovibrational perturbations, which are discussed. In particular, the rotational structure of the 2ν1 + (ν4 + ν5)0 Σu+–Σg+ band near 7994 cm−1 exhibits a particularly surprising intensity distribution: while the P(19) and R(17) transitions share the same J = 18 upper level, the R(17) line has an intensity about 4 orders of magnitude smaller than the P(19) line. This unusual situation is quantitatively interpreted as resulting from a Coriolis interaction between the ν1 + 2ν2 + ν51 and 2ν1 + (ν4 + ν5)0 bands with a energy crossing at J = 18. The accidental nearly perfect cancelation of the two terms contributing to the line strength of the R(17) line leads to the near disappearance of this line.

The room temperature absorption spectrum of water vapor highly enriched in 17O has been recorded by Cavity Ring Down Spectroscopy (CRDS) between 5850 and 6671 cm−1. Two series of recordings were performed with pressure values of 1.0 and 12.0 Torr. The investigated spectral region corresponds to the important 1.55 μm transparency window of the atmosphere where water absorption is very weak. The high sensitivity of the recordings (αmin ~ 5×10−11 cm−1) allows detecting lines with intensity spanning six orders of magnitude (1.4×10−30–3.6×10−24 cm/molecule at room temperature). The experimental list includes more than 10,300 lines. The assignments of water lines were performed using known experimental energy levels as well as calculated line lists based on the results of Partridge and Schwenke. More than 8500 lines were assigned to 9619 transitions of six water isotopologues (H216O, H217O, H218O, HD16O, HD17O and HD18O). All but four transitions of the 16O and 18O isotopologues were assigned using known experimental energy levels. More than half of the assigned H217O and HD17O transitions correspond to new (or corrected) upper energy levels. About 1000 new H217O transitions associated with upper states of the second triad and of the first hexad were identified. Most of the newly assigned HD17O transitions belong to the ν1+ν3 and 2ν2+ν3 bands. The assigned transitions allowed to newly determine or correct 20 highly excited rotational levels of the vibrational ground state of this isotopologue. Overall 791 and 266 energy levels are newly determined for H217O and HD17O, respectively. A few additional levels were corrected compared to literature values. The obtained experimental results are compared to the spectroscopic parameters provided by the HITRAN database and to the empirical energy levels recommended by an IUPAC task group.

The high-resolution absorption spectrum of acetylene has been recorded at room temperature by high sensitivity cavity ring down spectroscopy (CRDS) in the 6627–7065 cm–1 region. The studied spectral range corresponds to a spectral interval of very weak absorption (an acetylene transparency window). The positions and intensities of more than 6500 lines are determined in the considered interval where previous intensity information was mostly missing. On the basis of previous studies and on effective Hamiltonian predictions, 3062 12C2H2, 462 12C13CH2 and 104 12C2HD absorption lines belonging to a total of 123 vibrational bands are assigned. For comparison, the HITRAN2016 database provides line parameters of only ten 12C2H2 bands in the same region. Spectroscopic parameters of 113 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 0.003 cm–1). Many bands are found to be affected by perturbations. The vibrational transition dipole moment squared and Herman-Wallis coefficients of 47 bands were derived from a fit of the measured intensity values. In order to generate a recommended line list in the region, the derived spectroscopic parameters and Herman-Wallis coefficients were used to compute the line parameters for these 47 bands while experimental position and intensity values were kept for the other bands. Overall, the obtained recommended list including a total of 5260 transitions will help to fill a spectral gap around 1.47 µm where very scarce spectroscopic information is provided in the current spectroscopic databases. When compared to the HITRAN list in the region, some important deviations concerning both line positions and line intensities are evidenced as a result of inaccurate high J extrapolations.

An accurate empirical list of 57,995 transitions is constructed for natural water in the 5690–8340 cm−1 near infrared region (1.76–1.20 µm). The new list represents an updated version of the list reported in Mikhailenko et al. (2016). The spectral range is extended to lower energy and the transition frequencies benefited from a series of recent measurements by comb-assisted cavity ring down spectroscopy (CA-CRDS). The line list construction uses as starting point the variational line lists computed on the basis of the results of Schwenke and Partridge for the six most abundant water isotopologues (H2 16O, H2 18O, H2 17O, HD16O, HD18O, HD17O). Variational line positions are replaced by position values calculated from empirical rotation-vibration energy levels. The set of required empirical energy levels is improved in accuracy and enlarged, in particular for the minor isotopologues. A large number of energy levels and thus transition frequencies, relying on spectra recorded by CA-CRDS, have accuracy on the order of 10−4 cm−1. All the transitions are provided with unique vibrational labeling supported by effective Hamiltonian calculations in case of ambiguity. A detailed comparison is presented with the list of natural water included in the HITRAN2016 database and with the very recent H2 16O and H2 18O lists reported in Conway et al. (2020). The advantage of our list in terms of line position accuracy is demonstrated and illustrated by direct comparison with CRDS recordings at disposal. Intensity comparison shows a general agreement but a number of weaknesses of the most recent intensity calculations are evidenced. All the considered theoretical line lists include a few bands (e.g. 4ν2, 5ν2, ν1+2ν2 and ν1+3ν2) with intensities deviating significantly from the observations. © 2020 Elsevier Ltd E.K. Conway (Center for Astrophysics, Cambridge and University College London) is acknowledged for providing us the submitted version of Ref. [44] together with the corresponding H216O and H218O lists, prior publication. The support of the University Grenoble Alpes and CNRS (France) in the frame of International Research Project SAMIA is acknowledged. SNM activity was also partly supported in the frame of the Russian Science Foundation, grant no. 18-11-00024.

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 room temperature absorption spectrum of water vapour highly enriched in 17O is recorded by cavity ring down spectroscopy (CRDS) near 1.73 µm. Two series of recordings were performed with pressure values of about 0.12 and 8.5 Torr from 5693 to 5850 cm−1. The noise equivalent absorption (αmin) of the spectra is better than 10−10 cm−1 allowing for the measurements of water lines with intensity down to 10−29 cm/molecule. A total of 1132 lines were assigned to 1220 transitions of five water isotopologues (H216O, H217O, H218O, HD16O, and HD17O). Their intensities span near five orders of magnitude from 10−29 to 10−24 cm/molecule at 296 K. The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Schwenke and Partridge. Most of the new results concern the H217O isotopologue: 483 transitions were measured while only the 27 strongest were previously known. Overall 104 levels were newly determined for H217O (64 levels), H218O (16), HD17O (23) and HD16O (1) and a few additional levels were corrected compared to the literature. The obtained results are compared to the water line list in the HITRAN2016 database, to the ExoMol energy levels and to the empirical energy levels recommended by an IUPAC task group.

The very weak absorption spectrum of the minor isotopologues of carbon dioxide near 1.74 µm (5702–5879 cm−1) is studied by high sensitivity cavity ring down spectroscopy (CRDS) with an 18O enriched sample. The investigated spectral 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 measured. On the basis of the predictions of the effective Hamiltonian models, 3202 lines of nine carbon dioxide isotopologues - 12C16O2, 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 17O12C18O, 17O13C18O, 12C18O2 and 13C18O2 - were rovibrationnally assigned to 59 bands, 44 of which were observed for the first time. The accurate spectroscopic parameters of 53 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are 8 × 10−4 cm−1). Three bands are found to be strongly perturbed by resonance first order Coriolis interaction. The new measured line intensities allowed determining or improving the ΔP = 8 sets of the effective dipole moment (EDM) parameters for five non-symmetrical isotopologues - 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O and 17O12C18O - and ΔP = 9 sets for the 16O12C18O and 12C18O2 isotopologues (P = 2V1+ V2+ 3V3 is the polyad number, Vi being the vibrational quantum numbers). The set of EDM parameters available for eleven isotopologues is used to discuss their isotopic dependence. These newly observed bands provide critical validation tests for the most recent spectroscopic databases. The comparison to the Carbon Dioxide Spectroscopic Databank (CDSD-296), HITRAN2016 database and ab initio Ames line list is presented. Deficiency is evidenced for the weak 41104–00001 band of 16O12C18O in the HITRAN2016 list and identified as due to inaccurate CDSD intensities which were preferred to ab initio intensities.

The absorption spectrum of 13CH4 is recorded in the center of the tetradecad near 1.73 μm (5695–5850 cm−1) at 296 K and 80 K by direct absorption spectroscopy (DAS). The achieved noise equivalent absorption of the spectra is αmin ≈ 5 × 10−8 cm−1 leading to line intensity detectivity threshold on the order of 5 × 10−26 and 5 × 10−27 cm/molecule at 296 K and 80 K, respectively. As a result, two empirical line lists are constructed including about 3350 and 2070 lines at room temperature and liquid nitrogen temperature, respectively. For comparison, the HITRAN database provides in the region only the strongest 13CH4 lines (about 440 lines in total). From the intensity ratios of the lines measured at the two temperatures, 1529 empirical values of the lower state energy level (Eemp) were derived. Their accuracy is reflected by the clear propensity of the corresponding empirical values of the lower state rotational quantum number, Jemp, to be close to integer values. They provide accurate temperature dependence for 91% and 99% of the total 13CH4 absorption in the region at 296 K and 80 K, respectively. The comparison to the TheoReTS ab initio line list shows significant deviations 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.

In a companion paper, rovibrational assignments of acetylene in the 9280–10,740 cm–1 region were extended on the basis of a long path absorption spectrum recorded by Fourier-transform spectroscopy. Thirty-three and seven bands of 12C2H2 and 12C13CH2 were assigned, respectively, twelve 12C2H2 bands being newly assigned. In the present work, the vibrational transition dipole moments squared and Herman–Wallis coefficients of the bands are derived from a fit of the measured intensity values. An empirical recommended line list is provided with positions calculated using empirical spectroscopic band parameters and intensities calculated using the derived Herman–Wallis coefficients. As a result the constructed line list in the 9450–10,740 cm-1 region includes a total of 2774 lines belonging to 32 bands of 12C2H2 and seven bands of 12C13CH2. For comparison the HITRAN database in the same region includes 305 lines of 4 bands, all belonging to 12C2H2. The recommended acetylene line list is compared to the HITRAN line list and to the Acetylene Spectroscopic Database (ASD) constructed using the global effective operator approach. The measured bands belong to the ΔP = 15 and 16 series of bands where P = 5V1 + 3V2 + 5V3 + V4 + V5 is the polyad quantum number. An improved set of ΔP = 15 effective dipole moment (EDM) parameters is derived from a fit of the measured intensity values. The ΔP = 16 EDM parameters are derived for the first time. The derived sets of EDM will allow extending the Acetylene Spectroscopic Database at higher energy.

A tubular furnace is combined with a diode laser spectrometer to record the high temperature near infrared absorption spectrum of methane at a pressure of 80 Torr. The investigated spectral range covers the 5693–6257 cm−1 (1.75–1.60 µm) range of the tetradecad dominated by the 2ν3 band near 6000 cm−1. Various determinations (thermocouples, Doppler line broadening, rotational temperature) provide a value of about 964 K for the gas temperature. Lines with intensity larger than 5 × 10−24 cm/molecule at 1000 K are detected. As a result of the high temperature, high-J rovibrational transitions up to J ≈ 20 and hot bands are identified in the spectrum. The recorded spectra provide tests of various methane line lists recently released in the literature: HITRAN2016, experimental list derived from emission spectra, the MeCaSDa empirical line list and the TheoReTs and ExoMol theoretical line lists. The agreement with the TheoReTs line list is found to be very good in the studied region.

The high-resolution absorption spectrum of acetylene is studied by Fourier-transform spectroscopy (FTS) in the 9280–10740 cm–1 region dominated by the 3ν3 band near 9640 cm−1. Line positions and intensities of 1899 12C2H2 and 151 12C13CH2 absorption lines are retrieved from a spectrum recorded at room temperature (298.5 K) with a pressure of 87.6 hPa and a path length of 105 m. The measured 12C2H2 lines belong to thirty-three bands, twelve of them being newly assigned. The lines of 12C13CH2 in normal abundance (2.2%) belong to seven bands. For comparison the HITRAN database in the same region includes 301 lines of four 12C2H2 bands. Spectroscopic parameters of the upper vibrational levels are derived from band-by-band fits of the line positions (typical rms values are on the order of 0.002 cm–1). The comparison to the HITRAN line list and to results obtained using the global effective operator approach reveals a number of significant deviations. The occurrence of local rovibrational perturbations affecting a number of the analyzed bands is illustrated by the case of the strong 3ν3 band.

The room temperature absorption spectrum of water vapour highly enriched in 17 O is studied by Comb Assisted-Cavity Ring Down Spectroscopy (CA-CRDS) near 1.4 µm. The investigated spectral region (6667–7443 cm −1 ) is a strong absorbing region corresponding to the first hexade of interacting vibrational states. As a consequence of the high sensitivity of the recordings (Noise Equivalent Absorption, α min ∼ 10 −10 cm −1 ), a series of spectra could be recorded at very low pressure (less than 0.1 Torr) allowing for accurate determination of line centres and the spectral resolution of highly blended multiplets. For instance, 85 lines of the main isotopologue located near much stronger lines are measured for the first time. The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Schwenke and Partridge. Overall, the experimental list includes 9144 water lines which were assigned to 9988 transitions of six isotopologues (H 2 16 O, H 2 17 O, H 2 18 O, HD 16 O, HD 17 O and HD 18 O). Their intensities span six orders of magnitude from 10 −27 to 10 −21 cm/molecule at 296 K. Most of the new results concern the H 2 17 O isotopologue: more than 2300 new lines were measured, 64 new levels were determined and seven levels were corrected. In the case of HD 17 O, 152 new transitions were assigned and ten levels were newly determined. The center values of non-blended lines are reported with an accuracy better than 3 MHz (10 −4 cm −1 ) which represents an improvement compared to previous determinations. The comparison to the water vapor line list provided by the recently released 2016 version of the HITRAN database reveals a number of issues.

A Cavity Ring Down Spectrometer has been developed for high sensitivity absorption spectroscopy in the near infrared at pressure up to 10 bar. In order to strictly avoid perturbations of the optical alignment by pressure forces, the pre-aligned CRDS cavity is inserted inside the high pressure cell. The stability of the spectra baseline has been validated by filling the CRDS cell with Ar and N2 up to 10 bar. We present here the first application of this CW-CRDS spectrometer to the study of the high pressure spectrum of CO2 at room temperature. The spectra were recorded between 5850 and 5960 cm−1 for a series of pressure values up to 6400 Torr. The studied spectral interval corresponds to the high energy range of the 1.75 µm transparency window of CO2 of particular interest for Venus. The CO2 absorption coefficient at a given pressure value was obtained as the increase of the CRDS loss rate from its value at zero pressure taking into account the small contribution due to Rayleigh scattering. The CO2 absorption spectrum includes the contribution of the self broadened local rovibrational lines together with a broad and weak continuum. The CO2 continuum was obtained as the difference of the CO2 absorption coefficient and of a local lines simulation using the CO2 HITRAN line list and a truncated Voigt profile. A quadratic pressure dependence of the absorption continuum was observed, with an average binary absorption coefficient increasing smoothly from 3.7 to 11.5×10−9 cm−1 amagat−2 between 5850 and 5960 cm−1. The derived continuum shows a spectral feature located in the region of a band of 16O12C18O (present in natural abundance) which dominates the spectrum in the region. This spectral feature was found to arise from collisional interferences between local lines and quantitatively accounted for using a theoretical approach based on the impact and Energy Corrected Sudden (ECS) approximations. The impact of the chosen far wings CO2 line shape model on the retrieved continuum absorption is discussed.

The highly congested absorption spectrum of methane near 1 µm was recorded by Fourier Transform Spectroscopy at room temperature. The detectivity threshold of the recordings corresponds to an intensity cut off on the order of 2×10−26 cm/molecule. An empirical line list is constructed for the 9028–10,435 cm−1 spectral region. It consists of (i) 7212 lines in the 9520–10,435 cm−1 interval corresponding to the tetracontad and (ii) 574 lines in the 9028–9200 cm−1 interval corresponding to the high energy region of the triacontad, dominated by the 3ν3 band near 9046 cm−1. The first line list fills an important gap in the HITRAN database. The obtained data set constitutes a solid basis for future rovibrational assignments on the basis of advanced theoretical methods.

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded at room temperature by high sensitivity Continuous Wave Cavity Ring Down Spectroscopy (CW-CRDS) between 7911 and 8337 cm −1 . The investigated region covers most of the 1.25 µm transparency window of importance for atmospheric applications. The recordings were performed with sensitivity on the order of α min ~2×10 –11 cm −1 , more than two orders of magnitude better than previous investigations by Fourier Transform Spectroscopy (FTS). Measured line intensities cover a range of seven orders of magnitude (3×10 –30 –2×10 –23 cm/molecule at room temperature). The experimental line list provided as Supplementary Material includes more than 5000 transitions. As a result of the achieved sensitivity, more than 1150 lines of the experimental list were identified as being due to ammonia present as an impurity at the 5 ppm concentration level in the water sample. Although incomplete, the obtained ammonia line list seems to be the first one in the region. More than 3193 water lines were assigned to 3560 transitions of five water isotopologues (H 2 16 O, H 2 18 O, H 2 17 O, HD 16 O and HD 18 O). The assignments were performed using known experimental energy levels and calculated spectra based on variational calculations by Schwenke and Partridge. The obtained results are compared to the most relevant previous studies by Fourier Transform Spectroscopy in the region and to the exhaustive review of rovibrational line positions and levels performed recently by an IUPAC sponsored task group. Two-hundred and sixty-six levels are newly determined and 46 are corrected by more than 0.015 cm −1 compared to those recommended by the water IUPAC task group. The overall agreement between variational and measured intensities is satisfactory. A complete empirical list of 4473 transitions incorporating all the experimental information at disposal was constructed for water in the studied region. The intensity cut-off was fixed to 1×10 –29 cm/molecule at 296 K. A detailed comparison with the line list as provided by the HITRAN database illustrates the advantages of the new list.

The room temperature spectrum of carbon monoxide in natural isotopic abundance is recorded by Cavity Ring Down Spectroscopy between 8094 and 8317 cm −1 . The investigated range covers the low frequency region of the third overtone band centered at 8414 cm −1 . The achieved sensitivity of the recordings corresponds to a noise equivalent absorption, α min ~ 5×10 –12 cm −1 . 94 transitions are measured with intensity ranging between 3×10 –27 and 1×10 –30 cm/molecule. They include the first observation of (i) high J lines of the P branch of the 4-0 band of 12 C 16 O, (ii) the 4-0 band of 13 C 16 O and 12 C 18 O present in natural abundance in the sample (35 and 38 transitions, respectively), (iii) a few lines of the 4-0 band of 12 C 17 O and of the 5-1 hot band of 12 C 16 O. The spectroscopic parameters of the v =4 upper level of 13 C 16 O and 12 C 18 O are obtained from a fit of the measured line positions. The line positions reported with an accuracy of 5×10 −4 cm −1 and the derived line intensities are used for comparison to various theoretical line lists of carbon monoxide available in the literature. The agreement between the obtained experimental data and the most recent theoretical line lists available in the literature is discussed.

Six studies have been recently devoted to a systematic analysis of the high-resolution near infrared absorption spectrum of acetylene recorded by Cavity Ring Down spectroscopy (CRDS) in Grenoble and by Fourier-transform spectroscopy (FTS) in Brussels and Hefei. On the basis of these works, in the present contribution, we construct an empirical database for acetylene in the 5850–9415 cm–1 region excluding the 6341–7000 cm−1 interval corresponding to the very strong ν1+ν3 manifold. Our database gathers and extends information included in our CRDS and FTS studies. In particular, the intensities of about 1700 lines measured by CRDS in the 7244–7920 cm−1 region are reported for the first time together with those of several bands of 12C13CH2 present in natural isotopic abundance in the acetylene sample. The Herman-Wallis coefficients of most of the bands are derived from a fit of the measured intensity values. A recommended line list is provided with positions calculated using empirical spectroscopic parameters of the lower and upper energy vibrational levels and intensities calculated using the derived Herman-Wallis coefficients. This approach allows completing the experimental list by adding missing lines and improving poorly determined positions and intensities. As a result the constructed line list includes a total of 11113 transitions belonging to 150 bands of 12C2H2 and 29 bands of 12C13CH2. For comparison the HITRAN database in the same region includes 869 transitions of 14 bands, all belonging to 12C2H2. Our weakest lines have an intensity on the order of 10–29 cm/molecule, about three orders of magnitude smaller than the HITRAN intensity cut off. Line profile parameters are added to the line list which is provided in HITRAN format. The comparison of the acetylene database to the HITRAN2012 line list or to results obtained using the global effective operator approach is discussed in terms of completeness and accuracy.

Accurate rovibrational analysis of the upper part of the Tetradecad 12 CH 4 spectrum in the 5855–6250 cm −1 region is reported for J ≤ 10. The analysis uses the WKLMC experimental line list previously obtained in Grenoble by Cavity Ring Down Spectroscopy and Differential laser Absorption Spectroscopy at T = 296 K. Based on a previously published ab initio potential energy surface, the full Hamiltonian of methane nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformation method with a subsequent empirical optimization of parameters. Overall, more than 3200 12 CH 4 transitions are assigned adding about 1800 new assignments to those provided in the HITRAN database for 12 CH 4 in the region. The 12 CH 4 experimental line positions were fitted with RMS standard deviations of 0.0015 cm −1 and 2381 line intensities were modeled using an effective dipole moment with the RMS deviation of 8%. Rovibrational energy levels of sixteen vibrational states of the upper part of the Tetradecad system were determined. For the first time all three sub-levels of the weak 4ν 2 band were assigned. As a result, a new version of the WKLMC list for natural methane at 296 K is provided including the new assignments in the 5855–6250 cm −1 region.

The room temperature absorption spectrum of water vapor highly enriched in 17O has been recorded by Cavity Ring Down Spectroscopy (CRDS) between 7443 and 7921 cm−1. Three series of recordings were performed with pressure values around 0.1, 1 and 10 Torr. The frequency calibration of the present spectra benefited of the combination of the CRDS spectrometer to a self-referenced frequency comb. The resulting CRD spectrometer combines excellent frequency accuracy over a broad spectral region with a high sensitivity (Noise Equivalent Absorption, αmin∼ 10–11–10−10 cm−1). The investigated spectral region corresponds to the high energy range of the first hexade. The assignments were performed using known experimental energy levels as well as calculated line lists based on the results of Partridge and Schwenke. Overall about 4150 lines were measured and assigned to 4670 transitions of six water isotopologues (H216O, H217O, H218O, HD16O, HD17O and HD18O). Their intensities span six orders of magnitude from 10–28 to 10–22 cm/molecule. Most of the new results concern the H217O and HD17O isotopologues for which about 1600 and 400 transitions were assigned leading to the determination of 329 and 207 new energy levels, respectively. For comparison only about 300 and four transitions of H217O and HD17O were previously known in the region, respectively. By comparison to highly accurate H216O line positions available in the literature, the average accuracy on our line centers is checked to be on the order of 3 MHz (10−4 cm−1) or better for not weak well isolated lines. This small uncertainty represents a significant improvement of the line center determination of many H216O lines included in the experimental list provided as Supplementary Material .

This contribution is the second part of the analysis of the room temperature absorption spectrum of 18O enriched carbon dioxide by very high sensitivity Cavity Ring Down spectroscopy between 6977 and 7918 cm-1 (1.43–1.26 μm). Overall, more than 8600 lines belonging to 166 bands of eleven carbon dioxide isotopologues were rovibrationnally assigned. In a first part (Kassi et al. J Quant Spectrosc Radiat Transfer 187 (2017) 414–425, http://dx.doi.org/10.1016/j.jqsrt.2016.09.002 ), the results relative to mono-substituted isotopologues, 16O12C18O, 16O12C17O, 12C16O2 and 13C16O2, were presented. This second contribution is devoted to the multiply-substituted isotopologues or clumped isotopologues of particular importance in geochemistry: 16O13C18O, 16O13C17O, 12C18O2, 17O12C18O, 12C17O2, 13C18O2 and 17O13C18O. On the basis of the predictions of effective Hamiltonian models, a total of 3195 transitions belonging to 73 bands were rovibrationnally assigned for these seven species. Among the 73 observed bands, 55 are newly reported. All the identified bands correspond to ΔP=10 and 11 series of transitions, where P= 2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The accurate spectroscopic parameters of 70 bands have been determined from the standard band-by-band analysis. Global fits of the measured line intensities of the ΔP=10 series of transitions of 17O12C18O and 16O13C18O and of the ΔP=11 series of transitions of 12C18O2, 17O12C18O, 16O13C18O and 13C18O2 were performed to determine the corresponding sets of the effective dipole moment parameters.

The weak absorption spectrum of water vapor in the important 2.2 μm transparency window is investigated with very high sensitivity. Overall, about 400 absorption lines were measured by Cavity Ring Down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Laser Spectroscopy (OF-CEAS) in five spectral intervals: 4248.2–4257.3, 4298.4–4302.6, 4336.8.5-4367.5, 4422.4-4441.2 and 4514.6-4533.7 cm−1. The achieved sensitivity of the recordings (noise equivalent absorption, αmin, on the order of 2×10−10 cm−1) allowed detecting transitions with intensity values down to 1×10−28 cm/molecule, more than one order of magnitude better than previous studies by Fourier Transform spectroscopy. The rovibrational assignment was performed on the basis of variational calculations and of previously determined empirical energy values. Most of the newly assigned lines correspond to transitions of the ν1, ν3 and 3ν2 bands of H217O in natural isotopic abundance. Fourteen energy levels of H217O, H218O and HD18O are newly determined. An accurate and complete spectroscopic database is constructed for natural water in the 4190–4550 cm−1 region (2.39–2.20 µm). The list includes about 4500 transitions with intensity greater than 1×10−29 cm/molecule, for the six most abundant isotopologues in natural isotopic abundance. Line positions were obtained by difference of empirical energy values determined from literature data and complemented with the present CRDS results. The list is made mostly complete by including weak transitions not yet detected, with positions calculated from empirical levels and variational intensities. The variational intensities computed by a collaboration between the University College London and the Institute of Applied Physics in Nizhny Novgorod are found to improve significantly previous results by Schwenke and Partridge. Examples of comparison of the constructed line list to CRDS spectra and to simulations based on the HITRAN2012 list illustrate the advantages of the new list. The absence of many HDO lines is identified as most important deficiency of the HITRAN2012 list in the region.

The absorption spectrum of acetylene is studied by high-resolution Fourier-transform spectroscopy (FTS) between 8980 and 9420 cm–1. Positions and intensities of 432 12C2H2 absorption lines are retrieved from a spectrum recorded at room temperature (298.5 K) with a pressure of 87.6 hPa and a 105 m path length. The measured lines belong to 11 bands including three bands observed for the first time. The obtained intensity dataset constitutes the first intensity information in the region. The Herman-Wallis coefficients are derived from a fit of the measured intensity values. The reported results will be valuable to complete the spectroscopic databases of acetylene.

The extremely weak 2–0 O(14) electric quadrupole transition of N2 has been detected by very high sensitivity Cavity Ring Down spectroscopy near 4518 cm−1. It is the first N2 absorption line in the first overtone band reported so far from laboratory experiments. By combining a feedback narrowed Distributed Feedback laser diode with a passive cell tracking technique, a limit of detection of α min ∼ 1.2 × 10−11 cm−1 was achieved after one day of spectra averaging. The N2 2–0 O(14) line position and line intensity (about 1.5 × 10−30 cm/molecule) agree with calculated values provided in the HITRAN2012 database.

The room temperature absorption spectrum of 18O enriched carbon dioxide has been recorded by very high-sensitivity Cavity Ring Down spectroscopy between 6977 and 7918 cm−1 (1.43−1.26 μm). The achieved sensitivity (noise equivalent absorption αmin ~8×10−11 cm−1) has allowed for the detection of more than 8600 lines belonging to 166 bands of eleven carbon dioxide isotopologues. Line intensities of the weakest observed transitions are on the order of 2×10−30 cm/molecule. In this first part, we present the results relative to the 16O12C18O, 16O12C17O, 12C16O2 and 13C16O2 isotopologues. Their absorption lines were rovibrationally assigned on the basis of the predictions of their respective effective Hamiltonian model. Overall 5476 lines were measured and assigned to 93 bands. Forty nine of them, all belonging to 16O12C18O and 16O12C17O, are reported for the first time. The studied spectral region is formed by ΔP=10–12 series of transitions, where P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The spectroscopic parameters of 58 bands of 16O12C18O and 16O12C17O were determined from a fit of the measured line positions. An inter- and an intrapolyad resonance perturbation were identified and analyzed in the 16O12C18O spectrum. The comparison with the line positions and line intensities included in the AMES line list is discussed. Global fits of the line intensities were performed in order to (i) improve the ΔP=10 and 11 sets of the effective dipole moment parameters of 16O12C18O and the ΔP=11 set of parameters of 16O12C17O and (ii) derive for the first time the ΔP=10 and 12 parameters of 16O12C17O and 16O12C18O, respectively.