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The absorption spectrum of the O-18(3) isotopologue of ozone was recorded by cavity-ring-down spectroscopy between 7920 and 7985 cm(-1) with a routine noise equivalent absorption, alpha(min), on the order of a few 10(-11) cm(-1). This permitted to detect and analyze an extremely weak vibrational band assigned as 7 nu(1) + nu(3) following predictions from the ab initio potential energy surface reported in J Chem Phys 2013;139:134307. This is the most excited rovibrational band of the O-18(3) isotopologue detected so far. In total, 259 ro-vibrational transitions were measured and modeled using an effective Hamiltonian model. The vibrational dipole transition moment parameter of the band deduced from the analysis and the fit to 177 experimental line intensities was evaluated as 2.6 x 10(-6) Debye. The absorption coefficient of the recorded pure O-18(3) spectrum was found significantly smaller compared to that of the O-16(3) in the same range. The set of 171 upper state energies experimentally determined cover the range from 92.6% (at J = 1) to 97% (at J = 26) of the first dissociation threshold D-0. The comparison with ab initio predictions for the band origin and nu-dependent rotational constants is discussed. An absorption line list containing 477 transitions is provided as Supplementary material for the 7 nu(1) + nu(3) band. (C) 2021 Elsevier Ltd. All rights reserved.

International audience; Measurements of the water vapor absorption cross-sections at two spectral points of the 2.1 μm and 4.0 μm transparency windows are performed by optical feedback cavity enhanced absorption spectroscopy (OFCEAS). The self-continuum cross-section, C S , is measured for temperature values of 30 and 47 °C (303 and 320 K) at the 2853 cm −1 spectral point, corresponding to the lowest opacity region of the 4.0 μm transparency window. The C S values derived from the pressure squared dependence of the self-continuum, are found consistent with previous CEAS measurements in the considered window but significantly smaller than measurements by Fourier transform spectroscopy (FTS). The C S temperature dependence is discussed in relation with FTS measurements at high temperature. Foreign-continuum cross-sections, C F , are newly obtained from OFCEAS spectra of moist air in flow regime at the 4302 cm −1 spectral point of the low energy edge of the 2.1 μm window. After subtraction of the monomer and self-continuum contributions, C F values are derived from the linear variation of the foreign-continuum absorption with the product of the water vapor and air partial pressures. The measurements were performed for temperature values of 34 and 47 °C (307 and 320 K) and no significant temperature dependency was observed. The present C F value at 4302 cm −1 is gathered with previous CEAS measurements at seven spectral points of the 2.1 μm window. This consistent set of C F values is used to derive from a polynomial fit, the empirical frequency dependence of C F (ν) over the 4250-50 0 0 cm −1 range. Overall, the semi-empirical MT_CKD_3.5 values of C F are significantly underestimated in the centre of the considered window.

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 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 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.

Spectra of CO2 + H2 mixtures have been recorded at room temperature by using the cavity ring down technique, for four spectral intervals in the 2.12–2.35 µm CO2 transparency window which is within the (1-0) band of H2. The binary coefficients B C O 2 − H 2 + B H 2 − C O 2 have been retrieved from the spectra recorded at different pressures after subtraction of the CO2 monomer contribution and of the H2-H2 and CO2-CO2 collision induced absorptions (CIAs). In order to reduce the uncertainties, new measurement of the pure H2 CIA, the main subtracted contribution, at the percent level are also reported. The new set of experimental binary coefficients is compared to values provided by semi-empirical calculations made with the assumption of an isotropic CO2-H2 interaction potential and neglecting the short-range interaction-induced electric dipole. This comparison shows the limits of using such a model, which is the only one available, in that spectral region.

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.

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 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.

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 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.

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.

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.

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 absorption spectrum of the 13CH4 methane isotopologue has been recently recorded by Differential Absorption Spectroscopy (DAS) at 80 K in the 5853–6201 cm−1 spectral range. An empirical list of 3717 lines was constructed for this spectral range corresponding to the upper part of the Tetradecad dominated by the 2ν3 band near 5987 cm−1. In this work, we present rovibrational analyses of these spectra obtained via two theoretical approaches. Assignments of strong and medium lines were achieved with variational calculations using ab initio potential energy (PES) and dipole moment surfaces. For further analysis a non-empirical effective Hamiltonian (EH) of the methane polyads constructed by high-order Contact Transformations (CT) from an ab initio PES was employed. Initially predicted values of EH parameters were empirically optimized using 2898 assigned line positions fitted with an rms deviation of 5×10−3 cm−1. More than 1860 measured line intensities were modeled using the effective dipole transition moments approach with the rms deviation of about 10%. These new data were used for the simultaneous fit of the 13CH4 Hamiltonian parameters of the {Ground state/Dyad/Pentad/Octad/Tetradecad} system and the dipole moment parameters of the {Ground state-Tetradecad} system. Overall, 10 vibrational states and 28 vibration sublevels of the 13CH4 Tetradecad are determined. The comparison of their energy values with corresponding theoretical calculations is discussed.

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 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%.

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.

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.

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 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 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.

The very weak absorption continuum of CO 2 is studied by Cavity Ring Down Spectroscopy in three 20 cm −1 wide spectral intervals near the centre of the 1.74 µm window (5693–5795 cm −1 ). For each spectral interval, a set of room temperature spectra is recorded at pressures between 0 and 10 bar thanks to a high pressure CRDS spectrometer. The absorption continuum is retrieved after subtraction of the contributions due to Rayleigh scattering and to local lines of CO 2 and water (present as an impurity in the sample) from the measured extinction. Due to some deficiencies of the CO 2 HITRAN2012 line list, a composite line list had to be built on the basis of the Ames calculated line list with line positions adjusted according to the Carbon Dioxide Spectroscopic Databank and self-broadening and pressure shift coefficients calculated with the Complex Robert Bonamy method. The local line contribution of the CO 2 monomer is calculated using this list and a Voigt profile truncated at ±25 cm −1 from the line centre. Line mixing effects were taken into account through the use of the impact and Energy Corrected Sudden approximations. The density dependence of the retrieved continuum absorption was found to be purely quadratic in the low frequency interval below 5710 cm −1 but a small significant linear contribution was required to reproduce the observations above this value. This linear increase is tentatively attributed to the foreign-continuum of water vapor present in CO 2 sample with a relative concentration of some tens ppm. The retrieved binary coefficient is observed to vary smoothly with the wavenumber with a minimum value of 6×10 −10 cm −1 amagat −2 . By gathering the present data with the results reported in Kassi et al. J Quant Spectrosc Radiat Transf 2015;167:97 , a recommended set of binary coefficients is provided for the 5700–5950 cm −1 region.

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 .

In a recent contribution [A. Campargue, S. Kassi, D. Mondelain, S. Vasilchenko, D. Romanini, Accurate laboratory determination of the near infrared water vapor self-continuum: A test of the MT_CKD model. J. Geophys. Res. Atmos., 121,13,180–13,203, doi:10.1002/2016JD025531], we reported accurate water vapor absorption continuum measurements by Cavity Ring-down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OF-CEAS) at selected spectral points of 4 near infrared transparency windows. In the present work, the self-continuum cross-sections, CS, are determined for two new spectral points. The 2491 cm−1 spectral point in the region of maximum transparency of the 4.0 µm window was measured by OF-CEAS in the 23–52 °C temperature range. The 4435 cm−1 spectral point of the 2.1 µm window was measured by CRDS at room temperature. The self-continuum cross-sections were determined from the pressure squared dependence of the continuum absorption. Comparison to the literature shows a reasonable agreement with 1970 s and 1980 s measurements using a grating spectrograph in the 4.0 µm window and a very good consistency with our previous laser measurements in the 2.1 µm window. For both studied spectral points, our values are much smaller than previous room temperature measurements by Fourier Transform Spectroscopy. Significant deviations (up to about a factor 4) are noted compared to the widely used semi empirical MT_CKD model of the absorption continuum. The measured temperature dependence at 2491 cm−1 is consistent with previous high temperature measurements in the 4.0 µm window and follows an exp(D0/kT) law, D0 being the dissociation energy of the water dimer.

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.

A cavity ring down spectrometer referenced to a frequency comb is used to study the profile of air-broadened O2 lines of the 1.27 µm band. To this aim, spectra of O2 in dry air and in N2 with 2% relative abundance of O2 were measured, in the 7720–7920 cm−1 and 7868–7887 cm-1 spectral ranges, respectively. Spectra were recorded at room temperature and various pressures ranging from 50 to 700 Torr. Detailed line-profile analysis is reported for 85 transitions using the speed-dependent Nelkin-Ghatak model and a multi-spectrum treatment of the two series of spectra. Line mixing was found necessary to be taken into account in the analysis of lines in the region of the Q branch. The derived line parameters including the broadening and shifting coefficients, the speed-dependence components of the collisional line broadening and shifting, as well as the Dicke narrowing parameter are discussed and compared to literature data. In particular, the speed-dependence components of the collisional broadening are found to agree satisfactorily with predictions obtained by molecular dynamic simulations. This obtained set of line-shape parameters should allow for improved modeling of atmospheric spectra in the 1.27 µm spectral region.

Three very weak bands of the 18O16O18O isotopologue of ozone have been detected by high sensitivity CW-Cavity Ring Down Spectroscopy between 6340 and 6800 cm−1. They are vibrationally assigned as 2ν1+5ν3, ν1+4ν2+3ν3 and 3ν2+5ν3 and correspond to the highest frequency bands of this isotopologue detected so far. A total of 464, 318 and 194 transitions were rovibrationally assigned, respectively. The good agreement with theoretical values achieved for the derived band centres and rotational constants confirms the accuracy of the potential energy surface recently obtained via extensive ab initio calculations. A set of line intensities was measured and fitted to derive the first transition moment parameter of the three bands. The determined sets of effective Hamiltonian parameter and transition moment operators, as well as the experimental energy levels, were used to generate a complete list of 1526 transitions, provided as Supplementary materials . The calculated line-list allows generating a synthetic spectrum which reproduces satisfactorily the experimental spectrum.

The absorption spectrum of 13 CH 4 was recorded at two low temperatures in the icosad region near 1.38 µm, using direct absorption tunable diode lasers. Spectra were obtained using a cryogenic cell cooled at liquid nitrogen temperature (80 K) and a supersonic jet providing a 32 K rotational temperature in the 7173–7367 cm −1 and 7200–7354 cm −1 spectral intervals, respectively. Two lists of 4498 and 339 lines, including absolute line intensities, were constructed from the 80 K and jet spectra, respectively. All the transitions observed in jet conditions were observed at 80 K. From the temperature variation of their line intensities, the corresponding lower state energy values were determined. The 339 derived empirical values of the J rotational quantum number are found close to integer values and are all smaller than 4, as a consequence of the efficient rotational cooling. Six R (0) transitions have been identified providing key information on the origins of the vibrational bands which contribute to the very congested and not yet assigned 13 CH 4 spectrum in the considered region of the icosad.

The very weak absorption spectrum of the main isotopologue of nitrogen dioxide, 14N16O2, is investigated for the first time between 7760 and 7917 cm−1. The studied region corresponds to the highest energy range of the vibrational spectra of 14N16O2 investigated so far at high spectral resolution. The absorption spectra were recorded by very high sensitivity Continuous Wave-Cavity Ring Down Spectroscopy with a noise equivalent absorption of αmin≈5×10−11 cm−1. The spectrum results from the superposition of the rovibrational transitions of the 2ν1+5ν2+ν3, 2ν1+ν2+3ν3 and 5ν1+ν3 bands at 7790.9, 7888.2 and 7904.3 cm−1, respectively. The spectrum assignment and modeling were performed using the effective Hamiltonian approach, which involves altogether three bright – (2,5,1), (2,1,3) and (5,0,1) and three dark – (2,7,0), (2,3,2) and (5,2,0) states. As a result, 3020 rovibrational transitions were assigned including 51 extra lines of the 2ν1+3ν2+2ν3 and 5ν1+2ν3 bands. In this way, the overall set of 1494 spin-rotation energy levels were reproduced with an rms of 4.9×10−3 cm−1 for the (obs.−calc) deviations, leading to the determination of 66 fitted parameters. The effective Hamiltonian for the {(5,2,0), (2,3,2), (2,7,0), (2,5,1), (2,1,3), (5,0,1)} interacting states takes into account both the spin–rotation interactions within each vibrational state and C-type Coriolis and anharmonic resonances between different vibrational states, according to symmetry considerations. Indeed for NO2 the ( v , 1 v 2 ± 2 , v 3 ∓ 1 ) ↔ ( v , 1 v 2 , v 3 ) spin rotation energy levels are usually coupled through C-type Coriolis resonances, and accordingly the (2,7,0)↔(2,5,1)↔(2,3,2)↔(2,1,3) and (5,2,0)↔(5,0,1) interactions were included in the effective Hamiltonian model. Furthermore, these two blocks of interacting states are coupled by an additional C-type Coriolis and anharmonic resonances. Using the fitted values of the Hamiltonian parameters and the values of the 2ν1+5ν2+ν3, 2ν1+ν2+3ν3 and 5ν1+ν3 bands transition dipole moment operators determined from a fit of a selected set of experimental line intensities, a synthetic spectrum was generated for the entire investigated region and is provided as Supplementary material .

International audience; Our systematic investigation of the high sensitivity CW-Cavity Ring Down Spectra of 16O/18O ozone isotopologues at high vibrational excitation continues with the study of the 16O18O18O and 18O16O18O species. The first two papers of this series were devoted to the analysis of the same four bands of the 16O16O18O and 16O18O16O species in the 5930-6340 cm-1domain. Here, after a brief reminder of relevant experiment and theory, we report the analyses of two bands of 16O18O18O, vibrationally assigned as 2ν2+5ν3 and 2ν1+2ν2+3ν3_2 and three bands of 18O16O18O, assigned to 2ν1+2ν2+3ν3_1, 5ν1+ν3 and 3ν1+ν2+3ν3.They correspond to the highest vibration excitations observed so far for the 16O18O18O and 18O16O18O isotopologues. Altogether for the two new bands of 16O18O18O, 1214 rovibrational transitions were assigned up to Jmax=29 and for the three new bands of 18O16O18O, 948 rovibrational transitions were assigned up to Jmax=27. Observed line positions were fitted with root-mean squares deviations ranging from 0.005 to 0.011 cm-1, using effective Hamiltonian models accounting for dark state perturbations. The derived band centres and rotational constants are in good agreement with new theoretical calculations from the molecular potential function. The corresponding lists of 3365 lines are provided as Supplementary material.

The CO2 absorption continuum near 2.3 µm is determined for a series of sub atmospheric pressures (250–750 Torr) by high sensitivity Cavity Ring Down Spectroscopy. An experimental procedure consisting in injecting successively a gas flow of CO2 and synthetic air, keeping constant the gas pressure in the CRDS cell, has been developed. This procedure insures a high stability of the spectra baseline by avoiding changes of the optical alignment due to pressure changes. The CO2 continuum was obtained as the difference between the CO2 absorption coefficient and a local lines simulation using a Voigt profile truncated at ±25 cm−1. Following the results of the preceding analysis of the CO2 rovibrational lines (Vasilchenko S et al. J Quant Spectrosc Radiat Transfer 10.1016/j.jqsrt.2016.07.002 , a CO2 line list with intensities obtained by variational calculations and empirical line positions was preferred to the HITRAN line list. A quadratic pressure dependence of the absorption continuum is observed, with an average binary absorption coefficient increasing from 2 to 4×10−8 cm−1 amagat−2 between 4320 and 4380 cm−1. The obtained continuum is found in good agreement with a previous measurement using much higher densities (20 amagat) and a low resolution grating spectrograph and is consistent with values currently used in the analysis of Venus spectra.

An accurate and complete empirical spectroscopic database is constructed for natural water in the 5850–8340 cm−1 near infrared region (1.71–1.20 µm). The global list includes more than 46,500 transitions of the six most abundant isotopologues (H216O, H218O, H217O, HD16O, HD17O, HD18O) in natural isotopic abundance with intensity greater than 1×10−29 cm/molecule. All line positions were obtained by difference of empirically determined energy values. These empirical determinations are mostly based on extensive investigations of water vapor spectra by high-sensitivity CRDS complemented with literature data. In particular, the sets of energy levels of the minor isotopologues have been significantly enlarged from very recent analysis of CRDS spectra of D, 18O and 17O enriched water samples. The empirical line positions were associated to experimental intensity values from the literature obtained by FTS for the strong lines and CRDS for weaker lines. The list is made mostly complete by including a large number of weak transitions not yet detected, with empirical positions calculated from empirical levels associated with variational intensities. Air- and self-broadening coefficients and air-induced line shifts have been added to each transition using the most recent version of the algorithm used for the HITRAN and GEISA databases. Examples of comparison of CRDS spectra to simulations based on the HITRAN2012 list illustrate the advantages of our database. The relative merit of experimental and variational line intensities is discussed. A separate line list combining empirical line positions and variational intensities is provided. Future improvements from combination of experimental and variational intensities are suggested.

The very weak 3ν1+3ν2+ν3 absorption band of the main isotopologue of nitrogen dioxide, 14N16O2, is investigated for the first time near 7587 cm−1. The absorption spectrum was recorded by high sensitivity Continuous Wave-Cavity Ring Down Spectroscopy with a noise equivalent absorption of αmin≈1×10−10 cm−1. 414 lines of the 3ν1+3ν2+ν3 band were assigned with rotational quantum numbers N and Ka as high as 32 and 6, respectively, what corresponds to 518 rotation–vibration transitions. The overall set of spin–rotation energy levels was modeled in the frame of the effective Hamiltonian approach and reproduced with an RMS of 6×10−3 cm−1 for the (obs.–calc.) deviations. The effective Hamiltonian includes interactions with three nearby dark states – (350), (062) and (312) – in Coriolis interaction with the (331) bright state. Using a selected set of experimental line intensities and the fitted values of the vibration–rotation Hamiltonian parameters, the principal parameter in the dipole moment operator expansion is determined for the 3ν1+3ν2+ν3 band. With maximum line intensity on the order of 2.5×10−27 cm/molecule at 296 K, the 3ν1+3ν2+ν3 band is the weakest band of the NO2 molecule rovibrationnally assigned so far.

International audience; Using a cryogenic cell and a series of Distributed Feed Back (DFB) diode lasers, new high resolution spectra of methane have been recorded at 80 K and room temperature by differential absorption spectroscopy (DAS) between 6717 and 7589 cm-1 (1.49-1.32 μm). The investigated spectral region corresponds to the very congested icosad, which is not tractable by theory. Empirical lists of 19,940 and 24,001 lines were constructed from the 80 K and room temperature spectrum, respectively. The room temperature list adds about 8500 features to the empirical list of 15,375 lines at 296 K adopted in the HITRAN database from the original work of L. Brown (Brown, L. Empirical line parameters of methane from 1.1 to 2.1 μm. JQSRT 2005;96:251-70). A number of relatively strong CH4 lines located near strong water lines were found missing in the HITRAN line list. The improved sensitivity allowed adding more than 7000 lines to our previous list of about 12,000 transitions at 80 K (Campargue A, Wang L, Kassi S, Mašát M, Votava O. Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The Icosad region (1.49-1.30 μm). JQSRT 2010;111:1141-51). In order to facilitate identification of the transitions of the different methane isotopologues present in "natural" isotopic abundance, spectra of highly enriched CH3D and 13CH4 samples were recorded with the same experimental setup, both at room temperature and at 80 K.From the variation of the line strengths between 80 K and 294 K, the low energy values of about 12,000 transitions were determined. They allow accounting for the temperature dependence of 84 and 93% of the methane absorbance in the region, at room temperature and 80 K, respectively. As a result, we provide as supplementary material two complete line lists at 80 K and 294 K, including CH3D and 13CH4 identification and lower state energy values.

The absorption of carbon dioxide is very weak near 2.3 µm which makes this transparency window of particular interest for the study of Venus’ lower atmosphere. As a consequence of the weakness of the transitions located in this region, previous experimental data are very scarce and spectroscopic databases provide calculated line lists which should be tested and validated by experiment. In this work, we use the Cavity Ring Down Spectroscopy (CRDS) technique for a high sensitivity characterization of the CO 2 absorption spectrum in two spectral intervals of the 2.3 µm window: 4248–4257 and 4295–4380 cm −1 which were accessed using a Distributed Feed Back (DFB) diode laser and a Vertical External Cavity Surface Emitting Laser (VECSEL) as light sources, respectively. The achieved sensitivity (noise equivalent absorption, α min , on the order of 5×10 −10 cm −1 ) allowed detecting numerous new transitions with intensity values down to 5×10 −30 cm/molecule. The rovibrational assignments were performed by comparison with available theoretical line lists in particular those obtained at IAO Tomsk using the global effective operator approach. Hot bands of the main isotopologue and 16 O 12 C 18 O bands were found to be missing in the HITRAN database while they contribute importantly to the absorption in the region. Additional CRDS spectra of a CO 2 sample highly enriched in 18 O were recorded in order to improve the spectroscopy of this isotopologue. As a result about 700 lines of 16 O 12 C 18 O, 16 O 12 C 17 O, 17 O 12 C 18 O, 12 C 18 O 2 and 13 C 18 O 2 were newly measured. The status of the different databases (HITRAN, CDSD, variational calculations) in the important 2.3 µm transparency window is discussed. Possible improvements to correct evidenced deficiencies are suggested.

Accurate rovibrational analysis of the lower part of the Icosad 12 CH 4 spectrum in the 6539–6800 cm −1 region is reported. The analysis uses the WKLMC experimental line list previously obtained in Grenoble by Cavity Ring Down Spectroscopy and Differential Absorption Spectroscopy at T =80 K. Based on an ab initio potential energy surface, the full Hamiltonian of methane nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformations method with a subsequent empirical optimization of parameters. About 2445 experimental line positions were fitted with RMS standard deviations of 0.005 cm −1 and 1644 line intensities were modeled using effective dipole moment with the RMS deviation of 11.5%. Twenty five vibrational energy levels of the lower part of the Icosad were determined.

A self-referenced frequency comb has been combined with a cavity ring down (CRD) spectrometer to achieve a sub-MHz accuracy on the derived positions of the absorption lines. The frequency emitted by the distributed feedback (DFB) laser diode used in the spectrometer was obtained from the frequency of its beat note with the closest mode of the frequency comb. This delivers excellent frequency accuracy over a broad spectral region with sensitivity (noise equivalent absorption) of 1 x 10(-11) cm(-1) Hz(-1/2). This setup is used to measure the absorption spectrum of CO over a wide range corresponding to the 3-0 band (6172.5-6418.0 cm(-1)). Accurate values of line centers are measured for a total of 184 lines of four CO isotopologues, namely (CO)-C-12-O-60, (CO)-C-13-O-16, (CO)-C-12-O-18 and (CO)-C-12-O-17 present in "natural" abundances in our sample. The measurements include the first extensive study of the 3-0 band of (CO)-C-12-O-18 and (CO)-C-12-O-17, of the 4-1 hot band of (CO)-C-12-O-16 and the detection of new high-J transitions of the 3-0 band of (CO)-C-12-O-16 up to J=34. The line centers were corrected for the self-pressure shift and used to derive the upper state spectroscopic parameters. The obtained standard deviation of about 300 kHz and 500 kHz for the 3-0 band of (CO)-C-12-O-16 and of the minor isotopologues, respectively, is a good estimate of the average accuracy of the reported line centers. The resulting 3-0 line list of (CO)-C-12-O-16 provided as Supplementary material includes 69 reference line positions with a 300 kHz accuracy for the 6183-6418 cm(-1) region. (C) 2014 Elsevier Ltd. All rights reserved.

The absorption spectrum of 13 CH 4 has been recorded at 296 K and 80 K by differential absorption spectroscopy (DAS) in the high energy part of the tetradecad (5853–6201 cm −1 ) dominated by the 2ν 3 band near 5988 cm −1 . The achieved noise equivalent absorption of the spectra ( α min ≈1×10 −7 cm −1 ) allowed us to double the number of 13 CH 4 lines previously measured in the region (our lists include about 7200 and 3700 lines at 296 and 80 K, respectively). Empirical values of the lower state energy level, E emp , were systematically derived from the intensity ratios of the lines measured at 80 K and 296 K. Overall 2782 E emp values were determined extending significantly the previous set of about 1200 E emp values available in the literature. The corresponding empirical values of the rotational quantum number, J emp , show a clear propensity to be close to an integer, illustrating the validity of the method. The line lists at 296 K and 80 K, provided as Supplementary material , are discussed in relation with line lists and rovibrational assignments available in the literature.

The present contribution is devoted to the analysis of three extremely weak A-type bands of 16O3 recorded near 7686, 7739 and 7860 cm−1 i.e. only a few % below the dissociation limit, D0, at about 8560 cm−1. They correspond to the most excited vibration–rotation states of ozone observed so far via high-resolution absorption spectroscopy. They were detected by high sensitivity CW-cavity ring down spectroscopy with a typical noise equivalent absorption, αmin, on the order of 2×10−10 cm−1 and modelled using the effective operator approach. The derived band centres and rotational constants show a very good agreement with recent theoretical predictions based on a new ab initio potential energy surface.

The absorption spectrum of the 18 O 3 isotopologue of ozone is recorded by CW-Cavity Ring Down Spectroscopy between 7400 and 7920 cm −1 . The typical noise equivalent absorption of the recordings is α min ≈1×10 −10 cm −1 allowing for the detection of extremely weak vibrational bands located only a few % below the dissociation limit. The absorption spectrum also includes the weak 3 A 2 (000)–X(110) hot vibronic band at 7877.53 cm −1 affected by predissociation broadening. Overall, about 1000 lines were rovibrationnally assigned to six vibrational bands. Their line positions were modelled using effective Hamiltonian models covering three vibrational interacting systems and involving several “dark” states perturbing observed transitions. Line positions could be reproduced with rms deviations on the order of 0.01 cm −1 . The dipole transition moment parameters of the six bands were determined from the retrieved line intensities. The obtained set of effective parameters and the experimentally determined energy levels were used to generate a list of 1461 transitions provided as Supplementary materials .

An empirical line list has been constructed for “natural” water vapor at 296 K in the 5850–7920 cm −1 region. It was obtained by gathering separate line lists recently published on the basis of spectra recorded by high sensitivity Continuous Wave Cavity Ring Down Spectroscopy (CW-CRDS) of natural water, complemented with literature data for the strongest lines. The list includes 38,318 transitions of four major water isotopologues (H 2 16 O, H 2 18 O, H 2 17 O and HD 16 O) with an intensity cut-off of 1×10 −29 cm/molecule at 296 K. The list is made mostly complete over the whole spectral region by including a large number of weak lines with positions calculated using experimentally determined energy levels and intensities obtained from variational calculations. In addition, we provide HD 18 O and HD 17 O lists in the same region for transitions with intensities larger than 1×10 −29 cm/molecule. The HD 18 O and HD 17 O lists (1972 lines in total) were obtained using empirical energy levels available in the literature and variational intensities. The global list (40,290 transitions) for water including the contribution of the six major isotopologues will be adopted for the next edition of the GEISA database in the region. The advantages and drawbacks of our list are discussed in comparison with the list provided for the same region in the 2012 edition of the HITRAN database. The direct comparison of the CRDS spectra to simulations based on the HITRAN list has revealed some insufficiencies which could easily be corrected: missing HDO lines, duplicated lines, inaccurate line positions or line intensities from variational calculations.

More than 19,700 transitions belonging to 11 isotopologues of carbon dioxide have been assigned in the room temperature absorption spectrum of highly 18O enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990 cm−1 (1.71–1.43 μm). This third and last report is devoted to the analysis of the bands of five 17O containing isotopologues present at very low concentration in the studied spectra: 16O12C17O, 17O12C18O, 16O13C17O, 17O13C18O and 12C17O2 (627, 728, 637, 738 and 727 in short hand notation). On the basis of the predictions of effective Hamiltonian models, a total of 1759, 1786, 335, 273 and 551 transitions belonging to 24, 24, 5, 4 and 7 bands were rovibrationally assigned for 627, 728, 637, 738 and 727, respectively. For comparison, only five bands were previously measured in the region for the 728 species. All the identified bands belong to the ΔP=8 and 9 series of transitions, where P = 2 V 1 + V 2 + 3 V 3 is the polyad number (Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 61 bands from a fit of the measured line positions. Two interpolyad resonance perturbations were identified. Using the newly measured line positions and those collected from the literature, the global modeling of the line positions within the effective Hamiltonian approach was performed and a new set of Hamiltonian parameters was obtained for the 17O12C18O, 16O13C17O and 17O13C18O isotopologues. For the five studied isotopologues, the effective dipole moment parameters of the ΔP=8 and 9 series were derived from a global fit of the measured line intensities. The obtained results will be used for the improvement of the quality of the line positions and intensities in the most currently used spectroscopic databases of carbon dioxide.

More than 19000 transitions belonging to 11 isotopologues of carbon dioxide have been assigned in the room temperature absorption spectrum of highly 18O enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990 cm−1 (1.71–1.43 μm). The line positions were determined with accuracy better than 1×10−3 cm−1 while the absolute line intensities are reported with an uncertainty better than 10%. This second report is devoted to the analysis of the bands of three multiply substituted isotopologues: 12C18O2, 13C18O2 and 16O13C18O (828, 838 and 638 in short hand notation). On the basis of the predictions of effective Hamiltonian models, a total of 2870, 538 and 1375 transitions belonging to 59, 11 and 15 bands were rovibrationnally assigned for 828, 838 and 638, respectively. For comparison, only 11 bands were previously measured by Fourier Transform spectroscopy in the region, for the 828 species. All the identified bands correspond to a ΔP=9 variation of the polyad number (P=2V1+V2+3V3, where Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 81 bands from a fit of the measured line positions. A few resonance perturbations were identified. In particular, the 31113 and 51106 states of 638 belonging to different polyads (P=10 and P=11, respectively) are anharmonically coupled. Using the large set of newly measured line positions and those collected from the literature, the global modeling of the line positions within the effective Hamiltonian approach was performed and a new set of Hamiltonian parameters was obtained for each of the three considered isopotologues. Using a similar approach, the global fits of the obtained intensity values of the ΔP=9 series of transitions were used to derive the corresponding ΔP=9 effective dipole moment parameters of the three considered isotopologues. The obtained results will help to improve the quality of the spectral line parameters of the three considered minor isopotologues in the most currently used spectroscopic databases of carbon dioxide.