The Doppler broadened R(0), P(1) and P(2) lines of the (v' $ \leftarrow $ <- v'') = (3 $ \leftarrow $ <- 0) vibrational band of HD have been measured at the MHz accuracy level using a comb-referenced continuous-wave cavity ring-down spectrometer. The transition frequencies are found to be 305141769.4 +/- 5.0, 308138756.2 +/- 4.0 and 313148302.4 +/- 9.0 MHz for the P(2), P(1) and R(0) transitions, respectively. This is the first spectroscopic measurement of HD at this level of accuracy for such a high-vibrational excitation. It represents an accuracy improvement by a factor of 50 compared to the literature.

We present a coherent dataset of water absorption line parameters obtained by direct absorption spectroscopy with a setup based on a difference frequency terahertz (THz) spectrometer designed as described in L. Djevahirdjian et al., Nat. Commun., 2023, 14(1), 7162. This study includes a demonstration of system linearity and fringe analysis, revealing beyond-Voigt signatures in the line profiles. The results are compared with the literature values, and new line parameters are reported.

The SMAUG device is used to thermally populate the vibrational states of the methane molecule and depopulate its rotational states through its supersonic expansion in argon. The methane molecule is probed during expansion by cavity ringdown spectroscopy (CRDS) between 5880 and 6220 cm-1. The laser beam passes through both the isentropic core of the flow, characterized by a very low rotational temperature of 40.4 f 0.8 K, and the hotter boundary layers surrounding it, which are characterized by an average rotational temperature of 364.3 f 7.7 K. Analysis of the spectrum reveals that the vibrational population does not follow a Boltzmann distribution. A special procedure is developed to assign an effective vibrational temperature to each vibrational state, ranging from 532.4 f 32.2 to 1112.0 f 81.7 K for molecules in the isentropic core, and from 811.6 f 43.1 to 851.8 f 45.6 K for those in the shear layer. Only the first vibrational states of each methane polyad remain significantly populated leading to detectable transitions. A total of 2525 transitions from the cold gas of the isentropic core and from the warmer gas of the boundary layers are assigned from a new ab initio effective model and 1000 are confirmed by lower state combination differences (LSCD). Among these transitions, 718 originates from cold bands and 1807 from hot bands starting from vibrational states nu 4, nu 2 (dyad), 2 nu 4 (pentad) and 3 nu 4 (octad).

This work describes a technique exploiting a linear optical cavity to frequency stabilize, by optical feedback, an 8.5 µm QCL laser and perform, at the same time, cavity ring down spectroscopy. An arbitrary frequency step resolution is achieved thanks to an active control of the cavity length using a 1.6 µm tunable pilot laser. A detectivity of 4 × 10-10 cm-1 and a frequency resolution of 20 kHz are demonstrated, with a cavity finesse of 18800. A 3 GHz and a 4 MHz broad spectra are recorded with 8.5 MHz and 20 kHz step resolution, respectively. The first spectrum consists in a high-resolution overview showing two water lines that belong to H216O and H218O; the second one is a very high-resolution recording of a sharp Lamb dip structure observed at the top of the H216O line, illustrating the vast application fields this instrument opens.

Joint measurements of the 18O/16O and 17O/16O ratios of carbonate minerals and waters are increasingly used to investigate various geochemical, physical and biological processes. Diverse analytical methods, each of them technically challenging in one way or another, have been developed or refined in recent years to measure oxygen-17 anomalies (Δ17O) with instrumental precisions of 10 ppm or better. A critical underpinning of all these methods is how the international carbonate reference materials currently anchoring the VPDB 18O/16O scale are linked to the primary VSMOW-SLAP scale in (18O/16O, 17O/16O) space. For now, however, substantial systematic discrepancies persist between different groups and methods, even after all measurements are nominally standardized to VSMOW-SLAP. Here we take advantage of VCOF-CRDS, a novel spectroscopic method combining the ease and simplicity of near-infra-red absorption measurements in pure CO2 with metrological performance competitive with state-of-the-art IRMS techniques, to precisely characterize, based on previously reported equilibrium fractionation factors between water and CO2, the relative triple oxygen isotope compositions of international water standards (VSMOW2, SLAP2, GRESP) and CO2 produced by phosphoric acid reaction of carbonate standards (NBS18, NBS19, IAEA603, IAEA610, IAEA611, IAEA612). The robustness of our results derives from the demonstrated linearity of our measurements (RMSE ≈ 1 ppm), but also from the fact that, when equilibrated with or converted to CO2, all of these reference materials yield analytes with closely comparable oxygen-18 compositions. In light of these observations, we revisit potential causes of the large inter-laboratory discrepancies reported so far. Collectively reconciling the different types of measurements constraining the relative 17O/16O ratios of the two standards most often used to normalize carbonate analyses (NBS18, IAEA603) is a matter of high priority.

Satellite missions are considering the atmospheric O2 band at 1.27 mu m to determine the air-column. A prerequisite of these demanding atmospheric applications is an accurate knowledge of the spectroscopy of this band, in particular of the line profiles and their temperature dependence. In the present work, fifty-five transitions of the 1.27 mu m band of O2 have been studied with a cavity ring down spectrometer linked to an optical frequency comb referenced to a GPS-disciplined Rb oscillator. The comb-coherence transfer (CCT) technique was applied to obtain a RF tunable narrow-line comb-disciplined laser source from a set of distributed feedback laser diodes and a simple electro-optic modulator. High-quality spectra were obtained with a high-finesse cavity regulated at 253, 273 and 333 K. For each transition and each temperature, series of synthetic dry air spectra were recorded for five pressures, from 50 to 750 Torr. The line-shape parameters were retrieved thanks to a multi-spectrum fit procedure with a quadratic speed-dependent Nelkin-Ghatak profile and first-order line-mixing effect when required. For each transition, the temperature dependence exponents and coefficients of the different line profile parameters together with their values at the reference temperature of 296 K were determined. Absolute positions and intensities are provided by the fit with an average accuracy of 240 kHz (or 8 x 10-6 cm-1) and 0.2 %, respectively. An effect of intensity depletion with pressure on the order of 0.4 % atm-1 is evidenced. Comparison with literature, in particular with the HITRAN2020 database is discussed.

Light-matter interactions involving molecular oxygen (O2) span numerous decades in the frequency of electromagnetic radiation and are important to many thermophysical and thermochemical mechanisms, ranging from atmospheric remote sensing of greenhouse gases, aerosols, pollutants, temperature and pressure, visible and infrared radiative exchange in the upper atmosphere, ozone formation and decomposition, and the search for life beyond Earth, among many other examples. Here, we highlight advances in the quantitative spectroscopy of O2, for which updated band-specific, line-by-line parameters have been provided in the HITRAN2024 spectroscopic database. Theoretical results are presented for electric quadrupole transition intensities in the ground state of O 2 16 , and the Noxon band in the near-infrared region has been included in HITRAN for the first time. Particular focus is placed on the 1.27 μm, A- and B-bands of O2, in which intensities, line-shape (including beyond-Voigt parameterizations), and position parameters with improved accuracy and/or extended spectral coverage are presented. Corrections to the Schumann-Runge bands are also reported. The paper closes with recommendations and an outlook on key challenges in advancing our understanding of the spectroscopy of O2.

Kinetic isotopes effect (KIEs) describes a very common phenomenon related to change in chemical reaction rate due isotopic substitution. If in biological sciences, KIEs has received a lot of interest with the aim at understanding reaction mechanisms, their control on the isotopic composition of biogenic carbonate has long been overlooked. However, the initial assumption that isotopic fractionation primarily reflects a thermodynamic equilibrium process in the H2O-DIC-CaCO3 system is challenged by a growing number of observations. Not accounting for these disequilibrium effects leads to inaccurate estimates of carbonate growing temperature. In this scientific context, Triple oxygen isotopes systematic can help constraining kinetics isotopes fractionation associated with metabolic reactions implicated in biocarbonates formation. We thus took advantage from recent development in spectroscopic technique (VCOF-CRDS) to measured O17 isotopic anomalies in CO2 produced by carbonate acid reaction [1]. These samples were also analyzed for their δ13C, δ18O and Δ47 composition using a more classical mass spectroscopy technic. In this contribution we investigated cold-water corals (CWC) known to display strong isotopic disequilibria. For this 1st application, we selected four modern CWC species for which calcification conditions (T, S, pH, δ18Owater, Δ17Owater and δ13CDIC) are independently constrained. The measured isotopic signatures were compared to their respective expected values based on environmental constrains, assuming “pseudo-equilibrium” carbonate precipitation. In particular, corals Δ17O signatures were compared to the newly established equilibrium for O17 fractionation between calcite-water based on slow growing carbonates from Laghetto Basso and Devils Hole, measured using the same VCOF-CRDS technic [2]. We finally compared our experimental data with theoretical predictions for KIEs on DIC isotopic composition [3]. Interestingly, the correlation slope among Δ47 - Δ17O disequilibrium differ from the previous one derived from dual clumped (Δ47 - Δ48) isotopic measurements of the same species [4]. This founding suggesting that other biological parameter(s) should be taken into account to resolve CWC isotopic disequilibria. [1] Chaillot. J., Daëron. M., Casado, M., Landais. A., Pesnin. M., Clauzel. T., Kassi. S. (in prep) Triple oxygen analyses of carbon dioxide, water and carbonates using VCOF-CRDS. [2] Clauzel, T., Chaillot, J., Pesnin, M., Jautzy, J., Kessy, S., Daëron, M. (in prep) Advancing triple oxygen isotope analysis of carbonate and water using V-shaped Cavity Optical Feedback Cavity Ring-Down Spectroscopy (VCOF-CRDS): Calibration and implications for paleoclimate reconstruction. [3] Guo. W. (2020). Kinetic clumped isotope fractionation in the DIC-H2O-CO2 system: Patterns, controls, and implications. Geochimica et Cosmochimica Acta, 268, 230-257. [4] Davies. A. J., Guo. W., Bernecker. M., Tagliavento. M., Raddatz. J., Gischler. E., Floter. S., Fiebig. J. (2022). Dual clumped isotope thermometry of coral carbonate. Geochimica et Cosmochimica Acta, 338, 66-78.

In situ measurements of water vapour isotopic composition in polar regions has provided needed constrains of post-deposition processes involved in the archiving of the climatic signal in ice core records. During polar winter, the temperatures, and thus the specific humidity, are so low that current commercial techniques are not able to measure the vapour isotopic composition with enough precision. Here, we make use of new developments in infrared spectroscopy and combine an optical-feedback frequency-stabilised laser source (OFFS technique) using a V-shaped cavity optical feedback (VCOF) cavity and a high-finesse cavity ring-down spectroscopy (CRDS) cavity to increase the signal-to-noise ratio while measuring absorption transitions of water isotopes. We present a laboratory infrared spectrometer leveraging all these techniques dedicated to measure water vapour isotopic composition at low humidity levels. At 400 ppmv, the instrument demonstrates a precision of 0.01 ‰ and 0.1 ‰ in δ18O and d-excess, respectively, for an integration time of 2 min. This set-up yields an isotopic composition precision below 1 ‰ at water mixing ratios down to 4 ppmv, which suggests an extrapolated precision in δ18O of 1.5 ‰ at 1 ppmv. Indeed, thanks to the stabilisation of the laser by the VCOF, the instrument exhibits extremely low drift and very high signal-to-noise ratio. The instrument is not hindered by a strong isotope–humidity response which at low humidity can create extensive biases on commercial instruments.

We present the measurement and analysis of the 2OH stretching band of methanol between 7165 cm−1 and 7230 cm−1 cooled down to 26 ± 12 K in a buffer gas cooling experiment.

Absorption spectra of jet-cooled ethylene (ethene, C2H4) are recorded at three different rotational temperatures (6/8 K, 12 K, 38 K) using cavity ring-down spectroscopy (CRDS) in the 5880-6200 cm−1 spectral region. Rotational cooling is used to determine the various vibrational band centers by simplifying drastically the rotational band structure. A line-by-line assignment, based on a direct comparison with the TheoReTS variational line list and a systematic use of lower state combination difference (LSCD), is performed. Experimental line lists including line position and line integrated absorption cross sections are drawn up. The 6/8 K, 12 K and 38 K spectra contain 668, 1553 and 1679 absorption lines respectively. Overall, 320 rovibrational lines are assigned across 20 interacting vibrational bands. Among the 20 vibrational cold bands identified in this work, 14 had never been observed before. Line intensities are in the range of 10−24 - 10−20 cm/molecule. A direct comparison between our work and the TheoReTS and ExoMol theoretical line lists, as well as with the recent experimental work of Ben Fathallah et al. 2024 is provided.

Abstract. In situ measurements of water vapour isotopic composition in Polar Regions has provided needed constrains of post-deposition processes involved in the archiving of the climatic signal in ice core records. During polar winter, the temperatures are so low that current commercial techniques are not able to measure the vapour isotopic composition with enough precision. Here, we make use of new developments in infrared spectroscopy and combine an optical feedback frequency stabilised laser source (OFFS technique) using a V-shaped optical cavity (VCOF) and a high-finesse cavity ring down cavity (CRDS) which yield sufficient precision to measure isotopic composition at water mixing ratios down to 1 ppmv. Indeed, thanks to the stabilisation of the laser by the VCOF, the instrument suffers extremely low drift and very high signal to noise ratio. Using new constrains on the fitting technique, the instrument is additionally not hindered by a large isotope-humidity response which at low humidity can create extensive biases on commercial instruments.

Oxygen-17 excess (Δ17O) in carbonate minerals can provide valuable insights into past continental and marine environments, long-term trends in the temperature and oxygen-isotope composition of ancient oceans, isotopic disequilibrium effects in biogenic and abiotic carbonates, and cryptic diagenesis. Triple oxygen isotope analyses of carbonates and/or CO2 using isotope-ratio mass spectrometers (IRMS) remain challenging, however, because of isobaric interference between 16O13C16O and 16O12C17O. Using spectroscopic methods, the abundance of each CO2 isotopologue may be directly quantified, potentially providing simple, non-destructive measurements of δ13C, δ18O and Δ17O on small samples of CO2.Here we report new data characterizing the application of VCOF-CRDS (V-shaped Cavity Optical Feedback - Cavity Ring Down Spectroscopy [1]) to the analysis of small samples (<40 μmol) of pure CO2, as typically produced by phosphoric acid digestion of carbonate minerals.Instrumental drifts from various sources are observed to bias apparent isotopic abundances by a few tens of ppm, but these drifts are slow enough that they may be precisely monitored and corrected for by repeated analyses of a working gas interspersed between other analyses, requiring only ~8 mn per aliquot and 30 mn between consecutive “unkown” analyses. This approach was tested by analyzing repeated aliquots of another CO2 tank with a different isotopic composition, yielding instrumental repeatabilities of 12 ppm, 13 ppm and 7.4 ppm for δ13C, δ18O and Δ17O, respectively (95 % CL, Nf = 66).The accuracy of our measurements was tested over a wide range of Δ17O values spanning 130 ppm, by analyzing CO2 equilibrated at 25 °C with different waters whose triple oxygen compositions were independently constrained in the SMOW-SLAP scale by IRMS measurements and by simple nonlinear mixing predictions. We find that our Δ17O measurements are well within analytical uncertainties of predicted values (RMSE = 1.2 ppm), with analytical repeatabilities (including isotopic equilibration and gas manipulation) of 8.6 ppm (95 % CL, Nf = 27).We will also report the results of our ongoing investigation regarding the isotopic fractionation and analytical noise associated with different acid digestion protocols at different reaction temperatures, and the triple oxygen composition of various international reference materials already used for δ13C, δ18O, and clumped-isotope measurements.Based on these results, we conclude that VCOF-CRDS offers excellent accuracy, along with state-of-the-art levels of analytical precision/linearity, for straightforward analyses of 17O excess in CO2, water, and carbonate minerals.[1] Stoltmann et al. (2017) 10.1021/acs.analchem.7b02853

We present a robust approach to generate a continuously tunable, low phase noise, Hz linewidth and mHz/s stability THz emission in the 0.1 THz to 1.4 THz range. This is achieved by photomixing two commercial telecom, distributed feedback lasers locked by optical-feedback onto a single highly stable V-shaped optical cavity. The phase noise is evaluated up to 1.2 THz, demonstrating Hz-level linewidth. To illustrate the spectral performances and agility of the source, low pressure absorption lines of methanol and water vapors have been recorded up to 1.4 THz. In addition, the hyperfine structure of a water line at 556.9 GHz, obtained by saturation spectroscopy, is also reported, resolving spectral features displaying a full-width at half-maximum of 10 kHz. The present results unambiguously establish the performances of this source for ultra-high resolution molecular physics.

Metrological measurements of rovibrational frequencies in molecular hydrogen provide stringent tests for the most advanced theoretical calculations and for searching for physics beyond the standard model.We will present the accurate transition frequencies of a series of lines belonging to the (2-0) vibrational band of H 2 near 1.2 µm.These weak electricquadrupole transitions were measured at room temperature by comb referenced cavity ring-down spectroscopy and are the first H 2 (2-0) transition frequencies referenced to an absolute frequency standard.Accurate transition frequencies determination -up to three orders of magnitude better than previous measurements -will be presented.The impact of the line profile on zero-pressure line centers will be evaluated.These transition frequencies are used to infer the separation of lower energy levels in the vibrational ground state.All these experimental results will be compared to the most recent calculated frequencies.

Reaching low temperatures is of great interest for precision spectroscopy, as it simplifies rovibrationnal spectra of large molecules. Efficient cooling can be achieved via the supersonic expansion of a gas through a nozzle, which can be probed using cavity-enhanced spectroscopy [1]–[3]. We demonstrate comb-based Fourier transform spectroscopy (FTS) of acetylene in a supersonic jet. The experimental setup is shown on Fig. 1(a): the comb was an amplified Er:fiber source coupled to a 300-finesse enhancement cavity mounted perpendicular to the gas chamber, and the cavity transmission was analyzed using FTS. The comb was locked to the cavity using the two-point Pound-Drever-Hall scheme, and the repetition rate $f_{rep}$ was stabilized by acting on the cavity length with a piezo actuator [4]. The comb filtered by the cavity had a $f_{rep}=707 \ \text{MHz}$ , and two-burst interferograms were acquired, yielding comb mode resolution [4]. A mixture of 90% Ar and 10% C2H2 was expanded from a reservoir at 16 Torr into a chamber at 0.35 Torr through an aerospike nozzle. The isentropic core of the resulting supersonic jet exhibited a rotational temperature of 140 K and was surrounded by shear layers and residual gas at room temperature.

Laboratory spectroscopic data is essential for the modeling of hot exoplanet atmospheres, since molecules such as methane, a major component of hot-Jupiter-type exoplanet atmospheres, have a complex vibrational energy structure that makes computational predictions difficult at high temperatures for ro-vibrational transitions involving highly excited vibrational sates. To better inform line lists used in radiative transfer modeling, the ro-vibrational spectrum of methane has been recorded in the tetradecad region between 1.7 and 1.65 mu m (5880-6060 cm-1) through non-local thermodynamic equilibrium (non-LTE) cavity ringdown spectroscopy (CRDS). Non-LTE conditions, characterized by a low rotational temperature (-39 K) and a high vibrational temperature (up to 1130 K), have been obtained by hypersonic expansion of a pre-heated mixture of argon and methane in a contoured Laval nozzle. The high vibrational temperature increases the intensity of new hot bands, while the very low rotational temperature greatly simplifies their rotational structure, thus facilitating their identification. A close comparison of the recorded CRDS data to the TheoReTS database reveals both inefficient vibrational relaxation between polyads and efficient vibrational relaxation between vibrational states forming a polyad. These effects result in an overpopulation of the lowest vibrational energy level of each polyad, an effect not widely currently incorporated in non-LTE radiative transfer models. A series of new hot band transitions originating from the pentad and octad polyads were assigned and are provided as a line list for use in future databases.