Water Vapor Spectrum Research Articles

The spectrum of radioactive water vapor: the H219O radio-isotopologue

The absorption spectrum of H219O, a radioactive isotopologue of the water molecule, is predicted using variational nuclear motion calculated based on a high precision potential energy function and ab initio dipole moment surface. Vibrational - rotational energy levels and wave functions, line centers and Einstein coefficients for dipole transitions are calculated. Predicted transition wavenumbers are improved by extrapolating known empirical energy levels of the stable H216O, H217O and H218O isotopologues to H219O. A line list for possible atmospheric application is presented which includes air line broadening coefficients. The calculations span a wide spectral range covering infrared and visible wavelengths, and are appropriate for temperatures up to 1000 K. Windows suitable for observing absorption by H219O are identified and comparisons made with the infrared spectra of water vapor in natural abundance, H215O and H214O.

Femtosecond Terahertz Pulse Propagation Measurements and Simulations of Dewetting Kinetics in Real Time.

We report a terahertz time-domain study of dewetting kinetics on two time scales: femtoseconds and in real time (on the order of minutes). We recorded full electric field terahertz time domain signals with femtosecond time resolution during dewetting of water in cellulose. The femtosecond time-domain signals were analyzed with respect to the amplitude and signal emission times and how these two quantities changed over the course of dewetting kinetics. The femtosecond time-domain signals were modeled by a combination of finite-difference time-domain electromagnetic simulations of linear terahertz pulse propagation and an effective medium description of the dielectric permittivity. A logistic regression mechanism was incorporated into the electrodynamics simulations to account for the observed kinetics. In addition, analysis of the area-normalized, real-time time-dependent terahertz spectra was used to identify broad regions in the terahertz spectral range that correlated with the kinetic process. Real-time two-dimensional terahertz correlation maps were used to identify the pure rotational spectrum of water vapor, thus characterizing the evaporation part of the dewetting kinetics problem. We conclude with a kinetic model that accounts for our observations through a microscopic mechanism involving the interconversion among bulk water, water clusters, and individual water molecules in the gas phase. Overall, the approach presented here illustrates an application of femtosecond time-resolved experiments in the terahertz spectral range to the study of kinetic processes.

Estimation of the Global Equivalence Ratio of a Swirl Combustor from a Small Number of Absorption Spectra Using Machine Learning.

A new optical diagnostic method that predicts the global fuel-air equivalence ratio of a swirl combustor using absorption spectra from only three optical paths is proposed here. Under normal operation, the global equivalence ratio and total flow rate determine the temperature and concentration fields of the combustor, which subsequently determine the absorption spectra of any combustion species. Therefore, spectra, as the fingerprint for a produced combustion field, were employed to predict the global equivalence ratio, one of the key operational parameters, in this study. Specifically, absorption spectra of water vapor at wavenumbers around 7444.36, 7185.6, and 6805.6 cm-1 measured at three different downstream locations of the combustor were used to predict the global equivalence ratio. As it is difficult to find analytical relationships between the spectra and produced combustion fields, a predictive model was a data-driven acquisition. The absorption spectra as an input were first feature-extracted through stacked convolutional autoencoders and then a dense neural network was used for regression prediction between the feature scores and the global equivalence ratio. The model could predict the equivalence ratio with an absolute error of ±0.025 with a probability of 96%, and a gradient-weighted regression activation mapping analysis revealed that the model leverages not only the peak intensities but also the variations in the shape of absorption lines for its predictions.

A recommended line list for water vapor in the 12,969–13,418cm-1 interval

We have recently devoted two reports to the very weak absorption spectrum of water vapor in the 12,969 – 13,417 cm-1 region by high sensitivity cavity ring down spectroscopy (CRDS) [Vasilchenko et al. J. Quant. Spectrosc. Radiat. Transfer 275 (2021) 107,847; doi.org/10.1016/j.jqsrt.2021.107847; Vasilchenko et al. Molecular Physics e2051762; doi.org/10.1080/00,268,976.2022.2051762]. This spectral interval is important because it includes the region of the oxygen A-band near 760 nm. The achieved sensitivity allowed us to measure lines with intensity on the order of 10–29 cm molecule-1, about two orders of magnitude lower than the detectivity threshold of previous studies. A total of about 240 energy levels of H216O were newly determined. Our comparison to the W2020 empirical levels [Furtenbacher et al. J. Phys. Chem. Ref. Data 49 (2020) 043,103; doi.org/10.1063/5.0030680] led us to identify and correct about 300 W2020 energy levels of the main isotopologue differing from our energy value by more than 5 × 10–3 cm-1. In the present contribution, we consider in details the sources of the W2020 energy levels to identify the origin of these deviations. We confirm that more than 260 energy levels should be corrected but for the remaining thirty-two levels, the W2020 energy values are in fact, more reliable. As a result, we propose an improved list of energy levels retrieved from the CRDS data and a recommended line list for water vapor in natural isotopic abundance in the 12,969 – 13,417 cm-1 region, mostly based on the CRDS line parameters.

Direct measurement of the inertial-convective subrange above ocean surface waves

The −5/3 power law over the inertial subrange of the turbulence kinetic energy spectrum is one of the most well-known concepts in fluid physics. Obukhov and Corrsin extended the original hypothesis to a passive tracer, leading to the concept of an inertial-convective subrange. These postulates have been empirically validated in the atmospheric turbulence over land but have not been comprehensively studied in the marine air flow. During a recent oceanic campaign, the platform FLIP was deployed with an array of sensors to measure the perturbation wind velocity, temperature, and water vapor. Using these data, a previous study found that Kolmogorov's hypothesized −5/3 was not universally valid over the ocean. Here, we continue that work to analyze the spectrum of temperature and water vapor to empirically evaluate the theoretical extension by Obukhov-Corrsin. For temperature, the observed spectra were too noisy for thorough analysis; our conjecture for the source of noise and its implications for near-surface observations of atmospheric turbulence are discussed. For water vapor, we found strong agreement with the previous analysis of the kinetic energy spectrum. These findings corroborate (1) the theoretical notion of the scalar energy dissipation subrange driven by the inertial motions in the marine boundary layer and (2) evidence for non-Kolmogorov turbulence in the high Reynolds flow immediately above ocean waves. Our analysis shows a strong relationship with distance from the wavy surface; using linear extrapolation, we find that divergence from −5/3 persists in the lowest 25 m of the atmosphere.

Throughput-enhanced FTIR spectrometers with deep learning-based spectral recovery

Fourier transform infrared (FTIR) spectrometers are widely employed for spectroscopic characterization with high optical throughput, owing to the circular Jacquinot Stop (J-Stop). While the throughput increases with the J-Stop diameter, it has been theoretically and experimentally found that the divergent beam entering the Michelson interferometer induces spectral broadening and shifting, resulting in the obvious degradation of spectral resolution and wavenumber accuracy. This work has validated the deep learning-based spectral recovery for numerically eliminating the spectral distortions in a rapid and accurate way, effectively replacing the previously proposed time-consuming iterative calculation. Considering the influence of spectral complexity on the spectral recovery, the spectra are segmented and classified in terms of peak number with the convolutional neural network (CNN), before the parallel spectral reconstruction with a set of generative adversarial networks (GANs). The spectral recovery has been performed on the transmission spectra of water vapor collected by a commercial FTIR spectrometer, demonstrating that the spectra of 4 mm-diameter J-Stop with ∼12 times higher throughput can be recovered to coincide well with those of 1 mm-diameter J-Stop. With the enhanced throughput, the signal-to-noise ratio of FTIR spectrometers can be improved by >6 times for weak-light detection.

Multidimensional high-temperature field measurement method for flame based on near infrared radiation spectrum of water vapor

The temperature distribution is an important parameter in the design and optimization of :various engine types, and this paper begins by analyzing the temperature sensitivities of different waveband combinations. Based on an evaluation of the effects of self-absorption phenomena on the temperature measurement accuracy, a multidimensional temperature measurement method based on the integrated ratio of the intensity of the water vapor broadband radiation spectra is proposed. To address the multidimensional temperature inversion problem, the practicality of a nonlinear reconstruction approach is evaluated, and a multiple linear iteration algorithm is proposed. In addition, validation experiments are performed in the form of methane/oxygen laminar flame temperature measurements in combination with parallel rotating beam spectroscopy, and the results show that the method exhibits temperature measurement resolution of 10 K. The method proposed and developed in this work provides a new experimental concept for high-temperature measurements and is expected to provide reliable multidimensional temperature data for combustion chambers and plumes in engine ground experiments.

Accurate determination of line intensity of H[formula omitted]O near 7181 cm−1 : SI-traceable measurement using primary trace-moisture standard in N[formula omitted] gas

The absorption spectra of trace water vapor in N2 gas with a mole fraction of 500 nmol/mol in the pressure range of 20 kPa to 140 kPa were obtained near 7181 cm−1 using wavelength-meter-controlled cavity ring-down spectroscopy (WMC-CRDS). The reference gas (water vapor in N2 gas) was produced using a generation system of primary measurement standards for trace moisture in gases, where the amount of water vapor was measured using a gravimetric method. The obtained spectra of H2O were analyzed using a multispectrum fitting technique with a speed-dependent asymmetric Voigt profile (SDAVP). The values of the line intensity were determined with traceability to the International System of Units (SI). We could achieve the expanded uncertainty below 2 % for the line intensities of the strong lines.

DIAL hygrometer based on powerful laser diodes: calibration function and modulation of laser radiation

A differential absorption lidar method utilizing the spectral and energetic properties of high-power, pulsed laser diodes for remote sensing of atmospheric humidity is reported. The laser radiation of selected complementary laser diodes is multiplexed in dual spectral channels centered at optimal wavelength of 0.86µm and 0.911µm. Humidity profiles are retrieved integrating multiple resonance lines in the tunable range within the absorption spectrum of water vapor. The integral spectrum is less affected by the variable atmospheric pressure and temperature, which is an essential advantage allowing direct and reliable DIAL measurement.

Frequency comb-referenced cavity ring-down spectroscopy of natural water between 8041 and 8633 cm−1

The 1.25 µm atmospheric transparency window is of importance for a number of atmospheric applications. As a continuation of our previous works on the improvement of water vapor line parameters in the near infrared, the room temperature absorption spectrum of water vapor in natural isotopic abundance is recorded with unprecedented sensitivity between 8041 and 8633 cm−1, using comb-referenced cavity ring-down spectroscopy. The line positions and intensities of more than 5400 lines were retrieved. Their intensities range between 3.6 × 10−30 and 1.5 × 10−22 cm/molecule. The high sensitivity and low noise level of the recordings (αmin≈ 10−11 cm−1) allow for measuring more than 1600 new lines and determine their positions with an accuracy of about 10−4 cm−1 in the case of isolated features. The rovibrational assignments were performed using known experimental energy levels and calculated spectra based on variational calculations by Schwenke and Partridge. The final line list is assigned to more than 5400 transitions of the first six water isotopologues (H216O, H218O, H217O, HD16O, HD18O and HD17O). The measured line positions allow to determine the energy of 79 new levels of H216O, H218O, H217O, and HD16O, and to correct 139 previously reported term values. Although a good agreement is generally observed, the comparison to the HITRAN2020 spectroscopic database and to the W2020 transition frequencies reveals a number of discrepancies both for line positions and line intensities. The lack of traceability of some HITRAN line parameters and some biases in the derivation procedure of the W2020 energy levels are confirmed in the studied range. Validation tests of the theoretical values of the line intensities against measured values show both band-by-band variations of the deviations on the order of a few % and line-by-line fluctuations within a given band.

FT spectroscopy of water vapor in the 0.9 µm transparency window

Weak absorption spectrum of water vapor is recorded in the 0.9 µm transparency window using a Fourier transform spectrometer coupled with a 30-m base-length multipass cell. 780 vibration – rotation transitions of the H2O molecule were assigned on the base of accurate variational calculations, 410 of them are new. New experimental information is compared with the literature data and spectroscopic data base HITRAN2020. Significant distortions of the intensities of the (041)-(000) and (140)-(000) vibrational bands accepted in HITRAN2020 are discovered from the comparison with the experimental data. An accurate and detailed recommended list of the H216O absorption lines is reported in 9340–9790 cm−1 spectral region based on the experimental energy levels and variational calculation which reproduced the new intensity measurements in the best way.

Water vapor absorption spectroscopy and validation tests of databases in the far-infrared (50–720 cm-1). Part 1: Natural water

The rotational spectrum of water vapor in natural isotopic abundance has been recorded by high resolution (≈ 0.001 cm-1) Fourier transform spectroscopy at the AILES beam line of the SOLEIL synchrotron. The room temperature absorption spectrum has been recorded between 50 and 720 cm-1 using five pressure values up to 7 mbar and an absorption pathlength of 151.75 m. Line parameters were retrieved for the five recorded spectra and then combined in a global list of 2867 water lines with line intensity ranging between a few 10–26 and 10–19 cm/molecule. 454 of the measured lines are newly observed by absorption spectroscopy. The spectral calibration based on a statistical matching with about 700 accurate reference line positions allows for line center determinations with an accuracy of 5 × 10–5 cm-1 for well isolated lines of intermediate intensity.The large spectral coverage, the achieved position accuracy and sensitivity of the constructed line list make it valuable for validation tests of the current spectroscopic databases. Six water isotopologues (H218O, H216O, H217O, HD18O, HD16O, and HD17O) were found to contribute to the spectrum. The line position comparison to the recent HITRAN2020 spectroscopic database and to the W2020 line lists of H216O, H217O and H218O, [Furtenbacher et al. J. Phys. Chem. Ref. Data 49 (2020) 043103; https://doi.org/10.1063/5.0030680] shows an overall very good agreement. Nevertheless, a number of significant deviations are observed. Part of them has an amplitude largely exceeding the W2020 claimed error bars. On the basis of the experimental data at disposal for the main isotopologue (1310 transitions), the best agreement is achieved with the positions calculated using the effective Bending–Rotation Hamiltonian [Coudert et al. J Mol Spectrosc 2014;303:36–41. https://doi.org/10.1016/j.jms.2014.07.003].

Cavity ring down spectroscopy of water vapour near 750 nm: a test of the HITRAN2020 and W2020 line lists

Cavity ring down spectroscopy (CRDS) is used to measure with unprecedented sensitivity and accuracy the weak water vapour spectrum in the 13,171–13,417 cm−1 region. A total of more than 1400 water lines are rovibrationally assigned to four isotopologues in natural isotopic abundance (H2 16O, H2 18O, H2 17O and HD16O), leading to the determination of 151 new levels and correction of 160 levels. The review of previous experimental works in the region is discussed. The comparison to the recent HITRAN2020 spectroscopic databases and to the W2020 line lists [Furtenbacher et al. J. Phys. Chem. Ref. Data 49 (2020) 043103; doi:10.1063/5.0030680] shows important discrepancies both for line positions and line intensities. A significant fraction of the W2020 line positions is inaccurate and shows deviations compared to measurements largely exceeding their claimed error bars. Line intensities are poorly predicted by available ab initio calculations in the considered region. A recommended line list mostly based on the present CRDS measurements is proposed.

A novel parametric level set method coupled with Tikhonov regularization for tomographic laser absorption reconstruction

• Clear topological boundary of the combustion reaction flow is obtained. • Variations of temperature and species concentration in the chamber are diagnosed. • The accuracy, robustness and noise immunity of proposed method are the best. • The diagnosis of reaction flow with a large boundary gradient is highly accurate. Temperature and concentration distributions are essential parameters for understanding physicochemical processes in the in-cylinder/in-chamber engine and developing efficient combustion technology. However, due to the limited measurement space in the combustion chamber and the strong vibration and flame emission during the operation of the equipment, it is difficult to measure the multi-physical field by the traditional measurement technology. Tomographic laser absorption reconstruction based on laser absorption spectroscopy is a promising diagnostic for mapping the temperature and concentration images because it reduces the need for optical access. Since the inherently ill-posedness of the tomographic inverse problem leads to artifacts, low accuracy, poor robustness, and inability to visualize dynamic flow boundaries in the measured temperature and concentration images, the reconstructed algorithm must contain additional information to promote the presumed solution attributes. To address these problems, we propose a novel algorithm called Gaussian parametric level set method coupled with regularized Landweber to obtain the posterior topological structure of the turbulent reaction flow, which can compensate for the lack of a priori knowledge of the tomographic inverse problem. Numerical validation and algorithm comparison are performed using absorption spectra of water vapor at 7153.748 cm −1 and 7154.353 cm −1 and multi-angle parallel beam arrangement. The proposed approach significantly improves reconstructed quality and has excellent robustness. Even if the sparsely sampled data contains 10% random noise, the root mean square error is still within 0.12 in the temperature range 296–1600 K, approximately 50% of the error of the classical tomography methods. And the standard deviation is about 10% of the reconstructed results of Landweber. The proposed new method can obtain clear dynamic flow field boundaries, eliminate artifacts, improve measurement accuracy and robustness, and its applicability in harsh environments will benefit the supervision of combustion equipment, fuel utilization, pollutant control and optimal design of new combustion systems.

Study of a Mode Separation Due to Polarization Existing in a Cavity-Enhanced Absorption Spectroscopy.

A special phenomenon of resonance mode separation is observed during the study of a high sensitivity folded-cavity enhanced absorption spectroscopy for the measurement of trace gases. The phenomenon affects the measurement of gas absorption spectrum in the cavity. This resonant mode separation phenomenon of the resonant cavity is different from the resonant modes previously observed in linear-cavity enhanced absorption spectroscopy systems. To explore the mechanism of this phenomenon, a series of hypotheses are proposed. The most likely reason among these hypotheses is based on the different reflectance properties of the plane mirror at the fold of the cavity for S-polarized light and P-polarized light. Based on the matrix calculation method, the different reflectance and phase shift of the plane mirror for S-polarized light and P-polarized light are analyzed theoretically, and the results are in better agreement with the phenomena observed in the experiment. Finally, in order to eliminate the resonant mode separation phenomenon, line polarizers were added. By improving the system, the cavity enhanced absorption spectrum of residual water vapor in the cavity was successfully measured, and a minimum detectable absorption coefficient of αmin = 7.6 × 10−9 cm−1 can be obtained in a single laser scan of 10 s.

Analysis of the [formula omitted], [formula omitted], [formula omitted] and the [formula omitted] bands of HT[formula omitted

We present the ν1+2ν2, ν2+ν3, ν1+ν3 and the 2ν2+ν3 bands of HT16O that have been analyzed for the first time using a high-resolution infrared spectrum of tritiated water vapour. The spectrum has been recorded from a custom-built light-pipe cell at room temperature using a Bruker 125HR Fourier-transform spectrometer at a resolution of.0075 cm−1.In the range from 4715 to 5300 cm−1, we report 446 new experimental line positions assigned to the ν1+2ν2 and 611 new line positions belonging to the ν2+ν3 band.In the range of 5830 to 6440 cm−1, 165 new experimental line positions were determined for the ν1+ν3 band and 81 line positions were assigned to the 2ν2+ν3 band.The analysis reveals a systematic shift of the individual line positions compared to the variationally calculated line positions from the Tomsk database which uses the potential energy surface of Partridge and Schwenke. Furthermore, it is observed that the differences between prediction and experiment are depending on the rotational quantum number Ka′.For each band, the assigned lines were used to determine the spectroscopic constants in the A-reduced Watson Hamiltonian.With a total of 1303 new line positions for HT16O we roughly double the number of experimental line positions for this species.

Calibration method of instrument line shape for infrared radiometer

Interferometric infrared spectral radiometer has high luminous flux and large passing aperture, so the spectral data collected by the instrument are the convolution of the target spectral data and the instrument line shape (ILS). The main factors affecting the ILS include truncation effect, finite field of view effect, off-axis effect, defocus effect and relative position of detector and so on. In this paper the truncation effect, finite field of view effect, off-axis effect and defocus effect on ILS are expounded. These ILS errors all cause the ideal spectrum to drift towards the low wave number and widen. In this paper, the ideal absorption spectrum of water vapor is simulated by the line-by-line integration, through using MATLAB software and combining with the data of water vapor spectrum in HITRAN database, and the quantitative relationship between the error of instrument linear function and spectral distortion is established. According to the simulation results, a factor weight correction algorithm is proposed. It is believed that with this method, the error spectrum caused by ILS has the same optical properties as the ideal spectrum, but the optical path difference is different. Therefore, the coefficient matrix <i> <b>H</b> </i> can be constructed to establish the quantitative relationship between the error spectrum and the ideal spectrum, and the error spectrum can be corrected by using Landweber iterative algorithm. In this paper, the simulation data of water vapor absorption are used to verify the factor weight correction algorithm, and the spectral drift decreases from 0.51 cm<sup>–1</sup> to less than 0.01 cm<sup>–1</sup>. The accuracy of the factor weight correction algorithm is verified by the experimental observation of the standard black body with self-developed interferometric infrared spectral radiometer. The spectral drift of the measured data decreases from 0.226 cm<sup>–1</sup> to 0.012 cm<sup>–1</sup>, and the corrected spectral data are more accurate.

Study on dual-optical paths for simultaneous measurement method of water vapor absorption spectrum in 1 μm band

Based on the gas multi-pass absorption cell with dual-optical paths (long optical path: 72.46 m; short optical path: 36.23 m), a measurement method of simultaneously detecting water vapor absorption spectra is advanced. Combining with a narrow line-width external cavity diode laser and a high-precision Fabry-Perot etalon, a high-resolution simultaneous measurement device with dual-optical paths for water vapor absorption spectra in 1 μm band is developed. Since the external cavity diode laser has excellent polarization characteristics which could be combined with a half-wave plate and a polarization beam splitter to implement the laser transmissions in dual-optical paths simultaneously. Both the multi-pass absorption cell and the Fabry-Perot etalon in the measurement device have pressure and temperature control units, which are utilized for achieving ambient stability. The free spectral range of Fabry-Perot etalon is accurately measured by the method of optical comb frequency. Corresponding free spectral range with a deviation of only 0.02 % from the theoretical value is obtained to be a value of 749.52 MHz, and the influence of temperature on the frequency shift of etalon is less than 1 % of the measured value. The stability of the pressure and the temperature in the dual-optical path gas multi-pass absorption cell in the system are evaluated in detail, and the calculated relative errors are not more than 0.03 % and 0.02 %, respectively. At a temperature of 300 K, the system is used to measure the absorption spectra of water vapor at 9152.53 cm<sup>–1</sup> from 400 Pa to 2000 Pa on dual-optical paths, then the integrated absorbance and Lorentzian line-width of water vapor for long optical path and short optical path are inverted by fitting absorption spectra with Voigt profile respectively. The absorption line intensities and self-broadening coefficients are acquired by performing linear fitting to the integrated absorbance and Lorentzian line-width under different pressures. And the relative deviations of the average values of the dual-optical path absorption line intensities (converted to the reference temperature of 296 K) and the self-broadening coefficients and the corresponding data of the HITRAN2016 database are 0.78 % and 3.8 %, respectively. Consequently, the feasibility of the dual-optical path simultaneous measurement method and the reliability of the measurement device are demonstrated by the results.

Time series Fourier transform infrared spectroscopy for characterization of water vapor sorption in hydrophilic and hydrophobic polymeric films

This work investigates the nature of the molecular interactions between water vapor and polymers using time series Fourier transform infrared (FTIR) spectroscopy. A detailed analysis of the frequency shifts and relative peak intensities led to the conclusion that polyvinyl alcohol (PVOH) sorbed a large quantity of water vapor molecules, resulting in swelling and dissolving of polymer crystallites. Difference spectra were calculated to investigate spectral changes occurring upon sorption by dividing the spectra of polymers during the sorption time series by the spectrum of the dry sample and subsequently subtracting the water vapor spectrum. Based on the absorbance area of the OH stretching vibration region (4000–3000 cm-1) in difference spectra, the amount of water sorbed was significantly higher in poly-L-lactic acid (PLLA) and polyvinyl chloride (PVC) than in polyethylene (PE) and polytetrafluoroethylene (PTFE), increasing with the hydrophilicity of the surface. The OH stretching band of difference spectra shifted from 3499 cm-1 for PVC, to 3416 cm-1 for PE and finally to 3387 cm-1 for PTFE, indicating a more strengthened hydrogen-bonding network in the PTFE matrix upon water vapor sorption.

The far-infrared spectrum of 18O enriched water vapour (40–700 cm−1)

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