HITRAN Database Research Articles

NO-CO Monitoring Technique Using Ultraviolet Absorption Spectroscopy and Tunable Diode Laser Absorption Spectroscopy in High-Temperature and High-Pressure.

The single parameter detection of temperature (H2O) is no longer sufficient for the absorption combustion diagnosis. There is a huge demand for simultaneous computed tomography (CT) diagnosis of multi-parameters. This paper studied CO and NO, two representative combustion products based on tunable diode laser absorption spectroscopy (TDLAS) and ultraviolet absorption spectroscopy (UVAS). Different from the research on low detection limits, the absorbance needs to be corrected in high-temperature and high-pressure conditions due to the equipment performance of the CT system. A high-temperature and high-pressure chamber system was applied for the basic absorbance experiment. The corrected absorbance databases of 2325.2/2326.8 nm for CO, and 215/226 nm band for NO were established. The corrected absorbance databases were first compared with the HITRAN and ExoMol databases. The accuracy of the corrected databases was also analyzed by standard gas with 1D detection in the high-temperature and high-pressure chamber and two-dimensional (2D) reconstruction in a customed CT cell. The maximum CO mean relative error (MRE) of the 2D results is 2.75% while the maximum NO MRE is 4.99%. This study provides a basis for research on the CO and NO distribution in high-temperature and high-pressure combustion fields.

MARVEL Analysis of the Measured High-resolution Spectra of 12C16O

Abstract The Measured Active Rotational–Vibrational Energy Levels (MARVEL) algorithm is used to determine accurate empirical rotational–vibrational energy levels for the ground electronic state of the diatomic 12C16O molecule. 2293 energy levels have been obtained through a careful analysis of lines measured and assigned in high-resolution experimental spectra reported previously in 68 publications. Out of the 19,399 (7955) measured (unique) transitions in the limited wavenumber range of 0–14,470 cm−1, an analysis of the resulting experimental spectroscopic network (SN) validates 19,219 (7795), and only 11 transitions had to be deleted from the SN assembled (note that transitions within floating components of the SN cannot be validated). The measured transitions span states with vibrational and rotational quantum numbers less than or equal to 41 and 123, respectively, with the highest validated energy level lying at 67,148.1 cm−1. The validation procedure covers all transitions with a one-photon absorption intensity larger than 10−30 cm molecule−1 at 296 K. The validated line centers and the empirical rovibrational energy levels of 12C16O, with appropriate uncertainties and assignments, are provided in the appendix to this paper. Detailed comparisons are made with several existing data sets, such as the Kurucz and the HITRAN databases, NIST-certified wavelengths, and the list of lines protected by the International Astronomical Union, revealing occasional discrepancies.

Absolute line strength measurements of HO2 radical in the OO-stretching fundamental band between 1088 and 1124cm-1 using time-resolved dual-comb spectroscopy.

Absolute line strength measurements of hydroperoxyl (HO2) radical in the OO-stretching (ν3) fundamental band have been performed by means of mid-infrared time-resolved dual-comb spectroscopy. By employing two sets of dual-comb spectrometers, high-resolution time-resolved spectra of HO2 and HCl, formed in the photolysis reaction system of Cl2/CH3OH/O2, could be, respectively, measured near 1123 and 3059cm-1. With kinetic simulations, spectral analysis of both HO2 and HCl, as well as the accurate line strength of the HCl R(9) transition at 3059.316cm-1, an absolute line strength of the ν3 131,13 ← 121,12 F1,2 transitions in HO2 at 1122.983cm-1 was first determined to be 1.80 × 10-20cmmolecule-1 with a small uncertainty down to 4% under the conditions with low initial concentrations of Cl radical (1.63-1.81 × 1013moleculecm-3). Furthermore, broadband high-resolution spectra of the ν3 fundamental band of HO2 were recorded in the range of 1088-1124cm-1 with an average spectral resolution of 0.002cm-1. By contour fitting the measured broadband spectra with PGOPHER, the line strengths of hundreds of rovibrational transitions were obtained relative to the well-determined HO2 lines at 1122.983cm-1, and those values were observed to be higher than those tabulated in the HITRAN database by a factor of ∼2.8. Moreover, the absolute band strength of the ν3 fundamental band in HO2 was derived to be 22.3 km mol-1 with an uncertainty of 5%. This work providing precise and detailed spectral data would be crucial in revisiting the theoretical modeling of HO2 geometry and updating the database of the HO2 radical.

Broadband photothermal spectroscopy with a mid-infrared quantum cascade laser frequency comb.

We demonstrate a broadband photothermal spectroscopy in the mid-infrared region using a quantum cascade laser frequency comb operating between ∼7.7 and ∼8.2 µm covering a frequency range of ∼70 cm-1. The photothermal spectroscopy technique employs a Mach-Zehnder interferometer operating in a pump-probe configuration, where the mid-infrared pump beam is modulated by a Fourier transform spectrometer. A 76-m Herriott-type multipass cell is used for signal enhancement. As a proof-of-concept, we have measured the photothermal spectra of nitrous oxide that show good agreement with the HITRAN database. A minimum detection limit of 83 ppb of nitrous oxide in nitrogen is estimated from a broadband photothermal spectrum with 9.9 GHz spectral point spacing and acquired over 78 minutes. This detection scheme also provides over three orders of magnitude of photothermal signal linearity with gas concentration. This spectroscopic method combines the functionality of high sensitivity and background-free detection of photothermal spectroscopy as well as broadband mid-infrared operation of quantum cascade laser frequency comb, which could find applications in trace gas sensing systems that benefit from these features.

Coherent control in quartz-enhanced photoacoustics: fingerprinting a trace gas at ppm-level within seconds

Quartz-enhanced photoacoustic spectroscopy (QEPAS) has become a versatile tool for detection of trace gases at extremely low concentrations, leveraging the high quality (Q)-factor of quartz tuning forks. However, this high Q-factor imposes an intrinsic spectral resolution limit for fast wavelength sweeping with tunable laser sources due to the long ringing time of the tuning fork. Here, we introduce a technique to coherently control and damp the tuning fork by phase-shifting the modulation sequences of the driving laser. Particularly, we send additional laser pulses into the photoacoustic cell with a timing that corresponds to a π phase shift with respect to the tuning fork oscillation, effectively stopping its oscillatory motion. This enables acquisition of a complete methane spectrum spanning 3050–3450 nm in just three seconds, preserving the spectral shape. Our measured data is in good agreement with the theoretically expected spectra from the HITRAN database when convolved with the laser linewidth of . This will leverage the use of QEPAS with fast-sweeping OPOs in real-world gas sensing applications beyond laboratory environments with extremely fast acquisition speed enabled by our coherent control scheme.

Himitsu Bako of NO2 Mixtures: Characterization of NO2 Reference Material Using FTIR Spectroscopy in Middle Infrared Region

In this work, we investigate how much information a conventional infrared spectroscopic technique (FTIR) can yield for NO2 reference materials in the range of concentrations between 100 to 2500 μmol/mol. The amount fraction of 100 μmol/mol corresponds to the actual maximum for NO2 emissions by modern Euro 6 vehicles and is suitable for Portable Emissions Measurement Systems (PEMS) calibration. A set of measurements of four reference mixtures was performed. For the analysis, we developed an efficient and simple algorithm, based on the integration of rovibrational bands, yielding the molar fractions of NO2 (including dimer) and several impurities, such as N2O and HNO3. It resembles a Japanese puzzle box, Himitsu Bako, since different mixture components should be addressed in a certain order to unravel a complete composition. The algorithm was successfully applied to the recorded spectra. For example, the uncertainties for low NO2 amount fractions were shown to be limited essentially by the quality of reference spectroscopic data for the monomer (HITRAN database in the current work), and not by the measurement procedure. Shortcomings, further development, and improvements of the experimental set-up as well as of the evaluation algorithm are addressed.

Simulation of infrared polarized radiation transmission characteristics of high-temperature tail flame based on Monte Carlo method

Infrared polarization radiation of aircraft targets after being transmitted through high-temperature exhaust plumes is an important basis for infrared detection equipment to detect, identify, track and warn aircraft. At present, most of the studies on the transmission characteristics of gas polarized radiation focus on the visible wavelength band, and the research object is mainly the atmospheric environment. The study of infrared polarization radiation transmission characteristics in the special gas environment of high-temperature exhaust plume is still insufficient. In this paper, the Monte Carlo method is used to model the transmission of infrared polarized light in a high-temperature exhaust plume, and the absorption coefficients of H<sub>2</sub>O in 2.5−3.3 μm band and CO<sub>2</sub> in 4−5 μm band are calculated using the HITRAN database. The multiple scattering process of photons in the exhaust plume space is simulated, and the changes of the cosine of motion direction and cosine of vibration direction of the photons in the collision events are analyzed at the microscopic level. Additionally, the photon characteristics are statistically analyzed based on the principles of calculating polarization and transmittance. Based on the simulation results, the changes of radiative transmittance and polarization at different transmission distances are compared with each other, and the effects of exhaust plume temperature, pressure, gas component concentration, and detection wavelength on the transmission characteristics of infrared polarized light are analyzed as well. The experimental results demonstrate that the error between the calculated radiative transmittance in this study and the HITRAN database is within 2%. The effects of temperature and pressure on the transmission characteristics of polarized light become increasingly significant as the distance increases. The pressure is negatively correlated with transmittance and polarization, while the effect of temperature is related to the gas type and the temperature range. The radiant transmittance and polarization degree decay exponentially with the absorption coefficient and transmission distance of the gas in the exhaust plume space. Different detection wavelengths also lead to differences in the transmission characteristics of polarized light.

Measurement of carbon monoxide pressure broadening and temperature dependence coefficients in the 1 ← 0 band.

Two laser absorption spectroscopy (LAS)-based spectrometers have been developed for measuring carbon monoxide (CO) pressure broadening and temperature dependency coefficients in the 1 ← 0 band. Using a scanned-wavelength LAS at 140 Hz, pressure broadening coefficients of four CO transition lines P(16), P(20), P(26), and P(27), perturbed by Ar, He, H2, O2, N2, CO2, and Air have been systematically measured in a gas cell using a consistent metrological approach. Results indicate that the CO pressure broadening coefficient decreases monotonically as the line number |m| increases. The variation of pressure broadening coefficients at different buffer gases follow a consistent trend for all four measured lines: CO-H2 and CO-Ar show the highest and lowest pressure broadening coefficients, respectively. Compared to the literature results with relatively large uncertainties or even unavaible uncertainty information, the uncertainty of measured pressure broadening coefficients is below 1% for most cases. Further, using a scanned-wavelength LAS at 20 kHz, temperature dependence coefficients of P(20) in Ar, He, N2 and CO2 were measured at a temperature range of 430-1648 K in a shock tube. With this rapid scan frequency, the spectrum between incident shock and reflected shock was also used for temperature dependence coefficient calculation. The uncertainty of the measured temperature dependence coefficients are under 6.2%. Toward combustion systems as an application case, the CO mole fraction during CH4 oxidation in the shock tube was quantified using a fixed-wavelength LAS. The results reveal that the uncertainty in CO mole fraction was reduced by a factor of 2.7 when using the line parameters obtained in this study compared to those from the HITRAN database. Thus, the newly measured data with low uncertainties substantially enhance the spectroscopic database, enabling more precise CO mole fraction quantification across a range of application scenarios such as environmental monitoring, industrial control, safety monitoring, medicine, astronomy, and scientific research.

Tunable Continuous-Wave Terahertz Generator based on Difference Frequency Generation with DAST Crystal

Terahertz (THz) wave has been widely investigated recently due to the perspective of reflecting fingerprint characteristic of samples. As a promising method, THz technology has attracted great interests in various applications, especially in biological imaging, environmental monitoring, non-destructive evaluation, spectroscopy and molecular analysis. To reveal the intramolecular vibration/rotation information of various compound, of which linewidth of absorption lines typically in GHz or even MHz range, THz wave with wide tunability, narrow-linewidth, high frequency accuracy as well as high power stability is required. Currently, the linewidth with GHz level and low SNR at higher frequency still restrict its further applications in reveal intramolecular information. In this paper, the thermal distribution characteristics of DAST crystals based on diamond substrates under continuous laser pumping conditions were theoretically studied by COMSOL Multiphysics, and the effectiveness of diamond substrates in dissipating heat from DAST crystals was experimentally verified. Then, a narrow linewidth and tunable continuous-wave terahertz source with organic crystal has been demonstrated. Two narrow-linewidth CW fiber lasers were used as the pump sources for difference frequency generation. The terahertz wave can be continuously tunable in the range of 1.1-3 THz. The maximum output power of 3.39 nW was obtained at 2.493 THz. The power fluctuation in 30 minutes was measured to be 2.19%. In addition, the generated THz wave has a high polarization extinction ratio of 9.44 dB. Using this CW-THz source for high-precision spectral detection of air with different humidity, the results correspond well with the gas absorption spectral lines in the Hitran database, proving that the CW-THz source has narrow linewidth, high frequency accuracy and stability. Therefore, it could promote the practical prospect of tunable CW-THz source, which will have good potential in THz high-precision spectroscopic detection and multispectral imaging.

Line-shape parameters and their temperature dependence for self-broadened CO2 lines in the 296 K- 1250 K range by requantized classical molecular dynamics simulations

Line-shape parameters and their temperature dependence for self-broadened CO2 lines in the 296 K- 1250 K range by requantized classical molecular dynamics simulations

Spectral Calibration of the Spectrometer on Board the Colombian FACSAT-2 Satellite Mission

This paper presents the results of the integration, commissioning, and in-orbit calibration of the ARGUS 2000 SWIR wavelength spectrometer onboard the Colombian FACSAT-2 satellite, Colombia’s first satellite used for the measurement of greenhouse gases (GHG). The satellite has been in orbit for approximately one year, gathering spectral signatures in order to characterize the data and perform calibration. The calibration represents a certain behavior following a second-order adjustment. For data analysis, retrieval algorithms have been developed to obtain synthetic spectra using the Genspect 1.2 software code. These synthetic spectra were obtained from the spectroscopic data associated with atmospheric gases (H2O, O2, CO, and CO2), which are stored in the HITRAN database. Attempting to achieve a more accurate simulation of the experimental spectrum, certain instrumental parameters have been incorporated into the synthetic spectrum, including the resolution of the spectrometer, the field of view (FOV) angle of observation, the limited quantum efficiency of detection, and the slit function. As a result, six slit functions were tested, with the Gaussian and the diffraction functions proving to be the most effective. Finally, a profile of Total Carbon Column Observing Network (TCCON) concentrations was used for comparison with a spectral signature acquired by FACSAT-2, resulting in a close match between the synthetic spectrum and the measured spectrum.

On-chip mid-infrared dispersive wave generation at targeted molecular absorption wavelengths

The mid-infrared wavelength region is one of the most important spectral ranges for a variety of applications in monitoring and controlling molecules due to the presence of strong characteristic absorption modes of many molecules. Among various mid-infrared light sources, on-chip supercontinuum sources have garnered significant attention for their high spatial coherence, broad spectral bandwidth, compact size, and dispersion controllability. However, generating a supercontinuum that extends into the molecular fingerprint region typically requires high-energy mid-infrared pump pulses from complex optical systems. In contrast, supercontinuum generated with 1550 nm pump sources, which are generally more compact, has shown limited access to the molecular fingerprint region. In this study, we developed an on-chip supercontinuum source with a dispersive wave generated at a targeted wavelength of up to 4800 nm using a coupled pump energy of about 25 pJ. The pump pulses at a wavelength of 2340 nm were generated from a relatively compact Cr:ZnS laser oscillator. The wavelengths of the generated dispersive waves closely matched the numerically predicted wavelengths. To demonstrate the applicability of the generated dispersive waves for spectroscopic purposes, molecular absorption spectroscopy was performed on the fundamental vibrational modes of 12CO2, 13CO2, and N2O. In addition, their pressures were quantitatively estimated using cepstrum analysis on the measured absorption spectra. The uncertainty in the measured pressure was close to the theoretical limit determined by the uncertainties in the absorption line shape parameters in the HITRAN database, demonstrating the potential of this mid-infrared light source for advanced spectroscopic applications.

Expert Assessment of the Accuracy of Determining the Intensities of Vibrational-rotational Lines of Water Vapor in the HITRAN Database in the Range 2500–6500 cm–1

Expert Assessment of the Accuracy of Determining the Intensities of Vibrational-rotational Lines of Water Vapor in the HITRAN Database in the Range 2500–6500 cm–1

Experimental Study to Visualize a Methane Leak of 0.25 mL/min by Direct Absorption Spectroscopy and Mid-Infrared Imaging

Tunable laser spectroscopy (TLS) with infrared (IR) imaging is a powerful tool for gas leak detection. This study focuses on direct absorption spectroscopy (DAS) that utilizes wavelength modulation to extract gas information. A tunable interband cascade laser (ICL) with an optical power of 5 mW is periodically modulated by a sawtooth injection current at 10 Hz across the methane absorption around 3271 nm. A fast and sensitive thermal imaging camera for the mid-infrared range between 3 and 5.7 µm is operated at a frame rate of 470 Hz. Offline processing of image stacks is performed using different algorithms (DAS-F, DAS-f and DAS-2f) based on the Lambert–Beer law and the HITRAN database. These algorithms analyze various features of gas absorption, such as area (F), peak (f) and second derivative (2f) of the absorbance. The methane concentration in ppm*m is determined on a pixel-by-pixel analysis without calibration. Leak localization for methane leak rates as low as 0.25 mL/min is accurately displayed in a single concentration image with pixelwise sensitivities of approximately 1 ppm*m in a laboratory environment. Concentration image sequences represent the spatiotemporal dynamics of a gas plume with high contrast. The DAS-2f concept demonstrates promising characteristics, including accuracy, precision, 1/f noise rejection, simplicity and computational efficiency, expanding the applications of DAS.

Accurate reference spectra of HD in an H2–He bath for planetary applications

Context. The hydrogen deuteride (HD) molecule is an important deuterium tracer in astrophysical studies. The atmospheres of gas giants are dominated by molecular hydrogen, and the simultaneous observation of H2 and HD lines provides reliable information on the D/H ratios on these planets. The reference spectroscopic parameters play a crucial role in such studies. Under the thermodynamic conditions encountered in these atmospheres, spectroscopic studies of HD require not only the knowledge of line intensities and positions but also accurate reference data on pressure-induced line shapes and shifts. Aims. Our aim is to provide accurate collision-induced line-shape parameters for HD lines that cover any thermodynamic conditions relevant to the atmospheres of giant planets, namely any relevant temperature, pressure, and perturbing gas composition (the H2–He mixture). Methods. We performed quantum-scattering calculations on our new, highly accurate ab initio potential energy surface (PES), and we used scattering S matrices obtained in this way to determine the collision-induced line-shape parameters. We used cavity ring-down spectroscopy to validate our theoretical methodology. Results. We report accurate collision-induced line-shape parameters for the pure rotational R(0), R(1), and R(2) lines, the most relevant HD lines for investigations of the atmospheres of the giant planets. Besides the basic Voigt-profile collisional parameters (i.e., the broadening and shift parameters), we also report their speed dependences and the complex Dicke parameter, which can influence the effective width and height of the HD lines up to almost a factor of 2 for giant planet conditions. The sub-percent-level accuracy reached in this work is a considerable improvement over previously available data. All the reported parameters (and their temperature dependences) are consistent with the HITRAN database format, hence allowing for the use of the HITRAN Application Programming Interface (HAPI) for generating the beyond-Voigt spectra of HD.

NH3 line broadening coefficients and intensities measurement and impurities determination in emerging applications: CCUS, Biomethane and H2

NH3 line broadening coefficients and intensities measurement and impurities determination in emerging applications: CCUS, Biomethane and H2

Accurate Infrared Line Lists for 20 Isotopologues of CS2 at Room Temperature

To facilitate atmospheric and spectroscopic studies of carbon disulfide, or CS2, in both planetary and exoplanetary atmospheres, we adopt the “Best Theory + Reliable High-resolution Experiment” algorithm to generate semiempirical IR line lists for the 20 most abundant CS2 isotopologues, denoted as Ames-296K. The IR lists are computed using the Ames-1 potential energy surface, refined using the experimental transition set and an ab initio dipole moment surface fitted from CCSD(T)/aug-cc-pV(T/Q/5+d)Z dipoles extrapolated to a one-particle basis set limit. The IR lists cover the range of 0–10,000 cm−1, with an S 296K cutoff at 10−31 cm−1/molecule·cm−2 (abundance included). A “natural” IR line list at 296 K includes about 10 million lines of the 20 isotopologues, with their intensities scaled by the corresponding abundances. The zero-point energy, partition functions, and abundances are reported for each isotopologue. The energy levels in the global effective Hamiltonian model for 12C32S2 are adopted to improve the line position accuracy. This new IR list for the main isotopologue is denoted as A+I.296K. Reliable HITRAN2020 line positions are also utilized to improve the accuracy of the 32S12C34S, 32S12C33S, and 32S13C32S isotopologue line lists. The final composite line list is validated against Pacific Northwest National Laboratory experimental cross sections, showing excellent agreement. The agreement supports the quality of the composite line list and the power of synergy between experiment and theory. The new data are proposed for use in updating and expanding the CS2 data in HITRAN and other high-resolution IR databases. Supplementary files are available in Zenodo and AHED.

Analysis of the rotationally-resolved 3.3 µm region of C2H4 in natural isotopic abundance

Analysis of the rotationally-resolved 3.3 µm region of C2H4 in natural isotopic abundance

High-resolution investigation of the spin-rotation doublets of 14NO2 at 6.2 µm mid-infrared region using cavity ring-down spectroscopy

High-resolution investigation of the spin-rotation doublets of 14NO2 at 6.2 µm mid-infrared region using cavity ring-down spectroscopy

Refined line-shape parameters for CO lines broadened by air predicted from requantized classical molecular dynamics simulations

Refined line-shape parameters for CO lines broadened by air predicted from requantized classical molecular dynamics simulations