Wavenumber Difference Research Articles

Near-infrared microscopy reveals diabetic nephropathy in ob/ob mice

Diabetic nephropathy (DN) is a major cause of global kidney failure. While histological kidney biopsy is the gold standard for diagnosis, it primarily reveals tissue morphology. In contrast, near-infrared (NIR) microscopy offers a label-free method for detailed molecular characterization of kidney tissue. Hematoxylin and eosin-stained kidney tissue samples from 17 ob/ob mice with DN and 14 healthy mice were examined using Fourier transform-NIR microscopy. Four different spectra were obtained from both the mesangium and tubulus. NIR spectral analysis unveiled distinct differences in wavenumbers between DN-affected and healthy kidneys, notably in the carbohydrate and protein-associated region (5500-4200 cm−1). In the mesangium, DN tissue samples exhibited higher median values at 4235 cm−1, 4659 cm−1, 4844 cm−1, 4906 cm−1, and 5222 cm−1 compared to controls (P < 0.05, P < 0.01, P < 0.05, P < 0.05 and P < 0.001, respectively). In tubular spectra, higher median values were found at 4258 cm−1, 4659 cm−1, 5222 cm−1, and 5346 cm−1 in the DN group (P < 0.01, P < 0.05, P < 0.05 and P < 0.01, respectively). These spectral differences strongly correlated with metabolic, histologic, and urinary parameters, providing valuable DN progression insights. The classification model achieved a visible clustering between the control and DN group for both the mesangial and tubular measurements. NIR microscopy demonstrated significant spectral differences between DN and healthy kidney tissues in mice, hinting at its potential for providing chemical insights, aiding in more accurate diagnoses, and offering a foundation for further clinical exploration and potential therapeutic advancements in DN.

Generation of nano-to-microplastics from polypropylene surfaces via femtosecond laser ablation in liquids with different viscosities

Preparation of polypropylene (PP) nano and microparticles, crucial for investigating the effects of plastics on both human health and the environment, presents a significant and immediate challenge. Utilizing an fs laser system in different liquid mediums such as water, dodecane, and hexadecane, we have successfully generated PP particles with sizes ranging from 1.8 to 4911 nm. This outcome is partly attributed to the constraint on plasma expansion caused by the viscosity of the liquid media. We investigated the areas of material removal and observed a transition from ordered to disordered removal patterns during this process. The formation of filaments and pillars within the material removal cavity, along with the deposition layer at the cavity edge, primarily occurred due to insufficient plasma formation at low laser energy levels. Furthermore, we observed neck-shaped filaments and nano cracks on the deposition surface, which were attributed to the heat effect during laser interaction with the PP substrate. Moreover, we collected distinct nano-Fourier transform infrared spectroscopy (FTIR) signals from both the nanoparticle area and the deposition layer, revealing a 2 cm−1 wavenumber difference between the two regions. This discrepancy proved to be a valuable method for distinguishing between the nanoparticle area and the deposition layer.

Precision evaluation of Raman densimetry for carbon dioxide: improvement by correction for the drift effect.

To evaluate the precision of the wavenumber difference between the two main Raman bands of C O 2 (designated as Δ, an index of C O 2 density), we performed theoretical calculations for the uncertainties of the peak positions of the C O 2 Raman bands, and measured Raman spectra of C O 2 under the conditions used for the calculations. The Δ precision improves with increased peak intensity, but the peak intensity-precision relation does not hold beyond an intensity threshold corresponding to the measurement time of 1-2min. Correction for temporal variation of Δ by fitting a linear function to the data distribution improved the Δ precision to ±0.0005c m -1 at best, corresponding to C O 2 density precision as ±0.00015g/c m 3.

Characterization of Molybdenum (IV) Sulfide Prepared by Chemical Vapor Deposition Using Differential Reflectance Spectroscopy

Molybdenum (IV) sulfide is widely employed in electronic device applications. Recognized as one of the most efficacious methods for fabricating high-quality molybdenum (IV) sulfide, the chemical vapor deposition (CVD) method’s application necessitates the development of a straightforward, swift and nondestructive characterization tool. Thus, this paper presents a rapid and reliable differential reflectance spectroscopy (DRS) instrumentation, grounded on the optical microscope, capable of characterizing two-dimensional materials prepared by CVD. This universal nondestructive identification tool facilitates the investigation of two-dimensional materials on both opaque and transparent substrates. MoS2 samples prepared by CVD were characterized on SiO2/Si and sapphire substrate. The results indicate that the exciton absorption peak can be accurately identified, validating the instrumentation’s utility for material detection and monolayer identification. The characterization results, corroborated by the Raman spectra with a wavenumber difference of approximately 20 cm−1 and the triangular appearance of the optical image, affirm the application of this instrumentation. Ultimately, the DRS instrumentation provides a swift and nondestructive route to characterize physical properties such as bandgap and optical properties for two-dimensional materials.

Chemical structure and thermal maturation of the vitrinite-like maceral in the Lower Paleozoic shales: Insights from Raman spectroscopy of artificial pyrolysis residues

Vitrinite-like macerals (VLM) are ubiquitous in many pre-Devonian marine shales. The thermal maturity of these sediments, which are devoid of classical vitrinite, has been commonly evaluated using the reflectance of VLM as a substitute for vitrinite reflectance, but the molecular structure of VLM itself has seldom been examined. In this study, the immature VLM-rich Cambrian Alum shales from Scandinavia were selected and pyrolyzed at 300–550 ℃ to acquire a series of artificial pyrolysis samples with different ranks. The molecular structures and thermal evolution of VLM in natural and artificial shales were investigated by Raman spectroscopy. These Raman spectra and optical properties were compared with those of vitrinite, graptolite, and solid bitumen. The Raman spectra of VLM in natural samples of variable thermal maturities and immature samples altered by pyrolysis were generally comparable. The reduction of WD (D band position) and FWHM-G (full width at half maximum of the G band) and the increase of WG (G band position) and AD/AG (area ratio) in VLM spectra, which parallels the increasing thermal maturity of the samples, indicated an increased degree of aromatic conjugation and more structurally ordered carbon moieties. The increase in wavenumber difference between the D and G bands positions in Raman spectra (Raman band separation, RBS) demonstrated the gradual removal of oxygen-containing functional groups, the loss of aliphatic side chains, and the increased degree of aromatic ring condensation. In this way, with progressing maturity, the molecular structure of VLM gradually evolved from heterocyclic aromatic compounds and amorphous carbon structures at low maturity levels to structurally better-ordered, larger, aromatic fused-ring units characteristic of post-to-over mature samples. These molecular structures and their changes associated with thermal maturation were similar to those known from classical vitrinite. Aside from its reflectance, the thermal maturity of VLM-rich sediments could be assessed by Raman spectroscopy, notably through the RBS parameter of VLM Raman spectra, which closely correlated with VLM random reflectance throughout the reflectance interval between 0.5% and 5.5%.

Heating temperatures affect meat quality and vibrational spectroscopic properties of slow- and fast-growing chickens

This study determined the effect of water bath cooking (70°C and 90°C for 40 min) and the extreme heat treatment by an autoclave (121°C for 40 min) on the quality of breast meat of a fast-growing chicken, commercial broiler (CB), and slow-growing chickens, Korat chicken (KC), and Thai native chicken (NC) (Leung Hang Khao), by vibrational spectroscopic techniques, including synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy and Fourier transform Raman (FT-Raman) spectroscopy. Taste-enhancing compounds, including inosine-5'-monophosphate (IMP) and guanosine-5'-monophosphate (GMP), were better retained in cooked KC and NC meats than in cooked CB meat (P < 0.05). The high heat treatment at 121°C depleted the amount of insoluble collagen in all breeds (P < 0.05). Shear force values of slow-growing chicken meat were not affected by high heating temperatures (P > 0.05). In addition, the high heat treatment increased protein carbonyl (P < 0.05), while no effect on in vitro protein digestibility (P > 0.05). SR-FTIR microspectroscopy performed better in differentiating the meat quality of different chicken breeds, whereas FT-Raman spectroscopy clearly revealed differences in meat qualities induced by heating temperature. Based on principal component analysis (PCA), distinct characteristics of chicken meat cooked at 70°C were high water-holding capacity, lightness (L*), moisture content, and predominant α-helix structure, correlating with Raman spectra at 3,217 cm-1 (O-H stretching of water) and 1,651 cm-1 (amide I; α-helix). The high heating temperature at 90°C and 121°C exposed protein structure to a greater extent, as evidenced by an increase in β-sheets, which was well correlated with the Raman spectra at 2,968 and 2,893 cm-1 (C-H stretching), tryptophan (880 cm-1), tyrosine (858 cm-1), and 1,042, 1,020, and 990 cm-1 (C-C stretching; β-sheet). SR-FTIR and FT-Raman spectroscopy show potential for differentiation of chicken meat quality with respect to breeds and cooking temperatures. The marked differences in wavenumbers would be beneficial as markers for determining the quality of cooked meats from slow- and fast-growing chickens.

Towards high-throughput screening (HTS) of polyhydroxyalkanoate (PHA) production via Fourier transform infrared (FTIR) spectroscopy of Halomonas sp. R5-57 and Pseudomonas sp. MR4-99.

High-throughput screening (HTS) methods for characterization of microbial production of polyhydroxyalkanoates (PHA) are currently under investigated, despite the advent of such systems in related fields. In this study, phenotypic microarray by Biolog PM1 screening of Halomonas sp. R5-57 and Pseudomonas sp. MR4-99 identified 49 and 54 carbon substrates to be metabolized by these bacteria, respectively. Growth on 15 (Halomonas sp. R5-57) and 14 (Pseudomonas sp. MR4-99) carbon substrates was subsequently characterized in 96-well plates using medium with low nitrogen concentration. Bacterial cells were then harvested and analyzed for putative PHA production using two different Fourier transform infrared spectroscopy (FTIR) systems. The FTIR spectra obtained from both strains contained carbonyl-ester peaks indicative of PHA production. Strain specific differences in the carbonyl-ester peak wavenumber indicated that the PHA side chain configuration differed between the two strains. Confirmation of short chain length PHA (scl-PHA) accumulation in Halomonas sp. R5-57 and medium chain length PHA (mcl-PHA) in Pseudomonas sp. MR4-99 was done using Gas Chromatography-Flame Ionization Detector (GC-FID) analysis after upscaling to 50 mL cultures supplemented with glycerol and gluconate. The strain specific PHA side chain configurations were also found in FTIR spectra of the 50 mL cultures. This supports the hypothesis that PHA was also produced in the cells cultivated in 96-well plates, and that the HTS approach is suitable for analysis of PHA production in bacteria. However, the carbonyl-ester peaks detected by FTIR are only indicative of PHA production in the small-scale cultures, and appropriate calibration and prediction models based on combining FTIR and GC-FID data needs to be developed and optimized by performing more extensive screenings and multivariate analyses.

Evaluation of Plastic Deformation Considering the Phase-Mismatching Phenomenon of Nonlinear Lamb Wave Mixing

Nonlinear guided elastic waves have attracted extensive attention owing to their high sensitivity to microstructural changes. However, based on the widely used second harmonics, third harmonics and static components, it is still difficult to locate the micro-defects. Perhaps the nonlinear mixing of guided waves can solve these problems since their modes, frequencies and propagation direction can be flexibly selected. Note that the phenomena of phase mismatching usually occur due to the lack of precise acoustic properties for the measured samples, and they may affect the energy transmission from the fundamental waves to second-order harmonics as well as reduce the sensitivity to micro-damage. Therefore, these phenomena are systematically investigated to more accurately assessing the microstructural changes. It is theoretically, numerically, and experimentally found that the cumulative effect of difference- or sum-frequency components will be broken by the phase mismatching, accompanied by the appearance of the beat effect. Meanwhile, their spatial periodicity is inversely proportional to the wavenumber difference between fundamental waves and difference- or sum-frequency components. The sensitivity to micro-damage is compared between two typical mode triplets that approximately and exactly meet the resonance conditions, and the better one is utilized for assessing the accumulated plastic deformations in the thin plates.

Electromagnetic compatibility technologies based on multi-functional spoof surface plasmon polariton channels

High integration of modern microwave circuits and systems puts forward higher requirements for multi-function and electromagnetic compatibility (EMC) performance of transmission channels. In this paper, we propose two EMC technologies including the substrate integrated packaging (SIP) and tuneable wavenumber mismatching (TWM) based on multi-functional spoof surface plasmon polariton (SSPP) channels. The SIP technology can effectively improve the EMC performance of the SSPP channels in the whole frequency band by designing the packaging structure with easy fabrication and compact size; while the TWM technology can significantly suppress crosstalks in desired frequency bands by manipulating the wavenumber difference between two adjacent channels. Simulated and measured results demonstrate excellent multi-function and EMC performance of the integrated multi-functional SSPP channels by employing the two EMC technologies. The integrated multi-functional SSPP channels can realize continuous phase modulation in X-band and continuous amplitude modulation in Ku-band. The coupling coefficient of the integrated channels is about 8–10 dB lower than that of the channels without the package, and is 13–15 dB lower than that of the traditional microstrip channels in the whole X-band and Ku-band. Meanwhile, the coupling coefficient of the integrated multi-functional SSPP channels with a distance of 1/30 λ 0 can be reduced to around −30 dB in the desired narrow bands. Therefore, the proposed EMC technologies may find broad applications in highly integrated microwave circuits and systems.

Experimental realization of short-wavelength infrared half wave retarder fabricated from ZnO single crystal plates

With increasing interest in studying fundamental phenomena at near-infrared (NIR) and short-wavelength infrared (SWIR) frequencies, it is essential to find optical devices which can alter polarization state in the NIR and SWIR radiation range. However, simple optical components such as wave plates capable of generating and controlling polarization sates in the NIR and SWIR radiation are rare. Therefore, our use of channelled spectra of polarized white photons is reported to extract the dispersion of the phase birefringence Δnp(λ) of the 112‾0 and 11‾00 plates of ZnO single crystal acting as multiple order wave plates. The phase birefringence Δnp(λ) of the 112‾0 and 11‾00 ZnO plates was extracted using a calculation procedure named the wavenumber difference method. The correctness of the birefringence data obtained was also confirmed by recalculating the plate thickness using the Jones matrix technique. Furthermore, the birefringence group velocity factor of the 112‾0 and 11‾00 ZnO plates was also extracted from the channelled spectra of polarized white photons using simple method. For both 112‾0 and 11‾00 ZnO plates, a broad spectral full width at half maximum (FWHM) is observed in SWIR region (1100–2500 nm), therefore, 112‾0 and 11‾00 ZnO plates can act as if they are functioning as a zero-order wave plate.

Screech in transient supersonic jets

The starting processes of under-expanded free jets with nozzle pressure ratios of 2.15, 2.7, and 3.4 are systematically analyzed by large-eddy simulations, and the unified laws of the evolution of the screech frequency and the screech mode in the starting jet are given. Through the development of vortices, the critical time points of the generations of screech tones are investigated. The wavenumber spectra and dispersion relations are employed, showing that the screech feedback loops in the different starting jets are all closed by the neutral waves excited by the interaction between the Kelvin–Helmholtz wavepacket and shock cells of different wavenumbers. The screech frequency prediction during the starting process is put forward for the first time, which is achieved by combining the neutral acoustic wave mode with wavenumber differences between shock cells and the Kelvin–Helmholtz wavepacket. Spectral proper orthogonal decomposition is applied to explain the reason for the change in the interaction mechanism during the starting process.

Optical pulling using topologically protected one way transport surface-arc waves

Optical pulling is a counterintuitive phenomenon whereby light can pull particles against its propagation direction, but usually it is necessary to optimize both the incident beam and the manipulated particles. Here, we propose a robust optical pulling scheme using an air waveguide sandwiched between two chiral hyperbolic metamaterials carrying Weyl points. The pulling force is induced by mode conversion between two topologically protected chiral surface arcs supported on the two metamaterial surfaces of the waveguide. We prove that the optical pulling force is totally attributed to the Minkowski-type momentum of light and proportional to the wave-number difference between the two surface-arc waves, thus the pulling force is robust against the material, shape, and size of the particle. Thanks to the backscattering immunity of the surface-arc waves and the in-plane isotropy of the metamaterials, robust optical pulling can be achieved even in a curved waveguide, going beyond standard mechanisms of straight-line pulling.

Recovery of coherent reflection from rough-surface scattered acoustic fields via the frequency-difference autoproduct.

The acoustic field reflected from a random rough surface loses coherence with the incident field in the Kirchhoff approximation as kh cos θ increases, where k is the incident field wavenumber, h is the root mean square roughness height, and θ is the incidence angle. Thus, for fixed rough-surface properties and incidence angle, a reflected field at lower wavenumber should retain more coherence. Recent results suggest that the frequency-difference autoproduct formed from complex acoustic field amplitudes at two nearby frequencies can recover acoustic information at the difference of those frequencies even when the difference frequency is below the recorded field's bandwidth. Herein analytical, computational, and experimental results are presented for the extent to which the frequency-difference autoproduct recovers coherence from randomly rough-surface-scattered constituent fields that have lost coherence. The analytical results, developed from the Kirchhoff approximation and formal ensemble averaging over randomly rough surfaces with Gaussian height distributions and Gaussian correlation functions, indicate that the coherence of the rough-surface-reflected frequency-difference autoproduct depends on the surface correlation length and Δkh cos θ, where Δk is the difference of the autoproduct's constituent field wavenumbers. These results compare favorably with Monte Carlo simulations of rough surface scattering, and with laboratory experiments involving long surface correlation lengths where 1 ≤kh cos θ≤ 3.

Waveguide Invariant-based mitigation of reverberation and interference in active and passive sonar

Multipath propagation poses many challenges for broadband sonar signal processing in underwater acoustic channels. The waveguide invariant (WI) provides a useful relation between the temporal and frequency fading characteristics in shallow-water channels that can been exploited to improve broadband target detection in both active and passive sonars. In active sonar, the WI motivates an alternative to conventional constant-false-alarm rate (CFAR) normalization of the background by averaging over observed time-frequency striations to estimate the reverberation level. A WI-based generalized likelihood ratio test is reviewed and shown to outperform conventional cell-averaged and frequency-invariant CFAR detectors in both simulation and with real Mediterranean data. In passive towed-array sonar, targets near endfire are often masked by angularly spread broadband multipath interference whose statistics must be estimated with limited training data for effective suppression. A WI relationship characterizing the frequency-dependence of wavenumber differences permits averaging of narrowband array snapshots to form a low-rank broadband “focused” covariance matrix. Simulation experiments in a realistic ocean environment are reviewed showing that adaptive beamforming using WI focused covariance matrices can provide a significant array gain improvement over conventional adaptive methods with limited observation time. Finally, the potential for waveguide invariant-based blind source separation is discussed. [Work supported by ONR.]

Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions.

Rapidly developing mid-infrared quantum cascade laser (QCL) technology gives easy access to broadly tunable mid-IR laser radiation at a modest cost. Despite several applications of QCL in the industry, its usage for spectroscopic investigation of synthetically relevant organic compounds has been limited. Here, we report the application of an external cavity, continuous wave, mid-IR QCL to cryogenic ion vibrational predissociation spectroscopy to analyze a set of large organic molecules, organometallic complexes, and isotopically labeled compounds. The obtained spectra of test molecules are characterized by a high signal-to-noise ratio and low full width at half-maximum-values, allowing the assignment of two compounds with just a few wavenumber difference. Data generated by cw-QCL and spectra produced by another standard Nd:YAG difference-frequency generation system are compared and discussed.

FTIR-PCA analysis as an initial analysis to distinguish the origin of skin and leather

Leather products are parts of daily fashion in Indonesia, such as bags, shoes, jackets, and gloves. Adulteration of raw materials for leather products can occur if there are no labels on these products. Various methods such as PCR, GC-MS, HPLC, and FTIR have been carried out to distinguish the origin of leather products. The FTIR method is known as an easy and inexpensive method to use. The objective of this study was to evaluate the capability of FTIR spectroscopy and Principle Component Analysis (PCA) for lipid identifcation and initial analysis to distinguish the original materials on leather products. Lipid extracts obtained from the various skin were scanned using an FTIR spectrophotometer at 4000–450 cm -1 . It resulted in spectral differences in several wavenumbers (3000-2800 cm -1 and 1200-1000 cm -1 ). The same result is also found in lipid spectra from leather product extraction. The FTIR spectroscopy and PCA can differentiate pigskin and goatskin through specifc peaks in infrared spectra. This can be used as an initial analysis on determining the existence of skin adulteration in leather products. This study is prospective to be continued by chemometrics as quantitative analysis.

Sensitive Dependence of Ultrarelativistic Electron Precipitation on EMIC Wave Frequency

AbstractElectromagnetic ion cyclotron (EMIC) waves have long been considered to cause atmospheric precipitation loss of relativistic electrons, the quantitative evaluation of which is critical for understanding the radiation belt electron flux dropouts. In this study, we report test particle calculation results on precipitation loss rates of 5 MeV electrons with initial pitch angles of 4–10° at the equator by He+ band EMIC waves. We find a sensitive dependence of the precipitation loss rates on the wave frequency in that a preferred wave frequency (maximum loss frequency) exists at which the loss rate peaks predominantly and away from which it declines substantially. According to a cold plasma dispersion relation, a small difference in wave frequency just below the He+ gyrofrequency corresponds to a significant difference in wavenumber. Different frequencies lead to phase trapping of different extents, which determines the significance of loss cone scattering at the exit latitude from the wave zone. At frequencies below the maximum loss frequency, phase trapping causes large advective pitch angle changes, prohibiting loss cone scattering. At the maximum loss frequency, the phase‐trapping effect is optimized such that diffusion is dominant over advection and large enough to allow effective loss cone scattering. At frequencies above the maximum loss frequency, the phase‐trapping effect disappears, and the resulting (both diffusive and advective) scattering is too weak to drive loss cone scattering unless the initial pitch angle is close enough to the loss cone angle.

What Dictates Rashba Splitting in 2D van der Waals Heterobilayers.

Rashba spin-orbit coupling enables electric control of spin states, promising enormous advances from conventional charge-based computing. Until now, a general scheme or a descriptor to find an optimal system with isolated spin states with large tunable splitting is still lacking. Here, based on first-principles calculations, we explore the microscopic physicochemical mechanism responsible for the Rashba effect in 2D van der Waals heterobilayers. We find that the difference in the Born effective charge of atoms at the interface can be used as a single-layer descriptor to predict heteropairs with large Rashba splitting, thus reducing the scaling factor in materials search. Moreover, we discover that for most 2D materials, the routinely used Rashba parameter αR is not a good gauge of the effect's strength. From our general scheme, MoTe2|Tl2O and MoTe2|PtS2, with spin splitting above 120 meV, Rashba energy ER = 94 meV, and wavenumber difference 2k0 = 0.36 Å-1 ("effective" αR > 1 eVÅ), emerge as the best candidates for spin transistors at room temperature.

Experimental investigation of the return flow instability in magnetized spherical Couette flows

We conduct magnetized spherical Couette (MSC) flow experiments in the return flow instability regime with GaInSn as the working fluid, the ratio of the inner to the outer sphere radii ri/ro = 0.5, the Reynolds number Re = 1000, and the Hartmann number Ha ∈ [27.5, 40]. Rotating waves with different azimuthal wavenumbers m ∈ {2, 3, 4} manifest in certain ranges of Ha in the experiments, depending on whether the values of Ha were fixed or varied from different initial values. These observations demonstrate the multistability of rotating waves, which we attribute to the dynamical system representing the state of the MSC flow tending to move along the same solution branch of the bifurcation diagram when Ha is varied. In experiments with both fixed and varying Ha, the rotation frequencies of the rotating waves are consistent with the results of nonlinear stability analysis. A brief numerical investigation shows that differences in the azimuthal wavenumbers of the rotating waves that develop in the flow also depend on the azimuthal modes that are initially excited.

Experimental observation of the ν2+4ν3 bands of HD16O and HD18O between 14975 and 15275 cm−1

The ν2+4ν3 combination bands of HD16O and HD18O were measured using Fourier transform-incoherent broadband cavity-enhanced absorption spectroscopy (FT-IBBCEAS) with a spectral resolution of 0.08 cm−1. The ro-vibrational lines of these bands were assigned through comparison with ab-initio molecular lines from the Tomsk variational calculation database (http://spectra.iao.ru/). For HD18O and HD16O in total 114 and 141 strong lines were assigned in the region between 14975.3 cm−1 and 15243.3 cm−1 and between 14998.5 cm−1 and 15274.7 cm−1, respectively. While the very satisfactory agreement of line intensities was used for line assignments, a systematic average discrepancy of ~0.305 cm−1 in line positions was identified between the measured lines of HD18O and the theoretically predicted lines from the Tomsk database. Similarly for HD16O, an approximate wavenumber difference of ~0.361 cm−1 was observed. The wavenumber accuracy of the Fourier transform cavity enhanced absorption spectrometer was confirmed on basis of concurrently measured H216O spectra in the region between 15254.2 cm−1 and 15376.9 cm−1 and corroborated the systematic shifts of the ab initio data. A few lines of the ν1+4ν2+2ν3 bands of HD16O and HD18O were also identified. The data are compared and discussed on basis of existing literature data.