Ν3 Band Research Articles

Progress in understanding the infrared spectrum of the H2O-O2 dimer.

Spectra of the weakly bound H2O-O2 dimer are studied in the region of the H2O ν2 band using a tunable quantum cascade laser to probe a pulsed supersonic slit jet expansion. These are the first gas-phase infrared spectra of H2O-O2 and among only a few such results for O2-containing complexes. Almost 100 infrared lines are assigned based on the ground state combination differences from the microwave spectrum of H2O-O2. These lines belong to a main fundamental band, plus four combination bands lying 2 to 5cm-1 above the fundamental. All correspond to the ortho-H2O (I = 1) nuclear spin species. Interpretation of the observed rotational levels is discussed. The original microwave analysis conflicts with the infrared results but can be corrected by changing the signof a term or, better still, by using a published theory for weakly bound open shell complexes. The combination bands suggest that analogous ground state bands should be observable in the millimeter wave range. Many infrared transitions remain unassigned, including another extensive band apparently centered at 1603cm-1, and some of these are probably due to the para-H2O spin species (I = 0). Splittings due to the unpaired O2 electron spin (S = 1), due to large amplitude tunneling motions, and due to a-axis rotational motion all have similar magnitudes for H2O-O2, so the resulting energy levels will be heavily mixed and not amenable to simple modeling. Accurate theoretical predictions of these effects should be possible for obtaining an enhanced understanding of the observed spectra.

Measurements of He-collision-induced line-shape parameters of CO2 lines in the ν3 band

Measurements of He-collision-induced line-shape parameters of CO2 lines in the ν3 band

High Resolution Rovibrational Spectroscopy of the ν6 and ν3 + ν7 Bands of H2CCCH.

The molecular ion H2CCCH+ has been further investigated in a 4 K cryogenic ion trap instrument employing the leak-out spectroscopy (LOS) method. Transitions within two perpendicular bands, the fundamental ν6 (antisymmetric H-C-H stretch) and the combination band ν3 + ν7 (C≡C stretch and CH2 rock), have been measured in high resolution for the first time. The spectral analysis was aided by high level quantum chemical calculations and by our previous study of the parallel ν1 and ν3 + ν5 bands [Silva, W. G. D. P. ; Mol. Phys. 2023, e2296613]. The novel results presented here have allowed for a seventy-fold improvement on the accuracy of the value of the A0 rotational constant of this near-prolate asymmetric top.

Towards improved spectroscopic applications in multi-gas environments: CO2 spectral line parameter measurement and analysis

The ν1 + 2ν2 + ν3 band of 12CO2 is dominated by weak absorption lines near 2.0 uμm, which has potential application in planetary atmosphere, astrophysical, and hydrocarbon fuel combustion investigations. High-quality spectral line parameters are the foundation of spectroscopic technology. In this work, high-resolution infrared spectra of CO2 were recorded over 5005–5008 cm−1 range using a Distributed Feedback (DFB) laser with a linewidth of Δν < 0.0001 cm−1. H2-, N2-, O2-, Ar-, air- and CO2- line-intensity, collision broadening coefficients, pressure shift coefficients were determined for CO2 transitions R44e, R46 e, R48 e, R50 e at room temperature. Voigt and Rautian profiles were utilized to retrieve the measured line shape of each individual transition at various pressures. The new data extend and complement previous measurements over the target spectral region. In addition, a comprehensive analysis of the measured spectral line shape parameters is conducted to elucidate the characteristics of spectral line intensity, broadening, and pressure-induced shift coefficients under different molecular collision conditions. This has the potential to be valuable for modeling spectral calculations of multi-component systems, optimizing multi-gas environmental spectral calculation, and developing new spectral diagnostic methods.

The CH3D Absorption Spectrum Near 1.58 μm: Extended Line Lists and Rovibrational Assignments.

Monodeuterated methane (CH3D) contributes greatly to absorption in the 1.58 μm methane transparency window. The spectrum is dominated by the 3ν2 band near 6430 cm-1, which is observed in natural methane and used for a number of planetary applications, such as the determination of the D/H ratio. In this work, we analyze the CH3D spectrum recorded by high-sensitivity differential absorption spectroscopy in the 6099-6530 cm-1 region, both at room temperature and at 81 K. Following a first contribution to this topic by Lu et al., the room-temperature line list is elaborated (11,189 lines) and combined with the previous 81 K list (8962 lines) in order to derive about 4800 empirical lower-state energy values from the ratio of the line intensities measured at 81 K and 294 K (2T-method). Relying on the position and intensity agreements with the TheoReTS variational line list, about 2890 transitions are rovibrationally assigned to twenty bands, with fifteen of them being newly reported. Variational positions deviate from measurements by up to 2 cm-1, and the band intensities are found to be in good agreement with measurements. All the reported assignments are confirmed by Ground-State Combination Difference (GSCD) relations; i.e., all the upper-state energies (about 1370 in total) have coinciding determinations through several transitions (up to 8). The energy values, determined with a typical uncertainty of 10-3 cm-1, are compared to their empirical and variational counterparts. The intensity sum of the transitions assigned between 6190 and 6530 cm-1 represents 76.9 and 90.0% of the total experimental intensities at 294 K and 81 K, respectively.

The j and k dependencies of N2-, O2-, and air-broadened halfwidths of the CH3CN molecule

The N2-, O2, and air-broadened halfwidths of CH3CN lines in the parallel ν4 band have been calculated, along with the relaxation matrices W. These calculations employ our modified and refined versions of the Robert-Bonamy formalism and use all potential parameters from the literature without adjustments. Extensive comparisons between the predicted N2-broadened halfwidths in the qR and qP branches from the models at T = 296 K and experimental measurements are presented, showing that our latest model very closely matches the measurements. For the qQ branch, where measurements are unavailable, we compare our N2-broadened halfwidths with the converted air-broadened data from HITRAN 2008, obtaining similarly good agreement. The variation in the j and k dependencies of the N2-broadened halfwidths is discussed in detail. Additionally, the theoretically determined conversion factor from N2- to air-broadening is provided. Finally, based on our theoretical calculations of N2-broadened halfwidths of the qR(j,3) lines at five different temperatures, ranging from 250 K to 350 K, the temperature exponent N is determined and its dependence on j is analyzed.

Non-destructive Analytical Study of Raman Spectra Variations and Mechanisms of Calcite and Aragonite in Modern and Fossilized Oysters.

Oyster fossils are some of the most common bivalve mollusk fossils found all over the world, they are different from other fossils because the oyster is still alive in the present day, and the body structure of modern oyster is almost the same as that of ancient one. Therefore, we designed a control experiment comparing the Raman spectra of minerals from both modern oysters and fossil oysters to explore the mechanism of oyster's fossilization process, which is considered to be helpful for investigating biological evolution or paleoenvironment. The oyster fossil sample was found in Nagi-Cho, Okayama Prefecture, Japan. We focused on the variations of band position and full width half-maximum of ν1 Raman band (symmetric stretching mode) of calcite (CaCO3) from modern and fossil oysters and the mineral conversion between calcite and aragonite (CaCO3) around the adductor muscle inside the oyster. Compared to modern oysters, the ν1 band at around 1086 cm-1 of calcite from oyster fossils shifted to a high wavenumber region, and the possible reason for this phenomenon is considered an elemental substitution between Ca2+ and Mg2+. As for aragonite around adductor muscle in fossil oysters, it has been found by Raman spectra that most of the aragonite has been converted into calcite because calcite has a relatively more stable structure.

Helium Detection in Natural Gas Using Raman Spectroscopy.

Raman spectroscopy has great potential for quantitative analysis of natural gas. Helium is one of the components of natural gas and has a wide range of applications. It was believed that noble gases could not be detected using this technique due to the absence of their vibrational spectra. In this study, we demonstrated an approach to extracting the content of helium from the Raman spectrum of methane and carried out test measurements for the first time. The approach is based on the determination of changes in the ν1 band of methane caused by the influence of helium and other components. The necessary spectroscopic parameters characterizing the effect of methane (CH4), helium (He), nitrogen (N2), carbon dioxide (CO2), and ethane (C2H6) on the ν1 band of methane at a resolution of 0.35 cm-1 were obtained. The validation of the approach showed that the helium content in natural gas can be measured with an uncertainty of 1 mol% at a sample pressure of 50 bar. The measurement precision can be increased to 0.01 mol% by using a high-resolution spectrometer. The described method does not claim to replace helium detectors, but it can be considered a valuable addition to Raman gas analysis of natural gas in developing an all-in-one device. The possibilities for further improvement of the approach are also discussed.

High resolution analysis of the CD[formula omitted] deuterated methane: Extended investigation of the pentad region

A highly accurate rotational–vibrational analysis of Fourier transform infrared spectra of the 12CD4 molecule is presented. The high resolution infrared spectra were measured with a IFS125 HR Fourier transform interferometer from Bruker at an optical resolution of 0.003 cm−1 and analyzed in the 1750–2400 cm−1 region. Here the 2ν2, ν2+ν4, 2ν4, ν1 and ν3 bands (altogether, nine sub-bands of different symmetry) of the pentad are located. The number of 1213/1993/1576/77/1582 transitions with the Jmax = 23/23/23/14/32 were assigned to the 2ν2, ν2+ν4, 2ν4, ν1 and ν3 bands of 12CD4. The obtained experimental data were used for the determination of the upper ro-vibrational energy values. To provide more correct values of the upper energies, more than 7800 highly accurate “hot” transitions from the dyad region were additionally processed. In general, 4088 upper ro-vibrational energies of the pentad (for comparison, 2525 upper ro-vibrational energies with the value of Jmax=20 are known in the modern literature up to now) were determined, which were used then in the weighted fit procedure with a goal to determine the spectroscopic parameters (band centers, rotational, centrifugal distortion, tetrahedral splitting and resonance interaction parameters) of the effective Hamiltonian. The obtained drms value is 5.5×10−4 cm−1 which is almost one hundred times better than the reproduction of the same set of experimental data by the parameters known in the earlier literature.

Measurement and assignment of J = 5 to 9 rotational energy levels in the 9070-9370cm-1 range of methane using optical frequency comb double-resonance spectroscopy.

We use optical-optical double-resonance spectroscopy with a continuous wave (CW) pump and a cavity-enhanced frequency comb probe to measure the energy levels of methane in the upper part of the triacontad polyad (P6) with higher rotational quantum numbers than previously assigned. A high-power CW optical parametric oscillator, tunable around 3000 cm-1, is consecutively locked to the P(7, A2), Q(7, A2), R(7, A2), and Q(6, F2) transitions in the ν3 band, and a comb covering the 5800-6100cm-1 range probes sub-Doppler ladder-type transitions from the pumped levels with J' = 6 to 8, respectively. We report 118 probe transitions in the 3ν3 ← ν3 spectral range with uncertainties down to 300kHz (1 × 10-5cm-1), reaching 84 unique final states in the 9070-9370cm-1 range with rotational quantum numbers J between 5 and 9. We assign these states using combination differences and by comparison with theoretical predictions from a new abinitio-based effective Hamiltonian and dipole moment operator. This is the first line-by-line experimental verification of theoretical predictions for these hot-band transitions, and we find a better agreement of transition wavenumbers with the new calculations compared to the TheoReTS/HITEMP and ExoMol databases. We also compare the relative intensities and find an overall good agreement with all three sets of predictions. Finally, we report the wavenumbers of 27 transitions in the 2ν3 spectral range, observed as V-type transitions from the ground state, and compare them to the new Hamiltonian, HITRAN2020, ExoMol, and the WKMLC line lists.

Cavity ring-down spectroscopy of 14N216O near 0.83 µm

The cavity ring-down spectra (CRDS) of nitrous oxide were recorded at a pressure of 10 hPa in the 11,937–12,223 cm-1 range with a threshold sensitivity to absorption coefficient of the order of 6.5 × 10–11 cm-1. Three bands (ν1+5ν3, 6ν1+2ν3, and 3ν1+4ν3) were detected. The line centers and intensities were recovered from the observed spectra. The spectroscopic constants of the upper vibrational states and the vibrational transition dipole moment parameters were fitted to the measured line positions and intensities, respectively. It was found that the 3ν1+4ν3 band is in the interpolyad Coriolis resonance interaction with the 7ν1+7ν21 band. This interaction leads to the appearance in the spectra of the four extra lines of the 7ν1+7ν21 band.

First widespread occurrence of rare phosphate chladniite in a meteorite, winonaite Graves Nunataks (GRA) 12510: Implications for phosphide–phosphate redox buffered genesis in meteorites

Abstract The first widespread occurrence of rare Na-, Ca-, and Mg, Mn, Fe-bearing phosphate chladniite was observed in meteorite Graves Nunataks (GRA) 12510, which is a primitive achondrite that sits within the winonaite class. Numerous 1–500 µm chladniite grains were found, often on the margins between silicate clasts and the kamacite portions of the large metal veins that permeated through the sample. The largest chladniite grains are associated with merrillite, kamacite, taenite, troilite, albite, forsterite, diopside, and enstatite, with a few tiny chladniite grains and an apatite grain enclosed within merrillite. GRA 12510s average chladniite composition is Na2.7Ca1.25(Mg10.02Mn0.69Fe0.20)Σ10.91(PO4)9. Electron backscattered diffraction (EBSD) patterns indicate varying degrees of nucleation and growth of chladniite grains. Additionally, the first pure Raman spectrum of chladniite is described here, revealing primary ν1 bands at 954, 974, and especially 984 cm–1. The co-occurrence and close association of merrillite, apatite, chladniite, and P-bearing metallic phases within GRA 12510 suggests that the fO2 of IW-2 to IW-4 is an intrinsic property of the precursor chondritic material, and the phosphate-phosphide reaction may have buffered the final winonaite and IAB iron meteorite phase assemblages. Altogether, chladniite appears to form alongside other phosphates, with their chemistries reflecting the diverse environment of their formation. Meteoritic chladniite likely formed through subsolidus oxidation of schreibersite, scavenging Na from albite, Ca from diopside, Mg from enstatite/forsterite, Fe from kamacite/taenite, and Mn from alabandite/chromite when available. A P0-P5+ redox-buffered environment also has implications for thermometry and fast cooling rates, although more experiments are needed to extrapolate powder reaction rates to those of larger crystals. Furthermore, phosphide-phosphate buffered experiments may aid in investigating equilibrium chemistry at fO2 values between IW-2 and IW-4, which have been challenging to explore experimentally due to the limited availability of solid metal-metal oxide buffers between IW (Fe-FeO) and IW-5 (Cr-Cr2O3) at temperatures and pressures relevant to planetary interiors. Future investigations of phosphide-phosphate redox-buffered genesis at fO2 values between IW-2 and IW-4 have important implications for primitive meteorite constituents (e.g., CAI values), partially differentiated planetesimals and planets, including Mercury and core formation on Earth.

The ethylene absorption spectrum between 6075 and 8050 cm-1: Empirical line list and rovibrational assignments

The highly congested absorption spectrum of ethylene (C2H4) is analyzed between 6075 and 8050 cm-1. In the 6200–8050 cm-1 range, a list of about 32,650 lines is retrieved from a room temperature spectrum recorded by Fourier transform spectroscopy (P = 15.72 mbar, L = 45 m). This dataset was merged with a set of about 3460 lines available in the literature in the region of the strong ν5+ν9 band near 6150 cm-1. In addition, two FTS spectra at 130 K provide complementary information in the 6020–6320 cm-1 range (about 7570 lines).Relying on the position and intensity agreements with a line list of 12C2H4 transitions calculated by the variational method, a total of 4090 transitions is assigned to eighteen bands, ten of them being newly reported. All the reported assignments are confirmed by Lower State Combination Difference (LSCD) relations i.e. all the upper states (1749 in total) have coinciding determinations of their energies through several transitions (up to 6). The obtained empirical energy values are given and compared to their variational counterpart. As an additional validation test of the lower state assignments, the room temperature intensities are extrapolated at 130 K and compared to their experimental values. Overall, a large fraction of the strong lines of the region is assigned and the total intensity of the assigned transitions represents 46 and 55% of the total variational and experimental intensities at 296 K, respectively. In the considered range, variational positions deviate from measurements by a few cm-1 and the total variational absorption is underestimated by 40 %.

Mid-infrared high-resolution dual-comb spectroscopy: Intensity, broadening, and beyond-Voigt parameters of [formula omitted] and [formula omitted] lines

Using a high-resolution mid-infrared dual-comb spectrometer operating in the 1300 cm−1 spectral region, spectra of acetylene were recorded at room temperature. Spectroscopic parameters were measured in 3 vibrational bands of both 12C2H2 and 13C12CH2. Absolute line intensities (S0) and self-broadening coefficients (γ0self) were determined in the ν4+ν5, 2ν42+ν5−1⟵ν41 and ν41+2ν50⟵ν51 bands. For the main isotopologue, the collisional narrowing coefficients (ν0VC) as well as the speed-dependence of the broadening (γ2) and shifting (δ2) coefficients were measured in the ν4+ν5 band of the main isotopologue of acetylene. Theoretical line-shape models were fitted on experimental profiles using a homemade multi-spectrum fitting procedure to determine spectroscopic parameters. Excellent agreement with the literature was found for self-broadening coefficients and absolute line intensities in the ν4+ν5 band of 12C2H2. For the hot bands, good agreement with the literature is found within experimental uncertainties, while γ0self of those hot bands are also reported for the first time. Similarly, the rotational dependence of ν0VC is found to be close to previous works. γ2 and δ2 of 12C2H2, as well as S0 and γ0self of 13C12CH2 are also reported for the first time in this band.

Revisiting the IR Spectra of H2S in an Argon Matrix: Identification of (H2S)n (n ≤ 4) Clusters via the Spectral Assignment of νS-H Transitions.

Small-molecular clusters of H2S up to tetramer have been experimentally identified in a cold and solid argon matrix by the spectral assignment of νS-H fundamental transitions for different H2S:argon mixing ratios. Normal-mode frequency calculations at the MP2-CP/aug-cc-pV(Q + d)Z level have been used to support the spectral assignments. In addition, modulations in relative populations of different clusters due to the annealing of the deposited matrix and the preheating of the H2S-argon gas mixture before deposition reinforced the spectral assignments. Variations in mixing ratio, annealing of the matrix, and preheating of the gas mixture have also been used, in a combined manner, to unambiguously identify the ν1 and ν3 bands of the H2S monomer, which has been a matter of dispute for a long period. The two bands have been identified at 2634.4 and 2648.0 cm-1, respectively, while three bands at 2581.5, 2568.4, and 2547.6 cm-1 have been assigned to H-bonded dimers, cyclic trimers, and cyclic tetramers, respectively. Multiple bands within 2550-2580 cm-1 have been assigned to caged tetramers. The cooperative strengthening of S-H···S H bonds in cyclic H2S clusters was evident from the linear increment in νS-H spectral shifts with cluster size.

The D/H ratio in Titan’s acetylene from high spectral resolution IRTF/TEXES observations

We report observations of deuterated acetylene (C2HD) at 19.3μm (519 cm−1) with the Texas Echelon Cross Echelle Spectrograph on the NASA Infrared Telescope Facility in July 2017. Six individual lines from the Q-branch of the ν4 band were clearly detected with a S/N ratio up to 10. Spectral intervals around 8.0μm (745 cm−1) and 13.4μm (1247 cm−1) containing acetylene (C2H2) and methane (CH4) lines respectively, were observed during the same run to constrain the disk-averaged C2H2 abundance profile and temperature profile. Cassini observations with the Composite Infrared Spectrometer (CIRS) were used to improve the flux calibration and help to constrain the atmospheric model. The measured D/H ratio in acetylene, derived from the C2HD/C2H2 abundance ratio, is (1.22−0.21+0.27)× 10−4, consistent with that in methane obtained in previous studies. Possible sources of fractionation at different steps of the acetylene photochemistry are investigated.

Real-time monitoring of CH4 and N2O emissions from livestock using mid-infrared external cavity quantum cascade laser absorption spectroscopy

The largest share of greenhouse gas (GHG) emissions related to livestock originates from methane (CH4) and nitrous oxide (N2O) which have a far higher influence on global warming, it is therefore necessary to accurately monitor CH4 and N2O emissions to provide theoretical and practical basis for further estimating and regulating GHG emissions from livestock and improving livestock production performance. For the purpose of sensing CH4 and N2O emissions during livestock living process in real time, an optical sensor based on continuous-wave (CW) external cavity quantum cascade laser (EC-QCL) operating at room temperature was developed. CH4 and N2O absorption lines, located around 8 μm, of the ν4 and ν1 fundamental vibrational bands, respectively, were chosen for direct absorption spectroscopy, which allows for sensitive, selective and simultaneous measurement of CH4 and N2O concentrations. Use of a Herriot multi-pass cell with an effective path-length of 100 m, 1σ (SNR = 1) limits of detection of 26.8 ppbv, 20.3 ppbv and 0.01 % for CH4, N2O and H2O vapor were achieved, respectively. Field measurement of CH4 and N2O emissions from horses has been carried out in a stable over two weeks at the Vernaelde farm in Couderkerque Branche city, France. Concentrations of CH4 and N2O up to 10 times and 1.5 times higher than their levels in the local ambient air (∼ 2.12 ppmv and ∼ 427 ppbv) were observed, respectively.

New line list for the ν4 bands of the trans (790.117 cm–1) and cis (851.943 cm–1) conformers of nitrous acid (HONO): Accurate positions and absolute intensities

The goal of this work was to update and significantly improve the line lists that have been generated recently for 11 µm bands of the trans- and cis- conformer forms of nitrous acid (HONO) [Armante R, Perrin A, Kwabia Tchana F, Manceron L. The ν4 bands at 11 μm: linelists for the trans- and cis- conformer forms of nitrous acid (HONO) in the 2019 version of the GEISA database. Molecular Physics 2021;120:e1951860]. That 2019 version of the 11 µm line list was generated using the spectroscopic parameters that were available, at that time, in the literature. During the present study, we used high-resolution Fourier transform spectra recorded at 11 µm to perform a large investigation of line positions and intensities for the ν4 bands of the trans- and cis-conformer of HONO. The resulting set of experimental ν4 (absolute) intensities and of 41 energy levels were used to determine, by least squares fit computations, improved position and intensity parameters for the ν4 bands of the trans- and cis-conformer of HONO. For trans-HONO, the ν4 band appeared not to be perturbed, while for cis-HONO a weak high order B-type Coriolis, coupling together the 41 and 61 energy levels was evidenced for the first time. This new list is of potential interest for the IASI-NG (Infrared Atmospheric Sounding Interferometer - New Generation) instrument which will be launched on board the METOP-SG satellite in 2025.

Effect of Cage Occupancies on Molecular Vibrations of Methane in Structure H Clathrate Hydrate: Ab Initio Molecular Dynamics Simulation.

The structure H (sH) of methane hydrate, which has a distinctive structure with large (LL) cages capable of encapsulating multiple methane molecules, has been suggested as a methane reservoir in large icy bodies such as Titan, making it important in planetary science. This high-pressure phase, which exists in the GPa range, lends itself to the study of methane states and dynamics using powerful experimental techniques such as IR and Raman spectroscopy. However, the interpretation of the vibrational spectra of methane in the sH structure has been challenging because of the spectral complexities. The signals attributed to the methane molecules in the LL cage, as well as those of the other two cage types, overlap in the spectra. In this study, we investigated the microscopic origins of the shape of the C-H stretching vibration spectrum of methane in the LL cage using ab initio molecular dynamics (AIMD) simulations. For a single methane molecule in the LL cage, the ν3 band of the C-H stretching mode was observed at a higher frequency typical of isolated molecules in vacuum due to the large size of the LL cage. As the number of methane molecules in the LL cage increased beyond one, a tendency to blue-shift with increasing methane occupancy was observed, consistent with a loose-cage-tight-cage model. By characterizing the time correlation function of methane stretching vibrations based on the solvation number of methane and water molecules proximal to methane within the LL cage, we showed that the complicated spectral line shape observed in cases of higher methane occupancy in the LL cage resulted from the wider variation of the solvation shell states. Analysis of the solvation structures of the AIMD trajectories provided interpretations of the experimental spectral line shape, demonstrating the complementary nature of AIMD to the experiment and its effectiveness in analysis.

Coefficients of Carbon Dioxide Pressure-Induced Line Shift of Sulfur Dioxide at Room Temperature: The ν1 + ν3 Band

Coefficients of Carbon Dioxide Pressure-Induced Line Shift of Sulfur Dioxide at Room Temperature: The ν1 + ν3 Band