Mid- and long-wave infrared absorption cross sections for acetonitrile

Infrared absorption cross sections for acetonitrile (methyl cyanide; CH₃CN) have been determined in the 880–1700 cm^?1 spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR) and a multipass cell with a maximum optical pathlength of 19.3 m. Spectra of acetonitrile/dry synthetic air mixtures were recorded at 0.015 cm^?1 resolution (calculated as the Bruker instrument resolution of 0.9/MOPD) at a number of temperatures between 203 and 297 K and pressures appropriate for atmospheric conditions. Intensities were calibrated using three composite acetonitrile spectra recorded at the Pacific Northwest National Laboratory. These absorption cross sections will provide an accurate basis for upper tropospheric/lower stratospheric retrievals of acetonitrile in the mid-infrared spectral region from ACE satellite data.     

ICLAS of water in the 770 nm transparency window (12 746–13 558 cm−1). Comparison with current experimental and calculated databases

The absorption spectrum of water vapor has been investigated by intracavity laser spectroscopy (ICLAS) in the 12 746–13 558 cm^?1 spectral region corresponding to an interesting transparency window of the atmosphere, partly obscured by the A band of molecular oxygen.The achieved sensitivity—in the order of α_min～10^?9 cm^?1—has allowed one to measure 1062 water lines with intensities ranging from 1.6×10^?28 to 2.35×10^?24 cm/molecule at 296 K. A total of 169 new and improved energy levels belonging to 21 vibrational states could be determined from 374 newly measured transitions. The retrieved experimental line list is compared with the spectra calculated by Schwenke and Partridge, and Barber and Tennyson. Comparison with the available experimental databases shows that the obtained results represent a significant improvement of the knowledge of the water absorption in the considered region, in particular in the region of the oxygen A band.     

The absorption spectrum of methane at 80 and 294 K in the icosad (6717–7589 cm−1): Improved empirical line lists,isotopologue identification and temperature dependence

Using a cryogenic cell and a series of Distributed Feed Back (DFB) diode lasers, new high resolution spectra of methane have been recorded at 80 K and room temperature by differential absorption spectroscopy (DAS) between 6717 and 7589 cm^?1 (1.49–1.32 μm). The investigated spectral region corresponds to the very congested icosad, which is not tractable by theory. Empirical lists of 19,940 and 24,001 lines were constructed from the 80 K and room temperature spectrum, respectively. The room temperature list adds about 8500 features to the empirical list of 15,375 lines at 296 K adopted in the HITRAN database from the original work of L. Brown (Brown, L. Empirical line parameters of methane from 1.1 to 2.1 μm. JQSRT 2005;96:251–70). A number of relatively strong CH₄ lines located near strong water lines were found missing in the HITRAN line list. The improved sensitivity allowed adding more than 7000 lines to our previous list of about 12,000 transitions at 80 K (Campargue A, Wang L, Kassi S, Ma?át M, Votava O. Temperature dependence of the absorption spectrum of CH₄ by high resolution spectroscopy at 81 K: (II) The Icosad region (1.49–1.30 μm). JQSRT 2010;111:1141–51). In order to facilitate identification of the transitions of the different methane isotopologues present in “natural” isotopic abundance, spectra of highly enriched CH₃D and ¹³CH₄ samples were recorded with the same experimental setup, both at room temperature and at 80 K.From the variation of the line strengths between 80 K and 294 K, the low energy values of about 12,000 transitions were determined. They allow accounting for the temperature dependence of 84 and 93% of the methane absorbance in the region, at room temperature and 80 K, respectively. As a result, we provide as supplementary material two complete line lists at 80 K and 294 K, including CH₃D and ¹³CH₄ identification and lower state energy values.     

Ground-based solar absorption studies for the Carbon Cycle science by Fourier Transform Spectroscopy (CC-FTS) mission

Carbon cycle science by Fourier transform spectroscopy (CC-FTS) is an advanced study for a future satellite mission. The goal of the mission is to obtain a better understanding of the carbon cycle in the Earth's atmosphere by monitoring total and partial columns of CO₂, CH₄, N₂O, and CO in the near infrared. CO₂, CH₄, and N₂O are important greenhouse gases, and CO is produced by incomplete combustion. The molecular O₂ column is also needed to obtain the effective optical path of the reflected sunlight and is used to normalize the column densities of the other gases. As part of this advanced study, ground-based Fourier transform spectra are used to evaluate the spectral region and resolution needed. Spectra in the 3950–7140 cm^?1 region with a spectral resolution of 0.0042 cm^?1 recorded at Kiruna (67.84°N, 20.41°E, and 419 m above sea level), Sweden, on 1 April 1998, were degraded to the resolutions of 0.01, 0.1, and 0.3 cm^?1. The effect of spectral resolution on the retrievals has been investigated with these four Kiruna spectra. To obtain further information on the spectral resolution, optical components and spectroscopic parameters required by the future mission, high-resolution solar absorption spectra between 2000 and 15000 cm^?1 were recorded using Fourier transform spectrometers at Kitt Peak (31.9°N, 111.6°W, and 2.1 km above sea level), Arizona, on 25 July 2005 and Waterloo (43.5°N, 80.6°W, and 0.3 km above sea level), Ontario, on 22 November 2006 with spectral resolutions of 0.01 and 0.1 cm^?1, respectively. Dry air volume mixing ratios (VMRs) of CO₂ and CH₄ were retrieved from these ground-based observations. The HITRAN 2004 spectroscopic parameters are used with the SFIT2 package for the spectral analysis. The measurement precisions for CO₂ and CH₄ total columns are better than 1.07% and 1.13%, respectively, for our observations. Based on these results, a Fourier transform spectrometer (maximum spectral resolution of 0.1 cm^?1 or 5 cm maximum optical path difference (MOPD)) operating between 2000 and 15000 cm^?1 is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO₂, CH₄, and O₂ requires new laboratory measurements of the spectroscopic line parameters.     

Validation of HNO3 spectroscopic parameters using atmospheric absorption and emission measurements

The improved database of HNO₃ spectroscopic parameters in the 600–950 cm^?1 spectral region presented in [Gomez L, Tran H, Perrin A, Gamache RR, Laraia A, Orphal J, et al. Some improvements of the HNO₃ spectroscopic parameters in the spectral region from 600 to 950 cm^?1. JQSRT 2008, in press] is tested by comparisons between calculations and atmospheric remotely sensed absorption and emission spectra. The line parameters in the 11.3 μm region are validated using ground-based Fourier transform solar absorption measurements, whereas those in the 13.1 μm region are successfully tested using balloon-borne atmospheric emission spectra. In both regions, the quality of the line parameters and the consistency between band intensities is confirmed through comparisons with emission spectra collected by the satellite-borne MIPAS instrument.     

Analysis of the CRDS spectrum of 18O3 between 6950 and 7125 cm−1

The absorption spectrum of the ¹⁸O₃ isotopologue of ozone was recorded by CW-Cavity Ring Down Spectroscopy in the 6950–7125 cm^?1 region. The typical noise equivalent absorption of the recordings is α_min ≈1×10^?10 cm^?1. The spectrum is dominated by three very weak bands: 3ν₁+5ν₃ near 7009 cm^?1 and the ν₂+7ν₃ and 4ν₂+5ν₃ interacting bands near 7100 cm^?1. In total 260, 206 and 133 transitions were assigned for the 3ν₁+5ν₃, ν₂+7ν₃ and 4ν₂+5ν₃ bands, respectively. The line positions of the 3ν₁+5ν₃ band were modelled using an effective Hamiltonian (EH) model involving two dark states – (6 0 1) and (2 5 2) – in interaction with the (3 0 5) bright state. The EH model developed for the ν₂+7ν₃ and 4ν₂+5ν₃ bands involves only the (0 1 7) and (0 4 5) interacting bright states. Line positions could be reproduced with rms deviations on the order of 0.01 cm^?1 and the dipole transition moment parameters were determined for the three observed bands. The obtained set of parameters and the experimentally determined energy levels were used to generate a list of 984 transitions of the three bands which is provided as Supplementary Material.     

Effective line strengths of trans-nitrous acid near 1275 cm−1 and cis-nitrous acid at 1660 cm−1

We determined the effective line strengths of the trans conformer of nitrous acid (HONO) near 1275 cm^?1 (R-branch of ν₃ mode, NOH bend) and of the cis conformer at 1660 cm^?1 (R-branch of ν₂ mode, NO stretch), both at a spectral resolution of 0.001 cm^?1 by tunable infrared laser differential absorption spectroscopy (TILDAS) utilizing continuous-wave quantum cascade (cw-QC) lasers. Absorbance of one conformer was measured while simultaneously quantifying the mixing ratio of total HONO by catalytic conversion to nitric oxide (NO) followed by calibrated absorption spectroscopy. Line strengths obtained here are consistent with previously reported band strengths for the trans conformer but are lower by a factor of approximately 2.4 for the cis conformer.     

Vibrational spectroscopy of oxygen on the (100) and (111) surfaces of lanthanum hexaboride

Reflection absorption infrared spectroscopy (RAIRS) and high resolution electron energy loss spectroscopy (HREELS) have been used to study the adsorption of oxygen on the (100) and (111) surfaces of lanthanum hexaboride. Exposure of the surface at temperatures of 95 K and above to O₂ produces atomic oxygen on the surface and yields vibrational peaks in good agreement with those observed in previous HREELS studies. On the La-terminated (100) surface, RAIRS peaks correspond to vibrations of the boron lattice that gain intensity due to a decrease in screening of surface dipoles that accompanies oxygen adsorption. A sharp peak at ～ 734 cm^?1 in the HREEL spectrum shows isotopic splitting with RAIRS into two components at 717 and 740 cm^?1 with full widths at half maxima of only 12 cm^?1. The sharpness of this mode is consistent with its interpretation as a surface phonon that is well separated from both the bulk phonons and other surface phonons of LaB₆. On the boron-terminated LaB₆(111) surface, broad and weak features are assigned to both vibrations of the boron lattice and of boron oxide. On the (100) surface, oxygen blocks the adsorption sites for CO, and adsorbed CO prevents the dissociative adsorption of O₂.     

Comment on “Spectroscopic database of CO2 line parameters: 4300–7000 cm–1”

The “Spectroscopic database of CO₂ line parameters: 4300–7000 cm^–1” constructed by Toth et al., has been considered in relation with our previous and current studies of the absorption spectrum of carbon dioxide (CO₂) by high-sensitivity CW-cavity ring down spectroscopy (CW-CRDS) in the 5850–7000 cm^?1 region. Part of the line parameters of the database are based on accurate spectroscopic measurements by Fourier transform spectroscopy (FTS) but Toth et al. have chosen to fix to a very low value (4×10^?30 cm/molecule) the lower intensity cut off. This value which is far below the FTS detection limit has led to long range extrapolations to high J values and to the inclusion of weak unobserved bands which were theoretically predicted. In the 5850–7000 cm^?1 region, most of these calculated transitions were previously observed by CW-CRDS. The comparison with the CW-CRDS ¹³CO₂ spectrum in this region, has evidenced that (i) many weak bands above the intensity cut off are missing; (ii) there are important deviations between the line parameters provided in the database and our previous observations both for line positions (up to 1.7 cm^?1) and line intensities (up to a factor 80). Our discussion was limited to the three ¹³C species (¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O and ¹⁶O¹³C¹⁷O) but the conclusions should apply to the other isotopologues in particular ¹²C¹⁶O₂ and to the full spectral range of the database.Alternatively, the global effective operators models for CO₂ can reproduce satisfactorily all the experimental line positions and line intensities available in the literature. This polyad model, which has been developed for most of the CO₂ isotopologues, constitutes an interesting alternative for the most accurate and complete CO₂ database. In particular, very weak bands, accidental resonances, intensity transfers and extra lines are accurately accounted for and predicted by this polyad model.     

Photo-absorption studies on carbonyl sulphide in 30,000–91,000 cm−1 region using synchrotron radiation

Photo-absorption spectrum of carbonyl sulphide (OCS) is recorded in 30,000–91,000 cm^?1 (3300–1050 Å) region at an average resolution of 1.2 Å using Photo-physics beamline on the 450 MeV Indus-1 synchrotron radiation source at RRCAT Indore, India. Owing to significant absorption cross section dependence, spectra of OCS are recorded at various pressures (0.001–5 mbar) to optimize the S/N ratio for band systems appearing at different energy regions. The spectral region below 70,000 cm^?1 has contributions from dissociation mechanism of the ground state of OCS and three valence band systems arising from promotion of a 3π electron to 4π and 10σ orbital. Improved S/N ratio helped in unambiguous assignment of the valence band progressions at 42,000–48,000 cm^?1, 53,000–62,000 cm^?1 and 63,500–70,000 cm^?1 regions to the ¹Δ←X¹Σ⁺ transition, the relatively intense and sharp bands of ¹Π←X¹Σ⁺ transition and intense but broad bands of ¹Σ⁺←X¹Σ⁺ transition, respectively, and obtain the vibrational frequencies. Above 70,000 cm^?1 Rydberg series arising from s, p, d and f orbitals converging to the ionic ground state X²Π of OCS⁺ (90,121 cm^?1) are identified. Long progression in the first few members of the Rydberg series is suggestive of mixed valence character. Quantum defects are evaluated and used to discuss the nature of the molecular orbital. The present study provides a unifying picture of the VUV photo-absorption spectrum of OCS up to its first ionization limit.     

Extended line positions,intensities, empirical lower state energies and quantum assignments of NH3 from 6300 to 7000 cm−1

Nearly 4800 features of ammonia between 6300 and 7000 cm^?1 with intensities ≥4×10^?24 cm^?1/(molecule·cm^?2) at 296 K were measured using 16 pure NH₃ spectra recorded at various temperatures (296–185 K) with the McMath–Pierce Fourier Transform Spectrometer at Kitt Peak National Observatory, AZ. The line positions and intensities were retrieved by fitting individual spectra based on a Voigt line shape profile and then averaging the values to form the experimental linelist. The integrated intensity of the region was 4.68×10^?19 cm^?1/(molecule·cm^?2) at 296 K. Empirical lower state energies were also estimated for 3567 absorption line features using line intensities retrieved from 10 spectra recorded at gas temperature between 185 and 233 K. Finally, using Ground State Combination Differences (GSCDs) and the empirical lower state energy estimates, the quantum assignments were determined for 1096 transitions in the room temperature linelist, along with empirical upper state energies for 434 levels. The assignments correspond to seven vibrational states, as confirmed from recent ab initio calculations. The resulting composite database of ¹⁴NH₃ line parameters will provide experimental constraints to ab initio calculations and support remote sensing of gaseous bodies including the atmospheres of Earth, (exo)planets, brown dwarfs, and other astrophysical environments.     

Detection and analysis of four new bands in CRDS 16O3 spectra between 7300 and 7600 cm−1

The absorption spectrum of the ¹⁶O₃ isotopologue of ozone was recorded in the 7000–7920 cm^?1 region by using high sensitivity CW-Cavity Ring Down Spectroscopy (α_min ～ 10^?10 cm^?1). This report is devoted to the analysis of the 7300–7600 cm^?1 region dominated by four A-type bands: 6ν₁ + ν₃ centred around 7395 cm^?1, 3ν₁ + 5ν₂ + ν₃ and 2ν₁ + 4ν₂ + 3ν₃ lying in the 7450 cm^?1 region and 5ν₁ + 2ν₂ + ν₃ centred around 7579 cm^?1. 213 transitions of the 6ν₁ + ν₃ band were assigned and the corresponding line positions were modeled using an effective Hamiltonian including a Coriolis resonance interaction between the (601) upper state and a A-type dark state. The two very close 3ν₁ + 5ν₂ + ν₃ and 2ν₁ + 4ν₂ + 3ν₃ bands were analysed using a similar effective Hamiltonian scheme involving the anharmonic resonance coupling between the (351) and (243) states. For these two bands, 304 transitions were assigned. The modelling also includes a first Coriolis resonance interaction between the (351) bright state and the (530) dark state, and a second one between the (243) bright state and the (144) dark state. In the 7579 cm^?1 region, 205 transitions of the 5ν₁ + 2ν₂ + ν₃ band were assigned and modelled taking into account the Coriolis resonance interactions between the (521) upper state and the (700), (342) and (280) dark states.The dipole transition moment parameters of the four analysed bands were determined by a least-squares fit to the measured line intensities. For the studied band systems, the effective Hamiltonian and transition moment operator parameters were used to generate line lists provided as Supplementary Materials.     

Refinements of the WKMC empirical line lists (5852–7919 cm−1) for methane between 80 K and 296 K

During the last 4 years, empirical line lists for methane at room temperature and at 80 K were constructed from spectra recorded by (i) differential absorption spectroscopy (DAS) in the high energy part of the tetradecad (5852?6195 cm^?1) and in the icosad (6717–7589 cm^?1) and (ii) high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) in the 1.58 μm and 1.28 μm transparency windows (6165–6750 cm^?1 and 7541–7919 cm^?1, respectively). We have recently constructed the global line lists for methane in “natural” isotopic abundance, covering the spectral region from 5854 to 7919 cm^?1 (Campargue A, Wang L, Kassi S, Mondelain D, Bézard B, Lellouch E, et al., An empirical line list for methane in the 1.26–1.71 μm region for planetary investigations (T=80–300 K). Application to Titan, Icarus 219 (2012) 110–128). These WKMC (Wang, Kassi, Mondelain, Campargue) empirical lists include about 43,000 and 46,420 lines at 80±3 K and 296±3 K, respectively. The “two temperature method” provided lower state energy values, E_emp, for about 24,000 transitions allowing us to account satisfactorily for the temperature dependence of the methane absorption over the considered region. The obtained lists have been already successfully applied in a large range of temperature conditions existing on Titan, Uranus, Pluto, Saturn and Jupiter.In the present contribution, we provide some improvements to our lists by using literature data to extend the set of lower state energy values and by correcting the distortion of the high E_emp values (J>10) due to the temperature gradient existing in the cryogenic cell used for the recordings. The proposed refinements are found to have an overall limited impact but they may be significant in some spectral intervals below 6500 cm^?1.The new version of our lists at 80 K and 296 K is provided as Supplementary Material: the WKMC@80K+ and WKMC@296K lists are adapted for planetary and atmospheric applications, respectively. The WKMC@80K+ list is made applicable over a wider range of temperatures and shows satisfactory extrapolation capabilities up to room temperature. It was obtained by transferring to the 80 K list the 27,580 single lines present only in the 296 K list, with corresponding lower state energy values chosen to make them below the detectivity limit at 80 K.In the discussion, the different line lists and databases available for methane in the near infrared are compared and some suggestions are given.     

High-resolution spectrum of the ν9 band and reinvestigation of the ν8 band of cis-CH3ONO

The infrared spectrum of methyl nitrite CH₃ONO has been recorded at a spectral resolution of 0.003 cm^?1 using a Fourier-transform spectrometer Bruker IFS125HR. The ν₈ band of the cis isomer has been reinvestigated in the 780–880 cm^?1 spectral range to complete the study made by Goss et al. (2004) [3] and to fit the internal rotor splittings. The BELGI-IR program, which enables us to treat an isolated infrared band for asymmetric molecules containing one internal methyl rotor has been used for the analysis and predictions of spectra. Finally 1036 lines (913 A-type and 123 E-type lines for J≤50 and K_a≤28) have been assigned for the cis isomer and fitted with a standard deviation of 0.00047 cm^?1.Furthermore, for the first time, the ν₉ band of cis-CH₃ONO was investigated in the 540–660 cm^?1 spectral range and rather large internal rotation splittings were also observed at higher J values. For the ν₉ band, the effective approach performed with the BELGI-IR program allowed us to analyze and reproduce 682 lines up to J=50 and K_a=18 with a standard deviation of 0.00051 cm^?1. The multiple vibration–rotation–torsion interactions, which are likely to occur between the excited v₉=1 and v₈=1 states and the torsional manifolds are discussed.     

Stability of widely tuneable,continuous wave external-cavity quantum cascade laser for absorption spectroscopy

The performance of widely tuneable, continuous wave (cw) external-cavity quantum cascade laser (EC-QCL) has been evaluated for direct absorption spectroscopy measurements of nitric oxide (NO) in the wavenumber range 1872–1958 cm^?1 and with a 13.5 cm long optical cell. In order to reduce the absorption measurement errors due to the large variations of laser intensity, normalisation with a reference channel was used. Wavelength stability within the scans was analysed using the Allan plot technique for the reduced wavenumber range of 1892.4–1914.5 cm^?1. The Allan variances of the NO absorption peak centres and areas were observed to increase with successive scan averaging for all absorption peaks across the wavelength scan, thus revealing short- and long-term drifts of the cw EC-QCL wavelength between successive scans. As an example application, the cw EC-QCL was used for NO measurements in the exhaust of an atmospheric pressure packed-bed plasma reactor applied to the decomposition of dichloromethane in waste gas streams. Etalon noise was reduced by subtracting a reference spectrum recorded when the plasma was off. The NO limit of detection (SNR = 1) was estimated to be ～2 ppm at atmospheric pressure in a 20.5 cm long optical cell with a double pass and a single 7 s scan over 1892.4–1914.5 cm^?1.     

Broadband 2.84 μm luminescence properties and Judd–Ofelt analysis in Dy3+ doped ZrF4–BaF2–LaF3–AlF3–YF3 glass

2.84 μm luminescence with a bandwidth of 213 nm is obtained in Dy³⁺ doped (ZrF₄–BaF₂–LaF₃–AlF₃–YF₃) ZBLAY glass. Three intensity parameters and radiative properties have been determined from the absorption spectrum based on the Judd–Ofelt theory. The 2.84 μm emission characteristics and energy transfer mechanism upon excitation of a conventional 808 nm laser diode are investigated. The prepared Dy³⁺ doped ZBLAY glass possessing high predicted spontaneous transition probability (45.92 s^?1) along with large calculated emission cross section (1.17×10^?20 cm²) has potential applications in 2.8 μm laser.     

Infrared absorption cross sections for methanol

Infrared absorption cross sections for methanol, CH₃OH, have been determined near 3.4 and 10 μm from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. Methanol/dry synthetic air mixtures were prepared and spectra were recorded at 0.015 cm^?1 resolution (calculated as 0.9/MOPD) at a number of temperatures and pressures (50–760 Torr and 204–296 K) appropriate for atmospheric conditions. Intensities were calibrated using composite methanol spectra taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new measurements in the 10 μm region indicate problems with the existing methanol spectroscopic line parameters in the HITRAN database, which will impact the accuracy of satellite retrievals.     

Structural investigation of Te-based chalcogenide glasses using Raman spectroscopy

Structural changes of metals (Zn, Sb, In, Ga) and metal halides (AgI, ZnI₂, CdI₂, PbI₂, BiI₃) modified GeTe₄ glasses were investigated with the aid of Raman spectroscopy. The Raman spectra of these glasses in the frequency region between 100 cm^?1 and 300 cm^?1 display four main bands at about 124, 140, 159 and 275 cm^?1 which are contributed by Ge–Te, Te–Te, Te–Te and Ge–Ge vibration modes. The intensity of 159 cm^?1 and 275 cm^?1 bands vary with the addition of different glass modifiers. While the relative intensity of the 124 cm^?1 and 140 cm^?1 bands are insensitive to composition changes. Glass modifiers like Zn, In and Sb act as glass network unstabilizer which will disorganize the glass network by opening up the chain structures of Ge–Te and Te–Te. In the case of Ga and metal halides, Ga can open up Ge–(Te–Te)_4/2 tetrahedra and form Ga–(Te–Te)_3/2 triangle. Iodine can form covalent bonds with tellurium and decrease the tendency of microcrystal formation. Thus both Ga and iodine ultimately act as glass network stabilizer.     

High sensitivity cavity ring down spectroscopy of 13C16O2 overtone bands near 806 nm

The absorption spectrum of ¹³C¹⁶O₂ near 806 nm has been recorded with a continuous-wave cavity ring-down spectrometer. Two cold bands and one associated hot band are observed in this region. The line positions of these bands are determined with an accuracy of 0.003 cm^?1. The absolute line intensities have also been retrieved with an estimated accuracy of 4% for majority of the unblended lines. The vibrational transition dipole moment squared values and the empirical Herman–Wallis coefficients are determined for all the three bands. The comparison of the retrieved line positions and intensities to those given in the Carbon Dioxide Spectroscopic Databank shows large deviations in the line intensities of the 10052–00001 band. The effective dipole moment parameters describing the line intensities of ¹³C¹⁶O₂ near 806 nm are fitted according to the observed line intensities.     

First analysis of the 3ν9−ν9 hot band of difluoroboric acid (BF2OH). Further evidence of large amplitude effects for the OH torsion

The hot band 3ν₉?ν₉ of the isotopologue ¹¹BF₂OH (difluoroboric acid) located at 1034.78 cm^?1 was investigated for the first time by Fourier transform infrared spectroscopy. During previous studies both, the ν₉ mode (OH-torsion relative to the BF₂ moiety, at 522.87 cm^?1) and the ν₄ mode (in-plane OH bend) had been shown to exert large amplitude motion, and splittings of 0.0051 and 0.0038 cm^?1 had been observed in the interacting 2ν₉ and ν₄ bands located at 1042.87 and 961.49 cm^?1, respectively. The present work establishes large amplitude effects also for the 9³ excited state located at 1557.655 cm^?1. Numerous P and R transitions of the 3ν₉–ν₉ hot band were identified in the 2ν₉ manifold, and doublets corresponding to a torsional splitting of 0.031 cm^?1 in the 9³ state were observed. The vibrational assignment of the 9³ state was confirmed by the detection of the 3ν₉?2ν₉ hot band Q branch in the 19 μm region.