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.     

High sensitivity CW-Cavity Ring Down Spectroscopy of N2O between 6950 and 7653 cm−1 (1.44–1.31 μm): I. Line positions

The absorption spectrum of nitrous oxide, N₂O, has been recorded by CW-Cavity Ring Down Spectroscopy between 6950 and 7653 cm^?1. The spectra were obtained at Doppler limited resolution using a CW-CRDS spectrometer based on a series of fibered DFB laser diodes. The typical noise equivalent absorption, in the order of α_min≈1×10^?10 cm^?1, allowed for the detection of lines with intensity as small as 1×10^–29 cm/molecule.The positions of 7203 lines of four isotopologues (¹⁴N₂¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O and ¹⁴N₂¹⁸O) were measured with a typical accuracy of 1.0×10^?3 cm^?1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian models developed for each isotopologue. The band by band analysis allowed for the determination of the rovibrational parameters of more than 95 bands, most of them being newly reported while new rotational transitions are measured for the others. The measured line positions of the main isotopologue are found to be in good agreement with the predictions of the effective Hamiltonian model but a few deviations up to 0.20 cm^?1 are observed. Local rovibrational perturbations were evidenced for several bands. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian models.     

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.     

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.     

The near infrared cavity-enhanced absorption spectrum of methyl cyanide

The absorption spectrum of methyl cyanide (CH₃CN) has been measured in the near IR between 6000 and 8000 cm^?1 with a resolution of 0.12 cm^?1 using Fourier transform incoherent broadband cavity-enhanced absorption spectroscopy. The spectrum contains several weakly perturbed spectral regions; potential vibrational combination bands contributing to the spectrum are outlined. Line positions and cross-sections of CH₃CN between 6814 and 7067 cm^?1 have been measured at high-resolution of 0.001 cm^?1 using diode laser based off-axis cavity-enhanced absorption spectroscopy. A total of 4630 new absorption lines of CH₃CN are identified in this region. A value for the self-broadening coefficient has determined to be (3.3±0.2)×10^?3 cm^?1 mbar^?1 for one isolated line at 7034.171 cm^?1. Several line series have been identified in these regions and an autocorrelation analysis performed with a view to aiding future assignments of the rotational-vibrational transitions.     

The far infrared spectrum of trans-formic acid: An extension up to 175 cm−1

The far infrared spectrum of HCOOH was recorded at a high resolution (0.0009 cm^?1) and long path length (72 m) at the far-infrared beamline, Canadian Light Source. Spectra were recorded in the region 62–300 cm^?1, showing transitions from the trans-isomer.Ground state rotational transitions with K_a up to 30, were identified up to 175 cm^?1, extending the observation reported in the literature. A total of 3321 transitions were assigned and fitted together with previous (4149) published data. An improved set of rotational parameters was obtained adopting the symmetric top (A) reduction of the rotational Hamiltonian in the I^r representation. The newly measured far infrared transitions allowed the determination of all diagonal and off diagonal 8th order parameters L and of some of the diagonal 10th order parameters P.     

Line lists for H218O and H217O based on empirical line positions and ab initio intensities

New line lists for isotopically substituted water are presented. Most line positions were calculated from experimentally determined energy levels, while all line intensities were computed using an ab initio dipole moment surface. Transitions for which experimental energy levels are unavailable use calculated line positions. These line lists cover the range 0.05–20 000 cm^?1 and are significantly more complete and potentially more accurate than the line lists available via standard databases. All lines with intensities (scaled by isotopologue abundance) greater than 10^?29 cm/molecule at 296 K are included, augmented by weaker lines originating from pure rotational transitions. The final line lists contain 39 918 lines for H₂¹⁸O and 27 546 for H₂¹⁷O and are presented in standard HITRAN format. The number of experimentally determined H₂¹⁸O and H₂¹⁷O line positions is, respectively, 32 970 (83% of the total) and 17 073 (62%) and in both cases the average estimated uncertainty is 2×10^?4 cm^?1. The number of ab initio line intensities with an estimated uncertainty of 1% is 16 621 (42%) for H₂¹⁸O and 13 159 (48%) for H₂¹⁷O.     

Line intensities for the ν1, ν3 and ν1+ν3 bands of 34SO2

Using both high resolution (0.0018 cm^?1) and medium resolution (0.112 cm^?1) Fourier transform spectra of an enriched ³⁴S (95.3%) sample of sulfur dioxide, it has been possible to accurately measure a large number of individual line intensities for some of the strongest of the SO₂ bands, i.e. ν₁, ν₃ and ν₁₊ν₃. These intensities were least-squares fitted using a theoretical model which takes into account the vibration–rotation interactions linking the upper energy levels where needed, and, in this way, expansions of the various transition moment operators were determined. The Hamiltonian parameters determined in previous analyses together with these moments were then used to generate synthetic spectra for the bands studied and their corresponding hot bands providing one with an extensive picture of the absorption spectrum of ³⁴SO₂ in the spectral domains, 8.7, 7.4, and 4 μm.     

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.     

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.     

First high-resolution analysis of the ν15, ν12, ν5, ν10 and ν2 bands of oxirane

Fourier transform spectra of oxirane (ethylene oxide, c-C₂H₄O) have been recorded in the 730–1560 cm^?1 (6.4–13.7 μm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.0019 cm^?1. A total of six vibration bands, ν₁₅, ν₁₂, ν₅, ν₃, ν₁₀ and ν₂, have been observed and analyzed. The corresponding upper state ro-vibrational levels were fit using Hamiltonian matrices accounting for various interactions. Satisfactory fits were obtained using the following polyads {15¹, 12¹, 5¹} and {10¹, 2¹} of interacting states. As a result, an accurate and extended set of Hamiltonian constants were obtained. The following band centers were derived: ν₀ (ν₁₅) = 808.13518(60) cm^?1, ν₀ (ν₁₂) = 822.27955(37) cm^?1, ν₀ (ν₅) = 876.72592(15), ν₀ (ν₃) = 1270.37032(10) cm^?1, ν₀ (ν₁₀) = 1471.35580(50) cm^?1 and ν₀ (ν₂) = 1497.83309(15) cm^?1 where the uncertainties are one standard deviation.     

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.     

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.     

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.     

Analysis of the Coriolis interaction between ν6 and ν4 bands of ethylene-cis-d2(cis-C2H2D2) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν₆ band of ethylene-cis-d₂(cis-C₂H₂D₂) was recorded with a unapodized resolution of 0.0063 cm^?1 in the 990–1100 cm^?1 region. A total of 609 transitions were assigned to this band centred at 1039.7682 ± 0.0003 cm^?1. The ν₆ band was found to be coupled to the ν₄ band by a-type Coriolis resonance. Both perturbed and unperturbed transitions were assigned and fitted to give eight rovibrational constants with high accuracy for the v₆ = 1 state with a standard deviation of 0.00097 cm^?1 using a Watson’s A-reduced Hamiltonian in the I^r representation. From a rovibrational analysis of the Coriolis interaction between the ν₆ band and non-infrared active ν₄ band of cis-C₂H₂D₂, the band centre of ν₄ at 984.9 ± 0.2 cm^?1 was derived. Furthermore, the second-order a-type Coriolis coupling constant between the two bands was obtained for the first time.     

The high-resolution FTIR spectrum of the ν4 + ν8 band of trans-d2-ethylene (trans-C2H2D2)

The FTIR absorption spectrum of the hybrid A–B type ν₄ + ν₈ combination band of trans-C₂H₂D₂ centered at 1845.98737 cm^?1 in the 1730–1940 cm^?1 region was recorded at an unapodized resolution of 0.0063 cm^?1. A total of 2725 a- and b-type transitions was assigned and fitted to upper state (ν₄ + ν₈ = 1) rovibrational constants up to sextic terms using Watson’s A-reduced Hamiltonian in I^r representation. The b-type feature of the band was analyzed for the first time. The root-mean-square deviation of the IR fit was 0.00059 cm^?1. The most accurate set of ground state rovibrational constants up to sextic terms was also derived from the simultaneous fit of 3340 ground state combination differences from the present analysis and the ν₄ band of trans-C₂H₂D₂. The transition dipole moment ratio $\left|\frac{{\mu }_a}{{\mu }_b}\right|$ was found to be 1.95 ± 0.06.     

Effect of changes of the HITRAN database on transmittance calculations in the near-infrared region

In order to retrieve from high spectral resolution measurements with high accuracy, it is necessary to be able to evaluate the transmittance precisely. However, the uncertainty of the spectroscopic parameters is one of the most important contributions that affect the accuracy of transmittance. HITRAN is a compilation of spectroscopic parameters which has been updated several times. The transmittance calculations using the line parameters from the HITRAN’2000 database and the HITRAN’2004 database have been compared over the near infrared range from 4200 to 10,000 cm^?1. The differences between calculated transmittances over this spectral range are mainly caused by changes of the line parameters for H₂O, CO₂ and CH₄. For the tropical atmosphere, the differences are very prominent. Transmittance calculations for the sub-arctic winter atmosphere are less sensitive to the changes in the HITRAN database than those for the tropical atmosphere; but, the changes of line parameters still can not be ignored when considering the relative differences. For example, the relative difference is ～35% at 5073.3 cm^?1 with 0.2 cm^?1 spectral resolution. The comparisons have shown that it is important to pay attention to the changes of line parameters of the HITRAN database or to use the latest edition so as to improve the accuracy of atmospheric sounding with high spectral resolution.     

Rotational analysis of bands in the high-resolution infrared spectra of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d1

Pure samples of cis,cis- and trans,trans-1,4-difluorobutadiene-2-d₁ have been synthesized, and high-resolution (0.0015 cm^?1) infrared spectra have been recorded for these nonpolar molecules in the gas phase. For the cis,cis isomer, the rotational structure in two C-type bands at 775 and 666 cm^?1 and one A-type band at 866 cm^?1 has been analyzed to yield a combined set of 2020 ground state combination differences (GSCDs). Ground state rotational constants fit to these GSCDs are A₀ = 0.4195790(4), B₀ = 0.0536508(8), and C₀ = 0.0475802(9) cm^?1. For the trans,trans isomer, three C-type bands at 856, 839, and 709 cm^?1 have been investigated to give a combined set of 1624 GSCDs. Resulting ground state rotational constants for this isomer are A₀ = 0.9390117(8), B₀ = 0.0389225(4), and C₀ = 0.0373778(3) cm^?1. Small inertial defects confirm the planarity of both isomers in the ground state. Upper state rotational constants have been determined for most of the transitions. The ground state rotational constants for the two isotopologues will contribute to the data set needed for determining semiexperimental equilibrium structures for the nonpolar isomers of 1,4-difluorobutadiene.     

High-resolution Fourier transform study of the ν3 fundamental band of trans-formic acid

Using high-resolution Fourier transform spectra of trans-HCOOH recorded at 5.6 μm, we carried out an extensive analysis of the strong ν₃ fundamental band (carbonyl stretching mode) at 1776.83 cm^?1, starting from results of a previous analysis [Weber WH, Maker PD, Johns JWC, Weinberger E. J Mol Spectrosc 1987; 121: 243–60]. As pointed out in the literature, the ν₃ band is significantly perturbed by resonances due to numerous dark bands. We were able to assign series belonging to the ν₅+ν₇, ν₅+ν₉, ν₆+ν₇ and ν₆+ν₉ dark bands, located at 1843.48, 1792.63, 1737.96 and 1726.40 cm^?1, respectively. The model used to calculate energy levels accounts partly for the observed resonances, and enabled us to reproduce most of the observed line positions, within their experimental uncertainties. We also determined absolute line intensities with an accuracy estimated to 15%. Finally, we generated, for the first time, a list of line parameters for the 5.6 μm region of trans-formic acid.