Multispectrum analysis of the ν9 band of C2H6: Positions, intensities, self- and N2-broadened half-width coefficients

Line positions, intensities, Lorentz self- and N₂-broadened half-width coefficients have been measured for ^PQ₃, ^PQ₂, ^PQ₁, ^RQ₀, ^RQ₁, ^RQ₂, and ^RQ₃ sub-band transitions in the ν₉ fundamental band of ¹²C₂H₆. A multispectrum nonlinear least-squares fitting technique was used to fit up to 17 high-resolution (∼0.00156 cm⁻¹), room temperature absorption spectra of pure (99.99% chemical purity) natural sample of ethane and lean mixtures of the high-purity ethane diluted with N₂. A Bruker IFS 120HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington was used to record the data. A standard Voigt line shape was assumed to fit all the data since no line mixing or other non Voigt line shapes were required to fit any of the spectra used in the analysis. Short spectral intervals (∼2-2.5 cm⁻¹) of all 17 spectra covering a specific ^PQ or ^RQ sub-band were fit simultaneously. For the first time in an ethane band, pressure-broadened half-width coefficients were determined for the torsional-split components. However, for better reliability of the retrieved coefficients for the weaker components (transitions with large intensity ratios of 4:1 or 3:1 for most K levels between the strong and weak components), constraints were used such that the half-width coefficients of both torsional-split components for a given J were identical for a specific broadening gas. No pressure-induced shift coefficients were necessary to fit the spectra to their noise level. The present study revealed for the first time the dependence of self- and N₂-broadened half-width coefficients upon the J, K quantum numbers of the transitions in ethane. A number of transitions belonging to the ν₉+ν₄−ν₄ and the ν₉+2ν₄−2ν₄ hot bands were also observed in the fitted regions and measurements were made when possible.     

Temperature dependence of self- and N2-broadening coefficients of CH3Br ν6 band

Using absorption FT spectra (Bruker IFS 120, unapodized FWHM resolution ≈0.001 cm⁻¹), about 1400 lines, between 880 and 1050 cm⁻¹, and belonging to the ν₆ band of both ¹²CH₃⁷⁹Br and ¹²CH₃⁸¹Br isotopologues have been studied. Self- and N₂-broadening coefficients are measured at various temperatures with an accuracy estimated to be around 10%. Their temperature-dependence exponents n_self and n_N2 have been derived with an accuracy estimated to be between 10% and 20%. A rotational dependence with the quantum number J has been observed for both n_self and n_N2, and has been empirically modeled using average values and polynomial expansions.     

New Analysis of the ν3 fundamental band of HDCO: Positions and intensities

Using high-resolution Fourier transform spectra of mono deuterated formaldehyde (HDCO) recorded in the 5.8-μm spectral range at Giessen (Germany), we carried out an extensive analysis of the strong ν₃ fundamental band (carbonyl stretching mode) at 1724.2676 cm⁻¹, starting from results of a previous analysis [J.W.C. Johns, A.R.W. McKellar, J. Mol. Spectrosc. 64 (1977) 327-339]. For this hybrid band (with both A- and B-type transitions) the analysis was pursued up to high rotational quantum numbers. In this way, it was possible to evidence a resonance which perturbs the ν₃ lines for high K_a values which is due to the existence of the 2ν₅ and ν₅ + ν₆ dark bands in the same spectral region. In addition a local resonance is perturbing the 3¹ levels in  = 8 which is due to a crossing with the 4¹ energy levels in K_a = 11. The model used to calculate the energy levels accounts for the observed A- type, B- type C-type Coriolis (and/or) Fermi resonances which couple the 3¹ and the 5¹6¹, 5², and 4¹ energy levels. However the 4¹ state is also involved in strong vibration-rotation interactions coupling the {5¹,6¹,4¹} system of resonation states of HDCO [A. Perrin, J.M. Flaud, L. Margulès, J. Demaison, H. Mäder, S. Wörmke, J. Mol. Spectrosc. 216 (2002) 214-224]. Therefore the final energy levels calculation was performed for the {5¹,6¹,4¹,3¹,5²,5¹6¹} resonating states and in this way it was possible to reproduce the observed line positions, within their experimental uncertainties. The present work also led to the determination of the intensity ratio of the B- to A-type components of the ν₃ band I_A/I_B ∼24 band from spectral fittings performed in several parts of the observed spectrum. Finally, using the 5.8 μm band intensity available in the literature we generated, for the first time, a list of line parameters (positions and intensities) for the 5.8 μm region of HDCO.     

Simultaneous analysis of the 2ν2, 2ν5, and ν2 + ν5 vibration-rotation bands of CH3Br

Previous studies of the parallel bands 2ν₂ and $\text{2ν}{}_5{}^0$ of CH₃Br by the two first authors have been completed by the analysis of the weaker perpendicular band ν₂ + ν₅, centered near 2745 cm^?1. It is well known that the v₂ = 1 and v₅ = 1 states of methylbromide are linked by an x-y-type Coriolis interaction. Therefore, in the 2500–2900-cm^?1 range, the levels

$\text{(v}{}_2\text{=2), (v}{}_5\text{2, l}{}_5\text{=0), (v}{}_5\text{=2, l}{}_5\text{±2), (v}{}_5\text{=v}{}_2\text{=1, l=5±1)}$

are linked by a similar interaction. Least-squares and prediction programs have been written to treat this kind of problems and they have been satisfactorily applied to both isotopic species, CH₃⁷⁹Br and CH₃⁸¹Br. A localized resonance in the K = 0 subband of ν₂ + ν₅ has been shown to be due to the 3ν₃ + ν₆ band. No evidence for a strong Fermi resonance between ν₁ and $\text{2ν}{}_5{}^0$ has been found.     

H2-broadening coefficients in the ν2 and ν4 bands of PH3

H₂-broadening coefficients are measured for 41 transitions of PH₃ in the QR branch of the ν₂ band and the PP, RP, and PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 2 to 16 and K from 0 to 11 are located between 995 and . The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. These coefficients γ₀(J,K) are found to decrease slightly on the whole as J increases and they decrease significantly for K values approaching or equal to J(J?4). The H₂-broadenings are also calculated on the basis of a semiclassical model of interacting linear molecules, using an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. The theoretical results are in satisfactory agreement with the experimental data and reproduce the J and K dependencies of the broadenings, but the decrease observed for the QR(J,K) transitions with K=J is notably overestimated.     

Line shifts in the ν2, 2ν2, and ν4 bands of NH3 perturbed by O2

Pressure-induced line shift coefficients have been measured for more than 200 rovibrational lines of NH₃ perturbed by O₂ at room temperature (T = 295 K) in some branches of the ν₂, 2ν₂, and ν₄ bands. These lines with J values ranging from 1 to 13 are located in the spectral range 800-1800 cm⁻¹. Experiments were made with a high-resolution Fourier transform spectrometer. The treatment of vibration-rotation lines includes interference effects caused by the overlapping of lines. The O₂ pressure-induced shift coefficients have been derived from the non-linear least-squares multi-pressure fitting technique. The results illustrate a vibrational dependence of line shifts with vibrational quantum number. Most of the measured shifts are negative in the ν₄ band. They are positive for the ν₂ and 2ν₂ bands. The measured shift coefficients are compared with previous measurements and with those calculated from a semiclassical theory based upon the Robert-Bonamy formalism extended to the case of symmetric top molecule with inversion motion. The predictions are generally in satisfactory agreement with the experimental data. Analyses of measured and predicted results illustrate that these shifts mainly originate from the isotropic part of the intermolecular potential.     

Diode-laser measurements and calculations of H2-broadening coefficients in the ν3 band of CH3D

Using a tunable diode-laser spectrometer, we have measured at room temperature the H₂-broadening coefficients of for 36 lines belonging to QP and QR branches in the ν₃ parallel band. The recorded lines with J values ranging from 1 to 15 and K from 0 to 9 (K?J) are located between 1196 and 1412 cm⁻¹. The H₂-broadening coefficients were determined by fitting each spectral line with Voigt, Rautian, and Galatry profiles. They were also calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the weak electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results are in reasonable agreement with the experimental data, except for high J transitions where they are overestimated and for K approaching or equal to J with J?3 where they are underestimated. The latter discrepancy may be caused by the assumption to consider only ΔK=0 collision-induced transitions, associated with |ΔJ| transitions up to 4.     

First assignment of the 5ν4 and ν2+4ν4 band systems of CH4 in the 6287-6550 cm region

This paper reports the first assignment of rovibrational transitions of the 5ν₄ and ν₂+4ν₄ band systems of ¹²CH₄ in the 6287-6550 cm⁻¹ region, which is usually referred to as part of the 1.58 μm methane transparency window. The analysis was based on two line lists previously obtained in Grenoble by cavity ring down spectroscopy at T=297 and 79 K completed by three long-path Fourier transform spectra recorded in Reims (at 290 K, L=1603 m, P=1-34 mbar). In order to determine the dipole transition moment parameters and quantify the intensity borrowing due to the resonance interactions, we had to include in the fit of the effective Hamiltonian model some lines of the stronger ν₁+3ν₄ and ν₂+4ν₄ bands. For this purpose, intensities of 179 additional lines were retrieved from FTS spectra above 6550 cm⁻¹ though the analysis of these higher bands is not complete. About 1955 experimental line positions and 1462 line intensities were fitted with RMS standard deviations of 0.003 cm⁻¹ and 13.1%, respectively. A line list of 8029 calculated and observed transitions which are considered as dominant was constructed for ¹²CH₄ in the 6287-6550 cm⁻¹ region. This is the first high-resolution analysis and modelling of 5-quanta band systems of ¹²CH₄.     

New analysis of the ν5+ν9−ν9 hot band of HNO3

Nitric acid which is an important NO_x atmospheric reservoir molecule exhibits a strong absorption in the spectral region. Since this region, which corresponds to an atmospheric window, is one of the most commonly used for the retrieval of HNO₃ in the atmosphere it is essential to have the best possible corresponding spectral parameters. Updates of these spectral line parameters were recently performed in the last versions of the atmospheric databases. They concern the line positions and intensities not only of the two interfering cold bands ν₅ and 2ν₉ but also of the ν₅+ν₉−ν₉ hot band. This hot band exhibits indeed a sharp and strong Q branch at which is clearly observable in atmospheric spectra and is used for the retrievals. However, in spite of these recent updates, it proved that the spectral parameters of the hot band are not accurate enough to reproduce accurately the observed atmospheric HNO₃ absorption in ATMOS spectra. The present paper is dedicated to a more accurate analysis of this hot band using new laboratory high-resolution (0.002-) Fourier transform spectra. As a consequence, new and more precise line positions and line intensities (about 35% weaker than in HITRAN2K) were derived leading to a significant improvement in the simulation of atmospheric spectra.     

High-resolution infrared and theoretical study of the fundamental bands ν2, ν4 and ν9 and the c-Coriolis interacting dyad ν5, ν14 of 1,3,4-thiadiazole

The Fourier transform gas-phase IR spectrum of 1,3,4-thiadiazole, C₂H₂N₂S, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 800-1500 cm⁻¹ spectral region. Five fundamental bands ν₂(A₁; 1391.9 cm⁻¹), ν₄(A₁; 964.4 cm⁻¹), ν₅(A₁; 894.6 cm⁻¹), ν₉(B₁; 821.5 cm⁻¹), and ν₁₄(B₂; 898.4 cm⁻¹) have been analysed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from fits. The ν₄ and ν₉ bands are unperturbed while a strong c-Coriolis resonance perturbs the close-lying ν₅ and ν₁₄ bands. This dyad system has been analysed by a model including first and second order c-Coriolis resonance using the theoretically predicted Coriolis coupling constant . The ν₂ band is strongly perturbed by a local resonance, and we obtain a set of spectroscopic parameters using a model including second order a-Coriolis resonance with the inactive ν₁₀ + ν₁₄ band. Ground state rotational and quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational α-constants predicted by quantum chemical calculations using a cc-pVTZ basis and B3LYP methodology, have been compared with the present experimental data, where there is generally good agreement.     

The 2ν1, 2ν2 and 2ν3 overtones of FClO3

The infrared spectra of the 2ν₁, 2ν₂ and 2ν₃ overtones of perchloryl fluoride, FClO₃, have been recorded at high resolution using monoisotopic pure samples. Four symmetric top species have been investigated: F³⁵Cl¹⁶O₃, F³⁷Cl¹⁶O₃, F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃. The v_i = 2, i = 1, 2, 3 vibrationally excited states are totally symmetric, so these overtones correspond to parallel bands of medium/weak intensity, centered from 2010 to 2120 cm⁻¹ (2ν₁), from 1390 to 1430 cm⁻¹ (2ν₂) and from 1070 to 1100 cm⁻¹ (2ν₃). Most of the bands are unperturbed and their analysis was straightforward. The band origins, the rotational and centrifugal molecular constants in the v₁ = 2, v₂ = 2 and v₃ = 2 states have been determined, with standard deviations of the fits from 0.00024 to 0.00067 cm⁻¹. The 2ν₁ overtones of F³⁵Cl¹⁶O₃ and F³⁷Cl¹⁶O₃ are perturbed by an A₁/E Coriolis resonance between the v₁ = 2 state and one E component of the v₄ = 1, v₆ = 2 manifold. The 2ν₂ of F³⁷Cl¹⁸O₃ is perturbed by the same kind of interaction involving the v₁ = v₆ = 1 (E) state, at about 1396 cm⁻¹. In these bands the resonance is localized on rotational levels with specific J and K values. As a consequence, a few transitions of the perpendicular bands involving the interacting levels could be identified in the spectra. A simultaneous fit of the transitions assigned to the dyads has been performed and the parameters of the excited states have been determined, including the high order Coriolis interaction coefficient . The anharmonic constants x₁₁, x₂₂, x₃₃ of all the studied isotopologues of FClO₃, x₄₆ of F³⁵Cl¹⁶O₃, x₄₆ + g₄₆ of F³⁷Cl¹⁶O₃ and x₁₆ of F³⁷Cl¹⁸O₃, have been derived.     

The ν1, ν4 and 3ν6 bands of methyl chloride in the 3.4-μm region: Line positions and intensities

Methyl chloride (CH₃Cl) is one of the most abundant chlorine-containing molecules in the atmosphere. For this reason a recent update was performed in HITRAN in the 640-2600 cm⁻¹ region based on the line parameters generated in Nikitin et al. [Nikitin A, Champion JP, Bürger H. J Mol Spectrosc 2005;230:174-84] with the intensities scaled to existing experimental data. CH₃Cl has a rather strong signature around 3000 cm⁻¹ which was used recently by the Atmospheric Chemistry Experiment (ACE) satellite mission to produce the first study of the global distribution of methyl chloride in the upper troposphere and stratosphere. However, it was mentioned that the CH₃Cl line positions and intensities spectroscopic parameters are of very low quality in this spectral region in the public access HITRAN or GEISA databases. We present a complete update of the line positions and line intensities for the ν₁, ν₄, 3ν₆ bands of CH₃ ³⁵Cl and CH₃ ³⁷Cl in the 3.4 μm region. For this task, Fourier transform spectra have been recorded at high resolution at the Laboratoire de Dynamique, Interactions et Réactivité in France. Measurements of line positions and line intensities have been retrieved for both isotopologues ¹²CH₃ ³⁵Cl and ¹²CH₃ ³⁷Cl in the ν₁, ν₄, 3ν₆ bands. The theoretical model accounts for the interactions coupling the (ν₁=1; ?=0), (ν₄=1; ?=±1) and (ν₆=3; ?=±1) energy levels, together with additional resonances involving several dark states.     

Structure and broadening coefficients (He, Ar and N2) of the ν4 band of CF4

Spectra of CF₄ in the ν₄ fundamental band region have been recorded in pure gas and in mixtures with He, Ar and N₂ at resolution up to . Obtained data allowed us to evaluate the integrated band intensity, line intensity distribution and effective broadening coefficients for J-multiplets. The broadening coefficient behavior is similar to that previously registered for linear molecules: they coincide for P and R branches; the J-dependence in the case of argon is more pronounced than that for helium. The broadening coefficients for nitrogen and helium are practically the same but the values for nitrogen are scattered around the general trend.Q-branch broadening is different from that for J-manifolds. The coefficients of branch broadening are noticeably smaller. Nitrogen broadening is very close to result for the case of argon though there is a marked difference between them for J-manifolds. Collisions with argon and nitrogen broaden the Q-branch almost 3 times more effectively than collisions with helium.     

FTIR spectra and rovibrational analysis of the ν11 band of trans-ClHCCHF and ν10 of trans-ClHCCDF

High-resolution Fourier transform infrared spectra of natural trans-ClHCCHF and of its isotopologue trans-ClHCCDF have been recorded in the region between 700 and 1150 cm⁻¹ with the purpose to analyze the ν₁₁ fundamental of the main species and the ν₁₀ of its deuterated compound. Both bands, of symmetry species A″, present c-type envelope absorptions. Beside the expected features, the K structure of the P(J), Q(J), and R(J) manifolds was resolved and identified; the assignment of the rovibrational transitions was extended up to J = 92 and K_a = 13 for the trans-³⁵ClHCCHF and up to J = 86 and K_a = 10 for trans-³⁵ClHCCDF. More than 2900 and 2700 lines for the main and deuterated species, respectively, were analyzed by a least-squares procedure and reliable spectroscopic molecular parameters were determined for both isotopologues.     

High resolution analysis of the ν7 and ν9 bands of DCOOH

The 7¹ and 9¹ vibrational states of deuterated species of formic acid molecule DCOOH have been recorded by a FTIR spectrometer in the region 450- at a resolution of and a millimeter wave spectrometer. In the analysis microwave transitions from literature were used in addition to 14 835 assigned IR and 114 millimeter wave lines in the 7¹ and 9¹ vibrational states. The analysis resulted in band origins, rotational, centrifugal distortion, and eight interaction parameters of the Coriolis coupled 7¹ and 9¹ vibrational states. RMS deviation of the fit was for the IR data and the maximum values of J and K_a quantum numbers in the fit were 64, 28 and 64, 30 for 7¹ and 9¹ states, respectively.     

High-resolution infrared spectroscopy of the interacting ν9, ν5 + ν6 and 3ν6 levels of CH2BrF

The high-resolution (0.0030 cm⁻¹) Fourier transform infrared spectrum of CH₂⁷⁹BrF has been studied in part of the atmospheric window between 910 and 980 cm⁻¹, the region of the ν₉ (935.847 cm⁻¹) and ν₅ + ν₆ (961.239 cm⁻¹) bands. The ν₉ fundamental consists of a pseudo a-type band induced by Coriolis coupling with ν₅ + ν₆, in turn exhibiting a predominant a-type structure. Several interactions connecting these levels and the dark state 3ν₆ have been assessed. The whole data set is treated using Watson’s A-reduced Hamiltonian in the I^r representation implemented with first order a- and b- and c-type Coriolis terms. A detailed analysis of the rotational structure yields a set of accurate upper-state parameters up to quartic distortion terms for ν₉ and ν₅ + ν₆. In addition, spectroscopic information about the dark ternary overtone of ν₆ has been obtained.