The simulation of infrared bands from the analyses of rotational spectra: the 2ν9-ν9 and ν5-ν9 hot bands of HNO3

The results of millimeter and submillimeter wave rotational spectroscopy are used to simulate the complex structure of the 2ν₉-ν₉ and ν₅-ν₉ hot bands. The comparison data were obtained with a high-resolution Bruker FTIR. The combination of the quality of these data and the complexity of the spectra of these interacting states represents a stringent test for the simulation. It is shown that the agreement is very good and that this approach is generally advantageous. From this simulation, the ratios of the transition dipole moments for the 2ν₉-ν₉ and ν₅-ν₉ hot bands with respect to the ν₉ fundamental band were found to be 1.38(11) and 0.67(20), respectively. Using these results, the calculated integrated band intensities for the hot bands at were determined to be and . These results were used to successfully simulate high-resolution stratospheric spectra obtained from a balloon flight of the FIRS-2 spectrometer. The more general problem of the rotation-vibration database and the optimal use of both microwave and infrared data to define it is discussed. It is concluded that it is best if the combination of data takes place at the level of the original spectra.     

Analysis of the hot bands in the 2ν9 band region of propyne-d3

The rovibrational spectrum of 2ν₉ band of CD₃CCH is overlapped by two prominent hot bands identified as (2ν₉⁰+ν₁₀^±1)(E)←ν₁₀^±1(E) and 3ν₉^±1(E)←ν₉^±1(E), where ν₁₀ and ν₉ are the degenerate CCC and CCH bending fundamental vibrations, respectively. Assignment of lines to the transitions of these hot bands were carried out with the help of the high-resolution spectra recorded at ∼195 K and at room temperature. Molecular parameters for these hot bands have been obtained from the rotational analysis of the partially resolved K-structure lines. Only Q-head of the third hot band , originating from the lower 2ν₁₀ state could be identified.     

The first high-resolution analysis of the low-lying ν9 band of propane

The ν₉ fundamental band (C-C-C deformation) of propane (C₃H₈) at 369 cm⁻¹ has been studied at high-resolution (0.0011 cm⁻¹) with spectra recorded using the synchrotron radiation from the French light source facility at SOLEIL coupled to a Bruker IFS 125HR Fourier transform spectrometer. A 2.526 m base multipass cell with optical paths from 10.296 to 151.78 m was used. In addition, a spectrum was also recorded using a conventional globar source. Comparison of these experimental spectra shows clearly the gain obtained on the signal-to-noise ratios with the synchrotron radiation. The spectra have been thoroughly analyzed and transitions up to J=65 and K_a=33 have been assigned. The upper-state rotational levels were fitted using an A-type Watson Hamiltonian written in the I^r representation. An accurate band center ν₀ (ν₉)=369.228080(25) cm⁻¹ as well as accurate rotational and centrifugal distortion constants have been obtained and used to simulate a synthetic spectrum. These parameters should be useful to simulate hot bands of propane involving the 9¹ vibrational level as their lower state.     

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.     

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 study of the ν1/ν5 and 2ν1/ν1+ν5 P-H stretching bands of PH2D

The P-H stretching bands ν₁/ν₅ and 2ν₁/ν₁+ν₅ were recorded using a Bruker 120 HR interferometer with a resolution of 0.0042 and 0.0088 cm⁻¹, respectively, and analyzed. From the fits 33 and 50, respectively, vibrational, rotational, centrifugal distortion, and resonance interaction parameters were obtained. These reproduce 668 and 497 rovibrational energies of the pairs of states ν₁/ν₅ and 2ν₁/ν₁+ν₅ with experimental accuracies, rms=0.00016 and , respectively. “Local mode” behavior of the PH₂ fragment is established and discussed in detail.     

The ν3 fundamental band of HDCO

The ν₃ fundamental band (CO stretch) of HDCO at 1724 cm^?1 has been studied using both conventional infrared absorption and CO laser Stark spectroscopy. In addition to the excited-state (v₃ = 1) rotational constants, improved constants for the ground state of HDCO have been obtained by combining previous microwave data with some infrared combination differences. The following constants were determined:

     

9.

The overtone spectrum of carbonyl sulfide in the region of the ν₁+4ν₃ and 5ν₃ bands by ICLAS-VECSEL     

E. Bertseva  Y. Ding  A. Garnache  D. Romanini 《Journal of Molecular Spectroscopy》2003,219(1):81-87

The high-resolution overtone spectrum of OCS has been recorded in the region of the ν₁+4ν₃ and 5ν₃ bands by intracavity laser absorption spectroscopy based on an optically pumped vertical external cavity surface emitting laser (VECSEL). The extremely weak ν₁+4ν₃ band at was found to be isolated. The 5ν₃ band at is accompanied by two weaker bands at 9933.53 and assigned to the 12⁰4-00⁰0 and 04⁰4-00⁰0 bands, respectively. In addition, the 01¹5-01¹0 hot band was detected together with the extremely weak band heads of the R branch of the 02^0,25-02^0,20 hot bands. Finally, the 5ν₃ band of the ¹⁶O¹²C³⁴S minor isotopomer, present in natural abundance in the sample, was also observed and rotationally analyzed. Effective state parameters could be retrieved by standard band-by-band rotational fitting of the line positions, leading to a typical rms of . The observed line positions were compared to the predictions of the global model described by Rhaibi et al. [J. Mol. Spectrosc. 191 (1998) 32-44]. In general, the agreement is excellent, close to the experimental uncertainty () thus confirming the high predictive ability of this effective Hamiltonian model. Weak but significant deviations up to were, however, identified for two rotational levels of the highly excited 2,16⁰,0 dark state, observed through a local interaction with the 00⁰5 state. In the case of the ¹⁶O¹²C³⁴S isotopomer, the predicted line wavenumbers of the 5ν₃ band were globally overestimated by about . The new data have been included in the corresponding global model, leading to almost unchanged values of the molecular parameters and a statistical agreement with the experiment.     

10.

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

A.V. Nikitin  X. Thomas  L. Daumont  Vl.G. Tyuterev  S. Kassi 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(1):28-40

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.     

11.

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     

F. Hegelund  R. Wugt Larsen  M.H. Palmer 《Journal of Molecular Spectroscopy》2008,248(2):161-167

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.     

12.

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

R. Visinoni  A. Baldacci 《Journal of Molecular Spectroscopy》2011,269(2):226-230

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.     

13.

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

L. Gomez  G. Mellau 《Journal of Molecular Spectroscopy》2009,256(1):28-34

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.     

14.

Microwave spectroscopy of the ν₈-ν₆ band of diacetylene     

Keiji Matsumura  Tohru Etoh  Takehiko Tanaka 《Journal of Molecular Spectroscopy》1981,90(1):106-115

Vibration-rotation transitions of diacetylene between the first excited states of the ν₆ (CCH symmetric bending) and the ν₈ (CCH antisymmetric bending) vibrations were observed with a Stark modulation microwave spectrometer. The rotational, centrifugal distortion and l-type doubling constants of the two vibrational states were determined as follows with 2.5 σ uncertainties in parentheses.

Constant	Ground state	$\text{v}{}_3\text{= 1}$ state	Units
$\text{ν}{}_0$		1724.267	cm?1
$\text{A}$	198 119.75	198 210.4	MHz
$\text{B}$	34 910.646	34 676.6	MHz
$\text{C}$	29 561.488	29 331.3	MHz
$\text{μ}{}_{\mathrm{a}}$	2.3302	2.3486	D
$\text{μ}{}_{\mathrm{b}}$	0.195	0.190	D

     

15.

Tunable diode laser study of the ν₃ band of oxirane     

Douglas K. Russell  Ralf Wesendrup 《Journal of Molecular Spectroscopy》2003,217(1):59-71

We have measured and fitted over 600 well-resolved lines in the ν₃ ring breathing band of oxirane. The spectrum is accurately reproduced by previously determined rotational and centrifugal distortion constants for the ground state, together with newly determined rotational, quartic and some sextic distortion constants for the upper state. The magnitudes of the distortion constants reveal some evidence of Coriolis interactions with nearby states. The band centre was determined as .     

16.

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

Alberto Gambi  Paolo Stoppa 《Journal of Molecular Spectroscopy》2008,252(1):47-51

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.     

17.

High-resolution infrared and theoretical study of the fundamental bands ν₆, ν₇, ν₉ and ν₁₃ of 1,2,3-thiadiazole     

F. Hegelund  R. Wugt Larsen  P. Melec 《Journal of Molecular Spectroscopy》2008,250(1):8-19

The Fourier transform gas-phase IR spectrum of 1,2,3-thiadiazole, C₂H₂N₂S, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 700-1100 cm⁻¹ spectral region. Four fundamental bands ν₆(A^/; 1101.8 cm⁻¹), ν₇(A^/; 1038.8 cm⁻¹), ν₉(A^/, 858.9 cm⁻¹), and ν₁₃(A^//; 746.2 cm⁻¹) have been analyzed using the Watson model in A-reduction. Two additional bands, ν₈ (A^/; 894.6 cm⁻¹) and ν₁₂(A^//; 881.2 cm⁻¹) were assigned by their weak Q-branches. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from fits. A number of weak global and local interactions are present in the bands. The resonances identified were qualitatively explained by Coriolis type perturbations with neighboring levels. 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.     

18.

The high resolution infrared bands ν₁, ν₂, ν₄ and ν₂ + ν₅ of FClO₃     

E. Cané  K. Burczyk 《Journal of Molecular Spectroscopy》2006,239(2):146-153

The high resolution infrared spectrum of mono-isotopic F³⁷Cl¹⁶O₃ has been studied in the regions of ν₁, ν₂, ν₄ and ν₂ + ν₅ bands, centered at 1060.20, 707.16, 1301.71 and 1292.15 cm⁻¹, respectively. The ν₁ and ν₂ parallel bands are unperturbed so their analysis was straightforward and 3355 and 2433 transitions were assigned, respectively. The band origins, the rotational and centrifugal molecular constants in the v₁ = 1 and v₂ = 1 states have been determined, with standard deviation of the fits σ = 0.00019 and 0.00018 cm⁻¹. The ν₄ fundamental is affected by an anharmonic resonance with the ν₂ + ν₅ combination band. The kl > 0 sublevels cross at kl ? 27 because of the opposite values of and . The anharmonic resonance constant  cm⁻¹ has been derived. The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances have been found to be effective in ν₄, while in ν₂ + ν₅ only the Δl = Δk = ±2 one was active. A total of 5721 transitions have been assigned, 25% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants of F³⁷Cl¹⁶O₃ have been obtained. The standard deviation of the fit is 0.0006 cm⁻¹, six times the estimated data precision. The equilibrium geometry of perchloryl fluoride has been determined from the A_e and B_e constants of F³⁵Cl¹⁶O₃ and F³⁷Cl¹⁶O₃. Using the A₀ and B₀ constants of all the symmetric species the r₀ geometry has also been derived.     

19.

High resolution infrared spectrum and global analysis of ν₅, ν₁₂, and ν₁₂ + ν₆ − ν₆ in CH₃SiH₃     

L. Borvayeh  A. Bauder 《Journal of Molecular Spectroscopy》2009,255(2):122-133

The vibration-torsion-rotation spectrum of CH₃SiH₃ has been measured from 470 to 725 cm⁻¹ at near-Doppler resolution. The full-width at half - maximum of the lines observed near 600 cm⁻¹ was 0.0011 cm⁻¹. The spectra were obtained using a Bruker IFS 125 HR Fourier transform spectrometer with the broadband source radiation being supplied from the synchrotron emission of the storage ring at the Canadian Light Source. Three vibrational bands were investigated: the lowest lying perpendicular fundamental ν₁₂ centred near 524 cm⁻¹, the lowest lying parallel fundamental ν₅ near 703 cm⁻¹, and the torsional hot band ν₁₂ + ν₆ − ν₆ near 534 cm⁻¹. For ν₁₂ and ν₅, the resolution and sensitivity are much improved over those in earlier studies, with many of the torsional multiplets now being resolved even in the cases where the upper levels are unperturbed. The primary motivation for the present work was the hot band, here reported for the first time, where the dependence of the silyl rock in ν₁₂ on the torsional motion is much more pronounced. In addition, for the vibrational ground state (gs), two “forbidden” high torsional overtones v₆ = 3 ← 0 and 5 ← 0 have been observed that become allowed through resonant mixing of the upper states with ν₁₂ and ν₅, respectively. In each case, two (K, σ) series have been measured where the mixing is largest. Here σ = 0, 1, −1 labels the torsional sub-levels. Using the Fourier transform waveguide spectrometer at E. T. H., the three σ-components of the (J = 1 ← 0) transition in ν₁₂ + ν₆ were observed, and a series of direct l-doubling transitions in ν₁₂ + ν₆ were measured for σ = 0. In a global fit, all the new data have been analysed along with the frequencies for other transitions obtained in earlier investigations. The analysis takes into account the relevant interactions among the torsional stacks of levels in the gs, ν₁₂, and ν₅. These include the previously known (gs, ν₁₂) Coriolis-like and (gs, ν₅) Fermi-like interactions along with a higher order (ν₁₂, ν₅) Coriolis-like coupling introduced here. This last is responsible for the strong perturbation of the ν₅ series with K = 10, 11, and 12, and of the corresponding hot band series. A good fit to 9282 frequencies including 7942 new measurements was obtained both with the Free Rotor model in which the torsion is classified as a rotation, and with the High Barrier model in which the torsion is classified as a vibration. The Hamiltonian is discussed with emphasis on the new terms required for treating ν₁₂ + ν₆ − ν₆.     

20.

High resolution study of the 3ν₁ band of SO₂     

O.N. Ulenikov  E.S. Bekhtereva  S. Alanko 《Journal of Molecular Spectroscopy》2009,255(2):111-121

The second overtone band 3ν₁ of sulfur dioxide has been studied for the first time with high resolution rotation-vibration spectroscopy. About 3000 transitions involving about 900 upper state energy levels with have been assigned to the 3ν₁ band. In the analysis, an effective Hamiltonian taking into account accidental interactions between the vibrational states (3 0 0), (2 2 0), and (0 4 1) was used. The Watson operator in A-reduction and I^r representation was used in the diagonal blocks of the Hamiltonian. As the result of analysis a set of parameters reproducing the initial experimental data with the rms = 0.00028 cm⁻¹ was obtained.     

	$\text{B}{}_{\mathrm{v}}\text{(}\text{MHz}\text{)}$	$\text{D}{}_{\mathrm{v}}\text{(}\text{kHz}\text{)}$	$\text{q}{}_{\mathrm{v}}\text{(}\text{MHz}\text{)}$
$\text{ν}{}_6$	4391.3230(84)	0.582(154)	2.4830(32)
$\text{ν}{}_8$	4391.1921(94)	0.594(179)	2.4073(37)

The overtone spectrum of carbonyl sulfide in the region of the ν1+4ν3 and 5ν3 bands by ICLAS-VECSEL

The high-resolution overtone spectrum of OCS has been recorded in the region of the ν₁+4ν₃ and 5ν₃ bands by intracavity laser absorption spectroscopy based on an optically pumped vertical external cavity surface emitting laser (VECSEL). The extremely weak ν₁+4ν₃ band at was found to be isolated. The 5ν₃ band at is accompanied by two weaker bands at 9933.53 and assigned to the 12⁰4-00⁰0 and 04⁰4-00⁰0 bands, respectively. In addition, the 01¹5-01¹0 hot band was detected together with the extremely weak band heads of the R branch of the 02^0,25-02^0,20 hot bands. Finally, the 5ν₃ band of the ¹⁶O¹²C³⁴S minor isotopomer, present in natural abundance in the sample, was also observed and rotationally analyzed. Effective state parameters could be retrieved by standard band-by-band rotational fitting of the line positions, leading to a typical rms of . The observed line positions were compared to the predictions of the global model described by Rhaibi et al. [J. Mol. Spectrosc. 191 (1998) 32-44]. In general, the agreement is excellent, close to the experimental uncertainty () thus confirming the high predictive ability of this effective Hamiltonian model. Weak but significant deviations up to were, however, identified for two rotational levels of the highly excited 2,16⁰,0 dark state, observed through a local interaction with the 00⁰5 state. In the case of the ¹⁶O¹²C³⁴S isotopomer, the predicted line wavenumbers of the 5ν₃ band were globally overestimated by about . The new data have been included in the corresponding global model, leading to almost unchanged values of the molecular parameters and a statistical agreement with the experiment.     

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.     

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.     

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.     

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.     

Microwave spectroscopy of the ν8-ν6 band of diacetylene

Vibration-rotation transitions of diacetylene between the first excited states of the ν₆ (CCH symmetric bending) and the ν₈ (CCH antisymmetric bending) vibrations were observed with a Stark modulation microwave spectrometer. The rotational, centrifugal distortion and l-type doubling constants of the two vibrational states were determined as follows with 2.5 σ uncertainties in parentheses.

Tunable diode laser study of the ν3 band of oxirane

We have measured and fitted over 600 well-resolved lines in the ν₃ ring breathing band of oxirane. The spectrum is accurately reproduced by previously determined rotational and centrifugal distortion constants for the ground state, together with newly determined rotational, quartic and some sextic distortion constants for the upper state. The magnitudes of the distortion constants reveal some evidence of Coriolis interactions with nearby states. The band centre was determined as .     

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 infrared and theoretical study of the fundamental bands ν6, ν7, ν9 and ν13 of 1,2,3-thiadiazole

The Fourier transform gas-phase IR spectrum of 1,2,3-thiadiazole, C₂H₂N₂S, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 700-1100 cm⁻¹ spectral region. Four fundamental bands ν₆(A^/; 1101.8 cm⁻¹), ν₇(A^/; 1038.8 cm⁻¹), ν₉(A^/, 858.9 cm⁻¹), and ν₁₃(A^//; 746.2 cm⁻¹) have been analyzed using the Watson model in A-reduction. Two additional bands, ν₈ (A^/; 894.6 cm⁻¹) and ν₁₂(A^//; 881.2 cm⁻¹) were assigned by their weak Q-branches. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from fits. A number of weak global and local interactions are present in the bands. The resonances identified were qualitatively explained by Coriolis type perturbations with neighboring levels. 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 high resolution infrared bands ν1, ν2, ν4 and ν2 + ν5 of FClO3

The high resolution infrared spectrum of mono-isotopic F³⁷Cl¹⁶O₃ has been studied in the regions of ν₁, ν₂, ν₄ and ν₂ + ν₅ bands, centered at 1060.20, 707.16, 1301.71 and 1292.15 cm⁻¹, respectively. The ν₁ and ν₂ parallel bands are unperturbed so their analysis was straightforward and 3355 and 2433 transitions were assigned, respectively. The band origins, the rotational and centrifugal molecular constants in the v₁ = 1 and v₂ = 1 states have been determined, with standard deviation of the fits σ = 0.00019 and 0.00018 cm⁻¹. The ν₄ fundamental is affected by an anharmonic resonance with the ν₂ + ν₅ combination band. The kl > 0 sublevels cross at kl ? 27 because of the opposite values of and . The anharmonic resonance constant  cm⁻¹ has been derived. The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances have been found to be effective in ν₄, while in ν₂ + ν₅ only the Δl = Δk = ±2 one was active. A total of 5721 transitions have been assigned, 25% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants of F³⁷Cl¹⁶O₃ have been obtained. The standard deviation of the fit is 0.0006 cm⁻¹, six times the estimated data precision. The equilibrium geometry of perchloryl fluoride has been determined from the A_e and B_e constants of F³⁵Cl¹⁶O₃ and F³⁷Cl¹⁶O₃. Using the A₀ and B₀ constants of all the symmetric species the r₀ geometry has also been derived.     

High resolution infrared spectrum and global analysis of ν5, ν12, and ν12 + ν6 − ν6 in CH3SiH3

The vibration-torsion-rotation spectrum of CH₃SiH₃ has been measured from 470 to 725 cm⁻¹ at near-Doppler resolution. The full-width at half - maximum of the lines observed near 600 cm⁻¹ was 0.0011 cm⁻¹. The spectra were obtained using a Bruker IFS 125 HR Fourier transform spectrometer with the broadband source radiation being supplied from the synchrotron emission of the storage ring at the Canadian Light Source. Three vibrational bands were investigated: the lowest lying perpendicular fundamental ν₁₂ centred near 524 cm⁻¹, the lowest lying parallel fundamental ν₅ near 703 cm⁻¹, and the torsional hot band ν₁₂ + ν₆ − ν₆ near 534 cm⁻¹. For ν₁₂ and ν₅, the resolution and sensitivity are much improved over those in earlier studies, with many of the torsional multiplets now being resolved even in the cases where the upper levels are unperturbed. The primary motivation for the present work was the hot band, here reported for the first time, where the dependence of the silyl rock in ν₁₂ on the torsional motion is much more pronounced. In addition, for the vibrational ground state (gs), two “forbidden” high torsional overtones v₆ = 3 ← 0 and 5 ← 0 have been observed that become allowed through resonant mixing of the upper states with ν₁₂ and ν₅, respectively. In each case, two (K, σ) series have been measured where the mixing is largest. Here σ = 0, 1, −1 labels the torsional sub-levels. Using the Fourier transform waveguide spectrometer at E. T. H., the three σ-components of the (J = 1 ← 0) transition in ν₁₂ + ν₆ were observed, and a series of direct l-doubling transitions in ν₁₂ + ν₆ were measured for σ = 0. In a global fit, all the new data have been analysed along with the frequencies for other transitions obtained in earlier investigations. The analysis takes into account the relevant interactions among the torsional stacks of levels in the gs, ν₁₂, and ν₅. These include the previously known (gs, ν₁₂) Coriolis-like and (gs, ν₅) Fermi-like interactions along with a higher order (ν₁₂, ν₅) Coriolis-like coupling introduced here. This last is responsible for the strong perturbation of the ν₅ series with K = 10, 11, and 12, and of the corresponding hot band series. A good fit to 9282 frequencies including 7942 new measurements was obtained both with the Free Rotor model in which the torsion is classified as a rotation, and with the High Barrier model in which the torsion is classified as a vibration. The Hamiltonian is discussed with emphasis on the new terms required for treating ν₁₂ + ν₆ − ν₆.     

High resolution study of the 3ν1 band of SO2

The second overtone band 3ν₁ of sulfur dioxide has been studied for the first time with high resolution rotation-vibration spectroscopy. About 3000 transitions involving about 900 upper state energy levels with have been assigned to the 3ν₁ band. In the analysis, an effective Hamiltonian taking into account accidental interactions between the vibrational states (3 0 0), (2 2 0), and (0 4 1) was used. The Watson operator in A-reduction and I^r representation was used in the diagonal blocks of the Hamiltonian. As the result of analysis a set of parameters reproducing the initial experimental data with the rms = 0.00028 cm⁻¹ was obtained.