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.     

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 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 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.     

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 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.     

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.     

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.     

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.     

Rovibrational analysis of the ν2 and 2ν2 P-D stretching bands of PH2D

The infrared spectral regions of the P-D stretching fundamental band ν₂ and the first overtone band 2ν₂ of PH₂D were recorded with a resolution of 2.7×10⁻³ and , respectively. In the analysis about 710 and 440 transitions were assigned to the ν₂ and 2ν₂ bands. These provided 358 and 268 upper rovibrational energy terms, respectively. Resonance interactions between the states (010000) and (000200) were taken into account in the Hamiltonian used to fit upper energies of the (010000) state. The rovibrational energies of the (020000) state were fitted with a Hamiltonian for an isolated vibrational state.     

CO2 laser Stark spectroscopy of the Coriolis-coupled ν2 and ν5 bands of CD3Br

The ν₂ (CD₃ symmetrical deformation) and ν₅ (CD₃ degenerate deformation) fundamental bands of CD₃Br were studied by 9.4- and 10.4-μm CO₂ laser Stark spectroscopy. Stark resonances originating from 28 and 53 rovibrational transitions of the ν₂ and ν₅ bands, respectively, were assigned for each of the isotopic species, CD₃⁷⁹Br and CD₃⁸¹Br. These two bands were simultaneously analyzed with explicit inclusion of the ν₂-ν₅ Coriolis interaction, yielding precise molecular constants in the ν₂ and ν₅ excited states as well as the Coriolis coupling constant. The molecular constants obtained are consistent between the two isotopic species and are in good agreement with the results of high-resolution infrared studies. The band origins and dipole moments are

     

13.

High resolution rovibrational spectroscopy of pyrimidine: Analysis of the B₁ modes ν_10b and ν₄ and B₂ mode ν_6b     

Sieghard Albert  Martin Quack 《Journal of Molecular Spectroscopy》2007,243(2):280-291

We report the first high resolution rovibrational analysis of the infrared spectrum of pyrimidine (C₄H₄N₂) based on measurements using our Fourier transform spectrometer, the Bruker IFS 125 HR Zürich Prototype (ZP) 2001. Measurements were conducted at room temperature in a White-type cell with effective optical path lengths between 3.2 and 9.6 m and with resolutions ranging from 0.0008 to 0.0018 cm⁻¹ in the region between 600 and 1000 cm⁻¹. The spectrum was analyzed in the ν₄ (), ν_10b () and ν_6b regions of pyrimidine () using an effective Hamiltonian. A total of about 15 000 rovibrational transitions were assigned. The root mean square deviations of the fitted data are in the ranges d_rms = 0.00018-0.00024 cm⁻¹, indicating an excellent agreement of experimental line data with the calculations. The results are discussed briefly in relation to possible extensions to spectra of DNA bases and to intramolecular vibrational redistribution at higher energy. The analysis of the ν_10b and ν₄ bands will also be useful in the interstellar search for pyrimidine in the infrared region.     

14.

Study of vibration-rotation levels in formamide with high resolution FTIR spectroscopy: The ν₁₂, 2ν₁₂, ν₁₁, and ν₉ bands     

Lajos Sztraka  Veli-Matti Horneman 《Journal of Molecular Spectroscopy》2009,255(2):172-182

The far infrared and infrared spectra of formamide (HCONH₂) have been recorded at high resolution (0.00125 cm⁻¹) in the region of 90-1060 cm⁻¹. Over 20,000 transitions from the out-of-plane NH₂ wagging motion (n₁₂ = 1 ← 0 fundamental, n₁₂ = 2 ← 0 overtone, n₁₂ = 2 ← 1 difference bands), torsion (n₁₁ = 1 ← 0 bands), and out-of-phase NCO/NH₂ bend (n₉ = 1 ← 0 bands) have been assigned. Molecular parameters have been obtained for the ground state and the unperturbed n₁₂ = 1 state. The least-squares fit calculations were completed with the microwave data available in the literature. The complicated resonance system between the n₁₂ = 2, n₁₁ = 1, and n₉ = 1 states has been investigated carefully. Thus, we have been able to verify almost all resonances (avoided crossing) existing in the region J, K investigated. In the coupled Hamiltonian used for the fit, all Watson’s reduced parameters, including the octic ones and 16 Coriolis coupling parameters were taken into account. The rms deviation obtained from the fit was 0.000247 cm⁻¹.     

15.

High resolution analysis of the ν₇ and ν₉ bands of DCOOH     

O.I. Baskakov  V.-M. Horneman 《Journal of Molecular Spectroscopy》2003,219(2):191-199

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.     

16.

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

Jean-Pierre Bouanich  Jamel Salem  Jacques Walrand 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(2):195-205

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.     

17.

High resolution Fourier transform infrared spectra and analysis of the ν₁₄, ν₁₅ and ν₁₆ bands of azetidine     

Taras Zaporozan 《Journal of Molecular Spectroscopy》2010,264(2):105-110

Rotationally resolved vibrational spectra of the three lowest frequency bands of the four-membered heterocycle azetidine (c-C₃H₆NH) have been collected with a resolution of 0.00096 cm⁻¹ using the far infrared beamline at the Canadian Light Source synchrotron. The modes observed correspond principally to motions best described as: β-CH₂ rock (ν₁₄) at 736.701310(7) cm⁻¹, ring deformation (ν₁₅) at 648.116041(8) cm⁻¹, and the ring puckering mode (ν₁₆) at 207.727053(9) cm⁻¹. A global fit of 14 276 rovibrational transitions from the three bands provided an accurate set of ground state spectroscopic constants as well as excited state parameters for each of the three vibrational modes. The ground state structure was determined to be that of the puckered conformer having the NH bond in an equatorial arrangement.     

18.

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

E. Cané  K. Burczyk 《Journal of Molecular Spectroscopy》2008,247(1):57-63

The high resolution infrared spectra of monoisotopic F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃ have been studied in the region of the ν₄ fundamentals, centered at 1278.3 and 1263.3 cm⁻¹, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν₂ + ν₅ combination bands, centered at 1270.7 cm⁻¹ in F³⁵Cl¹⁸O₃ and 1257.3 cm⁻¹ in F³⁷Cl¹⁸O₃. In particular, they affect the kl > 0 levels of the v₄ = 1 and v₂ = v₅ = 1 states which cross at kl ? 18 in F³⁵Cl¹⁸O₃ and kl ? 3 in F³⁷Cl¹⁸O₃, due to the opposite values of and . The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances are also effective in the excited states of the dyad in F³⁵Cl¹⁸O₃, while in F³⁷Cl¹⁸O₃ only the Δl = Δk = ±2 one is active. In the spectrum of F³⁵Cl¹⁸O₃ 3423 transitions have been assigned, 10% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants between the v₄ = 1 and v₂ = v₅ = 1 levels have been obtained. The depertubed band origins of ν₄ and ν₂ + ν₅ are 1277.310567(165) and 1271.753733(195) cm⁻¹, respectively, and the anharmonic resonance constant is 2.804416(153) cm⁻¹. For F³⁷Cl¹⁸O₃, 3022 transitions have been assigned, 38% belonging to the ν₂ + ν₅ combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134) cm⁻¹, for ν₄and ν₂ + ν₅ and the constant is 2.9350669(405) cm⁻¹. The equilibrium geometry of perchloryl fluoride, r_e (ClO) = 139.7(3) pm, r_e (ClF) = 161.0(5) pm, and α_e (OClO) = 115.7(4) degree, has been determined using the A_e and B_e equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F^35/37Cl¹⁶O₃ and F^35/37Cl¹⁸O₃.     

19.

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

D.T. Petkie  B.P. Winnewisser  R.A.H. Butler  F.C. De Lucia 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,92(2):129-141

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.     

20.

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.     

		CD379Br		CD381Br
$\text{ν}{}_2$		991.396 82 (18)		991.388 46 (17)		cm?1
$\text{ν}{}_5$		1055.469 00 (12)		1055.466 32 (12)		cm?1
$\text{μ}{}_0$		1.830 42 (52)		1.829 84 (47)		D
$\text{μ}{}_2$		1.829 93 (48)		1.829 57 (46)		D
$\text{μ}{}_5$		1.832 23 (60)		1.831 19 (56)		D

High resolution rovibrational spectroscopy of pyrimidine: Analysis of the B1 modes ν10b and ν4 and B2 mode ν6b

We report the first high resolution rovibrational analysis of the infrared spectrum of pyrimidine (C₄H₄N₂) based on measurements using our Fourier transform spectrometer, the Bruker IFS 125 HR Zürich Prototype (ZP) 2001. Measurements were conducted at room temperature in a White-type cell with effective optical path lengths between 3.2 and 9.6 m and with resolutions ranging from 0.0008 to 0.0018 cm⁻¹ in the region between 600 and 1000 cm⁻¹. The spectrum was analyzed in the ν₄ (), ν_10b () and ν_6b regions of pyrimidine () using an effective Hamiltonian. A total of about 15 000 rovibrational transitions were assigned. The root mean square deviations of the fitted data are in the ranges d_rms = 0.00018-0.00024 cm⁻¹, indicating an excellent agreement of experimental line data with the calculations. The results are discussed briefly in relation to possible extensions to spectra of DNA bases and to intramolecular vibrational redistribution at higher energy. The analysis of the ν_10b and ν₄ bands will also be useful in the interstellar search for pyrimidine in the infrared region.     

Study of vibration-rotation levels in formamide with high resolution FTIR spectroscopy: The ν12, 2ν12, ν11, and ν9 bands

The far infrared and infrared spectra of formamide (HCONH₂) have been recorded at high resolution (0.00125 cm⁻¹) in the region of 90-1060 cm⁻¹. Over 20,000 transitions from the out-of-plane NH₂ wagging motion (n₁₂ = 1 ← 0 fundamental, n₁₂ = 2 ← 0 overtone, n₁₂ = 2 ← 1 difference bands), torsion (n₁₁ = 1 ← 0 bands), and out-of-phase NCO/NH₂ bend (n₉ = 1 ← 0 bands) have been assigned. Molecular parameters have been obtained for the ground state and the unperturbed n₁₂ = 1 state. The least-squares fit calculations were completed with the microwave data available in the literature. The complicated resonance system between the n₁₂ = 2, n₁₁ = 1, and n₉ = 1 states has been investigated carefully. Thus, we have been able to verify almost all resonances (avoided crossing) existing in the region J, K investigated. In the coupled Hamiltonian used for the fit, all Watson’s reduced parameters, including the octic ones and 16 Coriolis coupling parameters were taken into account. The rms deviation obtained from the fit was 0.000247 cm⁻¹.     

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.     

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.     

High resolution Fourier transform infrared spectra and analysis of the ν14, ν15 and ν16 bands of azetidine

Rotationally resolved vibrational spectra of the three lowest frequency bands of the four-membered heterocycle azetidine (c-C₃H₆NH) have been collected with a resolution of 0.00096 cm⁻¹ using the far infrared beamline at the Canadian Light Source synchrotron. The modes observed correspond principally to motions best described as: β-CH₂ rock (ν₁₄) at 736.701310(7) cm⁻¹, ring deformation (ν₁₅) at 648.116041(8) cm⁻¹, and the ring puckering mode (ν₁₆) at 207.727053(9) cm⁻¹. A global fit of 14 276 rovibrational transitions from the three bands provided an accurate set of ground state spectroscopic constants as well as excited state parameters for each of the three vibrational modes. The ground state structure was determined to be that of the puckered conformer having the NH bond in an equatorial arrangement.     

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

The high resolution infrared spectra of monoisotopic F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃ have been studied in the region of the ν₄ fundamentals, centered at 1278.3 and 1263.3 cm⁻¹, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν₂ + ν₅ combination bands, centered at 1270.7 cm⁻¹ in F³⁵Cl¹⁸O₃ and 1257.3 cm⁻¹ in F³⁷Cl¹⁸O₃. In particular, they affect the kl > 0 levels of the v₄ = 1 and v₂ = v₅ = 1 states which cross at kl ? 18 in F³⁵Cl¹⁸O₃ and kl ? 3 in F³⁷Cl¹⁸O₃, due to the opposite values of and . The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances are also effective in the excited states of the dyad in F³⁵Cl¹⁸O₃, while in F³⁷Cl¹⁸O₃ only the Δl = Δk = ±2 one is active. In the spectrum of F³⁵Cl¹⁸O₃ 3423 transitions have been assigned, 10% of them belonging to ν₂ + ν₅. The rovibrational parameters and the interaction constants between the v₄ = 1 and v₂ = v₅ = 1 levels have been obtained. The depertubed band origins of ν₄ and ν₂ + ν₅ are 1277.310567(165) and 1271.753733(195) cm⁻¹, respectively, and the anharmonic resonance constant is 2.804416(153) cm⁻¹. For F³⁷Cl¹⁸O₃, 3022 transitions have been assigned, 38% belonging to the ν₂ + ν₅ combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134) cm⁻¹, for ν₄and ν₂ + ν₅ and the constant is 2.9350669(405) cm⁻¹. The equilibrium geometry of perchloryl fluoride, r_e (ClO) = 139.7(3) pm, r_e (ClF) = 161.0(5) pm, and α_e (OClO) = 115.7(4) degree, has been determined using the A_e and B_e equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F^35/37Cl¹⁶O₃ and F^35/37Cl¹⁸O₃.     

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.     

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.