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.     

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.     

High resolution study of AsHD2: Ground state and the three bending fundamental bands ν3, ν4, and ν6

For the first time the infrared spectrum of the AsHD₂ molecule has been measured in the region of the bending fundamental bands ν₃, ν₄, and ν₆ on a Fourier transform spectrometer with a resolution of 0.0024 cm⁻¹ and analyzed. More than 5500 transitions with J^max = 26 have been assigned and used both to obtain “ground state combination differences” and for the determination of upper state ro-vibrational energies of the triad (001000), (000100), and (000001). Rotational parameters including centrifugal distortion coefficients up to octic terms of the ground vibrational state were calculated by fitting more than 500 “ground state combination differences” with J^max and . The obtained set of 24 parameters provides a rms-deviation of 0.00011 cm⁻¹. The upper energies were fitted with 52 parameters of an effective Hamiltonian which takes into account strong resonance interactions between all vibrational states of the triad (001000), (000100), and (000001). The rms-deviation for the energy levels considered in the fit is 0.00014 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.     

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.     

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:

     

8.

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.     

9.

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.     

10.

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.     

11.

The 2ν₄ overtone bands of FClO₃     

E. Cané  K. Burczyk 《Journal of Molecular Spectroscopy》2010,262(1):16-21

The high resolution infrared spectrum of the mono-isotopic species F³⁵Cl¹⁶O₃ has been studied in the region of the 2ν₄ overtone, from 2560 to 2680 cm⁻¹. The perpendicular component is strong and clearly observed while the parallel component is very weak and almost completely hidden by the perpendicular one. Their origins differ by 12.6 cm⁻¹, the being located at higher wavenumbers. The band is perturbed by the anharmonic interaction between the v₄ = 2, l₄ = ?2 and v₂ = v₄ = v₅ = 1, l₄ = l₅ = ±1 excited states, both of E symmetry. In total 3157 transitions have been assigned, 83% of these to , 12% to , and 5% to . The three bands have been analyzed simultaneously, taking into account the Fermi resonance effective between the excited states of E symmetry. The ro-vibration parameters of the excited states have been obtained, including the deperturbed band origins of and , at 2628.5890(4) and 2619.3342(5) cm⁻¹, respectively. The W₂₄₅ anharmonic constant is equal to 4.0161(4) cm⁻¹. The x₄₄+g₄₄ and x₂₄+x₄₅+g₄₅ anharmonicity constants have been derived from the obtained band origins and those of ν₄ and ν₂ + ν₅.     

12.

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.     

13.

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

O.N. Ulenikov  E.S. Bekhtereva  O.L. Petrunina  H. Bürger 《Journal of Molecular Spectroscopy》2003,219(1):13-29

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.     

14.

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.     

15.

High resolution infrared study of SbHD₂: The ground state and the Sb-H stretching bands ν₁ and 2ν₁     

E. Cané  R. Tarroni  H. Bürger 《Journal of Molecular Spectroscopy》2011,265(1):1-9

High resolution infrared spectra of ¹²¹SbHD₂ and ¹²³SbHD₂ have been studied in the region of ν₁, the Sb-H stretching fundamental, from 1780 to 1990 cm⁻¹. The 2ν₁ stretching overtone band of ¹²³SbHD₂, located in the 3640-3790 cm⁻¹ range, has also been investigated. The SbHD₂ molecule is an asymmetric rotor of C_s symmetry with the asymmetry parameter κ = 0.61. The ν₁ band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For ¹²³SbHD₂, 2092 transitions have been assigned: 70% of these belong to the C component, the other 30% are of B-type. The assigned transitions have been fitted using a Watson type S-reduced Hamiltonian in the III^l representation, with a standard deviation of the fit σ = 0.45 × 10⁻³ cm⁻¹. In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the ν₁ transitions. In total, 3942 GSCD up to J^″ = 27,  = 25, and  = 20 have been fitted with σ = 0.52 × 10⁻³ cm⁻¹. Only C-type transitions have been observed in the weak 2ν₁ overtone band. The 556 assigned transitions have been fitted with σ = 2.6 × 10⁻³ cm⁻¹ using the same Hamiltonian as for ν₁. In the ν₁ band of ¹²¹SbHD₂ 771 C-type transitions have been assigned, and the v₁=1 spectroscopic constants obtained from a fit with σ = 0.70 × 10⁻³ cm⁻¹. Using 618 GSCD the ground state spectroscopic constants of ¹²¹SbHD₂ have been derived with σ = 1.0 × 10⁻³ cm⁻¹. The molecular parameters for the ground and the v₁=1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH₃ has been used to predict all relevant spectroscopic parameters for ¹²³SbHD₂, ¹²¹SbHD₂, ¹²³SbH₂D, and ¹²¹SbH₂D. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH₃ → XH₂D/XHD₂ isotopic substitution, have been compared with those obtained in the present study.     

16.

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

C. Bray  A. Perrin  D. Jacquemart  N. Lacome 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(15):2446-2462

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.     

17.

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

E. Cané  G. Pawelke 《Journal of Molecular Spectroscopy》2007,244(1):24-32

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.     

18.

High-resolution synchrotron infrared spectroscopy of thiophosgene: The ν₂ and ν₄ fundamental bands near 500 cm     

A.R.W. McKellar  B.E. Billinghurst 《Journal of Molecular Spectroscopy》2010,260(1):66-34

Thiophosgene (Cl₂CS) is a favorite model system for studies of photophysics, vibrational dynamics, and intersystem interaction effects. But there are no previous rotationally-resolved infrared studies because the spectra are very congested due to hot bands and multiple isotopic species. This paper reports a detailed study of the ν₂ (∼504 cm⁻¹) and ν₄ (∼471 cm⁻¹) fundamental bands for the two most abundant isotopomers, ³⁵Cl₂CS and ³⁵Cl³⁷ClCS, based on spectra with observed line widths of ∼0.0008 cm⁻¹ obtained at the Canadian Light Source far-infrared beamline using synchrotron radiation and a Bruker IFS125 Fourier transform spectrometer.     

19.

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

C Betrencourt-Stirnemann  G Graner  D.E Jennings  W.E Blass 《Journal of Molecular Spectroscopy》1978,69(2):179-198

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.     

20.

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.     

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

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.     

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 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 2ν4 overtone bands of FClO3

The high resolution infrared spectrum of the mono-isotopic species F³⁵Cl¹⁶O₃ has been studied in the region of the 2ν₄ overtone, from 2560 to 2680 cm⁻¹. The perpendicular component is strong and clearly observed while the parallel component is very weak and almost completely hidden by the perpendicular one. Their origins differ by 12.6 cm⁻¹, the being located at higher wavenumbers. The band is perturbed by the anharmonic interaction between the v₄ = 2, l₄ = ?2 and v₂ = v₄ = v₅ = 1, l₄ = l₅ = ±1 excited states, both of E symmetry. In total 3157 transitions have been assigned, 83% of these to , 12% to , and 5% to . The three bands have been analyzed simultaneously, taking into account the Fermi resonance effective between the excited states of E symmetry. The ro-vibration parameters of the excited states have been obtained, including the deperturbed band origins of and , at 2628.5890(4) and 2619.3342(5) cm⁻¹, respectively. The W₂₄₅ anharmonic constant is equal to 4.0161(4) cm⁻¹. The x₄₄+g₄₄ and x₂₄+x₄₅+g₄₅ anharmonicity constants have been derived from the obtained band origins and those of ν₄ and ν₂ + ν₅.     

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 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.     

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.     

High resolution infrared study of SbHD2: The ground state and the Sb-H stretching bands ν1 and 2ν1

High resolution infrared spectra of ¹²¹SbHD₂ and ¹²³SbHD₂ have been studied in the region of ν₁, the Sb-H stretching fundamental, from 1780 to 1990 cm⁻¹. The 2ν₁ stretching overtone band of ¹²³SbHD₂, located in the 3640-3790 cm⁻¹ range, has also been investigated. The SbHD₂ molecule is an asymmetric rotor of C_s symmetry with the asymmetry parameter κ = 0.61. The ν₁ band is of hybrid type, formed by strong C-type and weak B-type transitions, and almost unperturbed. For ¹²³SbHD₂, 2092 transitions have been assigned: 70% of these belong to the C component, the other 30% are of B-type. The assigned transitions have been fitted using a Watson type S-reduced Hamiltonian in the III^l representation, with a standard deviation of the fit σ = 0.45 × 10⁻³ cm⁻¹. In order to determine the ground state parameters all possible ground state combination differences (GSCD) have been generated from the ν₁ transitions. In total, 3942 GSCD up to J^″ = 27,  = 25, and  = 20 have been fitted with σ = 0.52 × 10⁻³ cm⁻¹. Only C-type transitions have been observed in the weak 2ν₁ overtone band. The 556 assigned transitions have been fitted with σ = 2.6 × 10⁻³ cm⁻¹ using the same Hamiltonian as for ν₁. In the ν₁ band of ¹²¹SbHD₂ 771 C-type transitions have been assigned, and the v₁=1 spectroscopic constants obtained from a fit with σ = 0.70 × 10⁻³ cm⁻¹. Using 618 GSCD the ground state spectroscopic constants of ¹²¹SbHD₂ have been derived with σ = 1.0 × 10⁻³ cm⁻¹. The molecular parameters for the ground and the v₁=1 states of the two isotopologues agree well. The quartic theoretical ab initio force field of SbH₃ has been used to predict all relevant spectroscopic parameters for ¹²³SbHD₂, ¹²¹SbHD₂, ¹²³SbH₂D, and ¹²¹SbH₂D. Relations between the harmonic frequencies and between the anharmonicity constants obtained in the expanded local mode theory, for the XH₃ → XH₂D/XHD₂ isotopic substitution, have been compared with those obtained in the present study.     

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.     

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.     

High-resolution synchrotron infrared spectroscopy of thiophosgene: The ν2 and ν4 fundamental bands near 500 cm

Thiophosgene (Cl₂CS) is a favorite model system for studies of photophysics, vibrational dynamics, and intersystem interaction effects. But there are no previous rotationally-resolved infrared studies because the spectra are very congested due to hot bands and multiple isotopic species. This paper reports a detailed study of the ν₂ (∼504 cm⁻¹) and ν₄ (∼471 cm⁻¹) fundamental bands for the two most abundant isotopomers, ³⁵Cl₂CS and ³⁵Cl³⁷ClCS, based on spectra with observed line widths of ∼0.0008 cm⁻¹ obtained at the Canadian Light Source far-infrared beamline using synchrotron radiation and a Bruker IFS125 Fourier transform spectrometer.     

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 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.