High resolution FTIR spectra and analysis of the ν11 fundamental and of the ν2 + ν11, ν5 + ν12 and ν7 + ν16 combination bands of 12C6D6

We report results from measurements of the high resolution FTIR spectrum for the fully deuterated benzene molecule C₆D₆ in the range 450–3500 cm^?1. Accurate spectroscopic constants have been obtained for the fundamental vibration ν₁₁ at 496.208 cm^?1 and improved ground state constants have been deduced from a fit of ground state combination differences. The J structure of the combination parallel bands ν₂ + ν₁₁ (at 2798.1 cm^?1), ν₅ + ν₁₂ (1802.5 cm_?1) and ν₇, + ν₁₆ (2619.3 cm^?1) of C₆D₆ has been analysed as well, from which improved values of the band origin and of the B and D _j constants of the excited states have been obtained. The strongest hot bands accompanying these parallel transitions have been assigned by means of the anharmonic force field calculated by Maslen et al. [1992, J. chem. Phys., 97, 4233]. In particular (ν₁₁ + ν₁₆) ? ν₁₆ is assigned to the band at 492.4 cm^?1 even though its shape is typical of a perpendicular transition (PAPE). New values for the ν₅, ν₁₂ and ν₁₆ band origins are determined from the band origins of combination bands and from calculated anharmonic constants. Numerous anharmonic constants are derived from the assignment of hot band and combination transitions.     

Simultaneous analysis of the ν2 and ν4 bands of methane

Vibration-rotation spectra of the ν₂ and ν₄ bands of CH₄ have been analysed by a simultaneous diagonalization of the hamiltonian matrices for the v ₂=1 and v ₄=1 states coupled by the Bξ_2,4 Coriolis interaction term. The effective hamiltonians used extend to sextic centrifugal distortion terms. The results are a significant improvement on any previous analysis; 438 assigned transitions up to J′=16 have been fitted with an overall standard deviation of 0·016 cm^-1. The method used is compared with an alternative theoretical approach given by Berger.     

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

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

High-resolution spectroscopy of difference and combination bands of SF6 to elucidate the ν3 + ν1 − ν1 and ν3 + ν2 − ν2 hot band structures in the ν3 region

The strong infrared absorption in the ν₃ S–F stretching region of sulphur hexafluoride (SF₆) near 948 cm^?1 makes it a powerful greenhouse gas. Although its present concentration in the atmosphere is very low, it is increasing rapidly, due to industrial pollution. The ground state population of this heavy species is only 32% at room temperature and thus many hot bands are present. Consequently, a reliable remote-sensing spectroscopic detection and monitoring of this species require an accurate modelling of these hot bands. We used two experimental set-ups at the SOLEIL French synchrotron facility to record some difference and combination bands of SF₆: (1) a new cryogenic multiple pass cell with 93 m optical path length and regulated at 163 ± 2 K temperature and (2) the Jet-AILES supersonic expansion set-up. With this, we could obtain high-resolution absorption spectra of the ν₃ ? ν₁, ν₃ ? ν₂, ν₁ + ν₃ and ν₂ + ν₃ bands at low temperature. These spectra could be assigned and analysed, thanks to the SPVIEW and XTDS computer programs developed in Dijon. We performed two global fits of effective Hamiltonian parameters. The first one is a global fit of the ground state, ν₂, ν₃, ν₃ ? ν₂, ν₂ + ν₃, 2ν₃ and 2ν₃ ? ν₃ rovibrational parameters, using the present spectra and previous infrared, Raman and two-photon absorption data. This allows a consistent refinement of the effective Hamiltonian parameters for all the implied vibrational levels and a new simulation of the 2ν₃ + ν₂ ? ν₂ hot band. The second global fit involves the present ν₃ ? ν₁ and ν₁ + ν₃ lines, together with previous ν₁ Raman data, in order to obtain refined ν₁ parameters and also ν₁ + ν₃ parameters in a consistent way. This allows to simulate the ν₃ + ν₁ ? ν₁ hot band.     

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^?1 and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.     

The ν1 and ν3 bands of 16O3: Line positions and intensities

Using 0.005 cm⁻¹ resolution Fourier transform spectra of samples of ozone, the ν₁ and ν₃ bands of ¹⁶O₃ have been reanalyzed to obtain accurate line positions and an extended set of upper state rotational levels (J up to 69, K_a up to 20). Combined with the available microwave data, these upper state rotational levels were satisfactorily fitted using a Hamiltonian which takes explicitly into account the strong Coriolis interaction affecting the rotational levels of these two interacting states. In addition, 350 relative line intensities were measured from which the rotational expansions of the transition moment operators for the ν₁ and ν₃ states have been deduced. Finally, a complete listing of line positions, intensities, and lower state energies of the ν₁ and ν₃ bands of ¹⁶O₃ has been generated.     

First high-resolution analysis of the ν1, ν3 and ν1 + ν3 bands of sulphur dioxide 33S16O2

• High-resolution spectra of ³³S¹⁶O₂ have been recorded for the first time in the 8 and 4 µm spectral regions.

• The ν₁, ν₃ and ν₁ + ν₃ bands of the ³³S¹⁶O₂ have been analysed up to very high quantum numbers.

• Accurate ro-vibrational upper states constants have been determined.

     

High-resolution Fourier transform spectroscopy of the ν2 and ν3 fundamentals of nitrosyl fluoride,FNO

The ν₂ and ν₃ fundamentals of FNO have been recorded with a Fourier transform spectrophotometer at an apodized resolution of approximately 0.004 cm^?1. The Fourier infrared data have been analyzed together with previous microwave data to yield improved molecular parameters for the (000) and (010) vibrational states and the first set of constants for the (001) state. The main results (in cm^?1) are

     

9.

Diode laser spectroscopy of the ν1 and ν3 bands of thiazyl fluoride (FSN)     

《Journal of Molecular Spectroscopy》1987,126(2):270-281

The ν₁ (FS stretch) and ν₃ (SN stretch) bands of FSN have been measured with Dopplerlimited resolution using a diode laser spectrometer. An accurate set of band constants were determined for ν₁ from a simultaneous fit to 265 infrared data and 73 ground state rotational transitions. The ν₃ band was found to be perturbed as the result of a Coriolis-type interaction between the states (0, 0, 1) and (1, 2, 0). Further difficulties with ν₃ were produced by the presence of many strong absorption lines from an SO₂ impurity. A limited set of effective band constants were determined for this band. Some general aspects of Q-branch absorption line patterns are briefly discussed.     

10.

A simultaneous analysis of ν5, ν6, and the ground state of hydrazoic acid     

《Journal of Molecular Spectroscopy》1987,124(2):306-316

The pure rotational spectrum in the vibrational ground state [J. Bendtsen and F. M. Nicolaisen, J. Mol. Spectrosc. 119, 456–466 (1986)] and the infrared spectrum of the fundamental bands ν₅ and ν₆ [J. Bendtsen, F. Hegelund, and F. M. Nicolaisen, J. Mol. Spectrosc. 118, 121–131 (1986)] of HN₃ have been simultaneously analyzed using a three-level model taking into account resonance between the ground state and ν₅ due to centrifugal distortion [K. Yamada, J. Mol. Spectrosc. 81, 139–151 (1980)] and a- and b-Coriolis interactions between ν₅ and ν₆. A set of ground- and upper-state constants have been obtained and values for the centrifugal distortion parameter C₅^ab and the Coriolis coupling constant ζ_5,6^b are derived. A complete set of ground-state energies for J ≦ 50 and K_a ≦ 10 is tabulated.     

11.

High-resolution analysis of the ν1 and ν5 bands of phosgene 35Cl2CO and 35Cl37ClCO     

F. Kwabia Tchana  W.J. Lafferty  L. Manceron  M. Ndao 《Molecular physics》2013,111(21):3241-3246

Fourier transform spectra of phosgene (Cl₂CO) have been recorded in the 11.75 and 5.47 μm spectral regions using a Bruker IFS125HR spectrometer at resolutions of 0.00102 and 0.0015 cm^?1, respectively, leading to the observation of the ν₅ and ν₁ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper state ro-vibrational levels were fit using Watson-type Hamiltonians and/or a Hamiltonian matrix accounting for resonance effects when necessary. In this way, it was possible to reproduce the upper state ro-vibrational levels to within the experimental accuracy, i.e. ～0.17 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band centres: ν₀(ν_5, ³⁵Cl₂CO) = 851.012737(20) cm^?1, ν₀(ν_5, ³⁵Cl³⁷ClCO) = 849.995451(90) cm^?1, ν₀(ν_{2 +} ν_3, ³⁵Cl³⁷ClCO) = 864.42370(50) cm^?1, ν₀(ν_1, ³⁵Cl₂CO) = 1828.202514(40) cm^?1 and ν₀(ν_1, ³⁵Cl³⁷ClCO) = 1827.246444(20) cm^?1.     

12.

Vibration-rotation spectrum of formaldehyde: CH stretching fundamentals ν1 and ν5     

Toru Nakagawa  Koichi Yamada  Kozo Kuchitsu 《Journal of Molecular Spectroscopy》1976,63(3):485-508

The infrared vibration-rotation spectrum of formaldehyde vapor has been measured in the region from 2600 to 3400 cm^?1 with resolution from 0.04 to 0.07 cm^?1. An extensive rotational analysis of the ν₁ and ν₅ bands has confirmed and superseded the previous band-contour analysis of a medium-resolution spectrum. A large number of subbranches of both the ν₁ and ν₅ bands are perturbed by the combination bands ν₃ + ν₆, ν₂ + ν₄, and ν₂ + ν₆, whereas the Coriolis interaction between ν₁ and ν₅ is weak. The following effective rotational constants (in cm^?1) are obtained:

$\text{ν}{}_1\text{= 2782.49(1), A}{}_1\text{= 9.250(5), B}{}_1\text{= 1.2968(6), C}{}_1\text{= 1.1321(2)}$

,

$\text{ν}{}_0\text{= 2843.35(2), A}{}_0\text{= 9.224(2), B}{}_0\text{= 1.2936(2), C}{}_0\text{= 1.1303(1)}$

, where the number given in parentheses is three times the standard error in the last digit.     

13.

High-resolution infrared spectroscopy of CH281BrF near 8 μm: rovibrational analysis of the ν3 and ν8 fundamentals and resonances with the dark states 2ν5 and ν6 + ν9     

P. Stoppa  N. Tasinato  A. Baldacci  A. Pietropolli Charmet  S. Giorgianni  R. Wugt Larsen 《Molecular physics》2014,112(13):1799-1807

The infrared spectrum of isotopically enriched CH₂⁸¹BrF was investigated in the ν₃ and ν₈ region between 1150 and 1370 cm^?1 at a resolution of 0.003 cm^?1. The ν₃ vibration of symmetry species A^′ gives rise to an a-/b-hybrid band with a-type predominance, while the ν₈ mode of A^″ symmetry produces c-type absorption. Due to the proximity of the band origins to those of closely lying overtones and combination bands, the v₃ = 1 and v₈ = 1 levels were found perturbed through Coriolis resonance by the v₅ = 2 (A^′) and v₆ = v₉ = 1 (A^″) states, respectively. The spectral analysis resulted in the identification of 3132 transitions (J^″ ≤ 98 and K_a^″ ≤ 14) for the ν₃ and 2958 transitions (J^″ ≤ 68 and K_a^″ ≤ 19) for the ν₈ bands. The assigned data were fitted using the Watson's A-reduction Hamiltonian in the I^r representation and the perturbation operators. Although no transitions belonging to the perturbers were observed, the band origins and excited state parameters for fundamentals and ‘dark states’ together with coupling terms for the ν₃/2ν₅ and ν₈/ν₆ + ν₉ dyads were determined.     

14.

Analysis of FTIR spectra of CH2 79Br35Cl; the ν3 and ν9 fundamentals     

Marcel Snels  El Bachir Mkadmi 《Molecular physics》2013,111(13):1469-1473

The infrared spectrum of isotopically pure CH₂ ⁷⁹BrCl has been recorded at a resolution of 0.0025?cm^?1 and 0.0023?cm^?1 (FWHM) in the range 600–1600?cm^?1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν₃ and ν₉ fundamentals of the most abundant species CH₂ ⁷⁹Br³⁵Cl . Improved ground state constants, up to quartic terms, have been obtained from ground state combination differences (GSCD) involving transitions of the fundamentals ν₃, ν₄, ν₅ and ν₉. Both ν₃ and ν₉ transitions were fitted to a Watson-type Hamiltonian in the S-reduction, yielding accurate molecular constants for the ν₃ and ν₉ excited states. Small local perturbations were observed in both bands. Prominent features in the spectra were assigned to the ν₃ and ν₉ fundamentals of the CH₂ ⁷⁹Br³⁷Cl isotopic species and the hot-bands ν₃+ν₆???ν₆ and ν₉+ν₆???ν₆ of CH₂ ⁷⁹Br³⁵Cl.     

15.

Laser Stark spectroscopy of formaldehyde-d2: The Coriolis coupled ν4 and ν6 fundamentals     

Dewitt Coffey  Chikashi Yamada  Eizi Hirota 《Journal of Molecular Spectroscopy》1977,64(1):98-108

Using CO₂ and N₂O lasers, we have measured and assigned nineteen ν₄ and nine ν₆ rotation-vibration resonances of the type ΔM = 0 and M = J. These transitions were combined with the zero-field pure rotational spectra in order to determine the two fundamental vibrational frequencies, the rotational constants of both excited states, the Coriolis coupling constant, and the dipole moments of each of the three states. The ground-state rotational constants and centrifugal distortion constants were taken from a microwave study and the centrifugal distortion constants of the excited states were assumed equal to those of the ground state. The following results were obtained (standard deviations in parentheses):

	Ground state	$\text{ν}{}_2$	$\text{ν}{}_3$
A	3.1751882 (17)	3.1861249 (12)	3.1958722 (15)
B	0.39508266 (12)	0.39407878 (14)	0.39211484 (14)
C	0.35051504 (11)	0.34899779 (16)	0.34747411 (14)
$\text{ν}{}_0$	0	765.3551 (4)	519.5980 (4)

     

16.

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

J.-M. Flaud  W.J. Lafferty  R.L. Sams 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(9-10):669-674

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

17.

First far-infrared high-resolution analysis of the ν2 and ν4 bands of phosgene 35Cl2CO and 35Cl37ClCO     

J.-M. Flaud  F. Kwabia Tchana  W. J. Lafferty  A. Perrin  L. Manceron  M. Ndao 《Molecular physics》2018,116(23-24):3463-3467

ABSTRACT

A Fourier transform spectrum of phosgene (Cl₂CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm^?1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν₂ and ν₄ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 2¹ and 4¹ vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ～0.30 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν₀(ν_2, ³⁵Cl₂CO) = 572.526299(30) cm^?1, ν₀(ν_4, ³⁵Cl₂CO) = 582.089026(30) cm^?1, ν₀(ν_2, ³⁵Cl³⁷ClCO) = 568.951791(35) cm^?1 and ν₀(ν₄, ³⁵Cl³⁷ClCO) = 581.758279(35) cm^?1.     

18.

Reduced effective Hamiltonian for Coriolis-interacting νn and νt fundamentals of C3v molecules     

《Journal of Molecular Spectroscopy》1987,126(1):159-170

Reduction of the effective Hamiltonian for Coriolis-interacting ν_n(A₁) and ν_t(E) fundamentals in C_3v molecules is caried out. Formulas for the parameters of the reduced Hamiltonian in terms of the parameters of the unreduced one are derived. The reduction procedure allows interperation of the disagreement between the results reported by various authors on simultaneous fitting of interacting ν₂ and ν₅ bands of CH₃F. It is found also that the reduction of the effective Hamiltonian for the isolated degenerate band ν_t(E) should be carried out in order to provide a correct interpretation of the fitted parameters in terms of molecular constants.     

19.

High resolution FTIR study of the ν5 and ν6 bands of CH2D35Cl: analysis of resonances and determination of ground and upper state constants     

A. Baldacci  P. Stoppa  A. Pietropolli Charmet  S. Giorgianni  G. Nivellini 《Molecular physics》2013,111(20):2803-2811

The isotopically pure form of methyl chloride, CH₂D³⁵Cl, was synthesized and investigated by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004?cm^?1 in the range 650–900?cm^?1, the region of the lowest fundamentals ν₅ (827?cm^?1) and ν₆ (714?cm^?1). These distinct bands have been analysed in detail in the P-, Q- and R-branches. In spite of their expected a/b-hybrid nature, both envelopes show the peculiar characteristic of only a-type bands of near prolate asymmetric top molecules. Ground state parameters have been determined for the first time through ground state combination differences from both bands. Parameters of the excited vibrational states and coupling constants have been obtained using a model which accounts for c-type Coriolis interaction and ΔK_a?=?±?2 anharmonic resonance.     

20.

High-resolution Fourier-transform infrared spectroscopy of the ν1 and ν8 fundamental bands of sulphur tetrafluoride (SF4)     

KEVIN D. RAFFAEL  DAVID M. SMITH  DAVID A. NEWNHAM 《Molecular physics》2013,111(8):1095-1104

The vibration-rotation spectra of the ν₁ and ν₈ fundamental bands of ³²SF₄ have been observed using Fourier-transform infrared spectroscopy. The band centre of the c-type ν₁ symmetric sulphur-equatorial-fluorine stretching vibration was observed at 891.6 cm^?1 and that for the b-type ν₈ asymmetric sulphur-equatorial-fluorine stretching vibration at 864.6 cm^?1. In total, 2044 rovibrational transitions have been assigned. Analysis of the spectra showed that the rotational states of the ν₁ = 1 and ν₈ = 1 upper vibrational levels are coupled by an a-type Coriolis interaction. This coupling has been treated both using perturbation theory and by the explicit inclusion of an appropriate Hamiltonian matrix element in a combined fit of the data for both bands. Spectroscopic parameters have been determined for the ground, ν₁ = 1 and ν₈ = 1 vibrational levels. Weaker transitions resulting from difference bands and the fundamental bands of the ³⁴SF₄ isotopomer have been identified but could not be assigned, because of the density of lines in the room-temperature spectrum. The possibility that discrepancies between the observed and predicted spectra of the ν₁ fundamental may result from either a Coriolis interaction with the states of another vibrational level, or the effects of intramolecular exchange of axial and equatorial fluorine atoms is considered. The discussion is supported by theoretical calculations which show that the likely path for intramolecular exchange is via a C _4v transition state.     

		$\text{ν}{}_4$		$\text{ν}{}_6$
$\text{ν}{}_0$		938.0345 (6)		989.2519 (18)		(cm?1)
$\text{A}$		139 579 (150)		143 323 (150)		(MHz)
$\text{B}$		31 873.6 (5)		32 379.5 (7)		(MHz)
$\text{C}$		26 242.9 (6)		25 994.4 (8)		(MHz)
$\text{ξ}{}_{64}{}^{\mathrm{(a)}}$			136 178 (770)			(MHz)
μ		2.319 (10)		2.347 (4)		(D)
μ(ground state)			2.3464 (8)			(D)

Diode laser spectroscopy of the ν1 and ν3 bands of thiazyl fluoride (FSN)

The ν₁ (FS stretch) and ν₃ (SN stretch) bands of FSN have been measured with Dopplerlimited resolution using a diode laser spectrometer. An accurate set of band constants were determined for ν₁ from a simultaneous fit to 265 infrared data and 73 ground state rotational transitions. The ν₃ band was found to be perturbed as the result of a Coriolis-type interaction between the states (0, 0, 1) and (1, 2, 0). Further difficulties with ν₃ were produced by the presence of many strong absorption lines from an SO₂ impurity. A limited set of effective band constants were determined for this band. Some general aspects of Q-branch absorption line patterns are briefly discussed.     

A simultaneous analysis of ν5, ν6, and the ground state of hydrazoic acid

The pure rotational spectrum in the vibrational ground state [J. Bendtsen and F. M. Nicolaisen, J. Mol. Spectrosc. 119, 456–466 (1986)] and the infrared spectrum of the fundamental bands ν₅ and ν₆ [J. Bendtsen, F. Hegelund, and F. M. Nicolaisen, J. Mol. Spectrosc. 118, 121–131 (1986)] of HN₃ have been simultaneously analyzed using a three-level model taking into account resonance between the ground state and ν₅ due to centrifugal distortion [K. Yamada, J. Mol. Spectrosc. 81, 139–151 (1980)] and a- and b-Coriolis interactions between ν₅ and ν₆. A set of ground- and upper-state constants have been obtained and values for the centrifugal distortion parameter C₅^ab and the Coriolis coupling constant ζ_5,6^b are derived. A complete set of ground-state energies for J ≦ 50 and K_a ≦ 10 is tabulated.     

High-resolution analysis of the ν1 and ν5 bands of phosgene 35Cl2CO and 35Cl37ClCO

Fourier transform spectra of phosgene (Cl₂CO) have been recorded in the 11.75 and 5.47 μm spectral regions using a Bruker IFS125HR spectrometer at resolutions of 0.00102 and 0.0015 cm^?1, respectively, leading to the observation of the ν₅ and ν₁ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper state ro-vibrational levels were fit using Watson-type Hamiltonians and/or a Hamiltonian matrix accounting for resonance effects when necessary. In this way, it was possible to reproduce the upper state ro-vibrational levels to within the experimental accuracy, i.e. ～0.17 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band centres: ν₀(ν_5, ³⁵Cl₂CO) = 851.012737(20) cm^?1, ν₀(ν_5, ³⁵Cl³⁷ClCO) = 849.995451(90) cm^?1, ν₀(ν_{2 +} ν_3, ³⁵Cl³⁷ClCO) = 864.42370(50) cm^?1, ν₀(ν_1, ³⁵Cl₂CO) = 1828.202514(40) cm^?1 and ν₀(ν_1, ³⁵Cl³⁷ClCO) = 1827.246444(20) cm^?1.     

Vibration-rotation spectrum of formaldehyde: CH stretching fundamentals ν1 and ν5

The infrared vibration-rotation spectrum of formaldehyde vapor has been measured in the region from 2600 to 3400 cm^?1 with resolution from 0.04 to 0.07 cm^?1. An extensive rotational analysis of the ν₁ and ν₅ bands has confirmed and superseded the previous band-contour analysis of a medium-resolution spectrum. A large number of subbranches of both the ν₁ and ν₅ bands are perturbed by the combination bands ν₃ + ν₆, ν₂ + ν₄, and ν₂ + ν₆, whereas the Coriolis interaction between ν₁ and ν₅ is weak. The following effective rotational constants (in cm^?1) are obtained:

$\text{ν}{}_1\text{= 2782.49(1), A}{}_1\text{= 9.250(5), B}{}_1\text{= 1.2968(6), C}{}_1\text{= 1.1321(2)}$

,

$\text{ν}{}_0\text{= 2843.35(2), A}{}_0\text{= 9.224(2), B}{}_0\text{= 1.2936(2), C}{}_0\text{= 1.1303(1)}$

, where the number given in parentheses is three times the standard error in the last digit.     

High-resolution infrared spectroscopy of CH281BrF near 8 μm: rovibrational analysis of the ν3 and ν8 fundamentals and resonances with the dark states 2ν5 and ν6 + ν9

The infrared spectrum of isotopically enriched CH₂⁸¹BrF was investigated in the ν₃ and ν₈ region between 1150 and 1370 cm^?1 at a resolution of 0.003 cm^?1. The ν₃ vibration of symmetry species A^′ gives rise to an a-/b-hybrid band with a-type predominance, while the ν₈ mode of A^″ symmetry produces c-type absorption. Due to the proximity of the band origins to those of closely lying overtones and combination bands, the v₃ = 1 and v₈ = 1 levels were found perturbed through Coriolis resonance by the v₅ = 2 (A^′) and v₆ = v₉ = 1 (A^″) states, respectively. The spectral analysis resulted in the identification of 3132 transitions (J^″ ≤ 98 and K_a^″ ≤ 14) for the ν₃ and 2958 transitions (J^″ ≤ 68 and K_a^″ ≤ 19) for the ν₈ bands. The assigned data were fitted using the Watson's A-reduction Hamiltonian in the I^r representation and the perturbation operators. Although no transitions belonging to the perturbers were observed, the band origins and excited state parameters for fundamentals and ‘dark states’ together with coupling terms for the ν₃/2ν₅ and ν₈/ν₆ + ν₉ dyads were determined.     

Analysis of FTIR spectra of CH2 79Br35Cl; the ν3 and ν9 fundamentals

The infrared spectrum of isotopically pure CH₂ ⁷⁹BrCl has been recorded at a resolution of 0.0025?cm^?1 and 0.0023?cm^?1 (FWHM) in the range 600–1600?cm^?1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν₃ and ν₉ fundamentals of the most abundant species CH₂ ⁷⁹Br³⁵Cl . Improved ground state constants, up to quartic terms, have been obtained from ground state combination differences (GSCD) involving transitions of the fundamentals ν₃, ν₄, ν₅ and ν₉. Both ν₃ and ν₉ transitions were fitted to a Watson-type Hamiltonian in the S-reduction, yielding accurate molecular constants for the ν₃ and ν₉ excited states. Small local perturbations were observed in both bands. Prominent features in the spectra were assigned to the ν₃ and ν₉ fundamentals of the CH₂ ⁷⁹Br³⁷Cl isotopic species and the hot-bands ν₃+ν₆???ν₆ and ν₉+ν₆???ν₆ of CH₂ ⁷⁹Br³⁵Cl.     

Laser Stark spectroscopy of formaldehyde-d2: The Coriolis coupled ν4 and ν6 fundamentals

Using CO₂ and N₂O lasers, we have measured and assigned nineteen ν₄ and nine ν₆ rotation-vibration resonances of the type ΔM = 0 and M = J. These transitions were combined with the zero-field pure rotational spectra in order to determine the two fundamental vibrational frequencies, the rotational constants of both excited states, the Coriolis coupling constant, and the dipole moments of each of the three states. The ground-state rotational constants and centrifugal distortion constants were taken from a microwave study and the centrifugal distortion constants of the excited states were assumed equal to those of the ground state. The following results were obtained (standard deviations in parentheses):

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

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

First far-infrared high-resolution analysis of the ν2 and ν4 bands of phosgene 35Cl2CO and 35Cl37ClCO

ABSTRACT

A Fourier transform spectrum of phosgene (Cl₂CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm^?1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν₂ and ν₄ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 2¹ and 4¹ vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ～0.30 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν₀(ν_2, ³⁵Cl₂CO) = 572.526299(30) cm^?1, ν₀(ν_4, ³⁵Cl₂CO) = 582.089026(30) cm^?1, ν₀(ν_2, ³⁵Cl³⁷ClCO) = 568.951791(35) cm^?1 and ν₀(ν₄, ³⁵Cl³⁷ClCO) = 581.758279(35) cm^?1.     

Reduced effective Hamiltonian for Coriolis-interacting νn and νt fundamentals of C3v molecules

Reduction of the effective Hamiltonian for Coriolis-interacting ν_n(A₁) and ν_t(E) fundamentals in C_3v molecules is caried out. Formulas for the parameters of the reduced Hamiltonian in terms of the parameters of the unreduced one are derived. The reduction procedure allows interperation of the disagreement between the results reported by various authors on simultaneous fitting of interacting ν₂ and ν₅ bands of CH₃F. It is found also that the reduction of the effective Hamiltonian for the isolated degenerate band ν_t(E) should be carried out in order to provide a correct interpretation of the fitted parameters in terms of molecular constants.     

High resolution FTIR study of the ν5 and ν6 bands of CH2D35Cl: analysis of resonances and determination of ground and upper state constants

The isotopically pure form of methyl chloride, CH₂D³⁵Cl, was synthesized and investigated by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004?cm^?1 in the range 650–900?cm^?1, the region of the lowest fundamentals ν₅ (827?cm^?1) and ν₆ (714?cm^?1). These distinct bands have been analysed in detail in the P-, Q- and R-branches. In spite of their expected a/b-hybrid nature, both envelopes show the peculiar characteristic of only a-type bands of near prolate asymmetric top molecules. Ground state parameters have been determined for the first time through ground state combination differences from both bands. Parameters of the excited vibrational states and coupling constants have been obtained using a model which accounts for c-type Coriolis interaction and ΔK_a?=?±?2 anharmonic resonance.     

High-resolution Fourier-transform infrared spectroscopy of the ν1 and ν8 fundamental bands of sulphur tetrafluoride (SF4)

The vibration-rotation spectra of the ν₁ and ν₈ fundamental bands of ³²SF₄ have been observed using Fourier-transform infrared spectroscopy. The band centre of the c-type ν₁ symmetric sulphur-equatorial-fluorine stretching vibration was observed at 891.6 cm^?1 and that for the b-type ν₈ asymmetric sulphur-equatorial-fluorine stretching vibration at 864.6 cm^?1. In total, 2044 rovibrational transitions have been assigned. Analysis of the spectra showed that the rotational states of the ν₁ = 1 and ν₈ = 1 upper vibrational levels are coupled by an a-type Coriolis interaction. This coupling has been treated both using perturbation theory and by the explicit inclusion of an appropriate Hamiltonian matrix element in a combined fit of the data for both bands. Spectroscopic parameters have been determined for the ground, ν₁ = 1 and ν₈ = 1 vibrational levels. Weaker transitions resulting from difference bands and the fundamental bands of the ³⁴SF₄ isotopomer have been identified but could not be assigned, because of the density of lines in the room-temperature spectrum. The possibility that discrepancies between the observed and predicted spectra of the ν₁ fundamental may result from either a Coriolis interaction with the states of another vibrational level, or the effects of intramolecular exchange of axial and equatorial fluorine atoms is considered. The discussion is supported by theoretical calculations which show that the likely path for intramolecular exchange is via a C _4v transition state.