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.     

High-resolution FTIR spectra of CH2 = CClF in the 930-1050 cm−1 region

The gas-phase infrared spectra of natural CH₂ = CClF have been measured in the v ₆ and 2v ₁₂ band regions (930–1050 cm^?1) by high-resolution Fourier transform spectroscopy at room temperature. 1-Chloro-1-fluoroethylene is a planar asymmetric rotor (κ = ?0.54) belonging to the symmetry point group C_s and the vibrations investigated of symmetry species A′ give rise to a/b-hybrid bands with contributions of comparable intensity from both the components.

The rovibrational analysis of the fine structure led to the identification of 1894 (J ? 73, K_a ? 20) and 718 (J ? 53, K_a ? 8) transitions for the v ₆ and 2v ₁₂ bands of the ³⁵Cl isotopic species, respectively. Using the Watson's A-reduction Hamiltonian in the I^r representation a set of accurate spectroscopic parameters for both the excited states u ₆ = 1 and u12 = 2 of ³⁵Cl has been obtained for the first time. Transitions of ³⁷Cl isotopomer could also be assigned in the Q branch region of the 2v ₁₂ overtone; the determined band origin shift of 0.782 cm^?1 towards the lower wavenumbers led to describing the v ₁₂ fundamental as a vibration mainly involving the CFCl bending motion.     

High resolution study of the v 7 + v 8 band of ethylene (C2H4) at 1889 cm-1

The v ₇ + v ₈ A-type band of C₂H₄ has been recorded between 1932 and 1847 cm^-1 with a resolution of 0·06 cm^-1. The transitions with K _-1 ? 8> and J ? 2>5 have been assigned. Although slight Coriolis resonances perturb the band, the analysis has been made easy through the use of an elaborate set of asymmetric top computer programmes. The band centre and a set of upper state constants have been obtained. With these constants, 288 observed upper state energy levels have been fitted with a standard deviation of 0·021 cm^-1.

Using very simple expressions, we have predicted all the resonance effects perturbing the levels of ethylene near 2000 cm^-1. This led us to the identification of the v ₄ + v ₈ and v ₈ + v ₁₀ combination bands in low resolution spectra.     

High resolution FTIR spectroscopy of CH2DF: analysis of the v 3 and v 4 interacting bands

The high resolution (0.004cm^?1) Fourier transform infrared spectrum of the monodeuterated form of methyl fluoride, CH₂DF, has been recorded and analysed in the v ₃ and v ₄ band region around 1420cm^?1. Both bands, coming from A′ symmetry vibrations, have a/b hybrid character, although in v ₃ the b-type component prevails over the a-type. The rotational structure has been analysed using a dyad model including c-type Coriolis coupling and high order vibrational resonance between these states. Accurate upper state molecular parameters and interaction terms have been obtained by fitting about 3270 assigned transitions to Watson's A-reduced Hamiltonian in the I^r representation. In addition, from a simultaneous fit of ground state combination differences coming from this analysis and 42 literature microwave transitions, an improved and more complete set of ground state constants, including three new sextic centrifugal distortion terms (Φ_JK, Φ_KJ and Φ_K), has been derived.     

High-resolution FTIR spectroscopy of the v11 and v2 + v7 bands of ethylene-d4

The Fourier transform infrared spectrum of the v₁₁ band of ethylene-d₄ (C₂D₄) has been recorded with an unapodized resolution of 0.006 cm^?1 in the frequency range 2150 to 2250cm^?1. The v₁₁ band, with a band centre of about 2201 cm^?1, was found to be perturbed by the nearby v₂ + v₇ band centred at about 2235 cm^?1 by a b-type Coriolis interaction. By fitting a total of 772 infrared transitions of v₁₁ using a Watson's A-reduced Hamiltonian in the I^r representation with the inclusion of b-type Coriolis interaction term, two sets of constants, up to quartic distortion constants for the v₁₁ = 1 state, and principal rotational constants for the v₂ + v₇ = 1 dark state, were derived. The inertia defect of the v₁₁ state was found to be 0.0693 ± 0.0004u Ų.     

The perpendicular fundamental v5 of chloroform 12CH35Cl3: high resolution infrared study of the v5 band together with the millimetre-wave rotational spectrum

The infrared spectrum of the perpendicular fundamental v₅ of chloroform around 776 cm^?1 has been studied by applying two high resolution methods. A short range from the central part of the spectrum was measured with a diode laser by using a cold jet sample including chloroform in natural isotopic abundancies. More than 100 rotational lines of ¹²CH³⁵Cl₃ could be assigned. The whole band region was measured by a Fourier transform spectrometer at a resolution of 0.0010cm^?1. In this case an isotopically pure sample of ¹²CH³⁵Cl₃ was used. Starting from the results of the diode laser investigation more than 2000 lines could be assigned with J_max = 91 and K_max = 58. In addition to the infrared spectra, millimetre-wave lines also were measured. A total of 58 lines corresponding to J values 22, 23 and 35 at the excited vibration state v₅ = 1 were assigned and analysed. All the data from three different spectra were simultaneously fitted and, for example, the results v₀ = 775.961 50(3) cm^?1, 98, B₅-B₀ = ?0.180171(22) × 10^?3cm^?1, C₅ ? C₀ = ?0.170 57(15) × 10^?3cm^?1, and (Cζ)₅ = 0.047 5294(11) cm^?1 were obtained.     

Infrared-microwave double resonance in CH3OH using a Zeeman-tuned 3.5-μm HeXe laser

Infrared microwave double resonance signals have been observed for CH₃OH using the 3.5-μm HeXe laser line. When microwave transitions in the ground vibrational state are pumped, the double resonance signals are obtained on two infrared transitions v = 1 ← 0 of ν^CH(a′); v = 1, J, K, μ = 4, 2, 1 ← v = 0, J, K, μ = 3, 2, 1, and 4, 3, 1 ← 3, 3, 1. Three weak double resonance signals are due to the collision-induced transitions. Their relative intensities have been explained successfully by using the rate constants of collision-induced transitions which are proportional to the dipole matrix elements between the states involved in the transitions.     

High-resolution FTIR spectroscopy of CHD279Br: ro-vibrational analysis of the v4 fundamental and determination of the ground state constants

The first high-resolution infrared spectrum of CHD₂⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 940–1100 cm^?1 at an unapodised resolution of 0.0025 cm^?1. This spectral region is characterised by the v₄ (1036.8389 cm^?1) fundamental band, corresponding to the CD₂ wagging mode. The rotational structure of the a- and c-type components of the hybrid band has been extensively assigned for transitions involving values of J and K_a up to 65 and 15, respectively. The ground state constants up to the quartic centrifugal distortion terms have been obtained for the first time by ground state combination differences from 5251 assigned transitions and subsequently employed for the evaluation of the band origin and the excited state parameters of v₄. Watson’s S-reduced Hamiltonian in the I^r representation has been used in the ro-vibrational analysis. The dipole moment ratio |Δμ_a/Δμ_c| of the band has been estimated to be 1.3?±?0.1 from spectral simulations.     

Analysis of the ν6 band of 12CH3D at 8.6 μm

The ν₆(E) fundamental vibration-rotation band of monodeuteromethane (¹²CH₃D) has been recorded in the spectral range 1033–1270 cm^?1 with a resolution of approximately 0.04 cm^?1. Of the 669 transitions with J′ ≤ 17 identified, 633 have been retained for the determination of the rotational levels in the upper state v₆ = 1. The Coriolis interaction between the v₆ = 1(E) and v₃ = 1 (A₁) vibrational states of ¹²CH₃D results in large A₁A₂ splittings of levels with v₆ = 1 and |K ? l₆| = 0 or 3; the mixing in K and l₆ also gives rise to some ten forbidden transitions observed in the spectra. These effects have been very well explained within the formulation based on the contact transformation method. Values of 15 molecular structure constants of the v₆ = 1 state have been determined from a least-squares analysis of the 633 retained transitions. These constants can be used to estimate values of the upper-state energies up to fourth order, and through them the spectral positions of the 633 retained transitions are reproduced with an overall standard deviation of 0.013 cm^?1, which is within experimental uncertainties.     

Laser infrared spectroscopy of vinyl fluoride in the 1280–1400 cm−1 region

The infrared spectra of CH₂=CHF have been investigated in the ν₅ and ν₆ band regions between 1280 and 1400?cm^?1, at a resolution of about 0.002?cm^?1, using a tunable diode laser spectrometer. These vibrations of symmetry species A′ give rise to a/b-hybrid bands with different contributions from both the components. Spectral analysis resulted in the identification of 1565 (J≤46, K _a ≤11) and 1651 (J≤48, K _a ≤15) transitions of the ν₅ and ν₆ fundamentals, respectively. Both bands are perturbed by the nearby states ν₈?+?ν₉ and ν₉?+?ν₁₁ through different Coriolis resonances and an anharmonic interaction. Using Watson's A-reduction Hamiltonian in the I^r representation and perturbation operators almost all the transitions have been fitted simultaneously to a model including six resonances within the tetrad ν₅/ν₆/ν₈?+?ν₉/ν₉?+?ν₁₁. A set of spectroscopic constants for the ν₅ and ν₆ bands, as well as parameters for the dark states ν₈?+?ν₉ and ν₉?+?ν₁₁ and coupling constants, have been determined. From spectral simulations the dipole moment ratio |Δμ _a /Δμ _b | was estimated to be 0.6?±?0.1 and 2.0±0.3 for the ν₅ and ν₆ bands, respectively.     

N2-broadening coefficients of methyl chloride at room temperature

Methyl chloride is of interest for atmospheric applications, since this molecule is directly involved in the catalytic destruction of ozone in the lower stratosphere. In a previous work [Bray et al. JQSRT 2011;112:2446], lines positions and intensities of self-perturbed ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl have been studied into details for the 3.4 μm spectral region. The present work is focused on measurement and calculation of N₂-broadening coefficients of the ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl isotopologues. High-resolution Fourier Transform spectra of CH₃Cl–N₂ mixtures at room-temperature have been recorded between 2800 and 3200 cm^?1 at LADIR (using a classical source) and between 47 and 59 cm^?1 at SOLEIL (using the synchrotron source on the AILES beamline). 612 mid-infrared transitions of the ν₁ band and 86 far-infrared transitions of the pure rotational band have been analyzed using a multispectrum fitting procedure. Average accuracy on the deduced N₂-broadening coefficients has been estimated to 5% and 10% in the mid- and far-infrared spectral regions, respectively. The J- and K-rotational dependences of these coefficients have been observed in the mid-infrared region and then a simulation has been performed using an empirical model for 0≤J≤50, K≤9. The ¹²CH₃³⁵Cl–N₂ line widths for 0≤J≤50 and K≤10 of the ν₁ band and for 55≤J≤67 and K≤15 of the pure rotational band have been computed using a semi-classical approach involving exact trajectories and a real symmetric-top geometry of the active molecule. Finally, a global comparison with the experimental and theoretical data existing in the literature has been performed. Similar J- and K-rotational dependences have been appeared while no clear evidence for any vibrational or isotopic dependences have been pointed out.     

New measurements and global analysis of chloromethane in the region from 0 to 1800 cm

New high resolution Fourier transform spectra of pure ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm⁻¹. New rotational transitions within the v₂=1, v₅=1, and v₃=2 states have been measured at Lille. A first global analysis of the lower four band systems of the molecule (700-1800 cm⁻¹) is reported. The model was based on an effective Hamiltonian and dipole moment expressed in terms of irreducible tensor operators. A common set of 125 effective hamiltonian parameters (sixth order) has been adjusted to fit simultaneously some 11 000 IR data for each of the isotopomers including 153 mm wave data for 12CH₃35Cl. The assignments involve 12 sets of transitions (6 cold bands, 3 hot bands, and 3 pure rotational systems for ¹²CH₃³⁵Cl). The standard deviation was on average 0.00014 cm⁻¹ and 175 kHz for the IR and MMW data, respectively. The v₃=v₆=1 state was analysed for the first time principally from observed hot band transitions.     

Microwave spectrum of CH3OD

The microwave spectrum of CH₃OD has been observed in the frequency region between 14 and 92 GHz. All the ground-state transitions with J ≤ 8 and J = 2 ← 1, a-type transitions in the excited torsional states (v = 1 and v = 2) have been observed. The spectrum has been analyzed and rotational constants, torsional constants, torsion-vibration-rotation interaction constants, and centrifugal distortion constants have been evaluated. The Stark effect measurements have been made and the dipole moment components have been determined as μ_a = 0.833 ± 0.008 D and μ_b = 1.488 ± 0.015 D.     

Doppler-limited dye laser excitation spectroscopy of HCCl

The cw dye laser excitation spectrum of the $\text{A}\text{?}{}^1\text{A″(050) ←}\text{X}\text{?}{}^1\text{A′(000)}$ vibronic band of HCCl was observed between 16 539 and 16 656 cm^?1 with the Doppler-limited resolution, 0.03 cm^?1. The HCCl molecule was generated by the reaction of discharged CF₄ with CH₃Cl. The observed spectra were assigned to c-type transitions with ΔK_a = ±1 and also to axis-switching transitions with ΔK_a = 0 or ?2, but all with K′_a = 0, both for HC³⁵Cl and HC³⁷Cl. A rotational analysis yielded the rotational constants and quartic centrifugal distortion constants for the ground vibronic state and the band origin. A weak vibronic band, about one-third as intense as the main band, was found at about 57 cm^?1 to the violet of the main band for both isotopic species, and was ascribed to a transition from the ground vibronic state to a vibrational level, possibly (041), of the à state. The rotational levels of HC³⁵Cl in the à state showed a large perturbation; the J′ = 8, 9, and 10 levels were found to be split into two components. A normal coordinate analysis was carried out to calculate the centrifugal distortion constants and the inertia defect, which were in fair agreement with the observed values. The molecular structure of HCCl in the ground vibronic state was recalculated from the rotational constants of the two isotopic species combined with the 0.75B₀ + 0.25C₀ value previously reported for DC³⁵Cl.     

The 2v 2, v 1 and v 3 bands of H2 16O

The 2v ₂, v ₁ and v ₃ bands of H₂ ¹⁶O occurring in the region 2930–4255 cm^-1 were studied from a spectrum recorded with a high resolution Fourier transform spectrometer (resolution: 0·005 cm^-1). The set of the observed transitions leads by a least squares method to the determination of very accurate values of the rotational levels belonging to the vibrational states (000), (020), (100), (001). From these levels, using Watson's Hamiltonian, we have obtained respectively 21 and 17 rotational constants for the states (000) and (020).     

The high-resolution infrared spectra of the ν2 and ν3 bands of HOCl

The infrared spectra of the a-type transitions of the ν₂ and ν₃ bands of HO³⁵Cl and HO³⁷Cl have been obtained under high resolution. Line assignments of both bands have been made, and the spectroscopic constants have been obtained for both bands using a Watson Hamiltonian. Lines of the K_a = 5 subband of the ν₂ band of the HO³⁵Cl molecule were found to be slightly shifted by an interaction with the K_a = 4 level of the 2ν₃ vibrational state. The b-type transitions permitted for both bands were too weak to observe. Relative intensities of selected lines of both bands have been measured, and empirical Herman-Wallis factors have been determined.     

Ground-state constants A 0 and DK 0 of 12CH3I from perturbation-allowed transitions

The upper levels of the bands v ₅ and v ₃ + v ₆ of CH₃I are coupled through a Fermi and an l(2, -1) resonance. This gives rise to perturbation-allowed transitions. Altogether, more than 200 such lines corresponding to three different K-value pairs have been observed between 1320 cm^-1 and 1520 cm^-1. By fixing the sextic constant H^K ₀ equal to zero, the following values were obtained: A ₀ = 5·173931(2) cm^-1 and D^K ₀ = 87·36(6) × 10^-6 cm^-1. The possible values of H^K ₀ and their effects on the results are discussed.     

10-μm sub-doppler laser-Stark spectroscopy of methyl chloride: Analysis of the ν6 bands of the CH335Cl and CH337Cl

About 900 Stark transitions from 70 vibration-rotation transitions in CH₃³⁵Cl and about 400 transitions from 38 transitions in CH₃³⁵Cl in the ν₆ band have been assigned. These data were analyzed simultaneously with previously published microwave data on the ν₆ = 1 state. The fit has a standard deviation of about 2 MHz for the data for both isotopes. The isoptopic shift ν₆35 ? ν₆37 = 0.3766(6) cm^?1. Rotational dependence of the dipole moment was also just apparent at about μ_J = μ_K = 1 × 10^?5 D, and a complete set of molecular constants is given.