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 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.     

High-resolution infrared spectroscopy of CH2D79Br: ro-vibrational analysis of the ν4 and ν8 fundamental bands

The high-resolution Fourier transform infrared spectrum of CH₂D⁷⁹Br has been recorded and analysed in the region of the ν₄ and ν₈ fundamentals located in the range 1125?1360 cm^?1. The strong ν₄ band, centred at 1225 cm^?1, shows an a/b-hybrid structure with predominant a-type character, whereas ν₈, at 1253 cm^?1, generates a c-type contour comparable in intensity to the b-type component of ν₄. The upper states of these fundamentals are coupled through a- and b-type Coriolis resonances; further complications in this band system arise from perturbations due to the ν₆ = 2 (1183 cm^?1) and ν₅ = ν₆ = 1 (1359 cm^?1) dark states. The former interacts with ν₈ = 1 by b-type Coriolis coupling, whereas the latter perturbs the ν₄ = 1 and ν₈ = 1 levels by anharmonic and a-type Coriolis resonances, respectively. Accurate upper state parameters and interaction terms have been determined for the tetrad system ν₄/ν₈/2ν₆/ν₅+ν₆ by also including in the dataset the assigned transitions of the 2ν₆?ν₆ and ν₅+ν₆?ν₆ hot bands obtained from previous analysis.     

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.     

FTIR spectrum of vinyl fluoride near 3.6 μm: rovibrational analysis of the ν4+ν7 band and modelling Coriolis resonances in a seven-level polyad

ABSTRACT

The Fourier transform infrared (FTIR) spectrum of vinyl fluoride, H₂C=CHF, has been widely investigated in the region of the ν₄+ν₇ combination band around 2800 cm^?1 at a resolution of 0.005 cm^?1. This vibration of A' symmetry gives rise to an a/b-hybrid band with a predominant a-type component. The rovibrational structure is strongly perturbed and the analysis has been rather complicated since this combination band is involved at least in a seven-level interacting polyad, including the ν₈+2ν₁₀, 2ν₈+ν₁₀, 2ν₇+ν₉, ν₇+ν₈+ν₁₂, ν₅+ν₉+ν₁₀ and ν₇+ν₁₀+ν₁₂ vibrational states. The study has been further complicated by the absence of transitions coming from the perturbers that were considered as dark states. The spectral analysis resulted in the identification of 936 transitions with J" ≤ 46 and K_a" ≤ 11, all belonging to the a-type component. Most of the assigned data have been fitted using the Watson's A-reduction Hamiltonian in the I^r representation and proper Coriolis perturbation operators. The model employed includes seven different resonances within a complex polyad resonant system and a set of spectroscopic constants for the ν₄+ν₇ combination band, for the dark states, and Coriolis coupling coefficients have been determined.     

High-resolution measurements of the ν2 and 2ν2-ν2 bands of SO2

Infrared measurements have been made on SO₂ between 450 and 602 cm⁻¹ with a resolution of 0.005 cm⁻¹. The B-type bands due to the bending mode transitions 010-000 and 020-010 have been assigned and analyzed for the ³²S¹⁶O₂ molecule. A total of 3007 transitions were measured and fit for ³²S¹⁶O₂ with a standard deviation of 0.0004 cm⁻¹. Ro-vibrational constants are given that fit the current measurements and the pure rotational transitions reported in the literature.     

FTIR spectra and rovibrational analysis of parallel bands involving the ν1, ν2, and ν3 levels of natural and monoisotopic FClO3

Fourier Transform infrared spectra of gaseous natural FClO₃ and monoisotopic F³⁵ClO₃ have been recorded at 293 and 225 K with a resolution of 0.04 cm⁻¹. Rotational J structure and, in part, K structure were resolved for the parallel fundamentals, combination bands, and overtones ν₁, ν₂, ν₃, ν₁ + ν₂, ν₁ + ν₃, ν₂ + ν₃, 2ν₁, 2ν₂, and 2ν₃. Band origins ν₀, anharmonicity constants χ_ij, and vibration-rotation interaction constants α_i^A and α_i^B have been determined. For F³⁵ClO₃, ν₀ values are ν₁ = 1063.238(6), ν₂ = 716.814(6), and ν₃ = 549.877(3) cm⁻¹. No perturbation was found at the present level of accuracy.     

Line intensities in the ν1 + 2ν2, 2ν2 + ν3, 2ν1, ν1 + ν3, 2ν3, and ν1 + ν2 + ν3 − ν2 bands of H216O,between 6300 and 7900 cm−1

Using Fourier transform spectra, the intensities of 428 weak lines belonging to the ν₁ + 2ν₂, 2ν₂ + ν₃, 2ν₁, ν₁ + ν₃, 2ν₃, and ν₁ + ν₂ + ν₃ − ν₂ bands of the H₂¹⁶O molecule have been measured, between 6300 and 7900 cm⁻¹, with an average uncertainty of 7%.     

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.     

Infrared microwave sideband laser spectroscopy of the ν3 and 2ν3 ← ν3 bands of 13CH3F

A large number of transitions in the ν₃ and 2ν₃ ← ν₃ bands of ¹³CH₃F have been recorded at Doppler-limited resolution by means of an infrared laser microwave sideband spectrometer. The sidebands were generated in a CdTe crystal that was simultaneously irradiated by a CO₂ infrared laser and a high-power microwave source operating in the 8- to 18-GHz region. The J and K structures of the bands were well resolved except for the lowest K values. Frequencies of transitions involving J values up to 47 and K values up to 16 are reported. Vibration-rotation parameters for the v₃ = 0, 1, and 2 states were obtained by fitting to the experimental frequencies. These parameters reproduce the experimental values with an rms deviation of 3.8 MHz for the fundamental band and 2.5 MHz for the hot band.     

Study of the ν3 and 2ν3 ← ν3 bands of 12CH3F by infrared laser sideband and submillimeter-wave spectroscopy

An infrared laser sideband spectrometer operating in the CO₂ laser region with 8- to 18-GHz sidebands has been used to record 266 transitions in the ν₃ band and 84 transitions in the 2ν₃ ← ν₃ band of ¹²CH₃F. The accuracy of the measured frequencies is estimated to be 1–3 MHz. A millimeter/submillimeter-wave spectrometer has been used to record the spectra of 48 pure rotational transitions in the ground vibrational state and 55 transitions in the v₃ = 1 vibrational state with an accuracy of 20–90 kHz. The new measurements have been combined with previous radio frequency and infrared laser results to derive sets of constants for the ground, v₃ = 1, and v₃ = 2 states for this molecule. Tables of the vibrational dependence of the parameters and of the near coincidences of the ν₃ and 2ν₃ ← ν₃ band transitions with CO₂ laser frequencies are given.     

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.     

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.