A. Pietropolli Charmet

Jet-cooled diode laser spectrum and FTIR integrated band intensities of CF3Br: rovibrational analysis of 2ν5 and ν2 + ν3 bands near 9 μm and cross-section measurements in the 450–2500 cm−1 region

The high resolution (up to 0.0007 cm−1) infrared diode laser spectrum of CF3Br (Halon 1301) with natural isotopic abundance has been investigated in the region 1090–1130 cm−1, characterized by the presence of the 2ν5 and ν2 + ν3 absorptions and several weaker hot bands. The rovibrational analysis of the data, obtained employing a slit-jet system (rotational temperature of about 50 K) together with those recorded at 200 K, led to a complete and accurate set of spectroscopic constants for the bands of both the bromine isotopologues. Integrated band intensities have been obtained for all the absorptions in the spectral range 450–2500 cm−1. The high resolution data and information concerning the cross-sections of this molecule can be useful for its remote sensing and for better modelling its contribution to global warming.

Tunable diode laser spectra and analysis of the ν3 fundamental of CH279BrF

Abstract The infrared absorption spectra of CH 2 79 BrF ν 3 band have been recorded using a TDL spectrometer in the region 1270–1355 cm −1 , at a resolution of about 0.003 cm −1 . A detailed analysis of the a / b -hybrid band, centered at 1314.2559 cm −1 , with predominant a -type character, has been performed leading to the assignment of about 8500 transitions with K a ⩽20 and J ⩽95. Excited state perturbation effects, caused by first order c -type Coriolis interaction with the nearby v 5 =2 state, have been locally observed in different subbands. The analysis of the data was performed using Watson’s A -reduced Hamiltonian in the I r representation and Coriolis operators. Parameters up to sextic coefficients for the v 3 =1 state and the band origin as well as the rotational constants for the v 5 =2 dark state have been determined along with the coupling terms.

High resolution FTIR spectroscopy of chlorofluoromethane near 13 µm: rovibrational analysis and resonances of ν5 and 2ν 6 bands in ClF and ClF

The FTIR spectra of CH2ClF (natural isotopic mixture) and ClF (isotopically enriched sample) were investigated in the ν5 and 2ν6 region between 700 and 800 cm−1 at a resolution of 0.004 cm−1. The ν5 and 2ν6 vibrations of A′ symmetry give rise to a/b hybrid bands with a very predominant a-type component. Due to the proximity of their band origins, the v 5 = 1 and v 6 = 2 levels perturb each other by Fermi and Coriolis resonances. The interaction mechanisms, previously investigated in the rotational spectra of ClF, were extended to the less abundant isotopic species ClF and to higher J and Ka values in the main isotopologue. The spectral analysis resulted in the identification of 4188 and 5392 transitions for ClF and ClF, respectively. All the assigned data were simultaneously fitted using the Watsons A-reduction Hamiltonian in the I r representation and perturbation operators. Excited state parameters, band origins and coupling terms for the ν5/2ν6 dyad of both isotopologues were determined.

Infrared laser spectroscopy and rovibrational analysis of the ν5 fundamental of cis-1-chloro-2-fluoroethylene

The infrared spectrum of cis-1-chloro-2-fluoroethylene (cis-CHClCHF) has been investigated in the ν5 band region between 1220 and 1250 cm−1, at a resolution of about 0.002 cm−1, using a tunable diode laser spectrometer. This fundamental of symmetry species A′ yields a strong a/b-hybrid band with contributions of comparable intensity from both the components. The rovibrational analysis led to the identification of 3800 lines (J⩽69, Ka⩽25) for the ν5 band of 35Cl species, whose origin is at 1231.849 cm−1. Using Watsons A-reduction Hamiltonian in the Ir representation, a set of spectroscopic parameters up to sextic centrifugal distortion terms was obtained for the v5=1 state, which turned out to be free from perturbations.

High resolution FTIR study of the v5 and v6 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 ΔKa = ± 2 anharmonic resonance.

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 Watsons A-reduction Hamiltonian in the Ir 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.

High-resolution FTIR spectroscopy of HCFC-31 in the 950−1160 cm−1 region: rovibrational analysis and resonances in the ν4, ν9 and ν5+ν6 bands of CH235ClF

The FTIR spectrum of CH2ClF (natural isotopic mixture) was investigated in the ν4, ν9 and ν5+ν6 band region between 950 and 1160 cm−1 at the resolution of 0.004 cm−1. The ν4 and ν5+ν6 vibrations of A′ symmetry give rise to a/b hybrid bands with a predominant a-type component. The ν9 vibration of A″ symmetry, expected with a c-type band contour, shows an intense Coriolis-induced parallel component (ΔKa = 0, ΔKc = 0) derived from mixing with the v4 = 1 vibrational state. The high-resolution spectra of ν9 and ν5+ν6 have been analyzed for the first time, while the assignments of the ν4 band, previously investigated, have been extended to higher J and Ka values in the b-type component. The spectral analysis resulted in the identification of 1508, 809 and 349 transitions for the ν4, ν9 and ν5+ν6 bands of CH235ClF, respectively. Besides the strong first-order a- and b-type Coriolis resonances between ν4 and ν9, the ν5+ν6 vibration was found to interact through a c-type Coriolis with the ν4 and 3ν6. High-order anharmonic resonance (ΔKa = ±2) between ν4 and ν5+ν6 was also established. All the assigned data were simultaneously fitted using the Watsons A-reduction Hamiltonian in the Ir representation and the relevant perturbation operators. The model employed includes five types of resonances within the tetrad ν4/ν9/ν5+ν6/3ν6. Α set of spectroscopic constants for ν4, ν9 and ν5+ν6 bands as well as parameters for the dark state 3ν6 and seven coupling terms have been determined. The simulations performed in different spectral regions satisfactorily reproduce the experimental data.

Jet-cooled diode laser spectra of CF3Br in the 9.2 μm region and rovibrational analysis of symmetric CF3 stretching mode

Pulsed slit-jet high resolution (up to 0.0009 cm(-1) FWHM) infrared diode laser spectra of CF(3)Br, with natural isotopic abundance, were obtained in the region around 9.2 microm at the rotational temperature of about 50 K. In addition, diode laser spectra at reduced temperature (200 K) were recorded. We present here the rovibrational analysis of the nu(1) fundamental in the range 1075-1090 cm(-1). The fine structure of many P(J) and R(J) clusters has been well resolved for the first time. The assignment of rovibrational transitions has been accomplished up to K = 27, J = 63 for CFBr and K = 33, J = 62 for CFBr. A total of 636 (CFBr) and 880 (CFBr) lines were used in the final fit and a very accurate set of molecular constants, including the quartic centrifugal distortion coefficients for the v(1) = 1 state of both the bromine isotopologues, was obtained. In addition, spectral features belonging to the nu(1) + nu(6)-nu(6) hot band were unambiguously identified and a set of spectroscopic parameters 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 Cs 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, Ka ⩽ 20) and 718 (J ⩽ 53, Ka ⩽ 8) transitions for the v 6 and 2v 12 bands of the 35Cl isotopic species, respectively. Using the Watsons A-reduction Hamiltonian in the Ir 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.

Rovibrational analysis of the v1 fundamental of CF3Cl from diode laser spectra in a supersonic slit-jet expansion

Spectra of the ν1 fundamental band of CF3Cl (CFC-13), with natural isotopic abundance, were recorded with a tunable diode laser spectrometer in the range 1100–1116 cm−1 using a supersonic pulsed slit-jet expansion. A rotational temperature of about 50 K was reached and a significant simplification of the spectra was achieved. The reduced Doppler broadening obtained using the slit source led to a FWHM up to 0.0007 cm−1 and so it was possible to resolve almost completely the K-structure in the P(J) and R(J) clusters for the first time. From the final fit of the assigned transitions a reliable set of molecular constants including the quartic centrifugal distortion coefficients for the v1 = 1 state of CF335Cl and CF337Cl has been obtained.