High-resolution FTIR spectroscopy of HCFC-31 in the 950−1160 cm−1region: rovibrational analysis and resonances in the ν4, ν9and ν5+ν6bands 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 ν4 = 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 CH2 35ClF, 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 Watson's 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. A 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.