High-resolution FTIR spectroscopy of HCFC-31 in the 950−1160 cm−1 region: rovibrational analysis and resonances in the nu4, nu9 and nu5+nu6 bands of CH235ClF

The FTIR spectrum of CH2ClF (natural isotopic mixt.) was investigated in the ν4, ν9 and ν5+ν6 band region between 950 and 1160 cm-​1 at the resoln. 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-​resoln. 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 anal. resulted in the identification of 1508, 809 and 349 transitions for the ν4, ν9 and ν5+ν6 bands of CH235ClF, resp. 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-​redn. 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 consts. for ν4, ν9 and ν5+ν6 bands as well as parameters for the dark state 3ν6 and seven coupling terms have been detd. The simulations performed in different spectral regions satisfactorily reproduce the exptl. data.