High resolution IR spectrum of the nu8 band of CH2DF: analysis of the interactions with the near vibrational levels

The IR spectrum of the ν8 band of monodeutero methyl fluoride has been recorded with a resolution of 0.004 cm−1 using a Fourier transform spectrometer. The ν8 vibration, of A′′ symmetry species, gives rise to a pure c-type envelope centred at 1298.58 cm−1, resembling a perpendicular band of a prolate symmetric rotor. From the spectral analysis it has been found that ν8 is coupled with ν4 for the low Ka sublevels while for the higher ones other vibrational states, directly or indirectly, are also interacting. For satisfactory reproduction of the rovibrational data of ν8, the Watson's Hamiltonian in the Ir representation has been implemented with interaction parameters, which included first- and second-order a-, b-type and c-type Coriolis couplings with ν4 and ν9, respectively. Being these states also interacting with other levels, the effective spectroscopic parameters of the analysed band up to fourth order have been obtained from a data set formed by the six fundamentals located below 1500 cm−1