ABSTRACT
The FTIR spectra of CH2[double bond]CHF have been investigated in the nu(8), nu(10), and nu(11) region between 750 and 1050 cm(-1) at a resolution of about 0.002 cm(-1). The nu(8) vibration of symmetry species A' gives rise to an a/b-type hybrid band, while the nu(10) and nu(11) modes of A' ' symmetry produce c-type absorptions. Due to the proximity of their band origins, the three vibrations perturb each other by Coriolis and high-order anharmonic resonances. In particular, the interactions between the nu(8) and nu(10) modes are very strong and widespread with band origins separated by only 1.37 cm(-1). Besides the expected c-type characteristics, the nu(10) band shows a very intense pseudo a-type component caused by the strong first-order Coriolis resonances with the nu(8) state. Furthermore, the 2nu(9) "dark state" was found to be involved in the interacting band systems. The spectral analysis resulted in the identification of 3144, 3235, and 3577 transitions of the nu(8), nu(10), and nu(11) vibrations, respectively. Almost all the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the Ir representation and the perturbation operators. The model employed includes nine types of resonances within the tetrad nu(8)/nu(10)/nu(11)/2nu(9) and a set of spectroscopic constants for the nu(8), nu(10), and nu(11) fundamentals as well as parameters for the "dark state" 2nu(9), and fourteen coupling terms have been determined.
ABSTRACT
The vapor-phase infrared spectrum of monofluoroacetonitrile (CH(2)FCN) has been recorded at high resolution in the nu(4) band region (1363-1398 cm(-1)) using a tunable diode laser spectrometer. A detailed assignment of the rotational structure of the expected a-/b-hybrid band has been made for a-type transitions with K(a)=19, J=61. The b-type transitions were too weak to be observed. Upper state spectroscopic constants including the sextic terms have been obtained from a set of unperturbed data employing the Watson A-reduced Hamiltonian in the I(r) representation. A number of perturbed transitions have been accounted for, including b- and c-type Coriolis resonances and anharmonic resonances between nu(4) and the nearby levels nu(5)+nu(12) and nu(11)+nu(12). The vibrational energies of these perturbing levels have been obtained from the reanalysis of the low-resolution infrared spectrum. Rotational constants and the band origin of the perturbers along with the interaction parameters with the v(4)=1 state have also been determined. Copyright 2001 Academic Press.