Knowledge Bank

The gas phase infrared spectrum of natural $CF2Cl2$ has been recorded in the range $1094-1109cm-1$ at a resolution of about $0,002cm-1$ using a tunable diode laser spectrometer. Besides the strong $v1$ fundamental $(\sim 1101cm-1)$ and related hot-hands, at least two other bands, i.e. $\nu 2+\nu 7$ and $\nu 2+\nu 9$, are expected to absorb in this region. The low temperature spectrum $(\sim 200K)$, providing a significant depletion of the hot-band contributions, still shows the rotational structure extremely crowded and difficult to assign due to the presence of different overlapping chlorine isotopic lines. At present, only the structure of the $\nu 1$ band of $CF235Cl2$ (8-type) has been interpreted: about 600 transitions of the allowed subbranches and covering J' values up to 46 and $Ka\prime$ values up to 8 have been identified. From single subband analyses there is evidence that many rotational levels are influenced by perturbation. Although the main interaction may be due to a first order a-Coriolis resonance with $\nu 8(\zeta 1,8a=0.77$) lying about $60cm-1$ above $\nu 1$, second order a-Coriolis perturbation with $\nu 8$ as well as first order c-Coriolis resonance with $\nu 2+\nu 7$ are reasonably to be expected. The assigned transitions were fitted to a set of effective upper state parameters in terms of fixed ground state constants, using the Watson's A-reduced Hamiltonian in the $Ir$ representation. It is worthy noting that the symmetry $(C8)$ of $CF235Cl37Cl$ species predicts for the corresponding $\nu 1$ vibration a hybrid band consisting of both a-type and b-type transitions; the situation is so complex that a serious attempt at analyzing the involved structure was unsuccessful. Spectra, details of the interpretation and results obtained from the analysis will be discussed.