TUNABLE DIODE LASER SPECTROSCOPY OF $CF_{2}Cl_{2}$ IN THE $9 \mu m$ REGION
Loading...
Date
1990
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The gas phase infrared spectrum of natural $CF_{2}Cl_{2}$ has been recorded in the range $1094-1109 cm^{-1}$ at a resolution of about $0,002 cm^{-1}$ using a tunable diode laser spectrometer. Besides the strong $v_{1}$ fundamental $(\sim 1101 cm^{-1})$ 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 $CF_{2}^{35}Cl_{2}$ (8-type) has been interpreted: about 600 transitions of the allowed subbranches $^{e}P(1,-1), ^{o}P(-1,-1), ^{e}R(1,1)$ and $^{o}R(-1,1)$ covering J' values up to 46 and $K'_{a}$ 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 $\nu_{8} (\zeta ^{a}_{1,8} = 0.77$) lying about $60 cm^{-1}$ 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 $I^{r}$ representation. It is worthy noting that the symmetry $(C_{8})$ of $CF_{2}^{35}Cl^{37}Cl$ 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.
Description
Author Institution: Dipartimento di Chimica Fisica, Universita' di Venezia