Knowledge Bank

Diode laser spectra of $CF3X$ where $X=Cl,Br$ and I, with natural isotopic abundance, have been measured in the $9-9.5\mu m$ region using the SP 5000 Tunable Laser Source Spectrometer (from Spectra Physics) set up in appropriate configuration at the University of Venice. The frequency range considered mainly comprises the v1 fundamental (CF3 symmetric stretching and the $2\nu 5$ overtone; of the latter, only the parallel component $(2\nu 50)$ has been observed. The measurements were carried out at low temperature $(\ast 200K)$ in order to simplify the complex structure due to ``hot'' band congestion. The rotational fine structure within the P(J) and R(J) manifolds as well as in the Q-branch of the bands mentioned above has been resolved and a least-squares fit of the observed transitions to the energy expression including the quartic centrifugal distortion coefficients was performed. Some lines were found to be rotationally perturbed by 2v5 and*** and the different mechanisms involving $\Delta R=\Delta k=\pm 2$, and $\Delta R=\pm 2,\Delta k=\pm 1$ interactions have been considered in the interpretation. Accurate molecular parameters of $\nu 1$ and $2\nu 5o$ bands of the two different isotopic species of $CF3Cl$ and $CF3Br$ have been determined. Work on the spectrum of $CF3I$ is also in progress; however its fine structure appears so strongly perturbed that the rotational assignments are not quite easy in the scheme of isolated vibro-rotational systems. Interpretation, details of the spectra, and results obtained will be discussed.