VIBRATION-ROTATIONAL INTERACTIONS IN THE STATES $\nu_{2} = 1$ and $\nu_{5}=1$ OF $^{13}CH_{3}F$.

Abstract

The submillimeterwave spectra were measured of the rotational transitions in the $\nu_{2}=1$ and $\nu_{5}=1$ states of $^{13}CH_{3}F$. Almost 3000 lines were assigned in the high resolution infrared spectra of the $\nu_{2}$ and $\nu_{5}$ bands including 142 lines of the $Ak = \pm 2$ forbidden transitions. A variational approach was applied to the analysis of the $\nu_{2}$ and $\nu_{5}$ bands which are strongly perturbed by the $x-y$ Coriolis and $``2. 1''$ I-type interactions ($E_{2} = 1453.658 cm^{-1}$ and $E_{5} = 1465.576 cm^{-1}$). Combination differences were generated from these wavenumbers to determine very precise ground state parameters of $^{13}CH_{3}F$. The results of a computer search for the coincidences between the energy levels of the ortho-and para-states of $12CH_{3}F$ and $^{13}CH_{3}F$ were used in a new theoretical interpretation of the ortho-para conversion rates in both molecules.