Knowledge Bank

The submillimeterwave spectra were measured of the rotational transitions in the $\nu 2=1$ and $\nu 5=1$ states of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH3F$. 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 ($E2=1453.658cm-1$ and $E5=1465.576cm-1$). Combination differences were generated from these wavenumbers to determine very precise ground state parameters of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH3F$. The results of a computer search for the coincidences between the energy levels of the ortho-and para-states of $12CH3F$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH3F$ were used in a new theoretical interpretation of the ortho-para conversion rates in both molecules.