Knowledge Bank

The hyperfine structure of the $J=1\leftarrow 0$ transition of $CCl3F$ has been completely resolved for both $K=0$ and $K=1$ using a pulsed molecular beam Fabry- Perot cavity microwave spectrometer. Using previously available rotational $constants1$ for this molecule it is shown that the hyperfine splitting is qualitatively, but not quantitatively predicted using the classic method of Wolf, $etal.2$ and the effective hyperfine constants, $eqQ\ast \ast \ast =29.047$ MHz and $eqQxx-eqQyy=-110.95MHz$. To adequately describe the nuclear quadrupole coupling interaction in this heavy, oblate symmetrical top molecule it is necessary to consider in addition to those matrix elements off-diagonal in the quantum number J those off diagonal in K. Such matrix elements include not only additional ones arising from the $eqQzz-rqQyy$ term in the hyperfine Hamiltonian, but also those which find their origin in the usually ignored eqQxy term. The ability to measure this additional term will place more stringent limits on the assumption of cylindrical symmetry about the C-Cl bond.