New Method of Studying Internal Rotation in a Symmetric Rotor

A technique has been developed for the first time to study the internal rotation splittings in the ground torsional state of a symmetric rotor. Normally forbidden transitions obeying the selection rules $\Delta K=\pm 1, \pm 2, \pm 3$ and $\Delta \sigma =0, \pm 1$ have been observed in an avoided-crossing experiment using molecular-beam electric-resonance spectroscopy. For C${\mathrm{H}}_3$C${\mathrm{F}}_3$, it has been found that the barrier height $V_3=3.16\mathrm{}\left(11\right)\mathrm{}$ kcal/mol and the moment of inertia $I_{\alpha }$ of the methyl top is 3.17(11) amu ${\mathrm{\AA }}^2$.