Knowledge Bank

The ground internal rotation state $(m = 0) $ microwave spectrum of benzene$\bullet SO2$ has been reported previously [1]. It was shown that the spectrum is characteristic of an asymmetric top and displays a- and c-type transitions. It was also pointed out that numerous additional transitions occurred in the microwave spectrum of this complex. Using the Principal Axis Method (PAM) internal rotation Hamiltonian, the $m=0$ state transitions and the ``additional” transitions have been assigned. The existence of a rich spectrum for benzene $\bullet SO2$ is due to the internal rotation of benzene about its $C6$ axis with a 6-fold potential barrier. The barrier height, $V6$, is $0.3cm-1$. Transitions arising from internal rotation states as high as m = $\pm 5$ were seen with our FTMW spectrometer. The internal rotation microwave spectrum of benzene-$d6\bullet SO2$ was also assigned. Further information on the magnitude of the tilt angle of the benzene plane and the tilt angle of the $C2$ axis of $SO2$ with respect to the line joining their centers of mass was obtained.