THE MICROWAVE SPECTRUM OF BENZENE$\bullet SO_{2}$: A NEARLY FREE INTERNAL ROTOR

$^{1A}$. M. Andrews, M. S. LaBarge, A. Taleb-Bendiab, K. W. Hillig II and R. L. Kuczkowski, TF5, 45th Symposium on Molecular Spectroscopy, Ohio State University (1989). See also: Chem. Phys. Lett. 159, 559 (1989).""Author Institution: Department of Chemistry, University of MichiganThe ground internal rotation state $(m = 0) $ microwave spectrum of benzene$\bullet SO_{2}$ 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 $\bullet SO_{2}$ is due to the internal rotation of benzene about its $C_{6}$ axis with a 6-fold potential barrier. The barrier height, $V_{6}$, is $0.3 cm^{-1}$. 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-$d_{6}\bullet SO_{2}$ was also assigned. Further information on the magnitude of the tilt angle of the benzene plane and the tilt angle of the $C_{2}$ axis of $SO_{2}$ with respect to the line joining their centers of mass was obtained