THE MICROWAVE SPECTRUM AND STRUCTURE OF THE METHANOL-$SO_{2}$ COMPLEX

Author Institution: The University of Michigan, Ann Arbor, MI 48109-1055, U.S.A.; Sookmyung Women's University, Seoul 140-742, Korea.The rotational spectra of nine isotopomers of the methanol-sulfur dioxide complex were observed with a pulsed molecular beam Fourier transform microwave spectrometer. Each rotational transition was split into an A state (m=0) and an E state $(m=\pm1)$ component due to methyl top internal rotation effects. The A and E transitions showed an additional splitting ranging from a few MHz to a few tens of MHz in seven of the isotopomers. This so-called inversion splitting was absent in the two $S^{16}O^{18}O$ isotopomers. The center frequencies of the inversion doublets were used in a simultaneous fit of both A and E state transitions. Analysis of the moments of inertia indicated that the complex had a stacked structure. The centers of mass distance between the two monomers was $3.081 {\AA}$. The effective torsional barrier height was determined as $V_{3} = 128.6 cm^{-1}$ on the assumption that the methyl group rotates against a heavy frame. The dipole moment was determined as $\mu_{T} = 1.94 (3) D$