Knowledge Bank

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 $(m=\pm 1)$ 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 $S16O18O$ 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 $3.081\backslash AA$. The effective torsional barrier height was determined as $V3=128.6cm-1$ on the assumption that the methyl group rotates against a heavy frame. The dipole moment was determined as $\mu T=1.94(3)D$.