MICROWAVE-SPECTRUM, DIPOLE-MOMENT, STRUCTURE, AND INTERNAL-ROTATION OF THE CYCLOPROPANE-SULFUR DIOXIDE VAN DER WAALS COMPLEX

The rotational spectrum of the cyclopropane-sulfur dioxide complex was observed by Fourier transform microwave spectroscopy. The spectrum exhibited a- and c-dipole selection rules with the c-dipole transitions split into doublets of unequal intensity separated by about 150 kHz. The structure has C5 symmetry with the sulfur and carbon atoms all lying in the ac plane; the oxygen and hydrogen atoms straddle the plane. The sulfur dioxide plane is nearly parallel to a C-C bond edge. The distance from the center of mass of the SO2 to the C-C bond center is 3.295 angstrom. The dipole moment of the complex is 1.681(1) D, with components-mu(a) = 0.815(1) D and mu(c) = 1.470(1) D. The splittings in the spectrum arise from an internal rotation of the cyclopropane subunit about its local C2 axis which lies nearly along the line connecting the centers of mass.