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 Cs 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 Å. The dipole moment of the complex is 1.681(1) D, with components μa=0.815(1) D and μc=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