THE MICROWAVE-SPECTRUM, STRUCTURE, AND DIPOLE-MOMENT OF THE BUTADIENESULFUR-DIOXIDE COMPLEX

The microwave spectrum of the butadiene.SO2 complex has been observed with a Fourier transform microwave spectrometer. The rotational consta nts were determined as A = 2793.8856(3) MHz, B = 1325.4117(2) MHz, and C = 1123.0275(2) MHz. In addition to the normal species, the spectra of eight other isotopic species were assigned. The structure was deter mined from the moments of inertia of all the isotopic species in a lea st-squares fitting procedure. The centers of mass of the two monomers are separated by 3.32(5) angstrom with SO2 sitting above the center of the butadiene plane. The two molecular planes are close to parallel w ith the C2 axis of SO2 rotated 44(5)degrees relative to the C-C single bond of butadiene. The dipole moment was determined to be mu(total) = 1.475(15) D. Electrostatic and ab initio calculations have also been carried out to better understand the structure and binding of this com plex.