Knowledge Bank

The rotational spectra of nine isotopomers of the carbon dioxide - sulfur dioxide van der Waals complex were observed with a pulsed molecular beam.Fourier transform microwave spectrometer. All odd K energy levels were missing in the symmetric isotopic species, but were present in the singly substituted $C12O16O$ or $S12O16O$ isotopomers. No inversion splittings were observed in any of the isotopic species. The observed frequencies for each isotopomer were fit to obtain rotational and centrufugal distortion constants. Consideration of the moments of inertia, selection rules and missing levels indicate that the complex has a cross structure with $C2$ symmetry. The $C2$ axis of $SO2$ is perpendicular to the $C2$ axis of $CO2$. The negative end of the $SO2$ dipole moment points to the carbon atom. The center of mass distance between the two monomers is 3.29(5)\AA. The dipole moment is 1.771(2) D. Distributed multipole electrostatic calculations support the cross structure.