The microwave spectrum and structure of the carbon dioxide-sulphur dioxide complex

Abstract

The rotational spectra of nine isotopomers of the carbon dioxide–sulphur 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 C¹⁸O¹⁶O or S¹⁸O¹⁶O isotopomers. No inversion splittings were observed in any of the isotopic species. The observed frequencies for each isotopomer were fit to obtain rotational and centrifugal distortion constants. Consideration of the moments of inertia, selection rules and missing levels indicate that the complex has a cross structure with C_2v symmetry. The C₂ axis of SO₂ is perpendicular to the C_∞ axis of CO₂. The negative end of the SO₂ dipole moment points to the carbon atom. The centre of mass distance between the two monomers is 3⋅29(5) Å. The dipole moment is 1⋅771(2) D. Distributed multipole electrostatic calculations support the cross structure.