MICROWAVE-SPECTRUM, STRUCTURE, DIPOLE-MOMENT, AND DEUTERIUM NUCLEAR-QUADRUPOLE COUPLING-CONSTANTS OF THE ACETYLENE SULFUR-DIOXIDE VANDERWAALS COMPLEX

Thirty-three a- and c-dipole transitions of the acetylene-SO2 van der Waals complex have been observed by Fourier transform microwave spectroscopy and fit to rotational constants A = 7176.804(2) MHz, B = 2234.962(1) MHz, C = 1796.160(1) MHz. The complex has C(s) symmetry with the C2H2 and SO2 moieties both straddling an a-c symmetry plane (i.e., only the S atom lies in the plane). The two subunits are separated by a distance R(cm) = 3.430(1) angstrom and the C2 axis of the SO2 is tilted 14.1 (1)-degrees from perpendicular to the R(cm) vector, with the S atom closer to the C2H2. The dipole moment of the complex is 1.683(5) D. The deuterium nuclear quadrupole hyperfine structure was resolved for several for transitions in both C2HD.SO2 and C2D2.SO2. A lower limit for the barrier to internal rotation of the C2H2 was estimated to be 150 cm-1 from the absence of tunneling splittings. The binding energy was estimated by the pseudo-diatomic model as 2.1 kcal/mol. A distributed multipole analysis was investigated to rationalize the structure and binding of the complex.