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MICROWAVE SPECTRUM AND STRUCTURE OF HBr-SO₃ AND THE QUADRUPOLE COUPLING CONSTANT OF Ar-³³SO₃.

DENISE FIACCO, M. E. OTT, B. HARMS, W. A. BURNS, M. CANAGARATNA AND K. R. LEOPOLD, Department of Chemistry, University of Minnesota, 207 Pleasant St., SE, Minneapolis, MN 55455.

We report the microwave spectrum and structure of HBr-SO₃ as determined by pulsed nozzle Fourier transform microwave spectroscopy. Like its previously studied HF and HCl analogs, the complex exhibits a symmetric top spectrum and has a structure in which the halogen approaches the sulfur along the C₃ axis of the SO₃. The S--Br distance is 3.24 A and the HBr subunit forms an angle of approximately 73 deg. (or 107 deg.) with the a-axis of the complex. The structures of the three HX-SO₃ complexes are compared. We also report a measurement of the ³³S nuclear quadrupole coupling constant in Ar-³³SO₃. The value obtained (-15.296(14) MHz) is compared with a recent theoretical calculation of the monomer value and discussed in terms of the angular oscillations of the SO₃ unit.