Structures of the van der Waals Isomers of Halosulfuric Acids: Microwave Spectra of HX–SO3(X= F, Cl, Br)

Abstract

The complexes of SO3with HF, HCl, and HBr have been studied by microwave spectroscopy. In all three systems, the halogen atom approaches the SO3on or near its C3axis, and the vibrationally averaged structure is that of a symmetric top. The S–X bond lengths are 2.655(10), 3.1328(57), and 3.2339(85) Å for the HF, HCl, and HBr complexes, respectively, and in all three systems the out-of-plane distortion of the SO3is negligible. In HF–SO3, the hydrogen points away from the SO3and hyperfine structure in the DF complex gives an average angle of 47.7° with respect to the vibrationally averaged C3axis of the complex. In the HCl and HBr complexes, however, the HX unit is nearly parallel to the SO3plane. In HCl–SO3, the HCl forms a 72.8° angle with the average C3axis of the complex, with the proton tilting slightly toward the SO3. In HBr–SO3, the average orientation of the HBr is 73.0° off the symmetry axis of the complex, but the direction of the tilt (toward or away from the SO3) is not determined. Although the hydrogen halides react with SO3in bulk to produce halosulfuric acids, these gas-phase complexes are much like weakly bound dimers.