17O and 33S NMR studies of sulfur dioxide and sulfur trioxide

17O and 33S NMR chemical shifts of sulfur dioxide (SO2) were measured for the range of density (0.05–0.3 mol l21) in the gas phase at 300 and 333 K. The chemical shifts for both nuclei are linearly dependent on density showing an increase of 17O magnetic shielding and a decrease of 33S shielding due to intermolecular interactions. The present measurements have permitted the quantitative separation of the shielding contributions due to intermolecular interactions ðs1Þ and the shielding parameters of isolated molecules ðs0Þ: Analogous 17O NMR measurements were also carried out for gaseous sulfur trioxide (SO3) at 333 K. A decrease of oxygen shielding was observed here for larger densities, but the latter compound could be examined only in the very small range of density (,0.02–0.08 mol l21) and the shielding parameters were determined with lower accuracy. It was confirmed by the 17O and 33S NMR spectra of liquid SO2 and SO3 that intermolecular interactions in gases and liquids change the shielding constants in the same directions. q 2004 Elsevier B.V. All rights reserved.