Structure and energetics of weakly bound water-sulfur dioxide complexes

Optimal structures, interaction energies and harmonic vibrational frequencies of the H2O⋯SO2 dimers, 1:2 and 2:1 trimers have been determined from the MP2 calculations with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. Some properties of the complexes have been calculated at the CCSD(T) levels. The nature of the intermolecular interactions in the dimers have been investigated by symmetry-adapted perturbation theory (SAPT). We have located two stable configurations as well as two transition states on the potential energy surface for the dimer. Six low-energy configurations on the potential energy surface for 1:2 and 2:1 trimers have been found. The contribution of the three-body term represents as much as 19% for the (H2O)2⋯SO2. The calculated frequency shifts are presented for trimers to facilitate the frequency assignments of the experimental spectra.