The N2O·N2O, N2O·SO2, and (N2O)2·SO2van der Waals Complexes: An ab Initio Theoretical Analysis

The potential energy surfaces of the N 2 O·SO 2, N 2 O·N 2 O, and (N 2 O) 2 ·SO 2 van der Waals systems were extensively explored at the MP2 level of theory using Pople's 6-31G(d,p) and Dunning's cc-pVDZ, aug-cc-pVDZ, and cc-pVTZ basis sets. A total of 19 structures (seven for the trimer and six for each dimer) corresponding to stationary points on the potential energy surfaces were located and characterized. A dynamic structure corresponding to the interconversion of a number of configurations, which are of similar geometries and close in energy, is proposed for the N 2 O·SO 2 dimer. It is consistent with the asymmetric structure derived from microwave spectroscopic studies and explains the splitting of the rotational bands experimentally observed. The slipped-parallel configuration theoretically predicted for the N 2 O·N 2 O structure agrees with the geometry derived from infrared spectroscopy. One of the lower energy configurations predicted by ab initio methodologies for the (N 2 O) 2 ·SO 2 trimer structure agrees rather well with that derived from Fourier transform microwave spectroscopy. Symmetry-adapted perturbation theory throws light into the physically meaningful contributions to the interaction energy and helped us to rationalize the trimer geometry in terms of dimer interactions present in the isolated dimers located on the ab initio potential energy surfaces, most of them experimentally undetected.