Acetylene center dot center dot center dot sulfur dioxide van der Waals complexes: a theoretical study

Ab initio calculations at the MP2 and QCISD levels of theory using Pople's 6-31G(d,p) and Dunning's aug-cc-pVDZ basis sets were carried out to explore the potential energy surfaces corresponding to the C2H2... SO2 complex. A C-s stacked structure was found to be the most stable one in agreement with microwave experiments. The structural information on other dimers and trim ers located may be useful to fit a number of unassigned transitions. The la ck of tunneling splittings in the microwave spectrum is explained in terms of the high barrier computed for the internal rotation of the C2H2 subunit. (C) 2001 Elsevier Science B.V. All rights reserved.