Ab Initio Study on the (OCS)2·CO2van der Waals Trimers

Abstract

Ab initio calculations [MP2, MP4SDTQ, and QCISD(T)] using different basis sets [6-31G(d,p), cc-pVXZ (X = D, T, Q), and aug-cc-pVDZ] were carried out to study the (OCS)2·CO2 van der Waals trimers. Three barrel-like structures [C1 (two) and C2 symmetry] and three planar (Cs) structures were located on the potential energy surface. Their CBS-MP2/cc-pVXZ (X = D, T, Q) stabilization energies are 1760 (C1), 1514 (C2), 1660 (C1), 1325 (Cs), 1556 (Cs), and 1398 (Cs) cm-1, respectively. The most stable structure (one of the C1 barrel-like isomers) has bond lengths, angles, rotational constants, and dipole moment that agree quite well with the corresponding experimental values of the only structure observed in recent microwave spectroscopic studies. The energetic proximity of the rest of the isomers strongly suggests that the experimentally unobserved structures might also be present in the supersonic adiabatic expansion of the gas in the microwave spectroscopic studies as in the case of the (CO2)3 trimer where bot...