Theoretical study of the CO₂-O₂ van der Waals complex: potential energy surface and applications

A four-dimensional-potential energy surface (4D-PES) of the atmospherically relevant carbon dioxide-oxygen molecule (CO₂-O₂) van der Waals complex is mapped using the ab initio explicitly correlated coupled cluster method with single, double, and perturbative triple excitations (UCCSD(T)-F12b), and extrapolation to the complete basis set (CBS) limit using the cc-pVTZ-F12/cc-pVQZ-F12 bases and the l^-3 formula. An analytic representation of the 4D-PES was fitted using the method of interpolating moving least squares (IMLS). These calculations predict that the most stable configuration of CO₂-O₂ complex corresponds to a planar slipped-parallel structure with a binding energy of V ∼ -243 cm^-1. Another isomer is found on the PES, corresponding to a non-planar cross-shaped structure, with V ∼ -218 cm^-1. The transition structure connecting the two minima is found at V ∼ -211 cm^-1. We also performed comparisons with some CO₂-X van der Waals complexes. Moreover, we provide a SAPT analysis of this molecular system. Then, we discuss the complexation induced shifts of CO₂ and O₂. Afterwards, this new 4D-PES is employed to compute the second virial coefficient including temperature dependence. A comparison between quantities obtained in our calculations and those from experiments found close agreement attesting to the high quality of the PES and to the importance of considering a full description of the anisotropic potential for the derivation of thermophysical properties of CO₂-O₂ mixtures.