Ab initio investigation of internal rotation in the ethylene–sulfur dioxide dimer

Abstract

The phenomenon of tunneling motion in the C₂H₄...SO₂ dimer has been studied in the ab initio Hartree–Fock (HF) and Mo/ller–Plesset second‐order perturbation theory (MP2) levels, employing the DZP basis set. Basis set superposition errors (BSSE) were accounted for using the counterpoise correction method. A simple model for treating the problem in one dimension was utilized, where coupling of intramolecular vibration and dimer internal rotation have been neglected. A comparative study between two potentials was carried out. The first potential is based on pointwise ab initio calculations of the intermolecular potential energy surface (PES) including BSSE correction, and the second is based on the expression V_N=V₀ [1−cos(Nα)]/2, where V₀ was obtained from the ab initio fully optimized equilibrium and transition state structures. The resultant Hamiltonian was solved using the variational method, and the calculated splitting of transition frequencies compared with experimental data.