Ab initio study of van der Waals interaction of formamide with a nonpolar partner. Ar⋅⋅⋅H2NCOH complex

Abstract

The potential energy surface (PES) of the ground state of the Ar–formamide van der Waals complex is calculated by using the supermolecular Moller–Plesset perturbation theory and the related perturbation formalism of intermolecular interactions. Six stationary points (five minima) are identified on the PES. The structure with the Ar atom coplanar with formamide and located between O and H atoms of the COH fragment is found to correspond to the global minimum. The best estimates of Re and De are 3.75 Å, and 217 cm−1, respectively. The structure with Ar located above the C atom proved to be another important minimum, only slightly shallower than the global one. The best estimates of related Re, and De are 3.625 Å, and 210 cm−1, respectively. Behavior of the different fragments of the formamide molecule in van der Waals interactions is discussed in the context of different components of the interaction energy, in particular the exchange repulsion term. The relationship between the lowest energy structures of the Ar–formamide complex and the local depletions of the formamide charge density is elucidated.