Ab initio study of the F2(X 1Σg+)–H(2S) van der Waals complex Original Research Article

The F2(X 1Σg−)–H(2S) van der Waals complex, described by Jacobi coordinates (r, R, Θ), was investigated using the supermolecular unrestricted Møller–Plesset perturbation theory approach and analyzed using the second-order intermolecular perturbation theory based on the single determinant UHF and RHF wave function. The UMP4 calculations predict two minima. One minimum was found for the linear configuration (R=3.62 Å, De=48.6 cm−1) and the other one for the T-shaped geometry (R=3.31 Å, De=33.3 cm−1). The presented potential energy surface reveals that these two minima are separated by a barrier of 21.0 cm−1 at R=3.71 Å and Θ=52∘. The energy partitioning using the intermolecular perturbation theory scheme shows that the stability and the structure of the studied system is primarily determined by the anisotropy of the exchange penetration and dispersion components, which is typical for the extremely weak bounded van der Waals complexes.