Ab Initio Study of the HF(Χ )−H(2S) van der Waals Complex

Abstract

The adiabatic potential energy surface (PES) of the HF(X 1 )−H(2S) van der Waals complex, described by Jacobi coordinates (r = 0.918 Å, R, ϑ), was investigated using the supermolecular unrestricted fourth-order Møller−Plesset perturbation theory. Our calculations indicate two minima for the linear arrangements. The primary minimum was found for the H···HF geometry at R = 3.13 Å with a well depth of De = 98.01 cm-1 and the secondary one for the H···FH orientation at R = 3.21 Å with a well depth of De = 31.36 cm-1. The presented PES reveals that these minima are separated by a barrier of 81.73 cm-1 (with respect to the primary minimum) at R = 3.17 Å and ϑ = 99°. The physical origin of the studied weak interaction was analyzed by the intermolecular perturbation theory on the basis of the single determinant UHF wave function. The separation of the interaction energy shows that the locations of the predicted stable structures are primarily determined by the anisotropy of the repulsive Heitler−London exchange−penetration and attractive dispersion + induction energy components. Dynamical calculations have also been performed to determine the bound states of the studied complex. They show that the ground state is 21.01 cm-1 below the dissociation to HF(X 1 ) + H(2S).