Ab initio study of the F-2(X-1 Sigma(+)(g))-H(S-2) van der Waals complex

The F-2(X(1)Sigma(g)(-))-H(S-2) van der Waals complex, described by Jacobi coordinates (r, R, Theta), was investigated using the supermolecular unrest ricted Moller-Plesset perturbation theory approach and analyzed using the s econd-order intermolecular perturbation theory based on the single determin ant UHF and RHF wave function. The UMP4 calculations predict two minima. On e minimum was found for the linear configuration (R = 3.62 Angstrom, D-e = 48.6 cm(-1)) and the other one for the T-shaped geometry (R = 3.31 Angstrom , D-e = 33.3 cm(-1)). The presented potential energy surface reveals that t hese two minima are separated by a barrier of 21.0 cm(-1) at R = 3.71 Angst rom and Theta = 52 degrees. The energy partitioning using the intermolecula r perturbation theory scheme shows that the stability and the structure of the studied system is primarily determined by the anisotropy of the exchang e penetration and dispersion components, which is typical for the extremely weak bounded van der Waals complexes. (C) 2000 Elsevier Science B.V. All r ights reserved.