Theoretical study of some small van der Waals complexes containing inert gas atoms
The van der Waals complexes benzene-argon, benzene-argon 2 , perylene-argon and neon-hydrogen fluoride are investigated theoretically. The principal objective is to discover how the potential energy surfaces of such systems evolve in terms of the minima and transition states present when different approximations to the atom-molecule potential function are employed. This enables us to compare the effects of the electrostatic and dispersion-repulsion contributions to the energy, employing Stone's distributed multipole and distributed polarizability representations for the former contribution. New theories are described and applied to find minima, transition states and van der Waals vibrational frequencies, and these are compared with previous theoretical and experimental results. The calculations demonstrate that accurate characterization of model potential surfaces including distributed multipole terms is feasible. We find that the simplest Buckingham-Fowler approximations can still give useful geometrical predictions in regions of the surface that are not dominated by dispersion effects. For benzene-argon the first order approximation to the dipole moment agrees well with experiment, and we find that charge iteration is undesirable. The calculated stationary points, energies and van der Waals frequencies from model calculations including dispersion-repulsion effects are generally in reasonable agreement with experimental data and previous theoretical analyses. The calculated barrier heights for migration of argon atoms between different sides of aromatic rings are in agreement with rates found in previous simulations.
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Document Type: Research Article
Affiliations: University Chemical Laboratories, Lensfield Road, Cambridge, CB2 1EW, UK
Publication date: 01 September 1991