A quantum chemical study of the F- and H-bonded isomers of HF/ClF

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The F- and H-bonded isomers of HF/ClF are studied using an extended group function model. Two different basis sets are adopted: basis A comprises a [9s,6p,2d/7s,4p,2d/4s,2p] contracted gaussian-type basis, and basis B a [9s,6p,4d,2f/7s,4p,4d,2f/6s,4p,2d] contracted gaussian-type set. By freezing the monomer bond lengths at the optimized values for the isolated monomers and assuming a planar geometry for the complexes, the geometry is optimized with respect to an intersystem distance and two angular variables defining the geometries of the isomers. For both basis sets the F-bonded isomer is found to have the largest binding energy. For the F- and H-bonded isomers the calculated binding energies are respectively 9.12 (basis A) and 10.11 kJmol −1 (basis B), and 8.63 (basis A) and 8.96kJmol −1 (basis B). The changes in the one-electron density during formation of the complexes are analyzed in terms of charge centroids and charge ellipsoids of the geminal densities. The intermolecular potential is decomposed into a sum of distortion energies for the subsystems and the interaction energy between the distorted subsystems. The partitioning scheme suggests a very simple physical explanation concerning the prediction of the shapes of van der Waals complexes by pure electrostatic interactions.