The van der Waals potential-energy surfaces and the structures of ArClF and ArCl2

The potential-energy surfaces of the ArClF and ArCl2 complexes are determined by the Hartree-Fock (HF) and Mo/ller–Plesset calculations (up to MP4) in an efficient basis set of 6-31+G(2df ) for the intermolecular energy. The interaction energies are calculated by the supermolecular approach with the full counterpoise corrections for the basis-set superposition error. Three local potential minima are found for ArClF corresponding to the linear Ar–Cl–F and Ar–F–Cl and the asymmetric T-shaped structures. For these the well depths and the distances are D(Ar–Cl–F)=233.5 (MP2) or 219.7 cm−1 (MP4), RArCl=3.38 Å; D(Ar–F–Cl)=119.2 (MP2) or 127.2 cm−1 (MP4), RArF=3.3 Å; and D(T-shaped)=130.4 (MP2) or 132.6 cm−1 (MP4), RArCl=3.83 Å. The results are in accord with the linear ArClF structure as the most-stable structure determined by experiment with the estimate of De=228 cm−1 at RArCl=3.33 Å. For the ArCl2 complex, minima are found corresponding to the linear and the T-shaped structures. At the MP2 level the well depths and distances are D(linear)=220.1 cm−1, RArCl=3.5 Å; D(T-shaped)=183.6 cm−1, RArCl=3.9 Å. Only a small change results at the MP4 level D(linear)=195.3 cm−1, D(T-shaped)=165.2 cm−1. The results for the T-shaped ArCl2 are in good agreement with the experimental results of De=185±1 cm−1 and RArCl=3.8±0.1 Å. Estimates for the effects of differences in zero-point energy show the two structures may be of similar stablity.