THE VANDERWAALS 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 Moller-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), R(ArCl) = 3.38 angstrom; D(Ar-F-Cl) = 119.2 (MP2) or 127.2 cm - 1 (MP4), R(ArF) = 3.3 angstrom; and D(T-shaped) = 130.4 (MP2) or 132.6 cm - 1 (MP4), R(ArCl) = 3.83 angstrom. The results are in accord with the linear ArClF structure as the most-stable structure determined by experiment with the estimate of D(e) = 228 cm - 1 at R(ArCl) = 3.33 angstrom. 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, R(ArCl) = 3.5 angstrom; D(T-shaped) = 183.6 cm - 1, R(ArCl) = 3.9 angstrom. 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 D(e) = 185 +/- 1 cm - 1 and R(arCl) = 3.8 +/- 0.1 angstrom. Estimates for the effects of differences in zero-point energy show the two structures may be of similar stablity.