The rovibrational spectrum of the ArCO complex calculated from a semiempirically extrapolated coupled pair functional potential energy surface

The rovibrational spectrum of the ArCO van der Waals complex has been calculated using a recently published ab initio potential energy surface determined by the coupled pair functional approach. Comparison with known experimental values for some of the transitions shows that the anisotropy of this surface comes out reasonably well, although its well depth of 72 cm(-1) is too small. Based on a comparison of coupled pair functional interaction energies for Ne-2, NeAr, and Ar-2 with empirical potential energy curves an extrapolation scheme for the differential correlation energy is suggested. This semiempirical extrapolation scheme, with a slight modification to account for anisotropy, is also applied to the coupled pair functional interaction energies for ArCO, resulting in a surface which is characterized by a well depth of 109 cm(-1) at a T-shaped geometry and a barrier of 20 cm(-1) for rotation of Ar around the oxygen end of CO and of 26 cm(-1) for rotation around the carbon end. The rovibrational spectrum calculated from this potential is in very good agreement with the known experimental data, so that for the first time a realistic level scheme for the ArCO complex can be presented. Couplings between rotational levels of different van der Waals modes play an important role and are analysed in some detail. The intensities of infrared transitions have also been calculated in order to help in the experimental determination of the predicted new van der Waals modes. (C) 1996 American Institute of Physics.