The rovibrational spectrum of the ArCO van der Waals complex was calcd. using a recently published ab initio potential energy surface detd. by the coupled pair functional approach. Comparison with known exptl. 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 Ne2, NeAr, and Ar2 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 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 O end of CO and of 26 cm-1 for rotation around the C end. The rovibrational spectrum calcd. from this potential is in agreement with the known exptl. data, so that a realistic level scheme for the ArCO complex can be presented. Couplings between rotational levels of different van der Waals modes play a role and are analyzed. The intensities of IR transitions were calcd. to help in the exptl. detn. of the predicted new van der Waals modes.