In the present contribution, we performed ab initio calculations at the CCSD(T) level of theory in the framework of the supermolecule approach on the weakly bound CO-Ar van der Waals (vdW) complex in its "near T-shaped" most-stable ground state structure. The corresponding vertical excitation energies from the ground CO(X1Σ)-Ar(1S) to the excited CO(A1Π)-Ar(1S) and CO(A3Π)-Ar(1S) states are calculated as a guideline for future theoretical and experimental work. © 2006 Elsevier B.V. All rights reserved.