The ground-state potential energy surfaces of Rg-N-2 and Rg-C-2 (where Rg=He, Ne, or Ar) have been investigated at the coupled cluster singles, doubles, noniterative triples [CCSD(T)] level of theory using aug-cc-pVDZ and aug-cc-pVTZ basis sets. A basis set extrapolation procedure was employed to estimate the complete basis set limit, and the extrapolated potential energy surface was then utilized to calculate the bound intermolecular states and microwave transition frequencies of each complex. The Rg-N-2 complexes were chosen to demonstrate the reliability of the extrapolation scheme, since there are abundant theoretical and experimental data already available for these complexes. The calculated binding energies and equilibrium structures of the Rg-N-2 complexes compare favorably with previous semiempirical and ab initio calculations. The calculated microwave transition frequencies for Ar-N-2 are in excellent agreement with experimental values (deviation <0.1% rms) whereas the equivalent Ne-N-2 transitions show a greater deviation (1.3% rms). There are currently no experimental data with which to compare the binding energies and rovibrational energy levels of the Rg-C-2 complexes. However, the rovibrational energy level predictions should serve as a useful guide to any future spectroscopic studies of Rg-C-2 complexes. (C) 2003 American Institute of Physics.