The rovibrational energy level structure of (X) over tilde (3)Sigma(-) CNN has been investigated theoretically in order to assist the possible detection of CNN in interstellar space. The potential energy surface was calculated with the CCSD(T) ab initio method, using the aug-cc-pVTZ basis set. Potential energy parameter values were obtained in least-squares fittings to the ab initio data and used to calculate rotation-vibration energies with the MORBID program. For the ground and fundamental vibrational states, the spectroscopic constants have been calculated. The results obtained are found to be in a good agreement with existing experimental data and previous ab initio studies. (C) 2004 Elsevier B.V. All rights reserved.