The potential energy curves have been examined for the ground (X (2)Pi) and excited states (1 (2)Delta, 1 (2)Sigma (+), 2 (2)Sigma (+), and 1 Sigma (-)) of CCl using complete active space SCF (CASSCF) and multiconfiguration reference internally contracted configuration interaction (MRCI) with the aug-cc-pVTZ basis set. The active spaces are comprised of all valence molecular orbitals and include some nonvalence virtual molecular orbitals, which are used to further confirm the nature of the excited states. The anharmonic vibrational energy levels are also obtained for the ground and excited states based on the potential energy curves calculated with different active spaces. A comparison with experimental results is made and discussed. (C) 2001 American Institute of Physics.