The six-dimensional potential energy surface of the ground state X(1)Sigma(+) of C3O has been generated by the CCSD(T) approach. The spectroscopic constants of this molecule are calculated and the vibrational spectrum is derived. The fundamentals are accurate to within 10 cm(-1) compared to the available experimental data. The ground state correlates to the closed shell C-2(X(1)Sigma(+)) + CO(X(1)Sigma(+)) dissociation limit. The bonding in this molecule can be explained by charge transfer from CO to C-2. The lowest electronic excited states are also investigated. (C) 2001 Elsevier Science.