DFT calculations were carried out on the carbon and oxygen isotopomers of CO and Ni(CO)(4) and results compared with (Spindel's) experimental results on the carbon and oxygen isotope exchange equilibria between CO and Ni(CO)(4). The isotopic equilibrium constants, K-B, of carbon and oxygen exchange reactions between CO and Ni(CO)(4) complexes were theoretically calculated as the ratio of the reduced partition function ratios (RPFRs) of the C-13/C-12 and O-18/O-16 isotopic pairs for CO and Ni(CO)(4) on the assumption of the internal harmonic vibrations. The agreement between calculated separation factor and Spindel's experimental data are surprisingly good, including the temperature dependence. (C) 2004 Elsevier B.V. All rights reserved.