Using literature data on the gas phase reaction between free lanthanide atoms and carbon dioxide, we have found an isokinetic relation for seven of the twelve investigated elements with an isokinetic temperature, T-iso of 2500 +/- 330 K. This value is analyzed in the framework of the model of selective energy transfer, SET, indicating that metal-CO2 complexes are formed as pre-reaction states. The result is in accordance with the fundamental concepts of SET.