Carbon dioxide activation by La atom and La+ cation in the gas phase: A density functional theoretical study

The potential energy surfaces for the La + CO2 and La+ + CO2 reactions have been theoretically investigated by using the DFT (B3LYP/ECP/6-311+G(2d)) level of theory. To obtain an accurate evaluation of the activation barrier and reaction energy, the QCISD(T) single-point calculations using the B3LYP structures were performed. Both ground and excited state potential energy surfaces are discussed. These results show that the reaction mechanism is insertion mechanism along the C-O bond activation branch. The reaction of La atom with CO2 was shown to occur preferentially on the ground state (doublet) PES throughout the reaction process, and the experimentally observed species, has been explained according to the mechanisms revealed in this work. As for the reaction between La+ cation with CO2, it involves potential energy curve-crossing which dramatically affects reaction mechanism, and the crossing points (CPs) have been localized by the approach suggested by Yoshizawa et al. Due to the intersystem crossing existing in the reaction process of La+ with CO2, the intermediate (OLa(η2-CO))+ may not form. This mechanism is different from that of La + CO2 system. All our theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction.