Infrared photodissociation spectroscopy of mass-selected [MO(CO2)n]+ (M=Sc,Y,La) complexes indicates that the conversion from the solvated structure into carbonate one can be achieved by the ScO+ cation at n=5 and by the YO+ cation at n=4,while only the solvated structures are observed for the LaO+ cation.These findings suggest that both the ScO+and YO+ cations are able to fix CO2 into carbonate.Quantum chemical calculations are performed on [MO(CO2)n]+ to identify the structures of the low-lying isomers and to assign the observed spectral features.Theoretical analyses show that the [YO(CO2)n]+ complex has the smallest barrier for the conversion from the solvated structure into carbonate one,while [LaO(CO2)n]+ exhibits the largest conversion barrier among the three metal oxide cations.The present system affords a model in clarifying the effect of different metals in catalytic CO2 transformation at the molecular level.