The chemical transformation of the greenhouse gas CO2 into useful compounds is one of the most challenging problems in small molecule activation.1 Carbon dioxide fixation and activation at uranium centers have received considerable attention.2 In this work,the possible structures of reaction products of U(IV)O2 and CO2 are investigated by using DFT methods.Comparing with the matrix isolation infrared spectroscopy data3,the structure of UO(CO3) has been established.The electronic structure indicates that the product complex has a triplet ground state correlated to the 3Hg state of UO2,and CO2 coordination can also induce a reversal of the ground state of UO2 (the ground state changed from 5f17s1 to 5f2).4 The result provides a better understanding on CO2 activation by U(IV)O2.