An attempt has been made to study the reaction between a uranium atom and a nitrogen molecule theoretically using multiconfigurational wave functions. The C2v part of the reaction surface has been computed for several electronic states of various spin multiplicities. The system proceeds from a neutral uranium atom in its (5f)3(6d)(7s)2, 5L ground state to the linear molecule NUN, which has a 1Σ+g ground state and uranium in a formal U(VI) oxidation state. The effect of spin–orbit coupling has been estimated at crucial points along the reaction. These preliminary results shows that the system proceeds from a quintet state for U + N2, via a triplet transition state to the final closed shell molecule. An eventual energy barrier for the insertion reaction is caused by the spin–orbit coupling energy.