Exploring the different mechanisms involved in the application of actinide is necessary to obtain a more comprehensive understanding of actinide science. In this study, the mechanisms of gas-phase Np and Pu atoms dissociating NH3 molecules forming Neptunimine and Plutonimine complexes were systematically investigated using different approaches of density functional theory. A new dehydrogenation channel was discovered. The results reveal that the intermediates HAn-NH2 are the lowest energy in the overall reaction, and the direct planar evolution dehydrogenations are the lowest energy reaction path. Besides, the mechanism of the initial complexation process is discussed on the electron localization function, atoms-in-molecules, atomic dipole moment corrected Hirshfeld atomic charges, and electron density difference analysis. The results indicate that An-N in complex I exhibits a very weak covalent interaction, and it comes down to pulling the original dipole moment of the NH3 molecule and stretched between An atom and three H atoms. Graphical abstract.
Keywords: Activation mechanism; Ammonia; Neptunimine; Plutonimine.