The reactions of laser-ablated thorium and uranium metals in condensing pure dinitrogen streams as well as argon/dinitrogen mixtures have provided spectroscopic Evidence for the presence of several previously uncharacterized actinide metal nitrides and dinitrogen complexes. Infrared spectra of the matrix isolated product species indicate that thorium and uranium atoms have a significant bond weakening effect on dinitrogen upon initial complexation and in some cases complete dinitrogen bond cleavage is observed. In the reactions of laser-ablated thorium and uranium atoms with pure dinitrogen, the primary products are the metal mononitride (M-N), the metal dinitride (N-M-N), and in the uranium reactions, two dinuclear products U(mu-N)(2)U and NU(mu-N)(2)U. In the reactions of thorium with dinitrogen in argon, the primary products are N-Th-N, Th(mu-N)(2)Th, and the dinitrogen complexes Th-eta(1)-N-2 and Th-eta(1):eta(1)-(N-2)(2). The complete ground-state electronic structure and vibrational spectrum cf each product molecule has been modeled using quasirelativistic density functional calculations in order to lend support to the spectral assignments and to give insight into the electronic structure of these new species.