Reactions of laser-ablated niobium and tantalum atoms with dinitrogen in solid neon have been investigated using matrix-isolation infrared spectroscopy. The Nb(NN)(x) and Ta(NN)(x) (x = 1-4) molecules formed during sample deposition or on annealing are the major products. The products are characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, stepwise annealing, and change of reagent concentration and laser energy. Density functional theory calculations have been performed to understand the structures, ground electronic states, and bonding characteristics of niobium and tantalum dinitrogen complexes. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. The molecular orbital analyses and plausible reaction pathways for the formation of the products are also discussed.