Reactions of laser-ablated early lanthanoid atoms (Ce, Pr, Nd, Sm, and Eu, except for radioactive Pm) with N2O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. Lanthanoid monoxide-dinitrogen complexes, OLn(N-2) (Ln = Ce, Pr, Nd, and Sm), are observed during sample deposition and identified on the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments, whereas no new product is observed for Eu. The OLnNN(+) (Ln = Ce, Pr, Nd, and Sm) cations appear during sample deposition and increase visibly upon broadband irradiation (lambda > 250 nm) at the expense of the neutral OLn(N-2) complexes. Density functional theory calculations have been performed on the new products, which support identification of the OLn(N-2) and OLnNN(+) complexes from the matrix infrared spectra.