The high-resolution spectrum of O-2-N2O, the first for a complex containing more than one unpaired electron, has been studied in the region of the nu(3) N2O monomer vibrational band using a molecular beam diode laser absorption spectrometer. The spectrum has been completely analyzed using a newly developed effective Hamiltonian. The rotational constants are accurately determined for both ground and excited vibrational states. The equilibrium structure of the complex is planar, with a separation between the centers of the mass of two monomers of 3.423 Angstrom. The structural angles have been experimentally determined as: either theta(O2) = 58 degrees and theta(N2O) = 77 degrees, or theta(O2) = 122 degrees and theta(N3O) = 100 degrees. The large amplitude motion of the monomers leads to the complex having an effective out-of-plane root mean square angle of phi = phi(1)-phi(2) approximate to 23 degrees. In addition, an interpretation of the structure of the complex is given in terms of an intermolecular potential using a model described by Muenter. (C) 1997 American Institute of Physics.