The geometries and harmonic vibrational frequencies for the structural isomers of CN2 and the corresponding cations are calculated at the B3LYP/6-311+g(2df) level. Adiabatic ionization energies are calculated at the G1, G2(MP2) and G2 levels for each of the isomers. Of the cations, the linear C-infinityv molecule CNN+ is found to have the lowest energy. NCN+ (D-infinityh) lies 0.2 eV higher in energy than CNN+. The CN2+ isomer has a cyclic structure with C-2v symmetry. The adiabatic ionization energies of the radicals determined at the G2 level are IP(NCN, (X) over tilde (3)Sigma (-)(g)) = 12.52 +/- 0.07 eV, IP(CNN, (X) over tilde (3)Sigma (-)(g)) = 11.01 +/- 0.07 eV and IP(cyc-CN2, (X) over tilde (1)A(1)) = 11.94 +/- 0.07 eV. +/- 2000 Elsevier Science B.V. All rights reserved.