The ionization energies of the isomers of CN2

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∞v molecule CNN+ is found to have the lowest energy. NCN+ (D∞h) lies 0.2 eV higher in energy than CNN+. The CN2+ isomer has a cyclic structure with C2v symmetry. The adiabatic ionization energies of the radicals determined at the G2 level are IP(NCN, X̃3Σg−)=12.52±0.07 eV, IP(CNN, X̃3Σ−)=11.01±0.07 eV and IP(cyc-CN2, X̃1A1)=11.94±0.07 eV.