Conical and glancing Jahn-Teller intersections in the cyclic trinitrogen cation
The ground and electronically excited states of cyclic N3+ are characterized at the equilibrium D3h geometry and along the Jahn-Teller distortions. Lowest excited states are derived from single excitations from doubly degenerate HOMO to doubly degenerate LUMO, which gives rise to two exactly and two nearly degenerate states. The interaction of two degenerate states with two other states eliminates linear terms and results in a glancing rather than conical Jahn-Teller intersection. HOMO-2 → LUMO excitations give rise to two regular Jahn-Teller states. Optimized structures, vertical and adiabatic excitation energies, frequencies and ionization potential (IP) are presented. IP is estimated to be 10.595 eV, in agreement with recent experiments.