Topology of the complicated Jahn-Teller intersection in the cyclic trinitrogen cation
We characterized the ground and electronically excited states of cyclic N3+ at the equilibrium D3h geometry and along Jahn-Teller distortions.
Potential energy surfaces of the cyclic N3+ lowest electronic excited states.
The lowest excited states are derived from excitations from the doubly degenerate HOMO to the doubly degenerate LUMO, which gives rise to two exactly and two nearly degenerate electronic states [1,2]. In each multiplicity, the potential energy surfaces (PES) of four singlet and four triplet states are close in energy in equilateral geometry and form a complicated network of conical intersection's seams. A similar pattern will occur in other molecules with doubly degenerate HOMO and LUMO, e.g., benzene and sym-triazine.
Relevant molecular orbitals of cyclic N3+. Both HOMO and LUMO are doubly degenerate.
Topological features of D3h intersection seam for the PES scan along the fully symmetric stretch.
Virtually every possible topological feature is present on the PESs along the D3h distortion of this simple beautiful molecule: conical intersection (CI) seams, triple conical intersections, intersection of D3h CI with three C2v CIs, glancing (Renner-Teller) intersection of the potential energy surfaces. Cyclic N3+ can be considered a "molecule with the smallest Jahn-Teller effect".
Scans of increased resolution along Jahn-Teller distortions (bending normal mode) of the four lowest triplet excited states' PESs. The Jahn-Teller linear term is extremely small which makes the intersection appear glancing rather than conical.
Cyclic N3 is being investigated both experimentally [see P.C.Samartzis, J.J.M.Lin, et al. The simplest all-nitrogen ring: Photolytically filling the cyclic-N3 well . J. Chem. Phys. 126 (4): 041101 (2007)] and theoretically [see J.J.Dillon and D.R.Yarkony. Seams near Seams: The Jahn-Teller Effect in the 1E'' State of N3+. J. Chem. Phys. 126 (12): 124113 (2007)].