Electronic structure of the 1,3,5-tridehydrobenzene triradical in its ground and excited states
The ground and low-lying electronic states of the 1,3,5-tridehydrobenzene triradical are characterized by electronic structure calculations. It is found that the ground state is the 2A1 doublet of C2v symmetry. Another doublet state lies 0.1 – 0.2 eV higher in energy, and the lowest quartet state of D3h symmetry is 1.2 – 1.4 eV higher in energy. Both doublets are degenerate at D3h geometries and undergo different Jahn-Teller distortions. Structurely, the triradical is tighter than the parent neutral molecule (benzene), because the interaction among the unpaired electrons results in additional bonding even in the high-spin state (quartet). The adiabatic doublet-quartet energy gap and the excitation energies calculated at the equilibrium geometries of the 3,5-dehydrophenyl anion are provided to aid in the design and interpretation of photoelectron experiments.