Phenide anion

Fig. 3 Schematic diagram of the canonical MOs of benzene, phenide anion and phenylacetylene. The highest occupied molecular orbital (HOMO) and three lower ones HOMO-1, HOMO-2 and HOMO-3 are shown along with their symmetry representations...

To analyze the vibronic structures of the X, A and B electronic states Ph we constructed a vibronic Hamiltonian in a diabatic electronic basis which treats the nuclear motion in the X state adiabatically, and includes the nonadiabatic coupling between the A and B electronic states. The Hamiltonian terms of the dimensionless normal coordinates of the electronic ground state (XMi) of phenide anion is given by [19]... 

Here I3 represents a 3 x 3 unit matrix. (T/y + Vo) represents the zeroth-order Hamiltonian of unperturbed electronic ground state of phenide anion given by (21-22). The elements of the electronic Hamiltonian AH are expanded in a Taylor series as follows... 

The vibronic coupling in the PA + is bit more involved than in Ph [21], The De/, equilibrium mmetry of benzene breaks to Civ pon acetyjene substitution. The degenerate X Eig JT state of BZ + splits into X Bi and A Ax electronic states in PA + as revealed by Fig. 3. Contrary to the phenide anion, where removal of a proton splits the JT degeneracy of benzene, in phenylacetylene (PA), perturbation caused by substitution breaks the JT symmetry. 

---