Evidence of dynamical Jahn-Teller effect on triphenylene radical cation: Resonance Raman spectrum and ab initio quantum-chemical calculations

We report resonance Raman spectrum of the triphenylene radical cation gener ated by gamma -irradiation in a Freon glass at 77 K. Raman spectra were obt ained using excitation in resonance with the strong cation absorption band near 400 nm. Ab initio calculations (Hartree-Fock, B-LYP, and B3-LYP, all w ith 6-31G basis set) were performed to obtain the equilibrium structures an d vibrational force fields of triphenylene neutral and radical cation speci es. In addition, semiempirical calculations were carried out to identify th e state in resonance with the excitation light and to simulate the vibronic structure of the resonance Raman spectrum. From these experimental and the oretical results, it is concluded that the bands observed in the resonance Raman spectrum of the radical cation contain the signatures of the Jahn-Tel ler effect on the cation which, similarly to benzene cation, is dynamical i n nature.