Molecular structures in the non-adiabatic relaxaiton processes of excited states of pentafluoropyridine

In this work, the molecular structure and energy of some critical points in nonradiative relaxation process of the excited state of pentafluoropyridine are studied through quantum chemistry calculation. The structures and the vertical excitation energies and adiabatic excitation energies of the ground state and two lowest exited states are calculated. The geometry of the ground state is a planar structure with C-2v symmetry, while the geometries of the two lowest excited states are half-boat structures with out-of-plane distortions. Furthermore, the topology structures and energy of the conical intersections of S-2/S-1, S-1/S-0 and S-2/S-0 are determined. The topology structures of the conical intersections S-2/S-1, S-1/S-0 and S-2/S-0 in the branching space are all peaked with asymmetric structures, and are determined to be structure of boat, half-boat, and chair, respectively. Their corresponding energy values are estimated at 6.39, 5.16 and 8.51 eV, respectively. The results show that the primary non-adiabatic relaxation pathway is the wavepacket of the S-2 state rapidly evolving into the S-1 state via the S-2/S-1, and then directly relaxing to the ground state via the S-1/S-0. In addition, the probability of directly relaxing to the ground state through S-2/S-0 is smaller.