Theoretical evaluation of potential surfaces,equilibrium geometries and vibronic transition intensities of excimers: the pyrene crystal excimer

A general method for evaluation of equilibrium geometries and vibronic transition intensities of crystalline excimers is described. The method provides realistic potential surfaces which include, in addition to the α electron surfaces, also the repulsive hard core of the α electrons and the effect of the crystal potential. The method is applied to the study of the potential surfaces of the pyrene excimer, both in the crystal and in the gas phase. The method is also used for a direct evaluation of the vibronic structure of the excimer emission. The calculations reproduce the main experimentally observed properties including the structureless envelope of the emission band and the temperature dependence of its line width.