Excimer fluorescence XII. The pyrene crystal excimer interaction potential

Abstract

The excimer fluorescence spectra of pure single pyrene crystals were observed from 4 to 353 °K. The data are analysed to determine the vibrational zero-point energy of the excimer (= 90 cm -1 ), the force constants of the excited state (= 1.93 x 10 5 dyn/cm) and ground state (= 3.25 x 10 5 dyn/cm) of the dimer, and the equilibrium intermolecular separation (= 3.34 Å) of the excimer. The repulsive intermolecular potential, the excimer energy, and the attractive excimer interaction potential, V' = 51330 - 1.136 x 10 6 / r 3 (cm -1 ) are determined as functions of the intermolecular separation r (Å). V' is shown to be consistent with an exciton resonance state originating from the 1 B a state of the pyrene molecule.