Excimer fluorescence XII. The pyrene crystal excimer interaction potential

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 105 dyn/cm) and ground state (= 3.25 x 105 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 106/r3(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 1Ba state of the pyrene molecule.